Discovery of novel antigiardiasis drug candidates

Thieno[3,2-b]pyrrole 5-carboxamides as potent and selective inhibitors of Giardia duodenalis

Giardia duodenalis is the causative agent of the neglected diarrhoeal disease giardiasis. While often self-limiting, giardiasis is ubiquitous and impacts hundreds of millions of people annually. It is also a common gastro-intestinal disease of domestic pets, wildlife, and livestock animals. However, despite this impact, there is no vaccine for Giardia currently available. In addition, treatment relies on chemotherapies that are associated with increasing failure rates. To identify new treatment options for giardiasis we recently screened the Compounds Australia Scaffold Library for new chemotypes with selective anti-Giardia activity, identifying three compounds with sub-μM activity and promising selectivity. Here we extended these studies by examining the anti-Giardia activity of series CL9569 compounds. This compound series was of interest given the promising activity (IC50 1.2 μM) and selectivity demonstrated by representative compound, SN00798525 (1). Data from this work has identified an additional three thieno [3,2-b]pyrrole 5-carboxamides with anti-Giardia activity, including 2 which displayed potent cytocidal (IC50 ≤ 10 nM) and selective activity against multiple Giardia strains, including representatives from both human-infecting assemblages and metronidazole resistant parasites. Preclinical studies in mice also demonstrated that 2 is well-tolerated, does not impact the normal gut microbiota and can reduce Giardia parasite burden in these animals.

Tubulin as a potential molecular target for resveratrol in Giardia lamblia trophozoites, in vitro and in silico approaches

Giardia lamblia is a globally distributed protozoan parasite that causes intestinal disease. Recently, there is an increase in refractory cases of giardiasis to chemotherapeutic agents, and drugs available cause side effects that may limit its use or cause therapeutic non-compliance. Therefore, search for alternative and less harmful drugs to treat giardiasis is an important task. In this sense, resveratrol (RSV) is a polyphenol with a wide range of pharmacological effects such as antimicrobial, anticarcinogenic and antioxidant. The aim of this study was to evaluate the effects of RSV on Giardia lamblia trophozoites in vitro and in silico, focusing on tubulin affectation, a major protein of the Giardia cytoskeleton which participates in relevant processes for cell survival. In vitro determinations showed that RSV inhibits parasite growth and adherence, causes morphological changes, and induces apoptosis-like cell death through tubulin alterations demonstrated by immunolocalization and Western blot assays. Bioinformatic analysis by molecular docking suggested that RSV binds to Giardia tubulin interface heterodimer, sharing binding residues to those reported with depolymerization inhibitors. These findings suggest that RSV affects microtubular dynamics and make it an interesting compound to study for its safety and antigiardiasic potential.

An Improved Method to Enrich Large Extracellular Vesicles Derived from Giardia intestinalis through Differential Centrifugation

Giardia intestinalis is a flagellated unicellular protozoan that colonizes the small intestine, causing the diarrheal disease called giardiasis. The production of extracellular vesicles (EVs) by G. intestinalis and the role of these EVs in the parasite's interaction with the host have been described. According to biogenesis, EVs are grouped mainly into large (microvesicles-derived from the plasma membrane) and small (exosomes-derived from multivesicular bodies). Populations of EVs are heterogeneous, and improved methods to separate and study them are needed to understand their roles in cell physiology and pathologies. This work aimed to enrich the large extracellular vesicles (LEVs) of G. intestinalis in order to better understand the roles of these vesicles in the interaction of the parasite with the host. To achieve the enrichment of the LEVs, we have modified our previously described method and compared it by protein dosage and using Nano tracking analysis. Giardia intestinalis vesiculation was induced by incubation in a TYI-S-33 medium without serum, to which 1 mM of CaCl2 was added at 37 °C for 1 h. Then, the supernatant was centrifuged at 15,000× g for 1 h (15 K 1 h pellet), 15,000× g for 4 h (15 K 4 h pellet) and 100,000× g for 1.5 h (100 K 1h30 pellet). The pellet (containing EVs) was resuspended in 1× PBS and stored at 4 °C for later analysis. The EVs were quantified based on their protein concentrations using the Pierce BCA assay, and by nanoparticle tracking analysis (NTA), which reports the concentration and size distribution of the particles. The NTA showed that direct ultracentrifugation at 100,000× g for 1.5 h and centrifugation at 15,000× g for 4 h concentrated more EVs compared to centrifugation at 15,000× g for 1 h. Additionally, it revealed that centrifugation at 15,000× g 4 h was able to concentrate at the same particle concentration levels as a direct ultracentrifugation at 100,000× g for 1.5 h. As for the enrichment of LEVs, the NTA has shown a higher concentration of LEVs in direct ultracentrifugation at 100,000× g for 1.5 h, and in centrifugation at 15,000× g for 4 h, compared to centrifugation at 15,000× g for 1 h. Our results have shown that the most used method at 15,000× g for 1 h is not enough to obtain a representative population of large EVs, and we suggest that LEVs released by G. intestinalis can be better enriched by direct ultracentrifugation at 100,000× g for 1.5 h, or by centrifugation at 15,000× g for 4 h.

