Structure-activity effects in the anti-leishmanial activity of di-alkyl gallium quinolin-8-olates.

Six (G1-G6) novel organogallium complexes of the general formula [Ga(R)2quin] (where R = Et, iPr, nBu, tBu, sBu and hexyl; quin = quinolin-8-olate, C9H6NO) have been synthesised and fully characterised. Single crystal X-ray diffraction shows the complexes adopt a five-coordinate geometry through dimerisation. Complexes G1-G5 were analytically pure and could undergo further biological analysis. [Ga(hex)2quin] G6 could not be satisfactorily purified and was excluded from biological assays. 1H NMR spectroscopy indicated the complexes are stable to hydrolysis over 24 hours in 'wet' d6-DMSO. Complexes G1-G5 were assessed for their anti-leishmanial activity towards three separate strains: L. major, L. amazonensis and L. donovani, with varied results toward the promastigote form. G1 and G2 were found to be the most selective with little to no toxicity towards mammalian cell lines. Amastigote invasion assays on the three strains showed that [Ga(nBu)2quin] G3 and [Ga(tBu)2quin] G4 gave the best all round anti-parasitic activity with percentage infection ranges of 1.50-3.00% and 3.25-7.50% respectively, with G3 out-performing the drug control amphotericin B in all three assays. The activity was found to correlate with lipophilicity and water solubility, with the most effective G3 proving the most lipophilic and least water soluble.

Enhanced antibacterial activity of dimethyl gallium quinolinolates toward drug-resistant Klebsiella pneumoniae in low iron environments.

A series of dimethylgallium quinolinolate [GaMe2L] (L = 5-chloroquinolinolate, 5, 7-dichloroquinolinolate, 5, 7-dibromoquinolinolate or 5, 7-doiodoquinolinolate) complexes, shown previously to be active toward the Leishmania parasite, have been studied for their antibacterial activity toward a reference and drug resistant strain of Klebsiella pneumoniae (KP). The assays were conducted in standard iron-rich LB media and in the iron depleted RPMI and RPMI-HS media to better understand the effect of Fe concentration on the activity of the Ga complexes. In LB broth the parent quinolinols and the gallium complexes were inactive up to the highest concentration tested, 100 µM. In the more physiologically relevant 'iron-poor' RPMI-HS media the quinolonols remained inactive, however, the gallium complexes showed exceptional activity in the range 48-195 nM. Only in RPMI without any added HS did both the quinolinols and the gallium complexes show good activity. The significant differences in activity across the various media types suggest that the unnaturally high iron content of conventional LB media may provide false negative results for potentially potent Ga therapeutics. A protein binding assay on the organometallic gallium complexes showed a much slower uptake of Ga by Fe-binding proteins than is typically observed for gallium salts. This indicates that their greater lipophilicity and greater hydrolytic stability could account for their increased biological activity in RPMI-HS media.

Gallium reactivates first and second generation quinolone antibiotics towards drug-resistant Klebsiella pneumoniae.

Herein, we report on a series of homoleptic [GaL3] and heteroleptic organometallic [GaMe2L] complexes of inactive quinolone antibiotics; nalidixic acid, oxolinic acid and norfloxacin with their antibacterial activity (MIC 0.024-0.781 µM) towards four multi-drug resistant strains of Klebsiella pneumoniae through complexation to gallium.

Synchrotron-Infrared Microspectroscopy of Live Leishmania major Infected Macrophages and Isolated Promastigotes and Amastigotes.

