Moving toward improved immune checkpoint immunotherapy for advanced prostate cancer

Human prostate cancer is a heterogenous malignancy that responds poorly to immunotherapy targeting immune checkpoints. The immunosuppressive tumor microenvironment that is typical of human prostate cancer has been the main obstacle to these treatments. The effectiveness of these therapies is also hindered by acquired resistance, leading to slow progress in prostate cancer immunotherapy. Results from the highly anticipated late-stage clinical trials of PD-1/PD-L1 immune checkpoint blockade in patients with advanced prostate cancer have highlighted some of the obstacles to immunotherapy. Despite the setbacks, there is much that has been learned about the mechanisms that drive resistance, and new strategies are being developed and tested. Here, we review the status of immune checkpoint blockade and the immunosuppressive tumor microenvironment and discuss factors contributing to innate and adaptive resistance to immune checkpoint blockade within the context of prostate cancer. We then examine current strategies aiming to overcome these challenges as well as prospects.

Abstract 640: Exploring the relationships between prostate cancer, colorectal cancer, and ulcerative colitis

Studies suggest that certain immune-mediated diseases may be associated with cancer risk beyond local organs. Prolonged systemic inflammation from inflammatory bowel diseases such as ulcerative colitis (UC) and Crohn’s disease (CD) pose a greater risk to colorectal cancer (CRC) and accumulating data suggests that prostate cancer (PCa) risk is higher in patients with UC but not CD and that patients with PCa may be at a greater risk for CRC. A better understanding of the biological interactions between these conditions could have important implications for cancer screening, detection, and prevention in high-risk populations. However, data to establish the relationships and relative contributions of these diseases are lacking. Here, we explored these relationships using preclinical mouse models of dextran sulfate sodium (DSS)-induced colitis (DSS-UC) and DSS/azoxymethane (AOM)-induced CRC (DSS/AOM-CRC) in young and aged healthy wildtype mice and transgenic mice harboring Pten-deficient PCa. In the DSS/AOM-CRC model, aged PCa-bearing conditional Pten-knockout (KO) mice experienced poorer overall survival compared to age-matched wildtype (WT) without PCa because of CRC. DSS/AOM-CRC incidence was not affected by the presence of PCa, however tumor burden was higher in KO mice compared to WT and in KO mice, DSS/AOM-CRC accelerated PCa growth and progression. Prostates from WT DSS/AOM-CRC mice showed higher incidence of hyperplasia and greater myeloid cell infiltration compared to healthy controls. Systemic changes associated with DSS/AOM-CRC in both WT and KO mice included splenomegaly, lymphadenopathy, and immune cell composition. The impact of DSS-UC was investigated conditional Pten/Trp53-double knockout (DKO) mice with DDS only treatments starting at an age prior to the development of PCa. In this setting, cycling DSS led to the development of UC after 10 weeks of treatment and accelerated prostate tumor development characterized by high grade prostatic intraepithelial neoplasia (PIN) grade dysplasia and increased cell proliferation. Prostate tumors from mice with DSS-UC exhibited an altered tumor immune microenvironment characterized by a higher degree of inflammatory cell infiltrate. Changes in immune cell composition were also observed in peripheral blood and secondary lymphoid organs. These preclinical models recapitulated disease relationships observed in humans and provide a platform to further investigate biological mechanisms and therapeutic interventions.

Citation Format: Marco A. De Velasco, Yurie Kura, Kazuko Sakai, Naomi Ando, Noriko Sako, Kazutoshi Fujita, Shogo Adomi, Eri Banno, Yasunori Mori, Takafumi Minami, Masahiro Nozawa, Kazuhiro Yoshimura, Kazuto Nishio, Hirotsugu Uemura. Exploring the relationships between prostate cancer, colorectal cancer, and ulcerative colitis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 640.

Abstract 3044: Integrative gut microbiome analysis of human and mouse prostate cancer

Gut microbes are intricately involved in maintaining normal physiology and homeostasis and have become a major area of study to determine their relevance in human disease. In cancer, alterations to gut microbiota has been associated to resistance to chemo- and immuno-therapy, whereas supplementation with specific taxa improves antitumor treatment responses. Mouse models have been essential to study disease biology and drug discovery. However, mice are fundamentally quite different from humans, thus, questions have arisen regarding their utility as pertinent tools to study microbial influences and their impact on human disease. To address these questions, we have performed a cross-species comparative analysis of the fecal microbiota from a human cohort of prostate cancer patients and a preclinical mouse model of prostate cancer. Microbiota composition was determined by 16s RNA gene sequencing on stool samples from tumor-bearing prostate-specific conditional Pten-knockout and disease-free wildtype mice and 16s RNA gene sequencing data from a human cohort of patients with suspected prostate cancer was used. Human cases were assigned to no cancer and cancer groups based on diagnosis from prostate biopsy and as low-risk (negative biopsy of Gleason grade <3) or high-risk (Gleason grade ≥3). Community composition differed significantly between stool samples of cancer and disease-free individuals in mice but not humans. Operational taxonomic units (OTUs) corresponding to taxa associated with cancer in both mice and humans included Odoribacter spp. and Desulfovibrio spp. Comparing the profiles predicted with Tax4Fun revealed KEGG metabolic pathways associated prostate cancer. Pathways enriched in cancer bearing-mice and that are also associated in patients with prostate cancer included folate biosynthesis, biotin metabolism and ubiquinone & other terpenoid-quinone biosynthesis. Carbon metabolism was a pathway discordant between high-risk prostate cancer patients and cancer bearing mice. Although the basal composition of gut microbes differed between humans and mice, the functional microbiome showed greater similarities. Our cross-species comparative analysis shows that gut microbial dysbiosis is connected to prostate cancer provides additional insights into the biological processes involved. This study provides additional data that may help to bridge the gap between humans and mice.

Citation Format: Chisato Wakamori, Marco A. De Velasco, Yurie Kura, Naomi Ando, Noriko Sako, Kazutoshi Fujita, Kazuko Sakai, Makoto Matsushita, Eri Banno, Yasunori Mori, Masahiro Nozawa, Mitsuhisa Nishimoto, Kazuhiro Yoshimura, Norio Nonomura, Kazuto Nishio, Hirotsugu Uemura. Integrative gut microbiome analysis of human and mouse prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3044.

Abstract 2877: Profiling of myeloid-derived suppressor cells in Pten-deficient in prostate cancer progression

Myeloid-derived suppressor cells (MDSCs) are a heterogenous population of immature immune cells that expand during cancer and can induce potent immune suppression. These cells play critical roles in supporting tumor growth and progression and their induction has been associated with the inactivation of PTEN. To date, few therapies targeting these cells are available which is partly due to their increasingly complex nature and context-dependent functions. Moreover, there is no clear definition to identify these cells. Enhancing our understanding of this cell population will aid in developing more effective cancer therapies. Here, we used gene expression profiling, flow cytometry, and quantitative immunohistochemistry to characterize tumor-infiltrating and circulating MDSCs in prostate carcinogenesis and progression in transgenic mouse models of prostate cancer driven by the conditional inactivation of Pten and Trp53. Transcriptomic profiling revealed enrichment of various myeloid-derived cell signatures in the early stages of prostate cancer including MDSCs, macrophages, and neutrophils. Flow cytometric analysis confirmed the increased infiltration of CD11b+/Ly6G+ (polymorphonuclear MDSCs (pMDSCs)) and CD11b+/Ly6C+ (monocytic MDSCs (mMDSCs)) cells in prostate tumors. The temporal dynamics of tumor-infiltrating myeloid cells were further profiled and showed that pMDSC and mMDSC abundances were 1.6 and 5.7-fold higher, respectively, in older mice with late-stage locally invasive adenocarcinomas (AdCa) compared to younger mice with early-stage prostatic intraepithelial neoplasia (PIN). In both instances, pMDSCs comprised most of the leukocyte infiltrate, however, mMDSCs tended to be positively correlated with tumor burden in AdCa but not PIN. In peripheral blood, CD44+/CD62L+ immature neutrophils were associated with high tumor burden in aged mice. Treatments targeting the androgen receptor (AR) signaling further exacerbated pMDSC infiltration in tumors and was associated with resistance to second androgen receptor-targeted agent (ARTA) therapy in a model of castration resistant prostate cancer. Our findings indicate that MDSCs are a prominent population in Pten-null prostate cancer and are implicated with resistance to prostate cancer treatment. MDSCs constitute a potentially targetable population and these models serve as viable platforms to further investigate their biological activity and further evaluate novel MDSC-directed therapies.

Citation Format: Marco A. De Velasco, Yurie Kura, Noriko Sako, Naomi Ando, Kazuko Sakai, Eri Banno, Shogo Adomi, Mitsuhisa Nishimoto, Takafumi Minami, Yasunori Mori, Kazutoshi Fujita, Masahiro Nozawa Nozawa, Kazuhiro Yoshimura, Kazuto Nishio, Hirotsugu Uemura. Profiling of myeloid-derived suppressor cells in Pten-deficient in prostate cancer progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2877.

Abstract 5604: Targeting CD73 augments the efficacy of A2aR blockade in PTEN-deficient prostate cancer

Extracellular adenosine is an immunosuppressive molecule that is generated from ATP by the CD39 and CD73 ectoenzymes and exerts its antitumor effects through its interaction with the adenosine 2A receptor (A2AR) on immune cells. Approaches to curtail the immunosuppressive effects of extracellular adenosine primarily target CD73 and A2aR. In this study, we examined the immunomodulatory effects and antitumor effects of CD73 and A2aR blockade in the context of PTEN-deficient prostate cancer. The immunomodulatory effects of anti-CD73 antibody blockade (aCD73) or A2aR inhibition with the small molecule inhibitor AZD4635 were characterized in transgenic mice bearing Pten-null prostate tumors after one week of dosing. qPCR-based tumor immune profiling revealed distinct differences between the treatment groups that were characterized by the enrichment of gene signatures related to T cell, natural killer cell, and NK T cell in AZD4635 treated mice and macrophage and B cell in mice treated with aCD73. Immunohistochemical analysis showed significant 2.5- and 4.6-fold increases of granzyme B positive immune cells in the cancer glands of aCD73 and AZD4635 treated mice, respectively. Efficacy studies showed that tumors from mice after long-term treatment with AZD4635 were characterized with high adenosinergic signatures and particularly increased levels of Nt5e, the gene encoding CD73. Treatment with aCD73 and AZD4635 alone or in combination led to tumor burden reductions of 4.4%, 15.1% and 16.7%, respectively, after four weeks of treatment and -8.58%, 4.6% and 29.5%, respectively after eight weeks of treatment. Additional analyses showed that androgen deprivation therapy induced an adenosine high signature, and increased Nt5e expression levels and CD73-positive infiltrating MDSCs/neutrophils. The efficacy of AZD4635 versus aCD73 plus AZD4635 was evaluated in an in vivo castration-sensitive model of Pten-null prostate cancer treated with apalutamide plus androgen deprivation therapy via surgical castration. In this model, mice were treated for eight weeks to allow for the progression to castration-resistant prostate cancer (CRPC) and in this setting, the treatment combination of aCD73/AZD4635 improved tumor burden reduction to 34.3% from 23.1% in AZD4635 treated mice. Moreover 75% (6/8) of mice treated with aCD73/AZD4635 had tumor burden reductions greater than 30% relative to vehicle treated controls versus 28.6% (2/7) of mice in the AZD4635 only group. Our findings show that extracellular adenosine is a key immunosuppressive molecule in PTEN-deficient prostate cancer and provide evidence that implicates adenosinergic signaling via CD73 as a contributing factor to decreased efficacy of A2aR blockade and progression to CRPC.

Citation Format: Marco A. De Velasco, Yurie Kura, Naomi Ando, Noriko Sako, Kazuko Sakai, Alwin Schuller, Kris Sachsenmeier, Kazutoshi Fujita, Eri Banno, Masahiro Nozawa, Kazuhiro Yoshimura, Kazuto Nishio, Hirotsugu Uemura. Targeting CD73 augments the efficacy of A2aR blockade in PTEN-deficient prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5604.

Abstract 5282: Preclinical efficacy of abiraterone plus capivasertib in mouse Pten-deficient prostate cancer

Prostate tumors are characterized with constitutively activated AKT signaling primarily through the loss of PTEN. Second generation antiandrogens such as abiraterone acetate have improved the survival of prostate cancer patients, however, resistance remains a problem and patients with PTEN-deficient tumors have poorer outcomes to abiraterone treatments. Moreover, PTEN-deficient tumors are also characterized with immunosuppressive tumor microenvironments. In this study we investigate the benefit of adding capivasertib, a potent pan-Akt inhibitor, to abiraterone therapy in a preclinical model of Pten-deficient prostate cancer and examine the antitumor efficacy and its influence on antitumor immunity. The temporal effects of abiraterone and capivasertib alone and as combination therapy were evaluated after one and four weeks of dosing in conditional transgenic mice harboring Pten-deficient prostate tumors. While abiraterone therapy alone reduced genitourinary tract weights, which contain both AR-sensitive normal accessory sex organs and prostate tumor, the treatment had no overall effect on prostate tumor burden. Mice treated with capivasertib monotherapy experienced tumor burden reductions of 8.2% and 15.6% at week 1 and 8, respectively, moreover, the treatment combination of abiraterone + capivasertib significantly improved the therapeutic effect with tumor burden reductions of 35.6% and 37.8% at weeks 1 and 4, respectively versus vehicle control. qRT-PCR analysis of Ar target genes showed decreased expression in mice treated with abiraterone. All treatment combinations showed increased gene expression levels of Casp3 in tumors from mice at week one but were greatest in those treated with abiraterone alone or in combination and increased expression levels were sustained only in the combination cohort at week four. Immunological profiling of tumors from mice treated with abiraterone + capivasertib using qRT-PCR-based panel of immune-related genes revealed enrichments in genes associated with phagocytosis, antigen processing and dendritic cell function. Examination of the tumor draining lymph nodes by flow cytometric analysis showed ~1.5-fold-increases in the abundance of migratory dendritic cells (CD11b+\CD11c+\XCR1+) in all pharmacologically treated mice (versus vehicle control) and remained elevated only in mice receiving capivasertib as monotherapy or combination at week four. Additionally, mice treated with combination therapy also had enrichments in genes sets associated to T cell, NK cell and as well as T cell activation, cytotoxicity, and interferon gamma signature. The findings from this study provide preclinical evidence for the efficacy of combination therapy with abiraterone plus capivasertib and provides insights into its immunomodulatory effects and influence on antitumor immunity.

Citation Format: Marco A. De Velasco, Yurie Kura, Naomi Ando, Keiko Kuroka, Kazutoshi Fujita, Eri Banno, Kazuko Sakai, Masahiro Nozawa, Kazuhiro Yoshimura, Kazuto Nishio, Hirotsugu Uemura. Preclinical efficacy of abiraterone plus capivasertib in mouse Pten-deficient prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5282.

