Towards molecular imaging and treatment of disease with radionuclides: the role of inorganic chemistry

Exploring Aqueous Coordination Chemistry of Highly Lewis Acidic Metals with Emerging Isotopes for Nuclear Medicine

Nuclear medicine harnesses radioisotopes for the diagnosis and treatment of disease. While the isotopes 99mTc and 111In have enabled the clinical diagnosis of millions of patients over the past 3 decades, more recent clinical translation of numerous 68Ga/177Lu-based radiopharmaceuticals for diagnostic imaging and therapy underscores the clinical utility of metal-based radiopharmaceuticals in mainstream cancer treatment. In addition to such established radionuclides, advancements in radioisotope production have enabled the production of radionuclides with a broad range of half-lives and emission properties of interest for nuclear medicine. Chemical means to form kinetically inert, in vivo-compatible species that can be modified with disease-targeting vectors is imperative. This presents a challenge for radiosiotopes of elements where the aqueous chemistry is still underdeveloped and poorly understood. Here, we discuss our efforts to date in exploring the aqueous, radioactive coordination chemistry of highly Lewis acidic metal ions and how our discoveries apply to the diagnosis and treatment of cancer in preclinical models of disease. The scope of this Account includes approaches to aqueous coordination of to-date understudied highly Lewis acidic metal ions with radioisotopes of emerging interest and the modulation of well-understood coordination environments of radio-coordination complexes to induce metal-catalyzed reactivity for separation and pro-drug applications.First, we discuss the development of seven-coordinate, small-cavity macrocyclic chelator platform mpatcn/picaga as an exemplary case study, which forms robust complexes with 44Sc/47Sc isotopes. Due to the high chemical hardness and pronounced Lewis acidity of the Sc3+ ion, the displacement of ternary ligand H2O by 18/natF- can be achieved to form an inert Sc-18/natF bond. Corresponding coordination complex natSc-18F is in vivo compatible and forms a theranostic tetrad with corresponding 44Sc/47Sc, 177Lu complexes all exhibiting homologous biodistribution profiles. Another exceptionally hard, highly Lewis acidic ion with underdeveloped aqueous chemistry and emerging interest in nuclear medicine is 45Ti4+. To develop de novo approaches to the mononuclear chelation of this ion under aqueous conditions, we employed a fragment-based bidentate ligand screening approach which identified two leads. The screen successfully predicted the formation of [45Ti][Ti(TREN-CAM)], a Ti-triscatechol complex that exhibits remarkable in vivo stability. Furthermore, the fragment-based screen also identified approaches that enabled solid-phase separation of Ti4+ and Sc3+ of interest in streamlining the isotope production of 45Ti and accessing new ways to separate 44Ti/44Sc for the development of a long-lived generator system. In addition to establishing the inert chelation of Ti4+ and Sc3+, we introduce controlled, metal-induced reactivity of corresponding coordination complexes on macroscopic and radiotracer scales. Metal-mediated autolytic amide bond cleavage (MMAAC) enables the temperature-dependent release of high-molar-activity, ready-to-inject radiopharmaceuticals; cleavage is selectively triggered by coordinated trivalent Lewis acid nat/68Ga3+ or Sc3+. Following the scope of reactivity and mechanistic studies, we validated MMAAC for the synthesis of high-molar-activity radiopharmaceuticals to image molecular targets with low expression and metal-mediated prodrug hydrolysis in vivo.This Account summarizes how developing the aqueous coordination chemistry and tuning the chemical reactivity of metal ions with high Lewis acidity at the macroscopic and tracer scales directly apply to the radiopharmaceutical synthesis with clinical potential.

Recent advances in the synthesis of (99mTechnetium) based radio-pharmaceuticals

Technetium radionuclide (99mTc) has excellent extent of disintegration properties and occupies a special place in the field of nuclear medicinal chemistry and other health disciplines. Current review describes recent approaches of synthesis in detailed ways for radio-pharmaceuticals of technetium which have been developed to treat and diagnose the biotic disorders. These technetium labeled radio-pharmaceuticals have been established to apply in the field of diagnostic nuclear medicine especially for imaging of different body parts such as brain, heart, kidney, bones and so on, through single photon emission computed tomography (SPECT) that is thought to be difficult to image such organs by using common X-ray and MRI (Magnetic Resonance Imaging) techniques. This review highlights and accounts an inclusive study on the various synthetic routes of technetium labeled radio-pharmaceuticals using ligands with various donor atoms such as carbon, nitrogen, sulphur, phosphorus etc. These compounds can be utilized as next generation radio-pharmaceuticals.

