Abstract 757: Identification and characterization of small molecule activators of BRCA1 expression

Abstract

Abstract Breast cancer susceptibility gene 1 (BRCA1) has been intensely investigated in normal and cancerous cells and mutations in the BRCA1 gene have been found to account for half of the hereditary breast cancer cases. Although the role of BRCA1 in sporadic breast cancer is still uncertain, 30-40% of such cases show downregulation of BRCA1 expression. Because BRCA1 is a tumor suppressor gene, decreased expression of BRCA1 accelerates growth of mammary tumor cells, while increased expression leads to growth arrest and apoptosis. Furthermore, overexpression of BRCA1 in the murine mammary gland provides protection against mutagen-induced mammary neoplasia. In 2009, the American Cancer Society estimates that 254,650 new cases of invasive and in situ breast cancer will be diagnosed among women. Based on estimates of BRCA1 dysfunction in sporadic breast cancers, over 80,000 newly diagnosed malignancies would have decreased BRCA1 expression. Therefore, a novel prevention or therapeutic strategy targeting BRCA1 could have significant impact on incidence and/or survival. We developed an MCF-7 breast cancer cell line containing stably integrated copies of a BRCA1 promoter-driven firefly luciferase reporter plasmid and screened over 100,000 compounds for their ability to increase BRCA1-firefly luciferase expression. Six hundred and sixty two compounds (hits) increased BRCA1-firefly luciferase activity greater than 2 standard deviations above the control, DMSO. Secondary dose-response BRCA1-firefly luciferase assays confirmed 27 of the top 32 hits as true active compounds. Potency and efficacy of the active compounds were characterized quantitatively as effective concentration (EC50) and area under the curve (AUC), respectively. Cell viability assays determined that the active compounds had little cytotoxic effects. Non-cytotoxic compounds that increased BRCA1-firefly luciferase activity in a dose-dependent manner with a potency (EC50) and efficacy (AUC) greater than or equal to that of genistein, the positive control, were selected to move forward as lead compounds. Thus far, several lead compounds have been identified. Western blot analysis indicates lead compound 17 increases endogenous BRCA1 expression. Furthermore, DNA foci formation assays indicate compound 17 enhances the ability of BRCA1 to localize to sites of ionizing radiation-induced DNA damage. Because BRCA1 appears to play a role as a growth inhibitor and tumor suppressor in adult breast tissues, identification and characterization of a plausible active compound that enhances BRCA1 expression could potentially translate into a novel prevention or therapeutic option for patients afflicted with breast cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 757.