Abstract 5952: Curcumin monoglucuronide modulates the tumor microenvironment of Pten-null prostate tumors and exhibits antitumor activity

Curcumin is a naturally occurring compound found in turmeric and is well-known for its anticancer and anti-inflammatory properties, however, low solubility, poor absorption and fast clearance resulting in low systemic bioavailability has hindered therapeutic applications for free curcumin and has prompted the development of curcumin-based formulations with improved bioavailability. Curcumin monoglucuronide (CMG) is a water-soluble injectable prodrug that shows improved bioavailability over oral free curcumin and has demonstrated anticancer activity. In this study, we examine the therapeutic efficacy and immunomodulatory effects of CMG in mouse prostate cancer models driven by the conditional inactivation of Pten. The acute immunomodulatory effects of CMG were profiled in tumors from 28-week-old conditional Pten/Trp53 double knockout mice one-week after intraperitoneal dosing with CMG and were evaluated using a focused panel of qRT-PCR-based immune related genes, flow cytometry and immunohistochemistry (IHC). Overall, mice receiving CMG showed a higher inflammation profile compared to vehicle controls and was characterized with enrichments in macrophage, dendritic cell, and T cell gene signatures. CMG treated mice showed enhanced dendritic cell activity in tumors including an increased abundance of activated of migratory dendritic cells (CD11b+\CD11c+\XCR1+\MHC-II+\CD80+). Tumors from CMG-treated mice also contained increased T cell infiltration (including CD8+ and CD4+ T cells) as well as enrichment of genes related to T cell differentiation and activation and an increased abundance of CD4+\CD25+ regulatory T cells. While one week of dosing did not result in a significant reduction of tumor burden for CMG-treated mice, there was a 1.9-fold increase in cancer cell apoptosis as measures by cleaved caspase-3 IHC expression (P=0.004) and was correlated to leukocyte infiltration particularly in the ventral lobes of the prostate. The antitumor efficacy and long-term immunomodulatory effects of CMG were further evaluated in 16-week-old conditional Pten knockout after four weeks of dosing. In this model, tumor from mice treated with CMG showed a 10% reduction of tumor burden compared to vehicle controls (P=0.065). Tumors from CMG treated mice also had a 1.7-fold increase in apoptosis compared to vehicle treated mice (P=0.009) and tended to have reduced cancer cell proliferation compared to vehicle controls (P=0.148). Gene expression and flow cytometry analyses showed that tumors from mice treated with CMG for four weeks maintained improved tumor inflammation and showed an increased T cell infiltration over vehicle treated controls including effector cytotoxic T cells (CD8+\Granzyme B+). These findings provide preclinical evidence for the antitumor and immune modulatory activity of CMG in mouse hormone sensitive Pten-deficient prostate cancer.

Citation Format: Yurie Kura, Marco A. De Velasco, Naomi Ando, Kazuko Sakai, Kazutoshi Fujita, Eri Banno, Yoshihiko Fujita, Mamoru Hashimoto, Masahiro Nozawa, Kazuhiro Yoshimura, Kazuto Nishio, Hirotsugu Uemura. Curcumin monoglucuronide modulates the tumor microenvironment of Pten-null prostate tumors and exhibits antitumor activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5952.

Abstract 5637: Transformation of the gut microbiome in response to androgen deprivation and the transition to castration-resistant prostate cancer

Androgen deprivation therapy (ADT) remains the standard care for men with advanced prostate cancer. Although initially effective, many patients fail to maintain durable responses and progress to lethal castration-resistant prostate cancer. Commensal bacteria play important role in maintaining homeostasis and proper immune function. However, ADT alters gut bacterial compositions and the ramifications being investigated. In this study, we used a mouse model of Pten-deficient prostate cancer to characterize differences in bacterial composition of gut bacteria in mice with castration naïve-prostate cancer (CNPC) and gut microbiota from mice three and six weeks after treatment ADT via surgical castration representing castration-sensitive prostate cancer (CSPC) and CRPC, respectively. Fecal samples were collected and processed for 16s rRNA amplicon sequencing. ADT resulted in significant changes to biological diversity and local diversity was highest in CSPC (Shannon index, P=0.04). Community composition also differed significantly different between the groups (Adonis OTU Bray-Curtis, P=0.001, NMDS stress=0.07). Despite dissimilarities between bacterial communities among the groups, CNPC and CRPC shared a greater similarity. Taxa associated with CNPC included Unclassified S247, Prevotella L. reuteri, unclassified Rikenellaceae and unclassified Bacteroidales; taxa associated with CSPC included R. gnavus, Dorea, unclassified Desulfovibrionaceae, Dehalobacterium, A. muciniphilia, Bifidobacterium, and B. producta; and taxa associated with CRPC included Turicibacter, R. flavefaciens, L. garvieae, unclassified Peptostreptococcaceae and unclassified Bacilli. Mice with CSPC and CRPC had an increased abundance genes associated with of catabolic metabolic pathways associated with aromatic compound, steroid Benzoate, and toluene degradation as well as genes associated to pathways corresponding to methane metabolism, phosphonate and phosphinate metabolism, and nitrogen metabolism. Genes enriched in fecal taxa from CNPC and CRPC mice were associated with folate biosynthesis, galactose metabolism, amino sugar and nucleotide sugar metabolism, and carbon fixation pathways in prokaryotes. This study provides preclinical evidence to support the association between the gut microbiome and prostate cancer phenotypes associated with sensitivity to ADT.

Citation Format: Chisato Wakamori, Marco A. De Velasco, Kazuko Sakai, Yurie Kura, Naomi Ando, Kazutoshi Fujita, Eri Banno, Kazuhiro Yoshimura, Masahiro Nozawa, Kazuto Nishio, Hirotsugu Uemura. Transformation of the gut microbiome in response to androgen deprivation and the transition to castration-resistant prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5637.

Abstract 5211: Therapeutic resistance to anti-AR signal pathway therapies is related to compensatory pathway activation and immune suppression in mouse Pten/Trp53-deficient CRPC

Prostate cancers depend on androgens and the androgen receptor (AR) to drive androgen signaling pathways. Androgen-deprivation therapy (ADT) and second-generation antiandrogens have become the new standard of care for men with prostate cancer. However, resistance to these therapies remains a problem. TP53 mutations and PTEN loss have been associated with patients who fail to respond to anti-androgen therapies and complex interactions between AR signaling and the immune system means that these therapies have the potential to affect antitumor immune responses. Here, we characterize treatment responses of ADT alone and in combination with antiandrogen therapy using apalutamide (Apa) in a mouse model of Pten/Trp53-deficeint castrate-resistant prostate cancer (CRPC). Twenty-eight-week-old conditional Pten/Trp53-double knockout mice were randomized as untreated control or treated with ADT via orchidectomy for four weeks followed by vehicle or Apa therapy for an additional four weeks. While both treatments reduced tumor burden, there was no difference between treatments. Treatment responses in were further evaluated and were judged as favorable or non-favorable, relative to median tumor burden. Analysis of individual treatment responses indicated that 31.3% (5/16) of mice treated with ADT+Apa had tumor burden reductions >20% (relative to the median) compared to 6.3% (1/16) in ADT, and in both instances, 37.5% (6/16) of mice treated with ADT or ADT+Apa had tumor burden increases >20%. IHC showed lower nuclear/cytoplasm expression of AR in ADT+Apa treated mice and the reduction was more pronounced in favorable responders. ADT+Apa treated mice had lower gene expression levels of Ar than ADT alone and AR target genes (Fkbp5, Tmprss2, Timp4 and Nkx3.1) were decreased in ADT+Apa favorable responders whereas these target genes as well as AR-regulating genes (Myc and Igf1r, Igf1) were higher in ADT+Apa non-favorable responders. Cancer cell proliferation did not differ between treatments, but cancer glands in ADT+Apa treated mice had significantly greater IHC expression levels of cleaved caspase 3, a marker for apoptosis, and were greatest in ADT+Apa favorable responders. Levels of p-S6 ribosomal protein, a downstream target of Akt, were higher in the cancer glands of ADT+Apa but were reduced in stromal and infiltrating immune cells. Immune profiling by gene expression and flow cytometry showed enhanced macrophage involvement and reduced MDSC/granulocyte activity in ADT+Apa treated mice. There were no differences in CD8 T cell and NK cell abundance between the two cohorts, but greater cytotoxic activity was noted in all favorable responders. This study provides preclinical data that links therapeutic resistance to anti-AR signal pathways therapies in Pten/Trp53-deficeint CRPC to compensatory pathway activation and immune suppression.

Citation Format: Marco A. De Velasco, Yurie Kura, Naomi Ando, Noriko Sako, Kazuko Sakai, Kazutoshi Fujita, Eri Banno, Masahiro Nozawa, Kazuhiro Yoshimura, Kazuto Nishio, Hirotsugu Uemura. Therapeutic resistance to anti-AR signal pathway therapies is related to compensatory pathway activation and immune suppression in mouse Pten/Trp53-deficient CRPC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5211.

Intestinal Microbiota and Gene Expression Reveal Similarity and Dissimilarity Between Immune-Mediated Colitis and Ulcerative Colitis

Immune checkpoint inhibitors (ICIs) have become the standard of care for several cancers. However, ICI therapy has also been associated with various immune-related adverse events (irAEs). Clinical manifestations of immune-related colitis resemble those of inflammatory bowel diseases such as ulcerative colitis (UC). The composition of the bowel microflora is thought to influence the development of inflammatory bowel disease and irAE colitis. We profiled the gene expressions and microbe compositions of colonic mucosa from patients with solid cancers receiving anti-PD-L1 antibody treatment; we then compared the expression profiles associated with irAE colitis with those associated with UC. The pathway enrichment analysis revealed functional similarities between inflamed regions of irAE colitis and UC. The common enriched pathways included leukocyte extravasation and immune responses, whereas non-inflamed mucosa from patients with irAE colitis was distinct from patients with UC and was characterized by the recruitment of immune cells. A similarity between the microbiota profiles was also identified. A decreased abundance of Bacteroides species was observed in inflamed regions from both irAE colitis and UC based on a microbiota composition analysis of 16S rDNA sequencing. Pathways associated with molecule transport systems, including fatty acids, were enriched in inflamed and non-inflamed irAE colitis and inflamed UC, similar to Piphillin-inferred KEGG pathways. While UC is characterized by local regions of inflammation, ICI treatment extends to non-inflammatory regions of the colonial mucosa where immune cells are reconstituted. This analysis of the similarity and heterogeneity of irAE colitis and UC provides important information for the management of irAE colitis.

Abstract 1780: Associations between gut microbiota and PD-L1 immunotherapy/JAK1/2 inhibition in mouse Pten-deficient prostate cancer

The gut microbiome is now known to influence host immune function, malignancies, and response to therapy. We previously showed that sequencing PD-L1/JAK1/2 blockade prior to androgen deprivation therapy (ADT) could promote immune activity to potentiate antitumor responses in mouse Pten-deficient prostate cancer. Here, we investigate the associations between the treatment pairings of PD-L1 antibody (aPD-L1, clone D265A, mouse/IgG1 kappa) blockade and the JAK1/2 inhibitor AZD1480 with ADT in mouse Pten-deficient prostate cancer and fecal gut microbiomes. We used 16S rRNA amplicon sequencing to survey fecal samples of tumor bearing conditional Pten-knockout (KO) mice treated for four weeks with aPD-L1 and AZD14870 alone and as combination therapy in intact mice, and as concurrent (Conc) therapy with ADT (via surgical castration), or sequenced as adjuvant (Adj) or neoadjuvant (NeoAdj) therapy. In this model, PD-L1 blockade was ineffective as monotherapy in all treatment settings and as combination therapy in intact and Conc combination settings and hyperprogression was observed in some mice treated with aPD-L1 monotherapy in intact and Adj settings. In the NeoAdj setting, aPDL1/AZD1480 therapy demonstrated superiority over monotherapy. Significant differences in microbial composition were observed between groups (P<0.001), drugs (P<0.001), castration status (P<0.001) and treatment responses (P<0.001). AZD1480 as monotherapy or in combination with aPD-L1 was associated with the greatest changes in microbial composition followed by surgical castration. In the neoadjuvant setting Allobaculum, Lactobacillus, Sutturella, Turcibacter and Prevotella were associated with responders whereas Hellicobacter, Oscillospora, and Ruminococcus gnavus were associated with hyperprogression. Functionally, enrichments in fatty acid biosynthesis/metabolism, tetracycline biosynthesis, phenylalanine, tyrosine and tryptophan biosynthesis, and glycolysis/gluconeogenesis were revealed in responders whereas lipopolysaccharide biosynthesis, glycosaminoglycan degradation, fructose and mannose metabolism, histidine metabolism, glyoxylate and dicarboxylate metabolism, and the citrate cycle (TCA) were enriched in low responders. This study provides insight into the complex interactions between gut microbiota and cancer-burdened hosts, and reveals associations between gut microbial composition and treatment responses to androgen deprivation, immune modulation via JAK1/2 inhibition and PD-L1 blockade in a mouse model of Pten-deficient prostate cancer.

Citation Format: Marco A. De Velasco, Kazuko Sakai, Yurie Kura, Naomi Ando, Noriko Sako, Kazutoshi Fujita, Masahiro Nozawa, Kazuhiro Yoshimura, Kazuto Nishio, Hirotsugu Uemura. Associations between gut microbiota and PD-L1 immunotherapy/JAK1/2 inhibition in mouse Pten-deficient prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1780.

Abstract 1568: A2aR inhibition enhances the antitumor activity of CTLA4 blockade in mouse Pten-deficient prostate cancer

Extracellular adenosine impairs immune function in tumors and limits the efficacy of anti-CTAL4 immune checkpoint blockade. We previously showed that adenosine 2A receptor (A2aR) blockade with AZD4635 moderately inhibited tumor growth, in part by improving antigen presentation and cytotoxic T cell (CTL) activity in mouse Pten-deficient prostate cancer. Here, we continue to investigate the antitumor activity of AZD4635 and its effects when combined with CTLA4 blockade (aCTLA4) in preclinical models of Pten-deficient prostate cancer. Prostate tumors from Pten conditional knockout (KO) mice treated with aCTLA4 for five days had increased expression levels of adenosinergic genes. Furthermore, gene expression, flow cytometric and IHC analyses showed increased T regulatory cell differentiation and accumulation that was offset with the addition of AZD4635. Moreover, expression levels of genes associated with Th 1 cell differentiation and T cell-mediated cytotoxicity were increased in AZD4635/aCTLA4 treated tumors. Adding AZD4635 to a four-week regimen of aCTLA4 therapy improved the antitumor response by two-fold in an early-stage intervention model of Pten-deficient prostate cancer. Androgen deprivation (AD) has the potential to promote T cell infiltration in prostate tumors and using the AZD4635/aCTLA4 treatment combination as neoadjuvant therapy to AD via surgical castration led to a greater antitumor response. The antitumor activity of this treatment combination was further examined and confirmed in a subcutaneous syngeneic genome-derived allograft model using tumor-bearing conditional Pten-deficient knockout mice grafted with Pten-deficient CRPC tumor fragments. In a Pten/Trp53 conditional double knockout (DKO) mouse model of advanced prostate cancer, the AZD4635/aCTLA4 treatment combination did not improve overall survival rates. However, when AZD4635/aCTLA4 was used as neoadjuvant therapy to AR inhibition with the anti-androgen apalutamide, it improved median survival time from 21 days in monotherapy treated mice to 34 days in AZD4635/aCTLA4 treated mice. These results provide preclinical evidence to support the rational combination of A2AR blockade with AZD4635 and aCTLA4 immune checkpoint inhibition for PTEN-deficient prostate cancer.

Citation Format: Marco A. De Velasco, Yurie Kura, Noriko Sako, Naomi Ando, Kazuko Sakai, Alwin Schuller, Kazutoshi Fujita, Masahiro Nozawa, Kazuhiro Yoshimura, Kazuto Nishio, Hirotsugu Uemura. A2aR inhibition enhances the antitumor activity of CTLA4 blockade in mouse Pten-deficient prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1568.

