Abstract 2147: IDH1 mutation-inspired α-ketoglutaric acid mimics for epigenetic therapy of higher grade gliomas

Mutations at the active site of isocitrate dehydrogenase 1 gene (IDH1; R132H) occur at a high frequency (>70%) early in the oncogenesis of lower grade malignant gliomas, and result in a dramatic accumulation of the oncometabolite D-2 hydroxyglutarate ( D-2HG), that effectively replaces the normal metabolite α-ketoglutarate (α-KG) in cell physiology. Surprisingly, IDH1 mutations bestow superior therapeutic responses to alkylating agents and better patient survival. D-2HG, effectively competes with α-KG and potently inhibits various dioxygenase reactions, including the TET1, TET2 DNA -demethylases and histone demethylases (5m-cytosine to 5-OH cytosine, H3-K-meX to H3-K-meX-1) thereby, re-shaping and reprogramming the epigenetic landscape, and consequent transcriptional silencing; the DNA repair protein O6-methlguanine DNA methyltransferase (MGMT), which confers drug resistance is one major target for such repression. As a novel and innovative strategy of turning the tide against GBMs by exploiting the mechanistic aspects of the oncometabolite, we hypothesized that D-2HG and α-KG derivatives that can replace the natural metabolite in epigenomic dioxygenase reactions will serve as potent anti-glioma drugs either by themselves or in combination with the alkylating agents. To this end, we first synthesized a D-2HG diethyl ester to enhance its cellular uptake and tested its effects on four human brain tumor cell lines (DAOY, T98G, SF188 and UW18). This compound, at 5-10 mM and 24 h treatments, moderately inhibited the DNA repair activity of MGMT, increased temozolomide cytotoxicity by 1.5 to 3-fold, and induced histone H3-methylations as determined by western blot analyses. To increase the potency and design better compounds mimicking the oncometabolite and validate its impact on epigenesis, we synthesized a 2,4-dimethyleneglutaric acid (DMG), a α-KG mimic with methylene groups inserted at the C2 and C4 positions. The hydrophobic DMG ester, by itself, was cytotoxic with IC50 values up to 500 µM against brain tumor cell lines, however, when combined at 100 µM with TMZ resulted in a great synergistic cell killing (generally-9 fold, but 28-fold with UW-18 GBM cells). 0.25 mM DMG inhibited the cellular MGMT activity by >80%, induced degradation of TET1 protein and highly increased the methylation levels of histones (H1K25me1, me2 and H2BK25me2). Currently, experiments to determine the BBB-penetrance of DMG, its ability to induce genomic and MGMT-specific methylations in glioma cells and GBM regression in intracranial xenograft models developed in nude mice are underway. Collectively, these data reveal that acute treatments of α-KG analogs can alter the cellular epigenetic makeup in a manner ascribed to D-2HG, and open up the much-needed novel and exciting avenues of oncometabolite therapy for brain tumors (supported by CPRIT grants RP130266 & RP170207 to KSS). Citation Format: Hanumantha Rao Madala, Surendra Reddy Punganuru, Kalkunte S. Srivenugopal. IDH1 mutation-inspired α-ketoglutaric acid mimics for epigenetic therapy of higher grade gliomas [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 2147. doi:10.1158/1538-7445.AM2017-2147