Interaction of the P-glycoprotein multidrug transporter (MDR1) with high affinity peptide chemosensitizers in isolated membranes, reconstituted systems, and intact cells

P-Glycoprotein-mediated multidrug resistance can be reversed by the action of a group of compounds known as chemosensitizers. The interactions with P- glycoprotein of two novel hydrophobic peptide chemosensitizers (reversins 1 21 and 205) have been studied in model systems in vitro, and in a variety o f MDR1-expressing intact tumor cells. The reversins bound to purified P-gly coprotein with high affinity (77-154 nM), as assessed by a quenching assay using fluorescently labeled purified protein. The peptides modulated P-glyc oprotein ATPase activity in Sf9 insect fell membranes expressing human MDR1 , plasma membrane vesicles from multidrug-resistant cells, and reconstitute d proteoliposomes. Both peptides induced a large stimulation of ATPase acti vity; however, higher concentrations, especially of reversin 205, led to in hibition. This pattern was different from that of simple linear peptides, a nd resembled that of chemosensitizers such as verapamil. In both membrane v esicles and reconstituted proteoliposomes, 1-2 mu M reversins were more eff ective than cyclosporin A at blocking colchicine transport. Reversin 121 an d reversin 205 restored the uptake of [H-3]daunorubicin and rhodamine 123 i n MDR1-expressing cells to the level observed in the drug-sensitive parent cell lines, and also effectively inhibited the extrusion of calcein acetoxy methyl ester from intact cells. In cytotoxicity assays, reversin 121 and re versin 205 eliminated the resistance of MDR1-expressing tumor cells against MDR1-substrate anticancer drugs, and they had no toxic effects in MDR1-neg ative control cells. Me suggest that peptides of the reversin type interact with the MDR1 protein with high affinity and specificity, and thus they ma y be good candidates for the development of MDR1-modulating agents to sensi tize drug resistance in cancer. (C) 1999 Elsevier Science Inc.