Salicylanilide inhibitors of Toxoplasma gondii

Drug repurposing for parasitic protozoan diseases

Protozoan parasites are major hazards to human health, society, and the economy, especially in equatorial regions of the globe. Parasitic diseases, including leishmaniasis, malaria, and others, contribute towards majority of morbidity and mortality. Around 1.1 million people die from these diseases annually. The lack of licensed vaccinations worsens the worldwide impact of these diseases, highlighting the importance of safe and effective medications for their prevention and treatment. However, the appearance of drug resistance in parasites continuously affects the availability of medications. The demand for novel drugs motivates global antiparasitic drug discovery research, necessitating the implementation of many innovative ways to maintain a continuous supply of promising molecules. Drug repurposing has come out as a compelling tool for drug development, offering a cost-effective and efficient alternative to standard de novo approaches. A thorough examination of drug repositioning candidates revealed that certain drugs may not benefit significantly from their original indications. Still, they may exhibit more pronounced effects in other disorders. Furthermore, certain medications can produce a synergistic effect, resulting in enhanced therapeutic effectiveness when given together. In this chapter, we outline the approaches employed in drug repurposing (sometimes referred to as drug repositioning), propose novel strategies to overcome these hurdles and fully exploit the promise of drug repurposing. We highlight a few major human protozoan diseases and a range of exemplary drugs repurposed for various protozoan infections, providing excellent outcomes for each disease.

An updated review of chemical compounds with anti-Toxoplasma gondii activity

The opportunistic apicomplexan parasite Toxoplasma gondii is the etiologic agent for toxoplasmosis, which can infect a widespread range of hosts, particularly humans and warm-blooded animals. The present chemotherapy to treat or prevent toxoplasmosis is deficient and is based on diverse drugs such as atovaquone, trimethoprim, spiramycine, which are effective in acute toxoplasmosis. Therefore, a safe chemotherapy is required for toxoplasmosis considering that its responsible agent, T. gondii, provokes severe illness and death in pregnant women and immunodeficient patients. A certain disadvantage of the available treatments is the lack of effectiveness against the tissue cyst of the parasite. A safe chemotherapy to combat toxoplasmosis should be based on the metabolic differences between the parasite and the mammalian host. This article covers different relevant molecular targets to combat this disease including the isoprenoid pathway (farnesyl diphosphate synthase, squalene synthase), dihydrofolate reductase, calcium-dependent protein kinases, histone deacetylase, mitochondrial electron transport chain, etc.

Microwave-assisted chemoselective synthesis and photophysical properties of 2-arylazo-biphenyl-4-carboxamides from hydrazonals

The reaction of 3-oxo-2-arylhydrazonopropanals with acetoacetanilide in an equimolar ratio, under DBU/1,4-dioxane/microwave irradiation reaction conditions, resulted in chemoselective formation of 4-arylazo-5-hydroxy-benzamide derivatives. The structures of the obtained biphenyl-4-carboxamides were characterized by several spectroscopic techniques including IR, 1H- and 13C-NMR, MS and HRMS, and X-ray single crystals of three examples. The photophysical properties of the new products were also evaluated, with a particular focus on their absorption and emission spectra, which provided valuable information regarding their optical properties. The new compounds emitted 513-549 nm green fluorescence in acetone solution under UV irradiation.

Design and synthesis of novel halogen rich salicylanilides as potential antileishmanial agents

The available therapeutic treatment for leishmaniasis is inadequate and toxic due to side effects, expensive and emergence of drug resistance. Affordable and safe antileishmanial agents are urgently needed and toward this objective, we synthesized a series of 32 novel halogen rich salicylanilides including niclosamide and oxyclozanide and investigated their antileishmanial activity against amastigotes of Leishmania donovani. In vitro data showed fifteen compounds inhibited intracellular amastigotes with an IC₅₀ of below 5 μM and selectivity index above 10. Among 15 active compounds, 14 and 24 demonstrated better activity with an IC₅₀ of 2.89 μM and 2.09 μM respectively and selectivity index is 18. Compound 24 exhibited significant in vivo antileishmanial efficacy and reduced 65% of the splenic parasite load on day 28th post-treatment in the experimental visceral leishmaniasis golden hamster model. The data suggest that 24 can be a promising lead candidate possessing potential to be developed into a leishmanial drug candidate.

