Insight into the cytotoxicity of polynuclear Cu(I) camphor complexes

Interaction with bioligands and in vitro cytotoxicity of a new dinuclear dioxido vanadium(V) complex

One centrosymmetric bis(μ-oxido)-bridged vanadium(V) dimer with molecular formula [(V^VO₂)₂(pedf)₂] (1) has been synthesized from the reaction of VOSO₄·5H₂O with a Schiff base ligand (abbreviated with pedf^-) obtained from 2-acetylpyridine and 2-furoic hydrazide in methanol. Complex 1 was characterized by elemental analysis, UV-visible (UV-Vis), Fourier-transform infrared spectra (FT-IR), cyclic voltammetry (CV), electron paramagnetic resonance spectroscopy (EPR) and electrospray ionization-mass spectrometry (ESI-MS) techniques along with single crystal X-ray diffraction (SCXRD). The FT-IR spectral data of 1 indicated the involvement of oxygen and azomethine nitrogen in coordination to the central metal ion. The crystallographic studies revealed a dinuclear oxovanadium(V) complex with the Schiff base coordinated via the ONN donor set with formation of two five-membered chelate rings resulting in a distorted octahedral geometry. The interaction of 1 with calf thymus DNA (CT-DNA) was investigated by spectroscopic measurements and results suggested that the complex binds to CT-DNA via moderate intercalative mode with a binding constant (K_b) around 10³ M^-1. In addition, the in vitro protein binding behavior was studied by fluorescence spectrophotometric method using both bovine serum albumin (BSA) and human serum albumin (HSA) and a static quenching mechanism was observed for the interaction of the complex with both albumins that occurs with a K_b in the range (5-6) × 10³ M^-1. In vitro cytotoxicity of complex 1 on lung cancer cells (A549) and human skin carcinoma cell line (A431) demonstrated that the complex had a broad-spectrum of anti-proliferative activity with IC₅₀ value of 64.2 μM and 56.2 μM.

Tuning the Biological Activity of Camphorimine Complexes through Metal Selection

The cytotoxic activity of four sets of camphorimine complexes based on the Cu(I), Cu(II), Ag(I), and Au(I) metal sites were assessed against the cisplatin-sensitive A2780 and OVCAR3 ovarian cancer cells. The results showed that the gold complexes were ca. one order of magnitude more active than the silver complexes, which in turn were ca. one order of magnitude more active than the copper complexes. An important finding was that the cytotoxic activity of the Ag(I) and Au(I) camphorimine complexes was higher than that of cisplatin. Another relevant aspect was that the camphorimine complexes did not interact significantly with DNA, in contrast with cisplatin. The cytotoxic activity of the camphorimine complexes displayed a direct relationship with the cellular uptake by OVCAR3 cells, as ascertained by PIXE (particle-induced X-ray emission). The levels of ROS (reactive oxygen species) formation exhibited an inverse relationship with the reduction potentials for the complexes with the same metal, as assessed by cyclic voltammetry. In order to gain insight into the toxicity of the complexes, their cytotoxicity toward nontumoral cells (HDF and V79 fibroblasts) was evaluated. The in vivo cytotoxicity of complex 5 using the nematode Caenorhabditis elegans was also assessed. The silver camphorimine complexes displayed the highest selectivity coefficients (activity vs. toxicity).

Mo(VI) Potential Metallodrugs: Explaining the Transport and Cytotoxicity by Chemical Transformations

