Designing metallodrugs with nuclease and protease activity

Impact of Conjugation of the Reactive Oxygen Species (ROS)-Generating Catalytic Moiety with Membrane-Active Antimicrobial Peptoids: Promoting Multitarget Mechanism and Enhancing Selectivity

Antimicrobial peptides (AMPs) represent promising therapeutic modalities against multidrug-resistant bacterial infections. As a mimic of natural AMPs, peptidomimetic oligomers like peptoids (i.e., oligo-N-substituted glycines) have been utilized for antimicrobials with resistance against proteolytic degradation. Here, we explore the conjugation of catalytic metal-binding motifs─the amino terminal Cu(II) and Ni(II) binding (ATCUN) motif─with cationic amphipathic antimicrobial peptoids to enhance their efficacy. Upon complexation with Cu(II) or Ni(II), the conjugates catalyzed hydroxyl radical generation, and 22 and 22-Cu exhibited over 10-fold improved selectivity compared to the parent peptoid, likely due to reduced hydrophobicity. Cu-ATCUN-peptoids caused bacterial membrane disruption, aggregation of intracellular biomolecules, DNA oxidation, and lipid peroxidation, promoting multiple killing mechanisms. In a mouse sepsis model, 22 demonstrated antimicrobial and anti-inflammatory efficacy with low toxicity. This study suggests a strategy to improve the potency of membrane-acting antimicrobial peptoids by incorporating ROS-generating motifs, thereby adding oxidative damage as a killing mechanism.

Anticancer Activity of Metallodrugs and Metallizing Host Defense Peptides-Current Developments in Structure-Activity Relationship

This article provides an overview of the development, structure and activity of various metal complexes with anti-cancer activity. Chemical researchers continue to work on the development and synthesis of new molecules that could act as anti-tumor drugs to achieve more favorable therapies. It is therefore important to have information about the various chemotherapeutic substances and their mode of action. This review focuses on metallodrugs that contain a metal as a key structural fragment, with cisplatin paving the way for their chemotherapeutic application. The text also looks at ruthenium complexes, including the therapeutic applications of phosphorescent ruthenium(II) complexes, emphasizing their dual role in therapy and diagnostics. In addition, the antitumor activities of titanium and gold derivatives, their side effects, and ongoing research to improve their efficacy and reduce adverse effects are discussed. Metallization of host defense peptides (HDPs) with various metal ions is also highlighted as a strategy that significantly enhances their anticancer activity by broadening their mechanisms of action.

Diruthenium Paddlewheel Complexes Attacking Proteins: Axial versus Equatorial Coordination

Metallodrugs are an important group of medicinal agents used for the treatment of various diseases ranging from cancers to viral, bacterial, and parasitic diseases. Their distinctive features include the availability of a metal centre, redox activity, as well as the ability to multitarget. Diruthenium paddlewheel complexes are an intensely developing group of metal scaffolds, which can securely coordinate bidentate xenobiotics and transport them to target tissues, releasing them by means of substitution reactions with biomolecular nucleophiles. It is of the utmost importance to gain a complete comprehension of which chemical reactions happen with them in physiological milieu to design novel drugs based on these bimetallic scaffolds. This review presents the data obtained in experiments and calculations, which clarify the chemistry these complexes undergo once administered in the proteic environment. This study demonstrates how diruthenium paddlewheel complexes may indeed embody a new paradigm in the design of metal-based drugs of dual-action by presenting and discussing the protein metalation by these complexes.

Transition metal complexes as self-activating chemical nucleases: proficient DNA cleavage without any exogenous redox agents

Chemical nucleases have found potential applications in the research fields of chemistry, biotechnology and medicine. A variety of metal complexes have been explored as good to outstanding therapeutic agents for DNA cleavage activity most likely via hydrolytic, oxidative or photoinduced cleavage pathways. However, most of these DNA cleaving agents lack their utility in in vivo applications due to their dependence on exogenous oxidants or reductants to achieve successful DNA damage. In view of addressing these issues, the development of metal complexes/organic molecules serving as self-activating chemical nucleases has received growing attention from researchers. In only the last decade, this field has dramatically expanded for the usage of chemical nucleases as therapeutic agents for DNA damage. The present study provides an overview of the opportunities and challenges in the design and development of self-activating chemical nucleases as improved DNA therapeutic candidates in the absence of an external redox agent. The reports on DNA nuclease activity via self-activation, especially with copper, zinc and iron complexes, and their mechanistic investigation have been discussed in this review article.

