The Search for Antimalarial Drugs and the Discovery of Artemisinin

With its novel chemical structure, artemisinin is an antimalarial component isolated from the traditional Chinese medicine qinghao(Artemisia annua L.). Nowadays, artemisinin and its derivatives are used compatibly with new synthesized chemical antimalarial compounds to create artemisinin-based combination therapies(ACTs). These have become the first choice in treating malaria p.f. all over the world, providing an effective solution for the global challenge of curing drug-resistant malaria. Among the five ACTs recommended by the WHO, two were initiated in China and are used as the first-line treatment of falciparum malaria in all malaria endemic areas. As the use of artemisinin-based compound drugs have made such significant contributions to rolling back malaria, regarded as one of the great achievements globally in public health of the early twenty-first century, Tu Youyou, one of the most important researchers in the discovery of artemisinin, was made the first Nobel Prize laureate in Physiology or Medicine from the Chinese mainland. Artemisinin was discovered in a special social and cultural context through a combination of the exploration of traditional Chinese medical literature with the modern research approach of pharmaceutical sciences. This(Project 523) is a typical case of goal-oriented research leading to scientific advance, and the result of scientific research driven by the national needs.

Comparison of Molecular Properties (Stabilities, Reactivity and Interaction) of Manzamenones and Two Antimalarial Drugs (Quinine and Artemisinin) Using Mixed Method Calculations (ONIOM) and DFT (B3LYP)

Malaria is a real public health problem. It’s one of the pathologies that mobilize the scientific community. Resistance to existing treatments is the basis for the search for new treatments. Some molecules such as Manzamenones have shown important antimalarial properties. These molecules belong to the family of atypical fatty acid derivatives. This work presents the relative stabilities, some reactivity properties and the privileged sites of interaction by hydrogen bond of fourteen Manzamenones and two antimalarial drugs: quinine and Artemisinin. These analyses were performed using quantum chemical calculations. We employed the two-layer ONIOM calculation method;namely ONIOM (B3LYP/6-311++G (d, p): AM1) for the fourteen Manzamenones. The geometries of the two antimalarials are calculated at B3LYP/6-311++G (d, p). The electrostatic potential (ESP) calculation of all molecules is done at the B3LYP/6-31++G (d, p) level. The formation processes of the molecules are discussed from the thermodynamic quantities we have calculated. The relative stabilities, the energies of the frontier orbitals, the energy gaps, the dipole moment, etc., are evaluated and discussed. The electrostatic potential at the molecular surface has been used to identify the sites favorable to the formation of hydrogen bonds.

Alternatives to currently used antimalarial drugs: in search of a magic bullet

Malaria is a major cause of morbidity and mortality in many African countries and parts of Asia and South America.Novel approaches to combating the disease have emerged in recent years and several drug candidates are now being tested clinically.However,it is long before these novel drugs can hit the market,especially due to a scarcity of safety and efficacy data.To reduce the malaria burden,the Medicines for Malaria Venture(MMV)was established in 1999 to develop novel medicines through industry and academic partners’collaboration.However,no reviews were focused following various preclinical and clinical studies published since the MMV initiation(2000)to till date.We identify promising approaches in the global portfolio of antimalarial medicines,and highlight challenges and patient specific concerns of these novel molecules.We discuss different clinical studies focusing on the evaluation of novel drugs against malaria in different human trials over the past five years.The drugs KAE609 and DDD107498 are still being evaluated in Phase I trials and preclinical developmental studies.Both the safety and efficacy of novel compounds such as KAF156 and DSM265 need to be assessed further,especially for use in pregnant women.Synthetic non-artemisinin ozonides such as OZ277 raised concerns in terms of its insufficient efficacy against high parasitic loads.Aminoquinoline-based scaffolds such as ferroquine are promising but should be combined with good partner drugs for enhanced efficacy.AQ-13 induced electrocardiac events,which led to prolonged QTc intervals.Tafenoquine,the only new anti-relapse scaffold for patients with a glucose-6-phosphate dehydrogenase deficiency,has raised significant concerns due to its hemolytic activity.Other compounds,including methylene blue(potential transmission blocker)and fosmidomycin(DXP reductoisomerase inhibitor),are available but cannot be used in children.At this stage,we are unable to identify a single magic bullet against malaria.Future studies should focus on effective single-dose molecules that can act against all stages of malaria in order to prevent transmission.Newer medicines have also raised concerns in terms of efficacy and safety.Overall,more evidence is needed to effectively reduce the current malaria burden.Treatment strategies that target the blood stage with transmission-blocking properties are needed to prevent future drug resistance.