Estimating thermodynamic equilibrium solubility and solute-solvent interactions of niclosamide in eight mono-solvents at different temperatures

Niclosamide is an FDA-approved oral anthelmintic drug currently being repurposed for COVID-19 infection. Its interesting applicability in multiple therapeutic indications has sparked interest in this drug/ scaffold. Despite its therapeutic use for several years, its detailed solubility information from Chemistry Manufacturing & Controls perspective is unavailable. Thus, the present study is intended to determine the mole fraction solubility of niclosamide in commonly used solvents and cosolvents at a temperature range of 298.15–323.15 K. The polymorphic changes from crystalline to monohydrate forms post-equilibration in various solvents were observed. The maximum mole fraction solubility of niclosamide at 323.15 K is 1.103 × 10^-3 in PEG400, followed by PEG200 (5.272 × 10^-4), 1-butanol (3.047 × 10^-4), 2-propanol (2.42 × 10^-4), ethanol (1.66 × 10^-4), DMSO (1.52 × 10^-4), methanol (7.78 × 10^-5) and water (3.27 × 10^-7). The molecular electrostatic potential showed a linear correlation with the solubility. PEG400 has higher electrostatic potential, and H-bond acceptor count, which forms a hydrogen bond with phenolic –OH of niclosamide and thus enhances its solubility. This data is valuable for the drug discovery and development teams working on the medicinal chemistry and process chemistry of this scaffold.

Study of Biological Activities and ADMET-Related Properties of Salicylanilide-Based Peptidomimetics

A series of eleven benzylated intermediates and eleven target compounds derived from salicylanilide were tested against Staphylococcus aureus ATCC 29213 and Enterococcus faecalis ATCC 29212 as reference strains and against three clinical isolates of methicillin-resistant S. aureus (MRSA) and three isolates of vancomycin-resistant E. faecalis. In addition, the compounds were evaluated against Mycobacterium tuberculosis H37Ra and M. smegmatis ATCC 700084. The in vitro cytotoxicity of the compounds was assessed using the human monocytic leukemia cell line THP-1. The lipophilicity of the prepared compounds was experimentally determined and correlated with biological activity. The benzylated intermediates were found to be completely biologically inactive. Of the final eleven compounds, according to the number of amide groups in the molecule, eight are diamides, and three are triamides that were inactive. 5-Chloro-2-hydroxy-N-[(2S)- 4-(methylsulfanyl)-1-oxo-1-{[4-(trifluoromethyl)phenyl]amino}butan-2-yl]benzamide (3e) and 5-chloro-2-hydroxy-N-[(2S)-(4-methyl-1-oxo-1-{[4-(trifluoromethyl)phenyl]amino)pentan-2-yl)benzamide (3f) showed the broadest spectrum of activity against all tested species/isolates comparable to the used standards (ampicillin and isoniazid). Six diamides showed high antistaphylococcal activity with MICs ranging from 0.070 to 8.95 μM. Three diamides showed anti-enterococcal activity with MICs ranging from 4.66 to 35.8 μM, and the activities of 3f and 3e against M. tuberculosis and M. smegmatis were MICs of 18.7 and 35.8 μM, respectively. All the active compounds were microbicidal. It was observed that the connecting linker between the chlorsalicylic and 4-CF3-anilide cores must be substituted with a bulky and/or lipophilic chain such as isopropyl, isobutyl, or thiabutyl chain. Anticancer activity on THP-1 cells IC50 ranged from 1.4 to >10 µM and increased with increasing lipophilicity.

Chemotherapeutics for Toxoplasma gondii: Molecular Biotargets, Binding Modes, and Structure-Activity Relationship Investigations

Toxoplasmosis, an infectious zoonotic disease caused by the apicomplexan parasite Toxoplasma gondii (T. gondii), is a major worldwide health problem. However, there are currently no effective options (chemotherapeutic drugs or prophylactic vaccines) for treating chronic latent toxoplasmosis infection. Accordingly, seeking more effective and safer chemotherapeutics for combating this disease remains a long-term and challenging objective. In this paper, we summarize possible molecular biotargets, with an emphasis on those that are druggable and promising, including, without limitation, calcium-dependent protein kinase 1, bifunctional thymidylate synthase-dihydrofolate reductase, and farnesyl diphosphate synthase. Meanwhile, as important components of medicinal chemistry, the binding modes and structure-activity relationship profiles of the corresponding inhibitors were also illuminated. We anticipate that this information will be helpful for further identification of more effective chemotherapeutic interventions to prevent and treat zoonotic infections caused by T. gondii.

The antimicrobial and immunomodulatory effects of Ionophores for the treatment of human infection

Ionophores are a diverse class of synthetic and naturally occurring ion transporter compounds which demonstrate both direct and in-direct antimicrobial properties against a broad panel of bacterial, fungal, viral and parasitic pathogens. In addition, ionophores can regulate the host-immune response during communicable and non-communicable disease states. Although the clinical use of ionophores such as Amphotericin B, Bedaquiline and Ivermectin highlight the utility of ionophores in modern medicine, for many other ionophore compounds issues surrounding toxicity, bioavailability or lack of in vivo efficacy studies have hindered clinical development. The antimicrobial and immunomodulating properties of a range of compounds with characteristics of ionophores remain largely unexplored. As such, ionophores remain a latent therapeutic avenue to address both the global burden of antimicrobial resistance, and the unmet clinical need for new antimicrobial therapies. This review will provide an overview of the broad-spectrum antimicrobial and immunomodulatory properties of ionophores, and their potential uses in clinical medicine for combatting infection.

