Download or read book The Malaria Parasite s Chloroquine Resistance Transporter written by Robert Leon Summers and published by . This book was released on 2017 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The malaria parasite's chloroquine resistance transporter: An exploration of its interactions with drugs and of its evolution as a drug transporter Abstract: Initially identified as the primary determinant of chloroquine resistance in the malaria parasite Plasmodium falciparum, mutations in the 'chloroquine resistance transporter' (PfCRT) can influence the parasite's susceptibility to diverse molecules. The ability of PfCRT to affect the activity of so many compounds is likely to be a product of its location at the membrane of the parasite's digestive vacuole - an acidic compartment in which many types of drugs accumulate, act, and/or are activated. The Xenopus laevis oocyte system enables the functional expression of PfCRT and has been used to demonstrate that a mutant isoform of PfCRT mediates the efflux of chloroquine from the vacuole (i.e., away from its site of action), whereas the wild-type protein lacks this activity. However, the evolution of chloroquine transport activity by PfCRT has yet to be explored, and little is known of how PfCRT interacts with diverse compounds. The overarching aim of this study was to understand how mutations in PfCRT confer chloroquine transport activity and alter the parasite's susceptibility to diverse pharmacons. A kinetic analysis of the inhibition of PfCRT-mediated chloroquine transport by verapamil, a compound which partially restores the activity of chloroquine against drug-resistant parasites, was undertaken in the oocyte system. The findings of this work revealed verapamil to be a partial-mixed-type inhibitor of the transporter, and suggested that the mutations required for chloroquine transport introduce multiple substrate-binding sites into PfCRT. A series of complementary assays were then applied to examine the interactions of PfCRT with a range of compounds to identify, and distinguish between, PfCRT substrates and inhibitors. Using the oocyte system, two new classes of compounds were identified as potent inhibitors of the PfCRT-mediated transport of chloroquine. Transgenic parasite lines that are isogenic except for their pfcrt allele were employed, in conjunction with an assay that indirectly detects the transport of drugs out of the parasite's digestive vacuole, to further characterise these compounds. The resulting data revealed that most of these molecules are not substrates of the mutant transporter. Furthermore, parasite proliferation assays demonstrated that the compounds possessed enhanced activities against parasites harbouring mutant PfCRT. Structure-activity relationships were consistent with these compounds binding to multiple points of attachment within PfCRT via lipophilic and electrostatic interactions. Measurements of chloroquine transport via diverse isoforms of PfCRT (as well as by a series of chimeric proteins) were also undertaken in the oocyte system. These analyses revealed that multiple mutational pathways lead to saturable chloroquine transport via PfCRT. The finding that diverse PfCRT variants are all limited in their capacity to transport chloroquine suggests that resistance could be overcome by re-optimising the chloroquine dosage. Moreover, the results of this study indicated that the remodelling of PfCRT for chloroquine transport required a complex reorganisation of interacting residues. These studies support the idea that, in addition to being a mediator of multidrug resistance, PfCRT is itself a viable drug target. Antimalarial therapies could be formulated to exert opposing selection forces upon PfCRT, thereby exploiting a key resistance mechanism and prolonging drug efficacy against this important human pathogen.
Download or read book Identifying the Minimal Number of Mutations Required for Chloroquine Transport Via the Malaria Parasite s Chloroquine Resistance Transporter written by Tegan Dolstra and published by . This book was released on 2014 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: As resistance to the current frontline antimalarial drug, artemisinin, begins to spread through the malaria parasite population, efficacious alternatives are desperately required. One potential, relatively cheap source of new drugs is previously efficacious antimalarials that have fallen out of use due to widespread resistance. Of these, chloroquine (CQ) is particularly promising. CQ kills malaria parasites by interfering with the neutralisation of toxic haem waste products generated during haemoglobin digestion in the parasite's digestive vacuole (DV). A gold-standard antimalarial in the mid-20th century, the use of CQ is now severely limited due to the emergence and subsequent spread of CQ resistant (CQR) parasites. CQR parasites accumulate far less CQ in their DV than do CQ sensitive parasites. The main determinant of CQ resistance is mutations in a transport protein, the Plasmodium falciparum Chloroquine Resistance Transporter (PfCRT), which is located in the DV membrane. Martin et al. (2009) have shown using a heterologous Xenopus oocyte system that a CQR haplotype of PfCRT is capable of CQ transport, whereas the wild-type protein is not. Thus, it is proposed that CQ resistance is mediated by mutant PfCRT transporting CQ out of the DV and away from the drug's site of action. Here, I present a detailed analysis of the roles of the eight PfCRT mutations found in the CQR strain 'Dd2'. I expressed 29 PfCRT variants harbouring different combinations of these mutations in Xenopus oocytes. I then measured the ability of each variant to transport CQ to determine the minimal mutational requirements for CQ transport via PfCRT. I found that the combination of two mutations - K76T and N75E - was sufficient to induce low-level CQ transport, while a combination of four mutations - K76T, N75E, A220S and Q271E - allowed the protein to transport CQ at levels comparable to the Dd2 version of PfCRT. These findings provide novel and unexpected insights into the workings of a protein that is a key determinant of drug resistance in the malaria parasite.
