Browsing by Author "Theron, Anjo"

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    Characterization, modelling and docking studies of Plasmodium falciparum kinase PfCDPK4
    (AOSIS, 2019-04) Makungo, T; Tsekoa, Tsepo L; Theron, Anjo; Mancama, Dalubuhle T; Van Ree, T
    Characterization, modelling and docking studies of Plasmodium falciparum kinase PfCDPK4: The increasing incidence of Plasmodium strains that are resistant to current frontline antimalarial drugs has become one of the greatest challenges of controlling malaria incidence and mortality. There is, therefore, an urgent need to develop novel targets and antimalarial drugs that are effective against drug-resistant malarial parasites. At the same time the need to develop antimalarial drugs that furthermore prevent disease transmission, has become an increasingly important consideration. Calcium dependent protein kinases (CDPKs) regulate a variety of biological processes in the malaria parasite Plasmodium falciparum, CDPK4 being of prime importance in Plasmodium biology. In this study the structure of PfCDPK4 was used as a template in the discovery of malaria drug leads. The model structure of PfCDPK4 was generated by homology modelling, and model validation confirmed that the model of PfCDPK4 is of stereochemical quality. The molecular modelling approach of in silico screening against the target molecule PfCDPK4 utilized a large library of chemical compounds, some natural chemical compounds, and clinically approved kinase inhibitors. In silico screening of the Biofocus library against PfCDPK4 resulted in twenty-six compounds being identified; in vitro screening confirmed that three of these compounds exhibit moderate antimalarial activity against the NF54 strain of Plasmodium falciparum, with the percentage inhibition ranging between 42% and 47%.
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    Characterization, modelling and docking studies of Plasmodium falciparum kinase PfCDPK4
    (AOSIS, 2019-04) Makungo, T; Tsekoa, Tsepo L; Theron, Anjo; Mancama, Dalubuhle T; Van Ree, T
    Characterization, modelling and docking studies of Plasmodium falciparum kinase PfCDPK4: The increasing incidence of Plasmodium strains that are resistant to current frontline antimalarial drugs has become one of the greatest challenges of controlling malaria incidence and mortality. There is, therefore, an urgent need to develop novel targets and antimalarial drugs that are effective against drug-resistant malarial parasites. At the same time the need to develop antimalarial drugs that furthermore prevent disease transmission, has become an increasingly important consideration. Calcium dependent protein kinases (CDPKs) regulate a variety of biological processes in the malaria parasite Plasmodium falciparum, CDPK4 being of prime importance in Plasmodium biology. In this study the structure of PfCDPK4 was used as a template in the discovery of malaria drug leads. The model structure of PfCDPK4 was generated by homology modelling, and model validation confirmed that the model of PfCDPK4 is of stereochemical quality. The molecular modelling approach of in silico screening against the target molecule PfCDPK4 utilized a large library of chemical compounds, some natural chemical compounds, and clinically approved kinase inhibitors. In silico screening of the Biofocus library against PfCDPK4 resulted in twenty-six compounds being identified; in vitro screening confirmed that three of these compounds exhibit moderate antimalarial activity against the NF54 strain of Plasmodium falciparum, with the percentage inhibition ranging between 42% and 47%.
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    Differential inhibition of adenylylated and deadenylylated forms of M. tuberculosis glutamine synthetase as a drug discovery platform
    (PLOS, 2017-10) Theron, Anjo; Roth, Robyn L; Hoppe, H; Parkinson, C; Van der Westhuyzen, Christiaan W; Stoychev, Stoyan H; Wiid, I; Pietersen, RD; Baker, B; Kenyon, CP
    Glutamine synthetase is a ubiquitous central enzyme in nitrogen metabolism that is controlled by up to four regulatory mechanisms, including adenylylation of some or all of the twelve subunits by adenylyl transferase. It is considered a potential therapeutic target for the treatment of tuberculosis, being essential for the growth of Mycobacterium tuberculosis, and is found extracellularly only in the pathogenic Mycobacterium strains. Human glutamine synthetase is not regulated by the adenylylation mechanism, so the adenylylated form of bacterial glutamine synthetase is of particular interest. Previously published reports show that, when M. tuberculosis glutamine synthetase is expressed in Escherichia coli, the E. coli adenylyl transferase does not optimally adenylylate the M. tuberculosis glutamine synthetase. Here, we demonstrate the production of soluble adenylylated M. tuberulosis glutamine synthetase in E. coli by the co-expression of M. tuberculosis glutamine synthetase and M. tuberculosis adenylyl transferase. The differential inhibition of adenylylated M. tuberulosis glutamine synthetase and deadenylylated M. tuberulosis glutamine synthetase by ATP based scaffold inhibitors are reported. Compounds selected on the basis of their enzyme inhibition were also shown to inhibit M. tuberculosis in the BACTEC 460TB™ assay as well as the intracellular inhibition of M. tuberculosis in a mouse bone-marrow derived macrophage assay.
