Fosfatriclaben, a prodrug of triclabendazole: Preparation, stability, and fasciolicidal activity of three new intramuscular formulations

In this study, we present the preparation, stability, and in vivo fasciolicidal activity of three new intramuscular formulations in sheep of a prodrug based on triclabendazole, named fosfatriclaben. The new formulations were ready-to-use aqueous solutions with volumes recommended for intramuscular administration in sheep. The use of poloxamers (P-407 and P-188) and polysorbates (PS-20 and PS-80) in the new formulations improved the aqueous solubility of fosfatriclaben by 8-fold at pH 7.4. High-performance liquid chromatography with UV detection was used to evaluate the stability of fosfatriclaben in the three formulations. High recovery (> 90%) of fosfatriclaben was found for all formulations after exposure at 57 ± 2 °C for 50 h. The three intramuscular formulations showed high fasciolicidal activity at a dose of 6 mg/kg, which was equivalent to the triclabendazole content. The fasciolicidal activity of fosfatriclaben was similar to commercial oral (Fasimec®) and intramuscular (Endovet®) triclabendazole formulations at a dose of 12 mg/kg. In the in vivo experiments, all formulations administered intramuscularly reduced egg excretion by 100%, and formulations F1, F2, and F3 presented fasciolicidal activities of 100%, 100%, and 99.6%, respectively.

Characterization of the Effect of N-(2-Methoxyphenyl)-1-methyl-1H-benzimidazol-2-amine, Compound 8, against Leishmania mexicana and Its In Vivo Leishmanicidal Activity

Chemotherapy currently available for leishmaniasis treatment has many adverse side effects and drug resistance. Therefore, the identification of new targets and the development of new drugs are urgently needed. Previously, we reported the synthesis of a N-(2-methoxyphenyl)-1-methyl-1H-benzimidazol-2-amine, named compound 8, with an IC50 value in the micromolar range against L. mexicana, it also inhibited 68.27% the activity of recombinant L. mexicana arginase. Herein, we report studies carried out to characterize the mechanism of action of compound 8, as well as its in vivo leishmanicidal activity. It was shown in our ultrastructural studies that compound 8 induces several changes, such as membrane blebbing, the presence of autophagosomes, membrane detachment and mitochondrial and kinetoplast disorganization, among others. Compound 8 triggers the production of ROS and parasite apoptosis. It reduced 71% of the parasite load of L. mexicana in an experimental model of cutaneous leishmaniasis in comparison with a control. Altogether, the data obtained suggest the potential use of compound 8 in the treatment of cutaneous leishmaniasis.

Structure-Based Optimization of Carbendazim-Derived Tubulin Polymerization Inhibitors through Alchemical Free Energy Calculations

Carbendazim derivatives, commonly used as antiparasitic drugs, have shown potential as anticancer agents due to their ability to induce cell cycle arrest and apoptosis in human cancer cells by inhibiting tubulin polymerization. Crystallographic structures of α/β-tubulin multimers complexed with nocodazole and mebendazole, two carbendazim derivatives with potent anticancer activity, highlighted the possibility of designing compounds that occupy both benzimidazole- and colchicine-binding sites. In addition, previous studies have demonstrated that the incorporation of a phenoxy group at position 5/6 of carbendazim increases the antiproliferative activity in cancer cell lines. Despite the significant progress made in identifying new tubulin-targeting anticancer compounds, further modifications are needed to enhance their potency and safety. In this study, we explored the impact of modifying the phenoxy substitution pattern on antiproliferative activity. Alchemical free energy calculations were used to predict the binding free energy difference upon ligand modification and define the most viable path for structure optimization. Based on these calculations, seven compounds were synthesized and evaluated against lung and colon cancer cell lines. Our results showed that compound 5a, which incorporates an α-naphthyloxy substitution, exhibits the highest antiproliferative activity against both cancer lines (SK-LU-1 and SW620, IC50 < 100 nM) and induces morphological changes in the cells associated with mitotic arrest and mitotic catastrophe. Nevertheless, the tubulin polymerization assay showed that 5a has a lower inhibitory potency than nocodazole. Molecular dynamics simulations suggested that this low antitubulin activity could be associated with the loss of the key H-bond interaction with V236. This study provides insights into the design of novel carbendazim derivatives with anticancer activity.

In Silico Exploration of the Trypanothione Reductase (TryR) of L. mexicana

Human leishmaniasis is a neglected tropical disease which affects nearly 1.5 million people every year, with Mexico being an important endemic region. One of the major defense mechanisms of these parasites is based in the polyamine metabolic pathway, as it provides the necessary compounds for its survival. Among the enzymes in this route, trypanothione reductase (TryR), an oxidoreductase enzyme, is crucial for the Leishmania genus' survival against oxidative stress. Thus, it poses as an attractive drug target, yet due to the size and features of its catalytic pocket, modeling techniques such as molecular docking focusing on that region is not convenient. Herein, we present a computational study using several structure-based approaches to assess the druggability of TryR from L. mexicana, the predominant Leishmania species in Mexico, beyond its catalytic site. Using this consensus methodology, three relevant pockets were found, of which the one we call σ-site promises to be the most favorable one. These findings may help the design of new drugs of trypanothione-related diseases.

Development and Pharmacokinetic Evaluation of Two Parenteral Formulations of Albendazole Using Prodrug and Cosolvent Approaches

Albendazole is a broad-spectrum anthelmintic drug used for parasitic infections. In addition, due to its mechanism of action, it has been studied as an anticancer agent. However, poor and highly variable bioavailability are limiting factors for its use in systemic illnesses. The present study aimed to develop two parenteral formulations of albendazole and to compare its pharmacokinetic profile with the conventional oral administration. Parenteral formulations were developed using two different approaches: a phosphonooxymethylated prodrug and cosolvents. For the albendazole prodrug, once synthetized, its solubility and hydrolysis with alkaline phosphatase were evaluated. A factorial design of experiments was used for the cosolvent formulation. Stability and hemolytic activity were assessed. A pharmacokinetic study was performed on New Zealand rabbits. Both formulations were administered intravenously, and the prodrug was also administered intramuscularly. Results were compared with those obtained after the oral administration of albendazole. A 20,000-fold and 6000-fold increase in albendazole solubility was found with the prodrug and cosolvent formulations, respectively. Both parenteral formulations displayed higher albendazole plasma concentrations for the first 2 h compared with oral administration, even when the oral dose was doubled. The absolute bioavailability of oral albendazole was 15.5% while for the intramuscular administration of the prodrug was 102.6%. Both parenteral formulations showed a significant decrease in the formation of albendazole sulfoxide (ANOVA p<0.05) and allowed greater exposure to albendazole. Albendazole cosolvent parenteral formulation could be a promising option in systemic illnesses considering its ease of preparation and superb pharmacokinetic performance.

