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Investigating the determinants of resistance to quinine and chloroquine using a novel Plasmodium falciparum genetic crossKanai, Mariko January 2023 (has links)
The repeated emergence of Plasmodium falciparum resistance to first-line antimalarial drugs necessitates understanding the underlying resistance mechanisms to detect and monitor resistance in the field and to inform drug discovery efforts. With the advent of the FRG NOD human liver-chimeric (huHep) mouse model for P. falciparum genetic crosses, interest has renewed in harnessing this forward genetics tool to study traits including drug resistance. The antimalarial quinine (QN) is of particular interest as it has retained efficacy over 400 years as parasite resistance has been slow to develop against the drug, likely due to a multifactorial mechanism of which only several genes have been partially implicated. Chloroquine (CQ) is a former first-line drug for P. falciparum (that is still in use for P. vivax), and it’s phasing out has been associated with the recent emergence of CQ-sensitive P. falciparum parasites. While the CQ resistance transporter (PfCRT) is known to be the primary driver of resistance, studies have provided evidence for secondary modulators of CQ, of which only the multidrug resistance protein 1 (PfMDR1) transporter has been identified. This thesis addresses the hypotheses that additional mediators are involved in the parasite resistance mechanism to QN and that genes other than pfmdr1 modulate parasite resistance to CQ.
In chapter 3, we present the P. falciparum genetic cross that we conducted between the QN- and CQ-sensitive African NF54 and QN- and CQ-resistant Cambodian Cam3.II parasites in huHep mice, in collaboration with Dr. Photini Sinnis’s laboratory at Johns Hopkins University. By applying different selective conditions to cross progeny bulk pools prior to cloning these bulks, we were able to recover 120 unique recombinant progeny from this cross. We observed minimal overlap in the progeny genotypes obtained from CQ and QN pressure, suggesting distinct mechanisms for parasite resistance to these drugs. Bulk progeny selection and progeny clone-based QN linkage mapping approaches identified quantitative trait loci (QTLs) on chromosomes 7 and 12, as well as minor QTLs on other chromosomes, consistent with a multifactorial resistance mechanism. We applied the latter approach to investigate parasite response to CQ and its active metabolite monodesethyl-CQ (md-CQ) and identified a novel chromosome 12 QTL in addition to pfcrt. Interestingly, while the chromosome 12 QTLs overlapped, the chromosome 7 QTL for high-grade QN resistance did not contain pfcrt.
In chapter 4, we used bioinformatic approaches, whole-genome sequence data from our cross and field isolates, and literature review to identify the drug/metabolite transporter 1 (DMT1) as the top candidate of the chromosome 7 QTL, and S-adenosylmethionine mitochondrial carrier protein (SAMC), hydroxyethylthiazole kinase (ThzK), and ATP-dependent zinc metalloprotease (FtsH1) as the top candidates for the chromosome 12 QTLs. By harnessing Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas9 gene editing methodologies (SNP-editing, knockout, and tagging), we obtained evidence favoring DMT1 as a marker of QN resistance and localized this transporter to structures associated with vesicular trafficking, PVM, lipid bodies, and the lysosome-like digestive vacuole. We also harnessed SNP-editing and identified FtsH1 as a potential mediator of QN resistance and a modulator of CQ and md-CQ resistance. QN, mefloquine, and lumefantrine belong to the same aryl-amino alcohol class, and we found that QN is structurally more similar to mefloquine than lumefantrine. We also showed that QN can partially inhibit heme detoxification.
While conducting the work outlined in chapters 3 and 4, we identified an unmet need for quickly identifying clonal recombinant progeny and validating parasite identity, which inspired the study presented in chapter 5. We developed a genotyping method that can assess drug resistance-conferring SNPs directly from P. falciparum culture or infected blood as well as a multiplexed microsatellite genotyping method with five broadly informative markers. Both methods were applied in chapter 3 to identify clonal recombinant progeny, and the SNP genotyping method was used in chapter 4 to validate gene editing and progeny identity. We also tested the resolution, sensitivity, time, and cost of each method as well as whole-genome sequencing and recommended the ideal application for each genotyping method.
Our data demonstrate that DMT1 is a novel marker for QN resistance, and a new chromosome 12 locus associates with CQ response, of which ftsh1 is a potential candidate. In chapter 6, we discuss the potential mechanisms by which DMT1 is involved in QN resistance, the potential impact of our findings, and future experiments that can further characterize the QN and CQ resistance mechanisms and the functional role of these candidate genes. Read more
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The Study of Autophagy in <i>Plasmodium falciparum</i>Walker, Dawn Marie January 2013 (has links)
No description available.
