Tumor localization of Lewis lung carcinoma with radiolabeled monoclonal antibodies

Mouse 6D6 IgG2a and 5B5 IgM monoclonal antibodies which specifically bind murine lung carcinoma cells (3LL cells) were injected to healthy and tumor-bearing mice. In vivo localization was analyzed by counting the tissue radioactivity and by external gamma ray scintigraphy at various times after IV injection of 125I- or 131I-labeled antibodies. The clearance of the two monoclonal antibodies was not modified by the presence of the tumor, and the 6D6 IgG2a was cleared at a rate slower than the 5B5 IgM. Both antibodies gave a high specific uptake at the tumor level; the tumor-to-healthy tissue ratios were higher with the 6D6 IgG2a than the 5B5 IgM; unspecific mouse immunoglobulins (IgG2) did not localize in the tumor. The amount of 6D6 IgG2a antibody still associated with the tumor after 2 days following IV injection was 10 times higher than that of 5B5 IgM, and was still high enough to localize the tumor after 5 days. Imaging experiments confirmed the ability of 6D6 IgG2a to detect the presence of tumor cells. The targeting kinetics determined by computer analysis of camera images indicated a rapid targeting of antibodies in tumor with a maximal concentration after 4-6 h; after 48 h the background was quite low and the 6D6 IgG2a appeared to be specifically localized in the tumor.