CD13 receptor plays a critical role in
tumor angiogenesis and
metastasis. We therefore aimed to develop (99m)Tc-labeled monomeric and dimeric NGR-containing
peptides, namely, NGR1 and NGR2, for SPECT imaging of CD13 expression in HepG2
hepatoma xenografts. Both NGR-containing monomer and dimer were synthesized and labeled with (99m)Tc. In vivo receptor specificity was demonstrated by successful blocking of
tumor uptake of (99m)Tc-NGR dimer in the presence of 20 mg/kg NGR2
peptide. Western blot and immunofluorescence staining confirmed the CD13 expression in HepG2 cells. The NGR dimer showed higher binding affinity and cell uptake in vitro than the NGR-containing monomer, presumably due to a multivalency effect. (99m)Tc-Labeled monomeric and dimeric NGR-containing
peptides were subjected to SPECT imaging and biodistribution studies. SPECT scans were performed in HepG2
tumor-bearing mice at 1, 4, 12, and 24 h post-injection of ~7.4 MBq tracers. The metabolism of tracers was determined in major organs at different time points after injection which demonstrated rapid, significant
tumor uptake and slow
tumor washout for both traces. Predominant clearance from renal and hepatic system was also observed in (99m)Tc-NGR1 and (99m)Tc-NGR2. In conclusion, monomeric and dimeric
NGR peptide were developed and labeled with (99m)Tc successfully, while the high
integrin avidity and long retention in
tumor make (99m)Tc-NGR dimer a promising agent for
tumor angiogenesis imaging.