Synthesis and biological evaluation against Leishmania donovani of novel hybrid molecules containing indazole-based 2-pyrone scaffolds

A series of novel indazole-pyrone hybrids were synthesized by a one pot reaction between N-alkyl-6(5)-nitroindazoles and 2-pyrone (4-hydroxy-6-methyl-2H-pyran-2-one) using indium or stannous chloride as the reducing system in the presence of acetic acid in tetrahydrofuran. The hybrid molecules were obtained in good to excellent yields (72-92%) and characterized by NMR and single crystal X-ray diffraction. Nineteen compounds were tested in vitro against both Leishmania donovani (MHOM/ET/67/HU3, also called LV9) axenic and intramacrophage amastigotes. Among all, five compounds showed anti-leishmanial activity against intracellular L. donovani with an IC₅₀ in the range of 2.25 to 62.56 μM. 3-(1-(3-Chloro-2-ethyl-2H-indazol-6-ylamino)ethylidene)-6-methyl-3H-pyran-2,4-dione 6f was found to be the most active compound for axenic amastigotes and intramacrophage amastigotes of L. donovani with IC₅₀ values of 2.48 ± 1.02 μM and 2.25 ± 1.89 μM, respectively. However, the cytotoxicity of the most promising compound justifies further pharmacomodulations.

Antiplasmodial Activity of Acetogenins and Inhibitory Effect onPlasmodium falciparumAdenylate Translocase

Three Annonaceous acetogenins exhibited in vitro antimalarial activities on a chloroquine-resistant Plasmodium falciparum strain, with IC50s ranging from 5 to 10 microM. Structure-activity relationships showed that maximal antimalarial activity occurred in the presence of at least one tetrahydrofuran moiety and a synergistic action with chloroquine was observed. These acetogenins partially inhibited the P. falciparum adenylate translocase.

Interactions of antileishmanial drugs with monolayers of lipids used in the development of amphotericin B-miltefosine-loaded nanocochleates

The emergence of strains of Leishmania resistant to existing drugs complicates the treatment of life-threatening visceral leishmaniasis. The development of new lipid formulation (nanocochleates), containing two active drugs: amphotericin B (AmB) and miltefosine (hexadecylphosphocholine, HePC), could increase effectiveness, decrease toxicity and reduce the risk of appearance of resistance. Nanocochleates are cigar-shaped structures of rolled negatively charged lipid bilayers bridged by calcium, prepared from dioleoylphosphatidylserine (DOPS) and cholesterol (Cho) and able to accommodate drugs. To determine the interaction, the orientation and the stability of the amphiphilic drugs in the lipid mixture and the optimal drugs/lipids ratio, the Langmuir film balance and BAM (Brewster angle microscopy) were used. The drugs were mixed with the lipids (DOPS or 9DOPS/1Cho) and spread at the air-water interface. A stability study showed that DOPS maintained HePC at the interface at low molar fraction of HePC; this effect became more marked in the presence of Cho. The fact that HePC can be stably associated with the monolayer at low molar fraction (below 10%) suggests that in the nanocochleates HePC is inserted between the lipid molecules rather than between the bilayers. Phase diagrams and BAM images showed that, even at low pressure, DOPS maintains AmB at low molar fraction (below 10%) in the "erect" rather than the horizontal form at the interface and that the presence of Cho reinforces this effect. These results allowed us to predict the organization and the orientation of these drugs in the nanocochleates and to determine the optimal drugs/lipids ratio.

In silico analysis of a therapeutic target in Leishmania infantum: the guanosine-diphospho-D-mannose pyrophosphorylase

Leishmaniases are tropical and sub-tropical diseases for which classical drugs (i.e. antimonials) exhibit toxicity and drug resistance. Such a situation requires to find new chemical series with antileishmanial activity. This work consists in analyzing the structure of a validated target in Leishmania: the GDP-mannose pyrophosphorylase (GDP-MP), an enzyme involved in glycosylation and essential for amastigote survival. By comparing both human and L. infantum GDP-MP 3D homology models, we identified (i) a common motif of amino acids that binds to the mannose moiety of the substrate and, interestingly, (ii) a motif that is specific to the catalytic site of the parasite enzyme. This motif could then be used to design compounds that specifically inhibit the leishmanial GDP-MP, without any effect on the human homolog.

Antileishmanial activity of a formulation of 2-n-propylquinoline by oral route in mice model

2-n-propylquinoline is presently a drug-candidate for the treatment of visceral leishmaniosis in pre-clinical development. As this compound is in an oily state, it needs to be formulated and the objectives of this study are: to prepare a formulation; to demonstrate that the new salted formulation did not alter the activity of the active ingredient; and finally, that this activity was quite good compared to the reference oral drug, miltefosine. Therefore, a 2-n-propylquinoline formulation, as camphorsulfonic salt, was prepared and characterised. On the Leishmania donovani / Balb/c mice model, a treatment by oral route at 60 μmoles/kg/day for ten consecutive days with this formulation was compared to 2-n-propylquinoline alone and to miltefosine, the oral reference drug. The salt formulation did not alter the activity of the 2-n-propylquinoline. The formulation reduced the parasite burden of 76% compared to 89% for miltefosine (not significant). The characteristics of this formulation results in a suitable drugability of 2-n-propylquinoline for further studies.

In vitro antileishmanial and antitrypanosomal activities of five medicinal plants from Burkina Faso

After ethnobotanical surveys in central and western regions of Burkina Faso, five plants namely Lantana ukambensis (Verbenaceae), Xeoderris sthulmannii (Fabaceae), Parinari curatellifollia (Chrysobalanaceae), Ozoroa insignis (Anacardiaceae), and Ficus platyphylla (Moraceae) were selected for their traditional use in the treatment of parasitic diseases and cancer. Our previous studies have focused on the phytochemical, genotoxicity, antioxidant, and antiproliferative activities of these plants. In this study, the methanol extract of each plant was tested to reveal probable antileishmanial and antitrypanosomal activities. Colorimetric and spectrophotometric methods were used for the detection of antileishmanial and antitrypanosomal activities. Leishmania donovani (LV9 WT) and Trypanosoma brucei brucei GVR 35 were used to test the antileishmanial and antitrypanosomal activities, respectively. All extracts of tested plants showed a significant antitrypanosomal activity with minimum lethal concentrations between 1.5 and 25 μg/ml, the L. ukambensis extract being the most active. In the antileishmanial test, only the extract from L. ukambensis showed significant activity with an inhibitory concentration (IC(50)) of 6.9 μg/ml. The results of this study contribute to the promotion of traditional medicine products and are preliminary for the isolation of new natural molecules for the treatment of leishmaniasis and trypanosomiasis.

