The FK506-binding protein of the malaria parasite, Plasmodium falciparum, is a FK506-sensitive chaperone with FK506-independent calcineurin-inhibitory activity

We have identified an immunophilin of the FKBP family in Plasmodium falciparum that contains a conserved peptidyl prolyl isomerase (PPIase) and tetratricopeptide repeat (TPR) domains. The 35 kDa protein was named FKBP35 and expressed in bacteria. Recombinant FKBP35 exhibited potent PPIase and protein folding activities against defined substrates in vitro, suggesting that it is a parasitic chaperone. Both activities were inhibited by macrolide immunosuppressant drugs, ascomycin (a FK506 derivative) and rapamycin, but not by cyclosporin A, providing biochemical evidence of its inclusion in the FKBP family. Interestingly, FKBP35 inhibited purified plasmodial calcineurin (protein phosphatase 2B) in the absence of any drug. In the parasite's cell, FKBP35 exhibited a stage-specific nucleocytoplasmic shuttling and did not co-localize with calcineurin. FKBP35 associated with plasmodial heat shock protein 90 (Hsp90), another member of the chaperone superfamily, via the TPR domain. Geldanamycin, a Hsp90 inhibitor, and ascomycin inhibited P. falciparum growth in a synergistic fashion. Extensive search of the P. falciparum genome revealed no other FKBP sequence, implicating PfFKBP35 as a highly significant antimalarial drug target. Thus, the single FKBP of Plasmodium is an essential parasitic chaperone with a novel drug-independent calcineurin-inhibitory activity.     

Antileishmanial and antimalarial chalcones: synthesis, efficacy and cytotoxicity of pyridinyl and naphthalenyl analogs

The antileishmanial and antimalarial activity of methoxy-substituted chalcones (1,3-diphenyl-2-propen-1-ones) is well established. The few analogs prepared to date where the 3-phenyl group is replaced by either a pyridine or naphthalene suggest these modifications are potency enhancing. To explore this hypothesis, sixteen 3-naphthalenyl-1-phenyl-2-prop-1-enones and ten 1-phenyl-3-pyridinyl-2-prop-1-enones were synthesized and their in vitro efficacies against Leishmania donovani and Plasmodium falciparum determined. One inhibitor with submicromolar efficacy against L. donovani was identified (IC50 = 0.95 microM), along with three other potent compounds (IC50 < 5 microM), all of which were 3-pyridin-2-yl derivatives. No inhibitors with submicromolar efficacy against P. falciparum were identified, though several potent compounds were found (IC50 < 5 microM). The cytotoxicity of the five most active L. donovani inhibitors was assessed. At best the IC50 against a primary kidney cell line was around two-fold higher than against L. donovani. Being more active than pentamidine, the 1-phenyl-3-pyridin-2-yl-2-propen-1-ones have potential for further development against leishmaniasis; however it will be essential in such a program to address not only efficacy but also their potential for toxicity.     

基于吩噻嗪类化合物的新型抗结核小分子化合物的设计、合成及活性研究

目的 借助计算机虚拟筛选技术设计并合成新型抗结核小分子化合物.方法 以氯丙嗪为模板分子,利用Discovery studio 3.0构建相应的3D药效团模型,并对虚拟化合物库进行筛选;对筛选结果进行手动择优选择,化学合成目标化合物并进行体外抗结核分枝杆菌的活性评价.结果 筛选得到活性化合物15个,并合成其中13个,其中化合物9(多巴胺)在体外对结核分枝杆菌表现出中等强度的抑制作用,MIC为8.0 μg/ml.结论 通过药效团的方法筛选得到了结构较吩噻嗪类化合物简单的抗结核活性小分子多巴胺,该化合物作为抗结核分枝杆菌的先导化合物,较吩噻嗪类具有更大的结构修饰空间.     