Download or read book Malaria written by Institute of Medicine and published by National Academies Press. This book was released on 1991-02-01 with total page 312 pages. Available in PDF, EPUB and Kindle. Book excerpt: Malaria is making a dramatic comeback in the world. The disease is the foremost health challenge in Africa south of the Sahara, and people traveling to malarious areas are at increased risk of malaria-related sickness and death. This book examines the prospects for bringing malaria under control, with specific recommendations for U.S. policy, directions for research and program funding, and appropriate roles for federal and international agencies and the medical and public health communities. The volume reports on the current status of malaria research, prevention, and control efforts worldwide. The authors present study results and commentary on the: Nature, clinical manifestations, diagnosis, and epidemiology of malaria. Biology of the malaria parasite and its vector. Prospects for developing malaria vaccines and improved treatments. Economic, social, and behavioral factors in malaria control.
Download or read book The Plasmodium Falciparum Chloroquine Resistance Transporter PFCRT Mediates the Activity of Chloroquine resistance Reversal Agents in the Malaria Parasite written by Kristin Lane and published by . This book was released on 2007 with total page 138 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Saving Lives Buying Time written by Institute of Medicine and published by National Academies Press. This book was released on 2004-09-09 with total page 384 pages. Available in PDF, EPUB and Kindle. Book excerpt: For more than 50 years, low-cost antimalarial drugs silently saved millions of lives and cured billions of debilitating infections. Today, however, these drugs no longer work against the deadliest form of malaria that exists throughout the world. Malaria deaths in sub-Saharan Africaâ€"currently just over one million per yearâ€"are rising because of increased resistance to the old, inexpensive drugs. Although effective new drugs called "artemisinins" are available, they are unaffordable for the majority of the affected population, even at a cost of one dollar per course. Saving Lives, Buying Time: Economics of Malaria Drugs in an Age of Resistance examines the history of malaria treatments, provides an overview of the current drug crisis, and offers recommendations on maximizing access to and effectiveness of antimalarial drugs. The book finds that most people in endemic countries will not have access to currently effective combination treatments, which should include an artemisinin, without financing from the global community. Without funding for effective treatment, malaria mortality could double over the next 10 to 20 years and transmission will intensify.
Download or read book Investigating Mutability and the Plasmodium Falciparum Chloroquine Resistance Transporter in Drug Resistant Malaria Parasites written by Andrew Hojin Lee and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Malaria persists today as a significant burden for a large part of the world. However, over the past few decades, a concerted effort by governments, non-governmental organizations, researchers, and community health workers worldwide has yielded progress in reducing the deadly impact of this disease. Today, some of these gains are threatened by the rise of antimalarial drug resistance, a recurring problem that has impeded global malaria reduction efforts before. Research on Plasmodium falciprum resistance to the numerous antimalarial compounds used today and in the past has made significant progress on determining which specific mutations modulate drug susceptibility and to what degree they do so. To gain a comprehensive understanding of drug resistance, we need to elucidate how and why it arises. Therefore, it is important to elucidate whether some malaria parasites acquire resistance-conferring mutations faster than others and why the native function of the genetic factors involved lend themselves to modulating drug resistance.
Download or read book World Malaria Report 2018 written by World Health Organization and published by World Health Organization. This book was released on 2019-02-12 with total page 210 pages. Available in PDF, EPUB and Kindle. Book excerpt: This year s report shows that after an unprecedented period of success in global malaria control progress has stalled. Data from 2015?2017 highlight that no significant progress in reducing global malaria cases was made in this period. There were an estimated 219 million cases and 435 000 related deaths in 2017. The World malaria report 2018 draws on data from 90 countries and areas with ongoing malaria transmission. The information is supplemented by data from national household surveys and databases held by other organizations.
