Field evaluation of diagnostic performance of malaria rapid diagnostic tests in western Kenya.

BACKGROUND: Malaria continues to be a major burden in the endemic regions of Kenya. Health outcomes associated with case management are dependent on the use of appropriate diagnostic methods. Rapid diagnostic tests (RDTs) have provided an important tool to help implement the WHO recommended parasite-based diagnosis in regions where expert microscopy is not available. One of the questions that must be answered when implementing RDTs is whether these tests are useful in a specific endemic region, as well as the most appropriate RDT to use. Data on the sensitivity and specificity of RDT test kits is important information to help guide test selection by national malaria control programmes. METHODS: This study evaluated the diagnostic performance of RDTs including First Response (FR), CareStart (CS), SD Bioline (SD), and Binax Now (BN). The performance of these malaria kits was compared to microscopy, the gold standard, for the detection of malaria parasites. The malaria RDTs were also compared to PCR which is a more sensitive reference test. Five-hundred participants were included in the study through community screening (50 %) and testing suspected malaria cases referred from health facilities. RESULTS: Of the 500 participants recruited, 33 % were malaria positive by microscopy while 51.2 % were positive by PCR. Compared to microscopy, the sensitivity of eight RDTs to detect malaria parasites was 90.3-94.8 %, the specificity was 73.3-79.3 %, the positive predictive value was 62.2-68.8 %, and the negative predictive value was 94.3-96.8 %. Compared to PCR, the sensitivity of the RDTs to detect malaria parasites was 71.1-75.4 %, the specificity was 80.3-84.4 %, the positive predictive value was 80.3-83.3 %, and the negative predictive value was 73.7-76.1 %. The RDTs had a moderate measure of agreement with both microscopy (>80.1 %) and PCR (>77.6 %) with a κ > 0.6. CONCLUSION: The performance of the evaluated RDTs using field samples was moderate; hence they can significantly improve the quality of malaria case management in endemic regions in Kenya by ensuring appropriate treatment of malaria positive individuals and avoiding indiscriminate use of anti-malarial drugs for parasite negative patients.

Assessment of the Worldwide Antimalarial Resistance Network Standardized Procedure for In Vitro Malaria Drug Sensitivity Testing Using SYBR Green Assay for Field Samples with Various Initial Parasitemia Levels.

The malaria SYBR green assay, which is used to profilein vitrodrug susceptibility ofPlasmodium falciparum, is a reliable drug screening and surveillance tool. Malaria field surveillance efforts provide isolates with various low levels of parasitemia. To be advantageous, malaria drug sensitivity assays should perform reproducibly among various starting parasitemia levels rather than at one fixed initial value. We examined the SYBR green assay standardized procedure developed by the Worldwide Antimalarial Resistance Network (WWARN) for its sensitivity and ability to accurately determine the drug concentration that inhibits parasite growth by 50% (IC50) in samples with a range of initial parasitemia levels. The initial sensitivity determination of the WWARN procedure yielded a detection limit of 0.019% parasitemia.P. falciparumlaboratory strains and field isolates with various levels of initial parasitemia were then subjected to a range of doses of common antimalarials. The IC50s were comparable for laboratory strains with between 0.0375% and 0.6% parasitemia and for field isolates with between 0.075% and 0.6% parasitemia for all drugs tested. Furthermore, assay quality (Z') analysis indicated that the WWARN procedure displays high robustness, allowing for drug testing of malaria field samples within the derived range of initial parasitemia. The use of the WWARN procedure should allow for the inclusion of more malaria field samples in malaria drug sensitivity screens that would have otherwise been excluded due to low initial parasitemia levels.

Molecular characterization of the cytochrome b gene and in vitro atovaquone susceptibility of Plasmodium falciparum isolates from Kenya.

The prevalence of a genetic polymorphism(s) at codon 268 in the cytochrome b gene, which is associated with failure of atovaquone-proguanil treatment, was analyzed in 227 Plasmodium falciparum parasites from western Kenya. The prevalence of the wild-type allele was 63%, and that of the Y268S (denoting a Y-to-S change at position 268) mutant allele was 2%. There were no pure Y268C or Y268N mutant alleles, only mixtures of a mutant allele(s) with the wild type. There was a correlation between parasite 50% inhibitory concentration (IC50) and parasite genetic polymorphism; mutant alleles had higher IC50s than the wild type.

