Identification of dehydroxy isoquine and isotebuquine as promising antileishmanial agents

Traditional antimalarial drugs based on 4‐aminoquinolines have exhibited good antiproliferative activities against Leishmania parasites; however, their clinical use is currently limited. To identify new 4‐aminoquinolines to combat American cutaneous leishmaniasis, we carried out a full in vitro evaluation of a series of dehydroxy isoquines and isotebuquines against two Leishmania parasites such as Leishmania braziliensis and Leishmania mexicana. First, the antiproliferative activity of the quinolines was studied against the promastigote forms of L. braziliensis and L. mexicana parasites, finding that five of them exhibited good antileishmanial responses with micromolar IC₅₀ values ranging from 3.84 to 10 μM. A structure‐activity relationship analysis gave evidence that a piperidine or a morpholine attached as N‐alkyamino terminal substituent as well as the inclusion of an extra phenyl ring attached at the aniline ring of the isotebuquine core constitute important pharmacophores to generate the most active derivatives, with antileishmanial responses by far superior to those found for the reference drug, glucantime. All compounds showed a relatively low toxicity on human dermis fibroblasts, with CC₅₀ ranging from 69 to >250 μM. The five most active compounds displayed moderate to good antileishmanial activity against the intracellular amastigote form of L. braziliensis, compared to the reference drug. In particular, compound 2j was identified as the most potent agent against antimony‐resistant amastigotes of L. braziliensis with acceptable biological response and selectivity, emerging as a promising candidate for further in vivo antileishmanial evaluation. Diverse mechanism‐of‐action studies and molecular docking simulations were performed for the most active 4‐aminoquinoline.     

C-Geranylated flavonoids from Paulownia tomentosa fruits with antimicrobial potential and synergistic activity with antibiotics

Context C-6-Geranylated flavonoids possess promising biological activities. These substances could be a source of lead compounds for the development of therapeutics.

Objective The study was designed to evaluate their antibacterial and antileishmanial activity.

Materials and methods C-6-Geranylated flavanones were tested in micromolar concentrations against promastigote forms of Leishmania brazilensis, L. donovani, L. infantum, and L. panamensis against methicillin-resistant Staphylococcus aureus (MRSA); and synergistic potential with antibiotics was analyzed. IC₅₀ values (after 72?h) were calculated and compared with that of miltefosine. Flow cytometry and DNA fragmentation analysis were used the mechanism of the effect. Geranylated flavanones or epigallocatechin gallate were combined with oxacillin, tetracycline, and ciprofloxacin, and the effects of these two-component combinations were evaluated. Minimal inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs) were established (after 24?h), the synergy was measured by the checkerboard titration technique, and the sums of the fractional inhibitory concentrations (∑FICs) were computed.

Results 3′-O-Methyl-5′-O-methyldiplacone and 3′-O-methyldiplacone showed good antileishmanial activities (IC₅₀ 8–42?μM). 3′-O-Methyl-5′-hydroxydiplacone activates the apoptotic death at leishmanias, the effect of 3′-O-methyl-5′-O-methyldiplacone has another mechanism. The test of the antibacterial activity showed good effects of 3′-O-methyldiplacol and mimulone against MRSA (MIC 2–16?μg/mL), and in six cases, the results showed synergistic effects when combined with oxacillin. Synergistic effects were also found for the combination of epigallocatechin gallate with tetracycline or oxacillin.

Conclusion This work demonstrates anti-MRSA and antileishmanial potential of geranylated flavanones and uncovers their promising synergistic activities with antibiotics. In addition, the mechanism of antileishmanial effect is proposed.     

