Reactivity of the [M(PS)2](+) building block (M = Re(III) and (99m)Tc(III); PS = phosphinothiolate) toward isopropylxanthate and pyridine-2-thiolate.

The coordination properties of isopropylxanthate (i-Pr-Tiox) and pyridine-2-thiolate (PyS) toward the [M(PS)2](+) moiety (M = Re and (99m)Tc; PS = phosphinothiolate) were investigated. Synthesis and full characterization of [Re(PS2)2(i-Pr-Tiox)] (Re1), [Re(PSiso)2(i-Pr-Tiox)] (Re2), [Re(PS2)2(PyS)] (Re3), and [Re(PSiso)2(PyS)] (Re4), where PS2 = 2-(diphenylphosphino)ethanethiolate and PSiso = 2-(diisopropylphosphino)ethanethiolate, and the structural X-ray analysis of complex Re3 were carried out. (99m)Tc analogues of complexes Re2 ((99m)Tc2) and Re4 ((99m)Tc4) were obtained in high radiochemical yield following a simple one-pot procedure. The chemical identity of the radiolabeled compounds was confirmed by chromatographic comparison with the corresponding rhenium complexes and by dual radio/UV HPLC analysis combined with ESI(+)-MS of (99g/99m)Tc complexes prepared in carrier-added conditions. The two radiolabeled complexes were stable with regard to trans chelation with cysteine, glutathione, and ethylenediaminotetraacetic acid and in rat and human sera. This study highlights the substitution-inert metal-fragment behavior of the [M(PS)2](+) framework, which reacts with suitable bidentate coligands to form stable hexacoordinated asymmetrical complexes. This feature makes it a promising platform on which to develop a new class of Re/Tc complexes that are potentially useful in radiopharmaceutical applications.

Cytotoxicity in human cancer cells and mitochondrial dysfunction induced by a series of new copper(I) complexes containing tris(2-cyanoethyl)phosphines.

Over the last few years a lot of research has been done to develop novel metal-based anti-cancer drugs, with the aim of improving clinical effectiveness, reducing general toxicity, and broadening the spectrum of activity. The search for novel metal-based antitumour drugs other than Pt agents includes the investigation of the cytotoxic activity of copper(I/II) compounds. Among these copper agents, particular attention has been recently devoted to hydrophilic copper(I) species bearing phosphines because of their noteworthy stability in aqueous media together with their remarkable in vitro cytotoxic activity. In this study we report on the synthesis, characterization and cytotoxic assays of a series of Cu(I) complexes with tris(2-cyanoethyl)phosphine (PCN) and bis(2-cyanoethyl)phenylphosphine (PCNPh). They were prepared by reaction of [Cu(CH(3)CN)(4)](+) or CuX(2) precursors with the pertinent phosphine in acetone or acetonitrile solutions producing compounds of the following formulation: [Cu(PCN)(2)](+) 2, [Cu(CH(3)CN)(PCN)](+) 3, [Cu(X)(PCN)] (X = Cl, 4; Br, 5), and [Cu(PCNPh)(2)](+) 6. The new copper(I) complexes were tested for their cytotoxic properties against a panel of several human tumour cell lines. Cellular copper uptake rate was correlated with cell growth inhibition in 2008 human ovarian cancer cells. Moreover, copper(I)-PCN complexes were evaluated for their ability to alter the most relevant mitochondrial pathophysiological parameters such as respiration, coupling, ATP-synthetase activity and membrane potential in isolated mitochondria. These data were correlated with changes in mitochondrial membrane potential and production of reactive oxygen species (ROS) in drug-treated 2008 cells.

Synthesis and biological evaluation of new [Tc(N)(PS)]-based mixed-ligand compounds useful in the design of target-specific radiopharmaceuticals: the 2-methoxyphenylpiperazine dithiocarbamate derivatives as an example.

