Complexation of histone deacetylase inhibitor belinostat to Cu(II) prevents premature metabolic inactivation in vitro and demonstrates potent anti-cancer activity in vitro and ex vivo in colon cancer.

PURPOSE: The histone deacetylase inhibitor (HDACi), belinostat, has had limited therapeutic impact in solid tumors, such as colon cancer, due to its poor metabolic stability. Here we evaluated a novel belinostat prodrug, copper-bis-belinostat (Cubisbel), in vitro and ex vivo, designed to overcome the pharmacokinetic challenges of belinostat. METHODS: The in vitro metabolism of each HDACi was evaluated in human liver microsomes (HLMs) using mass spectrometry. Next, the effect of belinostat and Cubisbel on cell growth, HDAC activity, apoptosis and cell cycle was assessed in three colon cancer cell lines. Gene expression alterations induced by both HDACis were determined using RNA-Seq, followed by in silico analysis to identify master regulators (MRs) of differentially expressed genes (DEGs). The effect of both HDACis on the viability of colon cancer patient-derived tumor organoids (PDTOs) was also examined. RESULTS: Belinostat and Cubisbel significantly reduced colon cancer cell growth mediated through HDAC inhibition and apoptosis induction. Interestingly, the in vitro half-life of Cubisbel was significantly longer than belinostat. Belinostat and its Cu derivative commonly dysregulated numerous signalling and metabolic pathways while genes downregulated by Cubisbel were potentially controlled by VEGFA, ERBB2 and DUSP2 MRs. Treatment of colon cancer PDTOs with the HDACis resulted in a significant reduction in cell viability and downregulation of stem cell and proliferation markers. CONCLUSIONS: Complexation of belinostat to Cu(II) does not alter the HDAC activity of belinostat, but instead significantly enhances its metabolic stability in vitro and targets anti-cancer pathways by perturbing key MRs in colon cancer. Complexation of HDACis to a metal ion might improve the efficacy of clinically used HDACis in patients with colon cancer.

Multi-targeted metallo-ciprofloxacin derivatives rationally designed and developed to overcome antimicrobial resistance.

Antimicrobial resistance is a major global threat to human health due to the rise, spread and persistence of multi-drug-resistant bacteria or 'superbugs'. There is an urgent need to develop novel chemotherapeutics to overcome this overarching challenge. The authors derivatized a clinically used fluoroquinolone antibiotic ciprofloxacin (Cip), and complexed it to a copper phenanthrene framework. This resulted in the development of two novel metallo-antibiotics of general formula [Cu(N,N)(CipHA)]NO3 where N,N represents a phenanthrene ligand and CipHA represents a hydroxamic acid of Cip derivative. Comprehensive studies, including a detailed proteomic study in which Staphylococcus aureus cells were exposed to the complexes, were undertaken to gain an insight into their mode of action. These new complexes possess potent antibacterial activity against S. aureus and methicillin-resistant S. aureus. In addition, they were found to be well tolerated in vivo in Galleria mellonella larvae, which has both functional and structural similarities to the innate immune system of mammals. These findings suggest that proteins involved in virulence, pathogenesis, and the synthesis of nucleotides and DNA repair mechanisms are most affected. In addition, both complexes affected similar cell pathways when compared with clinically used Cip, including cationic antimicrobial peptide resistance. The Cu-DPPZ-CipHA (DPPZ = dipyrido[3,2-a:2',3'-c]phenazine) analogue also induces cell leakage, which leads to an altered proteome indicative of reduced virulence and increased stress.

Vorinostat and Belinostat, hydroxamate-based anti-cancer agents, are nitric oxide donors.

Vorinostat (suberoylanilide hydroxamic acid; SAHA) and Belinostat are two hydroxamate-based histone deacetylase inhibitors that are used clinically as potent anti-cancer agents. Their metabolic breakdown into inactive metabolites such as carboxylic acid and glucuronic derivatives results in them having short half-lives, which can negatively impact their pharmacokinetic profiles. Herein we report the potential of both Vorinostat and Belinostat to also act as nitric oxide donors under both chemical and biological ex vivo experimental conditions. More specifically, using ruthenium(III) as an effective NO scavenger, we were able to establish, in the first instance, that both Vorinostat and Belinostat had the capacity to release NO under chemical conditions. Both Vorinostat and Belinostat were then shown to cause vascular relaxation of rat aorta via NO-mediated activation of the haem-containing guanylate cyclase enzyme. A summary of our findings is reported herein.

