Striking efficacy of a vaccine targeting TOP2A for triple-negative breast cancer immunoprevention

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer that has a poor prognosis. TOP2A is a key enzyme in DNA replication and is a therapeutic target for breast and other cancers. TOP2A-specific Th1-promoting epitopes with optimal binding affinity to MHC II were identified using a combined scoring system. The multi-peptide TOP2A vaccine elicited a robust immunologic response in immunized mice, as demonstrated by the significant production of Th1 cytokines from immunized animals' splenocytes stimulated in vitro with TOP2A peptides. Anti-tumor efficacy of the TOP2A vaccine was demonstrated in a syngeneic TNBC mouse model, in which pre-graft preventive vaccination was associated with significantly decreased tumor growth as compared to adjuvant control. In a genetically engineered mouse (GEM) model of TNBC, vaccinated animals demonstrated a significant reduction in tumor incidence and average tumor volume compared to adjuvant control. Finally, we examined TCR sequences in CD4 tumor Infiltrating lymphocytes (TIL) from vaccinated mice and found that the TIL contained TCR sequences specific to the three vaccine peptides. These data indicate that our newly developed multi-peptide TOP2A vaccine is highly immunogenic, elicits TILs with vaccine specific TCRs, and is highly effective in preventing and intercepting TNBC development and progression in vivo.

Primary Prevention and Interception Studies in RAS-Mutated Tumor Models Employing Small Molecules or Vaccines

Therapeutic targeting of RAS-mutated cancers is difficult, whereas prevention or interception (treatment before or in the presence of preinvasive lesions) preclinically has proven easier. In the A/J mouse lung model, where different carcinogens induce tumors with different KRAS mutations, glucocorticoids and retinoid X receptor (RXR) agonists are effective agents in prevention and interception studies, irrespective of specific KRAS mutations. In rat azoxymethane-induced colon tumors (45% KRAS mutations), cyclooxygenase 1/2 inhibitors and difluoromethylornithine are effective in preventing or intercepting KRAS-mutated or wild-type tumors. In two KRAS-mutant pancreatic models multiple COX 1/2 inhibitors are effective. Furthermore, combining a COX and an EGFR inhibitor prevented the development of virtually all pancreatic tumors in transgenic mice. In the N-nitroso-N-methylurea-induced estrogen receptor-positive rat breast model (50% HRAS mutations) various selective estrogen receptor modulators, aromatase inhibitors, EGFR inhibitors, and RXR agonists are profoundly effective in prevention and interception of tumors with wild-type or mutant HRAS, while the farnesyltransferase inhibitor tipifarnib preferentially inhibits HRAS-mutant breast tumors. Thus, many agents not known to specifically inhibit the RAS pathway, are effective in an organ specific manner in preventing or intercepting RAS-mutated tumors. Finally, we discuss an alternative prevention and interception approach, employing vaccines to target KRAS.

Major hurdles to the use of tyrosine kinase inhibitors in clinical prevention/interception studies: Do preclinical studies with EGFR inhibitors suggest approaches to overcome some of the limitations

There are major hurdles to the use of tyrosine kinase inhibitors (TKIs) and any other agents with significant toxicities (which means practically the preponderance of potential effective agents) in the context of prevention/anti-progression (interception) studies. We will discuss epidermal growth factor receptor (EGFR) inhibitors as examples, both in a primary prevention setting, where agent(s) are administered to individuals with no cancer but who might be considered at higher risk due to a variety of factors, and in anti-progression/interception studies, where agent(s) are administered to persons with known preinvasive lesions (e.g., colon adenomas, lung nodules, ductal carcinoma in situ (DCIS), or pancreatic intraepithelial neoplasia (PanIN) lesions in the pancreas) in an attempt to reverse or inhibit progression of these lesions. Multiple potential hurdles will be examined, including: a) toxicity of agents, b) the likely range of subtypes of cancers affected by a given treatment (e.g., EGFR inhibitors against EGFR mutant lung adenocarcinomas), c) the availability of practical endpoints besides the blocking of cancer formation or pharmacokinetics related to the agents administered in a primary prevention study, and d) the interpretation of the regression or blockage of new preinvasive lesions in the anti-progression study. Such an anti-progression approach may help address some of the factors commented on regarding primary prevention (toxicity, potential target organ cancer subtypes) but still leaves major questions regarding interpretation of modulation of preinvasive endpoints when it may not be clear how frequently they progress to clinical cancer. Additionally, we address whether certain recent preclinical findings might be able to reduce the toxicities associated with these agents and perhaps even increase their potential efficacy. Antibodies and TKIs other than the EGFR inhibitors are not discussed because few if any had been tested as monotherapies in humans, making their efficacy harder to predict, and because a number have relatively rare but quite striking toxicities. Furthermore, most of the practical hurdles raised regarding the EGFR inhibitors are relevant to the other TKIs. Finally, we briefly discuss whether early detection employing blood or serum samples may allow identification of high-risk groups more amenable to agents with greater toxicity.

Abstract IA015: Immunoprevention of triple negative breast cancer by TOP2A derived peptide vaccination

Top2A is a key enzyme involved in DNA replication and is a therapeutic target for several cancer types including breast cancer. Overexpression of Top2A has been observed in both human and mouse triple-negative breast cancer (TNBC). The present study evaluated both immunogenicity and antitumor efficacy of a newly formulated multi-peptide vaccine targeting multiple epitopes of the Top2A protein. Top2A-specific MHC II epitopes with optimal binding affinity were identified using a combined scoring system, which predicted their potential to elicit a Th1 immune response. The formulated vaccine contained top three Top2A peptides, which elicited the strongest immunologic response and showed 100% sequence homology between human and mouse. Anti-tumor efficacy of the Top2A vaccine was initially evaluated in a syngeneic TNBC mouse model, in which pre-graft preventive vaccination was associated with significantly decreased tumor growth as compared to the adjuvant controls. The Top2A peptide vaccine exhibited striking efficacy in a genetically engineered TNBC mouse model (C3(1)/Tag), reducing tumor burden by >90% when compared with adjuvant alone. Splenocytes collected from vaccinated animals showed a robust immunologic response to the immunizing peptides. There were no overt toxicities observed with the Top2A vaccination. To explore potential mechanisms underlying the anti-tumor response induced by Top2A vaccine treatment, scTCR-seq of tumors in both control and Top2A vaccine groups revealed new T cell clones as a consequence of Top2A vaccination. Furthermore, in vitro stimulation of these splenocytes by the vaccinated Top2A peptides resulted in the secretion of cytokines indicative of Th1 responses but with minimal secretion of Th2-related cytokines. Our data indicate that the newly developed multi-peptide Top2A vaccine is immunogenic and efficacious in the prevention of TNBC development and progression in vivo.

Citation Format: Sang Beom Lee, Jing Pan, Donghai Xiong, Katie Palen, Bryon Johnson, Jeffrey E. Green, Shizuko Sei, Robert H. Shoemaker, Ronald A. Lubet, Yian Wang, Ming You. Immunoprevention of triple negative breast cancer by TOP2A derived peptide vaccination [abstract]. In: Proceedings of the Second Biennial NCI Meeting: Translational Advances in Cancer Prevention Agent Development (TACPAD); 2022 Sep 7-9. Philadelphia (PA): AACR; Can Prev Res 2022;15(12 Suppl_2): Abstract nr IA015.

Targeting Glutamine Metabolism to Enhance Immunoprevention of EGFR-Driven Lung Cancer

Lung cancer is the leading cause of cancer death worldwide. Vaccination against EGFR can be one of the venues to prevent lung cancer. Blocking glutamine metabolism has been shown to improve anticancer immunity. Here, the authors report that JHU083, an orally active glutamine antagonist prodrug designed to be preferentially activated in the tumor microenvironment, has potent anticancer effects on EGFR-driven mouse lung tumorigenesis. Lung tumor development is significantly suppressed when treatment with JHU083 is combined with an EGFR peptide vaccine (EVax) than either single treatment. Flow cytometry and single-cell RNA sequencing of the lung tumors reveal that JHU083 increases CD8⁺ T cell and CD4⁺ Th1 cell infiltration, while EVax elicits robust Th1 cell-mediated immune responses and protects mice against EGFR^L858R mutation-driven lung tumorigenesis. JHU083 treatment decreases immune suppressive cells, including both monocytic- and granulocytic-myeloid-derived suppressor cells, regulatory T cells, and pro-tumor CD4⁺ Th17 cells in mouse models. Interestingly, Th1 cells are found to robustly upregulate oxidative metabolism and adopt a highly activated and memory-like phenotype upon glutamine inhibition. These results suggest that JHU083 is highly effective against EGFR-driven lung tumorigenesis and promotes an adaptive T cell-mediated tumor-specific immune response that enhances the efficacy of EVax.

COX-2 inhibitors decrease expression of PD-L1 in colon tumors and increase the influx of Type I tumor infiltrating lymphocytes

Colon cancer is initiated under inflammatory conditions associated with upregulation of immune checkpoint proteins. We evaluated immune modulation induced by non-steroidal anti-inflammatory agents used for colon cancer prevention. Both celecoxib and naproxen inhibited polyp growth in APC Min mice. Treatment of mice with either drug significantly decreased PD-L1 expression on polyps in a dose dependent manner (p<0.0001 for both). The decrease in PD-L1 was associated with an influx of CD8+ T-cells into polyps (p<0.0001, celecoxib; p=0.048, naproxen) compared to lesions from untreated animals and correlated with disease control. Naproxen is a nonselective inhibitor of both COX-1 and COX-2, and we questioned the role of the different cyclooxygenases in PD-L1 regulation. Silencing either COX-2 or COX-1 RNA in the murine colon cancer cell line MC38, reduced PD-L1 expression by 86% in COX-2-silenced cells (p<0.0001) while there was little effect with COX-1 siRNA compared to control. Naproxen could inhibit the growth of MC38 in vivo. Naproxen treated mice demonstrated a significant reduction in MC38 growth as compared to control (p<0001). Both Tbet+ CD4 and CD8 tumor infiltrating T-cells (TIL) were significantly increased (p=0.04 and p=0.038 respectively) without a concurrent increase in GATA3+ TIL (p>0.05). CD8+ TIL highly expressed the activation marker, CD69. Not only was PD-L1 expression decreased on tumors, but LAG3+CD8+ T-cells and PD-1 and LAG3 expression on T-regulatory cells was also reduced (p=0.008 and p=0.002 respectively). These data demonstrate COX-2 inhibitors significantly decrease PD-L1 in colonic lesions and favorably impact the phenotype of tumor infiltrating lymphocytes to control tumor growth.

Efficacy of EGFR Inhibitors and NSAIDs Against Basal Bladder Cancers in a Rat Model: Daily vs. Weekly Dosing, Combining EGFR Inhibitors with Naproxen, and Effects on RNA Expression

BACKGROUND: There are few effective treatments specifically aimed at basal bladder cancer. OBJECTIVE: Female F344 rats administered N-butyl-N-(4-hydroxybutyl)-nitrosamine (OH-BBN) develop large invasive bladder cancers. We determined the efficacy of daily vs weekly dosing of EGFR inhibitors, determined the efficacy of naproxen combined with an EGFR inhibitor, and performed RNA analysis of bladder tumors treated for 5 days with EGFR inhibitors or NO-naproxen to identify pharmacodynamic biomarkers. METHODS: Erlotinib (6 mg/Kg BW daily or 21 or 42 mg/Kg BW weekly), lapatinib (25 or 75 mg/Kg BW daily or 263 or 525 mg/Kg BW weekly) and/or naproxen (30 mg/Kg BW daily) were administered to OH-BBN-treated rats beginning 2–12 weeks post OH-BBN. Rats were sacrificed 28 weeks after the final OH-BBN treatment to determine the effects of the EGFR inhibitors + naproxen on bladder weights and tumor development. In a separate study, rats were treated with OH-BBN. When palpable tumors developed, rats were treated with erlotinib, lapatinib, gefitinib, or the NSAID NO-naproxen for 5 days. RNA analysis was performed on the tumors. RESULTS: Daily or weekly dosing of erlotinib or lapatinib and daily dosing of naproxen reduced large tumor formation up to 70%, while combining daily lapatinib and naproxen reduced tumors 100%. RNA Analysis: All EGFR inhibitors strongly reduced cell proliferation and chromosome replication pathways, while NO-naproxen altered the G protein receptor, oxygen homeostasis and immune function pathways. CONCLUSIONS: While daily and weekly dosing with EGFR inhibitors and naproxen were effective, combining lapatinib and naproxen yielded no tumors. This might encourage its clinical use in an adjuvant setting with superficial basal tumors, and perhaps even in a more advanced setting. Furthermore, RNA analysis identified specific pathways that might be potential pharmacodynamic biomarkers in clinical trials.