Download or read book Studies of Malarial Parasite Chloroquine Resistance Transporter and Kinase Proteins Key Targets for Evolving Drug Therapies written by Matthew Ryan Hassett and published by . This book was released on 2017 with total page 512 pages. Available in PDF, EPUB and Kindle. Book excerpt: I have continued the use of an optimized CRT expression system in S. cerevisiae to elucidate drug transport ability. CQ resistance (CQR) is well understood in P. falciparum, but in Plasmodium vivax (another species of malaria), CQR remains a mystery. Multiple mutations in PfCRT are characteristic of drug resistant isolates, and contrary to PfCRT, the P. vivax orthologue (named PvCRT) primarily shows only single mutations in CRT. In this thesis, I measure the drug transport efficiencies of multiple Pf and PvCRT isoforms. My results show that there is a range of quinolone drug transport across the isoforms analyzed. Additionally, some CQR isolates expressing certain CRT isoforms likely have other genetic events that shape CQR.
Download or read book Treatment and Prevention of Malaria written by Henry M. Staines and published by Springer Science & Business Media. This book was released on 2012-01-06 with total page 318 pages. Available in PDF, EPUB and Kindle. Book excerpt: Malaria has defeated previous efforts at eradication and remains a massive global public health problem despite being readily preventable and treatable. It is a devastating disease that also extracts huge economic costs from the poorest countries in endemic regions. Starting with an overview of the disease and its current political, financial and technical context, this Milestones in Drug Therapy volume describes the history, chemistry, mechanisms of action and resistance, preclinical and clinical use, pharmacokinetics and safety and tolerability of the current range of antimalarial drugs. There is particular emphasis on artemisinins and related peroxides, as these drugs have now become the frontline treatment for malaria. Next generation antimalarials, molecular markers for detecting resistance, the importance of diagnostics and disease prevention are also covered in detail.
Download or read book Malaria Drugs Disease and Post genomic Biology written by David Sullivan and published by Springer Science & Business Media. This book was released on 2006-01-09 with total page 447 pages. Available in PDF, EPUB and Kindle. Book excerpt: Despite rapid increases in knowledge, malaria continues to kill more than a million people each year and causes symptomatic disease in a further 300 million individuals. This volume brings some of the world's best investigators to describe recent advances in both the scientific and clinical aspects of malaria, and bridges between the two.
Download or read book Antimalarial Chemotherapy written by Philip J. Rosenthal and published by Springer Science & Business Media. This book was released on 2001-04-01 with total page 393 pages. Available in PDF, EPUB and Kindle. Book excerpt: Philip Rosenthal, MD, and a panel of leading malaria experts drawn from academia, the military, and international health organizations survey the latest scientific understanding of antimalarial chemotherapy, emphasizing the molecular mechanisms of resistance and the description of important new targets. Their survey covers the current status of malarial and antimalarial chemotherapy, the relevant biology and biochemistry of malaria parasites, the antimalarial drugs currently available, new chemical approaches to chemotherapy, and possible new targets for chemotherapy. Comprehensive and cutting-edge, Antimalarial Chemotherapy: Mechanisms of Action, Resistance, and New Directions in Drug Discovery clearly delineates all the basic and clinical research now addressing one of the world's major unresolved disease problems, work that is now powerfully driving the rapid pace of antimalarial drug discovery today.
