Immunodiagnosis of tumors in vivo using radiolabeled monoclonal antibody A2B5

Recently a murine monoclonal antibody (A2B5) has been described that reacts with a membrane associated GQ ganglioside common to peptide secreting normal cells and tumors. In vitro binding data demonstrated the presence of this ganglioside on neurons, adrenal medulla, and pancreatic islets, along with neuroendocrine tumors such as insulinomas, pheochromocytomas, melanomas and neuroblastomas. Negative binding has previously been shown for tissue sections from liver, kidney, colon, lung, stomach, and tumors not derived from the neural crest. Because of the specificity at A2B5 in vitro, this monoclonal antibody was labeled with 131I for in vivo tumor localization studies. Daily radionuclear scans were obtained in 5 KX rats bearing the radiation induced rat insulinoma with disappearance of the label from the blood pool and concentration in the tumor so that by the fourth day, the only activity present by scan was in the insulinoma. Tissue‐counting data showed tumor/blood ratios (av ± SE, 1.29 ± 0.25) of A2B5 activity two to ten times the average activity found in other organs (0.28 ± 0.05). No tumor concentration of the control nonspecific monoclonal antibody P3X63 was evident (0.27 ± 0.04). In addition A2B5 also localized to five different human melanoma cells lines grown in nude mice with high tumor/blood levels (1.04 ± 0.27) compared to normal tissues (0.32 ± 0.05) (P = .0005), while no localization is seen in nudes carrying osteosarcomas, colon, bladder, and renal cell carcinomas. In addition antibody A2B5 did not concentrate in any normal tissue though the antigen is present on several. The finding that A2B5 reacts across species lines (mouse, rat, man) lends itself to obvious diagnostic and therapeutic possibilities.