Multifunctional in Vivo EPR Imaging of Tumor Microenvironment

项目摘要/摘要 肿瘤微环境(TME)是影响肿瘤恶性的化学和生物学背景， 由于混乱的血管生成，肿瘤的增殖和转移活性变得更低 (低PO2)和更酸性(低pH)。而已知的氧分压和pH值是肿瘤生长和 最近，间质PI被确定为在肿瘤发生中起重要作用的新的信号分子。 新合成的稳定的顺磁分子，自旋探针，允许同时在体内监测 间质PO2、胞外pH(Phe)和间质无机磷浓度(PI)的电子学研究 顺磁共振(EPR)。由于肿瘤是高度异质性的，光谱-空间EPR成像是 在空间上解析感兴趣的参数所需的。空间分辨率由EPR敏感度定义。这个 体素内的自旋探测器分子的数量随着空间分辨率的立方而减少，并可能成为 如果太小，就无法检测到。敏感度还直接转化为函数分辨率，其准确性 PH、pO2和pI均可测量。PI和他的同事关于快速扫描(RS)EPR的建议 已经在250 MHz频率下探索了这项技术，并显示出信噪比提高到2 与标准的场调制连续波(CW)方法相比，该方法具有几个数量级的优势。一项额外的 对于基于三苯基的多功能探针，可以通过增加 EPR频率为700-800 MHz(小型动物RS EPR研究的最佳选择)，扫描频率为50-100 kHz (目前的数学算法将上限扫描频率限制在约10 kHz)。RS-EPR灵敏度 增强将需要硬件(SA1)和软件(SA2)的开发。此外，新的4D光谱- 空间算法将进一步开发，以实现多功能多线EPR成像，因为标准 滤波反投影(FBP)重建无法与多功能自旋探头一起工作 较宽的多谱线EPR谱。一种新开发的多功能EPR成像仪将首先进行测试 对已知几何形状、pO2、pH和PI模式的标准样品进行体外实验，然后进行体内概念验证 成像。一群自发性罹患乳腺癌的转基因小鼠将被用来进行 快速扫描多功能成像和构建TME和TME的空间分辨PO2、pH和PI分布 正常的乳腺。我们期望获得具有生理意义的体素特定的功能敏感性 大约1-2毫米汞柱的二氧化磷，0.05pH单位和0.1毫米的无机磷酸盐。估计的空间分辨率将 小于200m。总而言之，这个项目的成功可能对未来 活体功能成像研究TME及以后。

PROJECT SUMMARY/ABSTRACT The tumor microenvironment (TME) is the chemical and biological background that affects tumor malignancy, proliferation and metastatic activity because of chaotic angiogenesis tumors growing to become less oxygenated (low pO2) and more acidic (low pH). While pO2 and pH are known to be important factors for tumor growth and treatment, interstitial Pi has been recently identified as a new signaling molecule of importance in tumorigenesis. Newly synthesized stable paramagnetic molecules, spin probes, permit simultaneous in vivo monitoring of interstitial pO2, extracellular pH (pHe) and concentration of interstitial inorganic phosphate (Pi) using Electron Paramagnetic Resonance (EPR). Because tumors are highly heterogeneous, spectral-spatial EPR imaging is required to spatially resolve the parameters of interest. Spatial resolution is defined by EPR sensitivity. The amount of the spin probe molecules within a voxel decreases as spatial resolution is cubed, and may become undetectable if too small. Sensitivity also directly translates into functional resolution, the accuracy with which pH, pO2, and Pi can be measured. The proposal by the PI and his colleagues for a Rapid Scan (RS) EPR technique has been explored at 250 MHz frequency and showed improvement in signal-to-noise ratio up to two orders of magnitude compared to the standard field-modulated continuous wave (CW) method. An additional order of magnitude signal enhancement can be achieved for trityl-based multifunctional probes by increasing EPR frequency to 700 -800 MHz (optimal for small animal RS EPR studies) and scan frequency to 50-100 kHz (the current mathematical algorithm limits the upper scan frequency to about 10 kHz). RS EPR sensitivity enhancement will require both hardware (SA1) and software (SA2) developments. In addition, novel 4D spectral- spatial algorithm will be further developed to enable multi-functional multi-line EPR imaging, since the standard filtered backprojection (FBP) reconstruction fails to work with multi-functional spin probes that have a comparatively broad multi-line EPR spectra. A newly developed multi-functional EPR imager will first be tested in vitro on standard samples with known geometry, pO2, pH, and Pi patterns, followed by in vivo proof-of-concept imaging. A colony of PyMT transgenic mice will be used that spontaneously-develop breast cancer to perform the rapid scan multifunctional imaging and construct spatially-resolved pO2, pH, and Pi profiles of TME and normal mammary gland. We anticipate to achieve physiologically significant voxel-specific functional sensitivities of about 1-2 mmHg of pO2, 0.05 pH units and 0.1 mM of inorganic phosphate. Estimated spatial resolution will be smaller than 200 m. In summary, the success of this project may have a significant impact on the future of in vivo functional imaging to study TME and beyond.