This study presents the first application of a general procedure based on the use of the [Tc(N)Cl(PS)(PPh(3))] species (PS is an alkyl phosphinothiolate ligand) for the preparation of Tc(N) target-specific compounds. [Tc(N)Cl(PS)(PPh(3))] selectively reacts with an appropriate dithiocarbamate ligand (S(∧)Y) to give [Tc(N)(PS)(S(∧)Y)] compounds. 1-(2-Methoxyphenyl)piperazine, which displays a potent and specific affinity for 5HT(1A) receptors, was selected as a functional group and conjugated to the dithiocarbamate unit through different spacers (L( n )). [(99m)Tc(N)(PS)(L( n ))] complexes were prepared in high yield (more than 90%). The chemical identity of (99m)Tc complexes was determined by high performance liquid chromatography comparison with the corresponding (99g)Tc complexes. All complexes were found to be inert toward transchelation with an excess of glutathione and cysteine. No notable biotransformation of the native compound into different species by the in vitro action of the serum and liver enzymes was shown. Nanomolar affinity for the 5HT(1A) receptor was obtained for [(99m)Tc(N)(PSiso)L(3)] (IC(50) = 1.5 nM); a reduction of the affinity was observed for the other complexes as a function of the shortening of the alkyl chain interposed between the dithiocarbamate and the pharmacophore. Negligible brain uptake was found from in vivo distribution data of [(99m)Tc(N)(PSiso)L(3)]. The key finding of this study is that the complexes maintained good affinity and selectivity for 5HT(1A) receptors, and the IC(50) value for [(99g)Tc(N)(PSiso)L(3)] being comparable to the IC(50) value found for WAY 100635. This result confirmed the possibility of preparing [(99m)Tc(N)(PS)]-based target-specific compounds without affecting the affinity and selectivity of the bioactive molecules for the corresponding receptors.

Biological in vitro and in vivo studies of a series of new asymmetrical cationic [99mTc(N)(DTC-Ln)(PNP)]+ complex (DTC-Ln = alicyclic dithiocarbamate and 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 most 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 be increased with respect to the other cationic (99m)Tc-agents keeping almost unaltered the favorable target/nontarget ratios.

The relationship between the electrospray ionization behaviour and biological activity of some phosphino Cu(I) complexes.

Electrospray ionization mass spectrometry was usefully employed for the characterization of three phosphino copper(I) complexes of medicinal interest. This technique revealed that the original [CuL(4)](+) pro-drugs (L = hydrophilic tertiary phosphine) underwent dissociation with production of coordinative unsaturated [CuL(3)](+) and [CuL(2)](+) species, which represented key intermediates for the activation of potential biological properties. The more favoured was the displacement of the ligands from the [CuL(4)](+) parent complex, the more favoured was in turn the possibility for the metal ion to directly interact with biological substrates, including pharmacological targets related to cancer proliferation. An inverse correlation between the stability and the cytotoxic activity of the three copper(I) complexes investigated has been clearly established.

Transglutaminase-mediated conjugation and nitride-technetium-99m labelling of a bis(thiosemicarbazone) bifunctional chelator.

An assessment study involving the use of the transglutaminase (TGase) conjugation method and the nitride-technetium-99m labelling on a bis(thiosemicarbazone) (BTS) bifunctional chelating agent is presented. The previously described chelator diacetyl-2-(N4-methyl-3-thiosemicarbazone)-3-(N4-amino-3-thiosemicarbazone), H2ATSM/A, has been functionalized with 6-aminohexanoic acid (ε-Ahx) to generate the bifunctional chelating agent diacetyl-2-(N4-methyl-3-thiosemicarbazone)-3-[N4-(amino)-(6-aminohexanoic acid)-3-thiosemicarbazone], H2ATSM/A-ε-Ahx (1), suitable for conjugation to glutamine (Gln) residues of bioactive molecules via TGase. The feasibility of the TGase reaction in the synthesis of a bioconjugate derivative was investigated using Substance P (SP) as model peptide. Compounds 1 and H2ATSM/A-ε-Ahx-SP (2) were labelled with nitride-technetium-99m, obtaining the complexes [99mTc][Tc(N)(ATSM/A-ε-Ahx)] (99mTc1) and [99mTc][Tc(N)(ATSM/A-ε-Ahx-SP)] (99mTc2). The chemical identity of 99mTc1 and 99mTc2 was confirmed by radio/UV-RP-HPLC combined with ESI-MS analysis on the respective carrier-added products 99g/99mTc1 and 99g/99mTc2. The stability of the radiolabelled complexes after incubation in various environments was investigated. All the results were compared with those obtained for the corresponding 64Cu-analogues, 64Cu1 and 64Cu2. The TGase reaction allows the conjugation of 1 with the peptide, but it is not highly efficient due to instability of the chelator in the required conditions. The SP-conjugated complexes are unstable in mouse and human sera. However, indeed the BTS system can be exploited as nitride-technetium-99m chelator for highly efficient technetium labelling, thus making compound 1 worthy of further investigations for new targeted technetium and copper radiopharmaceuticals encompassing Single Photon Emission Computed Tomography and Positron Emission Tomography imaging.

