Prostate cancer immunotherapy: beyond immunity to curability

Development of Spherical Nucleic Acids for Prostate Cancer Immunotherapy

Although the strategy of therapeutic vaccination for the treatment of prostate cancer has advanced to and is available in the clinic (Sipuleucel-T), the efficacy of such therapy remains limited. Here, we develop Immunostimulatory Spherical Nucleic Acid (IS-SNA) nanostructures comprised of CpG oligonucleotides as adjuvant and prostate cancer peptide antigens, and evaluate their antitumor efficacy in syngeneic mouse models of prostate cancer. IS-SNAs with the specific structural feature of presenting both antigen and adjuvant CpG on the surface (hybridized model (HM) SNAs) induce stronger cytotoxic T lymphocyte (CTL) mediated antigen-specific killing of target cells than that for IS-SNAs with CpG on the surface and antigen encapsulated within the core (encapsulated model (EM) SNAs). Mechanistically, HM SNAs increase the co-delivery of CpG and antigen to dendritic cells over that for EM SNAs or admixtures of linear CpG and peptide, thereby improving cross-priming of antitumor CD8⁺ T cells. As a result, vaccination with HM SNAs leads to more effective antitumor immune responses in two prostate cancer models. These data demonstrate the importance of the structural positioning of peptide antigens together with adjuvants within IS-SNAs to the efficacy of IS-SNA-based cancer immunotherapy.

Immune landscape of human prostate cancer: immune evasion mechanisms and biomarkers for personalized immunotherapy

BACKGROUND

Despite recent advances in cancer immunotherapy, the efficacy of these therapies for the treatment of human prostate cancer patients is low due to the complex immune evasion mechanisms (IEMs) of prostate cancer and the lack of predictive biomarkers for patient responses.

METHODS

To understand the IEMs in prostate cancer and apply such understanding to the design of personalized immunotherapies, we analyzed the RNA-seq data for prostate adenocarcinoma from The Cancer Genome Atlas (TCGA) using a combination of biclustering, differential expression analysis, immune cell typing, and machine learning methods.

RESULTS

The integrative analysis identified eight clusters with different IEM combinations and predictive biomarkers for each immune evasion cluster. Prostate tumors employ different combinations of IEMs. The majority of prostate cancer patients were identified with immunological ignorance (89.8%), upregulated cytotoxic T lymphocyte-associated protein 4 (CTLA4) (58.8%), and upregulated decoy receptor 3 (DcR3) (51.6%). Among patients with immunologic ignorance, 41.4% displayed upregulated DcR3 expression, 43.26% had upregulated CTLA4, and 11.4% had a combination of all three mechanisms. Since upregulated programmed cell death 1 (PD-1) and/or CTLA4 often co-occur with other IEMs, these results provide a plausible explanation for the failure of immune checkpoint inhibitor monotherapy for prostate cancer.

CONCLUSION

These findings indicate that human prostate cancer specimens are mostly immunologically cold tumors that do not respond well to mono-immunotherapy. With such identified biomarkers, more precise treatment strategies can be developed to improve therapeutic efficacy through a greater understanding of a patient's immune evasion mechanisms.

Syngeneic murine model for prostate cancer using RM1 cells transfected with gp100

BACKGROUND

Prostate cancer (PC) is the most commonly diagnosed solid tumor in men. A major challenge in PC immunotherapy is the lack of an animal model that resembles human adenocarcinoma and allows for manipulation or monitoring of the immune response. Mouse models are needed for preclinical testing of new immunotherapies, whether used alone or in combination with established drugs, and to develop companion biomarkers that can be validated in clinical trials.

METHODS

To develop a syngeneic prostate adenocarcinoma model with a well-defined tumor antigen, murine RM1 PC cells were transfected with the endogenous mouse melanoma protein, gp100 (RM1-gp100). Gp100 was attractive because it is a self-protein and it instantly allowed us to use the large trove of immune research tools developed for melanoma research. A dendritic cell (DC) vaccine was used as model immunotherapy to demonstrate that adoptive immunotherapy against gp100 decreases the growth of RM1-gp100 but not RM1.

