Radiotheranostics coupled between an At-211-Labeled RGD peptide and the corresponding radioiodine-labeled RGD peptide

Alpha particle-emitting radionuclides have gained considerable attention for radionuclide therapy. Astatine-211 ( 211 At) is a promising alpha particle-emitting radionuclide. 211 At is a halogen that has similar chemical properties to iodine and exhibits a half-life of 7.2 h. However, direct labeling of proteins or peptides into the tyrosine residue with 211 At was shown to be impractical. Herein, we demonstrate a novel 211 At-labeling method using the RGD peptide as a model peptide. An 211 At-labeled RGD peptide, [ 211 At]c[RGDf(4-At)K], was prepared from a precursor with a tributylstannyl group on the phenylalanine residue in c(RGDfK) with a radiochemical yield of 63% and a radiochemical purity of >96%, and its potential for targeted radionuclide therapy was evaluated. Based on the results of biodistribution experiments, [ 125 I]c[RGDf(4-I)K] and [ 211 At]c[RGDf(4-At)K] showed high accumulation in the tumor and similar biodistribution. This study provides useful information for radiotheranostics between an 211 At-labeled peptide and the corresponding radioiodine-labeled peptide.