title: Orthogonally protected artificial amino acid as tripod ligand for automated peptide synthesis and labeling with [(99m)Tc(OH(2))(3)(CO)(3)](+).
abstract: 1,2-Diamino-propionic acid (Dap) is a very strong chelator for the [(99m)Tc(CO)(3)](+) core, yielding small and hydrophilic complexes. We prepared the lysine based Dap derivative l-Lys(Dap) in which the ε-NH(2) group was replaced by the tripod through conjugation to its α-carbon. The synthetic strategy produced an orthogonally protected bifunctional chelator (BFC). The -NH(2) group of the α-amino acid portion is Fmoc- and the -NH(2) of Dap are Boc-protected. Fmoc-l-Lys(Dap(Boc)) was either conjugated to the N- and C-terminus of bombesin BBN(7-14) or integrated into the sequence using solid-phase peptide synthesis (SPPS). We also replaced the native lysine in a cyclic RGD peptide with l-Lys(Dap). For all peptides, quantitative labeling with the [(99m)Tc(CO)(3)](+) core at a 10 μM concentration in PBS buffer (pH = 7.4) was achieved. For comparison, the rhenium homologues were prepared from [Re(OH(2))(3)(CO)(3)](+) and Lys(Dap)-BBN(7-14) or cyclo-(RGDyK(Dap)), respectively. Determination of integrin receptor binding showed low to medium nanomolar affinities for various receptor subtypes. The IC(50) of cyclo-(RGDyK(Dap[Re(CO)(3)])) for α(v)β(3) is 7.1 nM as compared to 3.1 nM for nonligated RGD derivative. Biodistribution studies in M21 melanoma bearing nude mice showed reasonable α(v)β(3)-integrin specific tumor uptake. Altogether, orthogonally protected l-Lys(Dap) represents a highly versatile building block for integration in any peptide sequence. Lys(Dap)-precursors allow high-yield (99m)Tc-labeling with [(99m)Tc(OH(2))(3)(CO)(3)](+), forming small and hydrophilic complexes, which in turn leads to peptide radiopharmaceuticals with excellent in vivo characteristics.
authors.affiliation: Institute of Inorganic Chemistry, University of Zürich, Winterthurerstr. 190, CH-8057 Zürich, Switzerland.
authors.forename: Yunjun
authors.initials: Y
authors.lastname: Shen
authors.forename: Margret
authors.initials: M
authors.lastname: Schottelius
authors.forename: Karel
authors.initials: K
authors.lastname: Zelenka
authors.forename: Mariarosaria
authors.initials: M
authors.lastname: De Simone
authors.forename: Karolin
authors.initials: K
authors.lastname: Pohle
authors.forename: Horst
authors.initials: H
authors.lastname: Kessler
authors.forename: Hans-Jürgen
authors.initials: HJ
authors.lastname: Wester
authors.forename: Paul
authors.initials: P
authors.lastname: Schmutz
authors.forename: Roger
authors.initials: R
authors.lastname: Alberto
mesh_terms: D000818:Animals; D001839:Bombesin / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry; D045744:Cell Line, Tumor; D002614:Chelating Agents / Q000138:chemical synthesis / Q000737:chemistry; D006801:Humans; D039302:Integrin alphaVbeta3 / Q000378:metabolism; D008239:Lysine / Q000031:analogs & derivatives* / Q000138:chemical synthesis; D008545:Melanoma / Q000175:diagnosis* / Q000378:metabolism; D051379:Mice; D008819:Mice, Nude; D009842:Oligopeptides / Q000138:chemical synthesis / Q000737:chemistry*; D015609:Organotechnetium Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000737:chemistry*; D011422:Propionates / Q000138:chemical synthesis / Q000737:chemistry*; D060327:Solid-Phase Synthesis Techniques / Q000379:methods*
chemical_list: D002614:Chelating Agents; D039302:Integrin alphaVbeta3; D009842:Oligopeptides; D015609:Organotechnetium Compounds; D010446:Peptide Fragments; D011422:Propionates; C118536:bombesin (7-14); C047981:arginyl-glycyl-aspartic acid; D008239:Lysine; D001839:Bombesin