CYP51 from Trypanosoma cruzi: a phyla-specific residue in the B' helix defines substrate preferences of sterol 14alpha-demethylase

Antifungal and Antiparasitic Activities of Metallocene-Containing Fluconazole Derivatives

The search for new anti-infectives based on metal complexes is gaining momentum. Among the different options taken by researchers, the one involving the use of organometallic complexes is probably the most successful one with a compound, namely, ferroquine, already in clinical trials against malaria. In this study, we describe the preparation and in-depth characterization of 10 new (organometallic) derivatives of the approved antifungal drug fluconazole. Our rationale is that the sterol 14α-demethylase is an enzyme part of the ergosterol biosynthesis route in Trypanosoma and is similar to the one in pathogenic fungi. To demonstrate our postulate, docking experiments to assess the binding of our compounds with the enzyme were also performed. Our compounds were then tested on a range of fungal strains and parasitic organisms, including the protozoan parasite Trypanosoma cruzi (T. cruzi) responsible for Chagas disease, an endemic disease in Latin America that ranks among some of the most prevalent parasitic diseases worldwide. Of high interest, the two most potent compounds of the study on T. cruzi that contain a ferrocene or cobaltocenium were found to be harmless for an invertebrate animal model, namely, Caenorhabditis elegans (C. elegans), without affecting motility, viability, or development.

Control Phytophagous Nematodes By Engineering Phytosterol Dealkylation Caenorhabditis elegans as a Model

Plant-parasitic nematodes ingest and convert host phytosterols via dealkylation to cholesterol for both structural and hormonal requirements. The insect 24-dehydrocholesterol reductase (DHCR24) was shown in vitro as a committed enzyme in the dealkylation via chemical blocking. However, an increased brood size and ovulation rate, instead compromised development, were observed in the engineered nematode Caenorhabditis elegans where the DHCR24 gene was knocked down, indicating the relationship between DHCR24 and dealkylation and their function in nematodes remains illusive. In this study, a defect in C. elegans DHCR24 causes impaired growth of the nematode with sitosterol (a major component of phytosterols) as a sole sterol source. Plant sterols with rationally designed structure (null substrates for dealkylation) can't be converted to cholesterol in wild-type worms, and their development was completely halted. This study underpins the essential function of DHCR24 in nematodes and would be beneficial for the development of novel nematocidal strategies.

Structural modeling of cytochrome P450 51 from a deep-sea fish points to a novel structural feature in other CYP51s

Cytochromes P450 (CYP), enzymes involved in the metabolism of endogenous and xenobiotic substrates, provide an excellent model system to study how membrane proteins with unique functions have catalytically adapted through evolution. Molecular adaptation of deep-sea proteins to high hydrostatic pressure remains poorly understood. Herein, we have characterized recombinant cytochrome P450 sterol 14α-demethylase (CYP51), an essential enzyme of cholesterol biosynthesis, from an abyssal fish species, Coryphaenoides armatus. C. armatus CYP51 was heterologously expressed in Escherichia coli following N-terminal truncation and purified to homogeneity. Recombinant C. armatus CYP51 bound its sterol substrate lanosterol giving a Type I binding spectra (KD 15 μM) and catalyzed lanosterol 14α-demethylation turnover at 5.8 nmol/min/nmol P450. C. armatus CYP51 also bound the azole antifungals ketoconazole (KD 0.12 μM) and propiconazole (KD 0.54 μM) as determined by Type II absorbance spectra. Comparison of C. armatus CYP51 primary sequence and modeled structures with other CYP51s identified amino acid substitutions that may confer an ability to function under pressures of the deep sea and revealed heretofore undescribed internal cavities in human and other non-deep sea CYP51s. The functional significance of these cavities is not known. PROLOGUE: This paper is dedicated in memory of Michael Waterman and Tsuneo Omura, who as good friends and colleagues enriched our lives. They continue to inspire us.

Relaxed Substrate Requirements of Sterol 14α-Demethylase from Naegleria fowleri Are Accompanied by Resistance to Inhibition

Naegleria fowleri is the protozoan pathogen that causes primary amoebic meningoencephalitis (PAM), with the death rate exceeding 97%. The amoeba makes sterols and can be targeted by sterol biosynthesis inhibitors. Here, we characterized N. fowleri sterol 14-demethylase, including catalytic properties and inhibition by clinical antifungal drugs and experimental substituted azoles with favorable pharmacokinetics and low toxicity. None of them inhibited the enzyme stoichiometrically. The highest potencies were displayed by posaconazole (IC₅₀ = 0.69 μM) and two of our compounds (IC₅₀ = 1.3 and 0.35 μM). Because both these compounds penetrate the brain with concentrations reaching minimal inhibitory concentration (MIC) values in an N. fowleri cellular assay, we report them as potential drug candidates for PAM. The 2.1 Å crystal structure, in complex with the strongest inhibitor, provides an explanation connecting the enzyme weaker substrate specificity with lower sensitivity to inhibition. It also provides insight into the enzyme/ligand molecular recognition process and suggests directions for the design of more potent inhibitors.

Transformation of berberine to its demethylated metabolites by the CYP51 enzyme in the gut microbiota

Berberine (BBR) is an isoquinoline alkaloid extracted from Coptis chinensis that improves diabetes, hyperlipidemia and inflammation. Due to the low oral bioavailability of BBR, its mechanism of action is closely related to the gut microbiota. This study focused on the CYP51 enzyme of intestinal bacteria to elucidate a new mechanism of BBR transformation by demethylation in the gut microbiota through multiple analytical techniques. First, the docking of BBR and CYP51 was performed; then, the pharmacokinetics of BBR was determined in ICR mice in vivo, and the metabolism of BBR in the liver, kidney, gut microbiota and single bacterial strains was examined in vitro. Moreover, 16S rRNA analysis of ICR mouse feces indicated the relationship between BBR and the gut microbiota. Finally, recombinant E. coli containing cyp51 gene was constructed and the CYP51 enzyme lysate was induced to express. The metabolic characteristics of BBR were analyzed in the CYP51 enzyme lysate system. The results showed that CYP51 in the gut microbiota could bind stably with BBR, and the addition of voriconazole (a specific inhibitor of CYP51) slowed down the metabolism of BBR, which prevented the production of the demethylated metabolites thalifendine and berberrubine. This study demonstrated that CYP51 promoted the demethylation of BBR and enhanced its intestinal absorption, providing a new method for studying the metabolic transformation mechanism of isoquinoline alkaloids in vivo.

