Self-Assembly of a Dipeptide with a Reduced Amount of Copper into Antifungal and Antibacterial Particles

With the growing concern over the environmental impact and health risks associated with conventional pesticides, there is a great need for developing safer and more sustainable alternatives. This study demonstrates the self-assembly of antimicrobial and antifungal spherical particles by a dipeptide utilizing a reduced amount of copper salt compared to the commonly employed formulation. The particles can be sprayed on a surface and form an antimicrobial coating. The effectiveness of the coating against the bacteria Pectobacterium brasiliense, a common pathogen affecting potato crops, was demonstrated, as the coating reduced the bacterial load by 7.3 log. Moreover, a comprehensive field trial was conducted, where the formulation was applied to potato seeds. Remarkably, it exhibited good efficacy against three prevalent potato pathogens (P. brasiliense, Pythium spp., and Spongospora subterranea) while demonstrating no phytotoxic effects on the potatoes. These findings highlight the tremendous potential of this formulation as a nonphytotoxic alternative to replace hazardous pesticides currently available in the market.

Titanium complexes affect Bacillus subtilis biofilm formation

Biofilms are surface or interface-associated communities of bacterial cells, embedded in a self-secreted extracellular matrix (ECM). Cells in biofilms are 100-1000 times more resistant to antibiotic treatment relative to planktonic cells due to various reasons, including the ECM acting as a diffusion barrier to antibiotic molecules, the presence of persister cells that divide slowly and are less susceptible to cell-wall targeting drugs, and the activation of efflux pumps in response to antibiotic stress. In this study we tested the effect of two titanium(iv) complexes that have been previously reported as potent and non-toxic anticancer chemotherapeutic agents on Bacillus subtilis cells in culture and in biofilm forming conditions. The Ti(iv) complexes tested, a hexacoordinate diaminobis(phenolato)-bis(alkoxo) complex (phenolaTi) and a bis(isopropoxo) complex of a diaminobis(phenolato) "salan"-type ligand (salanTi), did not affect the growth rate of cells in shaken cultures, however they did affect biofilm formation. Surprisingly, while phenolaTi inhibited biofilm formation, the presence of salanTi induced the formation of more mechanically robust biofilms. Optical microscopy images of biofilm samples in the absence and presence of Ti(iv) complexes suggest that Ti(iv) complexes affect cell-cell and/or cell-matrix adhesion, and that these are interfered with phenolaTi and enhanced by salanTi. Our results highlight the possible effect of Ti(iv) complexes on bacterial biofilms, which is gaining interest in light of the emerging relations between bacteria and cancerous tumors.

Phenolato Ti(IV) hexacoordinate complexes for anticancer chemotherapy: enhancement of solubility, hydrolytic stability, and cytotoxicity

A new series of five titanium(IV) complexes based on diaminobis(phenolato)-bis(alkoxo) ligands with different substitutions was synthesized and characterized. All complexes were analyzed by X-ray crystallography, and all structures indicated C₂ symmetrical octahedral compounds. All complexes exhibited enhanced solubility in aqueous media compared with the parent methylated derivative phenolaTi (up to 0.4 vs. 0.05 mg ml^-1 of phenolaTi) due to halogen and alkoxo/hydroxo substitutions, with particularly enhanced water solubility for the methoxylated and hydroxylated derivatives. In particular, high hydrolytic stability was recorded for all derivatives, with the t_½ for ligand hydrolysis of more than 8 days, as established by ¹H NMR and HR-MS. All complexes were cytotoxic toward human ovarian A2780, colon HT-29, and cervical HeLa cancer cell lines (IC₅₀ values in the range of 0.3-40 μM), with negligible activity toward non-cancerous MRC-5 cells. The halogenated compounds of this series exhibit the best combination of stability and activity, making them highly promising for anticancer applications.

