Platinum(II) Complexes with Antitumoral/Antiviral Aromatic Heterocycles: Effect of Glutathione upon in Vitro Cell Growth Inhibition

Enhanced potency of a chloro-substituted polyaromatic platinum(II) complex and its platinum(IV) prodrug against lung cancer

The present study investigates the anti-neoplastic activity of a platinum (II) complex, Pt(II)5ClSS, and its platinum (IV) di-hydroxido analogue, Pt(IV)5ClSS, against mesenchymal cells (MCs), lung (A549), melanoma (A375) and breast (MDA-MB-231) cancer cells. Both complexes exhibited up to 14-fold improved cytotoxicity compared to cisplatin. NMR was used to determine that ∼25 % of Pt(IV)5ClSS was reduced to Pt(II)5ClSS in the presence of GSH (Glutathione) after 72 h. The complex 1H NMR spectra acquired for Pt(II)5ClSS with GSH shows evidence of degradation and environmental effects (∼30 %). The prominence of the 195Pt peak at ∼ -2800 ppm suggests that a significant amount of Pt(II)5ClSS remained in the mixture. Pt(II)5ClSS and Pt(IV)5ClSS have shown exceptional selectivity to cancer cells in comparison to MCs (IC50 > 150 μM). Western blot analysis of Pt(II)5ClSS and Pt(IV)5ClSS on A549 cells revealed significant upregulation of cleaved PARP-1, BAX/Bcl2 ratio, cleaved caspase 3 and cytochrome thus suggesting apoptosis was induced through the intrinsic pathway. Flow cytometry also revealed significant cell death by apoptosis. Treatment with Pt(II)5ClSS and Pt(IV)5ClSS also showed significant amounts of free radical production while the COMET assay showed that both complexes cause minimal DNA damage. Cellular uptake results via ICP-MS suggest a time-dependent active mode of transport for both complexes with Pt(II)5ClSS being transported at a higher rate compared to Pt(IV)5ClSS. A Dose Escalation Study carried out on BALB/c mice showed that Pt(II)5ClSS and Pt(IV)5ClSS were approximately 8- folds and 12.5-folds, respectively, more tolerated than cisplatin. The present study provides evidence that both complexes may have the characteristics of an efficient and potentially safe anti-tumor drug that could support NSCLC treatment.

The Lung Microbiome in COPD and Lung Cancer: Exploring the Potential of Metal-Based Drugs

Chronic obstructive pulmonary disease (COPD) and lung cancer 17 are two of the most prevalent and debilitating respiratory diseases worldwide, both associated with high morbidity and mortality rates. As major global health concerns, they impose a substantial burden on patients, healthcare systems, and society at large. Despite their distinct aetiologies, lung cancer and COPD share common risk factors, clinical features, and pathological pathways, which have spurred increasing research interest in their co-occurrence. One area of particular interest is the role of the lung microbiome in the development and progression of these diseases, including the transition from COPD to lung cancer. Exploring novel therapeutic strategies, such as metal-based drugs, offers a potential avenue for targeting the microbiome in these diseases to improve patient outcomes. This review aims to provide an overview of the current understanding of the lung microbiome, with a particular emphasis on COPD and lung cancer, and to discuss the potential of metal-based drugs as a therapeutic strategy for these conditions, specifically concerning targeting the microbiome.

Antibacterial activity of metal-phenanthroline complexes against multidrug-resistant Irish clinical isolates: a whole genome sequencing approach

Antimicrobial resistance (AMR) is one of the serious global health challenges of our time. There is now an urgent need to develop novel therapeutic agents that can overcome AMR, preferably through alternative mechanistic pathways from conventional treatments. The antibacterial activity of metal complexes (metal = Cu(II), Mn(II), and Ag(I)) incorporating 1,10-phenanthroline (phen) and various dianionic dicarboxylate ligands, along with their simple metal salt and dicarboxylic acid precursors, against common AMR pathogens were investigated. Overall, the highest level of antibacterial activity was evident in compounds that incorporate the phen ligand compared to the activities of their simple salt and dicarboxylic acid precursors. The chelates incorporating both phen and the dianion of 3,6,9-trioxaundecanedioic acid (tdda) were the most effective, and the activity varied depending on the metal centre. Whole-genome sequencing (WGS) was carried out on the reference Pseudomonas aeruginosa strain, PAO1. This strain was exposed to sub-lethal doses of lead metal-tdda-phen complexes to form mutants with induced resistance properties with the aim of elucidating their mechanism of action. Various mutations were detected in the mutant P. aeruginosa genome, causing amino acid changes to proteins involved in cellular respiration, the polyamine biosynthetic pathway, and virulence mechanisms. This study provides insights into acquired resistance mechanisms of pathogenic organisms exposed to Cu(II), Mn(II), and Ag(I) complexes incorporating phen with tdda and warrants further development of these potential complexes as alternative clinical therapeutic drugs to treat AMR infections.

