Cellular pharmacokinetic aspects of reversal effect of itraconazole on P-glycoprotein-mediated resistance of anticancer drugs

The reversal effect of itraconazole on P-glycoprotein (P-gp)-mediated resis tance of vinblastine, daunorubicin and doxorubicin was analyzed from a cell ular pharmacokinetic point of view, namely by [H-3]azidopine photoaffinity labeling, intracellular accumulation and transcellular transport experiment s. The LLC-GA5-COL150 cells, which expressed human P-gp selectively on the apical membrane due to transfection of MDR1 cDNA into the porcine kidney ep ithelial cells (LLC-PK1 cells), was used here, since this cell line constru cts the monolayer with tight junction, being able to characterize the cellu lar pharmacokinetics. In LLC-GA5-COL150 cells, itraconazole caused a revers al from resistance as shown by a growth inhibition assay. [H-3]Azidopine ph otoaffinity labeling demonstrated that itraconazole, vinblastine, daunorubi cin and doxorubicin showed higher binding ability for P-gp compared with di goxin, suggesting the following results were via P-gp, The intracellular ac cumulation of [H-3]vinblastine, [H-3]daunorubicin and [C-14]doxorubicin aft er their application on the basal and apical sides was increased by itracon azole, These changes H ere similar to the dose modifying factors determined by the growth inhibition assay, However, their basal-to-apical transport w as hardly affected by itraconazole, and this was explained by the fact that itraconazole inhibited P-gp, and subsequently increased their intracellula r concentration and then the non-P-gp mediated transport from the intracell ular space to apical side. The apical-to-basal transport of [H-3]vinblastin e, [H-3]daunorubicin and [C-14]doxorubicin was increased by itraconazole, a nd this was reasonably explained by the inhibition of P-gp, and partly also by the increase of their intracellular concentration I ia the inhibition o f P-gp.