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1.  Inhibition of Cardiac Ca2+ Release Channels (RyR2) Determines Efficacy of Class I Antiarrhythmic Drugs in Catecholaminergic Polymorphic Ventricular Tachycardia 
Background
Catecholaminergic polymorphic ventricular tachycardia (CPVT) is caused by mutations in the cardiac ryanodine receptor (RyR2) or calsequestrin (Casq2) and can be difficult to treat. The class Ic antiarrhythmic drug flecainide blocks RyR2 channels and prevents CPVT in mice and humans. It is not known whether other class I antiarrhythmic drugs also block RyR2 channels and to what extent RyR2 channel inhibition contributes to antiarrhythmic efficacy in CPVT.
Methods and Results
We first measured the effect of all class I antiarrhythmic drugs marketed in the United States (quinidine, procainamide, disopyramide, lidocaine, mexiletine, flecainide, and propafenone) on single RyR2 channels incorporated into lipid bilayers. Only flecainide and propafenone inhibited RyR2 channels, with the S-enantiomer of propafenone having a significantly lower potency than R-propafenone or flecainide. In Casq2−/− myocytes, the propafenone enantiomers and flecainide significantly reduced arrhythmogenic Ca2+ waves at clinically relevant concentrations, whereas Na+ channel inhibitors without RyR2 blocking properties did not. In Casq2−/− mice, 5 mg/kg R-propafenone or 20 mg/kg S-propafenone prevented exercise-induced CPVT, whereas procainamide (20 mg/kg) or lidocaine (20 mg/kg) were ineffective (n=5 to 9 mice, P<0.05). QRS duration was not significantly different, indicating a similar degree of Na+ channel inhibition. Clinically, propafenone (900 mg/d) prevented ICD shocks in a 22-year-old CPVT patient who had been refractory to maximal standard drug therapy and bilateral stellate ganglionectomy.
Conclusions
RyR2 cardiac Ca2+ release channel inhibition appears to determine efficacy of class I drugs for the prevention of CPVT in Casq2−/− mice. Propafenone may be an alternative to flecainide for CPVT patients symptomatic on β-blockers.
doi:10.1161/CIRCEP.110.959916
PMCID: PMC3667204  PMID: 21270101
class I antiarrhythmic drugs; propafenone; RyR2; catecholaminergic polymorphic ventricular tachycardia; flecainide; ranolazine; tetrodotoxin; quinidine; procainamide; disopyramide; lidocaine; mexiletine
2.  EFFICACY AND POTENCY OF CLASS I ANTIARRHYTHMIC DRUGS FOR SUPPRESSION OF Ca2+ WAVES IN PERMEABILIZED MYOCYTES LACKING CALSEQUESTRIN 
Background
Ca2+ waves can trigger ventricular arrhythmias such as catecholaminergic-polymorphic ventricular tachycardia (CPVT). Drugs that prevent Ca2+ waves may have antiarrhythmic properties. Here, we use permeabilized ventricular myocytes from a CPVT mouse model lacking calsequestrin (casq2) to screen all clinically available class I antiarrhythmic drugs and selected other antiarrhythmic agents for activity against Ca2+ waves.
Methods and Results
Casq2−/− myocytes were imaged in line-scan mode and the following Ca2+ wave parameters analyzed: wave incidence, amplitude, frequency, and propagation speed. IC50 (potency) and maximum inhibition (efficacy) were calculated for each drug. Drugs fell into 3 distinct categories. Category 1 drugs (flecainide, R-propafenone) suppressed wave parameters with the highest potency (IC50 < 10 μM) and efficacy (> 50% maximum wave inhibition). Category 2 drugs (encainide, quinidine, lidocaine, verapamil) had intermediate potency (IC50 20 μ 40 μM) and efficacy (20% - 40% maximum wave inhibition). Category 3 drugs (procainamide, disopyramide, mexilitine, cibenzoline, ranolazine) had no significant effects on Ca2+ waves at the highest concentration tested (100 μM). Propafenone was stereoselective, with R-propafenone suppressing waves more potently than S-propafenone (IC50: R-propafenone 2±0.2 μM vs. S-propafenone 54±18 μM). Both flecainide and R-propafenone decreased Ca2+ spark mass and converted propagated Ca2+ waves into non-propagated wavelets and frequent sparks, suggesting that reduction in spark mass, not spark frequency, was responsible for wave suppression.
Conclusions
Among all class I antiarrhythmic drugs, flecainide and R-propafenone inhibit Ca2+ waves with the highest potency and efficacy. Permeabilized casq2−/− myocytes are a simple in-vitro assay for finding drugs with activity against Ca2+ waves.
doi:10.1016/j.yjmcc.2011.07.002
PMCID: PMC3184367  PMID: 21798265
catecholaminergic polymorphic ventricular tachycardia; calsequestrin 2; cardiac ryanodine receptor (RyR2) Ca2+ release channel; class I antiarrhythmic drugs; flecainide; R-propafenone
3.  Searching for New Antimalarial Therapeutics amongst Known Drugs 
Chemical biology & drug design  2006;67(6):409-416.
The need to discover and develop new antimalarial therapeutics is severe. The annual mortality attributed to malaria, currently approximately 2.5 million, is increasing due primarily to widespread resistance to currently used drugs. One strategy to identify new treatment alternatives for malaria is to examine libraries of diverse compounds for the possible identification of novel scaffolds. Beginning with libraries of drug or drug-like compounds is an ideal starting point because, in the case of approved drugs, substantial pharmacokinetic and toxicologic data should be available for each compound series. We have employed a high throughput screen of the MicroSource Spectrum and Killer collections, a library of known drugs, bioactive compounds, and natural products. Our screening assay identifies compounds that inhibit growth of Plasmodium falciparum cultured in human erythrocytes. We have identified 36 novel inhibitors of P. falciparum, of which 19 are therapeutics, and five of these drugs exhibit effective 50% inhibitory concentrations within similar ranges to therapeutic serum concentrations for their currently indicated uses: propafenone, thioridazine, chlorprothixene, perhexiline and azlocillin. The findings we report here indicate that this is an effective strategy to identify novel scaffolds and therefore aid in antimalarial drug discovery efforts.
doi:10.1111/j.1747-0285.2006.00391.x
PMCID: PMC1592519  PMID: 16882315
malaria; drug discovery; biological screening
4.  The Activities of Current Antimalarial Drugs on the Life Cycle Stages of Plasmodium: A Comparative Study with Human and Rodent Parasites 
PLoS Medicine  2012;9(2):e1001169.
Michael Delves and colleagues compare the activity of 50 current and experimental antimalarials against liver, sexual blood, and mosquito stages of selected human and nonhuman parasite species, including Plasmodium falciparum, Plasmodium berghei, and Plasmodium yoelii.
Background
Malaria remains a disease of devastating global impact, killing more than 800,000 people every year—the vast majority being children under the age of 5. While effective therapies are available, if malaria is to be eradicated a broader range of small molecule therapeutics that are able to target the liver and the transmissible sexual stages are required. These new medicines are needed both to meet the challenge of malaria eradication and to circumvent resistance.
Methods and Findings
Little is known about the wider stage-specific activities of current antimalarials that were primarily designed to alleviate symptoms of malaria in the blood stage. To overcome this critical gap, we developed assays to measure activity of antimalarials against all life stages of malaria parasites, using a diverse set of human and nonhuman parasite species, including male gamete production (exflagellation) in Plasmodium falciparum, ookinete development in P. berghei, oocyst development in P. berghei and P. falciparum, and the liver stage of P. yoelii. We then compared 50 current and experimental antimalarials in these assays. We show that endoperoxides such as OZ439, a stable synthetic molecule currently in clinical phase IIa trials, are strong inhibitors of gametocyte maturation/gamete formation and impact sporogony; lumefantrine impairs development in the vector; and NPC-1161B, a new 8-aminoquinoline, inhibits sporogony.
