NOVEL AGENTS FOR DETECTING BONE METASTASIS

这个子项目是许多研究子项目中的一个 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可以在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者所在的机构。 本论文的研究重点是合成具有亚甲基膦酸酯或双膦酸酯基序的大环类骨导向剂，并将其应用于骨转移瘤的非侵入性显像。目前，骨转移瘤的诊断成像通常使用99 mTc-MDP（亚甲基二膦酸盐）进行。由于缺乏高特异性和灵敏度，99 mTc-MDP骨扫描通常由其他成像方式辅助，如放射摄影，MRI，CT，PET扫描和/或骨髓活检，以进行最终诊断。最近的药理学研究表明，双膦酸盐对骨转移的抗吸收作用的机制涉及两个步骤：双膦酸盐结合到羟基磷灰石骨矿物表面，随后被破骨细胞选择性地内化，在那里它们抑制骨细胞活性。在该机制的第一步中，双膦酸盐与羟基磷灰石的长时间保留限制了99 mTc-MDP骨扫描用于早期检测骨转移的特异性和灵敏度，这是由于络合物的有限体内稳定性和99 mTc的短半衰期（t1/2 = 6.01 h）。基于双膦酸盐的药理学机制，我们建议解决的假设，骨转移检测的灵敏度和特异性将显着提高，如果骨寻求大环四胺配合物可用于骨转移的多模态影像诊断。众所周知，大环螯合剂比无环配体形成动力学上更稳定的金属络合物。 DO 1A 3 P和DO 2A 2 P被设计为与177 Lu（t1/2 = 6.71 d）和Gd（III）形成动力学稳定的络合物，而亚甲基膦酸酯部分用于破骨细胞靶向。DO 3A-BP是具有双膦酸盐（靶向破骨细胞）和DOTA（1，4，7，10-四氮杂环十二烷-1，4，7，10-四乙酸）的混合配体，DOTA是用于金属放射性药物和MRI造影剂的传统螯合剂。它们与放射性核素的螯合物（64 Cu：t1/2 = 12.7 h;和177 Lu：t1/2 = 6.71 d）将提供具有宽范围放射性半衰期的核骨显像剂，这不仅能够检测/监测骨转移，而且能够对骨异常进行机制研究。此外，我们假设这些相同的骨寻求螯合剂将与Gd（III）形成稳定的复合物，这赋予它们作为磁共振成像（MRI）骨造影剂的潜在应用。 这两个目标将推进体内癌症显像剂的开发，以改善骨转移的检测和诊断，并可能为癌症患者的治疗和管理提供新的成像/姑息/治疗剂。建议的具体目标如下： 艾姆岛合成并表征具有亚甲基膦酸酯或双膦酸酯基序的趋骨大环螯合剂，并研究其与Cu（II）、Lu（III）和Gd（III）的配位化学。 本目标的目的是合成和表征趋骨配体螯合剂（DO 1A 3 P、DO 2A 2 P和DO 3A-BP），并获得足够的量（约1 g）用于后续研究。建议的配体与Cu（II），Lu（III）和Gd（III）的配合物将制备，表征和评价其在水溶液中的动力学和热力学稳定性。 Aim II.制备和评价64 Cu和177 Lu标记的配合物作为PET/SPECT显像剂，用于骨转移瘤的检测和原位监测 本研究的目的是建立骨导向放射性药物制备的放射化学方案，评价其体内稳定性和组织摄取和清除，并评估其作为PET/SPECT骨显像剂与目前临床骨扫描剂99 mTc-MDP相比的潜在适用性。最有希望的候选药物将在小鼠前列腺癌异种移植物的骨内骨转移模型中使用小动物PET和小动物SPECT进行测试。 将进行破骨细胞靶向评价以初步评价我们提出的复合物对骨转移的特异性。 Aim III.制备和研究冷钆配合物，并确定作为骨转移诊断成像的MRI骨造影剂的最佳候选物 这一目的是为了检验所提出的骨导向螯合剂将与钆形成稳定复合物的假设，钆也可用作MRI骨造影剂。钆化合物将作为MRI骨造影剂在与Aim II相同的骨转移模型中进行骨转移诊断成像评价。 我们希望确定候选人，给予长期的高对比度增强选择性地在骨组织界面，从而帮助骨成像，使使用MRI研究骨结构的变化与骨转移的进展。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. This proposal is focused on the synthesis of novel macrocyclic bone-seeking agents with methylenephosphonate or bisphosphonate motif and their applications to noninvasive imaging of bone metastases. Currently the diagnostic imaging of bone metastases is commonly performed with 99mTc-MDP (methylene bisphosphonate). Due to the lack of high specificity and sensitivity, 99mTc-MDP bone scan is often aided by other imaging modalities, such as radiography, MRI, CT, PET scans, and/or bone marrow biopsy, for a final diagnosis. Recent pharmacological investigations have revealed that the mechanism of bisphosphonate anti-resorption effects on bone metastases involves two steps: bisphosphonates bind to hydroxyapatite bone mineral surface and subsequently are internalized by osteoclasts selectively where they inhibit the osteoclastic activity. The long retention of bisphosphonates with hydroxyapatite in the first step of the mechanism limits the specificity and sensitivity of a 99mTc-MDP bone scan for early detection of bone metastases due to the limited in vivo stability of the complex and the short half-life of 99mTc (t1/2 = 6.01 h). Based upon the pharmacological mechanism of bisphosphonates, we propose to address the hypothesis that the sensitivity and specificity of bone metastasis detection will be significantly improved if bone-seeking macrocyclic tetraamine complexes can be utilized for multimodality imaging diagnosis of bone metastases . It is well-known that macrocyclic chelators form kinetically more stable metal complexes than acyclic ligands. DO1A3P and