Multi-Epitope-Based Vaccines for Colon Cancer Treatment and Prevention

Background

Overexpression of nonmutated proteins involved in oncogenesis is a mechanism by which such proteins become immunogenic. We questioned whether overexpressed colorectal cancer associated proteins found at higher incidence and associated with poor prognosis could be effective vaccine antigens. We explored whether vaccines targeting these proteins could inhibit the development of intestinal tumors in the azoxymethane (AOM)-induced colon model and APC Min mice.

Methods

Humoral immunity was evaluated by ELISA. Web-based algorithms identified putative Class II binding epitopes of the antigens. Peptide and protein specific T-cells were identified from human peripheral blood mononuclear cells using IFN-gamma ELISPOT. Peptides highly homologous between mouse and man were formulated into vaccines and tested for immunogenicity in mice and in vivo tumor challenge. Mice treated with AOM and APC Min transgenic mice were vaccinated and monitored for tumors.

Results

Serum IgG for CDC25B, COX2, RCAS1, and FASCIN1 was significantly elevated in colorectal cancer patient sera compared to volunteers (CDC25B p=0.002, COX-2 p=0.001, FASCIN1 and RCAS1 p<0.0001). Epitopes predicted to bind to human class II MHC were identified for each protein and T-cells specific for both the peptides and corresponding recombinant protein were generated from human lymphocytes validating these proteins as human antigens. Some peptides were highly homologous between mouse and humans and after immunization, mice developed both peptide and protein specific IFN-γ-secreting cell responses to CDC25B, COX2 and RCAS1, but not FASCIN1. FVB/nJ mice immunized with CDC25B or COX2 peptides showed significant inhibition of growth of the syngeneic MC38 tumor compared to control (p<0.0001). RCAS1 peptide vaccination showed no anti-tumor effect. In the prophylactic setting, after immunization with CDC25B or COX2 peptides mice treated with AOM developed significantly fewer tumors as compared to controls (p<0.0002) with 50% of mice remaining tumor free in each antigen group. APC Min mice immunized with CDC25B or COX2 peptides developed fewer small bowel tumors as compared to controls (p=0.01 and p=0.02 respectively).

Conclusions

Immunization with CDC25B and COX2 epitopes consistently suppressed tumor development in each model evaluated. These data lay the foundation for the development of multi-antigen vaccines for the treatment and prevention of colorectal cancer.

Proton pump inhibitor omeprazole suppresses carcinogen induced colonic adenoma progression to adenocarcinoma in F344 rat

Colorectal cancer (CRC) causes over 53,000 deaths annually in the United States. Its rising incidences worldwide and particularly in young adults is a major concern. Here, we evaluated the efficacy of omeprazole (OME) that is clinically approved for treating acid-reflux, to enable its repurposing for CRC prevention. In the azoxymethane (AOM)-induced rat CRC model, dietary OME (250 and 500 ppm) was administered at early adenoma stage (8 weeks after AOM) to assess the progression of early lesions to adenocarcinoma. Administration of OME at 250 ppm or 500 ppm doses led to suppression of total colon adenocarcinoma incidence by 15.7% and 32% (p<0.01), respectively. Importantly, invasive carcinoma incidence was reduced by 59% (p<0.0005) and 90% (p<0.0001) in OME administered rats in a dose-dependent manner. There was also a strong and dose-dependent inhibition in the adenocarcinoma multiplicity in rats exposed to OME. Administration of 250 and 500 ppm OME inhibited total colon adenocarcinoma multiplicity by ~49% and ~65% (p<0.0001), respectively. While non-invasive adenocarcinomas multiplicity was suppressed by ~34% to ~48% (p<0.02), the invasive carcinomas multiplicity was reduced by ~74% to ~94% (p<0.0001) in OME exposed rats in comparison to the untreated rats. Biomarker analysis results showed a decrease in cell proliferation and anti-apoptotic/pro-survival proteins with an increase in apoptosis. Transcriptome analysis of treated tumors revealed a significant increase in adenocarcinoma inhibitory genes (Olmf4; Spink4) expression and down regulation of progression promoting genes (SerpinA1, MMP21, IL6). In summary, OME showed significant protection against the progression of adenoma to adenocarcinoma.

Abstract 1618: Inhibition of lung tumorigenesis by a novel small molecule CA170 targeting the immune checkpoint protein VISTA

Immunotherapy using monoclonal antibodies to block immune checkpoints is becoming a mainstream therapy for multiple late-stage cancers owing to their efficacy in improving clinical outcomes. However, relatively low response rates and persistent clinical side effects indicate the need for additional strategies to block immune-suppressive pathways. VISTA (V-domain Ig Suppressor of T cell Activation), which is expressed on cells of the myeloid and lymphoid lineages, is an emerging target for cancer immunotherapy. Blocking VISTA activates both innate and adaptive immunity to eradicate tumors in mice. We found that CA170, a novel orally bioavailable tripeptide small molecule antagonist of VISTA and PD-L1/PD-L2, has potent anticancer efficacy on carcinogen-induced mouse lung tumorigenesis. Remarkably, lung tumor development was almost completely suppressed when CA170 was combined with an MHC-II-directed KRAS peptide vaccine. Flow cytometry and single cell RNA sequencing (scRNA-seq) revealed that CA170 increases CD8+ T cell infiltration and effector functions by decreasing the tumor infiltration of myeloid derived suppressor cells (MDSCs) and regulatory T cells (Tregs), while the KRAS vaccine primarily induces expansion of CD4+ effector T cells. Inhibition of VISTA by CA170 has strong efficacy against lung tumorigenesis with broad immunoregulatory functions that influence effector, memory and regulatory T cells, and promotes an adaptive T cell tumor-specific immune response that enhances efficacy of the KRAS vaccine.

Citation Format: Jing Pan, Yao Chen, Qi Zhang, Achia Khatun, Katie Palen, Li Wang, Chuanjia Yang, Bryon D. Johnson, Charles R. Myers, Shizuko Sei, Robert H. Shoemaker, Ronald A. Lubet, Yian Wang, Weiguo Cui, Ming You. Inhibition of lung tumorigenesis by a novel small molecule CA170 targeting the immune checkpoint protein VISTA [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 1618.

Effects of High-Fructose Diet vs. Teklad Diet in the MNU-Induced Rat Mammary Cancer Model: Altered Tumorigenesis, Metabolomics and Tumor RNA Expression

Epidemiology, clinical and experimental animal studies suggest high fructose diets are detrimental to metabolic status and may contribute to tumor development. This due to increased obesity and metabolic syndrome, known risk factors for many types of cancer. We compared tumor development in N-methyl-N-nitrosourea (MNU)-treated rats fed either a high (60%)-fructose diet (HFD) or a standard diet (SD). Female Sprague-Dawley rats at 43 days of age (DOA) were fed a SD or HFD followed by administration of MNU at 50 DOA. Rats were palpated weekly and sacrificed at 190 DOA. MNU-treated rats on HFD exhibited decreased tumor latency and roughly a two-fold increase in tumor multiplicity. RNA-Seq on frozen tumors (SD vs. HFD rats) showed altered expression of approximately 10% of genes (P < 0.05). When examined by Ingenuity Pathway Analysis, multiple highly significant pathways were identified including A) mechanisms of cancer, B) Wnt pathway, C) immune response (e.g., "Th1 and Th2 activation" and "antigen presentation") and D) LXR/RXR nuclear receptor. These generalized pathways were indirectly confirmed by alterations of various interrelated disease pathways (epithelial cancers, T cell numbers and apoptosis). In a second study, serum was collected from rats on the HFD or SD pre-MNU and at the time of sacrifice. Metabolomics revealed that the HFD yielded: A) increased levels of fructose, B) increases of various monoglycerols, C) reduced levels of various diacylglycerols and oxygenated inflammatory lipids (9 and 13 HODE and 12,13 DHOME) and D) increased levels of secondary bile acids (hyodeoxycholate and 6-oxolithocholate), which may reflect microbiome changes. These metabolomic changes, which are distinct from those on a high-fat diet, may prove relevant when examining individuals who consume higher levels of fructose.

Abstract 4584: A novel combination of a multipeptide KRAS vaccine and an ACAT1 inhibitor to prevent lung cancer

Kirsten rat sarcoma viral oncogene homolog (KRAS) gene encodes a small GTPase that cycles between GDP and GTP-bound states, which modulates important cell surface receptors essential for cell proliferation and survival. It is one of the most common drivers for many types of cancers, is present in up to 25% all human tumors, and 80% of mutation occurs in codon12. Efforts to target KRAS-driven cancers preventively or therapeutically have been unsuccessful. We recently formulated a multi-peptide KRAS vaccine (KVAX), which targets both wild-type and G12D mutant forms of KRAS and has 100% sequence homology between human and mouse. KVAX elicited strong immunologic response and exhibited striking cancer preventive efficacy when administered prior to KRAS mutation induction. However, clinical high-risk individuals may already express mutant KRAS, which has known to promote an immunosuppressive environment. Therefore, we combined KVAX with avasimibe (AVA), an ACAT1 inhibitor that modulates lipid metabolism in T cells and facilitates better TCR/peptide/MHC interactions, in syngeneic lung cancer mouse model and genetically engineered mouse model, in which mutant KRAS initiated lung tumorigenesis before vaccination. We found that the combination significantly decreased the presence of regulatory T cells in the tumor microenvironment, facilitated CD8+ T cell infiltration in tumor sites, and ultimately led to enhanced anti-cancer efficacy. Using 10X Genomics, we performed single cell RNA-seq on lung tumors from mice treated with KVAX and AVA and found significant increases in APC monocytes and CD4+ Th1 cells, especially increases in the effector/memory T cell population. Meanwhile, KVAX also decreased Tregs and M2 macrophages. These studies include the evaluation of tumor-infiltrating immune cells by single-cell RNA-seq (scRNA-seq) and provide a more detailed mechanisms of action of KVAX alone or in combination with AVA in modulating the tumor immune microenvironment.

Citation Format: Jing Pan, Qi Zhang, Katie Palen, Bryon Johnson, Li Wang, Shizuko Sei, Robert H. Shoemaker, Ronald A. Lubet, Yian Wang, Ming You. A novel combination of a multipeptide KRAS vaccine and an ACAT1 inhibitor to prevent lung 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 4584.

Use of Biomarker Modulation in Normal Mammary Epithelium as a Correlate for Efficacy of Chemopreventive Agents Against Chemically Induced Cancers

In both estrogen receptor/progesterone receptor-positive (ER+/PR+) human breast cancer and in ER+/PR+ cancers in the methylnitrosourea (MNU)-induced rat model, short-term modulation of proliferation in early cancers predicts preventive/therapeutic efficacy. We determined the effects of known effective/ineffective chemopreventive agents on proliferative index (PI) in both rat mammary epithelium and small cancers. Female Sprague-Dawley rats were treated with MNU at 50 days of age. Five days later, the rats were treated with the individual compounds for a period of 14 days. At that time, normal mammary tissue from the inguinal gland area was surgically removed. After removal, the rats remained on the agents for an additional 5 months. This cancer prevention study confirmed our prior results of striking efficacy with tamoxifen, vorozole, Targretin, and gefitinib, and no efficacy with metformin, naproxen, and Lipitor. Employing a separate group of rats, the effects of short-term (7 days) drug exposure on small palpable cancers were examined. The PI in both small mammary cancers and in normal epithelium from control rats was >12%. In agreement with the cancer multiplicity data, tamoxifen, vorozole, gefitinib, and Targretin all strongly inhibited proliferation (>65%; P < 0.025) in the normal mammary epithelium. The ineffective agents metformin, naproxen, and Lipitor minimally affected PI. In the small cancers, tamoxifen, vorozole, and Targretin all reduced the PI, while metformin and Lipitor failed to do so. Thus, short-term changes in the PI in either normal mammary epithelium or small cancers correlated with long-term preventive efficacy in the MNU-induced rat model.

