The Role of Cidofovir and Structural Analogs as Adjuvant Therapy for Glioblastoma

描述(申请人提供)：胶质母细胞瘤(GBM)是一种致命的原发脑瘤，大多数患者在确诊后12-15个月存活，尽管接受了标准的护理治疗。我们发现人类巨细胞病毒(HCMV)存在于高比例的GBM中，这一发现已被多个小组证实。我们的合作者Nino Chiocca博士最近证明，在胶质瘤转基因小鼠模型中，CMV感染加速了肿瘤向GBM的进展。最近，针对巨细胞病毒的抗病毒治疗在GBM患者中显示出疗效。我们已经确定FDA批准的治疗CMV感染的抗病毒药物西多福韦(CDV)在体外和在原发GBM的异种小鼠颅内移植模型中都有效地抑制了GBM的增殖。此外，我们对CDV的研究表明，虽然CDV的抗病毒作用对于抗肿瘤反应是重要的，但即使在没有CMV感染的情况下，CDV也具有强大的抗肿瘤特性。重要的是，使用CDV体内GBM异种移植模型观察到的抗肿瘤反应比迄今在UCSF测试的除替莫唑胺以外的任何全身用药都要强，而对于替莫唑胺，实质性的肿瘤反应仅限于使用肿瘤细胞来源及其相应的具有甲基化MGMT启动子的异种移植。从机制上讲，我们已经确定CDV，一种胞嘧啶类似物，不仅整合到CMV DNA中，而且还整合到肿瘤细胞基因组DNA中。我们发现，肿瘤细胞摄取CDV激活了凋亡途径，阻断了正常的DNA修复机制，这与肿瘤细胞对放射治疗(RT)的抵抗和恢复有关，RT是新诊断的GBM的主要护理治疗方式。在我们的体外和体内研究中，CDV增强了RT的效果。虽然CDV用于治疗人类疾病的局限性是组织摄取不良和肾毒性，但我们的合作者Karl Hostetler博士已经合成了高度亲脂的CDV衍生物，并且可以口服，而造成的毒性最小。在我们的初步研究中，这些化合物在体外显示出300倍的抗肿瘤作用，因此与西多福韦相比，可以大大降低剂量，达到显著的抗肿瘤活性。在目标1中，我们计划使用加州大学旧金山分校我们的合作研究员David James博士开发的现有小鼠异种移植模型，以获得的研究药物药代动力学知识为基础来优化治疗，并确定将抑制剂与RT结合时使用的最佳方案。在目标2中，我们将利用Chiocca博士的自发发生的GLOMS+/-CMV感染的转基因小鼠模型来了解抗病毒治疗在CMV介导的GBM肿瘤发生中的影响。此外，我们还将从巨细胞病毒对肿瘤微环境和宿主对肿瘤的免疫反应的影响方面来研究抗病毒治疗的影响。最后，在目标3中，我们计划研究CDV和CDV衍生化合物引起DNA损伤和干扰DNA修复机制的机制。我们预计，这些化合物的主要优势之一将是它们的高治疗指数：即对正常细胞的毒性有限，但Dramati凋亡途径激活和阻止肿瘤细胞的DNA修复，可以显著延缓或可能防止对GBM复发至关重要的放射和化疗耐药性。

DESCRIPTION (provided by applicant): Glioblastoma (GBM) is a fatal primary brain tumor, with most patients surviving 12-15 months following diagnosis, despite receiving standard of care treatment. We discovered that human cytomegalovirus (HCMV) is present in a high percentage of GBM, and these findings have been confirmed by multiple groups. Our co- investigator, Dr. Nino Chiocca, has recently demonstrated that CMV infection accelerates tumor progression to GBM in a transgenic mouse model of glioma. Recently, antiviral therapies aimed at HCMV have demonstrated efficacy in patients with GBM. We have determined that Cidofovir (CDV), an FDA approved antiviral agent for CMV infection, potently inhibits GBM proliferation both in vitro and in an intracranial xenograft mouse model of primary GBM. Furthermore, our investigations of CDV have indicated that, while the antiviral effect is significant to the antitumr response, CDV possesses potent antitumor properties even in the absence of CMV infection. Importantly, the antitumor response seen using the in vivo GBM xenograft model with CDV is greater than any systemic agent tested thus far at UCSF other than temozolomide, and for temozolomide, substantial tumor response is limited to the use of tumor cell sources and their corresponding xenografts having methylated MGMT promoter. Mechanistically, we have determined that CDV, a cytosine analog, incorporates not only into CMV DNA but also into tumor cell genomic DNA. We find that CDV uptake by tumor cells activates apoptotic pathways and blocks normal DNA repair mechanisms, which are responsible for tumor cell resistance to and recovery following radiation therapy (RT), the primary standard of care treatment modality for newly-diagnosed GBM. In our in vitro and in vivo studies, CDV enhances the effect of RT. Although poor tissue uptake and nephrotoxicity are limitations of using CDV in treating human disease, our collaborator Dr. Karl Hostetler, has synthesized CDV derivatives that are highly lipophilic, and can be administered orally while causing minimum toxicity. In our preliminary studies, these compounds exhibit > 300-fold increased antitumor effect in vitro, thus allowing dramatically lower dosages to be administered, in comparison with cidofovir, for achieving significant anti-tumor activity. In Aim 1, we plan to use existing mouse xenograft models developed by our co-investigator Dr. David James at UCSF to optimize treatments based on acquired knowledge of investigational agent pharmacokinetics and to determine optimal regimens to use when combining inhibitors with RT. In Aim 2 we will utilize Dr. Chiocca's transgenic mouse model of spontaneously occurring glooms +/- CMV infection to understand the impact of antiviral therapy in the setting of CMV-mediated GBM tumor genesis. In addition, we will examine the impact of antiviral therapy with respect to the influence of CMV on the tumor microenvironment and host immune response to tumor. Finally, in Aim 3 we plan to investigate the mechanisms by which CDV and CDV-derived compounds elicit DNA damage and interfere with DNA repair mechanisms. We anticipate that one of the major advantages of these compounds will be their high therapeutic index: i.e., limited toxicity in normal cells, but dramati apoptotic pathway activation and prevention of DNA repair in tumor cells, which could significantly delay or possibly prevent radiation and chemo-resistance critical for GBM recurrence.