PURPOSE: Recent studies have shown that brain tumor cells, unlike normal brain cells, are largely dependent upon glucose for energy and are not able to use ketone bodies as a primary energy source. These findings are thought to be because of decreased expression of succinyl-coenzyme A:3-oxoacid coenzyme A transferase (SCOT), a key enzyme involved in ketone body metabolism. Because of their neural crest origin, we hypothesized that neuroblastoma cells would also be unable to use ketone bodies as a primary energy source.

METHODS: Human foreskin fibroblasts (control) and human neuroblastoma cells (SK-N-AS) were grown in standard media with glucose (glc+), standard media without glucose (glc-), glucose-free media with acetoacetate, or glucose-free media with beta-hydroxybutyrate. Cell viability was determined with MTT [3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide] assay and apoptosis with fluorescence-activated cell sorting analysis. Immunoblotting was performed to SCOT protein.

RESULTS: Neuroblastoma cell viability was significantly decreased in the acetoacetate and hydroxybutyrate media by 52% and 61%, respectively, compared with control media. In addition, neuroblastoma cells showed significantly more apoptosis in the ketone media. Viability and apoptosis in the normal fibroblasts were not affected by the culture media. The expression of SCOT protein was significantly less in human neuroblastoma cells compared with the control fibroblasts.

CONCLUSIONS: Unlike human fibroblasts, neuroblastoma cells were unable to use ketone bodies as an energy source, likely because of their decreased expression of SCOT protein. Dietary manipulation using ketone bodies in accordance with SCOT expression may be a novel therapeutic strategy for neuroblastoma.

Little progress has been made in the long-term management of glioblastoma multiforme (GBM), considered among the most lethal of brain cancers. Cytotoxic chemotherapy, steroids, and high-dose radiation are generally used as the standard of care for GBM. These procedures can create a tumor microenvironment rich in glucose and glutamine. Glucose and glutamine are suggested to facilitate tumor progression. Recent evidence suggests that many GBMs are infected with cytomegalovirus, which could further enhance glucose and glutamine metabolism in the tumor cells. Emerging evidence also suggests that neoplastic macrophages/microglia, arising through possible fusion hybridization, can comprise an invasive cell subpopulation within GBM. Glucose and glutamine are major fuels for myeloid cells, as well as for the more rapidly proliferating cancer stem cells. Therapies that increase inflammation and energy metabolites in the GBM microenvironment can enhance tumor progression. In contrast to current GBM therapies, metabolic therapy is designed to target the metabolic malady common to all tumor cells (aerobic fermentation), while enhancing the health and vitality of normal brain cells and the entire body. The calorie restricted ketogenic diet (KD-R) is an anti-angiogenic, anti-inflammatory and pro-apoptotic metabolic therapy that also reduces fermentable fuels in the tumor microenvironment. Metabolic therapy, as an alternative to the standard of care, has the potential to improve outcome for patients with GBM and other malignant brain cancers.

Information is presented on the calorically restricted ketogenic diet (CRKD) as an alternative therapy for brain cancer. In contrast to normal neurons and glia, which evolved to metabolize ketone bodies as an alternative fuel to glucose under energy-restricted conditions, brain tumor cells are largely glycolytic due to mitochondrial defects and have a reduced ability to metabolize ketone bodies. The CRKD is effective in managing brain tumor growth in animal models and in patients, and appears to act through antiangiogenic, anti-inflammatory, and proapoptotic mechanisms.

BACKGROUND: Malignant brain cancer persists as a major disease of morbidity and mortality in adults and is the second leading cause of cancer death in children. Many current therapies for malignant brain tumors fail to provide long-term management because they ineffectively target tumor cells while negatively impacting the health and vitality of normal brain cells. In contrast to brain tumor cells, which lack metabolic flexibility and are largely dependent on glucose for growth and survival, normal brain cells can metabolize both glucose and ketone bodies for energy. This study evaluated the efficacy of KetoCal, a new nutritionally balanced high fat/low carbohydrate ketogenic diet for children with epilepsy, on the growth and vascularity of a malignant mouse astrocytoma (CT-2A) and a human malignant glioma (U87-MG).

METHODS: Adult mice were implanted orthotopically with the malignant brain tumors and KetoCal was administered to the mice in either unrestricted amounts or in restricted amounts to reduce total caloric intake according to the manufacturers recommendation for children with refractory epilepsy. The effects KetoCal on tumor growth, vascularity, and mouse survival were compared with that of an unrestricted high carbohydrate standard diet.

RESULTS: KetoCal administered in restricted amounts significantly decreased the intracerebral growth of the CT-2A and U87-MG tumors by about 65% and 35%, respectively, and significantly enhanced health and survival relative to that of the control groups receiving the standard low fat/high carbohydrate diet. The restricted KetoCal diet reduced plasma glucose levels while elevating plasma ketone body (beta-hydroxybutyrate) levels. Tumor microvessel density was less in the calorically restricted KetoCal groups than in the calorically unrestricted control groups. Moreover, gene expression for the mitochondrial enzymes, beta-hydroxybutyrate dehydrogenase and succinyl-CoA: 3-ketoacid CoA transferase, was lower in the tumors than in the contralateral normal brain suggesting that these brain tumors have reduced ability to metabolize ketone bodies for energy.

CONCLUSION: The results indicate that KetoCal has anti-tumor and anti-angiogenic effects in experimental mouse and human brain tumors when administered in restricted amounts. The therapeutic effect of KetoCal for brain cancer management was due largely to the reduction of total caloric content, which reduces circulating glucose required for rapid tumor growth. A dependency on glucose for energy together with defects in ketone body metabolism largely account for why the brain tumors grow minimally on either a ketogenic-restricted diet or on a standard-restricted diet. Genes for ketone body metabolism should be useful for screening brain tumors that could be targeted with calorically restricted high fat/low carbohydrate ketogenic diets. This preclinical study indicates that restricted KetoCal is a safe and effective diet therapy and should be considered as an alternative therapeutic option for malignant brain cancer.

BACKGROUND:Cannabinoids represent unique compounds for treating tumors, including astrocytomas. Whether CB(1) and CB(2) receptors mediate this therapeutic effect is unclear.

PRINCIPAL FINDINGS:We generated astrocytoma subclones that express set levels of CB(1) and CB(2), and found that cannabinoids induce apoptosis only in cells expressing low levels of receptors that couple to ERK1/2. In contrast, cannabinoids do not induce apoptosis in cells expressing high levels of receptors because these now also couple to the prosurvival signal AKT. Remarkably, cannabinoids applied at high concentration induce apoptosis in all subclones independently of CB(1), CB(2) and AKT, but still through a mechanism involving ERK1/2.

SIGNIFICANCE:The high expression level of CB(1) and CB(2) receptors commonly found in malignant astrocytomas precludes the use of cannabinoids as therapeutics, unless AKT is concomitantly inhibited, or cannabinoids are applied at concentrations that bypass CB(1) and CB(2) receptors, yet still activate ERK1/2.