Antimalarial Candidates Research Articles

Design, synthesis, and antiprotozoal evaluation of new 2,9-bis[(substituted-aminomethyl)phenyl]-1,10-phenanthroline derivatives.

A series of new 2,9-bis[(substituted-aminomethyl)phenyl]-1,10-phenanthroline derivatives was synthesized, and the compounds were screened in vitro against three protozoan parasites (Plasmodium falciparum, Leishmania donovani, and Trypanosoma brucei brucei). Biological results showed antiparasitic activity with IC50 values in the μm range. The in vitro cytotoxicity of these molecules was assessed by incubation with human HepG2 cells; for some derivatives, cytotoxicity was observed at significantly higher concentrations than antiparasitic activity. The 2,9-bis[(substituted-aminomethyl)phenyl]-1,10-phenanthroline 1h was identified as the most potent antimalarial candidate with ratios of cytotoxic-to-antiparasitic activities of 107 and 39 against a chloroquine-sensitive and a chloroquine-resistant strain of P. falciparum, respectively. As the telomeres of the parasite P. falciparum are the likely target of this compound, we investigated stabilization of the Plasmodium telomeric G-quadruplexes by our phenanthroline derivatives through a FRET melting assay. The ligands 1f and 1m were noticed to be more specific for FPf8T with higher stabilization for FPf8T than for the human F21T sequence.

Assessing drug efficacy against Plasmodium falciparum liver stages in vivo.

Malaria eradication necessitates new tools to fight the evolving and complex Plasmodium pathogens. These tools include prophylactic drugs that eliminate Plasmodium liver stages and consequently prevent clinical disease, decrease transmission, and reduce the propensity for resistance development. Currently, the identification of these drugs relies on in vitro P. falciparum liver stage assays or in vivo causal prophylaxis assays using rodent malaria parasites; there is no method to directly test in vivo liver stage activity of candidate antimalarials against the human malaria-causing parasite P. falciparum. Here, we use a liver-chimeric humanized mouse (FRG huHep) to demonstrate in vivo P. falciparum liver stage development and describe the efficacy of clinically used and candidate antimalarials with prophylactic activity. We show that daily administration of atovaquone-proguanil (ATQ-PG; ATQ, 30 mg/kg, and PG, 10 mg/kg) protects 5 of 5 mice from liver stage infection, consistent with the use in humans as a causal prophylactic drug. Single-dose primaquine (60 mg/kg) has similar activity to that observed in humans, demonstrating the activity of this drug (and its active metabolites) in FRG huHep mice. We also show that DSM265, a selective Plasmodial dihydroorotate dehydrogenase inhibitor with causal prophylactic activity in humans, reduces liver stage burden in FRG huHep mice. Finally, we measured liver stage-to-blood stage transition of the parasite, the ultimate readout of prophylactic activity and measurement of infective capacity of parasites in the liver, to show that ATQ-PG reduces blood stage patency to below the limit of quantitation by quantitative PCR (qPCR). The FRG huHep model, thus, provides a platform for preclinical evaluation of drug candidates for liver stage causal prophylactic activity, pharmacokinetic/pharmacodynamics studies, and biological studies to investigate the mechanism of action of liver stage active antimalarials.

Correction: Recent updates in the discovery and development of novel antimalarial drug candidates.

Correction for ‘Recent updates in the discovery and development of novel antimalarial drug candidates’ by John Okombo et al., Med. Chem. Commun., 2018, DOI: ; 10.1039/c7md00637c.

Recent updates in the discovery and development of novel antimalarial drug candidates.

Though morbidity and mortality due to malaria have declined in the last 15 years, emerging resistance to first-line artemisinin-based antimalarials, absence of efficacious vaccines and limited chemotherapeutic alternatives imperil the consolidation of these gains. As a blueprint to steer future designs of new medicines, malaria drug discovery recently adopted a descriptive proposal for the ideal candidate molecules and drugs likely to successfully progress into the final stages of clinical development. As an audit of recent developments in the chemotherapy of malaria in the last five years, this review captures a landscape of diverse molecules at various stages of drug development and discusses their progress. In brief, we also discuss how omics data on Plasmodium has been extensively leveraged to identify potential vaccine candidates and putative targets of molecules in development and clinical use as well as map loci implicit in their modes of resistance. Future perspective on malaria drug development should involve a reconciliation of some of the challenges of the target candidate profiles (TCPs), specifically TCP3, with the promise of effective anti-hypnozoite medicines. Similarly, with the recent development of a humanized mouse model that can evaluate the prophylactic potential of candidate drugs, we argue for increased effort at identifying more liver-stage molecules, which are often only secondarily prioritized in conventional screening programs.

