Metal-based antitumour drugs in the post-genomic era: what comes next?

Synthesis, spectroscopic characterization, X-ray structure and electrochemistry of new bis(1,2-diaminocyclohexane)gold(iii) chloride compounds and their anticancer activities against PC3 and SGC7901 cancer cell lines

Promising cytotoxic gold(iii) complexes with general formula [Au{(1,2-DACH)}₂]Cl₃ are reported.

Targeting the endoplasmic reticulum with a membrane-interactive luminescent ruthenium(ii) polypyridyl complex†Electronic supplementary information (ESI) available: Experimental details, characterization of and Fig. S1-S6. See DOI: 10.1039/c3sc51725jClick here for additional data file

The characterization and bioactivity of the dinuclear ruthenium(ii) complex [(Ru(DIP)2)2(tpphz)]4+ (DIP = 4,7-diphenyl-1,10-phenanthroline and tpphz = tetrapyrido[3,2-a:2',3'-c:3'',2''-h:2''',3'''-j]phenazine) is reported. This new complex is found to be luminescent in acetonitrile, where excitation into MLCT (metal-to-ligand charge-transfer) bands in the visible area of the spectrum (λex = 450 nm, ε = 45 000 M-1 cm-1) result in red emission (λem,max = 620 nm, ΦMLCT = 0.017). Aqueous in vitro binding studies indicate that this complex binds to duplex DNA with an affinity of 1.8 × 106 M-1 through a non-classical groove-binding interaction, however, unlike the parent complex [(Ru(phen)2)2(tpphz)]4+ (phen = 1,10-phenanthroline), it also displays an increase in MLCT luminescence on addition of liposomes. Confocal microscopy and TEM studies show that this lipophilic complex targets the endoplasmic reticulum of eukaryotic cells, where it functions as an imaging agent for this organelle, and cytotoxicity studies in human cancer cell lines indicate a comparable potency to the anti-cancer drug cisplatin.

Heteronuclear gold(I)-silver(I) sulfanylcarboxylates: Synthesis, structure and cytotoxic activity against cancer cell lines

Heteronuclear complexes of the type [AgAu(PPh3)2(xspa)] [H2xspa=3-(aryl)-2-sulfanylpropenoic acids; (x=3-phenyl-; 3-(2-chlorophenyl)-; 3-(o-methoxyphenyl)-; 3-(p-methoxyphenyl)-; 3-(p-hydroxyphenyl)-; 3-(2-furyl)-; 3-(2-thienyl)-; spa=2-sulfanylpropenoate)] were prepared by reacting the appropriate [Au(PPh3)(Hxspa)] precursor with Ag(PPh3)NO3. The compounds were characterized by spectroscopic methods, (IR; (1)H, (13)C and (31)P NMR) and mass spectrometry and the structures of the phenyl and p-methoxyphenyl derivatives were determined by X-ray diffraction. The in vitro antitumor activity against the HeLa-229, A2780 and A2780cis cell lines was determined and compared with that of cisplatin and the equivalent homonuclear gold(I) complexes.

Lipid-coated nanoscale coordination polymers for targeted cisplatin delivery

Nanoscale coordination polymers (NCPs) containing a Pt(IV) cisplatin prodrug, disuccinatocisplatin, were formed by a surfactant-templated synthesis and were shown to have a prodrug loading of 8.2 wt% and a diameter of ~133 nm by dynamic light scattering. These NCPs were stabilized by coating with a DOPC/cholesterol/DSPE-Peg2K lipid layer; a release profile in phosphate buffered saline showed an initial drug release of ~25% within the first hour and no more release observed up to 192 h. The NCP was rendered target-specific for sigma receptors by addition of an AA-DSPE-Peg2K conjugate (AA = anisamide) in the lipid formulation. The AA-containing NCP showed a statistically significant decrease in IC50 (inhibitory concentration, 50%) compared to the non-targeted NCP. Enhanced uptake of the AA-containing NCP was further supported by confocal microscopy and competitive binding assays.

