DEVELOPMENT OF PET RADIOPHARMACEUTICALS TARGETING GRPR

描述（由申请人提供）：胃泌素释放肽受体（GRPR）在各种人类肿瘤上过表达，因此已成为检测和治疗这些癌症的成功靶点。蛙皮素（BN）是一种十四个氨基酸的肽，其以高亲和力结合GRPR，并且放射性标记的BN类似物已被评估用于表达GRPR的癌症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个评估BN类似物放射性标记的正电子发射放射性核素的PET成像。具体地，我们使用了BN的八个C-末端氨基酸（BN（7-14））与1，4，7，10-四氮杂环十二烷-1，4，7，10-四乙酸（DOTA）缀合并用铜-64（64 Cu）放射性标记。我们已经证明了GRPR特异性摄取和microPET成像在小鼠携带前列腺癌或乳腺癌异种移植物使用各种64 Cu标记的DOTA-BN类似物。然而，众所周知，金属螯合物的不稳定性会导致非靶组织如肝脏和肾脏中放射性金属吸收增加，从而导致对比度降低。特别地，已经显示64 Cu在体内从DOTA解离并转螯合到其他蛋白质，导致在非靶组织中的高吸收。最近，1，4，7-三氮杂环壬烷-1，4，7-三乙酸（NOTA）已经与BN（7-14）缀合并直接与DOTA缀合的BN（7-14）进行比较。64 Cu标记的NOTA缀合物表现出比DOTA缀合物更低的肿瘤摄取，但也表现出更低的肝脏积累，导致NOTA缀合物的更高的肿瘤与肝脏比率。因此，本提案将集中于开发可与BN类似物缀合的新型双功能NOTA配体。我们相信，可以对NOTA缀合的BN类似物进行显著改进，因为64 Cu标记的NOTA缀合的BN类似物的肿瘤摄取小于DOTA缀合的BN类似物，并且缀合策略利用了NOTA的羧酸酯臂之一，减少了配位数。因此，我们假设，与公开的NOTA缀合的BN类似物相比，与BN类似物缀合并用64 Cu放射性标记的新型双功能NOTA配体将导致改善的肿瘤摄取和肿瘤与正常组织的比率。次要假设是68 Ga标记的NOTA缀合的BN类似物将提供表达GRPR的肿瘤的高质量PET图像。该提案的具体目标是：（1）。合成双官能NOTA衍生物并将其表征为与Cu（II）和Ga（III）的配合物; 2.）以形成NOTA衍生物的64 Cu-和68 Ga-标记的复合物并在体外对其进行评价; 3.）将NOTA衍生物与BN类似物偶联，用64 Cu或68 Ga对其进行放射性标记，并在体外对其进行评价; 4.）在携带肿瘤异种移植物的小鼠体内评估放射性标记的BN类似物作为GRPR PET成像的放射性药物。在这项研究的结论，我们希望已经开发出一个64 Cu标记的BN类似物和68 Ga标记的BN类似物的GRPR的PET成像，这代表了显着的改善，比现有的BN类似物用于PET成像。公共卫生相关性：在这项研究的结论，我们希望已经开发出一个64 Cu标记的BN类似物和68 Ga标记的BN类似物的GRPR的PET成像，这代表了显着的改善，比现有的BN类似物用于PET成像。这些类似物应该可用于表达GRPR的癌症的临床检测和分期。

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.