A new class of prophylactic metallo-antibiotic possessing potent anti-cancer and anti-microbial properties.

Immunocompromised cancer patients are often at high risk of developing infections. Standard infection control measures are required to prevent the onset of infection but, under some circumstances, antimicrobial prophylaxis is necessary. We have developed a family of innovative metallo-antibiotics of general formula [Cu(N,N)(CipA)Cl] where N,N represents a phenanthrene ligand and CipA stands for a derivative of the clinically used fluoroquinolone antibiotic ciprofloxacin. The X-ray crystal structure of one member from this family, [Cu(phen)(CipA)Cl] (where phen is 1,10-phenanthroline), is also reported. These complexes combine into one drug entity a Cu-N,N-framework with DNA binding and DNA oxidant properties and an antibiotic derivative with known anti-proliferative and anti-microbial activities. The complexes were all found to exhibit excellent DNA recognition with binding affinity of lead agents in the order of ∼107 M(bp)-1. Biophysical studies involving calf thymus DNA indicate the complexes intercalate or semi-intercalate DNA via the minor groove. All complexes exhibited excellent nuclease activity with DNA strand scission being mediated predominantly via superoxide and hydroxyl radicals. The complexes were found to have promising anti-proliferative effects against a human breast adenocarcinoma cell line (MCF-7) and a human prostate carcinoma cell line (DU145) with low micromolar and, in some cases, nanomolar cytotoxicities observed. Selective targeting of Gram positive bacteria was also identified by this complex class with one lead compound having an order of magnitude greater potency against Methicillin-resistant S. aureus (MRSA) as compared to the CipA ligand. Importantly, from a clinical stand point, these complexes were also found to be well tolerated in an in vivo Galleria mellonella larvae model, which has both functional and structural similarities to that of the innate immune system of mammals.

Toward Multi-Targeted Platinum and Ruthenium Drugs-A New Paradigm in Cancer Drug Treatment Regimens?

While medicinal inorganic chemistry has been practised for over 5000 years, it was not until the late 1800s when Alfred Werner published his ground-breaking research on coordination chemistry that we began to truly understand the nature of the coordination bond and the structures and stereochemistries of metal complexes. We can now readily manipulate and fine-tune their properties. This had led to a multitude of complexes with wide-ranging biomedical applications. This review will focus on the use and potential of metal complexes as important therapeutic agents for the treatment of cancer. With major advances in technologies and a deeper understanding of the human genome, we are now in a strong position to more fully understand carcinogenesis at a molecular level. We can now also rationally design and develop drug molecules that can either selectively enhance or disrupt key biological processes and, in doing so, optimize their therapeutic potential. This has heralded a new era in drug design in which we are moving from a single- toward a multitargeted approach. This approach lies at the very heart of medicinal inorganic chemistry. In this review, we have endeavored to showcase how a "multitargeted" approach to drug design has led to new families of metallodrugs which may not only reduce systemic toxicities associated with modern day chemotherapeutics but also address resistance issues that are plaguing many chemotherapeutic regimens. We have focused our attention on metallodrugs incorporating platinum and ruthenium ions given that complexes containing these metal ions are already in clinical use or have advanced to clinical trials as anticancer agents. The "multitargeted" complexes described herein not only target DNA but also contain either vectors to enable them to target cancer cells selectively and/or moieties that target enzymes, peptides, and intracellular proteins. Multitargeted complexes which have been designed to target the mitochondria or complexes inspired by natural product activity are also described. A summary of advances in this field over the past decade or so will be provided.

Innovative DNA-Targeted Metallo-prodrug Strategy Combining Histone Deacetylase Inhibition with Oxidative Stress.

