Imaging of O6-Alkylguanine-DNA Alkyltransferase

O6-烷基鸟嘌呤-DNA 烷基转移酶的成像

基本信息

批准号：
6942764
负责人：
GANESAN VAIDYANATHAN
金额：
$ 30.8万
依托单位：
DUKE UNIVERSITY
依托单位国家：
美国
项目类别：
财政年份：
2002
资助国家：
美国
起止时间：
2002-09-30 至 2007-08-31
项目状态：
已结题

项目摘要

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.

描述（申请人提供）：化疗，特别是烷化剂化疗，是治疗癌症的主要方式之一；然而，回应率往往较低。许多患者预后不良的一个主要原因是耐药性的产生，导致肿瘤再生并最终导致患者死亡。耐药性是由于修复蛋白O6烷基-DNA烷基转移酶(AGT)对烷化剂对鸟嘌呤和胸腺嘧啶残基进行烷基化而产生的DNA损伤的修复所致。 AGT 通过将修饰 DNA 上的烷基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，因此耐药性或治疗效果取决于肿瘤中 AGT 含量的量。无创定量肿瘤 AGT 的方法将在烷化剂化疗的规划、治疗过程中监测药物对 AGT 水平的影响以及新型烷化剂化疗药物的开发中大有帮助。苄基鸟嘌呤 (BG) 已被证明是一种出色的 AGT 灭活剂，并且有多项临床试验正在进行中，评估在化疗前使用 BG 来消耗 AGT。该提案的长期目标是开发放射性碘或 18F 标记的 BG 类似物，用于通过闪烁显像进行无创 AGT 测绘。苄基4位含氟BG（4-FBG）已被证明是BG的优异类似物。将开发 4-FBG 以及放射性碘标记 BG 衍生物的 18F 标记方法。虽然有可能使用这些化合物来证明原理，但我们还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。所考虑的化合物包括4-苄氧基-2,6-二氨基-5-硝基/亚硝基-嘧啶的衍生物，以及在C-8和N-9位置带有取代基的各种BG衍生物。将首先使用转染 AGT 的中国仓鼠卵巢 (CHO) 细胞评估新型未标记化合物的 AGT 灭活能力。将评估标记化合物与纯 AGT 的结合以及它们在含有 AGT 的细胞中的摄取和保留。它们的体外代谢也将被研究。将建立肿瘤 AGT 含量和肿瘤摄取标记 BG 类似物的相关性。这些研究主要使用 TE-67 1 人髓母细胞瘤异种移植物。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，尤其是肿瘤中的代谢物。同样，肿瘤摄取和肿瘤 AGT 含量之间的相关性也将在异种移植模型中进行研究。总之，该提案旨在确定开发适合肿瘤 AGT 成像的试剂是否将有助于化疗计划，从而改善烷化剂化疗的结果。随后，这些示踪剂将在异种移植物的无胸腺小鼠中进行评估。这些研究主要使用 TE-671 人髓母细胞瘤异种移植物。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，尤其是肿瘤中的代谢物。同样，肿瘤摄取和肿瘤 AGT 含量之间的相关性也将在异种移植模型中进行研究。总之，该提案旨在确定开发适合肿瘤 AGT 成像的试剂是否将有助于化疗计划，从而改善烷化剂化疗的结果。