Peptides containing the asparagine-glycine-arginine (NGR) motif can target the tumor neovascular
biomarker CD13/aminopeptidase N receptor. D-K6L9 is a tumor-selective anti-cancer peptide. To improve the
capacity of NGR peptides to target tumors, we joined the NGR and D-K6L9 peptides to form NKL. Next, we
linked 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) to NKL and labeled it with gallium 68
(68Ga, t1/2 = 67.7 min) to form 68Ga-DOTA-NKL. This novel probe was characterized in vitro. 68Ga-DOTA-NKL
was stable in phosphate buffered saline at room temperature and in human serum at 37°C. We determined that the
uptake rate of 68Ga-DOTA-NKL in CD13 receptor-positive 22Rv1 tumor cells was 3.15% ± 0.04 after 2 h, and
tested 68Ga-DOTA-NKL using positron emission tomography (PET)/computed tomography imaging in vivo.
MicroPET imaging results revealed that 22Rv1 tumor uptake of 68Ga-DOTA-NKL was 8.69 ± 0.20, 6.61 ± 0.22,
3.85 ± 0.06, and 1.41 ± 0.23 percentage injected dose per gram of tissue (%ID/g) at 0.5, 1, 2, and 3 h postinjection
(pi), respectively. The tumor-to-background contrast in the subcutaneous human prostate cancer 22Rv1
mouse model was 9.97 ± 1.90. The 68Ga-DOTA-NKL probe has combined tumor-targeting and tumor-selective
properties, and may be used to diagnose CD13-positive tumors.
Multivalent Bifunctional Chelator Scaffolds for Gallium-68 Based Positron Emission Tomography Imaging Probe Design: Signal Amplification via Multivalency
