Imaging and biodistribution of 131I labeled anti-neuropilin-2 monoclonal antibody in lung adenocarcinoma-bearing mice

Abstract

Objective To prepare 131I-anti-neuropilin-2-monoclonal antibody (131I-anti-NRP-2-mAb), and investigate its biodistribution and imaging in nude mice bearing xenografted lung adenocarcinoma, in order to evaluate its feasibility as an imaging agent targeting to NRP-2 positive tumors. Methods (1) 131I-anti-NRP-2-mAb was prepared by Chloramine-T method under the optimum labeling conditions, then the labeling efficiency, radiochemical purity and stability were determined in vitro. (2) The binding fraction and receptor binding affinity of 131I-anti-NRP-2-mAb were measured in A549 human lung cancer cells by cell uptaking and binding experiments. (3) The A549 tumor-bearing mice were randomly divided into 4 groups with direct sampling method and were sacrificed at 6, 24, 48, and 72 h, respectively, after tail intravenous injection of 0.37 MBq 131I-anti-NRP-2-mAb. The distribution was measured, and the ratios of tumor/muscle (T/M) and tumor/blood (T/B) were calculated. (4) Gamma imaging was performed in 6 mice, including 3 in the competitive inhibition control group (injected with 3.7 MBq 131I-anti-NRP-2-mAb and 100 μg atni-NRP-2-mAb), at 6, 24, 48, and 72 h post-injection to observe the radioactivity in tumor. Two-sample t test was used for data analysis. Results (1) The labeling yield and radiochemical purity of 131I-anti-NRP-2-mAb were (94.69±3.63)% and (98.56±0.48)%, respectively. The radiochemical purity was more than 85% after incubating in phosphate-buffered solution at room temperature for 72 h. (2) At 60, 120, 180 and 240 min post-injection, the binding ratios of 131I-anti-NRP-2-mAb in A549 cells were (3.95±0.18)%, (5.19±0.65)%, (6.60±0.36)% and (5.58±0.63)%, respectively. When excessive anti-NRP-2-mAb were added, the binding ratios were reduced to (0.94±0.31)%, (1.12±0.17)%, (1.24±0.25)% and (1.04±0.18)%, respectively, which were significantly lower than those of non-inhibited group (t values: 9.89-19.66, all P<0.05). 131I-anti-NRP-2-mAb bound to NRP-2 with high affinity half maximal inhibitory concentration (IC50=(410.8±1.2) nmol/L). (3) Biodistribution study demonstrated that the T/M and T/B ratios increased with the time extension and were 3.83±0.18 and 1.10±0.20, respectively, at 72 h post-injection. (4) Gamma imaging studies revealed that 131I-anti-NRP-2-mAb could clearly identify A549 tumors 6 h post-injection, especially at 48 h post-injection. Tumors were not observed clearly in competitive inhibition control group. Conclusion 131I-anti-NRP-2-mAb has been successfully prepared, and it could target to NRP-2 specifically. Key words: Neuropilin-2; Antibodies, monoclonal; Isotope labeling; Iodine radioisotopes; Radionuclide imaging; Lung neoplasms; Mice, nude