Abstract 125: Differential effects of inhibitors of epigenetic modifiers on IDH mutant cell lines
Authors: Kayabolen Alişan , Onder Tugba Bagci 
Published: July 2017

Abstract
Our aim is to find effective drug treatments for IDH mutant glioma cells and investigate their mechanism of actions by analysing genetic and epigenetic alterations upon drug treatments.
Drug screen was performed on IDH mutant and wild type cell lines by using a library of epigenetic modifier inhibitors. Hits for IDH mutant cells were validated with individual treatments. Combination treatments of these inhibitors were also performed to see synergistic effects. Then, IDH wild type glioma cells and BJ fibroblasts were transduced with mutant IDH1 overexpression plasmid, and checked if they were sensitized to these drugs or not.
Based on drug screen performed on IDH mutant and wild type glioma cell lines, we found that IDH mutant cell lines, MGG119 and MGG152, were highly sensitive to 5-azacytidine, Chaetocin and GSK-J4. For IDH1 mutant MGG152 cell line, IC50 value for GSK-J4 is 5.2 ± 1.3 µM, for 5-azacytidine is 2.2 ± 0.3 µM, and for Chaetocin is 10.2 ± 1.0 nM at 48h. On the other hand, these drugs did not affect viability of IDH wild type glioma cell lines and fibroblasts around these concentrations. Moreover, combination of drugs, especially combination of Chaetocin and 5-azacytidine had a highly synergistic effect on IDH mutant cells while it was still ineffective on IDH wild type cells. After transduced with mutant IDH overexpression plasmid, fibroblasts became more sensitive to these drugs. On the other hand, although their growth rate was reduced, IDH wild type glioma cells were not significantly sensitized to these drugs upon mutant IDH overexpression.
IDH mutation mainly inhibits DNA and histone demethylation, and leads to hypermethylation phenotype. Therefore, it is an expected result that IDH mutant cell lines are sensitive to 5-azacytidine which is an inhibitor of DNA methyltransferases, and Chaetocin which is an inhibitor of H3K9 methyltransferases. However, it was interesting to observe that GSK-J4 which is an inhibitor of H3K27 demethylases is also effective on IDH mutant cells. This may be a result of dependency on low number of active genes since IDH mutation causes downregulation of many genes by methylation. GSK-J4 may downregulate these genes by increasing H3K27 methylation. On the other hand, these effects might also be results of induced cell stress upon drug treatment. To answer this question, now we are trying to knock-down target genes of these drugs by shRNA, and obtaining compatible results. We are also planning to perform RNA-seq analysis to see genes with altered expressions upon drug treatments.
To conclude, unlike IDH wild type glioma cells or healthy fibroblasts, IDH mutant glioma cells were found to be sensitive to few epigenetic drugs in low concentrations. This was confirmed by sensitization of fibroblasts to these drugs upon mutant IDH1 overexpression. In addition, combination of these drugs had a highly synergistic effect on mutant cells which may give opportunity to use drugs in very low concentrations efficiently.
Citation Format: Alişan Kayabolen, Tugba Bagci Onder. Differential effects of inhibitors of epigenetic modifiers on IDH mutant cell lines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 125. doi:10.1158/1538-7445.AM2017-125