Targeting BCAT1 Combined with α-Ketoglutarate Triggers Metabolic Synthetic Lethality in Glioblastoma

Abstract

Branched-chain amino acid transaminase 1 (BCAT1) is upregulated selectively in human isocitrate dehydrogenase (IDH) wildtype (WT) but not mutant glioblastoma multiforme (GBM) and promotes IDHWT GBM growth. Through a metabolic synthetic lethal screen, we report here that α-ketoglutarate (AKG) kills IDHWT GBM cells when BCAT1 protein is lost, which is reversed by re-expression of BCAT1 or supplementation with branched-chain α-ketoacids (BCKAs), downstream metabolic products of BCAT1. In patient-derived IDHWT GBM tumors in vitro and in vivo, co-treatment of BCAT1 inhibitor gabapentin and AKG resulted in synthetic lethality. However, AKG failed to evoke a synthetic lethal effect with loss of BCAT2, BCKDHA, or GPT2 in IDHWT GBM cells. Mechanistically, loss of BCAT1 increased the NAD+/NADH ratio but impaired oxidative phosphorylation, mTORC1 activity, and nucleotide biosynthesis. These metabolic alterations were synergistically augmented by AKG treatment, thereby causing mitochondrial dysfunction and depletion of cellular building blocks, including ATP, nucleotides, and proteins. Partial restoration of ATP, nucleotides, proteins, and mTORC1 activity by BCKA supplementation prevented IDHWT GBM cell death conferred by the combination of BCAT1 loss and AKG. These findings define a targetable metabolic vulnerability in the most common subset of GBM that is currently incurable.

The physiological metabolite α-ketoglutarate ameliorates osteoarthritis by regulating mitophagy and oxidative stress

“…The tricarboxylic acid (TCA) cycle, also known as citric acid or Krebs cycle, occurs in the mitochondria in eukaryotes and regulates mitochondrial function and oxidative stress [ [14] , [15] , [16] , [17] ]. α-ketoglutarate (α-KG) is a key intermediate metabolite in the TCA cycle, also known as 2-oxoglutarate [ 18 ], which contributes to a variety of metabolic processes, including the biogenesis of numerous amino acids, nucleotide, lipid, and carnitine biosynthesis, and as a cofactor in numerous dioxygenases [ [19] , [20] , [21] , [22] ]. There is an increasing consensus that α-KG is involved in maintaining mitochondrial metabolism homeostasis [ 23 ], collagen synthesis [ 24 ], antioxidative defense [ 25 ], anti-inflammation [ 26 ], promoting cell proliferation [ 27 ], epigenetic modification [ 28 ], and tumor suppression [ 29 ].…”

GPT2 Is Induced by Hypoxia-Inducible Factor (HIF)-2 and Promotes Glioblastoma Growth

“…The cellular α-ketoglutarate levels were measured using a α-ketoglutarate colorimetric/fluorometric assay kit (Cat.#: K677-100, Biovision, Milpitas, CA, USA), as described previously [ 27 ]. Cells were lysed in ice-cold a-ketoglutarate assay buffer, sonicated, and centrifuged at 13,000 rpm for 10 min at 4 °C.…”

“…Scrambled control (SC) and GPT2 KD#2 U87MG cells (3 million) were mixed with Matrigel (1:1) and subcutaneously implanted into the flank side of 6- to 8-week-old male NOD/SCID mice (Envigo, Indianapolis, IN, USA). Tumor volume was measured with a caliper as described previously [ 27 ].…”

The biological essence of synthetic lethality: Bringing new opportunities for cancer therapy

“…Based on the above facts, the researchers developed a synthetic lethal therapy targeting branchedchain amino acid (BCAA) catabolism, providing a new option for patients with IDH wildtype GBM. 146,147 Similarly, the aberrant silencing of Inositol-3-Phosphate Synthase 1 (ISYNA1), the rate-limiting enzyme for myoinositol production, results in Solute Carrier Family 5 Member 3 (SLC5A3)-dependent myo-inositol transport in AML. Because ISYNA1 has been epigenetically silenced, cancer cells must rely on the transport of myo-inositol by SLC5A3 to maintain intracellular myo-inositol levels.…”