NCI Resources for Cancer Immunoprevention Research

Cancer prevention and early detection, the first two of the eight primary goals of the National Cancer Plan released in April 2023, are at the forefront of the nation's strategic efforts to reduce cancer incidence and mortality. The Division of Cancer Prevention (DCP) of the NCI is the federal government's principal component devoted to promoting and supporting innovative cancer prevention research. Recent advances in tumor immunology, cancer immunotherapy, and vaccinology strongly suggest that the host immune system can be effectively harnessed to elicit protective immunity against the development of cancer, that is, cancer immunoprevention. Cancer immunoprevention may be most effective if the intervention is given before or early in the carcinogenic process while the immune system remains relatively uncompromised. DCP has increased the emphasis on immunoprevention research in recent years and continues to expand program resources and interagency collaborations designed to facilitate research in the immunoprevention field. These resources support a wide array of basic, translational, and clinical research activities, including discovery, development, and validation of biomarkers for cancer risk assessment and early detection (Early Detection Research Network), elucidation of biological and pathophysiological mechanistic determinants of precancer growth and its control (Translational and Basic Science Research in Early Lesions), spatiotemporal multiomics characterization of precancerous lesions (Human Tumor Atlas Network/Pre-Cancer Atlas), discovery of immunoprevention pathways and immune targets (Cancer Immunoprevention Network), and preclinical and clinical development of novel agents for immunoprevention and interception (Cancer Prevention-Interception Targeted Agent Discovery Program, PREVENT Cancer Preclinical Drug Development Program, and Cancer Prevention Clinical Trials Network).

Advances and challenges in cancer immunoprevention and immune interception

Invasive cancers typically evade immune surveillance through profound local and systemic immunosuppression, preventing their elimination or control. Targeting immune interventions to prevent or intercept premalignant lesions, before significant immune dysregulation has occurred, may be a more successful strategy. The field of cancer immune interception and prevention is nascent, and the scientific community has been slow to embrace this potentially most rational approach to reducing the global burden of cancer. This may change due to recent promising advances in cancer immunoprevention including the use of vaccines for the prevention of viral cancers, the use of cancer-associated antigen vaccines in the setting of precancers, and the development of cancer-preventative vaccines for high-risk individuals who are healthy but carry cancer-associated heritable genetic mutations. Furthermore, there is increasing recognition of the importance of cancer prevention and interception by national cancer organizations. The National Cancer Institute (NCI) recently released the National Cancer Plan, which includes cancer prevention among the top priorities of the institute. The NCI's Division of Cancer Prevention has been introducing new funding opportunities for scientists with an interest in the field of cancer prevention: The Cancer Prevention-Interception Targeted Agent Discovery Program and The Cancer Immunoprevention Network. Moreover, the Human Tumor Atlas Network is spearheading the development of a precancer atlas to better understand the biology of pre-invasive changes, including the tissue microenvironment and the underlying genetics that drive carcinogenesis. These data will inform the development of novel immunoprevention/immuno-interception strategies. International cancer foundations have also started recognizing immunoprevention and immune interception with the American Association for Cancer Research, Cancer Research UK and the Society for Immunotherapy of Cancer each implementing programming focused on this area. This review will present recent advances, opportunities, and challenges in the emerging field of cancer immune prevention and immune interception.

Frameshift mutations in peripheral blood as a biomarker for surveillance of lynch syndrome

BACKGROUND

Lynch syndrome (LS) is a hereditary cancer predisposition syndrome caused by germline mutations in DNA mismatch repair (MMR) genes, which lead to high microsatellite instability (MSI-H) and frameshift mutations (FSMs) at coding mononucleotide repeats (cMNRs) in the genome. Recurrent FSMs in these regions are thought to play a central role in the increased risk of various cancers. However, there are no biomarkers currently available for the surveillance of MSI-H-associated cancers.

METHODS

An FSM-based biomarker panel was developed and validated by targeted next generation sequencing of supernatant DNA from cultured MSI-H colorectal cancer cells. This supported selection of 122-FSM targets as potential biomarkers. This biomarker panel was then tested using matched tumor, adjacent normal tissue, and buffy coat (53 samples), and blood-derived cell-free DNA (cfDNA; 38 samples) obtained from 45 cases of MSI-H/MMR deficient (MMRd) patients/carriers. cfDNA from 84 healthy individuals was also sequenced to assess background noise.

RESULTS

Recurrent FSMs at cMNRs were detectable not only in tumors, but also in cfDNA from MSI-H/MMRd cases including a LS carrier with a varying range of target detection (up to 85.2%), whereas they were virtually undetectable in healthy individuals. ROC analysis showed high sensitivity and specificity (AUC = 0.94) of the investigated panel.

CONCLUSIONS

We demonstrated that FSMs can be detected in cfDNA from MSI-H/MMRd cases and asymptomatic carriers. The 122-target FSM panel described here has promise as a tool for improved surveillance of MSI-H/MMRd carriers with the potential to reduce the frequency of invasive screening methods for this high-cancer-risk cohort.

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.

Differential Effect of Non-Steroidal Anti-Inflammatory Drugs Aspirin and Naproxen against TMPRSS2-ERG (Fusion)-Driven and Non-Fusion-Driven Prostate Cancer

The consumption of the non-steroidal anti-inflammatory drug (NSAID) aspirin is associated with a significant reduction in the risk of developing TMPRSS2-ERG (fusion)-positive prostate cancer (PCa) compared to fusion-negative PCa in population-based case-control studies; however, no extensive preclinical studies have been conducted to investigate and confirm these protective benefits. Thus, the focus of this study was to determine the potential usefulness of aspirin and another NSAID, naproxen, in PCa prevention, employing preclinical models of both TMPRSS2-ERG (fusion)-driven (with conditional deletion of Pten) and non-TMPRSS2-ERG-driven (Hi-Myc+/- mice) PCa. Male mice (n = 25 mice/group) were fed aspirin- (700 and 1400 ppm) and naproxen- (200 and 400 ppm) supplemented diets from (a) 6 weeks until 32 weeks of Hi-Myc+/- mice age; and (b) 1 week until 20 weeks post-Cre induction in the fusion model. In all NSAID-fed groups, compared to no-drug controls, there was a significant decrease in higher-grade adenocarcinoma incidence in the TMPRSS2-ERG (fusion)-driven PCa model. Notably, there were no moderately differentiated (MD) adenocarcinomas in the dorsolateral prostate of naproxen groups, and its incidence also decreased by ~79-91% in the aspirin cohorts. In contrast, NSAIDs showed little protective effect against prostate tumorigenesis in Hi-Myc+/- mice, suggesting that NSAIDs exert a specific protective effect against TMPRSS2-ERG (fusion)-driven PCa.

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.

Organoids and metastatic orthotopic mouse model for mismatch repair-deficient colorectal cancer

Background

Genome integrity is essential for the survival of an organism. DNA mismatch repair (MMR) genes (e.g., MLH1, MSH2, MSH6, and PMS2) play a critical role in the DNA damage response pathway for genome integrity maintenance. Germline mutations of MMR genes can lead to Lynch syndrome or constitutional mismatch repair deficiency syndrome, resulting in an increased lifetime risk of developing cancer characterized by high microsatellite instability (MSI-H) and high mutation burden. Although immunotherapy has been approved for MMR-deficient (MMRd) cancer patients, the overall response rate needs to be improved and other management options are needed.

Methods

To better understand the biology of MMRd cancers, elucidate the resistance mechanisms to immune modulation, and develop vaccines and therapeutic testing platforms for this high-risk population, we generated organoids and an orthotopic mouse model from intestine tumors developed in a Msh2-deficient mouse model, and followed with a detailed characterization.

Results

The organoids were shown to be of epithelial origin with stem cell features, to have a high frameshift mutation frequency with MSI-H and chromosome instability, and intra- and inter-tumor heterogeneity. An orthotopic model using intra-cecal implantation of tumor fragments derived from organoids showed progressive tumor growth, resulting in the development of adenocarcinomas mixed with mucinous features and distant metastasis in liver and lymph node.

Conclusions

The established organoids with characteristics of MSI-H cancers can be used to study MMRd cancer biology. The orthotopic model, with its distant metastasis and expressing frameshift peptides, is suitable for evaluating the efficacy of neoantigen-based vaccines or anticancer drugs in combination with other therapies.

Abstract 5258: Preclinical testing of CD73 inhibitor AB680 for pancreatic cancer immunoprevention

Introduction: Pancreatic ductal adenocarcinoma (PDAC) is characterized by a profoundly immunosuppressive microenvironment. Innovative therapeutic strategies are urgently needed to stop the progression of precancerous lesions into aggressive PDAC, which remains a lethal malignancy. The goal of this research project is to test immunopreventive strategies by targeting the 5’ ectonucleotidase enzyme, CD73, one of the gatekeeper enzymes responsible for conversion of adenosine monophosphate (AMP), to an immunosuppressive metabolite, adenosine, in the tumor microenvironment (TME). We hypothesize that inhibition of CD73 will prevent pancreatic intraepithelial neoplasia (PanIN) formation and progression to PDAC by reversing adenosine directed immunosuppression. This research explores immunopreventive strategies aimed to restore tumor immune surveillance to prevent cancer initiation or progression.

Materials and methods: We used two models: a syngeneic model of PDAC using cells derived from KrasG12D;Trp53R172H/+;PdxCre (KPC) mice and a KrasG12D;PdxCre (KC) genetically engineered mouse model (GEM) of PDAC. Oral gavage of AB680 (small molecule CD73 inhibitor) was given three days/week at 10mg/kg starting the day after KPC injections and tumor sizes were measured weekly. In the GEM model, the same treatment regimen began when the mice were between 6 and 9 weeks old and were euthanized either between 15 and 20 weeks of age or around 27 weeks of age, and pancreas tissue was harvested. Histology was analyzed and 6 fields per mouse were quantified using ImageJ.

Results: As we have described (Singh, et al, bioRxiv), in the syngeneic model, there was a significant reduction in tumor growth and significant increase in activated CD8-positive T cells, dendritic cells, and macrophages from AB680 treated mice. The intratumoral adenosine levels were significantly decreased in AB680 treated mice compared to vehicle treated mice. In the KC GEM model, we quantified significantly fewer early PanIN lesions (p=0.0328), a trend in decreased advanced PanIN (p=0.0641), and significant decrease in PDAC (p=0.0058) in the AB680 treated mice when compared to the vehicle treated mice. We quantified abundance of collagen deposition as a marker of fibrosis and observed significantly decreased collagen (p<0.0001) in AB680 treated KC mice. In addition, we quantified abundance of CK19+ lesions and observed a significant decrease in CK19+ lesions in AB680 treated mice (p=0.0061) compared to vehicle treated mice.

Conclusion: Inhibiting CD73 restructures TME and reduces PanIN incidence and progression to PDAC. CD73 inhibition may be a candidate immunoprevention strategy in pancreatic cancer. [Supported by NCI 75N91019D00021/75N91020F00002]

Citation Format: Lincoln N. Strickland, Erika Y. Faraoni, Nicolette R. Mardik, Lana Vornik, Michelle I. Savage, Shizuko Sei, Mark S. Miller, Holger K. Eltzschig, Powel H. Brown, Florencia McAllister, Jennifer M. Bailey-Lundberg. Preclinical testing of CD73 inhibitor AB680 for pancreatic cancer immunoprevention. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5258.

