In recent years, a number of TKIs (tyrosine kinase inhibitors) targeting epidermal
growth factor receptor (EGFR) family have been synthesized and some have been approved
for clinical treatment of cancer by the FDA. We recently reported a new pharmacological
action of the 4-anilinoquinazoline derived EGFR TKIs, such as lapatinib (Tykerb) and
erlotinib (Tarceva), which significantly affect the drug resistance patterns in cells
expressing the multidrug resistance (MDR) phenotype. Previously, we showed that lapatinib
and erlotinib could inhibit the drug efflux function of P-glycoprotein (P-gp, ABCB1)
and ABCG2 transporters. In this study, we determined if these TKIs have the potential
to reverse MDR due to the presence of the multidrug resistance protein 7 (MRP7, ABCC10).
Our results showed that lapatinib and erlotinib dose-dependently enhanced the sensitivity
of MRP7-transfected HEK293 cells to several established MRP7 substrates, specifically
docetaxel, paclitaxel, vinblastine and vinorelbine, whereas there was no or a less
effect on the control vector transfected HEK293 cells. [(3)H]-paclitaxel accumulation
and efflux studies demonstrated that lapatinib and erlotinib increased the intracellular
accumulation of [(3)H]-paclitaxel and inhibited the efflux of [(3)H]-paclitaxel from
MRP7-transfected cells but not in the control cell line. Lapatinib is a more potent
inhibitor of MRP7 than erlotinib. In addition, the Western blot analysis revealed
that both lapatinib and erlotinib did not significantly affect MRP7 expression. We
conclude that the EGFR TKIs, lapatinib and erlotinib reverse MRP7-mediated MDR through
inhibition of the drug efflux function, suggesting that an EGFR TKI based combinational
therapy may be applicable for chemotherapeutic practice clinically.