Therapeutic resistance and aggressive malignancy in glioblastomas: the contribution of GTP metabolism through regulation by IMPDH2

摘要 多形性胶质母细胞瘤(GBM)是最具侵袭性和致命性的脑肿瘤。尽管做出了广泛的努力 为了改善治疗，目前的GBM疗法仅略微延长了中位生存期，从大约12个月延长到 超过14个月。已经尝试了各种策略来改善治疗，但都被证明是唯一的 循序渐进地好于目前的护理标准。如果没有发现胶质瘤的独特特性， 可能使其成为有效的治疗靶点，GBM的预后将继续非常差。这个 我们实验室的长期目标是了解GTP代谢在肿瘤生长中的基础作用 GBM作为一个模型系统。为此，我们在《分子细胞》(2016)上发表了脂蛋白激酶的发现 PI5P4Kβ作为细胞内的GTP传感器，调节细胞对GTP的需求。在调查GTP的过程中 新陈代谢，我们在《自然细胞生物学》(2019)上进一步发表，GTP合成增加与 与GBM肿瘤增殖的侵袭性有关。GTP代谢重编程是由 上调肌苷一磷酸脱氢酶-2(IMPDH2)，激活GTP的生物合成 促进核糖体的生物发生和蛋白质合成。重要的是，治疗耐药的一个独特特征 GBM干细胞样细胞(GSCs)完全依赖于从头合成GTP。在未出版的初步版本中 研究发现，IMPDH2具有明显的抗活性氧损伤作用。 种(ROS)。重要的是，电离辐射直接通过dna断裂对肿瘤细胞产生杀伤作用。 其次是ROS的产生，ROS占DNA损伤的60%-70%。如此高的ROS 耐药性似乎是IMPDH2的一个关键和特定的特征。指导这项提议的核心假设是 IMPDH2通过以下方式促进GBM生长：1)抵抗辐射诱导的ROS损伤效应；2) 诱导GSCs存活所需的从头合成GTP。我们将通过探索分子来测试这一点 利用IMPDH2及其突变体的结构和分子分析研究ROS抗性机制。 (目标1)和GSC对从头合成GTP的高度依赖(目标2)。在目标3中，我们将使用IMPDH2 霉酚酸及其前体药物霉酚酸酯(MMF)对大鼠GBM模型的抑制作用 跟踪肿瘤生长和GBM微环境，次要目标是确定这些抑制物， 由于其抗炎和抗血管生成的特性，可以减轻常见的脑水肿。 在GBM(目标3)。完成这些目标将确定监文信息系统通过哪些机制来规范 Novo GTP合成，从而推动GBM肿瘤的生长。这些洞察力，当结合临床前数据时 MMF是一种已经被批准具有免疫抑制作用的药物，它有可能导致快速翻译 到人类的GBM。 项目说明

Summary Glioblastoma multiforme (GBM) is the most aggressive and lethal of all brain tumors. Despite extensive efforts to improve treatment, current GBM therapy only marginally prolongs median survival from about 12 months to over 14 months. A variety of strategies have been attempted to improve treatment, but all have proven to be only incrementally better than the current standard of care. Without the discovery of unique properties of gliomas that could make them effective targets for treatment, GBM will continue to have an extremely poor prognosis. The long-term goal of our laboratory is to understand the fundamental role of GTP metabolism in cancer growth using GBM as a model system. To that end, we published in Molecular Cell (2016) the discovery of lipid kinase PI5P4Kβ as an intracellular GTP sensor regulating the cells needs for GTP. In the course of investigating GTP metabolism, we further published in Nature Cell Biology (2019) that increased GTP synthesis is directly linked to the aggressive nature of GBM tumor proliferation. The GTP metabolic reprogramming is induced by upregulation of inosine monophosphate dehydrogenase-2 (IMPDH2), activating de novo GTP biosynthesis for the promotion of ribosomal biogenesis and protein synthesis. Importantly, a unique feature of treatment resistant GBM stem-like cells (GSCs) is exclusive dependence on de novo GTP synthesis. In unpublished preliminary studies, we have discovered that IMPDH2 is markedly resistant to the damaging effects of reactive oxygen species (ROS). Importantly, ionizing radiation exerts its cell killing effect on tumor through DNA breaks directly and secondary to the generation of ROS, which accounts for 60-70 % of DNA lesions. This high ROS resistance appears to a critical and specific feature of IMPDH2. The central hypothesis guiding this proposal is that IMPDH2 promotes GBM growth by i) being resistant to the damaging effect radiation induced ROS, ii) inducing de novo GTP synthesis required for GSCs survival. We will test this by exploring the molecular mechanisms of the ROS resistance using the structural and molecular analyses of IMPDH2 and its mutants. (Aim 1) and GSC’s high dependence on de novo GTP biosynthesis (Aim 2). In Aim 3, we will use the IMPDH2 inhibitor, mycophenolic acid (MPA) and its prodrug, mycophenolate mofetil (MMF) on in vivo GBM models tracking tumor growth and GBM microenvironments with a secondary objective to determine if these inhibitors, by virtue of their anti-inflammatory and anti-angiogenic properties, reduce the cerebral edema commonly seen in GBM (Aim 3). Completion of these aims will identify the mechanisms through which IMPDH2 regulates de novo GTP synthesis thereby driving on GBM tumor growth. These insights, when combined preclinical data on MMF, a drug already approved for its immunosuppressive effects, has the potential to result in rapid translation to human GBM. Project Description