The effect of androgen receptor splice variant 7 on the growth of castration-resistant prostate cancer and the efficacy of taxane chemotherapy.

Abstract

302 Background: Expression of androgen receptor (AR) splice variant 7 (AR-V7) has been identified as a mechanism associated with the development of castration-resistant prostate cancer (CRPC), but a potential link between AR-V7 expression and resistance to taxanes, such as docetaxel or cabazitaxel, has not been unequivocally demonstrated. We clarify the relationship between AR-V7 expression and resistance to taxanes. Furthermore, we assess the inhibitory effect of EPI-002, an antagonist of AR amino-terminal domain (NTD), to an AR-V7 driven CRPC cell line with acquired resistance to docetaxel. Methods: LNCaP95-DR cells, which express AR-V7 and exhibit resistance to enzalutamide and docetaxel, was developed. WST-1 assay or BrdU ELISA assay was performed to evaluate the inhibitory effect of drugs. We examined alterations of AR and AR-V7 signaling using Western blot analyses, real-time RT-qPCR and reporter gene assay. Results: LNCaP95-DR cells showed cross-resistance to cabazitaxel. Although the LNCaP95-DR cells had increased expression of AR-V7 and its target genes (UBE2C, CDC20), knockdown of AR-V7 did not restore sensitivity to docetaxel or cabazitaxel. However, despite resistance to docetaxel and carbazitaxel, EPI-002 had an inhibitory effect on the proliferation of LNCaP95-DR cells that was similar to that achieved with the parental LNCaP95 cells, whereas enzalutamide had no effect on the proliferation of either cell line. Conclusions: Our results suggest that EPI-002 may be an option for the treatment of AR-V7-driven CRPC that is resistant to taxanes.