Abstract
Abstract Background Topotecan is a therapeutic option for women with platinum-resistant or -refractory ovarian cancer. However, the dose-limiting toxicity of topotecan is myelosuppression. This led us to seek a combination treatment to augment topotecan anti-cancer activity in a cancer-targeted manner. Ovarian serous cancers, a major subtype, show dysregulated DNA repair pathway and often display a high level of CHEK1, a cell cycle regulator and DNA damage sensor. CHEK1 inhibitors are a novel approach to treatment, and have been used as single agents or in combination chemotherapy in many cancers. Methods We evaluated the cellular effects of topotecan in a panel of high grade serous (HGS) and non-HGS ovarian cancer cells. We then determined IC50s of topotecan in the absence and presence of suboptimal concentrations of CHEK1 inhibitor, PF477736. Synergism between topotecan and PF477736 was calculated based on cellular viability assays. Cytotoxic effect of the combined treatment was compared with apoptotic activities by Caspase3/7 activity assay and Western blotting of cleaved-PARP1 and γH2A.X. Results Non-HGS ovarian cancer cells were generally more sensitive to topotecan treatment compared to HGS ovarian cancer cells. When combined with suboptimal concentrations of CHEK1 inhibitor, topotecan potently and synergistically inhibited the proliferation of HGS ovarian cancer cells. This dramatic synergism in cellular toxicity was consistent with increases in markers of apoptosis. Conclusions Our findings suggest that the addition of CHEK1 inhibitor increases the response of ovarian cancer cells to topotecan. Furthermore, reduced dosages of both drugs achieved maximal cytotoxic effects by combining topotecan with CHEK1 inhibitor. This strategy would potentially minimize side effects of the drugs for extended clinical benefit. Citation Format: Marianne K. H. Kim, Jana James, Christina Annunziata. Topotecan synergizes with CHEK1 inhibitor to induce apoptosis in ovarian cancer cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3490. doi:10.1158/1538-7445.AM2015-3490
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