Improvement of Kiteplatin Efficacy by a Benzoato Pt(IV) Prodrug Suitable for Oral Administration

Kiteplatin, [PtCl₂(cis-1,4-DACH)] (DACH = diaminocyclohexane), contains an isomeric form of the oxaliplatin diamine ligand trans-1R,2R-DACH and has been proposed as a valuable drug candidate against cisplatin- and oxaliplatin-resistant tumors, in particular, colorectal cancer. To further improve the activity of kiteplatin, it has been transformed into a Pt(IV) prodrug by the addition of two benzoato groups in the axial positions. The new compound, cis,trans,cis-[PtCl₂(OBz)₂(cis-1,4-DACH)] (1; OBz = benzoate), showed cytotoxic activity at nanomolar concentration against a wide panel of human cancer cell lines. Based on these very promising results, the investigation has been extended to the in vivo activity of compound 1 in a Lewis Lung Carcinoma (LLC) model and its suitability for oral administration. Compound 1 resulted to be remarkably stable in acidic conditions (pH 1.5 to mimic the stomach environment) undergoing a drop of the initial concentration to ~60% of the initial one only after 72 h incubation at 37 °C; thus resulting amenable for oral administration. Interestingly, in a murine model (2·10⁶ LLC cells implanted i.m. into the right hind leg of 8-week old male and female C57BL mice), a comparable reduction of tumor mass (~75%) was observed by administering compound 1 by oral gavage and the standard drug cisplatin by intraperitoneal injection, thus indicating that, indeed, there is the possibility of oral administration for this dibenzoato prodrug of kiteplatin. Moreover, since the mechanism of action of Pt(IV) prodrugs involves an initial activation by chemical reduction to cytotoxic Pt(II) species, the reduction of 1 by two bioreductants (ascorbic acid/sodium ascorbate and glutathione) was investigated resulting to be rather slow (not complete after 120 h incubation at 37 °C). Finally, the neurotoxicity of 1 was evaluated using an in vitro assay.

Structural analysis of metal chelation of the metalloproteinase thermolysin by 1,10-phenanthroline

Metalloproteases and their inhibitors are important in numerous fundamental biochemical phenomena and medical applications. The heterocyclic organic compound, 1,10-phenanthroline, forms a complex with transition metal ions and is a Zn²⁺-chelating metalloprotease inhibitor; however, the mechanism of 1,10-phenanthroline-based chelation inhibition has not been fully elucidated. This study aimed to understand the structural basis of zinc metalloproteinase inhibition by 1,10-phenanthroline. Herein, the crystal structure of thermolysin was determined in the absence and presence of 1,10-phenanthroline at 1.5 and 1.8 Å, respectively. In native thermolysin, Zn²⁺ at the active site is tetrahedrally coordinated by His142, His146, Glu166, and water molecule and contains three Ca²⁺ ions, which are involved in thermostability. In the crystal structure of 1,10-phenanthroline-treated thermolysin crystal, seven 1,10-phenanthroline molecules were observed on the surface of thermolysin. These molecules are stabilized by π- π stacking interactions with aromatic amino acids (Phe63, Tyr66, Tyr110, His216, and Try251) or between the 1,10-phenanthrolines. Moreover, interactions with Ser5 and Arg101 were also observed. In this structure, Zn²⁺ at the active site was completely chelated, but no large conformational changes were observed in Zn²⁺ coordination with amino acid residues. Ca²⁺ at the Ca3 site exposed to the solvent was chelated by 1,10-phenanthroline, resulting in a conformational change in the side chain of Asp56 and Gln61. Based on the surface structure, for 1,10-phenanthroline to chelate a metal, it is important that the metal is exposed on the protein surface and that there is no steric hindrance impairing 1,10-phenanthroline access by the amino acids around the metal.

