目的 基于七甲川菁染料MHI148构建新型PET/近红外荧光(NIRF)双模态探针,并初步评估其用于肿瘤模型小鼠成像的能力.方法 采用双功能螯合剂DOTA修饰MHI148构建MHI148-DOTA,对其光物理、光热性能进行表征;以放射性核素68 Ga标记M HI148-DOTA,合成探针68Ga-M HI148,测定其放射化学纯度及稳定性.建立小鼠乳腺癌4T1及人脑胶质母细胞瘤U-87MG皮下瘤模型,以68 Ga-M HI148探针对其进行小动物PET显像,观察成像效果及该探针在小鼠体内的生物分布.结果 MHI148-DOTA光物理及光热性能优异.以之构建的探针68Ga-M HI148放射化学纯度＞99％,稳定性良好;小动物PET成像可清晰显示肿瘤,肿瘤摄取随时间延长而逐渐升高,6 h时U-87MG及4T1肿瘤/肌肉摄取比值分别为4.55±0.20及8.08±2.26;68Ga-M HI148小鼠体内主要分布于血液、肺、肝及肾脏.结论 成功构建的双模态68Ga-MHI148探针标记简单、稳定性良好,肿瘤靶向潜力较好,并可在近红外激光照射下抑制小鼠肿瘤细胞生长.

Objective:To develop a radiolabeled peptide molecular tracer 99Tc m-His-Arg-Pro-Tyr-Ile-Ala-His ( 99Tc m-T7) targeting transferrin receptor and evaluate its micro SPECT/CT imaging effect in tumor-bearing nude mice models. Methods:The peptide probe 99Tc m-T7 was developed by indirect labeling method with the coordination of co-ligands N-tri (hydroxymethyl) methylglycine and ethylenediamine diacetate. The expression levels of TfR on the surface of human pancreatic PANC-1 tumor cells and human breast MX-1 tumor cells were measured through flow cytometry. Cell binding and competitive blocking assays was conducted to analyze the binding affinity and specificity of 99Tc m-T7 in vitro. Micro SPECT/CT imaging and biodistribution after the establishment of mouse xenograft models were performed in vivo to evaluate the affinity and feasibility of noninvasive tumor imaging. Radio-autograph assay and immunohistochemical staining were conducted to validate the correlation between the uptake of 99Tc m-T7 and expression of TfR in tumor tissues. Independent sample t-test was used for the comparison between the two groups. Results:The radiolabeled probe 99Tc m-T7 was successfully synthesized with a radiolabeling yield of greater than 95%. It exhibited great stability in vitro, with radiochemical purities of (95.3±0.3)% and (90.6±0.4)% after incubation in normal saline and fetal bovine serum for 4 hours, respectively. The results of flow cytometry showed that PANC-1 tumor cells overexpressed TfR on the surface with a high tendency to bind TfR monoclonal antibody ((98.9±0.1)%), whereas MX-1 tumor cells showed low TfR expression on the membrane((0.2±0.1)%). In vitro cell binding assay results showed that the binding rate of PANC-1 cells to 99Tc m-T7 reached a peak ((16.12±0.01)%) after 60 minutes of incubation, which was higher than that of MX-1 cells ((1.20±0.01)%), and the difference between them was statistically significant ( t=28.67, P<0.001). The results of cell competition inhibition experiment showed that the binding rate of PANC-1 blocking group to 99Tc m-T7 decreased to (2.40±0.01)%, which was significantly different from that of PANC-1 experimental group( t=26.91, P<0.001). The results of micro SPECT/CT imaging in nude mice bearing tumor showed that 99Tc m-T7 could be quickly cleared from the blood and mainly eliminated from the kidneys. PANC-1 tumor-bearing nude mice models showed clear tumor contour 30 minutes after injection of 99Tc m-T7, with a tumor-to-muscle ratio of 2.80±0.22. The results of biological distribution experiments showed that the uptake of 99Tc m-T7 by tumors and organs (percentage injection dose rate (%ID/g) per gram of tissue) was consistent with the imaging results, and the uptake of 99Tc m-T7 in PANC-1 cells ((0.55±0.18)%ID/g) was higher than that in MX-1 cells ((0.16±0.11)%ID/g), and the difference was statistically significant ( t=6.42, P<0.001). The radio-autograph assay showed that PANC-1 cells significantly absorbed 99Tc m-T7 compared with MX-1 cells 30 minutes after injection of 99Tc m-T7. The highest uptake in normal organs was observed in the kidney, followed by the liver. Hematoxylin-eosin and immunohistochemical staining revealed no obvious necrosis in the tumor parenchyma. The PANC-1 cells overexpressed TfR, and whereas the MX-1 cells had low TfR expression. Conclusion:A specific polypeptide molecular probe 99Tc m-T7 targeting TfR was successfully prepared, which has excellent imaging efficiency in tumor-bearing nude mice models, and is expected to provide a new imaging method for monitoring the expression of tumor TFR in vivo.