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The demethylation metabolism of natural drugs difficult to absorb through the gut microbiota was first reported.

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Six different methods were presented to explain the metabolic mechanism of natural isoquinoline alkaloids.

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The findings provided a new idea for studying the mechanism of drug metabolism of gut microbiota.

Concerning P450 Evolution: Structural Analyses Support Bacterial Origin of Sterol 14α-Demethylases

Sterol biosynthesis, primarily associated with eukaryotic kingdoms of life, occurs as an abbreviated pathway in the bacterium Methylococcus capsulatus. Sterol 14α-demethylation is an essential step in this pathway and is catalyzed by cytochrome P450 51 (CYP51). In M. capsulatus, the enzyme consists of the P450 domain naturally fused to a ferredoxin domain at the C-terminus (CYP51fx). The structure of M. capsulatus CYP51fx was solved to 2.7 Å resolution and is the first structure of a bacterial sterol biosynthetic enzyme. The structure contained one P450 molecule per asymmetric unit with no electron density seen for ferredoxin. We connect this with the requirement of P450 substrate binding in order to activate productive ferredoxin binding. Further, the structure of the P450 domain with bound detergent (which replaced the substrate upon crystallization) was solved to 2.4 Å resolution. Comparison of these two structures to the CYP51s from human, fungi, and protozoa reveals strict conservation of the overall protein architecture. However, the structure of an "orphan" P450 from nonsterol-producing Mycobacterium tuberculosis that also has CYP51 activity reveals marked differences, suggesting that loss of function in vivo might have led to alterations in the structural constraints. Our results are consistent with the idea that eukaryotic and bacterial CYP51s evolved from a common cenancestor and that early eukaryotes may have recruited CYP51 from a bacterial source. The idea is supported by bioinformatic analysis, revealing the presence of CYP51 genes in >1,000 bacteria from nine different phyla, >50 of them being natural CYP51fx fusion proteins.

The cholesterol synthesis enzyme lanosterol 14α-demethylase is post-translationally regulated by the E3 ubiquitin ligase MARCH6

Cholesterol synthesis is a tightly controlled pathway, with over 20 enzymes involved. Each of these enzymes can be distinctly regulated, helping to fine-tune the production of cholesterol and its functional intermediates. Several enzymes are degraded in response to increased sterol levels, whilst others remain stable. We hypothesised that an enzyme at a key branch point in the pathway, lanosterol 14α-demethylase (LDM) may be post-translationally regulated. Here, we show that the preceding enzyme, lanosterol synthase is stable, whilst LDM is rapidly degraded. Surprisingly, this degradation is not triggered by sterols. However, the E3 ubiquitin ligase membrane-associated ring-CH-type finger 6 (MARCH6), known to control earlier rate-limiting steps in cholesterol synthesis, also control levels of LDM and the terminal cholesterol synthesis enzyme, 24-dehydrocholesterol reductase. Our work highlights MARCH6 as the first example of an E3 ubiquitin ligase that targets multiple steps in a biochemical pathway and indicates new facets in the control of cholesterol synthesis.

Novel structural CYP51 mutation in Trypanosoma cruzi associated with multidrug resistance to CYP51 inhibitors and reduced infectivity

Ergosterol biosynthesis inhibitors, such as posaconazole and ravuconazole, have been proposed as drug candidates for Chagas disease, a neglected infectious tropical disease caused by the protozoan parasite Trypanosoma cruzi. To understand better the mechanism of action and resistance to these inhibitors, a clone of the T. cruzi Y strain was cultured under intermittent and increasing concentrations of ravuconazole until phenotypic stability was achieved. The ravuconazole-selected clone exhibited loss in fitness in vitro when compared to the wild-type parental clone, as observed in reduced invasion capacity and slowed population growth in both mammalian and insect stages of the parasite. In drug activity assays, the resistant clone was above 300-fold more tolerant to ravuconazole than the sensitive parental clone, when the half-maximum effective concentration (EC₅₀) was considered. The resistant clones also showed reduced virulence in vivo, when compared to parental sensitive clones. Cross-resistance to posaconazole and other CYP51 inhibitors, but not to other antichagasic drugs that act independently of CYP51, such as benznidazole and nifurtimox, was also observed. A novel amino acid residue change, T297M, was found in the TcCYP51 gene in the resistant but not in the sensitive clones. The structural effects of the T297M, and of the previously described P355S residue changes, were modelled to understand their impact on interaction with CYP51 inhibitors.

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A ravuconazole-resistant T. cruzi clone presented reduced in vitro and in vivo fitness.

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The ravuconazole-resistant clone presented cross-resistance to other CYP51 inhibitors.

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There was no cross-resistance to benznidazole and nifurtimox.

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Resistance is associated with a novel structural mutation in the TcCYP51 protein.

Searching for drugs for Chagas disease, leishmaniasis and schistosomiasis: a review

Chagas disease, leishmaniasis and schistosomiasis are neglected diseases (NDs) and are a considerable global challenge. Despite the huge number of people infected, NDs do not create interest from pharmaceutical companies because the associated revenue is generally low. Most of the research on these diseases has been conducted in academic institutions. The chemotherapeutic armamentarium for NDs is scarce and inefficient and better drugs are needed. Researchers have found some promising potential drug candidates using medicinal chemistry and computational approaches. Most of these compounds are synthetic but some are from natural sources or are semi-synthetic. Drug repurposing or repositioning has also been greatly stimulated for NDs. This review considers some potential drug candidates and provides details of their design, discovery and activity.

A new chemotype with promise against Trypanosoma cruzi

Pyridyl benzamide 2 is a potent inhibitor of Trypanosoma cruzi, but not other protozoan parasites, and had a selectivity-index of ≥10. The initial structure-activity relationship (SAR) indicates that benzamide and sulfonamide functional groups, and N-methylpiperazine and sterically unhindered 3-pyridyl substructures are required for high activity against T. cruzi. Compound 2 and its active analogs had low to moderate metabolic stabilities in human and mouse liver microsomes.

