The [Tc(N)(PNP)]2+ metal fragment labeled cholecystokinin-8 (CCK8) peptide for CCK-2 receptors imaging: in vitroand in vivo studies

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

New approach to the chemistry of technetium(V) and rhenium(V) phenylimido complexes: Novel [M(NPh)PNP](3+) metal fragments (M = Tc, Re; PNP = aminodiphosphine) suitable for the synthesis of stable mixed-ligand compounds

Ligand-exchange reactions of the aminodiphosphine ligand bis[(2-diphenylphosphino)ethyl]amine hydrochloride ((PNHPHCl)-H-.) with labile M(NPh)Cl-3(PPh3)(2) precursors (M = Re, Tc) in the presence of triethylamine yield monocationic phenylimido mer,cis-[M(NPh)Cl-2(PNHP)]Cl (M = Re, 1; Tc, 2) intermediate complexes. X-ray analyses show that. in both compounds the aminodiphosphine acts as a tridentate ligand dictating a mer,cis arrangement. Two chloride ligands, respectively in an equatorial and in the axial position trans to the linear M-NPh moiety, fill the remaining positions in a distorted-octahedral geometry, The chloride trans to the, metal-imido core is labile, and is replaced by an alcoholate group, without affecting the original geometry, as established in mer,cis-[Re(NPh)(OEt)Cl(PNHP)]Cl 4. Otherwise, ligand-exchange reactions involving the aminodiphosphine bis[(2-diphenylphosphino)ethyl]methylamine (PNMeP), in which the central secondary amine has been replaced by a tertiary amine function, or its hydrochloride salt ((PNMePHCl)-H-.) give rise to three different species, depending on the experimental conditions: fac,cis-[Re(NPh)Cl-2(PNMeP)]Cl 3a, cis,fac-Re(NPh)Cl-3(PNMeP)(HCl)-H-. 3b, and mer,trans-[Re(NPh)Cl-2(PNMeP)]Cl 3c, which are characterized in solution by multinuclear NMR studies. The monodentate groups incorporated in these intermediate compounds, either halides and/or ethoxide, undergo substitution reactions with bidentate donor ligands such as catechol, ethylene glycol, and 1,2-aminophenol to afford stable mixed ligand complexes of the type [M(NPh)(O,O-cat)(PNP)]Cl [PNP = PNHP M = Re 5, Tc 6; PNP = PNMeP M = Re 7], [Re(NPh)(O,O-gly)(PNP)]Cl [PNP = PNHP 8, PNMeP 9] and [Re(NPh)(O,N-ap)(PNMeP)]Cl 10. X-ray diffraction analyses of the representative compounds 5 and 8 reveal that the aminodiphosphine switches from the meridional to the facial coordination mode placing the heteroatom of the diphosphine trans to the phenylimido unit and the bidentate ligand in the equatorial plane. Solution-state NMR studies suggest an analogous geometry for 6, 7, 9, and 10. Comparison with similar mixed ligand complexes including the terminal nitrido group is discussed

Electrospray mass spectrometry of a series of mixed nitrido Tc- 99g-heterocomplexes conjugated with bio-active molecules

Electrospray ionization mass spectrometry (ESI-MS) was successfully employed for the identification of six nitrido technetium mixed ligand complexes with a general formula of [Tc-99g(N)(O,S-BID)(PNP)], where PNP represents a heterodiphosphine and O,S-BID represents a simple dianionic bidentate ligand (compounds 1-3) or a more sophisticated N-substituted O,S-cysteine framework conjugated with a bio-active molecule (BAM) (compounds 4-6). In spite of similar coordination spheres exhibited by all the complexes investigated, simple co-ordination compounds 1-3 displayed collisionally-induced fragmentation processes (MS") different from those observed in biomolecule-containing compounds 4-6. In the latter, more decomposition channels were observed. This behavior is likely to be associated with some additional intramolecular contacts of the biomolecule (or part of the biomolecule) with pendant group(s) incorporated in the PNP-co-ligand. This view is further supported by the observations arising from both in vitro binding affinity experiments and nuclear magnetic resonance investigations. The presence of cationized forms for all compounds 1-6 and the practical lack of the [2M + Na](+) species for biomolecule-containing compounds 4-6 provided further evidence of a subtly different structural conformation

