Aggressive Prostate Cancer Research Articles

Abstract 1853: Prostate specific membrane antigen (PSMA) glycoforms and prostate cancer progression

Abstract Introduction: Prostate cancer (PCa) is the most common non-skin malignancy and the second leading cause of cancer related death in men. Prostate cancer is a heterogeneous disease with diverse clinical outcomes ranging from indolent asymptomatic cases to very aggressive and potentially lethal metastatic forms of the disease. Early detection of PCa is predominantly through determination of serum PSA levels and digital rectal examinations (DRE). Subsequently, biopsy based Gleason Grade Scores and TNM staging, tumor size or mpMRI are used to assess disease severity and progression. However, due to the low specificity of PSA concentration in diagnosis and prognosis, biopsy complications, and high mpMRI costs, there is still a critical need to identify and develop novel noninvasive biomarkers that discriminate indolent from aggressive PCa upon diagnosis. Our long-term objective is to discover biomarkers for aggressive PCa, develop and to implement them into robust clinical testing minimally invasive assays for PCa risk stratification at diagnosis. The current focus is on Prostate-Specific Membrane Antigen (PSMA), a membrane bound glycoprotein, that is significantly over-expressed in aggressive and metastatic prostate carcinomas and with poor patient prognosis. The role of its glycosylation status and composition in disease progression and its glycoforms on biomarker development and therapeutics is unknown. Aberrant glycosylation of glycoproteins occurs in many cancers, and it influences disease progression. We rationalize that differential glycosylation of PSMA correlate with progression to aggressive PCa and that PSMA glycopeptides and glycoforms can be used as diagnostics and prognosticators for aggressive disease. Methods/Results: PSMA was isolated from risk Grade Group stratified post-DRE urines, seminal plasma and prostate cancer cell lines with different metastatic phenotypes cell line lysates. Intact glycopeptides were isolated, purified and analyzed by qualitative and quantitative mass spectrometry to identify site specific glycoforms. Our data demonstrate differential expression of unique PSMA glycoforms that correlate with disease risk and severity. Conclusions: Differential glycosylation of PSMA correlates with PCa disease progression to aggressive phenotypes and may have utility in disease stratification. Ongoing studies focus on determining if these qualitative and quantitative changes have diagnostic/prognostic value and if these be integrated with other PCa biomarkers to improve their prognostic power in discriminating aggressive PCa. Acknowledgements: This work was supported by the DOD, USAMRAA, through the Prostate Cancer Research Program under Award No. W81XWH18-1-0228. Opinions, interpretations, and conclusions are those of the author and are not necessarily endorsed by the USAMRAA. Citation Format: Stephen Mackay, Ian O. Oduor, Tanya Burch, Dean A. Troyer, Oliver J. Semmes, Julius O. Nyalwidhe. Prostate specific membrane antigen (PSMA) glycoforms and prostate cancer progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1853.

Abstract 5968: CDC7 is a targetable regulator of advanced prostate cancer

Abstract Prostate cancer is estimated to contribute to over 34,000 deaths in men residing in the United States, with the majority fatality due to metastatic disease. CDC7 is a kinase that regulates DNA replication and is an emerging cancer biomarker for poor prognosis in carcinomas such as Wilms tumor and hepatocellular carcinomas. In this study, we demonstrated that high level of CDC7 is associated with metastatic prostate cancer when compared to benign prostate tissues or localized prostate cancer. Furthermore, we found that CDC7 expression is highest in prostate cancer patient-derived xenografts (PDX) models of adenocarcinomas with neuroendocrine features. In vitro, we showed that inhibition of CDC7 with TAK-931, a CDC7 specific inhibitor, reduced the ability of aggressive prostate cancer cells to proliferate, migrate, and invade. Similarly, knock-down of CDC7 in prostate cancer cell lines inhibited cell growth in a colony formation assay. TAK-931 treated prostate cancer cell lines also showed an abnormal cell cycle profile, indicating that inhibiting CDC7 in aggressive prostate cancer could contribute to replication stress and promote apoptosis. Overall, this study demonstrates that CDC7 is a targetable protein that regulates advanced and aggressive prostate cancer growth. Citation Format: Alifiani Bonita Hartono, Sidharth Paparaju, Chung Lee, Shiqin Liu, Busola R. Alabi, En-Chi Hsu, James D. Brooks, Eva Corey, Tanya Stoyanova. CDC7 is a targetable regulator of advanced prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5968.

Abstract 850: Androgenic alopecia and risks of overall and aggressive prostate cancer: An updated meta-analysis

Abstract Background: Androgenic alopecia, known as male pattern baldness (MPB), is a common hair loss disorder among men. MPB has similar risk factors with prostate cancer (PrCa) including advancing age, family history, and sex hormones. Several studies have examined the associations between MPB and PrCa but the evidence remains unclear. We carried out a meta-analysis of epidemiological studies that examined the relationship between patterns of baldness: frontal, vertex, or both and PrCa risk. Methods: A literature search was performed in October 2022 using PubMed and Web of Science databases for epidemiological studies published between 1/1/2000 and 10/31/2022, which examined the above hypothesis. From each eligible study, relevant data were extracted on study design, population, sample size, prevalence of MPB at various ages, and corresponding associations with risks of total and aggressive PrCa. Pooled relative risks (RR) and corresponding 95% confidence intervals (CI) were calculated using the DerSimonian and Laird random-effects models. Heterogeneity across studies was assessed by I2 statistic. Results: A total of 14 studies: 14,573 cases and 132,434 controls/non-cases were included. The prevalence of MPB increased from 5% to 70% with aging and varied across studies. Vertex MPB at ages 40 years or older was associated with a pooled RR of 1.08 (95%CI 1.00-1.17) of total PrCa, but there was no association with frontal MPB. The onset of MBP at younger ages was also associated with RR=1.10 (95% CI 0.93 - 1.29) of PrCa, although results were not statistically significant. Results were similar when data were stratified by clinical features of PrCa, although there was large heterogeneity in the definition of aggressive PrCa across studies. Conclusions: Men with vertex MPB may have modest increased risk of PrCa. However, the majority of studies were conducted in Caucasian men and they did not evaluate effect modifications by genetic variations in androgen metabolism pathway genes or changes in serum levels of androgens. Further, large well-designed prospective cohort studies are needed to better understand the complex relationship between genetic susceptibility, endogenous hormones, MBP and risk of PrCa. Citation Format: Sapir Amar, David Hanelin, Ilir Agalliu. Androgenic alopecia and risks of overall and aggressive prostate cancer: An updated meta-analysis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 850.