RESULTS

Expressing gp100 did not change the growth of RM1 cell in vitro or in vivo. The DCs pulsed with RM1-gp100 could be used to stimulate Pmel-1 lymphocyte proliferation and activation. Pmel-1 lymphocytes could be adoptively transferred into C57Bl/6 mice that were treated with DCs pulsed with RM1-gp100. The resulting Pmel-1 lymphocytes were monitored to assess the primary cellular immune response and memory response.

CONCLUSION

We describe a murine model for prostate adenocarcinoma with a well-characterized antigen that can be used in an immunologically intact mice to monitor the temporal CD8+ lymphocyte-mediated antitumor immunity.

Differential Targeting of Gr-MDSCs, T Cells and Prostate Cancer Cells by Dactolisib and Dasatinib

Granulocytic myeloid-derived suppressor cells (Gr-MDSCs) promote immune evasion and resistance to immunotherapeutics in a variety of malignancies. Our previous study showed that dual PI3K/mTOR inhibitor Dactolisib impaired the viability and immunosuppressive function of Gr-MDSCs, and significantly synergized with immune checkpoint blockade (ICB) antibodies targeting PD1 and CTLA4 to eradicate metastatic castration-resistant prostate cancer (CRPC) in a preclinical transgenic mouse model. On the contrary, tyrosine kinase inhibitor Dasatinib diminished tumor-infiltrating T lymphocytes and showed no synergic activity with ICB. The understanding of the distinct effects of Dactolisib and Dasatinib on Gr-MDSCs, T cells and prostate neoplastic cells is inadequate, limiting the clinical translation of the combination immunotherapy. To address this question, we applied Reverse Phase Protein Array (RPPA) to profile 297 proteins and protein phosphorylation sites of Gr-MDSCs, T cells and prostate cancer cells isolated from the CRPC model. We found cell type-specific protein expression patterns and highly selective targets by the two drugs, including preferential inhibition of phospho-4E-BP1 in Gr-MDSCs by Dactolisib and preferential suppression of phospho-Src and phospho-p38 MAPK in T cells. Furthermore, transcriptomic profiling of Gr-MDSCs treated with the two inhibitors revealed downregulation of mitochondrial respiration pathways by Dactolisib but not Dasatinib. Overall, these results provide important mechanistic insight into the efficacious combination of Dactolisib and ICB as well as the detrimental effect of Dasatinib on anti-tumor immunity.

A review on the interactions between the tumor microenvironment and androgen receptor signaling in prostate cancer

Prostate cancer growth is controlled by androgen receptor signaling via both androgen-dependent and androgen-independent pathways. Furthermore, the prostate is an immune competent organ with inflammatory changes both within the systemic and local environment contributing to the reprogramming of the prostatic epithelium with consistently elevated lymphocyte infiltration and proinflammatory cytokines being found in prostate cancer. The crosstalk between the tumor microenvironment and androgen receptor signaling is complex with both protumorigenic and antitumorigenic roles observed. However, despite an increase in immune checkpoint inhibitors and inflammatory signaling blockades available for a range of cancer types, we are yet to see substantial progress in the treatment of prostate cancer. Therefore, this review aims to summarize the tumor microenvironment and its impact on androgen receptor signaling in prostate cancer.

Tumor Immuno-Environment in Cancer Progression and Therapy

The approvals of Provenge (Sipuleucel-T), Ipilimumab (Yervoy/anti-CTLA-4) and blockers of the PD-1 - PD-L1/PD-L2 pathway, such as nivolumab (Opdivo), pembrolizumab (Keytruda), or atezolizumab (Tecentriq), have established immunotherapy as a key component of comprehensive cancer care. Further, murine mechanistic studies and studies in immunocompromised patients have documented the critical role of immunity in effectiveness of radio- and chemotherapy. However, in addition to the ability of the immune system to control cancer progression, it can also promote tumor growth, via regulatory T cells (Tregs), myeloid-derived dendritic cells (MDSCs) and tumor associated macrophages (TAM), which can enhance survival of cancer cells directly or via the regulation of the tumor stroma.An increasing body of evidence supports a central role for the tumor microenvironment (TME) and the interactions between tumor stroma, infiltrating immune cells and cancer cells during the induction and effector phase of anti-cancer immunity, and the overall effectiveness of immunotherapy and other forms of cancer treatment. In this chapter, we discuss the roles of key TME components during tumor progression, metastatic process and cancer therapy-induced tumor regression, as well as opportunities for their modulation to enhance the overall therapeutic benefit.