Sitamaquine as a putative antileishmanial drug candidate: from the mechanism of action to the risk of drug resistance

Sitamaquine is a 8-aminoquinoline in development for the treatment of visceral leishmaniasis by oral route, no activity being observed on the experimental cutaneous leishmaniasis experimental models. Recent data explain how sitamaquine accumulate in Leishmania parasites, however its molecular targets remain to be identified. An advantage of sitamaquine is its short elimination half-life, preventing a rapid resistance emergence. The antileishmanial action of its metabolites is not known. The selection of a sitamaquine-resistant clone of L. donovani in laboratory and the phase II clinical trials pointing out some adverse effects such as methemoglobinemia and nephrotoxicity are considered for a further development decision.

Mechanism of interaction of sitamaquine with Leishmania donovani

OBJECTIVES

This study focuses on the mechanism of interaction of sitamaquine with Leishmania donovani membranes, and its accumulation within the parasites.

METHODS

A biomimetic model of the outer layer of a Leishmania plasma membrane was used to examine the interactions of sitamaquine with lipids. The plasma membranes of L. donovani promastigotes were depleted of sterol using cholesterol oxidase, in order to assess the importance of sterols in drug-membrane interactions. Sterols were quantified and sitamaquine susceptibility was assessed using the MTT test. Kinetics of sitamaquine accumulation and efflux were measured under different conditions.

RESULTS

Sitamaquine interacts first with phospholipid anionic polar head groups and then with phospholipid acyl chains to insert within biological membranes and accumulates rapidly in the Leishmania cytosol according to a sterol-independent process. The rapid sitamaquine efflux observed was related to an energy-dependent mechanism since the intracellular amount of sitamaquine was enhanced three times in the absence of glucose and the efflux was inhibited in energy-depleted conditions. (1)H NMR analysis of motile lipid showed that sitamaquine did not affect lipid trafficking in Leishmania.

CONCLUSIONS

We propose that sitamaquine rapidly accumulates in Leishmania by diffusion along an electrical gradient and is concentrated in the cytosol by an energy- and sterol-independent process. The affinity of sitamaquine for membranes was transitory and an energy-dependent efflux was demonstrated, suggesting the presence of an as yet uncharacterized transporter.

Membrane sterol depletion impairs miltefosine action in wild-type and miltefosine-resistant Leishmania donovani promastigotes

OBJECTIVES

This study focuses on the importance of sterols in the action of miltefosine (hexadecylphosphocholine, HePC) against Leishmania donovani.

METHODS

Plasma membranes of L. donovani promastigotes were depleted of sterol using methyl-beta-cyclodextrin (MCD) and cholesterol oxidase (CH-OX). Sterols were quantified and HePC susceptibility was assessed using the MTT test. A biomimetic model of the outer leaflet of a Leishmania plasma membrane was used to decipher the HePC-lipid interactions.

RESULTS

CH-OX, which is known to act more specifically on condensed membranes, therefore at the level of lipid rafts, gave a better extraction yield in HePC-resistant parasites, confirming the more rigid structure of their membranes than those of wild-type parasites. Sterol depletion was responsible for a 40% decrease in HePC susceptibility in both wild-type and HePC-resistant parasites. Sterol repletion of the sterol-depleted parasites restored HePC susceptibility. The biomimetic model of the outer leaflet of a Leishmania plasma membrane confirmed that condensed microdomains were able to incorporate higher quantities of HePC than fluid ones and this result was amplified when the sterol concentration was increased.

CONCLUSIONS

Sterol and lipid rafts probably play a significant role as an HePC reservoir providing a constant supply to the previously described transporter. In addition, (1)H NMR experiments suggested that HePC stimulated lipid trafficking in parasites.

Antifungal canthin-6-one series accumulate in lipid droplets and affect fatty acid metabolism in Saccharomyces cerevisiae

The mechanism of action of antifungal canthin-6-one series was investigated in Saccharomyces cerevisiae. After a rapid uptake, a preferential accumulation of the drug within lipid droplets was observed. The antifungal action of canthin-6-one was found as reversible. Canthin-6-one did not exhibit affinity for sterols, and membrane ergosterol was not necessary for the antifungal activity since the MICs were similar on an ergosterol-deleted and the wild-type S. cerevisiae clones. Relative amount of unsaturated alkyl chain fatty acids was significantly enhanced suggesting a stimulation of desaturase enzyme systems. No synergistic effect was observed between canthin-6-one and amphotericin B, ketoconazole and caspofungine. Canthin-6-one should now be evaluated in vivo against fungal pathogens.

Recent strategies for the chemotherapy of visceral leishmaniasis

Visceral leishmaniasis is a widespread and deadly disease. First-line drugs are antimonials, but amphotericin B and its lipid formulations B is used for treating visceral leishmaniasis that is unresponsive to antimony. New therapeutic approaches are being actively developed, including the following: use of drug carriers targeted specifically to the parasite location, thus reduce adverse effects of drug; use of immunomodulating drugs; evaluation of natural products; pharmacokinetic studies; and drug combinations. Recent clinical trials with paromomycin and miltefosine were successful and these drugs appear to be promising for the future therapy of visceral leishmaniasis. Furthermore, identification and therapeutic evaluation of specific targets in the Leishmania organism could lead to new compounds, such as antileishmanial drugs and reversal agents of drug resistance.

Amphotericin B-Gum Arabic Conjugates: Synthesis, Toxicity, Bioavailability, and Activities Against Leishmania and Fungi

PURPOSE

Gum arabic, a branched polysaccharide consisting of more than 90% arabinogalactan having a molecular weight around 250,000 Da is the oldest and best known of all natural gums. The objective of the present investigation was to examine whether amphotericin B (AmB), the polyene antibiotic when conjugated to periodate oxidized gum arabic still retained its anti-fungal and anti-leishmanial activity and to evaluate its toxicity and bioavailability.