The Antibacterial and Anti-biofilm Activity of Metal Complexes Incorporating 3,6,9-Trioxaundecanedioate and 1,10-Phenanthroline Ligands in Clinical Isolates of Pseudomonas Aeruginosa from Irish Cystic Fibrosis Patients

Chronic infections of Pseudomonas aeruginosa in the lungs of cystic fibrosis (CF) patients are problematic in Ireland where inherited CF is prevalent. The bacteria’s capacity to form a biofilm in its pathogenesis is highly virulent and leads to decreased susceptibility to most antibiotic treatments. Herein, we present the activity profiles of the Cu(II), Mn(II) and Ag(I) tdda-phen chelate complexes {[Cu(3,6,9-tdda)(phen)₂]·3H₂O·EtOH}_n (Cu-tdda-phen), {[Mn(3,6,9-tdda)(phen)₂]·3H₂O·EtOH}_n (Mn-tdda-phen) and [Ag₂(3,6,9-tdda)(phen)₄]·EtOH (Ag-tdda-phen) (tddaH₂ = 3,6,9-trioxaundecanedioic acid; phen = 1,10-phenanthroline) towards clinical isolates of P. aeruginosa derived from Irish CF patients in comparison to two reference laboratory strains (ATCC 27853 and PAO1). The effects of the metal-tdda-phen complexes and gentamicin on planktonic growth, biofilm formation (pre-treatment) and mature biofilm (post-treatment) alone and in combination were investigated. The effects of the metal-tdda-phen complexes on the individual biofilm components; exopolysaccharide, extracellular DNA (eDNA), pyocyanin and pyoverdine are also presented. All three metal-tdda-phen complexes showed comparable and often superior activity to gentamicin in the CF strains, compared to their activities in the laboratory strains, with respect to both biofilm formation and established biofilms. Combination studies presented synergistic activity between all three complexes and gentamicin, particularly for the post-treatment of established mature biofilms, and was supported by the reduction of the individual biofilm components examined.

Platinum(ii) non-covalent crosslinkers for supramolecular DNA hydrogels

Manipulation of non-covalent metal–metal interactions allows the fabrication of functional metallosupramolecular structures with diverse supramolecular behaviors. The majority of reported studies are mostly designed and governed by thermodynamics, with very few examples of metallosupramolecular systems exhibiting intriguing kinetics. Here we report a serendipitous finding of platinum(ii) complexes serving as non-covalent crosslinkers for the fabrication of supramolecular DNA hydrogels. Upon mixing the alkynylplatinum(ii) terpyridine complex with double-stranded DNA in aqueous solution, the platinum(ii) complex molecules are found to first stack into columnar phases by metal–metal and π–π interactions, and then the columnar phases that carry multiple positive charges crosslink the negatively charged DNA strands to form supramolecular hydrogels with luminescence properties and excellent processability. Subsequent platinum(ii) intercalation into DNA competes with the metal–metal and π–π interactions at the crosslinking points, switching on the spontaneous gel-to-sol transition. In the case of a chloro (2,6-bis(benzimidazol-2′-yl)pyridine)platinum(ii) complex, with [Pt(bzimpy)Cl]⁺ serving as a non-covalent crosslinker where the metal–metal and π–π interactions outcompete platinum(ii) intercalation, the intercalation-driven gel-to-sol transition pathway is blocked since the gel state is energetically more favorable than the sol state. Interestingly, the ligand exchange reaction of the chloro ligand in [Pt(bzimpy)Cl]⁺ with glutathione (GSH) has endowed the complexes with enhanced hydrophilicity, decreasing the planarity of the complexes, and turning off the metal–metal and π–π interactions at the crosslinking points, leading to GSH-triggered hydrogel dissociation.

We report a serendipitous finding of platinum(ii) complexes serving as non-covalent crosslinkers for the fabrication of supramolecular DNA hydrogels.

