New water-soluble platinum(ii) phenanthroline complexes tested as cisplatin analogues: first-time comparison of cytotoxic activity between analogous four- and five-coordinate species

Antitumor and antimigration effects of a new Pt compound on neuroblastoma cells

Among the new Pt complexes with anticancer properties, phenanthroline derivatives have aroused great interest due to their different mode of action compared to cisplatin. We previously examined cytotoxic effects of a new Pt(II)-complex containing 1,10-phenantroline (phen), [Pt(η¹-C₂H₄OMe)(DMSO)(phen)]Cl, in a panel of eight human cancer cell lines, and showed that it exerted the greatest cytotoxic effect in the neuroblastoma SH-SY5Y cell line. In this study, the antiproliferative and antimetastatic potential of [Pt(η¹-C₂H₄OMe)(DMSO)(phen)]⁺ (in short Pt-EtOMeSOphen) was investigated in neuroblastoma SH-SY5Y, SK-N-SH and SK-N-BE(2) cells. Pt-EtOMeSOphen provoked the early signs of apoptosis induction (cleavage of PARP and activation of caspases-9 and -7); it also increased the level of proapoptotic Bax protein whereas it decreased the level of the antiapoptotic Bcl-2 protein. The effects of Pt-EtOMeSOphen on migration and invasion processes were also evaluated. A decrease of cell migration/invasion by Pt-EtOMeSOphen was observed through 2D and 3D in vitro assays. Pt-EtOMeSOphen was found to exert its actions by decreasing MMP-9 and MMP-2 expressions and activities. Pt-EtOMeSOphen provoked the phosphorylation of both ERK1/2 and p38 MAPKs. All the effects of Pt-EtOMeSOphen on SH-SY5Y cell vitality, migration and metalloproteases activities described here were due to the activation of p38 MAPK since pharmacological p38 MAPK inhibition or small interfering RNAs to p38 MAPK mRNA blocked such effects. Results suggest that Pt-EtOMeSOphen inhibits neuroblastoma cancer cells survival, motility, and invasion. This could lead to the reduction of neuroblastoma metastatic potential.

Multifunctional Polyoxometalate Platforms for Supramolecular Light-Driven Hydrogen Evolution*

Multifunctional supramolecular systems are a central research topic in light‐driven solar energy conversion. Here, we report a polyoxometalate (POM)‐based supramolecular dyad, where two platinum‐complex hydrogen evolution catalysts are covalently anchored to an Anderson polyoxomolybdate anion. Supramolecular electrostatic coupling of the system to an iridium photosensitizer enables visible light‐driven hydrogen evolution. Combined theory and experiment demonstrate the multifunctionality of the POM, which acts as photosensitizer/catalyst‐binding‐site^[1] and facilitates light‐induced charge‐transfer and catalytic turnover. Chemical modification of the Pt‐catalyst site leads to increased hydrogen evolution reactivity. Mechanistic studies shed light on the role of the individual components and provide a molecular understanding of the interactions which govern stability and reactivity. The system could serve as a blueprint for multifunctional polyoxometalates in energy conversion and storage.

Square-Planar vs. Trigonal Bipyramidal Geometry in Pt(II) Complexes Containing Triazole-Based Glucose Ligands as Potential Anticancer Agents

This article describes the synthesis, characterization, and biological activity of novel square-planar cationic platinum(II) complexes containing glucoconjugated triazole ligands and a comparison with the results obtained from the corresponding five-coordinate complexes bearing the same triazole ligands. Stability in solution, reactivity with DNA and small molecules of the new compounds were evaluated by NMR, fluorescence, and UV–vis absorption spectroscopy, together with their cytotoxic action against pairs of immortalized and tumorigenic cell lines. The results show that the square-planar species exhibit greater stability than the corresponding five-coordinate ones. Furthermore, although the square-planar complexes are less cytotoxic than the latter ones, they exhibit a certain selectivity. These results simultaneously demonstrate that overall stability is a fundamental prerequisite for preserving the performance of the agents and that coordinative saturation constitutes a point in favor of their biological action.