Avidin-biotin system: a small library of cysteine biotinylated derivatives designed for the [99mTc(N)(PNP)]2+ metal fragment.

Using the avidin-biotin system as model, we investigate here the effective application of [Tc(N)L(PNP)](+/0) technology (L=N-functionalized cysteine [O(-),S(-)]; PNP=aminodiphosphine) to the preparation of target-specific radiopharmaceuticals. A series of (99m)Tc-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-avidin receptor interaction, the following N-functionalized cysteine-biotin 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/99m)Tc(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 (99m)Tc-nitrido precursor (yields >95%). 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 (99m)Tc(N)(Biot-Abu-CysOS)(PNP3) complex, whereas the (99m)Tc(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 tract.

Synthesis and characterization of rhenium(iii) complexes with (Ph2PCH2CH2)2NR diphosphinoamine ligands.

The synthesis and characterization of a new series of neutral, six-coordinated compounds [ReIIIX3(PNPR)], where X is Cl or Br and PNPR is a diphosphinoamine having the general formula (Ph2PCH2CH2)2NR (R = H, CH3, CH2CH3, CH2CH2CH3, CH2CH2CH2CH3 and CH2CH2OCH3) are reported. Stable [ReIIIX3(PNPR)] complexes were synthesized, in variable yields, starting from precursors where the metal was in different oxidation states (iii and v), by ligand-exchange and/or redox-substitution reactions. The compounds were characterized by elemental analysis, proton NMR spectroscopy, cyclic voltammetry, UV/vis spectroscopy, positive-ion electrospray ionization mass spectrometry (ESI(+)-MS) and X-ray diffraction analysis. Although the formulation of the complexes allows either meridional or facial isomers, the latter arrangement was prevalent both in the solid and solution states. Only [ReCl3(PNPH)] showed a meridional configuration both in solution and in the crystalline state. [ReBr3(PNPme)] prefers the meridional configuration in the crystalline state and the facial one in solution. While ESI(+)-MS and voltammetric data seem to indicate some dependency from the nature of the alkyl substituent at the nitrogen, the available structural data of the complexes show only slight differences both for angles and bond lengths upon change of the alkyl chain tethered to the nitrogen.

Melanoma targeting with [99mTc(N)(PNP3)]-labeled α-melanocyte stimulating hormone peptide analogs: Effects of cyclization on the radiopharmaceutical properties.

The purpose of this study was to evaluate the effect of cyclization on the biological profile of a [99mTc(N)(PNP3)]-labeled α-melanocyte stimulating hormone peptide analog. A lactam bridge-cyclized H-Cys-Ahx-ßAla3-c[Lys4-Glu-His-D-Phe-Arg-Trp-Glu10]-Arg11-Pro-Val-NH2 (NAP-NS2) and the corresponding linear H-Cys-Ahx-ßAla-Nle-Asp-His-D-Phe-Arg-Trp-Gly-NH2 (NAP-NS1) peptide were synthetized, characterized by ESI-MS spectroscopy and their melanocortin-1 receptor (MC1R) binding affinity was determined in B16/F10 melanoma cells. The consistent [99mTc(N)(PNP3)]-labeled compounds were readily obtained in high specific activity and their stability and biological properties were assessed. As an example, the chemical identity of [99mTc(N)(NAP-NS1)(PNP3)]+ was confirmed by carrier added experiments supported by radio/UV HPLC analysis combined with ESI(+)-MS. Compared with the linear peptide, cyclization negatively affected the biological properties of NAP-NS2 peptide by reducing its binding affinity for MC1R and by decreasing the overall excretion rate of the corresponding [99mTc(N)(PNP3)]-labeled peptide from the body as well as its in vivo stability. [99mTc(N)(NAP-NS1)(PNP3)]+ was evaluated for its potential as melanoma imaging probe in murine melanoma model. Data from in vitro and in vivo studies on B16/F10 melanoma model of [99mTc(N)(NAP-NS1)(PNP3)]+ clearly evidenced that the radiolabeled linear peptide keeps its biological properties up on the conjugation to the [99mTc(N)(PNP3)]-building block. The progressive increase of the tumor-to-nontarget ratios over the time indicates a quite stable interaction between the radio-complex and the MC1R.

