Kinetics of inhibition of human and rat dihydroorotate dehydrogenase by atovaquone, lawsone derivatives, brequinar sodium and polyporic acid

Chemical Synthetic Lethality Screens Identify Selective Drug Combinations against Pseudomonas aeruginosa

The emergence of bacterial ESKAPE pathogens presents a formidable challenge to global health, necessitating the development of innovative strategies for antibiotic discovery. Here, we leverage chemical synthetic lethality to locate therapeutic combinations of small molecules against multidrug-resistant Pseudomonas aeruginosa. Using a transposon screen, we identify PyrD as a target for sensitizing P. aeruginosa to subinhibitory doses of ceftazidime. High-throughput inhibitor screens identify two PyrD inhibitors, nordihydroguaiaretic acid (NDGA) and chlorhexidine (CHX), each of which does not significantly affect growth in isolation but exhibits chemical synthetic lethality when combined with low-dose ceftazidime. Downstream biochemical studies elucidate the mechanism of inhibition by NDGA and CHX. Remarkably, this combination is toxic to P. aeruginosa but leaves commensal bacteria, which are more susceptible to antibiotics, unscathed. Aside from advancing drug combinations that may be explored further in the future, our results offer a new approach for devising potent and specific drug combinations against recalcitrant pathogens.

Enhanced Anticancer Efficiency of Curcumin Co-Loaded Lawsone Solid Lipid Nanoparticles Against MCF-7 Breast Cancer Cell Lines: Optimization by Statistical JMP Software-Based Experimental Approach

The present study highlighted enhancing the therapeutic effectiveness of curcumin (CUR) co-loaded lawsone (LS) through a solid lipid nanoparticles (SLNs)-based delivery system. The cetyl palmitate (CP), polyethylene glycol 400 (PEG), and probe sonication time (PS) were considered as independent variables whereas particle size and % entrapment efficiency (EE) were selected as dependent variables. The CUR-LS-SLN was developed by hot emulsification followed by probe sonication. A 23 factorial design was utilized in formulation development using JMP software version 17. Notably, the particle size and %EE of all the formulations were about 500 nm and greater than 75%, respectively. The zeta potential value was found to be -46.8 mV. From leverage plots significant and sensitive factors on particle size and %EE were identified. Contour plots led to the identification of an optimized formula whereby maintaining CP at 100 mg, PEG 400 at 6 mL, and PS at 10 min the desired particle size and %EE was achieved. TEM studies indicated the spherical shape of the particles. MTT assays of Michigan Cancer Foundation-7 (MCF-7) cells showed enhanced efficacy and greater cell inhibition of CUR-LS-SLN and combining both drugs using nanocarriers gave superior inhibition as compared with using either of the drugs evident from IC50 values of 3.7, 9.4, and 2.5 μM, respectively, for CUR, LS, and CUR-LS-SLN. The cells in the combination mostly had irregular cell walls and cell shrinkage was noted and greater cell reduction was also seen. It was found that the enhanced cytotoxicity effect of MCF-7 cells on the developed formulation was attributed to the drug's synergistic actions, more efficient nanocarrier internalizations, and sustained drug release from the formulation. Stability studies indicated that the optimized SLN was stable for 6 months.

Molecular analysis of the 2022 mpox outbreak and antiviral activity of dihydroorotate dehydrogenase inhibitors against orthopoxviruses

Monkeypox virus (MPXV) has caused a large pandemic outbreak in 2022 with more than 90.000 confirmed cases and 181 deaths. Notably, signs of microevolution and host adaption have been observed. Here, we demonstrate that viral genomes from Franconia, Bavaria acquired different mutations. Three isolates obtained from diagnostic samples, submitted from suspected Mpox cases, show differences in their replication capacities. One MPXV isolate which shows the fastest replication kinetics and higher viral loads, possesses a unique non-synonymous mutation (D616L) in the A11L protein (gene OPG136), which encodes for a protein that is part of a major viral core structure. In regard to pandemic preparedness and future outbreaks, we analyzed the antiviral activity of dihydroorotate dehydrogenase (DHODH) inhibitors, and show that they are active against MPXV, vaccinia virus (VACV), and cowpox virus (CPXV) and therefore likely against orthopoxviruses in general. In agreement with that, we also demonstrated that chemical optimization leads to compounds with EC50 values in the sub-nanomolar range, associated with low cytotoxicity, which forms a good basis for future drug development from this chemical series.

Tumor-Targeted Metal-Organic Framework for Improved Photodynamic Therapy and Inhibited Tumor Metastasis in Melanoma

Tumor hypoxia and elevated intracellular glutathione (GSH) levels significantly compromise the effectiveness of photodynamic therapy (PDT) in treating melanoma. In this study, we synthesized positively charged nanoparticles through a self-assembly method, incorporating photosensitizer verteporfin (VER), mitochondrial respiratory inhibitor atovaquone (ATO), and Fe3+. Subsequently, the nanoparticles were modified with sodium hyaluronate (HA) to obtain HA-ATO-Fe3+-VER nanoparticles (HAFV NPs). The fabricated HAFV NPs demonstrated excellent stability and in vitro Fenton reaction activity. HA facilitated the cellular internalization of HAFV NPs by targeting CD44 receptors, hence relieving tumor hypoxia through the disruption of the mitochondrial respiratory chain and involvement in the Fenton reaction. Simultaneously, ATO directly impeded the biosynthesis of GSH by diminishing ATP levels, while Fe3+ was supposed to oxidate GSH to GSSG, thereby doubly depleting GSH. The integration of these multiple mechanisms markedly enhanced the PDT efficacy of VER. Following intravenous administration, HAFV NPs preferentially accumulated in tumor tissues with minimal accumulation in the skin, demonstrating favorable biocompatibility in vivo. Furthermore, HAFV NPs effectively inhibited tumor growth and lung metastasis, which presents a promising strategy for melanoma treatment.

Unveiling the Antiviral Capabilities of Targeting Human Dihydroorotate Dehydrogenase against SARS-CoV-2

The urgent need for effective treatments against emerging viral diseases, driven by drug-resistant strains and new viral variants, remains critical. We focus on inhibiting the human dihydroorotate dehydrogenase (HsDHODH), one of the main enzymes responsible for pyrimidine nucleotide synthesis. This strategy could impede viral replication without provoking resistance. We evaluated naphthoquinone fragments, discovering potent HsDHODH inhibition with IC50 ranging from 48 to 684 nM, and promising in vitro anti-SARS-CoV-2 activity with EC50 ranging from 1.2 to 2.3 μM. These compounds exhibited low toxicity, indicating potential for further development. Additionally, we employed computational tools such as molecular docking and quantitative structure-activity relationship (QSAR) models to analyze protein-ligand interactions, revealing that these naphthoquinones exhibit a protein binding pattern similar to brequinar, a potent HsDHODH inhibitor. These findings represent a significant step forward in the search for effective antiviral treatments and have great potential to impact the development of new broad-spectrum antiviral drugs.