In Vivo Antiplasmodial Activity of Two Sahelian Plant Extracts on Plasmodium berghei ANKA Infected NMRI Mice.

Up to now, the control of malaria remains a challenge. The World Health Organization (WHO) recommends the use of artemisinin-based combination therapies (ACTs) for uncomplicated malaria treatment. Despite this guideline, many people in Burkina Faso use herbal medicine as primary treatment against malaria. The aim of this study was to assess the in vivo activity of Guiera senegalensis J. F. Gmel and Bauhinia rufescens Lam. leaves extracts against Plasmodium berghei ANKA. A four-day treatment of leaves decoction of each plant was administrated orally to 7 groups of six NMRI (Naval Medical Research Institute) mice infected with Plasmodium berghei ANKA strain. The control group received distilled water as treatment while the treated groups each received daily 100, 250, and 500 mg extract/kg body weight. Thin blood smears were performed on day five and the percentage of reduction of parasitaemia was determined compared to the control. The percentages of reduction of the parasitaemia at the doses of 100, 250, and 500 mg extract/kg body weight were, respectively, 57.5%, 35.9%, and 44.9% for Guiera senegalensis and 50.6%, 22.2%, and 25.7% for Bauhinia rufescens. Our findings on antiplasmodial activity of these two plants justify the traditional use by local populations against malaria. Thus, the isolation of the active compounds from these two plants is suggested for possible antimalarial candidate drugs.

In vitro antimalarial activity of Calophyllum bicolor and hemozoin crystals observed by Transmission Electron Microscope (TEM)

Objective : In continuation of our antimalarial candidate drug discovery program on Indonesia medicinal plants especially from stem bark of Calophyllum bicolor. Metode : We extracted of bioactive crude extract with hexane, acetone and methanol from stem bark of Calophyllum bicolor and evaluated their antimalarial activity by using parasite Plasmodium falciparum in vitro. Results: Methanol fraction showed most active and potent antimalarial activity dose dependent in in vitro experiments with IC50 = 0.52 ppb, and hexane fraction showed moderate antimalarial activity, but dose not dependent, while acetone fraction have not antimalarial activity. TEM (Trasmission Electron Microscopy) analysis confirmed a remarkable reduction of hemozoin in the presence of the bioactive fraction. Conclusion: The results suggest that the antimalarial activity of Calophyllum bicolor is due, methanol fraction showed the best in vitro antimalarial activity then another fraction.

Bioactive compounds fractionated from endophyte Streptomyces SUK 08 with promising ex-vivo antimalarial activity

ObjectiveTo determine ex vivo antimalarial activity and cytotoxicity of endophytic Streptomyces SUK 08 as well as the main core structure fractionated from its crude extract. MethodsThe activities of SUK 08 crude extract were evaluated by using the Plasmodium lactate dehydrogenase assay and synchronization test against rodent malaria parasite Plasmodium berghei, instead of human malarial parasite Plasmodium falciparum. The cytotoxicity of the crude extract was determined by MTT assay. The crude extract was analyzed by thin-layer chromatography and gas chromatography–mass spectrophotometry. ResultsThe ethyl acetate crude extract showed very promising antimalarial activity with IC50 of 1.25 mg/mL. The synchronization tests showed that ethyl acetate extraction could inhibit all stages of the Plasmodium life cycle, but it was most effective at the Plasmodium ring stage. On the basis of a MTT assay on Chang Liver cells, ethyl acetate and ethanol demonstrated IC50 values of >1.0 mg/mL. The IC50 of parasitemia at 5% and 30% for this extract was lower than chloroquine. Thin-layer chromatography, with 1: 9 ratio of ethyl acetate: hexane, was used to isolate several distinct compounds. Based on gas chromatography–mass spectrophotometry analysis, three core structures were identified as cyclohexane, butyl propyl ester, and 2,3-heptanedione. Structurally, these compounds were similar to currently available antimalarial drugs. ConclusionsThe results suggest that compounds isolated from Streptomyces SUK 08 are viable antimalarial drug candidates that require further investigations.

