Integrated Approach Reveals Role of Mitochondrial Germ-Line Mutation F18L in Respiratory Chain, Oxidative Alterations, Drug Sensitivity, and Patient Prognosis in Glioblastoma

Abstract

Glioblastoma is the most common and malignant primary brain tumour in adults, with a dismal prognosis. This is partly due to considerable inter- and intra-tumour heterogeneity. Changes in the cellular energy-producing mitochondrial respiratory chain complex (MRC) activities are a hallmark of glioblastoma relative to the normal brain, and associate with differential survival outcomes. Targeting MRC complexes with drugs can also facilitate anti-glioblastoma activity. Whether mutations in the mitochondrial DNA (mtDNA) that encode several components of the MRC contribute to these phenomena remains underexplored. We identified a germ-line mtDNA mutation (m. 14798T > C), enriched in glioblastoma relative to healthy controls, that causes an amino acid substitution F18L within the core mtDNA-encoded cytochrome b subunit of MRC complex III. F18L is predicted to alter corresponding complex III activity, and sensitivity to complex III-targeting drugs. This could in turn alter reactive oxygen species (ROS) production, cell behaviour and, consequently, patient outcomes. Here we show that, despite a heterogeneous mitochondrial background in adult glioblastoma patient biopsy-derived cell cultures, the F18L substitution associates with alterations in individual MRC complex activities, in particular a 75% increase in MRC complex II_III activity, and a 34% reduction in CoQ10, the natural substrate for MRC complex III, levels. Downstream characterisation of an F18L-carrier revealed an 87% increase in intra-cellular ROS, an altered cellular distribution of mitochondrial-specific ROS, and a 64% increased sensitivity to clomipramine, a repurposed MRC complex III-targeting drug. In patients, F18L-carriers that received the current standard of care treatment had a poorer prognosis than non-carriers (373 days vs. 415 days, respectively). Single germ-line mitochondrial mutations could predispose individuals to differential prognoses, and sensitivity to mitochondrial targeted drugs. Thus, F18L, which is present in blood could serve as a useful non-invasive biomarker for the stratification of patients into prognostically relevant groups, one of which requires a lower dose of clomipramine to achieve clinical effect, thus minimising side-effects.

An Alternative Pipeline for Glioblastoma Therapeutics: A Systematic Review of Drug Repurposing in Glioblastoma

“…Moreover, combining imipramine with ticlopidine, an inducer of autophagy, further increased mouse survival with increased cAMP levels as well as dysregulation of autophagic regulatory gene 7 (ATG7). Another TCA, clomipramine, proved to be efficacious in treating GBM cells that have a phenylalanine for leucine mutation in the mitochondrial respiratory chain complex III cytochrome b subunit, a mutation enriched in GBM [ 27 ].…”

Inhibition of mitochondrial carrier homolog 2 (MTCH2) suppresses tumor invasion and enhances sensitivity to temozolomide in malignant glioma

“…Extensive studies established that mitochondrial dysfunction is a prominent mechanism by which glioma cells exert its metabolic shift from oxidative phosphorylation (OXPHOs) to glycolysis, regardless of oxygen availability. During this metabolic reprogramming, mitochondrial function in glioma is evidently suppressed through mutations of mitochondrial DNA (Keatley et al 2019 ), altered metabolic enzyme atlas (Deighton et al 2014 ; Franceschi et al 2018 ), and imbalanced morphological dynamics (Xie et al 2015 ). All these events offer a proliferation advantage to tumor cells and decrease mitochondria-dependent cell death to chemical drugs (Vyas et al 2016 ).…”

Inhibition of Mitochondrial Carrier Homolog 2 (MTCH2) Suppresses Tumor Invasion and Enhances Sensitivity to Temozolomide in Malignant Glioma 

“…Extensive studies established that mitochondrial dysfunction is a prominent mechanism by which glioma cells exert its metabolic shift from oxidative phosphorylation (OXPHOs) to glycolysis, regardless of oxygen availability. During this metabolic reprogramming, mitochondrial function in glioma is evidently suppressed through mutations of mitochondrial DNA (8), altered metabolic enzyme atlas (9,10), and imbalanced morphological dynamics (11). All these events offer a proliferation advantage to tumor cells and decrease mitochondria-dependent cell death to chemical drugs (12).…”