Hexadentate bispidine derivatives as versatile bifunctional chelate agents for copper(II) radioisotopes.
The preparation and use of bispidine derivatives (3,7-diazabicyclo[3.3.1]nonane) as chelate ligands for radioactive copper isotopes for diagnosis (64Cu) or therapy (67Cu) are reported. Starting from the hexadentate bispidine-based bis(amine)tetrakis(pyridine) ligand 1 with a keto and two ester substituents, the corresponding mono-ol 2 and two dicarboxylic acid derivatives 3 and 5 have been synthesized. A range of techniques, including single-crystal X-ray structure analysis, UV/vis spectroscopy, cyclic voltammetry, thin-layer- (TLC), and high-performance liquid chromatography (HPLC), have been used to characterize the structure and stability of the copper(II)-bispidine complexes. A rapid formation (within 1 min) of stable copper(II)-bispidine complexes under mild conditions (ambient temperature, aqueous solution) has been observed. Challenge experiments of these complexes in the presence of a high excess of competing ligands, such as glutathione, cyclam, or superoxide dismutase (SOD), as well as in rat plasma, gave no evidence of demetalation or transchelation. The bifunctional bispidine derivative 5 can be readily functionalized with biologically active molecules at the pendant carboxylate groups. The coupling of a bombesin analogue betahomo-Glu-betaAla-betaAla-[Cha(13),Nle(14)]BBN(7-14), by condensation of a carboxylate of the bispidine backbone with the N-terminus of the peptide produced the bifunctional ligand 6. The radiocopper(II) complex of this bombesin-bispidine conjugate has a considerable hydrophilicity (log D(o/w) < -2.4), and this leads to a very fast blood clearance (blood: 0.28 +/- 0.02 SUV, 1 h p.i.), low liver tissue accumulation (liver: 1.20 +/- 0.27 SUV, 1 h p.i.), and rapid renal-urinary excretion (kidneys: 6.06 +/- 2.96 SUV, 1 h p.i.) as shown by biodistribution studies of 64Cu-6 in Wistar rats. Preliminary in vivo studies of 64Cu-6 in NMRI nu/nu mice, bearing the human prostate tumor PC-3 showed an accumulation of the conjugate in the tumor (2.25 +/- 0.13 SUV, 12.5 min p.i.; 0.94 +/- 0.05 SUV, 55 min p.i.) and allowed a clear visualization of the gastrin-releasing peptide receptor distribution by positron emission tomography (PET).
Juran
Stefanie
S
Forschungszentrum Dresden-Rossendorf, Institute of Radiopharmacy, PF 510119, D-01314 Dresden, Germany.
Walther
Martin
M
Stephan
Holger
H
Bergmann
Ralf
R
Steinbach
Jörg
J
Kraus
Werner
W
Emmerling
Franziska
F
Comba
Peter
P
D000818:Animals; D001839:Bombesin / Q000378:metabolism; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000138:chemical synthesis / Q000737:chemistry* / Q000493:pharmacokinetics; D002614:Chelating Agents / Q000737:chemistry*; D003301:Copper Radioisotopes / Q000737:chemistry*; D003432:Cross-Linking Reagents / Q000737:chemistry*; D003998:Dicarboxylic Acids / Q000737:chemistry; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007700:Kinetics; D008024:Ligands; D008297:Male; D051379:Mice; D049268:Positron-Emission Tomography; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D011725:Pyridines / Q000737:chemistry; D011854:Radiochemistry; D051381:Rats; D018004:Receptors, Bombesin / Q000378:metabolism; D014018:Tissue Distribution
D019086:Bridged Bicyclo Compounds, Heterocyclic; D002614:Chelating Agents; D003301:Copper Radioisotopes; D003432:Cross-Linking Reagents; D003998:Dicarboxylic Acids; D008024:Ligands; D011725:Pyridines; D018004:Receptors, Bombesin; C495809:bispidine; C023666:pyridine; D001839:Bombesin