Synthesis and evaluation of the anticancer activity of [Pt(diimine)(N,N-dibutyl-N'-acylthiourea)]+ complexes

Despite the concerted efforts to develop targeted cancer treatments, these therapies are plagued by the rapid development of resistance and serious adverse drug reactions. Based on the wide clinical use and successes of the platinum drugs like cisplatin and oxaliplatin, we investigated the synthesis and potential anticancer efficacy of alternative platinum complexes. A series of nine cationic square planar platinum(ii) complexes were synthesized and characterized and then evaluated for their anticancer activity. The complexes were of the type [Pt(diimine)(Lⁿ-κO,S)]⁺ where diimine is either 1,10-phenanthroline (phen), 5,6-dimethyl-1,10-phenanthroline (dmp) or dipyrido[3,2-f:2',3'-h]quinoxaline (dpq) and Lⁿ-κO,S representing various N,N-dibutyl-N'-acylthiourea ligands. The anticancer activity of the synthesised complexes was evaluated against two lung cancer cell lines (A549 and H1975) and a colorectal cancer cell line, HT-29. The 50% inhibitory concentrations (IC₅₀) for the most cytotoxic compounds were determined and the mode of cell death evaluated. The structure-activity relationships indicated that complexes with the 5,6-dimethyl-1,10-phenanthroline variation of the diimine ligand were the most active against the cell lines tested, while the activity of complexes based on the acylthiourea ligand varied between the cell lines. IC₅₀ values for the three active platinum complexes were in the low micromolar range for the three cell lines and ranged between 0.68 μM and 2.28 μM. Changes to cell morphology indicate that the active platinum complexes induce cell death by both apoptosis and paraptosis. The complexes were able to induce the nuclear expression of the cyclin-dependent kinase inhibitor, p21, which is an indicator of DNA damage. The collective data indicate that these platinum complexes are valuable lead compounds for further analysis and cancer drug discovery.

Luminescent Platinum(II) Complexes with Bidentate Diacetylide Ligands: Structures, Photophysical Properties and Application Studies

A series of platinum(II) complexes supported by terphenyl diacetylide as well as diimine or bis-N-heterocyclic carbene (NHC) ligands have been prepared. The diacetylide ligands adopt a cis coordination mode featuring non-planar terphenyl moieties as revealed by X-ray crystallographic analyses. The electrochemical, photophysical and photochemical properties of these platinum(II) complexes have been investigated. These platinum(II) diimine complexes show broad emission with peak maxima from 566 nm to 706 nm, with two of them having emission quantum yields >60% and lifetimes <2 μs in solutions at room temperature, whereas the platinum(II) diacetylide complexes having bis-N-heterocyclic carbene instead of diimine ligand display photoluminescence with quantum yields of up to 28% in solutions and excited state lifetimes of up to 62 μs at room temperature. Application studies revealed that one of the complexes can catalyze photoinduced aerobic dehydrogenation of alcohols and alkenes, and a relatively non-toxic water-soluble Pt(II) complex displays anti-angiogenic activity.

Long-term effects after treatment with platinum compounds, cisplatin and [Pt(O,O'-acac)(γ-acac)(DMS)]: Autophagy activation in rat B50 neuroblastoma cells

Cisplatin (cisPt), among the best known components of multi-drug front-line therapies used for the treatments of solid tumors, such as the childhood neuroblastoma, acts through DNA linking. Nevertheless, the cisPt effectiveness is compromised by the onset of severe side effects, including neurotoxicity that results in neurodegeneration, cell death, and drug-resistance. In the field of experimental oncology, aimed at overcoming cytotoxicity and chemoresistance, great efforts are devoted to the synthesis of new platinum-based drugs, such as [Pt(O,O'-acac)(γ-acac)(DMS)] (PtAcacDMS), which shows a specific reactivity with sulfur residues of enzymes involved in apoptosis. Autophagy, an evolutionary conserved degradation pathway for recycling of cytoplasmic components, represents one of the mechanisms adopted by cancer cells which contribute to drug-resistance. In the present study, standard acute (48 h-exposure) and long-term effects (7 day-recovery after treatment or 7 day-recovery followed by reseeding and 96 h-growth), of cisPt and PtAcacDMS (40 and 10 μM, respectively) were investigated in vitro employing rat B50 neuroblastoma as a cancer model. Using fluorescence and electron microscopy, as well as biochemical techniques, our data highlight a key role of the autophagic process in B50 cells. Specifically, long-term effects caused by cisPt lead to inhibition of the apoptotic process and paralleled by the activation of autophagy, thus evidencing that autophagy has a protective role after cisPt exposure, allowing cells to survive. Whereas, long-term effects produced by PtAcacDMS lead toward both apoptosis and autophagy activation. In conclusion, autophagy may represents an alternative cell death pathway, circumventing drug-resistance strategies employed by cancer cells to survive chemoterapy.

