Myotonic dystrophy type-1 (DM1), the most prevalent form of adult muscular dystrophy, is caused by expansion of a CTG repeat in the 3′ untranslated region of the DM protein kinase (DMPK) gene. The pathogenic effects of the CTG expansion arise from the deleterious effects of the mutant transcript. RNA with expanded CUG tracts alters the activities of several RNA binding proteins, including muscleblind-like 1 (MBNL1). MBNL1 becomes sequestered in nuclear foci in complex with the expanded CUG repeat RNA. The resulting loss of MBNL1 activity causes mis-regulated alternative splicing of multiple genes, leading to symptoms of DM1. The binding interaction between MBNL1 and mutant RNA could be a key step in the pathogenesis of DM1 and serves as a potential target for therapeutic intervention. We have developed two high throughput screen (HTS) suitable assays using both homogenous time-resolved fluorescence energy transfer (HTRF) and AlphaScreen technologies to detect the binding of a C-terminally His-tagged MBNL1 and a biotinylated (CUG)12 RNA. These assays are homogenous and successfully miniaturized to 1536-well plate format. Both assays were validated and show robust signal-to-basal ratios and Z’ factors.
Myotonic dystrophy type 1; DM1; Muscleblind-like 1; MBNL1
Small-molecule compounds approved for use as drugs may be “repurposed” for new indications and studied to determine the mechanisms of their beneficial and adverse effects. A comprehensive collection of all small-molecule drugs approved for human use would be invaluable for systematic repurposing across human diseases, particularly for rare and neglected diseases, for which the cost and time required for development of a new chemical entity are often prohibitive. Previous efforts to build such a comprehensive collection have been limited by the complexities, redundancies, and semantic inconsistencies of drug naming within and among regulatory agencies worldwide; a lack of clear conceptualization of what constitutes a drug; and a lack of access to physical samples. We report here the creation of a definitive, complete, and nonredundant list of all approved molecular entities as a freely available electronic resource and a physical collection of small molecules amenable to high-throughput screening.
Malaria is a deadly infectious disease in many tropical and subtropical countries. Previous efforts to eradicate malaria have failed, largely due to the emergence of drug-resistant parasites, insecticide-resistant mosquitoes and, in particular, the lack of drugs or vaccines to block parasite transmission. ATP-binding cassette (ABC) transporters are known to play a role in drug transport, metabolism, and resistance in many organisms, including malaria parasites. To investigate whether a Plasmodium falciparum ABC transporter (Pf14_0244 or PfABCG2) modulates parasite susceptibility to chemical compounds or plays a role in drug resistance, we disrupted the gene encoding PfABCG2, screened the recombinant and the wild-type 3D7 parasites against a library containing 2,816 drugs approved for human or animal use, and identified an antihistamine (ketotifen) that became less active against the PfABCG2-disrupted parasite in culture. In addition to some activity against asexual stages and gametocytes, ketotifen was highly potent in blocking oocyst development of P. falciparum and the rodent parasite Plasmodium yoelii in mosquitoes. Tests of structurally related tricyclic compounds identified additional compounds with similar activities in inhibiting transmission. Additionally, ketotifen appeared to have some activity against relapse of Plasmodium cynomolgi infection in rhesus monkeys. Further clinical evaluation of ketotifen and related compounds, including synthetic new derivatives, in blocking malaria transmission may provide new weapons for the current effort of malaria eradication.
A hallmark of Huntington’s disease is the presence of a large polyglutamine expansion in the first exon of the Huntingtin protein and the propensity of protein aggregation by the mutant proteins. Aberrant protein aggregation also occurs in other polyglutamine expansion disorders, as well as in other neurodegenerative diseases including Parkinson’s, Alzheimer’s, and prion diseases. However, the pathophysiological role of these aggregates in the cell death that characterizes the diseases remains unclear. Identification of small molecule probes that modulate protein aggregation and cytotoxicity caused by aggregated proteins may greatly facilitate the studies on pathogenesis of these diseases and potentially lead to development of new therapies. Based on a detergent insoluble property of the Huntingtin protein aggregates, we have developed a homogenous assay to rapidly quantitate the levels of protein aggregates in a cellular model of Huntington’s disease. The protein aggregation assay has also been multiplexed with a protease release assay for the measurement of cytotoxicity resulting from aggregated proteins in the same cells. Through a testing screen of a compound library, we have demonstrated that this multiplexed cytotoxicity and protein aggregation assay has ability to identify active compounds that prevent cell death and/or modulate protein aggregation in cells of the Huntington’s disease model. Therefore, this multiplexed screening approach is also useful for development of high-throughput screening assays for other neurodegenerative diseases involving protein aggregation.
