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

描述（由申请人提供）：胶质母细胞瘤（GBM）是一种致命的原发性脑肿瘤，尽管接受了标准治疗，但大多数患者在诊断后仍存活12-15个月。我们发现人巨细胞病毒（HCMV）存在于高比例的GBM中，这些发现已被多个小组证实。我们的合作研究者，博士尼诺Chiocca，最近证明，巨细胞病毒感染加速肿瘤进展为GBM在转基因小鼠模型的胶质瘤。最近，针对HCMV的抗病毒疗法已在GBM患者中显示出疗效。我们已经确定，西多福韦（CDV），一种FDA批准的CMV感染的抗病毒剂，在体外和原发性GBM的颅内异种移植小鼠模型中有效地抑制GBM增殖。此外，我们对CDV的研究表明，虽然抗病毒作用对抗肿瘤反应是重要的，但CDV即使在没有CMV感染的情况下也具有有效的抗肿瘤特性。重要的是，使用具有CDV的体内GBM异种移植物模型观察到的抗肿瘤应答大于迄今为止在UCSF测试的除替莫唑胺以外的任何全身性药物，并且对于替莫唑胺，实质性肿瘤应答限于使用肿瘤细胞来源及其相应的具有甲基化MGMT启动子的异种移植物。从机制上讲，我们已经确定，CDV，胞嘧啶类似物，不仅纳入CMV DNA，但也进入肿瘤细胞基因组DNA。我们发现肿瘤细胞摄取CDV激活了凋亡途径并阻断了正常的DNA修复机制，这是肿瘤细胞对放射治疗（RT）的抵抗和恢复的原因，放射治疗是新诊断GBM的主要标准治疗方式。在我们的体外和体内研究中，CDV增强了RT的作用。尽管组织吸收差和肾毒性是使用CDV治疗人类疾病的局限性，但我们的合作者Karl Hostetler博士合成了高度亲脂性的CDV衍生物，并且可以口服给药，同时引起最小的毒性。在我们的初步研究中，这些化合物在体外表现出> 300倍的抗肿瘤作用，因此与西多福韦相比，允许施用显著更低的剂量以实现显著的抗肿瘤活性。在目标1中，我们计划使用现有的小鼠异种移植模型，该模型是由我们的合作研究者加州大学旧金山分校的大卫詹姆斯博士开发的，以根据所获得的研究药物药代动力学知识来优化治疗，并确定将抑制剂与RT组合使用时的最佳方案。在目标2中，我们将使用Chiocca博士的自发发生黑色素瘤的转基因小鼠模型+/-CMV感染，以了解抗病毒治疗对CMV介导的GBM肿瘤发生的影响。此外，我们将研究抗病毒治疗对CMV对肿瘤微环境和宿主对肿瘤免疫反应的影响。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。我们预期这些化合物的主要优点之一将是它们的高治疗指数：即，在正常细胞中的毒性有限，但在肿瘤细胞中的凋亡途径激活和DNA修复的预防是戏剧性的，这可以显著延迟或可能预防对GBM复发至关重要的放射和化学抗性。

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.