Anticancer activity of novel amino acid derivative of palladium complex with phendione ligand against of human colon cancer cell line

The aim of this work is the identification of the structural effect of amino acid-Pd complex on DNA as an intracellular target which was studied using various spectroscopic techniques such as fluorescence, UV-visible and circular dichroism in combination with a molecular docking study. Hence, a novel water-soluble palladium complex, [Pd(phendione)(isopentylglycine)]NO₃, has been synthesized and characterized by spectroscopic method. The anticancer activity of complex was investigated against human colon cancer cell line of HCT116 after 24 h of incubation using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. In addition, this complex was interacted with calf thymus DNA (ct-DNA) via positive cooperative interaction. The fluorescence data indicate that Pd complex is intercalated in DNA. These results were confirmed by circular dichroism spectra. The molecular docking results indicate that docking may be an appropriate method for the prediction and confirmation of experimental results. Complementary molecular docking results may be useful for the determination of the binding mechanism of DNA in pharmaceutical and biophysical studies providing new insight into the novel pharmacology and new solutions in the formulation of advanced oral drug delivery systems. Docking and spectroscopic studies show that new water-soluble Pd complex has anticancer activity and it can bind to DNA via intercalation and groove binding.

Development of a facile antibody-drug conjugate platform for increased stability and homogeneity

Despite the advances in the design of antibody-drug conjugates (ADCs), the search is still ongoing for novel approaches that lead to increased stability and homogeneity of the ADCs. We report, for the first time, an ADC platform technology using a platinum(ii)-based linker that can re-bridge the inter-chain cysteines in the antibody, post-reduction. The strong platinum-sulfur interaction improves the stability of the ADC when compared with a standard maleimide-linked ADC thereby reducing the linker-drug exchange with albumin significantly. Moreover, due to the precise conserved locations of cysteines, both homogeneity and site-specificity are simultaneously achieved. Additionally, we demonstrate that our ADCs exhibit increased anticancer efficacy in vitro and in vivo. The Pt-based ADCs can emerge as a simple and exciting proposition to address the limitations of the current ADC linker technologies.

Reactivity of kiteplatin with S-donor biomolecules and nucleotides

Kiteplatin, (cis-1,4-DACH)dichloridoplatinum(ii), contains an isomeric form of the carrier ligand present in the successful antitumor drug oxaliplatin and has been recently found to be very active against oxaliplatin-resistant colon cancers, confirming that, by changing the nature of the amine ligand, it is possible to obtain platinum drugs that are not cross-resistant to those already in clinical use. Apart from interaction with DNA, another factor that can affect the activity of platinum drugs is their metabolic fate in the cellular environment. Therefore, kiteplatin has been reacted with S-donor biomolecules, such as glutathione, cysteine, and methionine. The investigation has further confirmed the different reactivity of methionine as compared to cysteine-containing peptides and has unraveled the possibility of cis-1,4-DACH to become mono-coordinated with one free end (a situation never seen for isomeric 1,2-DACH ligands) and to labilize cis ligands as a consequence of its large steric hindrance. The reaction of kiteplatin-GSH adducts with 5'-GMP has also shown how the reaction products can be different depending upon the aerobic or anaerobic reaction conditions used.

Monofunctional platinum(II) complexes with potent tumor cell growth inhibitory activity: the effect of a hydrogen-bond donor/acceptor N-heterocyclic ligand

In this paper we investigate the possibility of further increase the role of the N-donor aromatic base in antitumor Hollis-type compounds by conferring the possibility to act as a hydrogen-bond donor/acceptor. Therefore, we synthesized the Pt(II) complex cis-[PtCl(NH3 )2 (naph)]NO3 (1) containing the 1,8-naphthyridine (naph) ligand. The naphthyridine ligand is generally monodentate, and the second nitrogen atom can act as H-bond donor/acceptor depending upon its protonation state. The possibility of forming such an H-bond could be crucial in the interaction of the drug with DNA or proteins. Apart from the synthesis of the compound, in this study we evaluated its in vitro antitumor activity in a wide panel of tumor cell lines, also including cells selected for their sensitivity/resistance to oxaliplatin, which was compared with that of previously reported complex 2 ([PtI(2,9-dimethyl-1,10-phenanthroline)(1-methyl-cytosine)]I) and oxaliplatin and cisplatin as reference compounds. The cytotoxicity data were correlated with the cellular uptake and the DNA platination levels. Finally, the reactivity of 1 towards guanosine 5'-monophosphate (5'-GMP) and glutathione was investigated to provide insights into its mechanism of action.