Abstract 2234: Cardiovascular disease risk among men with prostate cancer: Differences by prostate cancer aggressiveness

Abstract Background: Cardiovascular disease (CVD) is a major cause of morbidity and mortality among men diagnosed with prostate cancer. We evaluated the extent to which men with prostate cancer develop CVD accounting for potential factors that may contribute to the CVD burden in this population. Methods: We prospectively followed men diagnosed with prostate cancer and free from CVD (stroke and coronary heart disease, including myocardial infarction, coronary artery bypass graft, and percutaneous coronary intervention) before their cancer diagnosis in the Health Professionals Follow-up Study, between 1986 and 2016. Men were categorized by D’Amico prostate cancer risk groups as low-risk (stage T1-2a, Gleason score ≤6, and PSA at diagnosis ≤10 ng/mL), intermediate-risk (T2b and/or Gleason score 7 and/or PSA >10-20), or high-risk (≥T2c/N1/M1 or Gleason score 8-10 or PSA >20). Incident fatal and non-fatal CVD, defined as coronary heart disease and stroke after cancer diagnosis, were centrally adjudicated. CVD risk factors including smoking, hyperlipidemia, hypertension, diabetes mellitus, body mass index, were self-reported on biennial questionnaires. Deaths due to prostate cancer or other causes were treated as competing events when estimating cumulative incidence and cause-specific hazard ratios (HR). Results: Among 5,707 prostate cancer patients, 1,912 had low-risk, 2,261 had intermediate-risk, and 1,534 had high-risk cancer. 1,102 CVD events were documented over up to 30 years of follow-up after cancer diagnosis. The 10-year CVD risk was 8.1% for men with low-risk cancer, 8.8% for intermediate-risk, and 10.4% for high-risk cancer. The cause-specific HRs for CVD were 1.18 (95% CI 1.03, 1.36) in intermediate-risk and 1.59 (95% CI 1.36, 1.85) in high-risk prostate cancer, both compared to low-risk prostate cancer. Men with high-risk cancer tended to be older; after age adjustment, the HRs were 1.15 for intermediate-risk (95% CI 1.00, 1.33) and 1.35 for high-risk cancer (1.35, 95% CI 1.16, 1.58). Associations between cancer risk group and CVD were essentially unchanged after further adjustment for CVD risk factors present at cancer diagnosis, primary cancer treatment modality (surgery, radiation, androgen deprivation therapy, watchful waiting/active surveillance), and calendar year of diagnosis. Discussion: Despite the elevated risk of cancer mortality in men with intermediate-risk and high-risk prostate cancer compared to low-risk prostate cancer, CVD risk remains at least as common over time among these men as among men with low-risk prostate cancer. Incident CVD risk after cancer diagnosis among men with more aggressive cancers, which particularly occur in older men, is not primarily attributable to differences in pre-existing risk factor burden. These findings from a cohort with healthcare access and literacy indicate a need for continued clinical attention to CVD after cancer diagnosis. Citation Format: Caroline Himbert, Anna Plym, Jane B. Vaselkiv, Andreas Pettersson, Philip W. Kantoff, Lorelei A. Mucci, Kenneth J. Mukamal, Konrad H. Stosapck. Cardiovascular disease risk among men with prostate cancer: Differences by prostate cancer aggressiveness [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2234.

Abstract 7344: Role of ubiquitin receptor ADRM1 (Rpn13) in prostate cancer

Abstract Adhesion-regulating molecule 1 (ADRM1)/Rpn13 is a component of the 19S regulatory subunit of the 26S proteasome [1]. ADRM1 plays a crucial role in the recognition of polyubiquitinated substrates of the proteasome and their subsequent deubiquitination and degradation [2]. ADRM1 transcript levels are commonly upregulated in diverse tumor types [3]. The androgen receptor (AR) plays a predominant role in prostate cancer (PCa) pathology. In this study, we investigated the expression of ADRM1/Rpn13 in different stages of prostate cancer and its association with AR expression. TCGA data from UALCAN was used for understanding ADRM1 expression on different stages of diseases and single-cell RNA-sequencing data of prostate cancer cell line was obtained from Prostate Cancer Atlas. TCGA (cell, 2015) data set was used for investigating the correlation between ADRM1 and AR by using R programming. Our study from the TCGA dataset reveals that ADRM1 expression increased significantly with the aggressiveness of prostate cancer (increase consistently with the Gleason score) from the TCGA dataset. We analyzed ADRM1 and AR expression in different prostate cancer cell lines and obtained that ADRM1 expressed significantly higher in prostate cancer cell lines which had lower AR expression. TCGA (cell, 2015) dataset indicated a negative correlation between ADRM1 and AR expression in prostate cancer. Our preliminary analysis indicated that ADRM1 inhibitor might be a potential therapeutic option for AR-independent prostate cancer. Citation Format: Shahjalal Chowdhury, Honghe Wang, Chitra Nayak, Balasubramanyam Karanam. Role of ubiquitin receptor ADRM1 (Rpn13) in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7344.

Abstract 2756: Single cell analysis reveals treatment response-associated plastic cell state and lineage switching in aggressive variant prostate cancer

Abstract Prostate cancer (PCa) is a common malignancy in men over 65, ranking as the second leading cause of cancer-related deaths among men in the United States. While most prostate cancers respond to androgen receptor (AR) targeting therapies, Aggressive Variant Prostate Cancers (AVPCs), characterized by RB1, Tp53, and/or PTEN alterations, do not. AVPCs exhibit lineage plasticity in preclinical models, enabling the expression of non-prostate epithelial lineage markers to adapt to therapeutic pressures. However, a measurable definition of lineage plasticity as a potential therapeutic target for clinical trials is currently lacking. To arrive at said definition, we perform single-nuclei RNA sequencing (snRNA-seq) on lymph node metastases from twelve AVPC patients with matched sample pairs of both pre- and post-treatment. Additionally, we include snRNA-seq data from eight non-AVPC patients as a baseline. Expanding upon our prior establishment of tumor-specific total mRNA expression (TmS) as an indicator of tumor cell lineage plasticity (Nature Biotechnology, PMID: 35697807), we employ unique molecular identifier (UMI) counts from individual cells to quantify this plasticity. We reveal a distinct cluster of tumor cells with notably high UMI counts in resistant samples, indicative of a less differentiated state and increased transcriptional diversity. This high-UMI cluster is marked by significant enrichment in pathways associated with epithelial-mesenchymal transition (EMT), stemness, one-carbon metabolism, and arginine metabolism pathways. Concurrently, there is a reduction in activity within the androgen receptor (AR) and DNA damage repair pathways. These characteristics suggest an enhanced capacity for lineage switching in AVPC tumor cells, potentially contributing to evasion from targeted therapies. Moreover, immune components within resistant samples consistently display lower UMI counts, indicating a diminished propensity for lineage plasticity. In conclusion, we present a better understanding of lineage switching in therapeutic resistance in AVPCs, paving the way for novel treatment strategies in PCa management. Citation Format: Shuai Guo, Elavarasan Subramani, Daniel E. Frigo, Patrick G. Pilié, Sangeeta Goswami, Rama Soundararajan, Ana Aparicio, Wenyi Wang. Single cell analysis reveals treatment response-associated plastic cell state and lineage switching in aggressive variant prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2756.

