Novel inhibitors of Plasmodium falciparum dihydroorotate dehydrogenase with anti-malarial activity in the mouse model

To quest new targets of Plasmodium parasite and their potential inhibitors to combat antimalarial drug resistance

Malaria remains a global health challenge with significant mortality and morbidity annually, with resistant parasite strains complicating treatment efforts. There is an acute need for novel antimalarial drugs that can put a stop to the future public health crisis caused by the multi-drug resistance strains of the Plasmodium parasite. However, the discovery of these new components is very challenging in the context of the generation of multi-drug resistance properties of malaria. The novel drugs also need to have several properties involving enhanced therapeutic prospects, successful treatment capabilities, and novel mechanisms of action that will forestall the resistance. To successfully achieve this aim researchers are trying to focus on exploring promising malaria targets. Various approaches have been made for the development of drugs for malaria including the remodelling of existing drugs and the development of novel inhibitors which acts on new targets. Advancement in the study provides more information on the biology of parasites and the new targets which help in the development of novel drugs. The present review focuses on the study of novel targets of malaria parasites and subsequent inhibitors of those particular targets. Some of these targets include malarial protease, various transporter proteins, enzymes involved in the synthesis of DNA, and nucleic acids like dihydroorotate dehydrogenase, dihydrofolate reductase, apicoplast and dihydropteroate synthase. Other potential targets are also included in this review such as isoprenoid biosynthesis, farnesyl transferase of parasite, P. falciparum translational elongation factor 2, and phosphatidyl inositol 4 kinase. These promising targets have also been summed up along with their corresponding inhibitors for combating multi-drug resistance malaria.

A comprehensive review of synthetic strategies and SAR studies for the discovery of PfDHODH inhibitors as antimalarial agents. Part 2: Non-DSM compounds

Malaria remains a severe global health concern, with 249 million cases reported in 2022, according to the World Health Organization (WHO) [1]. PfDHODH is an essential enzyme in malaria parasites that helps to synthesize certain building blocks for their growth and development. It has been confirmed that targeting Plasmodium falciparum dihydroorotate dehydrogenase (PfDHODH) enzyme could lead to new and effective antimalarial drugs. Inhibitors of PfDHODH have shown potential for slowing down parasite growth during both the blood and liver stages. Over the last two decades, many species selective PfDHODH inhibitors have been designed, including DSM compounds and other non-DSM compounds. In the first chapter [2] of this review, we have reviewed all synthetic schemes and structure-activity relationship (SAR) studies of DSM compounds. In this second chapter, we have compiled all the other non-DSM PfDHODH inhibitors based on dihydrothiophenones, thiazoles, hydroxyazoles, and N-alkyl-thiophene-2-carboxamides. The review not only offers an insightful overview of the synthetic methods employed but also explores into alternative routes and innovative strategies involving different catalysts and chemical reagents. A critical aspect covered in the review is the SAR studies, which provide a comprehensive understanding of how structural modifications impact the efficacy of PfDHODH inhibitors and challenges related to the discovery of PfDHODH inhibitors. This information is invaluable for scientists engaged in the development of new antimalarial drugs, offering insights into the most promising scaffolds and their synthetic techniques.

Proposition of In silico Pharmacophore Models for Malaria: A Review

In the field of medicinal chemistry, the concept of pharmacophore refers to the specific region of a molecule that possesses essential structural and chemical characteristics for binding to a receptor and eliciting biological activity. Understanding the pharmacophore is crucial for drug research and development, as it allows the design of new drugs. Malaria, a widespread disease, is commonly treated with chloroquine and artemisinin, but the emergence of parasite resistance limits their effectiveness. This study aims to explore computer simulations to discover a specific pharmacophore for Malaria, providing new alternatives for its treatment. A literature review was conducted, encompassing articles proposing a pharmacophore for Malaria, gathered from the "Web of Science" database, with a focus on recent publications to ensure up-to-date analysis. The selected articles employed diverse methods, including ligand-based and structurebased approaches, integrating molecular structure and biological activity data to yield comprehensive analyses. Affinity evaluation between the proposed pharmacophore and the target receptor involved calculating free energy to quantify their interaction. Multiple linear regression was commonly utilized, though it is sensitive to multicollinearity issues. Another recurrent methodology was the use of the Schrödinger package, employing tools such as the Phase module and the OPLS force field for interaction analysis. Pharmacophore model proposition allows threedimensional representations guiding the synthesis and design of new biologically active compounds, offering a promising avenue for discovering therapeutic agents to combat Malaria.

Parasitic Protozoans: Exploring the Potential of N,N'-Bis[2-(5-bromo-7-azabenzimidazol-1-yl)-2-oxoethyl]ethylene-1,3-Diamine and Its Cyclohexyl-1,2-diamine Analogue as TryR and Pf-DHODH Inhibitors

PURPOSE

Major human parasitic protozoans, such as Plasmodium falciparum and Trypanosoma brucei, cause malaria and trypanosomiasis also known as sleeping sickness. In anti-parasitic drug discovery research, trypanothione reductase (TryR) and P. falciparum dihydroorotate dehydrogenase (Pf-DHODH) enzymes are key drug targets in T. brucei and P. falciparum, respectively. The possibility of co-infection of single host by T. brucei and P. falciparum is because both parasites exist in sub-Saharan Africa and the problem of parasite drug resistance necessitates the discovery of new scaffolds, which are strange to the organisms causing these infectious diseases-new scaffolds may help overcome established resistance mechanisms of the organisms.

METHOD

In this study, N,N'-bis[2-(5-bromo-7-azabenzimidazol-1-yl)-2-oxoethyl]ethylene-1,3-diamine and its cyclohexyl-1,2-diamine analogue were explored for their inhibitory potential against TryR and Pf-DHODH by engaging density functional study, molecular dynamic simulations, drug-likeness, in silico and in vitro studies RESULTS/CONCLUSION: Results obtained indicated excellent binding potential of the ligands to the receptors and good ADMET (adsorption, desorption, metabolism, excretion, and toxicity) properties.