Cancer remains a global health challenge. There is an urgent need to develop innovative therapeutics that can overcome the shortcomings of existing cancer therapies. DNA enzymes involved in nucleic acid compaction and organization are an attractive cancer drug target for therapeutic exploitation. In this work, a family of Cu(II) prodrugs containing suberoylanilide hydroxamic acid (SAHA), a well-established histone deacetylase inhibitor (HDACi) and clinically approved cancer drug, and phenanthrene ligands as DNA intercalative components have been rationally developed. The complexes, of general formula [Cu(SAHA-1H)( N, N'-phenanthrene)]+, exhibit excellent DNA recognition with binding affinity of lead agents in the order of ∼107 M(bp)-1. Biophysical studies involving nucleic acid polymers indicate intercalative binding at both adenine-thymine (A-T) and guanine-cytosine (G-C) rich sequences but thermodynamically stable interactions are favored in G-C tracts. The complexes mediate DNA damage by producing reactive oxygen species (ROS) with spin trapping experiments showing that superoxide, the hydroxyl radical, and hydrogen peroxide play critical roles in strand scission. The agents were found to have promising antiproliferative effects against a panel of epithelial cancers, and in two representative cell lines possessing mutated p53 (SK-OV-3 and DU145), enhanced cytotoxicity was observed. Significantly, mechanistic experiments with the most promising candidates revealed HDAC inhibition activity was achieved over a shorter time frame as compared to clinical standards with DNA damage-response markers identifying upregulation of both DNA synthesis and nucleotide excision repair (NER) pathways. Finally, confocal imaging and gene expression analysis show this metallodrug class exerts cytotoxic activity predominantly through an apoptotic pathway.

A novel dual-functioning ruthenium(II)-arene complex of an anti-microbial ciprofloxacin derivative - Anti-proliferative and anti-microbial activity.

7-(4-(Decanoyl)piperazin-1-yl)-ciprofloxacin, CipA, (1) which is an analogue of the antibiotic ciprofloxacin, and its ruthenium(II) complex [Ru(η(6)-p-cymene)(CipA-H)Cl], (2) have been synthesised and the x-ray crystal structures of 1·1.3H2O·0.6CH3OH and 2·CH3OH·0.5H2O determined. The complex adopts a typical pseudo-octahedral 'piano-stool' geometry, with Ru(II) π-bonded to the p-cymene ring and σ-bonded to a chloride and two oxygen atoms of the chelated fluoroquinolone ligand. The complex is highly cytotoxic in the low µM range and is as potent as the clinical drug cisplatin against the human cancer cell lines A2780, A549, HCT116, and PC3. It is also highly cytotoxic against cisplatin- and oxaliplatin-resistant cell lines suggesting a different mechanism of action. The complex also retained low µM cytotoxicity against the human colon cancer cell line HCT116p53 in which the tumour suppressor p53 had been knocked out, suggesting that the potent anti-proliferative properties associated with this complex are independent of the status of p53 (in contrast to cisplatin). The complex also retained moderate anti-bacterial activity in two Escherichia coli, a laboratory strain and a clinical isolate resistant to first, second and third generation ß-lactam antibiotics.

Exploiting developments in nanotechnology for the preferential delivery of platinum-based anti-cancer agents to tumours: targeting some of the hallmarks of cancer.

Platinum drugs as anti-cancer therapeutics are held in extremely high regard. Despite their success, there are drawbacks associated with their use; their dose-limiting toxicity, their limited activity against an array of common cancers and patient resistance to Pt-based therapeutic regimes. Current investigations in medicinal inorganic chemistry strive to offset these shortcomings through selective targeting of Pt drugs and/or the development of Pt drugs with new or multiple modes of action. A comprehensive overview showcasing how liposomes, nanocapsules, polymers, dendrimers, nanoparticles and nanotubes may be employed as vehicles to selectively deliver cytotoxic Pt payloads to tumour cells is provided.

A novel platinum complex of the histone deacetylase inhibitor belinostat: rational design, development and in vitro cytotoxicity.