Synthesis and antimalarial activity of novel side chain modified antimalarial agents derived from 4-aminoquinoline

Malaria is one of the foremost public health problems in developing countries affecting nearly 40% of the global population. Apart from this, the past two decade's emergence of drug resistance has severely limited the choice of available antimalarial drugs. Furthermore, the general trend emerging from the SAR-studies is that chloroquine resistance does not involve any change to the target of this class of drugs but involves compound specific efflux mechanism. Based on this premise a number of groups have developed short chain analogues of 4-aminoquinoline, which are active against CQ-resistant strains of P. falciparum in in vitro studies. However, these derivatives undergo biotransformation (de-alklyation) significantly affecting lipid solubility of the drug. In view of this background information, we thought that it would be interesting to study the effect of additional lipophilicity and cationic charge at the lateral side chain of 4-aminoquinoline. This prompted us to explore the cationic amino acid conjugates namely, lysine and ornithine of 4-aminoquinoline with a view to achieve improved antimalarial activity and to the best of our knowledge such amino acid conjugates have not been hitherto reported in the literature in the case of 4-aminoquinolines. In the present study, a new series of side-chain modified 4-aminoquinolines have been synthesized and found active against both susceptible and multidrug resistant strains of P. falciparum in vitro and P. yoelli in vivo. The seminal finding of the present study is that a new series of compounds having significantly more activity against CQ resistant parasites has been identified.     

In vitro antimalarial activity of extracts of Albizia gummifera,Aspilia mossambicensis,Melia azedarach and Azadirachta indica against Plasmodium falciparum

Since chemotherapy is presently the primary strategy of malaria control in the world, and some malaria parasites are developing resistance to the commonly used antimalarial drugs, new antimalarial compounds are required. Therefore, it is important to test antimalarial activities of medicinal plant extracts which most herbalists claim to cure malaria. We evaluated the antimalarial activities of extracts of Albizia gummiffera, Aspilia mossambicensis, Melia azedar and Azadirahchta indica against laboratory adapted isolates of Plasmodium falciparum using an in vitro radioisotopic uptake technique. Chloroquine was used as a reference antimalarial drug. Al. gummifera had the highest antimalarial activity (mean fifty percent inhibitory concentration {IC(50)S} in ug/ml of test culture =3.5 +1.6SD, n=3) followed by As. mossambicensis (mean IC(50)=29.3+11.8SD, n=4) and Me. Azedarach (mean IC(50) =299.7+202.0SD, n=4). And lastly Az. Indica (mean IC(50)=349.9+213.1 SD, n=4). The antimalarial activities of the reference drug, chloroquine, was far much higher (mean IC(50)=0.065+0.057SD, n=)4). These findings show that Al. gummifera and As. mossambicensis plant extracts have potent antimalarial compounds. Phytochemical analyses should be done on these two plants to isolate the compound(s) containing he active principles(s).     

Ultrastructural analysis of miltefosine-induced surface membrane damage in adult Schistosoma mansoni BH strain worms

Schistosomiasis is an infectious parasitic disease caused by helminths from the genus Schistosoma; it affects over 200 million people globally and is endemic in 70 countries. In Brazil, 6 million individuals are infected with Schistosoma mansoni. Furthermore, as the prevalence of S. mansoni infections is increasing, approximately 26 million citizens in 19 Brazilian states are at risk for infection. Schistosomiasis disease control involves predominately the administration of a single drug, praziquantel. Although praziquantel exhibits chemotherapeutic efficacy and safety, its massive use in endemic zones, the possibility of the emergence of drug-resistant Schistosoma parasites, and the lack of another efficacious antischistosomal drug demand the discovery of new schistosomicidal compounds. First developed as anti-tumor drug, miltefosine is an alkylphospholipid derivative that exhibits bioactivity against Leishmania and Trypanosoma parasites, free-living protozoa, bacteria, and fungi. With its anti-parasite activity, miltefosine was the first orally administered drug against visceral and cutaneous leishmaniasis approved. Previously, by means of the MTT cytotoxic assay and a DNA fragmentation test, we verified that, at doses of 100 and 200 μM (40 and 80 μg/mL), miltefosine exhibited in vitro schistosomicidal activity against adult S. mansoni worms. Here, we present ultrastructural evidence of rapid, severe miltefosine-induced surface membrane damage in S. mansoni following drug treatment. The number of dead parasites was concentration- and time-dependent following miltefosine treatment. At a miltefosine concentration of 200 μM (～80 μg/mL), in vitro parasite killing was initiated as early as 3 h post-incubation, and it was maximal after 24 h of treatment. The parasite death was preceded by progressive surface membrane damage, characterized by tegument peeling, spine reduction and erosion, blister formation and rupture, and the emergence of holes. According to our present results, miltefosine is very effective at inducing membrane destruction of S. mansoni with a short onset of pharmacological action.     

