γH2AX and Chk1 phosphorylation as predictive pharmacodynamic biomarkers of Chk1 inhibitor-chemotherapy combination treatments.

Rebecca Rawlinson,Andrew J Massey

doi:10.1186/1471-2407-14-483

Abstract

BackgroundChk1 inhibitors are currently in clinical trials in combination with a range of cytotoxic agents and have the potential to potentiate the clinical activity of a large number of standard of care chemotherapeutic agents. Utilizing pharmacodynamic biomarkers to optimize drug dose and scheduling in these trials could greatly enhance the likelihood of clinical success.MethodsIn this study, we evaluated the in vitro potentiation of the cytotoxicity of a range of cytotoxic chemotherapeutic drugs by the novel Chk1 inhibitor V158411 in p53 mutant colon cancer cells. Pharmacodynamic biomarkers were evaluated in vitro.ResultsV158411 potentiated the cytotoxicity of a range of chemotherapeutic agents with distinct mechanisms of action in p53 mutant colon cancer cell lines grown in anchorage dependent or independent culture conditions. Analysis of pharmacodynamic biomarker changes identified dependencies on the chemotherapeutic agent, the concentration of the chemotherapeutic and the duration of time between combination treatment and biomarker analysis. A reduction in total Chk1 and S296/S317/S345 phosphorylation occurred consistently with all cytotoxics in combination with V158411 but did not predict cell line potentiation. Induction of γH2AX levels was chemotherapeutic dependent and correlated closely with potentiation of gemcitabine and camptothecin in p53 mutant colon cancer cells.ConclusionsOur results suggest that Chk1 phosphorylation could be a useful biomarker for monitoring inhibition of Chk1 activity in clinical trials involving a range of V158411-chemotherapy combinations and γH2AX induction as a predictor of potentiation in combinations containing gemcitabine or camptothecin.

Highlights

Chk1 inhibitors are currently in clinical trials in combination with a range of cytotoxic agents and have the potential to potentiate the clinical activity of a large number of standard of care chemotherapeutic agents
The serine-threonine checkpoint kinases Chk1 and Chk2 are often described as the “central transducers” of the DNA damage response (DDR) and are activated by the ATM kinase in response to DNA breaks and ATR kinase by single-stranded regions of DNA and form the key link between the sensing kinases
We evaluated the potential for a novel, highly selective Chk1/2 inhibitor, V158411, to potentiate the cytotoxicity of a range of agents in p53 mutant colon cancer cells and the corresponding changes in a panel of potential pharmacodynamic biomarkers for predictors of V158411 combinatorial activity

Summary

Introduction

Chk inhibitors are currently in clinical trials in combination with a range of cytotoxic agents and have the potential to potentiate the clinical activity of a large number of standard of care chemotherapeutic agents. The serine-threonine checkpoint kinases Chk and Chk are often described as the “central transducers” of the DDR and are activated by the ATM kinase in response to DNA breaks and ATR kinase by single-stranded regions of DNA and form the key link between the sensing kinases. Recognition of DNA double strand breaks by the Mre complex (Mre, Rad and Nbs1) or replication stress by the Rad9-Hus1-Rad complex results in the activation of the ATR and ATM kinases respectively. These kinases, in turn, activate the effector kinases Chk and Chk. In the vast majority of human cancers, p53 (an important effector of the G1/S checkpoint) is mutated or functionally inactivated, rendering cancer cells reliant on Chk1/Chk for checkpoint activation, in the presence of endogenous or exogenous DNA damage

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