Why the Ala-His-His Peptide Is an Appropriate Scaffold to Remove and Redox Silence Copper Ions from the Alzheimer's-Related Aβ Peptide

The progressive, neurodegenerative Alzheimer's disease (AD) is the most widespread dementia. Due to the ageing of the population and the current lack of molecules able to prevent or stop the disease, AD will be even more impactful for society in the future. AD is a multifactorial disease, and, among other factors, metal ions have been regarded as potential therapeutic targets. This is the case for the redox-competent Cu ions involved in the production of reactive oxygen species (ROS) when bound to the Alzheimer-related Aβ peptide, a process that contributes to the overall oxidative stress and inflammation observed in AD. Here, we made use of peptide ligands to stop the Cu(Aβ)-induced ROS production and we showed why the AHH sequence is fully appropriate, while the two parents, AH and AAH, are not. The AHH peptide keeps its beneficial ability against Cu(Aβ)-induced ROS, even in the presence of ZnII-competing ions and other biologically relevant ions. The detailed kinetic mechanism by which AHH could exert its action against Cu(Aβ)-induced ROS is also proposed.

A General, Label-Free and Homogeneous Electrochemical Strategy for Probing of Protease Activity and Screening of Inhibitor

Proteases play a critical role in regulating various physiological processes from protein digestion to wound healing. Monitoring the activity of proteases and screening their inhibitors as potential drug molecules are of great importance for the early diagnosis and treatment of many diseases. In this work, we reported a general, label-free and homogeneous electrochemical method for monitoring protease activity based on the peptide-copper interaction. Cleavage of peptide substrate results in the generation of a copper-binding chelator peptide with a histidine residue in the first or third position (His1 or His3) at the N-terminal. The redox potential and current of copper coordinated with the product are different from the free copper or the copper complex with the substrate, thus allowing for the detection of protease activity. Angiotensin-converting enzyme (ACE) and thrombin were determined as the model analytes. The label-free and homogeneous electrochemical method can be used for screening protease inhibitors with high simplicity and sensitivity.

Nuclease-like metalloscissors: Biomimetic candidates for cancer and bacterial and viral infections therapy

Despite the extensive and rapid discovery of modern drugs for treatment of cancer, microbial infections, and viral illnesses; these diseases are still among major global health concerns. To take inspiration from natural nucleases and also the therapeutic potential of metallopeptide antibiotics such as the bleomycin family, artificial metallonucleases with the ability of promoting DNA/RNA cleavage and eventually affecting cellular biological processes can be introduced as a new class of therapeutic candidates. Metal complexes can be considered as one of the main categories of artificial metalloscissors, which can prompt nucleic acid strand scission. Accordingly, biologists, inorganic chemists, and medicinal inorganic chemists worldwide have been designing, synthesizing and evaluating the biological properties of metal complexes as artificial metalloscissors. In this review, we try to highlight the recent studies conducted on the nuclease-like metalloscissors and their potential therapeutic applications. Under the light of the concurrent Covid-19 pandemic, the human need for new therapeutics was highlighted much more than ever before. The nuclease-like metalloscissors with the potential of RNA cleavage of invading viral pathogens hence deserve prime attention.

