DEVELOPMENT OF PET RADIOPHARMACEUTICALS TARGETING GRPR

描述(申请人提供)：胃泌素释放肽受体(GRPR)在各种人类肿瘤上过度表达，因此已成为检测和治疗这些癌症的成功靶点。蛙皮素(BN)是一种与GRPR具有高亲和力的14个氨基酸的多肽，放射性标记的BN类似物已被用于GRPR表达肿瘤的单光子发射计算机断层扫描(SPECT)和正电子发射断层扫描(PET)成像。我们的实验室是第一批评估用发射正电子的放射性核素放射性标记的BN类似物用于PET成像的实验室之一。具体地说，我们使用了BN(BN(7-14))的八个C-末端氨基酸与1，4，7，10-tetraazacyclododecane-1，4，7，10-tetraacetic酸(DOTA)偶联，并用铜-(64Cu)进行放射性标记。我们使用各种64Cu标记的DOTA-BN类似物，在携带前列腺癌或乳腺癌移植瘤的小鼠中展示了GRPR特异性摄取和microPET成像。然而，众所周知，金属络合物的不稳定性会导致肝脏和肾脏等非靶组织对放射性金属的吸收增加，从而导致对比度降低。特别是，已有研究表明，64Cu在体内与DOTA解离，并与其他蛋白质交叉螯合，导致非靶组织的高吸收。最近，1，4，7-三氮杂环-1，4，7-三乙酸(NOTA)被直接与BN(7-14)偶联，并与DOTA偶联的BN(7-14)进行了比较。64铜标记的NOTA结合物显示出比DOTA结合物更低的肿瘤摄取率，但也有更低的肝脏蓄积，导致NOTA结合物的肿瘤与肝脏比率更高。因此，这项提议将集中于开发可与BN类似物共轭的新型双功能NOTA配体。我们认为，NOTA结合BN类似物的显著改善是因为64Cu标记的NOTA结合BN类似物对肿瘤的摄取少于DOTA结合BN类似物，并且结合策略利用了NOTA的一个羧基臂，减少了配位数目。因此，我们假设，与已发表的NOTA结合的BN类似物相比，新型双功能NOTA配体与BN类似物结合并标记64Cu将导致更好的肿瘤摄取和肿瘤与正常组织的比率。第二个假设是，68Ga标记的NOTA结合的BN类似物将提供高质量的GRPR表达肿瘤的PET图像。该提案的具体目标是：1.)合成双功能NOTA衍生物，并表征其与铜(II)、镓(III)的配合物；形成64Cu和68Ga标记的NOTA衍生物的配合物，并对其进行体外评价；将NOTA衍生物与BN类似物偶联，用64Cu或68Ga对其进行放射性标记，并进行体外评价；目的：评价放射性标记的BN类似物在荷瘤小鼠体内作为放射性药物用于GRPR的PET显像。在这项研究结束时，我们预计已经开发出用于GRPR PET成像的64Cu标记的BN类似物和68Ga标记的BN类似物，这比用于PET成像的现有BN类似物有了显着的改进。公共卫生相关性：在这项研究结束时，我们预计已经开发出用于GRPR PET成像的64Cu标记的BN类似物和68Ga标记的BN类似物，这比用于PET成像的现有BN类似物有了显着的改进。这些类似物对于临床检测和分期表达GRPR的癌症应该是有用的。

DESCRIPTION (provided by applicant): The gastrin-releasing peptide receptor (GRPR) is overexpressed on various human tumors and thus has been a successful target for the detection and treatment of these cancers. Bombesin (BN) is a fourteen amino acid peptide that binds with high affinity to GRPR and radiolabeled BN analogs have been evaluated for single photon emission computed tomography (SPECT) and positron emission tomography (PET) imaging of GRPR-expressing cancers. Our laboratory was amongst the first to evaluate BN analogs radiolabeled with positron-emitting radionuclides for imaging by PET. Specifically, we used the eight C-terminal amino acids of BN (BN(7-14)) conjugated to 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) and radiolabeled with copper-64 (64Cu). We have demonstrated GRPR-specific uptake and microPET imaging in mice bearing either prostate or breast cancer xenografts using various 64Cu-labeled DOTA-BN analogs. However, it is well known that metal chelate instability leads to increased radiometal absorption in non-target tissues such as the liver and kidneys, leading to decreased contrast. In particular, it has been shown that 64Cu dissociates from DOTA in vivo and transchelates to other proteins leading to high absorption in non-target tissues. Recently, 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) have been conjugated to BN(7-14) and compared directly to DOTA conjugated BN(7-14). The 64Cu-labeled NOTA conjugate demonstrated lower tumor uptake than the DOTA conjugate, but also lower liver accumulation leading to higher tumor to liver ratios for the NOTA conjugate. Therefore, this proposal will focus on the development of novel bifunctional NOTA ligands that can be conjugated to BN analogs. We believe that significant improvements in NOTA conjugated BN analogs can be made since the tumor uptake of the 64Cu-labeled NOTA conjugated BN analog was less than the DOTA conjugated BN analog and that the conjugation strategy utilized one of the carboxylate arms of NOTA, reducing the coordination number. Therefore, we hypothesize that novel bifunctional NOTA ligands conjugated to BN analogs and radiolabeled with 64Cu will result in improved tumor uptake and tumor to normal tissue ratios compared to the published NOTA conjugated BN analog. A secondary hypothesis is that 68Ga- labeled NOTA conjugated BN analogs will provide high quality PET images of GRPR expressing tumors. The Specific Aims of the proposal are: 1.) to synthesize bifunctional NOTA derivatives and characterize them as complexes with Cu(II) and Ga(III); 2.) to form the 64Cu- and 68Ga-labeled complexes of the NOTA derivatives and evaluate them in vitro; 3.) to conjugate the NOTA derivatives to BN analogs, radiolabel them with 64Cu or 68Ga, and evaluate them in vitro; 4.) to evaluate the radiolabeled BN analogs in vivo in mice bearing tumor xenografts as radiopharmaceuticals for PET imaging of GRPR. At the conclusion of this research we expect to have developed a 64Cu-labeled BN analog and a 68Ga-labeled BN analog for PET imaging of GRPR that represents a significant improvement over the existing BN analogs that are used for PET imaging. PUBLIC HEALTH RELEVANCE: At the conclusion of this research we expect to have developed a 64Cu-labeled BN analog and a 68Ga-labeled BN analog for PET imaging of GRPR that represents a significant improvement over the existing BN analogs that are used for PET imaging. These analogs should be useful for the clinical detection and staging of cancers that express GRPR.