Deciphering Interactions between Potential Inhibitors and the Plasmodium falciparum DHODH Enzyme: A Computational Perspective

Malaria is a parasitic disease that, in its most severe form, can even lead to death. Insect-resistant vectors, insufficiently effective vaccines, and drugs that cannot stop parasitic infestations are making the fight against the disease increasingly difficult. It is known that the enzyme dihydroorotate dehydrogenase (DHODH) is of paramount importance for the synthesis of pyrimidine from the Plasmodium precursor, that is, for its growth and reproduction. Therefore, its blockade can lead to disruption of the parasite's life cycle in the vertebrate host. In this scenario, PfDHODH inhibitors have been considered candidates for a new therapy to stop the parasitic energy source. Given what is known, in this work, we applied molecular fractionation with conjugated caps (MFCC) in the framework of the quantum formalism of density functional theory (DFT) to evaluate the energies of the interactions between the enzyme and the different triazolopyrimidines (DSM483, DMS557, and DSM1), including a complex carrying the mutation C276F. From these results, it was possible to identify the main features of each system, focusing on the wild-type and mutant PfDHODH and examining the major amino acid residues that are part of the four complexes. Our analysis provides new information that can be used to develop new drugs that could prove to be more effective alternatives to present antimalarial drugs.

Diverse evolutionary pathways challenge the use of collateral sensitivity as a strategy to suppress resistance

Drug resistance remains a major obstacle to malaria control and eradication efforts, necessitating the development of novel therapeutic strategies to treat this disease. Drug combinations based on collateral sensitivity, wherein resistance to one drug causes increased sensitivity to the partner drug, have been proposed as an evolutionary strategy to suppress the emergence of resistance in pathogen populations. In this study, we explore collateral sensitivity between compounds targeting the Plasmodium dihydroorotate dehydrogenase (DHODH). We profiled the cross-resistance and collateral sensitivity phenotypes of several DHODH mutant lines to a diverse panel of DHODH inhibitors. We focus on one compound, TCMDC-125334, which was active against all mutant lines tested, including the DHODH C276Y line, which arose in selections with the clinical candidate DSM265. In six selections with TCMDC-125334, the most common mechanism of resistance to this compound was copy number variation of the dhodh locus, although we did identify one mutation, DHODH I263S, which conferred resistance to TCMDC-125334 but not DSM265. We found that selection of the DHODH C276Y mutant with TCMDC-125334 yielded additional genetic changes in the dhodh locus. These double mutant parasites exhibited decreased sensitivity to TCMDC-125334 and were highly resistant to DSM265. Finally, we tested whether collateral sensitivity could be exploited to suppress the emergence of resistance in the context of combination treatment by exposing wildtype parasites to both DSM265 and TCMDC-125334 simultaneously. This selected for parasites with a DHODH V532A mutation which were cross-resistant to both compounds and were as fit as the wildtype parent in vitro. The emergence of these cross-resistant, evolutionarily fit parasites highlights the mutational flexibility of the DHODH enzyme.

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.

Discovery of dual-target natural antimalarial agents against DHODH and PMT of Plasmodium falciparum: pharmacophore modelling, molecular docking, quantum mechanics, and molecular dynamics simulations

Malaria is a lethal disease that claims thousands of lives worldwide annually. The objective of this study was to identify new natural compounds that can target two P. falciparum enzymes; P. falciparum Dihydroorotate dehydrogenase (PfDHODH) and P. falciparum phosphoethanolamine methyltransferase (PfPMT). To accomplish this, e-pharmacophore modelling and molecular docking were employed against PfDHODH. Following this, 1201 natural compounds with docking scores of ≤ -7 kcal/mol were docked into the active site of the second enzyme PMT. The top nine compounds were subjected to further investigation using MM-GBSA free binding energy calculations and ADME analysis. The results revealed favourable free binding energy values better than the references, as well as acceptable pharmacokinetic properties. Compounds ZINC000013377887, ZINC000015113777, and ZINC000085595753 were scrutinized to assess their interaction stability with the PfDHODH enzyme, and chemical stability reactivity using molecular dynamics (MD) simulation and density functional theory (DFT) calculations. These findings indicate that the three natural compounds are potential candidates for dual PfDHODH and PfPMT inhibitors for malaria treatment.

Menthol carbonates as potent antiparasitic agents: synthesis and in vitro studies along with computer-aided approaches

Introduction

Despite the number of deaths and the significant economic and social costs associated with Chagas, Leishmaniasis and Malaria diseases worldwide, available drugs are limited and have serious side effects and high toxicity for the patient. Therefore, there is an urgent need for safe, low-cost, and effective treatments. Natural products are an important source of bioactive compounds and there is current interest in finding natural bioactive molecules that can be used for treating these parasitic diseases. In the present study we proposed to evaluate the in vitro antiparasitic activity of new menthol derivatives against Trypanosoma cruzi, Leishmania braziliensis and Plasmodium falciparum; moreover, we propose to explore their mode of action through in silico approaches.

Material and methods

A series of carbonate prodrugs (1–9) were synthesized from menthol with different aliphatic alcohols. Spectroscopic techniques were used to confirm the structures of the synthesized compounds. The cytotoxicity of the compounds was assessed using U-937 cells. In vitro trypanocidal, leishmanicidal and antiplasmodial activity were evaluated using a T. cruzi, L. braziliensis and P. falciparum organism, respectively. In addition, in silico studies were also performed through molecular dynamics simulations and MM-PBSA analysis.

Results

The assay revealed that most of the compounds were highly active against intracellular amastigotes of T. cruzi and L. braziliensis, and had moderate activity against the total forms of P. falciparum. Compound 2 was one of the drugs that showed a high selectivity index (SI) for the three organisms evaluated. The prediction of the ADME properties suggests that all the compounds have drug-like molecular properties and the probability to be lead candidates. Finally, molecular dynamics simulations, and MM-PBSA studies indicate that menthol at the substrate binding site of TcDHODH, LbDHODH and PfDHODH is structurally stable in the same order as the natural substrate; also, interactions of menthol with residues involved in the inhibition of TcDHODH and PfDHODH proteins were predicted.

Conclusions

The present study demonstrates that menthol prodrugs are promising antiparasitic agents; however, the mechanisms of action proposed in this study need to be experimentally verified by future enzymatic assays.

