Abstract LBA027: Mechanistic insights on the effects of the lead next generation galeterone analog, VNPP433-3β in castration resistant prostate cancer

Abstract

Abstract Introduction Metastatic castration-resistant prostate cancer (mCRPC) remains the second leading cause of cancer-related death in men in the United States and the second most frequently diagnosed cancer among males worldwide. Dysregulated androgen receptor (AR) is associated with nearly all known cases of prostate cancer (PCa) and its expression level has been correlated with poor survival. This study describes the mechanism of action of VNPP433-3β, a next generation galeterone analog (NGGA) in inhibiting PCa. Methods PCa cell lines CWR22Rv1 and LNCaP were treated with VNPP433-3β and followed up using cellular thermal shift assay (CETSA), RNA seq, mRNA 5’ cap-binding assay, translation and proteasome inhibition assays. Co-immunoprecipitation, molecular docking and fluorescence spectroscopy were used to study the interactions. Results VNPP433-3β, the lead next generation galeterone analog (NGGA) directly interacts with AR and inhibits metastatic castration resistant PCa (mCRPC) by enhancing degradation of full-length AR (fAR) and its splice variant AR-V7 in a dose-dependent manner. Moreover, VNPP433-3β drives the proteasomal degradation of fAR and AR-V7 by augmenting the interaction between AR and E3 ligases MDM2 & CHIP but disrupting HSP90 binding to AR. VNPP433-3β also impedes eIF4E phosphorylation by depleting MNK1/2 besides disrupting binding of eIF4E and eIF4G to mRNA 5’ cap thereby impeding translational activity of the cancer cells. Finally, the transcriptome analyses by RNA-seq reveal that VNPP433-3β modulates transcription of several genes and activates more than 20 cellular pathways, each of which synergistically contribute to PCa inhibition. Hence, VNPP433-3β obstructs PCa by invoking 1) transcriptional regulation of AR-responsive oncogenes via degrading AR, 2) translational regulation by depleting MNK1/2 thereby impeding phosphorylation of eIF4E and subsequent mRNA 5’cap-dependent translation initiation and 3) affecting AR half-life through enhanced proteasomal degradation. Conclusion As VNPP433-3β promotes degradation of fAR and AR-V7, concurrently depletes Mnk1/2, prevents eIF4E phosphorylation and modulates several cellular pathways to halt PCa, it could potentially be developed for clinical trials in mCRPC patients. Citation Format: Elizabeth Thomas, Retheesh S Thankan, Puranik Purushottamachar, Vincent C.O. Njar. Mechanistic insights on the effects of the lead next generation galeterone analog, VNPP433-3β in castration resistant prostate cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr LBA027.