Combination of Erlotinib and Naproxen Employing Pulsatile or Intermittent Dosing Profoundly Inhibits Urinary Bladder Cancers

Daily dosing of either NSAIDs or EGFR inhibitors has been shown to prevent bladder cancer development in a N-butyl-(4-hydroxybutyl)nitrosamine (OH-BBN)-induced rat model. However, these inhibitors cause gastrointestinal ulceration and acneiform rash, respectively, limiting their continuous use in a clinical prevention setting. We studied chemopreventive efficacy of pulsatile dosing of EGFR inhibitor erlotinib (42 mg/kg BW, once/week) combined with intermittent or continuous low doses of the NSAID naproxen (30 mg/kg BW/day, 3 weeks on/off or 128 ppm daily in diet) in the OH-BBN induced rat bladder cancer model. The interventions were started either at 1 or 4 weeks (early intervention) or 3 months (delayed intervention) after the last OH-BBN treatment, by which time the rats had developed microscopic bladder lesions. All combination regimens tested as early versus late intervention led to the reduction of the average bladder tumor weights (54%-82%; P < 0.01 to P < 0.0001), a decrease in tumor multiplicity (65%-85%; P < 0.01 to P < 0.0001), and a decrease in the number of rats with large palpable tumors (>200 mg; 83%-90%; P < 0.01 to P < 0.0001). Levels of signal transduction markers, Ki-67, cyclin D1, IL1β, pSTAT3, and pERK, were significantly (P < 0.05 to P < 0.001) reduced in the treated tumors, demonstrating their potential utility as predictive markers for efficacy. These findings demonstrate that significant chemopreventive efficacy could be achieved with alternative intervention regimens designed to reduce the toxicity of agents, and that starting erlotinib and/or naproxen treatments at the time microscopic tumors were present still conferred the efficacy.

Potentiation of Kras peptide cancer vaccine by avasimibe, a cholesterol modulator

Background

No effective approaches to target mutant Kras have yet been developed. Immunoprevention using KRAS-specific antigenic peptides to trigger T cells capable of targeting tumor cells relies heavily on lipid metabolism. To facilitate better TCR/peptide/MHC interactions that result in better cancer preventive efficacy, we combined KVax with avasimibe, a specific ACAT1 inhibitor, tested their anti-cancer efficacy in mouse lung cancer models, where Kras mutation was induced before vaccination.

Methods

Control of tumor growth utilizing a multi-peptide Kras vaccine was tested in combination with avasimibe in a syngeneic lung cancer mouse model and a genetically engineered mouse model (GEMM). Activation of immune responses after administration of Kras vaccine and avasimibe was also assessed by flow cytometry, ELISpot and IHC.

Findings

We found that Kras vaccine combined with avasimibe significantly decreased the presence of regulatory T cells in the tumor microenvironment and facilitated CD8+ T cell infiltration in tumor sites. Avasimibe also enhanced the efficacy of Kras vaccines target mutant Kras. Whereas the Kras vaccine significantly increased antigen-specific intracellular IFN-γ and granzyme B levels in CD8+ T cells, avasimibe significantly increased the number of tumor-infiltrating CD8+ T cells. Additionally, modulation of cholesterol metabolism was found to specifically impact in T cells, and not in cancer cells.

Interpretation

Avasimibe complements the efficacy of a multi-peptide Kras vaccine in controlling lung cancer development and growth. This treatment regimen represents a novel immunoprevention approach to prevent lung cancer.

Intermittent Dosing Regimens of Aspirin and Naproxen Inhibit Azoxymethane-Induced Colon Adenoma Progression to Adenocarcinoma and Invasive Carcinoma

Chronic use of aspirin and related drugs to reduce cancer risk is limited by unwanted side effects. Thus, we assessed the efficacy associated with different dosing regimens of aspirin and naproxen. Azoxymethane (AOM)-rat colon cancer model was used to establish the pharmacodynamic efficacy of aspirin and naproxen under different dosing regimens. Colon tumors were induced in rats (36/group) by two weekly doses of AOM. At the early adenoma stage, rats were fed diets containing aspirin (700 and 1,400 ppm) or naproxen (200 and 400 ppm), either continuously, 1 week on/1 week off, or 3 weeks on/3 weeks off, or aspirin (2,800 ppm) 3 weeks on/3 weeks off. All rats were euthanized 48 weeks after AOM treatment and assessed for efficacy and biomarkers in tumor tissues. Administration of aspirin and naproxen produced no overt toxicities. Administration of different treatment regimens of both agents had significant inhibitory effects with clear dose-response effects. Aspirin suppressed colon adenocarcinoma multiplicity (both invasive and noninvasive) by 41% (P < 0.003) to 72% (P < 0.0001) and invasive colon adenocarcinomas by 67%-91% (P < 0.0001), depending on the treatment regimen. Naproxen doses of 200 and 400 ppm inhibited invasive adenocarcinoma multiplicity by 53%-88% (P < 0.0001), depending on the dosing regimen. Colonic tumor biomarker analysis revealed that proliferation (proliferating cell nuclear antigen and p21), apoptosis (p53 and Caspase-3), and proinflammatory mediators (IL1β and prostaglandin E₂) were significantly correlated with the tumor inhibitory effects of aspirin and naproxen. Overall, our results suggest that intermittent dosing regimens with aspirin or naproxen demonstrated significant efficacy on the progression of adenomas to adenocarcinomas, without gastrointestinal toxicities.

Pharmacometabolomic Pathway Response of Effective Anticancer Agents on Different Diets in Rats with Induced Mammary Tumors

Metabolomics is an effective approach to characterize the metabotype which can reflect the influence of genetics, physiological status, and environmental factors such as drug intakes, diet. Diet may change the chemopreventive efficacy of given agents due to the altered physiological status of the subject. Here, metabolomics response to a chemopreventive agent targretin or tamoxifen, in rats with methylnitrosourea-induced tumors on a standard diet (4% fat, CD) or a high fat diet (21% fat, HFD) was evaluated, and found that (1) the metabolome was substantially affected by diet and/or drug treatment; (2) multiple metabolites were identified as potential pharmacodynamic biomarkers related to targretin or tamoxifen regardless of diet and time; and (3) the primary bile acid pathway was significantly affected by targretin treatment in rats on both diets, and the lysolipid pathway was significantly affected by tamoxifen treatment in rats on the high fat diet.

Optimized Bexarotene Aerosol Formulation Inhibits Major Subtypes of Lung Cancer in Mice

Bexarotene has shown inhibition of lung and mammary gland tumorigenesis in preclinical models and in clinical trials. The main side effects of orally administered bexarotene are hypertriglyceridemia and hypercholesterolemia. We previously demonstrated that aerosolized bexarotene administered by nasal inhalation has potent chemopreventive activity in a lung adenoma preclinical model without causing hypertriglyceridemia. To facilitate its future clinical translation, we modified the formula of the aerosolized bexarotene with a clinically relevant solvent system. This optimized aerosolized bexarotene formulation was tested against lung squamous cell carcinoma mouse model and lung adenocarcinoma mouse model and showed significant chemopreventive effect. This new formula did not cause visible signs of toxicity and did not increase plasma triglycerides or cholesterol. This aerosolized bexarotene was evenly distributed to the mouse lung parenchyma, and it modulated the microenvironment in vivo by increasing the tumor-infiltrating T cell population. RNA sequencing of the lung cancer cell lines demonstrated that multiple pathways are altered by bexarotene. For the first time, these studies demonstrate a new, clinically relevant aerosolized bexarotene formulation that exhibits preventive efficacy against the major subtypes of lung cancer. This approach could be a major advancement in lung cancer prevention for high risk populations, including former and present smokers.

Comparison of Effects of Diet on Mammary Cancer: Efficacy of Various Preventive Agents and Metabolomic Changes of Different Diets and Agents

To determine the effects of diet, rats were placed on a standard diet (4% fat) or on a modified Western (high-fat diet, HFD) diet (21% fat) at 43 days of age (DOA) and administered methylnitrosourea (MNU) at 50 DOA. Rats were administered effective (tamoxifen, vorozole, and Targretin) or ineffective (metformin and Lipitor) chemopreventive agents either by daily gavage or in the diet beginning at 57 DOA and continuing until sacrifice (190 DOA). Latency period of the tumors was determined by palpation, and multiplicity and cancer weights per rat were determined at final sacrifice. Rats on the HFD versus standard diet had: (i) a 6% increase in final body weights; (ii) significant decreases in tumor latency; and (iii) significant increases in final tumor multiplicity and average tumor weight. Tamoxifen, vorozole, and Targretin were highly effective preventive agents, whereas Lipitor and metformin were ineffective in rats on either diet. Serum was collected at 78 DOA and at sacrifice (190 DOA), and metabolomics were determined to identify the metabolite changes due to diets and effective agents. Rats given the HFD had increased levels of saturated free fatty acids (including myristate) and decreased levels of 2-aminooctanoate. Furthermore, rats on the HFD diet had increased levels of 2-aminobutyrate and decreases in glycine markers previously identified as indicators of prediabetes. Targretin increased long-chain glycophospholipids (e.g., oleyl-linoleoyl-glycerophosphocholine) and decreased primary bile acids (e.g., taurocholate). Tamoxifen increased palmitoyl-linoleoyl-glycophosphocholine and decreased stearoyl-arachidonyl glycophosphocholine. Finally, increased levels of methylated nucleotides (5-methylcytidine) and decreased levels of urea cycle metabolites (N-acetylcitrulline) were associated with the presence of mammary cancers.

Screening of Chemopreventive Agents in Animal Models: Results on Reproducibility, Agents of a Given Class, and Agents Tested During Tumor Progression

Because of the importance of testing reproducibility of results, we present our findings regarding screening agents in preclinical chemoprevention studies in rodent models performed by the Chemopreventive Agent Development Research Group (CADRG) of the Division of Cancer Prevention of the NCI. These studies were performed via contracts to various commercial and academic laboratories. Primarily, results with positive agents are reported because positive agents may progress to the clinics. In testing reproducibility, a limited number of direct repeats of our standard screening assays were performed; which entailed initiating treatment shortly after carcinogen administration or in young transgenic mice and continuing treatment until the end of the study. However, three additional protocols were employed relating to reproducibility: (i) testing agents at lower doses to determine efficacy and reduced toxicity; (ii) testing agents later in tumor progression when microscopic lesions existed and, (iii) testing multiple agents of the same mechanistic class. Data with six models that were routinely employed are presented: MNU-induced ER-positive mammary cancer in rats; MMTV-Neu ER-negative mammary cancers in transgenic mice; AOM-induced colon tumors in rats; intestinal adenomas in Min mice; OH-BBN-induced invasive rat urinary bladder cancers in rats; and UV-induced skin squamous carcinomas in mice. It was found that strongly positive results were highly reproducible in the preclinical models evaluated. Cancer Prev Res; 11(10); 595-606. ©2018 AACR.

Abstract 1266: Downregulation of PD-L1 by NSAID administration augments the effects of a multi-antigen vaccine for the prevention of adenomatous polyps in APC(Min/+) mice

Introduction: We have shown that treatment of APC(Min/+) mice with NSAIDs will inhibit development of adenomatous polyps and induce significant levels of polyp-infiltrating CD8 T-cells. We sought to identify the mechanism of NSAID induced immune stimulation and questioned whether administration of NSAIDs concurrent with vaccination could further reduce polyp formation.

Methods: PD-L1 expression and T-cell infiltrates were assessed by IHC and flow cytometry. MC38 and RKO (murine/human colorectal carcinoma cell lines) were treated with naproxen (200uM-1000 uM) and harvested at 24, 48 and 72h. At 4-6 weeks, APC(Min/+) mice were given a multi-antigen peptide vaccine (COX2, CDC25B, EGFR) with CFA/IFA or adjuvant alone. Two groups received 400ppm naproxen orally 7d/wk for 18 weeks. Polyps were quantified at ≤24 weeks. Spleens and polyps were collected for IFN-gamma ELISPOT, flow cytometry, and IHC.

