[In vivo localization of labeled monoclonal antibody 3G9 against human gastric cancer in tumor-bearing nude mice].

3G9 is one of murine monoclonal antibodies against human gastric cancer produced by immunization of multiple human gastric cancer cell lines in sequence in our institute. In vitro 3G9 had a high specific binding capacity with human gastric cancer tissues and cell lines. 131I-labeled 3G9 and 125I-labeled normal murine IgG were injected into nude mice bearing xenograft or cells M85 and MGC803 of human gastric cancer in order to compare the differences between 3G9 and IgG distributions in tumor and various normal tissues. The distribution of radioactivity in vivo suggested that 131I-3G9 had a good ability of localization in tissues of gastric cancer. The tumor/blood, tumor/liver, tumor/stomach and tumor/muscle ratios were 1.23, 4.72, 7.25 and 10.28, respectively. The localization index of tumor was 2.62 at 48 hr and 4.13 at 96 hr. The radioactivity of 125I-IgG in tumor was much lower than that of 131I-3G9 and tended to decrease with time. The results of scintigraphy showed that there was distinct radioactivity in the tumor. In this group of nude mice, the minimum weight and diameter of tumor was 83 mg and 4 mm, respectively. The method of scintigraphy to analyse variation of radioactivity in tumor-bearing nude mice was established. The results showed that monoclonal antibody 3G9 could be useful in localization and treatment of human gastric cancer.