Synthesis, β-hematin inhibition studies and antimalarial evaluation of new dehydroxy isoquine derivatives against Plasmodium berghei: A promising antimalarial agent

Many people are affected by Malaria around the world, and the parasite is developing resistance against available drugs. Currently, isoquine and N-tert-butyl isoquine are some of the most promising antimalarial candidates that have already reached Phase I and II clinical trials, respectively. Nevertheless, pharmacodynamic studies have demonstrated that isoquine is highly sensitive to form O-glucuronide metabolite, which may affect its accumulation in tissues. To avoid the O-glucuronide formation and its negative influence in the accumulation process, a series of novel five dehydroxy isoquine derivatives were designed and prepared herein as potential antimalarial agents. By a simple three-step procedure, five dehydroxy isoquines were prepared and subsequently examined on the inhibition of haemozoin formation, the main target of the 4-aminoquinolines. Four derivatives displayed significant inhibitory activities at low IC50 values from 1.66 to 1.86 μM comparable to CQ. On the basis of the results, these four compounds were subsequently tested against Plasmodium berghei ANKA model in mice, showing to be as active as CQ with significant curative responses and parasitemia suppression in mice infected. On the other hand, these four compounds showed an acceptable non specific cytotoxicity on murine peritoneal macrophague and human erythrocyte cells. Thus, the presented data indicate that the dehydroxy isoquines 4b, 4c and 4e constitute promising cost-effective leads for the development of new antiplasmodial targeted at blood-stage malaria parasites.

Pharmacokinetics of a Novel Trioxane Antimalarial Drug 99/411: Alterations Upon Rifampicin Coadministration, Single and Multiple Oral Dose Drug–Drug Interactions in Sprague-Dawley Rats

Aim: Study was aimed to investigate the potential drug–drug interactions between antimalarial candidate 99/411 and antitubercular drug rifampicin. Methods: A single-dose drug-interaction study followed by multiple dose parallel study was designed to estimate the drug–drug interactions. Results: It was found that steady-state pharmacokinetics profile of 99/411 determined after multiple dosing for five successive days was consistent with the single-dose characteristics in both the cases, when 99/411 was given alone and co-administered with rifampicin. Conclusion: The compound was absorbed fast after each dosing and declined up to next 24 h to lower concentration. AUC showed accumulation of 99/411 day by day after multiple dosing, which may affect the therapeutic response of this molecule.

Newer series of trioxane derivatives as potent antimalarial agents

Among synthesized 1,2,4-trioxane derivatives, six compounds were found to be considerably potent, with better activity against resistant strain of P. falciparum than the sensitive strain. The IC50 values of the best compound with 4-hydroxyphenyl substitution were found to be 0.391 and 0.837 µg/mL against sensitive and resistant strain of P. falciparum, respectively. Results of the tested compounds were comparable with that of the standard drug, chloroquine (IC50 = 0.044 and 0.205 µg/mL against sensitive and resistant strain of P. falciparum, respectively). Docking simulation, in silico drug-likeness and ADMET studies further validated the results of in vitro antimalarial activity. Trioxane derivatives exhibited good binding affinity for the P. falciparum cysteine protease falcipain 2 receptor (PDB id: 3BPF) with well defined drug-like and pharmacokinetic properties based on Lipinski’s rule of five with additional physicochemical and ADMET parameters. In view of having antimalarial potential, newly reported 1,2,4-trioxane derivative(s) may be useful as novel antimalarial lead(s) in the discovery and development of future antimalarial drug candidates as P. falciparum falcipain 2 inhibitors against resistant malaria.

Alkoxycarbonate Ester Prodrugs of Preclinical Drug Candidate ELQ-300 for Prophylaxis and Treatment of Malaria.

ELQ-300 is a preclinical antimalarial drug candidate that is active against liver, blood, and transmission stages of Plasmodium falciparum. While ELQ-300 is highly effective when administered in a low multidose regimen, poor aqueous solubility and high crystallinity have hindered its clinical development. To overcome its challenging physiochemical properties, a number of bioreversible alkoxycarbonate ester prodrugs of ELQ-300 were synthesized. These bioreversible prodrugs are converted to ELQ-300 by host and parasite esterase action in the liver and bloodstream of the host. One such alkoxycarbonate prodrug, ELQ-331, is curative against Plasmodium yoelii with a single low dose of 3 mg/kg in a murine model of patent malaria infection. ELQ-331 is at least as fully protective as ELQ-300 in a murine malaria prophylaxis model when delivered 24 h before sporozoite inoculation at an oral dose of 1 mg/kg. Here, we show that ELQ-331 is a promising prodrug of ELQ-300 with improved physiochemical and metabolic properties and excellent potential for clinical formulation.