Advances in preclinical approaches to Chagas disease drug discovery

Introduction: Chagas disease affects 8-10 million people worldwide, mainly in Latin America. The current therapy for Chagas disease is limited to nifurtimox and benznidazole, which are effective in treating only the acute phase of the disease but with severe side effects. Therefore, there is an unmet need for new drugs and for the exploration of innovative approaches which may lead to the discovery of new effective and safe drugs for its treatment. Areas covered: The authors report and discuss recent approaches including structure-based design that have led to the discovery of new promising small molecule candidates for Chagas disease which affect prime targets that intervene in the sterol pathway of T. cruzi. Other trypanosome targets, phenotypic screening, the use of artificial intelligence and the challenges with Chagas disease drug discovery are also discussed. Expert opinion: The application of recent scientific innovations to the field of Chagas disease have led to the discovery of new promising drug candidates for Chagas disease. Phenotypic screening brought new hits and opportunities for drug discovery. Artificial intelligence also has the potential to accelerate drug discovery in Chagas disease and further research into this is warranted.

Unpacking the Pathogen Box-An Open Source Tool for Fighting Neglected Tropical Disease

The Pathogen Box is a 400-strong collection of drug-like compounds, selected for their potential against several of the world's most important neglected tropical diseases, including trypanosomiasis, leishmaniasis, cryptosporidiosis, toxoplasmosis, filariasis, schistosomiasis, dengue virus and trichuriasis, in addition to malaria and tuberculosis. This library represents an ensemble of numerous successful drug discovery programmes from around the globe, aimed at providing a powerful resource to stimulate open source drug discovery for diseases threatening the most vulnerable communities in the world. This review seeks to provide an in-depth analysis of the literature pertaining to the compounds in the Pathogen Box, including structure-activity relationship highlights, mechanisms of action, related compounds with reported activity against different diseases, and, where appropriate, discussion on the known and putative targets of compounds, thereby providing context and increasing the accessibility of the Pathogen Box to the drug discovery community.

NewN-phenylacetamide-incorporated 1,2,3-triazoles: [Et3NH][OAc]-mediated efficient synthesis and biological evaluation

A facile, highly efficient, and greener method for the synthesis of new 1,4-disubstituted-1,2,3-triazoles was conducted using [Et₃NH][OAc] as a medium by the implementation of ultrasound irradiation via click chemistry, affording excellent yields. The present synthetic method exhibited numerous advantages such as mild reaction conditions, excellent product yields, minimal chemical waste, operational simplicity, shorter reaction time, and a wide range of substrate scope. The synthesized compounds were further evaluated for in vitro antifungal activity against five fungal strains, and some of the compounds displayed equivalent or greater potency than the standard drug. A molecular docking study against the modelled three-dimensional structure of cytochrome P450 lanosterol 14α-demethylase was also performed to understand the binding affinity and binding interactions of the enzyme. Furthermore, the synthesized compounds were evaluated for DPPH radical scavenging activity and antitubercular activity against Mycobacterium tuberculosis H37Rv strain.

A facile, highly efficient, and greener method for the synthesis of new 1,4-disubstituted-1,2,3-triazoles was conducted using [Et₃NH][OAc] as a medium by the implementation of ultrasound irradiation via click chemistry, affording excellent yields.

CYP51 as drug targets for fungi and protozoan parasites: past, present and future

The efficiency of treatment of human infections with the unicellular eukaryotic pathogens such as fungi and protozoa remains deeply unsatisfactory. For example, the mortality rates from nosocomial fungemia in critically ill, immunosuppressed or post-cancer patients often exceed 50%. A set of six systemic clinical azoles [sterol 14α-demethylase (CYP51) inhibitors] represents the first-line antifungal treatment. All these drugs were discovered empirically, by monitoring their effects on fungal cell growth, though it had been proven that they kill fungal cells by blocking the biosynthesis of ergosterol in fungi at the stage of 14α-demethylation of the sterol nucleus. This review briefs the history of antifungal azoles, outlines the situation with the current clinical azole-based drugs, describes the attempts of their repurposing for treatment of human infections with the protozoan parasites that, similar to fungi, also produce endogenous sterols, and discusses the most recently acquired knowledge on the CYP51 structure/function and inhibition. It is our belief that this information should be helpful in shifting from the traditional phenotypic screening to the actual target-driven drug discovery paradigm, which will rationalize and substantially accelerate the development of new, more efficient and pathogen-oriented CYP51 inhibitors.

Sterol 14α-Demethylase Structure-Based Optimization of Drug Candidates for Human Infections with the Protozoan Trypanosomatidae

Sterol 14α-demethylases (CYP51) are cytochrome P450 enzymes essential for sterol biosynthesis in eukaryotes and therapeutic targets for antifungal azoles. Multiple attempts to repurpose antifungals for treatment of human infections with protozoa (Trypanosomatidae) have been undertaken, yet so far none of them have revealed sufficient efficacy. VNI and its derivative VFV are two potent experimental inhibitors of Trypanosomatidae CYP51, effective in vivo against Chagas disease, visceral leishmaniasis, and sleeping sickness and currently under consideration as antiprotozoal drug candidates. However, VNI is less potent against Leishmania and drug-resistant strains of Trypanosoma cruzi and VFV, while displaying a broader spectrum of antiprotozoal activity, and is metabolically less stable. In this work we have designed, synthesized, and characterized a set of close analogues and identified two new compounds (7 and 9) that exceed VNI/VFV in their spectra of antiprotozoal activity, microsomal stability, and pharmacokinetics (tissue distribution in particular) and, like VNI/VFV, reveal no acute toxicity.

Binding of a physiological substrate causes large-scale conformational reorganization in cytochrome P450 51

Sterol 14α-demethylases (CYP51s) are phylogenetically the most conserved cytochromes P450, and their three-step reaction is crucial for biosynthesis of sterols and serves as a leading target for clinical and agricultural antifungal agents. The structures of several (bacterial, protozoan, fungal, and human) CYP51 orthologs, in both the ligand-free and inhibitor-bound forms, have been determined and have revealed striking similarity at the secondary and tertiary structural levels, despite having low sequence identity. Moreover, in contrast to many of the substrate-promiscuous, drug-metabolizing P450s, CYP51 structures do not display substantial rearrangements in their backbones upon binding of various inhibitory ligands, essentially representing a snapshot of the ligand-free sterol 14α-demethylase. Here, using the obtusifoliol-bound I105F variant of Trypanosoma cruzi CYP51, we report that formation of the catalytically competent complex with the physiological substrate triggers a large-scale conformational switch, dramatically reshaping the enzyme active site (3.5-6.0 Å movements in the FG arm, HI arm, and helix C) in the direction of catalysis. Notably, our X-ray structural analyses revealed that the substrate channel closes, the proton delivery route opens, and the topology and electrostatic potential of the proximal surface reorganize to favor interaction with the electron-donating flavoprotein partner, NADPH-cytochrome P450 reductase. Site-directed mutagenesis of the amino acid residues involved in these events revealed a key role of active-site salt bridges in contributing to the structural dynamics that accompanies CYP51 function. Comparative analysis of apo-CYP51 and its sterol-bound complex provided key conceptual insights into the molecular mechanisms of CYP51 catalysis, functional conservation, lineage-specific substrate complementarity, and druggability differences.