The transport and cytotoxicity of molybdenum-based drugs have been explained with the concept of chemical transformation, a very important idea in inorganic medicinal chemistry that is often overlooked in the interpretation of the biological activity of metal-containing systems. Two monomeric, [MoO₂(L¹)(MeOH)] (1) and [MoO₂(L²)(EtOH)] (2), and two mixed-ligand dimeric Mo^VIO₂ species, [{MoO₂(L^1-2)}₂(μ-4,4'-bipy)] (3-4), were synthesized and characterized. The structures of the solid complexes were solved through SC-XRD, while their transformation in water was clarified by UV-vis, ESI-MS, and DFT. In aqueous solution, 1-4 lead to the penta-coordinated [MoO₂(L^1-2)] active species after the release of the solvent molecule (1 and 2) or removal of the 4,4'-bipy bridge (3 and 4). [MoO₂(L^1-2)] are stable in solution and react with neither serum bioligand nor cellular reductants. The binding affinity of 1-4 toward HSA and DNA were evaluated through analytical and computational methods and in both cases a non-covalent interaction is expected. Furthermore, the in vitro cytotoxicity of the complexes was also determined and flow cytometry analysis showed the apoptotic death of the cancer cells. Interestingly, μ-4,4'-bipy bridged complexes 3 and 4 were found to be more active than monomeric 1 and 2, due to the mixture of species generated, that is [MoO₂(L^1-2)] and the cytotoxic 4,4'-bipy released after their dissociation. Since in the cytosol neither the reduction of Mo^VI to Mo^V/IV takes place nor the production of reactive oxygen species (ROS) through Fenton-like reactions of 1-4 with H₂O₂ occurs, the mechanism of cytotoxicity should be attributable to the direct interaction with DNA that happens with a minor-groove binding which results in cell death through an apoptotic mechanism.

Synthesis and Characterization of Camphorimine Au(I) Complexes with a Remarkably High Antibacterial Activity towards B. contaminans and P. aeruginosa

Fourteen new camphorimine Au(I) complexes were synthesized and characterized by spectroscopic (NMR, FTIR) and elemental analysis. The structural arrangement of three selected examples were computed by Density Functional Theory (DFT) showing that the complexes essentially keep the {Au^I-CN} unit. The Minimum Inhibition Concentrations (MIC) were assessed for all complexes showing that they are active towards the Gram-negative strains E. coli ATCC25922, P. aeruginosa 477, and B. contaminans IST408 and the Gram-positive strain S. aureus Newman. The complexes display very high activity towards P. aeruginosa 477 and B. contaminans IST408 with selectivity towards B. contaminans. An inverse correlation between the MIC values and the gold content was found for B. contaminans and P. aeruginosa. However, plots of MIC values and Au content for P. aeruginosa 477 and B. contaminans IST408 follow distinct trends. No clear relationship could be established between the MIC values and the redox potentials of the complexes measured by cyclic voltammetry. The MIC values are essentially independent of the redox potentials either cathodic or anodic. The complexes K₃[{Au(CN)₂}₃(^A4L)] (8, Y = m-OHC₆H₄) and K₃[{Au(CN)₂}₃(^B2L)]·3H₂O (14, Z = p-C₆H₄) display the lower MIC values for the two strains. In normal fibroblast cells, the IC₅₀ values for the complexes are ca. one order of magnitude lower than their MIC values, although higher than that of the precursor KAu(CN)₂.

Thermodynamic Study of Oxidovanadium(IV) with Kojic Acid Derivatives: A Multi-Technique Approach

The good chelating properties of hydroxypyrone (HPO) derivatives towards oxidovanadium(IV) cation, VIVO2+, constitute the precondition for the development of new insulin-mimetic and anticancer compounds. In the present work, we examined the VIVO2+ complex formation equilibria of two kojic acid (KA) derivatives, L4 and L9, structurally constituted by two kojic acid units linked in position 6 through methylene diamine and diethyl-ethylenediamine, respectively. These chemical systems have been characterized in solution by the combined use of various complementary techniques, as UV-vis spectrophotometry, potentiometry, NMR and EPR spectroscopy, ESI-MS spectrometry, and DFT calculations. The thermodynamic approach allowed proposing a chemical coordination model and the calculation of the complex formation constants. Both ligands L4 and L9 form 1:1 binuclear complexes at acidic and physiological pHs, with various protonation degrees in which two KA units coordinate each VIVO2+ ion. The joined use of different techniques allowed reaching a coherent vision of the complexation models of the two ligands toward oxidovanadium(IV) ion in aqueous solution. The high stability of the formed species and the binuclear structure may favor their biological action, and represent a good starting point toward the design of new pharmacologically active vanadium species.

Ln(iii) complexes with a chiral 1H-pyrazolo[3,4-b]pyridine derivative fused with a (−)-α-pinene moiety: synthesis, crystal structure, and photophysical studies in solution and in the solid state

Novel chiral luminescent Ln(iii) complexes with a pyrazolo[3,4-b]pyridine derivative containing a natural monoterpene (−)-α-pinene moiety are reported.

