Induction by verapamil of a rapid increase in ATP consumption in multidrug‐resistant tumor cells

A marked increase in cellular ATP consumption was induced by verapamil in the multidrug‐resistant (MDR) cell line 2780 ad , but not in the drug‐sensitive parental cell line A2780. A group of structurally unrelated drugs in concentrations known to reverse MDR, but not the verapamil analog tiapamil, a weak modulator of MDR, had similar effects. This effect was saturated at verapamil concentrations of about 1 μM.These data demonstrate that verapamil concentrations in MDR cells are maintained at a low level at the expense of ATP hydrolysis, and provide a first indication of the amount of metabolic energy used in this process.— B roxterman , H. J.; P inedo , H. M.; K uiper , C. M.; K aptein , L. C. M.; S chuurhuis , G. J.; L ankelma , j . Induction by verapamil of a rapid increase in ATP consumption in multidrug‐resistant tumor cells. FASEB J. 2: 2278‐2282; 1988.