1,3‐Bis(aryloxy)propan‐2‐ols as potential antileishmanial agents

We describe herein the synthesis and antileishmanial activity of 1,3‐bis(aryloxy)propan‐2‐ols. Five compounds ( 2 , 3 , 13 , 17 , and 18 ) exhibited an effective antileishmanial activity against stationary promastigote forms of Leishmania amazonensis (IC₅₀ < 15.0 μm ), and an influence of compound lipophilicity on activity was suggested. Most of the compounds were poorly selective, as they showed toxicity toward murine macrophages, except 17 and 18 , which presented good selective indexes (SI ≥ 10.0). The five more active compounds ( 2 , 3 , 13 , 17 , and 18 ) were selected for the treatment of infected macrophages, and all of them were able to reduce the number of internalized parasites by more than 80%, as well as the number of infected macrophages by more than 70% in at least one of the tested concentrations. Altogether, these results demonstrate the potential of these compounds as new hits of antileishmanial agents and open future possibilities for them to be tested in in vivo studies.     

Chemical composition along with anti-leishmanial and cytotoxic activity of Zataria multiflora

Context: Natural products and their compounds are some of the most interesting sources of new drugs. Reviews have reported various pharmacological properties such as antimicrobial effects of Zataria multiflora Boiss (Lamiaceae).

Objective: The present study investigates the chemical composition of Z. multiflora essential oil and evaluates its cytotoxic effects and anti-leishmanial activities against Leishmania tropica in an in vitro model.

Materials and methods: The components of Z. multiflora oil were identified by gas chromatography/mass spectroscopy (GC/MS) analysis. Anti-leishmanial effects of the essential oil (0–100?μL/mL) and methanol extract of Z. multiflora (0–100 μg/mL) on promastigote forms as well as their cytotoxic activities against J774 cells were evaluated using MTT assay for 72 h. The leishmanicidal activity against amastigote forms of L. tropica was evaluated at the concentrations of 0–50 μg/mL in a macrophage model for 48 h.

Results: The chemical analyses demonstrated that the main components of essential oil were thymol (41.81%), carvacrol (28.85%), and p-cymene (8.36%). Regarding leishmanicidal activity, the IC₅₀ values for the essential oil and methanol extract were 3.2?μL/mL and 9.8 μg/mL against promastigote forms and 8.3?μL/mL and 34.6 μg/mL against amastigote forms, respectively. Essential oil (CC₅₀ 89.3?μL/mL) indicated a higher cytotoxic effect than the methanol extract (CC₅₀ 591.6 μg/mL) of Z. multiflora.

Conclusion: The present study revealed the chemical composition of Z. multiflora that might be a natural source of new anti-leishmanial agents in terms of use against cutaneous leishmaniasis.     

Effect of 3‐Alkylpyridine Marine Alkaloid Analogues in Leishmania Species Related to American Cutaneous Leishmaniasis

A series of oxygenated analogues of marine 3‐alkylpyridine alkaloids were synthesized, and their leishmanicidal activity was assayed. All compounds were prepared from 3‐pyridinepropanol in few steps and in good yields. The key step for the synthesis of these compounds was a classic Williamson etherification under phase‐transfer conditions. Besides toxicity in peritoneal macrophages, the compounds exhibited a significant leishmanicidal activity. Of twelve compounds tested, five showed a strong leishmanicidal activity against promastigote forms of Leishmania amazonensis and L. braziliensis with IC₅₀ below 10 μm . Compounds 11 , 14 , 15, and 16 showed a strong leishmanicidal activity on intracellular amastigotes (IC₅₀ values of 2.78; 0.27; 1.03, and 1.33 μm , respectively), which is unlikely to be owing to the activation of nitric oxide production by macrophages.     

Effectiveness of Novel 5‐(5‐amino‐1‐aryl‐1H‐pyrazol‐4‐yl)‐1H‐tetrazole Derivatives Against Promastigotes and Amastigotes of Leishmania amazonensis

In this research, a series of substituted 5‐(5‐amino‐1‐aryl‐1H‐pyrazol‐4‐yl)‐1H‐tetrazoles were synthesized and evaluated for in vitro antileishmanial activity. Among the derivatives, examined compounds 3b and 3l exhibited promising activity against promastigotes and amastigotes forms of Leishmania amazonensis. The cytotoxicity of these compounds was evaluated on murine cells, giving access to the corresponding selectivity index (SI).     

Activity of Extracts and Coumarins from the Leaves of Calophyllum brasiliense. on Leishmania braziliensis.

