TC-99M-LABELED MONOCLONAL-ANTIBODIES FOR IMMUNOSCINTIGRAPHY - SIMPLIFIED PREPARATION AND EVALUATION

Ascorbic acid incubated with monoclonal antibodies (22-degrees-C, 60 min, pH 6.5) at a molar ratio of 3500:1, reduced 2.7 +/- 0.2% of the available disulfides to sulfhydryl groups that strongly bind 99mTc, and provided greater than 95% labeling efficiency for several IgM, IgG and F(ab')2 antibodies. The colloid formation was consistently less than 3% and the stability of the tracer when challenged with DTPA and cysteine was excellent. The immunospecificity of labeled antibodies as determined by immobilized specific antigen assay was 84 +/- 1% for IgM and 82.6 +/- 1.1% for IgG antibodies. For in vivo evaluation in mice bearing experimental abscesses and tumors, corresponding I-125-labeled antibodies served as controls. The liver uptake was similar (P = 0.76 and P = 0.12) for Tc-99m or I-125 labeled antinuclear antibody TNT-1 in mice bearing abscesses as well as for Tc-99m-TNT-1-F(ab')2 and I-125-TNT-1-F(ab')2 in mice bearing tumors. Higher but statistically insignificant (P = 0.08, 0.18, and 0.73) urinary excretion was noted for Tc-99m-antibodies. For corresponding Tc-99m- and I-125-labeled antibodies, the abscess to muscle ratios (3.3 +/- 0.5 vs. 3.4 +/- 0.8) and tumor to muscle ratios (10.04 +/- 4.4 vs. 10.54 +/- 3.0) were similar. The high Tc-99m-TNT-1-F(ab')2 uptake permitted excellent scintigraphic visualization of tumors whereas the nonspecific Tc-99m-HSA did not (tumor/muscle ratio: 2.4 +/- 0.3). This method is simple, reliable, and adaptable to an instant labeling technique.