Mefloquine, a new type of compound against schistosomes and other helminthes in experimental studies

Up to date, schistosomiasis is still prevalent worldwide. It is estimated that more than 200 million individuals are infected, and 120 million suffer from clinical morbidity. Facing such huge cases of schistosomiasis, only heavy reliance on a single praziquantel for schistosomiasis control does not adapt and may promote the selection and spread of drug-resistant parasites. Therefore, it is an urgent need to develop the new antischistosomal drug. In 2008–2009, the antimalarial drug mefloquine, an arylaminoalcohol compound, has been found to be effective against schistosomes. According to the experimental studies, the deepest impression on the antischistosomal properties of mefloquine can be summarized as following points: (1) single dose of mefloquine possesses potential effect against three major species of schistosomes (Schistosoma mansoni, Schistosoma haematobium, and Schistosoma japonicum) infecting humans; (2) the drug displays similar effects against developing stages of juvenile and adult schistosomes, which are superior to that of artemisinins and praziquantel; (3) in vitro mefloquine exerts direct killing effect on juvenile and adult schistosomes, while in vivo, the efficacy of the drug is independent to host immune response, (4) mefloquine causes extensive and severe morphological, histopathological, and ultrastructural damage to adult and juvenile schistosomes, particularly, the worm tegument, musculature, gut, and vitelline glands of female worms are the key sites attacked by the drug; (5) combined treatment with mefloquine and praziquantel, or artemisinins shows synergistic effect against schistosome in experimental therapy,while in initially clinical trial, mefloquine in combination with artesunate also exhibits higher cure rates against schistosomiasis hematobia and schistosomiasis mansoni, and (6) several mefloquine-related arylmethanols exhibit potential effect against schistosomes in vivo, which is a useful clue helpful for development of new antischistosomal compound. In the present review, we have summarized the major results published in recent years, and the significance as well as the prospect for the future study of mefloquine have been discussed briefly.     

Effects of interferon in malaria infection

Earlier, we reported that prophylactic treatment with human interferon gamma (rHuIFN-gamma) protected monkeys against Plasmodium cynomolgi B malaria infection. We have tested the efficacy of rHuIFN-gamma on relapsing stage of experimental P. cynomolgi B malaria infection in rhesus monkeys. No effect of rHuIFN-gamma was seen against experimental relapsing stage compared with controls; however, it appears that chloroquine (CHL) may have interfered with the antimalarial effect of IFN, since treatment with CHL inhibits the antiviral activity of mouse alpha/beta IFN and polyinosinic-polycytidylic acid (poly I:C) against Semliki forest virus (SFV) in mice. These results may have clinical implications especially with the use of IFN against virus infection, cancer and in parasitic infections in malaria endemic areas where CHL is one of the most widely used antimalarial drugs. Our result also shows that CHL treatment enhances the virus replication in mice and suggest a possible connection between AIDS and malaria infection, since the spread of AIDS has been rapid in parts of tropical Africa that have a high incidence of malaria, and chloroquine has been frequently used in the chemotherapy of malaria.     

Antiplasmodial activity of alkaloid extracts from Pavetta crassipes (K. Schum) and Acanthospermum hispidum (DC), two plants used in traditional medicine in Burkina Faso

In the course of the search for new antimalarial compounds, a study of plants traditionally used against malaria in Burkina Faso was made. An ethnobotanical study permitted the identification of plants currently used by the traditional healers and herbalists. Two plants among them were selected for further study: Pavetta crassipes (K. Schum) and Acanthospermum hispidum (DC). Alkaloid extracts of these plants were tested in vitro against two reference clones of Plasmodium falciparum: the W2 chloroquine-resistant and the D6 chloroquine-sensitive strains. Significant inhibitory activity was observed with Pavetta crassipes (IC(50)=1.23 microg/ml) and A. hispidum (IC(50)=5.02 microg/ml). Antiplasmodial activity was also evaluated against six Plasmodium falciparum isolates from children between 4 and 10 years old. The IC(50) values for the alkaloid extracts were in the range 25-670 ng/ml. These results indicated that P. falciparum wild strains were more sensitive to the alkaloid extracts than strains maintained in continuous culture. Moreover, the alkaloid extracts exhibit good in vitro antimalarial activity and weak cytotoxicity against three human cell lines (THP1, normal melanocytes, HTB-66). Isolation and structural determination are now necessary in order to precisely determine the active compounds.     

