Vitamin C in combination with inhibition of mutant IDH1 synergistically activates TET enzymes and epigenetically modulates gene silencing in colon cancer cells

ABSTRACT

Mutations in the enzyme isocitrate dehydrogenase 1 (IDH1) lead to metabolic alterations and a sustained formation of 2-hydroxyglutarate (2-HG). 2-HG is an oncometabolite as it inhibits the activity of α-ketoglutarate-dependent dioxygenases such as ten-eleven translocation (TET) enzymes. Inhibitors of mutant IDH enzymes, like ML309, are currently tested in order to lower the levels of 2-HG. Vitamin C (VC) is an inducer of TET enzymes. To test a new therapeutic avenue of synergistic effects, the anti-neoplastic activity of inhibition of mutant IDH1 via ML309 in the presence of VC was investigated in the colon cancer cell line HCT116 IDH1^R132H/+ (harbouring a mutated IDH1 allele) and the parental cells HCT116 IDH1^+/+ (wild type IDH1). Measurement of the oncometabolite indicated a 56-fold higher content of 2-HG in mutated cells compared to wild type cells. A significant reduction of 2-HG was observed in mutated cells after treatment with ML 309, whereas VC produced only minimally changes of the oncometabolite. However, combinatorial treatment with both, ML309 and VC, in mutated cells induced pronounced reduction of 2-HG leading to levels comparable to those in wild type cells. The decreased level of 2-HG in mutated cells after combinatorial treatment was accompanied by an enhanced global DNA hydroxymethylation and an increased gene expression of certain tumour suppressors. Moreover, mutated cells showed an increased percentage of apoptotic cells after treatment with non-cytotoxic concentrations of ML309 and VC. These results suggest that combinatorial therapy is of interest for further investigation to rescue TET activity and treatment of IDH1/2 mutated cancers.

KEYWORDS:

• Vitamin C
• epigenetics
• IDH1
• TET
• cancer cells

Acknowledgments

This work was supported by NutriAct – Competence Cluster Nutrition Research Berlin-Potsdam funded by the Federal Ministry of Education and Research (FKZ: 01EA1408A-B). Special thanks go to Dr. Guy Yealland for language editing of the manuscript. We would like to thank Monika Haseloff and Caue Egea Rodrigues for the excellent technical assistance in conducting the experiments.

Disclosure statement

No potential conflict of interest was reported by the authors.

Author Contributions

CG and BK designed experiments; CG, FS and AB performed experiments; CG, FS, TH and AB analysed data; CG, FS, AB, TH and BK wrote the manuscript, CG and BK advised on experimental design and provided critical feedback, all authors reviewed the manuscript.

Supplementary material

Supplementary data for this article can be accessed here.

Additional information

Funding

This work was supported by NutriAct – Competence Cluster Nutrition Research Berlin-Potsdam funded by the Federal Ministry of Education and Research (FKZ: 01EA1408A-B); Bundesministerium für Bildung und Forschung [01EA1408A-B].