IN-VIVO LOCALIZATION OF DIGLYCYLCYSTEINE-BEARING SYNTHETIC PEPTIDES BY NUCLEAR IMAGING OF OXOTECHNETATE TRANSCHELATION

A phenomenon of in vivo transchelation of oxotechnetate from a complex with glucoheptonic acid to synthetic peptides bearing oxotechnetate-b inding motifs and a technique for in vivo visualization of these pepti des are described. Using two model peptides bearing two tandem diglycy lcysteine (GGC) motifs (P1) or three GGC motifs (P2), we demonstrated that: (i) these peptides efficiently transchelated oxo-[Tc-99m]technet ate from a complex with glucoheptonic acid in vitro (a complex with pe ptides was stable at least 24 h; radiochemical purity exceeded 95% by high performance liquid chromatography); (ii) injection of peptides in to the rectus femoris muscle (at 0.5-1 mu mol of SH groups) followed b y an intravenous injection of Tc-99m glucoheptonate (0.25-0.5 mCi per animal) yielded visualization of the injected muscle by nuclear imagin g within 1 h after injection; (iii) the experimental/control (contrala teral) thigh muscle ratio was 1.80 +/- 0.05 for peptide P1 and 3.0 +/- 0.1 for P2; (iv) the injection of a control peptide P2 with SH groups covalently modified with N-ethylmaleimide resulted in a ratio of 1.4 +/- 0.2. These findings argue for specific association of oxo [Tc-99m] technetate with free thiols within the binding motif of injected pepti des in vivo. In vivo transchelation of oxo-[Tc-99m]technetate may be u seful for the purpose of noninvasive imaging of gene expression, i.e., when the expression product bears GGC motifs. (C) 1997 Elsevier Scien ce Inc.