Abstract 474: Genome-wide DNA methylation profiling reveals novel candidate epigenetic gatekeepers in hepatocarcinogenesis

Epigenetic deregulation is a critical event in human malignancies. Besides mutations in TERT promoter, found in 20% of dysplastic nodules, little is known about the key molecular alterations driving early hepatocarcinogenesis. The aims of this study were: 1) to analyze DNA methylation changes during the transition from preneoplastic lesions to early hepatocellular carcinoma (HCC), and 2) to identify candidate epigenetic gatekeepers in the transition between dysplasia and early tumors. Methylome profiling was done with Illumina HumanMethylation450 (485,000 CpG, 96% of known CpG islands). We evaluated differentially methylated CpG sites between groups using an F-test. To detect novel epigenetic gatekeepers we defined hypermethylation as a B value higher than 0.5. We profiled 144 fresh-frozen tissues from resection or liver transplant specimens and integrated these data with our previously report on DNA methylation in HCC (Villanueva et al. Hepatology 2015) resulting in: 16 normal liver, 139 cirrhosis, 8 dysplastic nodules and 227 HCC samples. Correlation between methylation and RNA expression (n= 361) was quantified with the Pearson’s coefficient. Patients were mostly male (76%), with a median age of 66, and with underlying liver disease mainly due to hepatitis C (43%) and B (23%). All tumors were early stage according to BCLC classification, including 43 cases below 2 cm in diameter. A phylo-epigenetic tree derived from the euclidean distances between differentially DNA methylated sites (n=421,997) reveals a gradient of methylation changes that spans normal, cirrhotic, dysplastic nodules and HCC. Epigenetic analysis confirmed closer proximity of dysplasia to HCC than to cirrhotic tissue. We validated aberrant methylation of previously reported HCC epidrivers within the unpublished dataset (e.g. EFBN2, TBX15) (Villanueva et al. Hepatology 2015). Focusing on CpG sites located in promoter regions (i.e., TSS200, TSS1500, 5’UTR, and 1st exon), we selected candidates hypermethylated in less than 1% of normal and cirrhotic tissue, in all high grade dysplastic nodules, and in more than 50% of small HCC nodules (<2 cm). When we integrated DNA methylation and gene expression we found a significant (all P<0.001) inverse correlation in TSPYL5 (r=-0.31), KCNA3 (r=-0.33), LDBH (r=-0.46) and SPINT2 (r=-0.43). Whole-genome DNA methylation profiles accurately discriminate between different histological lesions along the human hepatocarcinogenesis spectrum. We report novel epigenetic gatekeepers in the transition between dysplastic nodules and early HCC. Citation Format: Gabriela Hernandez Meza, Johann von Felden, Amanda Craig, Sergi Sayols, Anna Portela, Manel Esteller, Myron Schwartz, Vincenzo Mazzaferro, Josep Llovet, Augusto Villanueva. Genome-wide DNA methylation profiling reveals novel candidate epigenetic gatekeepers in hepatocarcinogenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 474.