Controlling the reactivity of [Pd(II)(N^N^N)Cl]+ complexes using 2,6-bis(pyrazol-2-yl)pyridine ligands for biological application: Substitution reactivity, CT-DNA interactions and in vitro cytotoxicity study

Four [(N^N^N)Pd^(II)Cl]⁺ complexes [chloride-(2,2':6',2''-terpyridine)Pd(II)]Cl (PdL1), [chlorido(2,6-bis(N-pyrazol-2-yl)pyridine)Pd(II)]Cl (PdL2), [chlorido(2,6-bis(3,5-dimethyl-N-pyrazol-2-yl)pyridine)Pd(II)]Cl (PdL3) and [chlorido(2,6-bis(3,5-dimethyl-N-pyrazol-2-ylmethyl)pyridine)Pd(II)]BF₄ (PdL4) were synthesized and characterized. The rates of substitution of these Pd(II) complexes with thiourea nucleophiles viz; thiourea (Tu), N,N'-dimethylthiourea (Dmtu) and N,N,N',N'-tetramethylthiourea (Tmtu) was investigated under pseudo first-order conditions as a function of nucleophile concentration [Nu] and temperature using the stopped-flow technique. The observed rate constants vary linearly with [Nu]; k_obs = k₂[Nu] and decreased in the order: PdL1 > PdL2 > PdL3 ≫ PdL4. The lower π-acceptability of the cis-coordinated N-pyrazol-2-yl groups (which coordinates via pyrazollic-N π-donor atoms) of the PdL2-4 significantly decelerates the reactivity relative to PdL1. Furthermore, the six-membered chelates having methylene bridge in PdL4 do not allow π-extension in the ligand and introduces steric hindrance further lowering the reactivity. Trends in DFT calculated data supported the observed reactivity trend. Spectrophotometric titration data of complexes with calf thymus DNA (CT-DNA) and viscosity measurements of the resultant mixtures suggested that associative interactions occur between the complexes and CT-DNA, likely through groove binding with high binding constants (K_b = 10⁴ M^-1). In vitro MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] cytotoxic activity data showed that PdL1 was the most potent complex against MCF7 breast cancer cells; its IC₅₀ value is lower than that of cisplatin. The results demonstrate how modification of a spectator ligand can be used to slow down the reactivity of Pd(II) complexes. This is of special importance in controlling drug toxicity in both pharmaceutical and biomedical applications.

Visualizing Kinetically Robust CoIII4L6 Assemblies in Vivo: SPECT Imaging of the Encapsulated [99mTc]TcO4- Anion

Noncovalent encapsulation is an attractive approach for modifying the efficacy and physiochemical properties of both therapeutic and diagnostic species. Abiotic self-assembled constructs have shown promise, yet many hurdles between in vitro and (pre)clinical studies remain, not least the challenges associated with maintaining the macromolecular, hollow structure under nonequilibrium conditions. Using a kinetically robust Co^III₄L₆ tetrahedron we now show the feasibility of encapsulating the most widely used precursor in clinical nuclear diagnostic imaging, the γ-emitting [^99mTc]TcO₄^- anion, under conditions compatible with in vivo administration. Subsequent single-photon emission computed tomography imaging of the caged-anion reveals a marked change in the biodistribution compared to the thyroid-accumulating free oxo-anion, thus moving clinical applications of (metallo)supramolecular species a step closer.

Optimising the relaxivities of Mn2+ complexes by targeting human serum albumin (HSA)