Bio-evaluation of fluoro and trifluoromethyl-substituted salicylanilides against multidrug-resistant S. aureus

Methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Staphylococcus aureus (VRSA) are primary causes of skin and soft tissue infections worldwide. To address the emergency caused due to increasing multidrug-resistant (MDR) bacterial infections, a series of novel fluoro and trifluoromethyl-substituted salicylanilide derivatives were synthesized and their antimicrobial activity was investigated. MIC data reveal that the compounds inhibited S. aureus specifically (MIC 0.25–64 µg/mL). The in vitro cytotoxicity of compounds with MIC < 1 µg/mL against Vero cells led to identification of four compounds (20, 22, 24 and 25) with selectivity index above 10. These four compounds were tested against MDR S. aureus panel. Remarkably, 5-chloro-N-(4’-bromo-3’-trifluoromethylphenyl)-2-hydroxybenzamide (22) demonstrated excellent activity against nine MRSA and three VRSA strains with MIC 0.031–0.062 µg/mL, which is significantly better than the control drugs methicillin and vancomycin. The comparative time–kill kinetic experiment revealed that the effect of bacterial killing of 22 is comparable with vancomycin. Compound 22 did not synergize with or antagonize any FDA-approved antibiotic and reduced pre-formed S. aureus biofilm better than vancomycin. Overall, study suggested that 22 could be further developed as a potent anti-staphylococcal therapeutic.

Developments in Treatment Methodologies Using Dendrimers for Infectious Diseases

Dendrimers comprise a specific group of macromolecules, which combine structural properties of both single molecules and long expanded polymers. The three-dimensional form of dendrimers and the extensive possibilities for use of additional substrates for their construction creates a multivalent potential and a wide possibility for medical, diagnostic and environmental purposes. Depending on their composition and structure, dendrimers have been of interest in many fields of science, ranging from chemistry, biotechnology to biochemical applications. These compounds have found wide application from the production of catalysts for their use as antibacterial, antifungal and antiviral agents. Of particular interest are peptide dendrimers as a medium for transport of therapeutic substances: synthetic vaccines against parasites, bacteria and viruses, contrast agents used in MRI, antibodies and genetic material. This review focuses on the description of the current classes of dendrimers, the methodology for their synthesis and briefly drawbacks of their properties and their use as potential therapies against infectious diseases.

Discovery of degradable niclosamide derivatives able to specially inhibit small cell lung cancer (SCLC)

Small cell lung cancer (SCLC) is exceedingly tough to treat and easy to develop resistance upon long use of the first-line drug carboplatin or radiotherapy. Novel medicines effective and specific against SCLC are greatly needed. Herein, we focused on the discovery of such a medicine by exploring a drug niclosamide with repurposing strategy. Initial screening efforts revealed that niclosamide, an anthelmintic drug, possessed the in vitro anticancer activity and an obvious sensitivity towards SCLC. This observation inspired the evaluation for two different kinds of niclosamide derivatives. 2 with a degradable ester as a linker exhibited the comparable activity but slightly inferior selectivity to SCLC, by contrast, the cytotoxicities of 4 and 5 with non-degradable ether linkages completely disappeared, clearly validating the importance of 2-free hydroxyl group or 2-hydroxyl group released in the antitumor activity. Mechanism study unfolded that, similar to niclosamide, 2 inhibited growth of cancer cells via p 53 activation and subsequent underwent cytochrome c dependent apoptosis. Further structural modification to afford phosphate sodium 8 with significantly enhanced aqueous solubility (22.1 mg/mL) and a good selectivity towards SCLC demonstrated more promising druggability profiles. Accordingly, niclosamide as an attractive lead hold a huge potential for developing targeted anti-SCLC drugs.

Potent Tetrahydroquinolone Eliminates Apicomplexan Parasites

Apicomplexan infections cause substantial morbidity and mortality, worldwide. New, improved therapies are needed. Herein, we create a next generation anti-apicomplexan lead compound, JAG21, a tetrahydroquinolone, with increased sp3-character to improve parasite selectivity. Relative to other cytochrome b inhibitors, JAG21 has improved solubility and ADMET properties, without need for pro-drug. JAG21 significantly reduces Toxoplasma gondii tachyzoites and encysted bradyzoites in vitro, and in primary and established chronic murine infections. Moreover, JAG21 treatment leads to 100% survival. Further, JAG21 is efficacious against drug-resistant Plasmodium falciparum in vitro. Causal prophylaxis and radical cure are achieved after P. berghei sporozoite infection with oral administration of a single dose (2.5 mg/kg) or 3 days treatment at reduced dose (0.625 mg/kg/day), eliminating parasitemia, and leading to 100% survival. Enzymatic, binding, and co-crystallography/pharmacophore studies demonstrate selectivity for apicomplexan relative to mammalian enzymes. JAG21 has significant promise as a pre-clinical candidate for prevention, treatment, and cure of toxoplasmosis and malaria.

