Development of Enzyme-Activated PET and MRI Probes for Cancer Imaging

这项研究的总体目标是发展正电子发射断层扫描(PET)和磁学 基于磁共振成像(MRI)的分子成像系统，用于成像体内癌症特异性的蛋白酶的酶活性。到目前为止，蛋白酶活性的成像主要涉及利用荧光共振能量转移(FRET)提供的猝灭和激活机制的荧光探针的开发。不幸的是，光学成像有一个严重的局限性，特别是在临床翻译中，光光子对组织的穿透性有限，组织自发荧光背景高，阻碍了其对深层组织的成像能力。为了解决这一挑战，我们提出了一个新的平台，以成像体内的蛋白酶活性。在这里，我们概述了使这一新平台与具有深度组织穿透的医疗模式兼容的发展，特别是：PET和MRI。 我们建议建立并验证一个用于成像癌细胞中特定的蛋白酶活性的通用平台。该平台是基于两个化学基团(半胱氨酸和2-氰基苯并噻唑的氨基和硫醇基团)之间的蛋白酶活性引发聚合而成的小分子成像探针。这一聚合过程将把小分子探针转化为更大的分子(甚至纳米颗粒)，以实现探针在目标位置的浓缩和滞留，并产生放大的读出信号。特别是，我们将利用1，2-氨基和2-氰基苯并噻唑基团之间高度特异的缩合反应作为聚合的基本机理，添加其他功能来赋予不同的酶专一性或增强我们方法的有效性。将设计、准备和评估两种临床成像方式--PET和MRI的探头。 小分子PET和MRI探针的性质，加上放大的激活信号，应该会最大限度地将这些探针转移到临床上。 在这个项目中，我们选择了Furin作为靶标，因为它是一个重要的“大师” 这种方法应该普遍适用于其他癌症和疾病特异性的蛋白酶，特别是任何执行C-末端切割的内切酶。这再次可能极大地改善这一平台技术的最终临床移植的前景。

The general goal of this research is to develop positron emission tomography (PET) and magnetic resonance imaging (MRI) based molecular imaging systems to image cancer-specific enzymatic acfivity of proteases in vivo. To date the imaging of protease activity has primarily involved the development of fluorescent probes which exploit quenching and acfivation mechanisms offered by fiuorescence resonance energy transfer (FRET). Opfical imaging unfortunately has a serious limitafion, especially for clinical translation, which is the limited tissue penetrafion of light photons and high tissue autofluorescence background, hindering its ability to image deep tissues. To address this challenge, we propose a new platform for imaging protease activity in vivo. Here we outline developments to make this new platform compatible with modalities that have deep tissue penetrafion, specifically: PET and MRI. We propose to establish and validate a general platform for imaging specific protease activity in cancer cells. The platform is based on the protease activity triggered polymerization between two chemical moieties (the amino and thiol groups of cysteine and 2-cyanobenzothiazole) incorporated into a small-molecule imaging probe. This polymerization process will convert the small-molecule probe into larger molecules (or even nanoparticles) to achieve probe concentration and retention at the target site and to generate amplified readout signals. In particular, we will exploit the highly specific condensation reaction between 1,2-aminomercapto and 2-cyanobenzothlazole groups as the base mechanism for polymerization, adding other functionalities to impart specificity to different enzymes or to enhance the effectiveness of our approach. Probes for two clinical imaging modalities, PET and MRI, will be designed, prepared and evaluated. The nature of the small-molecule PET and MRI probes, combined with the amplified activation signal, should maximize the likelihood of moving these probes into the clinic. In this project, we have chosen furin as the target enzyme because of its important role as a "master switch" at different levels or stages during the process of cancer development and progression. The approach, however, should be generally applicable to other cancer- and disease-specific proteases, in particular, any endoproteases that perform C-terminal cleavage. This again may greatly improve the prospects for eventual clinical translafion of this platform technology.