Disruption of mitochondrial membrane potential during apoptosis induced by PSC833 and CsA in multidrug resistant lymphoid leukemia

LOPES EC; BUSTAMANTE J; GARCÍA MG; ALVAREZ E; HAJOS S

Chicago, Illinois, USA

Congreso; Annual Meeting of American Society of Clinical Oncology (ASCO); 2003

American Society of Clinical Oncology (ASCO)

Previous findings from our laboratory demonstrated that when used at low concentration (0.1 mg/ml), CsA as well as its analogue PSC 833 were able to revert the MDR phenotype, while at high concentration (1 mg/ml) were able to induce apoptosis. CsA induced apoptosis in both sensitive (LBR-) and resistant to vincristine (LBR-V160) and to doxorubicin (LBR-D160) cell lines, while PSC 833 only induced apoptosis in the vincristine resistant cell line (LBR-V160). In this work, we investigated some of the  mechanisms involved during the process of apoptosis induced PSC 833 and CsA. Evaluation of the mitochondrial function during induction of apoptosis was carried out by recording changes in its transmembrane potential and cytochrome c release, followed by the caspase activation cascade. Through the measurements of  two fluorescent probes JC-1 and DiOC6, we found that both drugs induced apoptosis  associated with mitochondrial depolarization. This finding was observed despite the ability of CsA and PSC833 to block MDR pump activity. In addition, mitochondrial potential collapse was followed by an increase in cytochrome c in the cytosol, reaching 2.61-fold in LBR-, 1.98-fold in untreated LBR-V160, and 3.01-fold in the case of LBR-D160 after CsA treatment. However, in the case of PSC 833 induced apoptosis, a lower increase in cytochrome c release of 1.15-fold was observed in LBR-V160 associated only with caspase 3 but neither caspase 6 nor 8 activation. These results suggest that apoptosis induced by CsA and PSC 833 in these cell lines may be mediated through dissimilar mitochondrial events.