In vivo evaluation of type 2 transglutaminase contribution to the metastasis formation in melanoma

Three strategies for chemoselective labeling of RGD peptides with ¹⁸F have been compared. Aminooxy ¹⁸F]fluorobenzaldehyde conjugation provided 40 ± 12% decay-corrected radiochemical yield using a fully automated method. An one-pot protocol for ‘click labeling’ of the RGD scaffold with 2-¹⁸F]fluoroethylazide afforded 47 ± 8% decay-corrected radiochemical yield. Attempted conjugation with 3-¹⁸F]fluoropropanethiol led to extensive decomposition and was therefore found unsuitable for labeling of the RGD peptide investigated. The results suggest that ‘click labeling’ of RGD peptides provides an attractive alternative to aminooxy aldehyde condensation, however, 2-¹⁸F]-fluoroethylazide may be too small to allow separation of large ¹⁸F-labeled RGD peptides from their precursors.