Activatable molecular probes for photoacoustic lifetime imaging

描述（由申请人提供）：该项目的最终目标是开发一种用于特定酶活性的非侵入性临床成像的新方法。已知基质金属蛋白酶（MMP）家族的酶在癌症、动脉粥样硬化和其它炎症相关疾病的进展中起重要作用。使用3D成像识别特定酶并定位其活性的能力将有助于医生更好地了解疾病进展和对治疗的反应。这里提出的方法结合了智能分子剂和三维光声成像（派）技术。派提供了一种在超声成像上嵌入光学信息的方法。该图像具有高分辨率和高穿透深度沿着以及光学成像的特异性和对比度。我们团队提出的派的具体实现依赖于探测激发寿命。该技术被称为光声寿命成像（帕利）。我们建议设计一种分子探针，由两个亚甲基蓝（MB）的发色团分子连接的肽链，限制发色团的二聚体配置。肽连接被设计为在与MMP-2酶相互作用时被切割。这将导致MB二聚体断裂并释放两个MB单体。探针的两种状态，MB二聚体与游离MB单体，在激发寿命方面表现出非常显著的差异。MB单体具有稳定的三重激发态，其自然寿命为70 ms。三重态在二聚体构型中被非常有效地淬灭，从而导致小于0.040 ms的非常短的寿命。探针在其初始状态和其活化状态下的寿命之间的这种极端差异为帕利成像提供了有效的对比机制。此外，由于发色团的激发寿命极长，探针的激活状态明显不同于任何其他组织成分。因此，该机制将产生用于酶活性的功能成像的高图像对比度。研究计划包括以下步骤：1。探针合成：合成并测试分子探针，该分子探针由连接至可被MMP-2切割的肽序列的MB对组成。2.探针表征：测量对MMP-2的灵敏度和特异性。3.在仿组织体模中测试成像特性，如穿透深度、灵敏度和对比度。4.在前列腺癌小鼠模型中测试新的体内成像系统。该项目将为转化研究奠定基础，重点是在癌症筛查，治疗计划和治疗监测等临床应用中实施该技术。

DESCRIPTION (provided by applicant): The ultimate goal of the project is developing a new method for non-invasive clinical imaging of activity of specific enzymes. Enzymes of the matrix metalloproteinase (MMP) family are known to play a significant role in progression of cancer, atherosclerosis, and other inflammation related disease. The ability to identify a specific enzyme and localize its activity using 3D imaging would help physicians to better understand disease progression and response to treatment. The method proposed here combines a smart molecular agent and a 3D photoacoustic imaging (PAI) technique. PAI provides a way to embed optical information on ultrasound imaging. The images feature high resolution and high penetration depth along with the specificity and contrast of optical imaging. The specific implementation of PAI that our team proposes relies on probing excitation lifetime. The technique is termed photoacoustic lifetime imaging (PALI). We propose designing a molecular probe that consists of two methylene blue (MB) chromophore molecules linked by a peptide chain that confines the chromophores to a dimer configuration. The peptide link is designed to be cleaved upon interaction with MMP-2 enzyme. This would result in breaking the MB dimer and releasing two MB monomers. The two states of the probe, MB dimer vs. free MB monomers, exhibit a very drastic difference in excitation lifetime. MB monomers have a stable triplet excited state that has a natural lifetime of 70 ms. The triplet state is very effectively quenched in a dimer configuration resulting in a very short lifetime of less than 0.040 ms. This extreme difference in lifetime between the probe in its initial state and its activated state provie an effective contrast mechanism for PALI imaging. Moreover, the activated state of the probe is clearly distinct from any other tissue component because of the extremely long excitation lifetime of the chromophores. This mechanism would therefore generate high image contrast for functional imaging of enzyme activity. The research plan entails the following steps: 1. Probe Synthesis: Synthesize and test a molecular probe consisting of MB pair tethered to a peptide sequence that can be cleaved by MMP-2. 2. Probe Characterization: Measure sensitivity and specificity to MMP-2. 3. Testing imaging features such as penetration depth, sensitivity, and contrast in tissue-mimicking phantoms. 4. Testing the new imaging system in vivo in mice models of prostate cancer. The project will lay the groundwork for a translational research that would focus on implementing the technique in clinical applications such as cancer screening, treatment planning, and treatment monitoring.