基于ProCA1靶向性MRI对比剂活体内评估MR靶向成像的影响因素

Magnetic resonance molecular imaging depends on not only the characteristics of molecular probe and specific binding to receptors, but also tumor angiogenesis and non-specific uptake of the probe in tissue. The application of MRI probes as targeted contrast agents in molecular imaging has matured in many research fields. However, several papers reported are proof-of-concept studies, and detailed knowledge on the in vivo effects of tumor angiogenesis and probe-targeting interactions remains limited. The use of MR molecular probes to assess tumor angiogenesis as well as probes specific and non-specific binding will facilitate more accurate assessment of tumor biology information and receptor density. .We have developed protein-based MRI contrast agents (ProCAs) by introducing a Gd3+ binding site into a scaffold protein, CD2 (ProCA1), with high relaxivity compared to clinical available MRI contrast agents both in vitro and in vivo. A novel ProCA1 targeted to epidermal growth factor receptor (EGFR), namely ProCA1-ZEGFR:1907, has been verified its target specificity previously. In this program, we intends to use ProCA1-ZEGFR:1907 to demonstrate the feasibility of assessment of tumor angiogenesis and probe specific binding of the probe to EGFR simultaneously. .Dual tracer optical molecular imaging is a study employing two near-infrared fluorescent reporters that emitted light at different wave lengths. One reporter (the targeted reporter) was bound to ProCA1-ZEGFR: 1907. The second reporter was left untargeted (ProCA1) and was mixed in equal concentrations with the targeted reporter. The similarities and differences of physiological processes between ProCA1-ZEGFR: 1907 and ProCA1 will be demonstrated with the use of dynamic dual tracer optical molecular imaging, and the feasibility of DCE-MRI and differentiation between probe specific binding and non-specific uptake, as well as their different time windows will be determined. .We aim to establish an imaging system with the capability to assess both tumor angiogenesis and the EGFR-specific binding information in vivo, and explore the impact of various factors of MR molecular imaging, through a single injection of dual tracer reporters and sequential DCE-MRI, dynamic dual-tracer optical molecular imaging, MR molecular imaging and image fusion. More accurate and more realistic expression of EGFR will be obtained in vivo by MR images based on this advanced imaging system.

影响MR分子成像的因素除靶点与探针特异性结合外，还包括肿瘤血管生成、组织对探针非特异性摄取等。MR分子成像同时评估肿瘤血管生成以及探针特异性、非特异结合对其影响，有利于更准确评估肿瘤生物学信息。本课题拟利用前期研制的基于蛋白质靶向表皮生长因子受体的MRI对比剂（ProCA1-ZEGFR:1907）探讨MR分子成像同时评价肿瘤血管生成和探针与EGFR特异性结合的可行性。先采用双示踪光学分子成像方法同时示踪靶向探针和非靶向探针（ProCA1），研究同一个体内靶向探针和非靶向探针生理过程的异同点，确定DCE-MRI以及区分探针特异性结合和非特异性摄取的可行性及不同的时间窗。最终通过单次注入双示踪探针，先后进行DCE-MRI、动态双示踪光学分子成像、MR分子成像，通过图像信息融合，建立一套可获得肿瘤血管信息和肿瘤细胞EGFR表达水平的成像系统，实现精确、实时和较全面的MR靶向成像。

多功能诊疗一体化探针的研究在肿瘤诊断及治疗领域均发挥重要的作用，目前，具有临床转化前景的探针屈指可数，故而急需发展可转化的诊疗探针。CT成像具有三维成像，穿透力强，成像便捷等特点，但是由于具有辐射，不适用于连续成像，光声成像是新兴的成像技术，敏感性高，故而可作为补充模式有效地弥补CT成像的不足。钽作为高原子序数的元素，安全，廉价，年产量高，适用于开发为新型CT对比剂。硫化铜同样是一种安全性高，成本低廉，合成简单的纳米材料，故而将两者结合，可以开发出新型的多功能诊疗探针。我们成功制备了核壳结构的多功能TaO@CuS探针，体内及体外分别验证了其安全性及成像效果，并将其用于成像引导下的近红外二区光热治疗，荷瘤小鼠的肿瘤生长明显受到了抑制。

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