A ruthenocene-PNA bioconjugate--synthesis, characterization, cytotoxicity, and AAS-detected cellular uptake

Synthesis and Characterization of Ruthenium-Paraphenylene-Cyclopentadienyl Full-Sandwich Complexes: Cytotoxic Activity against A549 Lung Cancer Cell Line and DNA Binding Properties

Novel full-sandwich (η5-Cp)-Ru-paraphenylene complexes with the general formula [(η5-Cp)nRu(η6-L)](PF6)n where n = 1-3 and L = biphenyl, p-terphenyl and p-quaterphenyl, were synthesized and characterized by means of spectroscopic and analytical techniques. The structures of the complexes [(η5-Cp)Ru(η6-biphenyl)](PF6) (1), [(η5-Cp)Ru(η6-terphenyl)](PF6) (3) and [(η5-Cp)2Ru(η6-terphenyl)](PF6)2 (4) was determined by X-ray single crystal methods. The interaction of the complexes [(η5-Cp)Ru(η6-quaterphenyl)]Cl, (6)Cl, and [(η5-Cp)2Ru(η6-quaterphenyl)]Cl2, (7)Cl2, with the DNA duplex d(5'-CGCGAATTCGCG-3')2 was studied using NMR techniques. The results showed that both complexes interacted non-specifically with both the minor and major grooves of the helix. Specifically, (6)Cl exhibited partial binding through intercalation between the T7 and T8 bases of the sequence without disrupting the C-G and A-T hydrogen bonds. Fluorometric determination of the complexes' binding constants revealed a significant influence of the number of connected phenyl rings in the paraphenylene ligand (L) on the binding affinity of their complexes with the d(5'-CGCGAATTCGCG-3')2. The complexes (6)Cl and (7)Cl2 were found to be highly cytotoxic against the A549 lung cancer cell line, with complex (6) being more effective than (7) (IC50 for (6)Cl: 17.45 ± 2.1 μΜ, IC50 for (7)Cl2: 65.83 ± 1.8 μΜ) and with a selectivity index (SI) (SI for (6)Cl: 1.1 and SI for (7)Cl2: 4.8).

Synthesis and DNA interaction studies of Ru(II) cell penetrating peptide (CPP) bioconjugates

The synthesis of the first bioconjugates of a set of ruthenium(II) dipyridophenazine complexes with two different cell penetrating peptides (CPPs) is described. The CPPs, an arginine rich TAT-9 (RKKRRQRRR) sequence and the Xentry peptide (LCLRPVG), were synthesized using standard SPPS protocols, and the bioconjugates were obtained by the microwave-assisted coupling of the HOBt/TBTU preactivated metal complexes with the respective peptides on Wang resin. The racemic metal complexes were obtained by modified literature procedures. The bioconjugates were cleaved from the resin, purified by semi-preparative HPLC and characterized by analytical HPLC, high resolution mass spectrometry (HR-MS), and NMR spectroscopy. Despite the bioconjugation of the peptides to the dppz ligand, DNA intercalation was observed by CD spectroscopy, viscometry and the characteristic switch-on fluorescence of this class of compounds. Furthermore, the cellular uptake of the Xentry bioconjugates was confirmed by live cell imaging. Like the parent metal complexes, the bioconjugates show low in vitro cytotoxicity (IC50 > 80 μM), which is similar to the respective metal complexes alone.

Can Electrochemical Measurements Be Used To Predict X-ray Photoelectron Spectroscopic Data? The Case of Ferrocenyl-β-Diketonato Complexes of Manganese(III)

