Fluorescent Copper(II) Bis(thiosemicarbazonates): Synthesis, Structures, Electron Paramagnetic Resonance, Radiolabeling, In Vitro Cytotoxicity and Confocal Fluorescence Microscopy Studies

Shedding light on the use of graphene oxide-thiosemicarbazone hybrids towards the rapid immobilisation of methylene blue and functional coumarins

Coumarins, methylene blue derivatives, as well as related functional organic dyes have become prevalent tools in life sciences and biomedicine. Their intense blue fluorescence emission makes them ideal agents for a range of applications, yet an unwanted facet of the interesting biological properties of such probes presents a simultaneous environmental threat due to inherent toxicity and persistence in aqueous media. As such, significant research efforts now ought to focus on their removal from the environment, and the sustainable trapping onto widely available, water dispersible and processable adsorbent structures such as graphene oxides could be advantageous. Additionally, flat and aromatic bis(thiosemicarbazones) (BTSCs) have shown biocompatibility and chemotherapeutic potential, as well as intrinsic fluorescence, hence traceability in the environment and in living systems. A new palette of graphene oxide-based hierarchical supramolecular materials incorporating BTSCs were prepared, characterised, and reported hereby. We report on the supramolecular entrapping of several flat, aromatic fluorogenic molecules onto graphene oxide on basis of non-covalent interactions, by virtue of their structural features with potential to form aromatic stacks and H-bonds. The evaluations of the binding interactions in solution by between organic dyes (methylene blue and functional coumarins) and new graphene oxide-anchored Zn(ii) derivatised bis(thiosemicarbazones) nanohybrids were carried out by UV-Vis and fluorescence spectroscopies.

Hint from an Enzymatic Reaction: Superoxide Dismutase Models Efficiently Suppress Colorectal Cancer Cell Proliferation

Superoxide dismutases (SODs) are essential antioxidant enzymes that prevent massive superoxide radical production and thus protect cells from damage induced by free radicals. However, this concept has rarely been applied to directly impede the function of driver oncogenes, thus far. Here, leveraging efforts from SOD model complexes, we report the novel finding of biomimetic copper complexes that efficiently scavenge intracellularly generated free radicals and, thereby, directly access the core consequence of colorectal cancer suppression. We conceived four structurally different SOD-mimicking copper complexes that showed distinct disproportionation reaction rates of intracellular superoxide radical anions. By replenishing SOD models, we observed a dramatic reduction of intracellular reactive oxygen species (ROS) and adenine 5'-triphosphate (ATP) concentrations that led to cell cycle arrest at the G2/M stage and induced apoptosis in vitro and in vivo. Our results showcase how nature-mimicking models can be designed and fine-tuned to serve as a viable chemotherapeutic strategy for cancer treatment.

Structural and Functional Diversity in Rigid Thiosemicarbazones with Extended Aromatic Frameworks: Microwave-Assisted Synthesis and Structural Investigations