Synthesis and biologic evaluation of monocationic asymmetric 99mTc-nitride heterocomplexes showing high heart uptake and improved imaging properties.

UNLABELLED: The preparation, characterization, and first biologic evaluation in rats of a novel class of monocationic (99m)Tc heart imaging agents are reported. The complexes are represented by the general formula [(99m)Tc(N)(PNP)(L)](+), where L is the monoanionic form of a dithiocarbamate ligand of the type [R(1)(R(2))-N-C(=S)S](-), PNP is a diphosphine ligand of the type [(R(3))(2)P-(CH(2))(2)](2)-N(R(4)), and R(1)-R(4) are organic functional groups. METHODS: The new complexes were prepared by use of both liquid and freeze-dried formulations through a 2-step procedure. The first step involved the formation of the [TcN](2+) group through the reaction of (99m)TcO(4)(-) with succinic dihydrazide as a donor of nitride nitrogen atoms (N(3-)) in the presence of Sn(2+) ions. This step was followed by the simultaneous addition to the reaction solution of the ligand PNP and of the sodium salt of the dithiocarbamate ligand (NaL) to afford the final products, [(99m)Tc(N)(PNP)(L)](+). The chemical identities of the resulting (99m)Tc complexes were determined by comparing their chromatographic properties with those of the corresponding (99g)Tc analogs prepared by use of the long-lived isotope (99g)Tc and characterized by spectroscopic and crystallographic techniques. Ex vivo biodistribution studies were conducted in rats. In vivo tomographic images of the rat heart were obtained by use of a small-animal SPECT scanner. RESULTS: The [(99m)Tc(N)(PNP)(L)](+) complexes are monocationic and possess a distorted square-pyramidal geometry in which the TcN multiple bond occupies an apical position and the diphosphine and dithiocarbamate ligands span the residual 4 coordination positions on the basal plane through the 2 phosphorus atoms and the 2 sulfur atoms, respectively. Imaging and biodistribution studies demonstrated that these radiopharmaceuticals localize selectively in the myocardium of rats and are retained in this region for a prolonged time. The kinetics of heart uptake and clearance were found to be influenced by variations in the lateral R(1)-R(4) groups. Blood and lung washouts were extremely fast. Elimination occurred mostly through the kidneys and the liver. Surprisingly, at 1 h after injection, liver activity was almost negligible. Analysis of heart-to-liver and heart-to-lung uptake ratios showed that these values increased exponentially over time and became much higher than those determined for (99m)Tc-sestamibi and (99m)Tc-tetrofosmin. These findings were confirmed by analysis of high-quality SPECT images collected in rats for the new complexes and compared with images obtained with (99m)Tc-sestamibi and (99m)Tc-tetrofosmin. CONCLUSION: The high myocardial uptake and the very high heart-to-lung and heart-to-liver uptake ratios indicate that the [(99m)Tc(N)(PNP)(L)](+) complexes exhibit very favorable distribution properties and could be used to obtain SPECT cardiac images with improved quality.

Synthesis and Characterization of Nitrido Tc(V) and Re(V) Complexes with Ferrocenedithiocarboxylate {FcCS(2) = [Fe(C(5)H(4)CS(2))(C(5)H(5))](-)}