An anticancer Ti(IV) complex increases mitochondrial reactive oxygen species levels in relation with hypoxia and endoplasmic-reticulum stress: A distinct non DNA-related mechanism

PhenolaTi is a promising Ti(IV) anticancer complex, with high stability and cytotoxicity, without notable toxic side-effects. Its cellular mechanism was proposed to relate to ER stress. Herein, we investigated the downstream effects of this mode of action in two cancer cell lines: ovarian carcinoma A2780 and cervical adenocarcinoma HeLa. First, although Ti(IV) is a non-redox metal, the formation of mitochondrial reactive oxygen species (ROS) was detected with live-cell imaging. Then, we inspected the effect of the mitochondrial ROS on cytotoxicity, using two methods: (a) addition of compounds that either elevate or reduce the mitochondrial glutathione concentration, thus affecting the oxidative state of the cells; and (b) scavenging mitochondrial ROS. Unlike the results observed for cisplatin, neither method influenced the cytotoxicity of phenolaTi, implying that ROS formation was a mere side effect of its activity. Additionally, live cell imaging displayed the hypoxia induced by phenolaTi, which can be associated with ROS formation. Overall, the results support the notion that ER-stress is the main cellular mechanism of phenolaTi, leading to hypoxia and mitochondrial ROS. The distinct mechanism of phenolaTi, which is different from that of cisplatin, combined with its stability and favorable anticancer properties, altogether make it a strong chemotherapeutic drug candidate.

Targeting Protein Interaction Hotspots Using Structured and Disordered Chimeric Peptide Inhibitors

The main challenge in inhibiting protein-protein interactions (PPI) for therapeutic purposes is designing molecules that bind specifically to the interaction hotspots. Adding to the complexity, such hotspots can be within both structured and disordered interaction interfaces. To address this, we present a strategy for inhibiting the structured and disordered hotspots of interactions using chimeric peptides that contain both structured and disordered parts. The chimeric peptides we developed are comprised of a cyclic structured part and a disordered part, which target both disordered and structured hotspots. We demonstrate our approach by developing peptide inhibitors for the interactions of the antiapoptotic iASPP protein. First, we developed a structured, α-helical stapled peptide inhibitor, derived from the N-terminal domain of MDM2. The peptide bound two hotspots on iASPP at the low micromolar range and had a cytotoxic effect on A2780 cancer cells with a half-maximal inhibitory concentration (IC₅₀) value of 10 ± 1 μM. We then developed chimeric peptides comprising the structured stapled helical peptide and the disordered p53-derived LinkTer peptide that we previously showed to inhibit iASPP by targeting its disordered RT loop. The chimeric peptide targeted both structured and disordered domains in iASPP with higher affinity compared to the individual structured and disordered peptides and caused cancer cell death. Our strategy overcomes the inherent difficulty in inhibiting the interactions of proteins that possess structured and disordered regions. It does so by using chimeric peptides derived from different interaction partners that together target a much wider interface covering both the structured and disordered domains. This paves the way for developing such inhibitors for therapeutic purposes.

Synthesis of asymmetrical diaminobis(alkoxo)-bisphenol compounds and their C1-symmetrical mono-ligated titanium(iv) complexes as highly stable highly active antitumor compounds

Asymmetrical 2,2'-((ethane-1,2-diylbis((2-hydroxyethyl)azanediyl))bis(methylene))diphenol substituted compounds and their C1-symmetrical diaminobis(phenolato)-bis(alkoxo) titanium(iv) complexes were synthesized, with one symmetrical analogue. X-ray crystallography corroborated tight ligand binding. Different substitutions on the two aromatic rings enabled fine-tuning of the complex properties, giving enhanced solubility, high anticancer activity (IC50 < 4 μM), and significant hydrolytic stability.

