Drug resistance hampers our capacity to roll back malaria

An updated review of chemical compounds with anti-Toxoplasma gondii activity

The opportunistic apicomplexan parasite Toxoplasma gondii is the etiologic agent for toxoplasmosis, which can infect a widespread range of hosts, particularly humans and warm-blooded animals. The present chemotherapy to treat or prevent toxoplasmosis is deficient and is based on diverse drugs such as atovaquone, trimethoprim, spiramycine, which are effective in acute toxoplasmosis. Therefore, a safe chemotherapy is required for toxoplasmosis considering that its responsible agent, T. gondii, provokes severe illness and death in pregnant women and immunodeficient patients. A certain disadvantage of the available treatments is the lack of effectiveness against the tissue cyst of the parasite. A safe chemotherapy to combat toxoplasmosis should be based on the metabolic differences between the parasite and the mammalian host. This article covers different relevant molecular targets to combat this disease including the isoprenoid pathway (farnesyl diphosphate synthase, squalene synthase), dihydrofolate reductase, calcium-dependent protein kinases, histone deacetylase, mitochondrial electron transport chain, etc.

The role of pharmacists in eliminating counterfeit medicines in Nigeria

Introduction

Over the years, counterfeit pharmaceuticals have posed immense concerns for global health and patient safety. This menace encompasses various classes of medications. Given the criticality of pharmacists' interventions in drug distribution and supply, this study aimed at exploring their role in the prevention and control of counterfeit pharmaceutical products in Nigeria.

Methods

A cross-sectional study was undertaken, using questionnaires to collect data from pharmacists across various sectors of pharmacy practice in Nigeria. Face and content validity was undertaken on the study tool prior to data collection. Ethical approval was obtained from the National Institute for Pharmaceutical Research and Development Health Research Ethics Committee, and confidentiality was strictly maintained during data collection process. Data were analyzed using Statistical Package for Social Sciences. Descriptive statistical analysis was undertaken and chi square was used to determine association between socio-demographic characteristics and variables.

Results

The responses comprised 205 (52.6%) female and 185 (47.4%) male participants. Almost all the participants (98.4%) agreed that strict enforcement of drug laws can contribute to adequate control of counterfeit medicines in Nigeria, and majority of the study sample (64.7%) indicated that the poor implementation of these laws was a major factor influencing the preponderance of counterfeit medicines in the country. Two-thirds (63.5%) of the participants supported the need for pharmacists to provide adequate education to patients on strategies to identify counterfeit medicines, and a similar proportion (68.0%) were of the opinion that it was the responsibility of pharmacists to ensure that drugs are purchased from credible sources.

Conclusion

Findings from this study, in addition to confirming pharmacists' instrumentality in the fight against counterfeit medicines, identified certain context specific factors that can strengthen the regulation, policy and the entire healthcare system. Government and relevant stakeholders can therefore begin to articulate strategic reforms for contextual policy intervention that address medicines' counterfeiting, whilst prioritising pharmacists' role in other critical areas in the healthcare system.

Biodereplication of Antiplasmodial Extracts: Application of the Amazonian Medicinal Plant Piper coruscans Kunth

Improved methodological tools to hasten antimalarial drug discovery remain of interest, especially when considering natural products as a source of drug candidates. We propose a biodereplication method combining the classical dereplication approach with the early detection of potential antiplasmodial compounds in crude extracts. Heme binding is used as a surrogate of the antiplasmodial activity and is monitored by mass spectrometry in a biomimetic assay. Molecular networking and automated annotation of targeted mass through data mining were followed by mass-guided compound isolation by taking advantage of the versatility and finely tunable selectivity offered by centrifugal partition chromatography. This biodereplication workflow was applied to an ethanolic extract of the Amazonian medicinal plant Piper coruscans Kunth (Piperaceae) showing an IC50 of 1.36 µg/mL on the 3D7 Plasmodium falciparum strain. It resulted in the isolation of twelve compounds designated as potential antiplasmodial compounds by the biodereplication workflow. Two chalcones, aurentiacin (1) and cardamonin (3), with IC50 values of 2.25 and 5.5 µM, respectively, can be considered to bear the antiplasmodial activity of the extract, with the latter not relying on a heme-binding mechanism. This biodereplication method constitutes a rapid, efficient, and robust technique to identify potential antimalarial compounds in complex extracts such as plant extracts.

Discovery of Selective Toxoplasma gondii Dihydrofolate Reductase Inhibitors for the Treatment of Toxoplasmosis

A safer treatment for toxoplasmosis would be achieved by improving the selectivity and potency of dihydrofolate reductase (DHFR) inhibitors, such as pyrimethamine (1), for Toxoplasma gondii DHFR ( TgDHFR) relative to human DHFR ( hDHFR). We previously reported on the identification of meta-biphenyl analog 2, designed by in silico modeling of key differences in the binding pocket between TgDHFR and hDHFR. Compound 2 improves TgDHFR selectivity 6.6-fold and potency 16-fold relative to 1. Here, we report on the optimization and structure-activity relationships of this arylpiperazine series leading to the discovery of 5-(4-(3-(2-methoxypyrimidin-5-yl)phenyl)piperazin-1-yl)pyrimidine-2,4-diamine 3. Compound 3 has a TgDHFR IC₅₀ of 1.57 ± 0.11 nM and a hDHFR to TgDHFR selectivity ratio of 196, making it 89-fold more potent and 16-fold more selective than 1. Compound 3 was highly effective in control of acute infection by highly virulent strains of T. gondii in the murine model, and it possesses the best combination of selectivity, potency, and prerequisite drug-like properties to advance into IND-enabling, preclinical development.

Adverse Event Profile of Pyrimethamine-Based Therapy in Toxoplasmosis: A Systematic Review

Introduction

Approximately a third of the population worldwide is chronically infected with Toxoplasma gondii. Pyrimethamine-based regimens are recommended for the treatment of toxoplasmosis.

Objective

The aim was to evaluate the safety profile of pyrimethamine-based treatment for the three main Toxoplasma manifestations: toxoplasmic encephalitis (TE), ocular toxoplasmosis, and congenital toxoplasmosis.