Garbage in, garbage out: how reliable training data improved a virtual screening approach against SARS-CoV-2 MPro

Introduction: The identification of chemical compounds that interfere with SARS-CoV-2 replication continues to be a priority in several academic and pharmaceutical laboratories. Computational tools and approaches have the power to integrate, process and analyze multiple data in a short time. However, these initiatives may yield unrealistic results if the applied models are not inferred from reliable data and the resulting predictions are not confirmed by experimental evidence. Methods: We undertook a drug discovery campaign against the essential major protease (MPro) from SARS-CoV-2, which relied on an in silico search strategy -performed in a large and diverse chemolibrary- complemented by experimental validation. The computational method comprises a recently reported ligand-based approach developed upon refinement/learning cycles, and structure-based approximations. Search models were applied to both retrospective (in silico) and prospective (experimentally confirmed) screening. Results: The first generation of ligand-based models were fed by data, which to a great extent, had not been published in peer-reviewed articles. The first screening campaign performed with 188 compounds (46 in silico hits and 100 analogues, and 40 unrelated compounds: flavonols and pyrazoles) yielded three hits against MPro (IC₅₀ ≤ 25 μM): two analogues of in silico hits (one glycoside and one benzo-thiazol) and one flavonol. A second generation of ligand-based models was developed based on this negative information and newly published peer-reviewed data for MPro inhibitors. This led to 43 new hit candidates belonging to different chemical families. From 45 compounds (28 in silico hits and 17 related analogues) tested in the second screening campaign, eight inhibited MPro with IC₅₀ = 0.12-20 μM and five of them also impaired the proliferation of SARS-CoV-2 in Vero cells (EC₅₀ 7-45 μM). Discussion: Our study provides an example of a virtuous loop between computational and experimental approaches applied to target-focused drug discovery against a major and global pathogen, reaffirming the well-known "garbage in, garbage out" machine learning principle.

Structure–Activity Relationship of N-Phenylthieno[2,3-b]pyridine-2-carboxamide Derivatives Designed as Forkhead Box M1 Inhibitors: The Effect of Electron-Withdrawing and Donating Substituents on the Phenyl Ring

We report synthesis, characterization, biological evaluation, and molecular-docking studies of 18 thieno[2,3-b]pyridines with a phenylacetamide moiety at position 2, which is disubstituted with F, Cl, Br, or I at position 4, and with electron-withdrawing and electron-donating groups (-CN, -NO₂, -CF₃, and -CH₃) at position 2, to study how the electronic properties of the substituents affected the FOXM1-inhibitory activity. Among compounds 1–18, only those bearing a -CN (regardless of the halogen) decreased FOXM1 expression in a triple-negative breast cancer cell line (MDA-MB-231), as shown by Western blotting. However, only compounds 6 and 16 decreased the relative expression of FOXM1 to a level lower than 50%, and hence, we determined their anti-proliferative activity (IC₅₀) in MDA-MB-231 cells using the MTT assay, which was comparable to that observed with FDI-6, in contrast to compound 1, which was inactive according to both Western blot and MTT assays. We employed molecular docking to calculate the binding interactions of compounds 1–18 in the FOXM1 DNA-binding site. The results suggest a key role for residues Val296 and Leu289 in this binding. Furthermore, we used molecular electrostatic potential maps showing the effects of different substituents on the overall electron density.

Benzimidazole Derivatives as New and Selective Inhibitors of Arginase from Leishmania mexicana with Biological Activity against Promastigotes and Amastigotes

Leishmaniasis is a disease caused by parasites of the Leishmania genus that affects 98 countries worldwide, 2 million of new cases occur each year and more than 350 million people are at risk. The use of the actual treatments is limited due to toxicity concerns and the apparition of resistance strains. Therefore, there is an urgent necessity to find new drugs for the treatment of this disease. In this context, enzymes from the polyamine biosynthesis pathway, such as arginase, have been considered a good target. In the present work, a chemical library of benzimidazole derivatives was studied performing computational, enzyme kinetics, biological activity, and cytotoxic effect characterization, as well as in silico ADME-Tox predictions, to find new inhibitors for arginase from Leishmania mexicana (LmARG). The results show that the two most potent inhibitors (compounds 1 and 2) have an I₅₀ values of 52 μM and 82 μM, respectively. Moreover, assays with human arginase 1 (HsARG) show that both compounds are selective for LmARG. According to molecular dynamics simulation studies these inhibitors interact with important residues for enzyme catalysis. Biological activity assays demonstrate that both compounds have activity against promastigote and amastigote, and low cytotoxic effect in murine macrophages. Finally, in silico prediction of their ADME-Tox properties suggest that these inhibitors support the characteristics to be considered drug candidates. Altogether, the results reported in our study suggest that the benzimidazole derivatives are an excellent starting point for design new drugs against leishmanisis.

Effectiveness of an experimental injectable prodrug formulation against Fasciola hepatica of different ages in experimentally infected sheep

In this work, we present an evaluation of the fasciolicidal efficacy of a new injectable formulation of fosfatriclaben in comparison with the subcutaneous closantel and oral triclabendazole formulations currently used in veterinary practice as fasciolicides. The study was carried out in vivo on Fasciola hepatica at 2, 4, 6 and 8 weeks of age in experimentally infected sheep. To evaluate the formulation, the percent reduction of the parasite load was measured and the number of fluke eggs. Fosfatriclaben was used at 6 mg/kg/IM (dose equivalent to triclabendazole content), closantel at 5% at 10 mg/kg/SC, and triclabendazole at 10 mg/kg/PO; the control group received no treatment. Fosfatriclaben showed fasciolicidal efficacies of 95.5 %, 100 %, 100 % and 100 %, and triclabendazole showed similar efficacies of 97.4 %, 100 %, 100 % and 100 %, at the different treatment weeks (P > 0.05). Closantel showed limited efficacy against 2-, 4- and 6-week-old flukes but 100 % efficacy in adult flukes. All three evaluated formulations eliminated all 8-week-old F. hepatica trematode eggs. Although fosfatriclaben and triclabendazole showed similar fasciolicidal efficacy, the intramuscular administration of fosfatriclaben has several advantages over the oral administration of triclabendazole, such as ease of administration for veterinary use and a reduced risk of accidents for both the operator and the animals. In addition, the dose used in this injectable formulation is only 60 % of the oral dose, which reduces environmental contamination.