From medium to endoplasmic reticulum: Tracing anticancer phenolato titanium(IV) complex by 19F NMR detection

Titanium(IV) complexes of diaminobis(phenolato)-bis(alkoxo) ligands are promising anticancer drugs, showing marked in-vivo efficacy with no toxic side-effects in mice, hence, it is of interest to elucidate their mechanism of action. Herein, we employed a fluoro-substituted derivative, FenolaTi, for mechanistic analysis of the active species and its cellular target by quantitative ¹⁹F NMR detection to reveal its biodistribution and reactivity in extracellular and intracellular matrices. Upon administration to the serum-containing medium, FenolaTi interacted with bovine serum albumin. 20 h post administration, the cellular accumulation of FenolaTi derivatives was estimated as 37% of the administered compound, in a concentration three orders-of-magnitude higher than the administered dose, implying that active membrane transportation facilitates cellular penetration. An additional 19% of the administered dose that was detected in the extracellular environment had originated from post-apoptotic cells. In the cell, interaction with cellular proteins was detected. Although some intact Ti(IV) complex localized in the nucleus, no signals for isolated DNA fractions were detected and no reactivity with nuclear proteins was observed. Interestingly, higher accumulation of FenolaTi-derived compounds in the endoplasmic reticulum (ER) and interaction with proteins therein were detected, supporting the role of the ER as a possible target for cytotoxic bis(phenolato)-bis(alkoxo) Ti(IV) complexes.

Targeting an Interaction Between Two Disordered Domains by Using a Designed Peptide

Intrinsically disordered regions in proteins (IDRs) mediate many disease-related protein-protein interactions. However, the unfolded character and continuous conformational changes of IDRs make them difficult to target for therapeutic purposes. Here, we show that a designed peptide based on the disordered p53 linker domain can be used to target a partner IDR from the anti-apoptotic iASPP protein, promoting apoptosis of cancer cells. The p53 linker forms a hairpin-like structure with its two termini in close proximity. We designed a peptide derived from the disordered termini without the hairpin, designated as p53 LinkTer. The LinkTer peptide binds the disordered RT loop of iASPP with the same affinity as the parent p53 linker peptide, and inhibits the p53-iASPP interaction in vitro. The LinkTer peptide shows increased stability to proteolysis, penetrates cancer cells, causes nuclei shrinkage, and compromises the viability of cells. We conclude that a designed peptide comprising only the IDR from a peptide sequence can serve as an improved inhibitor since it binds its target protein without the need for pre-folding, paving the way for therapeutic targeting of IDRs.

Effective Oral Administration of an Antitumorigenic Nanoformulated Titanium Complex

Orally administered anticancer drugs facilitate treatment, but the acidic conditions in the stomach often challenge their availability. PhenolaTi is a Ti^IV -based nontoxic anticancer drug with marked in-vivo efficacy. We report that nanoformulation protects phenolaTi from decomposition in stomach-like conditions. This is evidenced by similar NMR characteristics and similar in-vitro cytotoxicity toward murine (CT-26) and human (HT-29) colon cancer cells before and after incubation of nanoformulated phenolaTi (phenolaTi-F) at pH 2, unlike results with the unformulated form of the complex. Furthermore, administration of phenolaTi-F in animal drinking water revealed a notable inhibition of tumor growth in Balb/c and immune-deficient (Nude) mice inoculated with CT-26 and HT-29 cells, respectively. In-vivo efficacy was at least similar to that of the corresponding intraperitoneal treatment with phenolaTi-F and the clinically employed oral drug, capecitabine. No body weight loss or clinical signs of toxicity were evident in the phenolaTi-F-treated animals. These findings demonstrate a new convenient mode of cancer treatment through oral administration by safe titanium-based drugs.