Conclusions
These data enable objective comparisons of the strengths and weaknesses of each chemical class at targeting each stage of the lifecycle. Noting that the activities of many compounds lie within achievable blood concentrations, these results offer an invaluable guide to decisions regarding which drugs to combine in the next-generation of antimalarial drugs. This study might reveal the potential of life-cycle–wide analyses of drugs for other pathogens with complex life cycles.
Please see later in the article for the Editors' Summary
Editors' Summary
Background
Malaria is a life-threatening disease caused by the Plasmodium parasite, which is transmitted to people through the bites of infected mosquitoes. According to latest global estimates, about 250 million people are infected with malaria every year with roughly 800,000 deaths—most occurring among young children living in Africa. Malaria also causes severe morbidity in children, such as anemia, low birth weight, and neurological problems, which compromise the health and development of millions of children living in malaria endemic areas. In addition to strategies that scale up and roll out the prevention of malaria, such as country-wide programs to provide insecticide-treating bednets, in the goal to eradicate malaria, the global health community has refocused efforts on the treatment of malaria, including finding new compounds that target different stages of the parasite life cycle as it passes from vector to host and back.
The interruption of malaria transmission worldwide is one of the greatest challenges for the global health community. In January 2011, this journal published a series on The Malaria Eradication Research Agenda (malERA), which described a set of research and development priorities, identified key knowledge gaps and the necessary tools needed, and introduced a draft research and development agenda for the worldwide eradication of malaria.
Why Was This Study Done?
Most currently available antimalarial drugs primarily target the disease-causing parasites' stages in the human blood system. But to eradicate malaria, new drugs that block transmission of the parasite between the human host and the mosquito vector, and eliminate the various stages of the parasite during its cycle in the human body, are needed. In this laboratory study, the researchers compared the profiles of all available and experimental antimalarials and analyzed each drug for activity against each specific stage in the malaria parasite's life cycle to provide a reference set of methods and data, that might serve as a benchmark to help guide the malaria research community in assessing the potential of newly discovered antimalarials. Furthermore, this analysis could provide insights into which chemical drug classes might provide transmission-blocking capabilities—an essential component of malaria eradication.
What Did the Researchers Do and Find?
The researchers used novel laboratory techniques under standardized conditions to develop a series of novel assays to analyze the activities of 50 antimalarial compounds (current drugs and those under development) against three Plasmodium species encompassing every major cellular strategy of the malarial life cycle including drug resistant parasite strains. In their comparative analysis, the researchers undertook a chemical profiling approach to identify the drugs that block transmission from the host to the mosquito vector and additionally suppress transmission from the mosquito to the human host.
The researchers highlighted some encouraging results; for example, the potencies of some antimalarials against the asexual blood stage of cultivated P. falciparum and P. vivax isolates show a very good correlation, suggesting that most of the pathways inhibited by antimalarials in P. falciparum may also be valid targets in P. vivax. The researchers also have shown that approved drugs, such as pyronaridine and atovaquone, can target liver and sexual stages in addition to asexual blood stages. Furthermore, the researchers found promising results for new compounds currently in clinical trials, such as the endoperoxide OZ439, a stable synthetic molecule currently being studied in a phase IIa clinical trial, which seemed to be a strong inhibitor of gametocyte maturation and gamete formation. The new 8-aminoquinoline, NPC-1161B, also inhibited sporogony.
What Do These Findings Mean?
The results of this analysis provide a valuable guide to help researchers decide which drugs and compounds show most promise as potential future antimalarial drugs for blocking the transmission of malaria. This study could also help researchers make decisions about which molecules could be best combined to provide the next generation of drugs that will succeed artemisinin compound therapy and support the eradication of malaria. Furthermore, this comprehensive approach to drug discovery could be applied to test drugs against other pathogens with complex life cycles.
Additional Information
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001169.
The malERA a research agenda for malaria eradication sponsored collection, published by PLoS in January 2011, comprises 12 Review articles that discuss agendas in malaria research and development
doi:10.1371/journal.pmed.1001169
PMCID: PMC3283556  PMID: 22363211
5.  Syncope, Widened QRS Interval, and Left Ventricular Systolic Depression Coincident with Propafenone Therapy for Atrial Fibrillation 
Texas Heart Institute Journal  2010;37(4):476-479.
We report the case of a 46-year-old man who developed syncope, a widened QRS interval, and depressed left ventricular systolic function during propafenone therapy for atrial fibrillation. These acute findings may have been consequent to an increased dosage of propafenone combined with heavy alcohol consumption that led to decreased metabolism of propafenone. In addition, propafenone is known to interfere with liver function, although this patient's test results showed scant evidence of liver abnormalities. Yet another possible factor is the genetic spectrum in the metabolism of propafenone and other class I antiarrhythmic agents. When propafenone is prescribed, we recommend advising patients that alcohol consumption and interactions with other drugs can lead to increased levels of the antiarrhythmic agent, with resultant toxicity that can lead to adverse cardiovascular effects. Patients taking propafenone should also undergo periodic liver function testing. Finally, attention should be paid to voluntary or official recalls of specific antiarrhythmic medications that are of unreliable quality or potency.
PMCID: PMC2929852  PMID: 20844627
Anti-arrhythmia agents/administration & dosage/adverse effects; atrial fibrillation/diagnosis/drug therapy/etiology/prevention & control; cytochrome P-450 CYP2D6/genetics; dose-response relationship, drug; heart/drug effects; liver/enzymology/metabolism; propafenone/administration & dosage/adverse effects/therapeutic use
6.  Preclinical evaluation of marketed sodium channel blockers in a rat model of myotonia discloses promising antimyotonic drugs 
Experimental Neurology  2014;255(100):96-102.
Although the sodium channel blocker mexiletine is considered the first-line drug in myotonia, some patients experiment adverse effects, while others do not gain any benefit. Other antimyotonic drugs are thus needed to offer mexiletine alternatives. In the present study, we used a previously-validated rat model of myotonia congenita to compare six marketed sodium channel blockers to mexiletine. Myotonia was induced in the rat by injection of anthracen-9-carboxylic acid, a muscle chloride channel blocker. The drugs were given orally and myotonia was evaluated by measuring the time of righting reflex. The drugs were also tested on sodium currents recorded in a cell line transfected with the human skeletal muscle sodium channel hNav1.4 using patch-clamp technique. In vivo, carbamazepine and propafenone showed antimyotonic activity at doses similar to mexiletine (ED50 close to 5 mg/kg); flecainide and orphenadrine showed greater potency (ED50 near 1 mg/kg); lubeluzole and riluzole were the more potent (ED50 near 0.1 mg/kg). The antimyotonic activity of drugs in vivo was linearly correlated with their potency in blocking hNav1.4 channels in vitro. Deviation was observed for propafenone and carbamazepine, likely due to pharmacokinetics and multiple targets. The comparison of the antimyotonic dose calculated in rats with the current clinical dose in humans strongly suggests that all the tested drugs may be used safely for the treatment of human myotonia. Considering the limits of mexiletine tolerability and the occurrence of non-responders, this study proposes an arsenal of alternative drugs, which may prove useful to increase the quality of life of individuals suffering from non-dystrophic myotonia. Further clinical trials are warranted to confirm these results.
Highlights
•Seven sodium channel blockers show antimyotonic activity in a rat model of myotonia.•The ED50 value ranges from 0.1 (riluzole, lubeluzole) to 5 mg/kg (mexiletine, carbamazepine).•The drugs use-dependently block hNav1.4 channels in cells in myotonic-like conditions.•The IC50 values in vitro were well linearly correlated with the ED50 values in vivo.•The study discloses promising new therapeutic options for myotonic patients.
doi:10.1016/j.expneurol.2014.02.023
PMCID: PMC4004800  PMID: 24613829
Non-dystrophic myotonia; Sodium channel blockers; Mexiletine; Rat model; Patch-clamp; Over-excitability
7.  Effects of diltiazem and propafenone on the inactivation and recovery kinetics of fKv1.4 channel currents expressed in Xenopus oocytes 
Acta Pharmacologica Sinica  2011;32(4):465-477.
