Influence of proline and hydroxyproline as antimicrobial and anticancer peptide components on the silver(I) ion activity: structural and biological evaluation with a new theoretical and experimental SAR approach

Silver(I) complexes with proline and hydroxyproline were synthesized and structurally characterized and crystal structure analysis shows that the formulas of the compounds are {[Ag2(Pro)2(NO3)]NO3}n (AgPro) (Pro = L-proline) and {[Ag2(Hyp)2(NO3)]NO3}n (AgHyp) (Hyp = trans-4-hydroxy-L-proline). Both complexes crystallize in the monoclinic lattice with space group P21 with a carboxylate bidentate-bridging coordination mode of the organic ligands Pro and Hyp (with NH2+ and COO- groups in zwitterionic form). Both complexes have a distorted seesaw (C2v) geometry around one silver(I) ion with τ4 values of 58% (AgPro) and 51% (AgHyp). Moreover, the results of spectral and thermal analyses correlate with the structural ones. 1H and 13C NMR spectra confirm the complexes species' presence in the DMSO biological testing medium and their stability in the time range of the bioassays. In addition, molar conductivity measurements indicate complexes' behaviour like 1 : 1 electrolytes. Both complexes showed higher or the same antibacterial activity against Bacillus cereus, Pseudomonas aeruginosa and Staphylococcus aureus as AgNO3 (MIC = 0.063 mM) and higher than silver(I) sulfadiazine (AgSD) (MIC > 0.5 mM) against Pseudomonas aeruginosa. In addition, complex AgPro exerted a strong cytotoxic effect against the tested MDA-MB-231 and Jurkat cancer cell lines (IC50 values equal to 3.7 and 3.0 μM, respectively) compared with AgNO3 (IC50 = 6.1 (5.7) μM) and even significantly higher selectivity than cisplatin (cisPt) against MDA-MB-231 cancer cell lines (SI = 3.05 (AgPro); 1.16 (cisPt), SI - selectivity index). The binding constants and the number of binding sites (n) of AgPro and AgHyp complexes with bovine serum albumin (BSA) were determined at four different temperatures, and the zeta potential of BSA in the presence of silver(I) complexes was also measured. The in ovo method shows the safety of the topical and intravenous application of AgPro and AgHyp. Moreover, the complexes' bioavailability was verified by lipophilicity evaluation from the experimental and theoretical points of view.

Ga(III) pyridinecarboxylate complexes: potential analogues of the second generation of therapeutic Ga(III) complexes?

A series of novel Ga(III)-pyridine carboxylates ([Ga(Pic)3]·H2O (GaPic; HPic = picolinic acid), H3O[Ga(Dpic)2]·H2O (GaDpic; H2Dpic = dipicolinic acid), [Ga(Chel)(H2O)(OH)]2·4H2O (GaChel; H2Chel = chelidamic acid) and [Ga(Cldpic)(H2O)(OH)]2 (GaCldpic; H2Cldpic = 4-chlorodipicolinic acid)) have been synthesized by simple one-step procedure. Vibrational spectroscopy (mid-IR), elemental analysis, thermogravimetric analysis and X-ray diffraction confirmed complexes molecular structure, inter and intramolecular interactions and their influence to spectral and thermal properties. Moreover, complex species speciation was described in Ga(III)-HPic and Ga(III)-H2Dpic systems by potentiometry and 1H NMR spectroscopy and mononuclear complex species were determined; [Ga(Pic)2]+ (logβ021 = 16.23(6)), [Ga(Pic)3] (logβ031 = 20.86(2)), [Ga(Dpic)2]- (logβ021 = 15.42(9)) and [Ga(Dpic)2(OH)]2- (logβ-121 = 11.08(4)). To confirm the complexes stability in 1% DMSO (primary solvent for biological testing), timescale 1H NMR spectra were measured (immediately after dissolution up to 96 h). Antimicrobial activity evaluated by IC50 (0.05 mM) is significant for GaDpic and GaCldpic against difficult to treat and multi-resistant P. aeruginosa. On the other hand, the GaPic complex is most effective against Jurkat, MDA-MB-231 and A2058 cancer cell lines and significantly also decreases the HepG2 cancer cells viability at 75 and 100 μM concentrations in a relatively short time (up to 48 h). In addition, fluorescence measurements have been used to elucidate bovine serum albumin binding activity between ligands, Ga(III) complexes and bovine serum albumin.