Glutathione depletion and dihydroorotate dehydrogenase inhibition actuated ferroptosis-augment to surmount triple-negative breast cancer

Ferroptosis is a promising therapeutic approach for combating malignant cancers, but its effectiveness is limited in clinical due to the adaptability and self-repair abilities of cancer cells. Mitochondria, as the pivotal player in ferroptosis, exhibit tremendous therapeutic potential by targeting the intramitochondrial anti-ferroptotic pathway mediated by dihydroorotate dehydrogenase (DHODH). In this study, an albumin-based nanomedicine was developed to induce augmented ferroptosis in triple-negative breast cancer (TNBC) by depleting glutathione (GSH) and inhibiting DHODH activity. The nanomedicine (ATO/SRF@BSA) was developed by loading sorafenib (SRF) and atovaquone (ATO) into bovine serum albumin (BSA). SRF is an FDA-approved ferroptosis inducer and ATO is the only drug used in clinical that targets mitochondria. By combining the effects of SRF and ATO, ATO/SRF@BSA promoted the accumulation of lipid peroxides within mitochondria by inhibiting the glutathione peroxidase 4 (GPX4)-GSH pathway and downregulating the DHODH-coenzyme Q (CoQH2) defense mechanism, triggers a burst of lipid peroxides. Simultaneously, ATO/SRF@BSA suppressed cancer cell self-repair and enhanced cell death by inhibiting the synthesis of adenosine triphosphate (ATP) and pyrimidine nucleotides. Furthermore, the anti-cancer results showed that ATO/SRF@BSA exhibited tumor-specific killing efficacy, significantly improved the tumor hypoxic microenvironment, and lessened the toxic side effects of SRF. This work presents an efficient and easily achievable strategy for TNBC treatment, which may hold promise for clinical applications.

Synthesis and evaluation of biological effects of modified graphene oxide nanoparticles containing Lawson (Henna extract) on gastric cancer cells

PURPOSE

Targeted Graphene Oxide (GO) nanoparticles can play an important role in the treatment of cancer by increasing cancer cell targeting. This study was conducted to synthesize GO nanoparticles functionalized with chitosan-folate (CS-FA) to deliver a natural product Lawsone (LA) for cancer treatment.

METHODS

After characterization of the LA-GO-CS-FA, antioxidant activities of the nanoparticles were investigated by ABTS, DPPH, and FRAP tests. CAM assay was used to study the effect of nanoparticles on angiogenesis. The expression level of inflammatory and angiogenic genes in cells treated with nanoparticles was evaluated by real-time PCR.

RESULTS

The findings demonstrated the formation of nanoparticles with a size of 113.3 nm, a PDI of 0.31, and a surface charge of + 11.07 mV. The percentages of encapsulation efficiency were reported at 93%. Gastric cancer cells were reported as the most sensitive to treatment compared to the control, and the gastric cancer cells were used to study gene expression changes. The anti-angiogenic effects of nanoparticles were confirmed by reducing the average number and length of blood vessels and reducing the height and weight of embryos in the CAM assay. The reducing the expression of genes involved in angiogenesis in real-time PCR was demonstrated. Nanoparticles displayed high antioxidant properties by inhibiting DPPH and ABTS radicals and reducing iron ions in the FRAP method. The reduction of pro-inflammatory genes in AGS cells which were treated with nanoparticles indicates the anti-inflammatory properties of nanoparticles.

CONCLUSION

This study showed the efficacy of nanoparticles in inhibiting gastric cancer cells by relying on inhibiting angiogenesis.

Medicinal chemistry approaches for the discovery of Plasmodium falciparum dihydroorotate dehydrogenase inhibitors as antimalarial agents

Malaria is a severe human disease and a global health problem because of drug-resistant strains. Drugs reported to prevent the growth of Plasmodium parasites target various phases of the parasites' life cycle. Antimalarial drugs can inhibit key enzymes that are responsible for the cellular growth and development of parasites. Plasmodium falciparum dihydroorotate dehydrogenase is one such enzyme that is necessary for de novo pyrimidine biosynthesis. This review focuses on various medicinal chemistry approaches used for the discovery and identification of selective P. falciparum dihydroorotate dehydrogenase inhibitors as antimalarial agents. This comprehensive review discusses recent advances in the selective therapeutic activity of distinct chemical classes of compounds as P. falciparum dihydroorotate dehydrogenase inhibitors and antimalarial drugs.

Unveiling the membrane bound dihydroorotate: Quinone oxidoreductase from Staphylococcus aureus

Staphylococcus aureus is an opportunistic pathogen and one of the most frequent causes for community acquired and nosocomial bacterial infections. Even so, its energy metabolism is still under explored and its respiratory enzymes have been vastly overlooked. In this work, we unveil the dihydroorotate:quinone oxidoreductase (DHOQO) from S. aureus, the first example of a DHOQO from a Gram-positive organism. This protein was shown to be a FMN containing menaquinone reducing enzyme, presenting a Michaelis-Menten behaviour towards the two substrates, which was inhibited by Brequinar, Leflunomide, Lapachol, HQNO, Atovaquone and TFFA with different degrees of effectiveness. Deletion of the DHOQO coding gene (Δdhoqo) led to lower bacterial growth rates, and effected in cell morphology and metabolism, most importantly in the pyrimidine biosynthesis, here systematized for S. aureus MW2 for the first time. This work unveils the existence of a functional DHOQO in the respiratory chain of the pathogenic bacterium S. aureus, enlarging the understanding of its energy metabolism.

Screening for DAX1/EWS-FLI1 functional inhibitors identified dihydroorotate dehydrogenase as a therapeutic target for Ewing's sarcoma

OBJECTIVE

EWS-FLI1 is the most common oncogenic fusion protein in Ewing's sarcoma family tumors (ESFTs). DAX1, an orphan member of the nuclear receptor superfamily, is up-regulated by EWS-FLI1 and plays a key role in the transformed phenotype of ESFTs.

METHODS

To discover a functional inhibitor of DAX1 and EWS-FLI1, we screened small-molecular inhibitors using a DAX1 reporter assay system.

