RADIOIMMUNOGUIDED SURGERY USING IODINE-125-LABELED BIOTINYLATED MONOCLONAL-ANTIBODIES AND COLD AVIDIN

One of the limitations of intraoperative tumor detection with radiolab eled monoclonal antibody (Mab), by means of a gamma-detecting probe (G DP), is the long time interval needed between Mab injection and surger y to obtain low blood-pool activity. Such an interval can be shortened considerably, exploiting the high affinity between avidin and biotin. Methods: Twenty patients with colorectal cancer were injected with 1 mg of biotinylated I-125 monoclonal antibodies followed, 48 hr later, by a chase of cold avidin. During surgery, the GDP was used to detect radioactive emissions from the tumor and normal tissue. Tumor tissue s amples were analyzed in vitro by immunohistochemical tests for the pre sence of tumor antigens and in vivo antibody localization. Results: At the time of surgery (average 7 days postinjection), the mean value of circulating radioactivity was 6% +/- 3% of the injected dose. Of 20 p atients studied, tumors were localized in 13 cases (65%). Subclinical tumors were detected in 3 patients (15%). Conclusion: The use of I-125 -labeled biotinylated Mabs followed by avidin as a chase enhances the applicability and effectiveness of radioimmunoguided surgery technolog y and will allow the use of radioisotopes with a shorter half-life tha n I-125.