Identification of Fungus-Derived Natural Products as New Antigiardial Scaffolds

There is an unmet need for effective therapies for treating diseases associated with the intestinal parasite Giardia lamblia. In this study, a library of chemically validated purified natural products and fungal extracts was screened for chemical scaffolds that can inhibit the growth of G. lamblia. The phenotypic screen led to the identification of several previously unreported classes of natural product inhibitors that block the growth of G. lamblia. Hits from phenotypic screens of these naturally derived compounds are likely to possess a variety of mechanisms of action not associated with clinically used nitroimidazole and thiazolide compounds. They may therefore be effective against current drug-resistant parasite strains. IMPORTANCE There is a direct link between widespread prevalence of clinical giardiasis and poverty. This may be one of the reasons why giardiasis is a significant contributor to diarrheal morbidity, stunting, and death of children in resource-limited communities around the world. FDA-approved treatments for giardiasis include metronidazole, related nitroimidazole drugs, and albendazole. However, a substantial number of clinical infections are resistant to these treatments. The depth of the challenge is partly exacerbated by a lack of investment in the discovery and development of novel agents for treatment of giardiasis. Applicable interventions must include new drug development strategies that will result in the identification of effective therapeutics, particularly those that are inexpensive and can be quickly advanced to clinical uses, such as products from nature. This study identified novel chemical scaffolds from fungi that can form the basis of future medicinal chemistry optimization of novel antigiardial agents.

Ultrastructural Alterations of the Human Pathogen Giardia intestinalis after Drug Treatment

This review presents the main cell characteristics altered after in vitro incubation of the parasite with commercial drugs used to treat the disease caused by Giardia intestinalis. This important intestinal parasite primarily causes diarrhea in children. Metronidazole and albendazole are the primary compounds used in therapy against Giardia intestinalis. However, they provoke significant side effects, and some strains have developed resistance to metronidazole. Benzimidazole carbamates, such as albendazole and mebendazole, have shown the best activity against Giardia. Despite their in vitro efficacy, clinical treatment with benzimidazoles has yielded conflicting results, demonstrating lower cure rates. Recently, nitazoxanide has been suggested as an alternative to these drugs. Therefore, to enhance the quality of chemotherapy against this parasite, it is important to invest in developing other compounds that can interfere with key steps of metabolic pathways or cell structures and organelles. For example, Giardia exhibits a unique cell structure called the ventral disc, which is crucial for host adhesion and pathogenicity. Thus, drugs that can disrupt the adhesion process hold promise for future therapy against Giardia. Additionally, this review discusses new drugs and strategies that can be employed, as well as suggestions for developing novel drugs to control the infection caused by this parasite.