METHODS

AmB conjugated to the oxidized polysaccharide through Schiff's linkages in the unreduced (imine) and reduced (amine) forms were characterized for the drug content, hemolytic potential, molecular mass, in vitro release and were examined for anti-fungal activity against Candida albicans and Cryptococcus neoformans and for anti-leishmanial activity against promastigotes of Leishmania donovani in culture. Toxicity and bioavailability were evaluated by intravenous (i.v) injections of the conjugates in mice and rabbits respectively.

RESULTS

The conjugates were found to be non-hemolytic and mice withstood a dosage of 20 mg (AmB)/kg body weight of both conjugates. Histological examination of the internal organs of mice showed no lesions in kidney, brain, heart or liver. Estimation of the residual drug in the internal organs 7 days post injection showed that the spleen still retained 8.4 +/- 0.53 microg/g of tissue. AmB was found to be released from both conjugates in vitro although the release from the imine conjugate was much faster than from the amine conjugate. The concentrations inhibiting parasite growth by 50% (IC(50)) values for the imine conjugate against promastigotes of L. donovani LV9 and DD8 strains were 0.37 +/- 0.04 and 1.44 +/- 0.18 microM respectively. The IC(50) values for the amine conjugates were much higher. The minimum inhibitory concentration (MIC) against C. albicans and C. neoformans was in the range of 0.5-0.9 microg/mL for both imino and amino conjugates. The bioavailability of the conjugate in rabbits showed that the imine conjugate maintained a plasma concentration in the range of 20 to 5 microg/mL while for the amine conjugate it was in the range of 17 to 3 microg/mL over 24 h.

CONCLUSIONS

The drug conjugates were stable, non-hemolytic and non-toxic to the internal organs of the animal and showed good anti-fungal and anti-leishmanial activity in vitro. In spite of the large molecular weight of the polysaccharide, AmB from the conjugates showed bioavailability after i.v injection. Since the highest concentration of AmB was found in the spleen after a single injection, these conjugates may have potential in anti-leishmanial therapy.

In vitro and in vivo antileishmanial efficacy of a new nitrilquinoline against Leishmania donovani

The in vitro activity of a new analogue of 2-alkenylquinoline (2-nitrilquinoline or NQ) against Leishmania donovani was compared to oral reference drug miltefosine (HePC). IC(50) of NQ was found at 38.6 microM against promastigotes and 2.4 microM against intramacrophage amastigotes. In vivo evaluation in the L. donovani Balb/c mice model indicated that oral treatments at 12.5 and 25 mg/kg for 10 consecutive days significantly reduced the parasite burden in the liver by 68.9 and 68.5%, respectively. This activity was similar to those of HePC at 7.5 mg/kg for 10 days which reduced the parasite burden in liver by 72.5%. The present study shows the positive contribution of a nitril substitute being added into the alkenyl chain branched at the 2-position of the quinoline ring to the antileishmanial activity. In addition, any apparent toxicological disorder was observed during the experiments.

Miltefosine affects lipid metabolism in Leishmania donovani promastigotes

Miltefosine (hexadecylphosphocholine [HePC]) is the first orally active antileishmanial drug. Transient HePC treatment of Leishmania donovani promastigotes at 10 microM significantly reduced the phosphatidylcholine content and enhanced the phosphatidylethanolamine (PE) content in parasite membranes, suggesting a partial inactivation of PE-N-methyltransferase. Phospholipase D activity did not seem to be affected by HePC. In addition, the enhancement of the lysophosphatidylcholine content could be ascribed to phospholipase A2 activation. Moreover, transient HePC treatment had no effect on the fatty acid alkyl chain length or the fatty acid unsaturation rate. Concerning sterols, we found a strong reduction of the C24 alkylated sterol content, and the enhancement of the cholesterol content could be the result of the HePC condensation effect with sterols. Because some of the effects observed after transient HePC treatment were different from those previously observed in HePC-resistant parasites, it could be hypothesized that continuous in vitro drug pressure induces the mechanisms of regulation in Leishmania lipid metabolism.

Antileishmanial and trypanocidal activities of new miltefosine liposomal formulations

Liposomes composed of hexadecylphosphocholine/egg phosphatidylcholine/stearylamine (HePC/EPC/SA) 10:10:0.1, 10:10:0.5 and 10:10:1 (molar ratio) (1-3) were prepared and lyophilized. The liposomes were physicochemically characterized (size and zeta-potential) and they were found stable at 4 degrees C over a period of 4 weeks. In vitro, liposomes 1 and 2 were about twice more active than HePC against Leishmania donovani WT whereas liposomes 3 were about three times more active than HePC on HePC-resistant promastigotes. Although liposomes 1-3 were inactive on the in vitro intramacrophage amastigote model, the ability of the liposomes to accumulate within the liver where parasites are located justifies a further in vivo evaluation. We observed that liposome 1 was twice more active than HePC against Trypanosoma brucei brucei bloodstream forms maintained in vitro. In vivo results showed that liposomal HePC seemed to be less toxic than the free drug despite the absence of significant antitrypanosomal activity.

Alteration of fatty acid and sterol metabolism in miltefosine-resistant Leishmania donovani promastigotes and consequences for drug-membrane interactions

Miltefosine (hexadecylphosphocholine [HePC]) is the first orally active drug approved for the treatment of visceral leishmaniasis. In order to investigate the biochemical modifications occurring in HePC-resistant (HePC-R) Leishmania donovani promastigotes, taking into account the lipid nature of HePC, we investigated their fatty acid and sterol metabolisms. We found that the content of unsaturated phospholipid alkyl chains was lower in HePC-R parasite plasma membranes than in those of the wild type, suggesting a lower fluidity of HePC-R parasite membranes. We also demonstrated that HePC insertion within an external monolayer was more difficult when the proportion of unsaturated phospholipids decreased, rendering the HePC interaction with the external monolayer of HePC-R parasites more difficult. Furthermore, HePC-R parasite membranes displayed a higher content of short alkyl chain fatty acids, suggesting a partial inactivation of the fatty acid elongation enzyme system in HePC-R parasites. Sterol biosynthesis was found to be modified in HePC-R parasites, since the 24-alkylated sterol content was halved in HePC-R parasites; however, this modification was not related to HePC sensitivity. In conclusion, HePC resistance affects three lipid biochemical pathways: fatty acid elongation, the desaturase system responsible for fatty acid alkyl chain unsaturation, and the C-24-alkylation of sterols.