Abstract 6518: Time course genomic characterization reveals progressive accumulation of mutations during tumor development in a Lynch syndrome mouse model

DNA mismatch repair (MMR) genes (e.g., MLH1, MSH2, MSH6, PMS2, and EPCAM) play an important role in maintaining genomic stability during DNA replication and recombination. Deficiency in MMR resulting from mutations in these genes leads to mutations in microsatellite regions throughout the genome (microsatellite instability; MSI) and in cancer driver oncogenes or tumor suppressor genes, which accumulate over time and eventually lead to cancer formation. Monoallelic germline mutation in MMR genes causes Lynch syndrome (LS). Among LS-related cancer types, the lifetime risk for colorectal cancer (CRC) is the highest (~80%). Frameshift mutations (FSMs) in coding microsatellites produce neoantigens, which have been shown to elicit immune responses. It was thus postulated that they can serve as vaccine targets. To develop a prophylactic vaccine and prevention strategy for this high-risk population, we characterized a LS mouse model (Msh2LoxP/LoxP;Villin-Cre) to determine whether these mice recapitulate the human LS oncogenic process. We found that tumor development was already notable at 7-8 months of age and median survival was 11.5 months. Histopathological analysis showed that tumors were adenoma or adenocarcinoma mixed with mucinous features. Using a targeted sequencing approach, a panel of FSMs in mononucleotide regions were identified in both tumors and histologically normal mucosa, suggesting that Msh2 deletion and FSMs were not sufficient for tumor development. In addition, Apc, Ctnnb, and Trp53 mutations were also observed with low frequency in organoids derived from these tumors, indicating that other driver mutations may be required for tumor initiation and progression, and most FSMs detected in tumors and mucosa were probably passenger mutations. To determine if fecal samples can be used to monitor the FSM load, fecal DNA from different time points was sequenced. We found that FSMs can be detected at 1month of age although the number of FSMs was relatively low compared to that from older mice, indicating that FSMs accumulate over time. MSI detection via fragment analysis confirmed that these tumors were MSI-H. Interestingly, mucosa and fecal samples from a time course study showed progressive increase in microsatellite instability, suggesting the possibility of using MSI score for disease monitoring. Our preliminary data indicates that combined fecal FSM status and MSI score can be potentially used as a biomarker to monitor the tumor development and disease progression for LS colorectal cancer.

Funded by the National Cancer Institute, National Institutes of Health, under Contract No. HHSN261201500003I

Citation Format: Yurong Song, Shaneen Baxter, Lisheng Dai, Chelsea Sanders, Holli Loomans-Kropp, Brandon Somerville, Ryan N. Baugher, Stephanie D. Mellott, Todd B. Young, Heidi E. Lawhorn, Teri M. Plona, Bingfang Xu, Lei Wei, Qiang Hu, Song Liu, Alan Hutson, Baktiar Karim, Simone Difilippantonio, Ligia Pinto, Matthias Kloor, Steven M. Lipkin, Shizuko Sei, Robert H. Shoemaker. Time course genomic characterization reveals progressive accumulation of mutations during tumor development in a Lynch syndrome mouse model. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6518.

CD73-Dependent Adenosine Signaling through Adora2b Drives Immunosuppression in Ductal Pancreatic Cancer

The microenvironment that surrounds pancreatic ductal adenocarcinoma (PDAC) is profoundly desmoplastic and immunosuppressive. Understanding triggers of immunosuppression during the process of pancreatic tumorigenesis would aid in establishing targets for effective prevention and therapy. Here, we interrogated differential molecular mechanisms dependent on cell of origin and subtype that promote immunosuppression during PDAC initiation and in established tumors. Transcriptomic analysis of cell-of-origin-dependent epithelial gene signatures revealed that Nt5e/CD73, a cell-surface enzyme required for extracellular adenosine generation, is one of the top 10% of genes overexpressed in murine tumors arising from the ductal pancreatic epithelium as opposed to those rising from acinar cells. These findings were confirmed by IHC and high-performance liquid chromatography. Analysis in human PDAC subtypes indicated that high Nt5e in murine ductal PDAC models overlaps with high NT5E in human PDAC squamous and basal subtypes, considered to have the highest immunosuppression and worst prognosis. Multiplex immunofluorescent analysis showed that activated CD8+ T cells in the PDAC tumor microenvironment express high levels of CD73, indicating an opportunity for immunotherapeutic targeting. Delivery of CD73 small-molecule inhibitors through various delivery routes reduced tumor development and growth in genetically engineered and syngeneic mouse models. In addition, the adenosine receptor Adora2b was a determinant of adenosine-mediated immunosuppression in PDAC. These findings highlight a molecular trigger of the immunosuppressive PDAC microenvironment elevated in the ductal cell of origin, linking biology with subtype classification, critical components for PDAC immunoprevention and personalized approaches for immunotherapeutic intervention.

SIGNIFICANCE

Ductal-derived pancreatic tumors have elevated epithelial and CD8+GZM+ T-cell CD73 expression that confers sensitivity to small-molecule inhibition of CD73 or Adora2b to promote CD8+ T-cell-mediated tumor regression. See related commentary by DelGiorno, p. 977.

Abstract 5260: Chemopreventive efficacy of everolimus and naproxen combination against carcinogen induced bladder cancer in F344 rats

Bladder Cancer (BC) is the second common genitourinary cancer with high recurrence and mortality rate due to metastatic muscle invasive BC (MIBC). Since majority of BCs are non-invasive at diagnosis, developing agents that effectively block BC progression may be beneficial for clinical translation. In this study, clinically approved agents, everolimus, mTOR inhibitor, [0.19mg/kg;7x/week (low dose, LD) or 1.33mg/kg;1x or 2X/week (high dose, HD)] at various dosing schedules alone or in combination with naproxen, an NSAID (30mg/kg body weight) intermittent dosing (3 Wks ON/OFF) were tested for efficacy in an N-butyl-N-(4- hydroxybutyl)nitrosamine (BBN)-induced BC rat model. Female F344 rats (8 weeks age; N=30) were gavaged 16 doses of BBN (150mg/dose). Either one-week (early intervention) or 12-weeks (late intervention) after BBN treatment, rats in each group received respective drug treatments by gavage. At 50 weeks age, rats were euthanized, and tissues were analyzed. Results suggest that BBN-exposed rats developed high number of Non-MIBC (NMIBC) and MIBC and had significantly large bladders (430±57mg, Mean±SEM; p<0.0001) compared to normal bladders in vehicle group (68.8±1.3mg). Importantly, there was significant reduction in tumor growth and progression of hyperplasia/papilloma with naproxen alone (3 weeks intermittent dosing) by 70% (129.7±7.7mg; p<0.0001) and 58% (180.8±27.6mg; p<0.001) at early and later interventions respectively compared to untreated BBN-exposed rats. Continuous LD or HD everolimus regimens during early intervention showed significant inhibitory effect on papilloma progression, whereas its delayed administration had modest to insignificant inhibitory effect of papilloma progression to NMIBC/MIBC. Intermittent dosing of naproxen alone inhibited large tumors (>200mg) incidence by 90% (p<0.0001) and by 75% (p<0.0001) with early and late interventions respectively. Early treatment with combinations led to >72% reduction in tumor weight (120.8±7.8mg, 121.8±11.5mg, and 118.6±5.2mg; p<0.0001) while late intervention had 58%-65% tumor reductions (179.6±14.4mg, 150.6±12.6mg, and 172.5±15.6mg; p<0.0005) with the combination dosing regimens. Notably, all 3 regimens of naproxen plus everolimus combinations significantly inhibited large tumor incidence at both early intervention (90%-100%; p<0.0001) and late intervention (60%-70%; p<0.0005), with significant suppression of papilloma progression to NMIBC and MIBC, including squamous cell carcinoma (SCC). Protein biomarker analysis suggested decrease in markers of proliferation, inflammation and mTOR signaling with an increased apoptosis. In summary, our study indicated that naproxen and everolimus combination can prevent bladder cancer progression and warrants further evaluation. (Supported by NCI-PREVENT program 75N91019D00020-75N91020F00003)

Citation Format: Venkateshwar Madka, Gopal Pathuri, Surya P. Singh, Anil Singh, Anh Bao, Nicole Stratton, Stanley Lightfoot, Clinton J. Grubbs, Jennifer Fox, John L. Clifford, Brian Cholewa, Shizuko Sei, CV Rao. Chemopreventive efficacy of everolimus and naproxen combination against carcinogen induced bladder cancer in F344 rats. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5260.

Combination of naproxen and a chemically-stable eicosapentaenoic acid analog provide additive tumor protection in Pirc rats

Colorectal cancer (CRC) is the second leading cause of cancer-related deaths in the United States. Patients with the genetic disorder Familial Adenomatous Polyposis (FAP) develop hundreds to thousands of polyps that unless removed by prophylactic colectomy will progress to CRC at an early age. Nonsteroidal anti-inflammatory drugs (NSAIDs) and the ω-3 polyunsaturated fatty acid (PUFA) eicosapentaenoic acid (EPA), have been evaluated for their chemopreventive potential in delaying CRC onset in high-risk patients. In our study, we determined whether the NSAID, naproxen, alone or in combination with a chemically-stable EPA analog (TP-252), affects tumor formation in the Apc^Pirc rat model. When compared to control diet, animals fed naproxen or HD TP-252 had 66% and 82% fewer tumors, respectively. However, animals fed a combination of naproxen and HD TP-252, exhibited a 95% reduction in tumor formation and a 98% reduction in tumor volume, respectively. To elucidate potential mechanisms of tumor protection, a comprehensive, targeted lipidomic analysis was performed on colonic mucosa to determine changes in eicosanoid metabolism. Animals receiving TP-252 alone or in combination with naproxen had significantly reduced mucosal levels of proinflammatory ω-6 eicosanoids (PGE₂ , 5-HETE and 14,15-DiHETrE), along with a simultaneous increase in anti-inflammatory EPA-derived ω-3 eicosanoids. A comprehensive lipidomic analysis also uncovered several potential pharmacodynamic (PD) lipid biomarkers, including resolvin E2, 9-HEPE, 12-HEPE and 18-HEPE, that were significantly correlated with tumor protection. Further studies with this drug combination should be focused on dose optimization and the role of EPA-derived lipid mediators in CRC initiation and progression.

Treatment Strategies and Mechanisms Associated with the Prevention of NASH-Associated HCC by a Toll-like Receptor 4 Inhibitor

We evaluated the cancer preventive efficacy of TAK-242, an inhibitor of Toll-like receptor 4 (TLR4), in a mouse model of hepatocellular carcinoma (HCC) occurring in the context of nonalcoholic steatohepatitis (NASH). We also assessed the cellular events associated with the preventive treatment efficacy. We tested oral administration of TAK-242, at clinically relevant but toxicity-reducing doses and scheduling, in mice with hepatocyte-specific deletion of Pten (HepPten-). The optimal dose and oral gavage formulation of TAK-242 were determined to be 30 mg/kg in 5% DMSO in 30% 2-hydroxypropyl-β-cyclodextrin. Daily oral administration of 30 mg/kg TAK-242 over 18 weeks was well tolerated and resulted in reduced development of tumors (lesions > 7.5 mm3) in HepPten- mice. This effect was accompanied by reduced macrovesicular steatosis and serum levels of alanine aminotransferase. In addition, 30 mg/kg TAK-242 daily treatment of small preexisting adenomas (lesions < 7.5 mm3) over 18 weeks, significantly reduced their progression to HCC. RNA sequencing identified 220 hepatic genes significantly altered upon TAK-242 treatment, that significantly correlated with tumor burden. Finally, cell deconvolution analysis revealed that TAK-242 treatment resulted in reduced hepatic populations of endothelial cells and myeloid-derived immune cells (Kupffer cells, Siglec-H high dendritic cells, and neutrophilic granule protein high neutrophils), while the proportion of mt-Nd4 high hepatocytes significantly increased, suggesting a decrease in hepatic inflammation and concomitant increase in mitochondrial function and oxidative phosphorylation upon TLR4 inhibition. In conclusion, this study identified treatment strategies and novel molecular and cellular mechanisms associated with the prevention of HCC in the context of NASH that merit further investigations.

PREVENTION RELEVANCE

Means to prevent development of HCC or progression of small adenomas to HCC in patients with NASH are urgently needed to reduce the growing mortality due to HCC. We characterized the chemopreventive effect of oral administration of the TLR4 inhibitor TAK-242 in a model of NASH-associated HCC.

