Promoting Trail Apoptosis Signaling Using 17-Beta-Hydroxywithanolides

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. Treatment of cancer cells with WE induced a reduction in the levels of the antiapoptotic proteins cFLIPL and cFLIPS, resulting in an increased activation of caspase-8 on subsequent TRAIL binding to its death receptors DR4 or DR5. The reduction in cFLIPL and cFLIPS was due to their destabilization and increased degradation by the proteasome. Interestingly, WE (a 17-beta-hydoxywithanolide, 17-BHW) was a far superior TRAIL sensitizer than more widely studied withaferin A (WFA) and its analogues, which lack the 17-beta-hydroxy group and bear an opposite side chain orientation, exhibit more promiscuous reactivity and are much more directly toxic to cells. Therefore, over 30 natural and semi-synthetic 17-BHWs were evaluated for their ability to promote death ligand-mediated cancer cell death. 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. Our studies identified several 17-BHWs that were 4-8 fold more potent than WE in sensitizing the renal carcinoma cells ACHN to TRAIL-mediated apoptosis. These more active 17-BHWs were also more efficient at reducing cellular levels of cFLIPL and cFLIPS and enhancing caspase-8 activation. 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 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 TRAIL 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 TRAIL-mediated 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, Poonam Tewary, Curtis J. Henrich, Cheryl L. Thomas, A. A. Leslie Gunatilaka, Thomas J. Sayers. Promoting TRAIL apoptosis signaling using 17-beta-hydroxywithanolides. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3513.