Abstract LB-113: A novel role of Withaferin A as an effective pro-apoptotic receptor agonist (PARA) and insights into the underlying molecular mechanisms

Introduction: Despite significant progress towards screening efforts and targeted therapies, breast cancer is still a leading cause of cancer-related mortality among women. Novel therapeutic strategies are clearly needed for effective targeting of breast cancer. Natural products continue to generate interest for identification of potential chemopreventive and therapeutic agents. Withaferin A (WFA) is a bioactive small molecule that has been proposed as a new-generation molecule capable of eliciting growth inhibitory effect on cancer cells. The molecular mechanisms by which WFA mediates inhibition of breast cancer remain elusive. The present study was designed to systematically elucidate the underlying mechanisms by which WFA inhibits growth and metastatic potential of breast cancer cells. Results: Because many cellular signaling events involve induced-phosphorylation of key targets, in the present study we utilized phosphokinase arrays to gain insight into the intricacies of WFA-mediated signaling networks and discovered that WFA induces RSK phosphorylation in breast cancer cells. Further analysis revealed an integral role of ERK in WFA-mediated RSK activation and WFA-induced ERK/RSK signaling resulted in concomitant upregulation and activation of Elk1(ETS-like transcription factor-1) and CHOP (C-EBP homology protein) leading to transcriptional upregulation of Death Receptor protein-5 (DR5). It is interesting to note that in recent years, many phase 1 and 2 single agent and combination clinical trials have been conducted to examine the efficacy and safety of recombinant human TRAIL (dulanermin, (Amgen/Genentech)), and the agonistic monoclonal antibodies to DR5 (lexatumumab (Human Genome Sciences), conatumumab (Amgen), drozitumab (Genentech), tigatuzumab (Daiichi-Sankyo) and LBY135 (Novartis)). Studies with these pro-apoptotic receptor agonists (PARAs) have been encouraging but no full phase 3 studies have been performed suggesting the need for novel PARAs with improved properties. Here, we show that WFA is more effective than three other known DR5 activators, TRAIL, etoposide and celecoxib, in activation of DR5 in breast cancer cells hence, appears to be a good candidate for further development as an effective DR5 inducer. WFA treatment effectively inhibited breast tumorigenesis in vivo and analysis of WFA-treated xenografts and MMTV-neu mice tumors showed increased activation of ERK/RSK axis and DR5 along with elevated nuclear accumulation of Elk1 and CHOP. Conclusion: These data provided first in vitro and in vivo evidence of the integral role of a previously unrecognized crosstalk between WFA and ERK/RSK and CHOP/Elk1 axes in breast tumor growth inhibition. Also, our findings may potentially open new avenues of research on the role of withaferin A as a novel pro-apoptotic receptor agonist (PARA). Citation Format: Arumugam Nagalingam, Panjamurthy Kuppusamy, Neeraj Saxena, Dipali Sharma. A novel role of Withaferin A as an effective pro-apoptotic receptor agonist (PARA) and insights into the underlying molecular mechanisms. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-113. doi:10.1158/1538-7445.AM2014-LB-113