We report two novel macrocyclic ligands based on the 1,4-DO2AM platform (1,4-DO2AM = 2,2'-(1,4,7,10-tetraazacyclododecane-1,4-diyl)diacetamide) and containing two benzyl groups attached either to the nitrogen atoms of the macrocyclic unit (1,4-BzDO2AM) or to the amide pendant arms (1,4-DO2AMBz). The protonation constants of the ligands and the stability constants of their Mn²⁺ complexes were determined using pH potentiometry. The introduction of benzyl groups results in a slight decrease of the stability constants of the Mn²⁺ complexes and a slight increase of their acid-catalysed dissociation reactions. A detailed relaxometric characterisation of the complexes using nuclear magnetic dispersion relaxation (NMRD) and ¹⁷O NMR studies indicated that the increase in molecular weight associated with the presence of benzyl groups results in a remarkable increase of proton relaxivities r_1p, which take values of 3.8, 3.5 and 2.5 mM^-1 s^-1 for [Mn(1,4-BzDO2AM)]²⁺, [Mn(1,4-DO2AMBz)]²⁺ and [Mn(1,4-DO2AM)]²⁺ (at 25 °C and 20 MHz). The [Mn(1,4-BzDO2AM)]²⁺ and [Mn(1,4-DO2AMBz)]²⁺ complexes form relatively strong adducts with Human Serum Albumin (HSA) with association constants of (3.9 ± 0.6) × 10³ and (2.0 ± 0.3) × 10³ M^-1, respectively. The interaction with the protein slows down the rotational tumbling of the complex in solution, which results in adducts endowed with remarkably high proton relaxivities (r_1p^b = 18.5 ± 0.7 and 27.4 ± 1.4 mM^-1 s^-1 for [Mn(1,4-BzDO2AM)]²⁺ and [Mn(1,4-DO2AMBz)]²⁺, respectively).

Copper complexes with dissymmetrically substituted bis(thiosemicarbazone) ligands as a basis for PET radiopharmaceuticals: control of redox potential and lipophilicity

Copper(ii) bis(thiosemicarbazone) derivatives have been used extensively in positron emission tomography (PET) to image hypoxia and blood flow and to radiolabel cells for cell tracking. These applications depend on control of redox potentials and lipophilicity of the bis(thiosemicarbazone) complexes, which can be adjusted by altering peripheral ligand substituents. This paper reports the synthesis of a library of new dissymmetrically substituted bis(thiosemicarbazone) ligands by controlling the condensation reactions between dicarbonyl compounds and 4-substituted-3-thiosemicarbazides or using acetal protection. Copper complexes of the new ligands have been prepared by reaction with copper acetate or via transmetallation of the corresponding zinc complexes, which are convenient precursors for the rapid synthesis of radio-copper complexes. Well-defined structure-activity relationships linking ligand alkylation patterns with redox potential and lipophilicity of the complexes are reported.

Gallium(III) chelates of mixed phosphonate-carboxylate triazamacrocyclic ligands relevant to nuclear medicine: Structural, stability and in vivo studies

Three triaza macrocyclic ligands, H₆NOTP (1,4,7-triazacyclononane-N,N',N″-trimethylene phosphonic acid), H₄NO2AP (1,4,7-triazacyclononane-N-methylenephosphonic acid-N',N″-dimethylenecarboxylic acid), and H₅NOA2P (1,4,7-triazacyclononane-N,N'-bis(methylenephosphonic acid)-N″-methylene carboxylic acid), and their gallium(III) chelates were studied in view of their potential interest as scintigraphic and PET (Positron Emission Tomography) imaging agents. A ¹H, ³¹P and ⁷¹Ga multinuclear NMR study gave an insight on the structure, internal dynamics and stability of the chelates in aqueous solution. In particular, the analysis of ⁷¹Ga NMR spectra gave information on the symmetry of the Ga³⁺ coordination sphere and the stability of the chelates towards hydrolysis. The ³¹P NMR spectra afforded information on the protonation of the non-coordinated oxygen atoms from the pendant phosphonate groups and on the number of species in solution. The ¹H NMR spectra allowed the analysis of the structure and the number of species in solution. ³¹P and ¹H NMR titrations combined with potentiometry afforded the measurement of the protonation constants (log K_Hi) and the microscopic protonation scheme of the triaza macrocyclic ligands. The remarkably high thermodynamic stability constant (log K_GaL=34.44 (0.04) and stepwise protonation constants of Ga(NOA2P)^2- were determined by potentiometry and ⁶⁹Ga and ³¹P NMR titrations. Biodistribution and gamma imaging studies have been performed on Wistar rats using the radiolabeled ⁶⁷Ga(NO2AP)^- and ⁶⁷Ga(NOA2P)^2-chelates, having both demonstrated to have renal excretion. The correlation of the molecular properties of the chelates with their pharmacokinetic properties has been analysed.