Bathophenanthroline Disulfonate Ligand-Induced Self-Assembly of Ir(III) Complexes in Water: An Intriguing Class of Photoluminescent Soft Materials

Strong evidence of concentration-induced and dissolved electrolyte-induced chromophore aggregation has been universally observed in numerous water soluble bis-cyclometalated Ir(III) photosensitizers bearing the sulfonated diimine ligands bathophenanthroline disulfonate and bathocuproine disulfonate. This new class of aqueous-based soft materials was highly photoluminescent in their aggregated state where detailed spectroscopic investigations of this phenomenon revealed significant blue shifts of their respective photoluminescence emission spectra with concomitant increases in excited-state lifetimes and quantum yields initiating even at micromolar chromophore concentrations in water or upon the addition of a strong electrolyte. A combination of nanoscale particle characterization techniques, static and dynamic photoluminescence spectroscopic studies, along with atomistic molecular dynamics (MD) simulations of these soft materials suggests the formation of small, heterogeneous nanoaggregate structures, wherein the sulfonated diimine ancillary ligand serves as a pro-aggregating subunit in all instances. Importantly, the experimental and MD findings suggest the likelihood of discovering similar aqueous aggregation phenomena occurring in all transition-metal complexes bearing these water-solubilizing diimine ligands.

C-Glycosylation in platinum-based agents: a viable strategy to improve cytotoxicity and selectivity

The glycosylation of five-coordinate Pt(ii) compounds through a Pt–C linkage can be a very effective strategy for attacking cancer cells, while preserving the survival of the healthy ones.

Chemiluminescence detection with water-soluble iridium(III) complexes containing a sulfonate-functionalised ancillary ligand

The chemiluminescence from four cyclometalated iridium(III) complexes containing an ancillary bathophenanthroline-disulfonate ligand exhibited a wide range of emission colours (green to red), and in some cases intensities that are far greater than the commonly employed benchmark reagent, [Ru(bpy)3](2+). A similar complex incorporating a sulfonated triazolylpyridine-based ligand enabled the emission to be shifted into the blue region of the spectrum, but the responses with this complex were relatively poor. DFT calculations of electronic structure and emission spectra support the experimental findings.

Robust affinity standards for Cu(I) biochemistry

The measurement of reliable Cu(I) protein binding affinities requires competing reference ligands with similar binding strengths; however, the literature on such reference ligands is not only sparse but often conflicting. To address this deficiency, we have created and characterized a series of water-soluble monovalent copper ligands, MCL-1, MCL-2, and MCL-3, that form well-defined, air-stable, and colorless complexes with Cu(I) in aqueous solution. X-ray structural data, electrochemical measurements, and an extensive network of equilibrium titrations showed that all three ligands form discrete Cu(I) complexes with 1:1 stoichiometry and are capable of buffering Cu(I) concentrations between 10(-10) and 10(-17) M. As most Cu(I) protein affinities have been obtained from competition experiments with bathocuproine disulfonate or 2,2'-bicinchoninic acid, we further calibrated their Cu(I) stability constants against the MCL series. To demonstrate the application of these reagents, we determined the Cu(I) binding affinity of CusF (log K = 14.3 ± 0.1), a periplasmic metalloprotein required for the detoxification of elevated copper levels in Escherichia coli . Altogether, this interconnected set of affinity standards establishes a reliable foundation that will facilitate the precise determination of Cu(I) binding affinities of proteins and small-molecule ligands.

