Biological activity of modified and exchanged 2-amino-5-nitrothiazole amide analogues of nitazoxanide

New nitazoxanide derivatives: design, synthesis, biological evaluation, and molecular docking studies as antibacterial and antimycobacterial agents

A new series inspired by combining fragments from nitazoxanide (NTZ) and 4-aminosalicylic acid (4-ASA) was synthesized and screened for in vitro antibacterial and antimycobacterial activities. The majority showed higher antibacterial potency than NTZ against all the screened strains, notably, 5f, 5j, 5n and 5o with MICs of 0.87-9.00 μM. Compounds 5c, 5n and 5o revealed higher potency than ciprofloxacin against K. pneumoniae, while 5i was equipotent. For E. faecalis, 3b, 5j, and 5k showed higher potency than ciprofloxacin. 5j was more potent against P. aeruginosa than ciprofloxacin, while 5n was more potent against S. aureus with an MIC of 0.87 μM. 5f showed equipotency to ciprofloxacin against H. pylori with an MIC of 1.74 μM. Compounds 3a and 3b (4-azidoNTZ, MIC 4.47 μM) are 2 and 5-fold more potent against Mycobacterium tuberculosis (Mtb H37Rv) than NTZ (MIC 20.23 μM) and safer. 4-Azidation and/or acetylation of NTZ improve both activities, while introducing 1,2,3-triazoles improves the antibacterial activity. Molecular docking studies within pyruvate ferredoxin oxidoreductase (PFOR), glucosamine-6-phosphate synthase (G6PS) and dihydrofolate reductase (DHFR) active sites were performed to explore the possible molecular mechanisms of actions. Acceptable drug-likeness properties were found. This study may shed light on further rational design of substituted NTZ as broad-spectrum more potent antimicrobial candidates.

Amidinoquinoxaline N-oxides: synthesis and activity against anaerobic bacteria

We present herein an in-depth study on the activity of amidinoquinoxaline N-oxides 1 against Gram-positive and Gram-negative anaerobic bacteria. Based on 5-phenyl-2,3-dihydropyrimidoquinoxaline N-oxide 1a, the selected structural variations included in our study comprise the substituents α- to the N-oxide function, the benzofused ring, substitution and quaternization of the amidine moiety, and the amidine ring size. Compounds 1 showed good to excellent antianaerobic activity, evaluated as the corresponding CIM50 and CIM90 values, and an antimicrobial spectrum similar to metronidazole. Six out of 13 compounds 1 had CIM90 values significantly lower than the reference drug. Among them, imidazoline derivatives 1i-l were the most active structures. Such compounds were synthesized by base-promoted ring closure of the corresponding amidines. The N-oxides under study showed no significant cytotoxicity against RAW 264.7 cells, with high selectivity indexes. Their calculated ADME properties indicate that the compounds are potentially good oral drug candidates. The antianaerobic activity correlated satisfactorily with the electron affinity of the compounds, suggesting that they may undergo bioreductive activation before exerting their antibacterial activity.

Nitazoxanide Inhibits the Bifunctional Enzyme GlG6PD::6PGL of Giardia lamblia: Biochemical and In Silico Characterization of a New Druggable Target

Giardiasis, which is caused by Giardia lamblia infection, is a relevant cause of morbidity and mortality worldwide. Because no vaccines are currently available to treat giardiasis, chemotherapeutic drugs are the main options for controlling infection. Evidence has shown that the nitro drug nitazoxanide (NTZ) is a commonly prescribed treatment for giardiasis; however, the mechanisms underlying NTZ's antigiardial activity are not well-understood. Herein, we identified the glucose-6-phosphate::6-phosphogluconate dehydrogenase (GlG6PD::6PGL) fused enzyme as a nitazoxanide target, as NTZ behaves as a GlG6PD::6PGL catalytic inhibitor. Furthermore, fluorescence assays suggest alterations in the stability of GlG6PD::6PGL protein, whereas the results indicate a loss of catalytic activity due to conformational and folding changes. Molecular docking and dynamic simulation studies suggest a model of NTZ binding on the active site of the G6PD domain and near the structural NADP⁺ binding site. The findings of this study provide a novel mechanistic basis and strategy for the antigiardial activity of the NTZ drug.

