Role of CYP3A5 in modulating androgen receptor signaling and its relevance to African American men with prostate cancer

Background: Androgen receptor signaling is crucial for prostate cancer growth and is regulated by intratumoral CYP3A5. As African American (AA) men often carry the wild type CYP3A5 and express high level of CYP3A5 protein, we tested the effect of blocking the wild type CYP3A5 in prostate cancer cells from AA men on androgen receptor signaling. CYP3A5 processes several commonly prescribed drugs and many of these are CYP3A5 inducers (e.g. phenytoin and rifampicin) or inhibitors (e.g. ritonavir and amiodarone). In this study, we test the effect of these commonly prescribed CYP3A5 inducers/inhibitors on AR signaling in prostate cancer cells. Methods: Cell fractionation and immunofluorescence studies were performed to study AR nuclear localization and activation process using CYP3A5 siRNA and CYP3A5 inducers and inhibitors. A qPCR based array was employed to examine expression of AR downstream regulated genes after blocking CYP3A5 expression using a pool of CYP3A5 siRNA. Cell growth was monitored using MTS based assays. Since AAs tend to carry wild type CYP3A5 and non-Hispanic White Americans (NHWA) carry mutated CYP3A5 two cell lines one of AA origin (MDAPCA2b) carrying wt CYP3A5 and the other of NHWA origin (LNCaP) carrying mutant CYP3A5 were used for above experiments. Results: Similar to that observed in LNCaP (mutant CYP3A5) earlier, CYP3A5 siRNA treated MDACPA2b (AA, wild type CYP3A5) cells showed decreased AR nuclear translocation and PSA production. q-PCR based profiler assay identified several AR regulated genes which were downregulated with CYP3A5 siRNA pool treatment performed with cDNA from CYP3A5 siRNA pool and NT treated MDAPCA2b cells. These downregulated genes include SCL45A3, FKBP5, NCAPD3, MYC, MME, ELL2, PIK3R3, HPRT1 and SPDEF with p-value of ≤0.005. These genes are known to regulate AR nuclear translocation, cell cycle progression and cell growth. SCL45A3, FKBP5, MYC, and ELL2 also showed decreased protein levels after CYP3A5 siRNA treatment. Commonly prescribed drugs which are either CYP3A5 inhibitors (amiodarone, ritonavir) or inducers (phenytoin, rifampicin) were tested for their ability to alter AR signaling in both LNCaP and MDAPCa2b cells. The results show that the CYP3A5 inducers promoted AR nuclear translocation and downstream signaling whereas CYP3A5 inhibitors abrogated them. The increased nuclear AR observed with phenytoin and rifampicin (CYP3A inducers) treatment is abrogated in CYP3A5 siRNA treated MDAPCa2b cells, confirming that the activation of AR activity is specific to changes in CYP3A5 activity. Both the inducers tested demonstrated increased cell growth of prostate cancer cells, whereas the inhibitors showed reduced cell growth. The difference in growth is more pronounced in MDAPCa2b cells which carries a wild type CYP3A5 as compared to LNCaP with the exception of ritonavir which also downregulates total AR levels. Conclusions: Concomitantly prescribed CYP3A5 modulating drugs may alter downstream AR signaling, cell growth and ADT efficacy in men, more so in AAs expressing wild type CYP3A5. Further, characterization and utilization of this observation how CYP3A5 inducers and inhibitors can alter AR signaling may provide guidance to physicians co-prescribing CYP3A5 modulating drugs to treat comorbidities in elderly patients undergoing ADT, particularly AA.