Biodistribution and preparation of technetium-99m-labeled D-D3 monoclonal antibody against pro-gastrin-releasing peptide(31-98) in mice

Abstract

Background We previously reported that iodine-131(131I)-labeled anti-progastrin-releasing peptide (ProGRP(31-98)) monoclonal antibody D-D3 could selectively accumulate in the tumor sites of nude mice bearing small cell lung cancer (SCLC) xenografts. However, 131I-D-D3 was cleared slowly from the body, and the best radioimmunoimaging time for SCLC was 72-96 hours after injection. The aims of this study were to radiolabel anti-ProGRP(31-98) D-D3 monoclonal antibody with technetium-99m (99mTc) and to investigate the biodistribution of this antibody in healthy ICR mice. Methods D-D3 was labeled with 99mTc via the 2-mercaptoethanol reduction method. 99mTc-D-D3 was purified by the gel column separation method. The labeling efficiency and radiochemical purity were measured by thin-layer chromatography. The immunological activity of 99mTc-D-D3 was determined with cell conjugation assays. 99mTc-D-D3 was injected into healthy ICR mice via a tail vein, and all the healthy ICR mice were sacrificed by cervical dislocation at a designated time. Then, the blood and major organs were removed and weighed, and counted in a gamma scintillation counter to determine the percentage of the injected dose per gram (%ID/g). Results The labeling rate and the radiochemical purity of 99mTc-D-D3 were (73.87±2.89)% and (94.13±4.49)%, respectively. The immunobinding rates of 99mTc-D-D3 to the human small cell lung cancer NCI-H446 cell line and lung adenocarcinoma A549 cell line were (81.2±2.37)% and (24.3±1.46)%, respectively. The distribution data of normal ICR mice demonstrated that 99mTc-D-D3 was mainly distributed in the liver, kidney and lung, and less in the brain tissue and muscle. Conclusions 99mTc-D-D3 antibody not only had high radiochemical purity, but also had good stability both in vitro and in vivo, and maintained good immunological activity. 99mTc-D-D3 was metabolized mainly in the kidney and liver, and the blood radioactivity decreased rapidly. Thus, 99mTc-D-D3 is conducive to the radioimmunoimaging of SCLC.