Inhibiting sirtuin-dependent DNA repair and oxidative stress responses impairs DIPG cell survival

Background : Diffuse intrinsic pontine gliomas (DIPG) are universally fatal pediatric brain tumors often characterized by a H3 histone mutation (H3K27M) that leads to epigenetic alterations and gene dysregulation. Histone deacetylases (HDAC), key players in modulating epigenetic pathways in cancer, have emerged as potential therapeutic targets for DIPG. This study evaluates the class III HDAC inhibitor, sirtinol, as a potential therapeutic for DIPG. Methods : Sirtinol’s efficacy and cellular mechanism were investigated using two patient-derived DIPG cell lines and one immortalized normal human astrocyte (NHAi) cell line as a comparator. Clonogenic survival was assessed under different experimental conditions, and changes in protein expression were measured via western blot and enzymatic assays. Liquid chromatography tandem mass spectrometry (LC-MS-MS) was used to measure brain and blood penetrance of sirtinol in mice. Results : We found that sirtinol dose-dependently decreased clonogenic cell survival in DIPG cells while having negligible effects on NHAi cells. Combined treatment of sirtinol and radiation resulted in additive toxicity in DIPG, but not NHAi cells. Sirtinol was less toxic in DIPG cells overexpressing mitochondrial-targeted catalase, suggesting peroxide generation as one mode of cell killing. Moreover, sirtinol was found to increase DNA double strand breaks in DIPG cells and decrease phosphorylation of SIRT2-mediated DNA repair pathway kinase ataxia-telangiectasia and Rad3-related protein (ATR). Sirtinol was detected in the brains of sirtinol-treated mice, suggesting blood brain barrier penetrance. Conclusions : Based on our results, sirtinol shows promise as a selective, redox-modulating therapeutic for DIPG that enhances oxidative stress and interferes with DNA repair.