Abstract 2313: Promoting caspase-8-dependent apoptosis signaling using 17-beta-hydroxywithanolides

Abstract

Abstract We have previously reported that withanolide E (WE), a steroidal lactone from Physalis peruviana, was highly active in sensitizing various human carcinoma cell lines to TRAIL-mediated apoptosis. Therefore, over 100 natural and semi-synthetic withanolides were evaluated for their ability to promote caspase-8-dependent cancer cell death. Our studies identified several withanolides that were 4-8 fold more potent than WE in sensitizing the renal carcinoma cells and melanoma cells to caspase-8-dependent apoptosis in response to either TRAIL or the TLR3 ligand poly (I:C). All active withanolides were 17-beta-hydroxywithanolides (17-BHW). The highly active 17-BHWs were more efficient than withanolide E at reducing cellular levels of both cFLIPL and cFLIPS and enhancing caspase-8 activation. Furthermore, immunoprecipitation of the TRAIL death-inducing signaling complex (DISC), or the related ripoptosome, demonstrated enhanced levels of both FADD and RIP1 in these macromolecular apoptosis signaling complexes following treatment with active 17-BHWs. The 17-BHWs used in this work were obtained by the application of an efficient method of plant biomass production involving our innovative and patented soil-less aeroponic cultivation of P. crassifolia and P. peruviana and by chemical modification of natural withanolides produced by these plants. Preliminary structure activity relationship (SAR) studies suggested that the enone moiety in ring A was essential for activity. In addition, acetoxylation at C-18, an alpha orientation of the side-chain lactone group and the double bond at C-24(25) of the lactone ring played important roles in determining the activity of 17-BHWs as apoptosis sensitizers. This suggests that the 17-BHW scaffold is amenable to optimization by a medicinal chemistry approach, which could lead to the identification of highly active natural product-based sensitizers of cancer cells to caspase-8-dependent apoptosis. The cellular molecular target(s) of active 17-BHWs are currently under further investigation. Funded by FNLCR Contract HHSN261200800001E. Citation Format: Alan D. Brooks, Ya-ming Xu, E. M. Kithsiri Wijeratne, Curtis J. Henrich, Poonam Tewary, Leslie Gunatilaka, Thomas J. Sayers. Promoting caspase-8-dependent apoptosis signaling using 17-beta-hydroxywithanolides [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 2313. doi:10.1158/1538-7445.AM2017-2313