Immediate effects of anticancer drugs on mitochondrial oxygen consumption.

The evolving role of mitochondria as a target for many anticancer drugs (e.g. platinum-based compounds, alkylating agents and anthracyclines) prompted us to investigate their immediate effects on the mitochondrial respiratory chain. For this purpose, we used a phosphorescence analyzer that measures [O(2)] in solution. The [O(2)] of solutions containing an appropriate substrate and various cell lines, tumors from patients or beef heart submitochondrial particles (SMPs) declined almost linearly (r>0.99) as a function of time, indicating that the kinetics of cellular oxygen consumption were zero order. Rotenone inhibited respiration, confirming that oxygen was consumed by the respiratory chain. Exposure to a clinically relevant concentration of cisplatin (5 microM at 37 degrees for 1-3 hr) had no effect on the respiration in cells or in SMP. Higher cisplatin concentrations (10-99 microM at 37 degrees for 1-3 hr) produced <25% inhibition. Incubations with 4-hydroperoxycyclophosphamide (50-100 microM at 37 degrees for 1 hr) inhibited oxygen consumption in SMP ( approximately 70% inhibition at 50 microM) and in cells ( approximately 30% inhibition at 50 microM). Incubations (37 degrees for 1 hr) of SMP with doxorubicin (25-100 microM) and daunorubicin (25-100 microM) had no inhibitory effect on the respiration. By contrast, incubations (37 degrees for 1 hr) of cells with doxorubicin (5-20 microM) and daunorubicin (2-20 microM) produced significant inhibition. We conclude that cisplatin does not directly damage the energy converting mechanism of mitochondria. On the other hand, comparable exposures to alkylating agents and anthracyclines produce immediate and dose-dependent impairment of cellular respiration.