RADIOIMMUNOLOCALIZATION OF HUMAN PANCREATIC-CARCINOMA XENOGRAFT BY TC-99M-LABELED YPC3 MONOCLONAL-ANTIBODY

Monoclonal antibodies specific to tumor cells may be a useful tool for the diagnosis and treatment of carcinomas. In this study, YPC3 mAb, a specific monoclonal antibody against the human pancreatic carcinoma c ell line Capan-2, was labeled directly with Tc-99m after being pretrea ted with 2-mercaptoethanol. The radiolabeling efficiency was found to be high (88%-95%) and the immunoreactivity retained, as assessed by im munohistochemistry and enzyme-linked immunosorbent assay. The biodistr ibution of Tc-99m-YPC3 mAb in nude mice bearing Capan-2 pancreatic car cinoma xenografts was studied and compared with that of labeled mouse immunoglobulin G(Tc-99m-nmIgG). The xenograft uptake values per gram o f tissue 6 h and 24 h after injection of Tc-99m-YPC3 mAb were found to be, respectively, 4.72%ID/g and 8.42%ID/g, and the tumor/blood ratios 1.16 and 2.24. At 6 h and 24 h after injection of Tc-99m-nmIgG, the u ptakes were 2.89%ID/g and 1.80%ID/g, and the tumor/blood ratios 0.84 a nd 1.02 respectively. External imaging by single-proton emission compu ted tomography, 24 h after injection of Tc-99m-YPC3 mAb, revealed clea r scintigraphic visualization of Capan-2 xenografts, whereas injection of Tc-99m-nmIgG did not. This study suggests that Tc-99m labeling of monoclonal antibody YPC3 might be of practical value in localization d iagnosis of human pancreatic carcinoma.