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

本研究的总体目标是开发正电子发射断层扫描（PET）和磁共振成像（MRI）。 本发明涉及基于共振成像（MRI）的分子成像系统，以在体内对蛋白酶的癌症特异性酶活性进行成像。迄今为止，蛋白酶活性的成像主要涉及荧光探针的开发，其利用由荧光共振能量转移（FRET）提供的淬灭和活化机制。光学成像有着严重的局限性，尤其是在临床应用中，光子穿透组织的能力有限，组织自身荧光背景高，阻碍了其对深部组织的成像能力。为了应对这一挑战，我们提出了一个新的平台，在体内成像蛋白酶活性。在这里，我们概述了使这种新平台与具有深层组织穿透的模式兼容的发展，特别是：PET和MRI。 我们建议建立和验证一个通用的平台，成像特定的蛋白酶活性的癌细胞。该平台基于蛋白酶活性触发的两个化学部分（半胱氨酸和2-氰基苯并噻唑的氨基和巯基）之间的聚合，所述两个化学部分并入小分子成像探针中。这种聚合过程将小分子探针转化为更大的分子（或甚至纳米颗粒），以实现探针浓度和在靶位点的保留，并产生放大的读出信号。特别是，我们将利用1，2-氨基巯基和2-氰基苯并噻唑基团之间的高度特异性缩合反应作为聚合的基本机制，添加其他功能以赋予不同酶的特异性或提高我们方法的有效性。将设计、制备和评价两种临床成像模式（PET和MRI）的探头。 小分子PET和MRI探针的性质与放大的激活信号相结合，应该最大限度地提高将这些探针转移到临床的可能性。 在本项目中，我们选择弗林蛋白酶作为目标酶，因为它作为一个重要的“主酶”， 在癌症发展和进展的过程中，在不同的水平或阶段发生“开关”。然而，该方法应该通常适用于其他癌症和疾病特异性蛋白酶，特别是进行C末端切割的任何内切蛋白酶。这可能再次大大改善该平台技术最终临床验证的前景。

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.