Abstract 3335: Ouabain, a cardiac glycoside, inhibits the Fanconi Anemia-BRCA pathway activated by DNA crosslinking agents.

Abstract

Abstract Most cancer therapies, including conventional chemotherapy and radiotherapy, are based on DNA damage-induced tumor cell death. In tumor cells, cellular DNA repair machinery can decrease anticancer drug efficacy and induce drug resistance. The DNA repair pathway has been an emerging target for development of anticancer drugs. DNA intercrosslinking, one of the most severe forms of DNA damage which are caused by anticancer drugs, such as cisplatin and mitomycin C (MMC), could activate the Fanconi anemia (FA)-BRCA DNA repair pathway. Inhibition of the FA-BRCA pathway can enhance the cytotoxic effects of anticancer drugs which induce DNA crosslinking and can reduce anticancer drug resistance. To find FA-BRCA pathway inhibitory small molecules, we established a cell-based high-content screening method for detecting the FA-BRCA pathway by measuring ubiquitinated FANCD2 foci on DNA lesions after immunofluorescence staining and then we applied our method to chemical screening. Using commercial LOPAC1280 chemical library screening, ouabain was identified as a competent FA-BRCA pathway inhibitory molecule. Ouabain, a member of the cardiac glycoside family and an endogenous mammalian hormone, binds to and inhibits the plasma membrane protein Na+/K+-ATPase and has been used for the treatment of heart disease for many years. We observed that ouabain, as well as its cardiac glycoside family members―digitoxin and digoxin―reduced monoubiquitination of FANCD2, inhibited ubiquitinated FANCD2 foci formation on DNA lesions and abrogated cell cycle arrest induced by MMC treatment. These inhibitory activities of the FA-BRCA pathway were independent of the cellular Ca++ ion increase or the drug uptake-inhibition effect which is known to be a function of ouabain. Furthermore, we found that ouabain potentiated cytotoxic effects of MMC in tumor cells. Taken together, we identified an additional role of ouabain as a FA-BRCA pathway inhibitor which has chemosensitization activity. The results of this study suggest that ouabain may serve as a chemosensitizer to anticancer drugs which induce DNA crosslinking. Citation Format: Mihwa Hwang, Dong Wha Jun, Hyun Jung Kim, Soo Kyung Hwang, Chang-Hun Lee, Sunshin Kim. Ouabain, a cardiac glycoside, inhibits the Fanconi Anemia-BRCA pathway activated by DNA crosslinking agents. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3335. doi:10.1158/1538-7445.AM2013-3335