CLEARANCE OF INJECTED RADIOACTIVELY LABELED ANTIBODIES TO TUMOR PRODUCTS BY LIPOSOME-BOUND 2ND ANTIBODIES

Abstract

Liposomes containing anti-goat Ig were injected 24 h after administration of 125I-labeled goat antibody against the carcinoembryonic antigen (anti-CEA) to groups of nude mice bearing human tumor xenografts, and normal mice. Controls in each group received radioactively labeled anti-CEA only. In liposome-treated mice, blood 125I levels were lower than those of controls 30 min to 24 h after liposome administration, with corresponding accumulation of 125I activity in the liver and spleen for the first 2 h after liposome injection. [14C]Cholesterol or 99mTc labels in the bilayer were eliminated rapidly from the blood, with uptake in the liver and spleen. In xenograft-bearing mice, 125I activity detected in the tumors up to 6 h after liposome injection was identical to that detected in the tumors of controls. However, 24 h after liposome injection a reduction in the tumor concentration of 125I-labeled anti-CEA was obtained, but the tumor/blood radioactivity was still increased. In 2 mice given 27 .mu.mol lipid, the blood radioactivity count after 24 h was only 5% of that in the controls. In rabbits, 2 h after administration of liposomes containing anti-goat 2nd antibody, the circulating 125I activity had dropped by 28-40%. Administration of liposome-entrapped 2nd antibody .apprx. 2 h prior to external scintigraphy may clear circulating radioactively labeled primary antibody by up to 50%.