Loss of FBXW7 Correlates with Increased IDH1 Expression in Glioma and Enhances IDH1-Mutant Cancer Cell Sensitivity to Radiation

Abstract F-box and WD repeat domain containing 7 (FBXW7) is a substrate receptor of the ubiquitin ligase SKP1-Cullin1-F-box complex and a potent tumor suppressor that prevents unregulated cell growth and tumorigenesis. However, little is known about FBXW7-mediated control of cell metabolism and related functions in cancer therapy. Here, we report that FBXW7 expression inversely correlates with the expression levels of the key metabolic enzyme isocitrate dehydrogenase 1 (IDH1) in patients with glioma and public glioma datasets. Deletion of FBXW7 significantly increased both wild-type (WT) and mutant IDH1 expression, which was mediated by blocking degradation of sterol regulatory element binding protein 1 (SREBP1). The upregulation of neomorphic mutant IDH1 by FBXW7 deletion stimulated production of the oncometabolite 2-hydroxyglutarate at the expense of increasing pentose phosphate pathway activity and NADPH consumption, limiting the buffering ability against radiation-induced oxidative stress. In addition, FBXW7 knockout and IDH1 mutations induced nonhomologous end joining and homologous recombination defects, respectively. In vitro and in vivo, loss of FBXW7 dramatically enhanced the efficacy of radiation treatment in IDH1-mutant cancer cells. Taken together, this work identifies FBXW7 deficiency as a potential biomarker representing both DNA repair and metabolic vulnerabilities that sensitizes IDH1-mutant cancers to radiotherapy. Significance: Deficiency of FBXW7 causes defects in DNA repair and disrupts NADPH homeostasis in IDH1-mutant glioma cells, conferring high sensitivity to radiotherapy.