Our laboratories recent studies (Stegh and colleagues, Ce// Report, 2017; Wahl and colleagues, Cancer Research, 2017) indicated that IDH1 wild-type (IDH1-wt) is overexpressed in 2/3 of HGG (referred to here as 'IDH1-wthigh GBM') that lack IDH1R132H mutation. Both genetic and pharmacological inhibition of wt-lDH1, alone and in combination with radiation therapy (RT) slows the growth of patient-derived HGG xenografts5,6, while overexpression of wt-lDH1 promotes intracranial HGG growth. On molecular levels, wt-lDH1high GBM produce excess NADPH, which serves as a rate-limiting reductant that drives the biosynthesis of mono unsaturated fatty acids (MUFAs). In addition, enhanced NADPH production increases glutathione (GSH) level, reduces reactive oxygen species (ROS), activates phospholipid peroxidase glutathione peroxidase 4 (GPX4)-driven lipid repair, and dampens the accumulation of polyunsaturated fatty acid (PUFA)-containing lipid peroxides, known executioners of ferroptosis. Based on these findings, we hypothesize that wt-lDH1 through enhanced lipid repair, heightened MUFA biosynthesis and displacement of oxidizable PUFAs from plasma membrane phospholipids antagonizes ferroptosis, a recently discovered form of cell death has rapidly gained recognition as a paradigm shifting strategy to specifically target cancer cells. We further hypothesize that wt-IDH1 inhibition cooperates with known inducers of ferroptosis, including RT and immune-mediated checkpoint inhibition, to antagonize HGG progression. For the pharmacological inhibition of wt-lDH1, we have used and characterized 13i, a first-in c/ass competitive a,f]-unsaturated enone, developed by AbbVie. 13i potently inhibits wt-lDH1 enzymatic activity, by covalently binding to the NADP binding pocket. Our data indicate that 13i promotes ferroptosis, is brain-penetrant, and like genetic ablation, reduces progression and extends the survival of IDH1-wfhigh HGG bearing mice, alone and in combination with RT. We will test these hypotheses in three Specific Aims: Aim 1: Determine how wt-lDH1 impacts de novo fatty acid biosynthesis and membrane phospholipid composition to inhibit ferroptosis. Aim 2. Determine how wt-lDH1 promotes GPX4-dependent lipid repair and antagonizes ferroptosis. Aim 3: Determine if genetic and pharmacological inactivation of wt-lDH1 amplifies ferroptosis in response to RT and immune checkpoint blockade and antagonizes HGG progression. Objectives and long-term goals. We will credential wt-lDH1 as regulator of ferroptosis in HGG and will validate the pharmacological inhibition of wt-lDH1 using a novel NADP+ competitive inhibitor as a therapeutic strategy. Results from these studies are expected to inform the design of IND-enabling studies evaluating the potential of 13i as adjuvant for anti-HGG therapy.