Copper-64 Radiopharmaceuticals for Oncologic Imaging

The positron emitting radionuclide (64)Cu has a radioactive half-life of 12.7 hours. The decay characteristics of (64)Cu allow for PET images that are comparable in quality to those obtained using (18)F. Given the longer radioactive half-life of (64)Cu compared with (18)F and the versatility of copper chemistry, copper is an attractive alternative to the shorter-lived nuclides for PET imaging of peptides, antibodies, and small molecules that may require longer circulation times. This article discusses a number of copper radiopharmaceuticals, such as Cu-ATSM, that have been translated to the clinic and new developments in copper-based radiopharmaceuticals.

Opportunities and challenges for metal chemistry in molecular imaging: from gamma camera imaging to PET and multimodality imaging

The development of medical imaging is a highly multidisciplinary endeavor requiring the close cooperation of clinicians, physicists, engineers, biologists and chemists to identify capabilities, conceive challenges and solutions and apply them in the clinic. The chemistry described in this article illustrates how synergistic advances in these areas drive the technology and its applications forward, with each discipline producing innovations that in turn drive innovations in the others. The main thread running through the article is the shift from single photon radionuclide imaging towards PET, and in turn the emerging shift from PET/CT towards PET/MRI and further, combination of these with optical imaging. Chemistry to support these transitions is exemplified by building on a summary of the status quo, and recent developments, in technetium-99m chemistry for SPECT imaging, followed by a report of recent developments to support clinical application of short lived (Ga-68) and long-lived (Zr-89) positron emitting isotopes, copper isotopes for PET imaging, and combined modality imaging agents based on radiolabelled iron oxide based nanoparticles.

Chelator free gallium-68 radiolabelling of silica coated iron oxide nanorods via surface interactions

The commercial availability of combined magnetic resonance imaging (MRI)/positron emission tomography (PET) scanners for clinical use has increased demand for easily prepared agents which offer signal or contrast in both modalities. Herein we describe a new class of silica coated iron-oxide nanorods (NRs) coated with polyethylene glycol (PEG) and/or a tetraazamacrocyclic chelator (DO3A). Studies of the coated NRs validate their composition and confirm their properties as in vivo T2 MRI contrast agents. Radiolabelling studies with the positron emitting radioisotope gallium-68 (t1/2 = 68 min) demonstrate that, in the presence of the silica coating, the macrocyclic chelator was not required for preparation of highly stable radiometal-NR constructs. In vivo PET-CT and MR imaging studies show the expected high liver uptake of gallium-68 radiolabelled nanorods with no significant release of gallium-68 metal ions, validating our innovation to provide a novel simple method for labelling of iron oxide NRs with a radiometal in the absence of a chelating unit that can be used for high sensitivity liver imaging.

Final step gallium-68 radiolabelling of silica-coated iron oxide nanorods as potential PET/MR multimodal imaging agents

The investigation of iron oxide-based positron emission tomography/magnetic resonance (PET/MR) multimodal imaging agents is an expanding field in which a variety of nanoparticle sizes, shapes, surface coatings and radioisotopes are open for exploration. This study develops iron oxide nanorods which are coated with various mixtures of poly(ethylene glycol) (PEG) and macrocyclic ligand (DO3A) via the formation of a silica layer on the surface. Gallium-68 radiolabelling of the nanorods was carried out in high radiochemical yields (RCY) and their stability in human serum was demonstrated for all constructs, even in the absence of the macrocyclic chelating unit. Further studies were carried out in an attempt to determine the appropriate amount of PEG coating to give optimal properties for future in vivo studies.

New p-tolylimido rhenium(v) complexes with carboxylate-based ligands: synthesis, structures and their catalytic potential in oxidations with peroxides

Novel p-tolylimido rhenium(v) complexes were obtained and calculations at the DFT level were undertaken. The complexes exhibited high catalytic activity in oxidation of alkanes and alcohols with H₂O₂ or TBHP.

Inorganic chemistry in nuclear imaging and radiotherapy: current and future directions

Radiometals play an important role in diagnostic and therapeutic radiopharmaceuticals. This field of radiochemistry is multidisciplinary, involving radiometal production, separation of the radiometal from its target, chelate design for complexing the radiometal in a biologically stable environment, specific targeting of the radiometal to its in vivo site, and nuclear imaging and/or radiotherapy applications of the resultant radiopharmaceutical. The critical importance of inorganic chemistry in the design and application of radiometal-containing imaging and therapy agents is described from a historical perspective to future directions.

