Glioblastoma (GB) is the most common and aggressive primary malignant brain tumor. Despite aggressive treatment, including maximum surgical resection followed by both chemotherapy and radiotherapy, median survival for patients remains at approximately 1.5 years after diagnosis. Recent preclinical studies examining the potential of the ketogenic diet (KD) as an adjuvant therapy for the treatment of malignant gliomas demonstrated that animals fed a KD and treated with chemotherapy or radiation survived significantly longer than those treated with chemotherapy or radiation and fed a standard diet. One of the key results of the KD is an increase in the blood level of the ketone body β-hydroxybutyrate (BHB). To more fully examine the mechanism through which the KD potentiates radiation, we examined the potential of BHB to increase radiosensitivity in mouse glioma cells in vitro. Plating cells in 10mM BHB followed by treatment for 2 weeks following radiation prevented colony formation in both the control and the radiation groups. We therefore assessed the effect of pretreatment with 5mM or 10mM BHB alone prior to radiation with 4 Gy. A statistically significant change in survival was observed when cultures were pre-treated with 10mM BHB for 24 hours prior to irradiation but not with 5mM BHB. However, significant changes in clonogenic survival were observed with a dose of 5mM BHB when cells were treated for 7 days post irradiation, starting 24 hours after irradiation. The effect of BHB on cell growth was then assessed using live cell counts. Both 5mM and 10mM BHB were effective in significantly reducing the cell number by 192 hours post plating. Growth was similarly affected by 10mM BHB or 2 Gy of radiation alone; however, when 10mM BHB was added to 2 Gy of radiation there was a very strong potentiating effect. These data suggest that BHB is an effective radiosensitizer for mouse glioma cells when used alone. In addition, they provide evidence that the extended survival seen in our in vivo mouse model of glioma when radiation is used in addition to the ketogenic diet may be modulated, to a large extent, by blood ketone levels. Whether this is due to differences in radiation-induced DNA damage, DNA repair or changes in the growth rate of the tumor cells is currently under investigation. Citation Format: Alex P. Rossi, Eric C. Woolf, Kenneth S. Brooks, Marshall J. Fairres, Adrienne C. Scheck. The ketone body β-hydroxybutyrate increases radiosensitivity in glioma cell lines in vitro. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3346. doi:10.1158/1538-7445.AM2015-3346

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Glioblastoma multiforme (GBM) is an aggressive primary brain tumor with a 5 year survival rate of 25% in children and less than 10% in adults. Improvement in the prognosis of GBM patients requires the development of new therapeutic approaches. One emerging strategy is to target aberrant cell metabolism, a trait shared by virtually all tumor cells. The ketogenic diet (KD), a high fat, low carbohydrate and protein metabolic therapy has been shown to prolong survival in animal glioma models, and when used in conjunction with radiation cured 9 of 11 mice of their implanted tumors. We have also shown that the KD alters hypoxia, angiogenesis, and other hallmarks of glioma progression. To elucidate the underlying mechanisms through which ketones exert their effects on glioma, we are doing analyses of the effect of β-hydroxybutyrate (βHB), the most prevalent ketone body synthesized during ketosis, on glioma cells in vitro. We found that βHB both alone and in conjunction with radiation significantly inhibits proliferation of human and mouse glioma cells and human glioma stem cells (GSC). Alterations in passage through the cell cycle may affect proliferation, and cells are also more sensitive to radiation in the G2/M cell cycle phase. We therefore analyzed the effect of βHB on cell cycle distribution of cells treated with βHB and/or radiation. An analysis of cell cycle status by flow cytometry demonstrated that treating the GSC line L0 with 5mM βHB in combination with 4 Gy of radiation significantly increased the number of cells in G2/M cell cycle arrest. In GL261-Luc2 mouse glioma cells, 5mM βHB alone significantly enhanced G2/M cell cycle arrest, which could lead to radiosensitization. Currently we are analyzing proteins involved in cell cycle progression and apoptosis to better understand βHB mediated changes in growth and radioresistance. In summary, these data provide insight to the radiosensitization and anti-proliferative mechanisms of βHB and may hold implications for the use of the KD in the treatment of GBM. Citation Format: Helena B. Silva-Nichols, Alex P. Rossi, Eric C. Woolf, Marshall J. Fairres, Loic P. Deleyrolle, Brent A. Reynolds, Adrienne C. Scheck. Radiosensitization of glioma cells by the ketone body β-hydroxybutyrate is associated with enhanced cell cycle arrest in the G2/M phase. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1670.