Five-year tracking of Plasmodium falciparum allele frequencies in a holoendemic area with indistinct seasonal transitions.

BACKGROUND: The renewed malaria eradication efforts require an understanding of the seasonal patterns of frequency of polymorphic variants in order to focus limited funds productively. Although cross-sectional studies in holoendemic areas spanning a single year could be useful in describing parasite genotype status at a given point, such information is inadequate in describing temporal trends in genotype polymorphisms. For Plasmodium falciparum isolates from Kisumu District Hospital, Plasmodium falciparum chloroquine-resistance transporter gene (Pfcrt-K76T) and P. falciparum multidrug resistance gene 1 (PfMDR1-N86Y), were analyzed for polymorphisms and parasitemia changes in the 53 months from March 2008 to August 2012. Observations were compared with prevailing climatic factors, including humidity, rainfall, and temperature. METHODS: Parasitemia (the percentage of infected red blood cells per total red blood cells) was established by microscopy for P. falciparum malaria-positive samples. P. falciparum DNA was extracted from whole blood using a Qiagen DNA Blood Mini Kit. Single nucleotide polymorphism identification at positions Pfcrt-K76T and PfMDR1-N86Y was performed using real-time polymerase chain reaction and/or sequencing. Data on climatic variables were obtained from http://www.tutiempo.net/en/. RESULTS: A total of 895 field isolates from 2008 (n=169), 2009 (n=161), 2010 (n=216), 2011 (n=223), and 2012 (n=126) showed large variations in monthly frequency of PfMDR1-N86Y and Pfcrt-K76T as the mutant genotypes decreased from 68.4%±15% and 38.1%±13% to 29.8%±18% and 13.3%±9%, respectively. The mean percentage of parasitemia was 2.61%±1.01% (coefficient of variation 115.86%; n=895). There was no correlation between genotype or parasitemia and climatic factors. CONCLUSION: This study shows variability in the frequency of Pfcrt-K76T and PfMDR1-N86Y polymorphisms during the study period, bringing into focus the role of cross-sectional studies in describing temporal genotype trends. The lack of correlation between genotypes and climatic changes, especially precipitation, emphasizes the cost of investment in genotype change.

The use of a prodrug approach to minimize potential CNS exposure of next generation quinoline methanols while maintaining efficacy in in vivo animal models.

The use of mefloquine (MQ) for antimalarial treatment and prophylaxis has diminished largely in response to concerns about its neurologic side effects. An analog campaign designed to maintain the efficacy of MQ while minimizing blood-brain barrier (BBB) penetration has resulted in the synthesis of a prodrug with comparable-to-superior in vivo efficacy versus mefloquine in a P. berghei mouse model while exhibiting a sixfold reduction in CNS drug levels. The prodrug, WR319670, performed poorly compared to MQ in in vitro efficacy assays, but had promising in vitro permeability in an MDCK-MDR1 cell line BBB permeability screen. Its metabolite, WR308245, exhibited high predicted BBB penetration with excellent in vitro efficacy. Both WR319670 and WR308245 cured 5/5 animals in separate in vivo efficacy studies. The in vivo efficacy of WR319670 was thought to be due to the formation of a more active metabolite, specifically WR308245. This was supported by pharmacokinetics studies in non-infected mice, which showed that both IV and oral administration of WR319670 produced essentially identical levels of WR319670 and WR308245 in both plasma and brain samples at all time points. In these studies, the levels of WR308245 in the brain were 1/4 and 1/6 that of MQ in similar IV and oral studies, respectively. These data show that the use of WR319670 as an antimalarial prodrug was able to maintain efficacy in in vivo efficacy screens, while significantly lowering overall penetration of drug and metabolites across the BBB.

Polymorphisms in Pfmdr1, Pfcrt, and Pfnhe1 genes are associated with reduced in vitro activities of quinine in Plasmodium falciparum isolates from western Kenya.