Recent progress on anti-Toxoplasma drugs discovery: Design, synthesis and screening

Toxoplasma gondii severely threaten the health of immunocompromised patients and pregnant women as this parasite can cause several disease, including brain and eye disease. Current treatment for toxoplasmosis commonly have high cytotoxic side effects on host and require long durations ranging from one week to more than one year. The regiments lack efficacy to eradicate T. gondii tissue cysts to cure chromic infection results in the needs for long treatment and relapsing disease. In addition, there has not been approved drugs for treating the pregnant women infected by T. gondii. Moreover, Toxoplasma vaccine researches face a wide variety of challenges. Developing high efficient and low toxic agents against T. gondii is urgent and important. Over the last decade, tremendous progress have been made in identifying and developing novel compounds for the treatment of toxoplasmosis. This review summarized and discussed recent advances between 2009 and 2019 in exploring effective agents against T. gondii from five aspects of drug discovery.

Collaborative drug discovery and the Tres Cantos Antimalarial Set (TCAMS)

Malaria affects a population of over 200 million people worldwide. New drugs are needed because of widespread resistance, and the hunt for such drugs involves a coordinated research effort from the scientific community. The release of the Tres Cantos Antimalarial Set (TCAMS) in 2010 represented a landmark in the field of collaborative drug discovery for malaria. This set of >13 000 molecules with confirmed activity against several strains of Plasmodium falciparum was publicly released with the goal of fostering additional research beyond the GlaxoSmithKline (GSK) network of collaborators. Here, we examine the outcomes realized from TCAMS over the past 8 years and whether the expectations surrounding this initiative have become a reality.

New life for an old drug: In vitro and in vivo effects of the anthelmintic drug niclosamide against Toxoplasma gondii RH strain

Toxoplasma gondii is the causative agent of toxoplasmosis and causes serious public health problems. However, the current treatment drugs have many limitations, such as serious side effects. Niclosamide is a salicylanilide drug commonly used to treat worm infections. Herein, the effectiveness of niclosamide for the treatment of T. gondii infection was demonstrated. This study was to evaluate the in vitro and in vivo activities of niclosamide against T. gondii and to explore its mechanism of action. The in vitro cytotoxicity of niclosamide on human foreskin fibroblast cells was evaluated by MTT test. Niclosamide displayed low host toxicity and its 50% inhibitory concentration was 8.3 μg/mL. The in vitro anti-proliferation and anti-invasion effects of niclosamide on T. gondii were determined by quantitative PCR and Giemsa staining. Niclosamide also inhibited T. gondii tachyzoite proliferation, with a 50% effective concentration of 45.3 ng/mL, and reduced the invasion of cells by tachyzoites (17.8% for the parasite control versus 1.9% for the niclosamide group treated with 100 ng/mL). A model was established by infecting BALB/c mice with the virulent RH strain of T. gondii and used to determine the in vivo effects of niclosamide on acute infection. The mice infected with tachyzoites and treated with 160, 200 or 240 mg/kg·bw niclosamide for 7 days exhibited 20%, 40% and 50% survival, respectively. In addition, niclosamide reduced the parasite burden in the blood and tissues of acutely infected mice, and niclosamide induced decreases in the mitochondrial membrane potential (ΔΨm) and adenosine triphosphate (ATP) levels in extracellular tachyzoites, as assessed by laser confocal microscopy and a multilabel reader. These findings indicated that the mechanism of action of niclosamide might be associated with T. gondii mitochondria oxidative phosphorylation. In conclusion, our results support the efficacy of niclosamide as a potential compound for the treatment of T. gondii infection.

Application of Dendrimers for the Treatment of Infectious Diseases

Dendrimers are drug delivery systems that are characterized by a three-dimensional, star-shaped, branched macromolecular network. They possess ideal properties such as low polydispersity index, biocompatibility and good water solubility. They are made up of the interior and the exterior layers. The exterior layer consists of functional groups that are useful for conjugation of drugs and targeting moieties. The interior layer exhibits improved drug encapsulation efficiency, reduced drug toxicity, and controlled release mechanisms. These unique properties make them useful for drug delivery. Dendrimers have attracted considerable attention as drug delivery system for the treatment of infectious diseases. The treatment of infectious diseases is hampered severely by drug resistance. Several properties of dendrimers such as their ability to overcome drug resistance, toxicity and control the release mechanism of the encapsulated drugs make them ideal systems for the treatment of infectious disease. The aim of this review is to discuss the potentials of dendrimers for the treatment of viral and parasitic infections.