Results: Polyps from the APC(Min/+) mouse and both cancer cell lines highly express PD-L1. PD-L1 expression was significantly decreased in MC38 (p&lt;0.01) and RKO (p&lt;0.01) as compared to control after incubation with naproxen at all doses. The inhibitory effect of NSAIDs on PD-L1 expression was both time and dose dependent. We evaluated the in vivo effect of combination immunoprevention in the APC(Min/+). Animals receiving vaccine alone showed a 33% inhibition of polyp formation while naproxen alone showed 54% inhibition (p&lt;0.0001) compared to adjuvant alone. Combination treatment demonstrated significantly greater inhibition of polyps than either modality (p&lt;0.001), 81% inhibition vs. adjuvant. Antigen specific T-cells could be detected at higher levels than control antigen in both the vaccine alone (p=0.0001) and combination-treated animals (p&lt;0.0001). The antigen specific responses seen in combination treated animals were nearly two-fold that of vaccine alone (p=0.008). No antigen specific immunity was detected in naproxen and adjuvant only treated mice. The magnitude of the immune response was significantly correlated with lower polyp counts, with a Pearson correlation coefficient of -0.55 (p=0.0014). Detailed immunologic analysis of tumors will be presented.

Conclusions: NSAIDs, via modulation of PD-L1, synergize with vaccines to increase immunogenicity and enhance influx of polyp infiltrating lymphocytes. This synergy results in superior prevention of polyp formation compared to treatment with NSAID or vaccine alone and has high potential for clinical application.

Citation Format: Mary L. Disis, Lauren R. Corulli, Clinton Grubbs, Ronald A. Lubet, Paul Cowan, Ekram Gad. Downregulation of PD-L1 by NSAID administration augments the effects of a multi-antigen vaccine for the prevention of adenomatous polyps in APC(Min/+) mice [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 1266.

Abstract 4989: Efficacy of erlotinib and/or naproxen when administered by intermittent dosing schedules in the prevention of chemically induced urinary bladder cancers

Inflammation and epidermal growth factor receptor (EGFR) signaling dysregulation plays an important role in urinary bladder cancer development. We have previously shown that single agent regimens with erlotinib (EGFR inhibitor) or naproxen (nonsteroidal anti-inflammatory drug; NSAID) when given continuously were highly effective in the prevention of OH-BBN-induced urinary bladder cancers in rats. Better tolerated chemoprevention regimens can be obtained by reducing doses and frequency of administration. Low dose combinations may also achieve substantial efficacy with minimal toxicity by targeting complementary pathways. Female Fischer-344 rats were obtained at 28 days of age, placed on Teklad (4% fat) diet, and received OH-BBN (150 mg/gavage) 2x/week for 8 weeks beginning at 56 days of age. In the first study, beginning one week after the final OH-BBN treatment the rats (25/group) received either:

Group 1, erlotinib (42 mg/kg BW, 1x/week); Group 2, naproxen (30 mg/kg BW/day, 3 weeks on/ 3 weeks off); Group 3, the combination of erlotinib and naproxen (using the same treatment regimens), and Group 4, vehicle. The rats were palpated for urinary bladder tumors, weighed 1x/week and observed daily for signs of toxicity. At the end of the study (10 months after the initial OH-BBN), the average weights of the urinary bladders (bladder plus tumors combined) were determined. The weights in Groups 1-4 were: 194*, 186*, 136* and 354 mg (*P &lt;0.05, Wilcoxon Rank test). This was accompanied by an increase in tumor latency, a decrease in tumor multiplicity, and a decrease in the number of rats with large palpable tumors (&gt; 200 mg). The second study used the same treatment regimens, but administration of the agents was delayed until three months after the final OH-BBN treatment, at which point microscopic transitional cell carcinomas were present. At the end of the study (11 months after the initial OH-BBN), the weights of the individual bladders in Groups 1-4 were: 584, 234*, 138* and 779 mg (*P&lt; 0.05, Wilcoxon Rank test). Thus, naproxen and particularly the combination were still highly effective. This was accompanied by an increase in tumor latency and a decrease in the number of rats with large palpable tumors (&gt; 200 mg). These studies demonstrate that in protocols meant to reduce the toxicity of agents (weekly erlotinib or intermittent dosing with naproxen), high chemopreventive efficacy was achieved. Of importance, starting erlotinib and/or naproxen intermittent treatments at the time microscopic cancers were present still reduced the size of the urinary bladder cancers without showing observable toxicity. The latter is of particular interest based on the clinical FAP trial showing great efficacy of erlotinib and sulindac. Supported by NCI contract number HHSN261201500036I, Task Order HHSN26100002.

Citation Format: Altaf Mohammed, Mark S. Miller, Ronald A. Lubet, Chen Suen, Shizuko Sei, Robert H. Shoemaker, Clinton J. Grubbs. Efficacy of erlotinib and/or naproxen when administered by intermittent dosing schedules in the prevention of chemically induced urinary bladder cancers [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 4989.

Abstract B48: Animal models in use by the NCI PREVENT Cancer Preclinical Drug Development Program

The Chemopreventive Agent Development Research Group in the Division of Cancer Prevention at the National Cancer Institute administers the PREVENT Program to facilitate the development of cancer preventive interventions, including chemical and immunologic agents, and biomarkers for potential use in clinical trials (https://prevention.cancer.gov/major-programs/prevent-cancer-preclinical).

Recent technologic advances have enabled generation of newer preclinical animal models, which recapitulate the tumorigenic process of human cancers and have become the mainstay for translational research, as these models may be more likely to provide clinically translatable observations. Several carcinogen-induced rat and mouse models, along with genetically engineered mouse (GEM) and other transgenic animal models, are at the forefront of evaluating cancer-preventive efficacy of drugs and vaccines in various organ sites. A wide array of organ-specific animal cancer models is in use for agent efficacy and toxicity evaluations through the PREVENT program. Key characteristics of these animal models adopted by PREVENT studies include relevance to human cancers such as organ site pathology, involvement of genetic or carcinogenic drivers, and transformation of precursor lesions, as well as a consistent tumor burden within a well-defined time period.

Examples of organ site–specific animal models employed by the PREVENT studies include GEM/transgenic models: BRCA1ex11, TgMMTV-neu, TgN(C3-1-TAg)cJeg, MMTV-PPARδ BRCA1co/co, MMTVCre+/+, p53 (breast); APCMin/+, B6-Msh2loxP/loxP,Tg(Vil-Cre), AKRMin/+, ApcMin/FCCC, PIRC (Rat) (colon); AJp53wt/A135V, Trp53F2-10/F2-10, Rb1F19/F19, Adeno-Cre, A/J-ULp53, FVB-CCSPKrasG12D, B6-CCSP-EGFRL858R (lung); Asc−/−, Nf2+/−,Cdkn2a+/− (mesothelioma); LSL-KrasG12D/+ , p48Cre/+, Pdx1Cre, Ptf1Cre, SMAD4-/-, Trp53R172H, Ptf1aCreERTM, hMuc1, LSL-KrasG12V, ROSA_rtTA, p53L/+, iKRasG12D/+ (pancreas); TRAMP, PtenKO, Ptenflox/flox.R26ERG(CreERT2) (prostate); Dicer-/-, Pten-/-, Amhr2+/-, Ad-mCherry-Cre (ovarian); and the carcinogen induced cancer models: MNU, DMBA (breast); OH-BBN (bladder); AOM (colon); NNK, B[a]p, NTCU (lung); asbestos (mesothelioma), MNU (prostate); and 4NQO (head and neck). Agents/drugs that have been or are being evaluated for cancer-preventive efficacy using these models include chemoprevention agents: A438079, AR-509, AZ10606120, Aspirin, Atorvastatin, Bazedoxifene, Bexarotene, Brevail, Budesonide, Ciclesonide, ED-71, ERB-041, Erlotinib, Gefitinib, GLG-302, Gugglesterone, GW274150, INT-747, JNJ-26070109, Lapatinib, Licofelone, LFA9, LY500307, Metformin, Naproxen, Omeprazole, Onc-201, Pioglitazone, PX-102, Rapamycin, SC144, SD-6010, ShetA2, Selumitenib, SR-3029, Sulindac, YS-121, XL-147 and YF476; and immuno-prevention vaccines (DNA, peptide, protein): Plac1, α-enolase, Neu, IGF-1R, IGFBP-2, anti-Fusobacterium nucleatum vaccine, TERT, multivalent-peptide, DLK1, KRAS, EGFR, Muc1, α-enolase, and mesothelin vaccines.

Results from these studies will provide important data that will inform “go/no go” decisions in terms of advancing agents towards clinical trials targeting high-risk populations at the early stages of cancer development. Through the PREVENT program, different strategies including alternative dosing, lower dose drug combinations, and drug/vaccine combinations are being developed with the goal to minimize toxicity and improve efficacy. Importantly, the next generation of organ-site-specific inducible GEM models may allow for agent intervention at different stages of cancer development in adult animals representing human pathologies. We will present selected efficacy and mechanistic data for various chemopreventive agents/vaccines tested using these preclinical animal models.

Acknowledgments: These studies have been conducted by academic/industrial contract Principal Investigators as part of the NCI PREVENT Program.

Citation Format: Altaf Mohammed, Mark Steven Miller, Elizabeth Glaze, Romaine I. Fernando, Jennifer Fox, Ronald A. Lubet, Shizuko Sei, Robert H. Shoemaker. Animal models in use by the NCI PREVENT Cancer Preclinical Drug Development Program [abstract]. In: Proceedings of the AACR Special Conference: Advances in Modeling Cancer in Mice: Technology, Biology, and Beyond; 2017 Sep 24-27; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(10 Suppl):Abstract nr B48.

Daily or weekly dosing with EGFR inhibitors, gefitinib and lapatinib, and AKt inhibitor MK2206 in mammary cancer models

Daily vs. weekly dosing with EGFR inhibitors (gefitinib and lapatinib) and an AKT inhibitor (MK2206) were compared in two rodent breast cancer models. Female Sprague-Dawley rats were administered methylnitrosourea (MNU) at 50 days of age, and gefitinib (daily/weekly dosing at 10/70 mg/kg BW) or lapatinib (daily/weekly dosing at 75/525 mg/kg BW) were administered by gavage beginning 5 days after MNU. For the prevention studies, weekly or daily dosing with gefitinib or lapatinib reduced cancer multiplicity >75%, and all treatments reduced tumor weights by >90%. For the therapeutic studies, MNU-treated rats were followed until small palpable mammary cancers developed. The rats were then treated daily or weekly as above for 6 weeks. Either daily or weekly dosing with lapatinib or gefitinib caused regression in >50% of the tumors. Immunohistochemistry biomarker studies in palpable mammary cancers following a weekly dose of gefitinib showed that 1 day (but not 7 days) after treatment, the levels of phosphorylated EGFR1 were significantly decreased. In an ER-negative (ER⁻) Neu-overexpressing model employing MMTV-Neu/P53KO mice, daily (100 mg/kg BW/day, 5 days each week), or weekly dosing (500 or 250 mg/kg BW) with gefitinib reduced tumor multiplicity 65, 85 and 75%, respectively. In the MNU prevention model, daily dosing (100 mg/kg BW/day) with the allosteric AKT inhibitor MK2206 was ineffective, while weekly dosing (700 mg/kg BW) reduced the final tumor weight >70%. Combining weekly MK2206 with the aromatase inhibitor vorozole (0.12 mg/kg BW/day) showed that each compound alone reduced tumor multiplicity 40–50%. The combination reduced cancer multiplicity ~70%. These studies demonstrate the efficacy of weekly dosing with various protein kinase inhibitors; raising the possibility of employing these agents in a breast cancer preventive setting.

Novel mutational landscapes and expression signatures of lung squamous cell carcinoma

Lung squamous cell carcinoma (LUSC) is a major subtype of Non-Small Cell Lung Cancer. To increase our understanding of the LUSC pathobiology, we performed exome sequencing and RNA-seq in 16 murine carcinogen-induced LUSC tumors and 8 normal murine lung tissue samples. Additionally, we conducted single-cell RNA-seq on two independent tumors from the same murine model. We identified a list of 59 cancer genes recurrently mutated in the mice LUSC tumors, 47 (80%) of which were also mutated in human LUSCs. At the single cell level, we detected unique clonal mutation patterns for each of the two LUSC tumors, being initiated from clones carrying the mutant Igfbp7 and Trp53 genes, respectively. We also identified an expression signature serving as an effective classifier for LUSC tumors and a strong predictor of survival outcomes of lung cancer patients. Lastly, we found that some of the mutant LUSC genes were associated with the significantly altered tumoral expression of inhibitory immune checkpoint genes such as PD-L1, VISTA, TIM3 and LAG3 in human LUSCs. The novel findings of clonal evolution, mutational landscapes and expression signatures of LUSC suggested new targets for the overall LUSC therapy and the immunotherapy of LUSC.