The prevalence of neglected tropical diseases (NTDs) is advancing at an alarming rate. The NTD leishmaniasis is now endemic in over 90 tropical and sub-tropical low socioeconomic countries. Current diagnosis for this disease involves serological assessment of infected tissue by either light microscopy, antibody tests, or culturing with in vitro or in vivo animal inoculation. Furthermore, co-infection by other pathogens can make it difficult to accurately determine Leishmania infection with light microscopy. Herein, for the first time, we demonstrate the potential of combining synchrotron Fourier-transform infrared (FTIR) microspectroscopy with powerful discrimination tools, such as partial least squares-discriminant analysis (PLS-DA), support vector machine-discriminant analysis (SVM-DA), and k-nearest neighbors (KNN), to characterize the parasitic forms of Leishmania major both isolated and within infected macrophages. For measurements performed on functional infected and uninfected macrophages in physiological solutions, the sensitivities from PLS-DA, SVM-DA, and KNN classification methods were found to be 0.923, 0.981, and 0.989, while the specificities were 0.897, 1.00, and 0.975, respectively. Cross-validated PLS-DA models on live amastigotes and promastigotes showed a sensitivity and specificity of 0.98 in the lipid region, while a specificity and sensitivity of 1.00 was achieved in the fingerprint region. The study demonstrates the potential of the FTIR technique to identify unique diagnostic bands and utilize them to generate machine learning models to predict Leishmania infection. For the first time, we examine the potential of infrared spectroscopy to study the molecular structure of parasitic forms in their native aqueous functional state, laying the groundwork for future clinical studies using more portable devices.

Modulating aryl substitution: Does it play a role in the anti-leishmanial activity of a series of tetra-aryl Sb(V) fluorinated carboxylates?

Eight tetra-arylantimony carboxylates of the general formula Ar4SbOC(O)R with Ar = Ph (a), p-Tol (b), R = C6F5 (1), CH2CF3 (2), CF2Br (3), CF2CF2CF3 (4) have been synthesised and characterised. Two of them (2b, 3b) are structurally novel. All structures were analytically characterised by FT-IR, 1H, 13C NMR spectroscopy. Previously synthesised structures were also analysed by X-ray diffraction and their solid-state structures authenticated. The solid-state structures exhibited a typical trigonal-bipyramidal geometry at the antimony centre, with the carboxylic oxygen and one of the aryl group carbons occupying axial positions with the remaining three aryl groups in the equatorial plane. All complexes were screened for their anti-leishmanial activity and cytotoxicity towards mammalian macrophages. No anti-leishmanial testing on tetra-arylantimony carboxylates have been previously performed. It was observed that the tetra-phenylantimony analogues are far more effective in comparison to the tetra-(p-tolyl)antimony complexes, with IC50 values in the ranges of 2.90-7.75 µM and 64.97-124.71 µM, respectively, for the promastigote assay, and 70.87-76.28 µM, 9.08-10.18 µM for the macrophages. Interestingly, the dose-response curve for tetra-phenylantimony carboxylates is a standard sigmoid curve, while for all tetra-(p-tolyl)antimony complexes it has an unusual inverted U-shape, indicating they are effective only at a low dose. All tetra-phenylantimony carboxylates were assessed for their anti-amastigote activity and showed promising results: 1.00% ± 1.44 (1a), 5,25% ± 1.72 (2a), 20.75% ± 8.46 (3a), 5.75% ± 1.62 (4a) at 10 µM.

The thiol-based reduction of Bi(V) and Sb(V) anti-leishmanial complexes.

Low molecular weight thiols including trypanothione and glutathione play an important function in the cellular growth, maintenance and reduction of oxidative stress in Leishmania species. In particular, parasite specific trypanothione has been established as a prime target for new anti-leishmania drugs. Previous studies into the interaction of the front-line Sb(V) based anti-leishmanial drug meglumine antimoniate with glutathione, have demonstrated that a reduction pathway may be responsible for its effective and selective nature. The new suite of organometallic complexes, of general formula [MAr3(O2CR)2] (M = Sb or Bi) have been shown to have potential as new selective drug candidates. However, their behaviour towards the critical thiols glutathione and trypanothione is still largely unknown. Using NMR spectroscopy and mass spectrometry we have examined the interaction of the analogous Sb(V) and Bi(V) organometallic complexes, [SbPh3(O2CCH2(C6H4CH3))2] S1 and [BiPh3(O2CCH2(C6H4CH3))2] B1, with the trifluoroacetate (TFA) salt of trypanothione and L-glutathione. In the presence of trypanothione or glutathione at the clinically relevant pH of 4-5 for Leishmania amastigotes, both complexes undergo facile and rapid reduction, with no discernible difference. However, at a higher pH (6-7), the complexes behave quite differently towards glutathione. The Bi(V) complex is again reduced rapidly but the Sb(V) complex undergoes slow reduction over 8 h (t1/2 = 54 min.) These results give the first insights into why the highly oxidising Bi(V) complexes display low selectivity in their cytotoxicity towards leishmanial and mammalian cells, while the Sb(V) complexes show good selectivity.