Avidin\u2013biotin system: a small library of cysteine biotinylated derivativesdesigned for the [99mTc(N)(PNP)]2+ metal fragment

Using the avidin\u2013biotin system as model, we investigate here the effective application of [Tc(N)L(PNP)]+/0 technology (L=Nfunctionalized cysteine [O-,S-]; PNP=aminodiphosphine) to the preparation of target-specific radiopharmaceuticals. A series of 99mTc-nitrido complexes containing functionalized biotin ligands was prepared and their biological profile was determined. To minimize the steric and the electronic influences of the Tc-carrying complex on the biotin\u2013avidin receptor interaction, the following N-functionalized cysteine\u2013biotin derivatives were synthesized: (1) Biot-CysOSH; (2) Biot-Abu-CysOSH; (3) Biot-Abz-CysOSH; (4) Biot-L- (Ac)Lys-CysOSH; (5) Biot-D-(Ac)Lys-CysOSH; (6) Biot-Glu-CysOSH. The asymmetrical nitrido-Tc(V) 99g/99mTc(N)(Biot-X-CysOS)(PNP3) (X=spacer) complexes, where PNP3 was N,N-bis-[(dimethoxypropyl) phosphinoethyl] methoxy-ethylamine, were obtained by simultaneous addition of PNP3 and the relevant biotinylated ligand to a solution containing a 99mTc-nitrido precursor (yields N95%). In all cases, a mixture of syn- and anti isomers was observed. In vitro challenge experiments with glutathione and cysteine indicated that no transchelation reactions occurred. Assessment of the in vitro binding to avidin of the complexes revealed that only the complexes containing Biot-Abu-CysOS and Biot-Glu-CysOS ligand maintained a good affinity for the concentrator. Stability studies carried out in human and mouse plasma as well as in rat and mouse liver homogenate evidenced a rapid enzymatic degradation for the 99mTc(N)(Biot-Abu-CysOS)(PNP3) complex, whereas the 99mTc(N)(Biot-Glu-CysOS)(PNP3) one was stable in all conditions. Tissue biodistribution in normal Balb/C mice of the most stable candidate showed a rapid clearance both from the blood and the other tissues. The activity was eliminated both through the hepatobiliary system and the urinary trac

Biological in vitro and in vivo studies of a series of new asymmetrical cationic [99mTc(N)(DTC-Ln)(PNP)]+ complex (DTC-Ln = alicyclic dithiocarbamate, PNP = diphosphinoamine)

(99m)Tc(N)-DBODC5 is a cationic mixed compound under clinical investigation as potential myocardial imaging agent. In spite of this, analogously to the other cationic (99m)Tc-agents, presents a relatively low first-pass extraction. Thus, modification of (99m)Tc(N)-DBODC(5) direct to increase its first-pass extraction keeping unaltered the favorable imaging properties would be desirable. This work describes the synthesis and biological evaluation of a series of novel cationic (99m)Tc-nitrido complexes, of general formula [(99m)TcN(DTC-Ln)(PNP)](+) (DTC-Ln= alicyclic dithiocarbamates; PNP = diphosphinoamine), as potential radiotracers for myocardial perfusion imaging. The synthesis of cationic (99m)Tc-(N)-complexes were accomplished in two steps. Biodistribution studies were performed in rats and compared with the distribution profiles of (99m)Tc(N)-DBODC5 and (99m)Tc-Sestamibi. The metabolisms of the roost promising compounds were evaluated by HPLC methods. Biological studies revealed that most of the complexes have a high initial and persistent heart uptake with rapid clearance from nontarget tissues. Among tested compounds. 2 and 12 showed improved heart uptake with respect to the gold standard (99m)Tc-complexes with favorable heart-to-liver and slightly lower heart-to-lung ratios. Chromatographic profiles of (99m)Tc(N)radioactivity extracted from tissues and fluids were coincident with the native compound evidencing remarkable in vivo stability of these agents. This study shows that the incorporation of alicyclic dithiocarbamate in the [(99m)Tc(N)(PNP)](+) building block yields to a significant increase of the heart uptake at early injection point suggesting that the first-pass extraction fraction of these novel complexes may he increased with respect to the other cationic (99m)Tc-agents keeping almost unaltered the favorable target/nontarget ratios