CDBN-YGXZ, a Novel Small-Molecule Drug, Shows Efficacy against Clostridioides difficile Infection and Recurrence in Mouse and Hamster Infection Models

Clostridioides difficile infection (CDI) causes severe diarrhea and colitis, leading to significant morbidity, mortality, and high medical costs worldwide. Oral vancomycin, a first-line treatment for CDI, is associated with a high risk of recurrence, necessitating novel therapies for primary and recurrent CDI. A novel small-molecule compound, CDBN-YGXZ, was synthesized by modifying the benzene ring of nitazoxanide with lauric acid. The mechanism of action of CDBN-YGXZ was validated using a pyruvate:ferredoxin/flavodoxin oxidoreductase (PFOR) inhibition assay. The efficacy of CDBN-YGXZ was evaluated using the MIC test and CDI infection model in mice and hamsters. Furthermore, metagenomics was used to reveal the underlying reasons for the effective reduction or prevention of CDI after CDBN-YGXZ treatment. The inhibitory activity against PFOR induced by CDBN-YGXZ. MIC tests showed that the in vitro activity of CDBN-YGXZ against C. difficile ranging from 0.1 to 1.5 μg/mL. In the mouse and hamster CDI models, CDBN-YGXZ provided protection during both treatment and relapse, while vancomycin treatment resulted in severe relapse and significant clinical scores. Compared with global effects on the indigenous gut microbiota induced by vancomycin, CDBN-YGXZ treatment had a mild influence on gut microbes, thus resulting in the disappearance or reduction of CDI recurrence. CDBN-YGXZ displayed potent activity against C. difficile in vitro and in vivo, reducing or preventing relapse in infected animals, which could merit further development as a potential drug candidate for treating CDI.

N-(Trimethylsilyl)-2-amino-5-nitrothiazole: An Efficient Reagent for the Direct Synthesis of 2-Amino-5-nitrothiazole-Based Antimicrobial Agents

Here we report the synthesis of a novel reagent designed to prepare 2-amino-5-nitrothiazole (ANT) amides and analogues in high yields. N-(Trimethylsilyl)-2-amino-5-nitrothiazole (N-(TMS)-ANT) was prepared in 99% yield via silylation of ANT using 1,1,1,3,3,3-hexamethyldisilazane (HMDS), trimethylsilyl chloride (TMSCl), and catalytic saccharin. N-(TMS)-ANT is a superb reagent for the preparation of ANT amides in excellent yields. Notably, cyclic anhydrides and base-sensitive acyl chlorides can be utilized with N-(TMS)-ANT to furnish ANT amides that are difficult to prepare by previously reported procedures.

Design and synthesis of novel nitrothiazolacetamide conjugated to different thioquinazolinone derivatives as anti-urease agents

The present article describes the design, synthesis, in vitro urease inhibition, and in silico molecular docking studies of a novel series of nitrothiazolacetamide conjugated to different thioquinazolinones. Fourteen nitrothiazolacetamide bearing thioquinazolinones derivatives (8a-n) were synthesized through the reaction of isatoic anhydride with different amine, followed by reaction with carbon disulfide and KOH in ethanol. The intermediates were then converted into final products by treating them with 2-chloro-N-(5-nitrothiazol-2-yl)acetamide in DMF. All derivatives were then characterized through different spectroscopic techniques (1H, 13C-NMR, MS, and FTIR). In vitro screening of these molecules against urease demonstrated the potent urease inhibitory potential of derivatives with IC50 values ranging between 2.22 ± 0.09 and 8.43 ± 0.61 μM when compared with the standard thiourea (IC50 = 22.50 ± 0.44 μM). Compound 8h as the most potent derivative exhibited an uncompetitive inhibition pattern against urease in the kinetic study. The high anti-ureolytic activity of 8h was confirmed against two urease-positive microorganisms. According to molecular docking study, 8h exhibited several hydrophobic interactions with Lys10, Leu11, Met44, Ala47, Ala85, Phe87, and Pro88 residues plus two hydrogen bound interactions with Thr86. According to the in silico assessment, the ADME-Toxicity and drug-likeness profile of synthesized compounds were in the acceptable range.

Cationic Peptidomimetic Amphiphiles Having a N-Aryl- or N-Naphthyl-1,2,3-Triazole Core Structure Targeting Clostridioides (Clostridium) difficile: Synthesis, Antibacterial Evaluation, and an In Vivo C. difficile Infection Model