N-acetyl-β-d-hexosaminidase from Trichomonas vaginalis: substrate specificity and activity of inhibitors

Among chitinolytic activities previously described in Trichomonas vaginalis, N-acetyl-beta-D-hexosaminidase (NAHase) was the enzyme system expressing the highest level of specific activity. We report here some biochemical characteristics of NAHase purified from T. vaginalis. We found at first that the use of 4-methylumbellifferyl-substrate was responsible for a substrate affinity for the enzyme, about 1000-fold higher than those when using p-nitrophenyl-substrates (PNP). Whereas the optimum pH was 7.0 using PNP-substrate, it was at 4.5 using 4-methylumbelliferyl-substrate. Four different substrates were compared for their action on T. vaginalis NAHase and we have found that N-acetyl-beta-D-glucosaminide substrate was the most specific. DTT had no effect on enzyme activity suggesting that thiol group are not involved at the catalytic site. The use of previously described inhibitors showed a positive correlation between trichomonacidal activity and NAHase inhibition.

In vitro antileishmanial activity of acetogenins from Annonaceae

Twelve acetogenins from Annonaceae were evaluated in vitro for their antileishmanial activities in order to search for new lead-compounds having antileishmanial properties. The compounds were comparatively evaluated by the 50% inhibitory concentrations (IC50) determination on promastigote forms of wild-type and four drug-resistant lines of Leishmania donovani. In addition, after testing the toxicity on mouse peritoneal macrophages, the compounds were evaluated on amastigote infected macrophages and a therapeutic index was calculated. The IC50 of the acetogenins against promastigote forms of L. donovani was in a range 4.7-47.3 microM. The most active compound was Rolliniastatin 1 (IC50 at 4.7 microM). On the intramacrophage amastigote in vitro model, only seven compounds exhibited measurable antileishmanial activity with IC50 values in a range 2.5-29.7 microM. Rollinistatin 1 was the most interesting compound with IC50 of 2.5 microM and it appears as the most promising one on the basis of therapeutic index (18.08). Isoannonacin, which is active against intramacrophagic amastigotes (IC50 of 6.2 microM) with a therapeutic index of 2.05, exhibited a strong action on drug-resistant strains (IC50 from 5.1 to 9.8 microM). Acetogenins are a new chemical series with interesting in vitro antileishmanial activity and further studies will be focused on the understanding of this selectivity in regard to the membrane and mitochondrial action using specific probes.

The chitinase system from Trichomonas vaginalis as a potential target for antimicrobial therapy of urogenital trichomoniasis

Chitinolytic activities in Trichomonas vaginalis membrane extracts were assessed by assays of three enzyme systems: N-acetyl-beta-D-hexosaminidase (NAHase), chitobiosidase and chitotriosidase. N-acetyl-beta-D-hexosaminidase was the enzyme that showed the highest specific activity. After successive subcutaneous inoculations into mice and parasite recovery in culture, the enzyme activities increased significantly with the number of inoculations for up to eight passages. In addition, enzyme activities were maximum at the logarithmic phase of growth. Glycol chitin, a chitinase substrate, enhanced all chitinolytic activities by about 30% and a clear-cut correlation is shown between the capacity for erythrocyte lysis by parasites and NAHase expression. Chitobiosidase and chitotriosidase activities were both inhibited at 58% and 100%, respectively, by allosamidine, a chitinase inhibitor used at 3 microM, whereas NAHase activity was not affected. Seven putative NAHase inhibitors (compounds n, 1-7), ureido and thioureido derivatives of 2-amino-2-deoxy-D-glucose were evaluated and five of them had K(i) values in the range 30-70 microM. The most active compound (compound 6) was functionally competitive with respect to the substrate with a K(i) value of 30 microM. The IC(50) values of the most active compounds on T. vaginalis were in the range 62-85 microM. These results indicate that chitinases of T. vaginalis are involved in pathogenicity and they could be an interesting target for drugs since chitinase inhibitors also inhibit parasite growth.

In vitro antileishmanial activity of amphotericin B loaded in poly(epsilon-caprolactone) nanospheres

The activity of formulations for amphotericin B (AmB) associated with poly(epsilon-caprolactone) nanospheres and coated with variable amounts of a non ionic surfactant poloxamer 188, was evaluated against AmB-susceptible (WT) and AmB-resistant (AmB(r)) strains of Leishmania donovani amastigotes in thioglycolate-elicited peritoneal macrophages. AmB-nanospheres were more actives than free AmB only against amastigotes of wild strain. The activity was not influenced by the concentration of poloxamer 188 used to stabilize the nanospheres in spite of this surfactant was previously reported to synergy with AmB on the membrane of the resistant parasite. Similarly, this improvement was not mediated through macrophage activation. In fact, these nanoparticle formulations appeared to inhibit both NO and TNF-alpha production induced by the free drug. Therefore, we suggest that the association of AmB with nanospheres may improve the capability of the drug to interact with ergosterol. This hypothesis appears to be supported by the fact that nanospheres did not show any improvement of the AmB activity against the resistant strain (characterized by the absence of ergosterol).

Characterisation of atovaquone resistance in Leishmania infantum promastigotes

Atovaquone, an antiparasitic agent, could possibly represent an alternative therapy after relapse following classical treatment for visceral leishmaniasis. Atovaquone-resistant strains were selected in vitro by stepwise drug pressure to study the mechanism of resistance in Leishmania. Characteristics of a promastigote strain resistant to 250 microg/ml of atovaquone were compared with those of the wild type (WT) strain. Resistant strains were shown to have a high level of resistance (45 times). They were stable in drug-free medium for 6 months, and showed no cross-resistance with other antileishmanial drugs. Rhodamine uptake and efflux were studied. They were not modified in the resistant strain, indicating the absence of P-glycoprotein overexpession. The effect of atovaquone on membrane lipidic composition was determined in both WT and atovaquone-resistant promastigotes. Analysis of lipid composition of the atovaquone-resistant strain showed that sterol biosynthesis was decreased in atovaquone-resistant parasites. Cholesterol was found to be the major membrane sterol as opposed to the WT strain. Cholesterol, due to its ordering effect, could decrease membrane fluidity and subsequently block the passage of atovaquone through the membrane. Increased membrane cholesterol content and altered drug membrane fluidity resulted from possible decrease of ergosterol biosynthesis by atovaquone, incorporation of cholesterol by promastigotes in the culture medium, solubilisation of atovaquone by cholesterol and co-passage of the two compounds or influence of dimethylsulfoxide. These results indicate that different cellular alterations may participate in the resistant phenotype, by altering drug membrane permeability.

