In vitro and in vivo antimalarial activity of puberulic acid and its new analogs, viticolins A-C, produced by Penicillium sp. FKI-4410

In the course of screening for antimalarial agents, five tropolone compounds were isolated from the culture broth of Penicillium sp. FKI-4410. Two were known compounds, puberulic acid and stipitatic acid. Three were new analogs of puberulic acid, designated viticolins A-C. Among them, puberulic acid exhibited potent antimalarial inhibition, with IC(50) values of 0.01?μg?ml(-1) against chloroquine-sensitive and -resistant Plasmodium falciparum strains in vitro. Furthermore, puberulic acid showed weak cytotoxicity against human MRC-5 cells, with an IC(50) value of 57.2?μg?ml(-1). The compound also demonstrated a therapeutic effect in vivo, which compared well against the currently used antimalarial drugs, and thus shows promise as a leading candidate for development into a new antimalarial compound.     

吡唑杂合体的抗疟疾活性

疟疾是由按蚊叮咬或输入携带疟原虫血液引起的一类高传染性疾病,其临床症状包括发热、头痛、呕吐等,如不及时治疗可能危及生命。尽管临床上使用的抗疟疾药物对疟疾的防控不可或缺,但随着长期广泛使用甚至滥用,恶性疟原虫对抗疟药物产生了不同程度的耐药性。为克服耐药性,研发新型抗疟疾药物势在必行。吡唑类化合物具有包括抗疟疾在内的多种生物活性,且某些吡唑类药物已广泛用于临床,故这类化合物引起了药物化学家的持续关注。本文将归纳吡唑杂合体在抗疟疾领域的最新研究进展,并讨论此类化合物的构-效关系。     

吡唑杂合体的抗疟疾活性

疟疾是由按蚊叮咬或输入携带疟原虫血液引起的一类高传染性疾病,其临床症状包括发热、头痛、呕吐等,如不及时治疗可能危及生命。尽管临床上使用的抗疟疾药物对疟疾的防控不可或缺,但随着长期广泛使用甚至滥用,恶性疟原虫对抗疟药物产生了不同程度的耐药性。为克服耐药性,研发新型抗疟疾药物势在必行。吡唑类化合物具有包括抗疟疾在内的多种生物活性,且某些吡唑类药物已广泛用于临床,故这类化合物引起了药物化学家的持续关注。本文将归纳吡唑杂合体在抗疟疾领域的最新研究进展,并讨论此类化合物的构-效关系。     

Current progress in the chemistry, medicinal chemistry and drug design of artemisinin based antimalarials

This review covers developments in relation to artemisinin-based antimalarial agents. Topics covered include a brief introduction to the history and treatment of malaria, and more recently, drug resistant malaria; the discovery of the naturally occurring novel peroxidic antimalarial artemisinin; artemisinin biosynthesis, metabolism and biotransformations; the diversity of proposed mechanisms of action; pharmacokinetics; the insight into structure-toxicity relationships; the total syntheses and the progress made in the syntheses of its analogs; and, ultimately the contribution of these efforts towards rational drug design in order to access potent, non-toxic antimalarial drugs based on artemisinin.     

Novel drug targets in malaria parasite with potential to yield antimalarial drugs with long useful therapeutic lives

The status of chemotherapy as the main strategy in malaria control is rapidly being eroded by development of drug resistant Plasmodia, causing malaria to be dubbed a "re-emerging disease". To counter this misfortune, there is an urgent need to develop novel antimalarial drugs capable of delaying resistance, or circumventing it altogether. Mode of action of antimalarial drugs, inter alia, has a bearing on their useful therapeutic lives (UTLs), with single target drugs having short UTLs compared with drugs which possess pleiotropic action. Quinolines and artemisinins are the two classes of drugs with pleiotropic action and subsequently long UTLs. All other antimalarials are single-target drugs, and have been rendered ineffective within 1 to 5 years of their introduction for clinical use. This strongly underlines the need for development of new antimalarial therapies possessing long UTLs. The present review explores novel drug targets within the malaria parasite that may be exploited in the search for novel drugs that possess long and UTLs.     