Oriented immobilization of proteins on hydroxyapatite surface using bifunctional bisphosphonates as linkers

Oriented immobilization of proteins is an important step in creating protein-based functional materials. In this study, a method was developed to orient proteins on hydroxyapatite (HA) surfaces, a widely used bone implant material, to improve protein bioactivity by employing enhanced green fluorescent protein (EGFP) and β-lactamase as model proteins. These proteins have a serine or threonine at their N-terminus that was oxidized with periodate to obtain a single aldehyde group at the same location, which can be used for the site-specific immobilization of the protein. The HA surface was modified with bifunctional hydrazine bisphosphonates (HBPs) of various length and lipophilicity. The number of functional groups on the HBP-modified HA surface, determined by a 2,4,6-trinitrobenzenesulfonic acid (TNBS) assay, was found to be 2.8 × 10(-5) mol/mg of HA and unaffected by the length of HBPs. The oxidized proteins were immobilized on the HBP-modified HA surface in an oriented manner through formation of a hydrazone bond. The relative protein immobilization amounts through various HBPs were determined by fluorescence and bicinchoninic acid (BCA) assay and showed no significant effect by length and lipophilicity of HBPs. The relative amount of HBP-immobilized EGFP was found to be 10-15 fold that of adsorbed EGFP, whereas the relative amount of β-lactamase immobilized through HBPs (2, 3, 4, 6, and 7) was not significantly different than adsorbed β-lactamase. The enzymatic activity of HBP-immobilized β-lactamase was measured with cefazolin as substrate, and it was found that the catalytic efficiency of HBP-immobilized β-lactamase improved 2-5 fold over adsorbed β-lactamase. The results obtained demonstrate the feasibility of our oriented immobilization approach and showed an increased activity of the oriented proteins in comparison with adsorbed proteins on the same hydroxyapatite surface matrix.

Enhanced affinity bifunctional bisphosphonates for targeted delivery of therapeutic agents to bone

Skeletal diseases have a major impact on the worldwide population and economy. Although several therapeutic agents and treatments are available for addressing bone diseases, they are not being fully utilized because of their uptake in nontargeted sites and related side effects. Active targeting with controlled delivery is an ideal approach for treatment of such diseases. Because bisphosphonates are known to have high affinity to bone and are being widely used in treatment of osteoporosis, they are well-suited for drug targeting to bone. In this study, a targeted delivery of therapeutic agent to resorption sites and wound healing sites of bone was explored. Toward this goal, bifunctional hydrazine-bisphosphonates (HBPs), with spacers of various lengths, were synthesized and studied for their enhanced affinity to bone. Crystal growth inhibition studies showed that these HBPs have high affinity to hydroxyapatite, and HBPs with shorter spacers bind more strongly than alendronate to hydroxyapatite. The HBPs did not affect proliferation of MC3T3-E1 preosteoblasts, did not induce apoptosis, and were not cytotoxic at the concentration range tested (10(-6)-10(-4) M). Furthermore, drugs can be linked to the HBPs through a hydrazone linkage that is cleavable at the low pH of bone resorption and wound healing sites, leading to release of the drug. This was demonstrated using hydroxyapatite as a model material of bone and 4-nitrobenzaldehyde as a model drug. This study suggests that these HBPs could be used for targeted delivery of therapeutic agents to bone.

fac-[TcO3(tacn)]+: a versatile precursor for the labelling of pharmacophores, amino acids and carbohydrates through a new ligand-centred labelling strategy

Herein, we report a protocol for the synthesis of [(99m)TcO(3)(tacn)](+) ([1](+)) (tacn = 1,4,7-triazacyclononane) that is suitable for clinical translation. Bioconjugates containing pharmacophores ([TcO(NO(2)-Imi)(tacn)](+); [3](+)), artificial amino acids ([TcO(Fmoc-allyl-His)(tacn)](+); [5](+)), and glucose derivatives ([TcO(allyl-tetraacetylglucose)(tacn)](+); [7](+)) were synthesized by cycloaddition strategies and fully characterized ((99)Tc and (99m)Tc). These new technetium complexes are stable at neutral pH and demonstrate the potential and flexibility of the [3+2] cycloaddition labelling concept. In addition to the synthetic work, the first biodistribution studies of [1](+) and the small [3+2] cycloadduct [(99m)TcO(NO(2)-Imi)(tacn)](+) ([3](+)) were completed. The biodistribution studies suggest the stability of these complexes in vivo. Furthermore, it was demonstrated that the high hydrophilicity of the [(99m)TcO(3)(tacn)](+) building block is a complement to the complexes of the fac-{Tc(CO)(3)}(+) core.