Transport of platinum bonded nucleotides into proteoliposomes, mediated by Drosophila melanogaster thiamine pyrophosphate carrier protein (DmTpc1)

The results of the present study suggest that DmTpc1 is actively implicated in the specific uptake of free cytoplasmic Pt bonded nucleotides, and therefore could be linked to the mechanism of action of some platinum-based antitumor drugs. Although DmTpc1 has a low affinity for model [Pt(dien)(N7-5'-dGTP)] and cis-[Pt(NH3)2(py)(N7-5'-dGTP)] compared to dATP it's well known that DNA platination level of few metal atoms per double-stranded molecule may account for the pharmacological activity of platinum based antitumor drugs. This is the first investigation where it has been demonstrated that a mitochondrial carrier is directly involved in the transport of metalated purines related with the cisplatin mechanism of action. Moreover it is shown as a lower hindrance of nucleotide bonded platinum complexes could strongly enhance mitochondrial uptake. Furthermore, a new application of ICP-AES addressed to measure the transport of metalated nucleobases, by using a recombinant protein reconstituted into liposomes, has been here, for the first time, developed and compared with a standard technique such as the liquid scintillation counting.

In vitro and in vivo studies into the biological activities of 1,10-phenanthroline, 1,10-phenanthroline-5,6-dione and its copper(ii) and silver(i) complexes

1,10-Phenanthroline (phen, 5), 1,10-phenanthroline-5,6-dione (phendione, 6), [Cu(phendione)3](ClO4)2·4H2O (12) and [Ag(phendione)2]ClO4 (13) are highly active, in vitro, against a range of normal and cancerous mammalian cells, fungal and insect cell lines, with the metal complexes offering a clear enhancement in activity. Cytoselectivity was not observed between the tumorigenic and non-tumorigenic mammalian lines. In in vivo tests, using Galleria mellonella and Swiss mice, all four compounds were well tolerated in comparison to the clinical agent, cisplatin. In addition, blood samples taken from the Swiss mice showed that the levels of the hepatic enzymes, aspartate aminotransferase (AST) and alanine aminotransferase (ALT), remained unaffected. Immunocompromised nude mice showed a much lower tolerance to 13 and, subsequently, when these mice were implanted with Hep-G2 (hepatic) and HCT-8 (colon) human-derived tumors, there was no influence on tumor growth.

Effect of thioethers on DNA platination by trans-platinum complexes

Increasing evidence indicates that sulfur-containing molecules can play important roles in the activity of platinum anticancer drugs. Although nuclear DNA is retained to be the ultimate target, these platinum compounds can readily react with a variety of other substrates containing a soft donor atom, such as proteins, peptides, and low molecular weight biomolecules, before reaching DNA. In a recent study it was demonstrated that the DNA platination rate of a trans-geometry antitumor drug was dramatically enhanced by methionine binding, thus suggesting that the thioether could serve as a catalyst for DNA platination. In this work we performed detailed studies on the reactions of a widely investigated and very promising trans-platinum complex having two iminoethers and two chlorido ligands, trans-EE, with methionine (Met) and guanosine 5'-monophosphate (GMP). The results show that in the reaction of trans-EE with methionine the bisadduct is the dominant species in the early stage of the reaction. The reaction is also influenced by chloride concentration: at low NaCl the bis-methionine adduct is formed in preference, whereas the monoadduct is favored at high NaCl concentration. Not only the monomethionine complex, trans-PtCl(E-iminoether)(2)(AcMet), but also the bis-methionine adduct, trans-Pt(E-iminoether)(2)(AcMet)(2), which has already lost both leaving chlorides, can react with GMP to form the ternary platinum complex trans-Pt(E-iminoether)(2)(AcMet)(GMP). The latter reaction discloses the possibility of direct coordination to DNA of a platinum-protein adduct, in which the two carrier ligands remain intact; this is not the case of cis-oriented platinum complexes, like cisplatin, for which formation of a ternary complex is usually accompanied by loss of at least one carrier ligand. Interestingly, isomerization from S to N coordination of one methionine takes place in the bis-methionine complex at neutral pH, while the monoadduct appears to be stable. The shift from S to N coordination of one methionine in the trans-bis-methionine adduct can easily account for the obtainment of the cis isomer in the bis-chelated Pt(Met-S,N)(2) end product.