Development of new combination anti-leishmanial complexes: Triphenyl Sb(V) mono-hydroxy mono-quinolinolates.

In seeking to develop single entity combination anti-Leishmanial complexes six heteropletic organometallic Sb(V) hydroxido quinolinolate complexes of general formula [SbPh3(C9H4NORR')(OH)] have been synthesised and characterised, derived from a series of halide substituted quinolinols (8-hydroxyquinolines). Single crystal X-ray diffraction on all the complexes show a common distorted six-coordinate octahedral environment at the Sb(V) centre, with the aryl groups and nitrogen atom of quinolinolate ligand bonding in the equatorial planes, with the two oxygen atoms (hydroxyl and quinolinolate) occupying the axial plane in an almost linear configuration. Each complex was tested for their anti-promastigote activity and mammalian cytotoxicity and a selectivity indices established. The complexes displayed excellent anti-promastigote activity (IC50: 2.03-3.39 µM) and varied mammalian cytotoxicity (IC50: 12.7-46.9 µM), leading to a selectivity index range of 4.52-16.7. All complexes displayed excellent anti-amastigote activity with a percentage infection range of 2.25%-9.00%. All complexes performed substantially better than the parent quinolinols and comparable carboxylate complexes [SbPh3(O2CRR')2] indicating the synergistic role of the Sb(V) and quinolinol moieties in increasing parasite mortality. Two of the complexes [SbPh3(C9H4NOBr2)(OH)] 4, [SbPh3(C9H4NOI2)(OH)] 5, provide an ideal combination of high selective and good activity towards the leishmanial amastigotes and offer the potential as good lead compounds.

Impact of structural changes in heteroleptic bismuth phosphinates on their antibacterial activity in Bi-nanocellulose composites.

To study and evaluate the effect of ligand choice and distribution in bismuth phosphinates on toxicity and antibacterial activity, a series of novel diphenyl mono-phosphinato bismuth complexes, [BiPh2(O(O[double bond, length as m-dash])P(H)Ph)] 1, [BiPh2(O(O[double bond, length as m-dash])PPh2)] 2, [BiPh2(O(O[double bond, length as m-dash])PMe2)] 3 and [BiPh2(O(O[double bond, length as m-dash])P(p-MeOPh)2)] 4, were synthesised, characterised and structurally authenticated by X-ray crystallography. Evaluation of their antibacterial activity towards Staphylococcus aureus (S. aureus), methicillin-resistant S. aureus (MRSA), vancomycin-resistant Enterococci (VRE), Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa) showed all four mono-phosphinato bismuth complexes to be highly active. However, unlike their less soluble bis-phosphinato analogues, they displayed an increased level of toxicity towards mammalian cells (COS-7, human and murine fibroblasts), where it was shown the complexes disrupt cellular membranes leading to cytotoxicity. The mono-phosphinato bismuth complexes were used to produce antibacterial nanocellulose composites. Leaching studies showed that complex 1 had the highest levels of leaching, at 15% of the total available bismuth when the composite was soaked in water. The aqueous leachates of 1 were bacteriostatic towards MRSA and VRE at concentrations between 4.0 and 4.6 µM, while being bactericidal towards E. coli above 2.8 µM. At similar concentrations the complex showed toxicity towards human fibroblast cells, with cell viability reduced to 2% (1, 2.4 µM). The possibility to control leaching of the bismuth complexes from cellulose composites through structural changes is evidence for their potential application in antibacterial surfaces and materials.

