RADIOIMMUNODETECTION OF COLORECTAL-CANCER METASTASES WITH I-131-LABELED MONOCLONAL-ANTIBODY B72.3 - A PILOT-STUDY TO DETERMINE EFFICACY OF DETECTION AND PHARMACOKINETICS

We performed radioimmunoscintigraphy (RIS) and/or pharmacokinetic (PCK) studies in 12 patients with primary or metastatic colorectal carcinoma, utilizing an intravenous administration of 1-4 mCi (I mg) of I-131-B72.3 monoclonal antibody. Metastatic lesions were correctly identified in 418 patients by RIS. Two patients with small lesions (>2 cm diameter) had a false-negative RIS scan. Two patients had a true-negative RIS scan. Optimal images were obtained at 1 week postinjection. PCK studies showed that the plasma clearance of I-131-B72.3 was biexponential with an alpha-phase half-life ranging from 0.5 to 7.1 hr and a beta-phase half-life ranging from 47:5 to 85.3 hr. Systemic and renal clearance data indicated that I-131-B72.3 was cleared very slowly and almost entirely kv deiodination. This pilot study was conducted to gain an understanding of the pharmacokinetics of this radiolabeled antibody. On the basis of these data, we are now studying second-generation antibodies as part of our long-range objectives to incorporate them in early detection and treatment protocols.