A new tumor neovasculature imaging tracer: Radioiodine labeled small peptide

Objectives Tripeptide sequence motif Arg-Arg-Leu(RRL) can bind to tumor-derived endothelial cells. The purpose of this study was to redesign and synthesize a new tumor neovasculature imaging tracer for tumor neovasculature imaging.

Methods The 10-mer RRL peptide (Tyr-Cys-Gly-Gly-Arg-Arg-Leu-Gly-Gly-Cys-NH2) and the control peptide (Tyr-Cys-Gly-Gly-Gly-Gly-Gly-Gly-Gly-Cys-NH2) were assembled by the solid phase method and added an amino-terminal Tyrosine to facilitate radioiodination. The radiolabelling yield was measured by ITLC-SG thin-layer chromatography developed by acetone. The purified radioiodine labeled RRL peptide was put in human blood serumfor 24h, and radiochemical purities were checked. Animal biodistribution experiments and SPECT imaging were carried out in BALB/c nude mice implanted with PC3 human prostate carcinoma. Results are expressed as the percentage injected dose per gram of tissue (%ID/g).

Results The crude product after purification yielded a main peak containing 99.56% end product by HPLC. The 131I labeling rate of RRL was approximately 60% and radiochemical purity was 96.5%. The radiochemical purity of the labeled compound remained 90.3% at 24 hours in human blood serum. We performed in vivo SPECT imaging to determine the specific uptake of radioiodinated RRL in prostate carcinoma nude nice model. There is an intense accumulation of 131I-RRL in tumor tissue at 24 hours after administration via tail vein, whereas no such trend was found in other tissues and control agent group.

Conclusions This new molecular trace agent can be used to image and monitor tumor neovasculature in vivo as a noninvasive imaging method