Elucidating and targeting the molecular foundations of IDH Mutant glioma

描述（由申请人提供）：胶质母细胞瘤（GBM）是中枢神经系统（CNS）的一种原发恶性肿瘤，几乎普遍致命。我们的长期目标是了解胶质瘤发生的分子机制，并利用这些信息为 GBM 患者开发更好的治疗方式。最近的工作表明，GBM 由几个亚组组成，每个亚组由不同的基因改变驱动。 GBM 的原神经亚组是一个独特的类别，包括具有异柠檬酸脱氢酶 (IDH) 1 和 2 突变、PDGF 通路激活和神经胶质瘤高甲基化表型 (G-CIMP) 的肿瘤。这些改变可能是可逆的，并且作为潜在目标具有广阔的前景。然而，突变 IDH 介导的转化的作用机制仍不清楚。最近，我们的团队已经证明 IDH 突变通过重塑表观基因组来建立 G-CIMP 并阻止分化发挥作用。本申请的中心假设是突变 IDH 诱导的表观基因组变化是 GBM 亚群发育的关键事件。该提案的目的是了解突变 IDH 诱导的神经胶质瘤发生的分子基础，并评估通过追求 3 个具体目标来靶向这种改变的效用。在目标 1 中，我们将阐明突变 IDH1 相关表观遗传重编程背后的染色质状态动态。这里的工作假设是 IDH 突变通过重塑表观基因组和阻止分化来发挥作用，这种效应可能是可逆的。我们将系统地阐明 IDH1 突变引起的全局和个体效应基因水平的染色质状态变化的细节。我们将探讨突变 IDH 诱导效应的可逆性。在目标 2 中，我们将描述 IDH1 突变和 IDH1 突变相关遗传改变之间的致癌协同性。我们的数据表明，突变的 IDH1 通过促进去分化状态发挥作用，但不会单独转化细胞。我们的假设是 IDH1 突变与其他反复出现的遗传病变协同作用以实现转化。我们将定义这种致癌背景的租户。我们将使用人星形胶质细胞和鼠 RCAS-TVA 系统研究相关病变在转化中与突变 IDH1 配合的能力。在目标 3 中，我们将通过表观遗传疗法优化 IDH1 突变依赖性生物学改变的靶向。由于 IDH 诱导的变化原则上是可逆的，因此我们假设可以使用靶向小分子来逆转突变 IDH1 的影响，从而使组织特异性因子能够驱动分化。使用突变 IDH1 抑制剂 (AGI-5198) 单独抑制突变 IDH1 可阻止 2-HG 产生，但仅对肿瘤生长产生轻微影响。相比之下，DNMT 和 H3K9 甲基化酶抑制剂（DAC、BIX）可直接逆转病理甲基化，并且对 IDH 突变细胞非常有效。我们将使用这两种方法来优化治疗策略。使用体外和小鼠模型，我们将单独使用 DNA/组蛋白甲基化抑制剂或与 AGI-5198 联合使用，以逆转突变 IDH1 的影响。

DESCRIPTION (provided by applicant): Glioblastoma (GBM) is a primary malignancy of the central nervous system (CNS) that is nearly universally fatal. Our long-term goal is to understand the molecular mechanisms that underlie gliomagenesis and to use this information to develop better therapeutic modalities for GBM patients. Recent work has demonstrated that GBMs consist of several subgroups, each driven by different genetic alterations. The proneural subgroup of GBMs is a distinct class that includes tumors with isocitrate dehydrogenase (IDH) 1 and 2 mutation, PDGF pathway activation, and the glioma hypermethylator phenotype (G-CIMP). These alterations are potentially reversible and hold great promise as potential targets. However, the mechanisms of action underlying mutant IDH-mediated transformation remain unclear. Recently, our groups have shown that IDH mutation functions by remodeling the epigenome to establish G-CIMP and institute a block to differentiation. The central hypothesis of this application is that mutant IDH-induced epigenomic changes are critical events underlying the development of this subset of GBMs. The objective of this proposal is to understand the molecular foundations of mutant IDH-induced gliomagenesis and to evaluate the utility of targeting this alteration by pursuing 3 Specific Aims. In Aim 1, we will elucidate the chromatin state dynamics underlying mutant IDH1- associated epigenetic reprogramming. The working hypothesis here is that IDH mutation acts by remodeling the epigenome and blocking differentiation, an effect that may be reversible. We will systematically elucidate the details of IDH1 mutation-induced chromatin state changes globally and at the level of individual effector genes. We will interrogate the reversibility of mutant IDH-induced effects. In Aim 2, we will characterize oncogenic cooperativity between IDH1 mutation and IDH1 mutation-associated genetic alterations. Our data indicates that mutant IDH1 acts by promoting a dedifferentiated state, but does not transform cells alone. Our hypothesis here is that IDH1 mutation cooperates with other recurring genetic lesions to achieve transformation. We will define the tenants of this oncogenic context. We will investigate the ability of associated lesions to cooperate with mutant IDH1 in transformation using human astrocytes and the murine RCAS-TVA system. In Aim 3, we will optimize targeting of mutant IDH1-dependent biological alterations with epigenetic therapy. Since IDH-induced changes are in principle reversible, we hypothesize that the effects of mutant IDH1 can be reversed using targeted small molecules, which will then enable tissue-specific factors to drive differentiation. Inhibition of mutant IDH1 alone using a mutant IDH1 inhibitor (AGI-5198) blocks 2-HG production but affects tumor growth only modestly. In contrast, DNMT and H3K9 methylase inhibitors (DAC, BIX) directly reverse pathologic methylation and are very potent against IDH mutant cells. We will use these two approaches to optimize a therapeutic strategy. Using both in vitro and mouse models, we will use DNA/ histone methylation inhibitors, alone and in combination with AGI-5198, to reverse the effects of mutant IDH1.