In combination with antibiotics, quinine is recommended as the second-line treatment for uncomplicated malaria, an alternative first-line treatment for severe malaria, and for treatment of malaria in the first trimester of pregnancy. Quinine has been shown to have frequent clinical failures, and yet the mechanisms of action and resistance have not been fully elucidated. However, resistance is linked to polymorphisms in multiple genes, including multidrug resistance 1 (Pfmdr1), the chloroquine resistance transporter (Pfcrt), and the sodium/hydrogen exchanger gene (Pfnhe1). Here, we investigated the association between in vitro quinine susceptibility and genetic polymorphisms in Pfmdr1codons 86 and 184, Pfcrt codon 76, and Pfnhe1 ms4760 in 88 field isolates from western Kenya. In vitro activity was assessed based on the drug concentration that inhibited 50% of parasite growth (the IC50), and parasite genetic polymorphisms were determined from DNA sequencing. Data revealed there were significant associations between polymorphism in Pfmdr1-86Y, Pfmdr1-184F, or Pfcrt-76T and quinine susceptibility (P < 0.0001 for all three associations). Eighty-two percent of parasites resistant to quinine carried mutant alleles at these codons (Pfmdr1-86Y, Pfmdr1-184F, and Pfcrt-76T), whereas 74% of parasites susceptible to quinine carried the wild-type allele (Pfmdr1-N86, Pfmdr1-Y184, and Pfcrt-K76, respectively). In addition, quinine IC50 values for parasites with Pfnhe1 ms4760 3 DNNND repeats were significantly higher than for those with 1 or 2 repeats (P = 0.033 and P = 0.0043, respectively). Clinical efficacy studies are now required to confirm the validity of these markers and the importance of parasite genetic background.

Efficacy and safety of artemether-lumefantrine and dihydroartemisinin-piperaquine in the treatment of uncomplicated Plasmodium falciparum malaria in Kenyan children aged less than five years: results of an open-label, randomized, single-centre study.

BACKGROUND: This open-label, randomized study evaluated efficacy and safety of artemether-lumefantrine (AL) and dihydroartemisinin-piperaquine (DP) in treatment of uncomplicated falciparum malaria in children below five years of age, to build evidence on use of AL as first-line treatment and DP as second-line treatment in Kenya. METHODS: A total of 454 children aged six to 59 months with uncomplicated falciparum malaria were randomized (1:1) to receive AL dispersible or DP paediatric tablets and followed up for 42 days. Primary efficacy variable was corrected adequate clinical and parasitological response (ACPR) rate on day 28. Secondary variables included corrected (day 14, 28 and 42), uncorrected (day 3, 14, 28 and 42) cure rates, parasitological failure at days 3, 14 and 42. Acceptability and tolerability of both drugs were assessed by caregiver questionnaire. RESULTS: On day 28, corrected ACPR rates for AL dispersible and DP paediatric were 97.8% (95% CI: 94.9-99.3) and 99.1% (95% CI: 96.8-99.9), respectively, in intention-to-treat population, with no significant treatment differences noted between AL dispersible and DP paediatric arms. Additionally, no significant differences were observed for PCR corrected cure rates on days 14 and ACPR on day 42 for AL dispersible (100%; 96.8%) and DP paediatric (100%; 98.7%). Similarly, for PCR uncorrected cure rates, no significant differences were seen on days 3, 14, 28, and 42 for AL dispersible (99.1%; 98.7%; 81.1%; 67.8%) and DP paediatric (100%; 100%; 87.7%; 70.5%). Parasite clearance was rapid, with approximately 90% clearance achieved in 40 hours in both treatment arms. Incidence of adverse events was related to underlying disease; malaria being reported in both treatment arms. One serious adverse event was noted in AL dispersible (0.42%) arm, not related to study drug. Adherence to treatment regimen was higher for children treated with AL dispersible (93.6%) compared to DP paediatric (85.6%). Acceptability of AL dispersible regimen was assessed as being significantly better than DP paediatric. CONCLUSIONS: AL and DP were both efficacious and well tolerated, and had similar effects at day 42 on risk of recurrent malaria. No signs of Plasmodium falciparum tolerance to artemisinins were noted. TRIAL REGISTRATION: PACTR201111000316370.