The long-standing interest in thiosemicarbazones (TSCs) has been largely driven by their potential toward theranostic applications including cellular imaging assays and multimodality imaging. We focus herein on the results of our new investigations into: (a) the structural chemistry of a family of rigid mono(thiosemicarbazone) ligands characterized by extended and aromatic backbones and (b) the formation of their corresponding thiosemicarbazonato Zn(II) and Cu(II) metal complexes. The synthesis of new ligands and their Zn(II) complexes was performed using a rapid, efficient and straightforward microwave-assisted method which superseded their preparation by conventional heating. We describe hereby new microwave irradiation protocols that are suitable for both imine bond formation reactions in the thiosemicabazone ligand synthesis and for Zn(II) metalation reactions. The new thiosemicarbazone ligands, denoted HL, mono(4-R-3-thiosemicarbazone)quinone, and their corresponding Zn(II) complexes, denoted ZnL₂, mono(4-R-3-thiosemicarbazone)quinone, where R = H, Me, Ethyl, Allyl, and Phenyl, quinone = acenapthnenequinone (AN), aceanthrenequinone (AA), phenanthrenequinone (PH), and pyrene-4,5-dione (PY) were isolated and fully characterized spectroscopically and by mass spectrometry. A plethora of single crystal X-ray diffraction structures were obtained and analyzed and the geometries were also validated by DFT calculations. The Zn(II) complexes presented either distorted octahedral geometry or tetrahedral arrangements of the O/N/S donors around the metal center. The modification of the thiosemicarbazide moiety at the exocyclic N atoms with a range of organic linkers was also explored, opening the way to bioconjugation protocols for these compounds. The radiolabeling of these thiosemicarbazones with ⁶⁴Cu was achieved under mild conditions for the first time: this cyclotron-available radioisotope of copper (t_1/2 = 12.7 h; β+ 17.8%; β- 38.4%) is well-known for its proficiency in positron emission tomography (PET) imaging and for its theranostic potential, on the basis of the preclinical and clinical cancer research of established bis(thiosemicarbazones), such as the hypoxia tracer ⁶⁴Cu-labeled copper(diacetyl-bis(N4-methylthiosemicarbazone)], [⁶⁴Cu]Cu(ATSM). Our labeling reactions proceeded in high radiochemical incorporation (>80% for the most sterically unencumbered ligands) showing promise of these species as building blocks for theranostics and synthetic scaffolds for multimodality imaging probes. The corresponding "cold" Cu(II) metalations were also performed under the mild conditions mimicking the radiolabeling protocols. Interestingly, room temperature or mild heating led to Cu(II) incorporation in the 1:1, as well as 1:2 metal: ligand ratios in the new complexes, as evident from extensive mass spectrometry investigations backed by EPR measurements, and the formation of Cu(L)₂-type species prevails, especially for the AN-Ph thiosemicarbazone ligand (L^-). The cytotoxicity levels of a selection of ligands and Zn(II) complexes in this class were further tested in commonly used human cancer cell lines (HeLa, human cervical cancer cells, and PC-3, human prostate cancer cells). Tests showed that their IC₅₀ levels are comparable to that of the clinical drug cis-platin, evaluated under similar conditions. The cellular internalizations of the selected ZnL₂-type compounds Zn(AN-Allyl)₂, Zn(AA-Allyl)₂, Zn(PH-Allyl)₂, and Zn(PY-Allyl)₂ were evaluated in living PC-3 cells using laser confocal fluorescent spectroscopy and these experiments showed exclusively cytoplasmic distributions.

Synthesis of Carvacrol Derivatives as Potential New Anticancer Agent against Lung Cancer

Lung cancer remains a major public health concern among all cancer diseases due to the toxicity and side-effects of the available commercially synthesized drugs. Natural product-derived synthesized anticancer drugs are now of promising interest to fight against cancer death. Carvacrol is a major component of most essential oil-bearing plants with potential pharmacological activity, especially against various cancer cell lines. Among the other organometallic compounds, copper complexes have been reported to be effective anticancer agents against various cancer cell lines, especially lung and leukemia cancers, due to the nontoxic nature of copper in normal cells since it is an endogenic metal. In this study, we synthesized three carvacrol derivatives, i.e., carvacrol aldehyde, Schiff base, and copper–Schiff base complex, through an established synthesis protocol and characterized the synthesized product using various spectroscopic techniques. The synthesized derivatives were evaluated for in vitro cytotoxic activity against different cancer cell lines, including human lung cancer (A549) and human fibroblast (BALB-3T3). Our findings showed that the copper–Schiff base complex derived from carvacrol inhibited the proliferation and migration of the A549 cell lines in a dose-dependent manner. This activity might be due to the inhibition of cell proliferation and migration at the G₂/M cell-cycle phase, as well as apoptosis, possibly through the activation of the mitochondrial apoptotic pathway. To our knowledge, this is the first report on the activity of the copper–Schiff base complex of carvacrol against A549 cell lines. Our result highlights that a new synthesized copper complex from carvacrol could be a novel potential drug in the treatment of lung cancer.

