The effect of ABCG2 V12M, Q141K and Q126X, known functional variants in vitro, on the disposition of lamivudine

Abstract

Aims: To evaluate the effects of three ABCG2 variants (Q141K, V12M and Q126X), which are known to have altered transport properties in vitro, on the disposition of lamivudine in healthy subjects.

Methods: To evaluate whether lamivudine is a substrate of ABCG2, intracellular accumulation and vectorial transport of 3H-lamivudine were determined in MDCK-ABCG2 cells. The pharmacokinetic parameters of lamivudine were compared among subjects with four different ABCG2 genotypes, including wild type (seven subjects), K141/K141 (six subjects), Q126/Stop126 (four subjects) and M12/M12 (five subjects) after a single oral dose of 100 mg lamivudine.

Results: The intracellular accumulation of lamivudine in MDCK-ABCG2 cells was significantly lower than that in MDCK-mock cells, but fumitremorgin C reversed the intracellular lamivudine concentration to that of MDCK-mock cells. The ABCG2-mediated transport of lamivudine was saturable and the values of Km and Vmax were 216.5 +/- 58 microm and 20.42 +/- 2.9 nmol h(-1) per 10(6) cells, respectively. After lamivudine administration to healthy subjects, the AUC of lamivudine showed no difference among subjects with different ABCG2 genotypes; 2480 +/- 502, 2207 +/- 1019, 2422 +/- 239, 2552 +/- 698 ng h(-1) ml(-1) for wild type, K141/K141, Q126/Stop126 and M12/M12 genotype, respectively (P = 0.85). The estimated 95% confidence intervals for the mean difference between K141/K141, Q126/Stop126, M12/M12 and wild as reference were (-1053, 507), (-555, 439) and (-552, 696), respectively. No other pharmacokinetic parameters were estimated to be significantly different among four different ABCG2 genotypes tested.

Conclusions: Lamivudine appeared to be a substrate of ABCG2 in vitro, but the disposition of lamivudine was not significantly influenced by known in vitro functional variants of ABCG2, Q141K, V12M and Q126X in healthy subjects.

Figure 1

(A) Comparison of intracellular accumulation of ³H-lamivudine in the MCDK-mock cells and ABCG2-overexpressing MDCK (MDCK-ABCG2) cells. Cells were incubated for 30 min at 37°C with ³H-lamivudine applied from the apical sides of MDCK-mock cells or MDCK-ABCG2 cell monolayers in the absence or presence of 10 µm fumitremorgin C (FTC), the selective inhibitor of ABCG2. Data are presented as mean ± SD of three preparations. *P < 0.01. (B) Time course of apical to basal (○) and basal to apical (•) transport of 1 µm³H-lamivudine across MDCK-ABCG2 cell monolayer. Each data point represents the mean ± SD of four independent experiments. (C) Concentration-dependent basal to apical transport of lamivudine (1–1000 µm) across the MDCK-ABCG2 cell monolayer. Each data point represents the mean ± SD of four independent experiments

Figure 2

Mean concentration–time profiles of lamivudine after a single oral administration of 100 mg lamivudine in subjects with wild genotype (○), Lys141/Lys141 (▪), Gln126/Stop126 (▵), and Met12/Met12 () variant of ABCG2

Figure 3

The peak plasma drug concentration (C_max) (A), the area under the plasma drug concentration–time curve (AUC) (B) and the total clearance (CL/F) (C) of subjects with wild-type and three ABCG2 functional variants after oral administration of 100 mg lamivudine. Each symbol indicates the individual pharmacokinetic parameter of subjects with four different genotypes of ABCG2. Vertical lines with horizontal bar indicate mean ± SD