Discovery of piperine derivatives as inhibitors of human dihydroorotate dehydrogenase to induce ferroptosis in cancer cells.

Inhibition of human dihydroorotate dehydrogenase (hDHODH) represents a promising strategy for suppressing the proliferation of cancer cells. To identify novel and potent hDHODH inhibitors, a total of 28 piperine derivatives were designed and synthesized. Their cytotoxicities against three human cancer cell lines (NCI-H226, HCT-116, and MDA-MB-231) and hDHODH inhibitory activities were also evaluated. Among them, compound H19, exhibited the strongest inhibitory activities (NCI-H226 IC50 = 0.95 µM, hDHODH IC50 = 0.21 µM). Further pharmacological investigations revealed that H19 exerted anticancer effects by inducing ferroptosis in NCI-H226 cells, with its cytotoxicity being reversed by ferroptosis inhibitors. This was supported by the intracellular growth or decline of ferroptosis markers, including lipid peroxidation, Fe2+, GSH, and 4-HNE. Overall, H19 emerges as a promising hDHODH inhibitor with potential anticancer properties warranting development.

Structural and Functional Analyses of Inhibition of Human Dihydroorotate Dehydrogenase by Antiviral Furocoumavirin.

Natural products are important sources of seed compounds for drug discovery. However, it has become difficult in recent years to discover new compounds with valuable pharmacological activities. On the other hand, among the vast number of natural products that have been isolated so far, a considerable number of compounds with specific biological activities are thought to be overlooked in screening that uses biological activity as an index. Therefore, it is conceivable that such overlooked useful compounds may be found by screening compound libraries that have been amassed previously through specific assays. Previously, NPD723, a member of the Natural Products Depository library comprised of a mixture of natural and non-natural products developed at RIKEN, and its metabolite H-006 were found to inhibit growth of various cancer cells at low nanomolar half-maximal inhibitory concentration. Subsequent analysis revealed that H-006 strongly inhibited human dihydroorotate dehydrogenase (DHODH), the rate-limiting enzyme in the de novo pyrimidine biosynthetic pathway. Here, we elucidated the crystal structure of the DHODH-flavin mononucleotide-orotic acid-H-006 complex at 1.7 Å resolution to determine that furocoumavirin, the S-enantiomer of H-006, was the actual inhibitor. The overall mode of interaction of furocoumavirin with the inhibitor binding pocket was similar to that described for previously reported tight-binding inhibitors. However, the structural information together with kinetic characterizations of site-specific mutants identified key unique features that are considered to contribute to the sub-nanomolar inhibition of DHODH by furocoumavirin. Our finding identified new chemical features that could improve the design of human DHODH inhibitors.

Targeting DHODH reveals therapeutic opportunities in ATRA-resistant acute promyelocytic leukemia.

Although all-trans retinoic acid (ATRA)-induced differentiation has transformed acute promyelocytic leukemia (APL) from the most fatal to the most curable hematological disease, resistance to ATRA in high-risk APL patients remains a clinical challenge. In this paper, we discovered that dihydroorotate dehydrogenase (DHODH) inhibition overcame ATRA resistance. 416, a potent DHODH inhibitor previously obtained in our group, inhibited the occurrence of APL in cells and model mice. Excitingly, 416 effectively overcame ATRA resistance in vitro and in vivo by inducing apoptosis and differentiation. Further mechanistic studies showed that PML/RARα lost the regulation of Bcl-2 and c-Myc in NB4-R1 cells, which probably contributed to ATRA resistance. Notably, 416 maintained its Bcl-2 and c-Myc down-regulation effect in NB4-R1 cells and overcome ATRA resistance by inhibiting DHODH. In conclusion, our study highlights the potential of 416 for APL therapy and overcoming ATRA resistance, supporting the further development of DHODH inhibitors for clinical use in refractory and relapsed APL.

Synergistic Functional Nanomedicine Enhances Ferroptosis Therapy for Breast Tumors by a Blocking Defensive Redox System.