Design, synthesis and antimalarial activity of a new class of iron chelators

Iron is crucial for many biochemical reactions involved in the growth and multiplication of the malaria parasite Plasmodium falciparum. There are many reports indicating that the iron chelators have antimalarial activity in vitro, in vivo and in human studies. However, these compounds suffer from a number of serious problems such as limited membrane permeability, short half-life and require long subcutaneous infusions. To circumvent these drawbacks we have designed a new class of iron chelators, wherein EDTA is tethered to 4-aminoquinoline. Here 4-aminoquinoline scaffold is used as a carrier to penetrate biological membrane and facilitate targetting the compounds to acidic food vacuole of the parasite. This study describes the synthesis of novel iron chelators and their in vitro antimalarial activity against P. falciparum strain of NF-54. The calculated LogP values of these compounds suggest the importance of lipophilicity for the antimalarial activity. The EDTA esters are more active than the corresponding acids. The biophysical studies suggest that these compounds may inhibit the parasite growth by iron chelation mechanism.     

Developing artemisinin based drug combinations for the treatment of drug resistant falciparum malaria: A review

The emergence and spread of drug resistant malaria represents a considerable challenge to controlling malaria. To date, malaria control has relied heavily on a comparatively small number of chemically related drugs, belonging to either the quinoline or the antifolate groups. Only recently have the artemisinin derivatives been used but mostly in south east Asia. Experience has shown that resistance eventually curtails the life-span of antimalarial drugs. Controlling resistance is key to ensuring that the investment put into developing new antimalarial drugs is not wasted. Current efforts focus on research into new compounds with novel mechanisms of action, and on measures to prevent or delay resistance when drugs are introduced. Drug discovery and development are long, risky and costly ventures. Antimalarial drug development has traditionally been slow but now various private and public institutions are at work to discover and develop new compounds. Today, the antimalarial development pipeline is looking reasonably healthy. Most development relies on the quinoline, antifolate and artemisinin compounds. There is a pressing need to have effective, easy to use, affordable drugs that will last a long time. Drug combinations that have independent modes of action are seen as a way of enhancing efficacy while ensuring mutual protection against resistance. Most research work has focused on the use of artesunate combined with currently used standard drugs, namely, mefloquine, amodiaquine, sulfadoxine/pyrimethamine, and chloroquine. There is clear evidence that combinations improve efficacy without increasing toxicity. However, the absolute cure rates that are achieved by combinations vary widely and depend on the level of resistance of the standard drug. From these studies, further work is underway to produce fixed dose combinations that will be packaged in blister packs. This review will summarise current antimalarial drug developments and outline recent clinical research that aims to bring artemisinin based combinations to those that need them most.     

Current status of malaria and potential for control

Malaria remains one of the world's worst health problems with 1.5 to 2.7 million deaths annually; these deaths are primarily among children under 5 years of age and pregnant women in sub-Saharan Africa. Of significance, more people are dying from malaria today than 30 years ago. This review considers the factors which have contributed to this gloomy picture, including those which relate to the vector, the female anopheline mosquito; to human activity such as creating new mosquito breeding sites, the impact of increased numbers of people, and how their migratory behavior can increase the incidence and spread of malaria; and the problems of drug resistance by the parasites to almost all currently available antimalarial drugs. In a selective manner, this review describes what is being done to ameliorate this situation both in terms of applying existing methods in a useful or even crucial role in control and prevention and in terms of new additions to the antimalarial armory that are being developed. Topics covered include biological control of mosquitoes, the use of insecticide-impregnated bed nets, transgenic mosquitoes manipulated for resistance to malaria parasites, old and new antimalarial drugs, drug resistance and how best to maintain the useful life of antimalarials, immunity to malaria and the search for antimalarial vaccines, and the malaria genome project and the potential benefits to accrue from it.     