Antigiardial Activity of Novel Guanidine Compounds

From four focused compound libraries based on the known anticoccidial agent robenidine, 44 compounds total were synthesised and screened for antigiardial activity. All active compounds were counter-screened for antibiotic and cytotoxic action. Of the analogues examined, 21 displayed IC₅₀ <5 μM, seven with IC₅₀ <1.0 μM. Most active were 2,2'-bis{[4-(trifluoromethoxy)phenyl]methylene}carbonimidic dihydrazide hydrochloride (30), 2,2'-bis{[4-(trifluoromethylsulfanyl)phenyl]methylene}carbonimidic dihydrazide hydrochloride (32), and 2,2'-bis[(2-bromo-4,5-dimethoxyphenyl)methylene]carbonimidic dihydrazide hydrochloride (41) with IC₅₀ =0.2 μM. The maximal observed activity was a 5 h IC₅₀ value of 0.2 μM for 41. The clinically used metronidazole was inactive at this timepoint at a concentration of 25 μM. Robenidine off-target effects at bacteria and cell line toxicity were removed. Analogue 41 was well tolerated in mice treated orally (100 mg/kg). Following 5 h treatment with 41, no Giardia regrowth was noted after 48 h.

An Overview of Mucosa-Associated Protozoa: Challenges in Chemotherapy and Future Perspectives

Parasitic infections caused by protozoans that infect the mucosal surfaces are widely neglected worldwide. Collectively, Entamoeba histolytica, Giardia lamblia, Cryptosporidium spp. and Trichomonas vaginalis infect more than a billion people in the world, being a public health problem mainly in developing countries. However, the exact incidence and prevalence data depend on the population examined. These parasites ultimately cause pathologies that culminate in liver abscesses, malabsorption syndrome, vaginitis, and urethritis, respectively. Despite this, the antimicrobial agents currently used to treat these diseases are limited and often associated with adverse side effects and refractory cases due to the development of resistant parasites. The paucity of drug treatments, absence of vaccines and increasing problems of drug resistance are major concerns for their control and eradication. Herein, potential candidates are reviewed with the overall aim of determining the knowledge gaps and suggest future perspectives for research. This review focuses on this public health problem and focuses on the progress of drug repositioning as a potential strategy for the treatment of mucosal parasites.

Oxygen levels are key to understanding "Anaerobic" protozoan pathogens with micro-aerophilic lifestyles

Publications abound on the physiology, biochemistry and molecular biology of "anaerobic" protozoal parasites as usually grown under "anaerobic" culture conditions. The media routinely used are poised at low redox potentials using techniques that remove O₂ to "undetectable" levels in sealed containers. However there is growing understanding that these culture conditions do not faithfully resemble the O₂ environments these organisms inhabit. Here we review for protists lacking oxidative energy metabolism, the oxygen cascade from atmospheric to intracellular concentrations and relevant methods of measurements of O₂, some well-studied parasitic or symbiotic protozoan lifestyles, their homeodynamic metabolic and redox balances, organism-drug-oxygen interactions, and the present and future prospects for improved drugs and treatment regimes.

Encephalitozoon intestinalis: A new target for auranofin in a mice model

Despite the fact that many approaches have been developed over years to find efficient and well-tolerated therapeutic regimens for microsporidiosis, the effectiveness of current drugs remains doubtful, and effective drugs against specific targets are still scarce. The present study is the first that was designed to evaluate the potency of auranofin, an anti-rheumatoid FDA approved drug, against intestinal Encephalitozoon intestinalis. Evaluation of the drug was achieved through counting of fecal and intestinal spores, studying the intestinal histopathological changes, measuring of intestinal hydrogen peroxide level, and post therapy follow-up of mice for 2 weeks for detection of relapse. Results showed that auranofin has promising anti-microsporidia potential. It showed a promising efficacy in mice experimentally infected with E. intestinalis. It has revealed an obvious reduction in fecal spore shedding and intestinal tissue spore load, amelioration of intestinal tissue pathological changes, and improvement of the local inflammatory infiltration without significant changes in hydrogen peroxide level. Interestingly, auranofin prevented the relapse of infection. Thus, considering the results of the present work, auranofin could be considered a therapeutic alternative for the gold standard drug 'albendazole' against the intestinal E. intestinalis infection especially in relapsing cases.