Current status of experimental models for the study of malaria

Infection by malaria parasites (Plasmodium spp.) remains one of the leading causes of morbidity and mortality, especially in tropical regions of the world. Despite the availability of malaria control tools such as integrated vector management and effective therapeutics, these measures have been continuously undermined by the emergence of vector resistance to insecticides or parasite resistance to frontline antimalarial drugs. Whilst the recent pilot implementation of the RTS,S malaria vaccine is indeed a remarkable feat, highly effective vaccines against malaria remain elusive. The barriers to effective vaccines result from the complexity of both the malaria parasite lifecycle and the parasite as an organism itself with consequent major gaps in our understanding of their biology. Historically and due to the practical and ethical difficulties of working with human malaria infections, research into malaria parasite biology has been extensively facilitated by animal models. Animals have been used to study disease pathogenesis, host immune responses and their (dys)regulation and further disease processes such as transmission. Moreover, animal models remain at the forefront of pre-clinical evaluations of antimalarial drugs (drug efficacy, mode of action, mode of resistance) and vaccines. In this review, we discuss commonly used animal models of malaria, the parasite species used and their advantages and limitations which hinder their extrapolation to actual human disease. We also place into this context the most recent developments such as organoid technologies and humanized mice.

Repurposing the Pathogen Box compounds for identification of potent anti-malarials against blood stages of Plasmodium falciparum with PfUCHL3 inhibitory activity

Malaria has endured as a global epidemic since ages and its eradication poses an immense challenge due to the complex life cycle of the causative pathogen and its tolerance to a myriad of therapeutics. PfUCHL3, a member of the ubiquitin C-terminal hydrolase (UCH) family of deubiquitinases (DUBs) is cardinal for parasite survival and emerges as a promising therapeutic target. In this quest, we employed a combination of computational and experimental approaches to identify PfUCHL3 inhibitors as novel anti-malarials. The Pathogen Box library was screened against the crystal structure of PfUCHL3 (PDB ID: 2WE6) and its human ortholog (PDB ID: 1XD3). Fifty molecules with better comparative score, bioavailability and druglikeliness were subjected to in-vitro enzyme inhibition assay and among them only two compounds effectively inhibited PfUCHL3 activity at micro molar concentrations. Both MMV676603 and MMV688704 exhibited anti-plasmodial activity by altering the parasite phenotype at late stages of the asexual life cycle and inducing the accumulation of polyubiquitinated substrates. In addition, both the compounds were non-toxic and portrayed high selectivity window for the parasite over mammalian cells. This is the first comprehensive study to demonstrate the anti-malarial efficacy of PfUCHL3 inhibitors and opens new avenues to exploit UCH family of DUBs as a promising target for the development of next generation anti-malaria therapy.

Eugenol carbonate activity against Plasmodium falciparum, Leishmania braziliensis, and Trypanosoma cruzi

Neglected tropical diseases are a major health problem throughout the world, and there are few effective and safe drugs. In this study, we report the design and synthesis of a novel series of carbonates of eugenol using different aliphatic alcohols and N,N-carbonyldiimidazole. Spectroscopic techniques, including ¹ H nuclear magnetic resonance (NMR), ¹³ C NMR, Fourier transform infrared, and high-resolution mass spectrometry, were used to confirm the structures of the synthesized compounds. In vitro and in silico studies of prodrugs of eugenol were performed to determine their antiplasmodial, trypanocidal, and leishmanicidal activities, and also their cytotoxicity. Compounds were highly active against Leishmania braziliensis and Plasmodium falciparum, whereas the activity shown for Trypanosoma cruzi was moderate. Molecular docking was used to determine a possible mode of action of eugenol against the dihydroorotate dehydrogenase of the three parasites (TcDHODH, LbDHODH, and PfDHODH). Notably, the docking results showed that eugenol not only has binding energy similar to that of the natural substrate (-7.2 and -7.1, respectively) but also has interactions with relevant biological residues of PfDHODH. This result indicates that eugenol could act as a substrate for PfDHODH in the pyrimidine biosynthesis pathway of P. falciparum. In conclusion, the combination of certain aliphatic alcohols and eugenol through a carbonate bond could significantly increase the antiparasitic activity of this class of compounds, which merits further studies.

A Comparative Review on Current and Future Drug Targets Against Bacteria & Malaria

Long before the discovery of drugs like 'antibiotic and anti-parasitic drugs', the infectious diseases caused by pathogenic bacteria and parasites remain as one of the major causes of morbidity and mortality in developing and underdeveloped countries. The phenomenon by which the organism exerts resistance against two or more structurally unrelated drugs is called multidrug resistance (MDR) and its emergence has further complicated the treatment scenario of infectious diseases. Resistance towards the available set of treatment options and poor pipeline of novel drug development puts an alarming situation. A universal goal in the post-genomic era is to identify novel targets/drugs for various life-threatening diseases caused by such pathogens. This review is conceptualized in the backdrop of drug resistance in two major pathogens i.e. "Pseudomonas aeruginosa" and "Plasmodium falciparum". In this review, the available targets and key mechanisms of resistance of these pathogens have been discussed in detail. An attempt has also been made to analyze the common drug targets of bacteria and malaria parasite to overcome the current drug resistance scenario. The solution is also hypothesized in terms of a present pipeline of drugs and efforts made by scientific community.

MalDA, Accelerating Malaria Drug Discovery

The Malaria Drug Accelerator (MalDA) is a consortium of 15 leading scientific laboratories. The aim of MalDA is to improve and accelerate the early antimalarial drug discovery process by identifying new, essential, druggable targets. In addition, it seeks to produce early lead inhibitors that may be advanced into drug candidates suitable for preclinical development and subsequent clinical testing in humans. By sharing resources, including expertise, knowledge, materials, and reagents, the consortium strives to eliminate the structural barriers often encountered in the drug discovery process. Here we discuss the mission of the consortium and its scientific achievements, including the identification of new chemically and biologically validated targets, as well as future scientific directions.

Design, synthesis and antimicrobial activity of novel 2-aminothiophene containing cyclic and heterocyclic moieties

One of the major challenges in the community and healthcare was an impedance of pathogenic bacteria to antibiotics. This work developed 2-aminothiophene derivatives as novel antimicrobial agents. Various 2-aminothiophene derivatives (3a-f, 5a-c, 6a, b, 7, 8a, b and 9) with cyclic and heterocyclic moieties at 5-position were synthesized, and characterized using NMR, IR, and mass spectroscopic techniques. The newly synthesized compounds were evaluated for their antimicrobial activity against bacteria S. pneumoniae, B. subtilis, P. aeruginosa, E. coli, and fungi A. fumigatus, S. mracemosum, G. candidum, C. albicans. Compound 3a with OH group at para position of phenyl ring exhibited significant antibacterial activity stronger than that of the drug standards Ampicillin and Gentamicin. Compound 6b possess pyrazole ring and compound 9 bearing pyridine ring showed promising antifungal activity compare to the standard drug Amphotericin B. The remaining compounds exhibited good to moderate inhibitory activities. In summary, the results suggest that the compounds from 2-aminothiophene derivatives can be used as antimicrobial agents.