The first mixed technetium-iron complexes [(99g)Tc(N)(FcCS(2))(2)] {FcCS(2) = [Fe(II)(C(5)H(5))(C(5)H(4)CS(2))](-)} (1) and [(99g)Tc(N)(FcCS(2))(FcCS(2)( bigstar))](+) {FcCS(2) = [Fe(II)(C(5)H(5))(C(5)H(4)CS(2))](-); FcCS(2)( bigstar) = Fe(III)(C(5)H(5))(C(5)H(4)CS(2))} (2) have been prepared and characterized. Complex 1 was obtained by reaction of the precursor complex [(99g)Tc(N)Cl(2)(PPh(3))(2)] with the piperidinium salt of the ligand FcCS(2). The resulting biferrocene complex is formed by two FcCS(2) ligands bound to the Tc atom through the four sulfur atoms of the two CS(2)(-) groups and bridged by a Tc&tbd1;N multiple bond. The mixed-valence Fe(2+)-Fe(3+), monocationic complex 2 was isolated as secondary product of the reaction of the precursor complex [(99g)Tc(N)Cl(4)](-) with the ligand FcCS(2). It has the same composition as 1 except for the fact that the Fe(II) center of one FcCS(2) ligand has been oxidized to Fe(III). The electrochemical properties of 1 and 2 are consistent with their formulations. Cyclic voltammetric studies and controlled potential electrolyses showed that complex 1 undergoes a quasi-reversible, two-electron exchange at 0.320 V (vs ferrocene/ferrocenium couple) attributed to the oxidation of the two Fe(II) ions, while complex 2 undergoes a quasi-reversible, one-electron exchange at nearly the same potential (0.344 V) assigned to the oxidation of the residual Fe(II) ion. These results indicate that in complex 1 the two Fe(II) atoms behave as independent redox centers. The synthesis, characterization, and electrochemical behavior of the analogous, six-coordinated rhenium(V) complex [Re(N)(FcCS(2))(2)(PPh(3))] are also reported.

Synthesis of a Novel Class of Trigonal Bipyramidal Nitrido Tc(V) Complexes with Phosphino-Thiol Ligands. Crystal Structure of [(99g)Tc(N)(L(1))(2)] [L(1) = 2-(Diphenylphosphino)ethanethiolato] and [(99g)Tc(N)(L(5))(2)] [L(5) = 2-(Ditolylphosphino)propanethiolato].

Reactions of the precursor complexes [(99g)Tc(N)Cl(2)(PPh(3))(2)] and [(99g)Tc(N)Cl(4)](-) with phosphine-thiol ligands (HL(n)()) of the type R(2)PCH(2)CH(2)SH (R = phenyl, methoxypropyl), R(2)'PCH(2)CH(2)CH(2)SH (R' = phenyl, tolyl), and R(2)' 'P-o-C(6)H(4)SH (R' ' = phenyl) afforded the five-coordinated, disubstituted nitrido technetium(V) complexes [(99g)Tc(N)(L(n)())(2)]. The complexes were characterized by elemental analysis, (1)H and (31)P NMR spectroscopy, FT IR, and positive FAB MS spectra. Structural characterization of [(99g)Tc(N)(L(1))(2)] (1) [HL(1) = (C(6)H(5))(2)PCH(2)CH(2)SH] and [(99g)Tc(N)(L(5))(2)] (5) [HL(5) = (o-CH(3)C(6)H(4))(2)PCH(2)CH(2)CH(2)SH] showed that the bidentate phosphino-thiol ligands are coordinated to the technetium center through the neutral phosphorus atom and the deprotonated thiol sulfur atom. These complexes possess an uncommon trigonal bipyramidal geometry with the two phosphorus atoms occupying the two transaxial positions and the two sulfur atoms on the equatorial plane along with the nitrido nitrogen atom. Compound 1 crystallizes in the monoclinic space group C2/c, a = 24.84(2) Å, b = 7.327(6) Å, c = 31.52(2) Å, beta = 111.06(10) degrees, and Z = 8. Compound 5 crystallizes in the monoclinic space group P2(1)/n, a = 11.090(1) Å, b = 14.387(2) Å, c = 11.087(1) Å, beta = 113.62(1) degrees, and Z = 2.

Electrospray mass spectrometry of a series of mixed nitrido 99gTc- heterocomplexes conjugated with bioactive 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 [99gTc(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 (MSn) 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.

Novel [99mTcIII(PS)2(Ln)] mixed-ligand compounds (PS = phosphino-thiolate; L = dithiocarbamate) useful in design and development of TcIII-based agents: synthesis, in vitro, and ex vivo biodistribution studies.