Clostridioides (also known as Clostridium) difficile is a Gram-positive anaerobic, spore producing bacterial pathogen that causes severe gastrointestinal infection in humans. The current chemotherapeutic options are inadequate, expensive, and limited, and thus inexpensive drug treatments for C. difficile infection (CDI) with improved efficacy and specificity are urgently needed. To improve the solubility of our cationic amphiphilic 1,1′-binaphthylpeptidomimetics developed earlier that showed promise in an in vivo murine CDI model we have synthesized related compounds with an N-arytriazole or N-naphthyltriazole moiety instead of the 1,1′-biphenyl or 1,1′-binaphthyl moiety. This modification was made to increase the polarity and thus water solubility of the overall peptidomimetics, while maintaining the aromatic character. The dicationic N-naphthyltriazole derivative 40 was identified as a C. difficile-selective antibacterial with MIC values of 8 µg/mL against C. difficile strains ATCC 700057 and 132 (both ribotype 027). This compound displayed increased water solubility and reduced hemolytic activity (32 µg/mL) in an in vitro hemolysis assay and reduced cytotoxicity (CC₅₀ 32 µg/mL against HEK293 cells) relative to lead compound 2. Compound 40 exhibited mild efficacy (with 80% survival observed after 24 h compared to the DMSO control of 40%) in an in vivo murine model of C. difficile infection by reducing the severity and slowing the onset of disease.

Novel Nitro-Heteroaromatic Antimicrobial Agents for the Control and Eradication of Biofilm-Forming Bacteria

The synthesis and biological activity of several novel nitrothiazole, nitrobenzothiazole, and nitrofuran containing antimicrobial agents for the eradication of biofilm-forming Gram-negative and Gram-positive pathogens is described. Nitazoxanide (NTZ), nitrofurantoin, and furazolidone are commercial antimicrobials which were used as models to show how structural modification improved activity toward planktonic bacteria via minimum inhibitory concentration (MIC) assays and biofilms via minimum biofilm eradication concentration (MBEC) assays. Structure–activity relationship (SAR) studies illustrate the ways in which improvements have been made to the aforementioned antimicrobial agents. It is of particular interest in this regard that the introduction of a chloro substituent at the 5-position of NTZ (analog 1b) resulted in marked activity enhancement, as did the replacement of the 2-acetoxy substituent in the latter compound with a basic amine group (analog 7b). It is also of importance that analog 4a, which is a simple methacrylamide, displayed noteworthy activity against S. epidermidis biofilms. These lead compounds identified to have high activity towards biofilms provide promise as starting points in future pro-drug studies.

A review on the structures and biological activities of anti-Helicobacter pylori agents

Helicobacter pylori is one of the main causal risk factor in the generation of chronic gastritis, gastroduodenal ulcers and gastric carcinoma. Thus, the eradication of H. pylori infection is an important way for preventing and managing the gastric diseases. Multiple-therapy with several antibacterial agents is used for the eradication of H. pylori infections; however the increase of resistance to H. pylori strains has resulted in unsatisfactory eradication and unsuccessful treatment. Furthermore, the combination therapy with high dosing leads to the disruption of intestinal microbial flora and undesired side effects. Therefore, the search for new therapeutic agents with high selectivity against H. pylori is a field of current interest. In recent years, diverse compounds originating from natural sources or synthetic drug design programs were evaluated and tried to optimize for applying against H. pylori. In this review, we have described various classes of anti-H. pylori compounds, their structure-activity relationship studies, and mechanism of actions, which could be useful for the development of new drugs for the treatment of H. pylori infections.

Therapeutic Potential of Nitazoxanide: An Appropriate Choice for Repurposing versus SARS-CoV-2?

The rapidly growing COVID-19 pandemic is the most serious global health crisis since the "Spanish flu" of 1918. There is currently no proven effective drug treatment or prophylaxis for this coronavirus infection. While developing safe and effective vaccines is one of the key focuses, a number of existing antiviral drugs are being evaluated for their potency and efficiency against SARS-CoV-2 in vitro and in the clinic. Here, we review the significant potential of nitazoxanide (NTZ) as an antiviral agent that can be repurposed as a treatment for COVID-19. Originally, NTZ was developed as an antiparasitic agent especially against Cryptosporidium spp.; it was later shown to possess potent activity against a broad range of both RNA and DNA viruses, including influenza A, hepatitis B and C, and coronaviruses. Recent in vitro assessment of NTZ has confirmed its promising activity against SARS-CoV-2 with an EC50 of 2.12 μM. Here we examine its drug properties, antiviral activity against different viruses, clinical trials outcomes, and mechanisms of antiviral action from the literature in order to highlight the therapeutic potential for the treatment of COVID-19. Furthermore, in preliminary PK/PD analyses using clinical data reported in the literature, comparison of simulated TIZ (active metabolite of NTZ) exposures at two doses with the in vitro potency of NTZ against SARS-CoV-2 gives further support for drug repurposing with potential in combination chemotherapy approaches. The review concludes with details of second generation thiazolides under development that could lead to improved antiviral therapies for future indications.