Titanium Tackles the Endoplasmic Reticulum: A First Genomic Study on a Titanium Anticancer Metallodrug

PhenolaTi is an advanced non-toxic anticancer chemotherapy; this inert bis(phenolato)bis(alkoxo) Ti(IV) complex demonstrates the intriguing combination of high and wide efficacy with no detected toxicity in animals. Here we unravel the cellular pathways involved in its mechanism of action by a first genome study on Ti(IV)-treated cells, using an attuned RNA sequencing-based available technology. First, phenolaTi induced apoptosis and cell-cycle arrest at the G2/M phase in MCF7 cells. Second, the transcriptome of the treated cells was analyzed, identifying alterations in pathways relating to protein translation, DNA damage, and mitochondrial eruption. Unlike for common metallodrugs, electrophoresis assay showed no inhibition of DNA polymerase activity. Reduced in vitro cytotoxicity with added endoplasmic reticulum (ER) stress inhibitor supported the ER as a putative cellular target. Altogether, this paper reveals a distinct ER-related mechanism by the Ti(IV) anticancer coordination complex, paving the way for wider applicability of related techniques in mechanistic analyses of metallodrugs.

Targeting an Interaction Between Two Disordered Domains by Using a Designed Peptide

Invited for the cover of this issue is the group of Assaf Friedler at the Hebrew University of Jerusalem. The image depicts the protein-protein interactions reported in this work. Read the full text of the article at 10.1002/chem.202000465.

Cytotoxic homoleptic Ti(iv) compounds of ONO-type ligands: synthesis, structures and anti-cancer activity

Reacting variously substituted dianionic tridentate ONO-type acylhydrazone ligands with titanium(iv) tetra(isopropoxide) gave a new class of eight homoleptic titanium(iv) compounds showing exceptional stability and promising cytotoxicity.

Racemic vs. enantiopure inert Ti(iv) complex of a single diaminotetrakis(phenolato) ligand in anticancer activity toward human drug-sensitive and -resistant cancer cell lines

A tetrakis(phenolato) Ti(iv) complex was synthesized in racemic and optically pure form, exhibiting high hydrolytic stability, and similar cytotoxicity for all stereochemical forms on HT-29 and A2780 cancer cells. Higher activity of the racemate on drug-resistant A2780cp and A2780adr lines implies a beneficial activity of both enantiomers rendering enantiomeric resolution unnecessary.

In Vivo Anticancer Activity of a Nontoxic Inert Phenolato Titanium Complex: High Efficacy on Solid Tumors Alone and Combined with Platinum Drugs

Due to the toxicity of platinum compounds used in the clinic as anticancer chemotherapies, titanium serves as a safe and attractive alternative. Lately, we introduced a new family of Ti complexes based on readily available phenolato ligands, demonstrating incredibly high hydrolytic stability, with the lead compound phenolaTi demonstrating wide cytotoxic activity toward the NCI‐60 panel of human cancer cell lines, with an average GI₅₀ value of 4.7±2 μm. Herein, we evaluated in vivo: a) the safety, and b) the growth inhibitory capacity (efficacy) of this compound. PhenolaTi was found to be effective in vivo against colon (CT‐26) and lung (LLC‐1) murine cell lines in syngeneic hosts and toward a human colon cancer (HT‐29) cell line in immune‐deficient (Nude) mice, with an efficacy similar to that of known chemotherapy. Notably, no clinical signs of toxicity were observed in the treated mice, namely, no effect on body weight, spleen weight or kidney function, unlike the effects observed with the positive control Pt drugs. Studies of combinations of phenolaTi and Pt drugs provided evidence that similar efficacy with decreased toxicity may be achieved, which is highly valuable for medicinal applications.

Synthesis of Pure Enantiomers of Titanium(IV) Complexes with Chiral Diaminobis(phenolato) Ligands and Their Biological Reactivity