Functional, Aromatic, and Fluorinated Monothiosemicarbazones: Investigations into Their Structures and Activity toward the Gallium-68 Incorporation by Microwave Irradiation

We report on the synthesis and spectroscopic characterization of a new series of coordinating monothiosemicarbazones incorporating aromatic backbones, featuring O/N/S donor centers monosubstituted with different aliphatic, aromatic, fluorinated, and amine-functionalized groups at their N centers. Their ability to bind metal ions such as Zn(II) and Ga(III) was explored, and the formation of two different coordination isomers of the Zn(II) complex was demonstrated by X-ray diffraction studies using synchrotron radiation. These studies showed the planar geometry for the coordinated mono(thiosemicarbazone) ligand and that the metal center can adopt either a heavily distorted tetrahedral Zn center (placed in an N/S/S/N environment, with CN = 4) or a pseudo-octahedral geometry, where the Zn(II) center is in the O/N/S/S/N/O environment, and CN = 6. Furthermore, 2-(4,5-dimethyl-2-thiazolyl)-3,5-diphenyl-2H-tetrazolium bromide (MTT) assays and cellular imaging in living cells were subsequently performed in two different cancer cell lines: PC-3 (a standard cell line derived from a bone metastasis of a stage IV prostate cancer) and EMT6 (a commercial murine mammary carcinoma cell line). The radiolabeling of new functional and aromatic monothiosemicarbazones with either gallium-68 (under pH control) or fluorine-18 is discussed. The potential of this class of compounds to act as synthetic scaffolds for molecular imaging agents of relevance to positron emission tomography was evaluated in vitro, and the cellular uptake of a simultaneously fluorinated and [⁶⁸Ga]-labeled mono(thiosemicarbazone) was investigated and is reported here.

Synthesis of (3-nitro-2-oxo-benzaldehyde thiosemicarbazonato)–zinc(ii) complexes: the position of nitro group in phenyl ring alters antimicrobial activity against K. pneumoniae 1, S. typhimurium 2, MRSA and C. albicans

The antimicrobial activity of five coordinated 3-nitro-2-oxo-benzaldehyde-thiosemicarbazonato)zinc(ii) complexes is different from that of analogous 5-nitro-complexes.

Synthesis, Characterization, and in Vitro Anticancer Activity of Copper and Zinc Bis(Thiosemicarbazone) Complexes

A series of eight bis(thiosemicarbazone) ligands and 16 of their respective copper(II) and zinc(II) complexes containing a combination of hydrogen, methyl, pyridyl, phenyl, and/or ethyl substituents at the diimine position of the ligand backbone were synthesized and characterized. The objective of this study was to identify the structure-activity relationships within a series of analogues with different substituents at the diimine position of the backbone and at the terminal N atom. The Cu(II) complexes Cu(GTSM₂), Cu(GTSCM), Cu(PyTSM₂), Cu(EMTSM₂) and Cu(PGTSM₂) demonstrated a distorted square planar geometry, while the Zn(II) complexes Zn(ATSM₂)(DMSO), Zn(PyTSM₂)(DMSO), and Zn(PGTSM₂)(H₂O) formed a distorted square pyramidal geometry. Cyclic voltammetry showed that the Cu(II) complexes display quasi-reversible electrochemistry. Of the agents, Cu(II) glyoxal bis(4,4-dimethyl-3-thiosemicarbazone) [Cu(GTSM₂)] and Cu(II) diacetyl bis(4,4-dimethyl-3-thiosemicarbazone) [Cu(ATSM₂)] demonstrated the greatest antiproliferative activity against tumor cells. Substitutions at the diimine position and at the terminal N atom with hydrophobic moieties markedly decreased their antiproliferative activity. Complexation of the bis(thiosemicarbazones) with Zn(II) generally decreased their antiproliferative activity, suggesting the Zn(II) complex did not act as a chaperone to deliver the ligand intracellularly, in contrast to similar bis(thiosemicarbazone) cobalt(III) complexes [King et al. Inorg. Chem. 2017, 56, 6609-6623]. However, five of the eight bis(thiosemicarbazone) Cu(II) complexes maintained or increased their antiproliferative activity, relative to the ligand alone, and a mechanism of Cu-induced oxidative stress is suggested. Surprisingly, relative to normoxic growth conditions, hypoxia that is found in the tumor microenvironment decreased the antiproliferative efficacy of most bis(thiosemicarbazones) and their copper complexes. This was independent of the potential hypoxia-selectivity mediated by Cu(II/I) redox potentials. These results provide structure-activity relationships useful for the rational design of bis(thiosemicarbazone) anticancer agents.