Synthesis, in vitro bioassays, and computational study of heteroaryl nitazoxanide analogs

Antiprotozoal drug nitazoxanide (NTZ) has shown diverse pharmacological properties and has appeared in several clinical trials. Herein we present the synthesis, characterization, in vitro biological investigation, and in silico study of four hetero aryl amide analogs of NTZ. Among the synthesized molecules, compound 2 and compound 4 exhibited promising antibacterial activity against Escherichia coli (E. coli), superior to that displayed by the parent drug nitazoxanide as revealed from the in vitro antibacterial assay. Compound 2 displayed zone of inhibition of 20 mm, twice as large as the parent drug NTZ (10 mm) in their least concentration (12.5 µg/ml). Compound 1 also showed antibacterial effect similar to that of nitazoxanide. The analogs were also tested for in vitro cytotoxic activity by employing cell counting kit-8 (CCK-8) assay technique in HeLa cell line, and compound 2 was identified as a potential anticancer agent having IC50 value of 172 µg which proves it to be more potent than nitazoxanide (IC50  = 428 µg). Furthermore, the compounds were subjected to molecular docking study against various bacterial and cancer signaling proteins. The in vitro test results corroborated with the in silico docking study as compound 2 and compound 4 had comparatively stronger binding affinity against the proteins and showed a higher docking score than nitazoxanide toward human mitogen-activated protein kinase (MAPK9) and fatty acid biosynthesis enzyme (FabH) of E. coli. Moreover, the docking study demonstrated dihydrofolate reductase (DHFR) and thymidylate synthase (TS) as probable new targets for nitazoxanide and its synthetic analogs. Overall, the study suggests that nitazoxanide and its analogs can be a potential lead compound in the drug development.

Cationic biaryl 1,2,3-triazolyl peptidomimetic amphiphiles targeting Clostridioides (Clostridium) difficile: Synthesis, antibacterial evaluation and an in vivo C. difficile infection model

Clostridioides (formerly Clostridium) difficile is a Gram-positive anaerobic bacterial pathogen that causes severe gastrointestinal infection in humans. The current chemotherapeutic options are vastly inadequate, expensive and limited; this results in an exorbitant medical and financial burden. New, inexpensive chemotherapeutic treatments for C. difficile infection with improved efficacy are urgently needed. A streamlined synthetic pathway was developed to allow access to 38 novel mono- and di-cationic biaryl 1,2,3-triazolyl peptidomimetics with increased synthetic efficiency, aqueous solubility and enhanced antibacterial efficacy. The monocationic arginine derivative 28 was identified as a potent, Gram-positive selective antibacterial with MIC values of 4 μg/mL against methicillin-resistant Staphylococcus aureus and 8 μg/mL against C. difficile. Furthermore, the dicationic bis-triazole analogue 50 was found to exhibit broad-spectrum activity with substantial Gram-negative efficacy against Acinetobacter baumannii (8 μg/mL), Pseudomonas aeruginosa (8 μg/mL) and Klebsiella pneumoniae (16 μg/mL); additionally, compound 50 displayed reduced haemolytic activity (<13%) in an in vitro haemolysis assay. Membrane-disruption assays were conducted on selected derivatives to confirm the membrane-active mechanism of action inherent to the synthesized amphiphilic compounds. A comparative solubility assay was developed and utilized to optimize the aqueous solubility of the compounds for in vivo studies. The biaryl peptidomimetics 28 and 67 were found to exhibit significant efficacy in an in vivo murine model of C. difficile infection by reducing the severity and slowing the onset of disease.

Nitazoxanide Analogs Require Nitroreduction for Antimicrobial Activity in Mycobacterium smegmatis

In this study, we aimed to decipher the natural resistance mechanisms of mycobacteria against novel compounds isolated by whole-cell-based high-throughput screening (HTS). We identified active compounds using Mycobacterium aurum. Further analyses were performed to determine the resistance mechanism of M. smegmatis against one hit, 3-bromo-N-(5-nitrothiazol-2-yl)-4-propoxybenzamide (3), which turned out to be an analog of the drug nitazoxanide (1). We found that the repression of the gene nfnB coding for the nitroreductase NfnB was responsible for the natural resistance of M. smegmatis against 3. The overexpression of nfnB resulted in sensitivity of M. smegmatis to 3. This compound must be metabolized into hydroxylamine intermediate for exhibiting antibacterial activity. Thus, we describe, for the first time, the activity of a mycobacterial nitroreductase against 1 analogs, highlighting the differences in the metabolism of nitro compounds among mycobacterial species and emphasizing the potential of nitro drugs as antibacterials in various bacterial species.