Incorporation of β-Alanine in Cu(II) ATCUN Peptide Complexes Increases ROS Levels, DNA Cleavage and Antiproliferative Activity

Redox-active Cu(II) complexes are able to form reactive oxygen species (ROS) in the presence of oxygen and reducing agents. Recently, Faller et al. reported that ROS generation by Cu(II) ATCUN complexes is not as high as assumed for decades. High complex stability results in silencing of the Cu(II)/Cu(I) redox cycle and therefore leads to low ROS generation. In this work, we demonstrate that an exchange of the α-amino acid Gly with the β-amino acid β-Ala at position 2 (Gly2→β-Ala2) of the ATCUN motif reinstates ROS production (• OH and H2 O2 ). Potentiometry, cyclic voltammetry, EPR spectroscopy and DFT simulations were utilized to explain the increased ROS generation of these β-Ala2-containing ATCUN complexes. We also observed enhanced oxidative cleavage activity towards plasmid DNA for β-Ala2 compared to the Gly2 complexes. Modifications with positively charged Lys residues increased the DNA affinity through electrostatic interactions as determined by UV/VIS, fluorescence, and CD spectroscopy, and consequently led to a further increase in nuclease activity. A similar trend was observed regarding the cytotoxic activity of the complexes against several human cancer cell lines where β-Ala2 peptide complexes had lower IC50 values compared to Gly2. The higher cytotoxicity could be attributed to an increased cellular uptake as determined by ICP-MS measurements.

Tuning Receptor Properties of Metal-Amyloid Beta Complexes. Studies on the Interaction between Ni(II)-Aβ5-9 and Phosphates/Nucleotides

Amyloid-beta (Aβ) peptides, potentially relevant in the pathology of Alzheimer's disease, possess distinctive coordination properties, enabling an effective binding of transition-metal ions, with a preference for Cu(II). In this work, we found that a N-truncated Aβ analogue bearing a His-2 motif, Aβ5-9, forms a stable Ni(II) high-spin octahedral complex at a physiological pH of 7.4 with labile coordination sites and facilitates ternary interactions with phosphates and nucleotides. As the pH increased above 9, a spin transition from a high-spin to a low-spin square-planar Ni(II) complex was observed. Employing electrochemical techniques, we showed that interactions between the binary Ni(II)-Aβ5-9 complex and phosphate species result in significant changes in the Ni(II) oxidation signal. Thus, the Ni(II)-Aβ5-9 complex could potentially serve as a receptor in electrochemical biosensors for phosphate species. The obtained results could also be important for nickel toxicology.

Anti-Leishmania braziliensis activity of 1,10-phenanthroline-5,6-dione and its Cu(II) and Ag(I) complexes

Leishmaniasis, included in the priority list of the WHO, remains as a neglected disease caused by parasites of the Leishmania genus. There is no vaccine available for human leishmaniasis, and the current treatment is based on old drugs that cause serious side effects. Herein, we initially studied the cellular distribution of the virulence factor gp63, the major metallopeptidase, in a virulent strain of Leishmania braziliensis, and then we measured the inhibitory effects of 1,10-phenanthroline-5,6-dione (phendione), and its metal complexes, [Cu(phendione)₃](ClO₄)₂.4H₂O and [Ag(phendione)₂]ClO₄, on both cellular and extracellular metallopeptidases produced by promastigotes. The action of the three compounds on parasite viability and on parasite-macrophage interaction was also determined. Gp63 molecules were detected in several parasite compartments, including the cytoplasm, the membrane lining the cell body and flagellum, and in the flagellar pocket, which explains the presence of gp63 in the culture medium. The test compounds inhibited parasite metallopeptidases in a typical dose-dependent manner, and they also caused a significant and irreversible inhibition of parasite motility. Moreover, the pre-treatment of promastigotes with the test compounds induced a decrease in the association index with macrophages. Collectively, phendione and its Cu(II) and Ag(I) complexes are excellent prototypes for the development of new anti-L. braziliensis drugs.

Antimicrobial Polymer-Based Assemblies: A Review

An antimicrobial supramolecular assembly (ASA) is conspicuous in biomedical applications. Among the alternatives to overcome microbial resistance to antibiotics and drugs, ASAs, including antimicrobial peptides (AMPs) and polymers (APs), provide formulations with optimal antimicrobial activity and acceptable toxicity. AMPs and APs have been delivered by a variety of carriers such as nanoparticles, coatings, multilayers, hydrogels, liposomes, nanodisks, lyotropic lipid phases, nanostructured lipid carriers, etc. They have similar mechanisms of action involving adsorption to the cell wall, penetration across the cell membrane, and microbe lysis. APs, however, offer the advantage of cheap synthetic procedures, chemical stability, and improved adsorption (due to multipoint attachment to microbes), as compared to the expensive synthetic routes, poor yield, and subpar in vivo stability seen in AMPs. We review recent advances in polymer-based antimicrobial assemblies involving AMPs and APs.