Potent Antimalarials with Development Potential Identified by Structure-Guided Computational Optimization of a Pyrrole-Based Dihydroorotate Dehydrogenase Inhibitor Series

Dihydroorotate dehydrogenase (DHODH) has been clinically validated as a target for the development of new antimalarials. Experience with clinical candidate triazolopyrimidine DSM265 (1) suggested that DHODH inhibitors have great potential for use in prophylaxis, which represents an unmet need in the malaria drug discovery portfolio for endemic countries, particularly in areas of high transmission in Africa. We describe a structure-based computationally driven lead optimization program of a pyrrole-based series of DHODH inhibitors, leading to the discovery of two candidates for potential advancement to preclinical development. These compounds have improved physicochemical properties over prior series frontrunners and they show no time-dependent CYP inhibition, characteristic of earlier compounds. Frontrunners have potent antimalarial activity in vitro against blood and liver schizont stages and show good efficacy in Plasmodium falciparum SCID mouse models. They are equally active against P. falciparum and Plasmodium vivax field isolates and are selective for Plasmodium DHODHs versus mammalian enzymes.

Azacarbazole n-3 and n-6 polyunsaturated fatty acids ethyl esters nanoemulsion with enhanced efficacy against Plasmodium falciparum

Alternative therapies are necessary for the treatment of malaria due to emerging drug resistance. However, many promising antimalarial compounds have poor water solubility and suffer from the lack of suitable delivery systems, which seriously limits their activity. To address this problem, we synthesized a series of azacarbazoles that were evaluated for antimalarial activity against D10 (chloroquine-sensitive) and W2 (chloroquine-resistant) strains of P. falciparum. The most active compound, 9H-3-azacarbazole (3), was encapsulated in a novel o/w nanoemulsion consisting of ethyl esters of polyunsaturated fatty acids n-3 and n-6 obtained from flax oil as the oil phase, Smix (Tween 80 and Transcutol HP) and water. This formulation was further analyzed using transmission electron microscopy, dynamic light scattering and in vitro and in vivo studies. It was shown that droplets of the 3-loaded nanosystem were spherical, with satisfactory stability, without cytotoxicity towards fibroblasts and intestinal cell lines at concentrations corresponding to twice the IC50 for P. falciparum. Moreover, the nanoemulsion with this type of oil phase was internalized by Caco-2 cells. Additionally, pharmacokinetics demonstrated rapid absorption of compound 3 (tmax = 5.0 min) after intragastric administration of 3-encapsulated nanoemulsion at a dose of 0.02 mg/kg in mice, with penetration of compound 3 to deep compartments. The 3-encapsulated nanoemulsion was found to be 2.8 and 4.2 times more effective in inhibiting the D10 and W2 strains of the parasite, respectively, compared to non-encapsulated 3. Our findings support a role for novel o/w nanoemulsions as delivery vehicles for antimalarial drugs.

Amino Acid Metabolism in Apicomplexan Parasites

Obligate intracellular pathogens have coevolved with their host, leading to clever strategies to access nutrients, to combat the host's immune response, and to establish a safe niche for intracellular replication. The host, on the other hand, has also developed ways to restrict the replication of invaders by limiting access to nutrients required for pathogen survival. In this review, we describe the recent advancements in both computational methods and high-throughput -omics techniques that have been used to study and interrogate metabolic functions in the context of intracellular parasitism. Specifically, we cover the current knowledge on the presence of amino acid biosynthesis and uptake within the Apicomplexa phylum, focusing on human-infecting pathogens: Toxoplasma gondii and Plasmodium falciparum. Given the complex multi-host lifecycle of these pathogens, we hypothesize that amino acids are made, rather than acquired, depending on the host niche. We summarize the stage specificities of enzymes revealed through transcriptomics data, the relevance of amino acids for parasite pathogenesis in vivo, and the role of their transporters. Targeting one or more of these pathways may lead to a deeper understanding of the specific contributions of biosynthesis versus acquisition of amino acids and to design better intervention strategies against the apicomplexan parasites.

Driving antimalarial design through understanding of target mechanism

Malaria continues to be a global health threat, affecting approximately 219 million people in 2018 alone. The recurrent development of resistance to existing antimalarials means that the design of new drug candidates must be carefully considered. Understanding of drug target mechanism can dramatically accelerate early-stage target-based development of novel antimalarials and allows for structural modifications even during late-stage preclinical development. Here, we have provided an overview of three promising antimalarial molecular targets, PfDHFR, PfDHODH and PfA-M1, and their associated inhibitors which demonstrate how mechanism can inform drug design and be effectively utilised to generate compounds with potent inhibitory activity.

Molecular docking analysis of Plasmodium falciparum dihydroorotate dehydrogenase towards the design of effective inhibitors

Malaria remains a global public health burden with significant mortality and morbidity. Despite the several approved drugs available for its management, the parasite has developed resistance to virtually all known antimalarial drugs. The development of a new drug that can combat resistant to Artemisinin based Combination Therapies (ACTs) for malaria is imperative. Plasmodium falciparum dihydroorotate dehydrogenase (PfDHODH), a flavin-dependent mitochondrial enzyme is vital in the parasite's pyrimidine biosynthesis is a well-known drug target. Therefore, it is of interest to document the MOLECULAR DOCKING analysis (using Maestro, Schrodinger) data of DIHYDROOROTATE DEHYDROGENASE PfDHODH from P. falciparum towards the design of effective inhibitors. The molecular docking features of 10 compounds with reference to chloroquine with PfDHODH are documented in this report for further consideration.