Synthesis of 18 F-radiolabeled diphenyl gallium dithiosemicarbazone using a novel halogen exchange method and in vivo biodistribution

¹⁸ F-radiolabeled diphenyl gallium thiosemicarbazone was prepared by [¹⁸ F] fluoride exchange of a nitrato anion under mild conditions. The diphenyl gallium thiosemicarbazone chloride is easily prepared in gram quantities and can be used at room temperature in the presence of oxygen. The corresponding nitrate complex is prepared using silver nitrate in methanol solvent and can be stored under nitrogen for weeks before radiolabeling. The biodistribution of this new tracer was studied in mice using positron emission tomography (PET).

Synthesis, structures, antimicrobial activity and biosafety evaluation of pyridine-2-formaldehyde-N-susbtituted-thiosemicarbazonates of copper(ii)

Copper(ii) complexes with pyridine based thiosemicarbazones have shown high antimicrobial potential against different microbial strains, and were found to be biosafe with several complexes displaying high cell viability (90–98%).

A Novel Strategy to Introduce 18F, a Positron Emitting Radionuclide, into a Gallium Nitrate Complex: Synthesis, NMR, X-Ray Crystal Structure, and Preliminary Studies on Radiolabelling with 18F

A hexan-3,4-dione bis(4N-phenylthiosemicarbazone) gallium nitrate complex was synthesised and the structure was confirmed by NMR studies. The complex was prepared using an appropriately substituted dithiosemicarbazone and sodium methoxide in anhydrous methanol. The structure was further confirmed using single crystal X-ray crystallography. The crystal structure of gallium nitrate complex of diphenylthiosemicarbazone comprise a planar configuration of the tetradentate coordinated thiosemicarbazone with the Ga3+ ion, with the nitrate ligand occupying the apical coordination site. The X-ray structure of the gallium fluoride complex of pentan-2,3-dione bis(4N-phenylthiosemicarbazone) has been determined and confirms exchange of the nitrate can be achieved with fluoride. We show facile exchange of 18F, a positron emitter, to form the 18F-gallium complex under mild conditions, thus providing confirmation that such a transformation can be used to introduce 18F directly into nitrate-coordinated complexes of gallium-thiosemicarbozone complexes, a new labelling strategy for the preparation of imaging agents.

Lysosomal tracking with a cationic naphthalimide using multiphoton fluorescence lifetime imaging microscopy

A naphthalimide-based chemosensing motif capable of turning on the fluorescence emission in solution and in vitro is reported.

Applications of "Hot" and "Cold" Bis(thiosemicarbazonato) Metal Complexes in Multimodal Imaging

The applications of coordination chemistry to molecular imaging has become a matter of intense research over the past 10 years. In particular, the applications of bis(thiosemicarbazonato) metal complexes in molecular imaging have mainly been focused on compounds with aliphatic backbones due to the in vivo imaging success of hypoxic tumors with PET (positron emission tomography) using (64) CuATSM [copper (diacetyl-bis(N4-methylthiosemicarbazone))]. This compound entered clinical trials in the US and the UK during the first decade of the 21(st) century for imaging hypoxia in head and neck tumors. The replacement of the ligand backbone to aromatic groups, coupled with the exocyclic N's functionalization during the synthesis of bis(thiosemicarbazones) opens the possibility to use the corresponding metal complexes as multimodal imaging agents of use, both in vitro for optical detection, and in vivo when radiolabeled with several different metallic species. The greater kinetic stability of acenaphthenequinone bis(thiosemicarbazonato) metal complexes, with respect to that of the corresponding aliphatic ATSM complexes, allows the stabilization of a number of imaging probes, with special interest in "cold" and "hot" Cu(II) and Ga(III) derivatives for PET applications and (111) In(III) derivatives for SPECT (single-photon emission computed tomography) applications, whilst Zn(II) derivatives display optical imaging properties in cells, with enhanced fluorescence emission and lifetime with respect to the free ligands. Preliminary studies have shown that gallium-based acenaphthenequinone bis(thiosemicarbazonato) complexes are also hypoxia selective in vitro, thus increasing the interest in them as new generation imaging agents for in vitro and in vivo applications.

