P. Ryan Tacon

 Introduction: Glioblastoma multiforme (GBM) is an aggressive central nervous system tumor, often developing as a primary tumor from de novo mutations. GBM is the most common, and most life-threatening of brain tumors seen in practice, and treatment is often palliative due to high mutation rates and chemotherapy resistance in tumor populations1,2. Studies show that amplifications of the NLRP3 inflammasome and NF-kB signaling are pivotal in chemotherapy resistance and cancer progression3,4. These effects are mediated by Histone Deacetylase (HDAC) 1, 3, 4, and 6 activity5,6. Chronic inflammation from the NLRP3 inflammasome is a contributor to metastasis and proliferation via upregulation of VEGF and matrix metalloproteinases4,7. Studies have suggested that a ketone body, β-hydroxybutyrate, can downregulate these pathways, providing a potential adjunctive therapy in cancer treatment. β- hydroxybutyrate is an HDAC 1, 3, and 4 inhibitor8. Inhibition of HDAC 1 and 3 has been shown to overcome NF-kB signaling and temozolomide resistance in GBM models, and inhibition of HDAC 4 and 6 sensitizes GBM to radiation5,6. Additionally, β-hydroxybutyrate inhibits NLRP3 inflammasome assembly through ASC adaptor protein inhibition, and is a potent inducer of FOXO3A expression, which has been shown to induce Bim-mediated apoptosis in GBM models8-11. Methods: The VM-M3 syngeneic mouse model of GBM tagged with luciferase was utilized in vitro and in mouse implantations. Mice were assigned to a control group, a 1,3- butanediol or ketone ester experimental group, or caloric restriction group, and randomly assigned to treatment groups. Bioluminescence, in vitro proliferation assessment, and mean survival time were measured to assess experimental effect12. Results: In vitro, presence of ketone bodies reduced VM-M3 proliferation compared to control regardless of glucose concentration. Bioluminescence was highly variable, but demonstrated a trend of reduced tumor burden with ketone administration. Mean survival time was significantly increased in 1,3- butanediol and ketone ester groups compared to control12. Conclusion: Studies have demonstrated potential anti-tumor effects of ketone bodies in a model of GBM by ameliorating HDAC 1, 3, 4 and NLRP3 inflammasome activity. Additional studies have demonstrated clinical benefit of these compounds in a mouse model of GBM, suggesting the mechanisms observed in vitro may exert benefit in vivo. Additional studies using β-hydroxybutyrate as an adjunctive to temozolomide chemotherapy and radiation therapy after surgical resection may demonstrate benefit through sensitization of GBM tumor cells to radiation and chemotherapy and inhibition of metastasis, and should be investigated.

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