A new niclosamide derivatives-B17 can inhibit urological cancers growth through apoptosis-related pathway

The incidence and mortality rate of urological cancers is increasing yearly. Niclosamide has been repurposed as an anti‐cancer drug in recent years. Synthesized derivative of niclosamide was testified for its anti‐cancer activity in urological cancers. MTT assay was used to measure the cytotoxicity effect of niclosamide and its derivatives in urological cancer cell lines. Migratory ability was monitored by scratch migration assay. Apoptosis and cell cycle changes were analyzed by annexin V and PI staining. The apoptosis‐related signal proteins were evaluated by western blotting. T24 had the best drug sensitivity with the lowest IC₅₀ in niclosamide and B17 treatment than DU145 and Caki‐1 cells. After niclosamide and B17 treatment, the mitotic cells were decreased, but apoptotic bodies and morphology changes were not prominent in T24, Caki‐1, and DU145 cells. The migratory ability was inhibited in niclosamide treatment than control group on Caki‐1 cells and niclosamide and B17 treatment than control group on DU145 cells. Early apoptosis cells were increased after niclosamide and B17 treatment than control group without cell cycle changes in T24, Caki‐1, and DU145 cells. Programmed cell death was activated majorly through PAPR and bcl‐2 in T24 and caspase‐3 in Caki‐1 cells, respectively. Niclosamide and B17 derivative had good ability in inhibition proliferation and migratory ability in T24, Caki‐1, and DU145 cells without prominent morphology and apoptotic body changes. UCC cells are more sensitive to niclosamide and B17 treatment. Early apoptosis was induced after niclosamide and B17 treatment through different mechanisms in T24, Caki‐1, and DU145 cells.

Drugs in development for toxoplasmosis: advances, challenges, and current status

Toxoplasma gondii causes fatal and debilitating brain and eye diseases. Medicines that are currently used to treat toxoplasmosis commonly have toxic side effects and require prolonged courses that range from weeks to more than a year. The need for long treatment durations and the risk of relapsing disease are in part due to the lack of efficacy against T. gondii tissue cysts. The challenges for developing a more effective treatment for toxoplasmosis include decreasing toxicity, achieving therapeutic concentrations in the brain and eye, shortening duration, eliminating tissue cysts from the host, safety in pregnancy, and creating a formulation that is inexpensive and practical for use in resource-poor areas of the world. Over the last decade, significant progress has been made in identifying and developing new compounds for the treatment of toxoplasmosis. Unlike clinically used medicines that were repurposed for toxoplasmosis, these compounds have been optimized for efficacy against toxoplasmosis during preclinical development. Medicines with enhanced efficacy as well as features that address the unique aspects of toxoplasmosis have the potential to greatly improve toxoplasmosis therapy. This review discusses the facets of toxoplasmosis that are pertinent to drug design and the advances, challenges, and current status of preclinical drug research for toxoplasmosis.

A Systematic Review of In vitro and In vivo Activities of Anti-Toxoplasma Drugs and Compounds (2006-2016)

The currently available anti-Toxoplasma agents have serious limitations. This systematic review was performed to evaluate drugs and new compounds used for the treatment of toxoplasmosis. Data was systematically collected from published papers on the efficacy of drugs/compounds used against Toxoplasma gondii (T. gondii) globally during 2006-2016. The searched databases were PubMed, Google Scholar, Science Direct, ISI Web of Science, EBSCO, and Scopus. One hundred and eighteen papers were eligible for inclusion in this systematic review, which were both in vitro and in vivo studies. Within this review, 80 clinically available drugs and a large number of new compounds with more than 39 mechanisms of action were evaluated. Interestingly, many of the drugs/compounds evaluated against T. gondii act on the apicoplast. Therefore, the apicoplast represents as a potential drug target for new chemotherapy. Based on the current findings, 49 drugs/compounds demonstrated in vitro half-maximal inhibitory concentration (IC50) values of below 1 μM, but most of them were not evaluated further for in vivo effectiveness. However, the derivatives of the ciprofloxacin, endochin-like quinolones and 1-[4-(4-nitrophenoxy) phenyl] propane-1-one (NPPP) were significantly active against T. gondii tachyzoites both in vitro and in vivo. Thus, these compounds are promising candidates for future studies. Also, compound 32 (T. gondii calcium-dependent protein kinase 1 inhibitor), endochin-like quinolones, miltefosine, rolipram abolish, and guanabenz can be repurposed into an effective anti-parasitic with a unique ability to reduce brain tissue cysts (88.7, 88, 78, 74, and 69%, respectively). Additionally, no promising drugs are available for congenital toxoplasmosis. In conclusion, as current chemotherapy against toxoplasmosis is still not satisfactory, development of well-tolerated and safe specific immunoprophylaxis in relaxing the need of dependence on chemotherapeutics is a highly valuable goal for global disease control. However, with the increasing number of high-risk individuals, and absence of a proper vaccine, continued efforts are necessary for the development of novel treatment options against T. gondii. Some of the novel compounds reviewed here may represent good starting points for the discovery of effective new drugs. In further, bioinformatic and in silico studies are needed in order to identify new potential toxoplasmicidal drugs.