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Biochemical Characterization of Two Aminopeptidases Involved in Hemoglobin Catabolism in the Food Vacuole of Plasmodium falciparumRagheb, Daniel Raafat Tadros 29 April 2011 (has links)
The parasite Plasmodium falciparum is the causative agent of the most severe form of human malaria. During its intraerythocytic life cycle, P. falciparum transports red blood cell contents to its acidic organelle, known as the food vacuole, where a series of proteases degrade a majority of the host hemoglobin. Two metalloaminopeptidases, PfAPP and PfA-M1, have been previously localized to the food vacuole (in addition to distinct secondary locations for each), implicating them in the final stages of hemoglobin catabolism. Prior genetic work has determined these enzymes are necessary for efficient parasite proliferation, highlighting them as potential anti-malarial drug targets. This study presents the biochemical basis for the catalytic roles of these two enzymes in the hemoglobin degradation pathway. PfAPP, an aminopeptidase P homolog, is specific for hydrolyzing the N-termini of peptides containing penultimate prolines. PfA-M1 is a member of the expansive M1 family of proteases and exhibits a broad specificity towards substrates. The two enzymes are ubiquitous, found in organisms across all kingdoms of life. Their presence in an acidic environment is unique for aminopeptidase P proteins and rare for M1 homologs. Our immunolocalization results have confirmed the dual distribution of these two enzymes in the parasite. Vacuolar targeting was found to be associated with the Plasmodium specific N-terminal extension found in the PfA-M1 sequence by yellow fluorescent protein fusion studies. Kinetic analysis of recombinant forms of PfAPP and PfA-M1 revealed both enzymes are stable and catalytically efficient in the substrate rich, acidic environment of the parasite food vacuole. In addition, mutagenic exploration of the PfA-M1 active site has determined a residue important in dictating substrate specificity among homologs of the same family. These results provide insight into the parasite's functional recruitment of these enzymes to deal with the final stages of hemoglobin catabolism and necessary considerations for inhibitor design. / Ph. D. Read more
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Proteome-wide Functional Profiling of Serine Hydrolases in the Human Malaria ParasiteElahi, AEM Rubayet 14 June 2019 (has links)
The serine hydrolase (SH) enzyme superfamily is one of the largest and most diverse enzyme classes in eukaryotes and prokaryotes. The most virulent human malaria parasite Plasmodium falciparum has over 40 predicted serine hydrolases (SH). Prior investigation on a few of these have suggested their critical role in parasite biology. The majority of the SHs in P. falciparum have not been functionally characterized. Investigation of these uncharacterized SHs will provide new insights into essential features of parasite metabolism and possibly lead to new antimalarial targets. In this study, we have employed activity-based protein profiling (ABPP) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) to functionally characterize SHs. In our effort to profile plasmodial SHs using ABPP, we have identified a human erythrocyte SH, acylpeptide hydrolase (APEH) in the developing parasites. This finding is the first report of internalization of host hydrolytic enzyme by the parasite. Treatment of parasites with an APEH specific triazole urea inhibitor, AA74-1, caused growth inhibition in parasites with poor potency in the first replication cycle, however, the potency dramatically increased in the second cycle. We show that this unique growth inhibition profile is due to the inability of AA74-1 to inhibit parasite-internalized APEH in vivo. These findings suggest that internalization of active APEH by the parasite is essential for parasite survival.