A SYBR Green 1-based in vitro test of susceptibility of Ghanaian Plasmodium falciparum clinical isolates to a panel of anti-malarial drugs.

BACKGROUND: Based on report of declining efficacy of chloroquine, Ghana shifted to the use of artemisinin-based combination therapy (ACT) in 2005 as the first-line anti-malarial drug. Since then, there has not been any major evaluation of the efficacy of anti-malarial drugs in Ghana in vitro. The sensitivity of Ghanaian Plasmodium falciparum isolates to anti-malarial drugs was, therefore, assessed and the data compared with that obtained prior to the change in the malaria treatment policy. METHODS: A SYBR Green 1 fluorescent-based in vitro drug sensitivity assay was used to assess the susceptibility of clinical isolates of P. falciparum to a panel of 12 anti-malarial drugs in three distinct eco-epidemiological zones in Ghana. The isolates were obtained from children visiting health facilities in sentinel sites located in Hohoe, Navrongo and Cape Coast municipalities. The concentration of anti-malarial drug inhibiting parasite growth by 50% (IC50) for each drug was estimated using the online program, ICEstimator. RESULTS: Pooled results from all the sentinel sites indicated geometric mean IC50 values of 1.60, 3.80, 4.00, 4.56, 5.20, 6.11, 10.12, 28.32, 31.56, 93.60, 107.20, and 8952.50 nM for atovaquone, artesunate, dihydroartemisin, artemether, lumefantrine, amodiaquine, mefloquine, piperaquine, chloroquine, tafenoquine, quinine, and doxycycline, respectively. With reference to the literature threshold value indicative of resistance, the parasites showed resistance to all the test drugs except the artemisinin derivatives, atovaquone and to a lesser extent, lumefantrine. There was nearly a two-fold decrease in the IC50 value determined for chloroquine in this study compared to that determined in 2004 (57.56 nM). This observation is important, since it suggests a significant improvement in the efficacy of chloroquine, probably as a direct consequence of reduced drug pressure after cessation of its use. Compared to that measured prior to the change in treatment policy, significant elevation of artesunate IC50 value was observed. The results also suggest the existence of possible cross-resistance among some of the test drugs. CONCLUSION: Ghanaian P. falciparum isolates, to some extent, have become susceptible to chloroquine in vitro, however the increasing trend in artesunate IC50 value observed should be of concern. Continuous monitoring of ACT in Ghana is recommended.

Direct comparison of the histidine-rich protein-2 enzyme-linked immunosorbent assay (HRP-2 ELISA) and malaria SYBR green I fluorescence (MSF) drug sensitivity tests in Plasmodium falciparum reference clones and fresh ex vivo field isolates from Cambodia.

BACKGROUND: Performance of the histidine-rich protein-2 enzyme-linked immunosorbent assay (HRP-2 ELISA) and malaria SYBR Green I fluorescence (MSF) drug sensitivity tests were directly compared using Plasmodium falciparum reference strains and fresh ex vivo isolates from Cambodia against a panel of standard anti-malarials. The objective was to determine which of these two common assays is more appropriate for studying drug susceptibility of "immediate ex vivo" (IEV) isolates, analysed without culture adaption, in a region of relatively low malaria transmission. METHODS: Using the HRP-2 and MSF methods, the 50% inhibitory concentration (IC50) values against a panel of malaria drugs were determined for P. falciparum reference clones (W2, D6, 3D7 and K1) and 41 IEV clinical isolates from an area of multidrug resistance in Cambodia. Comparison of the IC50 values from the two methods was made using Wilcoxon matched pair tests and Pearson's correlation. The lower limit of parasitaemia detection for both methods was determined for reference clones and IEV isolates. Since human white blood cell (WBC) DNA in clinical samples is known to reduce MSF assay sensitivity, SYBR Green I fluorescence linearity of P. falciparum samples spiked with WBCs was evaluated to assess the relative degree to which MSF sensitivity is reduced in clinical samples. RESULTS: IC50 values correlated well between the HRP-2 and MSF methods when testing either P. falciparum reference clones or IEV isolates against 4-aminoquinolines (chloroquine, piperaquine and quinine) and the quinoline methanol mefloquine (Pearson r = 0.85-0.99 for reference clones and 0.56-0.84 for IEV isolates), whereas a weaker IC50 value correlation between methods was noted when testing artemisinins against reference clones and lack of correlation when testing IEV isolates. The HRP-2 ELISA produced a higher overall success rate (90% for producing IC50 best-fit sigmoidal curves), relative to only a 40% success rate for the MSF assay, when evaluating ex vivo Cambodian isolates. Reduced sensitivity of the MSF assay is likely due to an interference of WBCs in clinical samples. CONCLUSIONS: For clinical samples not depleted of WBCs, HRP-2 ELISA is superior to the MSF assay at evaluating fresh P. falciparum field isolates with low parasitaemia (<0.2%) generally observed in Southeast Asia.

