Melanoma localization in nude mice with monoclonal Fab against p97

The tumor targeting capacity of monoclonal antibody Fab fragments was explored in nude mice bearing human melanoma xenografts. Radioiodinated Fab 8.2 and 96.5, specific for melanoma-associated antigen p97, were tested in vitro for immunoreactivity and in vivo for tumor localization relative to a co-administered control, Fab 1.4. Fab was cleared rapidly from the blood with a T1/2 of 3-3.5 hr and greater than 90% of the injected radioactivity was excreted by 16 hr. The mean specific Fab in tumor reached a maximum of 3.5% injected dose/g at 4 hr and decreased to 1.5% at 16 hr. Over the same period, the ratio of specific/control Fab in tumor normalized to blood, the localization index, rose from 3 to 25 compared with ratios near unity for all other tissues. The concentration of specific Fab in tumor could be correlated to the amount of Fab protein administered as well as its immunoreactivity.