DO2A2P are designed to form kinetically stable complexes with 177Lu (t1/2 = 6.71 d) and Gd(III) while the methylenephosphonate moieties are for osteoclast-targeting. DO3A-BP is hybrid ligand featuring both bisphosphonate (targeting osteoclasts) and DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid), a traditional chelator used in metal radiopharmaceuticals and MRI contrast agents. Their chelates with radionuclides (64Cu: t1/2 = 12.7 h; and 177Lu: t1/2 = 6.71 d) will provide nuclear bone imaging agents with a wide range of radioactive half lives, which enables not only the detection/monitoring of bone metastases but also the mechanistic studies of bone abnormalities. In addition, we hypothesize that these same bone-seeking chelators will form stable complexes with Gd(III), which endows them with potential applications as magnetic resonance imaging (MRI) bone contrast agents as well. Both goals will advance the development of in vivo cancer imaging agents to improve the detection and diagnosis of bone metastases, and potentially provide novel imaging/palliative/therapeutic agents for the treatment and management of cancer patients. The specific aims are proposed as follows: Aim I. To synthesize and characterize bone-seeking macrocyclic chelators with a methylene-phosphonate or bisphosphonate motif and investigate their coordination chemistry with Cu(II), Lu(III), and Gd(III) The goal of this aim is to synthesize and characterize the bone-seeking ligand chelators (DO1A3P, DO2A2P, and DO3A-BP and obtain adequate amounts (~ 1 g) for follow-up studies. The complexes of proposed ligands with Cu(II), Lu(III), and Gd(III) will be prepared, characterized, and evaluated for their kinetic and thermodynamic stability in aqueous solution. Aim II. To prepare and evaluate 64Cu and 177Lu labeled complexes as PET/SPECT imaging agents specifically for the detection and in situ monitoring of bone metastases The objective of this aim is to establish radiochemical protocols for the preparation of the bone-seeking radiopharmaceuticals, evaluate their in vivo stability and tissue uptake and clearance, and assess their potential applicability as PET/SPECT bone imaging agents as compared to 99mTc-MDP, the current clinical bone-scan agent. The most promising candidates will be tested using small animal PET and small animal SPECT in an intra-osseous bone metastasis model of prostate cancer xenografts in mice. Osteoclast-targeting evaluation will be performed to preliminarily evaluate the specificity of our proposed complexes to bone metastases. Aim III. To prepare and investigate cold gadolinium complexes and identify optimal candidates as MRI bone-contrast agents for diagnostic imaging of bone metastases This aim is to test the hypothesis that the proposed bone-seeking chelators will form stable complexes with gadolinium, which can be used as MRI bone contrast agents as well. The gadolinium compounds will be evaluated as MRI bone-contrast agents for diagnostic imaging of bone metastases in the same bone metastasis model as in Aim II. We hope to identify candidates that give prolonged high contrast enhancement selectively at the bone-tissue interface, thus aiding bone imaging and enabling the use of MRI to study changes in bone structure with progression of bone metastases.