An insight into the anticancer activities of Ru(II)-based metallocompounds using docking methods

Unlike organic molecules, reports on docking of metal complexes are very few; mainly due to the inadequacy of force fields in docking packages to appropriately characterize the metal atoms that consequentially hinder the rational design of metal-based drug complexes. In this study we have made used Molegro and Autodock to predict the anticancer activities of selected Ru(II) complexes against twelve anticancer targets. We observed that introducing the quantum calculated atomic charges of the optimized geometries significantly improved the docking predictions of these anticancer metallocompounds. Despite several limitations in the docking of metal-based complexes, we obtained results that are highly correlated with the available experimental results. Most of our newly proposed metallocompounds are found theoretically to be better anticancer metallocompounds than all the experimentally proposed RAPTA complexes. An interesting features of a strong interactions of new modeled of metallocompounds against the two base edges of DNA strands suggest similar mechanisms of anticancer activities similar to that of cisplatin. There is possibility of covalent bonding between the metal center of the metallocompounds and the residues of the receptors DNA-1, DNA-2, HDAC7, HIS and RNR. However, the general results suggest the possibility of metals positioning the coordinated ligands in the right position for optimal receptor interactions and synergistic effects, rather than forming covalent bonds.

Improving the bioactivity of Zn(II)-curcumin based complexes

New Zn(II)-curcumin based heteroleptic complexes (1-5) have been synthesized and fully characterized, with the aim to improve the bioactivity of the precursor derivative [(bpy-9)Zn(curc)Cl] (A), a potentially intercalating antitumor agent recently reported. Some structural changes have been made starting from the reference complex A, in order to introduce new functionalities, such as electrostatic and/or covalent interactions. In particular, keeping the same N,N chelating ligand, namely bpy-9, two completely different Zn(II) species have been obtained: a tetracoordinated Zn(II) cation with tetrafluoroborate as counterion (1) and a dimeric neutral complex in which the sulfate anion acts as a bridging group through two Zn(II) centres (2). Moreover, by changing the N,N chelating unit, [(L(n))Zn(curc)Cl] complexes (3-5), in which the Zn(II) ion shows the same pentacoordination seen in the precursor complex A, have been obtained. The antitumour activity of all new Zn(II) complexes was tested in vitro against the human neuroblastoma cell line SH-SY5Y in a biohybrid membrane system and the results indicate that all species exhibit strong cytotoxic activity. In particular the ionic tetrafluoroborate Zn(II) complex, 1, and the neutral phenanthroline based Zn(II) derivative, 4, show the strongest growth inhibition, being even more effective than the model complex A. Both complexes have a dose-dependent anti-proliferative effect on cells as demonstrated by the decrease of viability and the increase of Annexin V and PI-positive cells with the increase of their concentration. Cells treated with complexes 1 and 4 undergo apoptosis that involves the activation of JNK, caspase 3 and MMP changes. Finally, complex 1 is more effective in the induction of caspase-3 activation demonstrating its ability to trigger the execution-phase of cell apoptosis.

Comparing the suitability of autodock, gold and glide for the docking and predicting the possible targets of Ru(II)-based complexes as anticancer agents

In cancer chemotherapy, metal-based complexes have been recognized as the most promising means of inhibiting cancer growth due to the successful application of cis-platin and its derivatives above many of the existing organic anticancer agents. The limitations in their rational design can be traced to the complexity of the mechanism of their operations, lack of proper knowledge of their targets and lack of force fields in docking packages to appropriately define the metal centre of the organometallic complexes. In this paper, some of the promising anticancer complexes of Ru(II) such as the rapta-based complexes formulated as [Ru(η6-p-cymene)L2(pta)] and those with unusual ligands are considered. CatB and kinases which have been experimentally confirmed as possible targets of the complexes are also predicted by the three methods as one of the most targeted receptors while TopII and HDAC7 are predicted by two and one of the methods as best targets. The interesting features of the binding of the complexes show that some of the complexes preferentially target specific macromolecules than the others, which is an indication of their specificity and possibility of their therapeutic combination without severe side effects that may come from competition for the same target. Also, introduction of unusual ligands is found to significantly improve the activities of most of the complexes studied. Strong correlations are observed for the predicted binding sites and the orientation of the complexes within the binding site by the three methods of docking. However there are disparities in the ranking of the complexes by the three method of docking, especially that of Glide.

Synthesis, Characterization, and Antibacterial Studies of Pd(II) and Pt(II) Complexes of Some Diaminopyrimidine Derivatives

Pd(II) and Pt(II) complexes of trimethoprim and pyrimethamine were synthesized and characterized by elemental analysis, UV-Vis, FTIR, and NMR spectroscopy. The complexes are formulated as four coordinate square planar species containing two molecules of the drugs and two chloride or thiocyanate ions. The coordination of the metal ions to the pyrimidine nitrogen atom of the drugs was confirmed by spectroscopic analyses. The complexes were screened for their antibacterial activities against eight bacterial isolates. They showed varied activities with the active metal complexes showing more enhanced inhibition than either trimethoprim or pyrimethamine. The Pd(II) complexes of pyrimethamine showed unique inhibitory activities against P. aeruginosa and B. pumilus, and none of the other complexes or the drugs showed any activity against these bacteria isolates. The MIC and MBC determinations revealed that these Pd(II) complexes are the most active. Structure activity relationship showed that Pt(II) complexes containing chloride ions are more active, while for Pd(II) complexes containing thiocyanate ions showed more enhanced activity than those containing chloride ions.

