Targeting hormone-resistant breast cancer cells with docetaxel:a look inside the resistance

Aim:The study aims to analyze the effect of long-term incubation of ERα-positive MCF7 breast cancer cells with 4-hydroxytamoxifen(HT)on their sensitivity to tubulin polymerization inhibitor docetaxel.Methods:The analysis of cell viability was performed by the MTT method.The expression of signaling proteins was analyzed by immunoblotting and flow cytometry.ERαactivity was evaluated by gene reporter assay.To establish hormone-resistant subline MCF7,breast cancer cells were treated with 4-hydroxytamoxifen for 12 months.Results:The developed MCF7/HT subline has lost sensitivity to 4-hydroxytamoxifen,and the resistance index was 2.Increased Akt activity(2.2-fold)and decreased ERαexpression(1.5-fold)were revealed in MCF7/HT cells.The activity of the estrogen receptorαwas reduced(1.5-fold)in MCF7/HT.Evaluation of class Ⅲβ-tubulin expression(TUBB3),a marker associated with metastasis,revealed the following trends:higher expression of TUBB3 was detected in triple-negative breast cancer MDA-MB-231 cells compared to hormone-responsive MCF7 cells(P<0.05).The lowest expression of TUBB3 was found in hormone-resistant MCF7/HT cells(MCF7/HT<MCF7<MDA-MB-231,approximately 1:2:4).High TUBB3 expression strongly correlated with docetaxel resistance:IC_(50)value of docetaxel for MDA-MB-231 cells was greater than that for MCF7 cells,whereas resistant MCF7/HT cells were the most sensitive to the drug.The accumulation of cleaved PARP(a 1.6-fold increase)and Bcl-2 downregulation(1.8-fold)were more pronounced in docetaxel-treated resistant cells(P<0.05).The expression of cyclin D1 decreased(2.8-fold)only in resistant cells after 4 nM docetaxel treatment,while this marker was unchanged in parental MCF7 breast cancer cells.Conclusion:Further development of taxane-based chemotherapy for hormone-resistant cancer looks highly promising,especially for cancers with low TUBB3 expression.