Low-dimensional compounds containing bioactive ligands. Part XVII: Synthesis, structural, spectral and biological properties of hybrid organic-inorganic complexes based on [PdCl4]2- with derivatives of 8-hydroxyquinolinium

In this study, four hybrid organic-inorganic compounds (8-H₂Q)₂[PdCl₄] (1), (H₂ClQ)₂[PdCl₄] (2), (H₂NQ)₂[PdCl₄] (3) and (H₂MeQ)₂[PdCl₄]·2H₂O (4) (where 8-H₂Q = 8-hydroxyquinolinium, H₂ClQ = 5-chloro-8-hydroxyquinolinium, H₂NQ = 5-nitro-8-hydroxyquinolinium and H₂MeQ = 2-methyl-8-hydroxyquinolinium) were synthesized through organic cation modulation. Single-crystal X-ray structure analysis of compounds 1 and 3 indicates that their structures are planar and consist of [PdCl₄]^2- anions and 8-H₂Q or H₂NQ cations, respectively. Both ionic components are held together through ionic interactions and hydrogen bonds forming infinite chains linked through π-π interactions to form 2D structures. Furthermore, NMR spectroscopy, UV-Vis spectroscopy, elemental analysis, and FT-IR spectroscopy were used to explore the synthesized compounds. The DNA interaction, antimicrobial activity, antiproliferative activity, and radical scavenging effect of the compounds were evaluated. The hybrid compounds and their free ligands can interact with the calf thymus DNA via an intercalation mode involving the insertion of the aromatic chromophore between the base pairs of DNA; compound 1 has the highest binding affinity. Moreover, they have high antimicrobial efficacy against the tested 14 strains of microorganisms with minimum inhibitory concentration values ranging from <1.95 to 250 μg/mL. The antiproliferative activity of the compounds was investigated against three different cancer cell lines, and their selectivity was verified on mesenchymal stem cells. Compounds 1 and 2 displayed selective and high cytotoxicity against human lung and breast cancer cells and showed moderate cytotoxicity against colon cancer cells. Accordingly, they might be auspicious candidates for future pharmacological investigations in lung and breast cancer research.

An in vitro selective inhibitory effect of silver(i) aminoacidates against bacteria and intestinal cell lines and elucidation of the mechanism of action by means of DNA binding properties, DNA cleavage and cell cycle arrest

Novel silver(i) aminoacidate complexes {[Ag(HVal)(H₂O)(NO₃)]}_n (AgVal) and {[Ag₃(HAsp)₂(NO₃)]}_n·nH₂O (AgAsp) were prepared, investigated and fully characterized by vibrational spectroscopy (mid-IR), elemental analysis, thermogravimetric analysis, X-ray crystallography and mass spectrometry. Their stability in D₂O and PBS buffer was verified by time-dependent ¹H and ¹³C NMR measurements. Their in vitro antibacterial activity (against pathogenic Staphylococcus aureus CCM4223, Escherichia coli CCM4787) and that against probiotic bacteria Lactobacillus plantarum CCM7102 and Lactobacillus reuteri (L26) were determined and potential dosing concentration was evaluated. The cytotoxicity of both the complexes against intestinal porcine epithelial (IPEC-1) and human epithelial colorectal adenocarcinoma (CaCo-2) cell lines was determined using the colorimetric MTT assay and against human metastatic melanoma (A2058), human pancreatic adenocarcinoma (PaTu 8902), human cervical adenocarcinoma (HeLa), human colorectal carcinoma (HCT116), human leukaemic T cell lymphoma (Jurkat), and human dermal fibroblasts (HDF) using colorimetric MTS assay. The selectivity index (SI) was identified for intestinal cancer (CaCo-2) and healthy (IPEC-1) cells. The mechanism of action of AgVal and AgAsp was further elucidated and discussed by the study of their binding affinity toward the CT DNA, the ability to cleave the supercoiled form of pUC19 DNA and the ability to influence numbers of cells within each cell cycle.

Multifunctional properties of novel tacrine congeners: cholinesterase inhibition and cytotoxic activity

This review describes the synthesis of a wide range of novel tetrahydroacridine derivatives (tiocyanates, selenocyanates, ureas, selenoureas, thioureas, isothioureas, disulfides, diselenides and several tacrine homo- and hetro-hybrids). These tacrine congeners exhibit significant anticholinesterase and cytotoxic properties and may therefore be of considerable potential for the development of new drugs for the treatment of Alzheimer's disease.

A review on acridinylthioureas and its derivatives: biological and cytotoxic activity

Acridines possess two characteristics that have led many researchers to consider the agents interesting targets for future development as potential farmacophores: the planar acridine skeleton, which is able to intercalate into DNA, and the intense fluorescence of the agents. This review offers a study of the multifunctional character of acridines and the synthesis of novel acridine derivatives, with particular focus being placed on isothiocyanates and their congeners, e.g. thioureas, isothioureas, quaternary ammonium salts and platinum/gold conjugates. The review provides an overview of the structure, spectral properties, DNA binding and biological activity of acridinylthiourea congeners. These acridinylthiourea derivatives display significant cytotoxic activities against different types of cancer cell lines at micromolar concentrations. Copyright © 2017 John Wiley & Sons, Ltd.