TriTOX: A novel Trichomonas vaginalis assay platform for high-throughput screening of compound libraries

Trichomonas vaginalis is a neglected urogenital parasitic protist that causes 170 million cases of trichomoniasis annually, making it the most prevalent non-viral, sexually transmitted disease. Trichomoniasis treatment relies on nitroheterocyclics, such as metronidazole. However, with increasing drug-resistance, there is an urgent need for novel anti-trichomonals. Little progress has been made to translate anti-trichomonal research into commercialised therapeutics, and the absence of a standardised compound-screening platform is the immediate stumbling block for drug-discovery. Herein, we describe a simple, cost-effective growth assay for T. vaginalis and the related Tritrichomonas foetus. Tracking changes in pH were a valid indicator of trichomonad growth (T. vaginalis and T. foetus), allowing development of a miniaturised, chromogenic growth assay based on the phenol red indicator in 96- and 384-well microtiter plate formats. The outputs of this assay can be quantitatively and qualitatively assessed, with consistent dynamic ranges based on Z' values of 0.741 and 0.870 across medium- and high-throughput formats, respectively. We applied this high-throughput format within the largest pure-compound microbial metabolite screen (812 compounds) for T. vaginalis and identified 43 hit compounds. We compared these identified compounds to mammalian cell lines, and highlighted extensive overlaps between anti-trichomonal and anti-tumour activity. Lastly, observing nanomolar inhibition of T. vaginalis by fumagillin, and noting this compound has reported activity in other protists, we performed in silico analyses of the interaction of fumagillin with its molecular target methionine aminopeptidase 2 for T. vaginalis, Giardia lamblia and Entamoeba histolytica, highlighting potential for fumagillin as a broad-spectrum anti-protistal against microaerophilic protists. Together, this new platform will accelerate drug-discovery efforts, underpin drug-resistance screening in trichomonads, and contributing to a growing body of evidence highlighting the potential of microbial natural products as novel anti-protistals.

Spirocyclic Scaffolds in Medicinal Chemistry

Spirocyclic scaffolds are incorporated in various approved drugs and drug candidates. The increasing interest in less planar bioactive compounds has given rise to the development of synthetic methodologies for the preparation of spirocyclic scaffolds. In this Perspective, we summarize the diverse synthetic routes to obtain spirocyclic systems. The impact of spirocycles on potency and selectivity, including the aspect of stereochemistry, is discussed. Furthermore, we examine the changes in physicochemical properties as well as in in vitro and in vivo ADME using selected studies that compare spirocyclic compounds to their nonspirocyclic counterparts. In conclusion, the value of spirocyclic scaffolds in medicinal chemistry is discussed.

Discovery and Preclinical Development of Antigiardiasis Fumagillol Derivatives

Giardiasis, caused by the intestinal parasite Giardia lamblia, is a severe diarrheal disease, endemic in poverty-stricken regions of the world, and also a common infection in developed countries. The available therapeutic options are associated with adverse effects, and G. lamblia resistance to the standard-of-care drugs is spreading. Fumagillin, an antimicrosporidiosis drug, is a therapeutic agent with potential for the treatment of giardiasis. However, it exhibits considerable, albeit reversible, toxicity when used to treat immunocompromised microsporidiosis patients.