Selective Effect of Qinghaosu on Different Stages of Plasmodium falciparum in Vitro

Using highly synchronous cultures of Plasmodium falciparum in vitro,the susceptibi- lity of the different stages of the intraerythrocytic parasites to Qinghaosu (QHS) was assessed.The anti- parasitic effect of QHS was measured by comparing the changes of irradiation of^3 H-hypoxanthine in- corporated into the nucleic acids of parasites exposed to various concentrations of QHS at different stages of growth.It was found that the trophozoite stage of the parasite was the most sensitive to QHS, whereas the early ring stage was the least sensitive,and the sensitivities of the late ring and schizont stages fell between those of the early ring and trophozoite stages.The results revealed the correlation of stage-dependent effects of QHS with the blockade of the protein metabolism of the parasite.

Surveillance of antimalarial drug resistance in China in the 1980s–1990s

Since the successful preparation of the microplates and the medium for field application,the resistance degree and its geographical distribution of chloroquine-resistant Plasmodium falciparum,the fluctuation of the resistance degree of P.falciparum to chloroquine,and the sensitivity of the parasite to commonly used antimalarial drugs were investigated between 1980 and 2003 by the in vitro microtest and the in vivo four-week test recommended by the World Health Organization(WHO).The results indicated that chloroquine-resistant falciparum malaria was present in all eight provinces/autonomous regions endemic for falciparum malaria in China,and the resistance was high and widely distributed in the Hainan and Yunnan provinces.When the use of chloroquine was stopped or administered in a decreased quanity,the drug resistance gradually decreased.In Hainan and Yunnan,P.falciparum was still highly resistant to chloroquine,amodiaquine and piperaquine,and sensitive to pyronaridine and artemisinin derivatives,but the sensitivity was gradually reduced.Based on these results,principles and therapeutic regimens for antimalarial drug use in China were formulated,the use of the antimalarials which had already developed resistance was stopped or reduced,and recommendations to use artemisinin derivatives or compound pyronaridine to promote a rational use of antimalarials and strengthen malaria control were made.The results showed that malaria incidence had declined,and endemic areas of falciparum malaria have been gradually reducing since the mid-1980s.

In vivo antimalarial activity and toxicological effects of methanolic extract of Cocos nucifera(Dwarf red variety) husk fibre

OBJECTIVE： Phytochemical constituents as well as antimalarial and toxicity potentials of the methanolic extract of the husk fi bre of Dwarf Red variety of Cocos nucifera were evaluated in this study.METHODS： The dried powdered husk fi bre was exhaustively extracted with hexane, ethyl acetate and methanol successively and the methanolic extract was screened for fl avonoids, phenolics, tannins, alkaloids, steroids, triterpenes, phlobatannins, anthraquinones and glycosides. A 4-day suppressive antimalarial test was carried out using Plasmodium berghei NK65-infected mice, to which the extract was administered at doses of 31.25, 62.5, 125, 250 and 500 mg/kg body weight（BW）. Toxicity of the extract was evaluated in rats using selected hematological parameters and organ function indices after orally administering doses of 25, 50 and 100 mg/kg BW for 14 d.RESULTS： Phytochemical analysis revealed the presence of alkaloids, tannins, phenolics, saponins, glycosides, steroids and anthraquinones in the extract. Moreover, the extract reduced parasitemia by 39.2% and 45.8% at doses of 250 and 500 mg/kg BW respectively on day 8 post-inoculation. Various hematological parameters evaluated were not significantly altered（P〉0.05） at all doses of the extract, except red blood cell count which was signifi cantly elevated（P〈0.05） at 100 mg/kg BW. The extract significantly increased（P〈0.05） urea, creatinine, cholesterol, high-density lipoprotein-cholesterol and bilirubin concentrations in the serum as well as atherogenic index, while it reduced albumin concentration significantly（P〈0.05） at higher doses compared to the controls. Alanine aminotransferase activity was reduced in the liver and heart signifi cantly（P〈0.05） but was increased in the serum signifi cantly（P〈0.05） at higher doses of the extract compared to the controls.CONCLUSION： The results suggest that methanolic extract of the Dwarf red variety has partial antimalarial activity at higher doses, but is capable of impairing normal kidney and liver function as well as predisposing subjects to cardiovascular diseases.