Low-dimensional compounds containing bioactive ligands. Part VI: Synthesis, structures, in vitro DNA binding, antimicrobial and anticancer properties of first row transition metal complexes with 5-chloro-quinolin-8-ol

A series of new 3d metal complexes with 5-chloro-quinolin-8-ol (ClQ), [Mn(ClQ)2] (1), [Fe(ClQ)3] (2), [Co(ClQ)2(H2O)2] (3), [Ni(ClQ)2(H2O)2] (4), [Cu(ClQ)2] (5), [Zn(ClQ)2(H2O)2] (6), [Mn(ClQ)3]·DMF (7) and [Co(ClQ)3]·DMF·(EtOH)0.35 (8) (DMF=N,N-dimethylformamide), has been synthesized and characterized by elemental analysis, IR spectroscopy and TG-DTA thermal analysis. X-ray structure analysis of 7 and 8 revealed that these molecular complexes contain three chelate ClQ molecules coordinated to the central atoms in a deformed octahedral geometry and free space between the complex units is filled by solvated DMF and ethanol molecules. Antimicrobial activity of 1-6 was tested by determining the minimum inhibitory concentration and minimum microbicidal concentration against 12 strains of bacteria and 5 strains of fungi. The intensity of antimicrobial action varies depending on the group of microorganism and can be sorted: 1>ClQ>6>3/4>2>5. Complexes 1-6 exhibit high cytotoxic activity against MDA-MB, HCT-116 and A549 cancer cell lines. Among them, complex 2 is significantly more cytotoxic against MDA-MB cells than cisplatin at all tested concentrations and is not cytotoxic against control mesenchymal stem cells indicating that this complex seems to be a good candidate for future pharmacological evaluation. Interaction of 1-6 with DNA was investigated using UV-VIS spectroscopy, fluorescence spectroscopy and agarose gel electrophoresis. The binding studies indicate that 1-6 can interact with CT-DNA through intercalation; complex 2 has the highest binding affinity. Moreover, complexes 1-6 inhibit the catalytic activity of topoisomerase I.

Spectroscopic, structural and theoretical studies of novel, potentially cytotoxic 4-acridonecarboxamide imines

Ten novel, potentially intercalating 4-acridonecarboxamide azomethines and ketimines have been prepared by the condensation reaction of 9-oxo-9,10-dihydroacridine-4-carboxylic acid hydrazide with various aldehydes and ketones. The structures of the compounds were characterized spectroscopically by NMR ((1)H, (13)C, (15)N nuclei and 2D experiments), UV-vis, IR and fluorescence methods and by quantum chemical calculations using DFT at the B3LYP/6-311+G(d,p) level of theory and semiempirical ZINDO and AM1 methods. NMR chemical shift variations for C-4' were assessed due to changes in the polarizability of the imine C(4')=N(3') bond rather than direct inductive effects arising from the C-4' substituents. In concert with this was the reversed order observed for the N-3' chemical shifts with DFT-calculated atomic charges confirming the bond polarization. Both intra- and intermolecular hydrogen bonds between the acridone NH hydrogen and the amidic carbonyl oxygen were found to exist by FT-IR spectroscopy. Quantum chemical calculations were used to evaluate the configurational, tautomeric, conformational and hydrogen bonding states of the molecules as well as predict the NMR and IR data. The hypsochromic shifts observed in the UV-vis spectra upon changing from m-cresol to DMA, DMF or methanol were evaluated in terms of solvent polarity (giving rise to solvated excited state destabilization) and solvent aromaticity (giving rise to solvated excited state stabilization). The fluorescence of the compounds were modest, except for the 2,6-dichloro derivative, with respect to 9-isothiocyanatoacridine.

DNA binding properties and evaluation of cytotoxic activity of 9,10-bis-N-substituted (aminomethyl)anthracenes

The results of DNA binding properties for four selected N-substituted 9,10-bis(aminomethyl)anthracenes are presented. DNA binding affinities were studied using UV-vis and fluorescence spectrophotometric titrations, CD spectroscopy, denaturation transition temperature (Tm) measurements and AM1 quantum chemical calculations. The results obtained indicate that the anthracene products intercalate into the stacked base pairs of DNA with binding constants, K, in the range 1.3-10.9 x 10(5)M(-1) and the binding site size in DNA-base pairs, n, extending over the range 2.4-4.6. Tm values increased in the presence of the anthryl probes, thereby reflecting an increased stability of the calf-thymus (CT) DNA double helix and rendering agreement with the spectrometric titration results. The synthesized compounds were tested against L1210 and HeLa tumor cell lines wherein the HeLa cells appeared to be more sensitive than the L1210 cells. 9,10-Bis{[2-(piperazin-1-yl)ethyl]aminomethyl}anthracene exhibited the highest activity of the tested compounds. Our findings were compared with those of a control drug bisantrene.

