MDR1 C2005T polymorphism changes substrate specificity

Abstract

The current study is to determine the alterations of efflux transport activity to Rh123 and sensitivity to anticancer agents mediated by a MDR1 C2005T polymorphism. Expressions of mRNA and protein of MDR1 were measured by real-time PCR and immunoblotting, respectively, and localization of P-glycoprotein (P-gp) by confocal microscopy. Cell cytotoxicity and efflux transport activity were determined by MTT and Rh123 transepithelial permeability assay, respectively. MDR1 C2005T polymorphism did not affect the expression level of the MDR1 mRNA and protein and had no effect on the trafficking of P-gp to plasma membrane. A cytotoxicity study showed that MDR1wt and MDR1 (2005T) cells exhibited similar resistance, as measured by IC(50) values, to vinblastine (30.3 +/- 2.5 vs. 32.5 +/- 1.7 nM) and vincristine (104.1 +/- 1.9 vs. 110.3 +/- 3.5 nM). However, MDR1 (2005T) cells were less resistant to paclitaxel (28.2 +/- 2.1 vs. 91.8 +/- 3.5 nM; P < 0.05) and etoposide (119.7 +/- 6.5 vs. 546.8 +/- 9.5 nM; P < 0.05). The apparent transepithelial permeability ratios of Rh123 in MDR1 (wt) and MDR1 (2005T) cells were 2.12 +/- 0.46 and 3.64 +/- 0.78 (P < 0.05), respectively. The MDR1 C2005T polymorphism alters the transepithelial permeability of a fluorescent substrate and sensitivity to select cytotoxic agents, which may influence drug disposition and the therapeutic efficacy of some P-gp substrates.