Designed Metal-ATCUN Derivatives: Redox- and Non-redox-Based Applications Relevant for Chemistry, Biology, and Medicine

The designed "ATCUN" motif (amino-terminal copper and nickel binding site) is a replica of naturally occurring ATCUN site found in many proteins/peptides, and an attractive platform for multiple applications, which include nucleases, proteases, spectroscopic probes, imaging, and small molecule activation. ATCUN motifs are engineered at periphery by conjugation to recombinant proteins, peptides, fluorophores, or recognition domains through chemically or genetically, fulfilling the needs of various biological relevance and a wide range of practical usages. This chemistry has witnessed significant growth over the last few decades and several interesting ATCUN derivatives have been described. The redox role of the ATCUN moieties is also an important aspect to be considered. The redox potential of designed M-ATCUN derivatives is modulated by judicious choice of amino acid (including stereochemistry, charge, and position) that ultimately leads to the catalytic efficiency. In this context, a wide range of M-ATCUN derivatives have been designed purposefully for various redox- and non-redox-based applications, including spectroscopic probes, target-based catalytic metallodrugs, inhibition of amyloid-β toxicity, and telomere shortening, enzyme inactivation, biomolecules stitching or modification, next-generation antibiotic, and small molecule activation.

A copper complex formed with neurokinin B: binding stoichiometry, redox properties, self-assembly and cytotoxicity

The tachykinin neuropeptide of neurokinin B (NKB) is a copper-binding amyloid peptide with important roles in the regulation of physiological functions and pathophysiological processes in the central and peripheral nervous systems. In this work, the formation of a NKB-Cu²⁺ complex in a 1 : 1 stoichiometry was confirmed by mass spectrometry. The self-assembly of NKB and its mutant species was investigated by Thioflavin T (ThT) fluorescence assay and atomic force microscopy (AFM), and at the same time, the effect of Cu²⁺ on the aggregation of NKB was studied. As evidenced by cyclic voltammetry, the redox potential of NKB-Cu²⁺ was determined to be 0.77 V (vs. Ag/AgCl). It has been demonstrated that NKB at low concentrations exerts its neuroprotective function by inhibiting Cu²⁺-mediated reactive oxygen species (ROS) production in the presence of ascorbic acid (AA). In comparison with equivalent Cu²⁺, the peptide-Cu²⁺ aggregates aggravated the viability of PC-12 cells more seriously in the absence of AA. These results should be extremely valuable for understanding the NKB/Cu²⁺ interactions and the toxicity mechanism of Cu²⁺ associated with neurodegenerative diseases.

Human Antimicrobial Peptide Hepcidin 25-Induced Apoptosis in Candida albicans

Hepcidin 25 (hep 25) is a cysteine-rich 25-amino acid antimicrobial peptide containing the amino-terminal Cu(II)/Ni(II)-binding (ATCUN) motif. Upon metal binding, the ATCUN motif is known to be involved in the generation of reactive oxygen species (ROS), especially hydrogen peroxide and hydroxyl radicals, which act against different bacterial species. However, the antifungal activity and its correlation to the Cu(II)-ATCUN complex of Hep 25 are still poorly understood. Here, we found that ROS accumulation plays an important role in the fungicidal activity of hep 25 against Candida albicans. In addition, Annexin V-FITC staining and TUNEL assay results provide clues about the apoptosis induced by hep 25. Moreover, hep 25 also increases the generation of ROS, possibly because of copper binding to the ATCUN motif, which is relevant to its activity against C. albicans. Finally, the C. albicans killing action of hep 25 is an energy- and temperature-dependent process that does not involve targeting the membrane. Taken together, our results provide new insights into the mechanisms of hep 25 against C. albicans cells and the potential use of hep 25 and its derivatives as novel antifungal agents.

