Functional characterization of SNP and haplotype of human MDR1 gene using a vaccinia virus expression system

Abstract

Background Many studies have shown that P-glycoprotein (P-gp) can alter the absorption, distribution, and excretion of many drugs. There has been much interest in whether common coding polymorphisms of MDR1 can affect the function of P-gp and/or whether polymorphic variants are linked to altered drug pharmacokinetics. Methods We have introduced three known MDR1 coding SNPs (C1236T, G2677T, C3435T) and four possible haplotypes (C1236T-G2677T, C1236T-C3435T, G2677T-C3435T, C1236T-G2677T-C3435T) by site-directed mutagenesis to determine if there are changes in expression or function of MDR1 due to polymorphisms. Results Using a vaccinia virus based transient expression system, we showed that HeLa cells stained with the P-gp specific monoclonal antibodies MRK-16 or Western blots and the confocal laser microscope study express similar cell surface expression for the SNP and haplotypes. However, MDR1 wild-type and haplotype showed different patterns using UIC2+Taxol. Furthermore, haplotype which included polymorphisms at positions 1236, 2677 and 3435 exhibited altered function in the presence of P-gp inhibitors such as verapamil or cyclosporine A. Conclusions Common coding SNP in P-gp have little or no effect on overall expression or function. However, haplotype which includes polymorphisms at positions 1236, 2677 and 3435 has an effect on overall function, and on conformational change of MDR1. Clinical Pharmacology & Therapeutics (2005) 77, P24–P24; doi: 10.1016/j.clpt.2004.11.091