Lead Optimization of a Pyrrole-Based Dihydroorotate Dehydrogenase Inhibitor Series for the Treatment of Malaria

Malaria puts at risk nearly half the world's population and causes high mortality in sub-Saharan Africa, while drug resistance threatens current therapies. The pyrimidine biosynthetic enzyme dihydroorotate dehydrogenase (DHODH) is a validated target for malaria treatment based on our finding that triazolopyrimidine DSM265 (1) showed efficacy in clinical studies. Herein, we describe optimization of a pyrrole-based series identified using a target-based DHODH screen. Compounds with nanomolar potency versus Plasmodium DHODH and Plasmodium parasites were identified with good pharmacological properties. X-ray studies showed that the pyrroles bind an alternative enzyme conformation from 1 leading to improved species selectivity versus mammalian enzymes and equivalent activity on Plasmodium falciparum and Plasmodium vivax DHODH. The best lead DSM502 (37) showed in vivo efficacy at similar levels of blood exposure to 1, although metabolic stability was reduced. Overall, the pyrrole-based DHODH inhibitors provide an attractive alternative scaffold for the development of new antimalarial compounds.

Antimalarial Properties of Isoquinoline Derivative from Streptomyces hygroscopicus subsp. Hygroscopicus: An In Silico Approach

Malaria is one of the life-threatening diseases in the world. The spread of resistance to antimalarial drugs is a major challenge, and resistance to artemisinin has been reported in the Southeast Asian region. In the previous study, the active compound of Streptomyces hygroscopicus subsp. Hygroscopicus (S. hygroscopicus), eponemycin, has been shown to have antimalarial effects. To further analyze the effects of other active compounds on the Plasmodium parasite, identifying and analyzing the effectiveness of compounds contained in S. hygroscopicus through instrumentation of liquid chromatography/mass spectrometry (LC/MS) and in silico studies were very useful. This study aimed at identifying other derivative compounds from S. hygroscopicus and screening the antimalarial activity of the compound by assessing the binding affinity, pharmacokinetic profile, and bond interaction. The derivative compounds were identified using LC/MS. Protein targets for derivative compounds were found through literature studies, and the results of identification of compounds and protein targets were reconstructed into three-dimensional models. Prediction of pharmacokinetic profiles was carried out using Swiss ADME. Screening of protein targets for the derivative compound was carried out using the reverse molecular docking method. Analyzing bond interaction was done by LigPlot. One compound from S. hygroscopicus, i.e., 6,7-dinitro-2-[1, 2, 4]triazole-4-yl-benzo[de]isoquinoline-1,3-dione, was successfully identified using LC/MS. This compound was an isoquinoline derivative compound. Through literature studies with inclusion criteria, thirteen protein targets were obtained for reverse molecular docking. This isoquinoline derivative had the potential to bind to each protein target. The pharmacokinetic profile showed that this compound had the drug-likeness criteria. Conclusion. 6,7-Dinitro-2-[1, 2, 4]triazole-4-yl-benzo[de]isoquinoline-1,3-dione has antimalarial activity as shown by reverse molecular docking studies and pharmacokinetic profiles. The best inhibitory ability of compounds based on bond affinity is with adenylosuccinate synthetase.

An exclusive computational insight toward molecular mechanism of MMV007571, a multitarget inhibitor of Plasmodium falciparum

Recently, two Malaria Box molecules namely MMV007571 and MMV020439 well known inhibitors of New Permeability Pathway (NPP) function also showed a secondary phenotype of inhibition of enzyme Plasmodium falciparum dihydroorotate dehydrogenase (PfDHODH) and cytochrome bc1 complex in metabolic profile assays. Intricacies of their binding at the newly identified targets was need of the hour which motivated us to study their binding using molecular docking and dynamics simulations approach. Interestingly, molecular docking results of both MMV007571 and MMV020439 showed good binding affinity toward the Q_o site of cytochrome bc1 complex while only MMV007571 illustrated notable binding characterstics for PfDHODH. Molecular Dynamics (MD) simulations when carried out for native-PfDHODH, PfDHODH-MMV007571 and PfDHODH-Genz667348 models (100 ns each) demonstrated the role of inhibitors over the N-terminus domain which experienced conformational transition from an open state (22 Å) to closed state (16 Å) in the protein-inhibitor models. Dynamics also indicated that the loop domain near cofactor flavin mononucleotide (FMN) attained more felxibility which further lead to its poor binding and may contribute to inhibition of the oxidation (catalytic) process. Moreover, the pharmacophoric features of MMV007571 was justified and may serve as a template for the design of novel series of more potent multitarget inhibitors against Plasmodium falciparum.AbbreviationsÅAngstromACTsArtemisinin combination therapiescyt bc1cytochrome bc1 complexhhour(s)KKelvinµMmicromolarMMVMedicine for malaria ventureNLucNanoluciferasenMnanomolarNPPNew permeation pathwayPDBProtein data bankPfDHODHPlasmodium falciparum dihydroorotate dehydrogenasePOPC1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholineRBCRed blood corpusclesRMSDRoot-mean-square deviationSPStandard precisionvdWvan der WaalsXPExtra precisionyDHODHYeast dihydroorotate dehydrogenaseCommunicated by Ramaswamy H. Sarma.

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.

Unpacking the Pathogen Box-An Open Source Tool for Fighting Neglected Tropical Disease

The Pathogen Box is a 400-strong collection of drug-like compounds, selected for their potential against several of the world's most important neglected tropical diseases, including trypanosomiasis, leishmaniasis, cryptosporidiosis, toxoplasmosis, filariasis, schistosomiasis, dengue virus and trichuriasis, in addition to malaria and tuberculosis. This library represents an ensemble of numerous successful drug discovery programmes from around the globe, aimed at providing a powerful resource to stimulate open source drug discovery for diseases threatening the most vulnerable communities in the world. This review seeks to provide an in-depth analysis of the literature pertaining to the compounds in the Pathogen Box, including structure-activity relationship highlights, mechanisms of action, related compounds with reported activity against different diseases, and, where appropriate, discussion on the known and putative targets of compounds, thereby providing context and increasing the accessibility of the Pathogen Box to the drug discovery community.

Triazole derivatives and their antiplasmodial and antimalarial activities

Malaria, caused by protozoan parasites of the genus Plasmodium especially by the most prevalent parasite Plasmodium falciparum, represents one of the most devastating and common infectious disease globally. Nearly half of the world population is under the risk of being infected, and more than 200 million new clinical cases with around half a million deaths occur annually. Drug therapy is the mainstay of antimalarial therapy, yet current drugs are threatened by the development of resistance, so it's imperative to develop new antimalarials with great potency against both drug-susceptible and drug-resistant malaria. Triazoles, bearing a five-membered heterocyclic ring with three nitrogen atoms, exhibit promising in vitro antiplasmodial and in vivo antimalarial activities. Moreover, several triazole-based drugs have already used in clinics for the treatment of various diseases, demonstrating the excellent pharmaceutical profiles. Therefore, triazole derivatives have the potential for clinical deployment in the control and eradication of malaria. This review covers the recent advances of triazole derivatives especially triazole hybrids as potential antimalarials. The structure-activity relationship is also discussed to provide an insight for rational designs of more efficient antimalarial candidates.