Zinc(II)-Thiosemicarbazone Complexes Are Localized to the Lysosomal Compartment Where They Transmetallate with Copper Ions to Induce Cytotoxicity

As the di-2-pyridylketone thiosemicarbazone (DpT) and 2-acetylpyridine thiosemicarbazone (ApT) series show potent antitumor activity in vitro and in vivo, we synthesized their fluorescent zinc(II) complexes to assess their intracellular distribution. The Zn(II) complexes generally showed significantly greater cytotoxicity than the thiosemicarbazones alone in several tumor cell-types. Notably, specific structure-activity relationships demonstrated the importance of the di-2-pyridyl pharmacophore in their activity. Confocal fluorescence imaging and live cell microscopy showed that the Zn(II) complex of our lead compound, di-2-pyridylketone 4-cyclohexyl-4-methyl-3-thiosemicarbazone (DpC), which is scheduled to enter clinical trials, was localized to lysosomes. Under lysosomal conditions, the Zn(II) complexes were shown to transmetallate with copper ions, leading to redox-active copper complexes that induced lysosomal membrane permeabilization (LMP) and cytotoxicity. This is the first study to demonstrate direct lysosomal targeting of our novel Zn(II)-thiosemicarbazone complexes that mediate their activity via transmetalation with copper ions and LMP.

Microwave gallium-68 radiochemistry for kinetically stable bis(thiosemicarbazone) complexes: structural investigations and cellular uptake under hypoxia

We report the microwave synthesis of several bis(thiosemicarbazones) and the rapid gallium-68 incorporation to give the corresponding metal complexes. These proved kinetically stable under 'cold' and 'hot' biological assays and were investigated using laser scanning confocal microscopy, flow cytometry and radioactive cell retention studies under normoxia and hypoxia. (68)Ga complex retention was found to be 34% higher in hypoxic cells than in normoxic cells over 30 min, further increasing to 53% at 120 min. Our data suggests that this class of gallium complexes show hypoxia selectivity suitable for imaging in living cells and in vivo tests by microPET in nude athymic mice showed that they are excreted within 1 h of their administration.

Heteronuclear NMR Spectroscopic Investigations of Gallium Complexes of Substituted Thiosemicarbazones Including X-Ray Crystal Structure, a New Halogen Exchange Strategy, and 18F Radiolabelling

Five thiosemicarbazone ligands have been synthesized, and their coordination chemistry with gallium was investigated. The reaction of these thiosemicarbazones with gallium chloride in alcohol solutions in the presence of a base yielded the corresponding penta-coordinated Ga-Cl metal complexes. In contrast, the reaction of gallium nitrate with the ligands in the presence of alkoxides resulted in the formation of the corresponding Ga-alkoxides, rather than the anticipated Ga-nitrate complex. The crystal structures of gallium chloride and gallium methoxide complexes of diphenylthiosemicarbazone comprise a planar configuration of the tetradentate-coordinated thiosemicarbazone with Ga3+ ion, with the chloride or methoxide groups occupying the apical coordination site. The corresponding ethoxido complex was also prepared in an identical fashion, and NMR analysis confirmed structural similarity to the methoxido complex. Facile halogen exchange reactions of the gallium chloride complexes were achieved by treatment with silver nitrate, followed by addition of KF or KI to generate the gallium fluoride and iodide complexes, respectively. This method of exchange using halogenated inorganic salts aids the preparation of group 13 fluorides, which are notoriously insoluble in organic solvents, for complexation with organic ligands. All compounds have been fully characterized by NMR, and the X-ray crystal structures of two of the complexes are reported. Additionally, the positron-emitting isotope 18F was introduced in the structure of the diphenyl gallium thiosemicarbazone complex.

