An Activatable Nanoparticle Probe for Molecular Imaging of Protease Activity by Dual Energy CT

 描述（由申请人提供）：背景：X射线计算机断层扫描（CT）是临床医生最有用的诊断工具之一，因为它广泛可用，扫描时间快，成本低。然而，使用现有的造影剂，使用CT进行分子成像是不可能的，因此临床医生必须依赖于更昂贵且不易获得的其他方式。双能量CT（DE CT）是一种相对较新的技术，其中两种X射线能量用于单次扫描，可以提供有关组织材料成分的有价值的信息。如果与适当设计的造影剂结合，则该信息可能用于分子成像。该提案的目标是首次开发可用于蛋白酶活性的分子成像的可活化DE CT造影剂。这一目标将在以下具体目标中实现：目标1：体外开发和表征蛋白酶可切割的纳米颗粒CT造影剂。目的2：使用双能量CT测试可切割纳米探针在健康小鼠和小鼠原发性肉瘤模型中的体内性能。研究方法：在目标1中，将开发一种复合纳米探针，由含碘脂质体（~120 nm）通过蛋白酶可切割肽连接到多个小（~5 nm）金纳米颗粒组成。将在体外研究探针的稳定性、切割和毒性。在目的2中，该纳米探针将在健康小鼠中进行生物分布/动力学研究，然后将用于原发性软组织肉瘤小鼠模型中肿瘤蛋白酶活性的体内成像。当将该探针注射到体内时，肿瘤蛋白酶活性将导致将金纳米颗粒连接到脂质体的肽的切割。切割后，小的金纳米颗粒将与较大的脂质体分离。因此，在低蛋白水解活性的区域中，DE CT金和碘信号应保持重叠，而在高蛋白水解活性的区域中，碘信号应保持高而金信号将降低。将使用组织内金与碘浓度的实测比值评价局部蛋白酶活性。蛋白酶活性的CT测量将通过蛋白酶可激活的光学探针和离体组织分析进行验证。长期目标：本研究将证明首次使用CT探针进行癌症蛋白酶活性的分子成像。这种可激活的探针具有用于表现出高蛋白酶活性的多种病理的CT成像的潜力，包括癌症、动脉粥样硬化和其他炎性病症。这种探针的开发将是非侵入性分子成像的重要一步，并有可能改善各种疾病的诊断和风险分层。 流程.

 DESCRIPTION (provided by applicant): Background: X-ray computed tomography (CT) is one of the most useful diagnostic tools for clinicians due to its widespread availability, fast scan times, and low cost. However, molecular imaging with CT is not possible with existing contrast agents, so clinicians must instead rely on other modalities which are more expensive and less readily available. Dual-energy CT (DE CT), a relatively new technique in which two x-ray energies are used for a single scan, can provide valuable information about tissue material composition. This information can potentially be used for molecular imaging if it is coupled with appropriately-designed contrast agents. The goal of this proposal is to develop for the first time an activatable DE CT contrast agent that can be used for the molecular imaging of protease activity. This goal will be met in the following specific aims: Aim 1: Develop and characterize in vitro a protease-cleavable nanoparticle CT contrast agent. Aim 2: Test in vivo performance of cleavable nanoprobes in healthy mice and in a mouse primary sarcoma model using dual energy CT. Methods: In Aim 1, a composite nanoprobe will be developed consisting of iodine-containing liposomes (~120 nm) linked to multiple small (~5 nm) gold nanoparticles by a protease-cleavable peptide. Stability, cleavage, and toxicity of the probe will be studied in vitro In Aim 2, this nanoprobe will undergo biodistribution/kinetics studies in healthy mice and then will be used for in vivo imaging of tumor protease activity in a mouse model of primary soft tissue sarcoma. When this probe is injected in vivo, tumor protease activity will cause cleavage of the peptide linking the gold nanoparticles to the liposome. After cleavage, the small gold nanoparticles will separate from the larger liposomes. Thus, in areas of low proteolytic activity, the DE CT gold and iodine signals should remain overlaid, whereas in areas of high proteolytic activity, the iodine signal should remain high while the gold signal will decrease. The measured ratio of gold to iodine concentration within tissues will be used to evaluate local protease activity. CT measurements of protease activity will be validated by protease-activatable optical probes and by ex vivo tissue analysis. Long-Term Objectives: This study will demonstrate the first use of a CT probe for molecular imaging of protease activity in cancer. This activatable probe has the potential to be used for CT imaging of multiple pathologies which exhibit high protease activity, including cancer, atherosclerosis, and other inflammatory conditions. Development of such a probe will be a significant step forward for non-invasive molecular imaging and has the potential to improve diagnosis and risk stratification for a variety of disease processes.