Effect of weekly or daily dosing regimen of Gefitinib in mouse models of lung cancer

Gefitinib showed response in phase II clinical trials and with better clinical response in lung cancer with activating mutations in the tyrosine kinase domain of the EGFR. Questions of toxicity and potential dosing regimens impede the use in a prevention setting. This study will provide scientific evidence for the utility of testing and comparing weekly and daily dosing regimens in clinical trials. We employed the adenocarcinoma (AD) and squamous cell carcinoma (SCC) models to compare the efficacy of Gefitinib in daily or weekly dosing regimens. We also assessed the effectiveness of Gefitinib in altering growth of the H3255 xenograft. Bioluminescent imaging (BLI) and tumor size was evaluated. Relative expression of phospho-EGFR, phospho-ERK and phospho-AKT in the xenograft were evaluated by Western Blot analysis. In the lung AD model, Gefitinib showed significant inhibition of tumor load when treated with weekly or weekly intermittent dosing regimens in AJ/p53^val135/wtmice whereas a daily dosing regimen did not decrease the tumor load significantly. In the H3255-Luciferase xenograft model, weekly treatment demonstrated better inhibition than daily treatment. The weekly dosing regimen exhibited greater inhibition of phospho-EGFR, phospho-ERK and phospho-AKT than the daily dosing regimen, which may be correlated with the antitumor effects of the different dosing regimens. Weekly dosing with Gefitinib had similar or better efficacy than the daily dosing regimen in pre-clinical models of NSCLC. The data provide scientific evidences for the utility of testing and comparing weekly and intermittent dosing regimens in clinical trials.

Immunoprevention of KRAS-driven lung adenocarcinoma by a multipeptide vaccine

Lung cancer remains the leading cause of cancer death worldwide. Mutations in KRAS are detected in up to 30% of lung cancer cases. No effective therapies specifically targeting mutant KRAS have been developed. Vaccination against KRAS mutants is one of the venues of active exploration. The present study evaluated both immunogenicity and antitumor efficacy of a newly formulated multipeptide vaccine targeting multiple epitopes of the KRAS molecule. The formulated vaccine contained top four peptides, which elicited the strongest immunologic response and showed 100% sequence homology between human and mouse. The multipeptide KRAS vaccine was tested in an inducible CCSP-TetO-KRAS^G12D mouse model, where the vaccine was administered prior to activating the mutant KRAS protein. The KRAS peptide vaccine exhibited striking efficacy, reducing tumor number and tumor burden by >80% when compared with adjuvant alone. Splenocytes collected from vaccinated animals showed a robust immunologic response to the immunizing peptides. Furthermore, in vitro stimulation of these splenocytes by the vaccinated peptides resulted in the secretion of cytokines indicative of Th1 responses but with minimal secretion of Th2-related cytokines. The multipeptide KRAS vaccine was immunogenic and efficacious in the primary prevention of KRAS-induced lung cancer, indicating that the approach potentially can be used to prevent other KRAS-driven cancers, either alone or in combination with other modalities.

Lack of chemopreventive efficacy of metformin in rodent models of urinary bladder, head and neck, and colon/intestine cancer

Metformin is a biguanide employed in treating type II diabetes. Its potential efficacy for treating cancer has been demonstrated epidemiologically (lower cancer incidence in metformin users compared with users of sulfonylureas or insulin) and mechanistically, primarily in cell culture. Metformin decreases the levels of insulin-like growth factor 1 and secondarily inhibits the mammalian target of rapamycin pathway to exhibit anticancer effects. The current study examined its cancer preventive efficacy in multiple standard in situ arising cancer models. Metformin was administered orally by gavage or in the diet, at human equivalent doses, in numerous cancer models. In the hydroxybutyl(butyl)nitrosamine-induced model of invasive urinary bladder cancer, metformin (50 or 150 mg/kg body weight/day, intragastric) was ineffective despite high urinary concentrations of metformin. Metformin (250 or 500 ppm in diet) failed to decrease the incidence or invasiveness of squamous cell cancer of the tongue in a 4-nitroquinoline-1-(4NQO)-induced model. Finally, in the Min mouse model of gastrointestinal cancer, metformin (400 or 1,200 ppm in diet) was ineffective. Notably, a slight increase in intestinal tumor multiplicity was observed at the higher dose. Therefore, metformin lacked efficacy in multiple standard cancer models in non-diabetic rodents. This lack of efficacy may discourage any large phase clinical cancer trials in non-diabetic individuals in the absence of clear phase-II studies.

Pioglitazone-mediated reversal of elevated glucose metabolism in the airway epithelium of mouse lung adenocarcinomas

Airway epithelial cells are prone to the damage caused by lung cancer risk factors, such as cigarette smoking. Little is known about surrogate biomarkers in the bronchial airway epithelium that can be used to assess the effect of potential chemoprevention drugs on lung adenocarcinoma formation/progression. Pioglitazone has been suggested as a chemoprevention drug for lung cancer. To study the mechanisms underlying the role of pioglitazone in lung cancer prevention, we performed transcriptome sequencing (RNA-Seq) and found that Kras signaling was repressed by pioglitazone treatment in the airway epithelial cells of mice with lung adenocarcinoma (FDR q = 9.8E-04). It was also found that glucose metabolic pathways were elevated in the airway epithelium of mice with lung adenocarcinomas and inhibited by pioglitazone treatment (FDR q = 0.01). Downregulation of glucose metabolism genes was also observed in lung tumors of mice treated with pioglitazone. The high-risk expression signature of elevated glucose metabolism was associated with poor survival outcome in multiple lung adenocarcinoma patient populations (P values ranging from 1.0E-9 to 5.5E-5). Our results suggest that the role of pioglitazone in preventing lung adenocarcinoma may depend on inhibiting Kras signaling and glucose metabolism, which may serve as biomarkers of agent action in the airway epithelium.

Abstract 188: Preventive effect of aerosolized bexarotene in three major subtypes of lung cancer: adenocarcinoma, squamous cell carcinoma and small cell lung cancer in mice

Lung cancer is the leading cause of cancer-related deaths in the United States. The 5 year survival rate for lung cancer patients has remained a dismal 15% for 3 decades. Thus, the development of chemopreventive agents that could prevent lung cancer could potentially reduce the incidence and mortality of pulmonary neoplasms. Bexarotene has exhibited inhibitory effects in preclinical in vivo models of mammary and lung tumorigenesis, has been approved for clinical use in the treatment of cutaneous T-cell lymphoma, and has shown efficacy in phase I/II trials of non-small cell lung cancer (NSCLC). Preclinical studies have demonstrated that it is highly effective in the prevention of all three major subtypes of lung cancer in mouse models: adenocarcinoma (AD), squamous cell carcinoma (SCC), and small cell lung cancer (SCLC). The major side effects of bexarotene when administered orally to rodents or human patients have been hypertriglyceridemia and hypercholesterolemia. Previous studies in a mouse model of lung AD have demonstrated that aerosol delivery of bexarotene through nasal inhalation exhibited potent chemopreventive activity similar to that observed following oral administration (59 to74% reductions in lung tumor multiplicity). The significant decreases in tumor multiplicity and tumor load were achieved without hypertriglycerides that accompany oral bexarotene administration. In this study, aerosolized delivery of 10-30 mg/ml bexarotene showed a significant chemopreventive effect in all three major subtypes. In the N-nitroso-tris-chloroethylurea (NTCU) induced mouse SCC model, 1 week after the first dose of NTCU a dose dependent decrease in tumor formation was observed, with the highest dose causing 75% (p&lt;0.001) and 42% (p&lt;0.01) decreases in SCC tumor burden and the percentage of SCC tumors, respectively. Tumor load was decreased by 73% in A/Jp53 mouse AD model and by 41% in A/Jp53Rb mouse SCLC model. Aerosol delivery of bexarotene had no effect on animal body weight and other signs of toxicity, and no effect on triglyceride and cholesterol level. Aerosolized bexarotene formulation was effective against all 3 major lung cancer cell types and would be a major advance achieving significant reductions in preventing lung cancer incidence in persons at high risk of lung cancer e.g. former or present smokers.

Citation Format: Qi Zhang, Jing Pan, Marker S. Miller, Ronald A. Lubet, Yian Wang, Ming You. Preventive effect of aerosolized bexarotene in three major subtypes of lung cancer: adenocarcinoma, squamous cell carcinoma and small cell lung cancer in mice [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 188. doi:10.1158/1538-7445.AM2017-188

Abstract 5255: Comparison of high-fructose and standard diets in methylnitrosourea (MNU)-induced ER+ mammary cancers: Altered carcinogenesis, differential effects of metformin, and metabolomic differences

The MNU-induced model of ER+ mammary cancers in Sprague-Dawley rats has routinely been employed in screening for chemopreventive agents. We recently reported that metformin was ineffective in preventing mammary cancers in rats on a standard diet (Thompson, et al, Cancer Prev. Res, 8, 231-9, 2015). In this study, we evaluated the carcinogenic response in Vehicle-treated rats and rats receiving Metformin (150 mg/Kg BW/day) on standard Teklad or isocaloric High-Fructose diets. In the first study, rats were placed on Teklad or High-Fructose diet at 43 days of age. At 100 days of age, animals were administered a single dose of MNU. Animals were administered Metformin or tamoxifen beginning 5 days later. Rats were palpated weekly for mammary tumors and sacrificed at 300 days of age. Body weights between groups were not different. Tumor multiplicity and tumor weights were: Vehicle-Teklad,1.15 and 1.44g; Vehicle- High-Fructose, 2.10 and 2.94g; Metformin-Teklad, 1.25 and 1.91g; Metformin -High-Fructose, 1.00 and1.99g. Tamoxifen resulted in the prevention of all tumors. High-Fructose alone resulted in a 2X increase in tumor multiplicity (P&lt;0.05) and tumor weights (P&lt;0.05). In the Teklad diet, Metformin marginally increased tumor multiplicity and weights (0.1&gt;P&lt;0.05). In the High-Fructose diet, Metformin decreased tumor multiplicity by 50% (P&gt;0.05). In the second study, which parallels the standard MNU model, rats were also placed on Teklad or High-Fructose diet at 43 days of age. At 50 days of age, rats were administered a single dose of MNU. Rats on High-Fructose diet were administered either Vehicle or Metformin, while rats on Teklad diet were given only Vehicle; beginning 5 days later. Rats were palpated weekly and sacrificed at 170 days of age. Body weights between groups were not different. Tumor multiplicity and tumor weights were: Vehicle-High-Fructose, 6.00 and 7.74g; Metformin High-Fructose, 5.00 and 6.17g; and Vehicle-Teklad, 2.70 and 5.75g. As indicated, Vehicle-treated rats on High-Fructose diet had twice the number of cancers as Vehicle-Teklad diet (P&lt;0.05). Metformin had a minimal effect in rats on a High-Fructose diet; unlike our previous results in rats ( receiving MNU at 50 days of age) on Teklad or High-Fat diet where metformin increased cancer multiplicity and cancer weights. Furthermore, we performed metabolomic studies on both serum and cancers from animals on Teklad and High-Fructose diets. It was observed (based on principal component analysis) that serum from rats on High-Fructose and standard Teklad diet were profoundly different. Furthermore, there appeared to be a metabolic signature in rats bearing cancers. These and other metabolomic changes will be presented. Supported by NCI contract number HHSN261201200021I, Task Order HHSN26100005.

