COMPARISON OF IODINE-123-VASOACTIVE INTESTINAL PEPTIDE RECEPTOR SCINTIGRAPHY AND INDIUM-111-CYT-103 IMMUNOSCINTIGRAPHY

Recently, we have shown that the expression of receptors for vasoactiv e intestinal peptide (VIP) on intestinal adenocarcinomas can be used f or in vivo targeting of primary or metastatic tumor sites using I-123- labeled VIP. Several other receptors and antigens including the TAG-72 protein have also been implemented for in vivo localization purposes. In this study, we have compared the in vitro and in vivo binding of I -123-VIP and of the In-111-labeled monoclonal antibody (MAb) directed against TAG-72 (OncoScint(R); In-111-CR-103) in patients with intestin al adenocarcinomas in a single-blinded, prospectively randomized trial . Methods: Twenty patients were administered either I-123-VIP (150-200 MBq; 1 mu g) or In-111-CYT-103 (150 MBq; 1 mg) for one imaging study. After interim analysis demonstrated superior imaging with I-123-VIP, the next 10 patients (accounting for a total of 50 patients) enrolled in this trial underwent both studies in random order to allow for a di rect comparison. Results: In total, I-123-VIP scans were true-positive in 28 of 30 patients (93%) versus 17 of 30 patients administered In-1 11-CYT-103 (56%). In the subgroup of 10 patients enrolled in the secon d part of the study, primary intestinal adenocarcinomas were imaged in five of five patients with I-123-VIP and in only two of these patient s with In-111-CYT-103. Liver metastases were visualized in five of six patients by I-123-VIP receptor scanning and in four of these patients with In-111-CYT-103, The in vitro results indicated significant bindi ng of I-123-VIP to primary colorectal tumors as well as to HT29 and CO LO320 adenocarcinoma cells. In vitro, adenocarcinoma cells also expres sed abundant numbers of the TAG-72 antigen. Conclusion: Intestinal ade nocarcinomas co-express VIP receptors and the TAG-72 antigen. Despite significant in vitro binding of both agents, however, the VIP receptor scan is more sensitive in localizing intestinal adenocarcinomas and m etastatic spread.