The successful design and synthesis of a novel Pt complex of the histone deacteylase inhibitor belinostat are reported. Molecular modelling assisted in the identification of a suitable malonate derivative of belinostat (mal-p-Bel) for complexation to platinum. Reaction of [Pt(NH3)2(H2O)2](NO3)2 with the disodium salt of mal-p-Bel gave cis-[Pt(NH3)2(mal-p-Bel-2H)] (where -2H indicates that mal-p-Bel is doubly deprotonated) in excellent yield. An in vitro cytotoxicity study revealed that cis-[Pt(NH3)2(mal-p-Bel-2H)] possesses (i) considerable cytotoxicity against reported ovarian cancer cell lines, (ii) enhanced cytotoxicity relative to the previously reported Pt histone deacetylase inhibitor conjugate, cis-[Pt(II)(NH3)2(malSAHA-2H)] and (iii) favourable cyto-selective properties as compared to cisplatin and belinostat.

Valuable insight into the anticancer activity of the platinum-histone deacetylase inhibitor conjugate, cis-[Pt(NH3)2malSAHA-2H)].

cis-[Pt(II)(NH3)2(malSAHA-2H)], a cisplatin adduct conjugated to a potent histone deacetylase inhibitor (HDACi), suberoylanilide hydroxamic acid (SAHA), was previously developed as a potential anticancer agent. This Pt-HDACi conjugate was demonstrated to have comparable cytotoxicity to cisplatin against A2780 ovarian cancer cells but significantly reduced cytotoxicity against a representative normal cell line, NHDF. Thus, with a view to (i) understanding more deeply the effects that may play an important role in the biological (pharmacological) properties of this new conjugate against cancer cells and (ii) developing the next generation of Pt-HDACi conjugates, the cytotoxicity, DNA binding, cellular accumulation and HDAC inhibitory activity of cis-[Pt(II)(NH3)2(malSAHA-2H)] were investigated and are reported herein. cis-[Pt(II)(NH3)2(malSAHA-2H)] was found to have marginally lower cytotoxicity against a panel of cancer cell lines as compared to cisplatin and SAHA. cis-[Pt(II)(NH3)2(malSAHA-2H)] was also found to accumulate better in cancer cells but bind DNA less readily as compared to cisplatin. DNA binding experiments indicated that cis-[Pt(II)(NH3)2(malSAHA-2H)] bound DNA more effectively in cellulo as compared to in cell-free media. Activation of the Pt-HDACi conjugate was therefore investigated. The binding of cis-[Pt(II)(NH3)2(malSAHA-2H)] to DNA was found to be enhanced by the presence of thiol-containing molecules such as glutathione and thiourea, and activation occurred in cytosolic but not nuclear extract of human cancer cells. The activity of cis-[Pt(NH3)2(malSAHA-2H)] as a HDAC inhibitor was also examined; the conjugate exhibited no inhibition of HDAC activity in CH1 cells. In light of these results, novel Pt-HDACi conjugates are currently being developed, with particular emphasis, through subtle structural modifications, on enhancing the rate of DNA binding and enhancing HDAC inhibitory activity.

Suberoylanilide hydroxamic acid, a potent histone deacetylase inhibitor; its X-ray crystal structure and solid state and solution studies of its Zn(II), Ni(II), Cu(II) and Fe(III) complexes.

Reaction of the potent hydroxamate-based histone deacetylase (HDAC) inhibitor, suberoylanilide hydroxamic acid (SAHA), with hydrated metal salts of Fe(III), Cu(II), Ni(II) and Zn(II) yielded a tris-hydroxamato complex in the case of Fe(III) and bis-hydroxamato complexes in the case of Cu(II), Ni(II) and Zn(II) both in the solid state and in solution. Reaction of the secondary hydroxamic acid, N-Me-SAHA, also yielded a tris-hydroxamato complex in the case of Fe(III) and bis-hydroxamato complexes in the case of Cu(II), Ni(II) and Zn(II) in solution. These metal complexes have the hydroxamato moiety coordinated in an O,O'-bidentate fashion. Stability constants of the metal complexes formed with SAHA and N-Me-SAHA in a DMSO/H(2)O 70/30%(v/v) mixture are described. A novel crystal structure of SAHA together with a novel synthesis for N-Me-SAHA are also reported.