Download or read book Functional Studies on the Chloroquine Resistance Transporter PfCRT and the HECT E3 Ubiquitin protein Ligase PfUT in Plasmodium Falciparum written by Monika Jankowska-Döllken and published by . This book was released on 2019* with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Posttranslational modifications (PTMs) affect fundamental cellular functions of the human malaria parasite Plasmodium falciparum, including regulation of protein stability, metabolism, proliferation, apoptosis and signal transduction. This study investigates the importance of phosphorylation and ubiquitination in modulating the parasite intraerythrocytic development, as well as their implication in antimalarial drug resistance. The chloroquine resistance transporter PfCRT is a drug-metabolite carrier annotated as a prominent determinant of parasite's reduced susceptibility to quinoline drugs. PfCRT is posttranslationally modified by phosphorylation and palmitoylation. However, the role of these PTMs in regulation of PfCRT function is not fully resolved. Chemical and genetic approaches employed in the current study revealed the relevance of PfCRT phosphorylation at serine 33 in regulating the drug resistance-mediating function of this transporter and in vitro fitness of the parasite. The PfCRT allelic exchange mutants, in which serine 33 was replaced by alanine showed increased sensitivity to chloroquine and quinine. Moreover, PfCRT serine 33 substitution by phospho-mimicking amino acids, glutamic and aspartic acid, could respectively partially and fully, restore the resistance phenotype. The fitness variation between the PfCRT mutants was linked to differences in merozoite numbers and their invasion efficiencies, with alanine mutants displaying a significant advantage in this regard. Identification of a kinase implicated in this phenomenon is desired, as its inhibition in combination with chloroquine could reduce or prevent the further spread of resistance. A HECT E3 ubiquitin ligase, termed ubiquitin transferase PfUT, is a novel candidate gene for multifactorial resistance to quinine. PfUT was shown to localize to the parasite's ER/Golgi complex, but its role in reduced susceptibility to quinine and its physiological function remain unclear. Characterization of PfUT was attempted by a glmS ribozyme-based conditional knockdown of encoding it gene, generated using the CRISPR-Cas9 genome editing technology. Unexpectedly, integration of the glmS sequence resulted in a 2-fold increase in PfUT transcripts correlated with protein levels. PfUT overexpression, in turn, led to S phase-associated lengthening of parasite's cycle, reflected in impaired growth. Glucosamine-induced incomplete downregulation partially restored the wild type phenotype. Moreover, the transgenic parasites exhibited an enhanced susceptibility to quinine and quinidine. An alternative disruption of the pfut locus via a selection-linked integration (SLI-TGD) strategy was unsuccessful, despite multiple attempts. These results underline the importance of PfUT in parasite proliferation and survival. However, a direct proof of PfUT's association with quinine resistance and identification of its biological substrates await further investigation.
Download or read book Global Technical Strategy for Malaria 2016 2030 written by World Health Organization and published by World Health Organization. This book was released on 2015-11-04 with total page 35 pages. Available in PDF, EPUB and Kindle. Book excerpt: The World Health Organization's Global Technical Strategy for Malaria 2016- 2030 has been developed with the aim to help countries to reduce the human suffering caused by the world's deadliest mosquito-borne disease. Adopted by the World Health Assembly in May 2015 it provides comprehensive technical guidance to countries and development partners for the next 15 years emphasizing the importance of scaling up malaria responses and moving towards elimination. It also highlights the urgent need to increase investments across all interventions - including preventive measures diagnostic testing treatment and disease surveillance- as well as in harnessing innovation and expanding research. By adopting this strategy WHO Member States have endorsed the bold vision of a world free of malaria and set the ambitious new target of reducing the global malaria burden by 90% by 2030. They also agreed to strengthen health systems address emerging multi-drug and insecticide resistance and intensify national cross-border and regional efforts to scale up malaria responses to protect everyone at risk.
Download or read book Biochemical Characterisation of the Plasmodium Falciparum Chloroquine Resistance Transporter written by Fadi Baakdah and published by . This book was released on 2020 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "The emergence of resistance to commonly used antimalarials significantly hindered global efforts in eliminating malaria and cost the human race losses of lives in millions. Plasmodium falciparum parasites are the most accountable for morbidity and mortality compared to the other species that infect humans. At the present time, artemisinin combination therapies is the approach used in the field to treat malaria infected people and has shown tremendous success. However, resistance to these combinations recently emerged and the pattern of progression and spreading is alarming. Chloroquine once was the first-line drug for treatment of malaria infected people, however, it became in-effective due to the spread of chloroquine resistant strains. Many attributes of chloroquine, at the time when it was effective, were desired and as such the field took on different approaches to revive it. Some people took an approach to withdraw the use of chloroquine for a significant period