Lipases catalyze the hydrolysis of ester bonds of lipid species such as neutral lipids and phospholipids. Although roles of lipases in propagation, as well as virulence in various organisms, have been acknowledged, in P. falciparum lipases remain understudied. We combined LC-MS/MS with the SH-directed ABPP to identify lipases of SH superfamily in P. falciparum. We have identified 16 plasmodial SHs with putative lipase activity. Bioinformatics analysis of our identified lipases is consistent with our findings. We have screened a panel of various classes of SH inhibitors in a competitive ABPP. A plasmodial putative lipase was potently and specifically inhibited by human monoacylglycerol lipase inhibitor. This inhibition profile suggests it as a monoacylglycerol lipase which plays a role in releasing fatty acids from neutral lipid. This finding shows that how inhibitor screening can aid in building hypotheses on biological roles of an enzyme. Altogether, in this dissertation, we have presented a robust strategy of identifying and functionally characterizing SHs in P. falciparum, which opens the door to the discovery of new biological processes. / Doctor of Philosophy / Malaria contributed to nearly a half a million deaths in 2017. The vast majority of malaria-related deaths are due to the parasite Plasmodium falciparum. This parasite resides inside human red blood cells (erythrocytes) and grows rapidly during a 48 hour cycle. There are over 40 serine hydrolase (SH) superfamily proteins in the parasite. Biological functions of the majority of SHs in the parasite remains unknown. Study on these SHs will provide new insights into parasite biology, and possibly present new antimalarial drug targets. We used chemical biology techniques to identify and functionally characterize parasite SHs. In one study, we show the parasite intenalized a human erythrocyte SH, acylpeptide hydrolase (APEH). We used an APEH-specific inhibitor to investigate the biological significance of internalized APEH in parasite biology. Treatment of the parasite with the inhibitor resulted in parasite growth inhibition suggesting internalization of APEH is essential for parasite survival. Lipases are enzymes that aid in break down of lipids and have shown to be crucial for growth and pathogenicity in various organisms. Lipases and lipid catabolism remain understudied in the malaria parasite. We used mass spectrometry in our approach to identify 16 lipases in asexual parasites. We have also shown that screening with highly specific inhibitors can help in predicting biological function of a particular enzyme. In summary, in this body of work, we have presented an approach of studying SHs in the malaria parasite, which will provide new insights into parasite biology. Read more
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Investigations into the Nature of the Endosomal System in Plasmodium falciparumKrai, Priscilla M. 27 August 2013 (has links)
The parasite Plasmodium falciparum causes the most virulent form of human malaria and is responsible for the vast majority of malaria-related deaths. During the asexual intraerythrocytic stage, the parasite must transport newly synthesized proteins and endocytosed cargo to a variety of organelles, many of which are formed de novo and have no human equivalent. This process in mammalian cells would utilize an endosomal protein trafficking system, but no endosomal structures or proteins have been described in the parasite. Prior work on the parasite genome indicated that several proteins, which could potentially coordinate an endosomal network, were encoded in the genome and expressed during the asexual parasite stages. In this study, we have localized and attempted to further characterize these proteins in the context of the endosomal system. Two well-conserved protein components of the late endosome, the retromer cargo-selective complex and Rab7, were found on a previously un-described inherited structure adjacent to the parasite Golgi apparatus and in close opposition to nascent rhoptries (specialized secretory organelles required for invasion). The retromer cargo-selective complex was also in close proximity to its putative cargo, a P. falciparum homolog of the sortilin family of protein sorting receptors, PfSortilin. Another protein, PfFCP, the sole FYVE domain-containing protein in the P. falciparum genome, was localized to the membrane of a specialized acidic organelle, known as the food vacuole, where the parasite catabolizes the majority of its host cell hemoglobin. We analyzed the effects of a PfFCP dominant negative mutant and found that it altered food vacuole morphology and trafficking. A previous report localized the early endosome phosphoinositide, phosphatidylinositol 3-phosphate, to the food vacuole membrane, and in conjunction with our studies on PfFCP, this has raised doubts about the food vacuole as a lysosome equivalent in the parasite. The combination of both early and late endosome protein homologs in the parasite, and their potential function, has led to a new model of protein trafficking within the parasite that includes the food vacuole as a terminal early endosome and the apical organelles as lysosome equivalents. / Ph. D. Read more
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Screening of Tanzanian medicinal plants against Plasmodium falciparum and human immunodeficiency virus.Maregesi, S., Van Miert, S., Pannecouque, C., Feiz-Haddad, M.H., Hermans, N., Wright, Colin W., Vlietinck, A. J., Aspers, S., Pieters, L. January 2010 (has links)