Abstract 5199: Protease-activated CDCP1 as a marker for aggressive primary prostate cancer and castration resistance

Abstract CUB domain-containing protein 1 (CDCP1) is a type 1 transmembrane protein overexpressed in many cancers, including prostate cancer. CDCP1 has been associated with tumor progression, metastasis, drug resistance and poor prognosis in prostate cancer, making it a potential prognostic biomarker and therapeutic target. It has been shown to be overexpressed in a subset of castration resistant prostate cancers (CRPC) and cooperate with the loss of tumor suppressor PTEN to promote metastatic dissemination. Extracellular serine proteases activate CDCP1 by cleaving it into an N-terminal and C-terminal fragments. Proteolytic cleavage has been associated with the tumor-promoting functions of CDCP1. We studied the expression of full-length and cleaved form of CDCP1 in grade group 2-4 primary prostate cancer tissues and CRPCs using immunohistochemistry. Total CDCP1 staining was observed in 60% of primary prostate cancer samples, while the staining of cleaved CDCP1 was somewhat less frequently observed (45%). The results will be further analyzed regarding the PTEN status and for association with survival of the patients. In conclusion, so far, our results have indicated that cleaved CDCP1, which likely represents activated CDCP1, is detectable in GG 2-4 prostate cancers. Citation Format: Ruusu-Maaria Merivirta, Timo-Pekka Lehto, Antti Rannikko, Tuomas Mirtti, Hannu Koistinen. Protease-activated CDCP1 as a marker for aggressive primary prostate cancer and castration resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5199.

Abstract 7330: Identifying proteomic risk factors for overall, aggressive and early onset prostate cancer using mendelian randomization and tumor spatial transcriptomics

Abstract Background: Understanding the role of circulating proteins in prostate cancer risk can reveal key biological pathways and identify novel targets for cancer prevention. Methods: We investigated the association of 2,002 genetically predicted circulating protein levels with risk of prostate cancer overall, and of aggressive and early onset disease, using cis-pQTL Mendelian randomization (MR) and colocalization. Findings for proteins with support from both MR, after correction for multiple-testing, and colocalization were replicated using two independent cancer GWAS, one of European and one of African ancestry. Proteins with evidence of prostate-specific tissue expression were additionally investigated using spatial transcriptomic data in prostate tumor tissue to assess their role in tumor aggressiveness. Finally, we mapped risk proteins to drug and ongoing clinical trials targets. Results: We identified 20 proteins genetically linked to prostate cancer risk (14 for overall [8 specific], 7 for aggressive [3 specific], and 8 for early onset disease [2 specific]), of which a majority were novel and replicated. Among these were proteins associated with aggressive disease, such as PPA2 [Odds Ratio (OR) per 1 SD increment = 2.13, 95% CI: 1.54-2.93], PYY [OR = 1.87, 95% CI: 1.43-2.44] and PRSS3 [OR = 0.80, 95% CI: 0.73-0.89], and those associated with early onset disease, including EHPB1 [OR = 2.89, 95% CI: 1.99-4.21], POGLUT3 [OR = 0.76, 95% CI: 0.67-0.86] and TPM3 [OR = 0.47, 95% CI: 0.34-0.64]. We confirm an inverse association of MSMB with prostate cancer overall [OR = 0.81, 95% CI: 0.80-0.82], and also find an inverse association with both aggressive [OR = 0.84, 95% CI: 0.82-0.86] and early onset disease [OR = 0.71, 95% CI: 0.68-0.74]. Using spatial transcriptomics data, we identified MSMB as the genome-wide top-most predictive gene to distinguish benign regions from high grade cancer regions that had five-fold lower MSMB expression. Additionally, ten proteins that were associated with prostate cancer risk mapped to existing therapeutic interventions. Conclusion: Our findings emphasize the importance of proteomics for improving our understanding of prostate cancer etiology and of opportunities for novel therapeutic interventions. Additionally, we demonstrate the added benefit of in-depth functional analyses to triangulate the role of risk proteins in the clinical aggressiveness of prostate tumors. Using these integrated methods, we identify a subset of risk proteins associated with aggressive and early onset disease as priorities for investigation for the future prevention and treatment of prostate cancer. Citation Format: Trishna A. Desai, Asa K. Hedman, Marios Dimitriou, Mine Koprulu, Sandy Figiel, Wencheng Yin, Matthias Johansson, Eleanor L. Watts, Joshua R. Atkins, Aleksandr V. Sokolov, Helgi B. Schioth, Marc J. Gunter, Konstantinos K. Tsilidis, Richard M. Martin, Maik Pietzner, Claudia Langenberg, Ian G. Mills, Alastair D. Lamb, Anders Malarstig, Tim J. Key, The PRACTICAL Consortium, Ruth C. Travis, Karl Smith-Byrne. Identifying proteomic risk factors for overall, aggressive and early onset prostate cancer using mendelian randomization and tumor spatial transcriptomics [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7330.