RESULTS

K-234 and its derivatives, which were dihydroorotate dehydrogenase (DHODH) inhibitors, showed inhibitory effects in the reporter assay. K-234 inhibited the growth of Ewing's sarcoma with various fusion types, and K-234 derivatives altered the expression of EWS-FLI1-regulated genes. The DAX1 expression had no effect on the growth inhibitory effect of the K-234 derivatives, while DHODH overexpression or uridine treatment attenuated their inhibitory effects, suggesting that inhibition by K-234 derivatives occurs through DHODH inhibition. An in vivo study showed that a K-234 derivative clearly inhibited tumor growth in an Ewing's sarcoma xenograft mouse model.

CONCLUSION

Taken together, the present results suggest that DHODH inhibitors can inhibit the function of DAX1/EWS-FLI1 in ESFTs and might be a therapeutic agent with potent anti-tumor activity for Ewing's sarcoma patients.

Active mitochondrial respiration in cancer: a target for the drug

The relative contribution of mitochondrial respiration and subsequent energy production in malignant cells has remained controversial to date. Enhanced aerobic glycolysis and impaired mitochondrial respiration have gained more attention in the metabolic study of cancer. In contrast to the popular concept, mitochondria of cancer cells oxidize a diverse array of metabolic fuels to generate a majority of the cellular energy by respiration. Several mitochondrial respiratory chain (MRC) subunits' expressions are critical for the growth, metastasis, and cancer cell invasion. Also, the assembly factors, which regulate the integration of individual MRC complexes into native super-complexes, are upregulated in cancer. Moreover, a series of anti-cancer drugs function by inhibiting respiration and ATP production. In this review, we have specified the roles of mitochondrial fuels, MRC subunits, and super-complex assembly factors that promote active respiration across different cancer types and discussed the potential roles of MRC inhibitor drugs in controlling cancer.

Protein production, kinetic and biophysical characterization of three human dihydroorotate dehydrogenase mutants associated with Miller syndrome

Miller syndrome is a rare Mendelian disorder caused by mutations in the gene encoding human dihydroorotate dehydrogenase (DHODH). Human DHODH, a Class II DHODH, is an integral protein of the inner mitochondrial membrane (IMM) catalyzing the fourth step of the de novo pyrimidine biosynthesis pathway. Here we present a summary of the state of knowledge regarding Miller syndrome in the absence of any current review on the topic. We then describe the production and characterization of three distinct DHODH missense mutations (G19E, E52G, R135C) associated with Miller syndrome by means of enzyme kinetics and biophysical techniques. These human DHODH mutants were produced both in E. coli and in insect cells using the baculovirus expression vector system. We can show that the effects of these mutations differ from each other and the wild-type enzyme with respect to decreased enzymatic activity, decreased protein stability and probably disturbance of the correct import into the IMM. In addition, our results show that the N-terminus of human DHODH is not only a structural element necessary for correct mitochondrial import and location of DHODH on the outer side of the IMM, but also influences thermal stability, enzymatic activity and affects the kinetic parameters.Supplemental data for this article is available online at https://doi.org/10.1080/15257770.2021.2023749 .

Mitochondrial DHODH regulates hypoxia-inducible factor 1 expression in OTSCC

Oral tongue squamous cell carcinoma (OTSCC) was one of the most hypoxic tumors with unfavorable outcomes. Hypoxia-inducible factor-1 (HIF-1) signaling was associated with cancer proliferation, lymph node metastasis, angiogenesis and poor prognosis of OTSCC. Dihydroorotate dehydrogenase (DHODH) catalyzed the rate-limiting step in the de novo pyrimidine biosynthesis. The aim of the study was to explore the biological function of DHODH and investigate whether DHODH regulated HIF-1 signaling in OTSCC. Proliferation, migration and anoikis resistance were used to determine the function of DHODH. Western blot and luciferase activity assays were used to determine the regulatory role of DHODH on HIF-1. We found that increased DHODH expression was associated with advanced tumor stage and poorly differentiated tumor in head and neck cancer patients in The Cancer Genome Atlas (TCGA). DHODH enhanced the proliferation and aggressiveness of OTSCC. Moreover, DHODH prompted tumor growth and metastasis in vivo. DHODH promoted transcription, protein stability, and transactivation activity of HIF1A. DHODH-induced HIF1A upregulation in OTSCC can be reversed by reactive oxygen species (ROS) scavenger, indicating that DHODH enhanced HIF1A expression via ROS production. DHODH inhibitor suppressed DHODH-mediated ROS generation and HIF1A upregulation. Targeting DHODH using clinically available inhibitor, atovaquone, might provide a new strategy to treat OTSCC.

Atovaquone and Berberine Chloride Reduce SARS-CoV-2 Replication In Vitro

Epidemic RNA viruses seem to arise year after year leading to countless infections and devastating disease. SARS-CoV-2 is the most recent of these viruses, but there will undoubtedly be more to come. While effective SARS-CoV-2 vaccines are being deployed, one approach that is still missing is effective antivirals that can be used at the onset of infections and therefore prevent pandemics. Here, we screened FDA-approved compounds against SARS-CoV-2. We found that atovaquone, a pyrimidine biosynthesis inhibitor, is able to reduce SARS-CoV-2 infection in human lung cells. In addition, we found that berberine chloride, a plant-based compound used in holistic medicine, was able to inhibit SARS-CoV-2 infection in cells through direct interaction with the virion. Taken together, these studies highlight potential avenues of antiviral development to block emerging viruses. Such proactive approaches, conducted well before the next pandemic, will be essential to have drugs ready for when the next emerging virus hits.

Antimalarial Inhibitors Targeting Epigenetics or Mitochondria in Plasmodium falciparum: Recent Survey upon Synthesis and Biological Evaluation of Potential Drugs against Malaria

Despite many efforts, malaria remains among the most problematic infectious diseases worldwide, mainly due to the development of drug resistance by P. falciparum. Over the past decade, new essential pathways have been emerged to fight against malaria. Among them, epigenetic processes and mitochondrial metabolism appear to be important targets. This review will focus on recent evolutions concerning worldwide efforts to conceive, synthesize and evaluate new drug candidates interfering selectively and efficiently with these two targets and pathways. The focus will be on compounds/scaffolds that possess biological/pharmacophoric properties on DNA methyltransferases and HDAC’s for epigenetics, and on cytochrome bc1 and dihydroorotate dehydrogenase for mitochondrion.