Identification and Mechanistic Understanding of Dihydroorotate Dehydrogenase Point Mutations in Plasmodium falciparum that Confer in Vitro Resistance to the Clinical Candidate DSM265

Malaria is one of the most challenging human infectious diseases, and both prevention and control have been hindered by the development of Plasmodium falciparum resistance to existing therapies. Several new compounds with novel mechanisms are in clinical development for the treatment of malaria, including DSM265, an inhibitor of Plasmodium dihydroorotate dehydrogenase. To explore the mechanisms by which resistance might develop to DSM265 in the field, we selected for DSM265-resistant P. falciparum parasites in vitro. Any of five different amino acid changes led to reduced efficacy on the parasite and to decreased DSM265 binding to P. falciparum DHODH. The DSM265-resistant parasites retained full sensitivity to atovaquone. All but one of the observed mutations were in the DSM265 binding site, and the remaining C276F was in the adjacent flavin cofactor site. The C276F mutation was previously identified in a recrudescent parasite during a Phase IIa clinical study. We confirmed that this mutation (and the related C276Y) accounted for the full level of observed DSM265 resistance by regenerating the mutation using CRISPR/Cas9 genome editing. X-ray structure analysis of the C276F mutant enzyme showed that conformational changes of nearby residues were required to accommodate the larger F276 residue, which in turn led to a restriction in the size of the DSM265 binding pocket. These findings underscore the importance of developing DSM265 as part of a combination therapy with other agents for successful use against malaria.

A dual regulatory circuit consisting of S-adenosylmethionine decarboxylase protein and its reaction product controls expression of the paralogous activator prozyme in Trypanosoma brucei

Polyamines are essential for cell growth of eukaryotes including the etiologic agent of human African trypanosomiasis (HAT), Trypanosoma brucei. In trypanosomatids, a key enzyme in the polyamine biosynthetic pathway, S-adenosylmethionine decarboxylase (TbAdoMetDC) heterodimerizes with a unique catalytically-dead paralog called prozyme to form the active enzyme complex. In higher eukaryotes, polyamine metabolism is subject to tight feedback regulation by spermidine-dependent mechanisms that are absent in trypanosomatids. Instead, in T. brucei an alternative regulatory strategy based on TbAdoMetDC prozyme has evolved. We previously demonstrated that prozyme protein levels increase in response to loss of TbAdoMetDC activity. Herein, we show that prozyme levels are under translational control by monitoring incorporation of deuterated leucine into nascent prozyme protein. We furthermore identify pathway factors that regulate prozyme mRNA translation. We find evidence for a regulatory feedback mechanism in which TbAdoMetDC protein and decarboxylated AdoMet (dcAdoMet) act as suppressors of prozyme translation. In TbAdoMetDC null cells expressing the human AdoMetDC enzyme, prozyme levels are constitutively upregulated. Wild-type prozyme levels are restored by complementation with either TbAdoMetDC or an active site mutant, suggesting that TbAdoMetDC possesses an enzyme activity-independent function that inhibits prozyme translation. Depletion of dcAdoMet pools by three independent strategies: inhibition/knockdown of TbAdoMetDC, knockdown of AdoMet synthase, or methionine starvation, each cause prozyme upregulation, providing independent evidence that dcAdoMet functions as a metabolic signal for regulation of the polyamine pathway in T. brucei. These findings highlight a potential regulatory paradigm employing enzymes and pseudoenzymes that may have broad implications in biology.

Trypanosoma brucei is a single-celled eukaryotic pathogen and the causative agent of human African trypanosomiasis (HAT). Polyamines are organic polycations that are essential for growth in T. brucei to facilitate protein translation and to maintain redox homeostasis. The pathway is the target of eflornithine, a current frontline therapy for treatment of HAT. Polyamine biosynthetic enzymes are regulated at multiple levels in mammals (e.g. transcription, translation and protein turnover), but in contrast, T. brucei lacks these mechanisms. Instead in T. brucei a central enzyme in polyamine metabolism called AdoMetDC must form a complex with a sister protein (termed a pseudoenzyme) to be active. Herein, we show that cellular levels of this sister protein we call prozyme are in turn feedback regulated by both AdoMetDC and by its reaction product in response to cell treatments that reduce pathway output. This regulatory paradigm highlights how pseudoenzymes can evolve to play an important role in metabolic pathway regulation and in organismal fitness.

Selective Cytotoxicity of Dihydroorotate Dehydrogenase Inhibitors to Human Cancer Cells Under Hypoxia and Nutrient-Deprived Conditions

Human dihydroorotate dehydrogenase (HsDHODH) is a key enzyme of pyrimidine de novo biosynthesis pathway. It is located on the mitochondrial inner membrane and contributes to the respiratory chain by shuttling electrons to the ubiquinone pool. We have discovered ascofuranone (1), a natural compound produced by Acremonium sclerotigenum, and its derivatives are a potent class of HsDHODH inhibitors. We conducted a structure–activity relationship study and have identified functional groups of 1 that are essential for the inhibition of HsDHODH enzymatic activity. Furthermore, the binding mode of 1 and its derivatives to HsDHODH was demonstrated by co-crystallographic analysis and we show that these inhibitors bind at the ubiquinone binding site. In addition, the cytotoxicities of 1 and its potent derivatives 7, 8, and 9 were studied using human cultured cancer cells. Interestingly, they showed selective and strong cytotoxicity to cancer cells cultured under microenvironment (hypoxia and nutrient-deprived) conditions. The selectivity ratio of 8 under this microenvironment show the most potent inhibition which was over 1000-fold higher compared to that under normal culture condition. Our studies suggest that under microenvironment conditions, cancer cells heavily depend on the pyrimidine de novo biosynthesis pathway. We also provide the first evidence that 1 and its derivatives are potential lead candidates for drug development which target the HsDHODH of cancer cells living under a tumor microenvironment.

