Monoclonal antibodies as reversible equilibrium carriers of radiopharmaceuticals.

We have prepared monoclonal antibodies (MoAbs) with the specific ability to bind metal chelates such as 111In benzyl EDTA. One, 10, 50 and 100 micrograms MoAb CHA255 Kb = 4 X 10E9 was complexed with 111In BLEDTA II, BLEDTA IV, and benzyl EDTA and injected i.v. in Balb/c mice with KHJJ tumor. The biological half-life by whole body counting was profoundly altered for all three compounds; from minutes to hours with 10 micrograms; to days with 100 micrograms. Tumor uptake increased 50 fold at 24 h with increasing MoAb but satisfactory tumor concentrations (3% per g) and tumor/blood ratios (1.8:1) were obtained with an amount equivalent to 7 mg for a human. Blood level and whole body activity were decreased 30-50% within 3 h or i.v. injection of a "flushing" dose of unlabeled indium benzyl EDTA, increasing tumor/blood ratios to 50:1.