The role of epithelial-mesenchymal transition drivers ZEB1 and ZEB2 in mediating docetaxel-resistant prostate cancer

Docetaxel is the main treatment for advanced castration-resistant prostate cancer; however, resistance eventually occurs. The development of intratumoral drug-resistant subpopulations possessing a cancer stem cell (CSC) morphology is an emerging mechanism of docetaxel resistance, a process driven by epithelial-mesenchymal transition (EMT). This study characterised EMT in docetaxel-resistant sublines through increased invasion, MMP-1 production and ZEB1 and ZEB2 expression. We also present evidence for differential EMT across PC-3 and DU145 in vitro resistance models as characterised by differential migration, cell colony scattering and susceptibility to the CSC inhibitor salinomycin. siRNA manipulation of ZEB1 and ZEB2 in PC-3 and DU145 docetaxel-resistant sublines identified ZEB1, through its transcriptional repression of E-cadherin, to be a driver of both EMT and docetaxel resistance. The clinical relevance of ZEB1 was also determined through immunohistochemical tissue microarray assessment, revealing significantly increased ZEB1 expression in prostate tumours following docetaxel treatment. This study presents evidence for a role of ZEB1, through its transcriptional repression of E-cadherin to be a driver of both EMT and docetaxel resistance in docetaxel-resistant prostate cancer. In addition, this study highlights the heterogeneity of prostate cancer and in turn emphasises the complexity of the clinical management of docetaxel-resistant prostate cancer.