Background. Although paclitaxel is used for hormone-resistant prostate cancer, relapse

These observations suggest that tranilast may be a useful therapeutic agent for treatment of HRPC via the direct inhibitory effect on cancer cells and suppression of TGF-beta1-associated osteoblastic changes in bone metastasis.

BACKGROUNDRecently, we established paclitaxel‐resistant prostate cancer cell lines (PC‐3‐TxR and DU145‐TxR). To determine the mechanisms of paclitaxel resistance in PC‐3‐TxR cells, we compared the gene expression profiles between PC‐3 and PC‐3‐TxR cells. Our results indicated that expression of the C‐terminal tensin like protein (CTEN, tensin 4) gene was down‐regulated by 10‐fold in PC‐3‐TxR cells. We investigated the possibility that CTEN overexpression restores paclitaxel sensitivity.METHODSWe investigated how knockdown and overexpression of CTEN in androgen‐independent cell lines affect paclitaxel sensitivity by colony formation assay and growth inhibition assay. To determine the mechanisms by which CTEN affects paclitaxel sensitivity, we investigated the relationships between CTEN and F‐actin or epidermal growth factor receptor (EGFR) in PC‐3 cells. We also examined the association between expression of CTEN and grade of prostate cancer by immunohistochemistry using tissue microarray analysis.RESULTSDown‐regulation of CTEN, which is located in the cytoskeleton, played an important role in paclitaxel resistance in PC‐3‐TxR cells. Knockdown of CTEN expression in PC‐3 cells induced paclitaxel resistance. Overexpression of CTEN in PC‐3‐TxR and DU145‐TxR cells restored paclitaxel sensitivity. CTEN expression was inversely correlated with F‐actin and EGFR expression. Then knockdown of actin and EGFR in PC‐3‐TxR cells recovered paclitaxel sensitivity, indicating that CTEN down‐regulation mediates paclitaxel resistance through elevation of EGFR and actin expression. Moreover, CTEN expression was inversely correlated with Gleason score.CONCLUSIONSThese results strongly suggested that CTEN plays an important role in paclitaxel sensitivity and that CTEN expression level may be a prognostic predictive factor for PCa patients. Prostate 70: 48–60, 2010. © 2009 Wiley‐Liss, Inc.