In order to better understand intramolecular communication between molecular fragments, a series of ferrocene-functionalized β-diketonato manganese(III) complexes, [Mn(FcCOCHCOR)₃] with R = CF₃, 1, CH₃, 2, Ph = C₆H₅, 3, and Fc = Fe^II(η⁵-C₅H₄)(η⁵-C₅H₅), 4, the mixed ligand β-diketonato complex [Mn(FcCOCHCOFc)₂(FcCOCHCOCH₃)], 5, as well as the acac complex [Mn(CH₃COCHCOCH₃)₃], 6, were subjected to an electrochemical and X-ray photoelectron spectroscopy (XPS) study. The ferrocenyl (Fe^II) and Mn^III redox potentials, E°', and photoelectron lines were sufficiently resolved in each complex to demonstrate a linear correlation between E°' and group electronegativities of ligand R groups, χ_R, or Σχ_R, as well as with binding energies of both the Fe 2p_3/2 and Mn 2p_3/2 photoelectron lines. These relationships are consistent with effective communication between molecular fragments of 1-5. From these relationships, prediction of Mn and Fe core electron binding energies in [Mn(R¹COCHCOR²)₃] complexes from known manganese and/or ferrocenyl redox potentials are, therefore, now possible. Ligand infrared carbonyl stretching frequencies were successfully related to binding energy as a measure of the energy required for inner-sphere reorganization. In particular it became possible to explain why, upon electrochemical oxidation or photoionization, the ferrocenyl Fe^II inner-shell of 1-5 needs more energy in complexes with ligands bearing electron-withdrawing (CF₃) groups than in ligands bearing electron-donating groups such as ferrocenyl. The XPS determined entity I_ratio (the ratio between the intensities of the satellite and main metal 2p_3/2 photoelectron lines) is an indication not only of the amount of charge transferred, but also of the degree of inner-sphere reorganization. Just as for binding energy, the quantity I_ratio was also found to be related to the energy requirements for the inner-sphere reorganization depicted by the vibrational frequency, v_co.

The development of ruthenium(ii) polypyridyl complexes and conjugates for in vitro cellular and in vivo applications

Ruthenium(ii) [Ru(ii)] polypyridyl complexes have been the focus of intense investigations since work began exploring their supramolecular interactions with DNA. In recent years, there have been considerable efforts to translate this solution-based research into a biological environment with the intention of developing new classes of probes, luminescent imaging agents, therapeutics and theranostics. In only 10 years the field has expanded with diverse applications for these complexes as imaging agents and promising candidates for therapeutics. In light of these efforts this review exclusively focuses on the developments of these complexes in biological systems, both in cells and in vivo, and hopes to communicate to readers the diversity of applications within which these complexes have found use, as well as new insights gained along the way and challenges that researchers in this field still face.

Oligonucleotide conjugates - Candidates for gene silencing therapeutics

The potential therapeutic and diagnostic applications of oligonucleotides (ONs) have attracted great attention in recent years. The capability of ONs to selectively inhibit target genes through antisense and RNA interference mechanisms, without causing un-intended sideeffects has led them to be investigated for various biomedical applications, especially for the treatment of viral diseases and cancer. In recent years, many researchers have focused on enhancing the stability and target specificity of ONs by encapsulating/complexing them with polymers or lipid chains to formulate nanoparticles/nanocomplexes/micelles. Also, chemical modification of nucleic acids has emerged as an alternative to impart stability to ONs against nucleases and other degrading enzymes and proteins found in blood. In addition to chemically modifying the nucleic acids directly, another strategy that has emerged, involves conjugating polymers/peptide/aptamers/antibodies/proteins, preferably to the sense strand (3'end) of siRNAs. Conjugation to the siRNA not only enhances the stability and targeting specificity of the siRNA, but also allows for the development of self-administering siRNA formulations, with a much smaller size than what is usually observed for nanoparticle (∼200nm). This review concentrates mainly on approaches and studies involving ON-conjugates for biomedical applications.

A DFT-Elucidated Comparison of the Solution-Phase and SAM Electrochemical Properties of Short-Chain Mercaptoalkylferrocenes: Synthetic and Spectroscopic Aspects, and the Structure of Fc-CH2CH2-S-S-CH2CH2-Fc