Abstract

In the current study, we evaluated the activity of extracts and (-)mammea A/BB from the leaves of Calophyllum brasiliense. Camb. (Clusiaceae), against Leishmania braziliensis.. The dichloromethane extract and the coumarin (-)mammea A/BB showed significant activity against the promastigote forms of L. braziliensis., with a 50% lethal dose (LD₅₀) at concentrations of 60 and 23.2 μ g/mL, respectively. However, the aqueous extract from the leaves and amentoflavone showed no activity against promastigote forms. For the intracellular amastigote form, the dichloromethane extract and the coumarin (-)mammea A/BB reduced by 50% the infection index of parasites in macrophages at concentrations of 22 and 29 μ g/mL, respectively. In addition, the dichloromethane extract did not show cytotoxic effects against mouse peritoneal macrophages at concentration up to 1000 μ g/mL. On the other hand, the coumarin (-)mammea A/BB showed more cytotoxicity than the dichloromethane extract. The compounds were characterized by one and two-dimensional ¹H and ¹³C NMR analyses, and LC/UV/MS was used to identify (-)mammea A/BB and amentoflavone in the dichloromethane extract. These results provide new perspectives on the development of novel drugs with leishmanicidal activities obtained from natural products.     

Design,synthesis, antileishmanial,and antifungal biological evaluation of novel 3,5-disubstituted isoxazole compounds based on 5-nitrofuran scaffolds

Nineteen 3,5-disubstituted-isoxazole analogs were synthesized based on nitrofuran scaffolds, by a [3 + 2] cycloaddition reaction between terminal acetylenes and 5-nitrofuran chloro-oxime. The compounds were obtained in moderate to very good yields (45–91%). The antileishmanial activity was assayed against the promastigote and amastigote forms of Leishmania (Leishmania) amazonensis. Alkylchlorinated compounds 14p–r were active on both the promastigote and amastigote forms, with emphasis on compound 14p , which showed strong activity against the amastigote form (IC₅₀ = 0.6 μM and selectivity index [SI] = 5.2). In the alkyl series, compound 14o stands out with an IC₅₀ = 8.5 μM and SI = 8.0 on the amastigote form. In the aromatic series, the most active compounds were those containing electron-donor groups, such as trimethoxy isoxazole 14g (IC₅₀ = 1.2 μM and SI = 20.2); compound 14h , with IC₅₀ = 7.0 μM and SI = 6.1; and compound 14j containing the 4-SCH₃ group, with IC₅₀ = 5.7 μM and SI = 10.2. In addition, the antifungal activity of 19 nitrofuran isoxazoles was evaluated against five strains of Candida (C. albicans, C. parapsilosis, C. krusei, C. tropicalis, and C. glabrata). Eleven isoxazole derivatives were active against C. parapsilosis, and compound 14o was found to be the most active (minimal inhibitory concentration [MIC] = 3.4 μM) for this strain. Compound 14p was active against all the strains tested, with an MIC = 17.5 μM for C. glabrata, lower than that of the fluconazole used as the reference drug.     

In vitro and in vivo antileishmanial activity of the hanging sedge flavonoids based on bio- guided fractionation assay

As a major public health issue, cutaneous leishmaniasis (CL) has a number of complications, including drug resistance and poor response to conventional treatments. Over the last decade, research on natural sources for finding new antileishmanial agents has been a critical part of tropical disease research. Natural products also should be regarded as one of the most valuable applications for CL infection drug development. In this study, we assessed the in vitro and in vivo antileishmanial potential of Carex pendula Huds. (hanging sedge) methanolic extract and its fractions against Leishmania major produced cutaneous infection. Although the methanolic extract and its fractions exhibited suitable activity, the ethyl acetate fraction showed the best activity (with the half maximal inhibitory concentration IC₅₀ = 1.627 ± 0.211 mg/mL). The toxicity and selectivity indices (SI) of all samples were determined in murine peritoneal macrophage cells (J774A.1) using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test. The flavonoid components of the ethyl acetate fraction were identified using liquid chromatography electrospray ionization mass spectrometry (LC-ESI MS/MS). Nine chemical compounds were identified in this fraction, including three flavonols, four flavanonols, and two flavan derivatives. L. major-infected mice were used as an in vivo model because the methanolic extract was effective against L. major promastigotes in the mammalian cell line J774A.1 with SI = 2.514 (tail lesion size model). In silico analysis of identified compounds also revealed a favorable interaction between compounds 2 – 5 and L. major protein targets (3UIB, 4JZX, 4JZB, 5L4N, and 5L42). According to the findings of this study, the ethyl acetate fraction (as flavonoid fraction) exhibited considerable in vitro antileishmanial activity.     