A new platinum(II) compound anticancer drug candidate with selective cytotoxicity for breast cancer cells

[Pt(O,O′-acac)(γ-acac)(DMS)] (PtAcD) is able to induce apoptosis in various human cancer cells, including the cisplatin-resistant human breast carcinoma MCF-7 cells. Here, to confirm that PtAcD has the potentiality for therapeutic intervention, we studied its effects in primary cultured epithelial breast cells obtained from cancers and also from the corresponding histologically proven non-malignant tissue adjacent to the tumor. We demonstrated that PtAcD (1) is more cytotoxic in cancer than in normal breast cells; (2) activated NAD(P)H oxidase, leading to PKC-ζ and PKC-α tanslocations; (3) activated antiapoptotic pathways based on the PKC-α, ERK1/2 and Akt kinases; (4) activated PKC-ζ and, only in cancer cell PKC-δ, responsible for the sustained phosphorylation of p38 and JNK1/2, kinases both of which are involved in the mitochondrial apoptotic process. Moreover, crosstalk between ERK/Akt and JNK/p38 pathways affected cell death and survival in PtAcD-treated breast cell. In conclusion, this study adds and extends data that highlight the pharmacological potential of PtAcD as an anti breast cancer drug.

Cisplatin-related drugs for nongenomic targets: Forcing the reactivity with nucleobases

The products obtained by forcing the reaction with nucleosides (guanosine, Guo, and adenosine, Ado) of potential anticancer drugs for nongenomic targets [PtCl(O,O'-acac)(L)] (L = dimethyl sulfoxide, DMSO; dimethyl sulfide, DMS), closely related to their very powerful organometallic analogues [Pt(O,O'-acac)(γ-acac)(L)], have been studied. [PtCl(O,O'-acac)(L)] and [Pt(O,O'-acac)(γ-acac)(L)] complexes were reported unreactive toward nucleobases. Aquo species [Pt(O,O'-acac)H2O(L)]+, obtained from [PtCl(O,O'-acac)(L)] by Ag+ driven coordinated Cl– removal, gave access to [Pt(O,O'-acac)(L)(nucleoside)]+ ([Pt(O,O'-acac)(DMSO)(Guo)]+, [Pt(O,O'-acac)(DMS)(Guo)]+, [Pt(O,O'-acac)(DMSO)(Ado)]+). The effect of the chelate oxygen donor acac (with respect to a chelate diammine), the role of the sulfur ligand (DMSO, DMS), and the influence of the purinic nucleoside itself on the coordinated Guo or Ado dynamic motions in [Pt(O,O'-acac)(L)(nucleoside)]+ complexes have been investigated by NMR spectroscopy. Interestingly, a slow rotation of nucleobase around the Pt–N(7) bond with formation of two rotamers was observed already at room temperature only in the case of [Pt(O,O'-acac)(DMSO)(Guo)]+. On the other hand, no hindered rotation at room temperature was detected in the analogous [Pt(O,O'-acac)(DMS)(Guo)]+ and [Pt(O,O'-acac)(DMSO)(Ado)]+ complexes. Data suggest that rotation of the nucleoside in [Pt(O,O'-acac)(L)(nucleoside)]+ is very different with respect to the analogous [Pt(diammine)(L)(nucleoside)]2+ systems, due to specific interactions between the acac chelate ligand, the DMSO, and the nucleobase.

Structure-cytotoxicity relationship for different types of mononuclear platinum(II) complexes with 5,7-ditertbutyl-1,2,4-triazolo[1,5-a]pyrimidine

To compare the in vitro cytotoxicity of platinum(II) complexes with 5,7-ditertbutyl-1,2,4-triazolo[1,5-a]pyrimidine (dbtp), three complexes were prepared: cis-[PtI(2)(dbtp)(2)] (1), cis-[Pt(NO(3))(2)(dbtp)(2)] (2) and cis-[Pt(C(4)H(4)O(5))(dbtp)(2)] (3). The coordination compounds have been structurally characterized by IR; (1)H, (13)C, (15)N, (195)Pt NMR and single-crystal X-ray diffraction (1). Spectroscopic studies reveal the monodentate coordination of the heterocycle ligand (dbtp) via N(3) to platinum(II) ions. In addition, the crystal structure of (1) shows that the platinum(II) ion is located in nearly square-planar PtI(2)N(2) environments with two heterocycle ligands (dbtp) arranged in a head-to-head orientation. The complexes have been screened for their cytotoxicity against two human cells: non-small cell lung carcinoma (A549) and breast cancer (T47D). All of the complexes demonstrated a significant antiproliferative activity against both cell lines. On the basis of these results, it is concluded that the cytotoxicity of the studied compounds against T47D follows the order: (3)<(1)<(2).