Abstract 622: Gene panel-based immune profiling of human cancers

It is now well accepted that patients with inflamed tumors are more likely to benefit from immunotherapies targeting immune checkpoints such as CTLA4, PD1 and PD-L1.Several factors determine a tumor's immune status and identifying patients who may benefit from immunotherapy and determining which immune therapy to administer depends largely on the patient's tumor immunophenotype. We have developed an approach for immunoprofiling using a focused gene set (115 genes) and scoring system that assesses cell specific types and immune functions. This approach was developed in a preclinical cancer models and is being evaluated and tested in human cancers. We previously extracted data for the gene set and employed unsupervised network clustering to differentiate and classify cancer samples of patients from The Cancer Genome Atlas (TCGA) into immunologically distinct clusters. Here continue or examination and overview clinical features associated with individual clusters. A total of 8477 patients from the TCGA research network were profiled which included 28 solid cancer types. A total of 10 immune clusters (IC 1-10) were identified with a median cluster size of 971 patients with sizes ranging from 178 to 1570. All cancer types were represented in the ICs with mostly normal distribution except for IC 6 which was composed of 40% breast cancer patients and IC10 of which 1/5 of the cases were head-neck squamous cell carcinomas. ICs 2, 5 and 8 were associated with the poorest survival with median times at 73, 51 and 65 months, respectively. Conversely, patients in IC 9 experienced the longest overall survival, median time 148 months. The aggregate inflammation score, which measures overall tumor inflammation was positively correlated to overall survival (P=0.0109). IC 9 was correlated with the highest survival times and was positively associated with primary signatures related antitumor immunity such as high IFN gamma, cytotoxicity, and CD8 T cell and NK cell signatures. IC 8 was characterized with poor survival times and was associated with signatures related with immunosuppressive cells including granulocytic myeloid derived suppressor cells, M2 polarized macrophages and TH17 T cells, and an adenosine high signature. In addition, cases from this cluster also had low CTL signatures. Our findings show that gene expression data from a focused gene and our scoring algorithm could be used to differentiate and classify patients into various groups of immunologically distinct tumors types.

Citation Format: Marco A. De Velasco, Yurie Kura, Kazuko Sakai, Kazutoshi Fujita, Masahiro Nozawa, Kazuhiro Yoshimura, Kazuto Nishio, Hirotsugu Uemura. Gene panel-based immune profiling of human cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 622.

Abstract 1781: Correlates of androgen deprivation and gut microbiome in mouse Pten-deficient prostate cancer

Androgen receptor (AR) signaling plays a key role in the progression of prostate cancer and androgen deprivation therapy (ADT) is one the standard of care for men with advanced prostate cancer. However, AR also exerts effects on androgen responsive tissues and accumulating data indicates that AR is implicated in influencing gut flora. Commensal bacteria are essential for maintaining a healthy immune system which plays a major role in cancer surveillance. Moreover, cancer is known to promote commensal dysbiosis which can further impair immune function. Here, we investigate associations between commensal fecal bacteria and androgen deprivation in an immunocompetent transgenic mouse model of Pten-deficient prostate cancer. 16S rRNA amplicon sequencing was used to comprehensive profile and compare the fecal microbiomes of bearing conditional Pten-knockout mice with those of mice 5 weeks after surgical castration. Tumor burden in surgically castrated mice was significantly lower compared to that of intact mice, 57.45%, P<0.001. With regards to fecal microbial composition, ADT via surgical castration enhanced alpha diversity (Shannon index, P=0.006). Moreover, microbial communities differed between castrated and intact mice (PERMANOVA, P=0.003, NMDS stress=0.042). Notably, an individual mouse with a strong response to ADT showed marked differences in fecal microbe composition compared to other mice in the cohort. Taxa associated with ADT included Dorea, Oscillospora, Sutturella, Dehalobacterium, Akkermansia muciniphila, and Flexispira while Prevoltella, Allobacalum, Ruminococcus flavefaciens, Candidatus Arthromitus and Bacteroides. Dehalobacterium, Coprococcus and Ruminococcus gnavus were more abundant in fecal samples from castrated, low tumor burden mouse. Overall, Bacteriodes and Parabacteriodes were positively correlated to tumor burden. Taxon enrichment analysis (TSEA) revealed functional enrichments of lipid translocation, carbohydrate transport, amino acid transport and proteoglycans in cancer in castrated mice, whereas, enrichment of low-density lipoprotein particle binding, extracellular matrix assembly, inflammatory response to antigenic stimulus and ADP metabolic process. Functional profiles inferred from metagenomic 16S rRNA data revealed enrichment of glyoxylate and dicarboxylate metabolism, carbon metabolism and geraniol metabolism in castrated mice. In intact mice, lipopolysaccharide biosynthesis, streptomycin biosynthesis and amino sugar and nucleotide sugar metabolism were enriched. Notably, lower tumor burden was associated with porphyrin and chlorophyll metabolism, propanoate metabolism, and valine, leucine and isoleucine degradation. This study models ADT in a preclinical model of prostate cancer and provides a broad characterization of the gut microbiome and its association to androgen deprivation.

Citation Format: Marco A. De Velasco, Kazuko Sakai, Yurie Kura, Eri Banno, Naomi Ando, Noriko Sako, Nobutaka Shimizu, Kazutoshi Fujita, Masahiro Nozawa, Kazuhiro Yoshimura, Kazuto Nishio, Hirotsugu Uemura. Correlates of androgen deprivation and gut microbiome in mouse Pten-deficient prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1781.

Abstract 1438: Acute immune responses to apalutamide in mouse Pten-deficient prostate cancer

The androgen receptor (AR) is a major therapeutic target for human prostate cancer and therapies targeting the AR pathway also impact local and systemic immunity. However, the influences over host immune function vary depending on the type of AR treatment. Androgen deprivation (AD) can improve immune cell infiltration by enhancing T cell trafficking, but it also attracts immunosuppressive myeloid cells and regulatory T cells. We previously showed that chronic dosing of apalutamide, an oral nonsteroidal AR antagonist, was effective in suppressing tumor growth in a preclinical mouse models of Pten-deficient prostate cancer and also changed the composition of the tumor immune microenvironment improving cytotoxic T cell activity. Moreover, we also showed that using AD as neoadjuvant therapy improved the antitumor activity and immune responses of combined JAK/PD-L1 blockade, whereas administered as concurrent or adjuvant therapy was ineffective. Our aim in this study is to determine the potential of using apalutamide in as combination therapy with immunotherapy and immune modulating agents. For this we have characterized the acute immune modulatory activity of apalutamide on mouse Pten-deficient and compared its activity against that of AD. Conditional prostate specific Pten/Trp53 double knockout mice were orchidectomized or treated with apalutamide (30 mg/kg/D) for five days. Tumor samples and lymphoid organs were collected and processed for immune profiling using a qRT-PCR focused panel, flow cytometry and/or immunohistochemistry. Prostates from orchidectomized mice tended to be smaller however there was no decrease in size for apalutamide treated mice. Notably, thymuses were significantly enlarged in both orchidectomized and apalutamide treated mice compared to control. Genes related to antigen presenting/dendritic cell (APC/DC) and activated DC were greater in apalutamide treated mice compared to vehicle treated or surgically castrated mice. This finding was consistent with an increased abundance of MHC-IIhi/CD80+ migratory DCs (CD11c+/XCR1+) in tumors of apalutamide treated mice. Tumor associated macrophage infiltration was also greater in apalutamide treated mice. Granulocyte infiltration was significantly greater after both castration and apalutamide therapy however the proportion of mature granulocytes was higher in castrated mice. T cell infiltration was comparable between orchidectomized and apalutamide treated mice, and regulatory T cell activity was increased in both groups compared to controls, but to a higher degree in orchidectomized mice. In summary, this provides critical data that will be essential when developing rational combinations with additional immunotherapies and immunomodulatory agents.

Citation Format: Marco A. De Velasco, Yurie Kura, Naomi Ando, Kazuko Sakai, Nobutaka Shimizu, Eri Banno, Masahiro Nozawa, Kazuhiro Fujita, Kazuhiro Yoshimura, Kazuto Nishio, Hirotsugu Uemura. Acute immune responses to apalutamide in mouse Pten-deficient prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1438.

Abstract 4468: Cross-species analysis and immunophenotyping using of a focused panel of immune-responsive genes

Immunotherapy has transformed the landscape of cancer therapy, unfortunately, not all patients can reap the benefits and identifying those patients that may benefit remains challenging. It is the consensus that patients with inflamed tumors are more likely to benefit from immunotherapies targeting immune checkpoints, and therapies aiming to stimulate or boost T cell anti-tumor immunity and modulate tumor inflammation are being investigated. Determining which type of immune therapy to administer depends largely on the patients immunophenotype. Various methods aimed at determining a tumor's immune profile are emerging or are available, of these, immune profiling by gene expression analysis is common. Several platforms are available, however, methods to analyze results vary. We previously used a transgenic mouse model of prostate cancer to identify target genes and developed a focused panel of immune-related genes. In addition, we designed a scoring system to profile the tumor's immune phenotype and assess tumor immune responses. Our aim is to extend the applicability of this analysis model to any platform capable of measuring these gene targets. As proof of concept for our analytical approach, we extended our assessment to human cancer by defining cancer specific immune profiles and assessing their clinical relevance. Our focused panel consisted of 115 genes (six reference/normalization genes and 109 immune-related genes) and our scoring system was based on an enrichment algorithm using various immune cell-specific signatures and immune related processes. We evaluated the robustness of this immunophenotyping approach using mRNA data from a cohort consisting of 8477 patients spanning 28 cancer types from The Cancer Genome Atlas (TCGA) Research Network. Our computational pipeline utilized unsupervised and machine learning approaches to identify and evaluate phenotype clusters from gene expression or immune signatures. In this study, Louvain clustering outperformed traditional hierarchical clustering. Using Louvain clustering, we identified distinct clusters from which immunophenotypes could be defined and compared these to various molecular and clinical features. Here, we summarize our findings and show that a minimal gene set effectively identified cancer immunophenotypes. This cross-species analysis corroborates our previous observation and paves the way for further development of our analysis model.

Citation Format: Marco A. De Velasco, Yurie Kura, Kazuko Sakai, Hideki Nakagaki, Kazuto Nishio, Hirotsugu Uemura. Cross-species analysis and immunophenotyping using of a focused panel of immune-responsive genes [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4468.

Abstract 1071: Targeting A2aR in mouse Pten-deficient prostate cancer

Inactivation of PTEN occurs frequently in advanced human prostate cancer and can promote an immunosuppressive tumor microenvironment (TME). Extracellular adenosine can be produced by tumors which can in turn modulate anti-inflammatory and immunosuppressive effects via interactions with the A2a receptor (A2aR). Here, we used a transgenic mouse model of Pten-deficient prostate cancer to characterize adenosine-mediated immunosuppression in the TME and evaluate the effects of A2aR blockade. Transcriptomic analysis of normal wildtype prostate and Pten-deficient prostate tumors revealed enriched signatures for genes downregulated after a A2aR knockdown or upregulated after A2aR stimulation. Moreover, androgen withdrawal led to increased expression of the A2aR-stimulated responsive genes Cxcl2/3/5, Il1b, S100a8, Ptgs2 and Thbs1. Immunohistochemical staining of CD73, the ecto-enzyme responsible for producing extracellular adenosine, showed heterogeneous staining ranging from negative to focally strong in epithelial cancer cells and was strongly expressed in immune cells. A2aR was also strongly expressed on immune infiltrates. We used the oral A2aR antagonist AZD4635 to determine the immunosuppressive activity of extracellular adenosine and evaluate its antitumor activity in the context of castration-naïve (CNPC), castration-sensitive (CSPC) and castration-resistant (CRPC) prostate cancer. Four weeks of treatment with AZD4635 led to a 12.1% (P=0.140) reduction of tumor burden compared to control mice. Notably a subset of these mice (4/8) had tumor reductions greater than 20%. For the CSPC/CRPC models, mice were orchidectomized and treated with apalutamide with or without AZD4635 for four or eight weeks to represent CSPC or CRPC phenotypes, respectively. In these settings, treatment with AZD4635 improved the reduction of tumor burden by 16.4% (P=0.165) and 16.8% (P=0.123) in CSPC and CRPC, respectively. Despite similar reduction rates between the cohorts, a greater proportion of AZD4635 treated mice were below the median distribution in the CRPC setting compared to the CSPC setting, 50% (4/8) vs 70% (7/10), respectively. Immunophenotyping showed an increase in the abundance of dendritic cells in tumors and tumor draining lymph nodes of AZD4635-treated mice in the CPNC setting. Whereas a shift in M2 to M1 macrophage, decrease of PD1hi CD8 T cells and an increase in genes related to cytotoxic lymphocyte activity (Gzma, Gzmb, Prf1, Klrg1, and B3gat1) were observed in AZDD4635 treated mice in the CRPC setting. Decreased expressions of immunosuppressive genes related to T regulatory cells (Ctla4, Il2ra, Itga2, Tigit, Foxp3) were noted in both CSPC and CRPC settings. Our findings show that targeting extracellular adenosine with AZD4635 is effective in a subset of mouse Pten-deficient tumors and provides evidence that suggests context-specific immune modulating activity by extracellular adenosine in prostate cancer.

Citation Format: Marco A. De Velasco, Yurie Kura, Noriko Sako, Naomi Ando, Kazuko Sakai, Masahiro Nozawa, Kazuhiro Yoshimura, Kazuhiro Yoshikawa, Alwin Schuller, Kazuto Nishio, Hirotsugu Uemura. Targeting A2aR in mouse Pten-deficient prostate cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1071.

Abstract 3416: Androgen deprivation following JAK1/2 and PD-L1 inhibition improves antitumor efficacy in mouse models of Pten-deficient prostate cancer

Recently, the tumor suppressor PTEN has been shown to function as an immune modulator and its inactivation is associated with mediating tumor immune evasion. We previously examined the effects of programmed death-ligand 1 (PD-L1) immune checkpoint blockade (ICB) in transgenic mouse models of Pten-null prostate cancer. However, anti-PD-L1 monotherapy was largely ineffective in immunologically cold castration-naïve tumors from intact mice but showed some activity when administered to castrated mice. Our previous immune profiling studies also revealed that while androgen withdrawal increased tumor inflammation, it also mediated the recruitment and accumulation of immunosuppressive cells such as regulatory T cells, M2-polarized macrophages and myeloid-derived suppressor cells (MDSCs). Interleukin-6 (IL-6)/signal transducer and activator of transcription-3 (STAT3) signaling is a key immune modulating pathway that is upregulated in both intact and androgen deprived tumors. Here, we evaluate the effectiveness of targeting PD-L1 and JAK/STAT signaling in preclinical models of Pten-null prostate cancer. Intact tumor bearing conditional Pten-knockout were treated for four weeks with an a-PD-L1 blocking antibody (clone D265A, mouse/IgG1 kappa) and/or the JAK1/2 inhibitor, AZD1480. Pharmacological treatments targeting PD-L1 and JAK1/2 (PJ) combinations were also evaluated as concurrent therapy with androgen deprivation (AD) by orchidectomy (PJ+AD), and as sequential therapy; two weeks AD followed by PJ (AD>PJ), and one week of PT followed by AD (PJ>AD). Combined PD-L1/JAK followed by AD was the only treatment combination that improved antitumor immune responses over monotherapy. Notably, flow cytometry studies showed that combined PD-L1/JAK potently abrogated PD-L1 expression in circulating dendritic cells in all settings. Evidence for enhanced antitumor immune response in PJ>AD was supported by increased numbers circulating effector memory CD8 T cells and CD355+CD8+ T cells (CD355 Class I MHC-restricted T cell-associated molecule (CRTAM) a marker for activated CD8 T cell), and increased CD8 T cell infiltration in tumors and a reduction of CD25+CD4+ regulatory T cells. The efficacy of the PJ>AD treatment combination was further tested and confirmed in a subcutaneous syngeneic allograft model using mice grafted with tumor blocks from Pten-deficient castration-resistant prostate cancer tumors. Together these results indicate that pretreatment with combined PD-L1/JAK blockade can decrease the immunosuppressive effects of androgen withdrawal and have the potential to restore antitumor immune activity in Pten-deficient prostate cancer.