The upregulation of dihydroorotate dehydrogenase (DHODH) redox systems inside tumor cells provides a powerful shelter against lipid peroxidation (LPO), impeding ferroptosis-induced antitumor responses. To solve this issue, we report a strategy to block redox systems and enhance ferroptotic cancer cell death based on a layered double hydroxide (LDH) nanoplatform (siR/IONs@LDH) co-loaded with ferroptosis agent iron oxide nanoparticles (IONs) and the DHODH inhibitor (siR). siR/IONs@LDH is able to simultaneously release IONs and siR in a pH-responsive manner, efficiently generate toxic reactive oxygen species (ROS) via an Fe2+-mediated Fenton reaction, and synergistically induce cancer cell death upon the acceleration of LPO accumulation. In vivo therapeutic evaluations demonstrate that this nanomedicine has excellent performance for tumor growth inhibition without any detectable side effects. This work thus provides a new insight into nanomaterial-mediated tumor ferroptosis therapy.

Synthesis and biological evaluation of new quinoline-4-carboxylic acid-chalcone hybrids as dihydroorotate dehydrogenase inhibitors.

Fourteen novel quinoline-4-carboxylic acid-chalcone hybrids were obtained via Claisen-Schmidt condensation and evaluated as potential human dihydroorotate dehydrogenase (hDHODH) inhibitors. The ketone precursor 2 was synthesized by the Pfitzinger reaction and used for further derivatization at position 3 of the quinoline ring for the first time. Six compounds showed better hDHODH inhibitory activity than the reference drug leflunomide, with IC50 values ranging from 0.12 to 0.58 µM. The bioactive conformations of the compounds within hDHODH were resolved by means of molecular docking, revealing their tendency to occupy the narrow tunnel of hDHODH within the N-terminus and to prevent ubiquinone as the second cofactor from easily approaching the flavin mononucleotide as a cofactor for the redox reaction within the redox site. The results of the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay revealed that 4d and 4h demonstrated the highest cytotoxic activity against the A375 cell line, with IC50 values of 5.0 and 6.8 µM, respectively. The lipophilicity of the synthesized hybrids was obtained experimentally and expressed as logD7.4 values at physiologicalpH while the solubility assay was conducted to define physicochemical characteristics influencing the ADMET properties.

N-Heterocyclic 3-Pyridyl Carboxamide Inhibitors of DHODH for the Treatment of Acute Myelogenous Leukemia.

Acute myelogenous leukemia (AML), a disease of the blood and bone marrow, is characterized by the inability of myeloblasts to differentiate into mature cell types. Dihydroorotate dehydrogenase (DHODH) is an enzyme well-known in the pyrimidine biosynthesis pathway; however, small molecule DHODH inhibitors were recently shown to induce differentiation in multiple AML subtypes. Using virtual screening and structure-based drug design approaches, a new series of N-heterocyclic 3-pyridyl carboxamide DHODH inhibitors were discovered. Two lead compounds, 19 and 29, have potent biochemical and cellular DHODH activity, favorable physicochemical properties, and efficacy in a preclinical model of AML.

A Broad Antiviral Strategy: Inhibitors of Human DHODH Pave the Way for Host-Targeting Antivirals against Emerging and Re-Emerging Viruses.

New strategies to rapidly develop broad-spectrum antiviral therapies are urgently required for emerging and re-emerging viruses. Host-targeting antivirals (HTAs) that target the universal host factors necessary for viral replication are the most promising approach, with broad-spectrum, foresighted function, and low resistance. We and others recently identified that host dihydroorotate dehydrogenase (DHODH) is one of the universal host factors essential for the replication of many acute-infectious viruses. DHODH is a rate-limiting enzyme catalyzing the fourth step in de novo pyrimidine synthesis. Therefore, it has also been developed as a therapeutic target for many diseases relying on cellular pyrimidine resources, such as cancers, autoimmune diseases, and viral or bacterial infections. Significantly, the successful use of DHODH inhibitors (DHODHi) against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection further supports the application prospects. This review focuses on the advantages of HTAs and the antiviral effects of DHODHi with clinical applications. The multiple functions of DHODHi in inhibiting viral replication, stimulating ISGs expression, and suppressing cytokine storms make DHODHi a potent strategy against viral infection.

Expanding the Repertoire of Low-Molecular-Weight Pentafluorosulfanyl-Substituted Scaffolds.