Design, synthesis and SARs of novel salicylanilides as potent inhibitors of RANKL-induced osteoclastogenesis and bone resorption

Inhibiting osteoclastogenesis is a promising therapeutic target for treating osteoclast-related diseases. Herein, we synthesized a series of modified salicylanilides and their corresponding 3-phenyl-2H-benzo[e][1,3]oxazine-2,4(3H)-dione and 10-phenyldibenzo[b,f][1,4]oxazepin-11(10H)-one derivatives, and investigated the effects of such compounds on RANKL-induced osteoclast formation. Among them, a salicylanilide derivative (A04) and its 3-phenyl-2H-benzo[e][1,3]oxazine-2,4(3H)-dione derivative (B04) markedly suppressed RANKL-induced osteoclast differentiation and showed no significant cytotoxic effects at doses higher than that required to inhibit osteoclast formation. Both compounds reduced osteoclast formation and bone resorptive activity of osteoclasts in a dose-dependent manner. Further, the anti-osteoclastogenic effects of A04 and B04 may operate through reducing the RANKL-induced nuclear translocation of NFATc1. Accordingly, we present the potent anti-osteoclastogenic compounds A04 and B04 as promising candidates for further optimization as anti-resorptive agents.

Screening of the Open Source Malaria Box Reveals an Early Lead Compound for the Treatment of Alveolar Echinococcosis

The metacestode (larval) stage of the tapeworm Echinococcus multilocularis causes alveolar echinococcosis (AE), a very severe and in many cases incurable disease. To date, benzimidazoles such as albendazole and mebendazole are the only approved chemotherapeutical treatment options. Benzimidazoles inhibit metacestode proliferation, but do not act parasiticidal. Thus, benzimidazoles have to be taken a lifelong, can cause adverse side effects such as hepatotoxicity, and are ineffective in some patients. We here describe a newly developed screening cascade for the evaluation of the in vitro efficacy of new compounds that includes assessment of parasiticidal activity. The Malaria Box from Medicines for Malaria Venture (MMV), comprised of 400 commercially available chemicals that show in vitro activity against Plasmodium falciparum, was repurposed. Primary screening was carried out at 10 μM by employing the previously described PGI assay, and resulted in the identification of 24 compounds that caused physical damage in metacestodes. Seven out of these 24 drugs were also active at 1 μM. Dose-response assays revealed that only 2 compounds, namely MMV665807 and MMV665794, exhibited an EC₅₀ value below 5 μM. Assessments using human foreskin fibroblasts and Reuber rat hepatoma cells showed that the salicylanilide MMV665807 was less toxic for these two mammalian cell lines than for metacestodes. The parasiticidal activity of MMV665807 was then confirmed using isolated germinal layer cell cultures as well as metacestode vesicles by employing viability assays, and its effect on metacestodes was morphologically evaluated by electron microscopy. However, both oral and intraperitoneal application of MMV665807 to mice experimentally infected with E. multilocularis metacestodes did not result in any reduction of the parasite load.

The fox tapeworm Echinococcus multilocularis causes a deadly disease in humans that is characterized by cancer-like parasite growth in the liver of patients. Hence E. multilocularis is ideally removed by radical resection. However, as this is not always possible, patients are treated by chemotherapy to stop further parasite growth. To date, the drugs in use cannot kill the parasite E. multilocularis and they also induce side-effects, therefore new options for treatment are needed. We here screened a library of 400 compounds with proven activity against Plasmodium falciparum, the cause of malaria, for their effects against E. multilocularis in vitro. We developed and refined an in vitro screening cascade and developed an assay that can identify compounds with parasiticidal effects against E. multilocularis cells. We here show that MMV665807 acts parasiticidal as demonstrated by in vitro viability tests and by electron microscopy. In the mouse infection model the drug was not active, but work will focus on the evaluation of derivatives with improved bioavailability and pharmacokinetic properties to achieve parasiticidal activity not only in vitro, but also in vivo.