Synthesis and trichomonacidal activity of perketals and hydroperoxides

Some perketals were synthesized by the Dussault procedure using simple bromides and 2-methoxyprop-2-yl hydroperoxide. Treatment with acetic acid gave the corresponding hydroperoxides. Both perketals and hydroperoxides were tested in vitro as trichomonacidal agents. Most of them exhibited very good activities. The most powerful compound was 2-methoxyprop-2-yl hexadec-l-yl peroxide which exhibited an IC50 value of 0.51 microM being 10 times more effective than the reference compound Metronidazole.

Design and antileishmanial activity of amphotericin B-loaded stable ionic amphiphile biovector formulations

A new delivery system, Ionic Amphiphilic Biovector (ABV), comprised of anionic lipids (dipalmitoyl phosphatidyl glycerol) included in a cationic cross-linked polysaccharide matrix was used as a reservoir for amphotericin B (AmB). Two ABV formulations exhibited an in vitro and in vivo efficacy similar to commercial AmBisome against Leishmania donovani-infected mice. The higher stability of these ABV formulations indicates their potential for further development and applications.

Synthesis and in vitro Trichomonacidal activities of some new dialkylperoxides and 1,2,4-trioxanes

Two series of three trioxanes and 18 disubstituted peroxides were synthesised and evaluated for their in vitro trichomonacidal activity against Trichomonas vaginalis. The most active compound, 2-methylprop-2-yl 2-methoxyeth-1-yl peroxide exhibited an IC(50) value of 1.0+/-0.2 microM whereas other dialkyl peroxides had various IC(50) values which could not be correlated to their molecule structure. The best compound was about five times more active than metronidazole. The amount of generated oxygen or free radicals cannot explain completely the activity suggesting another way of action for these compounds on T. vaginalis.

Antitrypanosomal properties of cis-platinum-pentamidine bromide, thiocyanate and seleniocyanate on Trypanosoma brucei brucei mouse and sheep models

Three organometallic complexes derived from pentamidine were evaluated for their trypanocidal effect on in vivo Trypanosoma brucei brucei models in comparison to pentamidine isethionate as reference compound. On the T. b.brucei mouse model, the most active compound was cis-platinum-pentamidine bromide. This compound was active when subcutaneously administered at the single dose of 1.5 micromol/kg and its chemotherapeutic index was 200 whereas pentamidine isethionate was active at 6 micromol/kg with a chemotherapeutic index of 13, when administered in the same conditions. Cis-platinum-pentamidine bromide was active at 1 mg/kg (1.44 mmoles/kg), in a single dose by subcutaneous route against the early stage of the T. b.brucei Antat 1-9 sheep model. Platinum kinetics in serum showed a Cmax of 0.2 mg/l reached 80 h after the treatment at this dose. Cis-platinum-pentamidine bromide, cis-platinum-pentamidine seleniocyanate, and cis-platinum-pentamidine thiocyanate were distributed in the deep compartment according to a monocompartmental model. In all cases, platinum was eliminated from the serum 700 hours post-treatment. All data obtained from these models show activity on the early stage of the disease and justify further investigations on the late stage of the disease.

Contribution of dithiol ligands to in vitro and in vivo trypanocidal activities of dithiaarsanes and investigation of ligand exchange in an aqueous solution

Twelve new dithiaarsanes were evaluated for their in vitro and in vivo trypanocidal properties in regard to their three parent molecules, 4-amino-phenylarsenoxide, melarsenoxide, and 4-dansylamino-phenylarsenoxide. The most potent dithiaarsane, compound 2b, had a minimum effective concentration of 1.5 nM after 48 h of incubation and at a dose of 0.39 micromol/kg of body weight (0.2 mg/kg) administered subcutaneously cured 100% of mice acutely infected with Trypanosoma brucei brucei CMP. With this model, the chemotherapeutic index of compound 2b was 512, compared to 256 for melarsamine dihydrochloride (Cymelarsan) under the same conditions. With a chronic infection produced by T. brucei brucei GVR, compound 2b cured 100% of mice after treatment at a dose of 25 micromol/kg (12.5 mg/kg) for 4 consecutive days, whereas melarsamine dihydrochloride and potassium melarsonyl (Trimelarsan) cured less than 50% mice at this dose. For both acute and late-stage infections, dithiaarsanes having a melaminophenyl ring exhibited the most-potent trypanocidal activity. Compound 2b is thus one of the most active organoarsenicals described in a mouse trypanosomiasis model. Considering that the main intracellular targets of organoarsenicals are thiol groups, we studied the possibility of ligand exchange between Cymelarsan and several dithiols. In aqueous solution, we observed a rapid exchange of cysteamine from melarsamine with free cysteamine and also with various dithiols always in favor of more stable cyclic derivatives. These ligand exchanges suggest the ability of trivalent organoarsenicals to react with targets such as trypanothione and dihydrolipoic acid. Among several ligands, a 1,3-dimercaptopropane moiety appeared the most suitable for trypanocidal activity.

In vitro reversion of amphotericin B resistance in Leishmania donovani by poloxamer 188

A micellar formulation of amphotericin B (AmB) solubilized with poloxamer 188 was evaluated against an AmB Leishmania donovani-resistant line. A concave isobologram showed a synergistic effect of this association against promastigotes. This result was confirmed with amastigotes since the 50% effective concentration of the new formulation was 100 times less than that of the control AmB formulation.

In vivo antileishmanial action of Ir-(COD)-pentamidine tetraphenylborate on Leishmania donovani and Leishmania major mouse models

Ir-(COD)-pentamidine tetraphenylborate which has previously been studied on promastigote forms of Leishmania, was investigated for its antileishmanial properties compared with pentamidine used as reference compound. In vitro, the iridium complex had the same IC50 value on intracellular forms of Leishmania as pentamidine (15 microM). In vivo, the compound could not be injected intravenously due to the DMSO excipient so that the treatments were performed intraperitoneally or subcutaneously. On the L. donovani LV9/Balb/C mouse model, the iridium complex was not toxic after intraperitoneal treatment at 232 mg/kg/day x 5 or 147 mumoles/kg/day x 5, whereas all the mice died within five days when treated at the same dose with pentamidine isethionate. However, only 23% of parasite suppression was observed with the iridium complex. On a L. major MON 74/Balb/C mouse model, susceptible to intravenously administered pentamidine at 6.7 mumoles/kg/day x 5 (54% of parasite suppression), the iridium complex exhibited 32% of parasite suppression after a treatment at 76 mumoles/kg/day x 5 administered subcutaneously. This slight activity is of interest since pentamidine isethionate is not active under these conditions. Transmission electron microscopy of amastigotes from infected and treated mice show aggregation of ribosomal material, distension of the nuclear membrane and kDNA depolymerization. The mechanism of action therefore involves several targets: membranes, ribosomes and kDNA. According to our results, the Iridium complex is a suitable candidate to be encapsulated in drug carriers such as liposomes or nanoparticles.