Citation Format: Marco A. De Velasco, Yurie Kura, Naomi Ando, Noriko Sako, Kazuko Sakai, Kazuhiro Yoshikawa, Kazuto Nishio, Hirotsugu Uemura. Androgen deprivation following JAK1/2 and PD-L1 inhibition improves antitumor efficacy in mouse models of Pten-deficient prostate cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3416.

Abstract 3341: Systemic targeted JAK1/2 therapy for mouse Pten-deficient prostate cancer model influences the diversity and composition of the gut microbiome

Modulation of immune response by gut microbiota is believed to play a key role in determining response to anticancer therapy. Conversely, anticancer therapies have the potential to alter resident microbiota and the implications are unknown. We previously showed the antitumor efficacy of targeted JAK1/2 inhibition in a preclinical mouse model of prostate cancer and are now exploring its effectiveness as an immune modulator in prostate cancer therapy. We have also shown that androgen withdrawal can turn a poorly inflamed tumor into an inflamed tumor. In this follow-up study, we examine the effects of targeted JAK1/2 cancer therapy on the gut microbiome. For this we utilize 16S rDNA amplicon sequencing to profile the fecal microbiota (proximal and distal colon) of normal wildtype (WT) and tumor bearing conditional Pten-knockout (KO) mice treated for four weeks with the JAK1/2 inhibitor AZD1480 alone or in combination with orchidectomy. Mice treated with AZD1480 had lower tumor burden compared to control mice. Alpha diversity of fecal microbiota was greater in castrated KO mice compared intact WT and KO mice and mice receiving AZD1480 tended to have lower diversity regardless of castration status. Significant compositional differences were observed between the colonic microbiota of all experimental groups. Overall, mice treated with AZD1480, regardless of castration status resulted in decreased abundance of Clostridiaceae, F16, Gemellaceae, Odoribacteraceae, Rikenellaceae, and Lactobacillaceae and an increase of Paraprevotellaceae, Porphyromonadaceae, Verrucomicrobiaceae, Bifidobacteriaceae bacterial families. In the castration-naïve prostate cancer setting, enrichments of Akkermansia, Coprobacillus, Prevotella and Dehalobacterium and decreases of Lactococcus, Bacilli, Gemella, Lactobacillus, Desulfovibrio, and Odoribacter. Bifidobacterium, Desulfovibrio, Allobaculum, and Lactococcus were enriched in androgen deprived AZD1480-treated mice while Ruminococcus, and unclassified Clostridiaceae and F16 were decreased. We further used weighted correlation network analysis (WGCNA) to identify relevant networks of fecal microbiota associated with systemic targeted JAK1/2 inhibition. Using this approach, we have identified clusters of highly correlated taxa in the context of poorly inflamed and inflamed prostate tumors. Our findings show that systemic anticancer therapies can modify host microbiomes and provides insights into interactions between tumor, host microbiomes and immune modulating cancer therapies.

Citation Format: Marco A. De Velasco, Kazuko Sakai, Yurie Kura, Naomi Ando, Noriko Sako, Kazuhiro Yoshikawa, Kazuto Nishio, Hirotsugu Uemura. Systemic targeted JAK1/2 therapy for mouse Pten-deficient prostate cancer model influences the diversity and composition of the gut microbiome [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3341.

Abstract 3340: Prostate cancer alters gut microbiota in mice

Commensal gut bacteria are essential for maintaining intestinal homeostasis, however, aging, environmental factors and pathological conditions can cause changes in microbial composition resulting in dysbiosis. Specific microbial communities can alter host immune functions and are implicated in promoting carcinogenesis, tumor progression and therapeutic resistance. In this study we use a genetically engineered mouse model of prostate cancer to characterize changes in gut microbiota. 16S marker sequencing data was used to perform a comprehensive profile of the fecal microbiomes of conditional Pten-knockout mice harboring prostate tumors versus wildtype mice with normal prostate. Unsupervised clustering of microbiota was performed by hierarchical clustering. Community composition (beta diversity) was determine by principal components analysis, principal coordinates analysis (PCoA) and Adonis (permutational manova (PERMANOVA)) and the Shannon index was used to determine alpha diversity. The linear discriminant analysis effect size method was used to identify features associated with cancer and multiple linear regression was performed to determine relevant features of fecal bacteria collected from the proximal and distal colon. Predictive biomarkers associated with prostate cancer were identified with the Wilcoxon rank test. Weighted correlation network analysis (WGCNA) was performed to identify clusters of taxa associated with the presence of prostate cancer. Taxon set enrichment analysis (TSEA) was carried out to identify taxon sets associated with host genetic variations, and host intrinsic and extrinsic factors. Overall, the presence of prostate cancer did not affect diversity, however, significant compositional differences were observed between the cohorts (Bray-Curtis Adonis, P=0.003). At the family level S24_7, Odoribacteraceae, and Peptococcaceae were associated with cancer bearing mice while Bifidobacteriaceae, Peptostreptococcaceae, Coriobacteriaceae, Ruminococcaceae and Erysipelotrichaceae were associated with healthy mice (P<0.05). Prevotella, Lactobacillus reuteri and various unclassified Clostridiales, S24_7 and Rikenellaceae were identified as predictive biomarkers associated with cancer. Clusters of highly correlated taxa were identified in both cohorts and their functional influences are summarized. Overall, our study provides an in-depth overview of fecal microbiome in the context of mouse prostate cancer and provides the foundation to further investigate the interactions with disease progression and cancer therapy.

Citation Format: Marco A. De Velasco, Kazuko Sakai, Yurie Kura, Eri Banno, Naomi Ando, Noriko Sako, Kazuhiro Yoshikawa, Kazuto Nishio, Hirotsugu Uemura. Prostate cancer alters gut microbiota in mice [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3340.

Targeting castration-resistant prostate cancer with androgen receptor antisense oligonucleotide therapy

Sustained therapeutic responses from traditional and next-generation antiandrogen therapies remain elusive in clinical practice due to inherent and/or acquired resistance resulting in persistent androgen receptor (AR) activity. Antisense oligonucleotides (ASO) have the ability to block target gene expression and associated protein products and provide an alternate treatment strategy for castration-resistant prostate cancer (CRPC). We demonstrate the efficacy and therapeutic potential of this approach with a Generation-2.5 ASO targeting the mouse AR in genetically engineered models of prostate cancer. Furthermore, reciprocal feedback between AR and PI3K/AKT signaling was circumvented using a combination approach of AR-ASO therapy with the potent pan-AKT inhibitor, AZD5363. This treatment strategy effectively improved treatment responses and prolonged survival in a clinically relevant mouse model of advanced CRPC. Thus, our data provide preclinical evidence to support a combination strategy of next-generation ASOs targeting AR in combination with AKT inhibition as a potentially beneficial treatment approach for CRPC.

Abstract 5023: Immunomodulation of the multi-tyrosine kinase inhibitor TAS-115 in a mouse model of prostate cancer

Increasingly, immunotherapeutic agents are making their way into the clinic for the management of cancer, however, not all patients respond to single agent treatments. Susceptibility to immunotherapy is highly dependent on a tumor’s immune composition. Agents that are able modulate the tumor’s microenvironment (TME) to improve the balance between cytotoxic T cells and immunosuppressive cells such as myeloid-derived suppressor cells (MDSCs) M2-polarized macrophages and T regulatory cells (Tregs) are highly sought. We previously evaluated the preclinical activity of the multikinase inhibitor TAS-115 on mouse model of prostate cancer and showed that its antitumor effect was due in large part to its influence on the TME. In this study we examine the consequences of TAS-115 administration alone or in combination with androgen withdrawal via surgical castration or anti-androgen therapy with apalutamide, and focus on its influence on antitumor immunity. Pten/Trp53-double knockout mice were treated with TAS-115 alone or in combination with surgical castration or apalutamide for 4 weeks. Overall, TAS-115 reduced prostate tumor burden by 10.5%, however, 37.5% (3/5) of mice experienced no response (7.5%), while reductions of 14% and 27% were observed in 25% (2/8), 37.5% (3/5) of the remaining mice, respectively. A similar trend was noted in mice treated with the TAS/apalutamide combination but TAS plus surgical castration. Changes in cancer cell proliferation and apoptosis were insignificant with TAS-115 treatment, however, 2 of 4 TAS-115-responsive mice used for immunohistochemical (IHC) analysis showed a ~3-fold increased cleaved caspase-3 expression over non responsive mice. All TAS-115-treated mice showed reduced levels of phosphorylated STAT-3. Flow cytometric analysis of dissociated tumor samples revealed a reduction of tumor associated macrophages (TAMs) particularly when TAS-115 was given in combination with castration or apalutamide. Further analysis by IHC and qRT-PCR showed a M2-M1 polarization switch after TAS-115 therapy accompanied with decreased accumulation of monocytic MDSCs. An increase in tumor infiltrating neutrophils was also observed in mice receiving TAS-115. Although overall T cell infiltration was not improved TAS-115, there was an enhanced of activated CD8+ T cells, which was especially evident in responders. However, Treg infiltration was also increased after the administration of TAS-115. Overall our findings suggest that TAS-115 induced the reduction of immunosuppressive MDSCs and TAMs and may have induced an M2-M1 switch to provide a less immunosuppressive tumor microenvironment resulting in improved T cell mediated responses and provides evidence to support further investigation into using molecular targeting agents such TAS-115 as immune-modulators in combination with other immunotherapies to enhance or restore cytotoxic T cell activity.

Citation Format: Marco A. De Velasco, Yurie Kura, Noriko Sato, Naomi Ando, Kazuko Sakai, Kazuhiro Yoshimura, Masahiro Nozawa, Kazuhiro Yoshikawa, Kazuto Nishio, Hirotsugu Uemura. Immunomodulation of the multi-tyrosine kinase inhibitor TAS-115 in a mouse model of prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5023.

Abstract 3951: Apalutamide reworks the immune composition of prostate tumors

Prostate cancers depend on androgen receptor (AR) signaling for survival making it a major therapeutic target. Apalutamide is an oral nonsteroidal AR antagonist that is currently indicated for the treatment of patients with non-metastatic castration-resistant prostate cancer. Apalutamide hinders AR-mediated transcriptional activity by impeding AR nuclear translocation and binding to DNA in cancer cells. AR is also expressed by stromal and immune cells and can modulate innate and adaptive immune responses, moreover, androgen ablation can both hinder and enhance antitumor immunity. Thus far, success from immune checkpoint blockade monotherapy has been lacking in prostate cancer patients and novel strategies using of other modalities are being investigated. Here, we characterize the effect of apalutamide therapy on antitumor immunity in a preclinical mouse model of prostate cancer to assess its value as potential partner for combination with immunotherapy. Conditional prostate-specific Pten-knockout mice were treated with apalutamide (30 mg/kg/d, 5 days on/2 days off) or vehicle for a period of 4 or 8 weeks to coincide with androgen sensitivity and the shift towards castration resistance. Tumor reductions after 4 or 8 weeks of treatment with apalutamide were 38.2% (P<0.01) and 46.2% (P<0.001), respectively. Flow cytometric analysis of tumor tissues revealed 1.3 (P=0.033) and 1.9 (P<0.001) -fold increases of leukocyte (CD45+) infiltration in mice treated with apalutamide for 4 or 8 weeks, respectively. CD8+ T cell infiltration was 2.7-fold higher at 8 weeks, however, tumor reactive PD1+/CD8 T cells were 2-3-fold greater for apalutamide-treated mice at weeks 4 and 8. Quantitative immunohistochemical analysis confirmed increased intraepithelial CD8+ T and granzyme B-positive cells. Apalutamide treatment was also associated with increased peritumoral T regulatory cells and intraepithelial neutrophils. Immuno-profiling using a qRT-PCR-based panel of immune-relevant genes associated apalutamide therapy with an increased IFN-γ inflammatory signature, antigen presentation/dendritic cell, natural killer cell, T regulatory cell, tumor associated macrophage, and myeloid-derived suppressor cells (MDSC). These data also revealed a trend towards decreased CD8 T cell activation at week 8 accompanied by increased expression of the immunological checkpoints Ctla4, Tim3, and 2b4. In conclusion, our findings suggests that apalutamide-induced tumor cell death attracted phagocytes (macrophages and dendritic cells) that led to a innate and adaptive immune cell responses. While, cytotoxic T cell activity was improved, it was limited by the development of an immunosuppressive tumor microenvironment replete with MDSCs and T regulatory cells. Nevertheless, treatment with apalutamide turned immunologically “cold” tumors into more immunologically reactive tumors that may become more susceptible to targeted immunotherapy.

Citation Format: Marco A. De Velasco, Yurie Kura, Naomi Ando, Noriko Sato, Masahiro Nozawa, Kazuhiro Yoshimura, Kazuko Sakai, Kazuhiro Yoshikawa, Kazuto Nishio, Hirotsugu Uemura. Apalutamide reworks the immune composition of prostate tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3951.

Abstract 1613: Dietary isoflavone decreases prostate cancer progression and improves survival in conditional Pten/Trp53-deficient mice

Epidemiological data has shown that dietary practices can greatly influence cancer rates. Men in East Asian countries, men have significantly lower prostate cancer rates compared to their counterparts the US and Europe. Soybeans are a versatile and rich source of protein and its products constitute a rich portion of Asian diets. Recent interest in healthy eating has expanded the consumption of soy products which also provide a rich source of naturally occurring isoflavones and 17β-estradiol. In this study, we used roasted soybean flour (kinako), which contains high levels isoflavones glycosides and estradiol, as dietary soy source to determine the influence of isoflavones rich diets on prostate cancer. Six-week old conditional Pten/Trp53 double knockout mice were randomized and fed plain AIN-93M (Control) diets or a diets supplemented with kinako ad libitum. Concentrations of kinako were adjusted to for daily intakes of aglycone isoflavones (genistein, daidzein, and glycetein) of 400 (LDI) and 800 (HDI) mg. Mice were sacrificed at 16 and 20 weeks (n=6 mice/group) or maintained for survival assessment (n=8 mice/group). Dietary intake of kinako-supplemented diets did not influence the onset of prostatic intraepithelial neoplasia or tumor burden at the early stages. However, tumors from mice fed the HDI diet experienced reduced tumor proliferation rates. Moreover, mice fed LDI and HDI diets showed reduced androgen receptor (AR) protein expression levels as well as mRNA levels for the AR target genes Fkbp5, Nk3x3.1 and Timp4. Interestingly, mice on the LDI diet, but not the HDI, experienced longer times to disease progression (median times 264, 299 and 250 days for Control, LDI and HDI, respectively, P=0.663), tumor doubling (median times 14, 27 and 14 days for Control, LDI and HDI, respectively, P=0.083), cumulative survival (median times 292, 348 and 320 days for Control, LDI and HDI, respectively, P=0.199), and overall survival times (median times 28, 43 and 35 days for Control, LDI and HDI, respectively, P=0.324). The metastatic incidence was 33%, 14% and 14% for Control, LDI and HDI groups, respectively, P=0.631. We also investigated whether dietary intervention with kinako would impact previously stablished tumors. For this we fed kinako supplemented diets to conditional Pten-knockout mice with established tumors but no changes were observed in tumor burden, proliferation, apoptosis and AR activity. Together our data shows that long-term continuous ingestion of a diet rich in isoflavones may be necessary in order suppress tumor growth. Interestingly, this protective effect appears to be lost with high-doses of the dietary isoflavones. Further studies will need to be performed in order to decipher complex dynamic interplay between survival pathways isoflavones chemoprevention.