Synthesis and Biological Activity of Sterol 14α-Demethylase and Sterol C24-Methyltransferase Inhibitors

Sterol 14α-demethylase (SDM) is essential for sterol biosynthesis and is the primary molecular target for clinical and agricultural antifungals. SDM has been demonstrated to be a valid drug target for antiprotozoal therapies, and much research has been focused on using SDM inhibitors to treat neglected tropical diseases such as human African trypanosomiasis (HAT), Chagas disease, and leishmaniasis. Sterol C24-methyltransferase (24-SMT) introduces the C24-methyl group of ergosterol and is an enzyme found in pathogenic fungi and protozoa but is absent from animals. This difference in sterol metabolism has the potential to be exploited in the development of selective drugs that specifically target 24-SMT of invasive fungi or protozoa without adversely affecting the human or animal host. The synthesis and biological activity of SDM and 24-SMT inhibitors are reviewed herein.

The Tetrazole VT-1161 Is a Potent Inhibitor of Trichophyton rubrum through Its Inhibition of T. rubrum CYP51

Prior to characterization of antifungal inhibitors that target CYP51, Trichophyton rubrum CYP51 was expressed in Escherichia coli, purified, and characterized. T. rubrum CYP51 bound lanosterol, obtusifoliol, and eburicol with similar affinities (dissociation constant [K_d ] values, 22.7, 20.3, and 20.9 μM, respectively) but displayed substrate specificity, insofar as only eburicol was demethylated in CYP51 reconstitution assays (turnover number, 1.55 min^-1; K_m value, 2 μM). The investigational agent VT-1161 bound tightly to T. rubrum CYP51 (K_d = 242 nM) with an affinity similar to that of clotrimazole, fluconazole, ketoconazole, and voriconazole (K_d values, 179, 173, 312, and 304 nM, respectively) and with an affinity lower than that of itraconazole (K_d = 53 nM). Determinations of 50% inhibitory concentrations (IC₅₀s) using 0.5 μM CYP51 showed that VT-1161 was a tight-binding inhibitor of T. rubrum CYP51 activity, yielding an IC₅₀ of 0.14 μM, whereas itraconazole, fluconazole, and ketoconazole had IC₅₀s of 0.26, 0.4, and 0.6 μM, respectively. When the activity of VT-1161 was tested against 34 clinical isolates, VT-1161 was a potent inhibitor of T. rubrum growth, with MIC₅₀, MIC₉₀, and geometric mean MIC values of ≤0.03, 0.06, and 0.033 μg ml^-1, respectively. With its selectivity versus human CYP51 and drug-metabolizing cytochrome P450s having already been established, VT-1161 should prove to be safe and effective in combating T. rubrum infections in patients.

Crystal Structure of the New Investigational Drug Candidate VT-1598 in Complex with Aspergillus fumigatus Sterol 14α-Demethylase Provides Insights into Its Broad-Spectrum Antifungal Activity

Within the past few decades, the incidence and complexity of human fungal infections have increased, and therefore, the need for safer and more efficient, broad-spectrum antifungal agents is high. In the study described here, we characterized the new tetrazole-based drug candidate VT-1598 as an inhibitor of sterol 14α-demethylase (CYP51B) from the filamentous fungus Aspergillus fumigatus VT-1598 displayed a high affinity of binding to the enzyme in solution (dissociation constant, 13 ± 1 nM) and in the reconstituted enzymatic reaction was revealed to have an inhibitory potency stronger than the potencies of all other simultaneously tested antifungal drugs, including fluconazole, voriconazole, ketoconazole, and posaconazole. The X-ray structure of the VT-1598/A. fumigatus CYP51 complex was determined and depicts the distinctive binding mode of the inhibitor in the enzyme active site, suggesting the molecular basis of the improved drug potency and broad-spectrum antifungal activity. These data show the formation of an optimized hydrogen bond between the phenoxymethyl oxygen of VT-1598 and the imidazole ring nitrogen of His374, the CYP51 residue that is highly conserved across fungal pathogens and fungus specific. Comparative structural analysis of A. fumigatus CYP51/voriconazole and Candida albicans CYP51/VT-1161 complexes supports the role of H bonding in fungal CYP51/inhibitor complexes and emphasizes the importance of an optimal distance between this interaction and the inhibitor-heme iron interaction. Cellular experiments using two A. fumigatus strains (strains 32820 and 1022) displayed a direct correlation between the effects of the drugs on CYP51B activity and fungal growth inhibition, indicating the noteworthy anti-A. fumigatus potency of VT-1598 and confirming its promise as a broad-spectrum antifungal agent.

Antitrypanosomal and antileishmanial activity of prenyl-1,2,3-triazoles

A series of prenyl 1,2,3-triazoles were prepared from isoprenyl azides and different alkynes. The dipolar cycloaddition reaction provided exclusively primary azide products as regioisomeric mixtures that were separated by column chromatography and fully characterized. Most of the compounds displayed antiparasitic activity against Trypanosoma cruzi and Leishmania donovani. The most active compounds were assayed as potential TcCYP51 inhibitors.