Novel trans-platinum complexes of the histone deacetylase inhibitor valproic acid; synthesis, in vitro cytotoxicity and mutagenicity.

The first examples of Pt complexes of the well known anti-epilepsy drug and histone deacetylase inhibitor, valproic acid (VPA), are reported. Reaction of the Pt(II) am(m)ine precursors trans-[PtCl(2)(NH(3))(py)] and trans-[PtCl(2)(py)(2)] with silver nitrate and subsequently sodium valproate gave trans-[Pt(VPA(-1H))(2)(NH(3))(py)] and trans-[Pt(VPA(-1H))(2)(py)(2)], respectively. The valproato ligands in both complexes are bound to the Pt(II) centres via the carboxylato functionality and in a monodentate manner. The X-ray crystal structure of trans-[Pt(VPA(-1H))(2)(NH(3))(py)] is described. Replacement of the dichlorido ligands in trans-[PtCl(2)(py)(2)] and trans-[PtCl(2)(NH(3))(py)] by valproato ligands (VPA(-1H)) to yield trans-[Pt(VPA(-1H))(2)(py)(2)] and trans-[Pt(VPA(-1H))(2)(NH(3))(py)] respectively, significantly enhanced cytotoxicity against A2780 (parental) and A2780 cisR (cisplatin resistant) ovarian cancer cells. The mutagenicity of trans-[Pt(VPA(-1H))(2)(NH(3))(py)] and trans-[Pt(VPA(-1H))(2)(py)(2)] was determined using the Ames test and is also reported.

Enzyme inhibition as a key target for the development of novel metal-based anti-cancer therapeutics.

Historically, DNA has been the target for many metal-based anti-cancer drugs, but drawbacks of prevailing therapies have stimulated the search for new molecular targets which may present unique opportunities for therapeutic exploitation. Enzyme inhibition has recently been identified as an alternative and significant target. The pursuit of novel metallodrug candidates that selectively target enzymes is now the subject of intense investigation in medicinal bioinorganic chemistry and chemical biology. In the field of drug design, it is recognised by many that exploiting the structural and chemical diversity of metal ions for the identification of potential hit and lead candidates can dramatically increase the number of possible drug candidates that may be added to the already abundant armoury of chemotherapeutic agents. This review will focus on recent key advancements in enzyme inhibition as a key target for the development of novel metal-based anti-cancer therapeutics. The enormous clinical success of classical platinum drugs, amongst others, coupled with the wealth of knowledge accumulated in recent years on enzyme structure and function, has undoubtedly been the impetus behind the development of new metallodrug candidates with enzyme inhibitory properties. Recent trends in this field will be reviewed with a particular emphasis on metal complexes that inhibit protein and lipid kinases, matrix metalloproteases, telomerases, topoisomerases, glutathione-S-transferases, and histone deacetylases.

A novel anti-cancer bifunctional platinum drug candidate with dual DNA binding and histone deacetylase inhibitory activity.

The successful design and synthesis of a novel multifunctional platinum drug candidate with DNA binding, histone deacetylase inhibitory activity and enhanced selectivity for cancer cells are described.

The reduction of platinum(IV) and palladium(IV) ions by 2,6-pyridinedihydroxamic acid.

Reaction of K(2)[Pt(IV)Cl(6)] and K(2)[Pd(IV)Cl(6)] with 2,6-pyridinedihydroxamic acid (2,6-pyha) and its disodium salt, 2,6-pyhaNa(2), yielded not the desired Pt(IV) and Pd(IV) 2,6-pyridinedihydroxamato complexes, but rather the Pt(II) and Pd(II) 2,6-pyridinedicarboxylato complexes, trans-[Pt(II)(2,6-pyca(H-1))(2)].2H(2)O and trans-[Pd(II)(2,6-pyca(H-1))(2)].2H(2)O respectively (2,6-pyca = 2,6-pyridinedicarboxylic acid). Thus in the presence of Pt(IV) and Pd(IV), the dihydroxamic acid was adventitiously hydrolysed to the corresponding dicarboxylic acid and Pt(IV) and Pd(IV) reduced to Pt(II) and Pd(II) in situ. The X-ray crystal structures of 2,6-pyha, 2,6-pyhaNa(2).8H(2)O, trans-[Pt(II)(2,6-pyca(H-1))(2)].2H(2)O and trans-[Pd(II)(2,6-pyca(H-1))(2)].2H(2)O are reported, together with a possible mechanism for the metal-assisted hydrolysis of the dihydroxamic acid and reduction of Pt(IV) and Pd(IV) to Pt(II) and Pd(II) respectively.