Molecular and cellular characterization of the biological effects of ruthenium(II) complexes incorporating 2-pyridyl-2-pyrimidine-4-carboxylic acid

A great majority of the Ru complexes currently studied in anticancer research exert their antiproliferative activity, at least partially, through ligand exchange. In recent years, however, coordinatively saturated and substitutionally inert polypyridyl Ru(II) compounds have emerged as potential anticancer drug candidates. In this work, we present the synthesis and detailed characterization of two novel inert Ru(II) complexes, namely, [Ru(bipy)(2)(Cpp-NH-Hex-COOH)](2+) (2) and [Ru(dppz)(2)(CppH)](2+) (3) (bipy = 2,2'-bipyridine; CppH = 2-(2'-pyridyl)pyrimidine-4-carboxylic acid; Cpp-NH-Hex-COOH = 6-(2-(pyridin-2-yl)pyrimidine-4-carboxamido)hexanoic acid; dppz = dipyrido[3,2-a:2',3'-c]phenazine). 3 is of particular interest as it was found to have IC(50) values comparable to cisplatin, a benchmark standard in the field, on three cancer cell lines and a better activity on one cisplatin-resistant cell line than cisplatin itself. The mechanism of action of 3 was then investigated in detail and it could be demonstrated that, although 3 binds to calf-thymus DNA by intercalation, the biological effects that it induces did not involve a nuclear DNA related mode of action. On the contrary, confocal microscopy colocalization studies in HeLa cells showed that 3 specifically targeted mitochondria. This was further correlated by ruthenium quantification using High-resolution atomic absorption spectrometry. Furthermore, as determined by two independent assays, 3 induced apoptosis at a relatively late stage of treatment. The generation of reactive oxygen species could be excluded as the cause of the observed cytotoxicity. It was demonstrated that the mitochondrial membrane potential in HeLa was impaired by 3 as early as 2 h after its introduction and even more with increasing time.

Anticancer metallodrug research analytically painting the "omics" picture--current developments and future trends

Anticancer metallodrug development has for a long time been characterised by the similarity of new drug candidates to cisplatin and DNA as the primary target. Recent advances in bioanalytical techniques with high sensitivity and selectivity have revealed that metal-based drugs can undergo a wide range of biomolecular interactions beyond DNA and have generated interest in proteins as possible targets for metallodrugs. In fact, implementation of metallomics approaches that are able to reveal the fate of the compounds in biological systems can help to move drug development towards more targeted and rational design of novel metallodrugs. Additionally, proteomic screening and gene expression analysis can provide insight into physiological response to drug treatment and identify the reasons for drug resistance. Herein, we review selected applications which led to a better understanding of the mode of action of clinically established metal-based anticancer agents and novel metallodrug candidates.

Features and full reversibility of the renal toxicity of the ruthenium-based drug NAMI-A in mice

The ruthenium-based compound imidazolium trans-imidazoledimethylsulfoxide-tetrachlororuthenate (NAMI-A) is free of cytotoxicity up to 1mM concentration after 1h in vitro exposure of the LLC-PK1 renal tubule cells. In vivo, one cycle of i.p. administrations of 35 mg/kg/day NAMI-A (1 cycle=6 consecutive days), is free of a measurable toxicity on mouse kidneys. After two cycles with a one-week drug-free washout between cycles, mitochondrial membrane potential of the renal cells drops by 37% (p<0.05), serum creatinine increases by 30% (p<0.05) and a significant decrease of body weight of 12% (p<0.05) occurs. These parameters return to normal within 7 days after the end of treatment. A cycle-dependent alteration of glomeruli and a diffused swelling of renal tubules are also evident leading to a significant alteration of these structures after the third cycle. These effects are completely prevented if a 2-week drug free washout is used between two consecutive cycles. These data support the toxic accumulation of NAMI-A or of its products of transformation in the kidneys and stress the need of at least 14 days washout between two treatment cycles when the drug is given daily for 6 consecutive days.

The selective synthesis of metallanucleosides and metallanucleotides: a new tool for the functionalization of nucleic acids

Nucleobases team up: the efficient and selective preparation of purine-derived metallanucleosides, metallanucleotides, and metalladinucleotides having M-C bonds (M=Ir(III), Rh(III)) is reported for the first time. The results presented may be applied to the synthesis of functionalized nucleic acids, or DNA/RNA-modified segments.

