EGF receptor targeted tumor imaging with biotin-PEG-EGF linked to 99mTc-HYNIC labeled avidin and streptavidin

IntroductionAs direct radiolabeled peptides suffer limitations for in vivo imaging, we investigated the usefulness of radioloabeled avidin and streptavidin as cores to link peptide ligands for targeted tumor imaging.MethodsHuman epidermal growth factor (EGF) was site specifically conjugated with a single PEG-biotin molecule and linked to ^99mTc-HYNIC labeled avidin-FITC (Av) or streptavidin-Cy5.5 (Sav). Receptor targeting was verified in vitro, and in vivo pharmacokinetic and biodistribution profiles were studied in normal mice. Scintigraphic imaging was performed in MDA-MB-468 breast tumor xenografted nude mice.ResultsWhereas both ^99mTc-Av-EGF and ^99mTc-Sav-EGF retained receptor-specific binding in vitro, the two probes substantially diverged in pharmacokinetic and biodistribution behavior in vivo. ^99mTc-Av-EGF was rapidly eliminated from the circulation with a T1/2 of 4.3 min, and showed intense hepatic accumulation but poor tumor uptake (0.6%ID/gm at 4 h). ^99mTc-Sav-EGF displayed favorable in vivo profiles of longer circulation (T1/2β, 51.5 min) and lower nonspecific uptake that resulted in higher tumor uptake (3.8 %ID/gm) and clear tumor visualization at 15 h.Conclusion^99mTc-HYNIC labeled streptavidin linked with growth factor peptides may be useful as a protein-ligand complex for targeted imaging of tumor receptors.