Tubulin-β-III overexpression by uterine serous carcinomas is a marker for poor overall survival after platinum/taxane chemotherapy and sensitivity to epothilones

Abstract

BACKGROUND Uterine serous carcinoma (USC) is a subtype of endometrial cancer associated with chemoresistance and poor outcome. Overexpression of tubulin-β-III and p-glycoprotein has been linked to paclitaxel resistance in many cancers but has been undercharacterized among USCs. Epothilones have demonstrated activity in certain paclitaxel-resistant malignancies. In this study, relationships are clarified, in USCs relative to ovarian serous carcinomas (OSCs), between tubulin-β-III and p-glycoprotein expression, clinical outcome, and in vitro chemoresponsiveness to epothilone B, ixabepilone, and paclitaxel. METHODS Tubulin-β-III and p-glycoprotein were quantified by real-time polymerase chain reaction in 48 fresh-frozen tissue samples and 13 cell lines. Copy number was correlated with immunohistochemistry and overall survival. Median inhibitory concentration (IC50) was determined using viability and metabolic assays. Impact of tubulin-β-III knockdown on IC50 was assessed with small interfering RNAs. RESULTS USC overexpressed tubulin-β-III but not p-glycoprotein relative to OSC in both fresh-frozen tissues (552.9 ± 106.7 versus 202.0 ± 43.99, P =.01) and cell lines (1701.0 ± 376.4 versus 645.1 ± 157.9, P =.02). Tubulin-β-III immunohistochemistry reflected quantitative real-time polymerase chain reaction copy number and overexpression stratified patients by overall survival (copy number ≤ 400: 615 days; copy number > 400: 165 days, P =.049); p-glycoprotein did not predict clinical outcome. USCs remained exquisitely sensitive to patupilone in vitro despite tubulin-β-III overexpression (IC50,USC 0.245 ± 0.11 nM versus IC 50,OSC 1.01 ± 0.13 nM, P =.006). CONCLUSIONS Tubulin-β-III overexpression in USCs discriminates poor prognosis, serves as a marker for sensitivity to epothilones, and may contribute to paclitaxel resistance. Immunohistochemistry reliably identifies tumors with overexpression of tubulin-β-III, and a subset of individuals likely to respond to patupilone and ixabepilone. Epothilones warrant clinical investigation for treatment of USCs. © 2013 American Cancer Society.