Abstract 4649: BLX-3030, a potent, selective, orally available small molecule CDK9 inhibitor for aggressive variant prostate cancers

Abstract Background: The use of novel, potent targeted therapies in prostate cancers has led to the development of highly aggressive variant cancers, including neuroendocrine prostate cancer (NEPC). Gene amplification of N-MYC and C-MYC oncogenes leads to its overexpression in NEPC and mCRPC patients, highly prevalent in these lethal subtypes of cancers detected in 2% of all Prostate Cancers (PCa) and over 10-17% of mCRPC patients. N-MYC is a transcriptional target of CDK9, which acts as an oncogenic driver sufficient to transform human-derived prostate cancer to take on NEPC phenotypic changes resulting in a more aggressive disease identified in late-stage human PCa patients. Additionally, N-MYC and C-MYC are required for tumor drug resistance, and their downregulation through CDK9 inhibition lowers tumor growth. Our efforts have demonstrated that targeting both N-MYC and C-MYC as a driver of NEPC and mCRPC with highly selective CDK9 inhibitor BLX-3030 is a viable approach for therapeutic intervention of mCRPC and NEPC. Materials and Methods: Our empirical data-driven AI/ML MolecuLernTM fragment library, workflows, LigEdit design strategies, and hit2-lead optimization methods are employed. In vitro experiments include kinase glo, cell titer glo, selectivity profiler, ADME-Tox, FACS/apoptosis, cell migration, live cell imaging, immunofluorescent, western blot, combination studies and in vivo experiments including PK, prostate tumor models, 7-day tox, BLX-3030 non (GMP) scaleup and safety pharmacology experiments conducted. Results: We synthesized a series of novel small molecule CDK9 inhibitors that reversibly bind to CDK9, competitively block the ATP site with an IC50 of 1.06 nM, and elicit pharmacological responses in N-MYC, C-MYC, and other prostate cancer cells in vitro and in vivo. We studied the CDK9 N-MYC expression detected in PC-3, DU-145, LNCaP, and in LASCPC-01, NCI-H660, and 22RV1 cell lines. BLX-3030 exhibited potent cellular efficacy with an IC50 of 22 to 590 nM in PC cell lines and in N-MYC expressed cells had an activity of 76, 470, and 132 nM respectively, and reduced pCDK9, C-MYC, Mcl-1, N-MYC and its downstream RNA Pol II (Ser-2) and pAR (Ser-81) dose-dependently. BLX-3030 exhibits in vivo antitumor activity in LASCPC-01, 22RV1, and C4-2 prostate cancer mouse models. Several ADME-Tox, MTD, dose range finding, hERG and other in vivo safety pharmacology experiments have advanced BLX-3030 to the IND enabling studies. Conclusions: BLX-3030 is currently being investigated in non-clinical toxicology, toxicokinetic, and core battery of safety pharmacology studies including the assessment of effects on cardiovascular, central nervous, and respiratory systems. Citation Format: Zhaoang li, Chenyu Lin, Kyle Medley, Hariprasad Vankayalapati, David J. Bearss. BLX-3030, a potent, selective, orally available small molecule CDK9 inhibitor for aggressive variant prostate cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4649.

Abstract 170: Targeting of macrophage PI3Kγin prostate cancer using Eganelisib (IPI-549) reprograms immune-suppressive infiltrating macrophages to enhance anti-tumor immune responses and promote immunologically mediated tumor growth

Abstract Background: Prostate cancer (PCa) is traditionally considered an immunologically 'cold’ indication, as evidenced in part by significant infiltration of immunosuppressive tumor associated macrophages (TAMs) and few activated effector CD8+ T cells. Attempts to (re)invigorate an anti-prostate cancer immune response with immune checkpoint blockade (ICB) such as anti-CTLA-4 and anti-PD-1 have been largely ineffective clinically, despite promising results in other cancers. This is likely due to a multitude of immunosuppressive cell types and secreted factors within the tumor microenvironment (TME) that diminish T cell activation and trafficking. Reducing the immunosuppressive burden intratumorally by targeting TAMs is a clinically attractive approach and offers opportunity to sensitize PCa to immune checkpoint blockade. While PI3K signaling is ubiquitous in most cell types, specific catalytic isoforms and regulatory elements are differentially expressed depending on cell type, with PI3Kγ being significantly enriched in myeloid cells and therefore offering a unique therapeutic opportunity for specific targeting. Methods: Utilizing novel syngeneic prostate cancer tumors, PI3Kγ deletion and antagonism using Eganelisib (a small molecule inhibitor for PI3Kγ), we tested our hypothesis that targeting PI3Kγ signaling in PCa TAMs would lead to tumor growth inhibition and anti-tumor immune responses. Results: We show here that PCa tumor cells do not express the PI3Kγ isoform and, therapeutic inhibition of PI3Kγ with Eganelisib reduces the TAM suppressive phenotype. We also show PI3Kγ signaling is essential to monocyte anti-apoptotic signaling, and inhibition of PI3Kγ can enhance anti-tumor immune responses in preclinical models of PCa. Specifically, inhibition of PI3Kγ alone is sufficient to enhance anti-tumor immune responses in the less aggressive B6CaP PCa model, but insufficient in the more aggressive RM-1 PCa model. However, treatment of RM-1 tumors with Eganelisib produces improved tumor control when combined with anti-PD-1 therapy, relative to Eganelisib or anti-PD1 as a monotherapy. Conclusions: Altogether, these data highlight the integral role of PI3Kγ signaling in TAMs and the potential for therapeutic targeting with Eganelisib to sensitize PCa to ICB. Citation Format: Kenneth M. Adusei, Thomas R. Nirschl, Alex J. Lee, Fan Shen, Xiaoxu Wang, Monali Praharaj, Jade Alvarez, Iyana Gross, Kara A. Lombardo, Tamara L. Lotan, Judith A. Varner, Jelani C. Zarif. Targeting of macrophage PI3Kγin prostate cancer using Eganelisib (IPI-549) reprograms immune-suppressive infiltrating macrophages to enhance anti-tumor immune responses and promote immunologically mediated tumor growth [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 170.