A small molecule screening to detect potential therapeutic targets in human podocytes

WIDMEIER E, TAN W, AIRIK M, HILDEBRANDT F

A small molecule screening to detect potential therapeutic targets in human podocytes. Am J Physiol Renal Physiol 312: F157-F171, 2017. First published October 19, 2016; doi:10.1152/ajprenal.00386.2016. Steroid-resistant nephrotic syndrome (SRNS) inevitably progresses to end-stage kidney disease, requiring dialysis or transplantation for survival. However, treatment modalities and drug discovery remain limited. Mutations in over 30 genes have been discovered as monogenic causes of SRNS. Most of these genes are predominantly expressed in the glomerular epithelial cell, the podocyte, placing it at the center of the pathogenesis of SRNS. Podocyte migration rate (PMR) represents a relevant intermediate phenotype of disease in monogenic causes of SRNS. We therefore adapted PMR in a high-throughput manner to screen small molecules as potential therapeutic targets for SRNS. We performed a high-throughput drug screening of a National Institutes of Health Clinical Collection (NCC) library (n = 725 compounds) measuring PMR by videomicroscopy. We used the Woundmaker to perform individual 96-well scratch wounds and screened compounds using a quantitative kinetic live cell imaging migration assay using IncuCyte ZOOM technology. Using a normal distribution for the average PMR in wild-type podocytes with a vehicle control (DMSO), we applied a 90% confidence interval to define "distinct" compounds (5% faster/slower PMR) and found that 12 of 725 compounds (at 10 μM) reduced PMR. Clusters of drugs that alter PMR included actin/tubulin modulators such as the azole class of antifungals and antineoplastic vinca-alkaloids. We hereby identify compounds that alter PMR. The PMR assay provides a new avenue to test therapeutics for nephrotic syndrome. Positive results may reveal novel pathways in the study of glomerular diseases such as SRNS.

Antitrypanosomal activity of 5-nitro-2-aminothiazole-based compounds

A small series of 5-nitro-2-aminothiazole-based amides containing arylpiperazine-, biphenyl- or aryloxyphenyl groups in their core were synthesized and evaluated as antitrypanosomatid agents. All tested compounds were active or moderately active against Trypanosoma cruzi amastigotes in infected L6 cells and Trypanosoma brucei brucei, four of eleven compounds were moderately active against Leishmania donovani axenic parasites while none were deemed active against T. brucei rhodesiense. For the most active/moderately active compounds a moderate selectivity against each parasite was observed. There was good correlation between lipophilicity (clogP value) and antileishmanial activity or toxicity against L6 cells. Similarly, good correlation existed between clogP values and IC50 values against T. cruzi in structurally related subgroups of compounds. Three compounds were more potent as antichagasic agents than benznidazole but were not activated by the type I nitrorectusase (NTR).

Synthesis and Antimicrobial Evaluation of Amixicile-Based Inhibitors of the Pyruvate-Ferredoxin Oxidoreductases of Anaerobic Bacteria and Epsilonproteobacteria

Amixicile is a promising derivative of nitazoxanide (an antiparasitic therapeutic) developed to treat systemic infections caused by anaerobic bacteria, anaerobic parasites, and members of the Epsilonproteobacteria (Campylobacter and Helicobacter). Amixicile selectively inhibits pyruvate-ferredoxin oxidoreductase (PFOR) and related enzymes by inhibiting the function of the vitamin B1 cofactor (thiamine pyrophosphate) by a novel mechanism. Here, we interrogate the amixicile scaffold, guided by docking simulations, direct PFOR inhibition assays, and MIC tests against Clostridium difficile, Campylobacter jejuni, and Helicobacter pylori Docking simulations revealed that the nitro group present in nitazoxanide interacts with the protonated N4'-aminopyrimidine of thiamine pyrophosphate (TPP). The ortho-propylamine on the benzene ring formed an electrostatic interaction with an aspartic acid moiety (B456) of PFOR that correlated with improved PFOR-inhibitory activity and potency by MIC tests. Aryl substitution with electron-withdrawing groups and substitutions of the propylamine with other alkyl amines or nitrogen-containing heterocycles both improved PFOR inhibition and, in many cases, biological activity against C. difficile Docking simulation results correlate well with mechanistic enzymology and nuclear magnetic resonance (NMR) studies that show members of this class of antimicrobials to be specific inhibitors of vitamin B1 function by proton abstraction, which is both novel and likely to limit mutation-based drug resistance.