Organometallic Palladium Complexes with a Water-Soluble Iminophosphorane Ligand as Potential Anticancer Agents

The synthesis and characterization of a new water-soluble iminophosphorane ligand TPA=N-C(O)-2BrC(6)H(4) (C,N-IM; TPA = 1,3,5-triaza-7-phosphaadamantane) 1 is reported. Oxidative addition of 1 to Pd(2)(dba)(3) affords the orthopalladated dimer [Pd(μ-Br){C(6)H(4)(C(O)N=TPA-kC,N)-2}](2) (2) as a mixture of cis and trans isomers (1:1 molar ratio) where the iminophosphorane moeity behaves as a C,N-pincer ligand. By addition of different neutral or monoanionic ligands to 2, the bridging bromide can be cleaved and a variety of hydrophilic or water-soluble mononuclear organometallic palladium(II) complexes of the type [Pd{C(6)H(4)(C(O)N=TPA-kC,N)-2}(L-L)] (L-L = acac (3); S(2)CNMe(2) (4); 4,7-Diphenyl-1,10-phenanthrolinedisulfonic acid disodium salt C(12)H(6)N(2)(C(6)H(4)SO(3)Na)(2) (5)); [Pd{C(6)H(4)(C(O)N=TPA-kC,N)-2}(L)Br] (L = P(mC(6)H(4)SO(3)Na)(3) (6); P(3-Pyridyl)(3) (7)) and, [Pd(C(6)H(4)(C(O)N=TPA)-2}(TPA)(2)Br] (8) are obtained as single isomers. All new complexes were tested as potential anticancer agents and their cytotoxicity properties were evaluated in vitro against human Jurkat-T acute lymphoblastic leukemia cells, normal T-lymphocytes (PBMC) and DU-145 human prostate cancer cells. Compounds [Pd(μ-Br){C(6)H(4)(C(O)N=TPA-kC,N)-2}](2) (2) and [Pd{C(6)H(4)(C(O)N=TPA-kC,N)-2}(acac)] 3 (which has been crystallographically characterized) display the higher cytotoxicity against the above mentioned cancer cell lines while being less toxic to normal T-lymphocytes (peripheral blood mononuclear cells: PBMC). In addition, 3 is very toxic to cisplatin resistant Jurkat shBak indicating a cell death pathway that may be different to that of cisplatin. The interaction of 2 and 3 with plasmid (pBR322) DNA is much weaker than that of cisplatin pointing to an alternative biomolecular target for these cytotoxic compounds. All the compounds show an interaction with human serum albumin (HSA) faster than that of cisplatin.

Cytotoxic hydrophilic iminophosphorane coordination compounds of d⁸ metals. Studies of their interactions with DNA and HSA

The synthesis and characterization of a new water-soluble N,N-chelating iminophosphorane ligand TPAN-C(O)-2-NC(5)H(4) (N,N-IM) (1) and its d(8) (Au(III), Pd(II) and Pt(II)) coordination complexes are reported. The structures of cationic [AuCl(2)(N,N-IM)]ClO(4) (2) and neutral [MCl(2)(N,N-IM)] M=Pd (3), Pt(4) complexes were determined by X-ray diffraction studies or by means of density-functional calculations. While the Pd and Pt compounds are stable in mixtures of DMSO/H(2)O over 4 days, the gold derivative (2) decomposes quickly to TPAO and previously reported neutral gold(III) compound [AuCl(2)(N,N-H)] 5 (containing the chelating N,N-fragment HN-C(O)-2-NC(5)H(4)). The cytotoxicities of complexes 2-5 were evaluated in vitro against human Jurkat-T acute lymphoblastic leukemia cells and DU-145 human prostate cancer cells. Pt (4) and Au compounds (2 and 5) are more cytotoxic than cisplatin to these cell lines and to cisplatin-resistant Jurkat sh-Bak cell lines and their cell death mechanism is different from that of cisplatin. All the compounds show higher toxicity against leukemia cells when compared to normal human T-lymphocytes (PBMC). The interaction of the Pd and Pt compounds with calf thymus and plasmid (pBR322) DNA is different from that of cisplatin. All compounds bind to human serum albumin (HSA) faster than cisplatin (measured by fluorescence spectroscopy). Weak and stronger binding interactions were found for the Pd (3) and Pt (4) derivatives by isothermal titration calorimetry. Importantly, for the Pt (4) compounds the binding to HSA was reversed by addition of a chelating agent (citric acid) and by a decrease in pH.