Lynch syndrome cancer vaccines: A roadmap for the development of precision immunoprevention strategies

Hereditary cancer syndromes (HCS) account for 5~10% of all cancer diagnosis. Lynch syndrome (LS) is one of the most common HCS, caused by germline mutations in the DNA mismatch repair (MMR) genes. Even with prospective cancer surveillance, LS is associated with up to 50% lifetime risk of colorectal, endometrial, and other cancers. While significant progress has been made in the timely identification of germline pathogenic variant carriers and monitoring and early detection of precancerous lesions, cancer-risk reduction strategies are still centered around endoscopic or surgical removal of neoplastic lesions and susceptible organs. Safe and effective cancer prevention strategies are critically needed to improve the life quality and longevity of LS and other HCS carriers. The era of precision oncology driven by recent technological advances in tumor molecular profiling and a better understanding of genetic risk factors has transformed cancer prevention approaches for at-risk individuals, including LS carriers. MMR deficiency leads to the accumulation of insertion and deletion mutations in microsatellites (MS), which are particularly prone to DNA polymerase slippage during DNA replication. Mutations in coding MS give rise to frameshift peptides (FSP) that are recognized by the immune system as neoantigens. Due to clonal evolution, LS tumors share a set of recurrent and predictable FSP neoantigens in the same and in different LS patients. Cancer vaccines composed of commonly recurring FSP neoantigens selected through prediction algorithms have been clinically evaluated in LS carriers and proven safe and immunogenic. Preclinically analogous FSP vaccines have been shown to elicit FSP-directed immune responses and exert tumor-preventive efficacy in murine models of LS. While the immunopreventive efficacy of "off-the-shelf" vaccines consisting of commonly recurring FSP antigens is currently investigated in LS clinical trials, the feasibility and utility of personalized FSP vaccines with individual HLA-restricted epitopes are being explored for more precise targeting. Here, we discuss recent advances in precision cancer immunoprevention approaches, emerging enabling technologies, research gaps, and implementation barriers toward clinical translation of risk-tailored prevention strategies for LS carriers. We will also discuss the feasibility and practicality of next-generation cancer vaccines that are based on personalized immunogenic epitopes for precision cancer immunoprevention.

Abstract P004: Targeting the RXR pathway for the prevention of triple-negative breast cancer

Background: Triple-negative breast cancer (TNBC) is an aggressive cancer that lacks expression of the estrogen receptor (ER), progesterone receptor, and Erb-B2 receptor tyrosine kinase 2. TNBC patients exhibit a poor prognosis, even if treated with chemotherapy. Although studies using selective estrogen receptor modulators (SERMs) and aromatase inhibitors (AIs) have shown that breast cancer prevention is feasible, these drugs do not prevent ER-negative or TNBC tumors. It has been shown by our laboratory and others that retinoid X receptor (RXR)-specific ligands (rexinoids) can prevent breast cancers that are both ER-positive and ER-negative in mice. In our previous studies in MMTV-erbB2 mice, IRX-4204, a fourth generation rexinoid, prevented the development of most HER2/erbB2-positive tumors in these mice. For this study, we hypothesized that by targeting RXR pathway, we can prevent the development of triple negative, BRCA1-mutant mammary tumors in mice. To test the hypothesis, we treated MMTV-Cre/BRCA1co/co/p53+/- mice prior to their developing tumors with IRX-4204 to determine whether this RXR agonist effectively prevents triple-negative breast tumors. Methods: We tested the tumor preventative effect of IRX-4204 using the established MMTV-Cre/BRCA1co/co/p53+/- mouse model. These mice were produced by breeding MMTV-Cre/BRCA1co/co/p53+/- males and MMTV-Cre/BRCA1co/co/p53+/+ females, and female pups were PCR genotyped. All mice were separated into 4 groups: 1) sesame oil control, 2) IRX-4204 (10 mg/kg), 3) IRX-4204 (20 mg/kg) and 4) 9-cis-UAB-30 (5 mg/kg). All treatments were given by oral gavage, five days a week from 4 months of age. Mice were observed daily for tumor formation and toxicity. The percentage of tumor free mice were recorded, from which tumor incidence and time to tumor formation was visualized using Kaplan Meier curves and analyzed using the Log-rank test. Results: In MMTV-Cre/BRCA1co/co/p53+/- mice, IRX-4204 reduced tumor incidence and was associated with an increase in median tumor free survival time from 209 days to 336 days at 10 mg/kg dose (p=0.005). At the higher dose (20 mg/kg) IRX-4204 also delayed tumor formation with median tumor free survival from 209 days to 260 days (p=0.039). The rexinoid 9-cis-UAB 30 also significantly delayed tumor formation in MMTV-Cre/BRCA1co/co/p53+/- mice with median survival from 209 days to 270 days (p=0.04). Long term treatment of IRX-4204 was not associated with any toxicity. Conclusion: RXR agonist IRX-4204 delayed ER-negative mammary tumor formation in BRCA1co/co; MMTV-Cre; p53+/- mice. Based on our results, IRX-4204 is an effective cancer preventive drug without observed toxicity. Our results suggest that studies with reduced IRX-4204 dose alone or in combination with other targeted therapies such as selective estrogen receptor modulators are warranted. In the future, clinical trials of the IRX-4204 should be considered for the prevention of breast cancer in high-risk patients. (Supported by NCI-PREVENT contract to P. Brown and A. Mazumdar HHSN26100008).

Citation Format: Cassandra Moyer, Jamal Hill, Darian Coleman, Shizuko Sei, Altaf Mohammed, Martin Sanders, Powel Brown, Abhijit Mazumdar. Targeting the RXR pathway for the prevention of triple-negative breast cancer. [abstract]. In: Proceedings of the AACR Special Conference: Precision Prevention, Early Detection, and Interception of Cancer; 2022 Nov 17-19; Austin, TX. Philadelphia (PA): AACR; Can Prev Res 2023;16(1 Suppl): Abstract nr P004.

Precision immunointerception of EGFR-driven tumorigenesis for lung cancer prevention

Epidermal growth factor receptor (EGFR) mutations occur in about 50% of lung adenocarcinomas in Asia and about 15% in the US. EGFR mutation-specific inhibitors have been developed and made significant contributions to controlling EGFR mutated non-small cell lung cancer. However, resistance frequently develops within 1 to 2 years due to acquired mutations. No effective approaches that target mutant EGFR have been developed to treat relapse following tyrosine kinase inhibitor (TKI) treatment. Vaccination against mutant EGFR is one area of active exploration. In this study, we identified immunogenic epitopes for the common EGFR mutations in humans and formulated a multi-peptide vaccine (E^mut Vax) targeting the EGFR L858R, T790M, and Del19 mutations. The efficacy of the E^mut Vax was evaluated in both syngeneic and genetic engineered EGFR mutation-driven murine lung tumor models with prophylactic settings, where the vaccinations were given before the onset of the tumor induction. The multi-peptide E^mut Vax effectively prevented the onset of EGFR mutation-driven lung tumorigenesis in both syngeneic and genetically engineered mouse models (GEMMs). Flow cytometry and single-cell RNA sequencing were conducted to investigate the impact of E^mut Vax on immune modulation. E^mut Vax significantly enhanced Th1 responses in the tumor microenvironment and decreased suppressive Tregs to enhance anti-tumor efficacy. Our results show that multi-peptide E^mut Vax is effective in preventing common EGFR mutation-driven lung tumorigenesis, and the vaccine elicits broad immune responses that are not limited to anti-tumor Th1 response.

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 &gt;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 the mTOR Pathway for the Prevention of ER-Negative Breast Cancer

PREVENTION RELEVANCE

Our results show that everolimus delays mammary tumor formation in multiple mouse models, suggesting that mTOR inhibitors will be useful for the prevention of ER-negative and triple-negative breast cancer in humans. See related Spotlight, p. 787.

Abstract IA007: PREVENT agent development pipeline

The NCI’s PREVENT Cancer Preclinical Drug Development Program is a peer-reviewed program designed to support the preclinical development of promising agents and biomarkers for cancer interception/prevention towards clinical applications. PREVENT is not a grant program but allocates NCI contract resources to advance approved projects in a milestone-driven manner. Results obtained through NCI contract resources are returned to the applicant PIs and used to support further development by the applicants or in partnership with NCI. Resources available to PREVENT Program applicants include preclinical efficacy testing, CGMP manufacturing, GLP pharmacokinetic and IND-enabling toxicology studies, and IND filings. The PREVENT Program is focused on preventive agent development in the areas of Immunoprevention (cancer vaccines and immunomodulatory agents), Chemoprevention (novel mechanisms, anti-inflammatory agents, drug repurposing, toxicity reduction via alternative dosing regimens and agent combinations) and clinically translatable mechanistic biomarkers (pharmacodynamics, immune correlates, and tumor preventive efficacy). Submission deadlines for PREVENT Concept Applications occur twice per year on the second Monday in January and July. Further information can be obtained at the PREVENT Program website: https://prevention.cancer.gov/major-programs/prevent-cancer-preclinical

Citation Format: Mark Stevn Miller, Brian Cholewa, John Clifford, Vignesh Gunasekharan, Altaf Mohammed, Shanker Gupta, Robert Shoemaker, Shizuko Sei. PREVENT agent development pipeline [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 IA007.

Abstract IA013: Preclinical testing of CD73 inhibitors for pancreatic cancer immunoprevention

Introduction: The all stages combined five-year survival rate for pancreatic adenocarcinoma (PDA) is 11%; however, the five-year survival rate for localized PDA is 42%. These statistics highlight the importance of early prevention strategies to prevent disease progression and metastatic dissemination. Through the NCI PREVENT program, this research program explores immunoprevention strategies for PDA by targeting CD73, a gatekeeper ectoenzyme responsible for production of extracellular adenosine. We have recently shown aggressive subtypes of pancreatic intraepithelial neoplasia (PanIN) and PDA arising in ductal pancreatic epithelium have elevated CD73 and intrapancreatic adenosine indicating adenosine generation may be an early trigger of immunosuppression. We hypothesize inhibition of CD73 and adenosine generation will promote a more robust anti-tumor immune response and prevent PanIN and PDA progression. Methods: We tested three small molecule CD73 inhibitors (APCP, OP-5244, and AB680) in a syngeneic PDA mouse model by injecting 100-200k murine PDA cells derived from KrasG12D;Trp53R172H/+;Pdx:Cre (KPC) mice in the flanks of C57BL/6 female mice.

Tumor sizes were measured weekly and tumor volume and mass were recorded at time of death. Dosage: APCP oral gavage (3x/week at 20mg/kg) and intraperitoneal (IP) (3x/week at 20 mg/kg). OP-5244 oral (3x/week at 25mg/kg and 10mg/kg). AB680 oral gavage (3x/week at 10mg/kg). HPLC analysis was performed for each inhibitor to quantify adenosine levels.

Results: IP delivery of APCP significantly reduced tumor growth and intratumoral adenosine levels; however oral gavage delivery did not reduce tumor growth. Similarly, oral gavage delivery of OP-5244 did not reduce tumor growth. AB680 significantly reduced tumor volume and intratumoral adenosine levels and CyTOF immunoprofiling showed activated CD8+ T cells, dendritic cells, and macrophages were significantly increased in the tumors from AB680 treated mice. Conclusion: APCP IP delivery is more effective than oral gavage delivery and OP-5244 oral gavage delivery does not significantly decrease tumor growth. AB680 oral gavage delivery significantly decreases tumor growth and tumor adenosine concentrations. We observed a significant increase in infiltration of activated CD8+ T cells. AB680 shows high translational potential for preclinical testing in spontaneous GEM models.

Citation Format: Lincoln Ballew, Kanchan Singh, Vidhi Chandra, Tingting Mills, Erika Y. Faraoni, Victoria Mota, Trent Clark, Lana Vornik, Michelle I. Savage, Shizuko Sei, Altaf Mohammed, Holger K. Eltzschig, Powel H. Brown, Florencia McAllister, Jennifer M. Bailey-Lundberg. Preclinical testing of CD73 inhibitors for pancreatic cancer immunoprevention [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 IA013.

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.

High-power laser experiment on developing supercritical shock propagating in homogeneously magnetized plasma of ambient gas origin

A developing supercritical collisionless shock propagating in a homogeneously magnetized plasma of ambient gas origin having higher uniformity than the previous experiments is formed by using high-power laser experiment. The ambient plasma is not contaminated by the plasma produced in the early time after the laser shot. While the observed developing shock does not have stationary downstream structure, it possesses some characteristics of a magnetized supercritical shock, which are supported by a one-dimensional full particle-in-cell simulation taking the effect of finite time of laser-target interaction into account.