A general procedure for the preparation of a new class of neutral six-coordinated mixed ligand [(99m)Tc(III)(PS)2(Ln)] compounds (PS = trisalkyl-phosphino-thiolate; Ln = dithiocarbamate) is reported as well as their in vitro stability and the ex vivo tissue distribution studies. [(99m)Tc(PS)2(Ln)] complexes were prepared in high yield in nearly physiologic conditions following a one-pot procedure. For instance, the chemical identity of [(99m)Tc(PSiso)2(L1)] (PSiso = 2-(diisopropylphosphino)ethanethiol; L1 = pyrrolidine dithiocarbamate) was determined by HPLC comparison with the corresponding (99g)Tc-complex. All complexes comprise the stable [(99m)Tc(III)(PS)2](+) moiety, where the remaining two coordination positions are saturated by a dithiocarbamate chelate, also carrying bioactive molecules (e.g., 2-methoxyphenylpiperazine). [(99m)Tc(PS)2(Ln)] complexes were inert toward ligand exchange reactions. No significant in vitro and in vivo biotransformation were observed, underlining their remarkable thermodynamic stability and kinetic inertness. These results could be conveniently utilized to devise a novel class of (99m)Tc(III)-based compounds useful in radiopharmaceutical applications.

Assessment of the best N(3-) donors in preparation of [M(N)(PNP)]-based (M=(99m)Tc-; (188)Re) target-specific radiopharmaceuticals: Comparison among succinic dihydrazide (SDH), N-methyl-S-methyl dithiocarbazate (HDTCZ) and PEGylated N-methyl-S-methyl dithiocarbazate (HO2C-PEG600-DTCZ).

Succinic dihydrazide (SDH), N-methyl-S-methyl dithiocarbazate (HDTCZ) and PEGylated N-methyl-S-methyl dithiocarbazate (HO2C-PEG600-DTCZ) are nitrido nitrogen atom donors employed for the preparation of nitride [M(N)]-complexes (M=(99m)Tc and (188)Re). This study aims to compare the capability and the efficiency of these three N(3-) group donors, in the preparation of [M(N)PNP]-based target-specific compounds (M=(99m)Tc, (188)Re; PNP=aminodiphosphine). For this purpose, three different kit formulations (SDH kit; HO2C-PEG600-DTCZ kit; HDTCZ kit) were assembled and used in the preparation of [M(N)(cys~)(PNP3)](0/+) complexes (cys~=cysteine derivate ligands). For each formulation, the radiochemical yield (RCY) of the [M(N)(~cys)(PNP3)] compounds, was determined by HPLC. The deviation of the percentage of RCY, due to changes in concentration of the N(3-) donors and of the exchanging ligand, was determined. For (99m)Tc, data clearly show that HDTCZ is the most efficient donor of N(3-); however, SDH is the most suitable nitrido nitrogen atom donor for the preparation of [(99m)Tc(N)(PNP)]-based target-specific agents with high specific activity. When HO2C-PEG600-DTCZ or HDTCZ are used in N(3-) donation, high amounts of the exchanging ligand (10(-4)M) were required for the formation of the final complex in acceptable yield. The possibility to use microgram amounts of HDTCZ also in [(188)Re(N)] preparation (0.050mg) reduces its ability to compete in ligand exchange reactions, minimizing the quantity of chelators required to obtain the final complex in high yield. This finding can be exploit for increasing the radiolabeling efficiency in [(188)Re(N)]-radiopharmaceutical preparations compared to the previously reported HDTCZ-based procedure, notwithstanding a purification process could be necessary to improve the specific activity of the complexes.

Neutral and charged phosphine/scorpionate copper(I) complexes: effects of ligand assembly on their antiproliferative activity.