Efficiency comparison of experimental fosfatriclaben with three commercial fasciolicides in experimentally infected sheep

In this work, we compare and evaluate the efficiency of fosfatriclaben with three commercial fasciolicides in experimentally infected sheep. Fosfatriclaben is a novel prodrug derived from triclabendazole; it is highly water-soluble with excellent aqueous stability at pH 7, properties that make it ideal for developing intramuscular pharmaceutical compositions in the form of solutions. In order to compare, 30 mixed breed sheep, previously diagnosed negative to fluke eggs, were infected with 200 metacercariae of Fasciola hepatica, twice. Five groups of six animals/each were formed for treatments. Group 1 (G1) was treated with closantel 5% injectable at 5 mg/kg subcutaneously, G2 with clorsulon at 2 mg/kg subcutaneously, G3 with triclabendazole at 12 mg/kg per os, G4 with fosfatriclaben at 6 mg/kg intramuscularly (dose equivalent to triclabendazole content), and G5 remained as the non-treated control. On day 110, fecal samples were examined to determine the percentage of egg reduction after treatment, and sheep were humanely euthanized. The livers were collected, the flukes were extracted, measured, and counted. Efficiency in egg reduction was of 86.8, 90.5, 98.4, and 97.3% for closantel, clorsulon, triclabendazole, and fosfatriclaben, respectively, and efficiency against flukes was of 96.2, 91.9, 99.4, and 95.7%, respectively. No statistical differences were found between treatments. It is concluded that fosfatriclaben at 6 mg/kg intramuscularly presented a high fasciolicide efficiency, similar to the best commercial fasciolicides, having advantage over its predecessor since it uses half of the dose required by triclabendazole to remove flukes in sheep under study.

Characterisation of the in vitro activity of a Nitazoxanide-N-methyl-1H-benzimidazole hybrid molecule against albendazole and nitazoxanide susceptible and resistant strains of Giardia intestinalis and its in vivo giardicidal activity

BACKGROUND

It was previously demonstrated that CMC-20, a nitazoxanide and N-methyl-1H-benzimidazole hybrid molecule, had higher in vitro activity against Giardia intestinalis WB strain than metronidazole and albendazole and similar to nitazoxanide.

OBJETIVES

To evaluate the in vitro activity of CMC-20 against G. intestinalis strains with different susceptibility/resistance to albendazole and nitazoxanide and evaluate its effect on the distribution of parasite cytoskeletal proteins and its in vivo giardicidal activity.

METHODS

CMC-20 activity was tested against two isolates from patients with chronic and acute giardiasis, an experimentally induced albendazole resistant strain and a nitazoxanide resistant clinical isolate. CMC-20 effect on the distribution of parasite cytoskeletal proteins was analysed by indirect immunofluorescence and its activity was evaluated in a murine model of giardiasis.

FINDINGS CMC-20

showed broad activity against susceptible and resistant strains to albendazole and nitaxozanide. It affected the parasite microtubule reservoir and triggered the parasite encystation. In this process, alpha-7.2 giardin co-localised with CWP-1 protein. CMC-20 reduced the infection time and cyst load in feces of G. muris infected mice similar to albendazole.

MAIN CONCLUSIONS

The in vitro and in vivo giardicidal activity of CMC-20 suggests its potential use in the treatment of giardiasis.

Partial inhibition of the tricarboxylic acid cycle in Taenia crassiceps cysticerci after the in vitro exposure to a benzimidazole derivative (RCB15)

The benzimidazole derivative, 6-chloro-5-(2,3-dichlorophenoxy)-2-(trifluoromethyl)-1H-benzimidazole (RCB15), has a similar mode of action and efficacy as albendazole, a commonly used anthelminthic drugs. The aim of this study was to evaluate its influence on the tricarboxylic acid cycle in Taenia crassiceps cysticerci. The parasites were cultured in supplemented RPMI medium containing albendazole sulfoxide (ABZSO) or RCB15, for 24 h. Then, frozen in liquid nitrogen for organic metabolites extraction. Samples were analyzed by high performance liquid chromatography and organic acids of the tricarboxylic acid cycle were detected. It was possible to observe changes in the concentrations of all acids involved in this metabolic pathway, with the exception of α-ketoglutarate, which was not detected in the control group neither in most of the treated groups. It indicates that the parasite presented a partial inhibition of the tricarboxylic acid cycle. The significant increase in the concentration of citrate, oxaloacetate and succinate in the RCB15 treated groups may indicate an activation of the fumarate reductase pathway, leading to metabolic distress. Therefore RCB15 may be considered an alternative for the treatment of tissue parasitic diseases, since it induced changes in the main metabolic pathway of the parasite.

Leishmania mexicana Trypanothione Reductase Inhibitors: Computational and Biological Studies

Leishmanicidal drugs have many side effects, and drug resistance to all of them has been documented. Therefore, the development of new drugs and the identification of novel therapeutic targets are urgently needed. Leishmania mexicana trypanothione reductase (LmTR), a NADPH-dependent flavoprotein oxidoreductase important to thiol metabolism, is essential for parasite viability. Its absence in the mammalian host makes this enzyme an attractive target for the development of new anti-Leishmania drugs. Herein, a tridimensional model of LmTR was constructed and the molecular docking of 20 molecules from a ZINC database was performed. Five compounds (ZINC04684558, ZINC09642432, ZINC12151998, ZINC14970552, and ZINC11841871) were selected (docking scores -10.27 kcal/mol to -5.29 kcal/mol and structurally different) and evaluated against recombinant LmTR (rLmTR) and L. mexicana promastigote. Additionally, molecular dynamics simulation of LmTR-selected compound complexes was achieved. The five selected compounds inhibited rLmTR activity in the range of 32.9% to 40.1%. The binding of selected compounds to LmTR involving different hydrogen bonds with distinct residues of the molecule monomers A and B is described. Compound ZINC12151998 (docking score -10.27 kcal/mol) inhibited 32.9% the enzyme activity (100 µM) and showed the highest leishmanicidal activity (IC₅₀ = 58 µM) of all the selected compounds. It was more active than glucantime, and although its half-maximal cytotoxicity concentration (CC₅₀ = 53 µM) was higher than that of the other four compounds, it was less cytotoxic than amphotericin B. Therefore, compound ZINC12151998 provides a promising starting point for a hit-to-lead process in our search for new anti-Leishmania drugs that are more potent and less cytotoxic.

