Semiquantitative in vitro binding assay of indium-111-labeled monoclonal antibodies to human cancer and normal tissues

We have developed a simple in vitro method for the semiquantitative assessment of the radiolabeled antibody binding to cancer and normal tissues. Indium-111-labeled F(ab')2 fragments of 17-1A and 19-9 monoclonal antibodies with well-characterized specificity for gastrointestinal cancer demonstrated similar binding properties between cultured cancer cells and membrane fractions of homogenates prepared from tumor tissues. All of the 17 colon cancer specimens and seven (64%) of 11 gastric cancer specimens obtained by surgery showed positive binding with 17-1A. Specific binding of 19-9 was observed in 9 (53%) colon cancers and 4 (36%) gastric cancers. However, some normal colon tissues were also positive with 111In-labeled 17-1A. Relative levels of CA 19-9 antigen expression, determined by the binding with radiolabeled antibodies, correlated with percent positive cells determined by the immunohistochemical assays. Furthermore, membrane fractions could be cryopreserved without losing antibody-binding activity. These results indicate that this assay can be used for testing the immunoreactivity of radiolabeled anti-tumor antibodies and in vitro binding properties to cancer and normal tissues.