Metabolic profiles of ketolysis and glycolysis in malignant gliomas: Possible predictors of response to ketogenic diet therapy.

Abstract

e13048 Background: The enzymatic differences in energy metabolism between normal brain tissues and malignant gliomas formed the basis for animal model studies that showed increased survival in mice with orthotopically transplanted glioblastoma multiforme (GBM) treated with energy restricted ketogenic diet (ERKD). To test the hypothesis that human brain tumors may also be sensitive to ERKD, we used immunohistochemistry reactions on formalin fixed paraffin embedded tumor samples to evaluate for the presence of enzymes important for the metabolism of ketones and glucose. Methods: Immunoreactivities were graded using a semi-quantitative scale based on the percentage of positive cells: low positive<5% (LOW); intermediate (INT) 5-20%; and highly positive (HIGH) >20%. Focal non-neoplastic “normal” brain tissue present within the specimens served as positive internal controls. Results: Succinyl CoA: 3-oxoacid CoA transferase (OXCT1) and 3-hydroxybutyrate dehydrogenase 1 (BDH1) are mitochondrial enzymes important for metabolizing beta hydroxy butyrate, the main ketone in blood. Both of these enzymes were either decreased or absent (INT or LOW) concordantly in 14 of the 17 (82%) GBMs, and in 1 of 6 (17%) anaplastic astrocytomas (AA). Two of the enzymes in the glycolytic pathway hexokinase-2 and pyruvate kinase M2 were concordantly LOW or INT in only 3 of the 17 GBMs that also were LOW or INT for both OXCT1 and BDH1. The remaining brain tumors were positive for at least one of these glycolytic enzymes. Mitochondrial enzymes were not globally deficient. The mitochondrial enzyme acetyl CoA transferase (ACAT1) was present in 9 of the 14 GBM specimens that were LOW or INT for the mitochondrial enzymes OXCT1 and BDH1. Conclusions: Our data showing that many, but not all, malignant gliomas lack ketolytic enzymes, support the rationale of ERKD as investigational treatment for patients with malignant gliomas. Moreover, we hypothesize that it is important to test individual tumor samples for the expression of these enzymes prior to ERKD, as patients with malignant gliomas that have diminished capacity to metabolize ketones likely may derive the most benefit from ERKD.