The role of Pfmdr1 and Pfcrt in changing chloroquine, amodiaquine, mefloquine and lumefantrine susceptibility in western-Kenya P. falciparum samples during 2008-2011.

Single Nucleotide Polymorphisms (SNPs) in the Pfmdr1, and Pfcrt, genes of Plasmodium falciparum may confer resistance to a number of anti-malaria drugs. Pfmdr1 86Y and haplotypes at Pfcrt 72-76 have been linked to chloroquine (CQ) as well as amodiaquine (AQ) resistance. mefloquine (MQ) and lumefantrine (LU) sensitivities are linked to Pfmdr1 86Y. Additionally, Pfcrt K76 allele carrying parasites have shown tolerance to LU. We investigated the association between Pfmdr1 86/Pfcrt 72-76 and P. falciparum resistance to CQ, AQ, MQ and LU using field samples collected during 2008-2011 from malaria endemic sites in western Kenya. Genomic DNA from these samples was genotyped to examine SNPs and haplotypes in Pfmdr1 and Pfcrt respectively. Additionally, immediate ex vivo and in vitro drug sensitivity profiles were assessed using the malaria SYBR Green I fluorescence-based assay. We observed a rapid but steady percent increase in wild-type parasites with regard to both Pfmdr1 and Pfcrt between 2008 and 2011 (p<0.0001). Equally, a significant reciprocate decrease in AQ and CQ median IC50 values occurred (p<0.0001) during the same period. Thus, the data in this study point to a significantly rapid change in parasite response to AQ and CQ in the study period. This may be due to releasing of drug pressure on the parasite from reduced use of AQ in the face of increased Artemisinin (ART) Combination Therapy (ACT) administration following the intervention of the Global Fund in 2008. LU has been shown to select for 76K genotypes, thus the observed increase in 76K genotypes coupled with significant cross resistance between LU and MQ, may herald emergence of tolerance against both drugs in future.

High-throughput analysis of antimalarial susceptibility data by the WorldWide Antimalarial Resistance Network (WWARN) in vitro analysis and reporting tool.

Assessment of in vitro susceptibility is a fundamental component of antimalarial surveillance studies, but wide variations in the measurement of parasite growth and the calculation of inhibitory constants make comparisons of data from different laboratories difficult. Here we describe a Web-based, high-throughput in vitro analysis and reporting tool (IVART) generating inhibitory constants for large data sets. Fourteen primary data sets examining laboratory-determined susceptibility to artemisinin derivatives and artemisinin combination therapy partner drugs were collated from 11 laboratories. Drug concentrations associated with half-maximal inhibition of growth (IC50s) were determined by a modified sigmoid Emax model-fitting algorithm, allowing standardized analysis of 7,350 concentration-inhibition assays involving 1,592 isolates. Examination of concentration-inhibition data revealed evidence of apparent paradoxical growth at high concentrations of nonartemisinin drugs, supporting amendment of the method for calculating the maximal drug effect in each assay. Criteria for defining more-reliable IC50s based on estimated confidence intervals and growth ratios improved correlation coefficients for the drug pairs mefloquine-quinine and chloroquine-desethylamodiaquine in 9 of 11 and 8 of 8 data sets, respectively. Further analysis showed that maximal drug inhibition was higher for artemisinins than for other drugs, particularly in ELISA (enzyme-linked immunosorbent assay)-based assays, a finding consistent with the earlier onset of action of these drugs in the parasite life cycle. This is the first high-throughput analytical approach to apply consistent constraints and reliability criteria to large, diverse antimalarial susceptibility data sets. The data also illustrate the distinct biological properties of artemisinins and underline the need to apply more sensitive approaches to assessing in vitro susceptibility to these drugs.

