Presentation Authors: Chengfei Liu*, Joy C. Yang, Wei Lou, Liangren Liu, Christopher P. Evans, Allen C. Gao, Sacramento, CA
Introduction: The resistant mechanisms of next generation anti-androgens in castration resistant prostate cancer are incompletely understood. Our previous work demonstrated that AKR1C3 and AR-V7 play important roles in enzalutamide and abiraterone resistance, and that targeting AKR1C3 or AR-V7 could overcome this resistance. The aim of this study is to investigate the interaction between AKR1C3 and AR-V7 and determine their coordinated roles in drug resistance.
Methods: Global gene expression analysis was analyzed by microarray analysis. Steroid profile including androgens in tumor tissues was analyzed by Liquid Chromatography-Mass Spectrometry (LC-MS). The effects of AKR1C3 expression and activation were examined by knockdown of AKR1C3 expression using lentiviral shRNA or inhibition of AKR1C3 enzymatic activity by indomethacin. AKR1C3 and AR-V7 interaction were determined by co-immunoprecipitation and dual immunofluorescence. The effects of AKR1C3 activation on anti-androgen sensitivity were examined in vitro and in vivo.
Results: AKR1C3 forms a complex with AR-V7 and induces AR-V7 overexpression through increasing its protein stabilization. Targeting AKR1C3 by indomethacin significantly decreases AR/AR-V7 protein expression through the ubiquitin mediated proteasome pathway activation. AKR1C3 activates steroid hormone biosynthesis pathway and reprograms AR signaling in enzalutamide resistant prostate cancer. Additionally, bioinformatic analysis of indomethacin treated resistant cells discovered that indomethacin significantly activates unfolded protein response (UPR) pathway and suppresses Myc, cell cycle and AR/AR-V7 pathways. Finally, we found that enzalutamide and abiraterone prostate cancer cells are cross resistant to apalutamide and darolutamide, possibly through activation of AKR1C3 and AR-V7 pathways. Targeting AKR1C3 re-sensitizes resistant cells to apalutamide and darolutamide treatment through the AR-V7 inhibition.
Conclusions: AKR1C3 induces AR-V7 overexpression and stabilizes AR-V7 protein in resistant cells through the ubiquitin proteasome system alteration. Apalutamide and darolutamide are cross resistant to enzalutamide and abiraterone via AKR1C3/AR-V7 complex regulation.
Source of Funding: This work was supported in part by grants NIH/NCI CA168601, CA179970, DOD PC150229, and the U.S. Department of Veterans Affairs, Office of Research & Development BL&D grant number I01BX0002653 (A.C. G) and by resources from the VA Northern California Heal