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Sharma R, Lawrenson AS, Fisher NE, Warman AJ, Shone AE, Hill A, Mbekeani A, Pidathala C, Amewu RK, Leung S, Gibbons P, Hong DW, Stocks P, Nixon GL, Chadwick J, Shearer J, Gowers I, Cronk D, Parel SP, O'Neill PM, Ward SA, Biagini GA, Berry NG. Identification of novel antimalarial chemotypes via chemoinformatic compound selection methods for a high-throughput screening program against the novel malarial target, PfNDH2: increasing hit rate via virtual screening methods. J Med Chem 2012; 55:3144-54. [PMID: 22380711 PMCID: PMC3324984 DOI: 10.1021/jm3001482] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
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Malaria is responsible for approximately 1 million deaths
annually; thus, continued efforts to discover new antimalarials are
required. A HTS screen was established to identify novel inhibitors
of the parasite's mitochondrial enzyme NADH:quinone oxidoreductase
(PfNDH2). On the basis of only one known inhibitor of this enzyme,
the challenge was to discover novel inhibitors of PfNDH2 with diverse
chemical scaffolds. To this end, using a range of ligand-based chemoinformatics
methods, ∼17000 compounds were selected from a commercial library
of ∼750000 compounds. Forty-eight compounds were identified
with PfNDH2 enzyme inhibition IC50 values ranging from
100 nM to 40 μM and also displayed exciting whole cell antimalarial
activity. These novel inhibitors were identified through sampling
16% of the available chemical space, while only screening 2% of the
library. This study confirms the added value of using multiple ligand-based
chemoinformatic approaches and has successfully identified novel distinct
chemotypes primed for development as new agents against malaria.
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Pidathala C, Amewu R, Pacorel B, Nixon GL, Gibbons P, Hong WD, Leung SC, Berry NG, Sharma R, Stocks PA, Srivastava A, Shone AE, Charoensutthivarakul S, Taylor L, Berger O, Mbekeani A, Hill A, Fisher NE, Warman AJ, Biagini GA, Ward SA, O'Neill PM. Identification, design and biological evaluation of bisaryl quinolones targeting Plasmodium falciparum type II NADH:quinone oxidoreductase (PfNDH2). J Med Chem 2012; 55:1831-43. [PMID: 22364416 PMCID: PMC3297363 DOI: 10.1021/jm201179h] [Citation(s) in RCA: 81] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
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A program was undertaken to identify hit compounds against
NADH:ubiquinone
oxidoreductase (PfNDH2), a dehydrogenase of the mitochondrial electron
transport chain of the malaria parasite Plasmodium falciparum. PfNDH2 has only one known inhibitor, hydroxy-2-dodecyl-4-(1H)-quinolone
(HDQ), and this was used along with a range of chemoinformatics methods
in the rational selection of 17 000 compounds for high-throughput
screening. Twelve distinct chemotypes were identified and briefly
examined leading to the selection of the quinolone core as the key
target for structure–activity relationship (SAR) development.
Extensive structural exploration led to the selection of 2-bisaryl
3-methyl quinolones as a series for further biological evaluation.
The lead compound within this series 7-chloro-3-methyl-2-(4-(4-(trifluoromethoxy)benzyl)phenyl)quinolin-4(1H)-one
(CK-2-68) has antimalarial activity against the 3D7 strain of P. falciparum of 36 nM, is selective for PfNDH2 over other
respiratory enzymes (inhibitory IC50 against PfNDH2 of
16 nM), and demonstrates low cytotoxicity and high metabolic stability
in the presence of human liver microsomes. This lead compound and
its phosphate pro-drug have potent in vivo antimalarial activity after
oral administration, consistent with the target product profile of
a drug for the treatment of uncomplicated malaria. Other quinolones
presented (e.g., 6d, 6f, 14e) have the capacity to inhibit both PfNDH2 and P. falciparum cytochrome bc1, and studies to determine
the potential advantage of this dual-targeting effect are in progress.
