Abstract 5360: Targeting H3K27 Methylation by 3-Deazaneplanocin A (DZNep) in lung and esophageal cancers.

Abstract

Abstract Polycomb repressor complex-2 (PRC-2) is aberrantly expressed in a variety of human malignancies including lung and esophageal cancers. PRC-2 contains three main core proteins, enhancer of zeste 2 (EZH2), suppressor of zeste 12 (SUZ12), and embryonic ectoderm development (EED). In the present study, we sought to examine the effects of PRC-2 expression in lung and esophageal cancers, and to determine if PRC-2 is a potential therapeutic target in these malignancies. qRT-PCR analysis demonstrated significant over-expression of EZH2, SUZ12, and EED in cultured lung and esophageal cancer cells as well as primary tumors relative to normal or immortalized aerodigestive tract epithelial cells, or normal lung or esophageal tissues. Over-expression of individual PRC-2 components appeared to coincide with tumor histology; for example EZH2 was particularly over-expressed in small cell lung cancers, whereas EED appeared to be over-expressed primarily in esophageal cancers. DZNep mediated dose-dependent depletion of EZH2, EED and SUZ12, with corresponding decreases in global H3K27Me3 levels in cultured lung and esophageal cancer cells. Depletion of PRC-2 expression/activity coincided with growth arrest in these cancer cells. The growth inhibitory effects of DZNep in lung cancer cells were recapitulated byshRNA-mediated knock-down of EZH2 in these cells. DZNep induced expression of Dkk-1, a putative tumor suppressor that we have previously reported to be repressed by polycomb-mediated mechanisms in lung cancer cells and cultured normal respiratory epithelia following exposure to cigarette smoke condensate (CSC). Chromatin immunoprecipitation (ChIP) experiments demonstrated that DZNep-mediated activation of Dkk-1 coincided with decreased levels of H3K27Me3 within the Dkk-1 promoter. qRT-PCR and immunoblot experiments revealed that exposure of lung cancer cells to DZNep before or concurrent with CSC abrogated tobacco-mediated repression of Dkk-1 in vitro. Subsequent experiments demonstrated that daily intra-peritoneal (IP) injections of CSC significantly decreased Dkk-1 gene expression in subcutaneous A549 and Calu-6 xenografts, and enhanced growth of these tumors in nude mice. IP administration of DZNep (2.5 mg/kg BID q4 days every 7 days) significantly abrogated the enhancement effect of cigarette smoke on growth of lung cancer xenografts; this phenomenon coincided with decreased EZH2 and increased Dkk-1 expression in these xenografts. Collectively, these findings support development of DZNep for inhibiting PRC-2 expression in thoracic malignancies. Citation Format: Mahadev Rao, Young Hong, Scott Atay, Trevor Upham, Julie Hong, Nicole Datrice, Mary Zhang, Enrique Zudaire, Victor Marquez, David Schrump. Targeting H3K27 Methylation by 3-Deazaneplanocin A (DZNep) in lung and esophageal cancers. [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 5360. doi:10.1158/1538-7445.AM2013-5360