Abstract 2822: Targeting Mcl-1 regulated apoptosis pathway as a novel therapy in pancreatic cancer

Abstract

Abstract Resistance of pancreatic cancer to current treatment protocols as a consequence of apoptosis defects is a major cause of treatment failure. Therapeutic approaches that specifically target components of these molecular mechanisms are urgently needed. The anti-apoptotic protein Mcl-1, a member of the Bcl-2 family proteins, has emerged as a promising therapeutic target. Consistent with its anti-apoptotic function, the overexpression of Mcl-1 in pancreatic cancer cells has been associated with tumor progression and resistance to current chemotherapeutics. Applying high throughput screening approach several promising lead compounds as selective Mcl-1 inhibitors were identified and evaluated. Based on one of the most promising lead compounds we have designed and synthesized several analogues. The most potent compound, UMI-77, binds to Mcl-1 protein with Ki = 205 nM determined by fluorescence polarization based assay and shows selectivity over Bcl-2 and Bcl-xL. NMR spectroscopy studies demonstrate that UMI-77 binds to the same BH3 domain of Mcl-1 as the Bim BH3 peptide and antagonizes Mcl-1 function. UMI-77 inhibits cell growth and induces apoptosis in pancreatic cancer cells with high Mcl-1 levels (BxPC-3 and Panc-1) in a time and dose-dependent manner, accompanied by caspase-3 activation. Applying siRNA approach, the transient suppression of Mcl-1 abrogated UMI-77 mediated apoptosis in BxPC-3 cells, demonstrating that UMI-77 as a single agent can inhibit cell growth and induce apoptosis in pancreatic cells in a Mcl-1 dependent manner. Co-immunoprecipitation experiments revealed that UMI-77 blocks the heterodimerization of Mcl-1/Bax and Mcl-1/Bak in cells. By using murine embryonic fibroblasts (MEFs), wild type and deficient in both Bax and Bak (double knock out), it was demonstrated that the cytotoxic activity and induction of apoptosis by UMI-77 mainly depend on Bax and/or Bak, suggesting that function as BH3 mimetic. In order to verify the clinical utility of UMI-77, we tested its in vivo efficacy using BxPC-3 xenograft model. The maximum tolerated dose (MTD) of UMI-77 in SCID mice was determined to be 60mg/kg i.v. We further demonstrated that UMI-77 at MTD showed statistically significant and effective tumor growth inhibition in BxPC-3 xenograft model. At the end of the treatment, western blot analysis for different molecular markers on lysates isolated from tumors harvested from SCID mice revealed enhancement of proapoptotic markers in UMI-77 treated animals compared to control. Collectively, these promising findings warrant further chemical modifications of this compound and optimization toward developing a new class of anticancer drugs, Mcl-1 inhibitors. 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 2822. doi:10.1158/1538-7445.AM2011-2822