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Leung SC, Gibbons P, Amewu R, Nixon GL, Pidathala C, Hong WD, Pacorel B, Berry NG, Sharma R, Stocks PA, Srivastava A, Shone AE, Charoensutthivarakul S, Taylor L, Berger O, Mbekeani A, Hill A, Fisher NE, Warman AJ, Biagini GA, Ward SA, O'Neill PM. Identification, design and biological evaluation of heterocyclic quinolones targeting Plasmodium falciparum type II NADH:quinone oxidoreductase (PfNDH2). J Med Chem 2012; 55:1844-57. [PMID: 22364417 PMCID: PMC3351724 DOI: 10.1021/jm201184h] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
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Following a program undertaken to identify hit compounds
against
NADH:ubiquinone oxidoreductase (PfNDH2), a novel enzyme target within
the malaria parasite Plasmodium falciparum, hit to
lead optimization led to identification of CK-2-68, a molecule suitable
for further development. In order to reduce ClogP and improve solubility
of CK-2-68 incorporation of a variety of heterocycles, within the
side chain of the quinolone core, was carried out, and this approach
led to a lead compound SL-2-25 (8b). 8b has
IC50s in the nanomolar range versus both the enzyme and whole cell P. falciparum (IC50 = 15 nM PfNDH2; IC50 = 54 nM (3D7 strain
of P. falciparum) with notable oral activity of ED50/ED90 of 1.87/4.72 mg/kg versus Plasmodium
berghei (NS Strain) in a murine model of malaria when formulated
as a phosphate salt. Analogues in this series also demonstrate nanomolar
activity against the bc1 complex of P. falciparum providing the potential added benefit of a
dual mechanism of action. The potent oral activity of 2-pyridyl quinolones
underlines the potential of this template for further lead optimization
studies.
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Hale I, O'Neill PM, Berry NG, Odom A, Sharma R. The MEP pathway and the development of inhibitors as potential anti-infective agents. MEDCHEMCOMM 2012. [DOI: 10.1039/c2md00298a] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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55
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Salcedo-Sora JE, Ochong E, Beveridge S, Johnson D, Nzila A, Biagini GA, Stocks PA, O'Neill PM, Krishna S, Bray PG, Ward SA. The molecular basis of folate salvage in Plasmodium falciparum: characterization of two folate transporters. J Biol Chem 2011; 286:44659-68. [PMID: 21998306 PMCID: PMC3247980 DOI: 10.1074/jbc.m111.286054] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Tetrahydrofolates are essential cofactors for DNA synthesis and methionine metabolism. Malaria parasites are capable both of synthesizing tetrahydrofolates and precursors de novo and of salvaging them from the environment. The biosynthetic route has been studied in some detail over decades, whereas the molecular mechanisms that underpin the salvage pathway lag behind. Here we identify two functional folate transporters (named PfFT1 and PfFT2) and delineate unexpected substrate preferences of the folate salvage pathway in Plasmodium falciparum. Both proteins are localized in the plasma membrane and internal membranes of the parasite intra-erythrocytic stages. Transport substrates include folic acid, folinic acid, the folate precursor p-amino benzoic acid (pABA), and the human folate catabolite pABAGn. Intriguingly, the major circulating plasma folate, 5-methyltetrahydrofolate, was a poor substrate for transport via PfFT2 and was not transported by PfFT1. Transport of all folates studied was inhibited by probenecid and methotrexate. Growth rescue in Escherichia coli and antifolate antagonism experiments in P. falciparum indicate that functional salvage of 5-methyltetrahydrofolate is detectable but trivial. In fact pABA was the only effective salvage substrate at normal physiological levels. Because pABA is neither synthesized nor required by the human host, pABA metabolism may offer opportunities for chemotherapeutic intervention.
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Berger O, Kaniti A, van Ba CT, Vial H, Ward SA, Biagini GA, Bray PG, O'Neill PM. Synthesis and antimalarial activities of a diverse set of triazole-containing furamidine analogues. ChemMedChem 2011; 6:2094-108. [PMID: 21905228 DOI: 10.1002/cmdc.201100265] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2011] [Revised: 07/29/2011] [Indexed: 11/07/2022]
Abstract
Four different series of triazole diamidines have been prepared by the Pinner method from the corresponding triazole dinitriles. Copper-catalyzed "click chemistry" was used for the synthesis of 1,4- and 4,5-substituted triazoles, aryl magnesium acetylide reagents for the 1,5-substituted triazoles, with a thermal dipolar addition reaction employed for the 2,4-substituted triazoles. In vitro antimalarial activity against two different PfCRT-modified parasite lines (Science 2002, 298, 210-213) of Plasmodium falciparum and inhibition of hemozoin formation were determined for each compound. Several diamidines with potent nanomolar antimalarial activities were identified, and selected molecules were resynthesized as their diamidoxime triazole prodrugs. One of these prodrugs, OB216, proved to be highly potent in vivo with an ED50 value of 5 mg kg(-1) (po) and an observed 100 % cure rate (CD100) of just 10 mg kg(-1) by oral (po) administration in mice infected with P. vinckei.