Discovery and Development of Artemisinin and Related Compounds

Artemisinin is isolated from the plant Artemisia annua,sweet wormwood,an herb employed in traditional Chinese medicine.Prof.You-you Tu discovered artemisinin in the 1960 s,so she was awarded the 2015 Nobel Prize in Physiology or Medicine.Artemisinin and its semi-synthetic derivatives are a group of drugs that possess the most rapid action of all current drugs against Plasmodium falciparum malaria.In this review,the author investigated history on discovery of artemisinin,ethnopharmacology of Artemisia plants,chemistry and pharmacological activities of the relative compounds,and introduced Tu and other Chinese and world scientists＇ contribution,development of artemisinin and the related compounds and registered and marketed artemisinin drugs in China,UK,and USA.The author also recalled the studies on the mechanism of action of artemisinins and artemisinin combination therapies and summed up the resistance issues.In Current Recommendations and the Global Plan for Insecticide Resistance Management in Malaria Vectors（CPIRM）,that the WHO prevents the development and manages the spread of insecticide resistance is summarized in the technical basis for coordinated action against insecticide resistance：preserving the effectiveness of modern malaria vector control.Prof.Tu re-emphasized the artemisinin resistant on five principles to the WHO.She called on the world＇s scientists to pay attention to the study of drug resistance,and hopes scientists to contribute to break resistance of artemisinins.

Expanding the Therapeutic Spectrum of Artemisinin:Activity Against Infectious Diseases Beyond Malaria and Novel Pharmaceutical Developments

The interest of Western medicine in Traditional Chinese Medicine(TCM) as a source of drug leads/new drugs to treat diseases without available efficient therapies has been dramatically augmented in the last decades by the extensive work and the outstanding findings achieved within this kind of medicine. The practice of TCM over thousands of years has equipped scientists with substantial experience with hundreds of plants that led to the discovery of artemisinin(qinghaosu), which is extracted from the medicinal plant Artemisia annua L.(qinghao). The unexpected success of artemisinin in combating malaria has drawn strong attention from the scientific community towards TCM. Artemisinin was discovered by Youyou Tu in 1972. Since then, several novel pharmacological activities based on the well-known properties of the sesquiterpene lactone structure with the oxepane ring and an endoperoxide bridge have been unravelled. Beyond malaria, artemisinin and its derivatives(artemisinins) exert profound activities towards other protozoans(Leishmania, Trypanosoma, amoebas, Neospora caninum, and Eimeria tenella), trematodes(Schistosoma, liver flukes), and viruses(human cytomegalovirus, hepatitis B and C viruses). Less clear is the effect against bacteria and fungi. Based on the promising results of artemisinin and the first generation derivatives(artesunate, artemether, arteether), novel drug development strategies have been pursued.These included the synthesis of acetal-and non-acetal-type artemisinin dimeric molecules as well as developing nanotechnological approaches, e.g.artemisinin-based liposomes, niosomes, micelles, solid lipid nanocarriers, nanostructured lipid carriers, nanoparticles, fullerenes and nanotubes. The current review presents an overview on different aspects of artemisinins, including sources, chemistry, biological/pharmacological properties, types of infectious pathogens that are susceptible to artemisinins in vitro and in vivo, in addition to the advancement in their drug delivery systems utilizing pharmaceutical technology. It would be expected that different therapeutic strategies based on the second and third generation artemisinin derivatives and artemisinin-based drug technologies would be available in the near future to treat specific infectious diseases.

Polymorphisms of potential drug resistant molecular markers in Plasmodium vivax from China-Myanmar border during 2008-2017

