Abstract 1623: Epigenetic regulation of tumor suppressor genes in esophageal cancer by berries

Squamous cell carcinoma (SCC) is one of two major types of esophageal cancer. Major etiological factors for this disease include the use of tobacco and alcohol, and the consumption of salt-cured and moldy foods that are frequently contaminated with N-nitrosamine carcinogens. Using a rat model of esophageal SCC, we have demonstrated the ability of freeze-dried black raspberries (BRBs) to inhibit tumors induced with the nitrosamine carcinogen, N-nitrosomethylbenzylamine (NMBA). BRBs inhibit the progression of NMBA-induced dysplastic lesions to papillomas and carcinomas by reducing cell proliferation, inflammation and angiogenesis and promoting apoptosis and cell differentiation. However, there is no information regarding the potential effects of BRBs on epigenetic events in NMBA-induced rat esophageal tumorigenesis. F344 male rats were given s.c. injections of NMBA, at 0.3 mg/kg, 3 times/wk for 5 wks, and their esophagi harvested at 9, 15, 17 and 35 wks. Histopathological studies revealed the presence of small dysplastic esophageal lesions at 17 wks but not at 15 wks. Immunohistochemical analysis of Ki-67 stained esophageal epithelial cells indicated that cell proliferation at 15 wks was significantly higher than at 9 wks. Genome-wide microarray analysis indicated that more genes were downregulated than upregulated by NMBA (n=153 vs. 69) in papillomas at 35 wks when compared to whole esophagus at 9 wks. Some of these genes such as Sfrp4, a soluble frizzled-related protein, are associated with Wnt signaling and cell proliferation. To investigate whether BRBs elicit effects on DNA methylation of putative tumor suppressor genes, genome-wide methylation analysis was applied using normal esophageal tissues and papillomas collected at the end of the bioassay (35 wks). BRBs significantly demethylated the promoter CpG islands of 81 genes, some of which are involved in the regulation of important cellular functions such as proliferation and Wnt signaling. Included among these is Sfrp4; NMBA treatment induced its promoter methylation in both preneoplastic lesions (a mixture of normal, hyperplastic and dysplastic epithelium) and in papillomas and reduced its mRNA expression. In contrast, BRBs decreased promoter methylation and increased mRNA expression of Sfrp4 in preneoplastic lesions and in papillomas, suggesting that BRBs might reactivate tumor suppressor genes silenced by methylation. Dnmt3b mRNA expression was induced in both preneoplastic lesions and in papillomas of NMBA-treated rat esophagus suggesting that Dnmt3b could be a major contributor to promoter hypermethylation in NMBA-treated tissues. In conclusion, DNA methylation of tumor suppressor genes appears to contribute to the development of NMBA-induced rat esophageal tumorigenesis and another mechanism for the protective effects of BRBs may be to reduce DNA methylation. This research was supported, in part, by NCI grant R01 CA103180 to GDS. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1623. doi:1538-7445.AM2012-1623