Vitamin B3 suppresses Ras(V12) -driven tumor growth in Drosophila via redox regulation, mitochondrial function, and autophagy activation.

BACKGROUND: Ras-driven cancers present a major therapeutic challenge. Vitamin B3 (nicotinamide), an NAD(+) precursor, shows potential anticancer activity, but its mechanisms in Ras-driven tumors require elucidation. This study aimed to investigate the antitumor efficacy of vitamin B3 in a Ras(V12)scrib(-/-) Drosophila model and explore its underlying mechanisms. METHODS: We treated Ras(V12)scrib(-/-) Drosophila with varying vitamin B3 concentrations (0-4.8 mg/mL). Tumor growth was monitored by fluorescence imaging. Molecular analyses included Western blotting, quantitative real-time polymerase chain reaction (qRT-PCR), and biochemical assays to assess oncogene expression, eIF2α phosphorylation, redox status (NAD(+)/NADH, ROS, SOD, MDA), mitochondrial function (ATP, lactate, respiratory chain components), and autophagy markers (Atg8a-II, Ref(2)P). Larval survival and p53 mRNA expression were also analyzed. RESULTS: Vitamin B3 at 2.4 mg/mL optimally suppressed tumor growth and delayed larval lethality. Treatment downregulated Ras, Hif-1α and Myc expression, enhanced eIF2α phosphorylation, and significantly increased p53 mRNA levels. It also improved redox balance (increased NAD(+)/NADH ratio and SOD activity, decreased ROS and MDA), restored mitochondrial function (elevated ATP, reduced lactate, upregulated respiratory chain genes), and activated autophagy (increased Atg8a-II, decreased Ref(2)P) which was further confirmed by chloroquine assay. CONCLUSIONS: Vitamin B3 exerts multi-mechanistic antitumor effects in Ras-driven tumors by coordinately regulating oncogenic signaling (including p53 upregulation), redox homeostasis, mitochondrial metabolism, and autophagy, supporting its potential as a therapeutic strategy.