Huntington’s disease; protein aggregation; high-throughput screen; polyglutamine expansion; multiplex assay.
The human cytochrome P450 (CYP450) isozymes are the most important enzymes in the body to metabolize many endogenous and exogenous substances including environmental toxins and therapeutic drugs. Any unnecessary interactions between a small molecule and CYP450 isozymes may raise a potential to disarm the integrity of the protection. Accurately predicting the potential interactions between a small molecule and CYP450 isozymes is highly desirable for assessing the metabolic stability and toxicity of the molecule. The National Institutes of Health Chemical Genomics Center (NCGC) has screened a collection of over seventeen thousand compounds against the five major isozymes of CYP450 (1A2, 2C9, 2C19, 2D6 and 3A4) in a quantitative high throughput screening (qHTS) format. In this study, we developed support vector classification (SVC) models for these five isozymes using a set of customized generic atom types. The CYP450 datasets were randomly split into equal-sized training and test sets. The optimized SVC models exhibited high predictive power against the test sets for all five CYP450 isozymes with accuracies of 0.93, 0.89, 0.89, 0.85 and 0.87 for 1A2, 2C9, 2C19, 2D6 and 3A4, respectively, as measured by the area under the receiver operating characteristic (ROC) curves. The important atom types and features extracted from the five models are consistent with the structural preferences for different CYP450 substrates reported in the literature. We also identified novel features with significant discerning power to separate CYP450 actives from inactives. These models can be useful in prioritizing compounds in a drug discovery pipeline, or recognizing the toxic potential of environmental chemicals.
We herein describe the rapid synthesis of a diverse set of dihydroquinazolin-4-ones and quinazolin-4-ones, their biological evaluation as thyroid stimulating hormone receptor (TSHR) agonists, and SAR analysis. Among the compounds screened, 8b was 60-fold more potent than the hit compound 1a, which was identified from a high throughput screen of over 73,000 compounds.
Spinal Muscular Atrophy (SMA) is an autosomal recessive disorder affecting the expression or function of survival motor neuron protein (SMN) due to the homozygous deletion or rare point mutations in the survival motor neuron gene 1 (SMN1). The human genome includes a second nearly identical gene called SMN2 that is retained in SMA. SMN2 transcripts undergo alternative splicing with reduced levels of SMN. Up-regulation of SMN2 expression, modification of its splicing, or inhibition of proteolysis of the truncated protein derived from SMN2 have been discussed as potential therapeutic strategies for SMA. In this manuscript, we detail the discovery of a series of arylpiperidines as novel modulators of SMN protein. Systematic hit-to-lead efforts significantly improved potency and efficacy of the series in the primary and orthogonal assays. Structure property relationships including microsomal stability, cell permeability and in vivo pharmacokinetics (PK) studies were also investigated. We anticipate that a lead candidate chosen from this series may serve as a useful probe for exploring the therapeutic benefits of SMN protein up-regulation in SMA animal models, and a starting point for clinical development.
Drug repurposing for cancer treatment is an emerging approach to discover clinically approved drugs that demonstrate antineoplastic effect. The effective therapeutics for patients with advanced adrenocortical carcinoma(ACC) are greatly needed. The objective of this study was to identify and validate drugs with antineoplastic effect in ACC cells using a novel quantitative high-throughput drug screening (qHTS) technique.
A quantitative high-throughput proliferation assay of 2,816 clinically approved drugs was performed in the NCI-H295R ACC cell line. We validated the antiproliferative effect of candidate compounds in NCI-H295R cells. Further validation was performed in 3-dimensional multicellular aggregates (MCA) of NCI-H295R and SW-13 cell lines.
We identified 79 active compounds against ACC cells; 21 had an efficacy ≥60% and IC50 <1 μM. The top drug categories enriched were cardiotonic, antiseptic, and antineoplastic. We selected Bortezomib, ouabain, Methotrexate, pyrimethamine for validation. All had an antiproliferative effect in monolayer culture of NCI-H295R cells at clinical achievable serum level. Bortezomib and ouabain inhibited growth of MCA in both cell lines at a low concentration (10 fold below IC50). Methotrexate inhibited growth and caused disintegration of MCA in both cell lines at concentrations well below the maximum serum level (10 to 100 fold of IC50). Pyrimethamine caused growth inhibition in both cell lines at 10 fold of IC50 concentration.
qHTS of previously approved compounds is an effective and efficient method to identify anticancer drugs for a rare cancer such as ACC. We have validated the antineoplastic effect of Bortezomib, ouabain, Methotrexate and pyrimethamine, which could be translated into clinical trials in patients with locally advanced and/or metastatic ACC.
