Study on labelling methods of~(125)I-RC-160 and its biodistribution in animals

A method for the iodination of peptide RC-160 with high efficiency was developed. RC-160 was iodinated with N-bromosuccinimide (NBS) as oxidant, the conventional chloramine T (Ch-T) method was used as control. The labelling condition of NBS method was optimized and radiolabelled conjugate 125I-RC-160 was assessed as follows: no further purification was needed, the measured labelling yield of 125I-RC-160 was 92% and the specific activity was 1.95×10 12Bq/mmoL. The yield increased as the amount of NBS increased. The optimal ratio of RC-160(μg): 125I(MBq):NBS(μg)was 3:7.4:1. For Ch-T method, the labelling yield is 56% and specific activity was 0.65×10 12Bq/mmoL, but after purification by SepPaK-C 18, the labelling yield may reach as high as 92%. 1h after injection, radioactivity in blood decreased by 87.2%. No obvious concentration of 125I-RC-160 in thyroid or kidney was observed.