NMR study on iridium(III) complexes for identifying disulfonate substituted bathophenanthroline regio-isomers

A series of novel biscyclometalated iridium (III) complexes with an ancillary disulfonated bathophenanthroline (DSBP(2-)) ligand, Ir(L)(2)DSBPNa, L = 2-phenylpyridine (ppy), 2,4-difluorophenylpyridine (fppy), and 1-phenylisoquinoline (piq) were found to have two isomeric forms. The chemical structures of the isomers were determined by the one- and two-dimensional (1)H and (13)C NMR studies. The isomeric state was proved to have originated from the disulfonate-related regio-isomer of the DSBP(2-) ligand.

In vitro and in vivo antitumor activities and DNA binding mode of five coordinated cyclometalated organoplatinum(II) complexes containing biphosphine ligands

New complexes [Pt(C(∧)N)Cl(dppa)] (1), and [Pt(C(∧)N)Cl(dppm)] (2), (C(∧)N. deprotonated 2-phenylpyridine; dppa. bis(diphenylphosphino)amine; dppm. bis(diphenylphosphino)methane) were suggested to have pentacoordinated geometry as investigated by NMR and conductometry. Pharmacological effects of 1 and 2 were evaluated for their proteasome-inhibitory and apoptosis-inducing activities under in vitro and in vivo conditions, showing significant proteasome-inhibitory activity against purified 20S proteasome, while 2 demonstrated superior inhibitory activity against cellular 26S proteasome. Consistently, this effect was associated with higher levels of proteasome target proteins and apoptosis induction in breast cancer cells. Importantly, preliminary studies show 1 and 2 were able to exert a similar effect in vivo by inhibiting the growth of breast cancer xenografts in mice, which was associated with proteasome inhibition and apoptosis induction. Interaction of 1 and 2 with herring sperm DNA was investigated by fluorimeteric emission, suggesting that Pt(II)-containing biphosphine complexes with DNA binding capabilities can also target and inhibit the tumor proteasome.

Mutagenic Tests Confirm That New Acetylacetonate Pt(II) Complexes Induce Apoptosis in Cancer Cells Interacting with Nongenomic Biological Targets

New platinum(II) complexes [PtCl(O,O'-acac)(L)] (1) and [Pt(O,O'-acac)(γ-acac)(L)] (2) (L = DMSO, a; DMS, b) containing a single chelated (O,O'-acac) (1), or one chelated and one σ-bonded (γ-acac) acetylacetonate (2) have been synthesized. The new Pt(II) complexes exhibited high in vitro cytotoxicity on cisplatin sensitive and resistant cell lines and showed negligible reactivity with nucleobases (Guo and 5'-GMP) but selective substitution of DMSO/DMS with soft biological nucleophiles, such as L-methionine. In order to assess the ability of the new complexes with respect to cisplatin to induce apoptosis by interaction with nongenomic targets, the Ames' test, a standard reverse mutation assay, was carried out on two Salmonella typhimurium strains (TA98 and TA100). Interestingly, the new complexes did not show the well-known mutagenic activity exhibited by cisplatin and are, therefore, able to activate apoptotic pathways without interacting with DNA.

Synthesis, characterization, and photophysical properties of three platinum(II) complexes bearing fluorescent analogues of the Di-2-pyridylmethane ligand

