Multiple mechanisms underlying acquired resistance to taxanes in selected docetaxel-resistant MCF-7 breast cancer cells.
BACKGROUND
Chemoresistance is a major factor involved in a poor response and reduced overall survival in patients with advanced breast cancer. Although extensive studies have been carried out to understand the mechanisms of chemoresistance, many questions remain unanswered.


METHODS
In this research, we used two isogenic MCF-7 breast cancer cell lines selected for resistance to doxorubicin (MCF-7DOX) or docetaxel (MCF-7TXT) and the wild type parental cell line (MCF-7CC) to study mechanisms underlying acquired resistance to taxanes in MCF-7TXT cells. Cytotoxicity assay, immunoblotting, indirect immunofluorescence and live imaging were used to study the drug resistance, the expression levels of drug transporters and various tubulin isoforms, apoptosis, microtubule formation, and microtubule dynamics.


RESULTS
MCF-7TXT cells were cross resistant to paclitaxel, but not to doxorubicin. MCF-7DOX cells were not cross-resistant to taxanes. We also showed that multiple mechanisms are involved in the resistance to taxanes in MCF-7TXT cells. Firstly, MCF-7TXT cells express higher level of ABCB1. Secondly, the microtubule dynamics of MCF-7TXT cells are weak and insensitive to the docetaxel treatment, which may partially explain why docetaxel is less effective in inducing M-phase arrest and apoptosis in MCF-7TXT cells in comparison with MCF-7CC cells. Moreover, MCF-7TXT cells express relatively higher levels of β2- and β4-tubulin and relatively lower levels of β3-tubulin than both MCF-7CC and MCF-7DOX cells. The subcellular localization of various β-tubulin isoforms in MCF-7TXT cells is also different from that in MCF-7CC and MCF-7DOX cells.


CONCLUSIONS
Multiple mechanisms are involved in the resistance to taxanes in MCF-7TXT cells. The high expression level of ABCB1, the specific composition and localization of β-tubulin isoforms, the weak microtubule dynamics and its insensitivity to docetaxel may all contribute to the acquired resistance of MCF-7TXT cells to taxanes.
Harris
H
Wang
The
T
Vo
Ali
A
Hajar
Sarah
S
Li
Xinmei
X
Chen
Amadeo M
AM
Parissenti
David N
DN
Brindley
Department of Medical Genetics, University of Alberta, Edmonton, AB T6G 2H7, Canada. zhixiang.wang@ualberta.ca.
Zhixiang
Z
Wang
D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D001943:Breast Neoplasms / Q000378:metabolism* / Q000473:pathology; D000077143:Docetaxel; D004305:Dose-Response Relationship, Drug; D004317:Doxorubicin / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm; D005260:Female; D006801:Humans; D059566:M Phase Cell Cycle Checkpoints / Q000187:drug effects; D061986:MCF-7 Cells; D008870:Microtubules / Q000187:drug effects / Q000378:metabolism; D017239:Paclitaxel / Q000494:pharmacology; D020033:Protein Isoforms; D043823:Taxoids / Q000494:pharmacology*; D013997:Time Factors; D014404:Tubulin / Q000378:metabolism; D050257:Tubulin Modulators / Q000494:pharmacology*
C513055:ABCB1 protein, human; D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000972:Antineoplastic Agents, Phytogenic; D020033:Protein Isoforms; D043823:Taxoids; D014404:Tubulin; D050257:Tubulin Modulators; D000077143:Docetaxel; D004317:Doxorubicin; D017239:Paclitaxel