Avalanche for shape and feature-based virtual screening with 3D alignment

This report introduces a new ligand-based virtual screening tool called Avalanche that incorporates both shape- and feature-based comparison with three-dimensional (3D) alignment between the query molecule and test compounds residing in a chemical database. Avalanche proceeds in two steps. The first step is an extremely rapid shape/feature based comparison which is used to narrow the focus from potentially millions or billions of candidate molecules and conformations to a more manageable number that are then passed to the second step. The second step is a detailed yet still rapid 3D alignment of the remaining candidate conformations to the query conformation. Using the 3D alignment, these remaining candidate conformations are scored, re-ranked and presented to the user as the top hits for further visualization and evaluation. To provide further insight into the method, the results from two prospective virtual screens are presented which show the ability of Avalanche to identify hits from chemical databases that would likely be missed by common substructure-based or fingerprint-based search methods. The Avalanche method is extended to enable patent landscaping, i.e., structural refinements to improve the patentability of hits for deployment in drug discovery campaigns.

Clinically Available Medicines Demonstrating Anti-Toxoplasma Activity

Toxoplasma gondii is an apicomplexan parasite of humans and other mammals, including livestock and companion animals. While chemotherapeutic regimens, including pyrimethamine and sulfadiazine regimens, ameliorate acute or recrudescent disease such as toxoplasmic encephalitis or ocular toxoplasmosis, these drugs are often toxic to the host. Moreover, no approved options are available to treat infected women who are pregnant. Lastly, no drug regimen has shown the ability to eradicate the chronic stage of infection, which is characterized by chemoresistant intracellular cysts that persist for the life of the host. In an effort to promote additional chemotherapeutic options, we now evaluate clinically available drugs that have shown efficacy in disease models but which lack clinical case reports. Ideally, less-toxic treatments for the acute disease can be identified and developed, with an additional goal of cyst clearance from human and animal hosts.

Carbohydrate-derived amphiphilic macromolecules: a biophysical structural characterization and analysis of binding behaviors to model membranes

The design and synthesis of enhanced membrane-intercalating biomaterials for drug delivery or vascular membrane targeting is currently challenged by the lack of screening and prediction tools. The present work demonstrates the generation of a Quantitative Structural Activity Relationship model (QSAR) to make a priori predictions. Amphiphilic macromolecules (AMs) "stealth lipids" built on aldaric and uronic acids frameworks attached to poly(ethylene glycol) (PEG) polymer tails were developed to form self-assembling micelles. In the present study, a defined set of novel AM structures were investigated in terms of their binding to lipid membrane bilayers using Quartz Crystal Microbalance with Dissipation (QCM-D) experiments coupled with computational coarse-grained molecular dynamics (CG MD) and all-atom MD (AA MD) simulations. The CG MD simulations capture the insertion dynamics of the AM lipophilic backbones into the lipid bilayer with the PEGylated tail directed into bulk water. QCM-D measurements with Voigt viscoelastic model analysis enabled the quantitation of the mass gain and rate of interaction between the AM and the lipid bilayer surface. Thus, this study yielded insights about variations in the functional activity of AM materials with minute compositional or stereochemical differences based on membrane binding, which has translational potential for transplanting these materials in vivo. More broadly, it demonstrates an integrated computational-experimental approach, which can offer a promising strategy for the in silico design and screening of therapeutic candidate materials.

The benzimidazole based drugs show good activity against T. gondii but poor activity against its proposed enoyl reductase enzyme target

The enoyl acyl-carrier protein reductase (ENR) enzyme of the apicomplexan parasite family has been intensely studied for antiparasitic drug design for over a decade, with the most potent inhibitors targeting the NAD(+) bound form of the enzyme. However, the higher affinity for the NADH co-factor over NAD(+) and its availability in the natural environment makes the NADH complex form of ENR an attractive target. Herein, we have examined a benzimidazole family of inhibitors which target the NADH form of Francisella ENR, but despite good efficacy against Toxoplasma gondii, the IC50 for T. gondii ENR is poor, with no inhibitory activity at 1 μM. Moreover similar benzimidazole scaffolds are potent against fungi which lack the ENR enzyme and as such we believe that there may be significant off target effects for this family of inhibitors.

New derivatives of salicylamides: Preparation and antimicrobial activity against various bacterial species

Three series of salicylanilides, esters of N-phenylsalicylamides and 2-hydroxy-N-[1-(2-hydroxyphenylamino)-1-oxoalkan-2-yl]benzamides, in total thirty target compounds were synthesized and characterized. The compounds were evaluated against seven bacterial and three mycobacterial strains. The antimicrobial activities of some compounds were comparable or higher than the standards ampicillin, ciprofloxacin or isoniazid. Derivatives 3f demonstrated high biological activity against Staphylococcus aureus (⩽0.03μmol/L), Mycobacterium marinum (⩽0.40μmol/L) and Mycobacterium kansasii (1.58μmol/L), 3g shows activity against Clostridium perfringens (⩽0.03μmol/L) and Bacillus cereus (0.09μmol/L), 3h against Pasteurella multocida (⩽0.03μmol/L) and M. kansasii (⩽0.43μmol/L), 3i against methicillin-resistant S. aureus and B. cereus (⩽0.03μmol/L). The structure-activity relationships are discussed for all the compounds.