Antimalarial activity of new gossypol derivatives

Gossypol, a disesquiterpene extracted from cotton seeds, is known to inhibit strongly the Plasmodium falciparum lactate dehydrogenase, but its high toxicity has stopped any antimalarial drug development. A series of Schiff's bases was synthesized from gossypol by modification of the aldehyde groups responsible for its toxicity. A total of 13 compounds showing low cytotoxicity were then selected and were compared with gossypol for activity against 2 chloroquine-resistant strains of P. falciparum (PFB, FCB1). These in vitro activities were evaluated using an isotope-based drug-susceptibility semiautomated microdilution test followed by determination of IC₅₀ values (50% inhibitory concentration). In all, 12 of the 13 compounds tested were active; 3 of them displayed antimalarial activity comparable with that of gossypol itself. Received: 27 November 1999 / Accepted: 28 January 2000     

Antimalarial activity of fractions isolated from Albizia gummifera and Aspilia mossambicensis crude extracts

To identify the fractions of medicinal plant extracts containing the highest concentration of antimalarial principles, we tested the antimalarial activities of the crude or total extracts and two fractions from Albizia gummifera (Leguminosae) and three fractions from Aspilia mossambicencis (Compositae) against laboratory adapted isolates of Plasmodium falciparum in vitro using the 3H-hypoxanthine uptake assay. Chloroquine was used as a reference antimalarial drug. The mean 50% inhibitory concentrations (IC50s) of A. gummifera total extract and fraction were both <2.2 microg/ml for three P. falciparum isolates while the mean IC50 of A. gummifera f raction-2 was higher (5.0+2.9sd) for the same isolates. Aspilia mossambicensis total extract and fractions-1,4 and 5 had mean IC50 values of 96.6+/-32.5,38.6+/-23.0,142.5+/-79.6 and >1250.0 microg/ml, respectively, against four P. falciparum isolates. These results show that fraction-1 of either A. gummifera or A, mossambicensis had the highest concentration of antimalarial principles. We now plan to concentrate our efforts on these promising fractions in order to isolate pure compounds which could eventually be used to effectively treat malaria.     

In vitro antiplasmodial activity of bacterium RJAUTHB 14 associated with marine sponge Haliclona Grant against Plasmodium falciparum

Malaria is the most important parasitic disease, leading to annual death of about one million people, and the Plasmodium falciparum develops resistance to well-established antimalarial drugs. The newest antiplasmodial drug from a marine microorganism helps in addressing this problem. In the present study, Haliclona Grant were collected and subjected for enumeration and isolation of associated bacteria. The count of bacterial isolates was maximum in November 2007 (18?×?10(4) colony-forming units (CFU)?g(-1), and the average count was maximum during the monsoon season (117?×?10(3) CFU g(-1)). Thirty-three morphologically different bacterial isolates were isolated from Haliclona Grant, and the extracellular ethyl acetate extracts were screened for antiplasmodial activity against P. falciparum. The antiplasmodial activity of bacterium RJAUTHB 14 (11.98 μg[Symbol: see text]ml(-1)) is highly comparable with the positive control chloroquine (IC(50) 19.59 μg[Symbol: see text]ml(-1)), but the other 21 bacterial extracts showed an IC(50) value of more than 100 μg[Symbol: see text]ml(-1). Statistical analysis reveals that significant in vitro antiplasmodial activity (P?相似文献   

Synergy of the antiretroviral protease inhibitor indinavir and chloroquine against malaria parasites in vitro and in vivo