Metallic radionuclides in the development of diagnostic and therapeutic radiopharmaceuticals

Metallic radionuclides are the mainstay of both diagnostic and therapeutic radiopharmaceuticals. Therapeutic nuclear medicine is less advanced but has tremendous potential if the radionuclide is accurately targeted. Great interest exists in the field of inorganic chemistry for developing target specific radiopharmaceuticals based on radiometals for non-invasive disease detection and cancer radiotherapy. This perspective will focus on the nuclear properties of a few important radiometals and their recent applications to developing radiopharmaceuticals for imaging and therapy. Other topics for discussion will include imaging techniques, radiotherapy, analytical techniques, and radiation safety. The ultimate goal of this perspective is to introduce inorganic chemists to the field of nuclear medicine and radiopharmaceutical development, where many applications of fundamental inorganic chemistry can be found.

A practical guide to the construction of radiometallated bioconjugates for positron emission tomography

Positron emission tomography (PET) has become a vital imaging modality in the diagnosis and treatment of disease, most notably cancer. A wide array of small molecule PET radiotracers have been developed that employ the short half-life radionuclides (11)C, (13)N, (15)O, and (18)F. However, PET radiopharmaceuticals based on biomolecular targeting vectors have been the subject of dramatically increased research in both the laboratory and the clinic. Typically based on antibodies, oligopeptides, or oligonucleotides, these tracers have longer biological half-lives than their small molecule counterparts and thus require labeling with radionuclides with longer, complementary radioactive half-lives, such as the metallic isotopes (64)Cu, (68)Ga, (86)Y, and (89)Zr. Each bioconjugate radiopharmaceutical has four component parts: biomolecular vector, radiometal, chelator, and covalent link between chelator and biomolecule. With the exception of the radiometal, a tremendous variety of choices exists for each of these pieces, and a plethora of different chelation, conjugation, and radiometallation strategies have been utilized to create agents ranging from (68)Ga-labeled pentapeptides to (89)Zr-labeled monoclonal antibodies. Herein, the authors present a practical guide to the construction of radiometal-based PET bioconjugates, in which the design choices and synthetic details of a wide range of biomolecular tracers from the literature are collected in a single reference. In assembling this information, the authors hope both to illuminate the diverse methods employed in the synthesis of these agents and also to create a useful reference for molecular imaging researchers both experienced and new to the field.

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.

Challenges in chelating positron emitting copper isotopes: tailored synthesis of unsymmetric chelators to form ultra stable complexes

The synthesis of chelators that form high stability complexes with copper(II) isotopes and do not suffer from transchelation in vivo has been a goal for many chemists. Such chelators will facilitate the exploitation of the (64)Cu isotope (t(1/2) = 12.7 h, β(+) (19%); β(-) (39%); EC (41%)) for positron emission tomography imaging studies, which has a longer half life relative to the more commonly used (18)F (t(1/2) = 109.8 min) and (11)C (t(1/2) = 20.4 min) isotopes. One option is the CBTE2A chelator, which has been championed by Weisman, Wong and Anderson, and, more recently, alternate bifunctional chelator (BFC) versions have been synthesised. Improved synthetic methods are required for unsymmetric derivatisation of these chelators to allow more selective biomolecule attachment. This work investigates synthetic routes to form new unsymmetric chelating ligands via stepwise reaction of the bisaminal precursor, determines their X-ray structures and demonstrates cold copper(II) isotope complex formation.

Rhenium(IV) compounds inducing apoptosis in cancer cells

The anticancer properties of a series of mononuclear Re(IV) compounds of formula ReCl(4)L (where L is bpy = 2,2'-bipyridine; bpym = 2,2'-bipyrimidine; dmbpy = 4,4'-dimethyl-2,2'-bipyridine; phen = 1,10-phenanthroline) were investigated for the first time. All compounds displayed potent in vitro antiproliferative activity against selected cancer cells.