Abstract
Background:ABCB1 expression is uncommon in ovarian cancers in the clinical setting so we investigated non-MDR mechanisms of resistance to taxanes.Methods:We established eight taxane-resistant variants from the human ovarian carcinoma cell lines A2780/1A9, ES-2, MES-OV and OVCAR-3 by selection with paclitaxel or docetaxel, with counter-selection by the transport inhibitor valspodar.Results:Non-MDR taxane resistance was associated with reduced intracellular taxane content compared to parental controls, and cross-resistance to other microtubule stabilising drugs. Collateral sensitivity to depolymerising agents (vinca alkaloids and colchicine) was observed with increased intracellular vinblastine. These variants exhibited marked decreases in basal tubulin polymer and in tubulin polymerisation in response to taxane exposure. TUBB3 content was increased in 6 of the 8 variants. We profiled gene expression of the parental lines and resistant variants, and identified a transcriptomic signature with two highly significant networks built around FN1 and CDKN1A that are associated with cell adhesion, cell-to-cell signalling, and cell cycle regulation. miR-200 family members miR-200b and miR-200c were downregulated in resistant cells, associated with epithelial to mesenchymal transition (EMT), with increased VIM, FN1, MMP2 and/or MMP9.Conclusions:These alterations may serve as biomarkers for predicting taxane effectiveness in ovarian cancer and should be considered as therapeutic targets.
Highlights
ABCB1 expression is uncommon in ovarian cancers in the clinical setting so we investigated non-MDR mechanisms of resistance to taxanes
P-gp confers a high level of cellular resistance to many anticancer drugs, many other drug resistance mechanisms are thought to play a role in determining cellular response to taxanes including alterations of microtubule structure and dynamics, tubulin isotypes, and factors that regulate programmed cell death
We have established two sets of taxane-resistant variants, one set selected in taxanes alone which express ABCB1/P-gp (Wang et al, 2006), and another set of non-MDR variants exposed to taxanes in the presence of the P-gp inhibitor valspodar
Summary
We established eight taxane-resistant variants from the human ovarian carcinoma cell lines A2780/1A9, ES-2, MES-OV and OVCAR-3 by selection with paclitaxel or docetaxel, with counter-selection by the transport inhibitor valspodar. Four lines (3 serous: A2780/1A9, MES-OV and OVCAR-3; and one clear cell: ES-2) were chosen as parental lines for the generation of taxane-resistant variants, and cultured as described previously (Wang et al, 2006). These lines were chosen because they were the most sensitive to taxanes, did not express high levels of ABCB1, and grew readily in vitro (doubling times of p48 h in standard tissue culture media). The 3 parental serous lines did not express P-gp, and the clear cell line expressed very low but detectable levels
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