BCRP/ABCG2 levels account for the resistance to topoisomerase I inhibitors and reversal effects by gefitinib in non-small cell lung cancer

Purpose: Breast cancer resistance protein (BCRP) confers resistance against topoisomerase I inhibitors in cancer cells. Very recently, we reported that gefitinib reverses BCRP-mediated drug resistance by direct inhibition. However, it remains undetermined how much BCRP contributes to the resistance to topoisomerase I inhibitors in non-small cell lung cancer (NSCLC). The present study was designed to examine whether BCRP levels in NSCLC cells are correlated with the resistance to topoisomerase I inhibitors and the reversal effect by gefitinib. Methods: BCRP levels and its function were evaluated by Western blotting and flowcytometry, respectively. Gefitinib-insensitive NSCLC cells expressed various levels of BCRP, which were closely correlated not only with the IC50 values of SN-38 (r=0.874, P < 0.05) and those of topotecan (r=0.968, P < 0.001), but also with the reversal effects of 1 mu M gefitinib on SN-38 resistance (r=0.956, P < 0.001) and topotecan resistance (r=0.977, P=0.0001). Results: BCRP levels accounted for between 80 and 90% of the variation in the resistance to topoisomerase I inhibitors and the reversal effects by gefitinib. Also, gefitinib increased intracellular topotecan accumulation in proportion to the BCRP levels. Conclusions: These findings suggest that BCRP is the most important molecule responsible for topoisomerase I inhibitor resistance, and that the development of BCRP inhibitors is an effective approach for overcoming this resistance. In addition, the examination of BCRP levels in NSCLC tissues may identify an optimal patient population for treatment with topoisomerase I inhibitors alone or in combination with BCRP inhibitors.

目的：乳腺癌耐药蛋白（BCRP）使癌细胞对拓扑异构酶I抑制剂产生耐药性。最近，我们报道吉非替尼通过直接抑制逆转BCRP介导的耐药性。然而，在非小细胞肺癌（NSCLC）中，BCRP对拓扑异构酶I抑制剂耐药性的贡献程度仍未确定。本研究旨在检测NSCLC细胞中的BCRP水平是否与对拓扑异构酶I抑制剂的耐药性以及吉非替尼的逆转作用相关。 方法：分别通过蛋白质印迹法和流式细胞术评估BCRP水平及其功能。对吉非替尼不敏感的NSCLC细胞表达不同水平的BCRP，其不仅与SN - 38的半数抑制浓度（IC50）值（r = 0.874，P < 0.05）和拓扑替康的IC50值（r = 0.968，P < 0.001）密切相关，还与1μM吉非替尼对SN - 38耐药性的逆转作用（r = 0.956，P < 0.001）和对拓扑替康耐药性的逆转作用（r = 0.977，P = 0.0001）密切相关。 结果：BCRP水平在对拓扑异构酶I抑制剂的耐药性以及吉非替尼的逆转作用的变异中占80% - 90%。此外，吉非替尼使细胞内拓扑替康的蓄积量与BCRP水平成比例增加。 结论：这些发现表明BCRP是导致拓扑异构酶I抑制剂耐药的最重要分子，开发BCRP抑制剂是克服这种耐药性的有效方法。此外，检测NSCLC组织中的BCRP水平可能确定适合单独使用拓扑异构酶I抑制剂或与BCRP抑制剂联合治疗的最佳患者人群。