title: The [Tc(N)(PNP)]2+ metal fragment labeled cholecystokinin-8 (CCK8) peptide for CCK-2 receptors imaging: in vitro and in vivo studies.
abstract: The radiolabeling of the natural octapeptide CCK8, derivatized with a cysteine residue (Cys-Gly-CCK8), by using the metal fragment [99mTc(N)(PNP3)]2+ (PNP3 = N,N-bis(dimethoxypropylphosphinoethyl)methoxyethylamine) is reported. The [99mTc(N)(NS-Cys-Gly-CCK8)(PNP3)]+ complex was obtained according to two methods (one-step or two-step procedure) that gave the desired compound in high yield. The complex is stable in aqueous solution and in phosphate buffer. In vitro challenge experiments with an excess of cysteine and glutathione indicate that no transchelation reactions occur, confirming the high thermodynamic stability and kinetic inertness of this compound. Stability studies carried out in human and mouse serum, as well as in mouse liver homogenates, show that the radiolabeled compound remains intact for prolonged incubation at 37 degrees C. Binding properties give Kd (19.0 +/- 4.6 nmol/l) and Bmax (approximately 10(6) sites/cell) values in A431 cells overexpressing the CCK2-R. In vivo evaluation of the compound shows rapid and specific targeting to CCK2-R, a fourfold higher accumulation compared to nonreceptor expressing tumors.
authors.affiliation: Department of Pharmaceutical Sciences, University of Padua, Via Marzolo, 5, 35131 Padua, Italy.
authors.forename: Stefania
authors.initials: S
authors.lastname: Agostini
authors.forename: Cristina
authors.initials: C
authors.lastname: Bolzati
authors.forename: Eliana
authors.initials: E
authors.lastname: Didonè
authors.forename: Mario
authors.initials: M
authors.lastname: Cavazza-Ceccato
authors.forename: Fiorenzo
authors.initials: F
authors.lastname: Refosco
authors.forename: Luigi
authors.initials: L
authors.lastname: Aloj
authors.forename: Claudio
authors.initials: C
authors.lastname: Arra
authors.forename: Michela
authors.initials: M
authors.lastname: Aurilio
authors.forename: Anna Lucia
authors.initials: AL
authors.lastname: Tornesello
authors.forename: Diego
authors.initials: D
authors.lastname: Tesauro
authors.forename: Giancarlo
authors.initials: G
authors.lastname: Morelli
mesh_terms: D000818:Animals; D002021:Buffers; D002766:Cholecystokinin / Q000737:chemistry* / Q000378:metabolism* / Q000493:pharmacokinetics; D006801:Humans; D007553:Isotope Labeling / Q000379:methods; D051379:Mice; D008819:Mice, Nude; D008967:Molecular Biology / Q000379:methods; D015609:Organotechnetium Compounds / Q000737:chemistry* / Q000493:pharmacokinetics*; D010446:Peptide Fragments / Q000737:chemistry* / Q000378:metabolism* / Q000493:pharmacokinetics; D019275:Radiopharmaceuticals / Q000737:chemistry; D043887:Receptor, Cholecystokinin B / Q000032:analysis* / Q000235:genetics / Q000378:metabolism; D014018:Tissue Distribution; D014183:Transplantation, Heterologous
chemical_list: D002021:Buffers; D015609:Organotechnetium Compounds; D010446:Peptide Fragments; D019275:Radiopharmaceuticals; D043887:Receptor, Cholecystokinin B; C410885:cholecystokinin 8; D002766:Cholecystokinin