Citation Format: Mark S. Miller, Clinton J. Grubbs, Steve Stirdivant, Ronald A. Lubet. Comparison of high-fructose and standard diets in methylnitrosourea (MNU)-induced ER+ mammary cancers: Altered carcinogenesis, differential effects of metformin, and metabolomic differences [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 5255. doi:10.1158/1538-7445.AM2017-5255

Abstract 1698: Immunoprevention of KRAS-driven lung adenocarcinoma by a multi-peptide KRAS vaccine

Lung cancer remains the leading cause of cancer death worldwide. Mutations in KRAS are detected in up to 30% of lung cancer cases, about 80% of which occur in codon 12, yet no effective therapies specifically targeting mutant KRAS have been developed. Boosting the host immune response to cancer cells by vaccinating against defined tumor-associated antigens (TAAs) as a means of treating established tumors or preventing the development of tumors in high risk individuals such as current or former smokers is an area of intense research. The present study evaluated both immunogenicity and anti-tumor efficacy of a newly formulated multipeptide (peptides 15-17 amino acids long) vaccine targeting multiple epitopes of the KRAS molecule in a mouse model of KRAS-driven lung tumor. Vaccination was performed in the prevention setting in a transgenic mouse model, where mutated mouse Kras (G12D) is conditionally over-expressed in the lungs of mice using a CCSP promoter. A multi-score prediction algorithm was used to identify likely immunogenic epitopes in the KRAS protein sequence. The identified peptides were synthesized and screened in naïve mice for immunogenicity. The formulated vaccine contained the top four peptides, which elicited the strongest immunologic response and showed 100% sequence homology between human and mouse. The multipeptide KRAS vaccine was then tested in an inducible CCSP-TetO-KRASG12D mouse model, where the vaccines mixed with the Freund’s adjuvant or adjuvant alone were administered prior to activating the mutant KRAS protein. Our results show the KRAS peptide vaccine exhibited striking efficacy, reducing tumor number and tumor burden by &gt;80% when compared with adjuvant alone. Splenocytes collected from vaccinated animals at the end of the study showed a robust immunologic response to the immunizing peptides. Furthermore, in vitro stimulation of these splenocytes by the vaccine peptides resulted in the secretion of cytokines indicative of Th1 (interferon gamma) and Th17 (IL17) responses but with minimal secretion of Th2 related cytokines e.g. IL3 and IL4. In the draining lymph nodes from vaccinated mice rejecting tumors, there was a substantial increase in CD4 cells but a limited increase in CD8 cells. In summary, the multipeptide KRAS vaccine was immunogenic and efficacious in the primary prevention of KRAS-induced lung cancer in mice, indicating that the approach can potentially be used for the prevention of KRAS-driven cancers either alone or in combination with other modalities.

Citation Format: Jing Pan, Qi Zhang, Shizuko Sei, Robert H. Shoemaker, Ronald A. Lubet, Yian Wang, Ming You. Immunoprevention of KRAS-driven lung adenocarcinoma by a multi-peptide KRAS vaccine [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 1698. doi:10.1158/1538-7445.AM2017-1698

Abstract 5246: Effects of bazedoxifene either alone or in combination with letrozole in the prevention of chemically induced mammary cancers

Bazedoxifene is a third-generation selective estrogen receptor modulator (SERM) that has been clinically approved in Europe for the prevention and treatment of postmenopausal osteoporosis. The agent has also been shown to have therapeutic activity against estrogen receptor positive (ER+) breast cancer. Our laboratory is currently evaluating bazedoxifene for chemopreventive efficacy when given alone or in combination with the aromatase inhibitor (AI) letrozole. Initially, the agents were evaluated alone to determine effective chemopreventive doses in the methylnitrosourea (MNU) ER+mammary cancer model using female Sprague-Dawley rats. Bazedoxifene was mixed directly into a standard (Teklad, 4% fat) diet, while letrozole was gavaged 7x/week (vehicle was ethanol: PEG 400, 10:90, v/v). When evaluated alone in rats receiving MNU at 50 days of age, bazedoxifene (started one week after MNU) at doses of 100 and 30 mg/kg diet decreased mammary cancer multiplicity by 93 and 88%, respectively. In a similar protocol, letrozole at a dose of 0.1 mg/kg BW/day reduced cancer number (multiplicity) by 89%, while a dose of 0.05 mg/kg BW/day reduced the number by 47%. In a separate study evaluating lower doses (MNU also given to rats at 50 days of age), bazedoxifene at a dose of 5 mg/kg diet and letrozole at a dose of 0.04 mg/kg BW/day both decreased mammary tumor multiplicity by 73%. When the agents were given in combination at these lower dose levels, cancer number was reduced by 91%. An additional study was done in which the agents were given to rats receiving MNU at an older age (100 days). Rats receiving the agents at the original doses beginning one week after MNU (bazedoxifene at 30 mg/kg diet; letrozole at 0.1 mg/kg BW/day) had identical decreases in mammary tumor development (96%). It is obvious that bazedoxifene is as effective as letrozole in the prevention of mammary cancers even when initiated in older rats. Furthermore, administration of the agents in combination suggests an additive effect. The large increase in body weight gain generally noted in letrozole treated rats was not observed in rats receiving bazedoxifene; of interest, rats receiving the combination also had no increase in body weights. These studies indicate that bazedoxifene may be superior to other SERMs in that chemopreventive efficacy is achieved at low doses, which may be associated with less toxicity. Supported by NCI contract HHSN261201200021I, Task Order HHSN26100007.

Citation Format: Barbara K. Dunn, Chen Suen, Ronald A. Lubet, Vernon E. Steele, Clinton J. Grubbs. Effects of bazedoxifene either alone or in combination with letrozole in the prevention of chemically induced mammary cancers [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 5246. doi:10.1158/1538-7445.AM2017-5246

Abstract 7: Ceftriaxone, an FDA-approved cephalosporin antibiotic, suppresses lung cancer growth by targeting Aurora B

Ceftriaxone, an FDA-approved third-generation cephalosporin antibiotic, has antimicrobial activity against both gram-positive and gram-negative organisms. Generally, ceftriaxone is used for a variety of infections such as community-acquired pneumonia, meningitis and gonorrhea. Its primary molecular targets are the penicillin-binding proteins. However, other activities of ceftriaxone remain unknown. Herein, we report for the first time that ceftriaxone has antitumor activity in vitro and in vivo. Kinase profiling results predicted that Aurora B might be a potential ‘off’ target of ceftriaxone. Pull-down assay data confirmed that ceftriaxone could bind with Aurora B in vitro and in A549 cells. Furthermore, ceftriaxone (500 µM) suppressed anchorage-independent cell growth by targeting Aurora B in A549, H520 and H1650 lung cancer cells. Importantly, in vivo xenograft animal model results showed that ceftriaxone effectively suppressed A549 and H520 lung tumor growth by inhibiting Aurora B. These data suggest the anticancer efficacy of ceftriaxone for the treatment of lung cancers through its inhibition of Aurora B.

Citation Format: Xiang Li, Haitao Li, Shengqing Li, Feng Zhu, Dong Joon Kim, Hua Xie, Yan Li, Janos Nadas, Naomi Oi, Tatyana Zykova, Dong Hoon Yu, Mee-Hyun Lee, Myoung Ok Kim, Lei Wang, Wei Ya Ma, Ronald A. Lubet, Ann M. Bode, Ziming Dong, Zigang Dong. Ceftriaxone, an FDA-approved cephalosporin antibiotic, suppresses lung cancer growth by targeting Aurora B [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 7. doi:10.1158/1538-7445.AM2017-7

Epidermal growth factor receptor derived peptide vaccination to prevent lung adenocarcinoma formation: An in vivo study in a murine model of EGFR mutant lung cancer

The ability to prevent disease is the holy grail of medicine. For decades, efforts have been made to extend the successes seen with vaccination against infectious diseases to cancer. In some instances, preventive vaccination against viruses (prototypically HPV) has successfully prevented tumorigenesis and will make a major impact on public health in the decades to come. However, the majority of cancers that arise are a result of genetic mutation within the host, or non-viral environmental exposures. We present compelling evidence that vaccination against an overexpressed self-tumor oncoprotein has the potential to prevent tumor development. Vaccination against the Epidermal Growth Factor Receptor (EGFR) using a multipeptide vaccine in a preventive setting decreased EGFR-driven lung carcinogenesis by 76.4% in a mouse model of EGFR-driven lung cancer. We also demonstrate that anti-EGFR vaccination primes the development of a robust immune response in vivo. This study provides proof of concept for the first time that targeting tumor drivers in a preventive setting in lung cancer using peptide vaccination can inhibit tumorigenesis and may provide useful clinical insights into the development of strategies to vaccinate against EGFR in populations where EGFR-mutant disease is highly prevalent. © 2015 Wiley Periodicals, Inc.

Abstract 837: Reproducibility of efficacy results for chemopreventive agents in the methylnitrosourea-induced rat mammary cancer model

Perhaps the greatest question in biological science is: Can results be reproduced? This problem is of particular concern for a group whose primary mission is to screen for potentially effective agents and rank results by activity. The reproducibility of testing specific agents for chemopreventive activity, testing the same agent in various protocols, and testing multiple agents of a given mechanistic class in the MNU-induced model of ER+ breast cancer in Sprague-Dawley rats is presented. The model employs female virgin Sprague-Dawley rats on a standard 4% Teklad diet which develop ER+ mammary cancers (adenocarcinomas) following MNU injection at 50 days of age (DOA). Preventive agents were given by gavage or diet starting at 55 DOA, and animals monitored for tumor development until approximately 170 DOA. Seven agents which we had previously studied and which were strongly positive [tamoxifen, vorozole (an aromatase inhibitor), Targretin, gefitinib] or strongly negative (naproxen, Lipitor, metformin) were examined in the assays presented. These study results confirmed our previous data. We next tested these same agents in animals given a Western diet (high fat, low calcium) and again obtained the same results. We had thought that the altered physiology and potentially altered pharmacokinetics of rats on a Western diet might alter the observed chemopreventive efficacy. These studies show that the direct repetition of clearly positive and negative agents can be achieved and, in fact, repeated with a significant variation in diet. Importantly, in terms of reproducibility, we find that multiple agents of the same mechanistic class give similar results. Thus, various SERMs (tamoxifen, toremifene, Arzoxifene), RXR agonists (targretin, UAB-30, 4Me-UAB-30), EGFR inhibitors (gefitinib, Erlotinib, lapatinib) are all highly positive (70-95% reduction of cancer multiplicity). In contrast, the negative classes COX inhibitors (naproxen, sulindac, aspirin) or statins (atorvastatin or simvastatin) have been consistently negative (&lt;20% reduction). Therefore, reproducibility of efficacy results appears to be quite solid in our chemoprevention agent development program for rat mammary cancer testing, and we can, with significant certainty, trust our results.

Citation Format: Vernon E. Steele, Ronald A. Lubet, Clinton J. Grubbs. Reproducibility of efficacy results for chemopreventive agents in the methylnitrosourea-induced rat mammary cancer model. [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 837.

Abstract 824: Effects of metfornin on mammary carcinogenesis and metabolic profiles in methylnitrosourea-treated rats on standard or Western diets

The methylnitrosourea-induced model of ER+ mammary cancer in female Sprague-Dawley rats has been routinely used to screen for chemopreventive agents. We recently reported that metformin was ineffective in reducing cancer formation in rats on a standard (4% fat) diet (Thompson, et al., Cancer Prev Res. 8, 231, 2015). In the present studies, rats were placed on a standard (Teklad) diet or on a Western diet (20% fat, low calcium) at 43 days of age (DOA), and administered MNU at 50 DOA. Rats were administered metformin or vehicle daily by gavage beginning at 57 days of age. Serum from the rats of the various groups was obtained both at 21 days following initial administration of metformin (or vehicle) and at the end of the study (when tumors had developed in most rats). We found an increase in the final body weights, number of mammary cancers, and the final weights of tumors in rats on western diet compared with standard diet. Furthermore, metformin failed to decrease tumor multiplicity in either diet, in fact, it increased final cancer weights (P&lt;.05). Serum from rats in the various groups were examined for approximately 500 metabolites (Metabolon; Research Triangle Park, NC). The Metabolites which were differentially expressed when comparing Western vs standard diets at either time point included myoinositol, scyllo-inositol, 2-hydroxydecanoate, carnitine, tocopherol, and nicotinamide. Certain of these were fatty acids and lipid soluble vitamins that one would expect to be altered by diet. We also compared serum from animals on standard or Western diets at the early or late time points to determine metabolites associated with cancer development. Metabolites whose levels changed in tumor bearing rats included 4-OH-butyrate, acetyl-carnitine, uranate, and threonate. Finally, we compared the effects of metformin treatment in rats on Western or standard diet and found that the metabolic changes associated with metformin treatment were dependent on the diet employed. Thus, metformin altered levels of arachidate and serotonin only in rats on standard diet, while carnnitine and N-delta-acetylornithine were only modulated in rats on Western diet. Again, the most striking result may be that we still failed to observe any efficacy of metformin in animals on standard or Western diet.

