ATM and cancer: Treatment with 20 μM VE-821 alone induced irreversible growth arrest and apoptosis in a large fraction of different cancer cell lines that were p53-deficient (human colorectal carcinoma cell lines HT23, HT29 or human malignant melanoma cell line HT144) or p53-proficient but with a defective ATM-mediated pathway (human colorectal carcinoma cells HCT116).