Structural analyses of Candida albicans sterol 14α-demethylase complexed with azole drugs address the molecular basis of azole-mediated inhibition of fungal sterol biosynthesis

With some advances in modern medicine (such as cancer chemotherapy, broad exposure to antibiotics, and immunosuppression), the incidence of opportunistic fungal pathogens such as Candida albicans has increased. Cases of drug resistance among these pathogens have become more frequent, requiring the development of new drugs and a better understanding of the targeted enzymes. Sterol 14α-demethylase (CYP51) is a cytochrome P450 enzyme required for biosynthesis of sterols in eukaryotic cells and is the major target of clinical drugs for managing fungal pathogens, but some of the CYP51 key features important for rational drug design have remained obscure. We report the catalytic properties, ligand-binding profiles, and inhibition of enzymatic activity of C. albicans CYP51 by clinical antifungal drugs that are used systemically (fluconazole, voriconazole, ketoconazole, itraconazole, and posaconazole) and topically (miconazole and clotrimazole) and by a tetrazole-based drug candidate, VT-1161 (oteseconazole: (R)-2-(2,4-difluorophenyl)-1,1-difluoro-3-(1H-tetrazol-1-yl)-1-(5-(4-(2,2,2-trifluoroethoxy)phenyl)pyridin-2-yl)propan-2-ol). Among the compounds tested, the first-line drug fluconazole was the weakest inhibitor, whereas posaconazole and VT-1161 were the strongest CYP51 inhibitors. We determined the X-ray structures of C. albicans CYP51 complexes with posaconazole and VT-1161, providing a molecular mechanism for the potencies of these drugs, including the activity of VT-1161 against Candida krusei and Candida glabrata, pathogens that are intrinsically resistant to fluconazole. Our comparative structural analysis outlines phylum-specific CYP51 features that could direct future rational development of more efficient broad-spectrum antifungals.

Challenges in the chemotherapy of Chagas disease: Looking for possibilities related to the differences and similarities between the parasite and host

Almost 110 years after the first studies by Dr. Carlos Chagas describing an infectious disease that was named for him, Chagas disease remains a neglected illness and a death sentence for infected people in poor countries. This short review highlights the enormous need for new studies aimed at the development of novel and more specific drugs to treat chagasic patients. The primary tool for facing this challenge is deep knowledge about the similarities and differences between the parasite and its human host.

The Investigational Drug VT-1129 Is a Highly Potent Inhibitor of Cryptococcus Species CYP51 but Only Weakly Inhibits the Human Enzyme

Cryptococcosis is a life-threatening disease often associated with HIV infection. Three Cryptococcus species CYP51 enzymes were purified and catalyzed the 14α-demethylation of lanosterol, eburicol, and obtusifoliol. The investigational agent VT-1129 bound tightly to all three CYP51 proteins (dissociation constant [Kd] range, 14 to 25 nM) with affinities similar to those of fluconazole, voriconazole, itraconazole, clotrimazole, and ketoconazole (Kd range, 4 to 52 nM), whereas VT-1129 bound weakly to human CYP51 (Kd, 4.53 μM). VT-1129 was as effective as conventional triazole antifungal drugs at inhibiting cryptococcal CYP51 activity (50% inhibitory concentration [IC50] range, 0.14 to 0.20 μM), while it only weakly inhibited human CYP51 activity (IC50, ∼600 μM). Furthermore, VT-1129 weakly inhibited human CYP2C9, CYP2C19, and CYP3A4, suggesting a low drug-drug interaction potential. Finally, the cellular mode of action for VT-1129 was confirmed to be CYP51 inhibition, resulting in the depletion of ergosterol and ergosta-7-enol and the accumulation of eburicol, obtusifolione, and lanosterol/obtusifoliol in the cell membranes.

Human sterol 14α-demethylase as a target for anticancer chemotherapy: towards structure-aided drug design

Rapidly multiplying cancer cells synthesize greater amounts of cholesterol to build their membranes. Cholesterol-lowering drugs (statins) are currently in clinical trials for anticancer chemotherapy. However, given at higher doses, statins cause serious side effects by inhibiting the formation of other biologically important molecules derived from mevalonate. Sterol 14α-demethylase (CYP51), which acts 10 steps downstream, is potentially a more specific drug target because this portion of the pathway is fully committed to cholesterol production. However, screening a variety of commercial and experimental inhibitors of microbial CYP51 orthologs revealed that most of them (including all clinical antifungals) weakly inhibit human CYP51 activity, even if they display high apparent spectral binding affinity. Only one relatively potent compound, (R)-N-(1-(3,4'-difluorobiphenyl-4-yl)-2-(1H-imidazol-1-yl)ethyl)-4-(5-phenyl-1,3,4-oxadiazol-2-yl)benzamide (VFV), was identified. VFV has been further tested in cellular experiments and found to decrease proliferation of different cancer cell types. The crystal structures of human CYP51-VFV complexes (2.0 and 2.5 Å) both display a 2:1 inhibitor/enzyme stoichiometry, provide molecular insights regarding a broader substrate profile, faster catalysis, and weaker susceptibility of human CYP51 to inhibition, and outline directions for the development of more potent inhibitors.

Azole Antifungal Sensitivity of Sterol 14α-Demethylase (CYP51) and CYP5218 from Malassezia globosa

Malassezia globosa cytochromes P450 CYP51 and CYP5218 are sterol 14α-demethylase (the target of azole antifungals) and a putative fatty acid metabolism protein (and a potential azole drug target), respectively. Lanosterol, eburicol and obtusifoliol bound to CYP51 with K_d values of 32, 23 and 28 μM, respectively, catalyzing sterol 14α-demethylation with respective turnover numbers of 1.7 min⁻¹, 5.6 min⁻¹ and 3.4 min⁻¹. CYP5218 bound a range of fatty acids with linoleic acid binding strongest (K_d 36 μM), although no metabolism could be detected in reconstitution assays or role in growth on lipids. Clotrimazole, fluconazole, itraconazole, ketoconazole, voriconazole and ketaminazole bound tightly to CYP51 (K_d ≤ 2 to 11 nM). In contrast, fluconazole did not bind to CYP5218, voriconazole and ketaminazole bound weakly (K_d ~107 and ~12 μM), whereas ketoconazole, clotrimazole and itraconazole bound strongest to CYP5218 (K_d ~1.6, 0.5 and 0.4 μM) indicating CYP5218 to be only a secondary target of azole antifungals. IC₅₀ determinations confirmed M. globosa CYP51 was strongly inhibited by azole antifungals (0.15 to 0.35 μM). MIC₁₀₀ studies showed itraconazole should be considered as an alternative to ketoconazole given the potency and safety profiles and the CYP51 assay system can be used in structure-activity studies in drug development.

