Pharmacological interplay between breast cancerresistance protein and gefitinib in epidermalgrowth factor receptor signaling

Background: It has been previously shown that gefitinib reverses breast cancer resistance protein (BCRP)-mediated drug resistance. Here, the impact of BCRP on gefitinib-mediated inhibition in epidermal growth factor receptor (EGFR) signaling is evaluated. Materials and Methods: Sensitivity to gefitinib was determined by growth inhibition assay, and intracellular gefitinib levels were measured with HPLC. Western blotting was performed to detect EGFR signaling molecules. Results: BCRP reduced intracellular gefitinib levels and attenuated inhibitory activities of gefitinib to EGF-dependent EGFR signalings including downstream MAPK and Akt pathways in gefitinib- sensitive PC-9 cells. However, gefitinib did not inhibit MAPK and Akt signalings in KB-3-1 and HCT-116 cells, and BCRP- mediated gefitinib-resistance shown in PC-9 cells was not observed in gefitinib-insensitive KB-3-1 and HCT-116 cells. Conclusion: BCRP transports gefitinib and suppresses its inhibitory effects on EGFR phosphorylation. However, effects of BCRP on gefitinib activity in the EGFR signaling and on gefitinib-resistance were limited in the gefitinib-sensitive cells only.