BACKGROUND

Understanding the mechanisms of drug resistance to epidermal growth factor receptor tyrosine kinase inhibitor (EGFR TKI) is essential to develop novel chemotherapies for non-small cell lung cancer (NSCLC). Therefore, we analyzed the expression and function of ATP-binding cassette (ABC) transporters in EGFR TKI-resistant NSCLC.

METHODS

In three newly established AG1478-resistant NSCLC cell lines, we evaluated the expression profile of ABC transporters and genotyping of ABCG2 by real-time polymerase chain reaction and elucidated their function by Hoechst dye efflux analyses. The growth-inhibitory effect of the topoisomerase I inhibitor Hoechst 33342, which is extruded by ABCG2, was also investigated in these cells using 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium assay.

RESULTS

In AG1478-resistant cells, significantly less ABCG2 was expressed, and the ratios of the cells with a strong ability to extrude Hoechst dye were remarkably smaller than in the parent cells. Because of the ABCG2 downregulation and loss of function due to C421A/C421A homozygosity, PC-14AG50R was thus considered to be more sensitive to Hoechst 33342 than the parental cells. All AG1478-resistant cells were more sensitive to the combination of Hoechst 33342 and AG1478 than to single agent.

CONCLUSIONS

Resistance to EGFR TKI in NSCLC is associated with the downregulation of ABCG2 expression. A topoisomerase I inhibitor alone or in combination with EGFR TKI might offer a promising strategy for treating NSCLC that is resistant to EGFR TKI.