Citation Format: Yasunori Mori, Marco A. De Velasco, Yurie Kura, Eri Banno, Naomi Ando, Noriko Sato, Masahiro Nozawa, Kazuhiro Yoshimura, Kazuko Sakai, Kazuhiro Yoshikawa, Kazuto Nishio, Hirotsugu Uemura. Dietary isoflavone decreases prostate cancer progression and improves survival in conditional Pten/Trp53-deficient mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1613.

Abstract 4996: A real-time PCR-based approach to quantitatively assess tumor immune profiles and immune responses

Exciting breakthroughs in tumor immunology have led to the discovery and development of several promising immunotherapeutic strategies for cancer patients. Thus far, immune checkpoint inhibitors have been the most encouraging for solid tumors, however, treatment responses are observed in only a subset of patients and these appear to be primarily dependent on a tumor’s baseline immune profile. Additionally, tumors respond differently to immunotherapy and criteria to assess treatment responses are still being refined. We have identified a set of immune-related genes and developed a scoring system to profile the tumor’s immune status and assess immunological responses. In this study, we used a qRT-PCR-based approach to assess this panel and determine baseline tumor immune-profiles in an immunocompetent mouse model of Pten-null prostate cancer. We also assessed and compared tumor immune responses following androgen withdrawal (via surgical castration) and anti-PD-L1 immune checkpoint blockade. A total of 96 genes were selected for this focused panel which consisted of cell-type, immuno-responsive and housekeeping control genes. Core modules were designated based on functional gene associations which included antigen presentation, tumor inflammation, effector cells, immunomodulatory cells, immunosuppressive signaling and immune checkpoints. Core modules were further subdivided in to appropriately relevant sub-modules. A score for each submodule was calculated and a weighed score was then assigned for each core module. Tumor immunophenotypes based on core and sub-core immune scores (IS) were corroborated with immunohistochemical and/or flow cytometric analyses. Mouse castration-naïve prostate tumors exhibited low scores indicating a ‘”cold tumor” phenotype with little variation between individual mice. Androgen withdrawal induced cancer cell death in these tumors that in turn promoted immune cell infiltration. Core and sub-core IS of individual mice identified varied signatures reminiscent of immune excluded and inflamed “hot tumor” phenotypes. Short-term treatment with anti-PD-L1 blockade (clone D265A, mouse/IgG1 kappa) elicited an increased immune response signature in tumors from surgically castrated mice, but not in tumors from intact mice. Notably, discernable differences were noted among individual responders supporting the notion that responses to immune checkpoint may indeed be dependent on baseline tumor immune-profiles. In summary, androgen withdrawal appears to promote a “hotter” immunological phenotype in this model of prostate cancer, that is increased further by PD-L1 inhibition. Moreover, this investigation provides proof of concept evidence for a qRT-PCR-based biomarker approach for immuno-oncology.

Citation Format: Marco A. De Velasco, Yurie Kura, Noriko Sato, Naomi Ando, Kazuko Sakai, Yasunori Mori, Barry R. Davies, Masahiro Nozawa, Kazuhiro Yoshimura, Kazuhiro Yoshikawa, Kazuto Nishio, Hirotsugu Uemura. A real-time PCR-based approach to quantitatively assess tumor immune profiles and immune responses [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4996.

Generation of PTEN‑knockout (‑/‑) murine prostate cancer cells using the CRISPR/Cas9 system and comprehensive gene expression profiling

Phosphatase and tensin homolog (PTEN) deficiency is associated with development, progression, and metastasis of various cancers. However, changes in gene expression associated with PTEN deficiency have not been fully characterized. To explore genes with altered expression in PTEN‑deficient cells, the present study generated a PTEN‑knockout cell line (ΔPTEN) from a mouse prostate cancer‑derived cell line using the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR‑associated protein 9 (CRISPR/Cas9) gene editing system. Following transfection of the CRISPR/Cas9 construct, DNA sequencing was performed to identify deletion of the Pten locus and PTEN inactivation was verified by western blotting. The ΔPTEN cell line exhibited enhanced RAC‑alpha serine/threonine‑protein kinase phosphorylation and cyclin D1 expression. In addition, an increase in cell proliferation and colony formation was observed in the ΔPTEN cell line. Gene expression profiling experiments were analyzed with microarray and microRNA (miRNA) arrays. In the microarray analysis, 111 genes exhibited ≥10‑fold increased expression compared with the parent strain and mock cell line and 23 genes were downregulated. The only miRNA with increased expression of 10‑fold or more was mmu‑miR‑210‑3p. Genes with enhanced expression included genes involved in the development, progression, and metastasis of cancer such as Tet methylcytosine dioxygenase 1, twist family BHLH transcription factor 2, C‑fos‑induced growth factor and Wingless‑Type MMTV Integration Site Family, Member 3, and genes involved in immunosuppression such as Arginase 1. The results of the present study suggest that PTEN deficiency mobilizes a variety of genes critical for cancer cell survival and host immune evasion.

Abstract 947: Influence of abiraterone therapy on anti-tumor immunity in genetically engineered mouse prostate cancer models

Recent evidence has suggested that androgen deprivation therapies (ADTs) can influence tumor immune responses via androgen receptor (AR) regulation. On one hand, reports have indicated that certain ADTs can compromise T cell immune responses and enhance PD-L1 immune suppression, while others indicate that ADT can enhance anti-tumor responses via modulation of the apoptotic pathway. Abiraterone is a steroidal CYP17 inhibitor approved for the treatment of late-stage metastatic castration-resistant prostate cancer. In this study we use genetically engineered mouse models of prostate cancer (GEMMs-PCa) to investigate the antitumor activity of abiraterone and its influence on tumor immunity. In a mouse Pten-deficient prostate cancer model, chronic treatment with abiraterone acetate (40 mg/kg/d, 5 days on, 2 days off) reduced prostate tumor burden by 13.1% ± 9.0 (P=0.499) after four weeks of dosing and 30.5% ± 8.1 (P=0.0275) after eight weeks. Downregulation of classical mouse Ar-responsive genes (Fkbp5, Nkx3.1, Msmb and Timp4) confirmed the inhibition AR transcriptional activity after abiraterone therapy. In a model of advanced prostate cancer, driven by the conditional inactivation of Pten and Trp53, treatment with abiraterone after surgical castration modestly improved median overall survival from 7 days to 16 days vs. castration alone (P=0.240, n=8 mice/group). qRT-PCR-based analysis of a panel of 54 immune-responsive genes, revealed distinct expression signatures in abiraterone-treated tumors compared to tumors from orchidectomized mice. Relative to orchidectomized mice, tumors from abiraterone treated mice consistently demonstrated reduced mRNA levels of the T regulatory cell gene markers Cd4, Foxp3, Cd4, Tgfb1 and Il10. Furthermore, mRNA expression levels of representative immune checkpoint genes Cd274, Pdcd1lg2, Pdcd1 and Ctla4 were also lower in abiraterone treated mice. Follow-up immunohistochemical analysis showed a 1.8-fold increase of tumor infiltrating granzyme B-positive cells in tumors of mice treated with abiraterone compared to surgical castration. Our results show that abiraterone suppressed AR transcriptional activity and reduced tumor growth and progression in GEMMs-PCa. Our data also suggests that abiraterone induces lesser immunosuppressive responses than surgical castration and supports further investigation into developing rational combinations of ADT and immunotherapy in order to enhance therapeutic responses for patients suffering with prostate cancer.

Citation Format: Eri Banno, Marco A. De Velasco, Yurie Kura, Naomi Ando, Noriko Sato, Masahiro Nozawa, Kazuhiro Yoshimura, Kazuko Sakai, Kazuhiro Yoshikawa, Kazuto Nishio, Hirotsugu Uemura. Influence of abiraterone therapy on anti-tumor immunity in genetically engineered mouse prostate cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 947.

Abstract 1715: Treatment-dependent effects of androgen receptor signaling suppression on immune modulation in mouse Pten-deficient prostate cancer

Androgen-deprivation therapy (ADT) is the mainstay treatment for advanced metastatic prostate cancer. Treatments targeting androgen receptor (AR) signaling by androgen withdrawal or AR antagonists have been implemented in clinical practice, and clinical trials evaluating treatment combinations with immunotherapy are ongoing. However, AR expression is not limited to prostate epithelial cells and is expressed in several cell types including stromal and immune cells. Preclinical studies have shown that ADT can positively or negatively influence antitumor immunity depending on the treatment approach. To gain insights into the influence of ADT on tumor immunity, we compared surgical castration (Cast), AR-antisense oligonucleotide (ISIS581088, ISI), nonsteroidal antiandrogen (apalutamide, Apa) and hormonal antiandrogen (chlormadinone acetate, CMA) treatments in a mouse model of Pten-deficient prostate cancer. Conditional PSACre/Ptenf/f mice were treated for eight weeks and the antitumor activity and effects on immune organs were assessed. Compared to control mice, treatments with Cast, ISI, Apa and CMA significantly reduced tumor growth by 69.8%, 65.0%, 37.8%, and 40.8%, respectively, P<0.001. A significant enlargement of the thymus was seen in Cast (125 %) and Apa (45.8%)-treated mice whereas significant involution occurred after ISI (-73.3%) and CMA (-60.0%) treatments. Enlargement of spleen was noted in Cast (201.2%, P=0.009) ISI (96.3%, P=0.004) and Apa (55%, P=0.256)-treated mice. Draining lymph nodes were significantly larger in mice treated with ISI (48%, P=0.027), whereas their size decreased after treatment with Apa (-31.6%) and CMA (-15.4%). Focused gene expression profiling of immune and AR responsive genes by qRT-PCR array was performed on prostate tumor samples. Functional enrichment analysis of differentially expressed genes indicated distinct patterns of expression between treatments. Overall, the expression signatures of Cast and ISI were more closely concordant than those of Apa and CMA. Notably, genes associated with abnormal immune tolerance were enriched in Cast, Apa and CMA treatment groups. Genes associated with abnormal T-cell proliferation and PD-1 signaling were enriched in castrated mice. Our study shows that the AR signaling axis influences immune modulation and its effects on tumor immunity vary greatly depending on the pharmacologic approach for AR signaling inhibition. Rational combinations of ADT and immunotherapy will have to be carefully characterized and optimized in order to achieve their full therapeutic potential.

Citation Format: Marco A. De Velasco, Yurie Kura, Naomi Ando, Kazuko Sakai, Barry R. Davies, Youngsoo Kim, A. Robert MacLeod, Masahiro Nozawa, Kazuhiro Yoshimura, Kazuhiro Yoshikawa, Kazuto Nishio, Hirotsugu Uemura. Treatment-dependent effects of androgen receptor signaling suppression on immune modulation in mouse Pten-deficient prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1715.

Abstract 4825: Targeting PIM and AKT kinases impairs tumor growth and improves overall survival in a murine model of advanced castration-resistant prostate cancer

Background: Castration-resistant prostate cancer (CRPC) is an incurable disease with few treatment options, thus novel treatment strategies are required. PIM serine/threonine kinases (PIM-1, PIM-2, and PIM-3) are overexpressed in various cancers and are correlated with human prostate cancer progression. We previously evaluated the antitumor activity of the pan-PIM kinase inhibitor AZD1208 and showed that it could effectively suppress tumor growth in early-stage mouse models of castration-naïve and castration-resistant Pten-deficient prostate cancer. To fully determine the therapeutic potential of PIM inhibition we examined the therapeutic efficacy of AZD1208 in a mouse model of advanced prostate using clinically relevant endpoints. Additionally, since AKT and PIM kinases modulate survival processes by the phosphorylation of common substrates, we also examined the treatment combination with the pan-AKT inhibitor, AZD5363.

Methods: PSACre:Ptenflox/flox/Trp53flox/flox double knockout (Pten/P53-DKO) mice bearing palpable tumors with an initial size of 0.5 cm were surgically castrated and randomized to treatments with control vehicle, AZD1208 (60 mg/kg/day), AZD5363 (100 mg/kg/b.i.d) or AZD1208 + AZD5363 upon tumor progression or two weeks after castration, whichever occurred first. Tolerability was assessed by comparing differences in bodyweight and mouse health performance status. Therapeutic efficacy was determined by overall survival and antitumor activity was assessed by comparing tumor growth rates.

Results: Treatments appeared to be well tolerated by the mice and no significant differences were noted in bodyweight changes between treatment groups. Median overall survival times were 21, 28, 28 and 35 days for vehicle, AZD1208, AZD5363 and AZD1208+AZD5363 treated mice , respectively, P=0.027. Median time to tumor doubling (1→2 cm) was longer for AZD1208 and AZD1208+AZD5363 treatment groups compared to vehicle or AZD5363, 28, 21, 14 and 14 days, respectively, P=0.005.

Conclusions: Treatments with AZD1208 suppressed CRPC growth and improved overall survival times in Pten/P53-DKO mice. Furthermore, targeting both PIM and AKT kinases with combination therapy improved overall survival. This study provides evidence to support further development of therapeutic strategies targeting PIM and AKT for the management of human advanced prostate cancer.

Citation Format: Marco A. De Velasco, Yurie Kura, Naomi Ando Ando, Noriko Sato, Barry R. Davies, Masahiro Nozawa, Kazuhiro Yoshimura, Kazuhiro Yoshikawa, Kazuto Nishio, Hirotsugu Uemura. Targeting PIM and AKT kinases impairs tumor growth and improves overall survival in a murine model of advanced castration-resistant prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4825.

Abstract 4439: Genetic alterations in specific RNA processing genes is associated with poor patient outcome in prostate cancer

Altered expression of splicing factors has been implicated in human cancers but their role in disease progression is complex due to the magnitude of potential protein products. We previously showed that androgen withdrawal led to increased alternatively spliced products in mouse Pten-deficient prostate tumors. Here, we perform gene expression analysis this mouse prostate cancer model to identify candidate mRNA processing genes implicated in the progression to castration-resistant disease. Genome-wide analysis revealed a set of 43 unique RNA processing and splicing factor genes associated with the progression to castration-resistant disease. Expression analysis of this gene set was examined in a pan-cancer analysis of 30 TCGA cancer studies covering 26 human cancer types. Alterations of this gene set (z-score threshold variances >2) were found in 70.5% (6978/9896) of cases. The median percentage of affected cases across the studies ranged from 28.2-98.2% with a median of 78.3%. In prostate cancer patients (TCGA-Prostate Adenocarcinoma (PRAD)), 65.7% (327/497) of the cases had mRNA alterations of this gene set. Twenty-seven of the 30 studies had survival data, of these only three studies indicated poor disease-free survival (DSF) outcomes with mRNA alterations: TCGA-PRAD, P=0.00616; TCGA-Brain Lower Grade Glioma (BLGG), P=0.0088; TCGA-Thymoma, P=0.0265. In the TCGA-PRAD study, the median time to DSF was 81.2 months in altered cases vs. median not reached in non-altered cases. In three studies, favorable outcomes were seen in cases with alterations in the gene set: TCGA-Uveal melanoma, TCGA- Glioblastoma Multiforme and TCGA-Lung Squamous Cell Carcinoma. TCGA-BLGG was the only study to show a statistically significant association between gene set alterations and overall survival (OS), P=0.0206. In TCGA-PRAD, median OS was 115 months in altered cases vs. median not reached in non-altered cases P=0.262. We further analyzed the scope of molecular alterations of this gene set in prostate cancer patients, overall, 78.9% (393/498) of the cases had gene alterations consisting of mutations, amplifications, deletions, and mRNA downregulation in six (1.2%), two (0.4%), 49 (9.8%), 193 (38.8%), and 143 (28.7%) cases, respectively. Notably a strong association was revealed for poor OS for cases with mutations/copy number alterations (P=0.00621). These data suggest that molecular alterations in specific RNA processing genes can cooperate to promote specific cancer types and further studies will be required to fully understand the prostate cancer-driving events in this gene set.

