COMBINATIONS OF NONLABELED, I-125 LABELED, AND ANTIIDIOTYPIC ANTIPLACENTAL ALKALINE-PHOSPHATASE MONOCLONAL-ANTIBODIES AT EXPERIMENTAL RADIOIMMUNOTARGETING

Purpose: Placental alkaline phosphatase (FLAP) is a membrane-bound onc ofetal antigen that can be used for radioimmunotargeting. Preinjection of nonlabeled monoclonal anti-FLAP antibody (H7) and postinjection of monoclonal anti-idiotypic anti-PLAP antibody (alpha H7) were used in order to improve the localization efficacy of I-125-labeled H7. Materi al and Methods: A human cervix adenocarcinoma cell line (HeLa Hep 2) w as inoculated subcutaneously in 24 nude mice. Repeated quantitative ra dioimmunoscintigraphic recordings were performed on 27 occasions in ea ch of the 24 mice during the observation period which lasted for nearl y 3 months. The tumor and nontumor doses were calculated according to the Medical International Radiation Dose Committee formula on the basi s of the scintigraphic data. Results: All tumors were clearly visualiz ed as early as one day after injection of I-125-labeled H7. The remain ing radioactivity was exclusively located in the tumors at days 30-81. As much as 12-16% of the injected dose/g accumulated in the tumors du ring the first 2 days after injection, and remained stable at this hig h level for approximately 10 days in all investigated groups. Radioact ivity in the whole body was rapidly eliminated during the same time pe riod. The highest tumor/nontumor dose ratio was obtained after a singl e injection of I-125-labeled H7. Conclusion: Neither a preinjection of nonlabeled H7 nor a postinjection of alpha H7 nor a combination of bo th strategies resulted in improved tumor/nontumor dose ratios compared to a single injection of labeled H7. The monoclonal antibody H7 has a rapid and high uptake, combined with a prolonged retention time in th e tumors. The kinetic properties of H7 are different from antibodies t argeting intracellular tumor antigens.