Giardiasis, caused by the intestinal parasite Giardia lamblia, is a severe diarrheal disease, endemic in poverty-stricken regions of the world, and also a common infection in developed countries. The available therapeutic options are associated with adverse effects, and G. lamblia resistance to the standard-of-care drugs is spreading. Fumagillin, an antimicrosporidiosis drug, is a therapeutic agent with potential for the treatment of giardiasis. However, it exhibits considerable, albeit reversible, toxicity when used to treat immunocompromised microsporidiosis patients. Fumagillin is also a highly unstable compound. To address these liabilities, we designed and synthesized stable fumagillol derivatives with lower levels of permeation across polarized epithelial Caco-2 cells and better potency against G. lamblia trophozoites than fumagillin. Metronidazole-resistant G. lamblia strains were also susceptible to the new fumagillol derivatives. In addition, these compounds were more potent against the amebiasis-causing parasite Entamoeba histolytica than fumagillin. Two compounds exhibited better thermal and acid stability than fumagillin, which should prolong the drug shelf life and reduce compound degradation in the stomach. Studies with a mouse model of giardiasis with the most stable compound, 4-(((((3R,4S,5S,6R)-5-methoxy-4-((2R,3R)-2-methyl-3-(3-methylbut-2-en-1-yl)oxiran-2-yl)-1-oxaspiro[2.5]octan-6-yl)oxy)carbonyl)amino)benzoic acid (compound 9), revealed that it had better efficacy (effective dose [ED]) than fumagillin at both the fully curative dose (the 100% ED) of 6.6 mg/kg of body weight and a 50% ED of 0.064 mg/kg. Plasma pharmacokinetics revealed the slow absorption of compound 9 through the gut, consistent with the in vitro characterization in Caco-2 cells. An acute-dose study yielded a maximum tolerated dose (MTD) of 1,500 mg/kg, 227-fold higher than the fully curative dose. Thus, along with improved stability, compound 9 also exhibited an excellent therapeutic window.

Anti-Giardia Drug Discovery: Current Status and Gut Feelings

Giardia parasites are ubiquitous protozoans of global importance that impact a wide range of animals including humans. They are the most common enteric pathogen of cats and dogs in developed countries and infect ∼1 billion people worldwide. While Giardia infections can be asymptomatic, they often result in severe and chronic diseases. There is also mounting evidence that they are linked to postinfection disorders. Despite growing evidence of the widespread morbidity associated with Giardia infections, current treatment options are limited to compound classes with broad antimicrobial activity. Frontline anti-Giardia drugs are also associated with increasing drug resistance and treatment failures. To improve the health and well-being of millions, new selective anti-Giardia drugs are needed alongside improved health education initiatives. Here we discuss current treatment options together with recent advances and gaps in drug discovery. We also propose criteria to guide the discovery of new anti-Giardia compounds.

Enhanced Antigiardial Effect of Omeprazole Analog Benzimidazole Compounds

Giardiasis is a diarrheal disease that is highly prevalent in developing countries. Several drugs are available for the treatment of this parasitosis; however, failures in drug therapy are common, and have adverse effects and increased resistance of the parasite to the drug, generating the need to find new alternative treatments. In this study, we synthesized a series of 2-mercaptobenzimidazoles that are derivatives of omeprazole, and the chemical structures were confirmed through mass, ¹H NMR, and ¹³C NMR techniques. The in vitro efficacy compounds against Giardia, as well as its effect on the inhibition of triosephosphate isomerase (TPI) recombinant, were investigated, the inactivation assays were performed with 0.2 mg/mL of the enzyme incubating for 2 h at 37 °C in TE buffer, pH 7.4 with increasing concentrations of the compounds. Among the target compounds, H-BZM2, O₂N-BZM7, and O₂N-BZM9 had greater antigiardial activity (IC₅₀: 36, 14, and 17 µM on trophozoites), and inhibited the TPI enzyme (K₂: 2.3, 3.2, and 2.8 M⁻¹ s⁻¹) respectively, loading alterations on the secondary structure, global stability, and tertiary structure of the TPI protein. Finally, we demonstrated that it had low toxicity on Caco-2 and HT29 cells. This finding makes it an attractive potential starting point for new antigiardial drugs.