Methods

PubMed, Cochrane Library, and Google Scholar databases were searched through August 1, 2016. Randomized, observational, prospective/retrospective, and cohort studies were eligible. Thirty-one studies were included with a total of 2975 patients. Of these, 13 were in congenital toxoplasmosis (n = 929), 11 in ocular toxoplasmosis (n = 1284), and seven in TE (n = 687). Across manifestations, adverse event (AE)-related treatment discontinuation and/or change in therapy involved ≤37% of patients and occurred in >55% of studies: 100% for ocular toxoplasmosis, 57.1% for TE, and 61.5% for congenital toxoplasmosis. The most commonly observed AEs were bone marrow suppression, dermatologic, and gastrointestinal (GI). The prevalence of bone marrow suppression-related AEs was ≤50% in congenital toxoplasmosis, ≤42.7% in TE, and ≤9.0% in ocular toxoplasmosis. The frequency of GI and dermatologic AEs were ≤100 and ≤11.1%, respectively, for ocular toxoplasmosis, ≤10.7 and ≤17.9% for TE, and ≤10.8 and ≤2.1% for congenital toxoplasmosis. Steven–Johnson syndrome was reported in two patients with ocular toxoplasmosis and one with TE.

Conclusion

The AE profile associated with pyrimethamine-based treatments differed by each manifestation of toxoplasmosis and within a given manifestation. Hematologic AEs occurred across all manifestations indicating the importance of monitoring the blood of patients administered pyrimethamine-based regimens.

Rapid and specific drug quality testing assay for artemisinin and its derivatives using a luminescent reaction and novel microfluidic technology

Globally, it is estimated that about 10–30% of pharmaceuticals are of poor quality. Poor-quality drugs lead to long-term drug resistance, create morbidity, and strain the financial structure of the health system. The current technologies for substandard drug detection either are too expensive for low-resource regions or only provide qualitative results. To address the current limitations with point-of-care technologies, we have developed an affordable and robust assay to quantify the amount of active pharmaceutical ingredients (APIs) to test product quality. Our novel assay consists of two parts: detection reagent (probe) and a microfluidic testing platform. As antimalarials are of high importance in the global fight against malaria and are often substandard, they are chosen as the model to validate our assay. As a proof-of-concept, we have tested the assay with artesunate pure and substandard samples (Arsuamoon tablets) from Africa and compared with the conventional 96-well plate with spectrophotometer to demonstrate the quantitative efficacy and performance of our system.

Improving the role and contribution of pharmacokinetic analyses in antimalarial drug clinical trials

It is now World Health Organization (WHO) policy that drug concentrations on day 7 be measured as part of routine assessment in antimalarial drug efficacy trials. The rationale is that this single pharmacological measure serves as a simple and practical predictor of treatment outcome for antimalarial drugs with long half-lives. Herein we review theoretical data and field studies and conclude that the day 7 drug concentration (d7c) actually appears to be a poor predictor of therapeutic outcome. This poor predictive capability combined with the fact that many routine antimalarial trials will have few or no failures means that there appears to be little justification for this WHO recommendation. Pharmacological studies have a huge potential to improve antimalarial dosing, and we propose study designs that use more-focused, sophisticated, and cost-effective ways of generating these data than the mass collection of single d7c concentrations.

Measuring resistant-genotype transmission of malaria parasites: challenges and prospects

Increased gametocytemia in infections with resistant strains of Plasmodium species and their enhanced transmissibility are a matter of concern in planning and evaluating the impact of malaria control strategies. Various studies have determined weekly gametocyte carriage in response to antimalarial drugs in clinical trials. The advent of molecular biology techniques makes it easy to detect and quantify gametocytes, the stages responsible for transmission, and to detect resistant genotypes of the parasite. With the validation of molecular markers of resistance to certain antimalarial drugs, there is a need to devise a simpler formula that could be used with these epidemiological antimalarial resistance tools. Theoretical models for transmission of resistant malaria parasites are difficult to deploy in epidemiological studies. Therefore, devising a simple formula that determines the potential resistant-genotype transmission of malaria parasites should provide further insights into understanding the spread of drug resistance. The present perspective discusses gametocytogenesis in the context of antimalarial treatment and drug resistance. It also highlights the difficulties in applying the available theoretical models of drug resistance transmission and suggests Rashad's devised formula that could perhaps be used in determining potentially transmissible resistant genotypes as well as in mapping areas with high potential risk for the transmission of drug-resistant malaria. The suggested formula makes use of the data on gametocytes and resistant genotypes of malaria parasites, detected by molecular techniques in a certain geographical area within a particular point in time, to calculate the potential risk of resistant genotype transmission.

High prevalence of mutation in the Plasmodium falciparum dhfr and dhps genes in field isolates from Sabah, Northern Borneo

Background

Sulphadoxine-pyrimethamine (SP) has been in use for the treatment of uncomplicated falciparum malaria in Malaysia since the 1970s and is still widely employed in spite of widespread clinical resistance. Resistance to SP is known to be mediated by mutations in the pfdhfr and pfdhps genes. The aim of the present study was to investigate the distribution of pfdhfr and pfdhps gene polymorphism in Plasmodium falciparum field isolates from Kalabakan, Sabah, in northern Borneo.

Methods

A total number of 619 individuals were screened from 23 study sites of which 31 were positive for P. falciparum. Analysis of restriction fragment length polymorphisms (RFLP) was used to identify polymorphism in the pfdhfr and pfdhps genes at positions 16, 51, 59, 108, 164 and 437, 540, 581, respectively.

Results

All samples had at least one mutation in each of the genes associated with drug resistance. The prevalence of pfdhfr 59arg, 164leu and 108asn were 100%, 80.65% and 58.06%, respectively. Pfdhps mutants 437gly and 581gly accounted for 100% and 74.19% respectively. In pfdhfr, the most common mutant genotypes were combination 59arg + 164leu (22.58%) and 59arg + 108asn + 164leu (51.61%). In pfdhps the most common genotype was 437gly + 581gly (74.19%). One individual (3.22%) harboured parasites with four pfdhfr (16 val + 59arg + 108asn + 164leu) and two pfdhps (437gly + 581gly) mutations. The highest quintuple pfdhfr/pfdhps (41.94%) was three pfdhfr (59arg + 108asn + 164gly) and two pfdhps (437gly + 581gly).

Conclusion

The data suggest a high prevalence of genetic variations conferring resistance to SP which can predict treatment failure before becoming clinically evident. In areas like this, the use of SP may no longer be indicated.