Adrenocortical cancer; High throughput drug screening; Chemotherapy; Drug repurposing; Indication switching
We describe how room temperature storage of a 1,120 member compound library prepared in either DMSO or in a hydrated DMSO/water (67/33) mixture affects the reproducibility of potency values as monitored using cytochrome P450 1A2 and 2D6 isozyme assays. The bioluminescent assays showed Z′-factors of 0.71 and 0.62, with 18% and 32% of the library found as active against the CYP 1A2 and 2D6 isozymes respectively. We tested the library using quantitative high-throughput screening to generate potency values for every library member which was measured at seven time intervals spanning 37 weeks. We calculated the minimum significant ratio (MSR) from these potency values at each time interval and we found that for the library stored in DMSO, the CYP 1A2 and 2D6 assay MSRs progressed from approximately 2.0 to 5.0. The hydrated conditions showed similar performance in both MSR progression and analytical QC results. Based on this study we recommend that DMSO samples be stored in 1,536-well plates for < 4 months at room temperature. Further, the study shows the magnitude of potency changes that can occur in a robust bioassay due to compound sample storage.
HTS; compound storage; DMSO; quantitative HTS
We measured the “druggability” of the ATP-dependent luciferase derived from the firefly Photuris pennsylvanica that was optimized using directed evolution (Ultra-Glo™, Promega). Quantitative high throughput screening (qHTS) was used to determine IC50’s of 198,899 samples against a formulation of Ultra-Glo luciferase (Kinase-Glo™). We found that only 0.1% of the Kinase-Glo inhibitors showed an IC50 < 10 μM compared to 0.9% found from a previous qHTS against the firefly luciferase from Photinus pyralis (lucPpy). Further, the maximum affinity identified in the lucPpy qHTS was 50 nM while for Kinase-Glo this value increased to 600 nM. Compounds with interactions stretching outside the luciferin binding pocket were largely lost with Ultra-Glo luciferase. Therefore, Ultra-Glo luciferase will show less compound interference when used as an ATP sensor compared to lucPpy. This study demonstrates the power of large-scale quantitative analysis of structure-activity relationships (>100K compounds) in addressing important questions such as a target's druggability.
chemical profiling; enzyme assay; PubChem; luciferase; quantitative high-throughput screening
Malaria remains a devastating disease largely because of widespread drug resistance. New drugs and a better understanding of the mechanisms of drug action and resistance are essential for fulfilling the promise of eradicating malaria. Using high-throughput chemical screening and genome-wide association analysis, we identified 32 highly active compounds and genetic loci and genes associated with differential chemical phenotypes (DCPs), defined as ≥5-fold differences in half-maximum inhibitor concentration (IC50) between parasite lines. Chromosomal loci associated with 49 DCPs were confirmed by linkage analysis and tests of genetically modified parasites, including three genes that were linked to 96% of the DCPs. Drugs whose responses mapped to wild type or mutant pfcrt alleles were tested in combination in vitro and in vivo, yielding promising new leads for antimalarial treatments.
Plasmodium falciparum; high-throughput screening; genetic mapping; chemical genomics; phenotype
Background: Oxidative stress has been implicated in the pathogenesis of a variety of diseases ranging from cancer to neurodegeneration, highlighting the need to identify chemicals that can induce this effect. The antioxidant response element (ARE) signaling pathway plays an important role in the amelioration of oxidative stress. Thus, assays that detect the up-regulation of this pathway could be useful for identifying chemicals that induce oxidative stress.
Objectives: We used cell-based reporter methods and informatics tools to efficiently screen a large collection of environmental chemicals and identify compounds that induce oxidative stress.
Methods: We utilized two cell-based ARE assay reporters, β-lactamase and luciferase, to screen a U.S. National Toxicology Program 1,408-compound library (NTP 1408, which contains 1,340 unique compounds) for their ability to induce oxidative stress in HepG2 cells using quantitative high throughput screening (qHTS).