The antiplasmodial and radical scavenging activities of flavonoids of Erythrina burttii.

The acetone extract of the root bark of Erythrina burttii showed in vitro antiplasmodial activity against the chloroquine-sensitive (D6) and chloroquine-resistant (W2) strains of Plasmodium falciparum with IC(50) values of 0.97 ± 0.2 and 1.73 ± 0.5 µg/ml respectively. The extract also had radical scavenging activity against 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical with an EC(50) value of 12.0 µg/ml. The isoflav-3-enes burttinol-A and burttinol-C, and the 2-arylbenzofuran derivative burttinol-D were identified as the most active antiplasmodial (IC(50)<10 µM) and free radical scavenging (EC(50)ca. 10 µM) principles. The acetone extract of E. burttii at 800 mg/kg/day, in a 4-day Plasmodium berghei ANKA suppressive test, showed in vivo antimalarial activity with 52% chemosuppression. In the same in vivo test, marginal activities were also observed for the extracts of the root and stem bark of Erythrina abyssinica and the root bark of Erythrina sacleuxii.

Inhibitory activity of ferroquine, versus chloroquine, against western Kenya Plasmodium falciparum field isolates determined by a SYBR Green I in vitro assay.

Ferroquine (FQ), a chloroquine (CQ) analog, is being developed to treat persons with Plasmodium falciparum malaria. In 146 P. falciparum field isolates from western Kenya, we measured 50% inhibitory concentrations (IC(50); nM) of CQ and FQ by a SYBR Green I in vitro assay. Reference clones included W2 (CQ resistant) and D6 (CQ sensitive). Mutation analysis was done for P. falciparum CQ-resistance transporter gene (Pfcrt K76T). Median IC(50) values for FQ were lower than CQ for field isolates and the W2 clone (both P < 0.05). The Pfcrt mutation (76T), which was detected in > 80% of isolates, conferred higher CQ IC(50) values (P < 0.05) and modestly lower FQ IC(50) values (P < 0.05), versus Pfcrt wild type (K76). FQ is more potent than CQ against CQ-resistant P. falciparum field isolates and the W2 clone, and is less affected by Pfcrt 76T. These findings support the notion that FQ could be useful in treating persons with P. falciparum malaria.

Antimalarial drug sensitivity profile of western Kenya Plasmodium falciparum field isolates determined by a SYBR Green I in vitro assay and molecular analysis.

In vitro drug sensitivity and molecular analyses of Plasmodium falciparum track drug resistance. DNA-binding fluorescent dyes like SYBR Green I may allow field laboratories, proximal to P. falciparum collection sites, to conduct drug assays. In 2007-2008, we assayed 121 P. falciparum field isolates from western Kenya for 50% inhibitory concentrations (IC(50)) against 6 antimalarial drugs using a SYBR Green I in vitro assay: 91 immediate ex vivo (IEV) and 30 culture-adapted, along with P. falciparum reference clones D6 (chloroquine [CQ] sensitive) and W2 (CQ resistant). We also assessed P. falciparum mdr1 (Pfmdr1) copy number and single nucleotide polymorphisms (SNPs) at four codons. The IC(50)s for IEV and culture-adapted P. falciparum isolates were similar, and approximated historical IC(50)s. For Pfmdr1, mean copy number was 1, with SNPs common at codons 86 and 184. The SYBR Green I assay adapted well to our field-based laboratory, for both IEV and culture-adapted P. falciparum, warranting continued use.

Use of the NP-40 detergent-mediated assay in discovery of inhibitors of beta-hematin crystallization.