A qualitative study exploring perspectives towards rational use of medicines in Pakistan's Malaria Control Program (MCP)

Malaria is one of the most important global public health problems threatening the health of the population owing to prevailing socio-economic conditions and epidemiological reasons in Pakistan. This qualitative study has focused on the perspectives held towards the rational use of medicine intervention among malaria control program officials. Eight semi-structured interviews with all officials working for the malaria control program in Islamabad were conducted. The interviews, which were audio-taped and transcribed verbatim, were evaluated by thematic content analysis and by all authors. All respondents agreed on successful implementation of the malaria control program in Pakistan for controlling malaria by improving diagnostic and treatment facilities and promoting rational case management through training of prescribers. However, funding is still the major challenge faced by the program for its future implementation.

Mutation analysis in pfmdr1 and pfmrp1 as potential candidate genes for artemisinin resistance in Plasmodium falciparum clinical isolates 4years after implementation of artemisinin combination therapy in Iran

The emergence and spread of Plasmodium falciparum resistant to the commonly used anti-malarial drugs is a major challenge in the control and elimination of malaria. The present study provides information on genetic analysis in multidrug resistance 1 (pfmdr1) (N86Y/Y184F/S1034C/N1042D/F1226Y/D1246Y) and multidrug resistance protein 1 (pfmrp1) (H191Y/S437A/I876V/F1390I/K1466R) genes that are probably associated with artemisinin as well as chloroquine resistance transporter (pfcrt) 76T in P. falciparum clinical isolates (N=200) exposed to artemisinin-based combination therapy (ACT) 4years after its adoption in Iran. Also, the copy number of pfmdr1 gene was screened for its association with pfmdr1 mutations to incriminate artemisinin resistance. By using nested PCR-RFLP and sequencing analysis, none of the samples had any mutation at codons 1034, 1042, 1226 and 1246 of pfmdr1, while 86Y and 184F mutations were detected in 46% and 2% of the examined samples, respectively. Also, no significant difference was identified among analyzed samples collected before (baseline, 2002-2005) and after adoption of ACT (2007-2010) (P>0.05). As with pfmrp1 gene, the mutations at positions 191Y (76.5%), 437A (69.5%), 876V (64.5%) and 1390I (17%) were detected and no samples displayed mutation at codon 1466R. In total, 42.5% of the examined isolates carried both pfmdr1 86Y and pfcrt 76T and none of the parasites simultaneously harbored pfcrt 76T, pfmdr1 86Y, 184F and pfmrp1 191Y, 437A, 876V, 1390I mutations. In addition, the copy number of pfmdr1 gene (N = 1) was similar as a sensitive isolate, 3D7, to artemisinin. In summary, none of the potential mutations associated with artemisinin and its derivatives resistance was significantly changed 4years after adoption of ACT in Iran.

Isoprenoid biosynthesis inhibition disrupts Rab5 localization and food vacuolar integrity in Plasmodium falciparum

The antimalarial agent fosmidomycin is a validated inhibitor of the nonmevalonate isoprenoid biosynthesis (methylerythritol 4-phosphate [MEP]) pathway in the malaria parasite, Plasmodium falciparum. Since multiple classes of prenyltransferase inhibitors kill P. falciparum, we hypothesized that protein prenylation was one of the essential functions of this pathway. We found that MEP pathway inhibition with fosmidomycin reduces protein prenylation, confirming that de novo isoprenoid biosynthesis produces the isoprenyl substrates for protein prenylation. One important group of prenylated proteins is small GTPases, such as Rab family members, which mediate cellular vesicular trafficking. We have found that Rab5 proteins dramatically mislocalize upon fosmidomycin treatment, consistent with a loss of protein prenylation. Fosmidomycin treatment caused marked defects in food vacuolar morphology and integrity, consistent with a defect in Rab-mediated vesicular trafficking. These results provide insights to the biological functions of isoprenoids in malaria parasites and may assist the rational selection of secondary agents that will be useful in combination therapy with new isoprenoid biosynthesis inhibitors.

Recent advances and perspectives on tropical diseases: Malaria

Malaria remains a major health problem in the world. It is a neglected disease because it occurs almost exclusively in poor developing countries, which offer negligible marketable and profitable opportunities. Malaria (together with Tuberculosis), is responsible for an unprecedented global health crisis with devastating effects in developing countries. The 2011 Word Malaria Report indicated that 106 countries showed endemic malaria. Malaria control depends mainly on drug treatment, which is increasingly difficult due to the spread of drug resistant parasites and requires expensive drug combinations. Part of the inability to combat this disease is attributed to an incomplete understanding of its pathogenesis and pathophysiology. Improving the knowledge of the underlying pathogenic mechanisms of malaria transmission and of the exclusive metabolic pathways of the parasites (protozoa of the genus Plasmodium), should promote efficient treatment of disease and help the identification of novel targets for potential therapeutic interventions. Moreover, the elucidation of determinants involved in the spread of malaria will provide important information for efficient planning of strategies for targeted control.

Lead optimization of antimalarial propafenone analogues

Previously reported studies identified analogues of propafenone that had potent antimalarial activity, reduced cardiac ion channel activity, and properties that suggested the potential for clinical development for malaria. Careful examination of the bioavailability, pharmacokinetics, toxicology, and efficacy of this series of compounds using rodent models revealed orally bioavailable compounds that are nontoxic and suppress parasitemia in vivo. Although these compounds possess potential for further preclinical development, they also carry some significant challenges.

Development of a TaqMan Allelic Discrimination assay for detection of single nucleotides polymorphisms associated with anti-malarial drug resistance

Background

Anti-malarial drug resistance poses a threat to current global efforts towards control and elimination of malaria. Several methods are used in monitoring anti-malarial drug resistance. Molecular markers such as single nucleotide polymorphism (SNP) for example are increasingly being used to identify genetic mutations related to anti-malarial drug resistance. Several methods are currently being used in analysis of SNP associated with anti-malarial drug resistance and although each one of these methods has unique strengths and shortcoming, there is still need to improve and/or develop new methods that will close the gap found in the current methods.

Methods

TaqMan Allelic Discrimination assays for detection of SNPs associated with anti-malarial drug resistance were designed for analysis on Applied Biosystems PCR platform. These assays were designed by submitting SNP sequences associated with anti-malarial drug resistance to Applied Biosystems website. Eleven SNPs associated with resistance to anti-malarial drugs were selected and tested. The performance of each SNP assay was tested by creating plasmid DNAs carrying codons of interests and analysing them for analysis. To test the sensitivity and specificity of each SNP assay, 12 clinical samples were sequenced at codons of interest and used in the analysis. Plasmid DNAs were used to establish the Limit of Detection (LoD) for each assay.