Background:Plasmodium vivax remains the predominant species at the China–Myanmar border,imposing a major challenge to the recent gains in regional malaria elimination.To closely supervise the emerging of drug resistance in this area,we surveyed the variations in genes potentially correlated with drug resistance in P.vivax parasite and the possible drug selection with time.Methods:A total of 235 P.vivax samples were collected from patients sufering uncomplicated malaria at Yingjiang,Tengchong,and Longling counties,and Nabang port in China,Yunnan province,and Laiza sub-township in Myanmar,from 2008 to 2017.Five potential drug resistance genes were amplifed utilizing nested-PCR and analyzed,including pvdhfr,pvdhps,pvmdr1,pvcrt-o,and pvk12.The Pearson’s Chi-squared test or Fisher’s exact test were applied to determine the statistical frequency diferences of mutations between categorical data.Results:The pvdhfr F57I/L,S58R,T61M and S117T/N presented in 40.6%,56.7%,40.1%,and 56.0% of the sequenced P.vivax isolates,and these mutations signifcantly decreased with years.The haplotype formed by these quadruple mutations predominated in Yingjiang,Tengchong,Longling and Nabang.While a mutation H99S/R(56.6%)dominated in Laiza and increased with time.In pvdhps,the A383G prevailed in 69.2% of the samples,which remained the most prevalent haplotype.However,a signifcant decrease of its occurrence was also noticed over the time.The S382A/C and A553G existed in 8.4% and 30.8% of the isolates,respectively.In pvmdr1,the mutation Y976F occurred at a low frequency in 5/232(2.2%),while T958M was fxed and F1076L was approaching fxed(72.4%).The K10 insertion was detected at an occurrence of 33.2% in pvcrt-o,whereas there was no signifcant diference among the sites or over the time.No mutation was identifed in pvk12.Conclusions:Mutations related with resistance to antifolate drugs are prevalent in this area,while their frequencies decrease signifcantly with time,suggestive of increased susceptibility of P.vivax parasite to antifolate drugs.Resistance to chloroquine(CQ)is possibly emerging.However,since the molecular mechanisms underneath CQ resistance is yet to be better understood,close supervision of clinical drug efciency and continuous function investigation is urgently needed to alarm drug resistance.

Binding Reaction of Hemin with Chloroquine, Quinine and Quinidine in Water-propylene Glycol Mixture

The interaction of hemin with chloroquine, quinine and quini-dine wasinvestigated in 50% water-propylene glycol mixture at pH = 9, 8.1, 7.4 and 6.8 using aspectrophotometric method. The data could be well fitted into a model consistent with the formationof a 1:1 complex between the reacting partners. In addition, the results indicated that hemincomplexed more strongly with quinidine than with chloroquine and quinine, and the binding constantswere pH-dependent. Moreover, it was proved that the water-propylene glycol mixture is well suitableto the study of the systems containing hemin and quinoline-based drugs.

High multiple mutations of Plasmodium falciparum-resistant genotypes to sulphadoxine-pyrimethamine in Lagos, Nigeria

Background Plasmodium falciparum-resistance to sulphadoxine-pyrimethamine(SP)has been largely reported among pregnant women.However,the profile of resistance markers to SP dihydrofolate reductase(dhfr)and dihydropteroate synthase(dhps)in the general population are varied and not frequently monitored.Currently,SP is used as partner drug for artemisinin combination therapy(SP-artesunate)in some sub-Saharan African countries or as a prophylactic drug in intermittent preventive treatment of malaria during pregnancy and infants and in seasonal malaria chemoprevention(SMC).Profiling of P.falciparum-resistant genotypes to SP is dynamic and critical in providing data that would be useful for malaria control programmes.This study assessed the profile of dhfr and dhps genes genotypes among individuals with malaria in Lagos,Nigeria.Methods Molecular markers of SP resistance were identified by nested PCR and sequenced among malaria positive dried blood spots(DBS)that were collected from individuals attending health facilities from January 2013 to February 2014 and during community surveys from October 2010 to September 2011 across different Local Government Areas of Lagos State,Nigeria.Results A total of 242 and 167 samples were sequenced for dhfr and dhps,respectively.Sequence analysis of dhfr showed that 95.5%(231/242),96.3%(233/242)and 96.7%(234/242)of the samples had N51I,C59R and S108N mutant alleles,respectively.The prevalence of dhps mutation at codons A437G,A613S,S436A,A581G,I431V and K540E were 95.8%(160/167),41.9%(70/167),41.3%(69/167),31.1%(52/167),25.1%(42/167),and 1.2%(2/167)respectively.The prevalence of triple mutations(CIRNI)in dhfr was 93.8%and 44.3%for the single dhps haplotype mutation(SGKAA).Partial SP-resistance due to quadruple dhfr-dhps haplotype mutations(CIRNI-SGKAA)and octuple haplotype mutations(CIRNI-VAGKGS)with rate of 42.6%and 22.0%,respectively has been reported.Conclusions There was increased prevalence in dhfr triple haplotype mutations when compared with previous reports in the same environment but aligned with high prevalence in other locations in Nigeria and other countries in Africa.Also,high prevalence of dhfr and dhps mutant alleles occurred in the study areas in Lagos,Nigeria five to eight years after the introduction of artemisinin combination therapy underscores the need for continuous monitoring.