Effectively Targeting Notch in Hypoxic Brain Tumor Cells

描述(由申请人提供)：由于肿瘤细胞对标准疗法的抵抗，胶质母细胞瘤(GBM)患者尚无治愈方法。干细胞样肿瘤亚群似乎对大多数治疗特别难治，而且越来越清楚的是，特定的肿瘤 微环境可以促进干细胞的特性和化疗耐药性。然而，对新兴靶向治疗如何与其他药物和肿瘤微环境相互作用的了解很少，限制了它们的发展。该项目的长期目标是开发Notch抑制剂，作为治疗胶质母细胞瘤和其他恶性脑瘤的有效新疗法。这项建议的目的是阐明Notch是如何与肿瘤微环境和其他治疗相互作用的，以便在临床上有效地使用通路抑制剂。Notch通路是产生和维持非肿瘤性神经干细胞所必需的，在GBM肿瘤干细胞(CSC)中也起着关键作用。已有研究表明，血管周围微环境通过激活Notch信号来促进CSC，目前已有许多靶向血管的药物被使用。随着肿瘤相关血管的移除，基底膜和其他肿瘤转移到低氧表型，而Notch将如何在这种微环境中发挥作用还不太清楚。在这项建议中要检验的中心假设是，Notch不仅在血管周围的壁龛中，而且在缺氧的微环境中，是GBM分化和治疗反应的关键调节因子。事实上，新出现的数据表明，低氧肿瘤细胞可以概括定义血管周围生态位的许多分子特征，而Notch在这一背景下诱导干细胞样表型并调节对传统化疗的反应。前两个具体目标集中在了解Notch是如何在缺氧的GBM细胞中被激活的，以及确定Notch阻断是否可以逆转缺氧促进的CSC和化疗耐药的增加。第二个目标集中在Notch抑制和替莫唑胺化疗之间的相互作用，并研究Notch阻断可以使GBM对这种常用的烷化剂增敏的新机制。这些研究将确定Notch活性是如何在低氧脑胶质瘤细胞中调节的，并建立在低氧微环境中对CSC诱导和侵袭性肿瘤行为的要求。他们还将研究一种新的表观遗传学机制，通过该机制，该途径可以调节MGMT的表达和替莫唑胺的敏感性。这些结果都具有很高的临床相关性，并将直接影响到针对CSC的胶质母细胞瘤新药的开发。

DESCRIPTION (provided by applicant): No cures exist for patients with glioblastoma (GBM) due to the resistance of tumor cells to standard therapies. Stem-like tumor subpopulations seem especially refractory to most treatments, and it is becoming increasingly clear that specific tumor microenvironments can promote stem cell properties and chemoresistance. However, poor understanding of how emerging targeted therapies interact with other agents and the tumor microenvironment has limited their development. The long-term goal of the project is to develop Notch inhibitors as effective new therapies for glioblastoma and other malignant brain tumors. The objective of this proposal is to elucidate how Notch interacts with the tumor microenvironment and other treatments so pathway inhibitors can be effectively used in the clinic. The Notch pathway, which is required for generation and maintenance of non-neoplastic neural stem cells, also plays a key role in GBM cancer stem cells (CSC). It has been shown that the perivascular microenvironment promotes CSC through activation of Notch signaling, and a number of agent targeting blood vessels are currently in use. As tumor-associated blood vessels are removed, GBM and other tumors shift towards a hypoxic phenotype, and it is less clear how Notch will function in this microenvironment. The central hypothesis to be tested in this proposal is that Notch is a key mediator of GBM differentiation and therapeutic response not just in the perivascular niche, but also in the hypoxic microenvironment. Indeed, emerging data suggest that hypoxic tumor cells can recapitulate many of the molecular features which define the perivascular niche, and that Notch induces a stem-like phenotype and modulates the response to traditional chemotherapy in this context. The first two specific aims focus on understanding how Notch is activated in hypoxic GBM cells, and determining if Notch blockade can reverse the increase in CSC and chemoresistance promoted by hypoxia. The second two specific aims focus on the interaction between Notch inhibition and temozolomide chemotherapy, and investigate a novel mechanism by which Notch blockade can sensitize GBM to this commonly used alkylating agent. These studies will determine how Notch activity is regulated in hypoxic glioma cells, and to establish a requirement for Notch in CSC induction and aggressive tumor behavior in the hypoxic microenvironment. They will also examine a novel epigenetic mechanism by which the pathway can modulate MGMT expression and temozolomide sensitivity. These results are all of high clinical relevance, and will have a direct impact on the development of a novel agent targeting CSC in glioblastoma.