PET IMAGING OF OSTEOSARCOMA IN DOGS USING A FLUORINE-18-LABELED MONOCLONAL-ANTIBODY FAB FRAGMENT

Four dogs with histologically confirmed osteogenic sarcoma were studie d with PET following intravenous injection of the F-18-labeled Fab fra gment of TP-3, a monoclonal antibody specific for human and canine ost eosarcomas. Methods: The antibody fragment was labeled using the N-suc cinimidyl 8-[(4'-[F-18]fluorobenzyl)amino]suberate acylation agent. Bl ood clearance of activity was biphasic in all dogs but half-times were variable (T-1/2 beta = 2-13 hr). Catabolism of labeled Fab was reflec ted by the decrease in protein-associated activity in serum from more than 90% at 1 min to 60%-80% at 4 hr. Results: PET images demonstrated increased accumulation of F-18 at the primary tumor site relative to normal contralateral bone in one dog as early as 15 min after injectio n. Biopsies obtained after euthanasia indicated higher uptake at the e dges of the tumor as observed on the PET scans. Tumor uptake was 1-3 x 10(-3)% injected dose/g, a level similar to that reported for other F ab fragments in human tumors. in the three dogs with metastatic diseas e, early PET images reflected activity in the blood pool but later upt ake was observed in suspected metastatic sites. Conclusions: These res ults, although preliminary, suggest that PET imaging of F-18-labeled a ntibody fragments is feasible and that dogs with spontaneous tumors co uld be a valuable model for preclinical research with radioimmunoconju gates.