Racemic and enantiomerically pure titanium(IV) complexes with ortho-brominated or para-nitrated chiral diaminobis(phenolato) ligands were prepared with NH and NMe cyclohexyldiamino bridges through ligand to metal chiral induction. The hydrolytic behavior of the complexes was evaluated, identifying the N-methylated complex as the most stable. A representative NH complex hydrolyzed to first give a dimeric structure in solution as deduced by NMR diffusion measurements, followed by formation of clusters with higher nuclearity, as was supported by X-ray characterization of a tetranuclear cluster obtained in trace amounts following 30 days in water solutions. The cytotoxicity of the enantiomerically pure and racemic complexes was measured on HT-29 human colon cancer cell line based on the MTT assay; all stereochemical configurations of the N-methylated complex were inactive, whereas for the NH complexes, the racemic mixtures were mostly inactive but the pure enantiomers exhibited similarly high cytotoxicity, supporting a polynuclear active species. Analysis of the two enantiomers of the most active brominated complex for their cytotoxicity on human ovarian A2780, cisplatin resistant A2780cp and multi-drug-resistant A2780adr cell lines as well as for their apoptosis induction on the A2780 line revealed similar reactivity, supporting a similar mechanism for the two enantiomers.

In vitro combinations of inert phenolato Ti(iv) complexes with clinically employed anticancer chemotherapy: synergy with oxaliplatin on colon cells

Advanced anticancer phenolato titanium(iv) complexes were combined with known chemotherapeutic anticancer drugs applied in the clinic and were analyzed in vitro on cell lines most sensitive to the Ti(iv) complex and relevant to the clinical application of the known drugs. Combination of the Ti(iv) complex with cisplatin on ovarian cells showed mostly an additive behavior, also on a line resistant to cisplatin. Combination of the Ti(iv) complex with fluorouracil on colon cells gave near additive behavior, and that with oxaliplatin gave a synergistic behavior at a wide range of Ti : Pt ratios, but only when the drugs were administered together. Increasing the time intervals between the administration of Ti and of Pt turned the behavior to antagonistic, suggesting some deactivation of Pt by the Ti agent. For combinations where the drugs were applied together, the behavior depended on the effect level, and higher effects gave greater synergism, implying that technical aspects such as solubility are influential. Nevertheless, more complex patterns recorded for combinations where the drugs had been applied separately suggested multiple mechanisms with different concentration dependence. Overall the results point to high medicinal potential for the tested compounds for anticancer combination treatments.

Coordination Complexes of Titanium(IV) for Anticancer Therapy

Titanium(IV) coordination complexes represent attractive alternatives to platinumbased anticancer drugs. The advantage of the titanium metal lies in its low toxicity, and the hydrolysis of titanium(IV) coordination complexes in biological water-based environment to the safe and inert titanium dioxide is an enormous benefit. On the other hand, the rapid hydrolysis of titanium(IV) complexes in biological environment and their rich aquatic chemistry hampered the exploration and the development of effective compounds. Titanium(IV) complexes were the first to enter clinical trials for cancer treatment following the success of platinum-based chemotherapy, with the pioneering compounds titanocene dichloride and budotitane. Despite the high efficacy and low toxicity observed in vivo, the compounds failed the trials due to insufficient efficacy to toxicity ratio and formulation complications. The rapid hydrolysis of the complexes led to formation of multiple undefined aggregates and difficulties in isolating and identifying the particular active species and its precise cellular target. Numerous derivatives with different labile ligands or substitutions on the inert ones contributed to improve the complex anticancer features, and the best ones were comparable with, and occasionally better than cisplatin. Hydrolytic stability was improved in some cases but remained challenging. The following generation of phenolato-based complexes that came three decades later exhibited high activity and markedly improved stability, where no dissociation was observed for weeks in biological solutions. Complexes of no labile ligands whatsoever that remain intact in solution demonstrated in vitro and in vivo efficacy, with no signs of toxicity to the treated animals. Mechanistic insights gained for the different complexes analyzed include, among others, possible interaction with DNA and induction of apoptosis. Such complexes are highly promising for future exploration and clinical development.

Fluorescent antitumor titanium(iv) salen complexes for cell imaging

First live cell imaging using florescent salen Ti(iv) complexes, which are cytotoxic and inactive, both entering the cell but with different subcellular accumulations.

