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Sirtuin activation targets IDH-mutant tumors.

BACKGROUND
IDH-mutant tumors exhibit an altered metabolic state and are critically dependent upon nicotinamide adenine dinucleotide (NAD+) for cellular survival. NAD+ steady-state levels can be influenced by both biosynthetic and consumptive processes. Here, we investigated activation of sirtuin (SIRT) enzymes, which consume NAD+ as a coenzyme, as a potential mechanism to reduce cellular NAD+ levels in these tumors.


METHODS
The effect of inhibition or activation of Sirtuin activity, using small molecules, CRISPR/Cas9 gene editing and inducible overexpression, was investigated in IDH-mutant tumor lines, including patient-derived IDH-mutant glioma lines.


RESULTS
We found that SIRT1 activation led to marked augmentation of NAD+ depletion and accentuation of cytotoxicity, when combined with nicotinamide phosphoribosyltransferase inhibition (NAMPTi), consistent with the enzymatic activity of SIRT1 as a primary cellular NAD+ consumer in IDH-mutant cells. Activation of SIRT1 through either genetic overexpression or pharmacologic SIRT1-activating compounds (STACs), an existing class of well-tolerated drugs, led to inhibition of IDH1-mutant tumor cell growth.


CONCLUSIONS
Activation of SIRT1 can selectively target IDH-mutant tumors. These findings indicate that relatively non-toxic STACs, administered either alone or in combination with NAMPTi, could alter the growth trajectory of IDH-mutant gliomas, while minimizing toxicity associated with cytotoxic chemotherapeutic regimens.