Many malaria-endemic areas are also associated with high rates of human immunodeficiency virus (HIV) infection. An understanding of the chemotherapeutic interactions that occur during malaria and HIV co-infections is important. Our previous studies have demonstrated that some antiretroviral protease inhibitors are effective in inhibiting Plasmodium falciparum growth in vitro. Currently, studies examining the interactions between antiretroviral protease inhibitors and antimalarial drugs are being conducted, but the data are limited. In this study, we examined the synergistic interactions between the antiretroviral protease inhibitor indinavir and chloroquine (CQ) in chloroquine-resistant and chloroquine-sensitive malaria parasites in vitro and in vivo. In vitro, by using modified fixed-ratio isobologram method, fractional inhibitory concentrations index (FICI) was calculated to indicate the interaction between the two drugs. The results demonstrated that indinavir interacted synergistically with chloroquine against both chloroquine-sensitive P. falciparum clone 3D7 (mean FICI 0.784) and multidrug-resistant P. falciparum clone Dd2 (mean FICI 0.599). In vivo drug interactions were measured using a 4-day suppressive test in a rodent malaria model infected with Plasmodium chabaudi. We observed that indinavir enhanced the antimalarial activity of chloroquine against both the chloroquine-sensitive line P. chabaudi ASS and the chloroquine-resistant line P. chabaudi ASCQ. More importantly, chloroquine had a 100% clearance of asexual parasites when used in combination with indinavir at an appropriate dose ratio (10 mg/kg CQ + 1.8 g/kg indinavir) where there was no obvious toxicity. We conclude from this study that the combination of indinavir and chloroquine may become a novel antimalarial drug regimen.     

In vitro and in vivo antimalarial activity of ferrochloroquine, a ferrocenyl analogue of chloroquine against chloroquine-resistant malaria parasites

Previous studies have shown that ferrochloroquine (FQ) exhibited an antimalarial activity against Plasmodium spp. The present work confirmed this activity, described the curative effect on P. vinckei and investigated the FQ toxicity in vitro and in vivo. The in vitro and in vivo growth inhibition of P. falciparum and P. berghei N, respectively, showed that FQ antimalarial activity was 1.5–10 times more potent than chloroquine. FQ completely inhibited the in vivo development of both chloroquine-susceptible and resistant P. vinckei strains and protected mice from lethal infection at a dose of 8.4 mg kg⁻¹ day⁻¹ given for 4 days subcutaneously or orally. This curative effect was 5–20 times more potent than chloroquine, according to the strains' resistance to chloroquine. At this curative dose, no clinical changes were observed in mice up to 14 days after the last administration. Nevertheless, the acute toxicity and lethality of ferrochloroquine seemed to be dependent on gastric surfeit. The FQ security index determined in vitro confirmed that it might be a promising compound. Received: 12 August 2000 / Accepted: 16 August 2000     

In vitro assays for evaluation of drug activity against Leishmania spp

Leishmania is a parasitic protozoan which causes severe disease in humans and dogs. Screening of new compounds against leishmaniasis is particularly needed to determine the toxicity of some existing drugs and the appearance of drug-resistant strains. Reliable and simple in vitro models are required for large-scale initial screenings. In this review different methods for in vitro evaluation of drug activity against Leishmania spp. are summarized.     

Synthesis and evaluation of trimethoxyphenyl isoxazolidines as inhibitors of secretory phospholipase A2 with anti-inflammatory activity

A series of trimethoxyphenyl isoxazolidine derivatives, 5a(i-v) and 5b(i-v), bearing different constituents at the 5th position of the isoxazolidine ring were synthesized and evaluated in vitro and in vivo for their inhibitory activity against purified group I and II phospholipase A2 (PLA2) enzymes from snake venom and human inflammatory synovial fluid. Irrespective of modification to the pharmacophore (isoxazolidine ring), they exhibited greater specificity for group II PLA2. The length of alkyl or aryl group at the 5th position, which alters the hydrophobic and aromatic property, was responsible for enhancing the inhibition towards PLA2 enzymes. All of the compounds quench the fluorescent property of the purified PLA2 enzyme, and quenching increases with the increase in length of alkyl or aryl group. The inhibitory effect of compounds appeared to be due to the direct interaction of compounds with the enzyme. Inhibition is substrate-dependent, and the inhibitor likely competes with the substrate for the same binding site of the enzyme. The IC50 value for the most potent interacting inhibitor 5b(v) was 54.8 microM. The most active interacting compounds 5a(v) and 5b(v) from in vitro inhibition of PLA2 activity showed similar potency in in vivo neutralization of PLA2-induced mouse paw edema and hemolytic activity.