Differential Expression and Alternative Splicing of Transcripts Associated With Cisplatin-Induced Chemoresistance in Nasopharyngeal Carcinoma

Radiotherapy and adjuvant cisplatin (DDP) chemotherapy are standard administrations applied to treat nasopharyngeal carcinoma (NPC). However, the molecular changes and functions of DDP in NPC chemo-resistance remain poorly understood. In the present study, transcriptomic sequencing between 5-8F and 5-8F/DDP cells was performed to identify differential expression and alternative splicing (AS) characteristics in DDP-resistant NPC cells. Transcriptomic profiling identified 1,757 upregulated genes and 1,473 downregulated differentially expressed genes (DEGs). Bioinformatic analysis revealed that these DEGs were associated with or participated in important biological regulatory functions in NPC. Validation of 20 significant DEGs using quantitative real-time reverse transcription PCR showed that the expression patterns of 17 mRNAs were in accordance with the sequencing data. Intron retention was identified as the major AS event in chemoresistant cells. Furthermore, the expression level of matrix metalloproteinase 1 (MMP1), which was one of the most upregulated mRNAs in the chemoresistant cell lines, was significantly associated with the migration, invasion, and proliferation of NPC cells in vitro. Our study revealed that dysregulated genes and AS-mediated DDP chemoresistance might play important roles in NPC development and progression. Targeting aberrantly expressed genes might clarify the pathogenesis of NPC and contribute to developing new therapeutic strategies for NPC.

Antimicrobial and Antibiofilm Activities of Helical Antimicrobial Peptide Sequences Incorporating Metal-Binding Motifs

Antimicrobial peptides (AMPs) represent alternative strategies to combat the global health problem of antibiotic resistance. However, naturally occurring AMPs are generally not sufficiently active for use as antibiotics. Optimized synthetic versions incorporating additional design principles are needed. Here, we engineered amino-terminal Cu(II) and Ni(II) (ATCUN) binding motifs, which can enhance biological function, into the native sequence of two AMPs, CM15 and citropin1.1. The incorporation of metal-binding motifs modulated the antimicrobial activity of synthetic peptides against a panel of carbapenem-resistant enterococci (CRE) bacteria, including carbapenem-resistant Klebsiella pneumoniae (KpC+) and Escherichia coli (KpC+). Activity modulation depended on the type of ATCUN variant utilized. Membrane permeability assays revealed that the in silico selected lead template, CM15, and its ATCUN analogs increased bacterial cell death. Mass spectrometry, circular dichroism, and molecular dynamics simulations indicated that coordinating ATCUN derivatives with Cu(II) ions did not increase the helical tendencies of the AMPs. CM15 ATCUN variants, when combined with Meropenem, streptomycin, or chloramphenicol, showed synergistic effects against E. coli (KpC+ 1812446) biofilms. Motif addition also reduced the hemolytic activity of the wild-type AMP and improved the survival rate of mice in a systemic infection model. The dependence of these bioactivities on the particular amino acids of the ATCUN motif highlights the possible use of size, charge, and hydrophobicity to fine-tune AMP biological function. Our data indicate that incorporating metal-binding motifs into peptide sequences leads to synthetic variants with modified biological properties. These principles may be applied to augment the activities of other peptide sequences.

Preparation, characterization and comparison of biological potency in two new Zn(II) and Pd(II) complexes of butanedione monoxime derivatives