Results: Roughly 3% (34 of 1,340) of the unique compounds demonstrated activity across both cell-based assays. Based on biological activity and structure–activity relationship profiles, we selected 50 compounds for retesting in the two ARE assays and in an additional follow-up assay that employed a mutated ARE linked to β-lactamase. Using this strategy, we identified 30 compounds that demonstrated activity in the ARE-bla and ARE-luc assays and were able to determine structural features conferring compound activity across assays.
Conclusions: Our results support the robustness of using two different cell-based approaches for identifying compounds that induce ARE signaling. Together, these methods are useful for prioritizing chemicals for further in-depth mechanism-based toxicity testing.
ARE; Nrf2; oxidative stress; qHTS; toxicity; Tox21
Finding specific small-molecule inhibitors of protein-protein interactions remains a significant challenge. Recently, attention has grown toward “hot-spot” interactions where binding is dominated by a limited number of amino acid contacts, theoretically offering an increased opportunity for disruption by small molecules. Inhibitors of the interaction between BRCT (C-terminal portion of BRCA1, a key tumor suppressor protein with various functions), and phosphorylated protein (Abraxas, BACH1, CtIP) implicated in DNA damage response and repair pathways, should prove useful in studies of BRCA1’s role in cancer and to potentially sensitize tumors to chemotherapeutic agents. We developed and miniaturized to 1536-well format and 3 μL final volume a pair of fluorescence polarization (FP) assays utilizing fluorescein- and rhodamine-labeled pBACH1 fragment. In order to minimize the effect of fluorescence artifacts and to increase the overall robustness of the screen, the 75,552 compound library members were each assayed against both the fluorescein- and rhodamine-labeled probe-protein complexes in separate but interleaved reactions. In addition, every library compound was tested over a range of concentrations, following the qHTS paradigm (Inglese et al, PNAS, 103, 1147 (2006)). Analyses of the screening results led to the selection and subsequent confirmation of 16 compounds active in both assays. Faced with a traditionally difficult protein-protein interaction assay, by performing two-fluorophore qHTS we were able to confidently select a number of actives for further studies.
The thyroid hormone receptors (TR) are members of the nuclear hormone receptor (NHR) superfamily that regulate development, growth, and metabolism. Upon ligand binding, TR releases bound corepressors and recruits coactivators to modulate target gene expression. Steroid Receptor Coactivator 2 (SRC2) is an important coregulator that interacts with TRβ to activate gene transcription. To identify novel inhibitors of the TRβ and SRC2 interaction, we performed a quantitative high throughput screen (qHTS) of a TRβ-SRC2 fluorescence polarization assay against more than 290,000 small molecules. The qHTS assayed compounds at six concentrations up to 92 uM to generate titration-response curves and determine the potency and efficacy of all compounds. The qHTS dataset enabled the characterization of actives for structure-activity relationships as well as for potential artifacts such as fluorescence interference. Selected qHTS actives were tested in the screening assay using fluoroprobes labeled with Texas Red or fluorescein. The retest identified 19 series and 4 singletons as active in both assays with 40% or greater efficacy, free of compound interference and not toxic to mammalian cells. Selected compounds were tested as independent samples and a methylsulfonylnitrobenzoate series inhibited the TRβ-SRC2 interaction with 5 uM IC50. This series represents a new class of thyroid hormone receptor-coactivator modulators.
thyroid receptor; small molecule; HTS; coactivator; protein-protein interaction
The human ether-a-go-go-related gene (hERG) channel, a member of a family of voltage-gated potassium (K+) channels, plays a critical role in the repolarization of the cardiac action potential. The reduction of hERG channel activity as a result of adverse drug effects or genetic mutations may cause QT interval prolongation and potentially lead to acquired long QT syndrome. Thus, screening for hERG channel activity is important in drug development. Cardiotoxicity associated with the inhibition of hERG channels by environmental chemicals is also a public health concern. To assess the inhibitory effects of environmental chemicals on hERG channel function, we screened the National Toxicology Program (NTP) collection of 1408 compounds by measuring thallium influx into cells through hERG channels. Seventeen compounds with hERG channel inhibition were identified with IC50 potencies ranging from 0.26 to 22 μM. Twelve of these compounds were confirmed as hERG channel blockers in an automated whole cell patch clamp experiment. In addition, we investigated the structure-activity relationship of seven compounds belonging to the quaternary ammonium compound (QAC) series on hERG channel inhibition. Among four active QAC compounds, tetra-n-octylammonium bromide was the most potent with an IC50 value of 260 nM in the thallium influx assay and 80 nM in the patch clamp assay. The potency of this class of hERG channel inhibitors appears to depend on the number and length of their aliphatic side-chains surrounding the charged nitrogen. Profiling environmental compound libraries for hERG channel inhibition provides information useful in prioritizing these compounds for cardiotoxicity assessment in vivo.
