The Preclinical Pharmacology and Therapeutic Activity of the Novel CHK1 Inhibitor SAR-020106

Genotoxic antitumor agents continue to be the mainstay of current cancer chemotherapy. These drugs cause DNA damage and activate numerous cell cycle checkpoints facilitating DNA repair and the maintenance of genomic integrity. Most human tumors lack functional p53 and consequently have compromised G1-S checkpoint control. This has led to the hypothesis that S and G2-M checkpoint abrogation may selectively enhance genotoxic cell killing in a p53-deficient background, as normal cells would be rescued at the G1-S checkpoint. CHK1 is a serine/threonine kinase associated with DNA damage–linked S and G2-M checkpoint control. SAR-020106 is an ATP-competitive, potent, and selective CHK1 inhibitor with an IC50 of 13.3 nmol/L on the isolated human enzyme. This compound abrogates an etoposide-induced G2 arrest with an IC50 of 55 nmol/L in HT29 cells, and significantly enhances the cell killing of gemcitabine and SN38 by 3.0- to 29-fold in several colon tumor lines in vitro and in a p53-dependent fashion. Biomarker studies have shown that SAR-020106 inhibits cytotoxic drug–induced autophosphorylation of CHK1 at S296 and blocks the phosphorylation of CDK1 at Y15 in a dose-dependent fashion both in vitro and in vivo. Cytotoxic drug combinations were associated with increased ?H2AX and poly ADP ribose polymerase cleavage consistent with the SAR-020106–enhanced DNA damage and tumor cell death. Irinotecan and gemcitabine antitumor activity was enhanced by SAR-020106 in vivo with minimal toxicity. SAR-020106 represents a novel class of CHK1 inhibitors that can enhance antitumor activity with selected anticancer drugs in vivo and may therefore have clinical utility.