Objective To investigate the preparation method of a molecular probe ¹³¹I-ch4E5 for targeting B-cell lymphoma and its anti-tumor effect in human B-cell lymphoma-bearing nude mouse model.

Methods The anti-CD80 human-mouse chimeric antibody ch4E5 was labeled with ¹³¹I through the Iodogen method, and its labeling rate and radiochemical purity were determined by radioactive thin layer chromatography scanning method. (1)In vitro experiments: ¹³¹I-ch4E5 solution was added to cytocentrifuge tubes containing 1×10⁸, 1×10⁹, 1×10¹⁰, 5×10¹⁰, and 1×10¹¹ cells/L of human B-cell lymphoma cells (Raji cells) and to non-specific binding control tubes. Radioactivity counts per tube of precipitation were measured to calculate the specific binding rate of Raji cells to ¹³¹I-ch4E5. (2) In vivo experiments: 7.4 MBq of ¹³¹I-ch4E5 was injected into three tumor-bearing nude mice via the tail vein. After 72 h, the tumor-bearing nude mice were sacrificed. Fourteen organs or tissues, such as tumor and blood, were harvested and weighed, and their radioactivity was measured. The radioactivity ratio of tumor to normal tissue (T/NT) was calculated. In the treatment study, 15 tumor-bearing nude mice were divided into three groups according to the random number table method and injected with ¹³¹I-ch4E5 (¹³¹I-ch4E5 group), unlabeled ch4E5 (ch4E5 group), and normal saline (control group) through the tail vein. Tumor growth was observed in the three groups. After 15 days, the tumor inhibition rate was calculated, and then the tumor-bearing nude mice were sacrificed to harvest tumor tissues for histopathological examination by hematoxylin-eosin staining. Comparisons between the two groups were performed using two independent samples t-test.

Results The labeling rate of ¹³¹I-ch4E5 was (84.2±2.4)%, and the radiochemical purity was (97.1±1.1)%. (1) In vitro experiments: the binding rate of ¹³¹I-ch4E5 to Raji cells increased with increasing cell concentration, and the maximum binding rate was (38.2±2.3)%. (2) In vivo experiments: the distribution of ¹³¹I-ch4E5 in human B-cell lymphoma-bearing nude mice was targeted, and the maximum T/NT ratio of tumor to muscle was 7.30. Compared with the ch4E5 and control groups, the ¹³¹I-ch4E5 group exhibited decreased tumor growth, and the difference was statistically significant (t=2.889, 6.516; both P<0.05). Fifteen days after the administration, the tumor inhibition rate was 71.7% in the ¹³¹I-ch4E5 group and 43.4% in the ch4E5 group. The histopathological examination results showed that tumor cell necrosis was observed in both treatment groups, and the therapeutic efficacy of the ¹³¹I-ch4E5 group was superior to that of the ch4E5 group.

Conclusion The self-made molecular probe ¹³¹I-ch4E5 has high labeling rate and radiochemical purity, and has a significant inhibitory effect on the tumor growth of human B-cell lymphoma-bearing nude mice, which provides an experimental basis for further research on the application of ¹³¹I-ch4E5 in radioimmunotherapy.