Abstract 1633: C-terminal binding proteins are novel drug targets

Abstract

Abstract The CtBP transcriptional corepressors have been identified as proto-oncogenes. CtBP represses pro-apoptotic genes and promotes cancer cell migration and invasion in a redox sensitive manner through a regulatory dehydrogenase domain. The CtBP dehydrogenase substrate 4-methylthio-2-oxobutyric acid (MTOB) can act as a CtBP inhibitor at high concentrations, and induces apoptosis in the human colorectal cancer cell line HCT116. MTOB induced apoptosis is dependent upon expression of the BH3 only protein BIK, a previously established CtBP target. Treatment of both native and transformed Mouse Embryonic Fibroblasts revealed a wide therapeutic index for CtBP inhibition. In human colon cancer cell peritoneal xenografts, MTOB treatment reduced tumor growth and induced apoptosis in vivo without notable toxicity. To verify the potential utility of CtBP as a therapeutic target in human cancer, the expression of CtBP and its negative regulator ARF was studied in a series of resected human colon adenocarcinomas. CtBP and ARF levels were inversely-correlated, with elevated CtBP levels (compared with adjacent normal tissue) observed in greater than 60% of specimens, with ARF absent in nearly all specimens exhibiting elevated CtBP levels. Thus, CtBP is a viable therapeutic target in human cancer. In order to identify novel CtBP inhibitors, a simple dehydrogenase assay was developed that utilizes the spectrophotometric measurement of enzymatic conversion of NADH to NAD+ by the CtBP dehydrogenase activity. This assay successfully detects MTOB substrate and inhibitor activity, as well as inhibition of CtBP activity by the related compound 4-methylthio-2-hydroxybutyric acid (MTHB). This assay will be adapted for high throughput screening of small molecule libraries for novel CtBP inhibitors that can be further characterized in pre-clinical models. 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 1633. doi:10.1158/1538-7445.AM2011-1633