Activity and property landscape modeling is at the interface of chemoinformatics and medicinal chemistry

Property landscape modeling (PLM) methods are at the interface of experimental sciences and computational chemistry. PLM are becoming a common strategy to describe systematically structure-property relationships of datasets. Thus far, PLM have been used mainly in medicinal chemistry and drug discovery. Herein, we survey advances on key topics on PLM with emphasis on questions often raised regarding the outcomes of the property landscape studies. We also emphasize on concepts of PLM that are being extended to other experimental areas beyond drug discovery. Topics discussed in this paper include applications of PLM to further characterize protein-ligand interactions, the utility of PLM as a quantitative and descriptive approach, and the statistical validation of property cliffs.

Clostridium difficile drug pipeline: challenges in discovery and development of new agents

In the past decade Clostridium difficile has become a bacterial pathogen of global significance. Epidemic strains have spread throughout hospitals, while community acquired infections and other sources ensure a constant inoculation of spores into hospitals. In response to the increasing medical burden, a new C. difficile antibiotic, fidaxomicin, was approved in 2011 for the treatment of C. difficile-associated diarrhea. Rudimentary fecal transplants are also being trialed as effective treatments. Despite these advances, therapies that are more effective against C. difficile spores and less damaging to the resident gastrointestinal microbiome and that reduce recurrent disease are still desperately needed. However, bringing a new treatment for C. difficile infection to market involves particular challenges. This review covers the current drug discovery pipeline, including both small molecule and biologic therapies, and highlights the challenges associated with in vitro and in vivo models of C. difficile infection for drug screening and lead optimization.

Synthesis of nitro(benzo)thiazole acetamides and in vitro antiprotozoal effect against amitochondriate parasites Giardia intestinalis and Trichomonas vaginalis

We synthesized four 5-nitrothiazole (1-4) and four 6-nitrobenzothiazole acetamides (5-8) using an easy two step synthetic route. All compounds were tested in vitro against amitochondriate parasites Giardia intestinalis and Trichomonas vaginalis, showing excellent antiprotozoal effects. IC₅₀'s of the most potent compounds range from nanomolar to low micromolar order, being more active than their drugs of choice. Compound 1 (IC₅₀=122 nM), was 44-times more active than Metronidazole, and 10-fold more effective than Nitazoxanide against G. intestinalis and showed good trichomonicidal activity (IC₅₀=2.24 μM). This compound did not display in vitro cytotoxicity against VERO cells. The in vitro inhibitory effect of compounds 1-8 and Nitazoxanide against G. intestinalis fructose-1,6-biphosphate aldolase (GiFBPA) was evaluated as potential drug target, showing a clear inhibitory effect over the enzyme activity. Molecular docking of compounds 1, 4 and Nitazoxanide into the ligand binding pocket of GiFBPA, revealed contacts with the active site residues of the enzyme. Ligand efficiency metrics of 1 revealed optimal combinations of physicochemical and antiprotozoal properties, better than Nitazoxanide.

2-acylamino-5-nitro-1,3-thiazoles: preparation and in vitro bioevaluation against four neglected protozoan parasites

The 2-acylamino-5-nitro-1,3-thiazole derivatives (1-14) were prepared using a one step reaction. All compounds were tested in vitro against four neglected protozoan parasites (Giardia intestinalis, Trichomonas vaginalis, Leishmania amazonensis and Trypanosoma cruzi). Acetamide (9), valeroylamide (10), benzamide (12), methylcarbamate (13) and ethyloxamate (14) derivatives were the most active compounds against G. intestinalis and T. vaginalis, showing nanomolar inhibition. Compound 13 (IC50=10nM), was 536-times more active than metronidazole, and 121-fold more effective than nitazoxanide against G. intestinalis. Compound 14 was 29-times more active than metronidazole and 6.5-fold more potent than nitazoxanide against T. vaginalis. Ureic derivatives 2, 3 and 5 showed moderate activity against L. amazonensis. None of them were active against T. cruzi. Ligand efficiency indexes analysis revealed higher intrinsic quality of the most active 2-acylamino derivatives than nitazoxanide and metronidazole. In silico toxicity profile was also computed for the most active compounds. A very low in vitro mammalian cytotoxicity was obtained for 13 and 14, showing selectivity indexes (SI) of 246,300 and 141,500, respectively. Nitazoxanide showed an excellent leishmanicidal and trypanocidal effect, repurposing this drug as potential new antikinetoplastid parasite compound.

