CYP3A5 regulates prostate cancer cell growth by facilitating nuclear translocation of AR.

BACKGROUND: The central role of androgen receptor (AR) signaling is established in prostate cancer growth and progression. We propose CYP3A5 is part of a feedback loop that modulates the sensitivity of AR to androgen exposure. The purpose of this study is to elucidate the mechanism of regulation of AR expression by CYP3A5.
METHODS: To identify the role of CYP3A5 in regulating AR signaling, CYP3A5 protein expression was inhibited using CYP3A5 siRNA and azamulin. Both cell fractionation and immunocytochemical approaches in combination with dihydrotestosterone (DHT) and R1881 treatment were used to evaluate changes in AR nuclear translocation.
RESULTS: CYP3A5 siRNA blocked growth of LNCaP and C4-2 cells by 30-60% (P ≤ 0.005). Azamulin, a CYP3A pharmacologic inhibitor, reduced the growth of LNCaP, C4-2 and 22RV1 lines by ∼ 40% (P ≤ 0.005). CYP3A5 siRNA inhibited growth in response to DHT and R1881 treatment in LNCaP and C4-2 by decreasing nuclear AR localization and resulting in diminished PSA and TMPRSS2 expression. Decreased AR nuclear localization resulting from CYP3A5 inhibition resulted in growth inhibition comparable to IC60 and IC40 of bicalutamide in LNCaP and C4-2 cell lines. Conversely, the CYP3A inducer rifampicin enhanced AR nuclear localization.
CONCLUSION: As CYP3A5 regulates the nuclear translocation of AR; co-targeting CYP3A5 may provide a novel strategy for enhancing the efficacy of androgen deprivation therapy. Consequentially, these data suggest that concomitant medications may impact androgen deprivation therapy's efficacy.