ABSTRACT
Humanized monoclonal antibody U36 and its F[ab']2 fragment, radio labeled with 125I, were tested for tumor localization in nude mice bearing a squamous cell carcinoma xenograft line derived from a head and neck carcinoma. Monoclonal antibody IgG or F[ab']2 fragment were injected in parallel and at days 1, 2 and 3, mice were dissected for determination of isotope biodistribution. IgG as well as F[ab']2 showed highly specific localization in tumor tissue. The mean tumor uptake [n=3] is expressed as the percentage of the injected dose per gram of tumor tissue [%ID/g].%ID/g of IgG was 11.7% at day 1 and decreased to 10.9% at day 3 whereas%ID/g of F[ab']2 was 2.9% at day 1 and decreased on following days. Tumor to blood ratios [T/B] at day 1 were 0.86 for IgG and 1.32 for F[ab']2 and reached a maximum at day 3 with values of 4.41 and 1.84 respectively. These findings suggest that the superior tumor to non-tumor ratios in the day of 1 render the F[ab']2 fragment more qualified for specific targeting radioisotopes to tumor xenografts in this exprimental setting