Ligand-exchange reactions of copper(I) precursors ([Cu(CH(3)CN)(4)]BF(4), CuCl) with a panel of bis(azolyl)borates or poly(pyrazolyl)methanes and a tertiary monodentate phosphine (PTA = 1,3,5-triaza-7-phosphaadamantane, PCN = tris(cyanoethyl)phosphine) produced two series of heteroleptic, either '2 + 1 + 1'- or '3 + 1'-type complexes, which have been characterized by elemental analysis, FT-IR, ESI-MS and multinuclear (31)P and (1)H NMR. '2 + 1 + 1'-type complexes include a N,N-bidentate chelate and two monodentate phosphines (1-8) and '3 + 1'-type complexes comprise a N,N,O- or N,N,N-tridentate chelate and one monodentate phosphine (9-12). All these complexes adopt a four-coordinate, tetrahedral geometry. '3 + 1' complexes show better red-ox stability and a greater tendency to retain the native '3 + 1' mixed-ligand structure. Conversely, '2 + 1 + 1' complexes exhibit increased propensity to dissociation as shown by ESI-MS measurements and X-ray structure determination at low temperature (150 K) of the polymeric complex {[H(2)B(tz(NO2))(2)]Cu[PCN]}(n)6b. In this complex, either the bis(triazolyl)borate and the PCN ligands act as bidentate, with PCN being also the µ(2)-bridiging linker between adjacent monomers. Compound 6b is the first reported example of a polymeric PCN compound with a tetra-coordinate metal centre. Cytotoxic activity of all compounds has been evaluated by MTT test against a panel of several human tumor cell lines including examples of breast (MCF-7), colon (HCT-15 and LoVo), lung (A549), cervix (A431) and ovarian (2008 and its cisplatin resistant variant, C13*) carcinoma, melanoma (A375) and promyelocytic leukemia (HL60). Copper complexes generally show in vitro antitumour activity comparable to that of cisplatin. In particular, neutral '3 + 1'-type complexes 9 and 10, show IC(50) values appreciably lower than those exhibited by the reference metallodrug.

Chelating systems for (99m)Tc/(188)Re in the development of radiolabeled peptide pharmaceuticals.

Currently, receptor based radiopharmaceuticals have received great attention in molecular imaging and radiotherapy of cancer, and provide a unique tool for target-specific delivery of radionuclides to pathological tissues. In this context, receptor binding peptides represent an attractive class of target vectors for Nuclear Medicine purposes. The rich chemistry of the group 7 elements elaborated in past years, has allowed the development of different procedures for the preparation of radiolabeled peptides in high yield. This, joint to the use of solid-phase peptide synthesis, has opened the possibility to explore new strategies for approaching the design of new class of radiolabeled receptor-targeted peptides, and to create new versatilities in targeting vehicle design e.g. in synthesis of metal-cyclized peptides or of multivalent targeting agents. This review provides an overview on several aspects of the development of new (99m)Tc/(188)Re-peptide based target specific radiopharmaceuticals, in particular on the synthetic strategies employed for modifying molecular vectors, and the application of the different metal-cores and/or building block for preparing high specific activity agents.

Insights into the failure of the potential, neutral myocardial imaging agent TcN-NOET: physicochemical identification of by-products and degradation species.

INTRODUCTION: The neutral complex [(99m)Tc(N)(NOEt)(2)], often referred to as TcN-NOET [NOEt=N-ethoxy,N-ethyldithiocarbamate(1-)], was proposed several years ago as a myocardial imaging agent. Despite some favorable clinical properties evidenced during phase I and phase II studies, the overall results of the European and American phase III clinical studies have been judged insufficient for a successful approval process by the regulatory agencies. METHODS: Non-carrier-added and carrier-added experiments using short-lived (99m)Tc and long-lived (99g)Tc have been utilized to prepare a series of bis-substituted [Tc(N)(DTC)(2)] complexes [DTC=dithiocarbamate(1-)]. They have been purified by means of chromatographic techniques (high-performance liquid chromatography and thin-layer chromatography) and identified via double detection (UV-vis and radiometry) by comparison with authenticated samples of (99g)Tc compounds prepared by conventional coordination chemistry procedures. RESULTS: The molecular structure of the lipophilic, neutral complex cis-[Tc(N)(NOEt)(2)] has been assigned by comparison with similar nitrido-Tc(V) complexes already reported in the literature. Novel bis-substituted nitrido-Tc complexes containing hydrolyzed portions of coordinated NOEt, namely, N-ethyldithiocarbamate [NHEt(1-)] and N-hydroxy, N-ethyldithiocarbamate [NOHEt(1-)], have been prepared and characterized by means of multinuclear nuclear magnetic resonance spectroscopy and mass spectrometry. CONCLUSIONS: Despite the identification of these "hydrolyzed" species, it is still unclear whether the failure to reach the clinical goal of the perfusion tracer [(99m)Tc(N)(NOEt)(2)] is related to the degradation processes evidenced in this study or is the result of the mediocre imaging properties of the tracer.

Synthesis, characterization and biological evaluation of [188Re(N)(cys ∼)(PNP)]+/0 mixed-ligand complexes as prototypes for the development of 188Re(N)-based target-specific radiopharmaceuticals.

