Antibodies labeled with 199Au: potential of 199Au for radioimmunotherapy.

We have investigated the direct labeling of antibodies with gold isotopes as an alternative to iodine and chelated metals for antibody guided therapy. Both 199Au and 195Au complex anions in citrate-buffered solutions (pH 3.8-7.2) are rapidly bound to sheep polyclonal anti-CEA with high efficiency. After purification by gel filtration, the antibody retained 80% of the bound gold for upto 6 days at 4 degrees C and was reactive with its target antigen in a solid phase assay. Incubation with the gold binding substance D-penicillamine reduced labeling efficiency and stability.