Insights into the Giardia intestinalis enolase and human plasminogen interaction

Giardia intestinalis is an intestinal parasite that causes diarrhea in humans and animals worldwide. The enolase of G. intestinalis (GiENO) participates in its glycolysis pathway and is abundantly expressed in the parasite cytosol; however, its localization on the surface of trophozoites and cysts has been demonstrated. Enolases from bacteria and parasites can have different functions and are considered moonlighting proteins, for example, as a cell surface plasminogen receptor. In relation to GiENO, no studies have been performed about its possible participation as a plasminogen receptor. In this work, we employed molecular docking and multiscale molecular dynamics (MD) simulations to explore the possible interactions of human plasminogen (HsPLG) with the open and closed GiENO conformations. Our proposed GiENO plasminogen binding site (PLGBs) was identified at Lys266 based on the sequence comparison with bacterial enolase known to act as a plasminogen receptor. Our docking results performed with multiple MD snapshots of the closed GiENO conformation showed that Lys266 preferentially binds to the K5 domain of HsPLG. On the other hand, open GiENO conformations from all-atom and coarse-grained simulations indicated a high preference of the HsPLG K4 domain for lysine residues 186 and 188. Furthermore, we identified a potential N-glycosylation site of GiENO which suggests a possible explanation for the parasite cell surface localization or host mucin oligosaccharide adhesion mechanism. Our study constitutes the first multiscale computational study to explore the plasminogen receptor function of GiENO for its further consideration as a potential therapeutic target for giardiasis treatment.

Assessment of the effective dose of an experimental intramuscular formulation against immature and adult Fasciola hepatica in sheep

The effective dose of an injectable prodrug, named compound alpha prodrug, against immature and adult Fasciola hepatica in experimentally infected sheep was determined. In a first experiment, 30 sheep were infected with Fasciola hepatica on day 0 and 50. After microscopic detection of faecal eggs on day 80, groups (n = 6) 1 to 3 were treated with 6, 8 and 10 mg/kg of the experimental water-soluble prodrug compound alpha intramuscularly, respectively. Group 4 was treated with closantel and group 5 remained untreated. Copromicroscopical examinations were made on day 0, 80 and 108. On day 110, trematodes were collected from the bile ducts. Fasciolicide efficacy was assessed as a percentage of fluke-egg and adult-fluke reduction. Fluke length was also recorded. In a second experiment aimed to assess the fasciolicide activity of compound alpha prodrug against four-week-old flukes, 12 sheep were infected on day 0 and allocated into two groups (n = 6). On day 50 post infection, group A was treated with the experimental water-soluble prodrug compound alpha at 6 mg/kg/IM and B remained untreated. Fasciolicide activity was assessed on day 80 after collection, microscopic observation and measurement of flukes present in the parenchyma for immature stages and on day 108 for adults. Egg output decreased 91.2, 96.0, 98.8 and 94.9% for groups 1, 2, 3 and 4, respectively. Compound alpha prodrug cleared 97.6%, 98.51% and 100% of adult stages in a dose-dependent manner. Closantel killed 81.95% flukes. Regarding the second experiment, 81.2% efficacy was achieved. Immature flukes were significantly smaller in the treated group. It is concluded that the intramuscular application of compound alpha prodrug exerted fasciolicide efficacy against adults of Fasciola hepatica.

Functional Outcomes 18 Months After Total and Midarm Transplantation: A Case Report

BACKGROUND

The function reported after arm transplantation is deemed beneficial relative to the marked disability that upper arm amputation causes.

OBJECTIVE

We report a 51-year-old man with a Disabilities of the Arm, Shoulder and Hand (DASH) score of 75.83 who underwent bilateral arm transplantation in October 2015.

PROCEDURE

The right arm was transplanted at the glenohumeral joint level, including transplantation of the humeral head, joint capsule, and rotator cuff ligaments and tendons. Additionally, neurorrhaphies were performed at the origin of the terminal branches of the brachial plexus, including the axillary and musculocutaneous nerves. Therefore, this was considered a total arm transplantation. The left arm was transplanted at the transhumeral level, with complete transplantation of the biceps and triceps brachii, and terminolateral neurorrhaphy of the donor musculocutaneous nerve to the receptor radial nerve. A maintenance triple immunosuppression scheme was administered, with tacrolimus levels kept at 10 ng/mL.

RESULTS

At 18 months post-transplantation, the intrinsic musculature in the left hand showed electrical registry, DASH score was 67.5, Carroll test score was 28 in both extremities, Hand Transplant Score System was 67.5 in the right extremity and 77.5 in the left extremity, and Short Form-36 score was 96.1. The patient was healthy, with restored body integrity. He could lift medium-sized weightless objects, eat and go to the bathroom by himself, drink liquids with bimanual grasp, swim, dress almost independently, and drive.

CONCLUSION

The functional evolution of the patient was similar to previously reported transplanted arms, even though the right arm transplant involved the glenohumeral joint and axillary and musculocutaneous nerve repair.

Novel Mixed-Type Inhibitors of Protein Tyrosine Phosphatase 1B. Kinetic and Computational Studies

The Atlas of Diabetes reports 415 million diabetics in the world, a number that has surpassed in half the expected time the twenty year projection. Type 2 diabetes is the most frequent form of the disease; it is characterized by a defect in the secretion of insulin and a resistance in its target organs. In the search for new antidiabetic drugs, one of the principal strategies consists in promoting the action of insulin. In this sense, attention has been centered in the protein tyrosine phosphatase 1B (PTP1B), a protein whose overexpression or increase of its activity has been related in many studies with insulin resistance. In the present work, a chemical library of 250 compounds was evaluated to determine their inhibition capability on the protein PTP1B. Ten molecules inhibited over the 50% of the activity of the PTP1B, the three most potent molecules were selected for its characterization, reporting Ki values of 5.2, 4.2 and 41.3 µM, for compounds 1, 2, and 3, respectively. Docking and molecular dynamics studies revealed that the three inhibitors made interactions with residues at the secondary binding site to phosphate, exclusive for PTP1B. The data reported here support these compounds as hits for the design more potent and selective inhibitors against PTP1B in the search of new antidiabetic treatment.