Synthesis and biological evaluation of copper(ii) pyrenethiosemicarbazone

A fluorescent Cu(ii) pyrenethiosemicarbazone complex exhibits enhanced DNA-cleavage and cytotoxicity on photoexcitation.

Synthesis and structures of 5-nitro-salicylaldehyde thiosemicarb-azonates of copper(ii): molecular spectroscopy, ESI-mass studies, antimicrobial activity and cytotoxicity

Salicylaldehyde thiosemicarbazonates of copper(ii) have shown significant growth inhibitory activity againstS. aureus, MRSA,K. pneumonia,S. flexneri,P. aeruginosaandC. albicansand are bactericidal in nature with low cytotoxicity.

Mitochondrial metals as a potential therapeutic target in neurodegeneration

Transition metals are critical for enzyme function and protein folding, but in excess can mediate neurotoxic oxidative processes. As mitochondria are particularly vulnerable to oxidative damage due to radicals generated during ATP production, mitochondrial biometal homeostasis must therefore be tightly controlled to safely harness the redox potential of metal enzyme cofactors. Dysregulation of metal functions is evident in numerous neurological disorders including Alzheimer's disease, stroke, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis and Friedrich's ataxia. This review describes the mitochondrial metal defects in these disorders and highlights novel metal-based therapeutic approaches that target mitochondrial metal homeostasis in neurological disorders.

Crystal structure of (2E)-N-methyl-2-(2-oxo-1,2-di-hydroacenaphthylen-1-ylidene)hydrazinecarbo-thioamide

In the title compound, the acenapthylene ring system and the hydrazinecarbo­thio­amide unit (=N—NH—C=S—NH–) are essentially coplanar, making a dihedral angle of 1.59 (9)°. The mol­ecular conformation is stabilized by two weak intra­molecular hydrogen bonds (N—H⋯O and N—H⋯N), which generate S(6) and S(5) ring motifs.

In the title compound, C₁₄H₁₁N₃OS, the ace­naphthyl­ene ring system and hydrazinecarbo­thio­amide unit (=N—NH—C=S—NH–) are essentially coplanar [with maximum deviations from their mean planes of −0.009 (2) and 0.033 (2) Å, respectively], and make a dihedral angle of 1.59 (9)°. The mol­ecular conformation is stabilized by two weak intra­molecular hydrogen bonds (N—H⋯O and N—H⋯N), which generate S(6) and S(5) ring motifs. In the crystal, mol­ecules are linked by N—H⋯S hydrogen bonds, forming chains along [010]. The chains are linked via pairs of C—H⋯O hydrogen bonds, enclosing R²₂(10) ring motifs, and C—H⋯π inter­actions, forming a three-dimensional framework. The absolute structure of the title compound was determined by resonant scattering.

Molecular mechanisms of the biological activity of the anticancer drug elesclomol and its complexes with Cu(II), Ni(II) and Pt(II)

The bis(thiohydrazide) amide elesclomol has extremely potent antiproliferative activity and is currently in clinical trials as an anticancer agent. Elesclomol strongly binds copper and may be exerting its cell growth inhibitory effects by generating copper-mediated oxidative stress. Nickel(II) and platinum(II) complexes of elesclomol were synthesized and characterized in order to investigate if these biologically redox inactive metal complexes could also inhibit cell growth. The nickel(II)-elesclomol and platinum(II) elesclomol complexes were 34- and 1040-fold less potent than the copper(II)-elesclomol complex towards human leukemia K562 cells. These results support the conclusion that a redox active metal is required for elesclomol to exert its cell growth inhibitory activity. Copper(II)-elesclomol was also shown to efficiently oxidize ascorbic acid at physiological ascorbic acid concentrations. Reoxidation of the copper(I) thus produced would lead to production of damaging reactive oxygen species. An X-ray crystallographic structure determination of copper(II)-elesclomol showed that it formed a 1:1 neutral complex with a distorted square planar structure. The kinetics and equilibria of the competition reaction of the strong copper(II) chelator TRIEN with copper(II)-elesclomol were studied spectrophotometrically under physiological conditions. These results showed elesclomol bound copper(II) with a conditional stability constant 24-fold larger than TRIEN. A log stability constant of 24.2 was thus indirectly determined for the copper(II)-elesclomol complex.

