Inhibition of wild-type IDH1 as a ferroptosis-inducing therapeutic approach for the treatment of malignant glioma.

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Our laboratories recent studies (Stegh and colleagues, Cell 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 alone while genetic and pharmacological inhibition of wt-IDH1, and in combination with radiation therapy (RT) slows the growth of patient-derived HGG xenografts 5,6 overexpression of wt-IDH1 promotes intracranial HGG growth molecular levels, wt-IDH1 high , . On 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 phospholipidperoxidase glutathione peroxidase 4 (GPX4)-drivenlipid repair, and dampensthe accumulation of polyunsaturated fatty acid (PUFA)-containing lipid peroxides, known executioners of ferroptosis. Based on these findings, we hypothesize that wt-IDH1 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-IDH1, we have used and characterized 13i, a first-in- class competitive -unsaturated enone, developed by AbbVie. 13i potently inhibits wt-IDH1 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-wthigh HGG bearing mice, alone and in combination with RT. We will test these hypotheses in three Specific Aims: Aim 1: Determine how wt-IDH1 impacts de novo fatty acid biosynthesis and membrane phospholipid composition to inhibit ferroptosis. Aim 2. Determine how wt-IDH1 promotes GPX4-dependent lipid repair and antagonizes ferroptosis. Aim 3: Determine if genetic and pharmacological inactivation of wt-IDH1 amplifies ferroptosis in response to RT and immune checkpoint blockade and antagonizes HGG progression. Objectives and long-term goals. We will credential wt-IDH1 as regulator of ferroptosis in HGG and will validate the pharmacological inhibition of wt-IDH1 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.