In vitro activity: AZD7762, a more selective Chk1 inhibitor, inhibits Chk1 phosphorylation of a cdc25C peptide by reversibly binding to the ATP-binding site of Chk1, with IC50 of 5 nM and Ki of 3.6 nM. AZD7762 induces cell arrest with EC50 of 0.620 μM, and significantly abrogates the camptothecin induced G2 arrest with an EC50 of 10 nM, by blocking the chk1 dependent degradation of Cdc25A and activation of Cyclin A. AZD7762 (300 nM) enhances the antitumor efficacy of gemcitabine against SW620 and topotecan against MDA-MB-231 by reducing the GI50 values from 24.1 nM and 2.25 μM to 1.08 nM and 0.15 μM, respectively. AZD7762 shows cytotoxicity against a variety of neuroblastoma cell lines bearing p53 wild type, p53 mutation, Mdm2 amplification or p14 deletion with IC50 values ranging from 82.6-505.9 nM.

Kinase Assay: Recombinant human Chk1 is expressed as a glutathione S-transferase fusion in insect cells using a baculovirus vector and purified by glutathione affinity chromatography. A synthetic peptide substrate (N-biotinylaminohexanoyl-KKVSRSGLYRSPMPENLNRPR) for Chk1 is synthesized. Final assay concentrations of peptide and ATP (cold + 40 nCi [33P]ATP) are 0.8 and 1 μM, respectively. Different concentrations of AZD7762, buffer containing peptide and chk1 kinase and ATP, are added sequentially to a 384-well assay plate. The plate is incubated for 2 hours, reaction is stopped by the addition of buffer containing EDTA and scintillation proximity assay beads, and plates are read using a TopCount reader. Data analysis is carried out to determinate a dose response (IC50).

Cell Assay: For the checkpoint abrogation assay, HT29 cells are treated for 2 hours with camptothecin (topoisomerase I inhibitor; 0.07 μg/mL) to induce the G2 checkpoint. Cells are then treated for 20 hours with a 12-point titration of AZD7762 (12.5 μM to 6 nM) plus nocodazole. Cells are fixed with 3.7% formaldehyde for 1 hour, permeabilized with PBS containing 0.05% Triton X, and incubated with anti-phH3 antibody for 1 hour followed by Alexa Fluor 488 anti-rabbit and Hoechst stain for 1 hour. Mitotic index is determined on the ArrayScan and expressed as the percentage of cells undergoing mitosis. For the potentiation assays, SW620 or MDA-MB-231 cells are dosed for 24 hours with a 9-point titration of gemcitabine ranging from 0.01 to 100 nM with a constant dose of AZD7762 (300 nM). After 24 hours, medium is removed and AZD7762 alone is added back to the wells for an additional 24 hours. Cells are then incubated in AZD7762-free medium for an additional 72 hours. The effect on cell proliferation is determined by MTT.

Mol Cancer Ther. 2008 Sep;7(9):2955-66.