Characterization of stage-specific tumor progression in TMPRSS2-ERG (fusion)-driven and non-fusion-driven prostate cancer in GEM models

In the present study, we performed a comparative stage-specific pathological and molecular marker evaluation of TMPRSS2-ERG fusion and PTEN loss-driven (TMPRSS2-ERG. Pten^flox/flox ) versus non-fusion-driven prostate tumorigenesis (Hi-Myc) in mice. Anterior, ventral, and dorsolateral prostates were collected from mice at different ages (or time points post-Cre induction). Results indicated that growth and progression of prostatic intraepithelial lesions to adenocarcinoma stages occurred in both mice models albeit at different rates. In the TMPRSS2-ERG. Pten^flox/flox mice, the initiation of tumorigenesis was slow, but subsequent progression through different stages became increasingly faster. Adenocarcinoma stage was reached early on; however, no high-grade undifferentiated tumors were observed. Conversely, in the Hi-Myc^+/- mice, tumorigenesis initiation was rapid; however, progression through different stages was relatively slower and it took a while to reach the more aggressive phenotype stage. Nevertheless, at the advanced stages in the Hi-Myc^+/- mice, high-grade undifferentiated tumors were observed compared to the later stage tumors observed in the fusion-driven TMPRSS2-ERG. Pten^flox/flox mice. These results were corroborated by the stage specific-pattern in the molecular expression of proliferation markers (PCNA and c-Myc); androgen receptor (AR); fusion-resultant overexpression of ERG; Prostein (SLC45-A3); and angiogenesis marker (CD-31). Importantly, there was a significant increase in immune cell infiltrations, which increased with the stage of tumorigenesis, in the TMPRSS2-ERG fusion-positive tumors relative to fusion negative tumors. Together, these findings are both novel and highly significant in establishing a working preclinical model for evaluating the efficacy of interventions during different stages of tumorigenesis in TMPRSS2-ERG fusion-driven PCa.

Abstract 719: Preclinical testing of CD73 inhibitors for pancreatic cancer immunoprevention

Introduction: Pancreatic ductal adenocarcinoma (PDAC) is characterized by a profoundly immunosuppressive microenvironment. Innovative therapeutic strategies are urgently needed to stop the progression of precancerous lesions into aggressive PDAC, which remains a lethal malignancy. The goal of this research project is to test the immunopreventive strategies by targeting the ectonucleotidase CD73, one of the gatekeeper enzymes responsible for adenosine production and the formation of immunosuppressive tumor microenvironment in this malignancy. We hypothesize that inhibition of CD73 will prevent pancreatic intraepithelial neoplasia (PanIN) formation and progression to PDAC by reversing immunosuppression.

Materials and methods: A syngeneic PDAC mouse model was employed by injecting 100k murine pancreatic cancer (KPC) cells in flanks of C57BL/6 female mice. Oral gavage of AB680 (small molecule CD73 inhibitor) was given three days/week at 10mg/kg starting the day after KPC injections and tumor sizes were measured weekly. Toxicity was analyzed by serum ALT analysis. At the time of death 6 weeks post-KPC inoculation, tumor volume and mass were recorded. In another experiment, AB680 was administered 3 days/week at 10mg/kg for 5 weeks. CyTOF immunoprofiling of digested tumors from control and AB680 treated mice and HPLC analysis on serum from the time of death were performed.

Results: In experiment 1, by week three of the study, there was a significant difference in tumor volume between the control and AB680 treated groups (P=0.02). However, in weeks 4-5 AB680 reduced tumor growth compared to vehicle controls, but the grouped statistical analysis was not significant. When observing individual tumors, there was a reduction in tumor size in 30% of the AB680 treated mice between weeks 3-5, but the difference was not statistically different. ALT analysis determined AB680 does not induce liver toxicity. For experiment 2 (3x/week treatment with AB680), there was a significant reduction in tumor growth. Activated CD8-positive T cells, dendritic cells, and macrophages were significantly increased in the syngeneic tumors from AB680 treated mice. The intratumoral adenosine levels were significantly decreased in AB680 treated mice compared to vehicle treated mice.

Conclusion: We conclude oral gavage delivery of CD73 inhibitor AB680 at 10mg/kg (6x/week) reduces tumor growth in KPC syngeneic tumor bearing mice. Treatment with AB680 at 10mg/kg 3x/week significantly increases tumor doubling time, significantly alters intratumoral immune cell populations, and results in a significant decrease in intratumoral adenosine levels. In addition, we observed a significant increase in infiltration of activated CD8-positive T cells indicating oral gavage delivery using AB680 reverses immunosuppression in vivo. [Supported by NCI 75N91019D00021/75N91020F00002]

Citation Format: Kanchan Singh, Vidhi Chandra, Lincoln Ballew, Tingting Mills, Erika Y. Faraoni, Trent Clark, Lana A. Vornik, Michelle I. Savage, Holger K. Eltzschig, Altaf Mohammed, Shizuko Sei, Powel H. Brown, Florencia McAllister, Jennifer Bailey-Lundberg. Preclinical testing of CD73 inhibitors for pancreatic cancer immunoprevention [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 719.

Abstract 5562: Development of a TERT-specific peptide/adjuvant vaccine in C57BL/6 mice

Telomerase plays a vital role in cell senescence and cellular replication and has been described as a leading regulator in several human cancers, including prostate, thyroid, breast, colon, and bladder cancer. Telomerase is responsible for elongating telomere length and prolonging cellular lifespan as well as acting as a transcriptional modulator in cancer signaling pathways. Because of its enhanced expression in primary tumor cells as well as incipient tumor-initiating stem cells and with limited distribution in normal somatic cells, the catalytic component of telomerase, TERT (telomerase reverse transcriptase), is regarded as a high-impact target for immunotherapeutic agents and vaccines. In order to derive a mouse TERT (mTERT)-specific vaccine which could be useful in a preventive approach, we implemented an epitope-mapping stratagem by which pools of 30-mer peptides overlapping by 5 spanning the entire mTERT sequence were used to immunize C57BL/6 mice. Several immunogenic peptides were identified by matrixed peptide pool IFN-ɣ ELISPOT screening in a 2-part process that first identified positive pools, then identified individual peptides. 15-mer and 31-mer versions of the top 7 immunogenic mTERT peptides were synthesized and used as a peptide pool combined separately with several adjuvants to optimize immunogenicity. Results suggested a peptide sequence-specific preference for TLR3-mediated Hiltonol versus TLR9-mediated CpG-based adjuvants. In addition, the majority of T cell responses specific to the TERT peptides was identified through flow cytometry as belonging to the CD4 compartment, although one class I-restricted epitope was also identified. Multifunctional CD4+ T cells expressing IFN-ɣ, TNF-α, IL-2, and CD107a were identified specific to several mTERT peptides. In vivo cytotoxic effects exerted on TERT peptide pool-loaded target cells were also uncovered that were specific to a CpG-adjuvanted version of the vaccine. Finally, multiple versions of the mTERT peptide/adjuvant vaccine with highest immunogenicity scores are being tested in a syngeneic graft mouse model using subcutaneous implantation of lung cancer-derived SPON10 cells expressing mTERT. If proven efficacious, these results will support the feasibility of a TERT peptide/adjuvant approach for prophylactically engendering broad antitumor immunity to TERT-expressing cancers. Funded by NCI Contract No. HHSN261200800001E

Citation Format: Jason D. Marshall, Yurong Song, Hamid Zarkesh, Rebecca L. Matthews, Chelsea Sanders, Simone Difilippantonio, Ligia A. Pinto, Shizuko Sei, Robert H. Shoemaker. Development of a TERT-specific peptide/adjuvant vaccine in C57BL/6 mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5562.

Abstract 715: Targeting the mTOR pathway for the prevention of er-negative breast cancer

Background: Triple-Negative breast cancer (TNBC) is an aggressive cancer that lacks expression of the estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2. These cancers have a poor prognosis and are treated predominantly with chemotherapy. Therefore, we are working to find preventive therapies for these potentially lethal cancers. Dysregulation of PI3K-mTOR pathway is commonly associated with TNBC and other ER-negative breast cancers. We hypothesized that targeting mTOR may prevent development of ER-negative breast cancers and in this study tested whether the mTOR inhibitor, everolimus, prevents cancer in several mouse models of ER-negative breast cancer.

Methods: MMTV-erbB2 mice were purchased from the Jackson Laboratory. C3(1)/SV40TAg and BRCA1co/co;MMTV-Cre;p53+/- were generated through breeding. P53-null and p53-mutant mammary gland mice were generated by transplanting p53-null or p53-mutant mammary glands into cleared fat pads of p53-wild type mice. The mice were treated with either control or everolimus (5mg/kg), administered by oral gavage daily (5X/week). All mice develop palpable mammary tumors within 8-12 months. Mice were observed daily for tumor formation and drug toxicity. The percentage of tumor free mice was recorded, and time to tumor development was visualized using Kaplan-Meier curves and analyzed using the generalized Wilcoxon test.

Results: Treatment with everolimus significantly increased median survival of all mouse models. Everolimus treatment was also able to completely prevent mammary tumor formation in 27% of C3(1)/SV40Tag mice and 44% p53-mutant mammary gland mice. In p53-null mammary gland mice, 46% of control mice had developed tumors after 420 days, compared to 7% of everolimus treated mice. Long term treatment of everolimus was associated with mild toxicity that includes slight weight loss (&lt;10%) and skin changes (matted hair, skin erythema).

Conclusions: Everolimus significantly delayed mammary tumorigenesis in all five breast cancer mouse models. Our results suggest that everolimus is a promising cancer preventive drug for ER-negative tumors, and that further studies of everolimus in combination with other targeted therapies are warranted. In the future, clinical trials of the everolimus should be considered for the prevention of breast cancer in high-risk patients. Supported by NCI PREVENT Cancer Preclinical Drug Development Program (HHSN-2612015000-18I (PB).

Citation Format: Abhijit Mazumdar, Jamal Hill, William Tahaney, Yanxia Ma, Alejandro Contreras, Shizuko Sei, Altaf Mohammed, Powel Brown. Targeting the mTOR pathway for the prevention of er-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 715.

Oral administration of TRAIL-inducing small molecule ONC201/TIC10 prevents intestinal polyposis in the Apc min/+ mouse model

Colorectal cancer (CRC) incidence is rising globally. Hence, preventing this disease is a high priority. With this aim, we determined the CRC prevention potential of the TRAIL-inducing small molecule ONC201/TIC10 using a preclinical model representing high-risk familial adenomatous polyposis (FAP) patients, Apc ^min/+ mice. Prior to the efficacy study, optimal and non-toxic doses of ONC201 were determined by testing five different doses of ONC201 (0-100 mg/kg body weight (BW); twice weekly by oral gavage) in C57BL/6J mice (n=6/group) for 6 weeks. BW gain, organ weights and histopathology, blood profiling, and the plasma liver enzyme profile suggested no toxicities of ONC201 at doses up to 100 mg/kg BW. For efficacy determination, beginning at six weeks of age, groups of Apc ^min/+ male and female mice (n≥20) treated with colon carcinogen azoxymethane (AOM) (AOM-Apc ^min/+) were administered ONC201 (0, 25, and 50 mg/kg BW) as above up to 20 weeks of age. At termination, efficacy was determined by comparing the incidence and multiplicity of intestinal tumors between vehicle- and drug-treated groups. ONC201 showed a strong suppressive effect against the development of both large and small intestinal tumors in male and female mice. Apc ^min/+ mice treated with ONC201 (50 mg/kg BW) showed >50% less colonic tumor incidence (P<0.0002) than controls. Colonic tumor multiplicity was also significantly reduced by 68% in male mice (0.44 ± 0.11 in treated vs. 1.4 ± 0.14 in controls; P<0.0001) and by 75% in female mice (0.30 ± 0.10 in treated vs. 1.19 ± 0.19 in controls; P<0.0003) with ONC201 treatment (50 mg/kg BW). Small intestinal polyps were reduced by 68% in male mice (11.40 ± 1.19 in treated vs. 36.08 ± 2.62 in controls; P<0.0001) and female mice (9.65 ± 1.15 in treated vs. 29.24 ± 2.51 in controls; P<0.0001). Molecular analysis of the tumors suggested an increase in TRAIL, DR5, cleaved caspases 3/7/8, Fas-associated death domain protein (FADD), and p21 (WAF1) in response to drug treatment. Serum analysis indicated a decrease in pro-inflammatory serum biomarkers, such as IL1β, IL6, TNFα, G-CSF, and GM-CSF, in the ONC201-treated mice compared with controls. Our data demonstrated excellent chemopreventive potential of orally administered ONC201 against intestinal tumorigenesis in the AOM-Apc ^min/+ mouse model.