Aim:
To investigate the effects of diltiazem, an L-type calcium channel blocker, and propafenone, a sodium channel blocker, on the inactivation and recovery kinetics of fKv1.4, a potassium channel that generates the cardiac transient outward potassium current.
Methods:
The cRNA for fKv1.4ΔN, an N-terminal deleted mutant of the ferret Kv1.4 potassium channel, was injected into Xenopus oocytes to express the fKv1.4ΔN channel in these cells. Currents were recorded using a two electrode voltage clamp technique.
Results:
Diltiazem (10 to 1000 μmol/L) inhibited the fKv1.4ΔN channel in a frequency-dependent, voltage-dependent, and concentration-dependent manner, suggesting an open channel block. The IC50 was 241.04±23.06 μmol/L for the fKv1.4ΔN channel (at +50 mV), and propafenone (10 to 500 μmol/L) showed a similar effect (IC50=103.68±10.13 μmol/L). After application of diltiazem and propafenone, fKv1.4ΔN inactivation was bi-exponential, with a faster drug-induced inactivation and a slower C-type inactivation. Diltiazem increased the C-type inactivation rate and slowed recovery in fKv1.4ΔN channels. However, propafenone had no effect on either the slow inactivation time constant or the recovery.
Conclusion:
Diltiazem and propafenone accelerate the inactivation of the Kv1.4ΔN channel by binding to the open state of the channel. Unlike propafenone, diltiazem slows the recovery of the Kv1.4ΔN channel.
doi:10.1038/aps.2010.234
PMCID: PMC4001977  PMID: 21468083
inactivation; recovery; Kv1.4; potassium channel; diltiazem; propafenone; two electrode voltage clamp technique
8.  In Vitro and In Vivo Activity of Solithromycin (CEM-101) against Plasmodium Species 
With the emergence of Plasmodium falciparum infections exhibiting increased parasite clearance times in response to treatment with artemisinin-based combination therapies, the need for new therapeutic agents is urgent. Solithromycin, a potent new fluoroketolide currently in development, has been shown to be an effective, broad-spectrum antimicrobial agent. Malarial parasites possess an unusual organelle, termed the apicoplast, which carries a cryptic genome of prokaryotic origin that encodes its own translation and transcription machinery. Given the similarity of apicoplast and bacterial ribosomes, we have examined solithromycin for antimalarial activity. Other antibiotics known to target the apicoplast, such as the macrolide azithromycin, demonstrate a delayed-death effect, whereby treated asexual blood-stage parasites die in the second generation of drug exposure. Solithromycin demonstrated potent in vitro activity against the NF54 strain of P. falciparum, as well as against two multidrug-resistant strains, Dd2 and 7G8. The dramatic increase in potency observed after two generations of exposure suggests that it targets the apicoplast. Solithromycin also retained potency against azithromycin-resistant parasites derived from Dd2 and 7G8, although these lines did demonstrate a degree of cross-resistance. In an in vivo model of P. berghei infection in mice, solithromycin demonstrated a 100% cure rate when administered as a dosage regimen of four doses of 100 mg/kg of body weight, the same dose required for artesunate or chloroquine to achieve 100% cure rates in this rodent malaria model. These promising in vitro and in vivo data support further investigations into the development of solithromycin as an antimalarial agent.
doi:10.1128/AAC.05039-11
PMCID: PMC3264280  PMID: 22083475
9.  Development of a New Generation of 4-Aminoquinoline Antimalarial Compounds Using Predictive Pharmacokinetic and Toxicology Models 
Journal of medicinal chemistry  2010;53(9):3685-3695.
Among the known antimalarial drugs, chloroquine (CQ) and other 4-aminoquinolines have shown high potency and good bioavailability, yet complications associated with drug resistance necessitate the discovery of effective new antimalarial agents. ADMETa prediction studies were employed to evaluate a library of new molecules based on the 4-aminoquinolone-related structure of CQ. Extensive in vitro screening and in vivo pharmacokinetic studies in mice helped to identify two lead molecules, 18 and 4, with promising in vitro therapeutic efficacy, improved ADMET properties, low risk for drug-drug interactions, and desirable pharmacokinetic profiles. Both 18 and 4 are highly potent antimalarial compounds, with IC50 values = 5.6 nM and 17.3 nM, respectively, against the W2 (CQ-resistant) strain of Plasmodium falciparum (IC50 for CQ = 382 nM). When tested in mice, these compounds were found to have biological half-lives and plasma exposure values similar to or higher than those of CQ; they are therefore desirable candidates to pursue in future clinical trials.
doi:10.1021/jm100057h
PMCID: PMC2866084  PMID: 20361799
ADMET studies; antimalarial; 4-aminoquinolines; pharmacokinetics; toxicology
10.  Exhaustive Sampling of Docking Poses Reveals Binding Hypotheses for Propafenone Type Inhibitors of P-Glycoprotein 
PLoS Computational Biology  2011;7(5):e1002036.
Overexpression of the xenotoxin transporter P-glycoprotein (P-gp) represents one major reason for the development of multidrug resistance (MDR), leading to the failure of antibiotic and cancer therapies. Inhibitors of P-gp have thus been advocated as promising candidates for overcoming the problem of MDR. However, due to lack of a high-resolution structure the concrete mode of interaction of both substrates and inhibitors is still not known. Therefore, structure-based design studies have to rely on protein homology models. In order to identify binding hypotheses for propafenone-type P-gp inhibitors, five different propafenone derivatives with known structure-activity relationship (SAR) pattern were docked into homology models of the apo and the nucleotide-bound conformation of the transporter. To circumvent the uncertainty of scoring functions, we exhaustively sampled the pose space and analyzed the poses by combining information retrieved from SAR studies with common scaffold clustering. The results suggest propafenone binding at the transmembrane helices 5, 6, 7 and 8 in both models, with the amino acid residue Y307 playing a crucial role. The identified binding site in the non-energized state is overlapping with, but not identical to, known binding areas of cyclic P-gp inhibitors and verapamil. These findings support the idea of several small binding sites forming one large binding cavity. Furthermore, the binding hypotheses for both catalytic states were analyzed and showed only small differences in their protein-ligand interaction fingerprints, which indicates only small movements of the ligand during the catalytic cycle.
Author Summary
A major reason for the failure of cancer, antibiotic and antiviral therapies is the development of multidrug resistance (MDR). P-glycoprotein (P-gp), an ATP-dependent transport protein located in the membrane of epithelial cells of the kidney, liver, pancreas, colon and the blood-brain barrier, has been linked to the export of a broad variety of xenotoxins. Overexpression of P-gp leads to extrusion of therapeutic drugs and therefore triggers MDR. Thus, identification of potential P-gp inhibitors represents a promising concept for treatment of multiresistant tumours. However, due to lack of high resolution structural information and the polyspecific ligand recognition pattern only very limited information is available on the molecular basis of ligand/transporter interaction. Within this study we characterized the propafenone binding site of P-gp by docking a set of derivatives with known SAR into homology models of P-gp which represent both the apo and the nucleotide-bound state. Poses retrieved are in accordance with results from previous photoaffinity labeling studies and thus pave the way for structure-based in silico screening approaches.
doi:10.1371/journal.pcbi.1002036
PMCID: PMC3093348  PMID: 21589945
11.  Propafenone Poisoning—A Case Report with Plasma Propafenone Concentrations 
Journal of Medical Toxicology  2010;6(1):37-40.