of time resulting in the emergence of chloroquine sensitive strains. Others looked into modifying the structure of chloroquine in order to make derivatives that would be an improvement on the original. Additionally, others went on to investigate the molecular mechanism by which the parasite confers resistance to chloroquine. Presently, it is well known that mutations in the chloroquine resistance transporter (PfCRT), expressed on the membrane of a lysosome-like organelle in the parasite, the digestive vacuole (DV), are the primary determinants of chloroquine resistance. The physiological role and normal substrates are still matters of speculation but the protein seems to be important for the parasite survival because knockout-PfCRT clones could not be established. The crystal structure was resolved showing the spatial arrangement of the polypeptide chain relative to the juxtaposition of the transmembrane domains forming the central cavity where drugs would interact with PfCRT. Given PfCRT’s role in chloroquine resistance, we thought if chloroquine was slightly modified it would bypass PfCRT resistance mechanism. The first experimental manuscript thesis, we examined the antimalarial activity of 16 novel chloroquine derivatives against chloroquine-sensitive and -resistant Plasmodium falciparum strains. Only two compounds (e.g., AQ-13 and AQ-129) showed effects that surpassed chloroquine’s effect on chloroquine resistant strains that were examined previously but not to the extent of their relationship with PfCRT. Our results demonstrate that AQ-13 and AQ-129 are poor substrates of PfCRT and thus more effective against chloroquine resistant parasites. In the 2nd manuscript, we describe the high resolution characterisation of an antiserum raised against the full-length C-terminal domain of PfCRT. An IgG pool that recognises a de-phosphorylated Ser411 epitope was extracted and used as a tool to monitor the phosphorylation status of residue Ser411. This pool of IgG`s identified the presence of an Ser411 de-phosphorylated homodimer form of PfCRT that does not localise to the DV membrane as does the monomer PfCRT. We also show that PfCRT monomer in chloroquine-sensitive strain (3D7) is significantly more phosphorylated than in chloroquine-resistant strain (Dd2-H) at Ser411, suggesting a possible functional role for this residue in drug resistance. In the last manuscript, we describe the adoption of mammalian HEK-293F cells as a heterologous system to study PfCRT function. Using HEK-293F cells stably expressing PfCRT wild-type and mutants, we show mutant-PfCRT to cause a significant acidification of the lysosomes, relative to wild-type PfCRT. We also provide direct evidence that acidification was mediated through mutant-PfCRT, since using a proline-165-modified mutant-PfCRT clone restored the acidification of lysosomes to wild-type PfCRT levels. Thus, results of this study show for the first time the role of Pro165 in mutant-PfCRT function"--
Download or read book Chemotherapy and Drug Resistance in Malaria written by Wallace Peters and published by . This book was released on 1987 with total page 822 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Synthesis and Development of Novel Inhibitors of the Plasmodium Falciparum Chloroquine Resistance Transporter written by Karen Joy Deane and published by . This book was released on 2014 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The work detailed in this thesis has been directed towards the synthesis of inhibitors of the Plasmodium falciparum chloroquine resistance transporter (PfCRT). Mutations in this protein are responsible for resistance of the malaria parasite to the antimalarial drug, chloroquine. Inhibitors of PfCRT are known as resistance reversers, and include the antihistamine chlorpheniramine, which has been used as the basis of all the structures that have been developed in this work. Chapter 1 provides an introduction to the disease malaria, caused by Plasmodium parasites. A brief review of antimalarial drugs is presented, with a focus on the most successful of these, chloroquine, and the development of resistance to this drug. Chapter 2 reports the synthetic route to the synthesis of 30 analogues of chlorpheniramine, which includes the preparation and characterisation of 29 previously unreported compounds. Analogues were assayed for and showed the ability to inhibit chloroquine transport by PfCRT, which was correlated to the ability to lower the IC50 of chloroquine in resistant strains of Plasmodium falciparum. The development and synthesis of 10 novel reversed chloroquines is presented in Chapter 3. The targeted structures were analogues of a hybrid structure based on chloroquine and chlorpheniramine, and possessed potent antimalarial activity in addition to their strong activity as inhibitors of PfCRT. 32 new compounds were prepared and characterised. A second generation approach is detailed in the synthesis of 10 reversed sontochins in Chapter 4. The sontochin/chlorpheniramine hybrids showed enhanced activity as inhibitors of PfCRT compared to the previous series. 25 new compounds were synthesised and characterised en route. Chapter 5 describes the synthesis of two chlorpheniramine analogues that have been adapted for inclusion in a reversed tetraoxane. These structures showed no improvement to the activity of chlorpheniramine at inhibiting PfCRT, but possess features for incorporation into an endoperoxide antimalarial. The preparation and characterisation of 20 new compounds is reported.
Download or read book Resistance of Malaria Parasites to Drugs written by World Health Organization. Scientific Group on Resistance of Malaria Parasites to Drugs and published by . This book was released on 1965 with total page 76 pages. Available in PDF, EPUB and Kindle. Book excerpt:
