Interactions of human P-glycoprotein transport substrates and inhibitors at the drug binding domain: Functional and molecular docking analyses

Rhodamine 123 (R123) transport substrate sensitizes P-glycoprotein (P-gp) to inhibition by compound 2c (cis-cis) N,N-bis(cyclohexanolamine)aryl ester isomer in a concentration-dependent manner in human MDR1-gene transfected mouse T-lymphoma L5178 cells as shown previously. By contrast, epirubicin (EPI) concentration changes left unaltered 2c IC50 values of EPI efflux. To clarify this discrepancy, defined molecular docking (DMD) analyses of 12 N,N-bis(cyclohexanolamine)aryl esters, the highly flexible aryl ester analog 4, and several P-gp substrate/non-substrate inhibitors were performed on human P-gp drug- or nucleotide-binding domains (DBD or NBD). DMD measurements yielded lowest binding e…