Propafenone is an anti-arrhythmic drug used in the management of supraventricular and ventricular arrhythmias. It is metabolised through cytochrome P450 2D6 pathways; the major metabolites possess anti-arrhythmic activity. The cytochrome P450 CYP2D6 is coded by more than 70 alleles resulting in great genetic polymorphism of CYP2D6 isoenzymes, and up to 7% of Caucasian population are poor metabolisers. This case report describes a patient with severe overdose of propafenone who presented with coma, seizures and cardiotoxicity. The patient was managed with intravenous glucagon, hypertonic sodium bicarbonate, hypertonic saline and inotropic support. The propafenone and its 5-hydroxypropafenone (5-OHP) metabolite were measured by high-performance liquid chromatography with ultraviolet detection (no assay was available at the time to measure N-despropyl propafenone concentrations). Toxicological screen showed propafenone concentrations at a maximum of 1.26 mg/L at 9–10 h post-presentation, falling to 0.25 mg/L at 27–28 h post-presentation. No propafenone metabolite 5-OHP was detected in any sample analysed. No antidepressant or analgesic drugs were detected in toxicological screen. Propafenone overdose has been reported to be associated with features of severe cardiovascular and CNS toxicity. Aggressive treatment, meticulous monitoring and supportive care was associated with a good outcome in this case.
doi:10.1007/s13181-010-0037-2
PMCID: PMC3550440  PMID: 20373066
Propafenone; Poisoning; Cardiogenic shock; Convulsions
12.  Cyclopropyl Carboxamides, a Chemically Novel Class of Antimalarial Agents Identified in a Phenotypic Screen ▿ 
Antimicrobial Agents and Chemotherapy  2011;55(12):5740-5745.
Malaria is one of the deadliest infectious diseases in the world, with the eukaryotic parasite Plasmodium falciparum causing the most severe form of the disease. Discovery of new classes of antimalarial drugs has become an urgent task to counteract the increasing problem of drug resistance. Screening directly for compounds able to inhibit parasite growth in vitro is one of the main approaches the malaria research community is now pursuing for the identification of novel antimalarial drug leads. Very recently, thousands of compounds with potent activity against the parasite P. falciparum have been identified and information about their molecular descriptors, antiplasmodial potency, and cytotoxicity is publicly available. Now the challenges are how to identify the most promising chemotypes for further development and how best to progress these compounds through a lead optimization program to generate antimalarial drug candidates. We report here the first chemical series to be characterized from one of those screenings, a completely novel chemical class with the generic name cyclopropyl carboxamides that has never before been described as having antimalarial or other pharmacological activities. Cyclopropyl carboxamides are potent inhibitors of drug-sensitive and -resistant strains of P. falciparum in vitro and show in vivo oral efficacy in malaria mouse models. In the present work, we describe the biological characterization of this chemical family, showing that inhibition of their still unknown target has very favorable pharmacological consequences but the compounds themselves seem to select for resistance at a high frequency.
doi:10.1128/AAC.05188-11
PMCID: PMC3232824  PMID: 21968362
13.  Structure–Activity Relationships, Ligand Efficiency, and Lipophilic Efficiency Profiles of Benzophenone-Type Inhibitors of the Multidrug Transporter P-Glycoprotein 
Journal of Medicinal Chemistry  2012;55(7):3261-3273.
The drug efflux pump P-glycoprotein (P-gp) has been shown to promote multidrug resistance (MDR) in tumors as well as to influence ADME properties of drug candidates. Here we synthesized and tested a series of benzophenone derivatives structurally analogous to propafenone-type inhibitors of P-gp. Some of the compounds showed ligand efficiency and lipophilic efficiency (LipE) values in the range of compounds which entered clinical trials as MDR modulators. Interestingly, although lipophilicity plays a dominant role for P-gp inhibitors, all compounds investigated showed LipE values below the threshold for promising drug candidates. Docking studies of selected analogues into a homology model of P-glycoprotein suggest that benzophenones show an interaction pattern similar to that previously identified for propafenone-type inhibitors.
doi:10.1021/jm201705f
PMCID: PMC3326594  PMID: 22452412
14.  In vitro activity of ferroquine (SSR 97193) against Plasmodium falciparum isolates from the Thai-Burmese border 
Malaria Journal  2007;6:81.
Background
On the borders of Thailand, Plasmodium falciparum has become resistant to nearly all available drugs, and there is an urgent need to find new antimalarial drugs or drug combinations. Ferroquine (SSR97193) is a new 4-aminoquinoline antimalarial active against chloroquine resistant and sensitive P. falciparum strains in vivo and in vitro. This antimalarial organic iron complex (a ferrocenyl group has been associated with chloroquine) is meant to use the affinity of Plasmodium for iron to increase the probability for encountering the anti-malarial molecule.
The aim of the present study was to investigate the activity of ferroquine against P. falciparum isolates from an area with a known high multi-drug resistance rate.
Methods
Parasite isolates were obtained from patients with acute falciparum malaria attending the clinics of SMRU. In vitro cultures of these isolates were set-up in the SMRU-laboratory on pre-dosed drug plates, and grown in culture for 42 hours. Parasite growth was assessed by the double-site enzyme-linked pLDH immunodetection (DELI) assay.
Results
Sixty-five P. falciparum isolates were successfully grown in culture. The ferroquine mean IC50 (95% CI) was 9.3 nM (95% C.I.: 8.7 – 10.0). The mean IC50 value for the principal metabolite of ferroquin, SR97213A, was 37.0 nM (95% C.I.: 34.3 – 39.9), which is four times less active than ferroquine. The isolates in this study were highly multi-drug resistant but ferroquine was more active than chloroquine, quinine, mefloquine and piperaquine. Only artesunate was more active than ferroquine. Weak but significant correlations were found between ferroquine and its principal metabolite (r2 = 0.4288), chloroquine (r2 = 0.1107) and lumefantrine (r2 = 0.2364).
Conclusion
The results presented in this study demonstrate that the new ferroquine compound SSR97193 has high anti-malarial activity in vitro against multi-drug resistant P. falciparum.
doi:10.1186/1475-2875-6-81
PMCID: PMC1934364  PMID: 17597537
15.  Structure-guided lead optimization of triazolopyrimidine-ring substituents identifies potent Plasmodium falciparum dihydroorotate dehydrogenase inhibitors with clinical candidate potential 
Journal of medicinal chemistry  2011;54(15):5540-5561.
Drug therapy is the mainstay of antimalarial therapy, yet current drugs are threatened by the development of resistance. In an effort to identify new potential anti-malarials we have undertaken a lead optimization program around our previously identified triazolopyrimidine-based series of Plasmodium falciparum dihydroorotate dehydrogenase (PfDHODH) inhibitors. The X-ray structure of PfDHODH was used to inform the medicinal chemistry program allowing the identification of a potent and selective inhibitor (DSM265) that acts through DHODH inhibition to kill both sensitive and drug resistant strains of the parasite. This compound has similar potency to chloroquine in the humanized SCID mouse P. falciparum model, can be synthesized by a simple route, and rodent pharmacokinetic studies demonstrated it has excellent oral bioavailability, a long half-life and low clearance. These studies have identified the first candidate in the triazolopyrimidine series to meet previously established progression criteria for efficacy and ADME properties, justifying further development of this compound towards clinical candidate status.
doi:10.1021/jm200592f
PMCID: PMC3156099  PMID: 21696174
16.  Plasmodium dihydroorotate dehydrogenase: a promising target for novel anti-malarial chemotherapy 
Infectious disorders drug targets  2010;10(3):226-239.
Malaria remains a globally prevalent infectious disease that leads to significant morbidity and mortality. While there are a number of drugs approved for its treatment, drug resistance has compromised most of them, making the development of new drugs for the treatment and prevention of malaria essential. The completion of the Plasmodium falciparum genome and a growing understanding of parasite biology are fueling the search for novel drug targets. Despite this, few targets have been chemically validated in vivo. The pyrimidine biosynthetic pathway illustrates one of the best examples of successful identification of anti-malarial drug targets. This review focuses on recent studies to exploit the fourth enzyme in the de novo pyrimidine biosynthetic pathway of P. falciparum, dihydroorotate dehydrogenase (PfDHODH), as a new target for drug discovery. Several chemical scaffolds have been identified by high throughput screening as potent inhibitors of PfDHODH and these show strong selectivity for the malarial enzyme over that from the human host. Potent activity against parasites in whole cell models with good correlation between activity on the enzyme and the parasite have also been observed for a number of the identified series. Lead optimization of a triazolopyrimidine-based series has identified an analog with prolonged plasma exposure, that is orally bioavailable, and which shows good efficacy against the in vivo mouse model of the disease. These data provide strong evidence that PfDHODH is a validated target for the identification of new antimalarial chemotherapy. The challenge remains to identify compounds with the necessary combination of potency and metabolic stability to allow identification of a clinical candidate.