Is Bismuth Really the "Green" Metal? Exploring the Antimicrobial Activity and Cytotoxicity of Organobismuth Thiolate Complexes.

Antimicrobial resistance is becoming an ever-increasing threat for human health. Metal complexes and, in particular, those that incorporate bismuth offer an attractive alternative to the typically used organic compounds to which bacteria are often able to develop resistance determinants. Herein we report the synthesis, characterization, and biological evaluation of a series of homo- and heteroleptic bismuth(III) thiolates incorporating either one (BiPh2L), two (BiPhL2), or three (BiL3) sulfur-containing azole ligands where LH = tetrazolethiols or triazolethiols (thiones). Despite bismuth typically being considered a nontoxic heavy metal, we demonstrate that the environment surrounding the metal center has a clear influence on the safety of bismuth-containing complexes. In particular, heteroleptic thiolate complexes (BiPh2L and BiPhL2) display strong antibacterial activity yet are also nonselectively cytotoxic to mammalian cells. Interestingly, the homoleptic thiolate complexes (BiL3) were shown to be completely inactive toward both bacterial and mammalian cells. Further biological analysis of the complexes revealed the first insights into the biological mode of action of these particular bismuth thiolates. Scanning electron microscopy images of methicillin-resistant Staphylococcus aureus (MRSA) cells have revealed that the cell membrane is the likely target site of action for bismuth thiolates against bacterial cells. This points toward a nonspecific mode of action that is likely to contribute to the poor selectivity's demonstrated by the bismuth thiolate complexes in vitro. Uptake studies suggest that reduced cellular uptake could explain the marked difference in activity between the homo- and heteroleptic complexes.

Alkyl gallium(III) quinolinolates: A new class of highly selective anti-leishmanial agents.

A series of eight alkyl gallium complexes of general formulae [GaMe2(L)] and [Ga(Me)2L] have been synthesised, characterised and their antimicrobial activity against bacteria, cancer cells and Leishmania assessed. All eight complexes are novel, with the solid-state structures of all complexes successfully authenticated by single crystal X-ray diffraction. The dimethyl complexes all adopt a four-coordinate tetrahedral confirmation, while the monomethyl complexes are five-coordinate trigonal bipyramidal. All complexes were screened for their anti-bacterial activity either by solution state diffusion, or a solid-state stab test. The five soluble complexes underwent testing against two differing mammalian cell controls, with excellent selectivity observed against COS-7 cells, with an IC50 range of 88.5 µM to ≥100 µM. Each soluble complex was also tested for their anti-cancer capabilities, with no significant activity observed. Excellent activity was exhibited against the protozoan parasite Leishmania major (strain: V121) in both the promastigote and amastigote forms, with IC50 values ranging from 1.11 µM-13.4 µM for their anti-promastigote activity and % infection values of 3.5% ± 0.65-11.5% ± 0.65 for the more clinically relevant amastigote. Selectivity indices for each were found to be in the ranges of 6.61-64.7, with significant selectivity noted for two of the complexes. At minimum, the gallium complexes show a 3-fold enhancement in activity towards the Leishmaniaamastigotes over the parent quinolinols alone.

Anti-leishmanial activity and cytotoxicity of a series of tris-aryl Sb(V) mandelate cyclometallate complexes.

A series of ten cyclometallates and two µ2-peroxo bridged tris-aryl Sb(V) complexes derived from R/S-mandelic acid (= R/S-ManH2) were synthesised and characterised. As confirmed by X-ray crystallography the complexes 1Sr/s, [Sb(o-tol)3(man)], 2Sr/s, [Sb(m-tol)3(man)], 4Sr/s, [Sb(o-PhOMe)3(man)], 5Sr/s, [Sb(Mes)3(man)] and 6Sr/s, [Sb(p-tert-BuPh)3(man)] are all cyclometallates. Complexes 3Sr/s, [(Sb(p-tol)3(manH)2O2], contain a bridging O22- anion in the solid-state but convert to the cyclometallates in DMSO solution with concomitant release of H2O2 and formation of complexes [Sb(p-tol)3(man)], 3Sr'/s'. All complexes underwent initial testing against both human fibroblasts and L. major V121 promastigotes. IC50 values were found to range from 2.07 (6Sr) to >100 (4Sr) µM and 0.21 (5Ss) to >100 (4Ss) µM for fibroblasts and parasites respectively. Two of the complexes were found to be ineffective, displaying no toxicity (4S/r). Despite the degree of mammalian toxicity, the selectivity of most complexes exceeded an SI of three and so were assessed for their anti-amastigote activity. Excellent anti-amastigote activity was observed for complexes at both 10 µM and 5 µM, with percentage infection value ranging from 0.15-3.00% for those tested at 10 µM and 0.25-2.50% for those at 5 µM.