Optimizing a multi cancer antigen plasmid-based vaccine using an in situ prediction model

Little is known about optimization of a class II restricted plasmid-based vaccine targeting multiple cancer antigens. We set out to define parameters of an in situ prediction model in vaccine design for optimal immunogenicity. Using previously defined immunogenic class II epitopes from five cancer antigens, we evaluated the effects of using linkers between antigens and varying the antigen order. The construct with linkers was superior to the construct without linkers. The mice receiving the vaccine with linkers developed a greater magnitude (p&lt;0.0001), incidence and breadth IFN-g immune response. To determine the optimal antigen order, the sequences of all possible permutations were generated. Each sequence was evaluated in four publicly available algorithms to assess potential generation of immunity and physiochemical properties of the fusion protein. Of all parameters assessed, only predicted class II immunogenicity, in vivo half-life and percent of epitopes in helical secondary structure differed considerably among the constructs. We evaluated three constructs with similarly high class II immunogenicity; one with (A) long in vivo half-life and high percent in helices, one with (B) short half-life and high percent in helices or one with (C) short half-life and low percent in helices. Construct A generated a higher magnitude IFN-g response than Construct B or C (p&lt;0.006 for all). While there was 100% incidence of an immune response to all constructs, the breadth of the response for Construct A was greater than the other two constructs. Class II immunogenicity, in vivo half-life and the percent of the protein in a helical secondary structure can be used to discern the most immunogenic multi-antigen plasmid vaccine construct.

High-power laser experiment forming a supercritical collisionless shock in a magnetized uniform plasma at rest

We present an experimental method to generate quasiperpendicular supercritical magnetized collisionless shocks. In our experiment, ambient nitrogen (N) plasma is at rest and well magnetized, and it has uniform mass density. The plasma is pushed by laser-driven ablation aluminum (Al) plasma. Streaked optical pyrometry and spatially resolved laser collective Thomson scattering clarify structures of plasma density and temperatures, which are compared with one-dimensional particle-in-cell simulations. It is indicated that just after the laser irradiation, the Al plasma is magnetized by a self-generated Biermann battery field, and the plasma slaps the incident N plasma. The compressed external field in the N plasma reflects N ions, leading to counterstreaming magnetized N flows. Namely, we identify the edge of the reflected N ions. Such interacting plasmas form a magnetized collisionless shock.

Recurrent Frameshift Neoantigen Vaccine Elicits Protective Immunity With Reduced Tumor Burden and Improved Overall Survival in a Lynch Syndrome Mouse Model

BACKGROUND & AIMS

DNA mismatch repair deficiency drives microsatellite instability (MSI). Cells with MSI accumulate numerous frameshift mutations. Frameshift mutations affecting cancer-related genes may promote tumorigenesis and, therefore, are shared among independently arising MSI tumors. Consequently, such recurrent frameshift mutations can give rise to shared immunogenic frameshift peptides (FSPs) that represent ideal candidates for a vaccine against MSI cancer. Pathogenic germline variants of mismatch repair genes cause Lynch syndrome (LS), a hereditary cancer syndrome affecting approximately 20-25 million individuals worldwide. Individuals with LS are at high risk of developing MSI cancer. Previously, we demonstrated safety and immunogenicity of an FSP-based vaccine in a phase I/IIa clinical trial in patients with a history of MSI colorectal cancer. However, the cancer-preventive effect of FSP vaccination in the scenario of LS has not yet been demonstrated.

METHODS

A genome-wide database of 488,235 mouse coding mononucleotide repeats was established, from which a set of candidates was selected based on repeat length, gene expression, and mutation frequency. In silico prediction, in vivo immunogenicity testing, and epitope mapping was used to identify candidates for FSP vaccination.

RESULTS

We identified 4 shared FSP neoantigens (Nacad [FSP-1], Maz [FSP-1], Senp6 [FSP-1], Xirp1 [FSP-1]) that induced CD4/CD8 T cell responses in naïve C57BL/6 mice. Using VCMsh2 mice, which have a conditional knockout of Msh2 in the intestinal tract and develop intestinal cancer, we showed vaccination with a combination of only 4 FSPs significantly increased FSP-specific adaptive immunity, reduced intestinal tumor burden, and prolonged overall survival. Combination of FSP vaccination with daily naproxen treatment potentiated immune response, delayed tumor growth, and prolonged survival even more effectively than FSP vaccination alone.

CONCLUSIONS

Our preclinical findings support a clinical strategy of recurrent FSP neoantigen vaccination for LS cancer immunoprevention.

Pulmonary Aerosol Delivery of Let-7b microRNA Confers a Striking Inhibitory Effect on Lung Carcinogenesis through Targeting the Tumor Immune Microenvironment

MicroRNAs are potential candidates for lung cancer prevention and therapy. A major limitation is the lack of an efficient delivery system to directly deliver miRNA to cancer cells while limiting systemic exposure. The delivery of miRNA via inhalation is a potential strategy for lung cancer prevention in high-risk individuals. In this study, the authors investigate the efficacy of aerosolized let-7b miRNA treatment in lung cancer prevention. Let-7b shows significant inhibition of B[a]P-induced lung adenoma with no detectable side effects. Single-cell RNA sequencing of tumor-infiltrating T cells from primary tumors reveals that Let-7b post-transcriptionally suppresses PD-L1 and PD-1 expression in the tumor microenvironment, suggesting that let-7b miRNAs may promote antitumor immunity in vivo. Let-7b treatment decreases the expression of PD-1 in CD8+ T cells and reduces PD-L1 expression in lung tumor cells. The results suggest that this aerosolized let-7b mimic is a promising approach for lung cancer prevention, and that the in vivo tumor inhibitory effects of let-7b are mediated, at least in part, by immune-promoting effects via downregulating PD-L1 in tumors and/or PD-1 on CD8+ T cells. These changes potentiate antitumor CD8+ T cell immune responses, and ultimately lead to tumor inhibition.

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.

Abstract 440: Potentiation of EGFR peptide cancer vaccine by an orally bioavailable glutamine antagonist prodrug JHU-083

Lung cancer is the leading cause of cancer mortality worldwide. More than 85% of lung cancers are non-small cell lung cancer (NSCLC). EGFR mutations occur in 47.9% of Asia-Pacific patients with NSCLC and 19.2% of Western patients. The most common EGFR mutations (&gt;90%) are deletions in exon 19 and/or point mutations in exon 21 (L858R). Th1 helper cellular immunity is critical for immunotherapy-mediated tumor regression. We have previously characterized an MHC-II-restricted EGFR multi-peptide vaccine (two peptides: “SCVRACGADSYEMEEDGVRK” and “VWSYGVTVWELMTFGSKPY”) (EGFR-V) that targets the EGFR protein and decreases EGFR-driven lung tumorigenesis by ~80% in EGFRL858R transgenic mice that were vaccinated before doxycycline-induction of the EGFR protein [1]. However, diminished efficacy was observed when this MHC-II-restricted EGFR multi-peptide vaccine was given two weeks after doxycycline induction of the EGFR protein, suggesting that expression of the EGFR oncoprotein significantly increased the immunosuppressive microenvironment. JHU083, an orally bioavailable glutamine antagonist, has recently been shown to not only inhibit tumor growth but also boost anti-cancer immunity [2]. To determine if JHU083 could potentiate the efficacy of EGFR vaccine in a post-initiation setting, we evaluated in vivo antitumor efficacy of EGFR vaccine combined with JHU083 using an EGFRL858R transgenic mouse model. JHU083 inhibited tumor burden by 31% and EGFR vaccine suppressed tumor burden by 33%, whereas combining JHU083 with anti-EGFR peptide vaccine had an additive effect (54% tumor inhibition). Mechanistically, JHU083 by itself, markedly reduced the immunosuppressive monocytic myeloid-derived suppressor cells (MDSCs) in lung tissues. The combination of JHU083 and the vaccine significantly reduced Tregs in lung tissues. The anti-EGFR vaccine primarily induced expansion of antigen specific antitumor CD4+ effector T cells. Long term administration of JHU-083 did not decrease bodyweight in mice. Together with previous results, these data suggest that JHU083 could be used to reshape the tumor microenvironment toward one that enhances antitumor T cell responses and could further enhance the efficacy of the EGFR anticancer vaccine.

References1.Ebben, J.D., et al., 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. Mol Carcinog, 2016. 55(11): p. 1517-1525.2.Leone, R.D., et al., Glutamine blockade induces divergent metabolic programs to overcome tumor immune evasion. Science, 2019. 366(6468): p. 1013-1021.

Citation Format: Mofei Huang, Jing Pan, Qi Zhang, Shizuko Sei, Robert Shoemaker, Ronald Lubet, Yian Wang, Barbara Slusher, Ming You. Potentiation of EGFR peptide cancer vaccine by an orally bioavailable glutamine antagonist prodrug JHU-083 [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 440.

Abstract SY17-02: Multiantigen vaccines for colon cancer prevention

Colorectal cancer (CRC) is the second leading cause of cancer-related deaths in the US when men and women are combined. While overall CRC incidence has declined over the years, there has been an increase in CRC diagnosis in young and middle-aged adults. The US Preventive Services Task Force has recently issued draft recommendations for CRC screening to begin at 45 years of age instead of the previously recommended age of 50 for asymptomatic healthy individuals, who are at average risk of CRC, i.e. without a family history of hereditary CRC syndromes such as Lynch syndrome and familial adenomatous polyposis, or with no prior diagnosis of CRC, adenomatous polyps, inflammatory bowel disease. While the evidence supports that CRC-screening and early detection confers a substantial benefit, additional CRC prevention strategies can greatly help reduce the cancer burden in the US and around the world. A number of previous studies have shown that the use of nonsteroidal anti-inflammatory drugs (NSAIDs) reduces the risk of cancers, including CRC. However, their extended use can be associated with serious side effects, including gastrointestinal bleeding. Safer and more efficacious preventive approaches are needed for durable long-term CRC prevention. The majority of newly diagnosed CRC are non-familial (sporadic) and non-hypermutated/microsatellite-stable (MSS). Compared to CRC with high microsatellite instability, MSS CRC and adenomas have significantly lower somatic mutation frequencies, thus lower neoantigen load. Furthermore, MSS CRC have generally lower levels of tumor-infiltrating lymphocytes (TILs), higher density of myeloid derived suppressor cells (MDSC), and downregulation of HLA molecules. These are characteristic of immunologically “cold” tumors, making it highly challenging to immunologically control tumor growth. If cancer vaccines can successfully prime the immune system, in particular before the development of invasive cancer, vaccine-induced adaptive antitumor immunity may render “cold” tumors “hot” and achieve a favorable tumor control. One of the key questions, however, is what tumor antigens can be targeted by vaccines if tumors have lower levels of neoantigens that are known to elicit robust antitumor immune responses. Another approach for cancer vaccine-mediated immune priming is to target tumor associated antigens (TAAs). Unlike tumor-specific neoantigens, TAAs are self-antigens that are overexpressed in tumors, but may also be expressed in normal cells at various levels. Therefore, it is highly critical to identify T cell epitopes that break tolerance and help elicit effective antitumor immunity. Clinically beneficial antitumor immunity is characterized by high-density infiltrates of effector CD8+ cytotoxic T lymphocytes and effector memory T cells and the low abundance of immunosuppressive elements (e.g. regulatory T cells, MDSC, and M2-polarized tumor-associated macrophages) in the tumor microenvironment. Disis and colleagues from University of Washington have previously established a systematic and stepwise approach to identify Th1-selective epitopes for efficacious cancer vaccines while eliminating Th2-epitopes. They have shown cancer vaccines targeting TAAs thus developed could elicit robust Th1 immune response associated with antitumor effects. The NCI PREVENT Cancer Preclinical Drug Development Program (PREVENT) is a peer-reviewed agent development program focused on preclinical development of innovative interventions, including cancer vaccines and drugs, for precision cancer prevention-interception towards clinical applications (https://prevention.cancer.gov/major-programs/prevent-cancer-preclinical). PREVENT and Disis team collaborated on the development of a multi-antigen multi-peptide colon cancer vaccine, named Colovac, for immunoprevention of CRC. It consists of highly immunogenic Th1-promoting epitopes from three TAAs that are selected through CRC genomic database and literature search. TAAs selected are overexpressed in CRC, known to play a role in CRC oncogenesis, and associated with poor disease outcomes. This presentation will cover the background of Colovac development, preclinical antitumor efficacy data on Colovac used alone or in combination with naproxen, characterization of immune correlates of protection, and current ongoing development efforts toward clinical trials.

