p53-defective tumors with a functional apoptosome-mediated pathway: A new therapeutic target

Abstract

Background: Although cancer cells appear to maintain the machinery for intrinsic apoptosis, defects in the pathway develop during malignant transformation, preventing apoptosis from occurring. How to specifically induce apoptosis in cancer cells remains unclear. Methods: We determined the apoptosome activity and p53 status of normal human cells and of lung, colon, stomach, brain, and breast cancer cells by measuring cytochrome c-dependent caspase activation and by DNA sequencing, respectively, and we used COMPARE analysis to identify apoptosome-specific agonists. We compared cell death, cytochrome c release, and caspase activation in NCI-H23 (lung cancer), HCT-15 (colon cancer), and SF268 (brain cancer) cells treated with Triacsin c, an inhibitor of acyl-CoA synthetase (ACS), or with vehicle. The cells were mock, transiently, or stably transfected with genes for Triacsin c-resistant ACSL5, dominant negative caspase-9, or apoptotic protease activating factor-1 knockdown. We measured ACS activity and levels of cardiolipin, a mitochondrial phospholipid, in mock and ACSL5-transduced SF268 cells. Nude mice carrying NCI-H23 xenograft tumors (n = 10) were treated with Triacsin c or vehicle, and xenograft tumor growth was assessed. Groups were compared using two-sided Student t tests. Results: Of 21 p53-defective tumor cell lines analyzed, 17 had higher apoptosome activity than did normal cells. Triacsin c selectively induced apoptosome-mediated death in tumor cells (caspase activity of Triacsin c-treated versus untreated SF268 cells; means = 1020% and 100%, respectively; difference = 920%, 95% CI = 900% to 940%; P