Specific Design of Titanium(IV) Phenolato Chelates Yields Stable and Accessible, Effective and Selective Anticancer Agents

Octahedral titanium(IV) complexes of phenolato hexadentate ligands were developed and showed very high stability for days in water solutions. In vitro cytotoxicity studies showed that, whereas tetrakis(phenolato) systems are generally of low activity presumably due to inaccessibility, smaller bis(phenolato)bis(alkoxo) complexes feature high anticancer activity and accessibility even without formulations, also toward a cisplatin-resistant cell line. An all-aliphatic control complex was unstable and inactive. A leading phenolato complex also revealed: 1) high durability in fully aqueous solutions; accordingly, negligible loss of activity after preincubation for three days in medium or in serum; 2) maximal cellular accumulation and induction of apoptosis following 24-48 h of administration; 3) reduced impact on noncancerous fibroblast cells; 4) in vivo efficacy toward lymphoma cells in murine model; 5) high activity in NCI-60 panel, with average GI50 of 4.6±2 μm. This newly developed family of Ti(IV) complexes is thus of great potential for anticancer therapy.

Insights into molecular mechanism of action of salan titanium(IV) complex with in vitro and in vivo anticancer activity

Titanium compounds, in particular, Ti(IV) based diaminobis(phenolato) "salan" complexes demonstrate high cytotoxicity towards a wide range of cancer cell lines in vitro, and still, very little is known on their mode of action. A representative salan Ti(IV) complex was tested both in vitro and in vivo on human HT-29 colorectal adenocarcinoma and A2780 ovarian carcinoma cells. Both cell lines were sensitive in vitro with A2780 demonstrating an enhanced rate of uptake and intracellular accumulation and thus an earlier response to the drug. HT-29 cells responded in vivo by impaired tumor development in nude mice. Both cell lines responded in vitro (but to a different extent) by upregulation of p53 with no apparent effect on p21 followed by cell cycle arrest, apoptosis and necrosis as demonstrated by sub-G1 cell accumulation and staining by Annexin-V and propidium iodide. Furthermore, time dependent activation of cysteine-aspartic proteases9 (caspase9) as well as some minor activation of cysteine-aspartic proteases3 (caspase3) support a direct effect on the apoptotic pathway. The differential response of the two cell lines to the salan titanium(IV) complex suggests that more than one pathway is involved in their growth regulation and thus could inhibit development of drug resistant variants.

Unbound position II in MXCXXC metallochaperone model peptides impacts metal binding mode and reactivity: Distinct similarities to whole proteins

The effect of position II in the binding sequence of copper metallochaperones, which varies between Thr and His, was investigated through structural analysis and affinity and oxidation kinetic studies of model peptides. A first Cys-Cu(I)-Cys model obtained for the His peptide at acidic and neutral pH, correlated with higher affinity and more rapid oxidation of its complex; in contrast, the Thr peptide with the Cys-Cu(I)-Met coordination under neutral conditions demonstrated weaker and pH dependent binding. Studies with human antioxidant protein 1 (Atox1) and three of its mutants where S residues were replaced with Ala suggested that (a) the binding affinity is influenced more by the binding sequence than by the protein fold (b) pH may play a role in binding reactivity, and (c) mutating the Met impacted the affinity and oxidation rate more drastically than did mutating one of the Cys, supporting its important role in protein function. Position II thus plays a dominant role in metal binding and transport.

Selenocysteine containing analogues of Atx1-based peptides protect cells from copper ion toxicity

Seleno-substituted model peptides of copper metallochaperone proteins display particularly high Cu(i) affinity andin vitroanti-oxidative reactivity.

