Kinetics of H2AX phosphorylation after exposure to cisplatin

Background: Cisplatin is a widely used cancer chemotherapeutic drug that causes DNA crosslinking and stimulates H2AX phosphorylation. Our goal was to assess the potential of cH2AX to help predict tumor response to cisplatin treatment. Methods: The kinetics of cisplatin-induced DNA interstrand crosslinks was measured using the alkaline comet assay and compared with cH2AX formation and clonogenic cell survival in several DNA repair proficient or deficient human and rodent cell lines. Results: The comet assay was effective in ranking cell lines according to their relative sensitivity to cisplatin based on reduced crosslink formation measured 6 h after drug exposure or by the failure of irs3 and UV41 cell lines to subsequently remove crosslinks. In comparison, the initial rate of phosphorylation of H2AX measured over the first 6 h after cisplatin treatment was unrelated to drug sensitivity or crosslinking proficiency. However, for proliferating cell cultures, the fraction of cells that retained cH2AX foci 24 h after cisplatin treatment was correlated with the fraction of cells that lost clonogenic potential (slope 5 1.1, r 2 = 0.85). Conclusions: H2AX phosphorylation occurs in response to replication fork damage caused by cisplatin induced DNA lesions, probably interstrand crosslinks. Although early kinetics of cH2AX formation was uninformative, retention of cH2AX foci 24 h after treatment was shown to be a useful indicator of cell response to killing by cisplatin. However, for cH2AX to serve as an indicator of cell viability after cisplatin treatment, cells must have the opportunity to transit S phase during the recovery period. q 2008