Citation Format: Shizuko Sei. Multiantigen vaccines for colon cancer prevention [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 SY17-02.

Abstract LB225: Colon cancer preventive efficacy of licofelone and its analogue LFA-9 in PIRC rat model of FAP

Inflammation is a key hallmark of many cancers and potent target for chemoprevention. Experimental and clinical intervention studies indicate strong cancer preventive efficacy of cyclooxygenase (COX)-2 inhibitors. Their use for chemoprevention is limited due to increased cardiovascular (CV) toxicities. Selective COX-2 inhibition diverts arachidonic acid to the 5-lipoxygenase (5-LOX) pathway resulting in accumulation of prothrombotic leukotrienes while depleting antithrombotic prostaglandin (PG)I2, leading to increased risk of CV events. To overcome side effects, balanced dual inhibitors targeting COX-2/5-LOX or microsomal PGE synthase (mPGES)-1/5-LOX enzymes are being developed for chemoprevention. In this study, the clinically advanced dual COX-2/5-LOX inhibitor, licofelone, and its glycine analogue (LFA-9), the mPGES-1/5-LOX dual inhibitor, were evaluated for colon cancer preventive efficacy in the FAP relevant PIRC rat model. In preclinical dose range finding and preliminary toxicity studies in F344 rats, dietary administration of licofelone &lt;500ppm and LFA9 &lt;1,600ppm for 8 weeks showed no signs of toxicity based on by body weight gain, organs histopathology, blood cell counts, and serum chemistry. For efficacy evaluation, male and female PIRC rats were randomized by age (n≥15/group/gender). All rats had pre-intervention colonoscopies (8 weeks age) to determine baseline colonic polyps and were fed AIN-76A diets containing licofelone (250 ppm), LFA-9 (800ppm) or control until 32 (male) or 40 (female) weeks of age. Colonoscopies were repeated every 8 weeks for longitudinal monitoring of tumor development. At the end of the treatment period, rats were euthanized and intestines were evaluated for tumor multiplicity as an efficacy endpoint. Colonoscopy data suggested no significant difference in pretreatment colonic polyp multiplicity. However, there was a marked delay in colon tumor development in rats in the intervention group compared to control. Colonic tumor multiplicity at termination indicated that licofelone treated male rats developed 32% less tumors (21.87±1.23 (Mean±SEM); p&lt;0.0001), while LFA-9 treated male rats had 31% less tumors (22.13±1.19; p&lt;0.0001) compared to controls (32.25±1.37). There was no significant difference in tumor multiplicity between licofelone and LFA-9 treatment groups. In females, licofelone treatment led to 51% inhibition of colonic tumors (9.18±1.25; p&lt;0.0002) while LFA-9 treatment led to 37% inhibition (11.89±0.86; p&lt;0.002) compared to control (18.91±1.88). Although licofelone trended toward better inhibitory effect in females, this was not significantly different from the LFA-9 group. Colon tumor volume and small intestinal tumor multiplicity was notably inhibited in both licofelone and LFA-9 treated rats when compared to control. Our data suggest both licofelone and LFA-9 exhibit moderate and uniform chemopreventive efficacy against FAP-associated intestinal tumorigenesis in the PIRC rat model. (Supported by NCI HHSN HHSN261201500024I)

Citation Format: Venkateshwar Madka, Nagendra S. Yarla, Gopal Pathuri, Yuting Zhang, Anh Bao, Nicole C. Stratton, Anil Singh, David L. McCormick, Altaf Mohammed, Shizuko Sei, Jennifer Fox, Chinthalapally V. Rao. Colon cancer preventive efficacy of licofelone and its analogue LFA-9 in PIRC rat model of FAP [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 LB225.

Abstract 1556: Retinoid X receptor agonists enhances Th1 antigen-specific and polyfunctional T cells with the HER2-IGFBP2-IGF1R vaccine

Bexarotene and 9cUAB30 are highly selective oral retinoid X receptor (RXR) agonists with anti-proliferative activity in breast cancer. We have demonstrated that bexarotene enhances efficacy of a multi-antigen vaccine to prevent breast cancer in the TgMMTV-neu model and increases CD8 T-cell tumor infiltration. We further have shown that RXRα expression is in 24.9±13% of macrophages, 38.6 ±14% of plasmacytic dendritic cells (pDC), and 33.1 ± 16% of monocytic dendritic cells (mDC). Furthermore, the RXR agonists increased Th1 pDC and mDC. We therefore evaluated whether RXR agonists could enhance the vaccine antigen-specific immunogenicity and polyfunctional T cells in the transgenic mouse mammary tumor model TgMMTV-neu. Vaccination with the 150 µg HER2-IGFBP2-IGF1R vaccine and 5 ug GMCSF adjuvant every 2 weeks for four doses significantly increased antigen-specific IFN-γ T cells, but not antigen-specific IL10 T cells, as compared to control vaccination with empty vector. Interestingly, daily oral administration of 30 mg/kg bexarotene for 5 days prior to the HER2-IGFBP2-IGF1R vaccination series increased the IFN-γ immune responses to HER2, IGFBP2, and IGF1R by 1.2, 2.4 and 2.2 fold, respectively, as compared to the HER2-IGFBP2-IGF1R vaccine alone. Daily administration of a higher dose (200 mg/kg) 9cUAB30 for 5 days prior to the HER2-IGFBP2-IGF1R vaccination series increased the IFN-γ immune responses to HER2, IGFBP2, and IGF1R by 2.0, 2.3 and 1.7 fold, respectively, as compared to the HER2-IGFBP2-IGF1R vaccine alone. Control vaccination with either 9cUAB30 or bexarotene had no impact on antigen-specific IFN-γ T cell response. Type I DCs are important for producing polyfunctional CD4+ T cells that release not only IFN-γ but also TNF-α and IL-2. Polyfunctional T cells induce a longer lasting and more effective immune response in vaccines both for infectious diseases and cancer. We demonstrated the addition of bexarotene or 9cUAB30 increased antigen-specific polyfunctional T cells in the TgMMTV-neu (n=15 mice) transgenic mouse mammary tumor model while vaccination alone did not. There were an average of 1.3±0.2% antigen-specific CD4 polyfunctional T cells and 2.7±0.7 antigen-specific CD8 polyfunctional T cells with empty vector and vehicle control (sesame oil). HER2-IGFBP2-IGF1R vaccination following 30 mg/kg bexarotene treatment increased polyfunctional T cells to an average of 6.1±2.0% antigen-specific CD4 polyfunctional T cells (p=0.07) and 20.3±4.1% antigen-specific CD8 polyfunctional T cells (p=0.0003). HER2-IGBP2-IGF1R vaccination after 200 mg/kg 9cUAB30 increased antigen-specific polyfunctional T cells to 7.6±2.0% (p=0.01) and antigen-specific CD8 polyfunctional T cells to 17.6±4.1% (p=0.003). These data indicate that RXR agonists have an immunostimulatory role with multi-antigen cancer vaccines and may augment the anti-tumor activity of vaccines.

Citation Format: Sasha Elizabeth Stanton, Erin Rodmaker, Nicholas Drovetto, Lauren Corulli, Flonia Levy, Venkatram Atigadda, Clinton Grubbs, Romaine Fernando, Shizuko Sei, Mary L. Disis. Retinoid X receptor agonists enhances Th1 antigen-specific and polyfunctional T cells with the HER2-IGFBP2-IGF1R vaccine [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 1556.

Naproxen chemoprevention promotes immune activation in Lynch syndrome colorectal mucosa

OBJECTIVE

Patients with Lynch syndrome (LS) are at markedly increased risk for colorectal cancer. It is being increasingly recognised that the immune system plays an essential role in LS tumour development, thus making an ideal target for cancer prevention. Our objective was to evaluate the safety, assess the activity and discover novel molecular pathways involved in the activity of naproxen as primary and secondary chemoprevention in patients with LS.

DESIGN

We conducted a Phase Ib, placebo-controlled, randomised clinical trial of two dose levels of naproxen sodium (440 and 220 mg) administered daily for 6 months to 80 participants with LS, and a co-clinical trial using a genetically engineered mouse model of LS and patient-derived organoids (PDOs).

RESULTS

Overall, the total number of adverse events was not different across treatment arms with excellent tolerance of the intervention. The level of prostaglandin E2 in the colorectal mucosa was significantly decreased after treatment with naproxen when compared with placebo. Naproxen activated different resident immune cell types without any increase in lymphoid cellularity, and changed the expression patterns of the intestinal crypt towards epithelial differentiation and stem cell regulation. Naproxen demonstrated robust chemopreventive activity in a mouse co-clinical trial and gene expression profiles induced by naproxen in humans showed perfect discrimination of mice specimens with LS and PDOs treated with naproxen and control.

CONCLUSIONS

Naproxen is a promising strategy for immune interception in LS. We have discovered naproxen-induced gene expression profiles for their potential use as predictive biomarkers of drug activity.

TRIAL REGISTRATION NUMBER

gov Identifier: NCT02052908.

Optimization of Erlotinib Plus Sulindac Dosing Regimens for Intestinal Cancer Prevention in an Apc-Mutant Model of Familial Adenomatous Polyposis (FAP)

A clinical trial in patients with familial adenomatous polyposis (FAP) demonstrated that sulindac plus erlotinib (SUL+ERL) had good efficacy in the duodenum and colon, but toxicity issues raised concerns for long-term prevention. We performed a biomarker study in the polyposis in rat colon (Pirc) model, observing phosphorylated Erk inhibition in colon polyps for up to 10 days after discontinuing ERL+SUL administration. In a follow-up study lasting 16 weeks, significant reduction of colon and small intestine (SI) tumor burden was detected, especially in rats given 250 ppm SUL in the diet plus once-a-week intragastric dosing of ERL at 21 or 42 mg/kg body weight (BW). A long-term study further demonstrated antitumor efficacy in the colon and SI at 52 weeks, when 250 ppm SUL was combined with once-a-week intragastric administration of ERL at 10, 21, or 42 mg/kg BW. Tumor-associated matrix metalloproteinase-7 (Mmp7), tumor necrosis factor (Tnf), and early growth response 1 (Egr1) were decreased at 16 weeks by ERL+SUL, and this was sustained in the long-term study for Mmp7 and Tnf. Based on the collective results, the optimal dose combination of ERL 10 mg/kg BW plus 250 ppm SUL lacked toxicity, inhibited molecular biomarkers, and exhibited effective antitumor activity. We conclude that switching from continuous to once-per-week ERL, given at one-quarter of the current therapeutic dose, will exert good efficacy with standard-of-care SUL against adenomatous polyps in the colon and SI, with clinical relevance for patients with FAP before or after colectomy. PREVENTION RELEVANCE: This investigation concludes that switching from continuous to once-per-week erlotinib, given at one-quarter of the current therapeutic dose, will exert good efficacy with standard-of-care sulindac against adenomatous polyps in the colon and small intestine, with clinical relevance for patients with FAP before or after colectomy.

