Tumor angiogenesis imaging agent:biodistribution of 131I-YG5 and 131I-Boc-YG5

The cyclic peptide YG5 and the t-butyloxycarbonyl (Boc)-modified analog (Boc-YG5) were labelled with radioiodine. The radiochemical purity of 131I-YG5 or 131I-Boc-YG5 was almost 100% after purification by RP-HPLC. Biodistribution in BALB/C nude mice bearing MCF-7 tumor was measured. After t-butyloxycarbonyl (Boc)-modification, the 131I-Boc-YG5 was quite resistant to deiodination in vivo, resulting in negligible radioactivity accumulation in thyroid. The radiotracer clearance in tumor became faster, the absolute tumor uptake decreased for 131I-Boc-YG5, but the tumor-to-tissue uptake ratios increased. The uptake ratios of tumor to muscle, blood, heart, and lung at 1 h post injection reached 4.73, 1.70, 4.09 and 1.70, respectively. It is demonstrated that Boc-group is an effective prosthetic one to prevent deiodination in vivo and improve tumor imaging for radioiodinated NGR. (authors)