Biodistribution of131I-labelled monoclonal antibodies in human colon tumours by anex vivo perfusion model

Abstract

We describe a model for the evaluation of anti-tumour antibody specificity, using a human carcinoma-bearing colon segment. After resection of the human colon tumour, the supplying artery was cannulated and perfused with fresh frozen plasma and heparin. Continuous control of pressure, flow, temperature, p~ and various metabolic parameters were performed after administration of I3'llabelled anti-CEA antibody. Highly differentiated adenocarcinomas of the colon showed a much higher antibody uptake than undifferentiated tumours. Between 3 and 7% of the injected antibody was found in the tumour tissue. Autoradiography showed non-homogeneous binding in the tumour tissue. The non-specific antibody perfusion showed no tumour binding. We conclude that the ex vivo perfusion of resected colon carcinomas can be used to measure the kinetics of binding and clearance of MAbs in tumour tissue by direct scintigraphy. The cellular biodistribution of the antibody can be documented by means of autoradiography.The use of monoclonal antibodies (MAbs) for diagnostic and therapeutic purposes depends on the uptake and retention of the antibodies in the target neoplastic tissues. The accuracy of presently available methods is subject to inherent limitations with respect to scintigraphic localization, while therapeutic application appears only rarely successful. Recent clinical trials in colon carcinomas have proved more or less disappointing (Beatty et al., 1986; Epenetos et al., 1986; Mach et al., 1987). The purpose of our study was to examine the binding characteristics of CEA antibodies and to investigate the biodistribution of specific and non-specific antibodies in resected human colon tumours. MATERIAL AND METHODSAfter resection of the human colon tumour, the supplying artery was cannulated. The carcinoma-bearing colon segment was then removed and interposed in a closed circulation system similar to that reported by Sears et al. (1981) (Fig. 1). During pulsed perfusion with fresh frozen plasma (200 ml plus 5,000 U heparin) continuous monitorin of pressure, flow, temperature, PH and various metabolic parameters was performed. After administration of the 13t-labelled antibody (300-400 pCi 0.4-0.8 mg) continuous circulation was carried out for 40-45 min. Thereafter unbound MAbs were eluted from the tumour-bearing colon segment (40 min, fresh frozen plasma/Ringer solution 1 +2). During the whole perfusion period continuous scintigraphic analysis was performed, yielding a ratio of maximal accumulation in tumour tissue to accumulation in surrounding non-tumour tissue. After perfusion, tissue samples were taken from the centre of the tumour, the tumour periphery, the non-tumorous intestinal wall, the mucosa, the lymph nodes and the perivascular tissues, for activity determination in counts per g. Cross-sections were performed for autoradiographic and immunohistological documentation, and for antibody and CEA distribution. The specific MAb was C1 P83 (IgGI) directed against 180 kDa CEA (IgG1); the control MAb B40 (IgGI) specificity was not...