Discovery of a first-in-class inhibitor of sulfide:quinone oxidoreductase that protects against adverse cardiac remodeling and heart failure

AIMS

Hydrogen sulfide (H2S) is a potent signaling molecule that activates diverse cardioprotective pathways by posttranslational modification (persulfidation) of cysteine residues in upstream protein targets. Heart failure patients with reduced ejection fraction (HFrEF) exhibit low levels of H2S. Sulfide: quinone oxidoreductase (SQOR) catalyzes the first irreversible step in the metabolism of H2S and plays a key role in regulating H2S-mediated signaling. Our aim here was to discover a first-in-class inhibitor of human SQOR and evaluate its cardioprotective effect in an animal model of HFrEF.

METHODS AND RESULTS

We identified a potent inhibitor of human SQOR (STI1, IC50 = 29 nM) by high-throughput screening of a small-molecule library, followed by focused medicinal chemistry optimization and structure-based design. STI1 is a competitive inhibitor that binds with high selectivity to the coenzyme Q-binding pocket in SQOR. STI1 exhibited very low cytotoxicity and attenuated the hypertrophic response of neonatal rat ventricular cardiomyocytes and H9c2 cells induced by neurohormonal stressors. A mouse HFrEF model was produced by transverse aortic constriction (TAC). Treatment of TAC mice with STI1 mitigated the development of cardiomegaly, pulmonary congestion, dilatation of the left ventricle, and cardiac fibrosis and decreased the pressure gradient across the aortic constriction. Moreover, STI1 dramatically improved survival, preserved cardiac function, and prevented the progression to HFrEF by impeding the transition from compensated to decompensated left ventricle hypertrophy.

CONCLUSION

We demonstrate that the coenzyme Q-binding pocket in human SQOR is a druggable target and establish proof of concept for the potential of SQOR inhibitors to provide a novel therapeutic approach for the treatment of HFrEF.

TRANSLATIONAL PERSPECTIVE

In HFrEF there is a compelling need for new drugs that mitigate the pathological remodeling induced by injury and improve patient survival. This study identifies SQOR-inhibiting drugs as a promising first-in-class therapy for HFrEF patients. Due to the well-established protective properties of H2S-induced signaling in renal physiology and disease, this novel class of heart failure therapeutics may also address the large unmet need of therapies for approximately 50% of heart failure patients that have coexisting chronic renal dysfunction.

Phytocompounds Targeting Metabolic Reprogramming in Cancer: An Assessment of Role, Mechanisms, Pathways, and Therapeutic Relevance

The metabolism of cancer is remarkably different from that of normal cells and confers a variety of benefits, including the promotion of other cancer hallmarks. As the rewired metabolism is a near-universal property of cancer cells, efforts are underway to exploit metabolic vulnerabilities for therapeutic benefits. In the continued search for safer and effective ways of cancer treatment, structurally diverse plant-based compounds have gained substantial attention. Here, we present an extensive assessment of the role of phytocompounds in modulating cancer metabolism and attempt to make a case for the use of plant-based compounds in targeting metabolic vulnerabilities of cancer. We discuss the pharmacological interactions of phytocompounds with major metabolic pathways and evaluate the role of phytocompounds in the regulation of growth signaling and transcriptional programs involved in the metabolic transformation of cancer. Lastly, we examine the potential of these compounds in the clinical management of cancer along with limitations and challenges.

Metabolic Rewiring in Radiation Oncology Toward Improving the Therapeutic Ratio

To meet the anabolic demands of the proliferative potential of tumor cells, malignant cells tend to rewire their metabolic pathways. Although different types of malignant cells share this phenomenon, there is a large intracellular variability how these metabolic patterns are altered. Fortunately, differences in metabolic patterns between normal tissue and malignant cells can be exploited to increase the therapeutic ratio. Modulation of cellular metabolism to improve treatment outcome is an emerging field proposing a variety of promising strategies in primary tumor and metastatic lesion treatment. These strategies, capable of either sensitizing or protecting tissues, target either tumor or normal tissue and are often focused on modulating of tissue oxygenation, hypoxia-inducible factor (HIF) stabilization, glucose metabolism, mitochondrial function and the redox balance. Several compounds or therapies are still in under (pre-)clinical development, while others are already used in clinical practice. Here, we describe different strategies from bench to bedside to optimize the therapeutic ratio through modulation of the cellular metabolism. This review gives an overview of the current state on development and the mechanism of action of modulators affecting cellular metabolism with the aim to improve the radiotherapy response on tumors or to protect the normal tissue and therefore contribute to an improved therapeutic ratio.

The pathway to pyrimidines: The essential focus on dihydroorotate dehydrogenase, the mitochondrial enzyme coupled to the respiratory chain

This paper is based on the Anne Simmonds Memorial Lecture, given by Monika Löffler at the International Symposium on Purine and Pyrimidine Metabolism in Man, Lyon 2019. It is dedicated to H. Anne Simmonds (died 2010) - a founding member of the ESSPPMM, since 2003 Purine and Pyrimidine Society - and her outstanding contributions to the identification and study of inborn errors of purine and pyrimidine metabolism. The distinctive intracellular arrangement of pyrimidine de novo synthesis in higher eukaryotes is important to cells with a high demand for nucleic acid synthesis. The proximity of the enzyme active sites and the resulting channeling in CAD and UMP synthase is of kinetic benefit. The intervening enzyme dihydroorotate dehydrogenase (DHODH) is located in the mitochondrion with access to the ubiquinone pool, thus ensuring efficient removal of redox equivalents through the constitutive activity of the respiratory chain, also a mechanism through which the input of 2 ATP for carbamylphosphate synthesis is balanced by Oxphos. The obligatory contribution of O₂ to de novo UMP synthesis means that DHODH has a pivotal role in adapting the proliferative capacity of cells to different conditions of oxygenation, such as hypoxia in growing tumors. DHODH also is a validated drug target in inflammatory diseases. This survey of selected topics of personal interest and reflection spans some 40 years of our studies from tumor cell cultures under hypoxia to in vitro assays including purification from mitochondria, localization, cloning, expression, biochemical characterization, crystallisation, kinetics and inhibition patterns of eukaryotic DHODH enzymes.

Dihydroorotate dehydrogenase inhibitors in anti-infective drug research

Pyrimidines are essential for the cell survival and proliferation of living parasitic organisms, such as Helicobacter pylori, Plasmodium falciparum and Schistosoma mansoni, that are able to impact upon human health. Pyrimidine building blocks, in human cells, are synthesised via both de novo biosynthesis and salvage pathways, the latter of which is an effective way of recycling pre-existing nucleotides. As many parasitic organisms lack pyrimidine salvage pathways for pyrimidine nucleotides, blocking de novo biosynthesis is seen as an effective therapeutic means to selectively target the parasite without effecting the human host. Dihydroorotate dehydrogenase (DHODH), which is involved in the de novo biosynthesis of pyrimidines, is a validated target for anti-infective drug research. Recent advances in the DHODH microorganism field are discussed herein, as is the potential for the development of DHODH-targeted therapeutics.