Comparative stability, cytotoxicity and anti-leishmanial activity of analogous organometallic Sb(V) and Bi(V) acetato complexes: Sb confirms potential while Bi fails the test.

A series of sixteen triphenyl Bi(V) and Sb(V) acetato complexes of general formula [MPh3(O2CCR)2] and one oxido-bridge antimony complex [(SbPh3(O2COC(O)Me))2O], have been synthesised and characterised, thirteen of which are novel. The solid-state structures of fifteen of the complexes have been successfully authenticated by single crystal X-ray diffraction. All structures, excluding the oxido-bridge antimony complex, adopt a typical trigonal bipyramidal confirmation with the phenyl rings in a propeller-like orientation in the equatorial plane. Fourteen of the complexes were screened for their anti-leishmanial activity and cytotoxicity towards mammalian cells. The Bi(V) complexes were found to be unstable in DMEM culture media and to be severely toxic towards mammalian cells, with IC50 values in the range 11.4 µM-19.8 µM. In contrast, the Sb(V) complexes demonstrated a high degree of stability and selectivity, with IC50 values 6.18-19.1 µM for the promastigote assay, and of 73.8-≤100 µM for the human fibroblasts. Assessment of the Sb(V) complexes against the clinically relevant amastigote form of these parasites at 10 µM showed all but the oxido-bridged complex to be effective, with % infection values ranging from 7.0 ±â€¯1.7-40.5 ±â€¯2.0.

Comparative stability, toxicity and anti-leishmanial activity of triphenyl antimony(v) and bismuth(v) α-hydroxy carboxylato complexes.

A series of triphenyl Sb(v) and Bi(v) α-hydroxy carboxylato complexes of the general formula [MPh3(O2CROH)2] and [MPh3(O2CRO)] have been successfully synthesised and characterised, and subsequently assayed for their comparative activity towards Leishmania parasites and human fibroblast cells. Four complexes are novel; [SbPh3Gly], [BiPh3(GlyH)2], [SbPh3(R-ManH)2] and [SbPh3(S-ManH)2], and have been structurally characterised through X-ray diffraction. These were combined in the study with the known complexes; ([SbPh3(R-Man)], [SbPh3(S-Man)], [BiPh3(R-ManH)2], [BiPh3(R-ManH)2], [SbPh3(BenzH)2], [BiPh3(BenzH)2], for which the crystal structures of [BiPh3(S-ManH)2] and [BiPh3(R-Man)2] have now been authenticated (GlyH2 = glycolic acid, R/S-ManH2 = mandelic acid, BenzH2 = benzilic acid). The complexes adopt a typical bipyramidal 7-coordinate geometry with the phenyl rings occupying the equatorial plane, and the ligands on the axial. In contrast to previous studies the Bi(v) compounds show a relatively high degree of stability in DMEM culture media. Promastigote and human fibroblast cell assays showed the Bi(v) analogues to be non-selectively toxic with a respective IC50 range of 3.58-6.33 µM and 5.83-7.01 µM. In contrast, the Sb(v) analogues provided much greater selectivity (promastigotes 12.5-20.7; fibroblasts 72.8-≥100 µM). Assessment of the Sb(v) complexes against amastigotes at 10 µM showed them to be effective with % infection values ranging from 9.5 ± 0.5-30 ± 1.3.