Synthesis and in vitro and in vivo antimalarial activity of novel 4-anilinoquinoline Mannich base derivatives

Development of resistance has severely limited the choice of available antimalarial drugs, which clearly highlights the urgent need of novel chemotherapeutic agents for the treatment of malaria. The purpose of this study was to develop new potential antimalarial agents with 4-anilinoquinoline ring. A series of novel 4-anilinoquinoline Mannich base drug molecules have been synthesized. The synthesis involves the preparation of Mannich base and these bases subsequently coupled with 4,7-dichloroquinoline to get targeted drug molecules (Burckhalter et al. in J Am Chem Soc 70:1363–1373, 1948). Their structures were confirmed by IR, NMR, and mass spectral data. The synthesized molecules were evaluated for in vitro and in vivo antimalarial activity against the chloroquine sensitive 3D7 (West Africa) and RKL-2 strain of Plasmodium falciparum and rodent malaria parasite Plasmodium yoelii (strain N-67) in Swiss mice model, respectively (Charmot et al. in Prev Med 15:889, 1986). Except one molecule (containing diphenylamine), all the tested molecules showed activity while one of them (containing morpholine) showed promising in vitro and significant in vivo antimalarial activity under given test conditions.     

Malaria and iron: history and review

To cause infection, nearly all protozoa, fungi, and bacteria must obtain growth-essential iron from their hosts. To suppress infection, hosts have evolved iron-withholding defense systems. Enhancement of iron withholding is a potential target for the development of novel therapeutic agents. This review focuses on the association of iron with current and emerging antimalarial drugs. Proposed mechanisms of antimalarial action of (1) iron-requiring agents, the artemisinins, are compared with (2) a spectrum of compounds that withdraw iron by chelation. A novel approach to malarial chemotherapy might involve the sequential use of a member of each of the two categories.     

Antimalarial compound identification and design: advances in the patent literature, 2000 – 2003

World patents filed from 2000 to 2003 claiming specific in vitro or in vivo antimalarial activity are examined and compiled in this review in a format that allows comparison across different chemical classes or drug targets. The most over-represented classes include the 1-desoxy-D-xylulose 5-phosphate (DOXP) reductoisomerase inhibitors and novel quinoline or artemisinin analogues. This finding can be linked to important trends in the clinical development of new antimalarial drugs. Patents disclosing novel classes of antimalarial drugs were scarce. This may mean that the target-directed screening effort in malaria has not yet come to fruition, has not been commercially exploited in an appropriate manner, or that next generation compounds in known drug classes are more viable commercial entities.     

Artemisinin and chloroquine: do mode of action and mechanism of resistance involve the same protagonists?

Considerable progress has been made in antimalarial research; however, further studies are required to improve the efficacy of clinically available drugs, to develop new agents with superior activity and to avoid the emergence of resistance. In particular, efforts must focus on understanding the mode of action of antimalarial agents and on the mechanism by which the parasite Plasmodium falciparum impedes the action of these drugs. In this review, the current status of the antimalarial agents chloroquine and artemisinin is discussed, and the link between mechanism of action and resistance highlighted.     

四氮唑杂合体在抗疟疾领域的研究进展

疟疾主要是由恶性疟原虫引起的一类可致命传染性疾病,与艾滋病、结核病一起被认为是全球最重要的三大公共卫生问题。临床上使用的抗疟疾药物如喹啉类和青蒿素类尽管对药敏型疟疾依然高度有效,但随着耐药疟疾的不断涌现和广泛传播,现有抗疟疾药物的疗效呈逐年下降之势。因此,亟需开发新型抗疟疾药物。四氮唑作为羧基的生物电子等排体可用来取代药物中的羧基以提高药物分子的脂溶性、增加药物的生物利用度和降低毒副作用,故四氮唑被认为是最具发展前景的一类化合物。本文将着重介绍近年来四氮唑杂合体在抗疟疾领域的研究进展,并讨论此类化合物的构-效关系。     

