Recent studies show that metabolites, beyond their metabolic roles, can induce significant changes in cell behavior. Herein, we investigate the non-canonical role of nicotinamide (vitamin B3) on glioblastoma (GB) cell behavior. Nicotinamide induced senescence in GB cells, characterized by reduced proliferation, chromatin reorganization, increased DNA damage, enhanced beta-galactosidase activity, and decreased Lamin B1 expression. Nicotinamide-induced senescence was accompanied by an unexpected reprogramming of its metabolism, marked by simultaneous downregulated transcription of NNMT (nicotinamide N-methyltransferase) and NAMPT (nicotinamide phosphoribosyl-transferase). Nicotinamide effects on GB cells were mediated by decreased levels of SOX2. Consistently, analyses of patients' single cell transcriptome datasets showed that GB cells with low NNMT and NAMPT expression levels were enriched in gene modules related to senescence. Remarkably, senescent GB cells retained tumor-forming ability in vivo, albeit to a lesser extent compared to control cells. Further experiments at the single-cell level and transcriptomic analyses demonstrated that nicotinamide-induced senescence in GB cells is fully reversible. Overall, our findings identify a novel reversible senescent state in GB tumors and highlight the non-canonical role of nicotinamide as a key driver of cancer cell plasticity.
