In vitro experimental system for evaluating inhibitory effect of investigational drugs on P‐glycoprotein‐mediated transcellular transport of tacrolimus (FK506)

In this study, an in vitro experimental system for evaluating the inhibitory effect of investigational drugs on the P-glycoprotein (P-gp, MDR1)-mediated transport of tacrolimus (FK506) was developed using LLC-PK1-MDR1 and LLC-PK1 wild-type (control) cells. The amount of tacrolimus (concentrations: 1 and 5 μm) transported into P-gp-expressing and control cells increased with time in both the apical-to-basal and basal-to-apical directions at incubation times ranging from 40 min to 2 h. The corrected apparent permeability (Papp) ratio, obtained by dividing the Papp ratio in P-gp-expressing cells by that in the control cells, ranged from 2.6 to 5.3, showing significant differences in the transport of tacrolimus between the P-gp-expressing cells and the control cells. This system was then subsequently used to examine the P-gp transport of tacrolimus in the presence of verapamil (30 μm), a model inhibitor for P-gp-mediated transport activity. The corrected Papp ratios in the absence and presence of verapamil were 6.9 and 0.8, respectively. Data derived in the present study suggest that our developed system has the ability to detect a sufficient difference in the P-gp transport of tacrolimus between P-gp-expressing and control cells, and we therefore believe our system to be suitable for use in evaluating the inhibitory effects of investigational drugs on the P-gp-mediated transport of tacrolimus. Copyright © 2013 John Wiley & Sons, Ltd.