Results

Data from genetic profiles of the Plasmodium falciparum laboratory strains and sequence data from 12 clinical samples was used as the reference method with which the performance of the SNP assays were compared to. The sensitivity and specificity of each SNP assay was establish at 100%. LoD for each assay was established at 2 GE, equivalent to less than 1 parasite/μL. SNP assays performed well in detecting mixed infection and analysis of clinical samples.

Conclusion

TaqMan Allelic Discrimination assay provides a good alternative tool in detection of SNPs associated with anti-malarial drug.

Molecular monitoring of Plasmodium falciparum resistance to antimalarial drugs after adoption of sulfadoxine-pyrimethamine plus artesunate as the first line treatment in Iran

The main objective of this investigation was whether the combination therapy of sulfadoxine pyrimethamine (SP) plus artesunate (AS) protects against the spread of resistance to SP in malaria-endemic south-eastern Iran. Infected blood samples of Plasmodium falciparum (n=170) were collected during 2008-2010 after the adoption of SP-AS as the first line treatment in Iran. Four different genes of P. falciparum [dihydropteroate synthetase (pfdhps), dihydrofolate reductase (pfdhfr), chloroquine (CQ) resistance transporter (pfcrt K76T) and multidrug resistance1 (pfmdr1 N86Y)], associated with SP and CQ resistance were analyzed using PCR-RFLP methods. The result showed 4.1, 95.9 and 100% prevalence of pfdhfr 51I, 59R and 108N, respectively and the majority of patients (95.9%) were found to carry both 59R and 108N. The prevalence of single mutation at pfdhps 437G gene was 26.9% before the adoption of SP-AS, but as SP was used as the first line treatment; this mutation started to increase and reached a high level of 55.5% in 2008 (χ(2) test, P<0.05). However, three years after the introduction of SP-AS, this prevalence was reduced from 55.5% (in 2008) to 39.1% (in 2009) and then 40.5% (in 2010). The frequency of parasites carrying pfdhfr/pfdhps mutations (N(51)R(59)N(108)/G(437)) decreased from 53.3% in 2008 to 39.1% in 2009 and 38% in 2010. In addition, no significant reduction was seen in the frequency of mutant alleles of pfcrt 76T and pfmdr1 86Y after CQ was discontinued from study areas as a treatment for P. falciparum. This is explained by the fixation of pfcrt 76T in the falciparum populations that need more time to recover from CQ sensitivity in the absence of drug pressure in this region. In conclusion, the present findings suggest that in Iran, SP is still effective for the treatment of uncomplicated falciparum malaria as a partner drug of Artemisinin Combination Therapy (ACT) in this region.

Optimization of propafenone analogues as antimalarial leads

Propafenone, a class Ic antiarrythmic drug, inhibits growth of cultured Plasmodium falciparum. While the drug's potency is significant, further development of propafenone as an antimalarial would require divorcing the antimalarial and cardiac activities as well as improving the pharmacokinetic profile of the drug. A small array of propafenone analogues was designed and synthesized to address the cardiac ion channel and PK liabilities. Testing of this array revealed potent inhibitors of the 3D7 (drug sensitive) and K1 (drug resistant) strains of P. falciparum that possessed significantly reduced ion channel effects and improved metabolic stability. Propafenone analogues are unusual among antimalarial leads in that they are more potent against the multidrug resistant K1 strain of P. falciparum compared to the 3D7 strain.

Pattern of the Antimalarials Prescription during Pregnancy in Bangui, Central African Republic

Introduction. The aim of this study was to identify the antimalarials prescribed during the pregnancy and to document their timing. Method. From June to September 2009, a survey was conducted on 565 women who gave birth in the Castors maternity in Bangui. The antenatal clinics cards were checked in order to record the types of antimalarials prescribed during pregnancy according to gestational age. Results. A proportion of 28.8% ANC cards contained at least one antimalarial prescription. The commonest categories of antimalarials prescribed were: quinine (56.7%), artemisinin-based combinations (26.8%) and artemisinin monotherapy (14.4%). Among the prescriptions that occurred in the first trimester of pregnancy, artemisinin-based combinations and artemisinin monotherapies represented the proportions of (10.9%) and (13.3%). respectively. Conclusion. This study showed a relatively high rate (>80%) of the recommended antimalarials prescription regarding categories of indicated antimalarials from national guidelines. But, there is a concern about the prescription of the artemisinin derivatives in the first trimester of pregnancy, and the prescription of artemisinin monotherapy. Thus, the reinforcement of awareness activities of health care providers on the national malaria treatment during pregnancy is suggested.

Binding modes of 2,4-diaminoquinazoline and 2,4-diaminopteridine analogs to P. falciparum dihydrofolate reductase enzyme: Molecular docking studies

A molecular docking study was carried out on 28 compounds belonging to 2,4-diaminoquinazoline and 2,4-diaminopteridine analogs using Glide, FlexX and GOLD programs and the X-ray crystallographic structures of the quadruple mutant (1J3K:pdb) and wild type (1J3I:pdb) Plasmodium falciparum dihydrofolate reductase enzyme. The experimental conformation the bound ligand WR99210 was precisely reproduced by the docking procedures as demonstrated by low (<2.00 Å) root-mean-square deviations. The results indicated that most of the compounds dock into the active sites of both the wild type and quadruple mutant P. falciparum dihydrofolate reductase enzymes. Visual inspection of the binding modes also demonstrated that most of the compounds could form H-bond interactions with the key amino acid residues (Asp54, Ile14 and Leu/Ile164) and with better docking scores than the bound compound (5). Their long side chains orient in the hydrophobic portion of the active site which is occupied by trichloro aryloxy side chain of WR99210 (5). Thus, avoid potential steric clashes with Asn108 (mutated from Ser108). Such a clash is known to be responsible for the resistance of the P. falciparum to pyrimethamine and cycloguanil.

ogaraK: a population genetics simulator for malaria

MOTIVATION

The evolution of resistance in Plasmodium falciparum malaria against most available treatments is a major global health threat. Population genetics approaches are commonly used to model the spread of drug resistance. Due to uncommon features in malaria biology, existing forward-time population genetics simulators cannot suitably model Plasmodium falciparum malaria.

RESULTS

Here we present ogaraK, a population genetics simulator for modelling the spread of drug-resistant malaria. OgaraK is designed to make malaria simulation computationally tractable as it models infections, not individual parasites. OgaraK is also able to model the life cycle of the parasite which includes both haploid and diploid phases and sexual and asexual reproduction. We also allow for the simulation of different inbreeding levels, an important difference between high and low transmission areas and a fundamental factor influencing the outcome of strategies to control or eliminate malaria.

