MOLECULAR-INTERACTIONS OF CYCLOSPORINE-A WITH P-GLYCOPROTEIN - PHOTOLABELING WITH CYCLOSPORINE DERIVATIVES

The interaction between P-glycoprotein (140-180 kDa) from the multidru g-resistant Chinese hamster ovary cell line CH(R)C5 and cyclosporin A was characterized using three different photoactivable cyclosporin A a nalogs. Two monoclonal antibodies, which are able to discriminate betw een two major domains of cyclosporin A (the cyclophilin and calcineuri n binding domains), were used to detect the photolabeled proteins. A p rotein of 155 kDa corresponding to P-glycoprotein was much more strong ly photolabeled in membranes of CH(R)C5 cells than in membranes of the ir drug-sensitive parent cell line AuxB1. The antitumor drug vinblasti ne and the reversal agents verapamil and cyclosporin A inhibited the p hotolabeling, and the nonimmunosuppressive derivative PSC-833 caused a stronger inhibition than cyclosporin A. P-glycoprotein photolabeled w ith cyclosporin A analogs was only detected with the monoclonal antibo dy that recognizes cyclosporin A and its metabolites, indicating that the calcineurin binding domain recognized specifically by the other an tibody is not exposed. These results suggest that the portion of cyclo sporin A that binds to calcineurin plays a role in the interaction of cyclosporin A with P-glycoprotein.