Phytophthora infestans Dihydroorotate Dehydrogenase Is a Potential Target for Chemical Control - A Comparison With the Enzyme From Solanum tuberosum

The oomycete Phytophthora infestans is the causal agent of tomato and potato late blight, a disease that causes tremendous economic losses in the production of solanaceous crops. The similarities between oomycetes and the apicomplexa led us to hypothesize that dihydroorotate dehydrogenase (DHODH), the enzyme catalyzing the fourth step in pyrimidine biosynthetic pathway, and a validated drug target in treatment of malaria, could be a potential target for controlling P. infestans growth. In eukaryotes, class 2 DHODHs are mitochondrially associated ubiquinone-linked enzymes that catalyze the fourth, and only redox step of de novo pyrimidine biosynthesis. We characterized the enzymes from both the pathogen and a host, Solanum tuberosum. Plant DHODHs are known to be class 2 enzymes. Sequence analysis suggested that the pathogen enzyme (PiDHODHs) also belongs to this class. We confirmed the mitochondrial localization of GFP-PiDHODH showing colocalization with mCherry-labeled ATPase in a transgenic pathogen. N-terminally truncated versions of the two DHODHs were overproduced in E. coli, purified, and kinetically characterized. StDHODH exhibited a apparent specific activity of 41 ± 1 μmol min^-1 mg^-1, a k_cat^app of 30 ± 1 s^-1, and a K_m^app of 20 ± 1 μM for L-dihydroorotate, and a K_m^app= 30 ± 3 μM for decylubiquinone (Qd). PiDHODH exhibited an apparent specific activity of 104 ± 1 μmol min^-1 mg^-1, a k_cat^app of 75 ± 1 s^-1, and a K_m^app of 57 ± 3 μM for L-dihydroorotate, and a K_m^app of 15 ± 1 μM for Qd. The two enzymes exhibited different activities with different quinones and napthoquinone derivatives, and different sensitivities to compounds known to cause inhibition of DHODHs from other organisms. The IC₅₀ for A77 1726, a nanomolar inhibitor of human DHODH, was 2.9 ± 0.6 mM for StDHODH, and 79 ± 1 μM for PiDHODH. In vivo, 0.5 mM A77 1726 decreased mycelial growth by approximately 50%, after 92 h. Collectively, our findings suggest that the PiDHODH could be a target for selective inhibitors and we provide a biochemical background for the development of compounds that could be helpful for the control of the pathogen, opening the way to protein crystallization.

Lawsone-loaded Niosome and its antitumor activity in MCF-7 breast Cancer cell line: a Nano-herbal treatment for Cancer

Phytochemicals like Lawsone have some drawbacks that stem from their poor solubility. Low solubility in aqueous mediums results in low bioavailability, poor permeability and instability of phytochemical compounds in biological environments. The aim of this study was to design nanoniosomes containing Lawsone (Law) using non-ionic surfactants and cholesterol. Niosomes were prepared by thin film hydration method (TFH). Then, they were loaded with Henna extract (HLaw) and standard Lawsone (SLaw), and two resulted formulations were compared. The henna extract was analyzed by mass gas chromatography. Size, zeta potential, polydispersity index (PDI) and morphology of the loaded formulations were evaluated by dynamic light scattering (DLS) and scanning electron spectroscopy (SEM). The incorporation and release rate of Law from niosome bilayers were evaluated by UV-Vis spectroscopy. In vitro experiments were carried out to evaluate antitumor activity in MCF-7 cell line. The results showed distinct spherical shapes and particle sizes were about 250 nm in diameter and have negative zeta potentials. Niosomes were stable at 4 °C for 2 months. Entrapment efficiently of both formulations was about 70% and showed a sustained release profile. In vitro study exhibited that using of niosome to encapsulating Law can significantly increase antitumor activity of formulation in MCF-7 cell line compared to Law solution (free Law). Thus, niosomes are a promising carrier system for delivery of phytochemical compounds that have poor solubility in biological fluids. Graphical abstract ᅟ.

Plasmodium falciparum dihydroorotate dehydrogenase: a drug target against malaria

Malaria remains one of the most lethal infectious diseases worldwide, and the most severe form is caused by Plasmodium falciparum. In recent decades, the major challenge to treatment of this disease has been the ability of the protozoan parasite to develop resistance to the drugs that are currently in use. Among P. falciparum enzymes, P. falciparum dihydroorotate dehydrogenase has been identified as an important target in drug discovery. Interference with the activity of this enzyme inhibits de novo pyrimidine biosynthesis and consequently prevents malarial infection. Organic synthesis, x-ray crystallography, high-throughput screening and molecular modeling methods such as molecular docking, quantitative structure-activity relationships, structure-based pharmacophore mapping and molecular dynamics simulations have been applied to the discovery of new inhibitors of P. falciparum dihydroorotate dehydrogenase.

Synthesis, Design, and Structure⁻Activity Relationship of the Pyrimidone Derivatives as Novel Selective Inhibitors of Plasmodium falciparum Dihydroorotate Dehydrogenase

The inhibition of Plasmodium falciparum dihydroorotate dehydrogenase (PfDHODH) potentially represents a new treatment option for malaria, as P. falciparum relies entirely on a de novo pyrimidine biosynthetic pathway for survival. Herein, we report a series of pyrimidone derivatives as novel inhibitors of PfDHODH. The most potent compound, 26, showed high inhibition activity against PfDHODH (IC₅₀ = 23 nM), with >400-fold species selectivity over human dihydroorotate dehydrogenase (hDHODH). The brand-new inhibitor scaffold targeting PfDHODH reported in this work may lead to the discovery of new antimalarial agents.

Development of small-molecule viral inhibitors targeting various stages of the life cycle of emerging and re-emerging viruses

In recent years, unexpected outbreaks of infectious diseases caused by emerging and re-emerging viruses have become more frequent, which is possibly due to environmental changes. These outbreaks result in the loss of life and economic hardship. Vaccines and therapeutics should be developed for the prevention and treatment of infectious diseases. In this review, we summarize and discuss the latest progress in the development of small-molecule viral inhibitors against highly pathogenic coronaviruses, including severe acute respiratory syndrome coronavirus and Middle East respiratory syndrome coronavirus, Ebola virus, and Zika virus. These viruses can interfere with the specific steps of viral life cycle by blocking the binding between virus and host cells, disrupting viral endocytosis, disturbing membrane fusion, and interrupting viral RNA replication and translation, thereby demonstrating potent therapeutic effect against various emerging and re-emerging viruses. We also discuss some general strategies for developing small-molecule viral inhibitors.