Microwave synthesis of mixed ligand diimine-thiosemicarbazone complexes of ruthenium(II): biophysical reactivity and cytotoxicity

A novel microwave-assisted synthetic method has been used to synthesise a series of mixed ligand ruthenium(II) compounds containing diimine as well as bidentate thiosemicarbazone ligands. The compounds contain the diimine 1,10-phenanthroline (phen) or 2,2'-bipyridine (bpy) and the thiosemicarbazone is derived from 9-anthraldehyde. Based on elemental analyses and spectroscopic data, the compounds are best formulated as [(phen)(2)Ru(thiosemicarbazone)](PF(6))(2) and [(phen)(2)Ru(thiosemicarbazone)](PF(6))(2) where thiosemicarbazone = 9-anthraldehydethiosemicarbazone, 9-anthraldehyde-N(4)-methylthiosemicarbazone, and 9-anthraldehyde-N(4)-ethylthiosemicarbazone. Fluorescence competition studies with ethidium bromide, along with viscometric measurements suggests that the complexes bind calf thymus DNA (CTDNA) relatively strongly via an intercalative mode possibly involving the aromatic rings of the diimine ligands. The complexes show good cytotoxic profiles against MCF-7 and MDA-MB-231 (breast adenocarcinoma) as well as HCT 116 and HT-29 (colorectal carcinoma) cell lines.

Synthesis, anti-virus and anti-tumour activities of dibenzylbutyrolactone lignans and their analogues

An efficient synthesis of dibenzylbutyrolactone lignans and their analogues has been developed. Based on a Stobbe condensation of piperonal or veratraldehyde with diethylsuccinate and alkylation with 3,4-methylenedioxybenzyl bromide to give the skeleton of the lignan. The (±)-diacid was resolved with quinine and the functional groups were transformed to obtain three benzylbutyrolactone lignans and seven analogues. Four natural lignans were prepared by this method, and five lignans were synthesised for the first time. The synthesised compounds were evaluated for anti-HIV, anti-HSV, and anti-tumour activities. Results showed that the dibenzylbutyrolactone lignans and their analogues were inactive against HIV Tat transactivation and HSV-1 in vitro, but some compounds displayed significant activity against MDA-MB-435 human breast cancer cell.

DNA interaction studies of a platinum(II) complex, PtCl(2)(NN) (NN=4,7-dimethyl-1,10-phenanthroline), using different instrumental methods

The Pt(II) complex, PtCl(2)(4,7-Me(2)phen) (4,7-Me(2)phen=chelating dinitrogen ligand: 4,7-dimethyl-1,10-phenanthroline) was synthesized and characterized by spectroscopic ((1)H, (13)C NMR) and elemental analysis techniques. Binding interaction of this complex with calf thymus (CT) DNA has been investigated by emission, absorption, circular dichroism, viscosity and DNA thermal denaturation studies. The complex displays significant binding properties to the CT DNA. In fluorimeteric studies, the binding mode of complex with CT DNA was studied by using methylene blue as a fluoresce probe. As evidenced by the increasing fluorescence of methylene blue-DNA solutions in presence of increasing amount of complex, PtCl(2)(NN) complex is able to displace the methylene blue intercalated into DNA completely as to indicate intercalation. Furthermore, mentioned complex induces detectable changes in the CD spectrum of CT-DNA, an increase in T(m) value, and an increase in its viscosity. The experimental results showed that Pt(II) complex bound to DNA by an intercalative mode of binding.

