MICRO-PET IMAGING OF ALKYLGUANINE-DNA ALKYLTRANSFERASE (AGT)

本子项目是利用由NIH/NCRR资助的中心赠款提供的资源的众多研究子项目之一。子项目和研究者（PI）可能已经从另一个NIH来源获得了主要资金，因此可以在其他CRISP条目中表示。列出的机构是中心的，不一定是研究者的机构。化疗用烷基化剂的细胞毒性作用源于DNA鸟嘌呤残基o6位置的DNA烷基化。烷基化之后，一连串的事件发生，最终导致DNA链断裂。在各种癌症的烷基化化疗中发现的耐药主要归因于DNA修复蛋白烷基鸟嘌呤-DNA烷基转移酶（AGT）。AGT将鸟嘌呤o6 -烷基转移到活性位点的半胱氨酸上，从而修复DNA。这是一个化学计量或自杀的过程；一旦其半胱氨酸-145烷基化，AGT通过泛素途径降解，新的AGT只能通过从头合成再生。许多临床前、回顾性和前瞻性临床研究表明，肿瘤AGT含量与烷基化剂化疗的阳性临床结果呈负相关。此外，肿瘤AGT含量不仅在不同肿瘤类型之间存在差异，而且在同一组恶性肿瘤患者中也存在差异。因此，对肿瘤AGT含量的先验知识可以帮助肿瘤学家根据患者的具体情况量身定制化疗方案。我们的目标是开发放射性标记剂，使其能够通过PET或SPECT成像以无创方式量化肿瘤AGT含量。o6 -苄基鸟嘌呤（BG）是AGT的底物，作为AGT调节剂正在进行临床研究。我们已经开发出一种放射性碘化的BG类似物，即O6-3-[*I]碘苄基鸟嘌呤（IBG），它已被证明可以特异性标记AGT。最近这种化合物被贴上了I-124的标签。这项工作的目标是在小鼠异种移植模型中追踪这种药物。我们想确定对照组和肿瘤AGT耗尽组的肿瘤是否可以分化。我们项目的最终目标是开发放射性标记剂，通过PET或SPECT成像来量化AGT。因此，首先证明它可以在动物模型中完成是至关重要的。此外，有必要确定使用I-124标记的放射性药物用DUMC微pet对动物模型成像是可能的。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The cytotoxic action of chemotherapeutic alkylating agents stems from the alkylation of DNA at the O6-position of DNA guanine residues. Subsequent to alkylation, a cascade of events takes place resulting in eventual DNA strand breaks. Drug resistance seen in alkylator chemotherapy of various cancers has been primarily attributed to the DNA repair protein Alkylguanine-DNA alkyltransferase (AGT). AGT transfers the guanine O6-alkyl group to a cysteine in its active site thereby repairing the DNA. This is a stoichiometric or suicidal process; once its cysteine-145 is alkylated, AGT undergoes degradation via ubiquitin pathway and new AGT can only be regenerated by de novo synthesis. A number of preclinical as well as retrospective and prospective clinical studies have demonstrated an inverse correlation between the tumor AGT content and the positive clinical outcome of alkylator chemotherapy. Also, tumor AGT content varies not only between different tumor types but also within a group of patients of same malignancy. Thus, a prior knowledge of the tumor AGT content can help oncologists to tailor chemotherapy on a patient-specific basis. Our goal is to develop radiolabeled agents with which it should be possible to quantify tumor AGT content in a noninvasive fashion by PET or SPECT imaging. O6-benzylguanine (BG) is a substrate for AGT and is undergoing clinical studies as an AGT modulator. We have developed a radioiodinated BG analogue namely, O6-3-[*I]iodobenzylguanine (IBG) which has shown to label AGT specifically. Recently this compound has been tagged with I-124. The goal of this work is to track this agent in a mouse xenograft model. We would like to determine whether tumors of a control group and of a group whose tumor AGT is depleted can be differentiated. The ultimate goal of our project is to develop radiolabeled agents with which it should be possible to quantify AGT by PET or SPECT imaging. Thus it is critical to demonstrate that it can be done in an animal model first. In addition, it is necessary to eatablish that it is possible to image animal models with DUMC microPET using I-124 tagged radiopharmaceuticals.