Abstract 7320: Expression of circadian rhythm genes and lethal prostate cancer

Abstract Background: The circadian rhythm regulates diverse physiological and oncologic processes. We have previously shown in epidemiology studies that disruption of the circadian rhythm may be associated with increased risk of aggressive prostate cancer, including germline polymorphisms in certain circadian rhythm genes. This study sought to investigate the relationship between tumor circadian rhythm gene expression and lethal prostate cancer. Methods: We studied patients with primary prostate cancer in the Health Professionals Follow-up Study (HPFS) and Physicians’ Health Study (PHS). We created a composite score of mRNA expression using principal components that incorporated 11 circadian rhythm genes: AANAT, ARNTL, CLOCK, CRY1, CSNK1E, MTNR1A, MTNR1B, NPAS2, PER1, PER2, PER3. An age-stratified analysis was performed, and the mean differences of the score both by Gleason score and compared to normal tissue were calculated. The relationship between the score in prostate tumor tissue and lethal prostate cancer (metastases/prostate cancer-specific death) vs. indolent disease (no metastases after >8 years of follow-up) was assessed using logistic regression. The contribution of each gene was evaluated by leave-one-out analysis, generating scores leaving out one gene and assessing the relationship between the modified score and lethal disease. Results: Among 404 cancer patients in HPFS/PHS, there were 119 lethal events over 30 years of follow-up (median: 17 years). The circadian rhythm gene score was lower in tumor tissue compared to tumor-adjacent, histologically normal tissue (mean difference in units of standard deviation [SD] of gene score: -0.31, 95% confidence interval [CI]: -0.48 to -0.15). In addition, the score was lower in Gleason 9-10 compared to Gleason 6 tumors (mean difference in SD units: -1.05, 95% CI: -1.55 to -0.54). The three PER genes were the most strongly correlated with each other and with the score (Spearman correlation coefficients from 0.52-0.88 for the score and 0.31-0.63 between PER genes). Higher circadian rhythm gene scores were inversely associated with lethal prostate cancer (odds ratio [OR] for highest vs. lowest quartile: 0.43, 95% CI: 0.20 to 0.90) in a dose-response fashion and after adjusting for clinical and pathologic factors. The association appeared to be stronger in patients aged ≥65 years (OR for highest vs. lowest quartile: 0.21, 95% CI: 0.08 to 0.47) compared to <65 years at diagnosis (OR: 0.78, 95% CI: 0.29, 2.17). Results were consistent in the leave-one-out analysis for all genes except PER2 (OR for highest vs. lowest quartile: 1.00, 95% CI: 0.55 to 1.83) and PER1 (OR: 0.55, 95% CI: 0.30 to 1). Conclusion: This study examining intratumoral circadian rhythm gene expression contributes further evidence in support of the relationship between circadian rhythm disruption and aggressive prostate cancer. Tumor expression of PER1 and PER2 may be a predominant factor in the association. Citation Format: Jane Bailey Vaselkiv, Sarah C. Markt, Hannah E. Guard, Anqi Wang, Kathryn L. Penney, Konrad H. Stopsack, Lorelei A. Mucci. Expression of circadian rhythm genes and lethal prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7320.

Abstract 4157: Combining hyperpolarized magnetic resonance and positron emission tomography to interrogate prostate cancer metabolism

Abstract Background: There is an unmet clinical need for imaging biomarkers to distinguish indolent from aggressive prostate cancer (PCa). Many advanced and aggressive PCa patients receiving anti-androgens (enzalutamide) develop resistance. It is hypothesized that dysregulated cell metabolism is a key driver for PCa progression and therapy resistance. Two pathways commonly involved in PCa are glycolysis and fatty acid metabolism. Therefore, metabolic imaging and metabolomics were performed on enzalutamide sensitive/resistant, Androgen Receptor dependent (AR+) and AR independent (AR-) patient derived xenograft (PDX) tumors. To interrogate both pathways, [1-13C]-pyruvate hyperpolarized magnetic resonance spectroscopy (HP-MRS) and [18F]-fluorodeoxyglucose positron emission tomography (18F-FDG) for glycolysis, and [18F]-fluoro-pivalic acid positron emission tomography (18F-FPIA) for fatty acid metabolism were employed. 1H Nuclear Magnetic Resonance (NMR) spectroscopy and liquid chromatography with tandem mass spectrometry (LC-MS-MS) were employed for validation purposes. Methods: [1-13C]-labeled pyruvic acid was hyperpolarized using a DNP HyperSense polarizer following standard protocol. Anatomical MRI and 13C-MRS were obtained on different PCa PDX mouse models at two different time points using a Bruker 7T scanner. The PDX models included AR+ enzalutamide sensitive (183-A, 180-30), AR+ enzalutamide resistant (274-4), and AR- (144-4, 114-B). The time points imaged were before and after 7 days of treatment with enzalutamide. 1H-NMR spectroscopy was performed on extracted tissue. Simultaneously, 18F-FPIA-PET imaging were acquired on the same models on an Albira trimodal PET station. Results: The dynamic metabolic flux ratio, lactate-to-pyruvate (Lac/Pyr) was determined in vivo and used as a treatment response marker. The Lac/Pyr ratios were significantly higher in resistant tumors compared to sensitive tumors (p<0.01). The enzalutamide sensitive group had a lower Lac/Pyr ratio after treatment, while the enzalutamide resistant group had a higher Lac/Pyr ratio. After treatment, there was also a decrease in [18F]-FDG uptake, corresponding to the HP-MRS data. This was expected as both Pyruvate and [18F]-FDG interrogate the glycolytic pathway. As for the fatty acid metabolic imaging, PET imaging also revealed that [18F]-FPIA is transported into the tumors, and we are currently exploring how its uptake varies between AR (+/-) PCa-PDX tumors and enzalutamide resistant/sensitive models. Ex vivo NMR and mass spectrometry-based metabolomics validated the in vivo HP-MRS data with higher lactate levels in drug resistant tumors. Conclusion: Combining HP-MRS and PET presents an exciting opportunity to realize imaging-based personalized medicine in different AR (+/-) PCa-PDX preclinical models by interrogating glycolysis and fatty acid oxidation pathways. Citation Format: Muxin Wang, José S. Enriquez, Prasanta Dutta, Jenny Han, Peter Shepherd, Daniel Frigo, Federica Pisaneschi, Pratip K. Bhattacharya. Combining hyperpolarized magnetic resonance and positron emission tomography to interrogate prostate cancer metabolism [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4157.

Abstract 4801: Clinical polygenic model to stratify risk of any, metastatic, and fatal prostate cancer in a randomized controlled trial of precision screening