Antimicrobial Activity of Silver Camphorimine Complexes against Candida Strains

Hydroxide [Ag(OH)L] (L = ^IVL, ^VL, ^VIL, ^VIIL), oxide [{AgL}₂}(μ-O)] (L = ^IL, ^IIL, ^IIIL, ^VL, ^VIL) or chloride [Ag^IIL]Cl, [Ag(^VIL)₂]Cl complexes were obtained from reactions of mono- or bicamphorimine derivatives with Ag(OAc) or AgCl. The new complexes were characterized by spectroscopic (NMR, FTIR) and elemental analysis. X-ray photoelectron spectroscopy (XPS), ESI mass spectra and conductivity measurements were undertaken to corroborate formulations. The antimicrobial activity of complexes and some ligands were evaluated towards Candida albicans and Candida glabrata, and strains of the bacterial species Escherichia coli, Burkholderia contaminans, Pseudomonas aeruginosa and Staphylococcus aureus based on the Minimum Inhibitory Concentrations (MIC). Complexes displayed very high activity against the Candida species studied with the lowest MIC values (3.9 µg/mL) being observed for complexes 9 and 10A against C. albicans. A significant feature of these redesigned complexes is their ability to sensitize C. albicans, a trait that was not found for the previously investigated [Ag(NO₃)L] complexes. The MIC values of the complexes towards bacteria were in the range of those of [Ag(NO₃)L] and well above those of the precursors Ag(OAc) or AgCl. The activity of the complexes towards normal fibroblasts V79 was evaluated by the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) assay. Results showed that the complexes have a significant cytotoxicity.

Search for cytotoxic compounds against ovarian cancer cells: Synthesis, characterization and assessment of the activity of new camphor carboxylate and camphor carboxamide silver complexes

Five silver camphor complexes of formulae [Ag₂(L)(L')₂] (1,3,5) or [Ag(L)₂(L')] (2,4) were synthesized from silver nitrate and the suitable camphor carboxylate (L¹) or camphor carboxamides (L³, L⁴). The complexes were characterized by elemental analysis and spectroscopic techniques (NMR, FTIR, XPS). Computational calculations support coordination of the carboxylate group to silver, in the case of complex 2 and combined mixed keto/carboxylate in the case of complex 1. The stability of the complexes highly relies on the tetrahedral geometry of the lithium ion that binds to four oxygen atoms of the camphor carboxylate ligands. The redox properties of complexes 1 and 4 studied by cyclic voltammetry confirm the facile reduction of the metal sites that depending on the experimental conditions may lead to formation of silver nanoparticles as confirmed by XPS and TEM. Complexes 1, 2 and 4 were tested for cytotoxic activities against A2780 (IC₅₀, 11-14 μM) and A2780 cisplatin resistant (A2780cisR) (IC₅₀, 4-7 μM) cells using the MTT assay. The result showed that the complexes have anticancer activity higher than cisplatin. Complex 1 was also probed for cytotoxicity against the non-tumoral human embryonic kidney (HEK 293, IC₅₀, 62.2 ± 16 μM) cells showing low toxicity in agreement with the silver camphor carboxylate complexes having a considerable selectivity for the ovarian cancer cells A2780 and cisplatin resistant A2780cisR which is a key point under pharmacological uses.

Silver Camphor Imine Complexes: Novel Antibacterial Compounds from Old Medicines

The emergence of bacterial resistance to available antimicrobials has prompted the search for novel antibacterial compounds to overcome this public health problem. Metal-based complexes have been much less explored than organic compounds as antimicrobials, leading to investigations of the antimicrobial properties of selected complexes in which silver may occupy the frontline due to its use as medicine since ancient times. Like silver, camphor has also long been used for medicinal purposes. However, in both cases, limited information exists concerning the mechanisms of their antimicrobial action. This work reviews the present knowledge of the antimicrobial properties of camphor-derived silver complexes, focusing on recent research on the synthesis and antimicrobial properties of complexes based on silver and camphor imines. Selected examples of the structure and antimicrobial activity relationships of ligands studied so far are presented, showing the potential of silver camphorimine complexes as novel antimicrobials.

