Abstract B174: The effect of histone deacetylase inhibition on BRCA1 expression: A potential novel mechanism for enhancing platinum sensitivity in breast and ovarian cancer

Abstract

Abstract Introduction: Targeting BRCA1 expression has been shown to sensitize Breast-Cancer 1 (BRCA1)-expressing tumor cells to platinum-based chemotherapies. The improved outcome of (BRCA1)-deficient breast and ovarian cancer is believed to be linked to the impaired ability to repair chemotherapy-induced DNA damage. However, therapeutically relevant agents that target BRCA1 expression have yet to be identified. In this study, we explore the effect of histone deacetylase inhibition (HDACi) on BRCA1 expression and platinum sensitivity in a breast and ovarian cancer cell line model. Experimental procedures: BRCA1 mRNA and protein expression was determined by Q-PCR and Western blot, respectively. The efficacy of the HDACi, M344, to potentiate the cytotoxicity of platinum-based chemotherapeutics was evaluated in a range of breast and ovarian tumor cell lines using the MTT cell viability assay and confirmed by flow cytometry. The effect on DNA damage was measured by immunofluorescence staining and flow cytometry for H2A.X foci, a hallmark for the presence of DNA double strand breaks. Results: Baseline BRCA1 mRNA and protein expression was variable in three breast (MCF7, T47D and HCC1937) and three ovarian (A2780s, A2780cp a cisplatin-resistant variant and OVCAR4) cancer cell lines. Expression of BRCA1 protein decreased in response to the addition of the HDACi, M344, in the four cell lines that express detectable levels of BRCA1 by Western blot analysis. BRCA1 mRNA levels decreased with the addition of this HDACi in all the breast and ovarian cancer lines evaluated. Treatment with M344 also increased the sensitivity of these tumor cells to cisplatin and carboplatin treatment in the cell lines with high BRCA1 expression. Furthermore, expression of BRCA1 protein and mRNA decreased in cells treated with the combination of HDACi and cisplatin. A2780s cells subjected to combination platinum and HDACi treatment demonstrated increased levels of DNA damage as assessed by the presence of phosphorylated H2A.X foci in comparison to either treatment alone. Conclusion: This study supports a novel mechanism of BRCA1 targeting using an HDACi resulting in enhanced platinum sensitivity in breast and ovarian cancer cells. Further studies are needed to determine if a HDACi/platinum combination has potential clinical relevance in a subset of breast and ovarian cancer patients. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B174.