Abstract Introduction: Lifetime risk of prostate cancer (PCa) is strongly associated with three factors: ancestry, family history, and genetics. We previously developed a polygenic hazard score (PHS) for PCa comprised of 290 common genetic variants (PHS290). When accounting for family history and ancestry (self-reported or genetically determined), PHS290 remained a powerful independent predictor of age at PCa diagnosis, metastatic PCa diagnosis, and PCa death. Additional variants associated with PCa susceptibility or benign elevation of prostate-specific antigen (PSA) have since been published. Here, we evaluate their impact on lifetime risk predictions for metastatic and fatal PCa and develop an updated polygenic score. This score will inform the design of the Prostate Cancer, Genetic Risk, and Equitable Screening Study (ProGRESS, ClinicalTrials.gov ID NCT05926102), a nationwide randomized controlled trial evaluating precision PCa screening in the VA healthcare system. Methods: We utilized a machine learning approach to update the PHS. Over 450 variants associated with PCa, aggressive PCa, benign prostatic hyperplasia, or benign PSA elevation were evaluated for inclusion. First, we identified pairs of variants with highly correlated genotype (defined as R2 > 0.95) and utilized univariable Cox proportional hazards models (using age at diagnosis of PCa) to exclude one variant from each pair. We then evaluated all remaining candidate variants for inclusion in a new PHS using a LASSO-regularized Cox proportional hazards model. We combined the new PHS with clinical predictors (ancestry and family history) to create a comprehensive, quantitative polygenic score in a diverse, population-based cohort of n=590,750 (Million Veteran Program). Both self-reported and genetic ancestry (based on 2,309 ancestry informative markers) were assessed. We estimated hazard ratios (HRs) to compare men with high versus low polygenic score and evaluated absolute predictions of any, metastatic, and fatal PCa. Results: The updated polygenic score included 356 variants, as well as family history and genetic ancestry. When comparing the highest to the lowest quintile of the population for polygenic score, the HRs for any PCa, metastatic PCa, and fatal PCa were 5.6, 5.8, and 5.2 respectively. These HRs are all greater than those achieved with PHS290, which yielded 5.2, 4.9, and 4.4 respectively. Risk stratification improved within each ancestry group, including within the >100,000 participants of African ancestry—a group known to have elevated risk of fatal PCa. Absolute risk prediction was accurate for both metastatic and fatal PCa. Conclusion: The polygenic score accurately predicts risk of metastatic and fatal PCa in multiple ancestry groups. A clinical polygenic model has potential utility for precision PCa screening and will now be evaluated prospectively in the ProGRESS trial. Citation Format: Anna M. Dornisch, Roshan Karunamuni, Kara N. Maxwell, Julie Lynch, Isla P. Garraway, Adam Kibel, Charles A. Brunette, Morgan E. Danowski, Kyung M. Lee, Scott L. DuVall, J M. Gaziano, Brent S. Rose, Richard L. Hauger, Jason L. Vassy, Tyler M. Seibert. Clinical polygenic model to stratify risk of any, metastatic, and fatal prostate cancer in a randomized controlled trial of precision screening [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4801.

Abstract 7645: Differentially expressed genes as prognostic markers in racial disparities of prostate cancer

Abstract Racial disparities in prostate cancer are prevalent, with African American (AA) men experiencing 60% greater incidence and 2 to 3 times higher mortality than Caucasian American (CA) men. Consequently, there is a pressing need for improved means of interrogating race/ethnicity-based prostate cancer biology in order to identify biomarkers to help stratify men at high-risk for prostate cancer-specific progression and death and offer treatment recommendation that would mostly benefit AA men undergoing early aggressive therapies. Current predictive models rely on clinical variables but do not account for these disparities. The overall goal is to construct a race-specific prostate cancer prognostic prediction model for risk assessment. Here we performed comprehensive bioinformatics analysis using the data from 17 pairs of gene expression array from AA and CA cohorts and identified 63 differentially expressed genes (DEGs) by race. Among them, chemokine receptor 4 (CXCR4), viz. p-Akt (Ser473), fatty acid synthase (FASN), interleukin-6 (IL-6) and matrix metallopeptidase 9 (MMP-9) gene expressions were significantly altered in AA groups. Immunohistochemistry was performed on 163 prostate cancer patient specimens to validate DEG expression and immunoreactive scores (IRS) were calculated. CXCR4 exhibited significantly higher expression in AA tumors, with > 85% of AA prostate tumors showing weak to strong CXCR4 expression, compared to < 5% in CA specimens. While immunostaining for IL-6, FASN, MMP9 and p-Akt did not provide a significant distinction between CA and AA cases. IRS analysis confirmed higher expression of CXCR4 in AA cancers, compared to CA prostate cancer (p < 0.001). MMP9 and IL6 expression were moderately higher in AA cancer compared to CA prostate cancer (p < 0.05). In contrast, FASN expression was significantly higher in CA cancer, compared to AA prostate cancer (p < 0.001). We further investigated the impact of these genes on biochemical recurrence-free survival (BCRFS) using Kaplan-Meier analysis to examine the differences between low-risk versus high-risk groups. BCRFS analysis demonstrated that CXCR4 is a determinant factor of recurrence risk in AA prostate cancer patients. The activation of the PI3K-Akt signaling pathway, particularly in AA patients, suggests its role in prostate cancer aggressiveness. Taken together, this study demonstrates the importance of differential expression of biomarkers which constitute the bulk tumors in driving cancer. The distinct gene expression patterns, especially the upregulation of CXCR4, in AA prostate cancer highlight its potential as a prognostic biomarker and a target for personalized treatment strategies. These findings encourage further study into the role of population-specific difference in adding CXCR4 in risk model construction, especially in machine learning models. Citation Format: Amel A. Ahmed, Shiv Verma, Ibrahim M. Atawia, Daniel L. Shen, Gregory T. MacLennan, Pingfu Fu, Sanjay Gupta. Differentially expressed genes as prognostic markers in racial disparities of prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7645.

Abstract 560: IGF1 induces the expression of CYR61 in metastatic prostate cancer

Abstract The cysteine-rich angiogenic inducer 61 (CYR61) is a member of the cellular communication network (CCN) protein family that can be induced by growth factors. CYR61-specific functions are dependent on cellular context. In prostate cancer (PCa), CYR61 contributes to cell growth and survival through its interactions with extracellular ligands, such as integrins avb3 and a6b4, in the extracellular matrix space. Interestingly, CYR61 contains an insulin-like growth factor-binding protein domain suggesting that it may interact with insulin-like growth factor-I (IGF1). High serum levels of IGF1 are directly linked to PCa development and recently have been studied as a predictor of metastatic disease. Given the important roles that IGF1 and CYR61 play in PCa and their potential interaction, it is critical to investigate their molecular interplay. The correlation between PCa aggressiveness and circulating levels of CYR61 and IGF1 is poorly studied. Our goal was to assess the contribution of CYR61-IGF1 interaction to PCa cell proliferation. Their combined role may explain a proportion of aggressive PCa. This study was designed to characterize the role of IGF1-induced expression of CYR61 in metastatic PCa cellular models and to determine if this interaction contributes to aggressive tumor properties (e.g., proliferation, migration, tumorsphere formation). Using immunoblotting, we demonstrated that CYR61 is upregulated in the metastatic cell line PC3. Furthermore, optimized knockdown of CYR61 using siRNA significantly reduced PC3 cell proliferation, viability, and prostasphere formation. To examine the underlying mechanisms associated with IGF1 signaling, we assessed the activation of either the PI3/Akt and MAPK pathways in PC3 cells with CYR61 silencing. CYR61 siRNA-mediated knockdown decreased activation of the PI3/Akt pathway but did not affect the MAPK pathway. In addition, we found that IGF1 induces protein expression of CYR61 in a time-dependent manner, validated by both immunoblotting and confocal microscopy. In conclusion, these data provided evidence that CYR61 expression is induced by IGF1, and its inhibition decreased the capacity of metastatic PCa cells to proliferate, indicating a potential utilization of CYR61 inhibition in the therapy of metastatic PCa. Citation Format: Greisha L. Ortiz Hernandez, Mya Walker, Leanne Woods-Burnham, Rick A. Kittles, Carlos A. Casiano, Susan Neuhausen. IGF1 induces the expression of CYR61 in metastatic prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 560.