AVAILABILITY

OgaraK is available as free software (GPL) from the address http://popgen.eu/soft/ogaraK.

Genetic polymorphism in pvmdr1 and pvcrt-o genes in relation to in vitro drug susceptibility of Plasmodium vivax isolates from malaria-endemic countries

Treatment failure of chloroquine for Plasmodium vivax infection has increased in endemic countries. However, the molecular mechanisms for resistance and in vitro susceptibility of P. vivax to chloroquine remain elusive. We investigated the prevalence of mutations in the pvmdr1 and pvcrt-o genes, and the copy number of the pvmdr1 gene in isolates from the Republic of Korea (ROK), Thailand, the Union of Myanmar (Myanmar), and Papua New Guinea (PNG). We also measured in vitro susceptibility of Korean isolates to antimalarial drugs. The pvmdr1 analysis showed that mutations at amino acid position Y976F of pvmdr1 were found in isolates from Thailand (17.9%), Myanmar (13.3%), and PNG (100%), but none from the ROK, and mutation at position F1076L was present in isolates from the ROK (100%), Thailand (60.7%), and Myanmar (46.7%). One copy of the pvmdr1 gene was observed in most isolates and double copy numbers of the gene were observed in two Thai isolates. In the exons of the pvcrt-o gene that were sequenced, a K10 insertion was present in isolates from Thailand (56.0%) and Myanmar (46.2%), and the wild type was found in all Korean isolates. The results suggest that gene polymorphisms and copy number variation was observed in isolates of P. vivax from Southeast Asian countries. In Korean isolates polymorphism as limited to the F1076L variant, and no isolates with high level of resistance were found by in vitro susceptibility determinations. Moreover, our results provide a baseline for future prospective drug studies in malaria-endemic areas.

Environmental, pharmacological and genetic influences on the spread of drug-resistant malaria

Plasmodium falciparum malaria is subject to artificial selection from antimalarial drugs that select for drug-resistant parasites. We describe and apply a flexible new approach to investigate how epistasis, inbreeding, selection heterogeneity and multiple simultaneous drug deployments interact to influence the spread of drug-resistant malaria. This framework recognizes that different human 'environments' within which treatment may occur (such as semi- and non-immune humans taking full or partial drug courses) influence the genetic interactions between parasite loci involved in resistance. Our model provides an explanation for how the rate of spread varies according to different malaria transmission intensities, why resistance might stabilize at intermediate frequencies and also identifies several factors that influence the decline of resistance after a drug is removed. Results suggest that studies based on clinical outcomes might overestimate the spread of resistant parasites, especially in high-transmission areas. We show that when transmission decreases, prevalence might decrease without a corresponding change in frequency of resistance and that this relationship is heavily influenced by the extent of linkage disequilibrium between loci. This has important consequences on the interpretation of data from areas where control is being successful and suggests that reducing transmission might have less impact on the spread of resistance than previously expected.

Activity of the histone deacetylase inhibitor FR235222 on Toxoplasma gondii: inhibition of stage conversion of the parasite cyst form and study of new derivative compounds

Bradyzoite-to-tachyzoite conversion plays a role in the pathogenesis of recrudescence of ocular toxoplasmosis and disease in immunocompromised persons. The currently available medicines are ineffective on cysts and fail to prevent reactivation of latent toxoplasmosis. A previous study showed that the histone deacetylase inhibitor FR235222 has a dramatic effect on tachyzoite growth and induces tachyzoite-to-bradyzoite conversion in vitro. The present study shows that FR235222 can target in vitro-converted cysts and bradyzoites. Moreover, the compound is active on ex vivo T. gondii cysts. Free bradyzoites isolated after lysis of the cell wall did not proliferate in vitro when the cyst was treated with FR235222. The results imply that this compound is able to cross the T. gondii cystic cell wall. Fluorescent labeling shows that the compound impairs the capacity of the bradyzoites to convert without damaging the cyst wall integrity. In vivo inoculation of formerly treated cysts fails to infect mice when these cysts were treated with FR235222. We used our structural knowledge of FR235222 and its target, T. gondii HDAC3, to synthesize new FR235222 derivative compounds. We identified two new molecules that are highly active against tachyzoites. They harbor a better selectivity index that is more suitable for a future in vivo approach. These results identify FR235222 and its derivatives as new lead compounds in the range of therapeutics available for acute and chronic toxoplasmosis.

In vitro sensitivity of Plasmodium falciparum clinical isolates from the China-Myanmar border area to quinine and association with polymorphism in the Na+/H+ exchanger

Quinine resistance (QNR) in Plasmodium falciparum has been detected in many regions of the world where malaria is endemic. Genetic polymorphisms in at least four genes are implicated in QN susceptibility, and their significance often depends on the genetic background of the parasites. In this study, we have culture-adapted 60 P. falciparum clinical isolates from the China-Myanmar border and assessed their in vitro responses to QN. Our results showed that >50% of the parasite isolates displayed reduced sensitivity to QN, with a half-maximal inhibitory concentration (IC(50)) above 500 nM. Genotyping of pfcrt found that an overwhelming proportion of the parasite population had the chloroquine-resistant genotype, whereas pfmdr1 mutation genotypes and gene amplification were rare. Genotyping of the P. falciparum Na(+)/H(+) exchanger gene (pfnhe1) at the minisatellite ms4760 locus identified 10 haplotypes. Haplotype 7, which harbors three copies of the DNNND repeat, was the most predominant, accounting for nearly half of the parasite isolates. Correlation studies did not reveal significant associations of the polymorphisms in pfcrt and pfmdr1 genes with QN response. However, the ms4760 haplotypes were highly associated with in vitro QN responses. In particular, parasite isolates with an increased DNNND copy number tended to have significantly reduced QN susceptibility, whereas parasite isolates with a higher NHNDNHNNDDD copy number had increased QN susceptibility. This study provided further support for the importance of pfnhe1 polymorphisms in influencing QNR in P. falciparum.

Early transcriptional response to chloroquine of the Plasmodium falciparum antioxidant defence in sensitive and resistant clones

Resistance to chloroquine (CQ) in Plasmodium falciparum has a major impact on malaria control worldwide. To gain insight into early parasite stress response, mRNA expression profiles were determined for a set of 10 antioxidant defence genes in synchronized CQ-sensitive (3D7) and CQ-resistant (Dd2) clones under transient IC50 CQ-exposure (Dd2, 200 nM; 3D7, 14 nM). Upon 2-h CQ challenge, the mRNA upregulation detected was greater in 3D7 (six genes overexpressed at 1/3 of the intraerythrocytic cycle) than in Dd2 clone (three genes responding), providing evidence of an early transcriptional response to CQ-induced oxidative stress which might underlie some of the parasite's metabolic adaptation to the drug.

