Abstract 1692: SR16388 impairs protein homeostasis and induces autophagy in diverse human cancer cell lines.

Abstract SR16388 is a novel amino steroid that targets estrogen-binding proteins including genomic estrogen receptors (ERs). Preclinical studies have demonstrated that SR16388 is a well-tolerated, orally active compound with compelling properties as an experimental antitumor agent: SR16388 has been demonstrated to 1) inhibit the proliferation and viability of diverse human cancer cell lines in vitro; 2) have antiangiogenic activity in vivo; and 3) reduce the growth of human tumor xenografts in mice. SR16388, which binds to and potently inhibits ERα and ERβ in breast cancer cells, also inhibits the widely expressed orphan nuclear receptor ERRα that has been implicated in the development of various human malignancies. ERRα is thought to regulate tumor cell energy metabolism associated with energy stress within solid tumor microenvironments. We have been exploring potential mechanisms that could explain SR16388’s broad anti-proliferative effects toward human tumor cell lines with different genotypes and tissues of origin. In these studies, we observed that SR16388 can initiate a cell-cycle arrest at G1 or G2 and ultimately cause cytotoxicity (e.g., by apoptosis) even in cells that do not express ERs or ERRα. We recently observed that SR16388 can induce persistent macroautophagy (autophagy) in diverse tumor cells, including cells from hematopoietic malignancies (e.g., multiple myeloma/MM cells) in addition to carcinomas such as prostate and breast cancers. We demonstrated induction of autophagy by using established assays (e.g., LC3I/II processing; fluorescent reporters for acidic vacuole formation; long-lived protein degradation). Here we present results demonstrating that SR16388 can rapidly and potently induce autophagy in cultures of MM cells (U266, RPMI-8226) and PC3 prostate cancer cells. Induction of autophagy in PC3 cells, in particular, was detected in tumor xenografts as early as 3 hours after dosing of mice with a therapeutic dose level of SR16388. We will present data supporting the hypothesis that SR16388 exerts its anti-proliferative and anti-tumor effects in part through the induction of stress pathways modulated by perturbations of protein homeostasis. These effects could yield therapeutic benefits that derive from targets within solid tumor microenvironments. Citation Format: Lidia C. Sambucetti, Wei Zhou, Joy Calaoagan, Laurie Kara, Xiaohe Liu, Barbara Sato, Steve Samuelson, Nathan Collins, Keith Laderoute. SR16388 impairs protein homeostasis and induces autophagy in diverse human cancer cell lines. [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 1692. doi:10.1158/1538-7445.AM2013-1692