Radionuclide-based Molecular Imaging of the DNA Repair Protein AGT

描述（由申请人提供）：烷化剂化疗在脑肿瘤和其他恶性肿瘤的治疗中起着重要作用。然而，它的有效性往往受到耐药性的限制，这导致肿瘤的致命生长，尽管进一步的烷化剂化疗。对烷化剂化疗的耐药性主要是由于蛋白烷基鸟嘌呤-DNA烷基转移酶（AGT）修复诱导的O 6-烷基鸟嘌呤DNA损伤。肿瘤AGT含量和治疗结果之间存在明确的负相关性;通常，当肿瘤的AGT含量低于阈值时，存活率较高。我们假设，根据治疗前肿瘤AGT水平的非侵入性成像来决定是否对个体患者进行烷化剂化疗是可能的。这项工作的目标是开发放射性标记剂，将允许使用SPECT或PET成像评估AGT水平。我们建议合成放射性碘标记的衍生物O 6-苄基鸟嘌呤（BG），一种有效的AGT灭活剂，耦合到核定位肽序列（NLS），以提高交付的标记底物AGT主要存在的细胞核。将使用纯AGT和AGT表达细胞系在体外以及使用异种移植模型在体内评价这些标记试剂。具体目标是：1.合成苄基鸟嘌呤衍生物及其NLS偶联物。2.评价放射性标记的苄基鸟嘌呤及其NLS偶联物与纯AGT的结合以及在体外肿瘤细胞中的结合。3.评价在无胸腺小鼠异种移植模型中开发的AGT特异性放射性标记药物。一个成功的AGT分子成像剂可能是一个重要的工具，可以用来避免不必要的化疗;除了经济效益，它可以免除患者的主要副作用烷化剂化疗，并允许他们更早地分流到替代治疗。公共卫生相关性：该项目的目标是开发放射性标记示踪剂，可用作分子成像剂，用于非侵入性评估脑癌和其他肿瘤中的DNA修复蛋白烷基鸟嘌呤-DNA烷基转移酶（AGT）。AGT是耐药性的主要原因，这种耐药性经常损害许多癌症基于烷化剂的化疗的有效性。由于耐药性是癌症治疗过程中的一个主要障碍，因此使用分子成像技术来定量AGT将具有显著的临床影响。有了这种技术，化疗可以个性化，因为它应该可以预测哪些患者将受益于化疗，哪些不会。这将有助于避免治疗烷化剂化疗在很大程度上无效的患者，使他们免受不必要的副作用和费用，并为寻求可能更成功的替代治疗提供更早的理由，考虑到他们的AGT状态。

DESCRIPTION (provided by applicant): Alkylator chemotherapy plays a significant role in the treatment of brain tumors and other malignancies. However, its effectiveness is all too often limited by drug resistance, which leads to lethal growth of tumors despite further rounds of alkylator chemotherapy. Drug resistance to alkylator chemotherapy is primarily due to the repair of induced O6-alkylguanine DNA lesions by the protein alkylguanine-DNA alkyltransferase (AGT). There is a well-established inverse correlation between tumor AGT content and therapeutic outcome; generally, survival rates are higher when the AGT content of tumor is below a threshold. We hypothesize that it should be possible to decide whether to administer alkylator chemotherapy in individual patients based on noninvasive imaging of tumor AGT levels prior to therapy. The goal of this work is to develop radiolabeled agents that will allow assessment of AGT levels using SPECT or PET imaging. We propose to synthesize radioiodinated derivatives of O6- benzylguanine (BG), a potent AGT inactivating agent, coupled to nuclear localizing peptide sequences (NLS) to enhance delivery of the labeled substrate to the cell nucleus where AGT is predominantly present. These labeled agents will be evaluated in vitro using pure AGT and AGT-expressing cell lines and in vivo using xenograft models. The specific aims are: 1. To synthesize benzylguanine derivatives and their NLS conjugates. 2. To evaluate the radiolabeled benzylguanines and their NLS conjugates for binding to pure AGT and in tumor cells in vitro. 3. To evaluate AGT-specific radiolabeled agents developed in athymic mouse xenograft models. A successful agent for the molecular imaging of AGT could be an important tool that can be used to avoid unnecessary chemotherapy; in addition to the economic benefits, it can spare patients from the major side effects of alkylator chemotherapy, and allow them to be triaged earlier to alternative treatments. PUBLIC HEALTH RELEVANCE: The goal of this project is to develop radiolabeled tracers that can be utilized as molecular imaging agents for the noninvasive assessment of the DNA repair protein alkylguanine-DNA alkyltransferase (AGT) in brain cancers and other tumors. AGT is primarily responsible for the drug resistance that frequently compromises the effectiveness of alkylator-based chemotherapy of many cancers. Because drug resistance is a major road block in the cancer treatment process, the availability of a molecular imaging technique to quantify AGT will have a significant clinical impact. With such a technique, chemotherapy can be personalized because it should be possible to predict which patients will benefit from chemotherapy and which will not. This will help avoid treating patients for whom alkylator chemotherapy will be largely ineffective, sparing them of unwarranted side effects and expense, and providing an earlier rationale for seeking alternative treatments that might be more successful, given their AGT status.