PMCID: PMC2883174  PMID: 20334617
Malaria; Plasmodium; pyrimidine biosynthesis; dihydroorotate dehydrogenase; drug discovery
17.  Regulation of Antiarrhythmic Drug Propafenone Effects on the C-type KV1.4 Potassium Channel by PHo and K+ 
The effects of the antiarrhythmic drug propafenone at c-type kv1.4 channels in Xenopus laevis oocytes were studied with the two-electrode voltage-clamp techinique. Defolliculated oocytes (stage V-VI) were injected with transcribed cRNAs of ferret Kv1.4ΔN channels. During recording, oocytes were continuously perfused with control solution or propafenone. Propafenone decreased the currents during voltage steps. The block was voltage-, use-, and concentration- dependent manners. The block was increased with positive going potentials. The voltage dependence of block could be fitted with the sum of monoexponential and a linear function. Propafenone accelerated the inactivate of current during the voltage step. The concentration of half-maximal block (IC50) was 121 µM/L. With high, normal, and low extracellular potassium concentrations, the changes of IC50 value had no significant statistical differences. The block of propafenone was PH- dependent in high-, normal- and low- extracellular potassium concentrations. Acidification of the extracellular solution to PH 6.0 increased the IC50 values to 463 µM/L, alkalization to PH 8.0 reduced it to 58 µM/L. The results suggest that propafenone blocks the Kv1.4ΔN channel in the open state and give some hints for an intracellular site of action.
doi:10.3346/jkms.2009.24.1.84
PMCID: PMC2650976  PMID: 19270818
Potassium Channels; Anti-arrhythmic drug; Ion Channels, Voltage-Gated; Voltage Clamp; Membrane Currents
18.  Synthesis and evaluation of 7-substituted 4-aminoquinoline analogs for antimalarial activity 
Journal of medicinal chemistry  2011;54(20):7084-7093.
We previously reported that substituted 4-aminoquinolines with a phenylether substituent at the 7-position of the quinoline ring and the capability of intramolecular hydrogen bonding between the protonated amine on the side chain and a hydrogen bond acceptor on the amine’s alkyl substituents exhibited potent antimalarial activity against the multi-drug resistant strain P. falciparum W2. We employed a parallel synthetic method to generate diaryl ether, biaryl, and alkylaryl 4-aminoquinoline analogs, in the background of a limited number of side chain variations that had previously afforded potent 4-aminoquinolines. All subsets were evaluated for their antimalarial activity against the chloroquine-sensitive strain 3D7 and the chloroquine-resistant K1 and cytotoxicity mammalian cell lines. While all three arrays showed good antimalarial activity, only the biaryl-containing subset showed consistently good potency against the drug-resistant K1strain good selectivity with regard to mammalian cytotoxicity. Overall, our data indicate that the biaryl-containing series contains promising candidates for further study.
doi:10.1021/jm200636z
PMCID: PMC3697074  PMID: 21910466
19.  Antimalarial Activity of Phenylthiazolyl-Bearing Hydroxamate-Based Histone Deacetylase Inhibitors▿ †  
Antimicrobial Agents and Chemotherapy  2008;52(10):3467-3477.
The antimalarial activity and pharmacology of a series of phenylthiazolyl-bearing hydroxamate-based histone deacetylase inhibitors (HDACIs) was evaluated. In in vitro growth inhibition assays approximately 50 analogs were evaluated against four drug resistant strains of Plasmodium falciparum. The range of 50% inhibitory concentrations (IC50s) was 0.0005 to >1 μM. Five analogs exhibited IC50s of <3 nM, and three of these exhibited selectivity indices of >600. The most potent compound, WR301801 (YC-2-88) was shown to cause hyperacetylation of P. falciparum histones, which is a marker for HDAC inhibition in eukaryotic cells. The compound also inhibited malarial and mammalian HDAC activity in functional assays at low nanomolar concentrations. WR301801 did not exhibit cures in P. berghei-infected mice at oral doses as high as 640 mg/kg/day for 3 days or in P. falciparum-infected Aotus lemurinus lemurinus monkeys at oral doses of 32 mg/kg/day for 3 days, despite high relative bioavailability. The failure of monotherapy in mice may be due to a short half-life, since the compound was rapidly hydrolyzed to an inactive acid metabolite by loss of its hydroxamate group in vitro (half-life of 11 min in mouse microsomes) and in vivo (half-life in mice of 3.5 h after a single oral dose of 50 mg/kg). However, WR301801 exhibited cures in P. berghei-infected mice when combined at doses of 52 mg/kg/day orally with subcurative doses of chloroquine. Next-generation HDACIs with greater metabolic stability than WR301801 may be useful as antimalarials if combined appropriately with conventional antimalarial drugs.
doi:10.1128/AAC.00439-08
PMCID: PMC2565884  PMID: 18644969
20.  A Collaborative Epidemiological Investigation into the Criminal Fake Artesunate Trade in South East Asia  
PLoS Medicine  2008;5(2):e32.
Background
Since 1998 the serious public health problem in South East Asia of counterfeit artesunate, containing no or subtherapeutic amounts of the active antimalarial ingredient, has led to deaths from untreated malaria, reduced confidence in this vital drug, large economic losses for the legitimate manufacturers, and concerns that artemisinin resistance might be engendered.
Methods and Findings
With evidence of a deteriorating situation, a group of police, criminal analysts, chemists, palynologists, and health workers collaborated to determine the source of these counterfeits under the auspices of the International Criminal Police Organization (INTERPOL) and the Western Pacific World Health Organization Regional Office. A total of 391 samples of genuine and counterfeit artesunate collected in Vietnam (75), Cambodia (48), Lao PDR (115), Myanmar (Burma) (137) and the Thai/Myanmar border (16), were available for analysis. Sixteen different fake hologram types were identified. High-performance liquid chromatography and/or mass spectrometry confirmed that all specimens thought to be counterfeit (195/391, 49.9%) on the basis of packaging contained no or small quantities of artesunate (up to 12 mg per tablet as opposed to ∼ 50 mg per genuine tablet). Chemical analysis demonstrated a wide diversity of wrong active ingredients, including banned pharmaceuticals, such as metamizole, and safrole, a carcinogen, and raw material for manufacture of methylenedioxymethamphetamine (‘ecstasy'). Evidence from chemical, mineralogical, biological, and packaging analysis suggested that at least some of the counterfeits were manufactured in southeast People's Republic of China. This evidence prompted the Chinese Government to act quickly against the criminal traders with arrests and seizures.
Conclusions
An international multi-disciplinary group obtained evidence that some of the counterfeit artesunate was manufactured in China, and this prompted a criminal investigation. International cross-disciplinary collaborations may be appropriate in the investigation of other serious counterfeit medicine public health problems elsewhere, but strengthening of international collaborations and forensic and drug regulatory authority capacity will be required.
Paul Newton and colleagues' international, collaborative study found evidence that counterfeit artesunate was being manufactured in China, which prompted a criminal investigation.
Editors' Summary
Background
Malaria is one of the world's largest public health problems, causing around 500 million cases of illness and at least one million deaths per year (the estimates vary widely). The most serious form of malaria is caused by the parasite Plasmodium falciparum, which has become resistant to multiple drugs that had previously been the cornerstones of antimalarial regimens. One group of drugs for treating malaria, the artemisinin therapies including artesunate, are based upon a Chinese herb called qinghaosu; these have now become vital to the treatment of P. falciparum malaria. But counterfeit artesunate, containing none or too little (“subtherapeutic levels”) of the active ingredient, is a growing problem especially in South and East Asia. Fake artesunate is devastating for malaria control: it causes avoidable death, reduces confidence in the drug, and takes away profit from legitimate manufacturers. Of major concern also is the potential for subtherapeutic counterfeit artesunate to fuel the parasite's resistance to the artemisinin group of drugs.