The pentafluorosulfanyl (-SF5 ) functional group is of increasing interest as a bioisostere in medicinal chemistry. A library of SF5 -containing compounds, including amide, isoxazole, and oxindole derivatives, was synthesised using a range of solution-based and solventless methods, including microwave and ball-mill techniques. The library was tested against targets including human dihydroorotate dehydrogenase (HDHODH). A subsequent focused approach led to synthesis of analogues of the clinically used disease modifying anti-rheumatic drugs (DMARDs), Teriflunomide and Leflunomide, considered for potential COVID-19 use, where SF5 bioisostere deployment led to improved inhibition of HDHODH compared with the parent drugs. The results demonstrate the utility of the SF5 group in medicinal chemistry.

Discovery of Orally Available Retinoic Acid Receptor-Related Orphan Receptor γ-t/Dihydroorotate Dehydrogenase Dual Inhibitors for the Treatment of Refractory Inflammatory Bowel Disease.

Inflammatory bowel disease (IBD) is a multifactorial autoimmune disease, representing a major clinical challenge. Herein, a strategy of dual-targeting approach employing retinoic acid receptor-related orphan receptor γ-t (RORγt) and dihydroorotate dehydrogenase (DHODH) was proposed for the treatment of IBD. Dual RORγt/DHODH inhibitors are expected not only to reduce RORγt-driven Th17 cell differentiation but also to mitigate the expansion and activation of T cells, which may enhance anti-inflammatory effects. Starting from 2-aminobenzothiazole hit 1, a series of 2-aminotetrahydrobenzothiazoles were discovered as potent dual RORγt/DHODH inhibitors. Compound 14d stands out with IC50 values of 0.110 µM for RORγt and of 0.297 µM for DHODH. With acceptable mouse pharmacokinetic profiles, 14d exhibited remarkable in vivo anti-inflammatory activity and dose-dependently alleviated the severity of dextran sulfate sodium (DSS)-induced acute colitis in mice. Taken together, the present study provides a novel framework for the development of therapeutic agents for the treatment of IBD.

Mitochondrial-Linked De Novo Pyrimidine Biosynthesis Dictates Human T-Cell Proliferation but Not Expression of Effector Molecules.

T-cell activation upon antigen stimulation is essential for the continuation of the adaptive immune response. Impairment of mitochondrial oxidative phosphorylation is a well-known disruptor of T-cell activation. Dihydroorotate dehydrogenase (DHODH) is a component of the de novo synthesis of pyrimidines, the activity of which depends on functional oxidative phosphorylation. Under circumstances of an inhibited oxidative phosphorylation, DHODH becomes rate-limiting. Inhibition of DHODH is known to block clonal expansion and expression of effector molecules of activated T cells. However, this effect has been suggested to be caused by downstream impairment of oxidative phosphorylation rather than a lower rate of pyrimidine synthesis. In this study, we successfully inhibit the DHODH of T cells with no residual effect on oxidative phosphorylation and demonstrate a dose-dependent inhibition of proliferation of activated CD3+ T cells. This block is fully rescued when uridine is supplemented. Inhibition of DHODH does not alter expression of effector molecules but results in decreased intracellular levels of deoxypyrimidines without decreasing cell viability. Our results clearly demonstrate the DHODH and mitochondrial linked pyrimidine synthesis as an independent and important cytostatic regulator of activated T cells.

Design, Synthesis, and Biological Evaluation of a Novel Series of Teriflunomide Derivatives as Potent Human Dihydroorotate Dehydrogenase Inhibitors for Malignancy Treatment.

Human dihydroorotate dehydrogenase (hDHODH), as the fourth and rate-limiting enzyme of the de novo pyrimidine synthesis pathway, is regarded as an attractive target for malignancy therapy. In the present study, a novel series of teriflunomide derivatives were designed, synthesized, and evaluated as hDHODH inhibitors. 13t was the optimal compound with promising enzymatic activity (IC50 = 16.0 nM), potent antiproliferative activity against human lymphoma Raji cells (IC50 = 7.7 nM), and excellent aqueous solubility (20.1 mg/mL). Mechanistically, 13t directly inhibited hDHODH and induced cell cycle S-phase arrest in Raji cells. The acute toxicity assay indicated a favorable safety profile of 13t. Notably, 13t displayed significant tumor growth inhibition activity with a tumor growth inhibition (TGI) rate of 81.4% at 30 mg/kg in a Raji xenograft model. Together, 13t is a promising inhibitor of hDHODH and a preclinical candidate for antitumor therapy, especially for lymphoma.

