Identification and Characterization of the Binding Sites of P-Glycoprotein for Multidrug Resistance-Related Drugs and Modulators

Abstract

A major problem in cancer treatment is the development of resistance to multiple chemotherapeutic agents in tumor cells. A major mechanism of this multidrug resistance (MDR) is overexpression of the MDR1 product P-glycoprotein, known to bind to and transport a wide variety of agents. This review concentrates on the progress made toward understanding the role of this protein in MDR, identifying and characterizing the drug binding sites of P-glycoprotein, and modulating MDR by P-glycoprotein-specific inhibitors. Since our initial discovery that Pglycoprotein binds to vinblastine photoaffinity analogs, many P-glycoprotein-specific photoaffinity analogs have been developed and used to identify the particular domains of Pglycoprotein capable of interacting with these analogs and other P-glycoprotein substrates. Furthermore, significant advances have been made in delineating the drug binding sites of this protein by studying mutant P-glycoprotein. Photoaffinity labeling experiments and the use of sitedirected antibodies to several domains of this protein have allowed the localization of the general binding domains of some of the cytotoxic agents and MDR modulators on P-glycoprotein. Moreover, site-directed mutagenesis studies have identified the amino acids critical for the binding of some of these agents to P-glycoprotein. Furthermore, equilibrium binding assays using plasma membranes from MDR cells and radioactive drugs have aided our understanding of the modes of drug interactions with P-glycoprotein. Based on the available data, a topological model of Pglycoprotein and the approximate locations of its drug binding sites, as well as a proposed classification of multiple drug binding sites of this protein, is presented in this review.

Human Multidrug Resistance ABCB and ABCG Transporters: Participation in a Chemoimmunity Defense System

“…The end products of the hydrolysis are intracellular ADP and inorganic phosphate (for recent reviews, see Refs. 13,34,48,102,118,123,156,210,213,300,313,322,331,389). Based on this molecular mechanism of action, the catalytic and transport properties of MDR-ABC transporters are significantly different from those of the P-type ATPases.…”

Identification of Putative Binding Sites of P‐glycoprotein Based on its Homology Model

“…[9] Summarizing data obtained by competition with photolabeling drugs Safa proposed seven binding sites that partly interacted with each other: a vinblastine binding site, which also bound verapamil and cyclosporine A; a taxol binding site; a binding site for dihydropyridine type calcium channel blockers; a binding site for bepridil, prenylamine, and megesterol acetate; for flupentixol; for prazosinlike structures; and Hoechst 33342. [10] Loo and Clarke reported many results from cross-linking experiments on the interaction and transport characterization of P-gp. [11][12][13][14] Differences in the cross-linking patterns observed upon binding of different drugs led them to suggest that P-gp could accommodate varying substrates through an induced-fit mechanism.…”

Insight into Pleiotropic Drug Resistance ATP-binding Cassette Pump Drug Transport through Mutagenesis of Cdr1p Transmembrane Domains*

“…Two distinct substrate-binding sites, H (Hoechst 33342 binding site) and R (Rhodamine 123 binding site), have been pharmacologically defined for P-glycoprotein (19). Competition experiments subsequently suggested that P-glycoprotein could contain at least seven different drug-binding sites (20). The crystal structures of mouse and nematode P-glycoprotein, together with biochemical data, indicate that these proteins contain a large internal binding cavity that can accommodate structurally unrelated compounds of different sizes and shapes (21,22).…”