Effects of dihydroorotate dehydrogenase (DHODH) inhibitors on the growth of Theileria equi and Babesia caballi in vitro

Theileria equi and Babesia caballi are the causative agents of equine piroplasmosis (EP), which affects equine production in various parts of the world. However, a safe and effective drug is not currently available for treatment of EP. Dihydroorotate dehydrogenase (DHODH) is the fourth enzyme in the de novo pyrimidine synthesis pathway and has been known as a novel drug target for several apicomplexan protozoan parasites. In this study, we evaluated four DHODH inhibitors; atovaquone (ATV), leflunomide (LFN), brequinar (Breq), and 7-hydroxy-5-[1,2,4] triazolo [1,5,a] pyrimidine (TAZ) on the growth of T. equi and B. caballi in vitro and compared them to diminacene aceturate (Di) as the control drug. The growth of T. equi and B. caballi was significantly hindered by all inhibitors except TAZ. The half maximal inhibitory concentration (IC₅₀) of ATV, LFN, Breq and Di against T. equi was approximately 0.028, 109, 11 and 40 μM, respectively, whereas the IC₅₀ of ATV, LFN, Breq and Di against B. caballi was approximately 0.128, 193, 5.2 and 16.2 μM, respectively. Using bioinformatics and Western blot analysis, we showed that TeDHODH was similar to other Babesia parasite DHODHs, and confirmed that targeting DHODHs could be useful for the development of novel chemotherapeutics for treatment of EP.

Lapachol, a compound targeting pyrimidine metabolism, ameliorates experimental autoimmune arthritis

Background

The inhibition of pyrimidine biosynthesis by blocking the dihydroorotate dehydrogenase (DHODH) activity, the prime target of leflunomide (LEF), has been proven to be an effective strategy for rheumatoid arthritis (RA) treatment. However, a considerable proportion of RA patients are refractory to LEF. Here, we investigated lapachol (LAP), a natural naphthoquinone, as a potential DHODH inhibitor and addressed its immunosuppressive properties.

Methods

Molecular flexible docking studies and bioactivity assays were performed to determine the ability of LAP to interact and inhibit DHODH. In vitro studies were conducted to assess the antiproliferative effect of LAP using isolated lymphocytes. Finally, collagen-induced arthritis (CIA) and antigen-induced arthritis (AIA) models were employed to address the anti-arthritic effects of LAP.

Results

We found that LAP is a potent DHODH inhibitor which had a remarkable ability to inhibit both human and murine lymphocyte proliferation in vitro. Importantly, uridine supplementation abrogated the antiproliferative effect of LAP, supporting that the pyrimidine metabolic pathway is the target of LAP. In vivo, LAP treatment markedly reduced CIA and AIA progression as evidenced by the reduction in clinical score, articular tissue damage, and inflammation.

Conclusions

Our findings propose a binding model of interaction and support the ability of LAP to inhibit DHODH, decreasing lymphocyte proliferation and attenuating the severity of experimental autoimmune arthritis. Therefore, LAP could be considered as a potential immunosuppressive lead candidate with potential therapeutic implications for RA.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-017-1236-x) contains supplementary material, which is available to authorized users.

Fluorescence assay of dihydroorotate dehydrogenase that may become a cancer biomarker

We developed an assay method for measuring dihydroorotate dehydrogenase (DHODH) activity in cultured HeLa cells and fibroblasts, and in stage III stomach cancer and adjacent normal tissues from the same patient. The assay comprised enzymatic reaction of DHODH with a large amount of dihydroorotic acid substrate, followed by fluorescence (FL) detection specific for orotic acid using the 4-trifluoromethyl-benzamidoxime fluorogenic reagent. The DHODH activities in the biologically complex samples were readily measured by the assay method. Our data indicate significantly higher DHODH activity in HeLa cells (340 ± 25.9 pmol/10⁵ cells/h) than in normal fibroblasts (54.1 ± 7.40 pmol/10⁵ cells/h), and in malignant tumour tissue (1.10 ± 0.19 nmol/mg total proteins/h) than in adjacent normal tissue (0.24 ± 0.11 nmol/mg total proteins/h). This is the first report that DHODH activity may be a diagnostic biomarker for cancer.

Development of ML390: A Human DHODH Inhibitor That Induces Differentiation in Acute Myeloid Leukemia

Homeobox transcription factor A9 (HoxA9) is overexpressed in 70% of patients diagnosed with acute myeloid leukemia (AML), whereas only a small subset of AML patients respond to current differentiation therapies. A cell line overexpressing HoxA9 was derived from the bone marrow of a lysozyme-GFP mouse. In this fashion, GFP served as an endogenous reporter of differentiation, permitting a high-throughput phenotypic screen against the MLPCN library. Two chemical scaffolds were optimized for activity yielding compound ML390, and genetic resistance and sequencing efforts identified dihydroorotate dehydrogenase (DHODH) as the target enzyme. The DHODH inhibitor brequinar works against these leukemic cells as well. The X-ray crystal structure of ML390 bound to DHODH elucidates ML390s binding interactions.

The anti-malarial atovaquone increases radiosensitivity by alleviating tumour hypoxia

Tumour hypoxia renders cancer cells resistant to cancer therapy, resulting in markedly worse clinical outcomes. To find clinical candidate compounds that reduce hypoxia in tumours, we conduct a high-throughput screen for oxygen consumption rate (OCR) reduction and identify a number of drugs with this property. For this study we focus on the anti-malarial, atovaquone. Atovaquone rapidly decreases the OCR by more than 80% in a wide range of cancer cell lines at pharmacological concentrations. In addition, atovaquone eradicates hypoxia in FaDu, HCT116 and H1299 spheroids. Similarly, it reduces hypoxia in FaDu and HCT116 xenografts in nude mice, and causes a significant tumour growth delay when combined with radiation. Atovaquone is a ubiquinone analogue, and decreases the OCR by inhibiting mitochondrial complex III. We are now undertaking clinical studies to assess whether atovaquone reduces tumour hypoxia in patients, thereby increasing the efficacy of radiotherapy.