Marked elevation of serum N-acetyl-beta-D-hexosaminidase activity in rheumatoid rheumatoid arthritis

OBJECTIVE

To study N-acetyl-beta-D-hexosaminidase (NAHase) activity in the sera of rheumatoid arthritis (RA) patients and to determine its source.

METHODS

NAHase activity in the serum and synovial fluid of RA patients was measured with p-nitrophenyl beta-N-acetylglucosaminide as substrate. The p-nitrophenol released was measured spectrophotometrically in an ELISA reader. Rabbit articular chondrocytes in primary culture were stimulated with interleukin-1 beta (IL-1 beta).

RESULTS

Serum NAHase activity was higher in 35% of the RA patients than in healthy patients. The median activity was about twice that of the serum of healthy volunteers. RA patients with high serum NAHase activity also had more joint destruction (85%) than those with normal NAHase activity (57%, p < 0.05), but their inflammatory status was similar. The source of NAHase in RA was investigated by assaying it in RA synovial fluids (SF) and measuring its release from articular chondrocytes in primary culture. NAHase activity was detected in all 23 RA SF, at a median concentration that was 2 times that of the serum. NAHase activity in the medium of articular chondrocytes was stimulated by IL-1 beta (p < 0.005 compared to unstimulated cells), suggesting that cartilage is a source of serum and SF NAHase activity.

CONCLUSION

The serum concentration of the matrix hydrolase, NAHase, is higher in destructive RA than in inflammatory RA.

Synthesis and in vitro anthelmintic properties of some new dithiaarsanes

Fifteen new trivalent organoarsenicals were synthesized and evaluated for anthelmintic properties on three in vitro models, infective larvae of the filaria Molinema dessetae, infective larvae of an intestinal nematode, Nippostrongylus brasiliensis and adults and larvae of Rhabditis pseudoelongata a free living nematode. On the M. dessetae model, the most active compound after a 24 h incubation period had an EC50 of 0.02 mumol/l (compound 3a). Twelve compounds had an EC50 lower than 1 mumol/l whereas potassium melarsonyl exhibited an EC50 of 45.6 mumol/l. After 7 days incubation time, compound 1d had an EC50 of 2 nmol/l. On the N. brasiliensis model, compound 1d was also the most efficient after a 4 day incubation period (EC50 of 1 mumol/l). This compound was 100 times more active than potassium melarsonyl used as a reference compound. Nevertheless, no compound had an EC50 less than 100 mumol/l on Rhabditis pseudoelongata. Concerning the effect of dithiol ligands on the anthelmintic activity of these trivalent organoarsenicals on M. dessetae and N. brasiliensis, 2,2'-dimercaptodiethyloxide was more efficient as dithiol ligand than 1,3-dimercaptopropane which was more efficient than 1,2-dimercaptoethane. Moreover, the para-amino haptophore was more efficient than the melaminyl haptophore. These results showed that the use of new dithiol ligands for trivalent arsenicals enhanced greatly the anthelmintic activity compared with potassium melarsonyl.

A new photometric assay with bromocresol purple for testing in vitro antitrichomonal activity in aerobic environment

A new colorimetric assay relying on the acidic metabolism of Trichomonas vaginalis was developed for in vitro screening of various compounds against axenically grown trichomonads. Parasites from continuous culture were exposed to series of drug dilutions in a microtiter plate. After an incubation period of 48 h at 37 degrees C, the pH indicator of the medium had changed its colour in non-inhibited cultures due to the production of lactate and acetate. Inhibited cultures showed no colour changes. The use of bromocresol purple, a pH indicator, was suitable for several reasons: it is not toxic at the concentration used in the assay; the absorbance of bromocresol purple at 405 nm showed a linear correlation with both the pH of the medium and the viability of the trichomonads observed microscopically; plates could easily be read by eye or using an enzyme-linked immunosorbant assay (ELISA) reader. By comparison of the decreases in absorbance in test cultures with those in control cultures, IC50 values could be determined. Thus, IC50 of metronidazole was calculated at 25.5 +/- 2.3 mumol/l (n = 5) with the bromocresol purple assay and about 25 mumol/l after microscope observation. Minimal lethal concentrations (MLCs) could be read by eye. This test is now routinely used for anti-trichomonas evaluation of various chemical compounds and natural products.

Synthesis and biological evaluation of ureido and thioureido derivatives of 2-amino-2-deoxy-D-glucose and related aminoalcohols as N-acetyl-beta-D-hexosaminidase inhibitors

Ureido and thioureido derivatives of 2-acetamido-2-deoxy-beta-D-glucose, 1-amino-1-deoxy-D-glucitol and 2-(2-aminoethoxy)ethanol were prepared as N-acetyl-beta-D-hexosaminidase (NAHase) inhibitors and were evaluated on Trichomonas vaginalis NAHase. Although none showed complete inhibition of the enzyme at 100 microM, 1-amino-1-deoxy-D-glucitol derivatives acted as competitive inhibitors of the NAHase of T. vaginalis.