MicroRNA-206 regulates the epithelial-mesenchymal transition and inhibits the invasion and metastasis of prostate cancer cells by targeting Annexin A2

The present study investigated the molecular mechanism by which microRNA-206 (miR-206) targets Annexin A2 (ANXA2) expression and inhibits the invasion and metastasis of prostatic cancer cells through regulation of the epithelial-mesenchymal transition (EMT). Using bioinformatics analysis, miR-206 was identified as the most promising candidate miRNA that targeted ANXA2. Prostate tissue specimens from 60 patients with prostate cancer, 30 patients with metastatic prostate cancer and 20 patients with benign prostatic hyperplasia (BPH) were examined for ANXA2 protein expression by immunohistochemistry and western blotting and for miR-206 expression by reverse transcription-quantitative polymerase chain reaction. Additionally, human prostate cancer PC-3 cells were transfected with miR-206 mimics, miR-206 inhibitors or a negative control sequence, and expression of ANXA2, E-cadherin and N-cadherin was detected by western blotting. Transwell assays were performed to determine the effect of altered miR-206 expression on the invasive behavior of PC-3 cells. Bioinformatics analysis predicted complementary binding between miR-206 and ANXA2 mRNA. ANXA2 protein expression was detected in a significantly higher proportion of BPH tissues (95%, 19/20) when compared with prostate cancer tissues (51.7%, 31/60; P<0.05). Similarly, ANXA2 was expressed in a significantly higher proportion of metastatic prostate cancer samples than that of prostate cancer samples (P<0.05). Expression of miR-206 was higher than that of ANXA2 in prostate cancer samples, but lower in BPH samples. Inhibition of miR-206 expression in PC-3 cells upregulated ANXA2 and E-cadherin protein expression levels, downregulated N-cadherin and vimentin, and promoted cell invasion in vitro. These data suggested that binding between miRNA-206 and ANXA2 mRNA may regulate EMT signaling, thereby suppressing the invasion and metastasis of prostatic cancer cells.

Vascular endothelial growth factor suppresses dendritic cells function of human prostate cancer

Purpose

Prostate cancer (PCa) patients often have dendritic cell (DC) function defects, but the mechanism is not clear. The aim of this study was to detect the effect of vascular endothelial growth factor (VEGF) in mature DCs.

Patients and methods

In this study, we chose 30 PCa patients, 10 prostatic intraepithelial neoplasia (PIN) patients and 30 benign prostatic hyperplasia (BPH) patients, and compared the composition of peripheral blood T cells, the composition and function of local dendritic cells in prostate tissue, and the density of local VEGF.

Results

The results showed that the numbers of total DCs, mature and functional DCs, and CD4⁺ T cells were inhibited in PCa, and the inhibitory effect was enhanced with increased malignancy. In addition, the infiltration density of VEGF-positive cells was increased in PCa, and this increase was associated with an increased malignant degree of PCa. The inhibition of tumor immunity in patients with PCa is achieved by inhibiting the function of dendritic cells.

Conclusion

VEGF plays an important role in the inhibition of the maturation and function of dendritic cells, and this inhibition is gradually increased with an increasing malignant degree of PCa.

Prostate cancer health disparities: An immuno-biological perspective

Prostate cancer (PCa) is the most commonly diagnosed malignancy in males, and, in the United States, is the second leading cause of cancer-related death for men older than 40 years. There is a higher incidence of PCa for African Americans (AAs) than for European-Americans (EAs). Investigations related to the incidence of PCa-related health disparities for AAs suggest that there are differences in the genetic makeup of these populations. Other differences are environmentally induced (e.g., diet and lifestyle), and the exposures are different. Men who immigrate from Eastern to Western countries have a higher risk of PCa than men in their native countries. However, the number of immigrants developing PCa is still lower than that of men in Western countries, suggesting that genetic factors are involved in the development of PCa. Altered genetic polymorphisms are associated with PCa progression. Androgens and the androgen receptor (AR) are involved in the development and progression of PCa. For populations with diverse racial/ethnic backgrounds, differences in lifestyle, diet, and biology, including genetic mutations/polymorphisms and levels of androgens and AR, are risk factors for PCa. Here, we provide an immuno-biological perspective on PCa in relation to racial/ethnic disparities and identify factors associated with the disproportionate incidence of PCa and its clinical outcomes.

