[Radiolabeling of a new agent for the study of colorectal tumors].

A new Monoclonal Antibody (AcMo) ior-C5, highly specific for the most part of colorectal adenocarcinomas has been developed. The AcMo was labeled with 99mTc by the Schwarz's direct method using molar ratios MAb: reductant of 1:1,000 and 1:2,000. The first molar ratio was the most adequate for the preparation of the radiopharmaceutical. A labeling yield greater than 95% was obtained. Several <<in vitro>> assays were carried out in order to evaluate the stability of the preparation, whose results reflected the presence of the stable complex 99mTc-IgG. The biodistribution patterns for both preparations were similar. The excreting organs behaved like normal. Nevertheless, a greater renal excretion was observed for the preparation of the molar ratio of 1:2.000, which could be due to the presence of low affinity sites observed in this preparation. They are vulnerable to the trans-chelation of the 99mTc toward cysteine or glutathione present in plasma and tissues.