Teriflunomide Treatment of Multiple Sclerosis Selectively Modulates CD8 Memory T Cells.

Background and Objectives: Inhibition of de novo pyrimidine synthesis in proliferating T and B lymphocytes by teriflunomide, a pharmacological inhibitor of dihydroorotate dehydrogenase (DHODH), has been shown to be an effective therapy to treat patients with MS in placebo-controlled phase 3 trials. Nevertheless, the underlying mechanism contributing to the efficacy of DHODH inhibition has been only partially elucidated. Here, we aimed to determine the impact of teriflunomide on the immune compartment in a longitudinal high-dimensional follow-up of patients with relapse-remitting MS (RRMS) treated with teriflunomide. Methods: High-dimensional spectral flow cytometry was used to analyze the phenotype and the function of innate and adaptive immune system of patients with RRMS before and 12 months after teriflunomide treatment. In addition, we assessed the impact of teriflunomide on the migration of memory CD8 T cells in patients with RRMS, and we defined patient immune metabolic profiles. Results: We found that 12 months of treatment with teriflunomide in patients with RRMS does not affect the B cell or CD4 T cell compartments, including regulatory TREG follicular helper TFH cell and helper TH cell subsets. In contrast, we observed a specific impact of teriflunomide on the CD8 T cell compartment, which was characterized by decreased homeostatic proliferation and reduced production of TNFα and IFNγ. Furthermore, we showed that DHODH inhibition also had a negative impact on the migratory velocity of memory CD8 T cells in patients with RRMS. Finally, we showed that the susceptibility of memory CD8 T cells to DHODH inhibition was not related to impaired metabolism. Discussion: Overall, these findings demonstrate that the clinical efficacy of teriflunomide results partially in the specific susceptibility of memory CD8 T cells to DHODH inhibition in patients with RRMS and strengthens active roles for these T cells in the pathophysiological process of MS.

Identification of Dihydroorotate Dehydrogenase Inhibitors─Indoluidins─That Inhibit Cancer Cell Growth.

Dihydroorotate dehydrogenase (DHODH) catalyzes the rate-limiting step in de novo pyrimidine biosynthesis and is a promising cancer treatment target. This study reports the identification of indoluidin D and its derivatives as inhibitors of DHODH. Cell-based phenotypic screening revealed that indoluidin D promoted myeloid differentiation and inhibited the proliferation of acute promyelocytic leukemia HL-60 cells. Indoluidin D also suppressed cell growth in various other types of cancer cells. Cancer cell sensitivity profiling with JFCR39 and proteomic profiling with ChemProteoBase revealed that indoluidin D is a DHODH inhibitor. Indoluidin D inhibited human DHODH activity in vitro; the DHODH reaction product orotic acid rescued indoluidin D-induced cell differentiation. We synthesized several indoluidin D diastereomer derivatives and demonstrated that stereochemistry was vital to their molecular activity. The indoluidin D derivative indoluidin E showed similar activity to its parent compound and suppressed tumor growth in a murine lung cancer xenograft model. Hence, indoluidin D and its derivatives selectively inhibit DHODH and suppress cancer cell growth.

Exploring Marine-Derived Ascochlorins as Novel Human Dihydroorotate Dehydrogenase Inhibitors for Treatment of Triple-Negative Breast Cancer.

Human dihydroorotate dehydrogenase (hDHODH) is an attractive tumor target essential to de novo pyrimidine biosynthesis. Novel potent hDHODH inhibitors with low toxicity are urgently needed. Herein, we demonstrate the isolation of 25 ascochlorin (ASC) derivatives, including 13 new ones, from the coral-derived fungus Acremonium sclerotigenum, and several of them showed pronounced inhibitions against hDHODH and triple-negative breast cancer (TNBC) cell lines, MDA-MB-231/-468. Interestingly, we found that hDHODH is required for proliferation and survival of TNBC cells, and several ASCs significantly inhibited TNBC cell growth and induced their apoptosis via hDHODH inhibition. Furthermore, the novel and potent hDHODH inhibitors (1 and 21) efficiently suppressed tumor growth in patient-derived TNBC xenograft models without obvious body weight loss or overt toxicity in mice. Collectively, our findings offered a novel lead scaffold as the hDHODH inhibitor for further development of potent anticancer agents and a potential therapeutic strategy for TNBC.

