BINDING-PROPERTIES OF MONOCLONAL-ANTIBODIES RECOGNIZING EXTERNAL EPITOPES OF THE HUMAN MDR1 P-GLYCOPROTEIN

Monoclonal antibodies (MAbs) recognizing external epitopes of the huma n MDR1 P-glycoprotein have been used both for the detection of multidr ug-resistant cells and as specific inhibitors of P-glycoprotein-mediat ed multidrug resistance. Using a panel of recently developed transfect ed or transgenic cell lines containing variants of the human MDR1 and MDR3 P-glycoproteins, we have compared the specificity and binding pro perties of the previously isolated MAbs MRK16, HYB-241, UIC2 and 4E3, and of the newly isolated MAb 7G4. The removal of 1, 2 or all 3 of the N-glycosylation sites present in the first extracellular loop of MDR1 P-glycoprotein did not significantly affect the binding of these MAbs . In contrast, a 20 amino acid deletion in the first extracellular loo p of MDR1 P-glycoprotein completely abolished binding of UIC2, whereas the binding of all other MAbs was hardly affected. None of the MAbs t ested bound detectably to cell lines containing a high level of the hu man MDR3 P-glycoprotein. The differences in the binding specificity be tween UIC2 and the other tested antibodies parallel the reported funct ional differences in the ability of these antibodies to inhibit P-glyc oprotein-mediated drug efflux. (C) 1993 Wiley-Liss, Inc.