One of the mechanisms of platinum resistance in cancer chemotherapy is the activation of DNA damage checkpoint pathways. Chk2 is a multifunctional key component of the DNA replication-monitoring S/G2 checkpoint system, which mediates DNA damage signaling following genotoxic stress and leads to DNA repair or apoptosis. Developing checkpoint kinase inhibitors for better treatment of cancer has been a major target in drug discovery over the past decade. In our study, flow cytometric experiments show that cisplatin induces an initial accumulation of cells at S phase of cell cycle followed by an increase of cell fraction at G2 phase, suggesting cisplatin-induced cell cycle arrest. Treatment of cisplatin in human ovarian carcinoma cells resulted in Chk2 phosphorylation at Thr-68 and p53 phosphorylation at Ser-15. The observed cisplatin-induced increase in p53 phosphorylation preceded (by about 12 hours) the observed increase in Chk2 phosphorylation. Elevated protein levels of ATM, p53 and P21 by cisplatin in these cells appear in a dose-dependent manner. In addition, overexpression of p53 by cDNA transfection in cells with wild type p53-function doubled the amount of Chk2 phosphorylation 48 hours after cisplatin treatment, whereas p53 knock-down by specific siRNA greatly reduced Chk2 phosphorylation. Furthermore, selective Chk2 Inhibitor (C3742) potentiated the cell-killing effect of cisplatin in both sensitive and resistant ovarian cancer cells. In conclusion, our results suggest that after cisplatin exposure the DNA damage response pathway is activated with greatly increased Chk2 phosphorylation which is modulated by p53. Inhibition of Chk2 with a small-molecule inhibitor may overcome cisplatin resistance in cancer chemotherapy.

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 2982.