In vitro activity of new N-benzyl-1H-benzimidazol-2-amine derivatives against cutaneous, mucocutaneous and visceral Leishmania species

The identification of specific therapeutic targets and the development of new drugs against leishmaniasis are urgently needed, since chemotherapy currently available for its treatment has several problems including many adverse side effects. In an effort to develop new antileishmanial drugs, in the present study a series of 28 N-benzyl-1H-benzimidazol-2-amine derivatives was synthesized and evaluated in vitro against Leishmania mexicana promastigotes. Compounds 7 and 8 with the highest antileishmanial activity (micromolar) and lower cytotoxicity than miltefosine and amphotericin B were selected to evaluate their activity against L. braziliensis 9and L. donovani, species causative of mucocutaneous and visceral leishmaniasis, respectively. Compound 7 showed significantly higher activity against L. braziliensis promastigotes than compound 8 and slightly lower than miltefosine. Compounds 7 and 8 had IC₅₀ values in the micromolar range against the amastigote of L. mexicana and L. braziliensis. However, both compounds did not show better activity against L. donovani than miltefosine. Compound 8 showed the highest SI against both parasite stages of L. mexicana. In addition, compound 8 inhibited 68.27% the activity of recombinant L. mexicana arginase (LmARG), a therapeutic target for the treatment of leishmaniasis. Docking studies were also performed in order to establish the possible mechanism of action by which this compound exerts its inhibitory effect. Compound 8 shows promising potential for the development of more potent antileishmanial benzimidazole derivatives.

Species-Specific Inactivation of Triosephosphate Isomerase from Trypanosoma brucei: Kinetic and Molecular Dynamics Studies

Human African Trypanosomiasis (HAT), a disease that provokes 2184 new cases a year in Sub-Saharan Africa, is caused by Trypanosoma brucei. Current treatments are limited, highly toxic, and parasite strains resistant to them are emerging. Therefore, there is an urgency to find new drugs against HAT. In this context, T. brucei depends on glycolysis as the unique source for ATP supply; therefore, the enzyme triosephosphate isomerase (TIM) is an attractive target for drug design. In the present work, three new benzimidazole derivatives were found as TbTIM inactivators (compounds 1, 2 and 3) with an I₅₀ value of 84, 82 and 73 µM, respectively. Kinetic analyses indicated that the three molecules were selective when tested against human TIM (HsTIM) activity. Additionally, to study their binding mode in TbTIM, we performed a 100 ns molecular dynamics simulation of TbTIM-inactivator complexes. Simulations showed that the binding of compounds disturbs the structure of the protein, affecting the conformations of important domains such as loop 6 and loop 8. In addition, the physicochemical and drug-like parameters showed by the three compounds suggest a good oral absorption. In conclusion, these molecules will serve as a guide to design more potent inactivators that could be used to obtain new drugs against HAT.

Effects of the Protonation State of Titratable Residues and the Presence of Water Molecules on Nocodazole Binding to β-Tubulin

Regulation of microtubule assembly by antimitotic agents is a potential therapeutic strategy for the treatment of cancer, parasite infections, and neurodegenerative diseases. One of these agents is nocodazole (NZ), which inhibits microtubule polymerization by binding to β-tubulin. NZ was recently co-crystallized in Gallus gallus tubulin, providing new information about the features of interaction for ligand recognition and stability. In this work, we used state-of-the-art computational approaches to evaluate the protonation effects of titratable residues and the presence of water molecules in the binding of NZ. Analysis of protonation states showed that residue E198 has the largest modification in its pK_a value. The resulting E198 pK_a value, calculated with pH-REMD methodology (pK_a =6.21), was higher than the isolated E amino acid (pK_a =4.25), thus being more likely to be found in its protonated state at the binding site. Moreover, we identified an interaction between a water molecule and C239 and G235 as essential for NZ binding. Our results suggest that the protonation state of E198 and the structural water molecules play key roles in the binding of NZ to β-tubulin.

Curcumin alters the cytoskeleton and microtubule organization on trophozoites of Giardia lamblia

Giardia lamblia is a worldwide protozoan responsible for a significant number of intestinal infections. There are several drugs for the treatment of giardiasis, but they often cause side effects. Curcumin, a component of turmeric, has antigiardial activity; however, the molecular target and mechanism of antiproliferative activity are not clear. The effects of curcumin on cellular microtubules have been widely investigated. Since tubulin is the most abundant protein in the cytoskeleton of Giardia, to elucidate whether curcumin has activity against the microtubules of this parasite, we treated trophozoites with curcumin and the cells were analyzed by scanning electron microscopy and confocal microscopy. Curcumin inhibited Giardia proliferation and adhesion in a time-concentration-dependent mode. The higher inhibitory concentrations of curcumin (3 and 15μM) disrupted the cytoskeletal structures of trophozoites; the damage was evident on the ventral disk, flagella and in the caudal region, also the membrane was affected. The immunofluorescence images showed altered distribution of tubulin staining on ventral disk and flagella. Additionally, we found that curcumin caused a clear reduction of tubulin expression. By docking analysis and molecular dynamics we showed that curcumin has a high probability to bind at the interface of the tubulin dimer close to the vinblastine binding site. All the data presented indicate that curcumin may inhibit Giardia proliferation by perturbing microtubules.

Synthesis, antiprotozoal activity, and chemoinformatic analysis of 2-(methylthio)-1H-benzimidazole-5-carboxamide derivatives: Identification of new selective giardicidal and trichomonicidal compounds

A series of twelve new 2-(methylthio)-1H-benzimidazole-5-carboxamide derivatives (1-12) were synthesized and their antiparasitic activity was tested in vitro against Giardia intestinalis, Trichomonas vaginalis and Entamoeba histolytica. Experimental evaluations showed IC₅₀ values within the nanomolar range for all tested compounds, some showing higher activity than metronidazole and albendazole. A chemoinformatic study was used to compare the structure-activity relationship of the synthesized carboxamides with those of 91 previously studied benzimidazoles, and with some Nitazoxanide-N-methylbenzimidazole hybrids recently synthetized by our group. Compounds 1 and 3 were identified as prominent selective compounds against T. vaginalis and G. intestinalis, respectively, while compound 4 was found to be of broad spectrum against the three protozoans.