The inflammatory microenvironment and microbiome in prostate cancer development

Chronic inflammation promotes the development of several types of solid cancers and might contribute to prostate carcinogenesis. This hypothesis partly originates in the frequent observation of inflammatory cells in the prostate microenvironment of adult men. Inflammation is associated with putative prostate cancer precursor lesions, termed proliferative inflammatory atrophy. Inflammation might drive prostate carcinogenesis via oxidative stress and generation of reactive oxygen species that induce mutagenesis. Additionally, inflammatory stress might cause epigenetic alterations that promote neoplastic transformation. Proliferative inflammatory atrophy is enriched for proliferative luminal epithelial cells of intermediate phenotype that might be prone to genomic alterations leading to prostatic intraepithelial neoplasia and prostate cancer. Studies in animals suggest that inflammatory changes in the prostate microenvironment contribute to reprogramming of prostate epithelial cells, a possible step in tumour initiation. Prostatic infection, concurrent with epithelial barrier disruption, might be a key driver of an inflammatory microenvironment; the discovery of a urinary microbiome indicates a potential source of frequent exposure of the prostate to a diverse number of microorganisms. Hence, current evidence suggests that inflammation and atrophy are involved in prostate carcinogenesis and suggests a role for the microbiome in establishing an inflammatory prostate microenvironment that might promote prostate cancer development and progression.

Tumor infiltrating T lymphocytes expressing FoxP3, CCR7 or PD-1 predict the outcome of prostate cancer patients subjected to salvage radiotherapy after biochemical relapse

Tumor immunologic microenvironment is strongly involved in tumor progression and the presence of tumor infiltrating lymphocytes (TIL) with different phenotypes has been demonstrated to be of prognostic relevance in different malignancies. We investigated whether TIL infiltration of tumor tissues could also predict the outcome of prostate cancer patients. To this end, we carried out a retrospective analysis correlating the outcome of locally advanced prostate cancer patients undergone salvage radiotherapy upon relapse after radical surgery with the infiltration by different TIL populations. Twenty-two patients with resectable prostate cancer, with a mean age of 67 (+/-3.93) years, who received salvage radiotherapy with a mean of 69.66 (+/- 3.178) Gy in 8 weeks, between June 1999 and January 2009 and with a median follow up of 123 (+/- 55.82) months, were enrolled in this study. We evaluated, by immunohistochemistry, the intratumoral (^t) and peripheral stroma (^p) infiltration by CD45, CD3, CD4, CD8, CCR7, FoxP3 or PD-1-positive cells on tumor samples taken at the diagnosis (^d) and relapse times (^R). We correlated these variables with patients' biochemical progression free survival (bPFS), post-radiotherapy progression free survival (PFS), and overall survival (OS). Substantial changes in the rate of TIL subsets were found between the first and the second biopsy with progressive increase in CD4, CCR7, FoxP3, PD-1⁺ cells. Our analysis revealed that higher CD8^p,R+ and lower PD-1^R+ TIL scores correlated to a longer bPFS. Higher CD8^p,R+ and CCR7^t,R+ TIL scores and lower CD45^p,R+ and FoxP3^p,R+ TIL scores correlated to a prolonged PFS and OS. These results suggest that the immunological microenvironment of primary tumor is strictly correlated with patient outcome and provide the rationale for immunological treatment of prostate cancer.