Progress in the discovery of treatments for C. difficile infection: A clinical and medicinal chemistry review

Clostridium difficile is an anaerobic, Gram-positive pathogen that causes C. difficile infection, which results in significant morbidity and mortality. The incidence of C. difficile infection in developed countries has become increasingly high due to the emergence of newer epidemic strains, a growing elderly population, extensive use of broad spectrum antibiotics, and limited therapies for this diarrheal disease. Because treatment options currently available for C. difficile infection have some drawbacks, including cost, promotion of resistance, and selectivity problems, new agents are urgently needed to address these challenges. This review article focuses on two parts: the first part summarizes current clinical treatment strategies and agents under clinical development for C. difficile infection; the second part reviews newly reported anti-difficile agents that have been evaluated or reevaluated in the last five years and are in the early stages of drug discovery and development. Antibiotics are divided into natural product inspired and synthetic small molecule compounds that may have the potential to be more efficacious than currently approved treatments. This includes potency, selectivity, reduced cytotoxicity, and novel modes of action to prevent resistance.

Amixicile, a novel inhibitor of pyruvate: ferredoxin oxidoreductase, shows efficacy against Clostridium difficile in a mouse infection model

Clostridium difficile infection (CDI) is a serious diarrheal disease that often develops following prior antibiotic usage. One of the major problems with current therapies (oral vancomycin and metronidazole) is the high rate of recurrence. Nitazoxanide (NTZ), an inhibitor of pyruvate:ferredoxin oxidoreductase (PFOR) in anaerobic bacteria, parasites, Helicobacter pylori, and Campylobacter jejuni, also shows clinical efficacy against CDI. From a library of ∼250 analogues of NTZ, we identified leads with increased potency for PFOR. MIC screens indicated in vitro activity in the 0.05- to 2-μg/ml range against C. difficile. To improve solubility, we replaced the 2-acetoxy group with propylamine, producing amixicile, a soluble (10 mg/ml), nontoxic (cell-based assay) lead that produced no adverse effects in mice by oral or intraperitoneal (i.p.) routes at 200 mg/kg of body weight/day. In initial efficacy testing in mice treated (20 mg/kg/day, 5 days each) 1 day after receiving a lethal inoculum of C. difficile, amixicile showed slightly less protection than did vancomycin by day 5. However, in an optimized CDI model, amixicile showed equivalence to vancomycin and fidaxomicin at day 5 and there was significantly greater survival produced by amixicile than by the other drugs on day 12. All three drugs were comparable by measures of weight loss/gain and severity of disease. Recurrence of CDI was common for mice treated with vancomycin or fidaxomicin but not for mice receiving amixicile or NTZ. These results suggest that gut repopulation with beneficial (non-PFOR) bacteria, considered essential for protection against CDI, rebounds much sooner with amixicile therapy than with vancomycin or fidaxomicin. If the mouse model is indeed predictive of human CDI disease, then amixicile, a novel PFOR inhibitor, appears to be a very promising new candidate for treatment of CDI.

Ionic liquid-supported synthesis of sulfonamides and carboxamides

An ionic liquid-supported aldehyde was designed and converted to ionic liquid-supported secondary aryl amines through reductive amination. The reaction of ionic liquid-supported aryl amines with sulfonyl chlorides and acid chlorides, respectively, followed by cleavage using trifluoroacetic acid (TFA) afforded sulfonamides and caboxamides. To introduce additional diversity in the synthesis of sulfonamides and caboxamides, ionic liquid-supported iodosubstituted aryl amine was synthesized using the same strategy, and underwent Suzuki coupling reaction, followed by reaction with a methanesulfonyl chloride to generate the corresponding biaryl sulfonamide. The advantages of the protocol over solid-phase synthesis are homogeneous reaction medium, high loading, easy separation of products, and characterization of intermediates.

Synthesis and biological evaluation of substituted 4-arylthiazol-2-amino derivatives as potent growth inhibitors of replicating Mycobacterium tuberculosis H₃₇Rv

In search of potential therapeutics for tuberculosis, we describe herein synthesis and biological evaluation of some substituted 4-arylthiazol-2-amino derivatives as modified analogues of the antiprotozoal drug Nitazoxanide (NTZ), which has recently been reported as potent inhibitor of Mtb H(37)Rv (Mtb MIC=52.12 μM) with an excellent ability to evade resistance. Among the synthesized derivatives, the two compounds 7a (MIC=15.28 μM) and 7c (MIC=17.03 μM) have exhibited about three times better Mtb growth inhibitory activity over NTZ and are free from any cytotoxicity (Vero CC(50) of 244 and 300 μM respectively). These two compounds represent promising leads for further optimization.

