Recent research involving chemotherapeutic drugs such as anthracyclines have aided in redefining the definition of apoptosis from a form of cell death that is immunologically silent to the one that can activate an anti-cancer immune response. This form of apoptosis has been characterized as immunogenic cell death (ICD) and possess certain hallmarks such as the cell surface expression of heat shock proteins (HSPs) including HSP70 and HSP90 as well as ER-stress mediated pre-apoptotic expression of the ER chaperone calreticulin (CRT). One of the mechanisms by which ICD occurs is linked to the induction of an unfolded protein response (UPR) due to prolonged chemotherapeutic stress on cancer cells. Our research focuses on the development of Withaferin A (WA), a steroidal lactone derived from the Indian ayurvedic medicinal plant Withania somnifera as a chemoimmunotherapeutic agent. The benefit of using natural plant derived products is their low toxicity, multimodal action and potential ability to enhance the immune system. We initially screened the effect of Withaferin A by microarray analysis on breast cancer cells. WA induced significant alteration of 1160 genes (p-value 0.005). A pathway analysis determined that WA induces a robust heat shock response through up-regulation of several genes related to this pathway including response to unfolded proteins. The gene expression data was confirmed by the induction of intracellular HSP70, HSP40 as well as the UPR marker Bip78 by western blot. Furthermore we are able to demonstrate that WA treatment results in the translocation of known immunogenic HSPs HSP70, CRT and gp96 to the cell surface of several cancer cell lines. Additionally, WA treatment results in the induction of apoptosis and these WA mediated apoptotic cells can confer immunological protection against re-challenge with live tumor cells in vivo. Our long-term goal is to elucidate the anti-tumor immunomodulatory mechanisms of WA.
Funded by: American Cancer Society (S.A.)
Citation Format: Annalise R. Smith, Darlah Lopez, Samita Andreansky. A natural plant-derived compound, Withaferin A, exploits the stress pathway to induce antitumor immunity. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology: Multidisciplinary Science Driving Basic and Clinical Advances; Dec 2-5, 2012; Miami, FL. Philadelphia (PA): AACR; Cancer Res 2013;73(1 Suppl):Abstract nr B57.