Studies on lipidomimetic derivatives of alpha-difluoromethylornithine (DFMO) to enhance the bioavailability in a Trypanosoma B. brucei murine trypanosomiasis model

DFMO, a trypanostatic drug, presents a satisfactory intestinal absorption but its elimination from the blood is rapid so that high doses are necessary to obtain to therapeutic effect. In this study, we propose a strategy to enhance the bioavailability of DFMO by using lipidomimetic derivatives. Three lipidomimetic DFMO derivatives called O-DFMO, S-DFMO and Chol-DFMO were designed to reach easily the plasma and to be cleaved preferentially by plasma esterases progressively liberating free DFMO. Chol-DFMO only could be cleaved partially whereas the other compounds appeared to be stable in reconstituted intestinal medium and mouse plasma. Nevertheless, the use of DFMO derivatives in T. b. brucei experimental chemotherapy appeared as an interesting approach. Thus, O-DFMO was trypanocidal in vitro whereas DFMO, the active principle, was only trypanostatic. Nevertheless, this compound did not release DFMO in mouse blood as expected and acted therefore not as a prodrug. Oral treatment using low doses of compound O-DFMO was able to cure 40% mice while the active principle (eflornithine) administered at 50 fold higher molarity failed to cure any mice. This indicates that compound O-DFMO acts by a specific mechanism which remains to be investigated. S-DFMO was less active and Chol-DFMO had no in vitro activity but released small amounts of DFMO in mice, however, too slight to obtain a therapeutic effect.

In vitro antifilarial activity of organometallic complexes against infective larvae of Molinema dessetae and adult females of Brugia pahangi

New organometallic complexes having protozoocidal properties were evaluated for their in vitro antifilarial activity using two models: infective larvae of Molinema dessetae and adult females of Brugia pahangi. The compound most active on the M. dessetae model was Ir(I)-COD-pentamidine tetraphenylborate with an EC50 = 6 +/- 1 microM after 7-day-incubation. In the 2-aminobenzothiazole series, Ruthenium was more potent than Iridium for antifilarial activity. A dithiocarbamate function significantly enhanced the antifilarial activity. The compounds derived from benzimidazole were inactive whatever the metal (Iridium or Rhodium). The other compounds exhibited EC50 ranging from 10 to 31 microM. On adult female Brugia pahangi in vitro, Pt-DDH-N-acetylleucine, Pt-diminazene and Pd-Cl4-piperazine at 20 microM began to kill both microfilariae and the developing embryos within the mothers on day 2. The compounds, except for Pd-Cl4-piperazine, killed the adults after 5 days. Rh-Cl-2-chloropyridine caused obvious slowing of the adults from day 3 onward but did not affect the viability of adults, microfilariae or developing embryos. In vivo antifilarial investigations are necessary to appreciate the real advantage of heavy metal complexes in the experimental treatment of filariasis.

Uptake into leishmania donovani promastigotes and antileishmanial action of an organometallic complex derived from pentamidine

Iridium (Ir)-(COD)-pentamidine tetraphenylborate (CAS 225-75-4) was selected from a primary screening to be evaluated in vitro on three Leishmania (L.) strains comparatively to pentamidine used as reference compound. The IC50 values obtained from in vitro evaluation on promastigotes of L. major CRE 26, L. donovani DD8 and L. donovani LV9 were 3.9, 23.5, and 3.3 mumol/l for Ir-(COD)-pentamidine tetraphenylborate and 1.6, 7.7, and 3.9 mumol/l for pentamidine isethionate, respectively. Cytotoxicity on mouse peritoneal macrophages led to determine a chemotherapeutic index of 1.7 for Ir-(COD)-pentamidine tetraphenylborate and 4 for pentamidine. Considering L. donovani DD8, the uptake of iridium complex by the promastigotes was shown to be saturable with a Km value of 17.4 mumol/l and Vmax of 1.3 nmol/mg protein/2 h. After 2 and 4 h incubation of treated promastigotes in drug free medium the absence of Ir-complex efflux is in favour of intracellular drug binding. As a matter of fact iridium complex was shown to bind ribosomal subunits in vitro, with no effect on macromolecular biosynthesis.

Chitinolytic activities in Trichomonas vaginalis

Chitinolytic activities were identified in the Protozoa Trichomonas vaginalis. Overall chitinase activity assessed using chitine-azure as substrate was 10.93 +/- 1.21 nmoles/min/mg prot. End nonreducing chitobiosidase (exochitinase) and chitotriosidase (endochitinase) activities were shown using p-nitrophenyl-substrates and had specific activities of 4.55 +/- 0.53 and 0.47 +/- 0.06 nmol/min/mg prot, Kmapp. = 1.32 mM and 5 microM and pH optimum = 7.0 and 6.1 respectively. beta-N-acetylhexosaminidase (NAHase) activity was also detected with a specific activity of 5.40 +/- 0.65 nmol/min/mg prot., Kmapp = 0.656 mM and pH optimum at 7.0. No release of these enzymes into the culture medium was found. The possible role of chitinases in T. vaginalis remains to be investigated.

Epoxyethane-/ethynesulfonamides with antifilarial activities. Degradation kinetics and inhibitory effect on filarial malate dehydrogenase and lactate dehydrogenase

Some epoxyethane-/ethynesulfonamides had shown strong filaricidal activity with inconstant reproducibility as a result of a lack of stability in aqueous solution. The degradation in hydroxylic and aprotic solutions of two epoxyethanesulfonamides and one ethynesulfonamide was investigated using TLC, HPLC, GC and mass spectrometry. For both epoxydes, the degradation rate followed first-order kinetics and was more rapid in hydroxylic than in aprotic solutions. The degradation increased with the temperature whereas it was not modified with and without light exposure. Four kinds of degradation products were found: the first one involved the oxidation of the epoxyde bond, the second the breaking of the N-S bond, the third a desulfonation product and the fourth was not identified. In contrast, the stability of ethynesulfonamide was better than those of epoxyethanesulfonamide. These results suggest that epoxyethanesulfonamides should be kept at +4 degrees C before being injected to animals during the study of biological activity. Since epoxyde compounds are known to have inhibitory effects on parasite energy metabolism enzymes, the compunds were evaluated on two major filarial enzymes: lactate dehydrogenase (LDH) and cytoplasmic malate dehydrogenase (MDH). Both epoxyethanesulfonamides showed only a slight inhibitory effect on filarial LDH and MDH confirming the evidence that the main mode of action of these compounds remains to discover. Moreover, ethynesulfonamide and the degradation products of both epoxyethane-sulfonamides had no effect on LDH and MDH.