Isoxazolopyrimidine-Based Inhibitors of Plasmodium falciparum Dihydroorotate Dehydrogenase with Antimalarial Activity

Malaria kills nearly 0.5 million people yearly and impacts the lives of those living in over 90 countries where it is endemic. The current treatment programs are threatened by increasing drug resistance. Dihydroorotate dehydrogenase (DHODH) is now clinically validated as a target for antimalarial drug discovery as a triazolopyrimidine class inhibitor (DSM265) is currently undergoing clinical development. We discovered a related isoxazolopyrimidine series in a phenotypic screen, later determining that it targeted DHODH. To determine if the isoxazolopyrimidines could yield a drug candidate, we initiated hit-to-lead medicinal chemistry. Several potent analogues were identified, including a compound that showed in vivo antimalarial activity. The isoxazolopyrimidines were more rapidly metabolized than their triazolopyrimidine counterparts, and the pharmacokinetic data were not consistent with the goal of a single-dose treatment for malaria.

Identification of Morpholino Thiophenes as Novel Mycobacterium tuberculosis Inhibitors, Targeting QcrB

With the emergence of multidrug-resistant strains of Mycobacterium tuberculosis there is a pressing need for new oral drugs with novel mechanisms of action. Herein, we describe the identification of a novel morpholino-thiophenes (MOT) series following phenotypic screening of the Eli Lilly corporate library against M. tuberculosis strain H37Rv. The design, synthesis, and structure-activity relationships of a range of analogues around the confirmed actives are described. Optimized leads with potent whole cell activity against H37Rv, no cytotoxicity flags, and in vivo efficacy in an acute murine model of infection are described. Mode-of-action studies suggest that the novel scaffold targets QcrB, a subunit of the menaquinol cytochrome c oxidoreductase, part of the bc1-aa3-type cytochrome c oxidase complex that is responsible for driving oxygen-dependent respiration.

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.

Comparison of the susceptibility of Plasmodium knowlesi and Plasmodium falciparum to antimalarial agents

Background

The simian malaria parasite Plasmodium knowlesi is now a well-recognized pathogen of humans in South-East Asia. Clinical infections appear adequately treated with existing drug regimens, but the evidence base for this practice remains weak. The availability of P. knowlesi cultures adapted to continuous propagation in human erythrocytes enables specific studies of in vitro susceptibility of the species to antimalarial agents, and could provide a surrogate system for testing investigational compounds against Plasmodium vivax and other non-Plasmodium falciparum infections that cannot currently be propagated in vitro.

Objectives

We sought to optimize protocols for in vitro susceptibility testing of P. knowlesi and to contrast outputs with those obtained for P. falciparum under comparable test conditions.

Methods

Growth monitoring of P. knowlesi in vitro was by DNA quantification using a SYBR Green fluorescent assay or by colorimetric detection of the lactate dehydrogenase enzyme. For comparison, P. falciparum was tested under conditions identical to those used for P. knowlesi.

Results

The SYBR Green I assay proved the most robust format over one (27 h) or two (54 h) P. knowlesi life cycles. Unexpectedly, P. knowlesi displays significantly greater susceptibility to the dihydrofolate reductase inhibitors pyrimethamine, cycloguanil and trimethoprim than does P. falciparum, but is less susceptible to the selective agents blasticidin and DSM1 used in parasite transfections. Inhibitors of dihydroorotate dehydrogenase also demonstrate lower activity against P. knowlesi.

Conclusions

The fluorescent assay system validated here identified species-specific P. knowlesi drug susceptibility profiles and can be used for testing investigational compounds for activity against non-P. falciparum malaria.

Drug targets for resistant malaria: Historic to future perspectives

New antimalarial targets are the prime need for the discovery of potent drug candidates. In order to fulfill this objective, antimalarial drug researches are focusing on promising targets in order to develop new drug candidates. Basic metabolism and biochemical process in the malaria parasite, i.e. Plasmodium falciparum can play an indispensable role in the identification of these targets. But, the emergence of resistance to antimalarial drugs is an escalating comprehensive problem with the progress of antimalarial drug development. The development of resistance has highlighted the need for the search of novel antimalarial molecules. The pharmaceutical industries are committed to new drug development due to the global recognition of this life threatening resistance to the currently available antimalarial therapy. The recent developments in the understanding of parasite biology are exhilarating this resistance issue which is further being ignited by malaria genome project. With this background of information, this review was aimed to highlights and provides useful information on various present and promising treatment approaches for resistant malaria, new progresses, pursued by some innovative targets that have been explored till date. This review also discusses modern and futuristic multiple approaches to antimalarial drug discovery and development with pictorial presentations highlighting the various targets, that could be exploited for generating promising new drugs in the future for drug resistant malaria.

Using in Vitro Evolution and Whole Genome Analysis To Discover Next Generation Targets for Antimalarial Drug Discovery

Although many new anti-infectives have been discovered and developed solely using phenotypic cellular screening and assay optimization, most researchers recognize that structure-guided drug design is more practical and less costly. In addition, a greater chemical space can be interrogated with structure-guided drug design. The practicality of structure-guided drug design has launched a search for the targets of compounds discovered in phenotypic screens. One method that has been used extensively in malaria parasites for target discovery and chemical validation is in vitro evolution and whole genome analysis (IVIEWGA). Here, small molecules from phenotypic screens with demonstrated antiparasitic activity are used in genome-based target discovery methods. In this Review, we discuss the newest, most promising druggable targets discovered or further validated by evolution-based methods, as well as some exceptions.

In silico identification of promiscuous scaffolds as potential inhibitors of 1-deoxy-d-xylulose 5-phosphate reductoisomerase for treatment of Falciparum malaria

CONTEXT

Malaria remains one of the prevalent infectious diseases worldwide. Plasmodium falciparum 1-deoxy-d-xylulose-5-phosphate reductoisomerase (PfDXR) plays a role in isoprenoid biosynthesis in the malaria parasite, making this parasite enzyme an attractive target for antimalarial drug design. Fosmidomycin is a promising DXR inhibitor, which showed safety as well as efficacy against Plasmodium falciparum malaria in clinical trials. However, due to its poor oral bioavailability and non-drug-like properties, the focus of medicinal chemists is to develop inhibitors with improved pharmacological properties.

OBJECTIVE

This study described the computational design of new and potent inhibitors for deoxyxylulose 5-phosphate reductoisomerase and the prediction of their pharmacokinetic and pharmacodynamic properties.

MATERIAL AND METHODS

A complex-based pharmacophore model was generated from the complex X-ray crystallographic structure of PfDXR using MOE (Molecular Operating Environment). Furthermore, MOE-Dock was used as docking software to predict the binding modes of hits and target enzyme.

