Abstract 5638: Combination use of EF2K and VPS34 inhibitors with anti-androgen against drug-resistant castration resistant prostate cancer

Abstract

Abstract INTRODUCTION AND OBJECTIVES: Modulating the activity of eukaryotic elongation factor 2 kinase (eEF2K) has been suggested to regulate protein elongation to block autophagy in the tumor microenvironment. Among inhibitors of eEF2K, one would also inhibit VPS34, a class III phosphatidylinositol-3 kinase, and abrogate autophage flux to impair the survival escape mechanism. We tested the eEF2K and VPS 34 inhibitors from Janssen alone or in combination with anti-androgens for their effects on proliferation of prostate cancer cell lines, especially some castration resistant PC (CRPC) lines. MATERIALS AND METHODS: Cell proliferation was assessed with various concentrations of the EF2K or VPS34 inhibitor on CRPC lines using WST-1 viability assay. Effect of combinations of EF2K or VPS34 inhibitor with anti-androgens abiraterone (Abi) or enzalutamide (Enza) on drug-resistant CRPC cells was further explored. Western blot analysis was performed to examine the response of key autophagic molecules, androgen receptor (AR) and variant. Real time RT-PCR (RT-qPCR) was used to elucidate the effect of EF2K or VPS34 inhibitor alone or together with anti-androgens on AR, AR variant and their downstream molecules. RESULTS: EF2K and VPS34 inhibitors suppressed CRPC cell growth in a dose-response manner with IC50 ranging from 1 to 5 µM. These inhibitors displayed synergy with Abi and Enza against drug-resistant CRPC cells; especially on the pair of enza + EF2K inhibitor with p = 0.02 for significant difference when compared to enza or EF2K inhibitor alone. To our surprise, no significant autophagy was induced by these two inhibitors according to the autophagy markers detected by Western blots. VPS34 inhibitor alone and when combined with Abi and Enza showed AR/variant degrading ability. This downregulation was at the expression level with significant change of AR and V7, together with their transactivation markers PSA, TMPRS2, NKx3.1 and FKBP5 detected by RT-qPCR. CONCLUSION: EF2K and VPS34 inhibitors when combined with anti-androgens may solicit profound inhibitory effect on drug-resistant CRPC cells. Molecular delineation demonstrated the direct target might be AR and its variants. These combinations offered a new therapeutic option for advanced PC treatments. Citation Format: Joy C. Yang, Vito Cucchiara, Allen C. Gao, Christopher P. Evans. Combination use of EF2K and VPS34 inhibitors with anti-androgen against drug-resistant castration resistant prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5638. doi:10.1158/1538-7445.AM2017-5638