Structure-based approaches for the design of benzimidazole-2-carbamate derivatives as tubulin polymerization inhibitors

Microtubules are highly dynamic assemblies of α/β-tubulin heterodimers whose polymerization inhibition is among one of the most successful approaches for anticancer drug development. Overexpression of the class I (βI) and class III (βIII) β-tubulin isotypes in breast and lung cancers and the highly expressed class VI (βVI) β-tubulin isotype in normal blood cells have increased the interest for designing specific tubulin-binding anticancer therapies. To this end, we employed our previously proposed model of the β-tubulin-nocodazole complex, supported by the recently determined X-ray structure, to identify the fundamental structural differences between β-tubulin isotypes. Moreover, we employed docking and molecular dynamics (MD) simulations to determine the binding mode of a series of benzimidazole-2-carbamete (BzC) derivatives in the βI-, βIII-, and βVI-tubulin isotypes. Our results demonstrate that Ala198 in the βVI isotype reduces the affinity of BzCs, explaining the low bone marrow toxicity for nocodazole. Additionally, no significant differences in the binding modes between βI- and βIII-BzC complexes were observed; however, Ser239 in the βIII isotype might be associated with the low affinity of BzCs to this isotype. Finally, our study provides insight into the β-tubulin-BzC interaction features essential for the development of more selective and less toxic anticancer therapeutics.

Insights into the structure and inhibition of Giardia intestinalis arginine deiminase: homology modeling, docking, and molecular dynamics studies

Giardia intestinalis arginine deiminase (GiADI) is an important metabolic enzyme involved in the energy production and defense of this protozoan parasite. The lack of this enzyme in the human host makes GiADI an attractive target for drug design against G. intestinalis. One approach in the design of inhibitors of GiADI could be computer-assisted studies of its crystal structure, such as docking; however, the required crystallographic structure of the enzyme still remains unresolved. Because of its relevance, in this work, we present a three-dimensional structure of GiADI obtained from its amino acid sequence using the homology modeling approximation. Furthermore, we present an approximation of the most stable dimeric structure of GiADI identified through molecular dynamics simulation studies. An in silico analysis of druggability using the structure of GiADI was carried out in order to know if it is a good target for design and optimization of selective inhibitors. Potential GiADI inhibitors were identified by docking of a set of 3196 commercial and 19 in-house benzimidazole derivatives, and molecular dynamics simulation studies were used to evaluate the stability of the ligand-enzyme complexes.

JVG9, a benzimidazole derivative, alters the surface and cytoskeleton of Trypanosoma cruzi bloodstream trypomastigotes

Trypanosoma cruzi has a particular cytoskeleton that consists of a subpellicular network of microtubules and actin microfilaments. Therefore, it is an excellent target for the development of new anti-parasitic drugs. Benzimidazole 2-carbamates, a class of well-known broad-spectrum anthelmintics, have been shown to inhibit the in vitro growth of many protozoa. Therefore, to find efficient anti-trypanosomal (trypanocidal) drugs, our group has designed and synthesised several benzimidazole derivatives. One, named JVG9 (5-chloro-1H-benzimidazole-2-thiol), has been found to be effective against T. cruzi bloodstream trypomastigotes under both in vitro and in vivo conditions. Here, we present the in vitro effects observed by laser scanning confocal and scanning electron microscopy on T. cruzi trypomastigotes. Changes in the surface and the distribution of the cytoskeletal proteins are consistent with the hypothesis that the trypanocidal activity of JVG9 involves the cytoskeleton as a target.

5-Chloro-2-methyl-sulfanyl-6-(naphtha-len-1-yl-oxy)-1H-benzimidazole methanol monosolvate

In the title compound, C18H13ClN2OS·CH3OH, the dihedral angle between the benzimidazole group and the naphth-yloxy moiety [82.89 (5)°] very near to orthogonality. The H atom in the five-membered ring is disordered with equal occupancies at the two N atoms and the H atom of the methano-lic hy-droxy group is disordered with equal occupancies over two sites at the O atom. The methanol mol-ecule acts as a hydrogen-bond acceptor for the amino H atom and donates a hydrogen bond to the nonprotonated ring N atom. As a result, chains are formed running along the a axis.

Synthesis and antiprotozoal activity of nitazoxanide-N-methylbenzimidazole hybrids

A series of a novel hybrid compounds between nitazoxanide and N-methylbenzimidazole were synthesized starting from the corresponding N-methyl-2-nitroanilines. The new hybrid compounds (1-13) were evaluated in vitro against Giardia intestinalis, Entamoeba histolytica, Trichomonas vaginalis. NTZ, MTZ and ABZ were used as drug standards. Experimental evaluations revealed all of the new compounds (1-13) were active and showed strong activity against the three protozoa, particularly with E. histolytica where the IC50 values ranged between 3 and 69 nM. Overall, compounds 2, 5, 7, 8, 9, 11 and 12 stood out with values lower than 87 nM for all three protozoa, comparatively better than the reference drugs.

Molecular basis for benzimidazole resistance from a novel β-tubulin binding site model

Benzimidazole-2-carbamate derivatives (BzCs) are the most commonly used antiparasitic drugs for the treatment of protozoan and helminthic infections. BzCs inhibit the microtubule polymerization mechanism through binding selectively to the β-tubulin subunit in which mutations have been identified that lead to drug resistance. Currently, the lack of crystallographic structures of β-tubulin in parasites has limited the study of the binding site and the analysis of the resistance to BzCs. Recently, our research group has proposed a model to explain the interaction between the BzCs and a binding site in the β-tubulin. Herein, we report the homology models of two susceptible (Haemonchus contortus and Giardia intestinalis) parasites and one unsusceptible (Entamoeba histolytica) generated using the structure of the mammal Ovis aries, considered as a low susceptible organism, as a template. Additionally, the mechanism by which the principal single point mutations Phe167Tyr, Glu198Ala and Phe200Tyr could lead to resistance to BzCs is analyzed. Molecular docking and molecular dynamics studies were carried out in order to evaluate the models and the ligand-protein complexes' behaviors. This study represents a first attempt towards understanding, at the molecular level, the structural composition of β-tubulin in all organisms, also suggesting possible resistance mechanisms. Furthermore, these results support the importance of benzimidazole derivative optimization in order to design more potent and selective (less toxic) molecules for the treatment of parasitic diseases.

Synthesis and antiprotozoal activity of novel 2-{[2-(1H-imidazol-1-yl)ethyl]sulfanyl}-1H-benzimidazole derivatives

A series of 19 new 2-{[2-(1H-imidazol-1-yl)ethyl]sulfanyl}-1H-benzimidazole derivatives was synthesized starting from the properly substituted 1,2-phenylendiamine. These compounds have hydrogen or methyl at position 1; while hydrogen, chlorine, ethoxy or methoxycarbonyl group is at position 5 and/or 6. The novel compounds were tested against protozoa Trichomonas vaginalis, Giardia intestinalis and Entamoeba histolytica. Experimental evaluations revealed strong activity for all tested compounds, having IC50 values in the nanomolar range, which were even better than metronidazole, the drug of choice for these parasites.

