Intraperitoneal radioâ localization of tumors preâ targeted by biotinylated monoclonal antibodies

We describe 2â step and 3â step strategies for intraperitoneal tumor radioâ localization by means of monoclonal antibodies (MAbs). Nude mice bearing intraperitoneal human colon carcinoma tumors were injected i.p. with biotinylated MAb AUAI, followed 24 hr later by radioiodinated streptavidin (2â step). The uptake of radioactivity in tumor and normal tissues was measured 4 hr after injection of radioactive compound. A 3â step strategy consisted in administering biotinylated antibody, cold avidin after 24 hr and 111Inâ labelled biotin after a further 4 hr; mice were then killed 2 hr later. Tumor localization of intraperitoneallyâ administered biotinylated antibody and direct targeting of radioactive streptavidin to biotinylated antibody bound to tumor sites were demonstrated using immunohistochemistry and autoradiography. Our results show that (i) the 2â step approach increased the percentage of radioactivity uptake by tumor with respect to directly labelled antibodies (24% vs. 6%) and improved the tumor/nonâ tumor ratio; (ii) the 3â step approach allowed faster blood clearance of the radioactive probe (111Inâ biotin) and yielded high tumor/nonâ tumor ratios. â Preâ targetingâ methods appear to have advantages over the conventional 1â step approach with directly radiolabelled antibody. Copyright © 1990 Wileyâ Liss, Inc., A Wiley Company