Cheminformatic Analysis of Antimalarial Chemical Space Illuminates Therapeutic Mechanisms and Offers Strategies for Therapy Development.

The clear and present danger of malaria, which has been amplified in recent years by climate change, and the progressive thinning of our drug arsenal over the past two decades raise uncomfortable questions about the current state and future of antimalarial drug development. Besides suffering from many of the same technical challenges that affect drug development in other disease areas, the quest for new antimalarial therapies is also hindered by the complex, dynamic life cycle of the malaria parasite, P. falciparum, in its mosquito and human hosts, and its role thereof in the elicitation of drug resistance. New strategies are needed in order to ensure economical and expeditious development of new, more efficacious treatments. In the present study, we employ open-source cheminformatics tools to analyze the chemical space traversed by approved antimalarial drugs and promising candidates at various stages of development to uncover insights that could shape future endeavors in the field. Our scaffold-centric analysis reveals that the antimalarial chemical space is disjointed and segregated into a few dominant structural groups. In fact, the structures of antimalarial drugs and drug candidates are distributed according to Pareto's principle. This structural convergence can potentially be exploited for future drug discovery by incorporating it into bioinformatics workflows that are typically employed for solving problems in structural biology. Significantly, we demonstrate how molecular scaffold hunting can be applied to unearth putative mechanisms of action of drugs whose activities remain a mystery, and how scaffold-centric analysis of drug space can also provide a recipe for combination therapies that minimize the likelihood of emergence of drug resistance, as well as identify areas on which to focus efforts. Finally, we also observe that over half of the molecules in the antimalarial space bear no resemblance to other molecules in the collection, which suggests that the pharmacobiology of antimalarial drugs has not been entirely surveyed.

The Candidate Antimalarial Drug MMV665909 Causes Oxygen-Dependent mRNA Mistranslation and Synergizes with Quinoline-Derived Antimalarials.

ABSTRACTTo cope with growing resistance to current antimalarials, new drugs with novel modes of action are urgently needed. Molecules targeting protein synthesis appear to be promising candidates. We identified a compound (MMV665909) from the Medicines for Malaria Venture (MMV) Malaria Box of candidate antimalarials that could produce synergistic growth inhibition with the aminoglycoside antibiotic paromomycin, suggesting a possible action of the compound in mRNA mistranslation. This mechanism of action was substantiated with a Saccharomyces cerevisiae model using available reporters of mistranslation and other genetic tools. Mistranslation induced by MMV665909 was oxygen dependent, suggesting a role for reactive oxygen species (ROS). Overexpression of Rli1 (a ROS-sensitive, conserved FeS protein essential in mRNA translation) rescued inhibition by MMV665909, consistent with the drug's action on translation fidelity being mediated through Rli1. The MMV drug also synergized with major quinoline-derived antimalarials which can perturb amino acid availability or promote ROS stress: chloroquine, amodiaquine, and primaquine. The data collectively suggest translation fidelity as a novel target of antimalarial action and support MMV665909 as a promising drug candidate.

ImmunoPEGliposomes for the targeted delivery of novel lipophilic drugs to red blood cells in a falciparum malaria murine model

Most drugs currently entering the clinical pipeline for severe malaria therapeutics are of lipophilic nature, with a relatively poor solubility in plasma and large biodistribution volumes. Low amounts of these compounds do consequently accumulate in circulating Plasmodium-infected red blood cells, exhibiting limited antiparasitic activity. These drawbacks can in principle be satisfactorily dealt with by stably encapsulating drugs in targeted nanocarriers. Here this approach has been adapted for its use in immunocompetent mice infected by the Plasmodium yoelii 17XL lethal strain, selected as a model for human blood infections by Plasmodium falciparum. Using immunoliposomes targeted against a surface protein characteristic of the murine erythroid lineage, the protocol has been applied to two novel antimalarial lipophilic drug candidates, an aminoquinoline and an aminoalcohol. Large encapsulation yields of >90% were obtained using a citrate-buffered pH gradient method and the resulting immunoliposomes reached invivo erythrocyte targeting and retention efficacies of >80%. In P.yoelii-infected mice, the immunoliposomized aminoquinoline succeeded in decreasing blood parasitemia from severe to uncomplicated malaria parasite densities (i.e. from ≥25% to ca. 5%), whereas the same amount of drug encapsulated in non-targeted liposomes had no significant effect on parasite growth. Pharmacokinetic analysis indicated that this good performance was obtained with a rapid clearance of immunoliposomes from the circulation (blood half-life of ca. 2 h), suggesting a potential for improvement of the proposed model.