Abstract 809: Neighborhood disadvantage and prostate tumor aggressiveness among African American and European American men

Abstract Introduction: African American (AA) men experience greater prostate cancer (PC) incidence and mortality compared to European American (EA) men, but the reasons are not fully understood. Some literature has identified connections between neighborhood disadvantage and aggressive PC, and AA men may be more likely to experience these factors than EA men. However, it is unclear if these associations may vary by race. We tested associations of two neighborhood disadvantage measures (neighborhood socioeconomic deprivation and racial segregation) with prostate tumor aggressiveness, overall and separately by race. We hypothesized that they would be positively associated and that associations would be stronger among AA men. Methods: We leveraged data from the University of Maryland Greenebaum Comprehensive Cancer Center Tumor Registry for AA and EA men who were diagnosed with PC from 2004-2021. We geocoded participants’ addresses at diagnosis to determine census tract-based Area Deprivation Index (ADI) and Racial Isolation Index (RI) values. ADI analyses included men diagnosed in 2005 or later (778 AA men and 687 EA men), and RI analyses included men diagnosed in 2009 or later (606 AA men and 454 EA men) based on data availability. We used logistic regression to model the odds of aggressive PC, defined as a Gleason pattern of 4+3 or a total Gleason score >=8, overall and by race. We fit models with scaled ADI or RI as the exposure variable, adjusting for race, age at diagnosis, and year of diagnosis. We also assessed an interaction between each neighborhood measure and race. Results: Median (interquartile range) ADI scores were 118 (101-137) for AA men and 92 (83-102) for EA men, and RI scores were 0.68 (0.35-0.87) for AA men and 0.11 (0.06-0.20) for EA men, indicating greater neighborhood deprivation and AA residential segregation among AA participants. The greatest values for these scores were concentrated in central and west Baltimore. A one-standard deviation (SD) increase in ADI was associated with significantly greater odds of aggressive tumors for AA men (OR=1.28, 95% CI: 1.10, 1.49; p<0.01), but not for EA men (OR=0.85, 95% CI: 0.67, 1.08; p=0.19), and the p-value for interaction (p<0.01) was statistically significant. Similarly, a one-SD increase in RI was significantly associated with aggressive tumors for AA men (OR=1.24, 95% CI: 1.03, 1.49; p=0.03), but not for EA men (OR=1.23, 95% CI: 0.84, 1.80; p=0.29), although the p-value for interaction was not statistically significant. Conclusions: Neighborhood disadvantage was significantly associated with higher odds of aggressive PC. The association of neighborhood deprivation and tumor aggressiveness was stronger among AA men. Additional analyses will consider other measures, including historical redlining, to further evaluate the relationship of neighborhood disadvantage with prostate tumor aggressiveness. Citation Format: Joseph Boyle, Jessica Yau, Jimmie L. Slade, Derrick A. Butts, Jessica Wimbush, Jong Y. Park, Arif Hussain, Eberechukwu Onukwugha, Cheryl L. Knott, David C. Wheeler, Kathryn Hughes Barry. Neighborhood disadvantage and prostate tumor aggressiveness among African American and European American men [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 809.

Abstract 3232: LSD1 inhibition transcriptionally reprograms neuroendocrine prostate cancer exposing unique therapeutic vulnerabilities

Abstract Therapeutics have been developed to target castration-resistant prostate cancer (CRPC) classified as adenocarcinoma (CRPC-Adeno). However, an increasing frequency of CRPC-Adeno tumors progress to the highly aggressive and lethal neuroendocrine prostate cancer (NEPC) by acquiring a neuroendocrine (NE) phenotype as a mechanism of therapeutic resistance. This transformation from CRPC-Adeno to NEPC requires distinct epigenetic reprogramming by lysine-specific demethylase 1 (LSD1), which can be exploited for development of novel therapies to target NEPC. LSD1 is upregulated in NEPC and promotes a stem-like transition state through lineage plasticity which enables the cancer cell to undergo NE differentiation. We have shown that LSD1 inhibition reduces the NE program, driving NEPC towards a non-neuroendocrine state through ASCL1 suppression and YAP1 re-expression. This less aggressive non-neuroendocrine state exposes unique vulnerabilities for the development of novel combination therapies to treat this lethal disease. Citation Format: Sumer M. Jasmine, Adel Mandl, Susan L. Dalrymple, Sunghyun Kim, Jennifer Dias, Maria Kleppe, Cassandra Celatka, Amy Tapper, Ilsa Coleman, Peter Nelson, Hugh Rienhoff, Samuel R. Denmeade, W. Nathaniel Brennen. LSD1 inhibition transcriptionally reprograms neuroendocrine prostate cancer exposing unique therapeutic vulnerabilities [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3232.

Abstract 7546: Targeting NSD2 to reverse lineage plasticity and drug resistance in neuroendocrine prostate cancer and subtypes of mCRPC

Abstract Treatment with highly potent anti-androgens, such as enzalutamide and abiraterone promotes lineage plasticity in metastatic castration-resistant prostate cancer (mCRPC), which results in intra-tumor heterogeneity and emergence of mCRPC subtypes. The histological transformation from adenocarcinoma to aggressive neuroendocrine prostate cancer (CRPC-NE) has been associated with a loss of dependency on lineage-survival signals, leading to targeted drug resistance. Epigenomic reprogramming might be a fundamental driver of lineage plasticity. To determine CRPC-NE vulnerabilities, we have performed image-based screening using a small library of antibodies targeting different histone marks on CRPC-NE organoids derived from genetically engineered mice. We find that the histone mark H3K36me2 and the histone methyltransferase NSD2 play important roles in maintain the CRPC-NE epigenetic state. Knockout of NSD2 or ablation of H3K36me2 using an oncohistone mutant H3.3K36M reverted CRPC-NE to an adenocarcinoma phenotype. Simultaneous profiling of the transcriptome and epigenome from single cells verified this lineage conversion and the generation of cell states with canonical AR signaling. Moreover, H3K36me2 or NSD2 depleted mouse and human CRPC-NE organoids responded to enzalutamide treatment in vitro and in vivo, suggesting a reversal of castration-resistance. Most importantly, a small molecule inhibitor of NSD2 in combination with enzalutamide leads to growth suppression or apoptosis of mouse and human CRPC-NE organoids, as well as organoids of other CRPC subtypes. In conclusion, inhibition of NSD2 reverts the epigenomic state of CRPC-NE, reversing lineage plasticity and restoring anti-androgen sensitivity. Thus, we suggest that the combination of NSD2 inhibition with AR inhibition may represent a novel therapeutic approach for patients with CRPC-NE or even other CRPC subtypes. Citation Format: Jia J. Li, Alessandro Vasciaveo, Dimitrios Karagiannis, Xiao Chen, Chen Yu, Andrea Califano, Chao Lu, Michael M. Shen. Targeting NSD2 to reverse lineage plasticity and drug resistance in neuroendocrine prostate cancer and subtypes of mCRPC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7546.