Highly Effective and Hydrolytically Stable Vanadium(V) Amino Phenolato Antitumor Agents

Vanadium(V) oxo complexes with no labile ligands, including six octahedral complexes with pentadentate diaminotris(phenolato) ligands and one pentacoordinate complex with a tetradentate aminotris(phenolato) ligand, were synthesized in high yields. All octahedral complexes demonstrated high hydrolytic stability with no signs of decomposition after days in the presence of water, whereas the pentacoordinate complex decomposed within minutes to release the free ligand, demonstrating the marked impact of coordination number and geometry on the complex electrophilicity. All complexes showed marked cytotoxicity toward human colon HT-29 and ovarian OVCAR-3 cells. In particular, the octahedral complexes exhibited especially high activity, higher than that of cisplatin by up to 200-fold. Selected complexes demonstrated similarly high activity also toward the A2780 and the A2780cis cisplatin-resistant line. High cytotoxicity was also recorded after prolonged incubation in a DMSO solution at 4 and 37 °C temperatures and in biological medium. In vivo studies pointed to high efficacy in reducing tumor size, where no clinical signs of toxicity were detected in the treated mice. These results overall indicate high potential of the tested compounds as antitumor agents.

Anti-proliferative activity of the combination of salan Ti(iv) complexes with other organic and inorganic anticancer drugs against HT-29 and NCI-H1229 cells: synergism with cisplatin

Cytotoxic salan Ti(iv) complex demonstrated synergism with cisplatin in vitro toward human colon and lung cancer cells at various ratios.

Anti-proliferative activity of nano-formulated phenolato titanium(IV) complexes against cancer cells

Nanoparticles of titanium(IV) complexes of phenolato ligands were formed and evaluated for cytotoxicity toward human HT-29 colon cancer, murine T-25 lymphoma, and murine HU-2 multidrug-resistant (MDR) cells. The nano-formulation, besides increasing the complexes' shelf lives, is particularly efficient in overcoming limitations in solubility and cell-penetration, thus enhancing biological accessibility; large complexes that were inactive when measured in a non-formulated form showed marked activity when nano-formulated. For active and accessible small complexes, the effect of the formulation was negligible. Most complexes showed similar activity toward MDR cells and their drug-sensitive analogues, further increasing their therapeutic potential. An exception is a particularly hydrophobic complex, which is presumably more accessible to interaction with the membrane ABCB1 (MDR1) transporter active in the multidrug resistance of HU-2 cells. The most efficient compound is a mononuclear complex of a single hexadentate ligand, combining particularly high activity and hydrolytic stability with accessibility aided by the nano-formulation.

C1-symmetrical titanium(IV) complexes of salan ligands with differently substituted aromatic rings: enhanced cytotoxic activity

Diaminobis(phenolato) ("salan") titanium(IV) complexes of differently substituted aromatic rings were synthesized, and their hydrolytic stability and cytotoxicity were analyzed and compared to those of the C2-symmertrical analogues and their equimolar mixtures. The hydrolytic stability of the asymmetrical complexes was in between those of the symmetrical analogues, implying an additive influence of the ligand structural parameters. Most mixed halogenated/nitrated complexes showed a marked improvement of cytotoxic activity relative to the symmetrical analogues and their mixtures, with IC50 values as low as <1 μM corresponding to activity exceeding that of cisplatin by up to 30-fold. In contrast, asymmetrical complexes with substitutions of similar properties revealed an added influence of both, with cytotoxicity in between those of the symmetrical analogues. With the presumption that the active species is generally a polynuclear hydrolysis product kept in mind, it is overall evident that particular ligand design and fine-tuning of the parameters of influence including hydrophilicity and hydrophobicity are essential for maximizing biological efficiency.

