Abstract 3065: Targeting androgen receptor and c-FLIP greatly reduces proliferation and invasion in castration resistant prostate cancer

Prostate cancer (PCa) is the most common cancer in males with an estimated 164,690 new cases and 29,430 deaths in the United States in 2018. Androgen receptor (AR) plays a vital role in the growth and function of normal prostate, however it is also a principal driver of prostate cancer (PCa). Androgen deprivation therapy, or blockage of androgen at the level of AR, remains the treatment options for this disease. Nevertheless, emergence of androgen resistance limits their therapeutic usefulness, and most patients with PCa progress from androgen-dependent status to invasive castration-resistant PCa (CRPCa). CRPCa continues to express AR and depends on functional AR signaling for growth. Studies have shown that c-FLIP, an anti-apoptotic protein, reduces the efficacy of AR-targeted therapy. In addition, the expression of c-FLIP correlates with progression to CRPCa. Currently, the management of CRPCa poses a great challenge, and there is no beneficial therapeutic treatment. Therefore, finding natural agents that can disrupt AR function, especially in conjunction with other small molecules that target c-FLIP, could dramatically improve the benefits of therapeutic intervention for CRPCa. We found that fisetin, a flavonoid, interacts with the ligand binding domain of the AR, and vorinostat, a HDAC inhibitor, increases the acetylation of Ku70 by disrupting the interaction of endogenous c-FLIP and Ku70 resulting in degradation of c-FLIP. We next determined whether fisetin in combination with vorinostat could offer therapeutic advantage against CRPCa. Treatment of CRPCa cells with fisetin and vorinostat in combination more effectively reduced cell growth and colony formation than individual agents. Combination treatment also resulted in increased apoptosis as revealed by cleaved PARP and modulation in Bcl2 family proteins. Furthermore, combination treatment more effectively reduced the protein expression of HDAC6, c-FLIP, and procaspase 8 than individual agents. Elevation of AR/AR signaling and induction of HDAC6 expression play an important role in cell migration and invasion by inducing epithelial-to-mesenchymal transition (EMT). We found that combination treatment more effectively reduced the invasion of CRPCa cells and inhibited EMT as revealed by decreased expression of mesenchymal marker proteins (N-cadherin, vimentin and fibronectin), and increased expression of E-cadherin, an epithelial marker protein. In summary, our findings demonstrate that combination treatment (fisetin plus vorinostat) exhibits more potent anti-proliferative, pro-apoptotic, and anti-invasive effects in CRPCa. Citation Format: Akanksha Udhav Salunkhe, Harish C. Pal, Farrukh Afaq. Targeting androgen receptor and c-FLIP greatly reduces proliferation and invasion in castration resistant prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3065.