Targeting the translational apparatus in MYCN-driven pediatric solid tumors

描述(申请人提供)：髓母细胞瘤是最常见的儿童恶性脑肿瘤，最具侵袭性的分子亚群对生物学知之甚少，没有针对性的治疗方法。这些亚群的特征是转录因子MYCN或MYC水平升高，并独立于sonic hedgehog(SHH)信号。我们最近开发了一种SHH非依赖性、NMYC驱动的小鼠髓母细胞瘤模型，在该模型中，高水平的NMYC蛋白驱动肿瘤的发生。先前的数据表明，哺乳动物雷帕霉素靶点(MTOR)下游的翻译装置的调节是MYC驱动的肿瘤发生所必需的，并且MYC和mTOR轴之间存在促进肿瘤形成的协同关系。MTOR信号通过两个初级输出，rpS6激酶(S6K)和翻译起始因子eIF4E。一类新的临床mTOR活性部位抑制剂通过两个效应器干扰信号，而变构结合物雷帕霉素仅干扰S6K。这些机制上不同的活性具有巨大的治疗意义--在我们的髓母细胞瘤模型中，mTOR的活性部位抑制剂，而不是雷帕霉素，在体外显示出有效性。综上所述，这支持了这样一种观点，即通过S6K发出的信号是可有可无的，而eIF4E是MYC驱动的肿瘤发生所必需的。我们假设MYCN与mTOR信号下游的eIF4E协同诱导小脑神经球的增殖，抑制mTOR激酶是SHH非依赖性髓母细胞瘤的关键治疗策略。我们将通过使用药理学方法和遗传学方法来研究这一假说，后者消除抑制剂的靶外效应，以验证mTOR活性部位抑制相对于mTOR变构抑制的重要性。首先，我们将确定MYCN如何影响翻译机构(目标1)。使用遗传学方法，我们将分别评估S6K和eIF4E在MYCN驱动的肿瘤发生中的重要性(目标2)。最后，我们将使用mTOR的临床抑制剂来评估S6K(使用mTOR的变构抑制剂)和eIF4E(使用mTOR活性部位抑制剂)作为潜在的治疗靶点在两个细胞系和我们的活体小鼠模型中(目标3)。这些目标的成功完成阐明了MYCN在最具侵袭性的髓母细胞瘤亚型中所起作用的基本和有针对性的机制。

DESCRIPTION (provided by applicant): Medulloblastoma is the most common malignant brain tumor in children, and the most aggressive molecular subgroups have poorly understood biology and no targeted therapies. These subgroups are characterized by increased levels of transcription factors MYCN or MYC, as well as independence from sonic hedgehog (SHH) signaling. We have recently developed a model of SHH-independent, murine NMYC-driven medulloblastoma in which high levels of NMYC protein drives oncogenesis. Previous data show that modulation of the translational apparatus downstream of the mammalian target of rapamycin (mTOR) is required for MYC-driven oncogenesis and that there is a synergistic relationship between MYC and the mTOR axis to promote tumor formation. mTOR signals through two primary outputs, rpS6 kinase (S6K) and the translation initiation factor eIF4E. A new class of clinical mTOR active site inhibitors disrupts signaling through both effectors, whereas the allosteric binder rapamycin disrupts only S6K. These mechanistically distinct activities have enormous therapeutic implications-in our medulloblastoma model, active site inhibitors of mTOR, but not rapamycin, demonstrate efficacy in vitro. Taken together, this supports the idea that signaling through S6K is dispensable, whereas eIF4E is required for MYC-driven oncogenesis. We hypothesize that MYCN cooperates with eIF4E downstream of mTOR signaling to induce proliferation of cerebellar neurospheres, and that mTOR kinase inhibition is a critical therapeutic strategy for SHH-independent medulloblastoma. We will investigate this hypothesis through the use of both pharmacological approaches and genetic approaches, the latter to eliminate the off-target effects of inhibitors, to validate the significace of mTOR active site inhibition as opposed to mTOR allosteric inhibition. First, we will determine how MYCN influences the translational apparatus (Aim 1). Using genetic approaches, we will separately evaluate the importance of S6K and eIF4E for MYCN-driven oncogenesis (Aim 2). Finally, we will use clinical inhibitors of mTOR to evaluate S6K (using allosteric inhibitors of mTOR) and eIF4E (using mTOR active site inhibitors) as potential therapeutic targets in both cell lines and our in vivo mouse models (Aim 3). Successful completion of these aims elucidates fundamental and targetable mechanisms underlying MYCN's role in the most aggressive subtypes of medulloblastoma.