Abstract B48: Effect of concomitant CYP3A5-modulating drugs on androgen-receptor signaling in African American men undergoing androgen deprivation therapy

Introduction: In a recent study we have established that CYP3A5 augments nuclear translocation of androgen receptor (AR) and promotes prostate cancer (PC) growth. CYP3A isoforms are responsible for metabolizing almost 50% of the commonly prescribed drugs, many of which are CYP3A5 inhibitors and inducers. PC patients are elderly with comorbidities and are often prescribed concomitant medications while undergoing androgen-deprivation therapy (ADT), the most preferred treatment for PC. CYP3A5 is polymorphic, and African Americans (AA, 73%) express higher levels of CYP3A5 due to presence of wild-type CYP3A5 (*1/*1) compared to Caucasians (95%) expressing the mutant (*3/*3) producing only 13% of the active full-length CYP3A5 protein. Due to the expression of wild-type CYP3A5 in AA, concomitant medications modulating CYP3A5 activity can drastically alter AR activity and ADT efficacy in these patients. Our current work is focused on deciphering the mechanism of how commonly used CYP3A5-modulating medications can alter AR signaling in AA carrying the wild-type CYP3A5. Method: We genotyped the androgen-responsive prostate cancer cell lines to determine their CYP3A5 status using TaqMan® Drug Metabolism assay. We used cDNA from cells treated with either nontarget or CYP3A5 siRNA in RT2 profiler PCR arrays to identify set of genes in AR signaling pathway that are affected by CYP3A5 inhibition. Confocal microscopy was used to study AR nuclear localization after exposure to commonly used CYP3A5 inducer/inhibitor drugs. Cell fractionation experiments were used to further confirm the effect of these drugs on AR signaling. Luciferase-based reporter assay was used to test effect of CYP3A5-modulating drugs on AR activity. Results: Our genotyping assay revealed that MDA PCa 2b (African American) carries *1/*3 CYP3A5 gene compared to LNCaP (Caucasian) carrying *3/*3 genotype. To compare the differences due to CYP3A5 genotype on AR signaling, we selected MDAPCa2b and LNCaP cells for further studies. Consistent with earlier observations with LNCaP, MDA PCa 2b cell lines also showed decreased nuclear translocation of AR with CYP3A5 siRNA in both confocal and cell fractionation experiments. We also observed blocking of AR nuclear localization with azamulin, a CYP3A-specific inhibitor in both cell lines. The q-PCR-based profiler assay revealed a set of nine AR-regulated genes (SCL45A3, FKBP5, NCAPD3, MYC, MME, ELL2, PIK3R3, HPRT1, and SPDEF) downregulated with CYP3A5 siRNA treatment with a p value of ≤0.005 in MDA PCa 2b cells. MYC is known to be involved in cell cycle progression and apoptosis whereas PIK3R3 codes for the regulatory subunit of PI3 kinase regulating cell growth. SPDEF codes for a transcription factor promoting PSA known to aid in the cell growth. Downregulation of these genes with CYP3A5 siRNA treatment indicates that CYP3A5 modifier medications can alter AR downstream signaling regulating growth. We tested some commonly prescribed drugs that are either CYP inhibitors (amiodarone, ritonavir) or inducers (phenytoin, rifampicin) and evaluated their ability to alter AR signaling. The results revealed that the CYP inducers promoted increased AR nuclear migration and increased PSA production whereas CYP3A5 inhibitors blocked AR nuclear migration, decreasing PSA expression in both cell lines. A luminescence-based reporter assay using androgen response elements also supported that these CYP3A inducer and inhibitor drugs alter AR signaling. Conclusion: Our results indicate that concomitant medications that can alter CYP3A5 activity can modify AR signaling and PC growth. These results suggest that these CYP-modulating drugs can alter efficacy of ADT severely in AA men predominantly expressing wild-type CYP3A5 (*1/*1). We hypothesize that AR-directed therapeutic efficacy can be optimized by proper drug selection through minimizing the use of AR inducers while maximizing the use of AR inhibitors in patients undergoing ADT. Citation Format: Priyatham Gorjala, Oscar B. Goodman Jr., Ranjana Mitra. Effect of concomitant CYP3A5-modulating drugs on androgen-receptor signaling in African American men undergoing androgen deprivation therapy [abstract]. In: Proceedings of the Tenth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2017 Sep 25-28; Atlanta, GA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2018;27(7 Suppl):Abstract nr B48.