Citation Format: Mark S. Miller, Matthew D. Thompson, Ronald A. Lubet, Vernon E. Steele, Harold E. Seifried, Clinton J. Grubbs. Effects of metfornin on mammary carcinogenesis and metabolic profiles in methylnitrosourea-treated rats on standard or Western diets. [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 824.

Abstract 2626: Metabolic profiles and potential pharmacodynamic biomarkers in female Sprague-Dawley rats on a standard (4% fat) or Western (20% fat) diet and treated with known active or inactive chemopreventive agents

The methylnitrosourea (MNU) - induced model of ER+ mammary cancers in female Sprague-Dawley rats has been routinely used in our laboratories for screening chemopreventive agents. In this study, we evaluated multiple known effective [tamoxifen, Targretin (an RXR agonist), Iressa (EGFR1 inhibitor)] or ineffective agents (Lipitor, metformin) in rats placed on either standard diet (20% fat) or a Western diet (20% fat, low calcium) at 43 days of age (DOA). Rats were given MNU at 50 DOA and administered the various agents or vehicle beginning at 57 DOA until the end of the study. Palpation of the rats showed that agents yielded the same results in rats on either diets. Somewhat surprisingly, metformin was ineffective in rats on either diet; confirming our lack of efficacy in a standard diet (Thompson, et al, Cancer Prev Res., 2015). To look for potential pharmacodynamics biomarkers, serum was obtained from the various groups at 78 days of age and at sacrifice; when a large tumor burden was observed in rats given vehicle, Lipitor, or metformin. Levels of approximately 500 metabolites were compared in the serum (Metabolon Research, Research Triangle Park, NC). We initially looked for metabolite changes related to different diets and found differential expression of alpha 10-undecanoate, 13-methylmyristic acid, 4-hydrox-benzoate, 2-amino-heptanpate, tocopherol and nicotinamide when comparing serum from rats on Western vs standard diets. Interestingly, each of the highly effective agents (tamoxifen, Targretin, and Iressa) yielded metabolic profiles that were strikingly different from rats given vehicle; based on unsupervised analysis. These metabolites become potential pharmacodynamic biomarkers for the highly effective doses of these agents. In contrast, the two negative agents did not yield a similar dichotomy between treated and vehicle serum. One could determine, however, metabolites which differed between metformin or Lipitor treated rats vs vehicle treated rats when performing a supervised analysis. We also compared serum for the early and late time points with either diet since the latter serum was from animals with a significant number of mammary cancers. We observed a number of metabolite changes including 4-OH butyrate, acetyl carnitine, oxalate, and threonate. These cancer related profiles will be discussed at greater length; in addition to the altered profiles caused by the administration of the various chemopreventive agents. Supported by NCI contract HHSN261201200021I.

Citation Format: Matthew D. Thompson, Clinton J. Grubbs, Vernon E. Steele, Mark S. Miller, Fariba Moeinpour, Edward D. Karoly, Ronald A. Lubet. Metabolic profiles and potential pharmacodynamic biomarkers in female Sprague-Dawley rats on a standard (4% fat) or Western (20% fat) diet and treated with known active or inactive chemopreventive agents. [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 2626.

5MeCDDO Blocks Metabolic Activation but not Progression of Breast, Intestine, and Tongue Cancers. Is Antioxidant Response Element a Prevention Target?

The preventive efficacy of the triterpenoid 5MeCDDO was tested in two models of mammary cancer, the Min model of intestinal cancer, and a chemically induced model of head and neck cancer. In one model of mammary cancer, female Sprague-Dawley rats were administered MNU at 50 days of age, and 5MeCDDO (27 ppm) was administered in the diet beginning 5 days later for the duration of the study; 5MeCDDO was ineffective. In contrast, in a model examining initiation of mammary cancers by the procarcinogen dimethyl-benzanthracene, 5, 6-benzoflavone (500 ppm, an Ah receptor agonist) or 5MeCDDO (27 or 2.7 ppm) decreased tumor multiplicity by 90%, 80%, and 50%, respectively. This anti-initiating effect which is presumably mediated by altered metabolic activation parallels our observation that 5MeCDDO induced proteins of various antioxidant response element (ARE)-related phase II drug-metabolizing enzymes [e.g., GST Pi, AKR 7A3 (aflatoxicol), epoxide hydrolase, and quinone reductase] in the liver. 5MeCDDO tested in the 4-nitroquinoline-l-oxide (4-NQO) head and neck cancer model failed to decrease tumor incidence or invasiveness. In the Min mouse model of intestinal cancer, a high dose of 5MeCDDO (80 ppm) was weakly effective in reducing adenoma multiplicity [∼30% (P < 0.05)]; however, a lower dose was totally ineffective. These findings question whether measuring increased levels of certain ARE-related genes (e.g., quinone reductase, GST Pi), indicating decreased carcinogen activation are sufficient to imply general chemopreventive efficacy of a given agent or mixture. Cancer Prev Res; 9(7); 616-23. ©2016 AACR.

Abstract P3-11-04: Metabolic profiles in female Sprague-Dawley rats receiving either a standard (4% fat) or Western (20% fat) diet and changes in rats bearing mammary cancers

The methylnitrosourea(MNU)-induced model of ER+ mammary cancers in female Sprague-Dawley rats has been routinely used in our laboratories for screening chemopreventive agents. We recently reported that metformin was ineffective in preventing mammary cancers in this model when given to rats on a standard diet (Thompson, et al, Cancer Prev Res. 2015;8:231-9). In this study, we evaluated metformin in rats placed on either standard diet (4% fat) or a Western diet (20% fat, low calcium). As fat calories, these diets were 8% and 42%, respectively. The rats were placed on standard diet or Western diet at 43 days of age, given MNU (via the jugular vein) once at 50 days of age, and administered metformin or vehicle at 57 days of age for the remainder of the study. Serum of the rats in the various groups was obtained at 78 days of age, and at the end of the study (when mammary tumors were present). The levels of approximately 500 metabolites were compared in the serum based on data obtained by Metabolon (Research Triangle Park, NC). These studies showed that each of the four groups [(standard diet (early and late) or Western diet (early and late)] yielded four clearly distinct patterns based on an unsupervised principal component analysis. Certain of the metabolites which were differentially expressed in serum from standard vs Western diets at the early time point were alpha-10-undecanoate, 13-methylmyristic acid, 4-hydroxy-benzoate, 2-amino-heptanpate, tocopherol, and nicotinamide. Certain of these were fatty acids and lipid soluble vitamins that one would expect to be altered. Comparing serum from standard vs Western diets at the late time point confirmed many of these metabolic differences. We also compared serum from the early and late time points since the latter serums were typically from animals with a significant number of mammary cancers. We observed a number of metabolite changes including 4-hydroxy-butyrate, acetyl-carnitine, oxalate, and threonate. These cancer- related profiles will be discussed at greater lengths. Altered profiles caused by the administration of metformin and other chemopreventive agents will also be discussed. Of interest, metformin was consistently ineffective in preventing mammary cancers in rats given either standard or Western diet. Supported by NCI contract HHSN261201200021I.

Citation Format: Thompson MD, Grubbs CJ, Moeinpour F, Steele VE, Miller MS, Lubet RA. Metabolic profiles in female Sprague-Dawley rats receiving either a standard (4% fat) or Western (20% fat) diet and changes in rats bearing mammary cancers. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P3-11-04.

Suppression of Rat Oral Carcinogenesis by Agonists of Peroxisome Proliferator Activated Receptor γ

Peroxisome-proliferator-activated receptor γ (PPARγ) is a ligand-activated transcription factor that regulates cell proliferation, differentiation, and apoptosis. In vivo studies were performed to evaluate the activities of two thiazolidinedione PPARγ agonists, rosiglitazone and pioglitazone, as inhibitors of oral carcinogenesis in rats. Oral squamous cell carcinomas (OSCC) were induced in male F344 rats by 4-nitroquinoline-1-oxide (NQO; 20 ppm in the drinking water for 10 weeks). In each study, groups of 30 NQO-treated rats were exposed to a PPARγ agonist beginning at week 10 (one day after completion of NQO administration) or at week 17 (7 weeks post-NQO); chemopreventive agent exposure was continued until study termination at week 22 (rosiglitazone study) or week 24 (pioglitazone study). Administration of rosiglitazone (800 mg/kg diet) beginning at week 10 increased survival, reduced oral cancer incidence, and reduced oral cancer invasion score in comparison to dietary controls; however, chemopreventive activity was largely lost when rosiglitazone administration was delayed until week 17. Administration of pioglitazone (500 mg/kg diet beginning at week 10 or 1000 mg/kg diet beginning at week 17) induced significant reductions in oral cancer incidence without significant effects on OSCC invasion scores. Transcript levels of PPARγ and its three transcriptional variants (PPARγv1, PPARγv2, and PPARγv3) were not significantly different in OSCC versus age- and site-matched phenotypically normal oral tissues from rats treated with NQO. These data suggest that PPARγ provides a useful molecular target for oral cancer chemoprevention, and that overexpression of PPARγ at the transcriptional level in neoplastic lesions is not essential for chemopreventive efficacy.

Abstract PR09: Intermittent dosing regimens maintain efficacy of several cancer preventing drugs

Many potential chemopreventive drugs have adverse effects on human subjects when given daily. One strategy to alleviate these adverse events is to give the drugs on an intermittent dosing schedule. Such intermittent dosing has proven effective in other settings to reduce toxicity with limited effect on efficacy. Two animal models were used: the rat methylnitrosourea (MNU) - induced mammary cancer model and the rat hydroxy-butyl(butyl)-nitrosamine (OH-BBN) -induced urinary bladder cancer model. For the mammary study female Sprague-Dawley rats were given 75 mg of MNU/kg body weight at 50 days of age and five days later the EGFR inhibitors, Erlotinib, Gefitinib or Lapatinib were administered either daily or once a week at two dose levels. Multiplicity of ER-positive mammary cancers was followed weekly for four months. For the urinary bladder study female Fischer 344 rats were given 150 mg OH-BBN/gavage twice weekly beginning at 56 days of age and continuing for 8 weeks. Two weeks after the last OH-BBN treatment the rats were given naproxen either daily, one week on/one week off, or 3 weeks on/3 weeks off. Bladders were excised after 8 months of naproxen treatment and bladders with tumors were excised and weighed. EGFR inhibitors and the NSAID, Naproxen, have similar efficacy when given intermittently compared to daily. The EGFR antagonists, Erlotinib and Lapatinib, decreased mammary cancer multiplicity by 90% given daily and 75 % given weekly. The NSAID, naproxen, decreased large bladder cancers by about 65-80% given either daily, one week on/one week off or 3 weeks on/3 weeks off. Therefore intermittent dosing can be used for agents in two different mechanistic classes in animal mammary and bladder cancer models to lower toxicity, yet show little reduction in chemoprevention efficacy compared to daily dosing. Intermittent dosing schedules in the clinic should reduce EGFR mediated rash and NSAID induced gastric toxicity clinically while retaining efficacy.

Citation Format: Vernon E. Steele, Clinton J. Grubbs, Ronald A. Lubet. Intermittent dosing regimens maintain efficacy of several cancer preventing drugs. [abstract]. In: Proceedings of the Thirteenth Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2014 Sep 27-Oct 1; New Orleans, LA. Philadelphia (PA): AACR; Can Prev Res 2015;8(10 Suppl): Abstract nr PR09.

Abstract 2809: Chemopreventive studies of multiple agents in the methylnitrosourea-induced ER+ mammary cancer model in animals on standard and Western diets

Multiple positive and negative preventive agents [tamoxifen, vorozole (aromatase inhibitor), targretin (RXR agonist), gefitinib (EGFR inhibitor), metformin, and Lipitor] were examined for efficacy in rats given either standard Teklad (4% fat) diet or a modified Western diet [high fat (42%)]. Female Sprague Dawley rats were placed on the high fat or standard diet at 43 days of age, and administered methylnitrosourea (MNU) at 50 days of age. Rats on high fat diet vs standard diet gained approximately 40% more weight, exhibited a 50% increase in cancer multiplicity, and a decrease in cancer latency. The strong preventive agents (tamoxifen, vorozole, targretin, and gefitinib) were highly effective in animals on standard or high fat diets (reducing cancer multiplicity &gt;75% in rats on either diet). It was unclear whether the altered physiology of animals on high fat diet or altered PK of agents in animals with higher fat content might alter activity of these agents. We had previously found that both metformin and Lipitor were ineffective in rats on a standard fat diet, but thought that they might be effective in rats on a high fat diet. Interestingly, neither compound decreased tumorigenesis; but, at least marginally, increased tumor incidence and final tumor weights in rats on both diets. The ability of the various agents to alter proliferation of normal mammary epithelium in MNU-treated rats exposed for 2 weeks to the various agents was determined. It was found that inhibition of proliferation in mammary epithelium corresponded well to the efficacy of these agents in long-term chemopreventive assays. These results demonstrated that: (1) a high fat diet can be employed in this rat model to increase tumor multiplicity; (2) tamoxifen, vorozole, targretin and gefitinib were highly effective in rats on standard or high fat diet; (3) metformin and Lipitor were ineffective with either diet; and (4) there is a correlation between inhibition of proliferation in normal mammary epithelium and long-term preventive efficacy of agents; but this may reflect the homogeneity of the rat mammary cancers. Supported by NCI contract HHSN261201200021I.

