Abstract 3552: Mirk kinase mediates cisplatin resistance in ovarian cancers

Abstract

Abstract Epithelial carcinoma of the ovary is the fifth most frequent cause of cancer death in women, and the second most frequent gynecological malignancy. Cisplatin based regimens are the standard of care, but efficacy is limited by drug resistance. Cisplatin treatment increased intracellular levels of toxic reactive oxygen species (ROS) in each of four ovarian cancer cell lines in a dose-dependent manner, while concomitantly reducing cell numbers, which suggested that further increasing ROS levels might increase cisplatin toxicity. The serine/threonine kinase Mirk/dyrk1B is known to increase the expression of a cohort of antioxidant genes in various cells. Targeting Mirk expression by RNA interference also increased ROS levels in these ovarian cancer cell lines while decreasing levels of ferroxidase (ceruloplamin) which prevents the generation of hydroxyl radicals. A combination of Mirk depletion and cisplatin treatment enabled low levels of drug to increase ROS to toxic levels in both SKOV3 cells and TOV21G cells. Increased tumor cell death by the combination treatment was confirmed by loss of viable cells capable of dye exclusion, a decrease in cell number, and an increase in pro-apoptotic proteins. Mirk has a second function in ovarian cancer cells, to maintain cells in quiescent state where they are less vulnerable to chemotherapeutic drugs and radiation. The majority of ovarian cancer cells in human tumors are not cycling as shown by lack of Ki67 expression. Some of these cells may be in a reversible quiescent state where they can contribute to cancer spread under favorable growth conditions. Depletion of Mirk in SKOV3 cells enabled them to escape quiescence. Studies using cisplatin revealed a Mirk-dependent G0/G1 checkpoint in SKOV3 and other p53 mutant ovarian cancer cells. The Mirk gene is on the 19q13 amplicon which is found in about one-third of all ovarian cancers. The Mirk gene was amplified in the OVCAR3 cell line where it mediated both quiescence and increased expression of antioxidant genes which decreased cellular ROS levels. Mirk protein was expressed in 21 of 28 resected human ovarian cancers as shown by immunohistochemical analysis, and was detected in each of 7 ovarian cancer cell lines, where it was an active kinase. Mirk is not an essential gene for either murine embryogenesis or the viability of human diploid fibroblasts. Targeting Mirk in ovarian cancers may sensitize these tumors to lower levels of cisplatin, both by increasing ROS levels and by releasing tumor cells from quiescence. 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 3552.