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

Abstract

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 G 1 -S checkpoint control. This has led to the hypothesis that S and G 2 -M checkpoint abrogation may selectively enhance genotoxic cell killing in a p53-deficient background, as normal cells would be rescued at the G 1 -S checkpoint. CHK1 is a serine/threonine kinase associated with DNA damage-linked S and G 2 -M checkpoint control. SAR-020106 is an ATP-competitive, potent, and selective CHK1 inhibitor with an IC 50 of 13.3 nmol/L on the isolated human enzyme. This compound abrogates an etoposide-induced G 2 arrest with an IC 50 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 γH2AX 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.

AT13148 Is a Novel, Oral Multi-AGC Kinase Inhibitor with Potent Pharmacodynamic and Antitumor Activity

“…Cells were harvested, lysates prepared, protein estimations conducted, and Western blots undertaken as described (18), using the following antibodies: pSer473 AKT, AKT, pSer9 GSK3b, GSK3b, pSer235/236 S6 ribosomal protein (S6RP), S6RP, pSer330 NDRG, NDRG, pSer157 VASP, VASP, pSer19 MLC2, MLC2, pThr24 FOX01/pThr32 FOX03a, FOX01, PRAS40, cleaved PARP, IRS2, pThr1135 Rictor, Rictor, cyclin E2, c-MYC (Cell Signaling Technology), PIK3IP1 (Abcam), pThr246 PRAS40 (Upstate), cleaved caspase-3 (Epitomics), cyclin D1, p27, and glyceraldehyde-3-phosphate dehydrogenase (GAPDH; Neomarkers).…”

“…iodide as described and analyzed by flow cytometry (18). The proportion of cells in each phase of the cell cycle was determined using either the Cell Quest Pro Software package (BD Biosciences) or WinMDI 2.8.…”

CCT241533 Is a Potent and Selective Inhibitor of CHK2 that Potentiates the Cytotoxicity of PARP Inhibitors

“…It has been suggested that abrogating the G 2 checkpoint may increase the efficacy of genotoxic agents preferentially in p53-deficient backgrounds, as normal tissue would be rescued at the p53-dependent G 1 /S checkpoint (3,9,10). There is increasing evidence that this is the case for inhibitors of CHK1 (11)(12)(13)(14)(15)(16), but the case for CHK2 is still unclear and may depend on the cell line and cytotoxic agent employed (17)(18)(19)(20)(21)(22)(23). However, in cells that possess a functional p53 pathway, there is evidence that CHK2 inhibitors protect against apoptosis induced by ionizing radiation (IR) and taxol (21,(24)(25)(26)(27), presumably by blocking CHK2-dependent activation of p53.…”

Selective radiosensitization of p53 mutant pancreatic cancer cells by combined inhibition of Chk1 and PARP1

“…Abrogation of the G 2 checkpoint (by Chk1 inhibition and other strategies) has been shown to preferentially sensitize p53 mutant tumor cells to chemotherapy and radiation. [10][11][12][13][14][15][16][17] The prevailing model for tumor cell selectivity of Chk1 inhibition is that tumor cells harbor aberrations in other DNA damage response machinery (i.e., p53, p16, Rb) and, thus, do not G 1 arrest in response to DNA damage leading to selective sensitization of tumor cells by Chk1 inhibition, while normal cells are protected from Chk1 inhibition by their other intact checkpoints (i.e., p53-mediated G 1 arrest).…”