Stability of an organometallic ruthenium-ubiquitin adduct in the presence of glutathione: relevance to antitumour activity

The interactions of the ruthenium(II) complex Ru(eta6-p-cymene)(pta)Cl2 (RAPTA-C), an effective anticancer and antimetastatic agent, with biological nucleophiles are important with respect to its mechanism of action, for example, the reaction with glutathione (GSH) potentially plays an important role in detoxification. RAPTA-C reacts rapidly with glutathione forming a series of adducts including Ru(eta6-p-cymene)(pta)(GS), Ru(eta6-p-cymene)(GS) and bis-GSH conjugates, which were characterised by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). In addition, the ability of glutathione to cleave ruthenium-ubiquitin bonds was assayed and it was shown that GSH is capable of removing the Ru moiety from the protein, although no ternary adducts were identified.

Degradation of bidentate-coordinated platinum(II)-based DNA intercalators by reduced L-glutathione

We have examined the interaction of [(5,6-dimethyl-1,10-phenanthroline)(1S,2S-diaminocyclohexane)platinum(II)] (2+) (1, 56MESS), [(5-methyl-1,10-phenanthroline)(1S,2S-diaminocyclohexane)platinum(II)] (2+) (2, 5MESS), [(5,6-dimethyl-1,10-phenanthroline)(1R,2R-diaminocyclohexane)platinum(II)] (2+) (3, 56MERR), and [(5,6-dimethyl-1,10-phenanthroline)(ethylenediamine)platinum(II)] (2+) (4, 56MEEN) with reduced L-glutathione and L-methionine. Both thiols degrade all four complexes, mainly by displacing the ancillary ligand and forming a doubly bridged dinuclear complex. The degradation half-life of all the complexes with methionine is >7 days, indicating that these reactions are not biologically relevant. The rate of degradation by glutathione appears to be particularly important and shows an inverse correlation to cytotoxicity. The least active complex, 4 (t 1/2 glutathione: 20 h), degrades fastest, followed by 3 (31 h), 2 (40 h), and 1 (68 h). The major degradation product, [bis-mu-{reduced L-glutathione}bis{5,6-dimethyl-1,10-phenanthroline}bis{platinum(II)}] (2+) (5, 56MEGL), displays no cytotoxicity and is excluded as the source of the anticancer activity. Once bound by glutathione, these metal complexes do not then form coordinate bonds with guanosine. Partial encapsulation of the complexes within cucurbit[n]urils is able to stop the degradation process.

Comparison of cis and trans-Platinum Mononucleobase Compounds with DNA and Protein Models

Reactions of 5′-guanosine monophosphate (5′-GMP) and N-acetylmethionine (N-ac-l-Met) with the mononucleobase compounds, cis-[PtCl(L)n(9-EtGH)]+ (L = NH3, 4-pic, n = 2; L = en, n = 1) in a 1:1 molar ratio have been studied in aqueous solutions at pH 7.3 using 1H and 195Pt NMR spectroscopy. There is a high kinetic preference for sulfur over nitrogen binding. These results are compared with the trans isomers. Based on low cytotoxicity and a high sulfur/nitrogen preference the cis isomers may also present suitable features for antiviral activity through interaction with specific proteins.

Pressure-Assisted Hetero- and Homodialkylation of Sulfide in [Pt2(μ-S)2(dppp)2]: One-Pot Conversion of {Pt2(μ-S)2} into {Pt2(SR)2} and {Pt2(SR)(SR′)}

Heterodialkylation of [Pt2(mu-S)2(dppp)2] (dppp = Ph2P(CH2)3PPh2) was achieved under high pressure (10 kbar). This enabled the synthesis of rare diplatinum complexes with structurally diverse thiolate bridges, such as [Pt2(mu-SC5H10CO2CH2CH3)(mu-SC3H7)-(dppp)2](PF6)2, which was crystallographically identified. Complete homodialkylation was also achieved under similar conditions (6 kbar at room temperature), thus permitting the isolation of [Pt2(mu-SC2H4CO2CH2CH3)2(dppp)2]-(PF6)2. The isolation of these complexes extends the applications of high-pressure chemistry to thiolato homo- and heterobridged complexes that are otherwise not accessible.

Synthesis and evaluation of an N-acylated photoactivatable analogue of glutathione as probe for glutathione-utilizing enzymes

The first synthesis of an N-acylated photoactivatable analogue of reduced glutathione is described. N-(4-Benzoylbenzoyl)glutathione (8) was found to be an inhibitor and a photoaffinity probe of purified rat liver glutathione S-transferases.