Abstract
A peptide containing Asn-Gly-Arg(NGR) sequence was synthesized and directly labeled with 99mTc. Its radiochemical characteristics, biodistribution, and SPECT imaging were evaluated in nude mice bearing human HepG2 hepatoma. Nude mice bearing HepG2 were randomly divided into 5 groups with 5 mice in each group and injected with ~7.4 MBq 99mTc-NGR. The SPECT images were acquired in 1, 4, 8, and 12 h postinjection via caudal vein. The metabolism of tracers was determined in major organs at different time points, which demonstrated rapid, significant tumor uptake and slow tumor washout. The control group mice were blocked by coinjecting unlabelled NGR (20 mg/kg). Tumor uptake was (2.52 ± 0.83%) ID/g at 1 h, with the highest uptake of (3.26 ± 0.63%) ID/g at 8 h. In comparison, the uptake of the blocked control group was (1.65 ± 0.61%) ID/g at 1 h after injection. The SPECT static images and the tumor/muscle (T/NT) value were obtained. The highest T/NT value was 7.58 ± 1.92 at 8 h. The xenografted tumor became visible at 1 h and the clearest image of the tumor was observed at 8 h. In conclusion, 99mTc-NGR can be efficiently prepared and it exhibited good properties for the potential SPECT imaging agent of tumor.
Highlights
Angiogenic tumor vessels are important element for tumor growth and metastasis and the metalloexopeptidase CD13/ aminopeptidase N (APN) plays a critical role in cancer angiogenesis
In tissues that undergo angiogenesis, blood vessels overexpress APN and proliferation of endothelial cells is well known to be an important factor in tumor angiogenesis [3, 4]
It is proved that NGR can bind with new vasculature by aminopeptidase N (CD13) and integrin αvβ3, the binding mechanisms are different
Summary
Angiogenic tumor vessels are important element for tumor growth and metastasis and the metalloexopeptidase CD13/ aminopeptidase N (APN) plays a critical role in cancer angiogenesis. Peptides containing NGR have shown high efficiency in targeted cells, tissues, and new vessels with CD13 receptor overexpression [1, 2]. In tissues that undergo angiogenesis, blood vessels overexpress APN and proliferation of endothelial cells is well known to be an important factor in tumor angiogenesis [3, 4]. CD13 receptor mediated binding to tumor vasculature is specific but not to the other CD13 rich tissues, which was proved by in vivo studies [5]. A new NGR peptide was synthesized and labeled with 99mTc, subjected to SPECT imaging of CD13 expression in a subcutaneous mouse HepG2 hepatoma xenograft model, which was proved to show positive CD13 receptor and easy formation of tumor
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