Radiolabeling LyP-1 peptide and preliminary biodistribution evaluation in mice bearing MDA-MB-435 xenografts.

Background Recent studies have shown the LyP-1 peptide can home to either tumor lymphatics or the tumor cells and be internalized by targeted cells. This study aimed to investigate the possibility of using (NaI)-I-131 labeled LyP-1 peptide as an imaging agent or a therapeutic radiopharmaceutical in breast carcinoma and its metastasis. Methods The 10-mer cyclic peptide contained the LyP-1 sequence (YCGNKRTRGC) was synthesized by the solid phase method. Disulfide bonds between the cysteines maintain the cyclic structure. The LyP-1 peptide was labeled with (NaI)-I-131 using the chloramine-T method. The [I-131] LyP-1 peptide and a [I-131] control peptide were injected via tail vein into nude mice bearing MDA-MB-435 tumor xenografts. Biodistribution and imaging results in vivo were obtained. Results The labeling efficiencies of LyP-1 peptide reached 80% +/- 5% (n=5). The radiochemical purity was about 96%. The radiochemical purity of the labeled compound remains 92% at 24 hours in human serum at 37 degrees C. In the biodistribution studies, the [I-131] LyP-1 peptide accumulated in the tumor to a higher level than in other organs. The [I-131] LyP-1 peptide can successfully image the tumor in nude mice bearing MDA-MB-435 tumor xenografts. Conclusions The LyP-1 peptide could be effectively labeled with (NaI)-I-131 and the labeled compound is stable in human serum at 37 degrees C for 24 hours. The high specificity of [I-131] LyP-1 peptide suggests it may be a promising new radiotracer for identifying tumors.