Preclinical evaluation of an "instant" 99mTc-labeling kit for antibody imaging

This communication presents information on the quality and stability of a new conjugate of 99mTc to an anticancer antibody fragment and results of animal imaging and distribution studies. Clinical studies have proved that this labeled antibody can image tumors within 2 hours of i.v. injection. It is produced using an "instant kit," merely requiring addition of [99mTc]pertechnetate to a lyophilized vial containing the fragment and a pertechnetate-reducing agent. Within 5 min of addition of pertechnetate to the vial containing the fragment, [99mTc]pertechnetate is reduced and quantitatively bound to an intrinsic high-affinity receptor present in the Fab'. The Fab'-bound 99mTc is completely stable to challenge with diethylenetriaminepentaacetic acid and human serum albumin. Minimal oxidation and release of 99mTc bound to the fragment were observed when the labeled fragment was incubated for 24 h at 37 degrees C. Animal biodistribution studies were consistent with the known metabolic elimination of a radiolabeled Fab' fragment by the kidney. Tumor localization studies in athymic nude mice bearing xenografts of human colonic carcinoma (GW-39) predicted the positive results later demonstrated in clinical studies.