Novel prostate cancer immunotherapy with a DNA-encoded anti-prostate-specific membrane antigen monoclonal antibody

Prostate-specific membrane antigen (PSMA) is expressed at high levels on malignant prostate cells and is likely an important therapeutic target for the treatment of prostate carcinoma. Current immunotherapy approaches to target PSMA include peptide, cell, vector or DNA-based vaccines as well as passive administration of PSMA-specific monoclonal antibodies (mAb). Conventional mAb immunotherapy has numerous logistical and practical limitations, including high production costs and a requirement for frequent dosing due to short mAb serum half-life. In this report, we describe a novel strategy of antibody-based immunotherapy against prostate carcinoma that utilizes synthetic DNA plasmids that encode a therapeutic human mAb that target PSMA. Electroporation-enhanced intramuscular injection of the DNA-encoded mAb (DMAb) plasmid into mice led to the production of functional and durable levels of the anti-PSMA antibody. The anti-PSMA produced in vivo controlled tumor growth and prolonged survival in a mouse model. This is likely mediated by antibody-dependent cellular cytotoxicity (ADCC) effect with the aid of NK cells. Further study of  this novel approach for treatment of human prostate disease and other malignant conditions is warranted.

Functional reprogramming of human prostate cancer to promote local attraction of effector CD8(+) T cells

BACKGROUND

Local infiltration of CD8(+) T cells (CTLs) in tumor lesions predicts overall clinical outcomes and the clinical benefit of cancer patients from immune checkpoint blockade. In the current study, we evaluated local production of different classes of chemokines in prostate cancer lesions, and the feasibility of their modulation to promote selective entry of CTLs into prostate tumors.

METHODS

Chemokine expression in prostate cancer lesion was analyzed by TaqMan-based quantitative PCR, confocal fluorescence microscopy and ELISA. For ex vivo chemokine modulation analysis, prostate tumor explants from patients undergoing primary prostate cancer resections were cultured for 24 hr, in the absence or presence of the combination of poly-I:C, IFNα, and celecoxib (PAC). The numbers of cells producing defined chemokines in the tissues were analyzed by confocal microscopy. Chemotaxis of effector CD8(+) T cells towards the untreated and PAC-treated tumor explant supernatants were evaluated in a standard in vitro migration assays, using 24 well trans-well plates. The number of effector cells that migrated was enumerated by flow cytometry. Pearson (r) correlation was used for analyzing correlations between chemokines and immune filtrate, while paired two tailed students t-test was used for comparison between treatment groups.

RESULTS

Prostate tumors showed uniformly low levels of CTL/NK/Th1-recruiting chemokines (CCL5, CXCL9, CXCL10) but expressed high levels of chemokines implicated in the attraction of myeloid derived suppressor cells (MDSC) and regulatory T cells (Treg ): CCL2, CCL22, and CXCL12. Strong positive correlations were observed between CXCL9 and CXCL10 and local CD8 expression. Tumor expression levels of CCL2, CCL22, and CXCL12 were correlated with intratumoral expression of MDSC/Treg markers: FOXP3, CD33, and NCF2. Treatment with PAC suppressed intratumoral production of the Treg -attractant CCL22 and Treg /MDSC-attractant, CXCL12, while increasing the production of the CTL attractant, CXCL10. These changes in local chemokine production were accompanied by the reduced ability of the ex vivo-treated tumors to attract CD4(+) FOXP3(+) Treg cells, and strongly enhanced attraction of the CD8(+) Granzyme B(+) CTLs.

CONCLUSIONS

Our data demonstrate that the chemokine environment in prostate cancer can be reprogrammed to selectively enhance the attraction of type-1 effector immune cells and reduce local attraction of MDSCs and Tregs . Prostate 76:1095-1105, 2016. © 2016 Wiley Periodicals, Inc.

Evaluation of hGM-CSF/hTNFα surface-modified prostate cancer therapeutic vaccine in the huPBL-SCID chimeric mouse model

To validate its efficacy in the context of the human immune system, a novel therapeutic vaccine of hGM-CSF/hTNFα surface-modified PC-3 cells against human prostate cancer was evaluated in the human peripheral blood lymphocytes-severe combined immunodeficiency (huPBL-SCID) chimeric mouse model. The hGM-CSF or/and hTNFα modified vaccines inhibited prostate cancer growth effectively so as to prolong the mouse survival significantly. The splenocytes from the hGM-CSF/hTNFα vaccine-inoculated mice showed the strongest tumor-specific cytotoxicity against PC-3 cells and the highest production of IFNɤ. These features indicated that type 1 protective immune response was induced efficiently against human prostate cancer and further enhanced through synergetic adjuvant effects of hGM-CSF and hTNFα.