Facile synthetic procedures to synthesize a series of difficult-to-obtain mercaptoalkylferrocenes, namely, Fc(CH2)nSH, where n = 1 (1), 2 (2), 3 (3), or 4 (4) and Fc = Fe(η(5)-C5H5)(η(5)-C5H4), are reported. Dimerization of 1-4 to the corresponding disulfides 19-22 was observed in air. Dimer 20 (Z = 2) crystallized in the triclinic space group P1̅. Dimers 20-22 could be reduced back to the original Fc(CH2)nSH derivatives with LiAlH4 in refluxing tetrahydrofuran. Density functional theory (DFT) calculations showed that the highest occupied molecular orbital of 1-4 lies exclusively on the ferrocenyl group implying that the electrochemical oxidation observed at ca. -15 < Epa < 76 mV versus FcH/FcH(+) involves exclusively an Fe(II) to Fe(III) process. Further DFT calculations showed this one-electron oxidation is followed by proton loss on the thiol group to generate a radical, Fc(CH2)nS(•), with spin density mainly located on the sulfur. Rapid exothermic dimerization leads to the observed dimers, Fc(CH2)n-S-S-(CH 2)nFc. Reduction of the ferrocenium groups on the dimer occurs at potentials that still showed the ferrocenyl group ΔE = Epa,monomer - Epc,dimer ≤ 78 mV, indicating that the redox properties of the ferrocenyl group on the mercaptans are very similar to those of the dimer. (1)H NMR measurements showed that, like ferrocenyl oxidation, the resonance position of the sulfhydryl proton, SH, and others, are dependent on -(CH2)n- chain length. Self-assembled monolayers (SAMs) on gold were generated to investigate the electrochemical behavior of 1-4 in the absence of diffusion. Under these conditions, ΔE approached 0 mV for the longer chain derivatives at slow scan rates. The surface-bound ferrocenyl group of the metal-thioether, Fc(CH2)n -S-Au, is oxidized at approximately equal potentials as the equivalent CH2Cl2-dissolved ferrocenyl species 1-4. Surface coverage by the SAMs is dependent on alkyl chain length with the largest coverage obtained for 4, while the rate of heterogeneous electron transfer between SAM substrate and electrode was the fastest for the shortest chain derivative, Fc-CH2-S-Au.

Consequences of Electron-Density Manipulations on the X-ray Photoelectron Spectroscopic Properties of Ferrocenyl-β-diketonato Complexes of Manganese(III). Structure of [Mn(FcCOCHCOCH3)3]

Reaction of [Mn3(OAc)6O·3H2O](+) (1) with ferrocenyl β-diketones of the type FcCOCH2COR with R = CF3 (2a) and CH3 (2b), Ph = C6H5 (2c), and Fc = Fe(II)(η(5)-C5H4)(η(5)-C5H5) (2d) yielded a series of ferrocene-functionalized β-diketonato manganese(III) complexes 3a-3d, respectively, of general formula [Mn(FcCOCHCOR)3]. The mixed-ligand β-diketonato complex [Mn(FcCOCHCOFc)2(FcCOCHCOCH3)] (4) was obtained by reacting mixtures of diketones 2b and 2d with 1. A single-crystal X-ray structure determination of 3b (Z = 2, triclinic, space group P1̅) highlighted a weak axial elongating Jahn-Teller effect and a high degree of bond conjugation. An X-ray photoelectron spectroscopic study, by virtue of linear relationships between group electronegativities of ligand R groups, χR, or ∑χR, and binding energies of both the Fe 2p3/2 and Mn 2p3/2 photoelectron lines, confirmed communication between molecular fragments of 2a-2d as well as 3a-3d. This unprecedented observation allows prediction of binding energies from known β-diketonato side group χR values.

Vesicular disruption of lysosomal targeting organometallic polyarginine bioconjugates

