Abstract 4718: Withaferin A, a potent and abundant component of Withania somnifera root extract, reduces myeloid-derived suppressor cell function.

Abstract

Abstract Myeloid cells play a crucial role in growth and metastasis of malignant tumors. Tumor infiltrating myeloid cells includes myeloid-derived suppressor cells (MDSC), tumor-associated macrophages (TAMS) and dendritic cells (DC). These cells infiltrate into tumor and suppress tumor immunity by their inherent immune suppressive activity which is enhanced by interactions with each other (cross-talk). Therapeutic strategies targeting manipulation of these cells are being developed. The root extract of the plant Withania somnifera (Ashwagandha) (WRE) has been reported to reduce tumor cell proliferation and angiogenesis. Whether the anti-tumor effects of WRE are due to direct effects on malignant cells, or whether WRE also impacts immune suppressive myeloid cells is unknown. We hypothesize that WRE or its constituents impact tumor infiltrating myeloid cells and thereby boost anti-tumor immunity. HPLC and mass spectrometry analysis revealed that Withaferin A (WA) is the most abundant constituent of Withania somnifera root powder (ChromaDex, Inc. Irvine, CA). In comparison with the other constituents, WA has the most potent effect on reducing suppressive functions of myeloid cells. A prominent effect of MDSC is their production of IL-10 which increases upon cross-talk with macrophages, thus polarizing immunity to a tumor promoting type-2 phenotype. WA reduces inherent and cross-talk induced IL-10 secretion from MDSC in a dose dependent manner. Macrophage secretion of IL-6 and TNFα cytokines that are characteristic of M1-type macrophages and that also increase MDSC accumulation and function, are also reduced by WA. Much of the T cell suppressive activity of MDSC is due to MDSC production of reactive oxygen species (ROS), and WA significantly reduces MDSC production of ROS. Thus adjunctive treatment with WA has the potential to concomitantly reduce myeloid cell mediated immune suppression, to polarize immunity towards a tumor-rejecting type I phenotype, and to facilitate the development of anti-tumor immunity. Supported by NIH RO1CA115880, RO1CA84232, and American Cancer Society IRG-97-153-07 Citation Format: Pratima Sinha, Suzanne Ostrand-Rosenberg. Withaferin A, a potent and abundant component of Withania somnifera root extract, reduces myeloid-derived suppressor cell function. [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 4718. doi:10.1158/1538-7445.AM2013-4718