Abstract 1311A: CYP3A5 regulation of androgen receptor signaling: Relevance in African American prostate cancer patients and its development as novel target

Abstract

Abstract Background: Previously we demonstrated that CYP3A5 positively regulates androgen receptor (AR) signaling and growth of prostate cancer (PC) cells. CYP3A5 inhibition decreases nuclear AR localization and downregulates AR downstream signaling (e.g. PSA and TMPRSS2), resulting in decreased PC cell growth both with and without dihydrotestosterone (DHT) induction. Our current work focusses on the effect of CYP3A5 modulation on AR signaling and therapeutic resistance, mostly in African Americans (AA) widely carrying (73%) wild type CYP3A5 (*1/*1). AAs and have higher incidence of PC and double the mortality rate compared to Non-Hispanic White Americans (NHWA) carrying mutated CY3A5 gene (*3/3, 95%) and expressing truncated non-functional CYP3A5 protein. Methods: Immunoprecipitation was used to identify binding partners of AR. q-RT-PCR based profiler assays was used to detect changes in AR downstream signaling and effect on genes responsible for therapeutic resistance after CYP3A5 inhibition. Effect of CYP3A5 on AR nuclear translocation and induction of synthetic lethality in combination with PARP inhibitors were evaluated using cell fractionation and immunocytochemistry studies. Results: Co-immunoprecipitation of flag-tagged CYP3A5 transfected LNCaP cell extracts showed that CYP3A5 was in a complex with HSP90, AR, HSP70 and HSP40, also confirmed with reverse immunoprecipitation using AR/ HSP90 antibodies and agarose A/G beads. AR regulated genes (SCL45A3, FKBP5, MYC, ELL2, and MT2A) were downregulated with CYP3A5 siRNA treatment in MDA PCa 2b cells (*1/*3, AA origin) in a qPCR-based profiler assay with high fold difference and a P value of ≤0.005. PC patients are often prescribed medications for comorbidities, many of which are CYP3A modulators. Our results indicate that CYP inhibitors (amiodarone, ritonavir, fluoxetine etc.) decrease AR nuclear translocation and inducers (phenytoin, rifampicin, pioglitazone and hyperforin) increase AR nuclear translocation and activation. CYP3A5 siRNA treatment downregulates genes involved in cancer drug therapeutic resistance (TOP2A, BRCA1/2, CCNE1, CDK2/4, DHFR, MVP, MYC, RARB and HPRT1, P ≤ 0.005 ). Loss of TOP2A, BRCA2 and BRCA1is known to impair homologous recombination (HR). In combination with topoisomerase inhibitor etoposide, CYP3A5 siRNA in PC cells increases number of gamma-H2AX foci indicating synthetic lethality. Conclusion: A-Developing CYP3A5-AR-HSP90 interface as a target may provide a novel strategy to block PC growth. B-CYP3A5 modulation of AR signaling can affect the efficacy of androgen deprivation therapy specifically AA patients carrying wild type CYP3A5. C-Since CYP3A5 inhibition, downregulates DNA damage repair genes and impairs HR, CYP3A5 inhibition in combination with PARP inhibitors can be a novel strategy to induce synthetic lethality in PC patients. Citation Format: Priyatham Gorjala, Oscar B. Goodman, Ranjana Mitra. CYP3A5 regulation of androgen receptor signaling: Relevance in African American prostate cancer patients and its development as novel target [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 1311A.