Targeting of Helicobacter pylori thymidylate synthase ThyX by non-mitotoxic hydroxy-naphthoquinones

ThyX is an essential thymidylate synthase that is mechanistically and structurally unrelated to the functionally analogous human enzyme, thus providing means for selective inhibition of bacterial growth. To identify novel compounds with anti-bacterial activity against the human pathogenic bacterium Helicobacter pylori, based on our earlier biochemical and structural analyses, we designed a series of eighteen 2-hydroxy-1,4-naphthoquinones (2-OH-1,4-NQs) that target HpThyX. Our lead-like molecules markedly inhibited the NADPH oxidation and 2′-deoxythymidine-5′-monophosphate-forming activities of HpThyX enzyme in vitro, with inhibitory constants in the low nanomolar range. The identification of non-cytotoxic and non-mitotoxic 2-OH-1,4-NQ inhibitors permitted testing their in vivo efficacy in a mouse model for H. pylori infections. Despite the widely assumed toxicity of naphthoquinones (NQs), we identified tight-binding ThyX inhibitors that were tolerated in mice and can be associated with a modest effect in reducing the number of colonizing bacteria. Our results thus provide proof-of-concept that targeting ThyX enzymes is a highly feasible strategy for the development of therapies against H. pylori and a high number of other ThyX-dependent pathogenic bacteria. We also demonstrate that chemical reactivity of NQs does not prevent their exploitation as anti-microbial compounds, particularly when mitotoxicity screening is used to prioritize these compounds for further experimentation.

A screen of approved drugs and molecular probes identifies therapeutics with anti-Ebola virus activity

Currently, no approved therapeutics exist to treat or prevent infections induced by Ebola viruses, and recent events have demonstrated an urgent need for rapid discovery of new treatments. Repurposing approved drugs for emerging infections remains a critical resource for potential antiviral therapies. We tested ~2600 approved drugs and molecular probes in an in vitro infection assay using the type species, Zaire ebolavirus. Selective antiviral activity was found for 80 U.S. Food and Drug Administration-approved drugs spanning multiple mechanistic classes, including selective estrogen receptor modulators, antihistamines, calcium channel blockers, and antidepressants. Results using an in vivo murine Ebola virus infection model confirmed the protective ability of several drugs, such as bepridil and sertraline. Viral entry assays indicated that most of these antiviral drugs block a late stage of viral entry. By nature of their approved status, these drugs have the potential to be rapidly advanced to clinical settings and used as therapeutic countermeasures for Ebola virus infections.

How mitochondrial dysfunction affects zebrafish development and cardiovascular function: an in vivo model for testing mitochondria-targeted drugs

BACKGROUND AND PURPOSE

Mitochondria are a drug target in mitochondrial dysfunction diseases and in antiparasitic chemotherapy. While zebrafish is increasingly used as a biomedical model, its potential for mitochondrial research remains relatively unexplored. Here, we perform the first systematic analysis of how mitochondrial respiratory chain inhibitors affect zebrafish development and cardiovascular function, and assess multiple quinones, including ubiquinone mimetics idebenone and decylubiquinone, and the antimalarial atovaquone.

EXPERIMENTAL APPROACH

Zebrafish (Danio rerio) embryos were chronically and acutely exposed to mitochondrial inhibitors and quinone analogues. Concentration-response curves, developmental and cardiovascular phenotyping were performed together with sequence analysis of inhibitor-binding mitochondrial subunits in zebrafish versus mouse, human and parasites. Phenotype rescuing was assessed in co-exposure assays.

KEY RESULTS

Complex I and II inhibitors induced developmental abnormalities, but their submaximal toxicity was not additive, suggesting active alternative pathways for complex III feeding. Complex III inhibitors evoked a direct normal-to-dead transition. ATP synthase inhibition arrested gastrulation. Menadione induced hypochromic anaemia when transiently present following primitive erythropoiesis. Atovaquone was over 1000-fold less lethal in zebrafish than reported for Plasmodium falciparum, and its toxicity partly rescued by the ubiquinone precursor 4-hydroxybenzoate. Idebenone and decylubiquinone delayed rotenone- but not myxothiazol- or antimycin-evoked cardiac dysfunction.

CONCLUSION AND IMPLICATIONS

This study characterizes pharmacologically induced mitochondrial dysfunction phenotypes in zebrafish, laying the foundation for comparison with future studies addressing mitochondrial dysfunction in this model organism. It has relevant implications for interpreting zebrafish disease models linked to complex I/II inhibition. Further, it evidences zebrafish's potential for in vivo efficacy or toxicity screening of ubiquinone analogues or antiparasitic mitochondria-targeted drugs.

Original 2-(3-alkoxy-1H-pyrazol-1-yl)pyrimidine derivatives as inhibitors of human dihydroorotate dehydrogenase (DHODH)

From a research program aimed at the design of new chemical entities followed by extensive screening on various models of infectious diseases, an original series of 2-(3-alkoxy-1H-pyrazol-1-yl)pyrimidines endowed with notable antiviral properties were found. Using a whole cell measles virus replication assay, we describe here some aspects of the iterative process that, from 2-(4-benzyl-3-ethoxy-5-methyl-1H-pyrazol-1-yl)pyrimidine, led to 2-(4-(2,6-difluorophenoxy)-3-isopropoxy-5-methyl-1H-pyrazol-1-yl)-5-ethylpyrimidine and a 4000-fold improvement of antiviral activity with a subnanomolar level of inhibition. Moreover, recent precedents in the literature describing antiviral derivatives acting at the level of the de novo pyrimidine biosynthetic pathway led us to determine that the mode of action of this series is based on the inhibition of the cellular dihydroorotate dehydrogenase (DHODH), the fourth enzyme of this pathway. Biochemical studies with recombinant human DHODH led us to measure IC50 as low as 13 nM for the best example of this original series when using 2,3-dimethoxy-5-methyl-6-(3-methyl-2-butenyl)-1,4-benzoquinone (coenzyme Q1) as a surrogate for coenzyme Q10, the cofactor of this enzyme.