cardiotoxicity; hERG; long QT syndrome; NTP 1408 library; patch clamp; qHTS; tetra-n-octylammonium bromide; thallium influx
Gaucher disease is a Lysosomal Storage Disorder (LSD) caused by deficiency in the enzyme glucocerebrosidase (GC). Small molecule chaperones of protein folding and translocation have been proposed as a promising therapeutic approach to this LSD. Most small molecule chaperones described in the literature contain an iminosugar scaffold. Here we present the discovery and evaluation of a new series of GC inhibitors with a quinazoline core. We demonstrate that this series can improve the translocation of GC to the lysosome in patient-derived cells. To optimize this chemical series, systematic synthetic modifications were performed and the SAR was evaluated and compared using three different readouts of compound activity – enzymatic inhibition, enzyme thermostabilization, and lysosomal translocation of GC.
Included among the quantitative high throughput screens (qHTS) conducted in support of the U.S. Tox21 program are those being evaluated for the detection of genotoxic compounds. One such screen is based on the induction of increased cytotoxicity in 7 isogenic chicken DT40 cell lines deficient in DNA repair pathways compared to the parental DNA repair-proficient cell line. To characterize the utility of this approach for detecting genotoxic compounds and identifying the type(s) of DNA damage induced, we evaluated nine of 42 compounds identified as positive for differential cytotoxicity in qHTS (actinomycin D, adriamycin, alachlor, benzotrichloride, diglycidyl resorcinol ether, lovastatin, melphalan, trans-1,4-dichloro-2-butene, tris(2,3-epoxypropyl)isocyanurate) and one non-cytotoxic genotoxic compound (2-aminothiamine) for (1) clastogenicity in mutant and wild-type cells; (2) the comparative induction of γH2AX positive foci by melphalan; (3) the extent to which a 72-hr exposure duration increased assay sensitivity or specificity; (4) the use of 10 additional DT40 DNA repair-deficient cell lines to better analyze the type(s) of DNA damage induced; and (5) the involvement of reactive oxygen species in the induction of DNA damage. All compounds but lovastatin and 2-aminothiamine were more clastogenic in at least one DNA repair-deficient cell line than the wild-type cells. The differential responses across the various DNA repair-deficient cell lines provided information on the type(s) of DNA damage induced. The results demonstrate the utility of this DT40 screen for detecting genotoxic compounds, for characterizing the nature of the DNA damage, and potentially for analyzing mechanisms of mutagenesis.
DT40 DNA repair-deficient cell lines; quantitative high throughput screens; cytotoxicity; genotoxicity; chromosomal aberrations; γH2AX positive foci
Gaucher disease (GD), the most common lysosomal storage disorder, results from the inherited deficiency of the lysosomal enzyme glucocerebrosidase (GCase). Previously, wildtype GCase was used for high throughput screening (HTS) of large collections of compounds to identify small molecule chaperones that could be developed as new therapies for GD. However, the compounds identified from HTS usually showed reduced potency later in confirmatory cell-based assays. An alternate strategy is to perform HTS on mutant enzyme to identify different lead compounds, including those enhancing mutant enzyme activities. We developed a new screening assay using enzyme extract prepared from the spleen of a patient with Gaucher disease with genotype N370S/N370S. In tissue extracts, GCase is in a more native physiological environment, and is present with the native activator saposin C and other potential cofactors. Using this assay, we screened a library of 250,000 compounds and identified novel modulators of mutant GCase including 14 new lead inhibitors and 30 lead activators. The activities of some of the primary hits were confirmed in subsequent cell-based assays using patient-derived fibroblasts. These results suggest that primary screening assays using enzyme extracted from tissues is an alternative approach to identify high quality, physiologically relevant lead compounds for drug development.
The U.S. Tox21 collaborative program represents a paradigm shift in toxicity testing of chemical compounds from traditional in vivo tests to less expensive and higher throughput in vitro methods to prioritize compounds for further study, identify mechanisms of action, and ultimately develop predictive models for adverse health effects in humans. The NIH Chemical Genomics Center (NCGC) is an integral component of the Tox21 collaboration due to its quantitative high throughput screening (qHTS) paradigm, in which titration-based screening is used to profile hundreds of thousands of compounds per week. Here, we describe the Tox21 collaboration, qHTS-based compound testing, and the various Tox21 screening assays that have been validated and tested at the NCGC to date.