The protozoan parasite responsible for malaria affects over 500 million people each year. Current antimalarials have experienced decreased efficacy due to the development of drug-resistant strains of Plasmodium spp., resulting in a critical need for the discovery of new antimalarials. Hemozoin, a crystalline by-product of heme detoxification that is necessary for parasite survival, serves as an important drug target. The quinoline antimalarials, including amodiaquine and chloroquine, act by inhibiting the formation of hemozoin. The formation of this crystal does not occur spontaneously, and recent evidence suggests crystallization occurs in the presence of neutral lipid particles located in the acidic digestive vacuole of the parasite. To mimic these conditions, the lipophilic detergent NP-40 has previously been shown to successfully mediate the formation of ß-hematin, synthetic hemozoin. Here, an NP-40 detergent-based assay was successfully adapted for use as a high-throughput screen to identify inhibitors of ß-hematin formation. The resulting assay exhibited a favorable Z' of 0.82 and maximal drift of less than 4%. The assay was used in a pilot screen of 38,400 diverse compounds at a screening concentration of 19.3 µM, resulting in the identification of 161 previously unreported ß-hematin inhibitors. Of these, 48 also exhibited ≥ 90% inhibition of parasitemia in a Plasmodium falciparum whole-cell assay at a screening concentration of 23 µM. Eight of these compounds were identified to have nanomolar 50% inhibitory concentration values near that of chloroquine in this assay.

Design of anti-parasitic and anti-fungal hydroxy-naphthoquinones that are less susceptible to drug resistance.

Atovaquone is a hydroxy-naphthoquinone that is used to treat parasitic and fungal infections including Plasmodium falciparum (malaria), Pneumocystis jivorecii (pneumonia) and Toxoplasma gondii (toxoplasmosis). It blocks mitochondrial oxidation of ubiquinol in these organisms by binding to the ubiquinol oxidation site of the cytochrome bc(1) complex. Failure of atovaquone treatment has been linked to the appearance of mutations in the mitochondrially encoded gene for cytochrome b. In order to determine the optimal parameters required for inhibition of respiration in parasites and pathogenic fungi and overcome drug resistance, we have synthesized and tested the inhibitory activity of novel hydroxy-naphthoquinones against blood stage P. falciparum and liver stage P. berghei and against cytochrome bc(1) complexes isolated from yeast strains bearing mutations in cytochrome b associated with resistance in Plasmodium, Pneumocystis, and Toxoplasma. One of the new inhibitors is highly effective against an atovaquone resistant Plasmodium and illustrates the type of modification to the hydroxy-naphthoquinone ring of atovaquone that might mitigate drug resistance.

A novel activity from an old compound: Manzamine A reduces the metastatic potential of AsPC-1 pancreatic cancer cells and sensitizes them to TRAIL-induced apoptosis.

PURPOSE: Pancreatic cancer is the fourth leading cause of cancer death in the United States, and new drugs to treat the disease are needed. Pancreatic cancer cells are highly metastatic and exhibit resistance to apoptosis. Small molecules that can restore sensitivity to apoptosis or reduce metastasis would have therapeutic potential against this disease. Manzamine A is an alkaloid isolated from marine sponges that was suspected to have inhibitory activity against the mitogen activated kinase kinase (MEK). Because of this, the effects of Manzamine A were studied in pancreatic cancer cells. METHODS: AsPC-1 cells were treated for 48 h in the presence of various concentrations of Manzamine A and their phenotype, cytotoxicity, cell invasion and susceptibility to apoptosis were observed. RESULTS: Manzamine A decreased single cell formation, abrogated cell migration and restored the susceptibility of the cells to TRAIL-induced apoptosis in AsPC-1 cells. Its mechanism of action remains unknown, as manzamine A does not inhibit MEK. CONCLUSIONS: Manzamine A appears to have a formerly unrecognized activity in blocking tumor cell invasion as well as in restoring cancer cell susceptibility to apoptosis in vitro and therefore has the potential to be used as an adjuvant to existing cancer therapies.

Lactococcus lactis fabH, encoding beta-ketoacyl-acyl carrier protein synthase, can be functionally replaced by the Plasmodium falciparum congener.