Development of a human dihydroorotate dehydrogenase (hDHODH) pharma-similarity index approach with scaffold-hopping strategy for the design of novel potential inhibitors

Human dihydroorotate dehydrogenase (hDHODH) is a class-2 dihydroorotate dehydrogenase. Because it is extensively used by proliferating cells, its inhibition in autoimmune and inflammatory diseases, cancers, and multiple sclerosis is of substantial clinical importance. In this study, we had two aims. The first was to develop an hDHODH pharma-similarity index approach (PhSIA) using integrated molecular dynamics calculations, pharmacophore hypothesis, and comparative molecular similarity index analysis (CoMSIA) contour information techniques. The approach, for the discovery and design of novel inhibitors, was based on 25 diverse known hDHODH inhibitors. Three statistical methods were used to verify the performance of hDHODH PhSIA. Fischer’s cross-validation test provided a 98% confidence level and the goodness of hit (GH) test score was 0.61. The q², r², and predictive r² values were 0.55, 0.97, and 0.92, respectively, for a partial least squares validation method. In our approach, each diverse inhibitor structure could easily be aligned with contour information, and common substructures were unnecessary. For our second aim, we used the proposed approach to design 13 novel hDHODH inhibitors using a scaffold-hopping strategy. Chemical features of the approach were divided into two groups, and the Vitas-M Laboratory fragment was used to create de novo inhibitors. This approach provides a useful tool for the discovery and design of potential inhibitors of hDHODH, and does not require docking analysis; thus, our method can assist medicinal chemists in their efforts to identify novel inhibitors.

On dihydroorotate dehydrogenases and their inhibitors and uses

Proper nucleosides availability is crucial for the proliferation of living entities (eukaryotic cells, parasites, bacteria, and virus). Accordingly, the uses of inhibitors of the de novo nucleosides biosynthetic pathways have been investigated in the past. In the following we have focused on dihydroorotate dehydrogenase (DHODH), the fourth enzyme in the de novo pyrimidine nucleosides biosynthetic pathway. We first described the different types of enzyme in terms of sequence, structure, and biochemistry, including the reported bioassays. In a second part, the series of inhibitors of this enzyme along with a description of their potential or actual uses were reviewed. These inhibitors are indeed used in medicine to treat autoimmune diseases such as rheumatoid arthritis or multiple sclerosis (leflunomide and teriflunomide) and have been investigated in treatments of cancer, virus, and parasite infections (i.e., malaria) as well as in crop science.

Disruption of uridine homeostasis links liver pyrimidine metabolism to lipid accumulation

We report in this study an intrinsic link between pyrimidine metabolism and liver lipid accumulation utilizing a uridine phosphorylase 1 transgenic mouse model UPase1-TG. Hepatic microvesicular steatosis is induced by disruption of uridine homeostasis through transgenic overexpression of UPase1, an enzyme of the pyrimidine catabolism and salvage pathway. Microvesicular steatosis is also induced by the inhibition of dihydroorotate dehydrogenase (DHODH), an enzyme of the de novo pyrimidine biosynthesis pathway. Interestingly, uridine supplementation completely suppresses microvesicular steatosis in both scenarios. The effective concentration (EC(50)) for uridine to suppress microvesicular steatosis is approximately 20 µM in primary hepatocytes of UPase1-TG mice. We find that uridine does not have any effect on in vitro DHODH enzymatic activity. On the other hand, uridine supplementation alters the liver NAD(+)/NADH and NADP(+)/NADPH ratios and the acetylation profile of metabolic, oxidation-reduction, and antioxidation enzymes. Protein acetylation is emerging as a key regulatory mechanism for cellular metabolism. Therefore, we propose that uridine suppresses fatty liver by modulating the liver protein acetylation profile. Our findings reveal a novel link between uridine homeostasis, pyrimidine metabolism, and liver lipid metabolism.

Discovery of diverse human dihydroorotate dehydrogenase inhibitors as immunosuppressive agents by structure-based virtual screening

This study applied an efficient virtual screening strategy integrating molecular docking with MM-GBSA rescoring to identify diverse human dihydroorotate dehydrogenase (hDHODH) inhibitors. Eighteen compounds with IC(50) values ranging from 0.11 to 18.8 μM were identified as novel hDHODH inhibitors that exhibited overall species-selectivity over Plasmodium falciparum dihydroorotate dehydrogenase (pfDHODH). Compound 8, the most potent one, showed low micromolar inhibitory activity against hDHODH with an IC(50) value of 0.11 μM. Moreover, lipopolysaccharide-induced B-cell assay and mixed lymphocyte reaction assay revealed that most of the hits showed potent antiproliferative activity against B and T cells, which demonstrates their potential application as immunosuppressive agents. In particular, compound 18 exhibited potent B-cell inhibitory activity (IC(50) = 1.78 μM) and presents a B-cell-specific profile with 17- and 26-fold selectivities toward T and Jurkat cells, respectively.

Discovery of 4-hydroxy-1,6-naphthyridine-3-carbonitrile derivatives as novel PDE10A inhibitors

A series of 1,6-naphthyridine-based compounds was synthesized as potent phosphodiesterase 10A (PDE10A) inhibitors. Structure-based chemical modifications of the discovered chemotype served to further improve potency and selectivity over DHODH, laying the foundation for future optimization efforts.

An aggregation sensing reporter identifies leflunomide and teriflunomide as polyglutamine aggregate inhibitors

Intracellular protein aggregation is a common pathologic feature in neurodegenerative diseases such as Huntington' disease, amyotrophic lateral sclerosis and Parkinson' disease. Although progress towards understanding protein aggregation in vitro has been made, little of this knowledge has translated to patient therapy. Moreover, mechanisms controlling aggregate formation and catabolism in cellulo remain poorly understood. One limitation is the lack of tools to quantitatively monitor protein aggregation and disaggregation. Here, we developed a protein-aggregation reporter that uses huntingtin exon 1 containing 72 glutamines fused to the N-terminal end of firefly luciferase (httQ72-Luc). httQ72-Luc fails to aggregate unless seeded by a non-luciferase-containing polyglutamine (polyQ) protein such as Q80-cfp. Upon co-aggregation, httQ72-luc becomes insoluble and loses its enzymatic activity. Using httQ72-Luc with Q80(CFP/YFP) as seeds, we screened the Johns Hopkins Clinical Compound Library and identified leflunomide, a dihydroorotate dehydrogenase inhibitor with immunosuppressive and anti-psoriatic activities, as a novel drug that prevents polyQ aggregation. Leflunomide and its active metabolite teriflunomide inhibited protein aggregation independently of their known role in pyrimidine biosynthesis, since neither uridine treatment nor other pyrimidine biosynthesis inhibitors affected polyQ aggregation. Inducible cell line and cycloheximide-chase experiments indicate that these drugs prevent incorporation of expanded polyQ into an aggregate. This study demonstrates the usefulness of luciferase-based protein aggregate reporters for high-throughput screening applications. As current trials are under-way for teriflunomide in the treatment of multiple sclerosis, we propose that this drug be considered a possible therapeutic agent for polyQ diseases.