Design, synthesis and antitrypanosomal activity of some nitrofurazone 1,2,4-triazolic bioisosteric analogues

Chagas disease, caused by Trypanosoma cruzi, is a parasitosis that predominates in Latin America. It is estimated that 25 million people are under the risk of infection and, in 2008, more than 10 thousand deaths were registered. The only two drugs available in the therapeutics, nifurtimox and benznidazole, showed to be more effective in the acute phase of the disease. However, there is no standard treatment protocol effective for the chronic phase. Nitrofurazone (NF), an antimicrobial drug, has activity against T. cruzi, although being toxic. Considering the need for new antichagasic drugs, the existence of promising new therapeutic targets, as 14α-sterol demethylase and cruzain, and employing the bioisosterism and molecular hybridization approaches, four novel compounds were synthesized, characterized by melting point range, elemental analysis, IR and NMR spectroscopy. The compounds were tested against T. cruzi amastigotes in infected U2OS cells. All compounds showed selectivity towards T. cruzi and showed trypanomicidal activity in low micromolar range. The compound 3 showed potency similar to benznidazole, but lower efficacy. These results highlight the importance of the 1,2,4-triazole, thiosemicarbazonic and nitro group moieties for designing new efficient compounds, potentially for the chronic phase of Chagas disease.

Current drug therapy and pharmaceutical challenges for Chagas disease

One of the most significant health problems in the American continent in terms of human health, and socioeconomic impact is Chagas disease, caused by the protozoan parasite Trypanosoma cruzi. Infection was originally transmitted by reduviid insects, congenitally from mother to fetus, and by oral ingestion in sylvatic/rural environments, but blood transfusions, organ transplants, laboratory accidents, and sharing of contaminated syringes also contribute to modern day transmission. Likewise, Chagas disease used to be endemic from Northern Mexico to Argentina, but migrations have earned it global. The parasite has a complex life cycle, infecting different species, and invading a variety of cells - including muscle and nerve cells of the heart and gastrointestinal tract - in the mammalian host. Human infection outcome is a potentially fatal cardiomyopathy, and gastrointestinal tract lesions. In absence of a vaccine, vector control and treatment of patients are the only tools to control the disease. Unfortunately, the only drugs now available for Chagas' disease, Nifurtimox and Benznidazole, are relatively toxic for adult patients, and require prolonged administration. Benznidazole is the first choice for Chagas disease treatment due to its lower side effects than Nifurtimox. However, different strategies are being sought to overcome Benznidazole's toxicity including shorter or intermittent administration schedules-either alone or in combination with other drugs. In addition, a long list of compounds has shown trypanocidal activity, ranging from natural products to specially designed molecules, re-purposing drugs commercialized to treat other maladies, and homeopathy. In the present review, we will briefly summarize the upturns of current treatment of Chagas disease, discuss the increment on research and scientific publications about this topic, and give an overview of the state-of-the-art research aiming to produce an alternative medication to treat T. cruzi infection.

A Multilayer Network Approach for Guiding Drug Repositioning in Neglected Diseases

Drug development for neglected diseases has been historically hampered due to lack of market incentives. The advent of public domain resources containing chemical information from high throughput screenings is changing the landscape of drug discovery for these diseases. In this work we took advantage of data from extensively studied organisms like human, mouse, E. coli and yeast, among others, to develop a novel integrative network model to prioritize and identify candidate drug targets in neglected pathogen proteomes, and bioactive drug-like molecules. We modeled genomic (proteins) and chemical (bioactive compounds) data as a multilayer weighted network graph that takes advantage of bioactivity data across 221 species, chemical similarities between 1.7 10⁵ compounds and several functional relations among 1.67 10⁵ proteins. These relations comprised orthology, sharing of protein domains, and shared participation in defined biochemical pathways. We showcase the application of this network graph to the problem of prioritization of new candidate targets, based on the information available in the graph for known compound-target associations. We validated this strategy by performing a cross validation procedure for known mouse and Trypanosoma cruzi targets and showed that our approach outperforms classic alignment-based approaches. Moreover, our model provides additional flexibility as two different network definitions could be considered, finding in both cases qualitatively different but sensible candidate targets. We also showcase the application of the network to suggest targets for orphan compounds that are active against Plasmodium falciparum in high-throughput screens. In this case our approach provided a reduced prioritization list of target proteins for the query molecules and showed the ability to propose new testable hypotheses for each compound. Moreover, we found that some predictions highlighted by our network model were supported by independent experimental validations as found post-facto in the literature.

Neglected tropical diseases are human infectious diseases that are often associated with poverty. Historically, lack of interest from the pharmaceutical industry resulted in the lack of good drugs to combat the majority of the pathogens that cause these diseases. Recently, the availability of open chemical information has increased with the advent of public domain chemical resources and the release of data from high throughput screening assays. Our aim in this work was to make use of data from extensively studied organisms like human, mouse, E. coli and yeast, among others, to prioritize and identify candidate drug targets in neglected pathogen proteomes, and drug-like bioactive molecules to foster drug development against neglected diseases. Our approach to the problem relied on applying bioinformatics and computational biology strategies to model large datasets spanning complete proteomes and extensive chemical information from publicly available sources. As a result, we were able to prioritize drug targets and identify potential targets for orphan bioactive drugs.

Synergistic Interactions of Eugenol-tosylate and Its Congeners with Fluconazole against Candida albicans

We previously reported the antifungal properties of a monoterpene phenol “Eugenol” against different Candida strains and have observed that the addition of methyl group to eugenol drastically increased its antimicrobial potency. Based on the results and the importance of medicinal synthetic chemistry, we synthesized eugenol-tosylate and its congeners (E1-E6) and tested their antifungal activity against different clinical fluconazole (FLC)- susceptible and FLC- resistant C. albicans isolates alone and in combination with FLC by determining fractional inhibitory concentration indices (FICIs) and isobolograms calculated from microdilution assays. Minimum inhibitory concentration (MIC) results confirmed that all the tested C. albicans strains were variably susceptible to the semi-synthetic derivatives E1-E6, with MIC values ranging from 1–62 μg/ml. The test compounds in combination with FLC exhibited either synergy (36%), additive (41%) or indifferent (23%) interactions, however, no antagonistic interactions were observed. The MICs of FLC decreased 2–9 fold when used in combination with the test compounds. Like their precursor eugenol, all the derivatives showed significant impairment of ergosterol biosynthesis in all C. albicans strains coupled with down regulation of the important ergosterol biosynthesis pathway gene-ERG11. The results were further validated by docking studies, which revealed that the inhibitors snugly fitting the active site of the target enzyme, mimicking fluconazole, may well explain their excellent inhibitory activity. Our results suggest that these compounds have a great potential as antifungals, which can be used as chemosensitizing agents with the known antifungal drugs.