Antileismanial activity,mechanism of action study and molecular docking of 1,4‐bis(substituted benzalhydrazino)phthalazines

To identify new agents for the treatment of American cutaneous leishmaniasis, a series of eight 1,4‐bis(substituted benzalhydrazino)phthalazines was evaluated against Leishmania braziliensis and Leishmania mexicana parasites. These compounds represent a disubstituted version of the 1‐chloro‐4‐(monoaryl/heteroarylhydranizyl)phthalazine that exhibited a significant response against L. braziliensis according to our previous findings. Two disubstituted phthalazines 3b and 3f were identified as potential antileishmanial agents against L. braziliensis parasites, exhibiting a submicromolar IC₅₀ response of 2.37 and 7.90 µM on the promastigote form, and of 1.82 and 4.56 µM against intracellular amastigotes, respectively. In particular, compound 3b showed interesting responses against amastigote isolates from reference, glucantime‐resistant and clinical human strains, which were by far superior to the biological response found for the glucantime drug. With regard to the toxicity results, both 3b and 3f exhibited moderate LD₅₀ values against murine macrophages (BMDM), with good selectivity indexes on promastigotes and intracellular amastigotes of L. braziliensis. A comparison of biological response was established between the monosubstituted and disubstituted versions of these benzalhydrazino‐phthalazines. Easy synthetic procedure and significant response against amastigote strains including against resistant lines made compound 3b a potential candidate for further pharmacokinetic and in vivo experiments as antileishmanial agent, and as a platform for further structural optimization. Mechanism‐of‐action studies and molecular docking simulations discarded to inhibition of superoxide dismutase as possible mode of action.     

Screening of medicinal plants against Leishmania amazonensis

Context: Leishmaniasis is a widespread tropical infection caused by different species of Leishmania protozoa. There is no immunoprophylaxis (vaccination) available for Leishmania infections and conventional treatments are unsatisfactory; therefore antileishmanial drugs are urgently needed. Natural products are attractive due to their structural diversity.

Objective: The present work investigated the antileishmanial action of 21 species of plants.

Materials and methods: Plants were collected and their hydroalcoholic extracts were screened against promastigotes and amastigotes of L. amazonensis. Their toxicity was also assayed against peritoneal macrophages from BALB/c mice.

Results: Five extracts showed significant growth inhibitory activity against promastigote form. Only the extracts from Bidens pilosa L. (Asteraceae) and Punica granatum L. (Punicaceae) inhibited the growth of intracellular amastigotes, with IC₅₀ values of 42.6 and 69.6 µg/mL, respectively. In addition, a low toxicity on macrophage from BALB/c mice was observed.

Discussion: The antiparasitic activities of B. pilosa and P. granatum have been reported against other parasitic agents and their actions can be the results of flavonoids present in the extracts.

Conclusion: This study supports the importance of natural products as potential sources in the search for new antileishmanial drugs.     

Leishmanicidal and cytotoxic activities of Nigella sativa and its active principle,thymoquinone

Abstract

Context: Leishmaniasis is a complex disease with a broad spectrum of clinical presentations.

Objective: We evaluated the anti-leishmanial effects of Nigella sativa L. (Ranunculaceae) against Leishmania tropica and Leishmania infantum with an in vitro model.