Plasmodium falciparum, in addition to scavenging essential fatty acids from its intra- and intercellular environments, possesses a functional complement of type II fatty acid synthase (FAS) enzymes targeted to the apicoplast organelle. Recent evidence suggests that products of the plasmodial FAS II system may be critical for the parasite's liver-to-blood cycle transition, and it has been speculated that endogenously generated fatty acids may be precursors for essential cofactors, such as lipoate, in the apicoplast. beta-Ketoacyl-acyl carrier protein (ACP) synthase III (pfKASIII or FabH) is one of the key enzymes in the initiating steps of the FAS II pathway, possessing two functions in P. falciparum: the decarboxylative thio-Claisen condensation of malonyl-ACP and various acyl coenzymes A (acyl-CoAs; KAS activity) and the acetyl-CoA:ACP transacylase reaction (ACAT). Here, we report the generation and characterization of a hybrid Lactococcus lactis strain that translates pfKASIII instead of L. lactis fabH to initiate fatty acid biosynthesis. The L. lactis expression vector pMG36e was modified for the efficient overexpression of the plasmodial gene in L. lactis. Transcriptional analysis indicated high-efficiency overexpression, and biochemical KAS and ACAT assays confirm these activities in cell extracts. Phenotypically, the L. lactis strain expressing pfKASIII has a growth rate and fatty acid profiles that are comparable to those of the strain complemented with its endogenous gene, suggesting that pfKASIII can use L. lactis ACP as substrate and perform near-normal function in L. lactis cells. This strain may have potential application as a bacterial model for pfKASIII inhibitor prescreening.

Assessment of malaria in vitro drug combination screening and mixed-strain infections using the malaria Sybr green I-based fluorescence assay.

Several drug development strategies, including optimization of new antimalarial drug combinations, have been used to counter malaria drug resistance. We evaluated the malaria Sybr green I-based fluorescence (MSF) assay for its use in in vitro drug combination sensitivity assays. Drug combinations of previously published synergistic (atovaquone and proguanil), indifferent (chloroquine and azithromycin), and antagonistic (chloroquine and atovaquone) antimalarial drug interactions were tested against Plasmodium falciparum strains D6 and W2 using the MSF assay. Fifty percent inhibitory concentrations (IC(50)s) were calculated for individual drugs and in fixed ratio combinations relative to their individual IC(50)s. Subsequent isobologram analysis and fractional inhibitory concentration determinations demonstrated the expected drug interaction pattern for each combination tested. Furthermore, we explored the ability of the MSF assay to examine mixed parasite population dynamics, which are commonly seen in malaria patient isolates. Specifically, the capacity of the MSF assay to discern between single and mixed parasite populations was determined. To simulate mixed infections in vitro, fixed ratios of D6 and W2 strains were cocultured with antimalarial drugs and IC(50)s were determined using the MSF assay. Dichotomous concentration curves indicated that the sensitive and resistant parasites composing the genetically heterogeneous population were detectable. Biphasic analysis was performed to obtain subpopulation IC(50)s for comparison to those obtained for the individual malaria strains alone. In conclusion, the MSF assay allows for reliable antimalarial drug combination screening and provides an important method to discern between homogenous and heterogeneous parasite populations.

Selective cytotoxic activity of the marine-derived batzelline compounds against pancreatic cancer cell lines.

Pancreatic cancer is the fourth leading cause of cancer death in the United States. The prognosis of the disease is very negative, because the cancer will be usually metastasized by the time a patient manifests symptoms. Although combination therapy shows some promise, new drugs to treat the disease are needed. Given our interest in finding new therapies for pancreatic cancer, we sought to determine whether the known cytotoxic activity of the batzellines extended to pancreatic cancer cell lines. The batzellines are pyrroloiminoquinones alkaloids obtained from the deep-water Caribbean sponge Batzella sp (family Esperiopsidae, order Poecilosclerida). We show here that batzellines exhibit selective cytotoxicity towards the pancreatic cancer cell lines AsPC-1, Panc-1, BxPC-3, and MIA PaCa2 compared with the normal African green monkey kidney epithelial cell line Vero. The batzellines cause cytotoxicity by inducing cell cycle arrest that is mediated by their ability to intercalate into DNA and/or inhibit topoisomerase II activity. The cytotoxic abilities of isobatzellines A and C against pancreatic cancer cell lines, their low toxicity against normal cells, and their reported ability to be synthesized makes them interesting compounds with potential chemotherapeutic effects that may merit further research.