DEVELOPMENT OF PET RADIOPHARMACEUTICALS TARGETING GRPR

描述（由申请人提供）：胃泌素释放肽受体（GRPR）在多种人类肿瘤中过表达，因此已成为检测和治疗这些癌症的成功靶点。Bombesin （BN）是一种含有14个氨基酸的肽，与GRPR具有高亲和力，放射性标记的BN类似物已被用于表达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类似物放射性标记与正电子发射放射性核素PET成像。具体来说，我们将BN（BN(7-14)）的8个c端氨基酸偶联到1,4,7,10-四氮杂环十二烷-1,4,7,10-四乙酸（DOTA）上，并用铜-64 （64Cu）进行放射性标记。我们已经证明了grpr特异性摄取和使用各种64cu标记的DOTA-BN类似物在携带前列腺癌或乳腺癌异种移植物的小鼠中进行微pet成像。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）对放射性金属的吸收增加，从而导致对比度降低。特别是，已经证明64Cu在体内与DOTA解离，并转运到其他蛋白质上，导致非靶组织的高吸收。最近，1,4,7-三氮杂环壬烷-1,4,7-三乙酸（NOTA）偶联BN(7-14)，并直接与DOTA偶联BN（7-14）进行了比较。64cu标记的NOTA偶联物比DOTA偶联物显示出更低的肿瘤摄取，但也更低的肝脏积聚导致NOTA偶联物的肿瘤与肝脏比例更高。因此，本研究将重点开发新型双功能NOTA配体，并将其与BN类似物偶联。我们认为，由于肿瘤对64cu标记的NOTA偶联BN类似物的摄取少于DOTA偶联BN类似物，并且该偶联策略利用了NOTA的一个羧酸臂，减少了配位数，因此可以显著改善NOTA偶联BN类似物。因此，我们假设与已发表的NOTA偶联BN类似物相比，新型双功能NOTA配体偶联BN类似物并以64Cu放射性标记将导致肿瘤摄取和肿瘤与正常组织的比率提高。第二个假设是，68Ga标记的NOTA共轭BN类似物将为表达GRPR的肿瘤提供高质量的PET图像。该提案的具体目的是：1.)合成双功能NOTA衍生物并将其表征为与Cu（II）和Ga（III）配合物；2.)形成NOTA衍生物的64Cu-和68ga -标记配合物并进行体外评价；3)将NOTA衍生物与BN类似物偶联，用64Cu或68Ga进行放射性标记，并在体外进行评价；4.)评估异种肿瘤移植小鼠体内放射性标记BN类似物作为放射性药物用于GRPR的PET成像。在这项研究的结论中，我们期望开发出一种64cu标记的BN模拟物和一种68ga标记的BN模拟物，用于GRPR的PET成像，这比现有的用于PET成像的BN类似物有了显著的改进。公共卫生相关性：在这项研究的结论中，我们期望开发出一种64cu标记的BN类似物和一种68ga标记的BN类似物，用于GRPR的PET成像，这比现有的用于PET成像的BN类似物有重大改进。这些类似物应该对表达GRPR的癌症的临床检测和分期有用。

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.