Materials and methods: Antileishmanial effects of essential oil and methanolic extract of N. sativa (0–200?µg/mL) and thymoquinone (0–25?µg/mL) on promastigotes of both species and their cytotoxicity activities against murine macrophages were evaluated using the MTT assay at 24, 48, and 72?h. Moreover, their leishmanicidal effects against amastigotes were investigated in a macrophage model, for 48 and 72?h.

Results: The findings showed that essential oil (L. tropica IC₅₀ 9.3?μg/mL and L. infantum IC₅₀ 11.7?μg/mL) and methanolic extract (L. tropica IC₅₀ 14.8?μg/mL and L. infantum IC₅₀ 15.7?μg/mL) of N. sativa, particularly thymoquinone (L. tropica IC₅₀ 1.16?μg/mL and L. infantum IC₅₀ 1.47?μg/mL), had potent antileishmanial activity on promastigotes of both species after 72?h. In addition, essential oil (L. tropica IC₅₀ 21.4?μg/mL and L. infantum IC₅₀ 26.3?μg/mL), methanolic extract (L. tropica IC₅₀ 30.8?μg/mL and L. infantum IC₅₀ 34.6?μg/mL), and thymoquinone (L. tropica IC₅₀ 2.1?μg/mL and L. infantum IC₅₀ 2.6?μg/mL) mediated a significant decrease in the growth rate of amastigote forms of both species. Thymoquinone (CC₅₀ 38.8?μg/mL) exhibited higher cytotoxic effects against murine macrophages than the other extracts.

Conclusion: N. sativa, especially its active principle, thymoquinone, showed a potent leishmanicidal activity against L. tropica and L.infantum with an in vitro model.     

Synthesis,Cytotoxicity and Antileishmanial Activity of Some N-(2-(indol-3-yl)ethyl)-7-chloroquinolin-4-amines

We report herein the condensation of 4,7-dichloroquinoline (1) with tryptamine (2) and D-tryptophan methyl ester (3) . Hydrolysis of the methyl ester adduct (5) yielded the free acid (6) . The compounds were evaluated in vitro for activity against four different species of Leishmania promastigote forms and for cytotoxic activity against Kb and Vero cells. Compound (5) showed good activity against the Leishmania species tested, while all three compounds displayed moderate activity in both Kb and Vero cells.     

Virtual screening identification of nonfolate compounds, including a CNS drug, as antiparasitic agents inhibiting pteridine reductase

Folate analogue inhibitors of Leishmania major pteridine reductase (PTR1) are potential antiparasitic drug candidates for combined therapy with dihydrofolate reductase (DHFR) inhibitors. To identify new molecules with specificity for PTR1, we carried out a virtual screening of the Available Chemicals Directory (ACD) database to select compounds that could interact with L. major PTR1 but not with human DHFR. Through two rounds of drug discovery, we successfully identified eighteen drug-like molecules with low micromolar affinities and high in vitro specificity profiles. Their efficacy against Leishmania species was studied in cultured cells of the promastigote stage, using the compounds both alone and in combination with 1 (pyrimethamine; 5-(4-chlorophenyl)-6-ethylpyrimidine-2,4-diamine). Six compounds showed efficacy only in combination. In toxicity tests against human fibroblasts, several compounds showed low toxicity. One compound, 5c (riluzole; 6-(trifluoromethoxy)-1,3-benzothiazol-2-ylamine), a known drug approved for CNS pathologies, was active in combination and is suitable for early preclinical evaluation of its potential for label extension as a PTR1 inhibitor and antiparasitic drug candidate.     

Antileishmanial and antibacterial activity of a new pyrazole derivative designated 4-[2-(1-(ethylamino)-2-methyl- propyl)phenyl]-3-(4-methyphenyl)-1-phenylpyrazole

