Effects of the Combination Therapy of a CDK4/6 and a MEK inhibitor in a Mouse Model of Diffuse Midline Glioma

Diffuse intrinsic pontine glioma (DIPG) arises in the brainstem of children, leading tumor-related death among children. A heterozygous histone H3.3K27M mutation has been shown to occur in ~80% of DIPGs, and results in brainstem gliomagenesis. There is no clinical trial for the patients with DIPG that proved to prolong survival time so far. Recently, CDK4/6 inhibitor showed feasibility and early therapeutic effect against DIPG. Also, recent research with human DIPG specimens have detected the MAPK pathway highly activated. Here, we evaluated a novel combination therapy with CDK4/6 inhibitor and MEK inhibitor to the mouse DIPG model. In order to generate DIPG-bearing mice, we are using the RCAS/Tv-a system, with which we are able to target specific genetic alterations in RCAS viruses (avian retroviruses) to specific cells-of-origin using transgenic Tv-a-expressing mice (Tv-a being the receptor for RCAS viruses). We injected P3-P5 Nestin-Tv-a;p53fl/fl mice (C56Bl/6 background) with RCAS-PDGF-A + RCAS-H3.3K27M, and RCAS-Cre. The mice are treated with vehicle (methylcellurose), ribociclib as monotherapy, trametinib as monotherapy, and ribociclib and combination as combination. For short-term use, tumor tissues treated with ribociclib showed cytostatic effect, and those treated with trametinib showed cytotoxic effect, and those with combination showed both. Long-term use showed that combination therapy modestly prolonged mice survival compared with vehicle. Therefore, we need to find how DIPG showed registence to the long-term chemotherapy. Overall design: Examination of gene expression differences in mouse DIPGs treated with vehicle, ribociclib, trametinib, and ribociclib and trametinib as combination

弥漫内生型桥脑胶质瘤（Diffuse intrinsic pontine glioma, DIPG）多发于儿童脑干，是导致儿童肿瘤相关死亡的主要病因。约80%的DIPG病例存在杂合型组蛋白H3.3K27M突变，该突变可诱发脑干胶质瘤发生。截至目前，尚无针对DIPG患者的临床试验被证实可延长其生存时长。近期研究表明，细胞周期蛋白依赖性激酶4/6（CDK4/6）抑制剂对DIPG展现出良好的可行性与早期治疗效果；此外，针对人类DIPG标本的最新研究发现，丝裂原活化蛋白激酶（MAPK）通路呈高度激活状态。本研究针对小鼠DIPG模型，评估了CDK4/6抑制剂与丝裂原活化蛋白激酶激酶（MEK）抑制剂的新型联合治疗方案。为构建携带DIPG的小鼠模型，本研究采用RCAS/Tv-a系统：该系统可借助表达Tv-a的转基因小鼠（Tv-a为RCAS病毒的受体），将RCAS病毒（禽逆转录病毒，avian retroviruses）携带的特定遗传改造靶向至特定细胞起源。我们向背景为C56Bl/6的P3-P5 Nestin-Tv-a;p53fl/fl小鼠注射RCAS-PDGF-A + RCAS-H3.3K27M以及RCAS-Cre。小鼠分别接受赋形剂（甲基纤维素）、单药瑞博西尼（ribociclib）、单药曲美替尼（trametinib）以及瑞博西尼与曲美替尼联合治疗。短期给药实验结果显示：经瑞博西尼处理的肿瘤组织呈现细胞静止效应，经曲美替尼处理的肿瘤组织表现出细胞毒性效应，而联合给药组则同时兼具两种效应。长期给药实验结果表明，联合治疗组小鼠的生存周期较赋形剂组有适度延长。因此，本研究亟需阐明DIPG对长期化疗产生耐药性的潜在机制。本研究的整体实验设计为：检测赋形剂、瑞博西尼单药、曲美替尼单药以及瑞博西尼与曲美替尼联合治疗的小鼠DIPG组织中的基因表达差异。