Cancer Immunoprevention: Challenges and Potential Opportunities for Use of Immune Checkpoint Inhibitors

Cancer immunoprevention is achieved through promoting antitumor immune surveillance to block tumor formation and progression. Following the success of prophylactic vaccines against human papillomavirus (HPV) in preventing HPV-associated cancer, immunopreventive cancer vaccines targeting tumor antigens have been increasingly evaluated against cancers of noninfectious origin. While advances in cancer immunotherapy with immune checkpoint inhibitors (ICI) have clearly shown that the host immune system can mount effective antitumor immunity against tumor antigens when immune checkpoints are optimally blocked, the use of ICIs in the prevention setting has not been widely explored because of concerns of ICI-associated adverse events. In this issue of Cancer Prevention Research, Chung and colleagues demonstrate that the human cirrhotic liver harbors neoantigens, which accumulate further as the disease progresses to hepatocellular carcinoma (HCC), suggesting that cirrhotic liver may be susceptible to ICI therapy. Utilizing an established mouse model of carcinogen-induced liver fibrosis and HCC, they show that intermittent intervention by ICI, anti-mouse PD-1 (CD279) antibody, can prevent the progression of the precancerous stage of cirrhosis to HCC accompanied by increased T-cell infiltrates in the liver parenchyma. Importantly, there were no overt ICI-associated toxicities in the treated mice, indicating that safe dosing regimens could be established. This work is both significant and timely, opening the door to future studies, where the utility of ICI therapy can be further investigated not only in cirrhosis but other high-risk precancerous conditions. In this perspective, we discuss the implications of their findings, and the challenges and potential opportunities for use of ICIs for cancer immunoprevention.See related article by Chung et al., p. 911.

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.

Abstract 1099: Combination of bazedoxifene and lapatinib profoundly inhibits estrogen receptor positive (ER+) and Negative (ER-) mammary tumorigenesis

Bazedoxifene (Baz), a 3rd Gen SERM, is approved for prevention and treatment of osteoporosis as Duavee in the US. Baz downregulates ERα and inhibits growth of ER+ breast cancer (BC) cells, without stimulating the uterine endometrium. It also inhibits hormone-independent BC cell growth, presumably by inhibiting IL-6/GP130 interaction and downmodulating pSTAT3-cyclin D1 pathway, resulting in induction of apoptosis and reduction of tumor growth. Lapatinib (Lap), an FDA approved, small molecule dual inhibitor of both the EGFR/HER1 and HER2, is commonly used to treat patients with HER2-positive (HER2+) BC. We evaluated the efficacy of these two FDA-approved drugs, Baz and Lap, at lower doses, alone and in combination, for the prevention of BC in rodent models. Lap was given either daily or Ix/week by oral gavage while Baz was added directly to the diet. For ER+ mammary cancers, female Sprague-Dawley rats were given methylnitrosourea (MNU) at 50 days of age. The agents were started one week prior to MNU treatment in the following 6 groups: 1) Baz (5.0 mg/kg diet, 7x/week); 2) Lap (350 mg/kg BW, Ix/week); 3) Lap (50 mg/kg BW, 7x/week); 4) Baz + Lap as in Groups 1 and 2; 5) Baz + Lap as in Groups 1 and 3; and 6) none. At the end of the study (20 weeks after MNU), mammary cancer multiplicities in Groups 1 to 6 were: 0.75, 0.6, 0.2, 0.15, 0.1, and 4.25, respectively, demonstrating a profound (82-98%) inhibition of ER+ mammary cancers (p&lt;0.0001). When the agents were started prior to dimethybenzanthracene (DMBA, 1.0 mg/gavage, Ix/week for 4 weeks) in MMTV/Neu mice (7 weeks age), cancer multiplicities at the end of the study (18 weeks after the initial DMBA treatment) were as follows: 1) Baz (5.0 mg/kg diet), 1.0; 2) Lap (625 mg/kg BW,1x/week), 2.1; 3) Lap (125 mg/kg BW, 5x/week), 2.65; 4) Baz + Lap as in Groups 1 and 2; 0.4; 5) Baz + Lap as in Groups 1 and 3, 0.2; and 6) none, 5.2, demonstrating similarly profound chemoprevention efficacy by the combination regimens with multiplicities reduced by 93-96% (p&lt;0.01). Of note, giving lap Ix/week either alone or in combination with Baz resulted in significant decreases in cancer incidence, multiplicities and weights in both models. In a 2-week biomarker study, female MMTV/Neu mice treated with the combinations had significantly decreased proliferation rate (Ki67) in mammary epithelial cells by 74% (p&lt;0.05). These findings indicate that the combination of low-dose daily Baz and weekly Lap is highly effective in preventing ER+ and ER- mammary cancers, and that treatment with the EGFR/HER2 inhibitor Lap once a week is similarly efficacious to daily treatment with divided doses in its cancer inhibitory activity without overt toxicity.

Citation Format: Altaf Mohammed, Shizuko Sei, Robert Shoemakers, Clinton J. Grubbs. Combination of bazedoxifene and lapatinib profoundly inhibits estrogen receptor positive (ER+) and Negative (ER-) mammary tumorigenesis [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 1099.

Abstract CT111: Naproxen chemoprevention promotes immune activation in Lynch syndrome colorectal mucosa

Patients diagnosed with germline mutations in MMR genes (Lynch Syndrome, LS) have up to 70-80% lifetime risk of colorectal cancer. Therefore, this high-risk population has the potential to benefit from effective chemopreventive strategies. Naproxen is an NSAID widely used for pain treatment with an excellent safety profile that has demonstrated to be more efficacious preventing colorectal cancer compared to aspirin in vivo using an intestinal tissue-specific mouse model of LS (VC-Msh2-LoxP). The ‘Naproxen trial' was designed to evaluate the modulation of PGE2 levels in colorectal mucosa, evaluate safety and tolerability, and discover novel molecular pathways involved in the chemopreventive activity of naproxen in LS patients. Methods: Participants were randomized to naproxen 440 mg (HD), 220 mg (LD) and placebo by mouth daily for 6 months. Modulation of prostaglandin levels, number of adverse events (AEs) observed in each treatment arm and gene expression profiles by next-generation sequencing (mRNAseq) in normal colorectal mucosa of LS patients after 6 months of intervention were examined. Results: Eighty participants diagnosed with LS were randomized, 25 participants to HD, 27 to LD, and 28 to placebo. From these patients, 54 were considered evaluable per-protocol analysis: 16 in the HD group, 15 in the LD and 23 in placebo. The level of prostaglandin E2 in the colorectal mucosa decreased significantly after treatment with both LD and HD naproxen when compared to placebo (-91.2%±14.1, -93.6%±7.9, and 23.8%±108.4, P-value&lt;0.001, respectively). Moreover, levels of PGE2 urinary metabolite (PGE-M) were significantly changed in both treatment groups when compared to placebo (-47.7%±56.9, -41.1%±40.5, 7.6%±94.3, P-Value&lt;0.018). The intervention was well tolerated, no severe AEs related to treatment were reported, and the total number of AEs was not different across treatment arms. LD and HD naproxen promoted the activity of the immune system by activating different immune cell types without any effect on lymphoid cellularity and changed the expression patterns of the intestinal crypt towards epithelial differentiation and stem cell regulation. Conclusions: Naproxen is a promising strategy for immune interception in LS that induces immune-modulation coupled with changes in the dynamics of the intestinal crypt. We have also discovered naproxen-induced gene expression profiles for their potential use as predictive biomarkers of drug activity.

Citation Format: Laura Reyes Uribe, Wenhui Wu, Ozkan Gelincik, Prashant V. Bommi, Alejandro Francisco-Cruz, Luisa M. Solis, Patrick M. Lynch, Ramona Lim, Elena Stoffel, Priyanka Kanth, N. Jewel Samadder, Maureen E. Mork, Melissa W. Taggart, Ginger L. Milne, Lawrence J. Marnett, Lana Vornik, Diane D. Liu, Maria Revuelta, Kyle Chang, Y. Nancy You, Levy Kopelovich, Ignacio I. Wistuba, J. Jack Lee, Shizuko Sei, Robert H. Shoemaker, Eva Szabo, Ellen Richmond, Asad Umar, Marjorie Perloff, Powell H. Brown, Steven M. Lipkin, Eduardo Vilar. Naproxen chemoprevention promotes immune activation in Lynch syndrome colorectal mucosa [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 CT111.

Abstract 15: Hypertension drug Olmesartan medoxomil promotes colonic tumorigenesis in AOM-induced CRC rat model

Some retrospective studies suggest an inverse risk-association between the use of angiotensin signaling inhibitors and colorectal cancer (CRC). The angiotensin receptor blocker olmesartan medoxomil (OLM) is commonly prescribed for hypertension treatment. Here we sought to determine the chemopreventive efficacy of OLM using the azoxymethane (AOM)-induced CRC rat model. Male and female F344 rats (n=6/gender/group) were randomized and subcutaneously injected with 20 mg/kg of AOM once weekly for two weeks. One week later, AIN76-A diets containing OLM (0 ppm to 480 ppm) were fed to rats. Six weeks after treatment, rats were euthanized and evaluated for toxicity and aberrant crypt foci (ACF) inhibition. OLM-fed rats, particularly at ≥160 ppm, showed signs of toxicity. There was a modest decrease in the total ACFs without any change in multicrypt ACFs in male rats; however in females there was an increase in multicrypt ACFs as compared to the control diet group. For tumor efficacy evaluation, 5-week-old F344 rats were randomized (n=30/gender/group) and CRC was induced as described above. At the adenoma stage (12-weeks after AOM-treatment), rats were administered OLM (0, 20 and 40 ppm) in the diet for 33 weeks, and colonic tumors were evaluated. In the control group, there was a huge disparity in colonic tumor incidence and multiplicity between genders with ~3-fold less tumors in female rats. Surprisingly, colon tumor incidence was significantly increased (3-fold; p&lt;0.0002) in the OLM-treated female rats (77% OLM vs 24% control). Colon tumor multiplicity analysis also showed tumor promoting effects. In the 20 ppm OLM-treated male and female rats, colonic adenocarcinoma multiplicities were increased by ~91% (p&lt;0.01) and ~362% (p&lt;0.0001), respectively, when compared with their respective controls. Although there was no dose response, similar tumor promoting effects were found in 40 ppm OLM-treated rats. To understand male vs female colon tumor disparities and OLM tumor promoting effects, we carried out RNA-Seq analysis of colonic tumors. Reflecting tumor data, gene expression analysis also showed significant differences between male and female rats with respect to type II-interferon, PI3K-AKT, cholesterol, lipid droplet, mucin, IL-3, cell-cycle and nucleotide GPCR signaling pathways. OLM treatment significantly upregulated 586 and 740 genes, and downregulated 648 and 564 genes in male and female rat tumors, respectively. Of the 293 common genes identified, Irx5, Lrrn1, Ly6g6e, Sccpdh, Hoxd12, Igfbp1, Krt81 and DSC3 were upregulated up to 245-fold; and Rfxapl1, Serpinb3a, REg3b, Bnc1 and Ak4 were down-regulated 10 - 200-fold with OLM treatment. In conclusion, chronic administration of OLM did not provide any chemopreventive benefit against colonic tumors in the AOM-induced F344 rat CRC model. Further studies are warranted to assess the risk of colon cancer associated with long-term OLM use, particularly in females. (Supported by NCI HHSN 261201500038I and VA Merit Award)

Citation Format: Venkateshwar Madka, Yuting Zhang, Gopal Pathuri, Janani Panneerselvam, Nicole Stratton, Anil Singh, Shizuko Sei, Jennifer Fox, Chinthalapally V. Rao. Hypertension drug Olmesartan medoxomil promotes colonic tumorigenesis in AOM-induced CRC rat model [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 15.