Drug resistance in Giardia: Mechanisms and alternative treatments for Giardiasis

The use of chemotherapeutic drugs is the main resource against clinical giardiasis due to the lack of approved vaccines. Resistance of G. duodenalis to the most used drugs to treat giardiasis, metronidazole and albendazole, is a clinical issue of growing concern and yet unknown impact, respectively. In the search of new drugs, the completion of the Giardia genome project and the use of biochemical, molecular and bioinformatics tools allowed the identification of ligands/inhibitors for about one tenth of ≈150 potential drug targets in this parasite. Further, the synthesis of second generation nitroimidazoles and benzimidazoles along with high-throughput technologies have allowed not only to define overall mechanisms of resistance to metronidazole but to screen libraries of repurposed drugs and new pharmacophores, thereby increasing the known arsenal of anti-giardial compounds to some hundreds, with most demonstrating activity against metronidazole or albendazole-resistant Giardia. In particular, cysteine-modifying agents which include omeprazole, disulfiram, allicin and auranofin outstand due to their pleiotropic activity based on the extensive repertoire of thiol-containing proteins and the microaerophilic metabolism of this parasite. Other promising agents derived from higher organisms including phytochemicals, lactoferrin and propolis as well as probiotic bacteria/fungi have also demonstrated significant potential for therapeutic and prophylactic purposes in giardiasis. In this context the present chapter offers a comprehensive review of the current knowledge, including commonly prescribed drugs, causes of therapeutic failures, drug resistance mechanisms, strategies for the discovery of new agents and alternative drug therapies.

Treatment-refractory giardiasis: challenges and solutions

Giardia is the commonest parasitic diarrheal pathogen affecting humans and a frequent cause of waterborne/foodborne parasitic diseases worldwide. Prevalence of giardiasis is higher in children, living in poor, low hygiene settings in developing countries, and in travelers returning from highly endemic areas. The clinical picture of giardiasis is heterogeneous, with high variability in severity of clinical disease. It can become chronic or be followed by post-infectious sequelae. An alarming increase in cases refractory to the conventional treatment with nitroimidazoles (ie, metronidazole) has been reported in low prevalence settings, such as European Union countries, especially in patients returning from Asia. In view of its relevance, we aim in this review to recapitulate present clinical knowledge about Giardia, with a special focus on the challenge of treatment-refractory giardiasis. We propose a working definition of clinically drug-resistant giardiasis, summarize knowledge regarding resistance mechanisms, and discuss its clinical management according to research-based evidence and medical practice. Advances in development and identification of novel drugs and potential non-pharmacological alternatives are also reviewed with the overall aim to define knowledge gaps and suggest future directions for research.

Novel giardicidal compounds bearing proton pump inhibitor scaffold proceeding through triosephosphate isomerase inactivation

Giardiasis is a worldwide parasitic disease that affects mainly children and immunosuppressed people. Side effects and the emergence of resistance over current used drugs make imperative looking for new antiparasitics through discovering of new biological targets and designing of novel drugs. Recently, it has determined that gastric proton-pump inhibitors (PPI) have anti-giardiasic activity. The glycolytic enzyme, triosephosphate isomerase (GlTIM), is one of its potential targets. Therefore, we employed the scaffold of PPI to design new compounds aimed to increase their antigiardial capacity by inactivating GlTIM. Here we demonstrated that two novel PPI-derivatives (BHO2 and BHO3), have better anti-giardiasic activity than omeprazole in concentrations around 120–130 µM, without cytotoxic effect on mammal cell cultures. The derivatives inactivated GlTIM through the chemical modification of Cys222 promoting local structural changes in the enzyme. Furthermore, derivatives forms adducts linked to Cys residues through a C-S bond. We demonstrated that PPI can be used as scaffolds to design better antiparasitic molecules; we also are proposing a molecular mechanism of reaction for these novel derivatives.