Structure and coordination determination of peptide-metal complexes using 1D and 2D ¹H NMR

Copper (I) binding by metallochaperone transport proteins prevents copper oxidation and release of the toxic ions that may participate in harmful redox reactions. The Cu (I) complex of the peptide model of a Cu (I) binding metallochaperone protein, which includes the sequence MTCSGCSRPG (underlined is conserved), was determined in solution under inert conditions by NMR spectroscopy. NMR is a widely accepted technique for the determination of solution structures of proteins and peptides. Due to difficulty in crystallization to provide single crystals suitable for X-ray crystallography, the NMR technique is extremely valuable, especially as it provides information on the solution state rather than the solid state. Herein we describe all steps that are required for full three-dimensional structure determinations by NMR. The protocol includes sample preparation in an NMR tube, 1D and 2D data collection and processing, peak assignment and integration, molecular mechanics calculations, and structure analysis. Importantly, the analysis was first conducted without any preset metal-ligand bonds, to assure a reliable structure determination in an unbiased manner.

Anticancer metal complexes: synthesis and cytotoxicity evaluation by the MTT assay

Titanium (IV) and vanadium (V) complexes are highly potent anticancer agents. A challenge in their synthesis refers to their hydrolytic instability; therefore their preparation should be conducted under an inert atmosphere. Evaluation of the anticancer activity of these complexes can be achieved by the MTT assay. The MTT assay is a colorimetric viability assay based on enzymatic reduction of the MTT molecule to formazan when it is exposed to viable cells. The outcome of the reduction is a color change of the MTT molecule. Absorbance measurements relative to a control determine the percentage of remaining viable cancer cells following their treatment with varying concentrations of a tested compound, which is translated to the compound anticancer activity and its IC50 values. The MTT assay is widely common in cytotoxicity studies due to its accuracy, rapidity, and relative simplicity. Herein we present a detailed protocol for the synthesis of air sensitive metal based drugs and cell viability measurements, including preparation of the cell plates, incubation of the compounds with the cells, viability measurements using the MTT assay, and determination of IC50 values.

Heteroleptic titanium(IV) catecholato/piperazine systems and their anti-cancer properties

In this paper we report the synthesis and full characterisation of a range of Ti(IV)-catecholato systems complexed to piperazine or homopiperazine salan ligands. The steric/electronic environment of the catecholate moiety has been varied and the effect this has on cytotoxicity discussed. It was observed that the 7-membered homopiperazine complexes are more stable to hydrolysis than their piperazine cousins in biological media. In general the homopiperazine complexes show higher cytotoxicity than the piperazine complexes, with the most cytotoxic complex exhibiting IC50 (μM) values of 3 ± 0.5 μM (HT-29) and 4 ± 1 μM (OVCAR).

Peptide models of Cu(I) and Zn(II) metallochaperones: the effect of pH on coordination and mechanistic implications

The first NMR structures of Cu(I) and Zn(II) peptide complexes as models of metallochaperones were derived with no predetermined binding mode. The cyclic peptide MDCSGCSRPG was reacted with Cu(I) and Zn(II) at low and moderate pH. This peptide features the conserved sequence of copper chaperones but with Asp at position 2 as appears in the zinc binding domain of ZntA. The structures were compared with those of the Cu(I) complexes of the wild-type sequence peptide MTCSGCSRPG. All analyses were conducted first with no metal-binding constraints to ensure accurate binding ligand assignment. Several structures included metal-Met binding, raising a possible role of Met in the metal transport mechanism. Both Cu(I) and Zn(II) gave different complexes when reacted with the peptide of the native-like sequence under different pH conditions, raising the possibility of pH-dependent transport mechanisms. Cu(I) bound the MTCSGCSRPG peptide through one Cys and the Met under acidic conditions and differently under basic conditions; Zn(II) bound the MDCSGCSRPG peptide through two Cys and the Met residues under acidic conditions and through one Cys and the Met under basic conditions, while Cu(I) bound the non-native Asp mutant peptide through the Asp and one Cys under both conditions, suggesting that Asp may inhibit pH-dependent binding for Cu(I). NOESY and ESI-HRMS supported the presence of an aqua ligand for Zn(II), which likely deprotonated under basic conditions to give a hydroxo group. Coordination similarities were detected among the model system and native proteins, which overall suggest that coordination flexibility is required for the function of metallochaperones.