Previous estimates have suggested that between 33% and 53% of artesunate tablets in mainland South East Asia are counterfeit. In this paper the authors report on an unprecedented international collaboration and criminal investigation that attempted to quantify and source counterfeit artesunate among some of the most malarious countries in Asia.
Why Was This Study Done?
Previous reports have identified the problem of fake artesunate, but as of yet there have been few reports on the potential solutions. Concerned health workers and scientists, the regional World Health Organization (WHO) office and the International Criminal Police Organization (INTERPOL) got together to discuss what could be done in May 2005 when it became clear the counterfeit artesunate situation was worsening in the Greater Mekong Sub-Region of South East Asia (comprising Cambodia, Lao People's Democratic Republic, Myanmar, Thailand, Vietnam, and Yunnan Province in the People's Republic of China). Their subsequent investigation combined the goals and methods of a range of concerned parties—police, scientists, and health workers—to identify the source of counterfeit artesunate in South East Asia and to supply the evidence to help arrest and prosecute the perpetrators.
What Did the Researchers Do and Find?
The researchers conducted forensic analyses of samples of genuine and counterfeit artesunate. They selected these samples from larger surveys and investigations that had been conducted in the region beginning in the year 2000. Genuine samples were supplied by a manufacturer to provide a comparator. The authors examined the physical appearance of the packages and subjected the tablets to a wide range of chemical and biological tests that allowed an analysis of the components contained in the tablets.
When comparing the collected packages and tablets against the genuine samples, the researchers found considerable diversity of fake artesunate in SE Asia. Sixteen different fake hologram types (the stickers contained on packages meant to identify them as genuine) were found. Chemical analysis revealed that all tablets thought to be fake contained no or very small quantities of artesunate. Other ingredients found in the artesunate counterfeit tablets included paracetamol, antibiotics, older antimalarial drugs, and a range of minerals, and there were a variety of gases surrounding the tablets inside the packaging. Biological analyses of pollen grains inside the packaging suggested that the packages originated in the parts of South East Asia along the Chinese border.
What Do these Findings Mean?
The results were crucial in helping the authorities establish the origin of the fake artesunate. For example, the authors identified two regional clusters where the counterfeit tablets appeared to be coming from, thus flagging a potential manufacturing site or distribution network. The presence of wrong active pharmaceutical ingredients (such as the older antimalarial drugs) suggested the counterfeiters had access to a variety of active pharmaceutical ingredients. The presence of safrole, a precursor to the illicit drug ecstasy, suggested the counterfeits may be coming from factories that manufacture ecstasy. And the identification of minerals indigenous to certain regions also helped identify the counterfeits' origin. The researchers concluded that at least some of the counterfeit artesunate was coming from southern China. The Secretary General of INTERPOL presented the findings to the Chinese government, which then carried out a criminal investigation and arrested individuals alleged to have produced and distributed the counterfeit artesunate.
The collaboration between police, public health workers and scientists on combating fake artesunate is unique, and provides a model for others to follow. However, the authors note that substantial capacity in forensic analysis and the infrastructure to support collaborations between these different disciplines are needed.
Additional Information.
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.0050032.
The World Health Organization in 2006 created IMPACT—International Medical Products Anti-Counterfeiting Taskforce—with the aim of forging international collaboration to seek global solutions to this global challenge and in raising awareness of the dangers of counterfeit medical products. The task force membership includes international organizations, nongovernmental organizations, enforcement agencies, pharmaceutical manufacturers' associations, and drug and regulatory authorities. IMPACT's Web site notes that trade in counterfeit medicines is widespread and affects both developed and developing countries but is more prevalent in countries that have weak drug regulatory systems, poor supply of basic medicines, unregulated markets, high drug prices and/or significant price differentials. IMPACT holds international conferences and maintains a rapid alert system for counterfeit drugs.
The drug industry's anticounterfeit organization, Pharmaceutical Security Institute, works to develop improved systems to identify the extent of the counterfeiting problem and to assist in coordinating international inquiries. Its membership includes 21 large pharmaceutical companies.
The Web site of David Pizzanelli, a world expert on security holography, contains a PowerPoint presentation co-authored by Paul Newton that illustrates the different types of fake holograms found on fake artesunate packages, and their implications for artemisinin resistance (http://www.pizzanelli.co.uk/content/artesunate.html).
doi:10.1371/journal.pmed.0050032
PMCID: PMC2235893  PMID: 18271620
21.  Quinine Dimers Are Potent Inhibitors of the Plasmodium falciparum Chloroquine Resistance Transporter and Are Active against Quinoline-Resistant P. falciparum 
ACS chemical biology  2014;9(3):722-730.
Chloroquine (CQ) resistance in the human malaria parasite Plasmodium falciparum is primarily conferred by mutations in the “chloroquine resistance transporter” (PfCRT). The resistance-conferring form of PfCRT (PfCRTCQR) mediates CQ resistance by effluxing the drug from the parasite’s digestive vacuole, the acidic compartment in which CQ exerts its antiplasmodial effect. PfCRTCQR can also decrease the parasite’s susceptibility to other quinoline drugs, including the current antimalarials quinine and amodiaquine. Here we describe interactions between PfCRTCQR and a series of dimeric quinine molecules using a Xenopus laevis oocyte system for the heterologous expression of PfCRT and using an assay that detects the drug-associated efflux of H+ ions from the digestive vacuole in parasites that harbor different forms of PfCRT. The antiplasmodial activities of dimers 1 and 6 were also examined in vitro (against drug-sensitive and drug-resistant strains of P. falciparum) and in vivo (against drug-sensitive P. berghei). Our data reveal that the quinine dimers are the most potent inhibitors of PfCRTCQR reported to date. Furthermore, the lead compounds (1 and 6) were not effluxed by PfCRTCQR from the digestive vacuole but instead accumulated to very high levels within this organelle. Both 1 and 6 exhibited in vitro antiplasmodial activities that were inversely correlated with CQ. Moreover, the additional parasiticidal effect exerted by 1 and 6 in the drug-resistant parasites was attributable, at least in part, to their ability to inhibit PfCRTCQR. This highlights the potential for devising new antimalarial therapies that exploit inherent weaknesses in a key resistance mechanism of P. falciparum.
doi:10.1021/cb4008953
PMCID: PMC4068143  PMID: 24369685
22.  Cryo-EM structure of the Plasmodium falciparum 80S ribosome bound to the anti-protozoan drug emetine 
eLife  2014;3:e03080.
Malaria inflicts an enormous burden on global human health. The emergence of parasite resistance to front-line drugs has prompted a renewed focus on the repositioning of clinically approved drugs as potential anti-malarial therapies. Antibiotics that inhibit protein translation are promising candidates for repositioning. We have solved the cryo-EM structure of the cytoplasmic ribosome from the human malaria parasite, Plasmodium falciparum, in complex with emetine at 3.2 Å resolution. Emetine is an anti-protozoan drug used in the treatment of ameobiasis that also displays potent anti-malarial activity. Emetine interacts with the E-site of the ribosomal small subunit and shares a similar binding site with the antibiotic pactamycin, thereby delivering its therapeutic effect by blocking mRNA/tRNA translocation. As the first cryo-EM structure that visualizes an antibiotic bound to any ribosome at atomic resolution, this establishes cryo-EM as a powerful tool for screening and guiding the design of drugs that target parasite translation machinery.
DOI: http://dx.doi.org/10.7554/eLife.03080.001
eLife digest
Each year, malaria kills more than 600,000 people, mostly children younger than 5 years old. Humans who have been bitten by mosquitoes infected with malaria-causing parasites become ill as the parasites rapidly multiply in blood cells. Although there are several drugs that are currently used to treat malaria, the parasites are rapidly developing resistance to them, setting off an urgent hunt for new malaria drugs.
Developing new antimalarial medications from scratch is likely to take decades—too long to combat the current public health threat posed by emerging strains of drug-resistant parasites. To speed up the process, scientists are investigating whether drugs developed for other illnesses may also act as therapies for malaria, either when used alone or in combination with existing malaria drugs.
