Somatic Cell Transfer to Model Medulloblastoma in Mice

描述(申请人提供)：髓母细胞瘤(MBS)是一种由儿童小脑神经前体细胞转化而产生的恶性脑肿瘤。积极的治疗方法结合手术、颅骨脊髓放疗和化疗可使5年存活率超过70%。与治疗相关的神经毒性产生了识别信号分子的迫切需要，这些信号分子可以作为治疗的靶点，以最大限度地抑制肿瘤生长，并将附带的脑损伤降至最低。本研究的总体目标是使用我们利用RCAS/TV-a基因转移系统开发的MB小鼠模型作为分子靶向MB治疗的临床前测试平台。这个实验系统使用了来自禽白血病病毒的逆转录病毒载体(RCAS)和在Nestin基因启动子控制下表达逆转录病毒受体的转基因小鼠系，Nestin基因启动子在正常小脑发育期间活跃在神经前体细胞中。利用该系统，我们证明了Sonic Hedgehog(Shh)基因在小鼠小脑中的异位表达诱导了小鼠的MBS。此外，我们鉴定了属于不同功能类别的蛋白质，它们与Shh合作促进MB的形成。这些促进因子是：(A)Myc癌蛋白，在正常发育过程中刺激神经前体细胞的增殖；(B)bcl2，有效地抑制细胞凋亡；(C)胰岛素样生长因子-II，通过激活磷脂酰肌醇3-激酶(PI3K)信号转导通路，同时刺激增殖和阻止细胞凋亡；以及(D)肝细胞生长因子，一种对肿瘤生长具有多效性的生长因子。所有这些蛋白都在人的MBS中高表达，这表明它们在小鼠体内的促肿瘤活性准确地反映了人类疾病的发病机制。此外，这些蛋白质及其下游的信号分子可以被认为是治疗靶点。具体目的1是确定抑制Shh信号与阻断HGF信号是否协同增强Shh诱导的MBS小鼠的治疗反应。具体目的2是确定是否可以通过药物抑制HGF受体c-Met或下游PI3K信号来增强HGF单抗治疗对MB生长的抑制作用。具体目标3是使用RCAS/TV-a系统来识别导致Shh诱导的MBS转移到脊柱的基因。脊椎转移是MBS患者非常不利的预后因素。这些目标的实现将有可能将机械发现转化为针对MB儿童的分子靶向治疗。

DESCRIPTION (provided by applicant): Medulloblastomas (MBs) are malignant brain tumors that arise by transformation of neural progenitor cells in the cerebellum in children. Aggressive treatment approaches combining surgery, craniospinal radiation, and chemotherapy result in 5-year survival rates exceeding 70%. Treatment- related neurotoxicity has created a critical need to identify signaling molecules that can be targeted therapeutically to maximize tumor growth suppression and minimize collateral brain damage. The overall objective of this research is to use a mouse model of MB, which we developed using the RCAS/tv-a gene transfer system, as a preclinical testing platform for molecular targeted MB therapy. This experimental system uses a retroviral vector (RCAS) derived from avian leukosis virus and a transgenic mouse line that expresses the retrovirus receptor under control of the Nestin gene promoter, which is active in neural progenitor cells during normal cerebellar development. Using this system, we showed that ectopic expression of Sonic Hedgehog (Shh) in the postnatal cerebellum induces MBs in mice. Furthermore, we identified proteins belonging to different functional classes that cooperate with Shh to enhance MB formation. These enhancing factors are (a) Myc oncoproteins, which stimulate proliferation of neural progenitors during normal development, (b) Bcl-2, which potently inhibits apoptosis, (c) insulin-like growth factor-II, which concomitantly stimulates proliferation and blocks apoptosis by activating the phosphatidylinositol 3-kinase (PI3K) signal transduction pathway, and (d) hepatocyte growth factor (HGF), a growth factor with pleiotropic effects on tumor growth. The fact that all of these proteins are highly expressed in human MBs indicates that their tumor-promoting activity in mice accurately reflects the pathogenesis of the human disease. Moreover, these proteins and their downstream signaling molecules can be considered therapeutic targets. Specific aim 1 is to determine whether inhibiting Shh signaling cooperates with blockade of HGF signaling to enhance treatment response in mice bearing Shh?induced MBs. Specific aim 2 is to determine whether MB growth suppression by HGF monoclonal antibody therapy can be enhanced by pharmacologic inhibition of the HGF receptor c- Met or downstream PI3K signaling. Specific aim 3 is to use the RCAS/tv-a system to identify genes that cause Shh-induced MBs to metastasize to the spine. Spinal metastasis is a highly unfavorable prognostic factor for patients with MBs. Achievement of these aims will make it possible to translate the mechanistic discoveries to molecular targeted therapies for children with MB.