Experimental radioimmunotherapy with 186Re-MAG3-A7 anti-colorectal cancer monoclonal antibody: comparison with...

A murine IgG1 against a Mr 45 kD tumor-associated glycoprotein in human colorectal cancer, A7, was radiolabeled with 186Re by a chelating method with a mercaptoacetyltriglycine (MAG3). Its specific activity was 119 MBq/mg, which would be high enough for a therapeutic purpose, and its immunoreactivity was preserved well as was 131I-A7 labeled by the chloramine-T method. Growth of human colon cancer xenografts, 9.14 +/- 0.44 mm in diameter, in nude mice was significantly suppressed by an intravenous dose of 4.48 MBq of 186Re-A7. The therapeutic outcome with 186Re-A7 was better than that with 4.63 MBq of 131I-A7. Toxicity of treatments assessed by body weight change was similar with both conjugates. These results are likely caused by the tumor size and more favorable physical properties of 186Re than those of 131I.