In this regard, 2 NGR peptide ligands, HYNIC-c(NGR) and HYNIC-PEG<sub>2</sub> -c(NGR), were synthesized, radiolabeled with <sup>99m</sup> Tc, and evaluated in CD13-positive human fibrosarcoma HT-1080 tumor xenografts.
The human fibrosarcoma (HT-1080) and human colorectal adenocarcinoma (HT-29) xenografts were respectively used as positive and negative reference groups for CD13.
The cytotoxic effect of the novel cyclic NGR peptide-Dau conjugates were examined in vitro on CD13 positive HT-1080 (human fibrosarcoma) and CD13 negative HT-29 (human colon adenocarcinoma) cell lines.