Fluorine‐18 labeling of phosphopeptides: A potential approach for the evaluation of phosphopeptide metabolism in vivo

Phosphopeptides are very useful reagents to study signal transduction pathways related with cellular protein phosphorylation/dephosphorylation. Phosphopeptides have also been identified as important drug candidates to modulate intracellular signaling mechanisms through targeting phosphotyrosine, phosphoserine, or phosphothreonine residue‐binding protein domains. In this report, we describe the development of a convenient method for the mild and sufficient radiolabeling of phosphopeptides with the short‐lived positron emitter fluorine‐18 ( 18 F) to allow radiopharmacological studies on phosphopeptide metabolism in vivo by means of positron emission tomography (PET). Radiolabeling was accomplished via conjugation of the N‐terminus of polo‐box domain (PBD)‐binding phosphopeptide H‐Met‐Gln‐Ser‐pThr‐Pro‐Leu‐OH with the bifunctional labeling agent N ‐succinimidyl‐4‐[ 18 F]fluorobenzoate ([ 18 F]SFB) in reproducible isolated radiochemical yields of 25–28%. Radiopharmacological evaluation in vitro and in vivo of radiolabeled phospheptide [ 18 F]FB‐Met‐Gln‐Ser‐pThr‐Pro‐Leu‐OH [ 18 F]‐3 and its non‐phosphorylated analog [ 18 F]FB‐Met‐Gln‐Ser‐Thr‐Pro‐Leu‐OH [ 18 F]‐4 involved metabolic stability, cell uptake studies, and small animal PET experiments. Radiolabeled phosphopeptide [ 18 F]‐3 showed a remarkable high metabolic stability in vivo compared to the corresponding non‐phosphorylated peptide [ 18 F]‐4 . The presented method indicates that radiolabeling of phosphopeptides with [ 18 F]SFB is a promising approach for studying phosphopeptide metabolism in vivo. © 2009 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 92: 479–488, 2009. This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com