BackgroundGlioblastoma multiforme is a highly aggressive brain tumor with a poor prognosis, and advances in treatment have led to only marginal increases in overall survival. We and others have shown previously that the therapeutic ketogenic diet (KD) prolongs survival in mouse models of glioma, explained by both direct tumor growth inhibition and suppression of pro-inflammatory microenvironment conditions. The aim of this study is to assess the effects of the KD on the glioma reactive immune response.MethodsThe GL261-Luc2 intracranial mouse model of glioma was used to investigate the effects of the KD on the tumor-specific immune response. Tumor-infiltrating CD8+ T cells, CD4+ T cells and natural killer (NK) cells were analyzed by flow cytometry. The expression of immune inhibitory receptors cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and programmed death 1 (PD-1) on CD8+ T cells were also analyzed by flow cytometry. Analysis of intracellular cytokine production was used to determine production of IFN, IL-2 and IFN- in tumor-infiltrating CD8+ T and natural killer (NK) cells and IL-10 production by T regulatory cells.ResultsWe demonstrate that mice fed the KD had increased tumor-reactive innate and adaptive immune responses, including increased cytokine production and cytolysis via tumor-reactive CD8+ T cells. Additionally, we saw that mice maintained on the KD had increased CD4 infiltration, while T regulatory cell numbers stayed consistent. Lastly, mice fed the KD had a significant reduction in immune inhibitory receptor expression as well as decreased inhibitory ligand expression on glioma cells.ConclusionsThe KD may work in part as an immune adjuvant, boosting tumor-reactive immune responses in the microenvironment by alleviating immune suppression. This evidence suggests that the KD increases tumor-reactive immune responses, and may have implications in combinational treatment approaches.Electronic supplementary materialThe online version of this article (doi:10.1186/s12885-016-2337-7) contains supplementary material, which is available to authorized users.

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

Altered metabolism was first identified in cancer cells by Otto Warburg, who identified a higher reliance on anaerobic glycolysis rather than cellular respiration even in the presence of sufficient oxygen levels, a phenomenon called the Warburg Effect. Deregulated metabolism is now considered a driving hallmark of cancer and an attractive therapeutic target. While a great deal of work is being done to find genetic therapeutic targets that can be used for personalized medicine, current targeted approaches are typically ineffective because tumors are heterogeneous and contain multiple genetic subpopulations. This often precludes a particular targeted molecule from being found on all cells. In contrast to many genetic alterations, dysregulation of metabolism resulting in the need for high amounts of glucose is found in virtually all cancer cells. Targeting metabolism by reducing blood glucose may be a way to inhibit tumor growth since this, to a large extent, should circumvent the inherent problems associated with tumor heterogeneity. Methods that also provide an energy source for normal tissues such as ketones should reduce side effects associated with an overall reduction in blood glucose. The high-fat, low carbohydrate, and protein ketogenic diet (KD) results in reduced blood glucose and increased blood ketones, as does caloric restriction and fasting. In preclinical mouse models of malignant brain tumors, animals fed a KD had increased survival, particularly when used in combination with radiation or chemotherapy. Metabolic modulation through the use of a KD, caloric restriction, or fasting has been found to change the expression of a number of genes and pathways thought to inhibit tumor growth. Metabolic therapy has also recently been explored in other cancer types. In this chapter, we will examine the mechanisms underlying the KD which suggests its potential as an adjuvant therapy for cancer treatment.

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