PD46-12: Preclinical studies using cisplatin/carboplatin to restore the Enzalutamide sensitivity via degrading the androgen receptor splicing variant 7 (ARv7) to further suppress Enzalutamide resistant prostate cancer

Fu-Ju Chou, Yixi Hu*, ChangYi Lin, Hao Tian, Deepak Sahasrabudhe, Jean Joseph, Edward M Messing, Shuyuan Yeh, Chawnshang Chang, Rochester, NY

Introduction: The FDA-approved anti-androgen Enzalutamide (Enz) has been used successfully as a promising therapy to extend castration-resistant prostate cancer (CRPC) patients' survival by an extra 4.8 months. However, CRPC patients eventually develop Enz-resistance that may involve the induction of the androgen receptor (AR) splicing variant ARv7. Our goal is to reveal the mechanism of Enz-resistance in CRPC and explore a promising therapy to solve the problem.

Methods: The human CRPC cells (C4-2 and CWR22Rv1), and  Enz-resistant (EnzR) cell lines (EnzR1_C4-2, EnzS4_C4-2B, and EnzR4_C4-2B) were used. PCa patients’ blood were collected to isolate circulating tumor cells. Lentiviral plasmids were transfected into 293T cells to produce gene engineering tools. qPCR was used to evaluate the mRNA levels. Western blot was performed to assess protein expressions. MTT cell proliferation assays were used to detect cell growth. Preclinical mouse model with EnzR tumor was used to detect Cisplatin/Carboplatin plus Enz therapy efficacy.

Results: Here we found that Cisplatin (Cis) or Carboplatin, currently used in chemotherapy/radiation therapy to suppress tumor progression, could restore the Enz sensitivity in multiple EnzR CRPC cells via directly degrading/suppressing the ARv7. Combining Cis or Carboplatin with Enz therapy could also delay the development of Enz-resistance in CRPC C4-2 cells. Mechanism dissection showed that Cis or Carboplatin treatment might decrease the ARv7 expression via multiple mechanisms including (i) regulating the lncRNA-Malat1/SF2 RNA splicing complex, and (ii) increasing the ARv7 degradation via altering ubiquitination. Preclinical studies using in vivo mouse model with implanted EnzR1-C4-2 cells also demonstrated that Cis plus Enz therapy resulted in better suppression of EnzR progression than Enz treatment alone.

Conclusions: These results not only unveil the previously unrecognized Cis mechanism to degrade ARv7 via targeting the Malat1/SF2 complex and ubiquitination signals, it may also provide a novel and ready therapy to further suppress the EnzR CRPC progression in the near future.

Source of Funding: This work was partially supported by URMC Urology Department Research fund and George Whipple Professorship Endowment.