111 In‐ and 203 Pb‐labeled cyclic arginine‐glycine‐aspartic acid peptide conjugate as an α v β 3 integrin‐binding radiotracer

Methodology for site‐specific modification and chelate conjugation of a cyclic arginine‐glycine‐aspartic acid (cRGD) peptide for the preparation of a radiotracer molecular imaging agent suitable for detecting α v β 3 integrin is described. The method involves functionalizing the peptide with an aldehyde moiety and conjugation to a 1,4,7,10‐tetraazacyclododecane‐ N,N′,N″,N ‴‐tetraacetic acid derivative that possesses an aldehyde reactive aminooxy group. The binding assay of the 111 In‐labeled peptide conjugate with α v β 3 integrin showed 60% bound when four equivalents of the integrin was added, a reasonable binding affinity for a monovalent modified RGD peptide.