Citation Format: Koichi Sugimoto, Marco A. De Velasco, Yurie Kura, Kazuko Sakai, Masahiro Nozawa, Kazuhiro Yoshimura, Kazuhiro Yoshikawa, Kazuto Nishio, Hirotsugu Uemura. Genetic alterations in specific RNA processing genes is associated with poor patient outcome in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4439.

Abstract 3737: Apalutamide (ARN-509) demonstrates therapeutic efficacy in genetically engineered mouse models of Pten-deficient prostate cancer

Apalutamide (ARN-509) is an oral nonsteroidal androgen receptor (AR) antagonist that is currently undergoing late-stage clinical development for the management of castration-resistant prostate cancer (CRPC). In this study, we use genetically engineered mouse prostate cancer (GEM-PCa) models to examine the preclinical activity of apalutamide in the setting of castration-naïve and castration-resistant disease and delve into the molecular mechanisms underlying CRPC progression. In an early-stage efficacy model of Pten-deficient prostate cancer, four weeks of treatment with apalutamide (30 mg/kg/d) significantly reduced tumor burden by 33.5% (P=0.002) in castration-naive mice but did not alter tumor burden in orchidectomized mice bearing castration-resistant tumors. Interim analyses from long-term survival studies, using models of advanced prostate cancer driven by the conditional inactivation of Pten and Trp53, have indicated improved median overall survival (OS) times in both castration-naïve (17 days, 95% CI 11.6-38.9 in control mice vs. 36 days, 95% CI 21.8-56.9 in apalutamide treated-mice, P=0.280) and CRPC settings (21 days, 95% CI 15.1-25.8 in control mice vs. 40 days, 95% CI 31.2-50.1 in apalutamide treated-mice, P=0.001). In the CRPC model, time to tumor progression was significantly longer for mice treated with apalutamide, median time 20 days 95% CI 9.8-20.6, in apalutamide treated-mice vs. 7 days, 95% CI 5.1-10.8, in control mice, P=0.029. Molecular characterization indicated increased PI3K-AKT signaling in response to treatment with apalutamide in castration-naïve prostate tumors. In vitro studies using four mouse prostate cancer cell lines revealed synergistic responses with apalutamide and AKT inhibition (GSK-690693), the mean combination index at 50% effective dose ranged from 0.585-0.791. In vivo efficacy studies of combination therapy in Pten-KO mice showed tumor burden reductions of 33.4%, 17.7% and 40.9% in apalutamide, GSK-690693 and combination treatments, respectively, P=0.002 in the castration-naïve setting, and reductions of 1.0%, 12.7% and 15.5% in apalutamide, GSK-690693 and combination treatments, respectively, P=0.101 in the CRPC setting. Studies to further evaluate the therapeutic benefit of apalutamide plus PI3K/AKT signal blockade in models of advanced prostate cancer are underway. In conclusion, our findings show that apalutamide is active in GEM-PCa models and support further investigation for developing rational treatment combinations for the management of advanced prostate cancer.

Citation Format: Marco A. De Velasco, Masahiro Nozawa, Yurie Kura, Naomi Ando, Noriko Sato, Kazuhiro Yoshimura, Kazuko Sakai, Kazuhiro Yoshikawa, Kazuto Nishio, Hirotsugu Uemura. Apalutamide (ARN-509) demonstrates therapeutic efficacy in genetically engineered mouse models of Pten-deficient prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3737.

Abstract 2868: Preclinical evaluation of the multi tyrosine kinase inhibitor TAS-115 in genetically engineered mouse models of prostate cancer

The tumor microenvironment (TME) is comprised of various cell types that can contribute to malignancy by promoting cancer cell proliferation, immune evasion, angiogenesis and metastasis. Here we use genetically engineered mouse models of prostate cancer to show that TAS-115, a multi-kinase inhibitor that targets c-MET, VEGF-R, and CSF1-R signal pathways, suppresses prostate cancer growth by targeting the TME. Conditional Pten-knockout (Pten-KO) and Pten/Trp53-double knockout (Pten/P53-DKO) mice were used to evaluate the pharmacodynamic activity of TAS-115 and efficacy studies were carried in 16-week-old Pten/P53-DKO mice. Four weeks of treatment with TAS-115 significantly suppressed prostate tumor growth in by 22.6%, P=0.041. Epithelial cancer cell proliferation in was reduced by 28.6%, (P=0.072) in TAS-115-treated mice, however, no changes were seen in the induction of apoptosis. Immunohistochemical (IHC) analysis revealed potent but focal inhibition of ERK phosphorylation in both epithelial and stromal cells. A tendency for reduced phosphorylation of AKT and STAT3 were also noted in mice receiving TAS-115. IHC analysis also revealed strong inhibition of CSF1-R phosphorylation in tumor infiltrating immune cells of mice treated with TAS-115. We also examined the effects of TAS-115 in a castration-resistant Pten/P53-DKO prostate tumor model. In this model, we did not note statistically significant reductions in tumor burden, however, 2 of 6 (33.3%) mice treated with TAS-115 had noticeably reduced tumor burden (>20% reduction relative to median overall tumor burden levels). No significant changes were observed in overall tumor proliferation, apoptotic rates or in AKT and ERK phosphorylation levels in the tumors of TAS-115-treated mice however, a significant reduction of STAT3 phosphorylation staining index (-39.3, P=0.0424) was observed, the prostates tumors of mice receiving TAS-115. Similar to castration-naïve treated tumors, CSF1-R phosphorylation was strongly inhibited in infiltrating immune cells of castration-resistant prostate tumors from TAS-115-treated mice. Unsupervised clustering from a qRT-PCR-based focused panel of immune-responsive genes showed greater consistency and a higher magnitude of response in TAS-115-treated mice in the castration-resistant tumor model. Further analysis of microvessel density showed a 20% reduction in tumor neovascularization in both intervention models. The direct antitumor effect of TAS-115 on cancer cells was examined in vitro using mouse prostate cancer cell lines. In these studies, TAS-115 showed moderate growth inhibition. Overall our studies show that TAS-115 is capable of suppressing prostate tumor growth by acting primarily on the TME and provide evidence to support further investigation of TME modulation using small molecule multi-kinase inhibitors.

Citation Format: Marco A. De Velasco, Yurie Kura, Naomi Ando, Noriko Sato, Masahiro Nozawa, Kazuhiro Yoshimura, Kazuko Sakai, Kazuhiro Yoshikawa, Kazuto Nishio, Hirotsugu Uemura. Preclinical evaluation of the multi tyrosine kinase inhibitor TAS-115 in genetically engineered mouse models of prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2868.

Efficacy of targeted AKT inhibition in genetically engineered mouse models of PTEN-deficient prostate cancer

The PI3K/AKT pathway is frequently altered in advanced human prostate cancer mainly through the loss of functional PTEN, and presents as potential target for personalized therapy. Our aim was to determine the therapeutic potential of the pan-AKT inhibitor, AZD5363, in PTEN-deficient prostate cancer. Here we used a genetically engineered mouse (GEM) model of PTEN-deficient prostate cancer to evaluate the in vivo pharmacodynamic and antitumor activity of AZD5363 in castration-naïve and castration-resistant prostate cancer. An additional GEM model, based on the concomitant inactivation of PTEN and Trp53 (P53), was established as an aggressive model of advanced prostate cancer and was used to further evaluate clinically relevant endpoints after treatment with AZD5363. In vivo pharmacodynamic studies demonstrated that AZD5363 effectively inhibited downstream targets of AKT. AZD5363 monotherapy significantly reduced growth of tumors in castration-naïve and castration-resistant models of PTEN-deficient prostate cancer. More importantly, AZD5363 significantly delayed tumor growth and improved overall survival and progression-free survival in PTEN/P53 double knockout mice. Our findings demonstrate that AZD5363 is effective against GEM models of PTEN-deficient prostate cancer and provide lines of evidence to support further investigation into the development of treatment strategies targeting AKT for the treatment of PTEN-deficient prostate cancer.

Abstract 751: Characterization of STAT3 activation in human prostate cancer

Signal transducers and activators of transcription (STATs) were initially associated with cytokine signal transduction pathways but are now also recognized as key modulators of key survival processes in in various cancers. Activation of STAT3 occurs by the binding of various cytokines to its receptors leading to the activation of the JAK/ STAT3 signaling pathway. Interleukin-6 (IL-6) has been implicated in regulating growth of various malignant tumors. Activated IL-6 has also been shown to be elevated in the sera from patients with metastatic prostate cancer, and persistent activation of STAT3 is a common feature. To better characterize the potential role of JAK/STAT3 as a therapeutic target for advanced prostate cancer, we examined expression patterns of activated STAT3 in 111 cases of localized prostate cancer from patients who underwent radical prostatectomy. Association studies were conducted with clinicopathological characteristics and biochemical recurrence. We also analyzed the expression of IL-6/KAK/STAT3 genes from RNA-sequencing data form the Cancer Genome Atlas Prostate Adenocarcinoma (TCGA-PRAD) data set and its association to long-term outcomes. Immunohistochemical analysis revealed that 11.7%, 42.3% and 45.9% of patients had high, moderate or low/negative expression of phosphorylated-STAT3 (Tyr705). Cancerous glands tended to have higher STAT3 expression compared to paired normal adjacent tissue, P=0.088. No correlations were observed between STAT3 expression and clinicopathological parameters. Patients with moderate-high p-STAT3 expression tended to experience shorter times to biochemical recurrence (median time, 15 months) compared to patients with low/negative STAT3 activity, (median time to recurrence not reached, P=0.064). Cluster analysis suggested a trend for decreased disease-free survival for patients with high IL-6/KAK/STAT3 gene expression signature. Our data suggests an association between STAT3 signaling and prostate cancer recurrence and provides clinical evidence to support JAK/STAT3 as a potential therapeutic target for patients with advanced prostate cancer.

Citation Format: Marco A. De Velasco, Yuji Hatanaka, Yurie Kura, Naomi Ando, Kazuko Sakai, Koichi Sugimoto, Masahiro Nozawa, Kazuhiro Yoshimura, Kazuhiro Yoshikawa, Kazuto Nishio, Hirotsugu Uemura. Characterization of STAT3 activation in human prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 751. doi:10.1158/1538-7445.AM2017-751

Abstract 4702: PD-L1 blockade in preclinical models of PTEN-deficient prostate cancer

Immune checkpoint blockade with antibodies aimed at enhancing antitumor immunity have become an attractive therapeutic option. Establishing immunocompetent and clinically relevant models that predict treatment response is essential for the development of novel immunotherapies. To gain better insights into the preclinical evaluation of novel immunotherapeutic strategies, we used genetically engineered mouse models of PTEN-deficient prostate cancer. We first analyzed the transcriptome in castration-naïve prostate tumors and the progression to castration-resistant disease. Comparative analyses were performed between age-matched normal prostate and PTEN-/- prostate tumor samples from castration-naïve mice and, at 4 weeks (castration-sensitive) and 10 weeks (castration-resistant) post-surgical castration. Pathway and gene-set enrichment analysis indicated that abnormal tumor immunity was strongly associated with the progression to castration resistance. Chemokine signaling, B cell receptor and T cell receptor signaling pathways were among the top dysregulated pathways, and gene signatures of suppressed tumor immunity were enriched in castration-resistant tumors. Higher expression patterns of the programmed cell death protein 1(PD-1) and its ligand (PD-L1) were observed in castration-resistant tumors compared to castration-naïve tumors. We also characterized immune expression profiles in more aggressive tumors from PTEN/P53 double knockout (DKO) mice. PD-L1 was strongly expressed cancer cells, but a higher presence of PD-1+, CD45+ and F4/80+ stromal infiltrating immune cells in was observed in castration-resistant tumors. PD-1/PD-L1 blockade with antibodies against mouse PD-L1 increased CD45+ tumor infiltrating lymphocytes (TILs) in an early model of PTEN/P53-deficient castration-resistant prostate cancer. PTEN/P53-DKO mice with advanced castration-naïve prostate cancer tended to experienced longer overall survival after treatment with PD-1/PD-L1 blockade compared to vehicle and isotype controls, median survival 23, 14 and 11 days, respectively, P=0.458. A higher number of CD45+ TILs was observed in tumors of mice receiving the anti-PD-L1 treatment. Interim analysis of PD-1/PD-L1 blockade on a model of advanced PTEN/P53-deficient castration resistant prostate cancer (CRPC) has thus far shown that mice receiving treatment experience significantly longer survival (P=0.017, median survival not yet reached). Our findings show that castration-resistance promotes tumor immune suppression in mouse PTEN-deficient prostate cancer and suggest that this phenomenon can be reversed pharmacologically with anti-PD-L1 blockade. Thus, we provide preclinical evidence for immune checkpoint blockade as a potentially promising prostate cancer therapy.

Citation Format: Marco A. De Velasco, Yurie Kura, Naomi Ando, Noriko Sato, Kazuko Sakai , Barry R. Davies, Koichi Sugimoto, Masahiro Nozawa, Kazuhiro Yoshimura, Kazuhiro Yoshikawa, Kazuto Nishio , Hirotsugu Uemura. PD-L1 blockade in preclinical models of PTEN-deficient prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4702. doi:10.1158/1538-7445.AM2017-4702

Abstract 1582: Therapeutic potential of combination therapy using a next generation antisense oligonucleotide targeting the androgen receptor and AKT inhibition with AZD5363 in genetically engineered mouse models of prostate cancer

Prostate cancer is highly dependent on androgen receptor (AR) and PI3K/AKT signaling pathways for survival and disease progression. Preclinical evidence suggests that combinatorial approaches targeting both AR and PI3K/AKT activity improves treatment efficacy. However, sustained responses from traditional and next-generation anti-androgen therapies targeting AR remain elusive in clinical practice due to inherent/acquired resistance resulting in lethal castration-resistant prostate cancer (CRPC). Mechanisms for continued AR transcriptional activity may be ligand dependent or independent but still require AR gene expression. Persistent AR gene expression is a key feature of CRPC. Thus, blocking AR gene expression by antisense oligonucleotides (ASO) is a logical approach to CRPC. We previously showed that monotherapy with ISIS581088, a generation 2.5 ASO targeting mouse AR, demonstrated strong antitumor activity in a transgenic mouse model of PTEN-deficient prostate cancer. In this study we show the antitumor effects of combined therapy of ISIS581088 and AZD5363, a potent AKT inhibitor and demonstrate the therapeutic benefit of combination therapy in a clinically relevant mouse model of CRPC. Sixteen-week-old mice with PTEN-/- castration-naïve prostate tumors were treated with ISIS581088 and AZD5363 alone or in combination for four weeks. Tumor growth inhibition rates were 41.2%, 20.2% and 54.4% for ISIS581088, AZD5363 and ISIS581088/AZD5363 treatment groups, respectively, P<0.001. In a model of mouse CRPC, 16-week-old mice with PTEN-/- castration-resistant prostate tumors (eight weeks post castration) experienced reduced tumor burden with all treatments but no enhancement was observed when the compounds were administered in combination compared with monotherapy drug treatments. In a randomized trial of advanced CRPC in PTEN/P53 double knockout mice, combination therapy significantly increased overall survival. Median survival were 18, 17 21, 22, and 38 days for control vehicle, control ASO, ISIS581088, AZD5363 and ISIS581088/AZD5363 treatment groups, respectively, P=0.041. In conclusion, our data shows that combination therapy significantly reduced tumor burden in mice with castration-naïve tumors compared to those treated with monotherapy. Notably, combination therapy did not produce an additive effect in an early stage CRPC intervention model. Still, combination therapy demonstrated a clear advantage in prolonging overall survival in a long-term randomized mouse trial of PTEN/P53-deficient CRPC. Thus, our data provides preclinical evidence to support that next generation ASOs targeting AR in combination with AKT inhibition is a potentially effective treatment approach for CRPC.

