Abstract 5415: Histone deacetylase inhibitors and 15-deoxy-Δ12,14-prostaglandin J2 synergistically induce apoptosis

Abstract

Abstract The histone deacetylase inhibitors (HDIs) valproic acid (VPA) and suberoylanilide hydroxamic acid (SAHA, vorinostat) are used clinically for the treatment of epilepsy and cutaneous T-cell lymphoma, respectively. HDIs have been shown to be more effectively utilized in combination with other agents despite the promising anti-tumor effect of HDIs alone. Therefore, additional mechanism-based therapeutic strategies for use of HDIs in combination with other agents should be investigated to overcome resistance to HDIs or to increase the efficacy of HDIs. The natural endogenous ligand of peroxisome proliferator-activated receptor γ (PPARγ) 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2) is a member of cyclopentenone prostaglandins and known to be a potent anti-neoplastic agent. Thus, we examined whether VPA or SAHA in combination with 15d-PGJ2 could show synergistic anti-tumor activitiy in colon cancer DLD-1 cells. Cell viability was determined using a Cell Counting Kit-8 assay. Apoptosis and reactive oxygen species (ROS) generation were determined using flow cytometry analysis. Western blotting and real-time RT-PCR analysis were carried out to investigate the expressions of apoptosis-related molecules. Small interfering RNA or transient transfection with plasmids was used for gene silencing, gene overexpression or luciferase assays. Mice bearing DLD-1 xenograft were divided into 4 groups (n=5) and injected everyday (i.p.) with diluent, VPA (100 mg/kg), 15d-PGJ2 (5 mg/kg) or a combination for 25 days. Cotreatment with VPA or SAHA at clinically achievable concentrations and 15d-PGJ2 synergistically induced cell death and drastically caused caspase-dependent apoptosis in DLD-1 cells. The apoptosis induced by VPA/15d-PGJ2 cotreatment was due to alterations of apoptosis-related genes such as an antiapoptotic Bcl-2 family member Bcl-XL, X-chromosome-linked inhibitor of apoptosis (XIAP), C/EBP homologous protein (CHOP) and death receptor 5 (DR5) via ROS generation, subsequent endoplasmic reticulum stress and/or histone deacetylase inhibition. Moreover, VPA/15d-PGJ2 cotreatment induced ROS-dependent apoptosis in other malignant tumor cells and was more effective than a VPA or 15d-PGJ2 monotherapy in vivo. These results suggest that cotreatment with the clinically relevant HDIs and 15d-PGJ2 may warrant clinical investigation as a rational combination therapy against a broad spectrum of malignant tumors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5415.