Abstract A10: Epigenetic mechanisms in liver tumors: Gene expression analysis of epigenetic machinery in hepatoblastomas

Liver tumors in children are rare and account for only 1-4% of all pediatric solid tumors. While hepatocellular carcinoma is predominant in adults, the most common liver cancer in children is hepatoblastoma, an embryonal tumor. The prognosis of patients with advanced tumor stages remains poor as well as surviving children often face severe effects following aggressive chemotherapy. Hepatoblastomas carry a low mutational burden, and the impairment of epigenetic mechanisms, which are the core of embryogenesis and development, stands out as an alternative route for tumorigenesis. The main objective of this study was to explore the role of genes associated with methylation and hydroxymethylation in hepatoblastomas. The expression of seven genes of the epigenetic machinery ( DNMT1, DNMT3A, DNMT3L, UHRF1, TET1, TET2 , and TET3 ) was analyzed by qPCR (Taqman). The cohort of tumors consisted of 21 hepatoblastomas and a control group of 8 non-tumor differentiated liver tissues. Additionally, a 5hmC quantification assay (Quest 5-hmC DNA ELISA Kit) was applied to assess the level of 5hmC in tumors. TET1 and TET2 genes, whose proteins are responsible for the active demethylation of 5-methylcytosine (5mC), and consequent production of 5-hydroxymethylcytosine (5hmC), were found to be upregulated. A significant increase in the 5hmC levels was also evident in tumor samples when compared to nontumoral tissues. We have shown in hepatoblastomas an upregulated profile of TET1 and TET2 enzymes with a resulting elevation of 5hmC level in tumors. Our data suggest that hepatoblastomas could present a pluripotency pattern of gene expression when compared to differentiated livers; to address this issue, the expression levels of three genes associated with pluripotency ( POU5F1, SOX2 and NANOG ) were evaluated, with no significant alteration. Therefore, although hepatoblastomas have a more undifferentiated molecular profile than mature hepatocytes, our results indicate that tumor cells are already commited with the differentiation process. Altogether, these data suggest that the development of hepatoblastomas is associated with a blockage in the stages of hepatoblasts. Citation Format: Maria Rivas, Cecilia da Costa, Silvia Toledo, Monica Cypriano, Luiz Caires, Ernesto Goulart, Dirce Carraro, Isabela Werneck, Carla Rosenberg, Mayana Zatz, Ana Krepischi. Epigenetic mechanisms in liver tumors: Gene expression analysis of epigenetic machinery in hepatoblastomas [abstract]. In: Proceedings of the AACR International Conference held in cooperation with the Latin American Cooperative Oncology Group (LACOG) on Translational Cancer Medicine; May 4-6, 2017; Sao Paulo, Brazil. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(1_Suppl):Abstract nr A10.