Glioblastoma utilizes fatty acids and ketone bodies for growth allowing progression during ketogenic diet therapy

Abstract

Glioblastoma (GBM) metabolism has traditionally been characterized by a dependence on aerobic glycolysis, prompting use of the ketogenic diet as a potential therapy. We observed growth-promoting effects on U87 GBM of both ketone body and fatty acid (FA) supplementation under physiological glucose conditions. An in vivo assessment of the unrestricted ketogenic diet surprisingly resulted in increased tumor growth and decreased animal survival. These effects are abrogated by FAO inhibition using knockdown of carnitine palmitoyltransferase 1 (CPT1).Primary patient GBM cultures revealed significant utilization of FAO regardless of tumorigenic mutational status and decreased proliferation, increased apoptosis, and elevated mitochondrial ROS production with CPT1 inhibition. Metabolomic tracing with 13 C-labeled fatty acids showed significant FA utilization within the TCA cycle, indicating that FAO is used for both bioenergetics and production of key intermediates. These data demonstrate important roles for FA and ketone body metabolism that could serve to improve targeted therapies in GBM.traditionally characterized by its reliance on the Warburg effect. Under normal physiological conditions the healthy adult brain meets most of its energy demand by complete oxidation of glucose. This produces pyruvate which is then converted into acetyl-CoA for entrance into the TCA cycle to support the electron transport chain 1 . Thus, glycolysis and respiration remain tightly connected and result in more efficient ATP production with little lactic acid production. In contrast, the Warburg effect dramatically increases the rate of aerobic glycolysis and lactic acid production in the cytosol. While the benefits of this phenomenon are not completely understood, it has been posited that its main advantages are increased biomass production and facilitated invasion due to acidification of the microenvironment 2 .GBMs have been identified as highly reliant on aerobic glycolysis to the point that they are sometimes referred to as being "glucose addicted". Several common signaling pathways found to be altered in GBM, such as PI3K-Akt-mTOR and Myc pathways, promote this phenotype by increasing expression of genes that allow cells to take up large amounts of glucose for increased glycolysis and lactate production 1, 3, 4 . Alterations to these pathways are often associated with mutations common to GBM such as EGFR and PTEN. EGFR, an activator of PI3K, is amplified in ~40% of GBMs with approximately half of those tumors expressing the constitutively active EGFRviii variant 5 . The tumor suppressor protein PTEN, a potent PI3K antagonist, is also altered in 30-40% of GBMs 6 . Similar to EGFR amplification, loss of PTEN function by either mutation or deletion results in hyperactivation of the PI3K/Akt signaling network. Despite these findings, little progress has been made therapeutically in targeting enzymes reported to regulate glucose metabolism in GBM.The interconnection between oncogenic signaling networks and metabolic pathways is complex in...

Energy Metabolism in IDH1 Wild-Type and IDH1-Mutated Glioblastoma Stem Cells: A Novel Target for Therapy?

“…For the synthesis of ATP, a thorough metabolic rewiring occurs in IDH1 mt cells, leading to a vast increase in the number of mitochondria as was shown in oligodendroglioma cells [ 49 ]. IDH1 wt glioblastoma cells mainly use glycolysis as a classical Warburg phenotype that produces lactate [ 50 , 51 ], whereas IDH1 mt secondary glioblastoma use OXPHOS for the generation of ATP using pyruvate and glutamate, which has been determined at the gene expression, protein, and metabolite levels [ 42 , 45 , 52 , 53 , 54 , 55 ].…”

“…It was found that ROS levels were increased in GSCs and apoptosis was induced, whereas ROS scavengers annihilated these effects [ 77 ]. However, an unrestricted ketogenic diet did not reduce tumor growth in vivo in various glioblastoma mouse models, whereas the inhibition of fatty acid oxidation by etomoxir reduced glioblastoma growth in the same mouse models [ 50 ]. It appeared that etomoxir prolonged the survival of mice whereas the ketogenic diet did not affect survival or even reduce the survival of the mice.…”

“…It appeared that etomoxir prolonged the survival of mice whereas the ketogenic diet did not affect survival or even reduce the survival of the mice. IDH1 wt and IDH1 mt glioblastoma cells were not differently affected by etomoxir [ 50 ]. We conclude that the long-standing conviction that a ketogenic diet is beneficial for glioblastoma patients has no scientific grounds.…”

“…The energy metabolism of IDH1 mt glioblastoma is forced to be dependent on OXPHOS instead of aerobic glycolysis because of the drain of αKG and NADPH by the IDH1 mt enzyme that converts αKG into D-2-HG with concomitant oxidation of NADPH into NADP + [ 42 , 45 , 52 , 53 , 54 , 55 ]. This altered metabolism causes metabolic stress, and it has been hypothesized by us and others that the increased metabolic stress induced by the therapeutic targeting of the mitochondrial energy metabolism prolongs the survival of IDH1 mt glioblastoma patients [ 10 , 50 , 61 ]. Candidate compounds in this respect are metformin or phenformin, chloroquine, and epigallocatechin-3-gallate (EGCG) to inhibit the production of αKG by glutamate dehydrogenase.…”

Systems level profiling of chemotherapy-induced stress resolution in cancer cells reveals druggable trade-offs

“…A similar metabolic state, which is characterized by minimal glycolysis and high dependency on fatty acid oxidation, has been described in rapidly cycling germinal-center B cells (78). Preclinical observations suggest that the reliance of some cancers on fatty acids to generate energy may be exploited therapeutically by means of pharmacological or dietary interventions (79,80). It is therefore tempting to speculate that such approaches could also be applied in the context of PIs in MM patients, particularly as our observations on the effects of metformin and GCN2 inhibition also link fatty acid metabolism to stress recovery in PI-treated MM cells.…”