Reversion of Epithelial–mesenchymal Transition (EMT) As a Mechanism of Action of Cabazitazel in Castration-Resistant Prostate Cancer

Background: The epithelial to mesenchymal transition (EMT) process is involved in de novo and acquired resistance to hormone-therapy and docetaxel (D) in metastatic castration resistant prostate cancer (mCRPC). Cabazitaxel (CZ) it active after D-progression and prior second-line hormone-therapies. Here we investigated the differences between CZ and D resistance related to the EMT phenotype acquisition and its potential clinical value. Methods: D and CZ resistant (R) cells lines were derived from parental DU-145 and PC-3. Cell line Molecular characterization was performed using Affymetrix GeneChip Human Gene 2.0 ST microarrays. Gene expression analysis was performed by quantitative real-time PCR in cell lines and in FFPE tumors from mCRPC treated with CZ. Protein levels were measured by Western Blot. Cell migration was assessed using the Cultrex cell migration kit (Trevigen) andcell viability by MTT assay. Gene inhibitory experiments were performed by siRNA transfection. Results: Microarray data, pathway analysis and EMT gene data in silico validation showed that EMT occurred in both D-R and CZ-R cells, being ZEB1 one of the top deregulated genes. However, we identified 55 EMT genes differentially deregulated between D-R and CZ-R vs parental cells. Among them CDH1, and ESRP1 (lost in D-R but maintained in Cz-R), and AXL (overexpressed in D-R and downregulated in CZ-R). D-R cells presented a more pronounced mesenchymal phenotype (morphology, higher migration and lower proliferation rates, higher expression of EMT markers at mRNA and protein level) than CZ-R. Dose-response experiments showed that CZ induced CDH1 and ESRP1 expression in different cell lines models. ZEB1 inhibition reverted D- resistance, but not CZ-resistance, and restored ESRP1 expression in D-R cells. In 29 CRPC patients treated with CZ, low level of expression of ESRP-1 in tumor correlated with a better PSA-PFS (6.2 vs 2.7 months, P = 0.006; HR: 0.31 P = 0.009) and radiological PFS (7.9 vs 3.3 months, P = 0.047; HR: 0.39 P = 0.055) and the EMT phenotype was not associated to resistance. Conclusions: The reversion of EMT phenotype, trough induction of CDH1 and ESRP1, may be a novel mechanism of action of CZ, which may explain its activity in patients progressing to prior therapies in CPRC. Legal entity responsible for the study: Hospital Clínic of Barcelona Funding: Sanofi-Aventis Disclosure: All authors have declared no conflicts of interest.