Abstract 5162: Effects of combined epigenetic therapy with histone methyltransferase EZH2 inhibitor 3-deazaneplanocin and histone deacetylase inhibitor SAHA on non-small cell lung cancer cells

Abstract

Abstract [Background] EZH2, a polycomb group protein, has histone methyltransferase activity, and is involved in malignant transformation of several cancers. We have previously shown that an EZH2 inhibitor, DZNep, inhibits growth of non-small cell lung cancer(NSCLC) cell lines via G1 arrest and apoptosis. Recently, cotreatment with DZNep and an histone deacetylase (HDAC) inhibitor has been shown to induce apoptosis synergistically in AML, ovarian cancers and renal cancers. Therefore, we determined the combined effect of DZNep and an HDAC inhibitor, SAHA, on NSCLC cells. [Methods] We evaluated the effect of combined therapy with DZNep and SAHA against four human NSCLC cell lines_H1299, H1975, A549 and PC-3. Cell proliferation was measured by MTT assay. Percentage of apoptotic cells was measured using Annexin V-FITC with a flow cytometer. Western blot analysis was performed on total cell lysates. For in vivo assay, H1975 cells were subcutaneously implanted into the flank of BALB/cAJcl nu/nu nude mice. When the average tumor volume reached approximately 50∼100mm3, the following treatments were intraperitoneally administered twice per week for 6 weeks; vehicle alone (5% DM SO), DZNep (4mg/kg), SAHA (40mg/kg), and DZNep (4mg/kg) plus SAHA (40mg/kg). [Results] Co-treatment with DZNep and SAHA inhibited cell proliferation synergistically, and reduced EZH2 expression and histone H3 lysine 27 trimethylation more effectively compared with each agent alone. The co-treatment greatly induced accumulation of p27 Kip1 and decrease in cyclin A expression. Flow cytometry analysis demonstrated that the apoptotic fraction was increased in an additive or synergistic manner by the combination therapy. These effects were more evident in H1975 and PC-3 cells with EGFR mutation, in which the co-treatment markedly reduced phosphorylation of EGFR, AKT and ERK1/2. The combined therapy reduced the levels of β-catenin, and its downstream pro-proliferative targets cyclin D1 and EGFR. The co-treatment with DZNep and SAHA also caused significantly greater inhibition of tumor growth of H1975 xenografts than each agent alone in nude mice without visible toxicity. [Conclusion] Combined epigenetic therapy with an EZH2 inhibitor and an HDAC inhibitor may represent an effective approach for NSCLCs. Citation Format: Taichi Takashina, Ichiro Kinoshita, Junko Kikuchi, Yasushi Shimizu, Jun Sakakibara Konishi, Satoshi Oizumi, Masaharu Nishimura, Hirotoshi Dosaka Akita. Effects of combined epigenetic therapy with histone methyltransferase EZH2 inhibitor 3-deazaneplanocin and histone deacetylase inhibitor SAHA on non-small cell lung cancer cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5162. doi:10.1158/1538-7445.AM2014-5162