Novel quinolone derivatives targeting human dihydroorotate dehydrogenase suppress Ebola virus infection in vitro.

Ebola virus (EBOV) has emerged as a significant public health concern since the 2013-2016 outbreak in West Africa. Currently, no effective antiviral treatments have been approved for clinical use. Compound 1 RYL-634 is a quinolone-derived compound that can inhibit dihydroorotate dehydrogenase, a rate-limiting enzyme in the de novo pyrimidine synthesis pathway and it exhibited antiviral activity against multiple RNA virus infection. In this study, we evaluated the efficacy of a panel of newly developed compounds based on RYL-634 against EBOV infection. Our data showed that RYL-634 as well as its derivatives are effective against EBOV transcription- and replication-competent virus-like particle (trVLP) infection and authentic EBOV infection in vitro at low nanomolar IC50 values and relatively high CC50. Of note, the new derivative RYL-687 had the lowest IC50 at approximately 7 nM and was almost 6 times more potent than remdesivir (GS-5734). Exogenous addition of different metabolites in the pyrimidine de novo synthesis pathway confirmed DHODH as the target of RYL-687. These data provide evidence that such quinolone-derived compounds are promising therapeutic candidates against EBOV infection.

DHODH Hot Spots: An Underexplored Source to Guide Drug Development Efforts.

BACKGROUND: Dihydroorotate dehydrogenase (DHODH) has long been recognized as an important drug target for proliferative and parasitic diseases, including compounds that exhibit trypanocidal action and broad-spectrum antiviral activity. Despite numerous and successful efforts in structural and functional characterization of DHODHs, as well as in the development of inhibitors, DHODH hot spots remain largely unmapped and underexplored. OBJECTIVE: This review describes the tools that are currently available for the identification and characterization of hot spots in protein structures and how freely available webservers can be exploited to predict DHODH hot spots. Moreover, it provides for the first time a review of the antiviral properties of DHODH inhibitors. METHODS: X-ray structures from human (HsDHODH) and Trypanosoma cruzi DHODH (TcDHODH) had their hot spots predicted by both FTMap and Fragment Hotspot Maps web servers. RESULTS: FTMap showed that hot spot occupancy in HsDHODH is correlated with the ligand efficiency (LE) of its known inhibitors, and Fragment Hotspot Maps pointed out the contribution of selected moieties to the overall LE. The conformational flexibility of the active site loop in TcDHODH was found to have a major impact on the druggability of the orotate binding site. In addition, both FTMap and Fragment Hotspot Maps servers predict a novel pocket in TcDHODH dimer interface (S6 site). CONCLUSION: This review reports how hot spots can be exploited during hit-to-lead steps, docking studies or even to improve inhibitor binding profile and by doing so using DHODH as a model, points to new drug development opportunities.

Low cytotoxic quinoline-4-carboxylic acids derived from vanillin precursors as potential human dihydroorotate dehydrogenase inhibitors.

Twenty novel 2-substituted quinoline-4-carboxylic acids bearing amide moiety were designed and synthesized by Doebner reaction. Human dihydroorotate dehydrogenase (hDHODH) was recognized as a biological target and all compounds were screened as potential hDHODH inhibitors in an enzyme inhibition assay. The prepared heterocycles were also evaluated for their cytotoxic effects on the healthy HaCaT cell line while lipophilic properties were considered on the basis of experimentally determined logD values at physiological pH. The most promising compound 5j, with chlorine at para-position of terminal phenyl ring, showed good hDHODH inhibitory activity, low cytotoxicity, and optimal lipophilicity. The bioactive conformation of 5j on the hDHODH, determined by means of molecular docking, revealed the compound's pharmacology and provide guidelines for further lead optimization.

Selective eradication of pluripotent stem cells by inhibiting DHODH activity.