Citation Format: Marco A. De Velasco, Yurie Kura, Naomi Ando, Koichi Sugimoto, Kazuko Sakai, Barry R. Davies, Youngsoo Kim, A. Robert MacLeod, Masahiro Nozawa, Kazuhiro Yoshimura, Kazuhiro Yoshikawa, Kazuto Nishio , Hirotsugu Uemura. Therapeutic potential of combination therapy using a next generation antisense oligonucleotide targeting the androgen receptor and AKT inhibition with AZD5363 in genetically engineered mouse models of prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1582. doi:10.1158/1538-7445.AM2017-1582

Abstract 1096: Co-targeting of AKT and Pim kinases in mouse PTEN-deficient prostate cancer

AKT and Pim kinases modulate programmed cell death by the phosphorylation of common substrates that regulate apoptosis and other survival processes. Evidence suggests that the antitumor effects of targeted Akt inhibition can be inhibited or diminished by the JAK/STAT-dependent induction of Pim kinases. In this study we examined the therapeutic potential of co-targeting AKT and Pim in a genetically engineered mouse model of prostate cancer driven by the conditional inactivation of PTEN. The antitumor effects of AZD5363, a pan AKT inhibitor, and AZD1208, a highly potent Pim kinase inhibitor, were investigated as monotherapy or in combination on mice harboring castration-naïve prostate tumors and mice that developed castration-resistant disease. Mice were randomized treated for four weeks. Safety and tolerability was assessed by bodyweight changes. Antitumor activity was determined by differences in tumor burden, proliferation and apoptosis and histology. Molecular activity was assessed by examining the phosphorylation of common substrates by western blot analysis. Treatments were well-tolerated and no significant differences in bodyweight changes were observed. In castration-naïve prostate tumors, treatments with AZD5363, AZD1208 and AZD5363/AZD1208 resulted in 11.9%, 13.5% and 36.9% reductions of tumor burden compared to vehicle treated controls, respectively, P<0.001. The treatment combination of AZD5363/AZD1208 demonstrated significant antitumor activity compared to monotherapy, P<0.001. In the castration-resistant tumors, treatments with AZD5363, AZD1208 and AZD5363/AZD1208 resulted in 21%, 9.5% and 27% reductions of tumor burden compared to vehicle treated controls, respectively, P<0.004. Although the differences in in tumor burden were not statistically between monotherapy and combination therapy, a notable degree of tumor gland regression was observed in tumors treated with AZD5363/AZD1208. Overall, combination therapy showed a synergistic effect by inhibited or impaired phosphorylation of PRAS40, eIF4B and BAD in both castration-naïve and castration-resistant tumor models. Inhibition of both pathways enhanced the reduction of tumor cell proliferation and increased apoptosis. Overall, our findings provide in vivo data to support redundancy between AKT/Pim survival pathways and suggest that a therapeutic approach of combined AKT/Pim kinase inhibition may be possible therapeutic approach for AKT-driven prostate cancer.

Citation Format: Marco A. De Velasco, Koichi Sugimoto, Yurie Kura, Naomi Ando, Noriko Sato, Kazuko Sakai, Barry R. Davies, Dennis Huszar, Masahiro Nozawa, Kazuhiro Yoshimura, Kazuhiro Yoshikawa, Kazuto Nishio, Hirotsugu Uemura. Co-targeting of AKT and Pim kinases in mouse PTEN-deficient prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1096. doi:10.1158/1538-7445.AM2017-1096

Abstract 2014: Alternative splicing is a frequent event in mouse PTEN-deficient prostate cancer

Castration-resistant prostate cancer (CRPC) remains an incurable disease and presents a major challenge for the development of novel treatment strategies. Alternative splicing occurs as a common natural phenomenon and promotes diversity, however, cancer-related alternative splicing events have been shown to contribute to disease progression and promote therapeutic escape. In prostate cancer, key genes required for normal biological function are frequently alternatively spliced resulting in altered phenotypes. Novel therapeutic strategies targeting the alternative splicing machinery are being developed and tested. Here, characterized the conditional PTEN-deficient mouse model of prostate cancer to determine its relevancy as preclinical tool for the development and efficacy determination of novel therapeutic strategies targeting aberrant alternative splicing. For this, we used the Affymetrix GeneChip mouse transcriptome assay to perform comparative analysis of the transcriptomes of normal prostate tissue and PTEN-deficient castration-naïve, castration-sensitive (4 weeks post-castration), and castration-resistant (10 weeks post-castration) prostate cancers. Clustering analysis revealed genes enriched with the functions involved in mRNA splicing and processing in mice with prostate tumors. Moreover, alternative splicing events were more prevalent in castration-sensitive tumors (>2.5-fold) compared to castration-naïve and castration resistant tumors. Exon skipping (cassette exon), was the most common splicing event observed in all conditions. Additionally, alternative splicing was observed in several genes frequently associated with human prostate cancer including CD44, AR, p53, Bcl2l1 and Klf6 among others. Collectively, our data shows that alternative mRNA splicing is a frequent event in mouse PTEN-deficient prostate cancer and supports a role for alternative splicing dysregulation and the pathogenesis of the disease. Furthermore, this mouse model may also provide a suitable platform to study current therapeutic approaches targeting alternative splicing.

Citation Format: Marco A. De Velasco, Yurie Kura, Kazuko Sakai, Yoshihiko Fujita, Yosuke Togashi, Masato Terashima, Kazuhiro Yoshikawa, Kazuto Nishio, Hirotsugu Uemura. Alternative splicing is a frequent event in mouse PTEN-deficient prostate cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2014.

Abstract 4315: Effects of increased dietary fat consumption on prostate cancer progression in genetically engineered mice

Prostate cancer is a highly heterogeneous disease and evidence indicates that lifestyle and environmental factors can contribute to cancer-related deaths. Accumulating data also suggests that increased dietary fat consumption may promote and increase the risk of prostate cancer-related morbidity and mortality. However, data between studies is inconsistent and a direct link between increased consumption of dietary fat and the promotion of prostate cancer remains unclear. Here, we present our findings from a preclinical study of increased dietary fat consumption and its effects on prostate tumor growth and progression using genetically engineered mouse models of prostate cancer. We determined the effects of a high fat diet on tumor cell proliferation and apoptosis in vivo using a well-established mouse model of prostate cancer. Twenty-week-old mice, with conditional biallelic deletion of PTEN, harboring castration-naïve or castration-resistant prostate tumors were randomized and assigned to a standard laboratory diet (4% fat) or a high-fat diet (HFD, 13.6% fat) for 8 weeks. In both tumor models, mice fed a HFD had increased expression levels of proteins associated with proliferation and decreased levels of apoptosis markers. To determine the long term effects of a HFD, we used a mouse model of advanced prostate cancer. Mice with concomitant inactivation of PTEN and p53 develop tumors that progress quickly and are characterized with increased metastatic development and decreased survival compared to PTEN knockout mice. PTEN/p53 double knockout mice were randomized and assigned to control or HFD experimental groups after weaning. Our findings revealed that mice fed a HFD resulted in obesity that led to decreased progression-free survival and overall survival rates compared to mice fed a standard diet. Our results provide evidence to support the effects of high dietary fat consumption and increased prostate cancer risk, and provide a platform to investigate chemoprevention strategies.

Citation Format: Marco A. De Velasco, Yurie Kura, Yuji Hatanaka, Takashi Oki, Yutaka Yamamoto, Koichi Sugimoto, Yasunori Mori, Kazuhiro Yoshimura, Masahiro Nozawa, Kazuhiro Yoshikawa, Kazuto Nishio, Hirotsugu Uemura. Effects of increased dietary fat consumption on prostate cancer progression in genetically engineered mice. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4315.

Abstract 954: Analysis of noncoding RNA expression in a mouse model of PTEN-deficient prostate cancer

Prostate cancer is a heterogeneous disease that is driven by combined genetic and epigenetic alterations. A significant portion of the mammalian genome consists of non-coding regions of RNA. Increasing evidence has shown that these noncoding RNAs (ncRNAs) have significant roles in the epigenetic regulation of several cellular processes, and their dysregulation can contribute to tumorigenesis and promote disease progression in many cancer types. In order to gain better insights into the potential roles of ncRNAs in prostate cancer, we used a genetically engineered mouse model of prostate cancer to perform a comparative analysis of the cancer transcriptome and the landscape of ncRNAs in castration-naïve prostate tumors and the progression to castration-resistant disease. Whole transcription arrays were used to explore both messenger (mRNA) and long intergenic non-coding RNA (LincRNA) transcript expression in normal prostate tissue from wildtype mice and prostate tumors from conditional PTEN-knockout mice. Comparative analyses were performed between prostate tumor samples from castration-naïve mice and, at 4 weeks and 10 weeks post-surgical castration. Altered expression of ncRNAs was most commonly observed and accounted for 56.2% (2370/4216), 47.6% (4460/9366) and 41.57% (1545/3717) of the total genes differentially expressed between normal mouse prostate and prostate tumors from castration-naïve, 4 weeks post-castration and 10 weeks post-castration, respectively. We also profile the expression of relevant cancer-related lincRNAs present in these models. Overall, our analyses provide data to support a role of LincRNA dysregulation in the pathogenesis of PTEN-deficient prostate cancer, and suggest that these mouse models might provide a potential preclinical tool to test candidate prospective therapies targeting ncRNAs.

Citation Format: Marco A. De Velasco, Yurie Kura, Kazuko Sakai, Yuji Hatanaka, Yoshihiko Fujita, Yosuke Togashi, Masato Terashima, Kazuhiro Yoshikawa, Kazuto Nishio, Hirotsugu Uemura. Analysis of noncoding RNA expression in a mouse model of PTEN-deficient prostate cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 954.

Abstract 3864: The Jak1/2 inhibitor AZD1480 suppresses tumor growth and metastasis in genetically engineered mouse models of PTEN-deficient prostate cancer

Activation of signal transducer and activator of transcription (STAT) 3 via the interleukin 6 (IL-6)/IL-6R/Janus kinase (JAK) signaling axis is a feature common in patients with advanced human prostate cancer and has been associated with poor prognosis. STAT3 can promote CRPC growth by activating the androgen receptor signaling pathway. It can also promote survival by modulating tumor cell proliferation, epithelial to mesenchymal transition, angiogenesis and immune response. However, recent preclinical data suggests that STAT3 may also act as a tumor suppressor in PTEN-deficient prostate cancer. In this study, we investigated the effectiveness of AZD1480, a potent JAK1/2 inhibitor, in genetically engineered mouse models of prostate cancer driven by the loss of PTEN and PTEN/P53. In vivo pharmacodynamic studies using conditional PTEN-deficient mice demonstrated that AZD1480 strongly inhibited STAT3 phosphorylation. Moreover, AZD1480 monotherapy in PTEN-deficient mice harboring castration-naïve or castration-resistant prostate tumors resulted in tumor growth reductions of 24.8%, P<0.001 and 15.8%, P<0.001, respectively, compared to vehicle treated control mice. Mice treated with AZD1480 also exhibited reduced levels of tumor cell proliferation and microvessel density, and increased apoptosis compared to controls. Clinically relevant outcomes were evaluated in a late-stage model of prostate cancer driven by the conditional inactivation of PTEN and P53. In this model, PTEN/P53 double knockout mice with established tumors were randomized to vehicle or AZD1480 treatment groups. Mice treated with AZD1480 demonstrated a modest but statistically significant improvement in overall survival compared to control mice, median time 20 days vs. 27 days, P = 0.03, respectively. Additionally, the metastatic tumor incidence decreased from 46.6% (7/15) in control mice to 20% (3/15) in AZD1480-treated mice. Our findings provide preclinical evidence supporting the potential use of Jak1/2 inhibitors for the targeted therapy of human prostate cancer.

Citation Format: Marco A. De Velasco, Yurie Kura, Naomi Ando, Emiko Fukushima, Yuji Hatanaka, Takashi Oki, Kazuhiro Yoshimura, Masahiro Nozawa, Barry R. Davies, Dennis Huszdar, Kazuhiro Yoshikawa, Kazuto Nishio, Hirotsugu Uemura. The Jak1/2 inhibitor AZD1480 suppresses tumor growth and metastasis in genetically engineered mouse models of PTEN-deficient prostate cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3864.

Abstract 3538: Effects of oral chloroquine administration on a preclinical mouse model of PTEN/p53-deficient prostate cancer

Autophagy is cellular process that can promote tumor survival during periods of metabolic and therapeutic stress. Inhibition of autophagy can promote senescence resulting in decreased tumor growth. Genetic alterations of PTEN and p53 are frequently present in advanced human prostate cancer and are associated with poor prognosis. In mouse models, the inactivation of PTEN leads to the development of prostate tumors that progress slowly, in part due to the induction of PTEN-(loss)-induced cellular senescence. Concomitant inactivation of both PTEN and P53 in prostate leads to the development of an aggressive cancer phenotype that can overcome PTEN-(loss)-induced cellular senescence and is characterized with accelerated growth, metastatic development and decreased survival. Published findings show that in some cancer models, the effects of autophagy inhibition are dependent on p53 status. In this study we assessed the effects of pharmacological inhibition of autophagy with chloroquine (CQ) on the growth and progression of mouse prostate tumors driven by the concomitant inactivation of PTEN and p53. CQ is a lysosomotropic agent that has widely used to impede autophagy and inhibit the growth of human tumor cells in vitro and in vivo. Genetically engineered mice with the conditional inactivation of PTEN and p53 were used to evaluate the antitumor effects and therapeutic benefit of CQ in a drug intervention model of prostate cancer. Twenty-seven-week-old PTEN/p53 double knockout mice bearing prostate tumors were randomized to control and oral CQ (100 mg/kg in drinking water) treatment groups. Progression-free survival was 145 days versus 161 days (P = 0.703) for control and CQ treated mice, respectively. Median overall survival was 170 days versus 147 days (P = 0.523) for control and CQ treated mice, respectively. Tumor burden assed by the median genitourinary tract weight was 2.42 grams versus 2.19 grams (P = 0.645) for control and CQ treated mice, respectively. Our molecular assays revealed that CQ failed to consistently inhibit autophagy in tumors at the present dose. Overall, our findings show that CQ alone did not provide treatment benefit in mouse prostate cancer with loss of p53.

Citation Format: Marco A. De Velasco, Koichi Sugimoto, Yurie Kura, Yuji Hatanaka, Yutaka Yamamoto, Takashi Oki, Kazuhiro Yoshimura, Masahiro Nozawa, Kazuhiro Yoshikawa, Kazuto Nishio, Hirotsugu Uemura. Effects of oral chloroquine administration on a preclinical mouse model of PTEN/p53-deficient prostate cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3538.

Conditional PTEN-deficient mice as a prostate cancer chemoprevention model

BACKGROUND

We generated a mouse model of prostate cancer based on the adult-prostate-specific inactivation of phosphatase and tensin homolog (PTEN) using the Cre-loxP system. The potential of our mice as a useful animal model was examined by evaluating the chemopreventive efficacy of the anti-androgen, chlormadinone acetate (CMA).

MATERIALS AND METHODS

Six-week-old mice were treated subcutaneously with 50 μg/g of CMA three times a week for 9 or 14 weeks and sacrificed at weeks 15 and 20. Macroscopic change of the entire genitourinary tract (GUT) and histologically evident prostate gland tumor development were evaluated. Proliferation and apoptosis status in the prostate were examined by immunohistochemistry.

