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The cyclic peptide YG5 and the t-butyloxycarbonyl(Boc)-modified analog(Boc-YG5) were labeled 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.
The cyclic peptide YG5 and the t-butyloxycarbonyl (Boc) -modified analog (Boc-YG5) were labeled 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 said that Boc-group is an effective prosthetic one to prevent deiodination in vivo and improve tumor imaging for radioiodinated NGR.