Hexahydroquinolines are antimalarial candidates with potent blood-stage and transmission-blocking activity.

Antimalarial compounds with dual therapeutic and transmission-blocking activity are desired as high-value partners for combination therapies. Here, we report the identification and characterization of hexahydroquinolines (HHQs) that show low nanomolar potency against both pathogenic and transmissible intra-erythrocytic forms of the malaria parasite Plasmodium falciparum. This activity translates into potent transmission-blocking potential, as shown by in vitro male gamete formation assays and reduced oocyst infection and prevalence in Anopheles mosquitoes. In vivo studies illustrated the ability of lead HHQs to suppress Plasmodium berghei blood-stage parasite proliferation. Resistance selection studies, confirmed by CRISPR-Cas9-based gene editing, identified the digestive vacuole membrane-spanning transporter PfMDR1 (P. falciparum multidrug resistance gene-1)as a determinant of parasite resistance to HHQs. Haemoglobin and haem fractionation assays suggest a mode of action that results in reduced haemozoin levels and might involve inhibition of host haemoglobin uptake into intra-erythrocytic parasites. Furthermore, parasites resistant to HHQs displayed increased susceptibility to several first-line antimalarial drugs, including lumefantrine, confirming that HHQs have a different mode of action to other antimalarials drugs for which PfMDR1 is known to confer resistance. This work evokes therapeutic strategies that combine opposing selective pressures on this parasite transporter as an approach to countering the emergence and transmission of multidrug-resistant P. falciparum malaria.

A pharmacokinetic comparison of homodimer ARB-92 and heterodimer ARB-89: novel, potent antimalarial candidates derived from 7β-hydroxyartemisinin

The ultimate goal of this study was to identify an orally active, affordable, potent and safe antimalarial drug based on the natural product artemisinin. During these efforts, a series of novel 7β-hydroxyartemisinin analogs were synthesized and characterized in vitro for their antimalarial activity against Plasmodium falciparum. Heterodimerization of 7β-hydroxyartemisinin provided the asymmetrical carbamate (ARB-89) while homodimerization provided the carbonate (ARB-92). These dimers were found to be highly active in vitro with an IC50 ≤ 0.50 nM against P. falciparum infected human red blood cells (RBC). For further development as potential antimalarial agents, a battery of in vitro and in vivo pharmacokinetic experiments was performed to distinguish the fate of the discovery compounds ARB-89 and ARB-92. Two UPLC-MS methods were developed and validated for the analysis of the compounds. Both ARB-89 and ARB-92 exhibited moderate affinity (51 and 56%, respectively) to parasitized RBC, which is a perquisite for antimalarial activity. Following a single dose oral and intravenous pharmacokinetic study in rats, ARB-89 displayed a high clearance (92.8 ± 5.6 L/h kg), short elimination half-life (t1/2, 1.2 ± 0.2 h) and moderate oral bioavailability (23.4%). ARB-89 was found to be excreted unchanged in feces, which may be due to its high lipophilicity, molecular weight and low oral exposure. In an attempt to identify a better lead antimalarial compound, ARB-92 was designed to be more water soluble than ARB-89 by incorporating a protonatable tertiary amine as part of the dimerizing ligand for 7β-hydroxyartemisinin. As anticipated, ARB-92 displayed a lower clearance (2.9 ± 0.7 L/h kg) and subsequently a longer t1/2 (2.3 ± 0.2 h) compared to ARB-89. The oral bioavailability of ARB-92 was found to be 34% in rats, a value somewhat better than the marketed artemisinin derivatives artenimol (19.3%), artemether (19.7%) or artesunate (29.5%).

Skrining Aktivitas Antimalaria Beberapa Tanaman Indonesia Hasil Eksplorasi Dari Hutan Raya Cangar, Batu-Malang, Jawa Timur

Background: Malaria is the most important parasitic disease. Malaria control which depends on specific chemotherapy now complicated by resistance of Plasmodium falciparum to most commonly available antimalarial drug. Such situation has heralded the need for alternative antimalarial therapy. Objective: This research aim was to find new antimalarial candidates from some Indonesia plants collected from Cangar National Forest, Batu-Malang, East Java. Methods: Eleven samples of leaves and stem extracts were screened against Plasmodium falciparum 3D7 culture which maintained in RPMI-1640 Medium. Samples tested in concentration of 0.01, 0.1, 1, 10 and 100 µg/ml. Probit analysis was used to determine IC50. Results: In vitro antimalarial activity revealed that only three crude extracts samples from Fraxinus griffithi stem extract, Piper sulcatum leaves extract and Eucalyptus globulus stem extract had good antimalarial activity with IC50 value of 0.33, 0.20 and 0.55 µg/ml, respectively. Conclusions: Fraxinus griffithi stem extract, Piper sulcatum leaves extract and Eucalyptus globulus stem extract might be a good candidate for antimalarial natural product resources.

