Abstract 843: Inhibition of AKT signaling promotes FOXO3a-dependent apoptosis in castration-resistant prostate cancer cells.

Abstract

Abstract Treatment for aggressive prostate cancers involves hormonal ablation therapy, radical prostatectomy, radiation therapy, chemotherapy or in combination. Despite their initial sensitivity to these treatments, prostate cancer eventually progresses to castration -resistant prostate cancer (CRPC), which is both aggressive and refractory to current therapeutic modalities. Hence, CRPC demands the identification of novel targeted therapies with minimal side effects. We identified Withaferin-A (WA) a major bioactive compound derived from the medicinal plant, Withania somnifera, is extensively used in Asian herbal medicines to treat a variety of ailments, including cancer. Earlier, we reported that WA induced the pro-apoptotic gene, prostate apoptosis response-4 (Par-4) and apoptosis in CRPC cells. These results encouraged us to determine the mechanism of action of WA on CRPC cells. It is known that activated AKT negatively regulates forkhead transcription factor class O family protein (FOXO3a) that regulates genes involved with tumorigenesis, cell cycle arrest or apoptosis. In the present study, we found that FOXO3a is an upstream of Par-4 signaling which transactivates Par-4 function in CRPC cells. Inhibition of AKT activation by WA facilitates nuclear translocation of FOXO3a which in turn activates Par-4 mediated apoptosis in CRPC cells. Our confocal and immuno-precipitation studies confirmed that upon activation. FOXO3a and Par-4 were co-localized in the nucleus. Similar results were found with overexpression of FOXO3a showing transactivation of Par-4 and growth arrest in CRPC cells. Treatment of actinomycin-D or cyclohexmide along with WA, confirmed that FOXO3a regulation on Par-4 function in CRPC cells. On contrary, inhibition of FOXO3a by siRNA resulted in down regulation of Par-4 and apoptosis by WA in CRPC cells suggesting FOXO3a activation is necessary for the induction of Par-4 mediated apoptosis. Promoter bashing studies suggest a direct interaction of FOXO3a with Par-4 promoter; a sequential deletion of FOXO3a DNA binding sites in Par-4 promoter fails to induce Par-4 activation upon WA treatment in CRPC cells. Overall, our studies conclude that Par-4 is a target of FOXO3a, and Par-4 activation is required for induction of apoptosis in CRPC cells. Activation of FOXO3a is an attractive target for the treatment of CRPC and molecules such as WA can be explored further for the treatment of CRPC. Citation Format: Trinath P. Das, Chendil Damodaran. Inhibition of AKT signaling promotes FOXO3a-dependent apoptosis in castration-resistant prostate cancer cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 843. doi:10.1158/1538-7445.AM2013-843