Clinical Candidate VT-1161's Antiparasitic Effect In Vitro, Activity in a Murine Model of Chagas Disease, and Structural Characterization in Complex with the Target Enzyme CYP51 from Trypanosoma cruzi

A novel antifungal drug candidate, the 1-tetrazole-based agent VT-1161 [(R)-2-(2,4-difluorophenyl)-1,1-difluoro-3-(1H-tetrazol-1-yl)-1-{5-[4-(2,2,2-trifluoroethoxy)phenyl]pyridin-2-yl}propan-2-ol], which is currently in two phase 2b antifungal clinical trials, was found to be a tight-binding ligand (apparent dissociation constant [Kd], 24 nM) and a potent inhibitor of cytochrome P450 sterol 14α-demethylase (CYP51) from the protozoan pathogen Trypanosoma cruzi. Moreover, VT-1161 revealed a high level of antiparasitic activity against amastigotes of the Tulahuen strain of T. cruzi in cellular experiments (50% effective concentration, 2.5 nM) and was active in vivo, causing >99.8% suppression of peak parasitemia in a mouse model of infection with the naturally drug-resistant Y strain of the parasite. The data strongly support the potential utility of VT-1161 in the treatment of Chagas disease. The structural characterization of T. cruzi CYP51 in complex with VT-1161 provides insights into the molecular basis for the compound's inhibitory potency and paves the way for the further rational development of this novel, tetrazole-based inhibitory chemotype both for antiprotozoan chemotherapy and for antifungal chemotherapy.

Ligand tunnels in T. brucei and human CYP51: Insights for parasite-specific drug design

BACKGROUND

Cytochrome P450 sterol 14α-demethylase (CYP51) is an essential enzyme for sterol biosynthesis and a target for anti-parasitic drug design. However, the design of parasite-specific drugs that inhibit parasitic CYP51 without severe side effects remains challenging. The active site of CYP51 is situated in the interior of the protein. Here, we characterize the potential ligand egress routes and mechanisms in Trypanosoma brucei and human CYP51 enzymes.

METHODS

We performed Random Acceleration Molecular Dynamics simulations of the egress of four different ligands from the active site of models of soluble and membrane-bound T. brucei CYP51 and of soluble human CYP51.

RESULTS

In the simulations, tunnel 2f, which leads to the membrane, was found to be the predominant ligand egress tunnel for all the ligands studied. Tunnels S, 1 and W, which lead to the cytosol, were also used in T. brucei CYP51, whereas tunnel 1 was the only other tunnel used significantly in human CYP51. The common tunnels found previously in other CYPs were barely used. The ligand egress times were shorter for human than T. brucei CYP51, suggesting lower barriers to ligand passage. Two gating residues, F105 and M460, in T. brucei CYP51 that modulate the opening of tunnels 2f and S were identified.

CONCLUSIONS

Although the main egress tunnel was the same, differences in the tunnel-lining residues, ligand passage and tunnel usage were found between T. brucei and human CYP51s.

GENERAL SIGNIFICANCE

The results provide a basis for the design of selective anti-parasitic agents targeting the ligand tunnels.

Structure-Functional Characterization of Cytochrome P450 Sterol 14α-Demethylase (CYP51B) from Aspergillus fumigatus and Molecular Basis for the Development of Antifungal Drugs

Aspergillus fumigatus is the opportunistic fungal pathogen that predominantly affects the immunocompromised population and causes 600,000 deaths/year. The cytochrome P450 51 (CYP51) inhibitor voriconazole is currently the drug of choice, yet the treatment efficiency remains low, calling for rational development of more efficient agents. A. fumigatus has two CYP51 genes, CYP51A and CYP51B, which share 59% amino acid sequence identity. CYP51B is expressed constitutively, whereas gene CYP51A is reported to be inducible. We expressed, purified, and characterized A. fumigatus CYP51B, including determination of its substrate preferences, catalytic parameters, inhibition, and x-ray structure in complexes with voriconazole and the experimental inhibitor (R)-N-(1-(2,4-dichlorophenyl)-2-(1H-imidazol-1-yl)ethyl)-4-(5-phenyl-1,3,4-oxadiazol-2-yl)benzamide (VNI). The enzyme demethylated its natural substrate eburicol and the plant CYP51 substrate obtusifoliol at steady-state rates of 17 and 16 min(-1), respectively, but did not metabolize lanosterol, and the topical antifungal drug miconazole was the strongest inhibitor that we identified. The x-ray crystal structures displayed high overall similarity of A. fumigatus CYP51B to CYP51 orthologs from other biological kingdoms but revealed phylum-specific differences relevant to enzyme catalysis and inhibition. The complex with voriconazole provides an explanation for the potency of this relatively small molecule, whereas the complex with VNI outlines a direction for further enhancement of the efficiency of this new inhibitory scaffold to treat humans afflicted with filamentous fungal infections.

Azole Antifungal Agents To Treat the Human Pathogens Acanthamoeba castellanii and Acanthamoeba polyphaga through Inhibition of Sterol 14α-Demethylase (CYP51)

In this study, we investigate the amebicidal activities of the pharmaceutical triazole CYP51 inhibitors fluconazole, itraconazole, and voriconazole against Acanthamoeba castellanii and Acanthamoeba polyphaga and assess their potential as therapeutic agents against Acanthamoeba infections in humans. Amebicidal activities of the triazoles were assessed by in vitro minimum inhibition concentration (MIC) determinations using trophozoites of A. castellanii and A. polyphaga. In addition, triazole effectiveness was assessed by ligand binding studies and inhibition of CYP51 activity of purified A. castellanii CYP51 (AcCYP51) that was heterologously expressed in Escherichia coli. Itraconazole and voriconazole bound tightly to AcCYP51 (dissociation constant [Kd] of 10 and 13 nM), whereas fluconazole bound weakly (Kd of 2,137 nM). Both itraconazole and voriconazole were confirmed to be strong inhibitors of AcCYP51 activity (50% inhibitory concentrations [IC50] of 0.23 and 0.39 μM), whereas inhibition by fluconazole was weak (IC50, 30 μM). However, itraconazole was 8- to 16-fold less effective (MIC, 16 mg/liter) at inhibiting A. polyphaga and A. castellanii cell proliferation than voriconazole (MIC, 1 to 2 mg/liter), while fluconazole did not inhibit Acanthamoeba cell division (MIC, >64 mg/liter) in vitro. Voriconazole was an effective inhibitor of trophozoite proliferation for A. castellanii and A. polyphaga; therefore, it should be evaluated in trials versus itraconazole for controlling Acanthamoeba infections.