Determination of the binding affinities of plasmid DNA using fluorescent intercalators possessing an acridine skeleton

Novel acridine derivatives, wherein the steric factor has been varied systematically through substitution at the 9 position of the acridine ring, were evaluated as convenient fluorescent probes for nucleic acid detection. The binding affinities of N-(9-acridinylthiocarbamoyl)amino acids (ATA) with plasmid DNA (pUC 19) were investigated using UV-vis spectrophotometry, fluorometric titration and quantum chemical calculations (AM1). From spectrofluorometric analysis, the binding constants for the DNA-ATA complexes were determined. To elucidate its DNA intercalation, the most preferable tautomeric structure of ATA was established by means of AM1 calculations.

Involvement of glutathione in the cytotoxicity of 9-isothiocyanatoacridine

Isothiocyanates (ITCs) are phytochemicals with promising cancer-preventive potential. To elucidate the mechanism of cytotoxicity of ITCs, their accumulation by cells and the role of intracellular glutathione, fluorescent 9-isothiocyanatoacridine (AcITC) was synthesized. The kinetic parameters for the reactions of AcITC with thiols were estimated and the influence of AcITC on human chronic myeloid leukemia cell line (K562) in regard to intracellular glutathione was studied. Cytotoxicity was evaluated by MTT assay, IC(50)=29.2 +/- 2.5 microM (48 h incubation). This acridine derivative was able to induce apoptosis of cells (morphological changes of cells and DNA fragmentation were observed) at least within certain dose that only decreased the level of intracellular glutathione, excessive doses (completely depleted intracellular pool of glutathione) induced necrosis rather than apoptosis. Our results indicated that apoptosis of leukemia cells induced by ITC is possible only if intracellular glutathione is not entirely depleted.

Involvement of glutathione in the cytotoxicity of 9-isothiocyanatoacridine

Isothiocyanates (ITCs) are phytochemicals with promising cancer-preventive potential. To elucidate the mechanism of cytotoxicity of ITCs, their accumulation by cells and the role of intracellular glutathione, fluorescent 9-isothiocyanatoacridine (AcITC) was synthesized. The kinetic parameters for the reactions of AcITC with thiols were estimated and the influence of AcITC on human chronic myeloid leukemia cell line (K562) in regard to intracellular glutathione was studied. Cytotoxicity was evaluated by MTT assay, IC(50)=29.2 +/- 2.5 microM (48 h incubation). This acridine derivative was able to induce apoptosis of cells (morphological changes of cells and DNA fragmentation were observed) at least within certain dose that only decreased the level of intracellular glutathione, excessive doses (completely depleted intracellular pool of glutathione) induced necrosis rather than apoptosis. Our results indicated that apoptosis of leukemia cells induced by ITC is possible only if intracellular glutathione is not entirely depleted.

Fluorescence Reagents for Labelling of Biomolecules. Part III. Study of the Reactions of 2- and 4-Substituted 9-Isothiocyanatoacridines with Glycine

Kinetics of nucleophilic addition reaction of 2- and 4-substituted 9-isothiocyanatoacridines I - VII with glycine in buffered aqueous dimethylformamide has been studied. The addition products, N-(9-acridinylthiocarbamoyl)glycines VIII - XIV, were characterized by IR, UV, 1H NMR, mass and fluorescence spectra. Derivatives VIII, X and XII exhibited higher fluorescence intensity than the starting isothiocyanates; the highest fluorescence was found for the unsubstituted compound X. The reaction mechanism is discussed on the basis of properties of the reaction products and kinetic characteristics.

Fluorescence Reagents for Labelling of Biomolecules. Part I. Synthesis and Spectral Characterization of 2- and 4-Substituted 9-Isothiocyanatoacridines

9-Isothiocyanatoacridines VIII - XIV were prepared from the corresponding 9-chloroacridines I - VII. The IR, 1H NMR, 13C NMR and fluorescence spectra of the products are given. The 13C NMR chemical shifts of the C-9 ipso carbon atom exhibit a trend that is in accord with the Hammett constants of substituents bonded to the C-2 carbon. Effect of these substituents on the chemical shift of C-NCS was only small. The dependence of hydrolysis of isothiocyanates VIII - XIV on pH of the medium was studied. It was found that 9-isothiocyanatoacridines do not undergo hydrolysis at pH 7 - 10. The relative fluorescence intensities (F/F0) of compounds VIII - XIV at pH 7.4 have been determined in comparison with that of 9-aminoacridine. No direct dependence between the fluorescence intensity and the polar character of substituents has been found.