Abstract 19: Examination of HJC0152, a putative modulator of glucose and energy metabolism, for mammary cancer prevention

Breast cancer (BC) is the most common cancer in women in the US. Approximately 30-40% of BC cases are estrogen-receptor (ER)-negative (ENBC); the majority of these are triple-negative (TNBC). No drugs have been shown to effectively prevent ENBC including TNBC. TNBC incidence is higher in young African American and Hispanic/Latina women, thus the need for preventive agents for TNBC is critical. Developing agents targeting non-ER-based oncogenic pathways will therefore offer alternative and potentially more effective approaches for preventing ENBC/TNBC. Glucose metabolism is an essential energy-producing process for normal cells and is aberrant and reprogrammed in cancer cells including BC cells. We recently developed HJC0152, a novel small-molecule glucose metabolism modulator as a potential cancer preventive agent. HJC0152 has been shown to inhibit glycolysis by differentially regulating glycolytic enzyme expression and the function of mitochondrial respiratory complexes in both EPBC and TNBC cells, leading to reduced production of energy molecule adenosine-triphosphate (ATP), induced apoptosis, and decreased proliferation and tumor progression. In this study, we determined the preventive anti-cancer efficacies of long-term and short-term (inhibition of premalignant lesions) HJC0152 administration in mouse models of ENBC and TNBC. HJC0152 was given orally 6 days/wk for 2-10 months in well-established ENBC model, MMTV-erbB2; and TNBC model, C3(1)/TAgSV40. HJC0152 at 50 and 75 mg/Kg doses delayed and partially prevented mammary tumor development in ENBC (MMTV-erbB2) mice (p=0.0034 for all groups). A maximum 6-week delay was achieved for median time to tumor formation (TTF). In the TNBC (C3(1)/TAgSV40) model, HJC0152 significantly delayed mammary tumor development (p=0.0114 for all groups) and achieved 3.3-week delay for median TTF. Up to 21% less mice developed mammary tumors in both models. In addition, TNBC mice developed less number of tumors per mouse than in ENBC mice, and the tumor volume doubling time increased from 6.9 to 9.2 days. In the short-term premalignant lesion study, the number of mammary intraepithelial neoplasia (MIN) lesion (representing human DCIS) was significantly decreased (p=0.034) in the HJC0152-treated MMTV-erbB2 mice. In the HJC0152-treated C3(1)/TAgSV40 mice, the number of hyperplasia and MIN lesions were significantly decreased (p=0.0014 and 0.0203, respectively). These results demonstrate that HJC0152 suppresses mammary tumor development in ENBC and TNBC models via reducing premalignant lesions, even in the most aggressive TNBC model, C3(1)/TAgSV40. There were no significant side effects or toxicity signs observed in both long- and short-term prevention experiments. We conclude that HJC0152 has promising cancer preventive efficacy by targeting non-ER-based signaling pathways such as STAT3 signaling and glucose metabolism. This study was supported by a NIH/NCI PREVENT Program fund. *Current Affiliation: LSUHSC.

Citation Format: Hyejin Kim, Xi Liu, Yefei Wen, Jia Zhou, Romaine Fernando, Shizuko Sei, Powel H. Brown, Qiang Shen. Examination of HJC0152, a putative modulator of glucose and energy metabolism, for mammary cancer prevention [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 19.

Abstract 21: Optimization of dosing regimens of sulindac in combination with erlotinib for small intestine and colorectal cancer prevention

Introduction: Familial adenomatous polyposis (FAP) is an autosomal dominant disorder caused by germline mutations in the APC (Adenomatous polyposis coli) gene. The combination of Sulindac (SUL) with Erlotinib (ERL) for 6 months was effective in reducing duodenal and colon polyp burden in FAP patients. However, toxicity of the two drugs in combination raised concerns about their long- term use in a prevention setting. Current preclinical studies in the polyposis in rat colon (Pirc) model of FAP examined lower and/or less frequent clinically relevant dosing of ERL and SUL.

Methods: Pirc males (n=14/group) at 5-6 wks of age were fed AIN93 diet with/without SUL (250 ppm in diet) daily and/or escalating doses of ERL (10, 21, or 42 mg/kg) by oral gavage, once weekly, in a 12-month Chemoprevention Efficacy/Toxicity/Resistance study. In a follow-on 3-month Dose Optimization study, Pirc males (n=10/group) were fed AIN93 diet with/without SUL (250 ppm in diet) and/or lower ERL doses (5 or 10 mg/kg), once or twice weekly. Colon polyps were examined by monthly colonoscopy, and at the end of the study assessed by histology, immunoblotting and RT- qPCR. Colon and small intestine (SI) polyps were recorded for location, multiplicity and volume. Tumors, adjacent normal tissues, and blood samples were collected.

Results: Efficacy/Toxicity/Resistance study: Weekly ERL (10, 21, or 42 mg/kg) + daily SUL (250 ppm) demonstrated excellent tumor inhibition (58%, 85.5%, 95.2%, respectively, p&lt;0.001 vs AIN), based on monthly colonoscopy. Treatment inhibited pErk and Wnt pathway genes in colon polyps. Results at necropsy demonstrated dose-dependent tumor inhibition by ERL (10, 21, or 42 mg/kg) + SUL (250 ppm) in the SI (89.1%, 98.8%, 99.3%, p&lt;0.001 vs AIN) and colon (55.2%, 78%, and 95.1%, p&lt;0.001 vs AIN), respectively, consistent with the colonoscopy data. The lowest most efficacious dose was ERL10+SUL (0.24X human loading dose), when compared to tumor inhibition by ERL10 (52.6%, p&lt;0.05 vs ERL10+SUL) or SUL alone (40%, p&lt;0.01 vs ERL10+SUL), indicating synergy, mainly in the SI. Moreover, ERL10+SUL normalized organ weights and hematocrits that were altered in the AIN controls. But, few rats had weight loss, blood in rectum, diarrhea, and skin toxicity. Dose Optimization study: dose and frequency of low-dose SUL and ERL are ongoing, to identify best clinically translatable combinations.

Conclusions: These studies have the potential to define new dosing strategies for SUL+ERL that are safe and effective, improving efficacy against colon and SI polyps, while circumventing toxicity and resistance. Outcomes from the current work, and dose optimization in Pirc, should be directly translatable to the clinical management of FAP patients.

Acknowledgements: Research supported by NCI Contract Number HHSN261201500018I, Task Order HHSN26100004, and NCI Contract Number 75N91019D00021, Task Order 75N91019F00130.

Citation Format: Praveen Rajendran, Ahmetmursel Ulusan, Wan-Mohaiza Dashwood, Sabeeta Kapoor, Altaf Mohammed, Shizuko Sei, Asif Rashid, Powel H. Brown, Eduardo Vilar-Sanchez, Roderick H. Dashwood. Optimization of dosing regimens of sulindac in combination with erlotinib for small intestine and colorectal cancer prevention [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 21.

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.

Abstract 5074: Optimizing erlotinib plus sulindac dosing regimens in a preclinical model of FAP

Introduction Colorectal cancer (CRC) involves sporadic cases and hereditary syndromes, such as familial adenomatous polyposis (FAP). In FAP patients, surgical intervention often is coupled to prevention strategies using nonsteroidal anti-inflammatory drugs. However, none of the current therapeutic options is fully effective. A recent trial in FAP patients combined standard of care Sulindac (SUL) treatment with daily Tarceva/erlotinib (ERL), and had good efficacy in reducing adenomatous polyp burden. Toxicity concerns, however, raised questions over the combination strategy for long-term prevention (Samadder et al. 2016). Using the Apc-mutant polyposis in rat colon (Pirc) model as a mimic of human FAP, we sought to optimize the dosing regimens for SUL+ERL for an improved safety profile, while retaining efficacy in the GI tract.

Methods In a short-term pharmacodynamic biomarker study, rats (n=7) were fed AIN control diet or AIN diet containing 250 ppm SUL, either alone or in combination with ERL, given by oral gavage at 6 or 12 mg/kg (daily), 21 mg/kg (twice weekly), or 42 mg/kg (once weekly). Colon and small intestine (SI) polyps were resected at 0.5, 1, 2, 3, 7, 10, and 14 days after dosing, and assessed by immunoblotting (IB) or RT-qPCR for changes in pErk/Erk, pAkt/Akt, and other biomarkers. In a follow-up efficacy study, rats (n=10) were given SUL, ERL, or ERL+SUL using dosing regimens that were dictated by recovery times for pErk in the biomarker study. Colon and SI polyps were recorded at necropsy for location, incidence, multiplicity, and volume. Tumors and adjacent normal tissues were taken for histopathology and molecular analyses.

Results The biomarker study revealed that pErk was inhibited in Pirc colon polyps for up to 10 days after discontinuing ERL treatment, with full recovery on or around day 14. Nuclear β-catenin, c-Myc, Mmp-7 and Cyclin D1 also were attenuated by ERL+SUL in colon polyps. In the efficacy study, results accrued via endoscopy at 3, 4 and 5 months were remarkably consistent with data obtained during final necropsy, at 6 months. Compared to AIN controls, multiple ERL+SUL groups exhibited significant suppression of polyps in the colon (78-98% inhibition, p&lt;0.001) and SI (91-100% inhibition, p&lt;0.001). Molecular analyses revealed that pErk was inhibited in adenomatous polyps, along with downregulation of β-catenin targets (c-Myc, Mmp-7). No overt toxicity was detected, other than mild skin changes in groups given ERL.

Conclusions These studies have the potential to define safe and effective dosing strategies for SUL+ERL, improving efficacy against colon and SI polyps, while circumventing toxicity and resistance. Outcomes from the current work, plus an ongoing one-year toxicity/resistance trial in Pirc, should be directly translatable to the clinical management of FAP patients exhibiting similar pathology and phenotype. Supported by NCI Contract Number HHSN261201500018I, Task Order HHSN26100004.

Citation Format: Ahmetmursel Ulusan, Praveen Rajendran, Wan-Mohaiza Dashwood, Altaf Mohammed, Shizuko Sei, Powel H. Brown, Eduardo Vilar-Sanchez, Roderick H. Dashwood. Optimizing erlotinib plus sulindac dosing regimens in a preclinical model of FAP [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5074.

Abstract 2732: Frameshift neoantigen vaccination prevent Lynch syndrome mouse model intestinal cancer

Microsatellite-unstable (MSI) cancers occurring in the context of Lynch syndrome elicit pronounced tumor-specific immune responses directed against frameshift peptide (FSP) neoantigens, which result from mismatch repair (MMR) deficiency-induced insertion/deletion mutations in coding microsatellites (cMS). We have recently completed a clinical phase I/IIa trial that successfully demonstrated safety and immunogenicity of an FSP neoantigen-based vaccine in MSI colorectal cancer patients (Clinical trial number: NCT01461148). The vaccine was safe and induced robust cellular and humoral immune responses in all vaccinated patients. To further develop a cancer preventive vaccine against MSI cancers in Lynch syndrome, we aimed to establish a preclinical mouse model. A systematic database search was performed to identify cMS sequences in the murine genome. Subsequently, intestinal tumors obtained from Lynch syndrome mice (Msh2flox/flox VpC+/+) were evaluated for mutations affecting these candidate microsatellites. Thirteen candidate cMS were detected that presented with a mutation frequency of 15% or higher. Epitope prediction using the netMHC4.0 algorithm was performed, and ten most promising FSP neoantigens were synthesized. Immunogenicity was evaluated after vaccination of C57BL/6 mice using IFN-gamma ELISpot. Four FSP neoantigens derived from cMS mutations in the genes Nacad, Maz, Xirp1, and Senp6 elicited strong antigen-specific cellular immune responses. CD4-specific T cell responses were detected for Maz, Nacad, and Senp6 and CD8-positive T cells were detected for Xirp1 and Nacad. Vaccination with peptides encoding these four intestinal cancer FSP neoantigens promoted anti-neoantigen immunity, reduced intestinal tumorigenicity and prolonged overall survival (P&lt;0.01). Additionally, NSAIDs, which have chemopreventive efficacy for Lynch syndrome, increase T cell immunity against neoantigens. Mechanistic tumor mutation burden and adaptive immune response studies will be shown. In summary, these data support the further development of vaccination strategies for preventing cancers associated with Lynch syndrome.

Citation Format: Ozkan Gelincik, Hamza Ibrahim, Mine Ozkan, Aysel Ahadova, Shizuko Sei, Robert Shoemaker, Mattias Kloor, Magnus Von Knebel Doeberitz, Steven M. Lipkin. Frameshift neoantigen vaccination prevent Lynch syndrome mouse model intestinal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2732.