Ag(I) camphorimine complexes with antimicrobial activity towards clinically important bacteria and species of the Candida genus

The present work follows a previous report describing the antibacterial activity of silver camphorimine complexes of general formula [Ag(NO3)L]. The synthesis and demonstration of the antifungal and antibacterial activity of three novel [Ag(NO3)L] complexes (named 1, 2 and 3) is herein demonstrated. This work also shows for the first time that the previously studied complexes (named 4 to 8) also exert antifungal activity. The antibacterial activity of complexes was evaluated against Staphylococcus aureus, Pseudomonas aeruginosa, Burkholderia contaminans and Escherichia coli strains, while antifungal activity was tested against the Candida species C. albicans, C. glabrata, C. parapsilosis and C. tropicalis. The antimicrobial activity of the complexes ranged from very high (complex 4) to moderate (complex 6) or low (complex 8), depending on the structural and electronic characteristics of the camphorimine ligands. Notably, the highest antibacterial and anti-Candida activities do not coincide in the same complex and in some cases they were even opposite, as is the case of complex 4 which exhibits a high anti-bacterial and low antifungal activity. These distinct results suggest that the complexes may have different mechanisms against prokaryotic and eukaryotic cells. The antifungal activity of the Ag(I) camphorimine complexes (in particular of complex 1) was found to be very high (MIC = 2 μg/mL) against C. parapsilosis, being also registered a prominent activity against C. tropicalis and C. glabrata. None of the tested compounds inhibited C. albicans growth, being this attributed to the ability of these yeast cells to mediate the formation of less toxic Ag nanoparticles, as confirmed by Scanning Electron Microscopy images. The high antibacterial and anti-Candida activities of the here studied camphorimine complexes, especially of complexes 1 and 7, suggests a potential therapeutic application for these compounds.

Synthesis of Ag(I) camphor sulphonylimine complexes and assessment of their cytotoxic properties against cisplatin-resistant A2780cisR and A2780 cell lines

Camphorsulphonylimine complexes [Ag(NO₃)(^IL)₂] (^IL=C₁₂H₁₉N₃SO₂, 1) and [(AgNO₃)₂(^IIL)] (^IIL=C₂₂H₂₃N₃SO₂, 2) were synthesized and characterized by elemental analysis, spectroscopy (IR, NMR) and cyclic voltammetry. [Ag(NO₃)(^IL)₂] crystalizes in the monoclinic C2 space group with a triangular geometry assuming a chalice-type shape. The anti-proliferative properties of the new complexes 1 and 2 and those of the previously reported [Ag(NO₃)(^IIIL)] (^IIIL=C₁₆H₁₈N₃SO₂, 3) were assessed against the human ovarian cancer cells (cisplatin-sensitive A2780, cisplatin-resistant A2780cisR) and the non-tumoral human HEK 293 cell line, using the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay. The NR (3-amino-7-dimethylamino-2-methylphenazine hydrochloride) assay was alternatively used to assess the cytotoxicity on the A2780 cells. Results from the MTT assay (48h exposure) show that the complexes display IC₅₀ values lower (by at least one order of magnitude) than cisplatin, while the cytotoxicity of AgNO₃ is of the same order of cisplatin. The camphorsulphonylimine ligands display irrelevant (^IL, ^IIIL) or no cytotoxicity (^IIL). The highest cytotoxicity (lower IC₅₀) was found for [(AgNO₃)₂(^IIL)]. The binding ability of the complexes to calf thymus-deoxyribonucleic acid (CT-DNA) was studied by fluorescence. Constants (K_sv, K_a) and the number (n) of binding centres to DNA were calculated showing that DNA intercalation possibly occurs in the cases of complexes 2 and 3, while a more complicated process operates for 1. As expected from the cytotoxicity, [(AgNO₃)₂(^IIL)] displays the highest binding affinity (K_a=1.61×105 M^-1). No binding to DNA was detected for AgNO₃ or ^IIL under the experimental conditions used. The binding trend to CT-DNA found by fluorescence was corroborated by cyclic voltammetry.

Antibacterial activity of silver camphorimine coordination polymers

[Ag(NO₃)(OC₁₀H₁₄NC₆H₄NC₁₀H₁₄O)] is the first bi-camphor silver coordination polymer structurally characterized. It displays bactericidal activity against Gram-negative and Gram-positive strains comparable to drugs in use.

Oxygen activation by copper camphor complexes

In situreduction of CuCl₂enables formation of Cu(i) complexes prone to activate molecular oxygen from air towards catalytic oxidation of 1,3-dicarbonyls.