Mechanism of amphotericin B resistance in Leishmania donovani promastigotes

Amphotericin B (AmB)-resistant Leishmania donovani promastigotes were selected by increasing drug pressure, and their biological features were compared with those of the wild-type parent strain. The 50% inhibitory concentration for resistant cells was 20 times higher than that for the wild-type. Resistance was stable after more than 40 passages in drug-free medium, and resistant promastigotes were infective to macrophages in vitro but lost their virulence in vivo. They had 2.5 times longer generation time, decreased AmB uptake, and increased AmB efflux in comparison to the wild type. Fluorescence measurement with a specific plasma membrane probe, 1-[4-(trimethylammonio)-1,6-diphenylhexa]-1,3,5-triene, showed increased membrane fluidity in drug-resistant promastigotes. Analysis of lipid composition showed that in resistant cells saturated fatty acids were prevalent, with stearic acid as the major fatty acid, and the major sterol was an ergosterol precursor, the cholesta-5, 7, 24-trien-3beta-ol and not ergosterol as in the AmB-sensitive strain.

Lymphotropic antifilarial agents derived from closantel and chlorambucil

New closantel and chlorambucil prodrugs expected to accumulate in the lymphatic system were evaluated on the filaria Molinema dessetae. The prodrugs of closantel had a delayed effect in vitro on the infective larvae compared to the free drug. The closantel prodrugs were less toxic in vivo than closantel itself. The most active prodrug after treatment at 200 mumol/kg by the oral route was the 1,3-dipalmitoyl-2-succinyl-glycerol-closantel. The macrofilaricidal delayed effect of closantel prodrugs was of interest to prevent anaphylactic shock. In vitro, chlorambucil was active on M. dessetae infective larvae with an IC50 of 26 microM. 1,3-Dipalmitoyl-2-chlorambucil-glycerol was slightly active while the addition of a thioether function between the drug and the lymphotropic ligand canceled the activity. However, no activity with chlorambucil and its prodrugs was observed in vivo. The lymphotropism of these prodrugs has now to be verified using comparative pharmacokinetics in serum and lymph to quantify the increase in drug concentration in lymph.

Synthesis and antiparasitic activities of amidinic azolated derivatives

A set of heterocyclic N-acetamidinium hydrochlorides were prepared from the corresponding N-acetonitriles. The antiparasitic screening showed that, while all amidines are practically inactive, some nitriles present leishmanicide properties.

Tissue distribution and metabolism in rat of an ethynesulphonamide with filaricidal activity

1. The tissue distribution and metabolism of a new filaricidal agent P903 (N-[(2-phenylethynyl)sulfonyl]morpholine) were studied in rat. 2. After s.c. administration of 14C and 13C P903, the Tmax in the blood was observed on day 2. Elimination was slow and > 95% was bound to protein. Radioactivity was distributed in the whole organism but particularly in erythrocytes and the lymphatic channel. Four days later, > 60% of the radioactivity was excreted in urine and faeces at equal amounts and 15% remained at the injection point. 3. In all biological fluids tested no P903 was found but only its metabolites. 4. One principal metabolite, the N-[(2-phenyloxo-2-ethane) sulphonyl] morpholine or oxosulphonamide was identified in blood, urine and faeces as compared with the reference compound by GC/MS and NMR. This latter molecule was detected following hydrolysis by hydrochloric acid but not with beta glucuronidase/sulphatase. 5. Unconjugated and conjugated oxosulphonamide represented > 85% of the radioactivity at all times tested in blood but only 38 and 35% respectively of urinary and faecal radioactivity on day 1 after the administration of the labelled drug. 6. Thus, P903 is rapidly converted to a reactive metabolite, probably an oxirene, which is then conjugated with endogenous components to form conjugated oxosulphonamide and an unknown metabolite. The role of this reactive metabolite in antifilarial activity seems to be very important in understanding the mechanism of action of P903.

Trypanocidal effect of Ir-(COD)-pentamidine tetraphenylborate on Trypanosoma brucei and T. b. gambiense rodent models and serum kinetics in sheep

Pentamidine di-(iridium cyclo-octadiene)tetraphenylborate, called Ir-(COD)-pentamidine tetraphenylborate, was selected from a primary screening as a promising trypanocidal compound. The compound was evaluated against three isolates: Trypanosoma brucei brucei CMP, T.b. brucei GVR 35 and T.b. gambiense Feo. On the T.b. brucei GVR 35 murine CNS model, no mouse was cured when the treatment was commenced 21 days post-infection whatever the treatment regimen. Nevertheless, in vitro the compound killed the trypomastigote forms of T. b. gambiense Feo at 0.6 microM. In vivo, the compound cured all mice infected 1 hour previously with T. b. gambiense Feo after a 10 mg/kg (6.3 mumol/kg) treatment subcutaneously administered in a single dose. Moreover, the compound was active at 1 mg/kg (0.6 mumol/kg) in a single dose against the early stage of the T. b. brucei Antat 1-9 sheep model. Serum kinetics data showed that pentamidine di-(iridium cyclo-octadiene) tetraphenylborate was distributed within deep compartment according to a monocompartmental model. The maximum iridium serum concentration was 198 micrograms/l corresponding to 1 mumol/kg of iridium derivative and this value remained stable for 30-50 hours post-treatment. Iridium was completely eliminated from the serum 700 hours post-treatment. all data obtained from these models are in favour of an activity in the early stage of the disease but indicate that the compound could not cross the blood-brain barrier despite its lipophilicity. Although iterative treatments with the compound rapidly induced the selection of iridium derivative refractory populations, the compound could be studied on pentamidine refractory strains.

Synthesis of catecholamide spiroarsoranes and their in vitro anthelmintic properties against Molinema dessetae and Nippostrongylus brasiliensis infective larvae

Catecholamide spiroarsoranes were synthesized and evaluated for anthelmintic properties on two in vitro models, infective larvae of the filaria Molinema dessetae and infective larvae of an intestinal nematode. Nippostrongylus brasiliensis. On the N dessetae model, the most active compound after 24 h incubation time had an EC50 of 0.1 mumol/l. Eleven compounds had EC50 's in a range from 2 to 200 mumol/l. After 7 days incubation time, the two most active compounds had EC50 's of 0.03 and 0.07 mumol/l, respectively. On the N brasiliensis model, only three compounds were slightly active after 4 days incubation time. The ligands used for the spiroarsoranes synthesis were also evaluated for anthelmintic activity in order to know the contribution of these structures in the spiroarsoranes activity. Spiroarsoranes as prodrugs of arsonic acids were very active on the filaria, nematode having predominantly transcuticular uptake of nutrients while the activity on the intestinal nematode having both the types, transcuticular and intestinal uptake was low. The high sensitivity of filarial infective larvae is probably in relation to their location in the mosquito whereas N. brasiliensis infective larvae are telluric and should be more unsensitive to survive in a variable environment.