The development of copper radiopharmaceuticals for imaging and therapy

The increasing use of positron emission tomography in preclinical and clinical settings has widened the demand for radiopharmaceuticals with high specificity that can image biological phenomena in vivo. While many PET tracers have been developed from small organic molecules labeled with carbon-11 or fluorine-18, the short half-lives of these radionuclides preclude their incorporation into radiotracers, which can be used to image biological processes that are not induced immediately after system perturbation. Additionally, the continuing development of targeted agents, such as antibodies and nanoparticles, which undergo extended circulation, require that radionuclides with half-lives that are complimentary to the biological half-lives of these molecules be developed. Copper radionuclides have received considerable attention since they offer a variety of half-lives and decay energies and because the coordination chemistry of cooper and its role in biology is well understood. However, in addition to the radiometal chelate, a successful copper based radiopharmaceutical depends upon the chemical structure of the entire radiotracer, which may include a biologically important molecule and a chemical linker that can be used to deliver the copper radionuclide to a specific target and modulate its in vivo properties, respectively. This review discusses the development of copper radiopharmaceuticals and the importance of factors such as chemical structure on their pharmacokinetics in vivo.

Fluorescent gallium and indium bis(thiosemicarbazonates) and their radiolabelled analogues: synthesis, structures and cellular confocal fluorescence imaging investigations

New fluorescent and biocompatible aromatic Ga(III)- and In(III)-bis(thiosemicarbazonato) complexes for dual mode optical and PET or SPECT molecular imaging have been synthesised via a synthetic method based on transmetallation reactions from Zn(II) precursors. Complexes have been fully characterised in the solid state by single crystal X-ray diffraction and in solution by spectroscopic methods (UV/Vis, fluorescence, (1)H and (13)C{(1)H} NMR). The bis(thiosemicarbazones) radiolabelled rapidly in high yields under mild conditions with (111)In (a gamma and Auger emitter for SPECT imaging and radiotherapy with t(1/2) = 2.8 d) and (68)Ga (a generator-available positron emitter for PET imaging with t(1/2) = 68 min). Cytotoxicity and biolocalisation studies using confocal fluorescence imaging and fluorescence lifetime imaging (FLIM) techniques have been used to study their in vitro activities and stabilities in HeLa and PC-3 cells to ascertain their suitability as synthetic scaffolds for future multimodality molecular imaging in cancer diagnosis and therapy. The observation that the indium complexes show certain nuclear uptake could be of relevance towards developing (111)In therapeutic agents based on Auger electron emission to induce DNA damage.

A novel zinc bis(thiosemicarbazone) complex for live cell imaging

Fluorescent zinc complexes have recently attracted a lot of interest owing to their vast applications in cellular imaging. We report the synthesis as well as physical, chemical and biological studies of a novel zinc glyoxalbis(4-methyl-4-phenyl-3-thiosemicarbazone), [Zn(GTSC)]₃, complex. As compared with the well-studied zinc biacetylbis(4-methyl-3-thiosemicarbazone), Zn(ATSM), complex, which was used as a reference, [Zn(GTSC)]₃ had 2.5-fold higher fluorescence. When cellular fluorescence was measured using flow cytometry, we observed that [Zn(GTSC)]₃ had 3.4-fold to 12-fold higher fluorescence than Zn(ATSM) in various cell lines (n = 9) of different tissue origin. Confocal fluorescence microscopy results showed that [Zn(GTSC)]₃ appeared to have a nuclear localization within 30 min of addition to MCF7 cells. Moreover, [Zn(GTSC)]₃ showed minimal cytotoxicity compared with Zn(ATSM), suggesting that [Zn(GTSC)]₃ may be less deleterious to cells when used as an imaging agent. Our data suggest that the novel [Zn(GTSC)]₃ complex can potentially serve as a biocompatible fluorescent imaging agent for live cells.