Certain antibiotics—including one called emetine—have already shown promise as antimalarial drugs. These antibiotics prevent the parasites from multiplying by interfering with the ribosome—the part of a cell that builds new proteins. However, humans become ill after taking emetine for long periods because it also blocks the production of human proteins.
Tweaking emetine so that it acts only against the production of parasite proteins would make it a safer malaria treatment. To do this, scientists must first map the precise interactions between the drug and the ribosomes in parasites. Wong et al. have now used a technique called cryo-electron microscopy to examine the ribosome of the most virulent form of malaria parasite. This technique uses very cold temperatures to rapidly freeze molecules, allowing scientists to look at molecular-level details without distorting the structure of the molecule—a problem sometimes encountered in other techniques.
The images of the parasitic ribosome taken by Wong, Bai, Brown et al. show that emetine binds to the end of the ribosome where the instructions for how to assemble amino acids into a protein are copied from strands of RNA. In addition, the images revealed features of the parasitic ribosome that are not found in the human form. Drug makers could exploit these features to improve emetine so that it more specifically targets the production of proteins by the parasite and is less toxic to humans.
DOI: http://dx.doi.org/10.7554/eLife.03080.002
doi:10.7554/eLife.03080
PMCID: PMC4086275  PMID: 24913268
malaria; Plasmodium falciparum; ribosome; drug development; cryo-EM; other
23.  Multidrug-Resistant Plasmodium vivax Associated with Severe and Fatal Malaria: A Prospective Study in Papua, Indonesia 
PLoS Medicine  2008;5(6):e128.
Background
Multidrug-resistant Plasmodium vivax (Pv) is widespread in eastern Indonesia, and emerging elsewhere in Asia-Pacific and South America, but is generally regarded as a benign disease. The aim of the study was to review the spectrum of disease associated with malaria due to Pv and P. falciparum (Pf) in patients presenting to a hospital in Timika, southern Papua, Indonesia.
Methods and Findings
Data were prospectively collected from all patients attending the outpatient and inpatient departments of the only hospital in the region using systematic data forms and hospital computerised records. Between January 2004 and December 2007, clinical malaria was present in 16% (60,226/373,450) of hospital outpatients and 32% (12,171/37,800) of inpatients. Among patients admitted with slide-confirmed malaria, 64% of patients had Pf, 24% Pv, and 10.5% mixed infections. The proportion of malarial admissions attributable to Pv rose to 47% (415/887) in children under 1 y of age. Severe disease was present in 2,634 (22%) inpatients with malaria, with the risk greater among Pv (23% [675/2,937]) infections compared to Pf (20% [1,570/7,817]; odds ratio [OR] = 1.19 [95% confidence interval (CI) 1.08–1.32], p = 0.001), and greatest in patients with mixed infections (31% [389/1,273]); overall p < 0.0001. Severe anaemia (haemoglobin < 5 g/dl) was the major complication associated with Pv, accounting for 87% (589/675) of severe disease compared to 73% (1,144/1,570) of severe manifestations with Pf (p < 0.001). Pure Pv infection was also present in 78 patients with respiratory distress and 42 patients with coma. In total 242 (2.0%) patients with malaria died during admission: 2.2% (167/7,722) with Pf, 1.6% (46/2,916) with Pv, and 2.3% (29/1260) with mixed infections (p = 0.126).
Conclusions
In this region with established high-grade chloroquine resistance to both Pv and Pf, Pv is associated with severe and fatal malaria particularly in young children. The epidemiology of P. vivax needs to be re-examined elsewhere where chloroquine resistance is increasing.
Ric Price and colleagues present data from southern Papua, Indonesia, suggesting that malaria resulting from infection withPlasmodium vivax is associated with substantial morbidity and mortality.
Editors' Summary
Background.
Malaria, a parasitic disease transmitted to people by mosquitoes, is common throughout the tropical and subtropical areas of the world. In sub-Saharan Africa, infections with Plasmodium falciparum cause most of the malaria-associated illness and death. Elsewhere, another related parasite—P. vivax—is often the commonest cause of malaria. Both parasites are injected into the human blood stream when an infected mosquito bites a person. From there, the parasites travel to the liver, where they multiply for 8–9 d and mature into a form of the parasite known as merozoites. These merozoites are released from the liver and invade red blood cells where they multiply rapidly for a couple of days before bursting out and infecting more red blood cells. This cyclical accumulation of parasites in the blood causes a recurring flu-like illness characterized by fevers, headaches, chills, and sweating. Malaria can be treated with antimalarial drugs but, if left untreated, infections with P. falciparum can cause anemia (by destroying red blood cells) and can damage the brain and other vital organs (by blocking the capillaries that supply these organs with blood), complications that can be fatal.
Why Was This Study Done?
Unlike falciparum malaria, vivax malaria is generally regarded as a benign or nonfatal disease even though there have been several reports recently of severe disease and deaths associated with vivax malaria. These reports do not indicate, however, whether P. vivax is responsible for a significant proportion of malarial deaths. Public health officials need to know this information because strains of P. vivax that are resistant to multiple antimalarial drugs are widespread in Indonesia and beginning to emerge elsewhere in Asia and South America. In this study, therefore, the researchers investigate the relative burden of vivax and falciparum malaria in Papua, Indonesia, a region where multidrug-resistant strains of both P. falciparum and P. vivax are common.
What Did the Researchers Do and Find?
The researchers examined data collected from all the patients attending the outpatient and inpatient departments of a hospital that serves a large area in the southern lowlands of Papua, Indonesia between January 2004 and December 2007. Among those inpatients in whom malaria had been confirmed by finding parasites in blood samples, two-thirds were infected with P. falciparum, a quarter with P. vivax, and the rest with a mixture of parasites. Nearly one in four patients infected with P. vivax developed severe malaria compared with roughly one in five patients infected with P. falciparum. However, about one in three patients infected with both parasites developed severe disease. Whichever parasite was responsible for the infection, the proportion of patients with severe disease was greatest among children below the age of five years. Severe anemia was the commonest complication associated with severe malaria caused by both P. vivax and P. falciparum (present in 87% and 73% of cases, respectively). Finally, one in 50 patients with malaria died; the risk of death was the same for patients infected with P. falciparum, P. vivax, or both parasites.
What Do These Findings Mean?
These findings provide important information about the burden of malaria associated with P. vivax infection. They show that in a region where multidrug-resistant strains of both P. falciparum and P. vivax are common, P. vivax infection (as well as P. falciparum infection) is associated with severe and fatal malaria, particularly in young children. The findings also show that infection with a mixture of the two parasites is associated with a higher risk of severe disease than infection with either parasite alone. Most importantly, they show that similar proportions of patients infected with P. falciparum, P. vivax, or a mixture of parasites die. Further studies need to be done in other settings to confirm these findings and to learn more about the pattern of severe malaria associated with P. vivax (in particular, with multidrug-resistant strains). Nevertheless, these findings highlight the need to consider both P. vivax and P. falciparum when implementing measures designed to reduce the malaria burden in regions where these parasites coexist.
Additional Information.
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.0050128.
A PLoS Medicine Research in Translation article by Stephen Rogerson further discusses this study and a related PLoS Medicine paper on vivax malaria in a community cohort from Papua New Guinea
The MedlinePlus encyclopedia has a page on malaria (in English and Spanish)
The US Centers for Disease Control and Prevention provides information on malaria (in English and Spanish)
Vivaxmalaria provides information on topics related to P. vivax
The Malaria Vaccine Initiative also provides a fact sheet on P. vivax malaria
Information is available from the Roll Back Malaria Partnership on the global control of malaria
doi:10.1371/journal.pmed.0050128
PMCID: PMC2429950  PMID: 18563962
24.  Estimating the Number of Paediatric Fevers Associated with Malaria Infection Presenting to Africa's Public Health Sector in 2007 
PLoS Medicine  2010;7(7):e1000301.