Abstract 3589: Understanding the role of Pax5 in development of taxane-resistant NE-like prostate cancer

Abstract Background: Resistance to the existing Androgen Receptor Signaling Inhibitor (ARSI) therapies led to higher incidences of aggressive therapy-induced neuroendocrine-like prostate cancer (t-NEPC) with predominant small cell-like characteristics, dismal overall survival, and an ultimate resistance to taxane chemotherapies. t-NEPCs are mostly treated with platinum-based drugs with etoposide and/or taxane but have less selectivity and high systemic toxicity, which often limits their clinical and therapeutic potential. During t-NEPC transformation, upon chromatin reprogramming associated with epigenetic alterations and altered transcriptional activity, adenocarcinoma loses its luminal features to adopt neurobasal characteristics. The following study aims to unravel the mechanism of developing t-NEPC taxane resistance upon acquiring such adaptive neuronal characteristics. Objective: The primary objective is to delineate how chromatin modifications along with epigenetic regulation facilitates the adaptive neuronal characteristics and dictates the development of t-NEPC taxane resistance. Methods: We generated various t-NEPC cell lines either by genetic modification (DKD) or therapeutic pressure (C4-2BER). We performed RNA-Seq, ATAC-Seq and acetylated Histone (H3K18 and H3K27) ChIP-Seq in our developed t-NEPC models and compared with adenocarcinoma. We next compared ATAC Seq and Acetylated histone ChIP Seq with RNA Seq in C4-2B and C4-2BER and performed functional assays. Results: Our ATAC Seq and acetylated histone footprints (Ac H3K18 and Ac H3K27 ChIP Seq) analyses revealed an enhanced chromatin accessibility during t-NEPC transformation. Overlapping RNA seq suggested newly transcribed neuronal genes with higher extent of promoter accessibility. Transcription Factor mapping among newly accessible gene promoters revealed preferential Pax5 binding, whose expression occurs selectively in t-NEPC unlike adenocarcinoma. Pathway analysis of differentially expressed neuronal genes in t-NEPC suggested an involvement of Pax5 in axonal guidance, neurotransmitter regulation, and neuronal adhesion, which are essential for strong cellular communication. Furthermore, Pax5 depletion disrupts cellular interaction in t-NEPC, thereby, sensitizing them to taxane therapies. Conclusions: Our study concludes that continuous AR ablation with ARSIs, leads to chromatin alterations with epigenetic changes, thereby allowing Pax5 transcriptional activation in t-NEPC. This altered transcriptional activity promotes gene expression necessary to govern taxane-resistant t-NEPC development. Citation Format: Sreyashi Bhattacharya, Ridwan Islam, Sanika Bodas, Juhi Mishra, Dipanwita Das, Kaustubh Datta, Samikshan Dutta. Understanding the role of Pax5 in development of taxane-resistant NE-like prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3589.

Abstract 3238: Therapeutic targeting of the genome guardian sirtuins in metastatic prostate cancer

Abstract Introduction: The effective treatment paradigm for the lethal form of metastatic prostate cancer (mPCa) remains challenging. Almost all mPCas eventually develops therapy resistance against androgen receptor (AR) inhibitors (e.g., Enzalutamide, Abiraterone) or to poly (adenosine diphosphate-ribose) polymerase (PARP) inhibitors (Olaparib, Niraparib, Talazoparib) (HRRd) when used as monotherapy. Although the patients in the ARSi+PARPi combination produced significantly longer radiologic progression-free survival (rPFS), a substantial number had attained therapy resistance by the end of the study tenure. So, a newer therapy is urgently needed. In recent years, a new targetable therapeutics development domain has been unfolding with an expanding understanding of the role of SIRTuins in prostate cancer cell survival, invasion, and progression to an aggressive metastatic state. Here, we will investigate the therapeutic efficacy of SIRT1/7 inhibitor (SIRT1/7i) and determine synergy with DNA-damaging PARP inhibitor combinations through a battery of cell and molecular assays using various prostate cancer cellular models. Methods: We have treated the mPCa cell lines 22Rv1, LAPC4, PC3 and LnCAP as well as prostate epithelial cell line RWPE1 with SIRT1 inhibitor SIRT1-IN-2 (MedChemExpress, HY-146689), SIRT7 inhibitor 97491 (MedChemExpress, HY-135899) and AR inhibitor Enzalutamide individually as well as in combination of PARP inhibitor Olaparib. The treatment of the SIRT1 and SIRT7 monotherapy arm was 72 hours long, and combination therapy continued for 7 days. The cell viability was assessed with CellTiter-Glo® 2.0 Cell Viability Assay (Promega). The cell cycle progression and proliferation analysis were done using flow cytometry through Propidium iodide staining and AnnexinV-FITC apoptosis detection chemistry. Cell survival was orthogonally assessed using colony counting assays. We adopt RAD51 foci counting assays and COMET assays for evaluating treatment-induced genome instability. Results: The preliminary result suggested that the SIRT1i+Olaparib and SIRT7i+Olaparib combination significantly sensitized the mPCa cell lines 22Rv1, PC3, and LnCAP for cell death compared to the prostate epithelial cell RWPE1. Upon the combination treatment, the mPCa cell lines showed elevated apoptotic cell death, reconfirmed through colony counting assay. Conclusion: Therapeutic combination treatment of SIRT1 and SIRT7 inhibition with Olaparib could be an effective treatment option for aggressive metastatic prostate cancer. Citation Format: Subhajit Giri. Therapeutic targeting of the genome guardian sirtuins in metastatic prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3238.