Abstract 979: Paclitaxel resistance in prostate cancer: rescue of resistance using HDAC inhibitor SAHA involves apoptosis.

Introduction and Objective: Although Paclitaxel has demonstrated antitumor activity against several cancers, the acquisition of resistance during treatment remains a significant problem. Several potential mechanisms were proposed and the recent studies determined that drug resistance may involve histone H3 acetylation. Histone deacetylases (HDACs) are overexpressed in prostate cancer (PCa) and HDAC inhibitors have greater anti-proliferative activity against prostate and breast cancer models. We have investigated the interaction of the HDAC inhibitors Valproic Acid (VPA) and SAHA (Vorinostat) with Paclitaxel in both susceptible and resistance PCa cell lines. We evaluated anti-proliferative activity, nuclear morphometry, expression of apoptotic genes: Caspases 3 and 9 and Annexin A5, and three keratins (8, 18 and 19) which are involved in cell differentiation. Methods: Four PCa cell lines PC3, PC3-TxR (Paclitaxel resistant), DU145 and DU145-TxR (Paclitaxel resistant) were grown in 96 well & 24 well tissue culture plates. After a day, the cells were exposed to 1.2mM of VPA and 5μM of SAHA for 24 hours followed by treatment with 4.5nM Paclitaxel for 48 hours. WST-1 cytotoxicity assay was performed in the 96 well plates. From the 24 well plates, RNA was isolated and the real-time PCR for expression of specific genes was done using gene specific primers and β-actin (to calculate relative expression). Nuclear morphometry was done in Feulgen stained nuclei using AutoCyteTM Pathology Workstation and QUIC-DNA software. Results: We found after 24hrs treatment: (i) VPA (1.2mM) reversed Paclitaxel resistance only in PC3 cell lines (50%) while (ii) SAHA made all the PCa cell lines more susceptible to Paclitaxel (50-60%). We observed specific changes in DNA ploidy and in nuclear structure in Paclitaxel resistant DU145-TxR cell lines when compared to DU145 cells. Our results showed different patterns of apoptotic and keratin gene expression occurred in DU145 and DU145-TxR cell lines following treatment with SAHA but no significant changes in PC3 and PC3-TxR cell lines. Expressions of Caspase 3, Caspase 9 and Annexin A5 were increased significantly in SAHA treated DU145-TxR cells, and KRT-8 and KRT-19 (keratins) were significantly downregulated in DU145-TxR cell lines irrespective of treatment. Conclusions: Hence, resistance to Paclitaxel can be rescued by HDAC inhibitors VPA and SAHA, but likely by different mechanisms that are yet to be established. Also, altered expression of apoptotic biomarkers, but not keratins shows that the rescue by SAHA involves apoptosis but not epithelial mesenchymal transition. Source of funding: National Cancer Institute of the National Institutes of Health through awards funded under Grant number 1U54CA143868-03 Citation Format: Christhunesa S. Christudass, Karan Sood, David Yeater, Robert W. Veltri. Paclitaxel resistance in prostate cancer: rescue of resistance using HDAC inhibitor SAHA involves apoptosis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 979. doi:10.1158/1538-7445.AM2013-979