Skrining Aktivitas Antimalaria Beberapa Tanaman Indonesia Hasil Eksplorasi Dari Hutan Raya Cangar, Batu-Malang, Jawa Timur

Background: Malaria is the most important parasitic disease. Malaria control which depends on specific chemotherapy now complicated by resistance of Plasmodium falciparum to most commonly available antimalarial drug. Such situation has heralded the need for alternative antimalarial therapy. Objective: This research aim was to find new antimalarial candidates from some Indonesia plants collected from Cangar National Forest, Batu-Malang, East Java. Methods: Eleven samples of leaves and stem extracts were screened against Plasmodium falciparum 3D7 culture which maintained in RPMI-1640 Medium. Samples tested in concentration of 0.01, 0.1, 1, 10 and 100 µg/ml. Probit analysis was used to determine IC50. Results: In vitro antimalarial activity revealed that only three crude extracts samples from Fraxinus griffithi stem extract, Piper sulcatum leaves extract and Eucalyptus globulus stem extract had good antimalarial activity with IC50 value of 0.33, 0.20 and 0.55 µg/ml, respectively. Conclusions: Fraxinus griffithi stem extract, Piper sulcatum leaves extract and Eucalyptus globulus stem extract might be a good candidate for antimalarial natural product resources.

Challenges to replace ACT as first-line drug

The spread of artemisinin and partner drug resistance through Asia requires changes in first-line therapy. The traditional modus has been the replacement of one first-line anti-malarial regimen with another. The number of anti-malarial drug candidates currently in development may have given false confidence in the expectation that resistance to artemisinin-based combination therapy (ACT) can be solved with a switch to the next anti-malarial drug regimen. A number of promising anti-malarial drug regimens did not succeed in becoming first-line drugs due to safety concerns or rapid development of resistance. Currently promising candidates for inclusion in first-line regimens, such as KAE 609, KAF 156, OZ 439, and OZ 277, have already triggered safety concerns or fears that point mutations could render the drugs inefficacious. An additional challenge for a new first-line drug is finding an appropriate partner drug. There is hope that none of the above-mentioned concerns will be substantiated in larger, upcoming trials. Meanwhile, combining already licensed anti-malarials may be a promising stop-gap measure. Practitioners in Vietnam have empirically started to add mefloquine to the current dihydroartemisinin-piperaquine. Practitioners in Africa could do worse than empirically combine already licensed co-artemether and amodiaquine when treatment with ACT no longer clears Plasmodium falciparum. Both combinations are currently undergoing trials.

Potential of synthetic endoperoxides against Trichomonas vaginalis in vitro

Metronidazole is well known for medicine against Trichomonas vaginalis infection, but it has side effects though it is effective, and especially because reports of metronidazole-tolerant species are increasing, the development of new medicine is being required. Here, we noticed the killing effects of endoperoxide compounds, N-89 and N-251 as new antimalarial drug candidates, on T. vaginalis and searched the possibility of development of new medicine. We added each of metronidazole, artemisinin, and two of new endoperoxides (N-89 and N-251) to metronidazole-resistant and -sensitive species and compared its anti-trichomonal efficacy. For metronidazole, IC50 value, 50% of killing concentration for T. vaginalis, was very low for metronidazole-sensitive isolates (11.7 to 22.8μM), but was high for metronidazole-resistant ones (182.9 to 730.4μM). The IC50 values of N-89 and N-251 were 41.0 to 60.0μM, and 82.0 to 300.0μM for metronidazole-sensitive and -resistant isolates, respectively. In conclusion, we found the endoperoxides, N-89 and N-251, have anti-trichomonal effect against metronidazole-resistant T. vaginalis as well as metronidazole-sensitive ones. These results indicate that the anti-trichomonal effects for our endoperoxides are equivalent or better in metronidazole-resistant T. vaginalis in comparison to metronidazole.