title: Mitochondrial permeability transition induced by the anticancer drug etoposide.
abstract: Etoposide (VP-16) is widely used for the treatment of several forms of cancer. The cytotoxicity of VP-16 has been assigned to the induction of apoptotic cell death but the signaling pathway for VP-16-induced apoptosis is essentially unknown. There is some evidence that this process depends on events associated with the loss of mitochondrial membrane potential (Delta Psi) and/or release of apoptogenic factors, putatively as a consequence of mitochondrial permeability transition (MPT) induction. This work evaluates the interference of VP-16 with MPT in vitro, which is characterized by the Ca(2+)-dependent depolarization of Delta Psi, the release of matrix Ca(2+) and by extensive swelling of mitochondria. Delta Psi depolarization and Ca(2+) release were measured with ion-selective electrodes, and mitochondrial swelling was monitored spectrophotometrically. Incubation of rat liver mitochondria with VP-16 results in a concentration-dependent induction of MPT, evidenced by an increased sensitivity to Ca(2+)-induced swelling, depolarization of Delta Psi, Ca(2+) release by mitochondria and stimulation of state 4 oxygen consumption. All of these effects are prevented by preincubating the mitochondria with cyclosporine A, a potent and specific inhibitor of the MPT. Therefore, VP-16 increases the sensitivity of isolated mitochondria to the Ca(2+)-dependent induction of the MPT. Together, these data provide a possible mechanistic explanation for the previously reported effects of VP-16 on apoptosis induction.
authors.affiliation: Laboratório de Bioquimíca, Faculdade de Farmácia, Universidade de Coimbra, Coimbra, Portugal. custodio@ci.uc.pt
authors.forename: J B
authors.initials: JB
authors.lastname: Custódio
authors.forename: C M
authors.initials: CM
authors.lastname: Cardoso
authors.forename: V M
authors.initials: VM
authors.lastname: Madeira
authors.forename: L M
authors.initials: LM
authors.lastname: Almeida
mesh_terms: D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D002458:Cell Fractionation; D005047:Etoposide / Q000494:pharmacology*; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000187:drug effects / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008930:Mitochondria, Liver / Q000187:drug effects* / Q000378:metabolism; D008933:Mitochondrial Swelling / Q000187:drug effects / Q000502:physiology; D010539:Permeability / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D005047:Etoposide; D002118:Calcium