Proteomic and functional analyses reveal pleiotropic action of the anti-tumoral compound NBDHEX in Giardia duodenalis

Giardiasis, a parasitic diarrheal disease caused by Giardia duodenalis, affects one billion people worldwide. Treatment relies only on a restricted armamentarium of drugs. The disease burden and the increase in treatment failure highlight the need for novel, safe and well characterized drug options. The antitumoral compound NBDHEX is effective in vitro against Giardia trophozoites and inhibits glycerol-3-phosphate dehydrogenase. Aim of this work was to search for additional NBDHEX protein targets. The intrinsic NBDHEX fluorescence was exploited in a proteomic analysis to select and detect modified proteins in drug treated Giardia. In silico structural analysis, intracellular localization and functional assays were further performed to evaluate drug effects on the identified targets. A small subset of Giardia proteins was covalently bound to the drug at specific cysteine residues. These proteins include metabolic enzymes, e.g. thioredoxin reductase (gTrxR), as well as elongation factor 1B-γ (gEF1Bγ), and structural proteins, e.g. α-tubulin. We showed that NBDHEX in vitro binds to recombinant gEF1Bγ and gTrxR, but only the last one could nitroreduce NBDHEX leading to drug modification of gTrxR catalytic cysteines, with concomitant disulphide reductase activity inhibition and NADPH oxidase activity upsurge. Our results indicate that NBDHEX reacts with multiple targets whose roles and/or functions are specifically hampered. In addition, NBDHEX is in turn converted to reactive intermediates extending its toxicity. The described NBDHEX pleiotropic action accounts for its antigiardial activity and encourages the use of this drug as a promising alternative for the future treatment of giardiasis.

A novel in vitro image-based assay identifies new drug leads for giardiasis

Giardia duodenalis is an intestinal parasite that causes giardiasis, a widespread human gastrointestinal disease. Treatment of giardiasis relies on a small arsenal of compounds that can suffer from limitations including side-effects, variable treatment efficacy and parasite drug resistance. Thus new anti-Giardia drug leads are required. The search for new compounds with anti-Giardia activity currently depends on assays that can be labour-intensive, expensive and restricted to measuring activity at a single time-point. Here we describe a new in vitro assay to assess anti-Giardia activity. This image-based assay utilizes the Perkin-Elmer Operetta^® and permits automated assessment of parasite growth at multiple time points without cell-staining. Using this new approach, we assessed the "Malaria Box" compound set for anti-Giardia activity. Three compounds with sub-μM activity (IC₅₀ 0.6-0.9 μM) were identified as potential starting points for giardiasis drug discovery.

Perspective on the Genetic Response to Antiparasitics: A Review Article

BACKGROUND

Drugs' pharmacokinetics and pharmacodynamics can be affected by diverse genetic variations, within which simple nucleotide polymorphisms (SNPs) are the most common. Genetic variability is one of the factors that could explain questions like why a given drug does not have the desired effect or why do adverse drug reactions arise.

METHODS

In this retrospective observational study, literature search limits were set within PubMed database as well as the epidemiological bulletins published by the Mexican Ministry of Health, from Jan 1st 2001 to Mar 31st 2017 (16 years).

RESULTS

Metabolism of antiparasitic drugs and their interindividual responses are mainly modified by variations in cytochrome P450 enzymes. These enzymes show high frequencies of polymorphic variability thus affecting the expression of CYP2C, CYP2A, CYP2A6, CYP2D6, CYP2E6 and CYP2A6 isoforms. Research in this field opens the door to new personalized treatment approaches in medicine.

CONCLUSION

Clinical and pharmacological utility yield by applying pharmacogenetics to antiparasitic treatments is not intended as a mean to improve the prescription process, but to select or exclude patients that could present adverse drug reactions as well as to evaluate genetic alterations which result in a diversity of responses, ultimately seeking to provide a more effective and safe treatment; therefore choosing a proper dose for the appropriate patient and the optimal treatment duration. Furthermore, pharmacogenetics assists in the development of vaccines. In other words, the aim of this discipline is to find therapeutic targets allowing personalized treatments.

An up-date on Giardia and giardiasis

Giardia intestinalis is a non-invasive protozoan parasite infecting the upper small intestine causing acute, watery diarrhea or giardiasis in 280 million people annually. Asymptomatic infections are equally common and recent data have suggested that infections even can be protective against other diarrheal diseases. Most symptomatic infections resolve spontaneously but infections can lead to chronic disease and treatment failures are becoming more common world-wide. Giardia infections can also result in irritable bowel syndrome (IBS) and food allergies after resolution. Until recently not much was known about the mechanism of giardiasis or the cause of post-giardiasis syndromes and treatment failures, but here we will describe the recent progress in these areas.