Peter Gething and colleagues compute the number of fevers likely to present to public health facilities in Africa and the estimated number of these fevers likely to be infected with Plasmodium falciparum malaria parasites.
Background
As international efforts to increase the coverage of artemisinin-based combination therapy in public health sectors gather pace, concerns have been raised regarding their continued indiscriminate presumptive use for treating all childhood fevers. The availability of rapid-diagnostic tests to support practical and reliable parasitological diagnosis provides an opportunity to improve the rational treatment of febrile children across Africa. However, the cost effectiveness of diagnosis-based treatment polices will depend on the presumed numbers of fevers harbouring infection. Here we compute the number of fevers likely to present to public health facilities in Africa and the estimated number of these fevers likely to be infected with Plasmodium falciparum malaria parasites.
Methods and Findings
We assembled first administrative-unit level data on paediatric fever prevalence, treatment-seeking rates, and child populations. These data were combined in a geographical information system model that also incorporated an adjustment procedure for urban versus rural areas to produce spatially distributed estimates of fever burden amongst African children and the subset likely to present to public sector clinics. A second data assembly was used to estimate plausible ranges for the proportion of paediatric fevers seen at clinics positive for P. falciparum in different endemicity settings. We estimated that, of the 656 million fevers in African 0–4 y olds in 2007, 182 million (28%) were likely to have sought treatment in a public sector clinic of which 78 million (43%) were likely to have been infected with P. falciparum (range 60–103 million).
Conclusions
Spatial estimates of childhood fevers and care-seeking rates can be combined with a relational risk model of infection prevalence in the community to estimate the degree of parasitemia in those fevers reaching public health facilities. This quantification provides an important baseline comparison of malarial and nonmalarial fevers in different endemicity settings that can contribute to ongoing scientific and policy debates about optimum clinical and financial strategies for the introduction of new diagnostics. These models are made publicly available with the publication of this paper.
Please see later in the article for the Editors' Summary
Editors' Summary
Background
Malaria —an infectious parasitic disease transmitted to people through the bite of an infected mosquito —kills about one million people (mainly children living in sub-Saharan Africa) every year. Although several parasites cause malaria, Plasmodium falciparum is responsible for most of these deaths. For the past 50 years, the main treatments for P. falciparum malaria have been chloroquine and sulfadoxine/pyrimethamine. Unfortunately, parasitic resistance to these “monotherapies” is now widespread and there has been a global upsurge in the illness and deaths caused by P. falciparum. To combat this increase, the World Health Organization recommends artemisinin combination therapy (ACT) for P. falciparum malaria in all regions with drug-resistant malaria. In ACT, artemisinin derivatives (new, fast-acting antimalarial drugs) are used in combination with another antimalarial to reduce the chances of P. falciparum becoming resistant to either drug.
Why Was This Study Done?
All African countries at risk of P. falciparum have now adopted ACT as first-line therapy for malaria in their public clinics. However, experts are concerned that ACT is often given to children who don't actually have malaria because, in many parts of Africa, health care workers assume that all childhood fevers are malaria. This practice, which became established when diagnostic facilities for malaria were very limited, increases the chances of P. falciparum becoming resistant to ACT, wastes limited drug stocks, and means that many ill children are treated inappropriately. Recently, however, rapid diagnostic tests for malaria have been developed and there have been calls to expand their use to improve the rational treatment of African children with fever. Before such an expansion is initiated, it is important to know how many African children develop fever each year, how many of these ill children attend public clinics, and what proportion of them is likely to have malaria. Unfortunately, this type of information is incompletely or unreliably collected in many parts of Africa. In this study, therefore, the researchers use a mathematical model to estimate the number of childhood fevers associated with malaria infection that presented to Africa's public clinics in 2007 from survey data.
What Did the Researchers Do and Find?
The researchers used survey data on the prevalence (the proportion of a population with a specific disease) of childhood fever and on treatment-seeking behavior and data on child populations to map the distribution of fever among African children and the likelihood of these children attending public clinics for treatment. They then used a recent map of the distribution of P. falciparum infection risk to estimate what proportion of children with fever who attended clinics were likely to have had malaria in different parts of Africa. In 2007, the researchers estimate, 656 million cases of fever occurred in 0–4-year-old African children, 182 million were likely to have sought treatment in a public clinic, and 78 million (just under half of the cases that attended a clinic with fever) were likely to have been infected with P. falciparum. Importantly, there were marked geographical differences in the likelihood of children with fever presenting at public clinics being infected with P. falciparum. So, for example, whereas nearly 60% of the children attending public clinics with fever in Burkino Faso were likely to have had malaria, only 15% of similar children in Kenya were likely to have had this disease.
What Do These Findings Mean?
As with all mathematical models, the accuracy of these findings depends on the assumptions included in the model and on the data fed into it. Nevertheless, these findings provide a map of the prevalence of malarial and nonmalarial childhood fevers across sub-Saharan Africa and an indication of how many of the children with fever reaching public clinics are likely to have malaria and would therefore benefit from ACT. The finding that in some countries more than 80% of children attending public clinics with fever probably don't have malaria highlights the potential benefits of introducing rapid diagnostic testing for malaria. Furthermore, these findings can now be used to quantify the resources needed for and the potential clinical benefits of different policies for the introduction of rapid diagnostic testing for malaria across Africa.
Additional Information
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1000301.
Information is available from the World Health Organization on malaria (in several languages) and on rapid diagnostic tests for malaria
The US Centers for Disease Control and Prevention provide information on malaria (in English and Spanish)
MedlinePlus provides links to additional information on malaria (in English and Spanish)
Information on the global mapping of malaria is available at the Malaria Atlas Project
Information is available from the Roll Back Malaria Partnership on the global control of malaria (in English and French) and on artemisinin combination therapy
doi:10.1371/journal.pmed.1000301
PMCID: PMC2897768  PMID: 20625548
25.  Ryanodine receptor inhibition potentiates the activity of Na channel blockers against spontaneous calcium elevations and delayed afterdepolarizations in Langendorff-perfused rabbit ventricles 
BACKGROUND
Na channel blockers are effective in suppressing delayed afterdepolarizations (DADs) in isolated Purkinje fibers. However, in isolated mouse ventricular myocytes lacking calsequestrin, only those Na channel blockers that also inhibit type 2 ryanodine receptor channels were effective against spontaneous Ca elevation (SCaE) and DADs.
OBJECTIVE
To test the hypothesis that combined Na channel and type 2 ryanodine receptor channel blocker ((R)-propafenone) is more effective than a Na channel blocker (lidocaine) in suppressing SCaE and DADs in the intact rabbit ventricles.
METHODS
We compared (R)-propafenone (3 μmol/L) with lidocaine (50 μmol/L) on SCaE and DADs by using epicardial optical mapping of intracellular calcium (Cai) and membrane voltage in Langendorff-perfused rabbit hearts. SCaE and DADs were induced by rapid pacing trains and isoproterenol (0.3 μmol/L) infusion. One arbitrary unit is equivalent to the Ca transient amplitude of paced beats.
RESULTS
SCaEs were observed at the cessation of rapid pacing in all hearts at baseline. (R)-Propafenone nearly completely inhibited DADs and SCaE (0.04 arbitrary units [95% confidence interval 0.02–0.06] vs 0.23 arbitrary units [95% confidence interval 0.18–0.28] at baseline; n = 6 hearts; P < .001). Lidocaine also significantly reduced the SCaE but was significantly (P < .05) less effective than (R)-propafenone. Both drugs increased the rise time of action potential upstroke and reduced conduction velocity to a similar extent, suggesting a significant inhibition of INa.
CONCLUSIONS
Both Na channel blockers significantly reduced tachycardia-induced SCaEs in the rabbit ventricles, but (R)-propafenone was significantly more effective than lidocaine. These data suggest that type 2 ryanodine receptor inhibition potentiates the activity of Na channel blockers against SCaE and DADs in the intact hearts.
doi:10.1016/j.hrthm.2012.02.031
PMCID: PMC3572724  PMID: 22387372
Depolarization; Action potentials; Calcium; Antiarrhythmic agents

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