Citation Format: Clinton J. Grubbs, Mark S. Miller, Vernon E. Steele, Fariba Moeinpour, Harold Seifried, Brandy M. Heckman-Stoddard, Ronald A. Lubet. Chemopreventive studies of multiple agents in the methylnitrosourea-induced ER+ mammary cancer model in animals on standard and Western diets. [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 2809. doi:10.1158/1538-7445.AM2015-2809

Abstract P5-11-01: Correlation of the effects of potential and known chemopreventive agents on proliferation rates in normal mammary glands and mammary cancers with their chemopreventive efficacy

Core needle biopsy, fine needle aspiration, or imaging (e.g., mammography) are currently used to examine chemopreventive agent efficacy in Phase II breast cancer trials. However, biomarker endpoints, such as proliferation rates using Ki67 in normal or "at risk" breast tissue, have not been formally validated relative to cancer outcome. The aim of this study was to validate Ki-67 in "normal" mammary tissue from the methylnitrosourea (MNU) rat mammary tumor model with mammary cancer multiplicity within the same animal as surrogate biomarker for agent efficacy. Multiple studies were performed in female Sprague-Dawley rats to correlate this proliferation biomarker in mammary tissue after two weeks of chemoprevention agent treatment with mammary cancer incidence and multiplicity at the end of the study. In brief, MNU was given at 50 days of age, one week later administration of the agent was started, and after two weeks a biopsy of the mammary gland was taken. Treatment with the agents continued for approximately 150 days, at which time the study was terminated and mammary tumor multiplicity was measured. Changes in proliferation and mammary tumor multiplicity were compared to a control group of untreated group of animals within the same experiment using a two-sided Student t-test.

[table1]AgentNormal Mammary Gland Proliferation IndexFinal Mammary Cancer MultiplicityVorozole (1.25 mg/kg BW/day)88%↓90%↓Lipitor (125 mg/kg diet)38%↓16%↓Targretin (150 mg/kg diet)90%↓92%↓Naproxen (200 mg/kg diet)6%↑45%↑Iressa (10 mg/kg BW/day)52%↓93%↓Tamoxifen (3.3 mg/kg diet)77%↓100%↓Metformin (150 mg/kg BW/day)25%↓71%↑

In general, highly effective agents to preventing cancers (e.g., tamoxifen) also prevented normal mammary gland proliferation after only two weeks of treatment, while inactive agents (e.g., naproxen) had minimal effects on normal gland proliferation. The effects of the agents on established mammary cancers (in which the agents were given for 7 days to rats bearing small MNU-induced mammary cancers) showed similar correlations. Additional biomarkers, as well as the proliferation change and efficacy of these agents in rats fed a high-fat (Western) diet, will also be presented. In conclusion, determining the effect of a potential chemopreventive agent on cell proliferation following short-term treatment appears to be an effective method for predicting its efficacy in preventing mammary cancers. These data further confirm that Ki67 measurements are useful in Phase II prevention trials as a biomarker of agent efficacy.

Citation Format: Brandy M Heckman-Stoddard, Clinton J Grubbs, Fariba Moeinpour, Vernon E Steele, Ronald A Lubet. Correlation of the effects of potential and known chemopreventive agents on proliferation rates in normal mammary glands and mammary cancers with their chemopreventive efficacy [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P5-11-01.

Prevention of chemically induced urinary bladder cancers by naproxen: protocols to reduce gastric toxicity in humans do not alter preventive efficacy

The COX inhibitors (NSAID/Coxibs) are a major focus for the chemoprevention of cancer. The COX-2-specific inhibitors have progressed to clinical trials and have shown preventive efficacy in colon and skin cancers. However, they have significant adverse cardiovascular effects. Certain NSAIDs (e.g., naproxen) have a good cardiac profile, but can cause gastric toxicity. The present study examined protocols to reduce this toxicity of naproxen. Female Fischer-344 rats were treated weekly with the urinary bladder-specific carcinogen hydroxybutyl(butyl)nitrosamine (OH-BBN) for 8 weeks. Rats were dosed daily with NPX (40 mg/kg body weight/day, gavage) or with the proton pump inhibitor omeprazole (4.0 mg/kg body weight/day) either singly or in combination beginning 2 weeks after the final OH-BBN. OH-BBN-treated rats, 96% developed urinary bladder cancers. While omeprazole alone was ineffective (97% cancers), naproxen alone or combined with omeprazole-prevented cancers, yielding 27 and 35% cancers, respectively. In a separate study, OH-BBN -: treated rats were administered naproxen: (A) daily, (B) 1 week daily naproxen/1week vehicle, (C) 3 weeks daily naproxen/3 week vehicle, or (D) daily vehicle beginning 2 weeks after last OH-BBN treatment. In the intermittent dosing study, protocol A, B, C, and D resulted in palpable cancers in 27%, 22%, 19%, and 96% of rats (P < 0.01). Short-term naproxen treatment increased apoptosis, but did not alter proliferation in the urinary bladder cancers. Two different protocols that should decrease the gastric toxicity of NSAIDs in humans did not alter chemopreventive efficacy. This should encourage the use of NSAIDs (e.g., naproxen) in clinical prevention trials.

Lack of effect of metformin on mammary carcinogenesis in nondiabetic rat and mouse models

Epidemiologic studies have shown that diabetics receiving the biguanide metformin, as compared with sulfonylureas or insulin, have a lower incidence of breast cancer. Metformin increases levels of activated AMPK (AMP-activated protein kinase) and decreases circulating IGF-1; encouraging its potential use in both cancer prevention and therapeutic settings. In anticipation of clinical trials in nondiabetic women, the efficacy of metformin in nondiabetic rat and mouse mammary cancer models was evaluated. Metformin was administered by gavage or in the diet, at a human equivalent dose, in standard mammary cancer models: (i) methylnitrosourea (MNU)-induced estrogen receptor-positive (ER(+)) mammary cancers in rats, and (ii) MMTV-Neu/p53KO ER(-) (estrogen receptor-negative) mammary cancers in mice. In the MNU rat model, metformin dosing (150 or 50 mg/kg BW/d, by gavage) was ineffective in decreasing mammary cancer multiplicity, latency, or weight. Pharmacokinetic studies of metformin (150 mg/kg BW/d, by gavage) yielded plasma levels (Cmax and AUC) higher than humans taking 1.5 g/d. In rats bearing small palpable mammary cancers, short-term metformin (150 mg/kg BW/d) treatment increased levels of phospho-AMPK and phospho-p53 (Ser20), but failed to reduce Ki67 labeling or expression of proliferation-related genes. In the mouse model, dietary metformin (1,500 mg/kg diet) did not alter final cancer incidence, multiplicity, or weight. Metformin did not prevent mammary carcinogenesis in two mammary cancer models, raising questions about metformin efficacy in breast cancer in nondiabetic populations.

Enhanced antitumor activity of 3-bromopyruvate in combination with rapamycin in vivo and in vitro

3-Bromopyruvate (3-BrPA) is an alkylating agent and a well-known inhibitor of energy metabolism. Rapamycin is an inhibitor of the serine/threonine protein kinase mTOR. Both 3-BrPA and rapamycin show chemopreventive efficacy in mouse models of lung cancer. Aerosol delivery of therapeutic drugs for lung cancer has been reported to be an effective route of delivery with little systemic distribution in humans. In this study, 3-BrPA and rapamycin were evaluated in combination for their preventive effects against lung cancer in mice by aerosol treatment, revealing a synergistic ability as measured by tumor multiplicity and tumor load compared treatment with either single-agent alone. No evidence of liver toxicity was detected by monitoring serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) enzymes. To understand the mechanism in vitro experiments were performed using human non-small cell lung cancer (NSCLC) cell lines. 3-BrPA and rapamycin also synergistically inhibited cell proliferation. Rapamycin alone blocked the mTOR signaling pathway, whereas 3-BrPA did not potentiate this effect. Given the known role of 3-BrPA as an inhibitor of glycolysis, we investigated mitochondrial bioenergetics changes in vitro in 3-BrPA-treated NSCLC cells. 3-BrPA significantly decreased glycolytic activity, which may be due to adenosine triphosphate (ATP) depletion and decreased expression of GAPDH. Our results demonstrate that rapamycin enhanced the antitumor efficacy of 3-BrPA, and that dual inhibition of mTOR signaling and glycolysis may be an effective therapeutic strategy for lung cancer chemoprevention.

Honokiol inhibits lung tumorigenesis through inhibition of mitochondrial function

Honokiol is an important bioactive compound found in the bark of Magnolia tree. It is a nonadipogenic PPARγ agonist and capable of inhibiting the growth of a variety of tumor types both in vitro and in xenograft models. However, to fully appreciate the potential chemopreventive activity of honokiol, a less artificial model system is required. To that end, this study examined the chemopreventive efficacy of honokiol in an initiation model of lung squamous cell carcinoma (SCC). This model system uses the carcinogen N-nitroso-trischloroethylurea (NTCU), which is applied topically, reliably triggering the development of SCC within 24 to 26 weeks. Administration of honokiol significantly reduced the percentage of bronchial that exhibit abnormal lung SCC histology from 24.4% bronchial in control to 11.0% bronchial in honokiol-treated group (P = 0.01) while protecting normal bronchial histology (present in 20.5% of bronchial in control group and 38.5% of bronchial in honokiol-treated group. P = 0.004). P63 staining at the SCC site confirmed the lung SCCs phenotype. In vitro studies revealed that honokiol inhibited lung SCC cells proliferation, arrested cells at the G1-S cell-cycle checkpoint, while also leading to increased apoptosis. Our study showed that interfering with mitochondrial respiration is a novel mechanism by which honokiol changed redox status in the mitochondria, triggered apoptosis, and finally leads to the inhibition of lung SCC. This novel mechanism of targeting mitochondrial suggests honokiol as a potential lung SCC chemopreventive agent.

Src is a novel potential off-target of RXR agonists, 9-cis-UAB30 and Targretin, in human breast cancer cells

9-cis-UAB30 (UAB30) and Targretin are well-known retinoid X receptor (RXR) agonists. They were highly effective in decreasing the incidence of methylnitrosourea (MNU)-induced mammary cancers. However, whether the anti-mammary cancer effects of UAB30 or Targretin originate from the activation of RXR is unclear. In the present study, we hypothesized that UAB30 and Targretin not only affect RXR, but likely influence one or more off-target proteins. Virtual screening results suggest that Src is a potential target for UAB30 and Targretin that regulates extracellular matrix (ECM) molecules and cell motility and invasiveness. In vitro kinase assay data revealed that UAB30 or Targretin interacted with Src and attenuated its kinase activity. We found that UAB30 or Targretin substantially inhibited invasiveness and migration of MCF-7 and SK-BR-3 human breast cancer cells. We examined the effects of UAB30 and Targretin on the expression of matrix metalloproteinases (MMP)-9, which are known to play an essential role in tumor invasion. We show that activity and expression of MMP-9 were decreased by UAB30 or Targretin. Western blot data showed that UAB30 or Targretin decreased AKT and its substrate molecule p70(s6k), which are downstream of Src in MCF-7 and SK-BR-3 cells. Moreover, knocking down the expression of Src effectively reduced the sensitivity of SK-BR-3 cells to the inhibitory effects of UAB30 and Targretin on invasiveness. Taken together, our results demonstrate that UAB30 and Targretin each inhibit invasion and migration by targeting Src in human breast cancer cells.