No / Medicinal plants used to treat infectious diseases in Bunda district, Tanzania, were screened for activity against Plasmodium falciparum and human Immunodeficiency Virus Type 1 (HIV-1, IIIB strain) and Type 2 (HIV-2, ROD strain). Antiplasmodial activity was observed for the 80% MeOH extract of Ormocarpum kirkii (root; MIC = =31.25 ¿g/mL). Combretum adenogonium (leaves), Euphorbia tirucalli (root), Harrisonia abyssinica (root), Rhyncosia sublobata (root), Sesbania sesban (root), Tithonia diversifolia (leaves), and Vernonia cinerascens (leaves; MIC value of 62.5 ¿g/mL). With regard to HIV, 80% MeOH extracts of Barleria eranthemooides (root), Cambretum adenogonium (leaves and stem bark), Elaeodedron schlechteranum (stem bark and root bark), Lannea schweinfurthii (stem bark), Terminalia mollis (stem bark and root bark), Acacia tortilis (stem bark), Ficus cycamorus (stem bark) and Indigofera colutea (shoot), as well as H2O extracts from Barleria eranthemoides (root), Combretum adenogonium (leaves and stem bark)and Terminalia mollis (stem bark and root bark) exhibited IC50 values below 10 ¿g/mL against HIV-1 (IIIB strain). The highest anti-HIV-1 activity value was obtained for the B. eranthemoides 80% MeOH root extract (IC50 value 2.1 ¿g/mL). Only a few extracts were active against HIV-2, such as the 80% MeOH extract from Lannea schweinfurthii (stem bark) and Elaeodedron schlechteranum (root bark), showing IC50 values < 10 ¿g/mL. Read more
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Metabolism of cryptolepine and 2-fluorocryptolepine by aldehyde oxidaseStell, J. Godfrey P., Wheelhouse, Richard T., Wright, Colin W. January 2012 (has links)
No / Objectives To investigate the metabolism of cryptolepine and some cryptolepine
analogues by aldehyde oxidase, and to assess the implications of the results on the
potential of cryptolepine analogues as antimalarial agents.
Methods The products resulting from the oxidation of cryptolepine and
2-fluorocryptolepine by a rabbit liver preparation of aldehyde oxidase were isolated
and identified using chromatographic and spectroscopic techniques. The antiplasmodial
activity of cryptolepine-11-one was assessed against Plasmodium falciparum
using the parasite lactate dehydrogenase assay.
Key findings Cryptolepine was oxidized by aldehyde oxidase give cryptolepine-11-
one. Although 2-fluorocryptolepine was found to have less affinity for the enzyme
than cryptolepine,it was a better substrate for aldehyde oxidase than the parent compound.
In contrast, quindoline, the 11-chloro- , 2,7-dibromo- and 2-methoxy analogues
of cryptolepine were not readily oxidized. Cryptolepine-11-one was found to
be inactive against P. falciparum in vitro raising the possibility that the effectiveness
of cryptolepine as an antimalarial, may be compromised by metabolism to an
inactive metabolite by liver aldehyde oxidase.
Conclusions Cryptolepine and 2-fluorocryptolepine are substrates for aldehyde
oxidase. This may have implications for the design and development of cryptolepine
analogues as antimalarial agents. Read more
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Screening Indian plant species for antiplasmodial properties – ethnopharmacological compared to random selection.Kantamreddi, Venkata Siva Satya Narayana, Wright, Colin W. 01 1900 (has links)
No / In the search for biologically active plant species, many studies have shown that an ethnopharmacological approach is more effective than a random collection. In order to determine whether this is true in the case of plant species used for the treatment of malaria in Orissa, India, the antiplasmodial activities of extracts prepared from 25 traditionally used species were compared with those of 25 species collected randomly. As expected, plant species used traditionally for the treatment of malaria were more likely to exhibit antiplasmodial activity (21 species (84%) active against Plasmodium falciparum strain 3D7) than plant species collected randomly (9 species (32%)). However, of the nine active randomly collected species, eight had not previously been reported to possess antiplasmodial activity while one inactive species had been reported to be active in another study. Of the 21 active species of traditional antimalarial treatments, only six had been reported previously. This study suggests that while the selection of traditional medicinal plants is more predictive of antiplasmodial study, random collections may still be of value for the identification of new antiplasmodial species. Read more
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Semi-Synthetic Analogues of Cryptolepine as a Potential Source of Sustainable Drugs for the Treatment of Malaria, Human African Trypanosomiasis and CancerAbacha, Yabalu Z., Forkuo, A.D., Gbedema, S.Y., Mittal, N., Ottilie, S., Rocamora, F., Winzeler, E.A., van Schalkwyk, D.A., Kelly, J.M., Taylor, M.C., Reader, J., Birkholtz, L-M., Lisgarten, D.R., Cockcroft, J.K., Lisgarten, J.N., Palmer, R.A., Talbert, R.C., Shnyder, Steven, Wright, Colin W. 26 April 2022 (has links)
Yes / The prospect of eradicating malaria continues to be challenging in the face of increasing
parasite resistance to antimalarial drugs so that novel antimalarials active against asexual,
sexual, and liver-stage malaria parasites are urgently needed. In addition, new antimalarials
need to be affordable and available to those most in need and, bearing in mind climate
change, should ideally be sustainable. The West African climbing shrub Cryptolepis
sanguinolenta is used traditionally for the treatment of malaria; its principal alkaloid,
cryptolepine (1), has been shown to have antimalarial properties, and the synthetic
analogue 2,7-dibromocryptolepine (2) is of interest as a lead toward new antimalarial
agents. Cryptolepine (1) was isolated using a two-step Soxhlet extraction of C.