Availability of antimalarial drugs and evaluation of the attitude and practices for the treatment of uncomplicated malaria in bangui, central african republic

National malaria management policy is based upon the availability of effective and affordable antimalarial drugs. This study was undertaken to evaluate the quality of the treatment of uncomplicated malaria cases in Bangui, an area with multidrug-resistant parasites, at a time preceding implementation of a new therapeutic policy relying on the artemisinin derivative combined treatment artemether-lumefantrine. A cross-sectional study was carried out in Bangui city to assess availability of antimalarial drugs and the performances of health workers in the management of uncomplicated malaria. Availability of drugs was recorded in all drugs wholesalers (n = 3), all pharmacies in health facilities (n = 14), private drugstores (n = 15), and in 60 non-official drug shops randomly chosen in the city. Despite a limited efficacy at the time of the survey, chloroquine remained widely available in the official and nonofficial markets. Artemisinin derivatives used in monotherapy or in combination were commonly sold. In health care facilities, 93% of the uncomplicated malaria cases were treated in the absence of any laboratory confirmation and the officially recommended treatment, amodiaquine-sulfadoxine/pyrimethamine, was seldom prescribed. Thus, the national guidelines for the treatment of uncomplicated malaria are not followed by health professionals in Bangui. Its use should be implemented while a control of importation of drug has to be reinforced.

A Plasmodium falciparum transcriptional cyclin-dependent kinase-related kinase with a crucial role in parasite proliferation associates with histone deacetylase activity

Cyclin-dependent protein kinases (CDKs) are key regulators of the eukaryotic cell cycle and of the eukaryotic transcription machinery. Here we report the characterization of Pfcrk-3 (Plasmodium falciparum CDK-related kinase 3; PlasmoDB identifier PFD0740w), an unusually large CDK-related protein whose kinase domain displays maximal homology to those CDKs which, in other eukaryotes, are involved in the control of transcription. The closest enzyme in Saccharomyces cerevisiae is BUR1 (bypass upstream activating sequence requirement 1), known to control gene expression through interaction with chromatin modification enzymes. Consistent with this, immunofluorescence data show that Pfcrk-3 colocalizes with histones. We show that recombinant Pfcrk-3 associates with histone H1 kinase activity in parasite extracts and that this association is detectable even if the catalytic domain of Pfcrk-3 is rendered inactive by site-directed mutagenesis, indicating that Pfcrk-3 is part of a complex that includes other protein kinases. Immunoprecipitates obtained from extracts of transgenic parasites expressing hemagglutinin (HA)-tagged Pfcrk-3 by using an anti-HA antibody displayed both protein kinase and histone deacetylase activities. Reverse genetics data show that the pfcrk-3 locus can be targeted only if the genetic modification does not cause a loss of function. Taken together, our data strongly suggest that Pfcrk-3 fulfils a crucial role in the intraerythrocytic development of P. falciparum, presumably through chromatin modification-dependent regulation of gene expression.

Plasmodium falciparum resistance to anti-malarial drugs in Papua New Guinea: evaluation of a community-based approach for the molecular monitoring of resistance

Background

Molecular monitoring of parasite resistance has become an important complementary tool in establishing rational anti-malarial drug policies. Community surveys provide a representative sample of the parasite population and can be carried out more rapidly than accrual of samples from clinical cases, but it is not known whether the frequencies of genetic resistance markers in clinical cases differ from those in the overall population, or whether such community surveys can provide good predictions of treatment failure rates.

Methods

Between 2003 and 2005, in vivo drug efficacy of amodiaquine or chloroquine plus sulphadoxine-pyrimethamine was determined at three sites in Papua New Guinea. The genetic drug resistance profile (i.e., 33 single nucleotide polymorphisms in Plasmodium falciparum crt, mdr1, dhfr, dhps, and ATPase6) was concurrently assessed in 639 community samples collected in the catchment areas of the respective health facilities by using a DNA microarray-based method. Mutant allele and haplotype frequencies were determined and their relationship with treatment failure rates at each site in each year was investigated.

Results

PCR-corrected in vivo treatment failure rates were between 12% and 28% and varied by site and year with variable longitudinal trends. In the community samples, the frequencies of mutations in pfcrt and pfmdr1 were high and did not show significant changes over time. Mutant allele frequencies in pfdhfr were moderate and those in pfdhps were low. No mutations were detected in pfATPase6. There was much more variation between sites than temporal, within-site, variation in allele and haplotype frequencies. This variation did not correlate well with treatment failure rates. Allele and haplotype frequencies were very similar in clinical and community samples from the same site.

Conclusions

The relationship between parasite genetics and in vivo treatment failure rate is not straightforward. The frequencies of genetic anti-malarial resistance markers appear to be very similar in community and clinical samples, but cannot be used to make precise predictions of clinical outcome. Thus, indicators based on molecular data have to be considered with caution and interpreted in the local context, especially with regard to prior drug usage and level of pre-existing immunity. Testing community samples for molecular drug resistance markers is a complementary tool that should help decision-making for the best treatment options and appropriate potential alternatives.

Discovery, mechanisms of action and combination therapy of artemisinin

Despite great international efforts, malaria still inflicts an enormous toll on human lives, especially in Africa. Throughout history, antimalarial medicines have been one of the most powerful tools in malaria control. However, the acquisition and spread of parasite strains that are resistant to multiple antimalarial drugs have become one of the greatest challenges to malaria treatment, and are associated with the increase in morbidity and mortality in many malaria-endemic countries. To deal with this grave situation, artemisinin-based combinatory therapies (ACTs) have been introduced and widely deployed in malarious regions. Artemisinin is a new class of antimalarial compounds discovered by Chinese scientists from the sweet wormwood Artemisia annua. The potential development of resistance to artemisinins by Plasmodium falciparum threatens the usable lifespan of ACTs, and therefore is a subject of close surveillance and extensive research. Studies at the Thai-Cambodian border, a historical epicenter of multidrug resistance, have detected reduced susceptibility to artemisinins as manifested by prolonged parasite-clearance times, raising considerable concerns on resistance development. Despite this significance, there is still controversy on the mode of action of artemisinins. Although a number of potential cellular targets of artemisinins have been proposed, they remain to be verified experimentally. Here, we review the history of artemisinin discovery, discuss the mode of action and potential drug targets, and present strategies to elucidate resistance mechanisms.

