Cano-Gauci D F, Seibert F S, Safa A R, Riordan J R
Research Institute, Hospital for Sick Children Toronto, Ontario, Canada.
Biochem Biophys Res Commun. 1995 Apr 17;209(2):497-505. doi: 10.1006/bbrc.1995.1529.
Multidrug resistant cells may become acutely sensitive to the calcium channel blocker verapamil, in spite of the fact that its accumulation by these cells is negligible. We selected verapamil-resistant mutants from multidrug resistant Chinese hamster ovary cells. Levels of P-glycoprotein expression and cross-resistance profiles remained unaltered in the verapamil-resistant multidrug resistant cells. As well, a photoactive verapamil analog specifically bound to P-glycoprotein in these cells. We had previously used a photoactive anthracycline to show that calcium antagonists and several anticancer drugs bind to P-glycoprotein at overlapping or interacting sites. Verapamil and its analogues no longer inhibit the binding of either anticancer drugs or calcium channel blockers to P-glycoprotein. Sequencing of P-glycoprotein revealed that no change had occurred in the coding sequence as a result of the selection procedure.
