Abstract 2580: Discovery of SINE: Selective inhibitors of nuclear export increase levels of regulatory proteins p53, p21, FOXO and IκB leading to apoptosis of malignant cells

Abstract

Abstract Transport of macromolecules across nuclear membrane is fundamental to the proper functioning of living cells. Nuclear localization of intact tumor suppressor proteins (TSPs) and other growth regulatory proteins (GRPs) such as p53, FOXO, pRB, p21, p27 and IκB are critical for their “policing” function. Conversely, mislocalization of a nuclear protein to the cytoplasm can render it ineffective as a TSP/GRP. Cancer cells appear to acquire intracellular mechanisms to export tumor-supressing nuclear proteins as they evolve and spread. In many cases, nuclear export is followed by proteasome dependent degradation. Most known TSP/GRP utilize the nuclear export protein CRM1 (chromosomal region maintenance 1; also called exportin 1 [XPO1]), to exit the nucleus, and overexpression of CRM1 has been reported as a poor prognostic factor in a variety of neoplasms. Therefore, inhibition of CRM1 can force the nuclear localization of key TSPs/GRPs, activating their pathways. This leads to cell cycle arrest followed by induction of cell death in cancer cells. Our SINE are novel, potent and selective, drug-like nuclear export inhibitors (IC50 ∼40-100nM) that derive their activity through direct covalent modification and inhibition of CRM1. SINE exert selective and prolonged inhibition of CRM1-mediated forkhead (FOXO), p53, p21 and IκB nuclear export in a variety of normal and transformed cell lines. Cell cycle analysis following incubation with the SINE compound KPT-0127 revealed that it blocks at both the G1/S and G2/M phases, consistent with arrest at multiple cell cycle checkpoints. SINE-induced apoptosis is observed in many cancer cell lines (e.g. A375, Jurkat, BL-40, HCT-116), but not in normal proliferating cells (e.g. 3T3, mouse embryo fibroblasts). In cytotoxicity assays, SINE compounds showed highly potent cytotoxicity in both hematologic and solid tumor cell lines (IC50s <100nM) with limited effects on normal cells (PBMCs, HUVEC, 3T3, MEF IC50s >2000nM). SINE show no significant effect on 37 proteins including several cysteine proteases, minimal CYP inhibition (> 10 μM for all major CYPs) and no hERG inhibition. In single dose mouse toxicology studies, KPT-0127 was generally well tolerated (p.o. or s.c.) up to 560 mg/kg, and no deaths were observed. The pharmacokinetics of KPT-0127 is adequate for s.c. and i.v. dosing in vivo. Tumor xenograft studies have been undertaken in colon cancer HCT-116 and myeloma MM.1S tumor bearing mice. SINE induce potent, dose dependent anticancer activity against both small (∼140mm3) and large (∼1400mm3) tumors. Together, these data demonstrate that SINE represent a novel mechanism of action with robust anti-tumor activity both in vitro and in vivo and promising applications as single agent and for combination therapies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2580. doi:10.1158/1538-7445.AM2011-2580