Epigenetic targeting of clear cell renal cell carcinoma (ccRCC) with ascorbic acid (AA) via upregulation of Ten-Eleven Translocation (TET) methylcytosine dioxygenase activity.

479 Background: We and others have previously shown that the ccRCC epigenome is characterized by widespread DNA hypermethylation (CCR 2014, Nature 2014). Various important tumor suppressor genes (TSGs), such as SMAD7 (inhibitor of oncogenic TGF-β signaling), are under-expressed due to aberrantly methylated promoters or enhancers. We hypothesized that the hypermethylation in ccRCC could be due to low activity of the TET enzymes, which convert methylcytosine (5-mc) to hydroxymethylcytosine (5-hmc). Loss of function of TET enzymes can occur with an inactivating mutation (TET-2 is mutated in about 6% of ccRCC (Science Signaling 2013) or hypoactivity of normal TET enzymes, through inhibition by metabolic intermediates. AA is an essential co-factor for TET enzymes (JACS 2015). We hypothesized that high dose AA treatment of ccRCC could potentially increase the functional activity of TET enzymes leading to demethylation of the RCC genome, and enhance expression of TSGs. Methods: In vitro TET activity was performed on ccRCC cell line 769P with increasing doses of AA (L-AA). Genome wide quantitative 5-mc and 5-hmc was evaluated using mass spectrometry. SMAD7 expression was determined using qRT-PCR. Proliferation assay (MTT) was performed with AA in combination with pazopanib. Cell cycle and apoptosis assays were performed. Results: AA, at doses achieved only by the intravenous route (1-10mM), increased TET activity in ccRCC cell line 769P. Genome wide 5-mc was significantly reduced and 5-hmc was increased, correlating with increase in TET activity. SMAD7 expression was increased with AA treatment. High dose AA led to proliferation inhibition with a cell cycle arrest in the G1 phase, and had a synergistic effect with pazopanib. Since AA leads to the generation of H2O2 in-vitro, catalase was used as control. This did not reverse the effect of AA on epigenetic changes; and proliferation inhibition was seen despite catalase control. Conclusions: High dose AA causes TET mediated DNA demethylation of the hypermethylated RCC genome, resulting in the re-expression of TSGs, and proliferation inhibition. Sequencing and xenograft studies are underway.