This project seeks to examine the role of gp150-180 in multidrug resistance (MDR) and its role in the circumvention of MDR by calcium channel blockers. A major 150-180 kDa Vinca alkaloid (gp150-180) was identified in purified plasma membranes from MDR cells by photoaffinity labeling. Gp150-180 exhibits cross binding specificity for Vinca alkaloids, actinomycin D, anthracycline antibiotics, calcium channel blockers, and calmodulin inhibitors suggesting a central functional role in MDR phenotype and its circumvention. The role of gp150-180 in MDR will be tested by examining the effect of specific drug photolabeling on cellular drug uptake and efflux, and by drug uptake and release using membrane vesicles from MDR cells. the role of this drug acceptor protein in circumventing MDR will be examined by competition experiments using agents previously shown to counteract multidrug resistance. The subcellular distribution of gp150-180 over time will be monitored. For further characterization of drug binding sites and exploring whether gp150-180 possesses multiple drug binding sites, or whether it may be a family of proteins, each with specificity for a distinct class of drugs, the protein will be purified using drug affinity chromatographic methods. The purified gp150-180 will be inserted into planar lipid bilayers for functional reconstitution experiments and analyzing the role of this protein in cellular drug accumulation. The purified gp150-180 will be used to prepare monoclonal antibodies to define plasma membrane orientation and drug binding sites, and to evaluate the possible microheterogeneity of gp150-180. Detailed characterization of drug binding sites of gp150-180 may elucidate some of the underlying mechanisms of multidrug resistance and might lead to the development of new compounds designed to prevent or reverse the development of the multidrug resistant phenotype.

National Institute of Health (NIH)
National Cancer Institute (NCI)
First Independent Research Support & Transition (FIRST) Awards (R29)
Project #
Application #
Study Section
Experimental Therapeutics Subcommittee 1 (ET)
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
University of Chicago
Schools of Medicine
United States
Zip Code
Safa, Ahmad R (2004) Identification and characterization of the binding sites of P-glycoprotein for multidrug resistance-related drugs and modulators. Curr Med Chem Anticancer Agents 4:1-17
Safa, A R (1998) Photoaffinity labels for characterizing drug interaction sites of P-glycoprotein. Methods Enzymol 292:289-307
Cano-Gauci, D F; Seibert, F S; Safa, A R et al. (1995) Selection and characterization of verapamil-resistant multidrug resistant cells. Biochem Biophys Res Commun 209:497-505
Safa, A R; Agresti, M; Bryk, D et al. (1994) N-(p-azido-3-[125I]iodophenethyl)spiperone binds to specific regions of P-glycoprotein and another multidrug binding protein, spiperophilin, in human neuroblastoma cells. Biochemistry 33:256-65
Safa, A R (1993) Photoaffinity labeling of P-glycoprotein in multidrug-resistant cells. Cancer Invest 11:46-56
Sinicrope, F A; Dudeja, P K; Bissonnette, B M et al. (1992) Modulation of P-glycoprotein-mediated drug transport by alterations in lipid fluidity of rat liver canalicular membrane vesicles. J Biol Chem 267:24995-5002
Fleming, G F; Amato, J M; Agresti, M et al. (1992) Megestrol acetate reverses multidrug resistance and interacts with P-glycoprotein. Cancer Chemother Pharmacol 29:445-9
Tamai, I; Safa, A R (1991) Azidopine noncompetitively interacts with vinblastine and cyclosporin A binding to P-glycoprotein in multidrug resistant cells. J Biol Chem 266:16796-800
Samuels, B L; Murray, J L; Cohen, M B et al. (1991) Increased glutathione peroxidase activity in a human sarcoma cell line with inherent doxorubicin resistance. Cancer Res 51:521-7
Tamai, I; Safa, A R (1990) Competitive interaction of cyclosporins with the Vinca alkaloid-binding site of P-glycoprotein in multidrug-resistant cells. J Biol Chem 265:16509-13

Showing the most recent 10 out of 17 publications