A novel Schiff base ligand (2-iminothiophenol-2,3-butanedione monoxime, ITBM) and its complexes with Pd(II) and Zn(II) metal ions ([M(ITBM)₂]Cl₂) were synthesized and characterized in the present study. The formulated complexes were evaluated for in vitro antioxidant activity as radical scavengers against 1,1-diphenyl-2-picrylhydrazyl radicals (DPPH^•). According to the results, antioxidant activity of Pd complex (IC₅₀=36 mg L^-1) was more effective than that of Zn(II) complex (IC₅₀=72 mg L^-1). Biophysical techniques along with computational modeling were employed to examine the binding of these complexes with human serum albumin (HSA) as the model protein. The trial findings revealed an interaction between Schiff base complexes and HSA with a modest binding affinity [K_b=6.31(±0.11)×10⁴ M^-1 for Zn(II) complex and 0.71(±0.05)×10⁴ M^-1 for Pd(II) complex at 310 K]. An intense fluorescence quenching of protein through a static quenching mechanism was occurred due to the binding of both complexes to HSA. Hydrogen bonds and van der Waals forces in both examined systems were the main stabilizing forces in the development of drug-protein complex. Based on far-UV-CD observations, the content of α-helical structure in the protein was reduced through induction by both complexes. Analysis of protein-ligand docking demonstrated binding of the two Schiff base complexes to residues placed in the IIA subdomain of HSA. In addition, Zn complex with HSA showed a stronger binding ability than that of Pd complex.Communicated by Ramaswamy H. Sarma.

Low catalytic activity of the Cu(ii)-binding motif (Xxx-Zzz-His; ATCUN) in reactive oxygen species production and inhibition by the Cu(i)-chelator BCS

The catalytic redox activity of Cu(ii) bound to the motif NH2-Xxx-Zzz-His (ATCUN) with ascorbate and H2O2/O2 is very low and can be stopped via Cu(i)-chelation. This impacts its application as an artificial Cu-enzyme to degrade biomolecules via production of reactive oxygen species in a Cu(i)-chelator rich environment like the cytosol.

Binding of Divalent Metal Ions with Deprotonated Peptides: Do Gas-Phase Anions Parallel the Condensed Phase?

Chelation complexes of the histidine-containing tripeptides HisAlaAla, AlaHisAla, and AlaAlaHis with Ni(II) and Cu(II) having a −1 net charge are characterized in the gas phase by infrared multiple-photon dissociation (IRMPD) spectroscopy and density functional theory calculations. We address the question of whether the gas-phase complexes carry over characteristics from the corresponding condensed-phase species. We focus particularly on three aspects of their structure: (i) square-planar chelation by the deprotonated amide nitrogens around the metal ion (low-spin for the Ni case), (ii) metal-ion coordination of the imidazole side chain nitrogen, and (iii) the exceptional preference for metal-ion chelation by peptides with His in the third position from the N-terminus, as in the amino terminal Cu and Ni (ATCUN) motif. We find that square-planar binding around the metal ion, involving bonds to both deprotonated backbone nitrogens, one of the carboxylate oxygens and the N-terminal nitrogen, is the dominant binding motif for all three isomers. In contrast to the condensed-phase behavior, the dominant mode of binding for all three isomers does not involve the imidazole side chain, which is instead placed outside the coordination zone. Only for the AlaAlaHis isomer, the imidazole-bound structure is also detected as a minority population, as identified from a distinctive short-wavelength IR absorption. The observation that this conformation exists only for AlaAlaHis correlates with condensed-phase behavior at neutral-to-basic pH, in the sense that the isomer with His in the third position is exceptionally disposed to metal ion chelation by four nitrogen atoms (4N) when compared with the other isomers. These results also emphasize the divergence between the conformational stabilities in the gas phase and in solution or crystalline environments: in the gas phase, direct metal binding of the imidazole is overall less favorable than the alternative of a remote imidazole that can act as an intramolecular H-bond donor enhancing the gas-phase stability.

N-Terminal Cu-Binding Motifs (Xxx-Zzz-His, Xxx-His) and Their Derivatives: Chemistry, Biology and Medicinal Applications

Peptides and proteins with N-terminal amino acid sequences NH2 -Xxx-His (XH) and NH2 -Xxx-Zzz-His (XZH) form well-established high-affinity CuII -complexes. Key examples are Asp-Ala-His (in serum albumin) and Gly-His-Lys, the wound healing factor. This opens a straightforward way to add a high-affinity CuII -binding site to almost any peptide or protein, by chemical or recombinant approaches. Thus, these motifs, NH2 -Xxx-Zzz-His in particular, have been used to equip peptides and proteins with a multitude of functions based on the redox activity of Cu, including nuclease, protease, glycosidase, or oxygen activation properties, useful in anticancer or antimicrobial drugs. More recent research suggests novel biological functions, mainly based on the redox inertness of CuII in XZH, like PET imaging (with 64 Cu), chelation therapies (for instance in Alzheimer's disease and other types of neurodegeneration), antioxidant units, Cu transporters and activation of biological functions by strong CuII binding. This Review gives an overview of the chemical properties of Cu-XH and -XZH motifs and discusses the pros and cons of the vastly different biological applications, and how they could be improved depending on the application.