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    Evaluating blood–brain barrier permeability, cytotoxicity, and activity of potential acetylcholinesterase inhibitors: In vitro and in silico study
    (2024-12) Maboko, LM; Theron, Anjo; Panayides, Jenny-Lee; Cordier, W; Fisher, D; Steenkamp, V
    Acetylcholinesterase inhibitors (AChEIs) remain the first-line treatment for Alzheimer's disease. However, these drugs are largely symptomatic and often associated with adverse effects. This study aimed to evaluate novel pharmacophores for their in vitro AChEI activity, blood–brain barrier (BBB) permeability, and cytotoxic potential, hypothesizing that a combination of AChEIs could enhance symptom management while minimizing toxicity. A library of 1453 synthetic pharmacophores was assessed using in vitro and in silico methods to determine their feasibility as an inhibitor of the AChE enzyme. An in-house miniaturized Ellman's assay determined acellular AChEI activities, while pharmacokinetic properties were evaluated using the SwissADME web tool. The combinational effects of in silico BBB-permeable pharmacophores and donepezil were examined using a checkerboard AChEI assay. Cytotoxicity of active compounds and their synergistic combinations was assessed in SH-SY5Y neuroblastoma and bEnd.5 cells using the sulforhodamine B assay. Cellular AChEI activity of active in silico BBB-permeable predicted compounds was determined using an SH-SY5Y AChE-based assay. An in vitro BBB model was used to assess the effect of compounds on the integrity of the bEnd.5 monolayer. Out of the screened compounds, 12 demonstrated 60% AChEI activity at 5 μM, with compound A51 showing the lowest IC50 (0.20 μM). Five compounds were identified as BBB-permeable, with the donepezil-C53 combination at ¼IC50 exhibiting the strongest synergy (CI = 0.82). Compounds A136 and C129, either alone or with donepezil, showed cytotoxicity. Notably, compound C53, both alone and in combination with donepezil, demonstrated high AChEI activity and promising BBB permeability, warranting further investigation.
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    New transmission-selective antimalarial agents through hit-to-lead optimization of 2-([1,1'-Biphenyl]-4-carboxamido)benzoic acid derivatives
    (2022-09) Reader, J; Opperman, DFL; Van der Watt, ME; Theron, Anjo; Leshabane, M; Da Rocha, S; Turner, J; Garrabrant, K; Piña, I; Mills, C
    Malaria elimination requires multipronged approaches, including the application of antimalarial drugs able to block human-to-mosquito transmission of malaria parasites. The transmissible gametocytes of Plasmodium falciparum seem to be highly sensitive towards epidrugs, particularly those targeting demethylation of histone post-translational marks. Here, we report exploration of compounds from a chemical library generated during hit-to-lead optimization of inhibitors of the human histone lysine demethylase, KDM4B. Derivatives of 2-([1,1'-biphenyl]-4-carboxamido) benzoic acid, around either the amide or a sulfonamide linker backbone (2-(arylcarboxamido)benzoic acid, 2-carboxamide (arylsulfonamido)benzoic acid and N-(2-(1H-tetrazol-5-yl)phenyl)-arylcarboxamide), showed potent activity towards late-stage gametocytes (stage IV/V) of P. falciparum, with the most potent compound reaching single digit nanomolar activity. Structure-activity relationship trends were evident and frontrunner compounds also displayed microsomal stability and favourable solubility profiles. Simplified synthetic routes support further derivatization of these compounds for further development of these series as malaria transmission-blocking agents.
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    The Tuberculosis Drug Candidate SQ109 and Its Analogs Have Multistage Activity against Plasmodium falciparum
    (2024-08) Watson, SJ; Van der Watt, ME; Theron, Anjo; Reader, J; Tshabalala, S; Erlank, E; Koekemoer, LL; Naude, M; Stampolaki, M; Adewole, F
    Toward repositioning the antitubercular clinical candidate SQ109 as an antimalarial, analogs were investigated for structure–activity relationships for activity against asexual blood stages of the human malaria parasite Plasmodium falciparum pathogenic forms, as well as transmissible, sexual stage gametocytes. We show that equipotent activity (IC50) in the 100–300 nM range could be attained for both asexual and sexual stages, with the activity of most compounds retained against a multidrug-resistant strain. The multistage activity profile relies on high lipophilicity ascribed to the adamantane headgroup, and antiplasmodial activity is critically dependent on the diamine linker. Frontrunner compounds showed conserved activity against genetically diverse southern African clinical isolates. We additionally validated that this series could block transmission to mosquitoes, marking these compounds as novel chemotypes with multistage antiplasmodial activity.