68Ga标记智能纳米PET探针的研制及其用于肿瘤诊断的性能研究

Early diagnosis of tumor is of great importance for human being fighting tumors. Among the techniques of tumor diagnosis, positron emission tomography (PET) has been widely used due to its advantages in early diagnosis of tumor with high sensitivity and accuracy. Therefore, development of novel PET probes is vital for broadening clinical applications of PET. Nanoparticles can be used as a carrier to load a large number of imaging agents, enhance the concentration in region of interest, and improve the sensitivity of imaging, are widely explored in nowadays. In this study, based on a new condensation reaction, we will design 68Ga-labeled PET probe targeting furin which is upregulated in many cancers. After being uptaken by tumor cells, the probes will be hydrolyzed by furin to initiate the condensation reaction and thereafter self-assemble into radioactive nanoparticles in tumor cells, and enhance the radioactivity in tumor cells for tumor-targeted PET imaging. Therefore, our radioactive nanoparticles are highly “smart” and tumor-targeting which are totally different from those premade nanoparticles with synthetic difficulty, low uptake in tumor, etc. From design and synthesis of the probe, nano preparation and characterization in vitro, targeting experiment of cell and micro-PET imaging of tumor-bearing nude mice, we hope that we could develop new tumor-targeting PET imaging agents with convenient radioactive labeling and higher sensitivity for early diagnosis of tumor.

肿瘤的早期诊断对于肿瘤的治疗至关重要。在肿瘤诊断技术中，正电子断层显像(PET)因其具有早期、灵敏的优点而得到广泛的应用。新型PET探针的开发能进一步扩展PET的临床应用。纳米粒子能作为一个载体来装载大量的显像剂以提高生物组织局部浓度，提高成像灵敏性，已成为PET探针的研究热点之一。本研究利用一个新型缩合反应，设计68Ga标记的小分子PET探针，该探针靶向肿瘤细胞高表达的furin酶，能被furin酶识别摄取进入细胞，剪切水解发生缩合反应然后自组装成放射性纳米粒子，在肿瘤细胞内浓聚放射性，用于肿瘤的靶向PET成像。该放射性纳米粒子具有智能组装和高度靶向性，从而克服普通纳米粒子合成难、低摄取等问题。我们希望通过本探针的设计合成、纳米粒子制备、细胞靶向性实验和荷瘤裸鼠micro-PET显像等研究，研制出具有标记简便、较高灵敏度、肿瘤靶向的新型PET探针用于肿瘤的早期诊断。

肿瘤的早期诊断对于肿瘤的治疗至关重要。在肿瘤诊断技术中，正电子断层显像(PET)因其具有早期、灵敏的优点而得广泛的应用。新型PET探针的开发能进一步扩展PET的临床应用。纳米粒子能作为一个载体来装载大量的显像剂以提高生物组织局部浓度，提高成像灵敏性，已成为PET探针的研究热点之一。本项目设计了一个新型PET探针68Ga-NODAGA-RVRRCKCBT，该探针靶向肿瘤细胞高表达的furin酶，能被furin酶识别摄取进入细胞，酶切缩合后自组装成放射性纳米粒子，在肿瘤细胞内浓聚放射性，用于肿瘤的靶向PET成像。首先我们合成了标记前体NODAGA-RVRRCKCBT、冷化合物Ga-NODAGA-RVRRCKCBT，进行了结构确证；标记制备了探针68Ga-NODAGA-RVRRCKCBT，放化纯大于97%；将冷化合物和furin酶共孵育进行体外纳米粒子制备，形成了平均直径为356.8±95.9 nm的纳米粒子；将冷化合物和前体分别与MDA-MB-468细胞共同培养，结果显示共培养的细胞里能看到纳米粒子；进行了MDA-MB-231和MDA-MB-468荷瘤裸鼠micro-PET显像实验，结果显示MDA-MB-231肿瘤热化合物组1h的肿瘤摄取率为1.01±0.23%ID/g，而冷热化合物共注射组为2.49±0.19%ID/g；而在MDA-MB-468肿瘤，热化合物组1 h的摄取率为0.88±0.24%ID/g，热化合物和前体共注射组的摄取率为2.12±0.13%ID/g，冷热化合物共注射组的显像效果最好，1 h的摄取率为3.72±0.27%ID/g。进行了MDA-MB-468的裸鼠组织分布和药代实验，验证了冷热共注射组具有较高的肿瘤摄取率和较长的血液代谢时间；进行了MDA-MB-468荷瘤裸鼠肿瘤纳米验证，能在共注射组的肿瘤细胞内看到纳米粒子。通过以上实验我们验证了探针和标记前体或冷化合物共注射可以在高表达furin酶的肿瘤细胞内形成含68Ga的纳米粒子，从而提高荷瘤裸鼠的micro-PET显像效果。通过本研究我们研制出了一个具有标记简便、较高灵敏度、肿瘤靶向的新型PET探针。