Pluripotent stem cells (PSCs), such as embryonic stem cells and induced pluripotent stem cells, give rise to all kinds of functional cells, making them promising for successful application in regenerative medicine. However, there is concern that a PSC-derived differentiated cell population may form teratomas when used for cell therapy if the population contains undifferentiated PSCs. Therefore, for the success of regenerative medicine, it is crucial to establish methods that induce complete PSC differentiation and eliminate the contamination of PSCs. Here, I show that the dihydroorotate dehydrogenase (DHODH) inhibitor brequinar (BRQ) induced cell cycle arrest, cell death, and stemness loss in mouse PSCs (mPSCs), whereas it was less toxic against normal tissue-specific stem cells and differentiating cells. I demonstrate that BRQ-pretreated mPSCs did not form teratomas after being transplanted into NOD/SCID mice. Moreover, BRQ administration to teratoma-bearing mice prevented tumor growth and decreased PSC marker levels in the tumor without any visible effects in the differentiated germ layer cells and the mice. Collectively, these data suggested that DHODH inhibitors such as BRQ can be indispensable in the fundamental methods of PSC-based therapy.

Effect of the Intramolecular Hydrogen Bond on the Active Metabolite Analogs of Leflunomide for Blocking the Plasmodium falciparum Dihydroorotate Dehydrogenase Enzyme: QTAIM, NBO, and Docking Study.

BACKGROUND: Leflunomide (LFM) and its active metabolite, teriflunomide (TFM), have drawn a lot of attention for their anticancer activities, treatment of rheumatoid arthritis and malaria due to their capability to inhibit dihydroorotate dehydrogenase (DHODH) and Plasmodium falciparum dihydroorotate dehydrogenase (PfDHODH) enzyme. In this investigation, the strength of intramolecular hydrogen bond (IHB) in five analogs of TFM (ATFM) was analyzed employing density functional theory (DFT) using B3LYP/6-311++G (d, p) level and molecular orbital analysis in the gas phase and water solution. A detailed electronic structure study was performed using the quantum theory of atoms in molecules (QTAIM) and the hydrogen bond energies (EHB) of stable conformer obtained in the range of 76-97 kJ/mol, as a medium hydrogen bond. The effect of substitution on the IHB nature was studied by natural bond orbital analysis (NBO). 1H NMR calculations showed an upward trend in the proton chemical shift of the enolic proton in the chelated ring (14.5 to 15.7ppm) by increasing the IHB strength. All the calculations confirmed the strongest IHB in 5-F-ATFM and the weakest IHB in 2-FATFM. Molecular orbital analysis, including the HOMO-LUMO gap and chemical hardness, was performed to compare the reactivity of inhibitors. Finally, molecular docking analysis was carried out to identify the potency of inhibition of these compounds against PfDHODH enzyme. TFM acts as an inhibitor of dihydroorotate dehydrogenase (DHODH) and Plasmodium falciparum dihydroorotate dehydrogenase (PfDHODH) enzyme. Leflunomide and its active metabolite teriflunomide have been identified as drugs for treatment of some diseases, such as multiple sclerosis (MS), rheumatoid arthritis (RA), malaria, and cancer. Hydrogen bonds play a key role in the interaction between drugs and enzymes. OBJECTIVES: The aim of the present work is to investigate the effect of the strength of intramolecular hydrogen bonds (IHBs) in the active metabolite analogs of leflunomide or analogs of teriflunomide (ATFMs) and study the interaction of these inhibitors against the PfDHODH enzyme using quantum mechanical methods. METHODS: At first, intramolecular hydrogen bonds in five ATFMs were evaluated by the DFT method, quantum theory of atoms in molecules (QTAIM), nuclear magnetic resonance (NMR), natural bond orbital (NBO), and molecular orbital (MO) analyses. Then, the interaction of these inhibitors against the PfDHODH enzyme were compared using molecular docking study. RESULTS: All the computed results confirm the following trend in the intramolecular hydrogen bond strength in five mono-halo-substituted 2-cyano-3-hydroxy-N-phenylbut-2-enamide (ATFM): 5-FATFM> 4-Br-ATFM ≈ 3-Br-ATFM>3-Cl-ATFM>TFM-Z>2-F-ATFM which is in agreement with QTAIM, NMR, and NBO results. Docking results show that 5-F-ATFM (EHB=97kJ/mol) has the minimum MolDock score due to its considerable IHB strength. CONCLUSION: For strong IHBs (EHB>100kJ/mol), C=O and O-H group are involved in the intramolecular interactions and do not contribute to the external interactions. Also, the docking study revealed maximum binding energy between TFM-Z and PfDHODH enzyme.