Tox21; National Research Council; National Toxicology Program; toxicity testing; in vitro assays; NIH Roadmap; NIH Chemical Genomics Center; quantitative high-throughput screening
Opiates are potent analgesics but also drugs of abuse mainly because they produce euphoria. Chronic use of opiates results in the development of tolerance and dependence. Dr Marshall Nirenberg’s group at the National Institutes of Health (NIH) was the first to use a cellular model system of Neuroblastoma×Glioma hybrid cells (NG108-15) to study morphine addiction. They showed that opiates affect adenylyl cyclase (AC) by two opposing mechanisms mediated by the opiate receptor. Although the cellular mechanisms that cause addiction are not yet completely understood, the most observed correlative biochemical adaptation is the upregulation of adenylyl cyclase. This model also provides the opportunity to look for compounds which could dissociate the acute effect of opiates from the delayed response, upregulation of AC, and thus lead to the discovery of non-addictive drugs. To identify small molecule compounds that can inhibit morphine-induced cAMP overshoot, we have validated and optimized a cell-based assay in a high throughput format that measures cellular cAMP production after morphine withdrawal. The assay performed well in the 1536-well plate format. The LOPAC library of 1280 compounds was screened in this assay on a quantitative high throughput screening (qHTS) platform. A group of compounds that can inhibit morphine induced cAMP overshoot were identified. The most potent compounds are eight naloxone related compounds, including levallorphan tartrate, naloxonazine dihydrochloride, naloxone hydrochloride, naltrexone hydrochloride, and naltriben methanesulfonate. The qHTS approach we used in this study will be useful in identifying novel inhibitors of morphine induced addiction from a larger scale screening.
adenylyl cyclase (AC); Adenosine- 3’,5’-monophosphate (cAMP); quantitative high- throughput screening (qHTS); µ opioid receptor (morphine receptor); Human embryonic kidney293- µ opioid receptor cell line (HEK-MOR); Homogeneous Time-Resolved Fluorescence (HTRF)
Antagonists of the Neuropeptide S Receptor have been postulated as promising therapeutics in the treatment of respiratory, sleep, anxiety, and addictive disorders. Here we present the SAR of a new series of orthosteric antagonists. Neuropeptide S Receptor signaling is coupled to both Gq and Gs proteins, and we observe that different analogues in this structural series can selectively antagonize these two pathways. Many G-protein coupled receptors transduce signals through multiple pathways. Selective antagonism of these pathways may lead the way to the development of more targeted pharmacological profiles and therapies.
Neuropeptide S Receptor antagonist; sleep disorders; addiction disorders; Naphtho Pyrano Pyrimidines; homogeneous time resolved fluorescence; Neuropeptide S radiolabel displacement assay
Antagonists of the neuropeptide S receptor have been postulated as promising therapeutics in the treatment of respiratory, sleep, anxiety, and addictive disorders. Here, we present the SAR of a new series of orthosteric antagonists. Neuropeptide S receptor signaling is coupled to both Gq and Gs proteins, and we observe that different analogues in this structural series can selectively antagonize these two pathways. Many G-protein coupled receptors transduce signals through multiple pathways. Selective antagonism of these pathways may lead the way to the development of more targeted pharmacological profiles and therapies.
Neuropeptide S receptor antagonist; sleep disorders; addiction disorders; naphtho pyrano pyrimidines; homogeneous time-resolved fluorescence; neuropeptide S radiolabel displacement assay
The human pathogen Giardia lamblia is an anaerobic protozoan parasite that causes giardiasis, one of the most common diarrheal diseases worldwide. Although several drugs are available for the treatment of giardiasis, drug resistance has been reported and is likely to increase, and recurrent infections are common. The search for new drugs that can overcome the drug-resistant strains of Giardia is an unmet medical need. New drug screen methods can facilitate the drug discovery process and aid with the identification of new drug targets. Using a bioluminescent ATP content assay, we have developed a phenotypic drug screen method to identify compounds that act against the actively growing trophozoite stage of the parasite. This assay is homogeneous, robust, and suitable for high-throughput screening of large compound collections. A screen of 4,096 pharmacologically active small molecules and approved drugs revealed 43 compounds with selective anti-Giardia properties, including 32 previously reported and 11 novel anti-Giardia agents. The most potent novel compound was fumagillin, which showed 50% inhibitory concentrations of 10 nM against the WB isolate and 2 nM against the GS isolate.