In silico design of anti-atherogenic biomaterials

Atherogenesis, the uncontrolled deposition of modified lipoproteins in inflamed arteries, serves as a focal trigger of cardiovascular disease (CVD). Polymeric biomaterials have been envisioned to counteract atherogenesis based on their ability to repress scavenger mediated uptake of oxidized lipoprotein (oxLDL) in macrophages. Following the conceptualization in our laboratories of a new library of amphiphilic macromolecules (AMs), assembled from sugar backbones, aliphatic chains and poly(ethylene glycol) tails, a more rational approach is necessary to parse the diverse features such as charge, hydrophobicity, sugar composition and stereochemistry. In this study, we advance a computational biomaterials design approach to screen and elucidate anti-atherogenic biomaterials with high efficacy. AMs were quantified in terms of not only 1D (molecular formula) and 2D (molecular connectivity) descriptors, but also new 3D (molecular geometry) descriptors of AMs modeled by coarse-grained molecular dynamics (MD) followed by all-atom MD simulations. Quantitative structure-activity relationship (QSAR) models for anti-atherogenic activity were then constructed by screening a total of 1164 descriptors against the corresponding, experimentally measured potency of AM inhibition of oxLDL uptake in human monocyte-derived macrophages. Five key descriptors were identified to provide a strong linear correlation between the predicted and observed anti-atherogenic activity values, and were then used to correctly forecast the efficacy of three newly designed AMs. Thus, a new ligand-based drug design framework was successfully adapted to computationally screen and design biomaterials with cardiovascular therapeutic properties.

Modification of triclosan scaffold in search of improved inhibitors for enoyl-acyl carrier protein (ACP) reductase in Toxoplasma gondii

Through our focused effort to discover new and effective agents against toxoplasmosis, a structure-based drug design approach was used to develop a series of potent inhibitors of the enoyl-acyl carrier protein (ACP) reductase (ENR) enzyme in Toxoplasma gondii (TgENR). Modifications to positions 5 and 4' of the well-known ENR inhibitor triclosan afforded a series of 29 new analogues. Among the resulting compounds, many showed high potency and improved physicochemical properties in comparison with the lead. The most potent compounds 16 a and 16 c have IC50 values of 250 nM against Toxoplasma gondii tachyzoites without apparent toxicity to the host cells. Their IC50 values against recombinant TgENR were found to be 43 and 26 nM, respectively. Additionally, 11 other analogues in this series had IC50 values ranging from 17 to 130 nM in the enzyme-based assay. With respect to their excellent in vitro activity as well as improved drug-like properties, the lead compounds 16 a and 16 c are deemed to be excellent starting points for the development of new medicines to effectively treat Toxoplasma gondii infections.

Development of a triclosan scaffold which allows for adaptations on both the A- and B-ring for transport peptides

The enoyl acyl-carrier protein reductase (ENR) enzyme is harbored within the apicoplast of apicomplexan parasites providing a significant challenge for drug delivery, which may be overcome through the addition of transductive peptides, which facilitates crossing the apicoplast membranes. The binding site of triclosan, a potent ENR inhibitor, is occluded from the solvent making the attachment of these linkers challenging. Herein, we have produced 3 new triclosan analogs with bulky A- and B-ring motifs, which protrude into the solvent allowing for the future attachment of molecular transporters for delivery.

Antibacterial activity of salicylanilide 4-(trifluoromethyl)-benzoates

The development of novel antimicrobial agents represents a timely research topic. Eighteen salicylanilide 4-(trifluoromethyl)benzoates were evaluated against Mycobacterium tuberculosis, M. avium and M. kansasii, eight bacterial strains including methicillin-resistant Staphylococcus aureus (MRSA) and for the inhibition of mycobacterial isocitrate lyase. Some compounds were further screened against drug-resistant M. tuberculosis and for their cytotoxicity. Minimum inhibitory concentrations (MICs) for all mycobacterial strains were within 0.5–32 μmol/L, with 4-chloro-2-[4-(trifluoromethyl)phenylcarbamoyl]phenyl 4-(trifluoromethyl)benzoate superiority. Gram-positive bacteria including MRSA were inhibited with MICs ≥ 0.49 μmol/L, while Gram-negative ones were much less susceptible. Salicylanilide 4-(trifluoromethyl)benzoates showed significant antibacterial properties, for many strains being comparable to standard drugs (isoniazid, benzylpenicillin) with no cross-resistance. All esters showed mild inhibition of mycobacterial isocitrate lyase and four compounds were comparable to 3-nitropropionic acid without a direct correlation between in vitro MICs and enzyme inhibition.