Imaging of O6-Alkylguanine-DNA Alkyltransferase

描述（由申请人提供）：化疗，尤其是烷化剂化疗，是治疗癌症的主要方式之一;然而，反应率通常较低。许多患者预后不良的主要原因是耐药性的发展，导致肿瘤再生长和最终患者死亡。耐药性是由于修复蛋白O 6烷基-DNA烷基转移酶（AGT）对DNA损伤的修复，DNA损伤是由烷化剂对鸟嘌呤和胸腺嘧啶残基的烷基化产生的。AGT通过将烷基从修饰的DNA转移到其活性位点的半胱氨酸来修复损伤。这是一个自杀过程，因为没有再生蛋白质的机制，因此抗性或治疗功效取决于肿瘤中AGT含量的量。非侵入性定量肿瘤AGT的方法将在烷化剂化疗的规划，监测药物对AGT水平的影响，在治疗过程中，并在新的烷化剂化疗药物的开发很长的路要走。苄基鸟嘌呤（BG）已被证明是一个很好的AGT灭活剂，有几个临床试验正在进行评估使用BG消耗AGT化疗前。本提案的长期目标是开发放射性碘或18F标记的BG类似物，用于通过放射性造影成像进行AGT的非侵入性标测。在其苄基的4-位上含有氟的BG（4-FBG）已经被证明是BG的优良类似物。将开发用于4-FBG以及放射性碘化BG衍生物的18 F标记的方法。虽然可以使用这些化合物来证明原理的证据，但也将努力开发更好的类似物，这些类似物更容易制备，更有效，并且具有更高的代谢稳定性和更长的肿瘤保留时间。在所考虑的化合物中有4-苄氧基-2，6-二氨基-5-硝基/亚硝基嘧啶的衍生物，以及在其C-8和N-9位具有取代基的各种BG衍生物。将首先使用用AGT转染的中国仓鼠卵巢（CHO）细胞评价新型未标记化合物的AGT灭活能力。将评价标记化合物与纯AGT的结合及其在含AGT细胞中的摄取和保留。 还将研究它们的体外代谢。将建立肿瘤AGT含量与标记BG类似物的肿瘤摄取的相关性。首先，TE-67 1人髓母细胞瘤异种移植物将用于这些研究。将研究肿瘤摄取作为药物浓度和时间的函数。将确定潜在的代谢物，特别是肿瘤中的代谢物。同样，也将在异种移植模型中研究肿瘤摄取和肿瘤AGT含量之间的相关性。总之，该提案旨在确定是否开发一种合适的肿瘤AGT成像剂将有助于化疗计划，从而改善烷化剂化疗的结果。 随后，将在接受异种移植物的无胸腺小鼠中评价这些示踪剂。 首先，TE-671人髓母细胞瘤异种移植物将用于这些研究。 将研究肿瘤摄取作为药物浓度和时间的函数。 将确定潜在的代谢物，特别是肿瘤中的代谢物。 同样，也将在异种移植模型中研究肿瘤摄取和肿瘤AGT含量之间的相关性。 总之，该提案旨在确定是否开发一种合适的肿瘤AGT成像剂将有助于化疗计划，从而改善烷化剂化疗的结果。

DESCRIPTION (provided by applicant): Chemotherapy, especially alkylator chemotherapy, is one of the primary modes for the treatment of cancer; however, the response rate is often low. A major reason for poor prognosis in many patients is the development of drug resistance, resulting in tumor regrowth and eventual patient death. The drug resistance is due to the repair of DNA lesions, generated by alkylation of guanine and thymine residues by the alkylating agents, by the repair protein O6 alkyl-DNA alkyltrasferase (AGT). AGT repairs the lesions by transferring the alkyl groups from the modified DNA to a cysteine in its active site. This is a suicidal process as there is no mechanism to regenerate the protein and hence the resistance, or alternatively the therapeutic efficacy, depends on the amount of AGT content in the tumor. A means to noninvasively quantitate tumor AGT will go a long way in the planning of alkylator chemotherapy, monitoring the effect of drugs on AGT levels during the therapeutic course, and in the development of newer alkylator chemotherapeutic agents. Benzylguanine (BG) has been shown to be an excellent inactivator of AGT and there are several clinical trials in progress evaluating the use of BG to deplete AGT prior to chemotherapy. The long-term objective of this proposal is to develop radioiodine- or 18F-labeled BG analogues useful in the noninvasive mapping of AGT by scintigraphic imaging. BG containing fluorine at the 4-position of its benzyl group (4-FBG) has already been shown to be an excellent analogue of BG. Methods will be developed for the 18F-labeling of 4-FBG as well as radioiodinated BG derivatives. While it may be possible to demonstrate the proof of principle using these compounds, efforts will also be directed in the development of better analogues that are easier to prepare, more potent, and will have higher metabolic stability, and longer tumor retention. Among the compounds considered are the derivatives of 4-benzyloxy-2,6-diamino-5-nitro/nitroso-pyrimidine, and various BG derivatives with substituents at its C-8 and N-9 positions. Novel unlabeled compounds will be first evaluated for their AGT inactivating ability using Chinese hamster ovary (CHO) cells transfected with AGT. Labeled compounds will be evaluated for their binding with pure AGT and for their uptake and retention in AGT-containing cells. Their in vitro metabolism also will be studied. Correlativity of tumor AGT content and tumor uptake of labeled BG analogues will be Established. Primarily, TE-67 1 human medulloblastoma xenografts will be utilized for these studies. Tumor uptake as a function of drug concentration and time will be studied. Potential metabolites, especially in the tumor, will be determined. Again, the correlativity between tumor uptake and tumor AGT content will be investigated in xenograft models as well. In summary, this proposal seeks to determine whether the development of a suitable agent for the imaging of tumor AGT will facilitate chemotherapy planning, thereby improving the outcome of alkylator chemotherapy. Subsequently these tracers will be evaluated in athymic mice hosting xenografts. Primarily, TE-671 human medulloblastoma xenografts will be utilized for these studies. Tumor uptake as a function of drug concentration and time will be studied. Potential metabolites, especially in the tumor, will be determined. Again, the correlativity between tumor uptake and tumor AGT content will be investigated in xenograft models as well. In summary, this proposal seeks to determine whether the development of a suitable agent for the imaging of tumor AGT will facilitate chemotherapy planning, thereby improving the outcome of alkylator chemotherapy.