Here, we report for the first time the synthesis and the antileishmanial activity of a new pyrazole derivative, namely 4-[2-(1-(ethylamino)-2-methylpropyl)phenyl]-3-(4-methyphenyl)-1-phenylpyrazole). Micromolar concentrations of this compound were found to inhibit the in vitro multiplication of Leishmania tropica, Leishmania major, and Leishmania infantum, three species causing different forms of leishmaniasis. Furthermore, the 50% inhibitory concentration (IC50) values for the compound are only slightly higher than those of amphotericin B, one of the most active antileishmanial agents used as a satisfactory substitute in cases not responding to pentostam. The IC50 values after 48 h for L. tropica, L. major, and L. infantum promastigote growth were 0.48 microg/mL, 0.63 microg/mL and 0.40 microg/mL, respectively for the compound, while they were 0.23 microg/mL, 0.29 microg/mL and 0.24 microg/mL, respectively for amphotericin B. We also tested this compound for its antibacterial activity against several bacteria. The strongest antibacterial activity was observed against Entrococcus feacalis and Staphylococcus aureus with a minimal inhibitory concentration (MIC) of 60 microg/mL.     

Design,synthesis and antitrypanosomatid activities of 3,5‐diaryl‐isoxazole analogues based on neolignans veraguensin,grandisin and machilin G

Using bioisosterism as a medicinal chemistry tool, 16 3,5‐diaryl‐isoxazole analogues of the tetrahydrofuran neolignans veraguensin, grandisin and machilin G were synthesized via 1,3‐dipolar cycloaddition reactions, with yields from 43% to 90%. Antitrypanosomatid activities were evaluated against Trypanosoma cruzi, Leishmania (L.) amazonensis and Leishmania (V.) braziliensis. All compounds were selective for the Leishmania genus and inactive against T. cruzi. Isoxazole analogues showed a standard activity on both promastigotes of L. amazonensis and L. braziliensis. The most active compounds were 15 , 16 and 19 with IC₅₀ values of 2.0, 3.3 and 9.5 μM against L. amazonensis and IC₅₀ values of 1.2, 2.1 and 6.4 μM on L. braziliensis, respectively. All compounds were noncytotoxic, showing lower cytotoxicity (>250 μM) than pentamidine (78.9 μM). Regarding the structure–activity relationship (SAR), the methylenedioxy group was essential to antileishmanial activity against promastigotes. Replacement of the tetrahydrofuran nucleus by an isoxazole core improved the antileishmanial activity.     

Discovery of benzimidazole‐based Leishmania mexicana cysteine protease CPB2.8ΔCTE inhibitors as potential therapeutics for leishmaniasis

Chemotherapy is currently the only effective approach to treat all forms of leishmaniasis. However, its effectiveness is severely limited due to high toxicity, long treatment length, drug resistance, or inadequate mode of administration. As a consequence, there is a need to identify new molecular scaffolds and targets as potential therapeutics for the treatment of this disease. We report a small series of 1,2‐substituted‐1H‐benzo[d]imidazole derivatives ( 9a–d ) showing affinity in the submicromolar range (K_i = 0.15–0.69 μM) toward Leishmania mexicanaCPB2.8ΔCTE, one of the more promising targets for antileishmanial drug design. The compounds confirmed activity in vitro against intracellular amastigotes of Leishmania infantum with the best result being obtained with derivative 9d (IC₅₀ = 6.8 μM), although with some degree of cytotoxicity (CC₅₀ = 8.0 μM on PMM and CC₅₀ = 32.0 μM on MCR‐5). In silico molecular docking studies and ADME‐Tox properties prediction were performed to validate the hypothesis of the interaction with the intended target and to assess the drug‐likeness of these derivatives.     

7‐Chloro‐4‐quinolinyl Hydrazones: A Promising and Potent Class of Antileishmanial Compounds

In this work, we report the antileishmanial evaluation of twenty 7‐chloro‐4‐quinolinyl hydrazone derivatives ( 1 – 20 ). Firstly, the compounds were tested against promastigotes of four different Leishmania species. After that, all derivatives were assayed against L. braziliensis amastigotes and murine macrophages. Furthermore, it was investigated whether the antiamastigote L. braziliensis effect of the compounds could be associated with nitric oxide production. Compounds 6 and 7 showed a strong leishmanicidal activity against intracellular parasite with IC₅₀ in nanogram levels (30 and 20 ng/mL, respectively). Appreciable activity of three compounds tested can be considered an important finding for the rational design of new leads for antileishmanial compounds.