sanguinolenta roots, followed by crystallization (yield 0.8% calculated as a base with
respect to the dried roots). Semi-synthetic 7-bromo- (3), 7, 9-dibromo- (4), 7-iodo- (5), and
7, 9-dibromocryptolepine (6) were obtained in excellent yields by reaction of 1 with
N-bromo- or N-iodosuccinimide in trifluoroacetic acid as a solvent. All compounds
were active against Plasmodia in vitro, but 6 showed the most selective profile with
respect to Hep G2 cells: P. falciparum (chloroquine-resistant strain K1), IC50 = 0.25 µM, SI
= 113; late stage, gametocytes, IC50 = 2.2 µM, SI = 13; liver stage, P. berghei sporozoites
IC50 = 6.13 µM, SI = 4.6. Compounds 3–6 were also active against the emerging zoonotic species P. knowlesi with 5 being the most potent (IC50 = 0.11 µM). In addition, 3–6 potently
inhibited T. brucei in vitro at nM concentrations and good selectivity with 6 again being the
most selective (IC50 = 59 nM, SI = 478). These compounds were also cytotoxic to wild-type
ovarian cancer cells as well as adriamycin-resistant and, except for 5, cisplatin-resistant
ovarian cancer cells. In an acute oral toxicity test in mice, 3–6 did not exhibit toxic effects at
doses of up to 100 mg/kg/dose × 3 consecutive days. This study demonstrates that C.
sanguinolenta may be utilized as a sustainable source of novel compounds that may lead
to the development of novel agents for the treatment of malaria, African trypanosomiasis,
and cancer. Read more
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MMV008138 and analogs: potential novel antimalarial agents for P. falciparumLiu, Lixuan 15 May 2018 (has links)
Malaria is a severe and deadly mosquito-borne disease. Although treatable, the continuous emergence of multi-drug resistant parasite strains urgently calls for the development of novel antimalarial agents. P. falciparum parasites synthesize essential isoprenoid precursors, isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP), via a non-mevalonate pathway: the methylerythritol phosphate (MEP) pathway. This pathway is not utilized by humans. Thus, compounds that target the MEP pathway and disrupt isoprenoid biosynthesis in P. falciparum hold promise as potent and safe new antimalarial agents, that engage new targets.
Previously, we and others identified MMV008138 from the Malaria Box as a MEP pathway targeting compound. Later work revealed that it targets the IspD enzyme within the MEP pathway. Work in the Carlier group has established preliminary structure-activity relationship (SAR) of MMV008138: 1) (1R,3S)-configuration is required; 2) 2', 4'-disubstitution of the D-ring with small, electronegative substituents; 3) functional importance of carboxylate acid at C3.
In this work, I aim to gain further insight into the C3 SAR and A-ring SAR of lead compound MMV008138. Synthesized acid bioisosteres and A-ring analogs of MMV008138 were evaluated in their ability to inhibit P. falciparum parasite growth. We showed that the C3 substituent of MMV008138 has a very tight SAR, and likely interacts with a very constricted pocket within the PfIspD enzyme. A-ring modifications are limited to certain positions of MMV001838 and need to be sterically small. However, we have yet to identify a modification that significantly improves drug lead potency.
Future work will continue towards understanding the A-ring SAR of MMV008138, as well as D-ring SAR and C1-SAR. Efforts will also be directed towards finding analogs with improved potency, transport and metabolic stability. / MS / Malaria is a severe and deadly mosquito-borne disease, caused by malaria parasites. Although treatable, the continuous emergence of drug resistance urgently calls for the development of novel antimalarial agents. Research in the Carlier group is aimed at finding drug molecules that can selectively target and kill the malarial parasite, and at the same time be safe to humans. The Carlier group has identified MMV008138 from the Malaria Box as a promising drug lead. In this work, I aim to understand the how the structure of MMV008138 play a role in its ability to kill malaria parasites. These results will help identify modification strategies that may significantly improve drug lead potency. Read more
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