Pharmacokinetics of a radioiodinated monoclonal antibody F(ab')2 fragment in a xenograft model with circulating antigen.

The pharmacokinetics of 131I-labeled OC 125 F(ab')2 antibody fragment were investigated in athymic mice bearing OVCAR-3 ovarian carcinoma xenografts, a model in which the CA 125 antigen is present in serum. Nine antibody doses between 0.1 and 650 micrograms were studied. Optimal tumor to normal tissue ratios were obtained at 100-200 micrograms of F(ab')2. At most antibody doses, the pre-injection level of circulating CA 125 appeared to influence the localization of 131I activity in tumor, liver and spleen.