Thiazolides as novel antiviral agents. 1. Inhibition of hepatitis B virus replication

We report the syntheses and activities of a wide range of thiazolides [viz., 2-hydroxyaroyl-N-(thiazol-2-yl)amides] against hepatitis B virus replication, with QSAR analysis of our results. The prototypical thiazolide, nitazoxanide [2-hydroxybenzoyl-N-(5-nitrothiazol-2-yl)amide, NTZ] 1 is a broad spectrum antiinfective agent effective against anaerobic bacteria, viruses, and parasites. By contrast, 2-hydroxybenzoyl-N-(5-chlorothiazol-2-yl)amide 3 is a novel, potent, and selective inhibitor of hepatitis B replication (EC(50) = 0.33 μm) but is inactive against anaerobes. Several 4'- and 5'-substituted thiazolides show good activity against HBV; by contrast, some related salicyloylanilides show a narrower spectrum of activity. The ADME properties of 3 are similar to 1; viz., the O-acetate is an effective prodrug, and the O-aryl glucuronide is a major metabolite. The QSAR study shows a good correlation of observed EC(90) for intracellular virions with thiazolide structural parameters. Finally we discuss the mechanism of action of thiazolides in relation to the present results.

Synthesis of benzologues of Nitazoxanide and Tizoxanide: a comparative study of their in vitro broad-spectrum antiprotozoal activity

We have synthesized two new benzologues of Nitazoxanide (NIT) and Tizoxanide (TIZ), using a short synthetic route. Both compounds were tested in vitro against six protozoa (Giardia intestinalis, Trichomonas vaginalis, Entamoeba histolytica, Plasmodium berghei, Leishmania mexicana and Trypanosoma cruzi). Compound 1 (benzologue of NIT) showed broad antiprotozoal effect against all parasites tested, showing IC(50)'s<5 μM. This compound was five-times more active than NIT, and 18-times more potent than metronidazole against G. intestinalis. It was 10-times more active than pentamidine against L. mexicana, and it was sevenfold more potent than benznidazole versus T. cruzi. This compound could be considered as a new broad spectrum antiprotozoal agent.

Nitroreductase (GlNR1) increases susceptibility of Giardia lamblia and Escherichia coli to nitro drugs

OBJECTIVES

The protozoan parasite Giardia lamblia causes the intestinal disease giardiasis, which may lead to acute and chronic diarrhoea in humans and various animal species. For treatment of this disease, several drugs such as the benzimidazole albendazole, the nitroimidazole metronidazole and the nitrothiazolide nitazoxanide are currently in use. Previously, a G. lamblia nitroreductase 1 (GlNR1) was identified as a nitazoxanide-binding protein. The aim of the present project was to elucidate the role of this enzyme in the mode of action of the nitro drugs nitazoxanide and metronidazole.

METHODS

Recombinant GlNR1 was overexpressed in both G. lamblia and Escherichia coli (strain BL21). The susceptibility of the transfected bacterial and giardial cell lines to nitazoxanide and metronidazole was analysed.

RESULTS

G. lamblia trophozoites overexpressing GlNR1 had a higher susceptibility to both nitro drugs. E. coli were fully resistant to nitazoxanide under both aerobic and semi-aerobic growth conditions. When grown semi-aerobically, bacteria overexpressing GlNR1 became susceptible to nitazoxanide.

CONCLUSIONS

These findings suggest that GlNR1 activates nitro drugs via reduction yielding a cytotoxic product.

Synthesis and antimicrobial evaluation of nitazoxanide-based analogues: identification of selective and broad spectrum activity

A library composed of nitazoxanide-based analogues was synthesized and assayed for increased antibacterial efficacy against the pyruvate-ferredoxin oxidoreductase (PFOR) using microorganisms Helicobacter pylori, Campylobacter jejuni and Clostridium difficile. Derivatives were found to recapitulate and improve activity against these organisms and select analogues were tested for their ability to disrupt the PFOR enzyme directly. The library was also screened for activity against staphylococci and resulted in the identification of analogues capable of inhibiting both staphylococci and all PFOR organisms at low micromolar minimum inhibitory concentrations with low toxicity to human foreskin cells.

Targeting bacterial membrane function: an underexploited mechanism for treating persistent infections

Persistent infections involving slow-growing or non-growing bacteria are hard to treat with antibiotics that target biosynthetic processes in growing cells. Consequently, there is a need for antimicrobials that can treat infections containing dormant bacteria. In this Review, we discuss the emerging concept that disrupting the bacterial membrane bilayer or proteins that are integral to membrane function (including membrane potential and energy metabolism) in dormant bacteria is a strategy for treating persistent infections. The clinical applicability of these approaches is exemplified by the efficacy of lipoglycopeptides that damage bacterial membranes and of the diarylquinoline TMC207, which inhibits membrane-bound ATP synthase. Despite some drawbacks, membrane-active agents form an important new means of eradicating recalcitrant, non-growing bacteria.