Synthesis and antimalarial activity of substituted pyrazole derivatives

The development of new antimalarial drugs is an urgent priority considering the increasing prevalence of drug-resistant Plasmodium falciparum parasites. A series of pyrazoles are described as part of efforts directed toward the synthesis of some potent antimalarial agents. The replacement of the ester group as a substituent in the pyrazole ring by nitrile group caused a precipitous loss of activity as antimalarial due to the lack of hydrogen-bond formation. Further modification of the heterocyclic ring to give substituted aryl derivatives afforded potent antimalarial derivatives: methyl 5-amino-3-anisidinepyrazole-4-carboxylic acid 3a (IC50: 0.149 mumol/l) and methyl 5-amino-3-(m anisidin)pyrazole-4-carboxylic acid 3c (IC50: 0.15 mumol/l). The synthesis, structure-activity relationships (SAR), X-ray crystallography and pharmacological activity associated with these series of compounds are discussed.     

Recent patent reviews on small molecule-based antimalarial drugs

Malaria is the number one disease in the world responsible for 1-3 million deaths each year. The world wide number of malaria patients is estimated at 400 to 900 million. Approximately one third of the world's population lives in malaria-endemic areas, including Central and South America, Asia, and Africa. Plasmodium falciparum, Plasmodium vivax, Plasmodium ovale and Plasmodium malariae are malaria parasites responsible for infecting humans. Mosquitoes that carry malaria parasites have become resistant to insecticides, and the deadliest parasites have become resistant to previously effective antimalarial drugs such as chloroquine, quinine and other clinically used agents. Because of the widespread incidence of malaria in certain parts of the world and because of the increasing parasite resistance to standard anti-malarial agents, there is an urgent need for introducing new effective drugs. This review presents the recent patents that reveal development of novel antimalarial drugs.     

Antimalarial quassinoids: past,present and future

This review is a compilation of the investigations reported to date on the sources, isolation, chemistry and antimalarial activities of natural quassinoids and their synthetic and semisynthetic analogs. It also provides an analysis of the in vitro structure–activity relationship of quassinoids for further evaluation in animal models. The introduction of non-nitrogenous antimalarial drugs has created a new era of malaria chemotherapy to treat Plasmodium falciparum strains that are resistant to existing nitrogenous drugs and the rising incidence of the deadly cerebral malaria. Many antimalarial quassinoids are discovered from simaroubaceous plants that are used traditionally to treat fever and malaria, thereby reiterating the critical role of ethnopharmacology as a rich source of novel drug discovery.     

Recent developments in naturally derived antimalarials: cryptolepine analogues

Increasing resistance of Plasmodium falciparum to commonly used antimalarial drugs has made the need for new agents increasingly urgent. In this paper, the potential of cryptolepine, an alkaloid from the West African shrub Cryptolepis sanguinolenta, as a lead towards new antimalarial agents is discussed. Several cryptolepine analogues have been synthesized that have promising in-vitro and in-vivo antimalarial activity. Studies on the antimalarial modes of action of these analogues indicate that they may have different or additional modes of action to the parent compound. Elucidation of the mode of action may facilitate the development of more potent antimalarial cryptolepine analogues.     

Chemotherapeutic agents against malaria: what next after chloroquine?

This is a general review of currently available antimalarial drugs, these compounds are gathered according with its chemical structure and the biological targets. A great number of these new antimalarial agents are now moving actively in the pipeline from basic science to clinical studies.     

The antimalarial activity of indole alkaloids and hybrids

Malaria, caused by the genus Plasmodium, remains a global public health concern. It is estimated by the World Health Organization that over 40% of the world's population lives in areas at risk for malarial transmission, and around half a million people succumb to this infectious disease annually, which is related to the rapid spread of drug-resistant parasite strains. Indole derivatives, which possess broad-spectrum pharmacological properties, play a crucial role in the discovery of new drugs. Many indole derivatives exhibited potential in vitro and in vivo activity against both drug-sensitive and drug-resistant malaria, suggesting that the indole moiety is a useful template for the development of novel antimalarial agents. This review outlines the advances in indole alkaloids and hybrids with antimalarial potential in the recent decade.     