Nickel(ii)-promoted specific hydrolysis of zinc finger proteins

The (S/T)XH sequence in Cys₂His₂zinc fingers can be hydrolytically cleaved by Ni(ii) ions. This reaction can be applied for purification, inhibition or activation of designed zinc finger fusion proteins.

NEDD4 is involved in acquisition of epithelial-mesenchymal transition in cisplatin-resistant nasopharyngeal carcinoma cells

Nasopharyngeal carcinoma (NPC) is a highly invasive head-neck cancer derived from the nasopharyngeal epithelium, mainly prevalent in southern China and Southeast Asia. Radiotherapy and adjuvant cisplatin (DDP) chemotherapy are standard administrations applied in the treatment of NPC. However, resistance to chemotherapeutic drugs has recently become more common, resulting in worse treatment outcome for NPC therapy. To elucidate the underlying molecular basis of drug resistance to DDP in NPC cells, we examined the morphocytology, cell motility and molecular changes in DDP-resistant NPC cells with respect to epithelial-mesenchymal transition (EMT) features. We found that EMT is closely associated with DDP-induced drug resistance in NPC cells, as DDP-resistant cells displayed morphological and molecular markers changes consistent with EMT. Wound healing and Transwell Boyden chamber assays revealed an enhanced migration and invasion potential in DDP-resistant NPC cells. Mechanistically, upregulation of NEDD4 was observed to relate to EMT in DDP-resistant cells. More importantly, depletion of NEDD4 in resistant cells led to a partial reversion of EMT phenotypes to MET characteristics. These data suggest that NEDD4 is largely involved in EMT features and chemoresistance of NPC cancer cells. NEDD4 could be a novel therapeutic target to overcome drug resistance in successful administrations of NPC.

Two New Oxovanadium(IV) Compounds Containing Amino Acid Schiff Base and 1,10-Bathophenanthroline Ligands: Syntheses, Crystal Structures, and In Vitro Evaluation of the Anticancer Activities

Two new oxovanadium(iv) compounds containing 1,10-bathophenanthroline (Bphen) and amino Schiff base derivatives [VO(hnd-napha)(Bphen)] (1) and [VO(o-van-met)(Bphen)] (2) were synthesised (where hnd-napha and o-van-met are N-Schiff bases derived from the reaction of 2-hydroxy-1-naphthaldehyde with 3-(1-naphthyl)-l-alanine and o-vanillin with l-methionine, respectively). These compounds were characterised by elemental analysis, infrared spectroscopy, high-resolution mass spectrometry, and single-crystal X-ray diffraction (XRD). Both compounds showed low molar conductance values, indicating that they are non-electrolytes. The XRD results showed that the VIV atoms in both compounds existed in the VO3N3 coordination geometry with Schiff base and Bphen ligands. The in vitro anticancer activities of compounds 1 and 2 were evaluated against A549 human lung carcinoma and HepG2 human hepatoma cell lines using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, and the results revealed that both compounds were cytotoxic with half maximal inhibitory concentration (IC50) values in the range of 8.22 ± 1.0 to 94.89 ± 3.2 μmol L−1. Notably, compound 2 exhibited much better anticancer activity in vitro against A549 cells (8.22 ± 1 μmol L−1) than [VO(acac)2] (24 ± 6 μmol L−1) or any of our previously reported oxovanadium(iv) compounds, making it comparable in activity to cisplatin (3.1 ± 0.5 μmol L−1). These results therefore suggest that compound 2 could be used as a promising lead for the development of anticancer agents for the treatment of lung cancer.