多功能稀土纳米探针用于VX2瘤靶向性CT造影剂和放疗增敏剂的影像学研究

Iodine ions in Iodinated contrast agent for CT has shortcomings such as weak X-ray attenuation, renal toxicity, and short plasma half-life. BaYbF5:2%Tm3+ is a newtype rare earth nanoprobe, which contains heavy metals such as Ba and Yb with higher X-ray attenuation coefficient and longer plasma half-life. It means that this newtype nanaprobe could be passive enriched in solid VX2 tumor because of enhanced permeability and retention (EPR) effect, targeting ligands also could be linked on the probe for active targeting enriched in VX2 tumor. Moreover, the heavy metal nanoparticles is a kind of radiosensitizer. Hereby, we will establish a rabbit lung VX2 tumor model as the research platform, rabbits in non-targeted nanoprobe group and RGD peptide modified targeted nanoprobe group were performed CT scan to evaluate the CT enhancement and active targeted effect in the tumor between two groups. Those rabbits also underwent radiotherapy and the radiosensitization of targeted nanoprobe were evaluated by comparing with radiotherapy only group and control group. CT enhancement effect, tumor size, and metabolic change of the tumor pre- and post radiotherapy were measured on enhanced CT and PET/CT, respectively. All rabbits were sacrificed, the tumor volume, tumor cell necrosis rate, EGFR, apoptosis rate, tumor cell cycle were tested and measured. Organs such as heart, kidney, liver were examined whether with damage or not. All analysis were taken pathology results and CT measurements as gold standard. This study will lay the foundation for the optimization and clinical application of the multifunctional rare-earth nanoprobe.

目前CT造影剂的主成分碘，存在对X射线衰减不强、一定的肾毒性、血半衰期短等不足。新型稀土纳米探针BaYbF5:2%Tm3+中重金属元素镱、钡的X射线衰减系数高于碘，血半衰期较长有利于EPR效应被动富集，还可连接靶向配体主动靶向富集，且稀土重金属纳米颗粒具有放疗增敏效应。据此，本项目拟建立肺VX2瘤大型哺乳动物深部脏器肿瘤模型为研究平台， RGD修饰靶向探针组与非靶向探针组CT扫描比较，观测CT造影剂效果、主动靶向效果； 比较对照组、单纯放疗组、非靶向探针+放疗组、靶向探针+放疗组的差别，判断靶向探针的放疗增敏效果。CT观测造影剂强化效果、肿瘤大小， FDG PET/CT测量肿瘤代谢变化，检测血VX2瘤标志物特异性DNA量的变化。病理测量肿瘤大小、瘤细胞坏死率、EGFR、凋亡率、细胞周期、重要脏器有无损伤。以病理和CT测量值为金标准，统计分析和评价。为多功能稀土纳米探针的优化及应用奠定基础。

目前临床使用的CT及MR显像剂均为单模态显像剂，且有一定肾毒性。纳米材料因粒径小，比表面积大，可与靶向配体连接等特点，可作为多功能生物医学材料使用。本课题通过水热法合成纳米材料BaGdF5并探究其材料性质以及在动物体内生物分布特点。经过修饰的PEG@BaGdF5有良好的生物相容性，具有CT/MRI双模态造影剂功能，且X线衰减系数高于临床常用造影剂碘海醇。使用靶向配体RGD连接后合成RGD-PEG@BaGdF5，通过连续多时间点CT/MR动物显像发现：尾静脉注射纳米材料后1 h，荷VX2瘤裸鼠肿瘤部位CT值在RGD-PEG@BaGdF5组与PEG@BaGdF5组之间存在差异，RGD-PEG@BaGdF5组CT值高于RGD-PEG@BaGdF5组，且RGD-PEG@BaGdF5组肿瘤强化持续时间更长，MR肿瘤显像结果类似。证明了RGD-PEG@BaGdF5在肿瘤部位主动靶向沉积提升了纳米材料CT/MR造影剂性能。显像后各脏器病理结果亦证实纳米材料无明显组织毒性。RGD-PEG@BaGdF5不仅可作为CT/MR双模态显像剂，因Ba、Gd均为高原子序数元素，还可作为放疗增敏剂。本课题分别对各组荷VX2瘤裸鼠瘤体注射纳米材料后使用普通X线局部外放射治疗，结果显示RGD-PEG@BaGdF5组肿瘤生长抑制效应明显优于PEG@BaGdF5组、单纯放疗组及对照组。此外，RGD-PEG@BaGdF5组Ki67染色阳性率最低，而TUNEL染色阳性率最高，也证明了RGD-PEG@BaGdF5具有良好的放疗增敏效能。另外，本课题还评估了ctDNA含量变化用于兔VX2瘤放疗疗效监测的价值，探究了BaGdF5在细胞水平放疗增敏效果与机制。综上所述，本研究为促进主动靶向性纳米诊疗一体化的发展提供了大量科学依据。

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