Design, synthesis, and in vitro activity of novel 2'-O-substituted 15-membered azalides

Malaria remains one of the most widespread human infectious diseases, and its eradication will largely depend on antimalarial drug discovery. Here, we present a novel approach to the development of the azalide class of antimalarials by describing the design, synthesis, and characterization of novel 2'-O-substituted-9-deoxo-9a-methyl-9a-aza-9a-homoerythromycin A derivatives consisting of different quinoline moieties covalently liked to a 15-membered azalide scaffold at position 2'. By multistep straightforward synthesis, 19 new, stable, and soluble compounds were created and biologically profiled. Most active compounds from the 4-amino-7-chloroquinoline series showed high selectivity for P. falciparum parasites, and in vitro antimalarial activity improved 1000-fold over azithromycin. Antimalarial potency was equivalent to chloroquine against the sensitive strain (3D7A) and up to 48-fold enhanced over chloroquine against the chloroquine-resistant strain (W2). Concurrently, the antibacterial activity of the compounds was eliminated, thus facilitating the development of malaria-specific macrolide agents.     

Plasmodium falciparum: Multidrug resistance

Malaria is the most lethal and debilitating disease caused by the protozoan parasite Plasmodium worldwide. The most severe forms of disease and the incidence rates of mortality are associated with P. falciparum infections. With the identification of disease source and symptoms, many chemical entities were developed naturally and synthetically for administration as a potential antimalarial drug. The major classes of approved antimalarial drugs that are governed as first‐line treatment in tropical and subtropical areas include quinolines, naphthoquinones, antifolates, 8‐aminoquinolines, and endoperoxides. However, the efficacy of antimalarial drugs has decreased due to ongoing multidrug resistance problem to current drugs. With increasing resistance to the current antimalarial artemisinin and its combination therapies, malaria prophylaxis has declined gradually. New‐generation antimalarial and novel drug target are required to check the incidence of malaria resistance. This review summarizes the emergence of multidrug resistance to known antimalarial and the development of new antimalarial to resolve drug resistance condition. Few essential proteins are also discussed that can be considered as novel drug target against malaria in future.     

Pharmacokinetic interactions of antimalarial agents.

Combination of antimalarial agents has been introduced as a response to widespread drug resistance. The higher number of mutations required to express complete resistance against combinations may retard the further development of resistance. Combination of drugs, especially with the artemisinin drugs, may also offer complete and rapid eradication of the parasite load in symptomatic patients and thus reduce the chance of survival of resistant strains. The advantages of combination therapy should be balanced against the increased chance of drug interactions. During the last decade, much of the pharmacokinetics and metabolic pathways of antimalarial drugs have been elucidated, including the role of the cytochrome P450 (CYP) enzyme complex. Change in protein binding is not a significant cause of interactions between antimalarial agents. CYP3A4 and CYP2C19 are frequently involved in the metabolism of antimalarial agents. Quinidine is a potent inhibitor of CYP2D6, but it appears that this enzyme does not mediate the metabolism of any other antimalarial agent. The new combinations proguanil-atovaquone and chlorproguanil-dapsone do not show significant interactions. CYP2B6 and CYP3A4 are involved in the metabolism of artemisinin and derivatives, but further studies may reveal involvement of more enzymes. Artemisinin may induce CYP2C19. Several artemisinin drugs suffer from auto-induction of the first-pass effect, resulting in a decline of bioavailability after repeated doses. The mechanism of this effect is not yet clear, but induction by other agents cannot be excluded. The combination of artemisinin drugs with mefloquine and the fixed combination artemether-lumefantrine have been studied widely, and no significant drug interactions have been found. The artemisinin drugs will be used at an increasing rate, particularly in combination with other agents. Although clinical studies have so far not shown any significant interactions, drug interactions should be given appropriate attention when other combinations are used.     

Metallocenes and malaria: a new therapeutic approach

Rapid development of significant resistance to antimalarial drugs has been a major force driving research to identify and develop new compounds. The use of synthetic organometallic complexes seems to be promising for treatment of malaria infections. Recent progress in identification and development of new drugs promises to lead to a much greater range of antimalarial agents. Organometallic complexes and metalloporphyrins have shown in vitro activity against Plasmodium falciparum. Ferroquine (ferrocenyl chloroquine) is more active than chloroquine against strains and isolates of P. falciparum and shows efficacy against murine parasites.