Three new ligands of the general formula [RNHCH(py)(2)] (py = pyridine; R = tosyl, Ts-dpm; R = dansyl, Ds-dpm; R = 7-nitro-1,2,3-benzoxadiazole, NBD-dpm) have been synthesized and characterized. Reactions of these ligands with cis-[Pt(DMSO)(2)Cl(2)] (DMSO = dimethyl sulfoxide) in methanol affords [Pt(Ts-dpm)Cl(2)] (1), [Pt(Ds-dpm)Cl(2)] (2), and [Pt(NBD-dpm)Cl(2)] (3). The crystal structures of these complexes reveal bidentate coordination of the ligands to the Pt center with nonplanar chelate rings. Because of inequivalent substituents on the methine carbon atom of the ligands, distinct exo and endo isomers exist in the three complexes. X-ray analyses indicate that 1 crystallizes in the endo conformation, 2 in the exo conformation, and 3 as a mixture of the two conformers. The (1)H NMR and (195)Pt NMR spectra of the complexes display two sets of independent signals corresponding to the chemically inequivalent exo and endo conformers. The exo conformer was determined by 2D NMR spectroscopy to be thermodynamically favored for all three complexes. Density functional theory (DFT), time-dependent DFT, and atoms in molecules calculations were carried out for both conformers of 3 to investigate differences in their electronic structures and to explore intramolecular interactions. In the presence of dioxygen, 1 thermally decomposes at 60 degrees C to form several unidentified products. Compound 2 is thermally stable even in the presence of dioxygen and water but upon light exposure decomposes to form a new platinum(II) species with a (195)Pt NMR shift of -2177 ppm. Compound 3 reacts both thermally and photochemically in the presence of dioxygen and trace amounts of water to form both 4-amino-7-nitro-2,1,3-benzoxadiazole and [Pt(dpk)Cl(2)] (dpk = di-2-pyridyl ketone). Oxidation of 1 and 3 with H(2)O(2) in acetic acid affords a mixture of compounds, two of which contain dpm ligands bound in a tridentate manner to platinum.

Inhibition of Aβ42 peptide aggregation by a binuclear ruthenium(II)-platinum(II) complex: Potential for multi-metal organometallics as anti-amyloid agents

Design of inhibitors for amyloid-β (Aβ) peptide aggregation has been widely investigated over the years towards developing viable therapeutic agents for Alzheimer's disease (AD). The biggest challenge seems to be inhibiting Aβ aggregation at the early stages of aggregation possibly at the monomeric level, as oligomers are known to be neurotoxic. In this regard, exploiting the metal chelating property of Aβ to generate molecules that can overcome this impediment presents some promise. Recently, one such metal complex containing Pt(II) ([Pt(BPS)Cl(2)]) was reported to effectively inhibit Aβ42 aggregation and toxicity (1). This complex was able bind to Aβ42 at the N-terminal part of the peptide and triggered a conformational change resulting in effective inhibition. In the current report, we have generated a mixed-binuclear metal complex containing Pt(II) and Ru(II) that inhibited Aβ42 aggregation at an early stage of aggregation and seemed to have different modes of interaction than the previously reported Pt(II) complex, suggesting an important role of the second metal center. This 'proof-of-concept' compound will help in developing more effective molecules against Aβ aggregation by modifying the two metal centers as well as their ligands, which will open doors to new rationale for Aβ inhibition.

Mono- and dinuclear platinum(II) compounds with 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine. Structure, cytotoxic activity and reaction with 5'-GMP

Mono- and dinuclear platinum(II) coordination compounds of formula cis-[PtCl(2)(NH(3))(dmtp)], 1, cis-[PtCl(2)(dmtp)(2)], 2 and {H(+)[C(28)H(32)Cl(2)N(16)Pt(2)](2+)(NO(3))(3)(H(2)O)(6)}, 3, in which dmtp is 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine have been synthesized and characterized by infrared and by (1)H, (13)C, (195)Pt NMR spectroscopy. The coordination units of the cationic species of formula [Pt(2)(mu-dmtp)(2)Cl(2)(dmtp)(2)](2+) are built up by two platinum atoms in a square-planar environment. Two sites are occupied by two 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine (dmtp) bridging ligands which are linked to both metal atoms through their nitrogen atoms in positions 3 and 4. The other two positions are occupied by one monodentate 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine (dmtp) molecule and a coordinated chloride. This compound is the first in which the same triazolopyrimidine ligand (dmtp) coordinates to a metal ion in two different ways, i.e. bridging bidentate and non-bridging monodentate. In addition, the interaction of compounds 1 and 2 with 5'-GMP was investigated in solution by (1)H NMR spectroscopy. The cytotoxicity of all the new platinum(II) compounds were studied by using two different cell lines: T47D (breast cancer) and HCV29T (bladder cancer).