We report on an efficient procedure for the preparation of [(188)Re(N)(PNP)]-based complexes (where PNP is diphosphinoamine) useful in the development of target-specific radiopharmaceuticals. The radiochemical yield of the compounds was optimized considering such reaction parameters as nature of the nitrido nitrogen donor, reaction times and pH level. The chemical identity of the (188)Re agents was determined by high-performance liquid chromatography comparison with the corresponding well-characterized cold Re compounds. (188)Re(N) mixed compounds have been evaluated with regard to stability toward transchelation with GSH and degradation by serum enzymes. The clearance of selected radiocompounds from normal tissues and their in vivo stability were evaluated in rats by biodistribution and imaging studies. [(188)Re(N)(cys ∼)(PNP)](+/0) mixed-ligand compounds were efficiently prepared in aqueous solution from perrhenate using a multistep procedure based on the preliminary formation of the labile (188)Re(III)-EDTA species, which easily undergo oxidation/ligand exchange reaction to afford the [(188)Re(V) ≡ N](2+) core in the presence of dithiocarbazate. The final mixed-ligand compounds were obtained, at 100 °C, by adding the two bidentate ligands to the buffered [(188)Re(V) ≡ N](2+) solution (pH 3.2-3.6). However, a relatively high amount of cys ∼ ligand was required to obtain a quantitative radiochemical yield. The complexes were stable toward reoxidation to perrhenate and ligand exchange reactions. In vivo studies showed rapid distribution and elimination of the complexes from the body. No specific uptakes in sensitive tissues/organs were detected. A positive correlation of the distribution of the complexes estimated with biodistribution studies (%ID) and with micro-SPECT semiquantification imaging analysis (standard uptake values) was observed. These results support the possibility of applying [(188)Re(N)(PNP)] technology to the preparation of target-specific agents.

Synthesis and structural characterization of copper(I) complexes bearing N-methyl-1,3,5-triaza-7-phosphaadamantane (mPTA): cytotoxic activity evaluation of a series of water soluble Cu(I) derivatives containing PTA, PTAH and mPTA ligands.

New copper(I) complexes containing the water soluble N-methyl-1,3,5-triaza-7-phosphaadamantane (mPTA) phosphine have been synthesized by ligand-exchange reactions starting from [Cu(CH(3)CN)(4)][BF(4)] or [Cu(CH(3)CN)(4)][PF(6)] precursors and (mPTA)X (X=CF(3)SO(3), I). Depending on the ligand counter ion, the hydrophilic [Cu(mPTA)(4)][(CF(3)SO(3))(4)(BF(4))] 3a and [Cu(mPTA)(4)][(CF(3)SO(3))(4)(PF(6))] 3c complexes or the iodine-coordinated [Cu(mPTA)(3)I]I(3)4 species were obtained respectively and fully characterized by spectroscopic methods. Single crystal structural characterization was undertaken for [Cu(mPTA)(3)I]I(3).H(2)O, 4.H(2)O, and [Cu(mPTA)(4)][(CF(3)SO(3))(2)(BF(4))(3)] .0.25H(2)O, 3b.0.25H(2)O, the latter obtained by crystallization of [Cu(mPTA)(4)][(CF(3)SO(3))(4)(BF(4))] 3a. The cytotoxicity of analogous tetrahedral homoleptic Cu(I) derivatives [Cu(PTA)(4)](BF(4)) 1, [Cu(PTAH)(4)][Cl(4)(BF(4))] 2, [Cu(mPTA)(4)][(CF(3)SO(3))(4)(BF(4))] 3a and [Cu(mPTA)(4)][(CF(3)SO(3))(4)(PF(6))] 3c was evaluated against a panel of several human tumor cell lines. All the complexes showed in vitro antitumor activity comparable to that of the reference metallodrug cisplatin. Tests performed on cisplatin sensitive and resistant cell lines showed that against human ovarian 2008/C13(*) cell line pair, the resistance factor of copper derivatives was roughly 7-fold lower than that of cisplatin, whereas against human cervix cancer A431/A431-Pt cell line pair it was about 2.5-fold lower. These results, confirming the circumvention of cisplatin resistance, support the hypothesis that phosphine copper(I) complexes follow different cytotoxic mechanisms than do platinum drugs.