Drug Development Against the Major Diarrhea-Causing Parasites of the Small Intestine, Cryptosporidium and Giardia

Diarrheal diseases are among the leading causes of morbidity and mortality in the world, particularly among young children. A limited number of infectious agents account for most of these illnesses, raising the hope that advances in the treatment and prevention of these infections can have global health impact. The two most important parasitic causes of diarrheal disease are Cryptosporidium and Giardia. Both parasites infect predominantly the small intestine and colonize the lumen and epithelial surface, but do not invade deeper mucosal layers. This review discusses the therapeutic challenges, current treatment options, and drug development efforts against cryptosporidiosis and giardiasis. The goals of drug development against Cryptosporidium and Giardia are different. For Cryptosporidium, only one moderately effective drug (nitazoxanide) is available, so novel classes of more effective drugs are a high priority. Furthermore, new genetic technology to identify potential drug targets and better assays for functional evaluation of these targets throughout the parasite life cycle are needed for advancing anticryptosporidial drug design. By comparison, for Giardia, several classes of drugs with good efficacy exist, but dosing regimens are suboptimal and emerging resistance begins to threaten clinical utility. Consequently, improvements in potency and dosing, and the ability to overcome existing and prevent new forms of drug resistance are priorities in antigiardial drug development. Current work on new drugs against both infections has revealed promising strategies and new drug leads. However, the primary challenge for further drug development is the underlying economics, as both parasitic infections are considered Neglected Diseases with low funding priority and limited commercial interest. If a new urgency in medical progress against these infections can be raised at national funding agencies or philanthropic organizations, meaningful and timely progress is possible in treating and possibly preventing cryptosporidiosis and giardiasis.

The Critical Role of the Cytoskeleton in the Pathogenesis of Giardia

Giardia lamblia is a flagellated parasite of the gut and causes significant morbidity worldwide. Novel druggable targets are sorely needed due to Giardia's prevalence and the growing threat of antibiotic resistance. Giardia's conserved and unique cytoskeletal features, such as its eight flagella and ventral disc, are required for host colonization by facilitating motility, attachment, and cell division. Therapies that target these processes could interfere with trophozoite colonization, reduce the time or severity of the infection, and reduce the number of infectious cysts shed into the environment. This requires vetting and prioritizing critical cellular processes and identifying specific Giardia proteins in those processes as targets. It is time to leverage the wealth of data gathered through genome sequencing and proteomic studies, and new insights on the cytoskeleton of Giardia to design effective new drugs to treat giardiasis.

Drug Resistance in the Microaerophilic Parasite Giardia lamblia

The microaerophilic parasite Giardia lamblia is a causative agent of dysentery affecting hundreds of millions of people around the globe every year. The symptoms of the disease, commonly referred to as giardiasis, are diarrhea, nausea, and malabsorption. Treatment of giardiasis is exclusively based on chemotherapy with antigiardial drugs, including metronidazole, albendazole, and nitazoxanide. In this review, all drugs currently used in the treatment of Giardia infections are discussed with a special emphasis on treatment failure and drug resistance.

Infections by Intestinal Coccidia and Giardia duodenalis

The coccidians Cryptosporidium spp, Cyclospora cayetanensis, and Cystoisospora belli and the flagellate Giardia duodenalis are pathogenic protozoa associated with gastrointestinal manifestations. Diagnosis relies heavily on microscopy, and although ova-and-parasite examinations can detect Giardia and Cystoisospora, Cryptosporidium and Cyclospora often require specific diagnostic requests. Approved non-microscopy methods are available for Giardia and Cryptosporidium, although negative results are frequently followed by microscopic assays. Polymerase chain reaction-based methods are not frequently used for diagnosis of Giardia and Cryptosporidium and have been used primarily for epidemiologic or outbreak investigations of Giardia and Cryptosporidium.