Compounds which are able to destabilize the lysosomal membrane have been proposed as interesting candidates for targeted anticancer drugs due to the pronounced lysosomal changes in cancer cells. For this purpose, metallocene derivatives of a cell penetrating polyarginine peptide M–(Arg)9(Phe)2Lys–NH2 (where M = ferrocene carboxylate or ruthenocene carboxylate) were designed and their biological activities were investigated in detail. The ferrocenoyl- and ruthenocenoyl polyarginine bioconjugates were synthesized via Fmoc solid-phase peptide synthesis (SPPS) protocols on a microwave-assisted synthesizer. After HPLC purification >98% purity was observed for all conjugates. Their interaction with supported biomimetic membranes was investigated on a quartz crystal microbalance (QCM) and revealed a very strong binding of the metallocene peptides and their metal-free congeners to an artificial eukaryotic membrane model (DMPC–cholesterol). To demonstrate their antiproliferative utility as cytotoxic compounds for a targeted anticancer drug, cell viability (by the crystal violet assay), apoptosis (flow cytometry, Ann V/PI staining), induction of reactive oxygen species (ROS, by flow cytometry with dihydroethidium staining), and changes in cancer cell metabolism, e.g. respiration and glycolysis, were studied. Our results reveal only a weak toxicity for the metal-free polyarginine peptide, which could be significantly enhanced (to ca. 50 μM against HeLa cells in the best case) by coupling ferrocene or ruthenocene carboxylates to the N-terminus of the peptide. The investigation of the cellular uptake and intracellular localization by fluorescence microscopy revealed an enhanced vesicular disruption by the metallocene bioconjugate compared to the metal-free derivative which could be triggered by light and chemicals. Further studies of apoptosis, respiration, glycolysis and ROS formation reveal the superior characteristics of the metallocene compounds. While most cells remain viable even at 300 μM of the metal free bioconjugate 1, most cells are dead or in late stages of apoptosis at 200 μM of the ruthenocene derivative 3, and at 100 μM of the most active ferrocene derivative 2, however, all show very little sign of necrosis. Also, the metal free compound 1 does not induce ROS formation but both metallocene–polyarginine bioconjugates are clearly associated with enhanced intracellular ROS levels, with levels for the redox-active ferrocene derivative being two times higher than for the structurally very similar but redox-silent ruthenocene derivative. We propose that such metallocene–polyarginine peptides induce lysosomal membrane permeabilization and thereby could be developed towards targeted anticancer drugs.

In vitro and in vivo evaluation of water-soluble iminophosphorane ruthenium(II) compounds. A potential chemotherapeutic agent for triple negative breast cancer

A series of organometallic ruthenium(II) complexes containing iminophosphorane ligands have been synthesized and characterized. Cationic compounds with chloride as counterion are soluble in water (70–100 mg/mL). Most compounds (especially highly water-soluble 2) are more cytotoxic to a number of human cancer cell lines than cisplatin. Initial mechanistic studies indicate that the cell death type for these compounds is mainly through canonical or caspase-dependent apoptosis, nondependent on p53, and that the compounds do not interact with DNA or inhibit protease cathepsin B. In vivo experiments of 2 on MDA-MB-231 xenografts in NOD.CB17-Prkdc SCID/J mice showed an impressive tumor reduction (shrinkage) of 56% after 28 days of treatment (14 doses of 5 mg/kg every other day) with low systemic toxicity. Pharmacokinetic studies showed a quick absorption of 2 in plasma with preferential accumulation in the breast tumor tissues when compared to kidney and liver, which may explain its high efficacy in vivo.

Small cationic antimicrobial peptides delocalize peripheral membrane proteins

Short antimicrobial peptides rich in arginine (R) and tryptophan (W) interact with membranes. To learn how this interaction leads to bacterial death, we characterized the effects of the minimal pharmacophore RWRWRW-NH2. A ruthenium-substituted derivative of this peptide localized to the membrane in vivo, and the peptide also integrated readily into mixed phospholipid bilayers that resemble Gram-positive membranes. Proteome and Western blot analyses showed that integration of the peptide caused delocalization of peripheral membrane proteins essential for respiration and cell-wall biosynthesis, limiting cellular energy and undermining cell-wall integrity. This delocalization phenomenon also was observed with the cyclic peptide gramicidin S, indicating the generality of the mechanism. Exogenous glutamate increases tolerance to the peptide, indicating that osmotic destabilization also contributes to antibacterial efficacy. Bacillus subtilis responds to peptide stress by releasing osmoprotective amino acids, in part via mechanosensitive channels. This response is triggered by membrane-targeting bacteriolytic peptides of different structural classes as well as by hypoosmotic conditions.

Sandwich complex-containing macromolecules: property tunability through versatile synthesis

Sandwich complexes feature unique properties as the physical and electronic properties of a hydrocarbon ligand or its derivative are integrated into the physical, electronic, magnetic, and optical properties of a metal. Incorporation of these complexes into macromolecules results in intriguing physical, electrical, and optical properties that were hitherto unknown in organic-based macromolecules. These properties are tunable through well-designed synthetic strategies. This review surveys many of the synthetic approaches that have resulted in tuning the properties of sandwich complex-containing macromolecules. While the past two decades have seen an ever-growing number of research publications in this field, gaps remain to be filled. Thus, we expect this review to stimulate research interest towards bridging these gaps, which include the insolubility of some of these macromolecules as well as expanding the scope of the sandwich complexes.