Exploring the interplay of physicochemical properties, membrane permeability and giardicidal activity of some benzimidazole derivatives

This study evaluated the relationship between the physicochemical properties, membrane permeability and in vitro giardicidal activity of twenty nine benzimidazole derivatives (1-7n). The retention time data from reverse phase high performance chromatography (RP-HPLC) were used to estimate aqueous solubility and lipophilicity of these compounds. The apparent permeability was determined using Caco-2 cell monolayer. The calculation of some descriptors, such as Clog P, PSA, was performed using ACD labs software. For benzimidazole derivatives with NHCOOCH(3), CH(3), NH(2), SH and SCH(3) groups at the 2-position, a quadratic type of regression model was obtained with giardicidal activity and aqueous solubility or lipophilicity. On the other hand, giardicidal activity of 2-(trifluoromethyl)-1H-benzimidazole derivatives was influenced by lipophilicity, hydrogen bond donors and molecular volume but it was not determined by their apparent permeability in Caco-2 cell line.

Impact of compound alpha treatment in vivo on egg production by the liver fluke, Fasciola hepatica

Sheep infected with the triclabendazole-susceptible Cullompton isolate of Fasciola hepatica were treated with compound alpha at a dosage of 15 mg/kg at 12 weeks post-infection. Adult flukes were recovered from the bile ducts at 24h, 48 h and 72 h post-treatment (pt). They were processed for whole mount analysis, histology and transmission electron microscopy of the female reproductive system: specifically, the uterus, Mehlis' gland, ovary and vitellaria. As judged by the appearance of the uterus, normal egg production ceased within 24h of treatment; this phenomenon preceded significant changes to the other reproductive organs. Over the 3-day pt period, there was a progressive decline in the number of oogonia in the ovary, together with an increase in the number of eosinophilic and apoptotic oocytes and vacuolation and shrinkage of the ovarian tubules. There was a shift in the cell population within the vitelline follicles at 48 h pt, with relatively greater numbers of mature vitelline cells and fewer immature cells. The follicles were vacuolated and the shell globule clusters in the mature cells were disorganised. Greater disruption was seen at 72 h pt, with a reduction in the size of the follicles and rupture of cells, releasing their content into the lumen of the follicles. These histological observations were confirmed and extended at the TEM level. Thus, examination of electron micrographs showed that disruption of the shell globule clusters was evident at 48 h pt, which coincided with the start of the breakdown of the mature cells and of the nurse cell network. These degenerative changes were more conspicuous at 72 h pt. In the Mehlis' gland, shrinkage and vacuolation of the cells and their cytoplasmic extensions became progressively greater from 48 h to 72 h pt, and secretory activity declined. The changes in the reproductive organs and inhibition of egg production are put in context of the overall time-course of drug action.

The design and inhibitory profile of new benzimidazole derivatives against triosephosphate isomerase from Trypanosoma cruzi: a problem of residue motility

To develop a new set of compounds with inhibitory activity against the triosephosphate isomerase of Trypanosoma cruzi (TcTIM), a group of benzimidazole derivatives was studied using four different docking procedures. These docking procedures differ in the number and type of mobile residues considered in the analysis. As a result of this methodology, a clustered analysis of plausible candidate structures was produced. A different set of previously synthesized compounds was used to validate this analysis. The validation showed that the best results correspond to the docking procedure in which the residues near the hydrophobic pocket of the protein's interface were considered mobile. A binding site for the best candidates was identified. Residues Tyr103, Glu105 and Lys113, among others, are important for the binding of this kind of compound. Residue Tyr103 is different in the human TIM, thus establishing a key feature for the future design of selective inhibitors.

Comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) of some benzimidazole derivatives with trichomonicidal activity

Trichomonosis is a common sexually transmitted infectious disease linked to reproductive health complications. Recently, the benzimidazole nucleus has emerged as a promising scaffold to develop new trichomonicidal agents. Despite the fact that large amounts of experimental data have been accumulated over the past eight years, no quantitative studies have yet been reported on this class of compounds. In our effort to develop new antiparasitic benzimidazole derivatives, we report in this paper CoMFA and CoMSIA studies with an initial set of 70 benzimidazole derivatives with trichomonicidal activity. Four CoMFA models and eight CoMSIA models were generated; ten of these models had values of r(2) > 0.6 and q(2) > 0.5. The best CoMFA model had r(2) = 0.936 and q(2) = 0.634, and the best CoMSIA model had r(2) = 0.858 and q(2) = 0.642. These models were generated by using two conformer selection methodologies (minimum energy conformations and 3D similarity), and three charge types (Mulliken, Gasteiger-Hükel and electrostatic potential atomic charges). The putative active tautomers of 1H-benzimidazole derivatives were selected using 3D-QSAR calculations. All models were validated via an external test set with 13 molecules. The best models satisfied additional validation criteria. The contour maps generated show the most important features that a benzimidazole derivative should have for trichomonicidal activity; they also, suggest that substituents at the 2- and 6-positions are important in the generation of derivatives with strong activity.

Towards a systematic characterization of the antiprotozoal activity landscape of benzimidazole derivatives

Parasitic infections caused by the protozoa Trichomonas vaginalis and Giardia intestinalis still represent a major problem in developing countries. Despite the fact that benzimidazoles are promising compounds with activity against both protozoa, systematic studies to characterize and compare their structure-activity relationships (SAR) are limited. Herein, we report a systematic characterization of the SAR of 32 benzimidazoles with activity against T. vaginalis and G. intestinalis. The analysis was based on pairwise comparisons of the activity similarity and molecular similarity using different molecular representations. Radial, MACCS keys, TGD and piDAPH3 fingerprints were used to develop consensus models of the landscape. The landscapes contained continuous regions and activity cliffs. Two 'deep consensus activity cliffs' and several pairs of compounds in smooth regions of the SAR were identified in the landscape of T. vaginalis. In contrast, a number of 'apparent and shallow cliffs' were found for G. intestinalis. Several compounds active for both parasites showed similar SAR suggesting a common mechanism of action. We also identified pairs of structurally similar molecules with dramatic changes in selectivity. Results suggested that while substitution at position 2 on the benzimidazole moiety plays an important role in increasing the potency against both parasites, substitutions at positions 4-7 could influence selectivity. This study represents a first step towards the systematic characterization of the antiprotozoal activity landscape of benzimidazoles, and has direct implications in the future development of other types of quantitative models. The landscape of larger data sets with other biological endpoints can be analyzed using the general approaches used in this work.