Monohydroxamic acids and bridging dihydroxamic acids as chelators to ruthenium(III) and as nitric oxide donors: syntheses, speciation studies and nitric oxide releasing investigations.

The synthesis and spectroscopic characterisation of novel mononuclear Ru(III)(edta)(hydroxamato) complexes of general formula [Ru(H2edta)(monoha)] (where monoha = 3- or 4-NH2, 2-, 3- or 4-C1 and 3-Me-phenylhydroxamato), as well as the first example of a Ru(III)-N-aryl aromatic hydroxamate, [Ru(H2edta)(N-Me-bha)].H2O (N-Me-bha = N-methylbenzohydroxamato) are reported. Three dinuclear Ru(III) complexes with bridging dihydroxamato ligands of general formula [{Ru(H2edta)}2(mu-diha)] where diha = 2,6-pyridinedihydroxamato and 1,3- or 1,4-benzodihydroxamato, the first of their kind with Ru(III), are also described. The speciation of all of these systems (with the exception of the Ru-1,4-benzodihydroxamic acid and Ru-N-methylbenzohydroxamic systems) in aqueous solution was investigated. We previously proposed that nitrosyl abstraction from hydroxamic acids by Ru(III) involves initial formation of Ru(III)-hydroxamates. Yet, until now, no data on the rate of nitric oxide (NO) release from hydroxamic acids has been published. We now describe a UV-VIS spectroscopic study, where we monitored the decrease in the ligand-to-metal charge-transfer band of a series of Ru(III)-monohydroxamates with time, with a view to gaining an insight into the NO-releasing properties of hydroxamic acids.

Ruthenium(III) dimethyl sulfoxide pyridinehydroxamic acid complexes as potential antimetastatic agents: synthesis, characterisation and in vitro pharmacological evaluation.

Reaction of 3-pyridinehydroxamic acid and 4-pyridinehydroxamic acid (3-pyha and 4-pyha) with either [NBu4][RuCl4(dmso-S)2] or [(dmso)2H][RuCl4(dmso-S)2] (dmso is dimethyl sulfoxide) in acetone afforded three new ruthenium(III) dimethyl sulfoxide pyridinehydroxamic acid complexes: [NBu4][trans-RuCl4(dmso-S)(4-pyha)] x CH3CO CH3 (1), [3-pyhaH][trans-RuCl4(dmso-S)(3-pyha)] (2) and [4-pyhaH][trans-RuCl4(dmso-S)(4-pyha)] (3). The solid-state structure of [NBu4][trans-RuCl4(dmso-S)(4-pyha)] x CH3COCH3 (1) was determined by X-ray crystallography. 2 and 3 were pharmacologically evaluated for their in vitro cytotoxicity, their ability to inhibit cell invasion and their gelatinase activity. 2 and 3 were devoid of cytotoxicity against the cell lines tested. 2 inhibited invasion of the highly invasive MDA-MB-231 cells to a much greater extent than 3. Contrary to expectations, neither 2 nor 3 had any inhibitory effect on matrix metalloproteinase (MMP) production and/or activity and in fact 3 was found to enhance the production and/or activity of both MMP-2 and MMP-9.

Synthesis, characterisation and speciation studies of heterobimetallic pyridinehydroxamate-bridged Pt(II)/M(II) complexes (M = Cu, Ni, Zn). Crystal structure of a novel heterobimetallic 3-pyridinehydroxamate-bridged Pt(II)/Cu(II) wave-like coordination polymer.