Rapid detection of point mutations in Plasmodium falciparum genes associated with antimalarial drugs resistance by using High-Resolution Melting analysis

We have developed a High-Resolution DNA Melting method to detect mutations related to Plasmodium falciparum resistance. This method is based on real-time PCR followed by High Resolution Melting ramping from 67 degrees C to 80 degrees C with fluorescence data acquisition set at 0.1 degrees C increments. The accuracy of the technique was assessed using 177 P. falciparum clinical isolates and two reference strains. Results perfectly matched those obtained by DNA sequencing for some important genetic markers of P. falciparum resistance. This technique could be of great value for epidemiological studies, especially in developing countries.

Antimicrobial resistance: international control strategies, with a focus on limited-resource settings

Microorganisms resistant to multiple anti-infective agents have increased worldwide. These organisms threaten both optimal care of patients with infection as well as the viability of current healthcare systems. In addition, antimicrobials are valuable resources that enhance both prevention and treatment of infections. As resistance diminishes this resource, it is a societal goal to minimise resistance and therefore to reduce forces that produce resistance. This review considers strategies for minimising resistance that are needed at several different levels of responsibility, ranging from the patient care provider to international agencies. It then describes responses that might be appropriate according to the resources available for control, focusing on limited-resource settings. Antimicrobial resistance represents an international concern. Response to this problem demands concerted efforts from multiple sectors both in developed and developing countries, as well as the strengthening of multinational/international partnerships and regulations. Both medical and public health agencies should be in the forefront of these efforts.

Disruption of the PfPK7 gene impairs schizogony and sporogony in the human malaria parasite Plasmodium falciparum

PfPK7 is an orphan protein kinase of Plasmodium falciparum with maximal homology to MEK3/6 and to fungal protein kinase A proteins in its C-terminal and N-terminal regions, respectively. We showed previously that recombinant PfPK7 is active on various substrates but is unable to phosphorylate the Plasmodium falciparum mitogen-activated protein kinase homologues, suggesting that it is not a MEK functional homologue. Using a reverse genetics approach to investigate the function of this enzyme in live parasites, we now show that PfPK7(-) parasite clones display phenotypes at two stages of their life cycle: first, a decrease in the rate of asexual growth in erythrocytes associated with a lower number of daughter merozoites generated per schizont, and second, a dramatic reduction in the ability to produce oocysts in the mosquito vector. A normal asexual growth rate and the ability to produce oocysts are restored if a functional copy of the PfPK7 gene is reintroduced into the PfPK7(-) parasites. Hence, PfPK7 is involved in a pathway that regulates parasite proliferation and development.

Molecular analysis of chloroquine resistance in Plasmodium falciparum in Yunnan Province, China

Resistance of Plasmodium falciparum to chloroquine (CQ) is determined by the mutation at K76T of the P. falciparum chloroquine resistance transporter (pfcrt) gene and modified by other mutations in this gene and in the P. falciparum multidrug resistance 1 (pfmdr1) gene. To determine the extent of polymorphisms in these genes in field P. falciparum isolates from Yunnan province of China, we genotyped the pfcrt codon 76, pfmdr1 codons 86 and 1246. Our results showed that although CQ has been withdrawn from treating falciparum malaria for over two decades, 90.3% of the parasites still carried the pfcrt K76T mutation. In contrast, mutations at pfmdr1 codons 86 and 1246 were rare. Sequencing analysis of the pfcrt gene in 34 parasite field isolates revealed CVIET at positions 72-76 as the major type, consistent with the theory of Southeast Asian origin of CQ resistance in the parasite. In addition, two novel pfcrt haplotypes (75D/144Y/220A and 75E/144Y/220A) were identified. Real-time polymerase chain reaction was used to determine pfmdr1 gene amplification, which is associated with mefloquine resistance. Our result indicated that in agreement with that mefloquine has not been used in this area, most (>90%) of the parasites had one pfmdr1 copy. Genotyping at two hypervariable loci showed relatively low levels of genetic diversity of the parasite population. Meanwhile, 28.4% of cases were found to contain mixed clones, which favour genetic recombination. Furthermore, despite a unique history of antimalarial drugs in Yunnan, its geographical connections with three malarious countries facilitate gene flow among parasite populations and evolution of novel drug-resistant genotypes. Therefore, continuous surveillance of drug resistance in this area is necessary for timely adjustment of local drug policies and more effective malaria control.

Rapid microarray-based method for monitoring of all currently known single-nucleotide polymorphisms associated with parasite resistance to antimalaria drugs

Parasite drug resistance is partly conferred by single-nucleotide polymorphisms (SNPs), and monitoring them has been proposed as an alternative to monitoring drug resistance. Therefore, techniques are required to facilitate analyses of multiple SNPs on an epidemiological scale. We report a rapid and affordable microarray technique for application in epidemiological studies of malaria drug resistance. We have designed a multiwell microarray that is used in conjunction with PCR-amplified target genes implicated in the drug resistance of malaria with subsequent one-tube minisequencing using two fluorochromes. The drug-resistance-associated genes pfdhfr, pfdhps, pfcrt, pfmdr1, and pfATPase were amplified and analyzed for cultured Plasmodium falciparum strains and from field samples. We obtained a specificity of 94%, and comparison of field sample results to those of restriction fragment length polymorphism (RFLP) typing resulted in an overall consistency of >90%, except for pfdhfr51, for which most discrepancies were due to false determinations by RFLP of mixed infections. The system is sufficiently sensitive to assay parasites in clinical malaria cases and in most asymptomatic cases, and it allows high throughput with minimal hands-on time. The cost for the assay has been calculated as 0.27 euros/SNP (US $0.33), which is below the cost incurred with other systems. Due to the simplicity of the approach, newly identified SNPs can be incorporated rapidly. Such a monitoring system also makes it possible to identify the reemergence of drug-susceptible parasites once a drug has been withdrawn.