Novel 3-nitrotriazole-based amides and carbinols as bifunctional antichagasic agents

3-Nitro-1H-1,2,4-triazole-based amides with a linear, rigid core and 3-nitrotriazole-based fluconazole analogues were synthesized as dual functioning antitrypanosomal agents. Such compounds are excellent substrates for type I nitroreductase (NTR) located in the mitochondrion of trypanosomatids and, at the same time, act as inhibitors of the sterol 14α-demethylase (T. cruzi CYP51) enzyme. Because combination treatments against parasites are often superior to monotherapy, we believe that this emerging class of bifunctional compounds may introduce a new generation of antitrypanosomal drugs. In the present work, the synthesis and in vitro and in vivo evaluation of such compounds is discussed.

Sterol biosynthesis is required for heat resistance but not extracellular survival in leishmania

Sterol biosynthesis is a crucial pathway in eukaryotes leading to the production of cholesterol in animals and various C24-alkyl sterols (ergostane-based sterols) in fungi, plants, and trypanosomatid protozoa. Sterols are important membrane components and precursors for the synthesis of powerful bioactive molecules, including steroid hormones in mammals. Their functions in pathogenic protozoa are not well characterized, which limits the development of sterol synthesis inhibitors as drugs. Here we investigated the role of sterol C14α-demethylase (C14DM) in Leishmania parasites. C14DM is a cytochrome P450 enzyme and the primary target of azole drugs. In Leishmania, genetic or chemical inactivation of C14DM led to a complete loss of ergostane-based sterols and accumulation of 14-methylated sterols. Despite the drastic change in lipid composition, C14DM-null mutants (c14dm(-)) were surprisingly viable and replicative in culture. They did exhibit remarkable defects including increased membrane fluidity, failure to maintain detergent resistant membrane fraction, and hypersensitivity to heat stress. These c14dm(-) mutants showed severely reduced virulence in mice but were highly resistant to itraconazole and amphotericin B, two drugs targeting sterol synthesis. Our findings suggest that the accumulation of toxic sterol intermediates in c14dm(-) causes strong membrane perturbation and significant vulnerability to stress. The new knowledge may help improve the efficacy of current drugs against pathogenic protozoa by exploiting the fitness loss associated with drug resistance.

Sequence variation in CYP51A from the Y strain of Trypanosoma cruzi alters its sensitivity to inhibition

CYP51 (sterol 14α-demethylase) is an efficient target for clinical and agricultural antifungals and an emerging target for treatment of Chagas disease, the infection that is caused by multiple strains of a protozoan pathogen Trypanosoma cruzi. Here, we analyze CYP51A from the Y strain T. cruzi. In this protein, proline 355, a residue highly conserved across the CYP51 family, is replaced with serine. The purified enzyme retains its catalytic activity, yet has been found less susceptible to inhibition. These biochemical data are consistent with cellular experiments, both in insect and human stages of the pathogen. Comparative structural analysis of CYP51 complexes with VNI and two derivatives suggests that broad-spectrum CYP51 inhibitors are likely to be preferable as antichagasic drug candidates.

Clotrimazole as a potent agent for treating the oomycete fish pathogen Saprolegnia parasitica through inhibition of sterol 14α-demethylase (CYP51)

A candidate CYP51 gene encoding sterol 14α-demethylase from the fish oomycete pathogen Saprolegnia parasitica (SpCYP51) was identified based on conserved CYP51 residues among CYPs in the genome. It was heterologously expressed in Escherichia coli, purified, and characterized. Lanosterol, eburicol, and obtusifoliol bound to purified SpCYP51 with similar binding affinities (Ks, 3 to 5 μM). Eight pharmaceutical and six agricultural azole antifungal agents bound tightly to SpCYP51, with posaconazole displaying the highest apparent affinity (Kd, ≤3 nM) and prothioconazole-desthio the lowest (Kd, ∼51 nM). The efficaciousness of azole antifungals as SpCYP51 inhibitors was confirmed by 50% inhibitory concentrations (IC50s) of 0.17 to 2.27 μM using CYP51 reconstitution assays. However, most azole antifungal agents were less effective at inhibiting S. parasitica, Saprolegnia diclina, and Saprolegnia ferax growth. Epoxiconazole, fluconazole, itraconazole, and posaconazole failed to inhibit Saprolegnia growth (MIC100, >256 μg ml(-1)). The remaining azoles inhibited Saprolegnia growth only at elevated concentrations (MIC100 [the lowest antifungal concentration at which growth remained completely inhibited after 72 h at 20°C], 16 to 64 μg ml(-1)) with the exception of clotrimazole, which was as potent as malachite green (MIC100, ∼1 μg ml(-1)). Sterol profiles of azole-treated Saprolegnia species confirmed that endogenous CYP51 enzymes were being inhibited with the accumulation of lanosterol in the sterol fraction. The effectiveness of clotrimazole against SpCYP51 activity (IC50, ∼1 μM) and the concentration inhibiting the growth of Saprolegnia species in vitro (MIC100, ∼1 to 2 μg ml(-1)) suggest that clotrimazole could be used against Saprolegnia infections, including as a preventative measure by pretreatment of fish eggs, and for freshwater-farmed fish as well as in leisure activities.

Structural basis for rational design of inhibitors targeting Trypanosoma cruzi sterol 14α-demethylase: two regions of the enzyme molecule potentiate its inhibition

Chagas disease, which was once thought to be confined to endemic regions of Latin America, has now gone global, becoming a new worldwide challenge with no cure available. The disease is caused by the protozoan parasite Trypanosoma cruzi, which depends on the production of endogenous sterols, and therefore can be blocked by sterol 14α-demethylase (CYP51) inhibitors. Here we explore the spectral binding parameters, inhibitory effects on T. cruzi CYP51 activity, and antiparasitic potencies of a new set of β-phenyl imidazoles. Comparative structural characterization of the T. cruzi CYP51 complexes with the three most potent inhibitors reveals two opposite binding modes of the compounds ((R)-6, EC₅₀ = 1.2 nM, vs (S)-2/(S)-3, EC₅₀ = 1.0/5.5 nM) and suggests the entrance into the CYP51 substrate access channel and the heme propionate-supporting ceiling of the binding cavity as two distinct areas of the protein that enhance molecular recognition and therefore could be used for the development of more effective antiparasitic drugs.