Application of Radiolabeled Monoclonal A7 Antibody for Radioimmunotherapy of Human Colon Cancer

利用表达于人恶性肿瘤细胞上的肿瘤相关抗原的单抗，可在体内将治疗性放射性核素输送到肿瘤病变部位。对于这种方法，需要稳定的放射性金属络合物。Re-186或Re-188有望成为放射免疫治疗的放射性核素选择。我们对MAG3和HYNIC络合物的偶联过程进行了评估。放射性标记物的稳定性令人满意。该项目使用的是一种单抗A7。该抗体识别多种人结肠癌细胞上的腺癌相关抗原。用Re-186标记A7抗体，比活性大于37MBq/mg。标记抗体的免疫反应性为67%，与I-131标记抗体相当。LS180人结肠癌细胞接种于Balb/c裸鼠。用I-131或Re-186标记的A7进行活体成像可以很好地显示肿瘤。治疗试验研究表明，Re-186A7对肿瘤的辐射是I-131A7的1.6倍。因此，Re-186抗体应该是有吸引力的放射免疫治疗方法。我们试图通过改变肿瘤组织的递送系统来增加肿瘤对放射性标记抗体的摄取。血管紧张素-II和激氨酸酶抑制剂马来酸依那普利的联合使用使小鼠的血压从95/61增加到153/67。在正常器官分布无明显变化的情况下，肿瘤摄取增加了1.62倍。综上所述，通过控制肿瘤组织的血流动力学和血管通透性可以增强肿瘤的摄取，这项技术可以用于有效的靶向。

Using monoclonal antibody specific for tumor associated antigen expressed on human malignant tumor cells, therapeutic radionuclides can be delivered to the tumor lesion in vivo. For this approach, the stable radiometal chelates is required. Re-186 or Re-188 are expected to be the choice of radionuclide for radioimmunotherapy. We have assessed the conjugation procedure of the MAG3 chelate and HYNIC chelate. The stability of the radiolabel was found to be satisfactory. A monoclonal antibody A7 was used for the project. This antibody recognizes adenocarcinoma related antigen on the variety of human colon cancer cells. The A7 antibody was labeled with Re-186, resulting in the specific activity of greater than 37 MBq/mg. And the immunoreactivity of the labeled antibody was 67%, which is equivalent for that of I-131 labeled counterpart.LS180 human colon cancer cells were inoculated to the Balb/c nude mice. In vivo imaging with either I-131 or Re-186 labeled A7 provided well-delineated tumor. Therapy trial study demonstrated that Re-186 A7 delivered 1.6 times higher radiation to the tumor than I-131 A7. Thus, Re-186 antibody should be the attractive modality for radioimmunotherapy.We have tried to increase the tumor uptake of radiolabeled antibodies by modifying the delivery system to the tumor tissue. The combination usage of angiotensin-II and a kininase inhibitor, enalapril maleate, increased the mouse blood pressure from 95/61 to 153/67. And the tumor uptake was also increased by the factor of 1.62 with little change in normal organ distribution. In conclusions, enhanced tumor uptake was achieved by manipulating hemodynamics and vascular permeability of the tumor tissue and this technique can be applied for effective targeting.