Efficacy, pharmacokinetics, and metabolism of tetrahydroquinoline inhibitors of Plasmodium falciparum protein farnesyltransferase

New antimalarials are urgently needed. We have shown that tetrahydroquinoline (THQ) protein farnesyltransferase (PFT) inhibitors (PFTIs) are effective against the Plasmodium falciparum PFT and are effective at killing P. falciparum in vitro. Previously described THQ PFTIs had limitations of poor oral bioavailability and rapid clearance from the circulation of rodents. In this paper, we validate both the Caco-2 cell permeability model for predicting THQ intestinal absorption and the in vitro liver microsome model for predicting THQ clearance in vivo. Incremental improvements in efficacy, oral absorption, and clearance rate were monitored by in vitro tests; and these tests were followed up with in vivo absorption, distribution, metabolism, and excretion studies. One compound, PB-93, achieved cure when it was given orally to P. berghei-infected rats every 8 h for a total of 72 h. However, PB-93 was rapidly cleared, and dosing every 12 h failed to cure the rats. Thus, the in vivo results corroborate the in vitro pharmacodynamics and demonstrate that 72 h of continuous high-level exposure to PFTIs is necessary to kill plasmodia. The metabolism of PB-93 was demonstrated by a novel technique that relied on double labeling with a radiolabel and heavy isotopes combined with radiometric liquid chromatography and mass spectrometry. The major liver microsome metabolite of PB-93 has the PFT Zn-binding N-methyl-imidazole removed; this metabolite is inactive in blocking PFT function. By solving the X-ray crystal structure of PB-93 bound to rat PFT, a model of PB-93 bound to malarial PFT was constructed. This model suggests areas of the THQ PFTIs that can be modified to retain efficacy and protect the Zn-binding N-methyl-imidazole from dealkylation.

High antiplasmodial activity of novel plasmepsins I and II inhibitors

The aim of this study was to develop new antiplasmodial compounds acting through distinct mechanisms during both the liver and the blood stages of the parasite life cycle. Compounds were designed on the basis of the "double-drug" approach: primaquine, which has been linked to statine-based inhibitors of plasmepsins (PLMs), the plasmodial aspartic proteases involved in degradation of hemeoglobin. The compounds were tested in vitro for anti-PLM I/PLM II activities and against chloroquine-sensitive (D10) and chloroquine-resistant (W2) strains of P. falciparum. An antiplasmodial activity (IC(50)) as low as 0.1 microM was obtained, an excellent improvement in comparison with inhibitors previously reported (IC(50) = 2-20 microM). The killing activity was equally directed against both P. falciparum strains and was correlated to lipophilicity (calculated as ALogP), for all compounds but one (9). All compounds inhibited PLM I and PLM II in the nanomolar range (K(i) = 1-700 nM). The most promising compounds (2, 6, 10) were not cytotoxic against human fibroblasts at 100 microM and were highly selective for PLMs vs human cathepsin D.

Trioxaquines are new antimalarial agents active on all erythrocytic forms, including gametocytes

Malaria is the third most significant cause of infectious disease in the world. The search for new antimalarial chemotherapy has become increasingly urgent due to parasite resistance to classical drugs. Trioxaquines are synthetic hybrid molecules containing a trioxane motif (which is responsible for the antimalarial activity of artemisinin) linked to an aminoquinoline entity (which is responsible for the antiplasmodial properties of chloroquine). These trioxaquines are highly potent against young erythrocytic stages of Plasmodium falciparum and exhibit efficient activity in vitro against chloroquine-sensitive and -resistant strains of P. falciparum (50% inhibitory concentration, 4 to 32 nM) and are also active in vivo against P. vinckei petteri and P. yoelii nigeriensis in suppressive and curative murine tests. The trioxaquine DU1302 is one of these promising antimalarial agents. The present study confirms the absence of toxicity of this drug on cell lines and in a mice model. Moreover, DU1302 exhibits potent activity against gametocytes, the form transmitted by mosquitoes, as killing of the gametocytes is essential to limit the spread of malaria. The ease of chemical synthesis of this trioxaquine prototype should be considered an additional advantage and would make these drugs affordable without perturbations of the drug supply.

Host–parasite interactions for virulence and resistance in a malaria model system

A rich body of theory on the evolution of virulence (disease severity) attempts to predict the conditions that cause parasites to harm their hosts, and a central assumption to many of these models is that the relative virulence of pathogen strains is stable across a range of host types. In contrast, a largely nonoverlapping body of theory on coevolution assumes that the fitness effects of parasites on hosts is not stable across host genotype, but instead depends on host genotype by parasite genotype interactions. If such genetic interactions largely determine virulence, it becomes difficult to predict the strength and direction of selection on virulence. In this study, we tested for host-by-parasite interactions in a medically relevant vertebrate disease model: the rodent malaria parasite Plasmodium chabaudi in laboratory mice. We found that parasite and particularly host main effects explained most of the variance in virulence (anaemia and weight loss), resistance (parasite burden) and transmission potential. Host-by-parasite interactions were of limited influence, but nevertheless had significant effects. This raises the possibility that host heterogeneity may affect the rate of any parasite response to selection on virulence. This study of rodent malaria is one of the first tests for host-by-parasite interactions in any vertebrate disease; host-by-parasite interactions typical of those assumed in coevolutionary models were present, but were by no means pervasive.

Identification of an effector protein and gain-of-function mutants that activate Pfmrk, a malarial cyclin-dependent protein kinase

Cyclin-dependent protein kinases (CDKs) are key regulators of cell cycle control. In humans, CDK7 performs dual roles as the CDK activating kinase (CAK) responsible for regulating numerous CDKs and as the RNA polymerase II carboxyl-terminal domain (CTD) kinase involved in the regulation of transcription. Binding of an effector protein, human MAT1, stimulates CDK7 kinase activity and influences substrate specificity. In Plasmodium falciparum, CDKs and their roles in regulating growth and development are poorly understood. In this study, we characterized the regulatory mechanisms of Pfmrk, a putative homolog of human CDK7. We identified an effector, PfMAT1, which stimulates Pfmrk kinase activity in a cyclin-dependent manner. The addition of PfMAT1 stimulated RNA polymerase II CTD phosphorylation and had no effect on the inability of Pfmrk to phosphorylate PfPK5, a putative CDK1 homolog, which suggests that Pfmrk may be a CTD kinase rather than a CAK. In an attempt to abrogate the requirement for PfMAT1 stimulation, we mutated amino acids within the active site of Pfmrk. We found that two independent mutants, S138K and F143L, yielded a 4-10-fold increase in Pfmrk activity. Significant kinase activity of these mutants was observed in the absence of either cyclin or PfMAT1. Finally, we observed autophosphorylation of Pfmrk that is unaffected by the addition of either cyclin or PfMAT1.