New benzo(b)thiophenesulphonamide 1,1-dioxide derivatives induce a reactive oxygen species-mediated process of apoptosis in tumour cells

In this work, we describe the process of cell death induced by a series of new benzo(b)thiophenesulphonamide 1,1-dioxide derivatives (BTS) that have been selected as candidate antineoplastic drugs. Human leukaemic CCRF-CEM cells incubated with BTS undergo a typical apoptotic process that includes cell shrinkage, phosphatidylserine translocation to the cell surface, mitochondrial dysfunction, caspase activation, chromatin condensation and internucleosomal DNA degradation. Mitochondrial alterations included dissipation of the mitochondrial membrane potential, oxidation of the phospholipid cardiolipin, release of cytochrome c and uncoupling of the mitochondrial respiratory chain, leading to a decrease of the intracellular ATP pool. Activation of caspase-8, -9 and -3 takes place during BTS-induced apoptosis. Either the addition of the specific caspase-8 inhibitor Z-IETD-fmk, or the overexpression of the antiapoptotic protein Bcl-2 significantly prevented BTS-induced apoptosis, suggesting the involvement of both caspase-8-regulated and mitochondria-dependent signalling pathways in this process. BTS induce a significant increase in the production and accumulation of intracellular reactive oxygen species (ROS) that can be observed within minutes after drug addition. Moreover, cytochrome c release, caspase-3 activation and cell death can be completely abrogated by a previous incubation with the antioxidant N-acetyl-cysteine. These results suggest that ROS are essential mediators in BTS-induced apoptosis.