Synthesis and biological activity of 2-(trifluoromethyl)-1H-benzimidazole derivatives against some protozoa and Trichinella spiralis

A series of 2-(trifluoromethyl)-1H-benzimidazole derivatives (1a-1i) were synthesized via Phillips cyclocondensation of a substituted 1,2-phenylenediamine and trifluoroacetic acid. The synthesized compounds were evaluated in vitro against various protozoan parasites: Giardia intestinalis, Entamoeba histolytica, Trichomonas vaginalis and Leishmania mexicana, and they showed nanomolar activities against the first three protozoa tested. The compounds were also tested in vitro and in vivo against the nematode Trichinella spiralis. Compounds 1b, 1c and 1e had the most desirable in vitro antiparasitic profile against all parasites studied. In the in vivo model against T. spiralis, compounds 1b and 1e showed good activity against the adult phase at 75 mg/Kg. However, against the muscle larvae stage, only compound 1f exhibited in vivo antiparasitic efficacy.

Anthelmintic activity of benzimidazole derivatives against Toxocara canis second-stage larvae and Hymenolepis nana adults

The anthelmintic activity of 11 benzimidazole derivatives (A1-A11) and 2 thioureides N,N'-disubstituted (B1-B2) was determined. Each compound and albendazole was tested in vitro against Toxocara canis larvae and in vivo against Hymenolepis nana adult. Compounds A1-A6 and B1-B2 were designed as albendazole prodrugs. Compounds A8-A11 were designed as direct analogues of A7, which had previously proved to be an effective agent against Fasciola hepatica. Results of the in vitro screening showed that A6 was more active than albendazole at 0.18 microM (relative mobility 40% and 80%, respectively). Whereas that the in vivo evaluation against H. nana, compounds A7-A11 demonstrated significant activity in terms of removing cestode adults in the range of 88-97%, displaying better efficacy than albendazole (83%).

Surface and internal tegumental changes in juvenile Fasciola hepatica following treatment in vivo with the experimental fasciolicide, compound alpha

Eight indoor-reared, crossbred sheep with no pre-exposure to Fasciola hepatica were infected, by oral gavage, with 200 metacercarial cysts of the triclabendazole-susceptible, Cullompton isolate of F. hepatica. Anthelmintic dosing occurred at 4 weeks post-infection using 15mg/kg compound alpha. Two treated sheep per time period were euthanized at 24h, 48h and 72h post-treatment with compound alpha. The two sheep from the control group were euthanized alongside the 24h alpha-treated sheep. Juvenile flukes were recovered from each of the sheeps' liver and processed for examination by electron microscopy. The surface morphology of the flukes' tegument was assessed using scanning electron microscopy (SEM). The ultrastructure of the tegumental syncytium and underlying tegumental cells and connections and somatic musculature were investigated using transmission electron microscopy (TEM). Both the SEM and TEM results revealed a level of disruption that increased with time, culminating at 72h with extensive tegumental loss and substantial degeneration of the cell bodies. The effects of compound alpha on the surface morphology were not particularly apparent until 48h post-treatment, when disruption included swelling and blebbing of the tegument. At 72h post-treatment, SEM revealed loss of the entire syncytial layer over large areas of the flukes. In the areas where the syncytium was lost and the basal lamina exposed, lesions of varying sizes had developed, revealing underlying tissues. Though minor forms of disruption to the ultrastructure of the syncytium were observed using TEM 24h post-treatment, it was at 48h post-treatment that substantial stress responses occurred. They included the presence of autophagic vacuoles and 'open' bodies at the apex of the syncytium and swelling of the basal infolds. The mitochondria within the syncytium and tegumental cells became progressively more disrupted over the three time periods and, by 72h post-treatment, they were frequently distorted and swollen in appearance, and contained severely swollen cristae. By 72h, the number of secretory bodies, particularly T1 bodies, had become significantly depleted in their respective cell bodies, cytoplasmic processes and in the tegumental syncytium. Both the circular and longitudinal muscle bundles were severely disrupted 72h post-treatment. They frequently contained a reduced number of muscle fibres and, in more severe instances, there was an absence of fibres altogether.

Biopharmaceutic evaluation of novel anthelmintic (1H-benzimidazol-5(6)-yl)carboxamide derivatives

Benzimidazole 2-carbamates, such as albendazole (ABZ) and mebendazole (MBZ), used for the treatment of helmintic infections, have low aqueous solubility and poor bioavailability, both of which lead to high interindividual variability when used for human systemic helmintiosis; therefore, it is necessary to search for new anthelmintics with better biopharmaceutical properties. In the present study the solubility, pKa, logP and apparent permeability in the Caco-2 cells system of four novel anthelmintic (1H-benzimidazol-5(6)-yl)carboxamide derivatives (compounds 1-4) with a 2-methylthyo group were evaluated. Also the pharmacokinetic parameters of compound 1 which in previous studies showed activity similar to ABZ against T. spirallis, was evaluated in BALB/c mice, as a representative molecule of the series. The novel anthelmintics, showed better solubility than ABZ in aqueous acid pH and in organic solvents. The logP, P(app) and Caco-2 data indicate that the 4 derivatives are highly permeable drugs, but it is possible that an efflux system could be involved in the transport of these compounds. Plasma levels of compound 1 and its sulfoxide (compound 5) were high after the first 5 min. This fact strongly suggests that compound 1 is rapidly metabolized in the small intestine. On the other hand, the sulfone metabolite (compound 6) levels were lower than those of compound 5. The half life and mean residence time (MRT) of compound 1 and its main metabolites indicate that their elimination is very rapid. More studies in mammalian species are necessary in order to understand the pharmacokinetic behavior of these novel compounds.

Molecular modeling of some 1H-benzimidazole derivatives with biological activity against Entamoeba histolytica: a comparative molecular field analysis study

Comparative molecular field analysis (CoMFA) was performed on a set of 1H-benzimidazole derivatives. Molecular modeling and 3D-QSAR were employed to determine the tautomeric form that would probably fit a target receptor in Entamoeba histolytica. CoMFA results suggest that the antiamoebic activity is favored with steric bulk at position 5 of the benzimidazole ring and low electron density on the group at position 2. To the best of our knowledge this is the first 3D-QSAR study performed for benzimidazoles as antiamoebic agents. The CoMFA models derived will be very valuable to design new and more potent compounds against E. histolytica.