The reaction of cis-[Pt(NH3)2(3-pyhaH)2]2+ (3-pyhaH = 3-pyridinehydroxamic acid) and cis-[Pt(NH3)2(4-pyhaH)2]2+ (4-pyhaH = 4-pyridinehydroxamic acid) with Cu(II), Ni(II) or Zn(II) in aqueous solution affords novel heterobimetallic pyridinehydroxamate-bridged complexes, {cis-[Pt(NH3)2(mu-3-pyha)M(mu-3-pyha)].SO4.xH2O}n and {cis-[Pt(NH3)2(mu-4-pyha)M(mu-4-pyha)].SO4.xH2O}n respectively. The crystal and molecular structure of one of these, {cis-[Pt(NH3)2(mu-3-pyha)Cu(mu-3-pyha)]SO4.8H2O}n 3a, has been determined and was found to be a novel heterobimetallic wave-like coordination polymer, the structure of which contains interlinked pyridinehydroxamate-bridged repeating units of Pt(II) and Cu(II) ions in slightly distorted square-planar N4 and O4 coordination environments respectively and extensive hydrogen-bonding through the Pt ammines and the deprotonated hydroxamate O and via the O of the SO4(2-) counterions and the H(N) of the hydroxamate moiety. Spectrophotometric and speciation studies on the other heterobimetallic systems confirm that very similar species are being formed in solution and based on elemental analysis and spectroscopic results analogous complexes are formed in the solid-state. In this paper, we report the first examples of coordination polymers incorporating both Pt(II)/Cu(II), Pt(II)/Ni(II) and Pt(II)/Zn(II) and containing pyridinehydroxamic acids as bridging scaffolds.

Novel platinum(II) ammine hydroxamate and hydroximate complexes and the platinum-assisted hydrolysis of hydroxamic acids.

The 2-pyridinecarboxylate (2-pyca) platinum(IV) complex [2-pycaH2][PtCl4(2-pyca)].H2O, 1, has been synthesised from K2[PtCl4] following the hydrolysis of 2-pyridinehydroxamic acid (2-pyhaH) in the presence of H2O2, and directly from K2[PtCl6] and picolinic acid. Structural characterisation of 1 reveals octahedral geometry about platinum(IV) consisting of a (N,O)-bidentate pyridinecarboxylate ligand and four chloride ligands. A mechanism for the hydrolysis of 2-pyridinehydroxamic acid to 2-pyridinecarboxylic acid is proposed. Two novel coordination modes of hydroxamic acids to platinum(II) are also reported. The dinuclear platinum ammine hydroximato complex, [{cis-Pt(NH3)2}2(mu-2-pyhaH(-1))](ClO4)2.H2O, 3, has been synthesised where the two platinum(II) centres are bridged via(O,O) and (N,N) coordination. The latter coordination mode is via the hydroximate nitrogen and the pyridine nitrogen. The corresponding mononuclear platinum(II) pyridinehydroxamate complex, [cis-Pt(NH3)2(2-pyha)]ClO4, 4, has been synthesised. Spectroscopic studies indicate that the coordination mode is through the pyridine nitrogen and hydroxamate oxygen atoms (N,O).

Ruthenium as an effective nitric oxide scavenger.

Whilst nitric oxide (NO) has emerged as one of the most versatile and ubiquitous molecules in the human body with a diverse range of physiological functions, dysfunction in NO biosynthesis or metabolism has led to the pathogenesis of a number of disease states. A variety of therapeutic strategies have therefore emerged that either reduce or increase endogenous NO levels depending on the disease pathology. The predominant strategy to date to reduce levels of NO is to utilise specific isoform selective inhibitors of nitric oxide synthases, the enzymes responsible for NO biosynthesis. An alternative line of attack, not related to specificity for a particular enzyme, but rather on compartmental localisation and pharmacokinetics, is to remove or scavenge the excess NO responsible for the disease pathology. In this regard, a number of NO scavenger molecules have demonstrated pharmacological activity across a broad spectrum of disease states. This review will highlight the rationale behind the development, and the current state of play, of one such class of NO scavengers, complexes of the d-block transition metal ruthenium. Prior to this, a brief overview of the remarkable diversity of NO, both from a chemical and biological viewpoint, will be provided for perspective.