RESULTS

CMA triggered significant shrinkage of not only the GUT but also prostate glands at 15 weeks compared to the control (p=0.017 and p=0.010, respectively), and the trend became more marked after a further five-weeks of treatment. The onset of prostate adenocarcinoma was not prevented but the proliferation of cancer cells was inhibited by CMA, which suggested the androgen axis is critical for cancer growth in these mice.

CONCLUSIONS

Conditional PTEN-deficient mice are useful as a preclinical model for chemoprevention studies and serve as a valuable tool for the future screening of potential chemopreventive agents.

Abstract 1845: Chloroquine demonstrates limited effectiveness in an autochthonous preclinical model of prostate cancer

Chloroquine (CQ) is a well-known compound that is used for the treatment of malaria and certain autoimmune diseases. CQ can also block autophagy, an essential cellular process that is implicated with resistance to chemotherapy. Preclinical studies have demonstrated the anticancer effects of CQ and hydroxychloroquine when used in combination with other anticancer agents suggesting that blocking autophagy inhibits therapeutic resistance. However, recent data shows that CQ can have antitumor effects independent of autophagy. Furthermore, given the specific roles of autophagy during tumorigenesis, the therapeutic effects of CQ observed in xenograft studies may differ than those in an autochthonous tumor model. The aim of our study was to investigate the antitumor effects of CQ in an autochthonous tumor model and to determine if CQ could reverse therapeutic resistance through the induction of autophagy. To test this hypothesis we tested the therapeutic administration of CQ in a genetically engineered mouse model of prostate cancer driven by the conditional inactivation of PTEN. We also characterized the combinatorial effects of CQ in combination with additional molecular targeting that included mTOR (everolimus), AKT (AZD5363), MEK (Selumetinib; AZD6244/ARRY142886), 5α-reductase (dutasteride) inhibitors. Oral administration of CQ demonstrated antitumor activity and moderately, but significantly, inhibited growth PTEN-deficient prostate tumors in a drug intervention model. However, combination therapy with CQ did not enhance therapeutic efficacy over inhibitor monotherapy alone. Mice with PTEN-mutant castration-resistant prostate cancer (CRPC) are resistant to treatment with everolimus. Therefore, we tested whether blocking autophagy could restore sensitivity to everolimus in CRPC. Mice with mutant PTEN and ATG7, an autophagy regulatory gene, CRPC demonstrated increased sensitivity and activity to everolimus suggesting that defective autophagy restored resistance to everolimus. On, the contrary, the treatment the combination of CQ and everolimus failed to produce any treatment effects in PTEN-deficient/ATG7-wildtype CRPC. Our findings suggest that combinatorial strategies with CQ lack therapeutic efficacy in autochthonous tumors and might be ineffective in the clinical setting.

Citation Format: Yurie Kura, Marco A. De Velasco, Naomi Ando, Emiko Fukushima, Barry R. Davies, Dennis Huzdar, Yutaka Yamamoto, Yuji Hatanaka, Takashi Oki, Nobutaka Shimizu, Kazuhiro Yoshimura, Masahiro Nozawa, Kazuhiro Yoshikawa, Kazuto Nishio, Hirotsugu Uemura. Chloroquine demonstrates limited effectiveness in an autochthonous preclinical model of prostate cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1845. doi:10.1158/1538-7445.AM2015-1845

Abstract 1856: Preclinical effects of dual AKT/MAPK inhibition in PTEN-deficient prostate cancer

Targeting signal molecules with single agent monotherapy is met with limited or transient clinical benefits. Therefore, establishing effective rational combinatorial treatment strategies provides a better option for achieving improved clinical outcomes. The AKT/PI3K and MAPK signaling pathways have been identified as key compensatory signal transduction pathways in prostate cancer. We have used genetically engineered mouse models of prostate cancer to show the treatment efficacy of monotherapy with the AKT inhibitor AZD5363 and the MAP/ERK kinase (MEK) inhibitor selumetinib (AZD6244, ARRY142886). We hypothesized that a rational combinatorial approach utilizing both of these inhibitors would improve treatment efficacy compared to single agent monotherapy. To test this hypothesis, we evaluated the treatment effects of AZD5363 and selumetinib in preclinical models of prostate cancer. In vitro experiments were carried out using a panel of human prostate cancer cell lines, and mouse prostate cancer cell lines, derived from PTEN-deficient castration-naïve prostate cancer (CNPC) and castration-resistant prostate cancer (CRPC). Treatments with AZD5363 and selumetinib demonstrated a synergistic combination effect in both human and mouse prostate cancer cell lines. We evaluated the antitumor effects in vivo by comparing the effects of AZD5363 and selumetinib alone or in combination in PTEN-deficient mice. Our studies show that combination therapy of AZD5363/selumetinib was well-tolerated by the mice and demonstrated significantly improved inhibition of tumor growth compared to single agent therapy. In the CNPC model, mice showed 16.7, 10.0 and 24.9% reductions in tumor burden after treatments with AZD5363, selumetinib and AZD5363/selumetinib, respectively (P<0.001). In the CRPC model, mice showed 15.8, 3.8 and 27.0% reductions in tumor burden after treatments with AZD5363, selumetinib and AZD5363/selumetinib, respectively (P<0.001). Target validation studies confirmed the inhibition of downstream targets. Overall, our findings suggest a potential role for targeting the PI3K/AKT and MAPK signaling pathways with AZD5363 and selumetinib for treatment of PTEN-deficient prostate cancer.

Citation Format: Marco A. De Velasco, Yutaka Yamamoto, Yurie Kura, Emiko Fukushima, Naomi Ando, Barry Davies, Yuji Hatanaka, Takashi Oki, Nobutaka Shimizu, Masahiro Nozawa, Kazuhiro Yoshikawa, Kazuhiro Yoshimura, Kazuto Nishio, Hirotsugu Uemura. Preclinical effects of dual AKT/MAPK inhibition in PTEN-deficient prostate cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1856. doi:10.1158/1538-7445.AM2015-1856

Abstract 1850: Evaluation of Pim-1 kinase inhibition in a preclinical model of mouse prostate cancer

Pim-1 is a serine/threonine kinase that is in involved in the transcription of genes that regulate apoptosis and cell cycle progression. Pim-1 has been shown to be overexpressed in a variety of cancers and has been implicated in human prostate tumorigenesis. The aim of our study was to clarify the role of Pim-1 during the prostate tumorigenesis and determine its potential as a molecular target for therapy. To accomplish this goal, we carried out a series of experiments using a genetically engineered mouse model of prostate cancer driven by the conditional inactivation of PTEN. High levels of Pim-1 were observed during the early stages of the tumorigenesis process which decreased as tumors progressed. Expression of Pim-1 was localized in the nucleus and cytoplasm of prostatic intraepithelial neoplasia (PIN), well-differentiated, and moderately-differentiated tumors. In poorly-differentiated tumors, Pim-1expression was heterogeneously expressed at lower levels and was predominantly localized to the cytoplasm of cancer cells. Levels of Pim-1 expression were increased in tumors from mice after surgical castration. To evaluate the therapeutic potential of Pim-1as a target for prostate cancer, we tested the antitumor effects of AZD1208, a highly potent Pim kinase inhibitor, on a panel of cell lines derived from castration-naïve and castration-resistant mouse prostate cancer. AZD1208 inhibited the tumor cell growth of several cell lines and demonstrated higher sensitivity to those derived from castration resistant tumors. In vivo, drug intervention studies show that treatment with AZD1208 reduced tumor growth of castration-naïve and castration-resistant prostate tumors by 12.1 (P = 0.162) and 24.3% (P<0.001), respectively. These findings provide further support for a role of Pim-1 during prostate tumorigenesis and could thus serve as a rational target for the development of novel combination strategies.

Citation Format: Marco A. De Velasco, Takashi Oki, Yurie Kura, Naomi Ando, Emiko Fukushima, Barry R. Davies, Dennis Huszar, Yutaka Yamamoto, Yuji Hatanaka, Nobutaka Shimizu, Kazuhiro Yoshimura, Masahiro Nozawa, Kazuhiro Yoshikawa, Kazuto Nishio, Hirotsugu Uemura. Evaluation of Pim-1 kinase inhibition in a preclinical model of mouse prostate cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1850. doi:10.1158/1538-7445.AM2015-1850

Abstract 4699: Preclinical activity of the AKT inhibitor AZD5363 in PTEN-deficient mouse models of prostate cancer

Increased phosphoinositide 3-kinase (PI3K) pathway activity is commonly observed in human prostate cancer and constitutes a potential target for therapeutic intervention. AZD5363 is a potent pan-AKT kinase inhibitor that is currently being investigated in phase 1 and 2 clinical trials in solid cancers including prostate. AZD5363 has demonstrated strong anti-tumor activity against human prostate cancer cells in vitro and in vivo. Genetically engineered mouse models mimic the genetic and biological evolution of human prostate cancer and address deficiencies encountered with xenograft models. In the present study, we examined in vivo target validation, pharmacodynamics, and antitumor responses of AZD5363 monotherapy in a PTEN-deficient mouse model of prostate cancer, and show the survival benefit in an advanced prostate cancer model driven by PTEN/P53 inactivation. Downstream targets of AKT were inhibited in a dose-dependent manner and activity of AZD5363 at was observed up to 8 hours after a single dose of 100 mg/kg. Tumor cell proliferation and the induction of apoptosis paralleled the activity of AZD5363. Compared to vehicle treated mice, chronic administration of AZD5363 at 100 mg/kg B.I.D. 5 times per week for 4 weeks inhibited growth of castration-naïve and castration-resistant prostate cancers by 15.9% ±4.3 and 20.2% ±4.4, respectively. Inhibition of S6 phosphorylation was effectively maintained the after chronic administration of AZD5363 and was accompanied by decreased proliferation rates and increase in apoptosis. Furthermore, in a long-term survival study of PTEN/P53 double knockout mice, treatment with AZD5363 significantly improved survival rates from 24 to 37 days, P<0.011. In conclusion, our findings indicate that AZD5363 is effective against autochthonous models of mouse prostate cancer and support further investigation of the AKT inhibitor for the treatment of PTEN-deficient prostate cancer.

Citation Format: Marco A. De Velasco, Yuji Hatanaka, Yurie Kura, Emiko Fukushima, Naomi Ando, Barry R. Davies, Yutaka Yamamoto, Takashi Oki, Nobutaka Shimizu, Kazuhiro Yoshimura, Masahiro Nozawa, Kazuhiro Yoshikawa, Kazuto Nishio, Hirotsugu Uemura. Preclinical activity of the AKT inhibitor AZD5363 in PTEN-deficient mouse models of prostate cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4699. doi:10.1158/1538-7445.AM2015-4699

Abstract 1857: Effects of long-term chloroquine chemotherapy in a preclinical model of PTEN-deficient prostate cancer

Chloroquine (CQ) and its derivative hydroxychloroquine are drugs that have been used to treat malaria and rheumatism. These drugs are also capable of producing antitumor effects in preclinical cancer models. In addition to mediating antitumor effects by impairing autophagy in certain cancer cells types, these agents have also been shown to effect antitumor responses independent of autophagy inhibition. Treatment strategies using CQ and its derivative alone or in combination with other anticancer drugs are being considered for clinical applications. However, the safety and long-term effects of CQ therapy for the treatment of cancers are unknown. In this study, we investigated the safety and efficacy of long-term CQ therapy in a PTEN-deficient model of prostate cancer. Twenty-eight-week-old tumor-bearing PTEN conditional knockout mice (PSA-CRE+/PTENf/f) were treated with CQ in the drinking water. Based on daily water consumption, the daily oral dose was adjusted to 100 mg/kg in distilled water. Timed sacrifices were scheduled 2, 4, 8, 16 and 32 weeks after the initiation of treatments and subset of mice was used for survival analysis. Mice receiving CQ were healthy in appearance and normal in demeanor. Compared to controls, mice receiving CQ began to exhibit lower body weights over the course of treatment beginning at 5 weeks after the initiation of treatment. At the completion of the study, mice receiving CQ averaged 27.3 grams of bodyweight compared to 33.8 grams in the control group (P<0.001). However, chronic treatment with CQ for 32 weeks inhibited tumor burden by 18.4% (P = 0.0118). For the long-term survival studies, median survival for control and CQ treated mice was 83.4 and 82.0 days, respectively (P = 0.782). Bodyweights of CQ mice were significantly reduced (44.8% of control, P = 0.029). Tumor burden at time of death decreased from 15.9% ±5.9 of bodyweight in control mice to 2.5% ±0.6 in CQ-treated mice (P<0.05). In summary, our studies show that long-term chronic administration of CQ was capable of inhibiting growth of PTEN-deficient tumors, however, CQ was poorly tolerated by mice and did not improve overall survival. Thus, caution should be exercised to carefully assess the safety and tolerability of this drug when using it long-term in human clinical trials.

Citation Format: Kazuhiro Yoshikawa, Marco A. De Velasco, Yurie Kura, Naomi Ando, Emiko Fukushima, Yutaka Yamamoto, Yuji Hatanaka, Takashi Oki, Nobutaka Shimizu, Kazuhiro Yoshimura, Kazuto Nishio, Hirotsugu Uemura. Effects of long-term chloroquine chemotherapy in a preclinical model of PTEN-deficient prostate cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1857. doi:10.1158/1538-7445.AM2015-1857

Evaluation of in vivo responses of sorafenib therapy in a preclinical mouse model of PTEN-deficient of prostate cancer

Background

Despite recent advances in the treatment for advanced prostate cancer, outcomes remain poor. This lack of efficacy has prompted the development of alternative treatment strategies. In the present study we investigate the effects of the multikinase inhibitor sorafenib in a genetically engineered mouse model of prostate cancer and explore the rational combination with the mTOR inhibitor everolimus.

Methods

Conditional prostate specific PTEN-deficient knockout mice were utilized to determine the pharmacodynamic and chemopreventive effects of sorafenib. This mouse model was also used to examine the therapeutic efficacy of sorafenib alone or in combination with everolimus. Preclinical efficacy was assessed by comparing the reduction of tumor burden, proliferation, angiogenesis and the induction of apoptosis. Molecular responses were assessed by immunohistochemical, TUNEL and western blot assays.

Results

Pharmacodynamic analysis revealed that a single dose of sorafenib decreased activation of the PI3K/AKT/mTOR signaling axis at doses of 30–60 mg/kg, but activated JAK/STAT3 signaling. Levels of cleaved casapase-3 increased in a dose dependent manner. Chemoprevention studies showed that chronic sorafenib administration was capable of inhibiting tumor progression through the reduction of cancer cell proliferation, angiogenesis and the induction of apoptosis. In intervention models of established castration-naïve and castration-resistant prostate cancer, treatment with sorafenib provided modest but statistically insignificant reduction in tumor burden. However, sorafenib significantly inhibited cancer cell proliferation and MVD but had minimal effects on the induction of apoptosis. Interestingly, the administration of sorafenib increased the expression levels of the androgen receptor, p-GSK3β and p-ERK1/2 in castration-resistant prostate cancers. In both intervention models, combination therapy demonstrated a clear tendency of enhanced antitumor effects over monotherapy. Notably, the treatment combination of sorafenib and everolimus overcame therapeutic escape from single agent therapy in castration-resistant prostate cancers.

Conclusions

In summary, we provide insights into the molecular responses of sorafenib therapy in a clinically relevant model of prostate cancer and present preclinical evidence for the development of targeted treatment strategies based on the use of multikinase inhibitors in combination with mTOR inhibitors for the treatment of advanced prostate cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-015-0509-x) contains supplementary material, which is available to authorized users.