ER−/ER+ breast cancer cell lines exhibited different resistance to paclitaxel through pulse selection

In this study, we established two PTX-resistant breast cancer cell lines, 231 TIM10 and MCF-7 TIM10, from ER-negative MDA-MB-231 cells and ER-positive MCF-7 cells by pulse selection, respectively. We found that 231 TIM10 variants acquired higher drug resistance than MCF-7 TIM10 variants by the pulse selection, although ER-positive MCF-7 cells were not as sensitive as ER-negative MDA-MB-231 to the initial pulses with PTX. 231 TIM10 had 11.9-fold greater resistance (RI = 11.9) than the parental MDA-MB-231 cells, while MCF-7 TIM10 got 5.5-fold resistance (RI = 5.5) when compared with the parental MCF-7 cells. In the presence of 5nM PTX, 231 TIM10 cells formed colonies, but no colony formed when MCF-7 TIM10 cells were cultured in the same condition. These data have two implications. First, the ER expression state might be an important determinant for the response of breast cancer cells to paclitaxel treatment. Second, ER-negative and ER-positive breast cancer cells develop drug-resistance phenotype with distinctive mechanisms. Our work not only established useful models for studying the paclitaxel resistance but also provides interesting clues to understand the mechanisms underlying the drug resistance of ER-negative and ER-positive breast cancer cells.