RESULTS

Finally, 14 compounds were selected as new and potent inhibitors of PfDXR on the basis of pharmacophore mapping, docking score, binding energy and binding interactions with the active site residues of the target protein. The predicted pharmacokinetic properties showed improved permeability by efficiently crossing blood-brain barrier. While, in silico promiscuity binding data revealed that these hits also have the ability to bind with other P. falciparum drug targets.

DISCUSSION AND CONCLUSION

In conclusion, innovative scaffolds with novel modes of action, improved efficacy and acceptable physiochemical/pharmacokinetic properties were computationally identified.

Checkpoint kinase 1 inhibition sensitises transformed cells to dihydroorotate dehydrogenase inhibition

Reduction in nucleotide pools through the inhibition of mitochondrial enzyme dihydroorotate dehydrogenase (DHODH) has been demonstrated to effectively reduce cancer cell proliferation and tumour growth. The current study sought to investigate whether this antiproliferative effect could be enhanced by combining Chk1 kinase inhibition. The pharmacological activity of DHODH inhibitor teriflunomide was more selective towards transformed mouse embryonic fibroblasts than their primary or immortalised counterparts, and this effect was amplified when cells were subsequently exposed to PF477736 Chk1 inhibitor. Flow cytometry analyses revealed substantial accumulations of cells in S and G2/M phases, followed by increased cytotoxicity which was characterised by caspase 3-dependent induction of cell death. Associating PF477736 with teriflunomide also significantly sensitised SUM159 and HCC1937 human triple negative breast cancer cell lines to dihydroorotate dehydrogenase inhibition. The main characteristic of this effect was the sustained accumulation of teriflunomide-induced DNA damage as cells displayed increased phospho serine 139 H2AX (γH2AX) levels and concentration-dependent phosphorylation of Chk1 on serine 345 upon exposure to the combination as compared with either inhibitor alone. Importantly a similar significant increase in cell death was observed upon dual siRNA mediated depletion of Chk1 and DHODH in both murine and human cancer cell models. Altogether these results suggest that combining DHODH and Chk1 inhibitions may be a strategy worth considering as a potential alternative to conventional chemotherapies.

2-Aminothiophene scaffolds: Diverse biological and pharmacological attributes in medicinal chemistry

2-Aminothiophenes are important five-membered heterocyclic building blocks in organic synthesis, and the chemistry of these small molecules is still developing based on the discovery of cyclization by Gewald. Another attractive feature of 2-aminothiophene scaffolds is their ability to act as synthons for the synthesis of biological active thiophene-containing heterocycles, conjugates and hybrids. Currently, the biological actions of 2-aminothiophenes or their 2-N-substituted analogues are still being investigated because of their various mechanisms of action (e.g., pharmacophore and pharmacokinetic properties). Likewise, the 2-aminothiophene family is used as diverse promising selective inhibitors, receptors, and modulators in medicinal chemistry, and these compounds even exhibit effective pharmacological properties in the various clinical phases of appropriate diseases. In this review, major biological and pharmacological reports on 2-aminothiophenes and related compounds have been highlighted; most perspective drug-candidate hits were selected for discussion and described, along with additional synthetic pathways. In addition, we focused on the literature dedicated to 2-aminothiophenes and 2-N-substituted derivatives, which have been published from 2010 to 2017.

The dihydroorotate dehydrogenases: Past and present

The flavoenzyme dihydroorotate dehydrogenase catalyzes the stereoselective oxidation of (S)-dihydroorotate to orotate in the fourth of the six conserved enzymatic reactions involved in the de novo pyrimidine biosynthetic pathway. Inhibition of pyrimidine metabolism by selectively targeting DHODHs has been exploited in the development of new therapies against cancer, immunological disorders, bacterial and viral infections, and parasitic diseases. Through a chronological narrative, this review summarizes the efforts of the scientific community to achieve our current understanding of structural and biochemical properties of DHODHs. It also attempts to describe the latest advances in medicinal chemistry for therapeutic development based on the selective inhibition of DHODH, including an overview of the experimental techniques used for ligand screening during the process of drug discovery.

Design, synthesis, crystal structure and in vitro cytotoxic properties of a novel Schiff base derived from indole and biphenyl

A novel and potentially active dihydroorotate dehydrogenase (DHODH) inhibitor, namely 3-({(E)-[(E)-1-(biphenyl-4-yl)ethylidene]hydrazinylidene}methyl)-1H-indole (BEHI) acetonitrile disolvate, C23H19N3·2CH3CN, has been designed and synthesized. The structure of BEHI was characterized by elemental analysis, Q-TOF (quadrupole time-of-flight) MS, NMR, UV–Vis and single-crystal X-ray diffraction. The antitumour activity of the target molecule was evaluated by the MTT method. Results indicated that BEHI exhibited rather potent cytotoxic activity against human A549 (IC50 = 20.5 µM) and mouse breast 4T1 (IC50 = 18.5 µM) cancer cell lines. Meanwhile, to rationalize its potencies in the target, BEHI was docked into DHODH and the interactions with the active site residues were analyzed. Single-crystal structure analysis indicated that hydrogen bonds are present only between BEHI and acetonitrile solvent molecules in the asymmetric unit. The interplay of weak π–π stacking and weak C(N)—H...π interactions between neighbouring BEHI molecules play crucial roles in the formation of the final supramolecular frameworks.

Discovery of Antimalarial Azetidine-2-carbonitriles That Inhibit P. falciparum Dihydroorotate Dehydrogenase

Dihydroorotate dehydrogenase (DHODH) is an enzyme necessary for pyrimidine biosynthesis in protozoan parasites of the genus Plasmodium, the causative agents of malaria. We recently reported the identification of novel compounds derived from diversity-oriented synthesis with activity in multiple stages of the malaria parasite life cycle. Here, we report the optimization of a potent series of antimalarial inhibitors consisting of azetidine-2-carbonitriles, which we had previously shown to target P. falciparum DHODH in a biochemical assay. Optimized compound BRD9185 (27) has in vitro activity against multidrug-resistant blood-stage parasites (EC₅₀ = 0.016 μM) and is curative after just three doses in a P. berghei mouse model. BRD9185 has a long half-life (15 h) and low clearance in mice and represents a new structural class of DHODH inhibitors with potential as antimalarial drugs.