Radiolabeled bivalent haptens for tumor immunodetection and radioimmunotherapy

The pretargeting technique referred to as the Affinity Enhancement System ( AES) uses bispecific antibodies and radiolabeled bivalent haptens that bind cooperatively to target cells in vivo. Experimental and clinical data demo nstrate that DTPA bivalent haptens can deliver large radiation doses to tum or cells with high tumor to normal tissue contrast ratios and long activity residence time in tumors, Preliminary clinical results of radioimmunothera py of medullary thyroid carcinomas and lung cancers look promising. Very en couraging results in biodistribution and radioimmunotherapy experiments in animals have been obtained with new haptens bearing two histamine-hemisucci nate suitable for I-131, Tc-99m and Re-188 labeling. Targeting isotopes to double antigen positive tumor cells provides a binding enhancement that inc reases specificity for tumor cells as compared to single antigen targeting on normal cells. This approach may be beneficial for targeting isotopes to B type acute lymphoblastic leukemia and Burkitt lymphoma, as well as others tumors co-expressing two markers of low specificity, and might increase tu mor irradiation with minimal irradiation of normal cells.