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Stevenson BJ, Bibby J, Pignatelli P, Muangnoicharoen S, O'Neill PM, Lian LY, Müller P, Nikou D, Steven A, Hemingway J, Sutcliffe MJ, Paine MJI. Cytochrome P450 6M2 from the malaria vector Anopheles gambiae metabolizes pyrethroids: Sequential metabolism of deltamethrin revealed. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2011; 41:492-502. [PMID: 21324359 DOI: 10.1016/j.ibmb.2011.02.003] [Citation(s) in RCA: 178] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/12/2010] [Revised: 02/03/2011] [Accepted: 02/07/2011] [Indexed: 05/30/2023]
Abstract
Resistance to pyrethroid insecticides in the malaria vector Anopheles gambiae is a major threat to malaria control programmes. Cytochome P450-mediated detoxification is an important resistance mechanism. CYP6M2 is over-expressed in wild populations of permethrin resistant A. gambiae but its role in detoxification is not clear. CYP6M2 was expressed in Escherichia coli and a structural model was produced to examine its role in pyrethroid metabolism. Both permethrin and deltamethrin were metabolized. Rates were enhanced by A. gambiae cytochrome b(5) with kinetic parameters of K(M)=11±1μM and k(cat)=6.1±0.4 per min for permethrin (1:1 cis-trans) and K(M)=2.0±0.3μM and k(cat)=1.2±0.1 per min for deltamethrin. Mass spectrometry and NMR analysis identified 4'-hydroxy deltamethrin and hydroxymethyl deltamethrin as major and minor deltamethrin metabolites respectively. Secondary breakdown products included cyano(3-hydroxyphenyl)methyl deltamethrate and deltamethric acid. CYP6M2 was most highly transcribed in the midgut and Malpighian tubules of adult A. gambiae, consistent with a role in detoxification. Our data indicates that CYP6M2 plays an important role in metabolic resistance to pyrethroids and thus an important target for the design of new tools to combat malaria.
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Chadwick J, Amewu RK, Marti F, Garah FBE, Sharma R, Berry NG, Stocks PA, Burrell-Saward H, Wittlin S, Rottmann M, Brun R, Taramelli D, Parapini S, Ward SA, O'Neill PM. Antimalarial Mannoxanes: Hybrid Antimalarial Drugs with Outstanding Oral Activity Profiles and A Potential Dual Mechanism of Action. ChemMedChem 2011; 6:1357-61. [DOI: 10.1002/cmdc.201100196] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2011] [Indexed: 11/11/2022]
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Mercer AE, Copple IM, Maggs JL, O'Neill PM, Park BK. The role of heme and the mitochondrion in the chemical and molecular mechanisms of mammalian cell death induced by the artemisinin antimalarials. J Biol Chem 2011; 286:987-96. [PMID: 21059641 PMCID: PMC3020783 DOI: 10.1074/jbc.m110.144188] [Citation(s) in RCA: 125] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2010] [Revised: 10/05/2010] [Indexed: 01/15/2023] Open
Abstract
The artemisinin compounds are the frontline drugs for the treatment of drug-resistant malaria. They are selectively cytotoxic to mammalian cancer cell lines and have been implicated as neurotoxic and embryotoxic in animal studies. The endoperoxide functional group is both the pharmacophore and toxicophore, but the proposed chemical mechanisms and targets of cytotoxicity remain unclear. In this study we have used cell models and quantitative drug metabolite analysis to define the role of the mitochondrion and cellular heme in the chemical and molecular mechanisms of cell death induced by artemisinin compounds. HeLa ρ(0) cells, which are devoid of a functioning electron transport chain, were used to demonstrate that actively respiring mitochondria play an essential role in endoperoxide-induced cytotoxicity (artesunate IC(50) values, 48 h: HeLa cells, 6 ± 3 μM; and HeLa ρ(0) cells, 34 ± 5 μM) via the generation of reactive oxygen species and the induction of mitochondrial dysfunction and apoptosis but do not have any role in the reductive activation of the endoperoxide to cytotoxic carbon-centered radicals. However, using chemical modulators of heme synthesis (succinylacetone and protoporphyrin IX) and cellular iron content (holotransferrin), we have demonstrated definitively that free or protein-bound heme is responsible for intracellular activation of the endoperoxide group and that this is the chemical basis of cytotoxicity (IC(50) value and biomarker of bioactivation levels, respectively: 10β-(p-fluorophenoxy)dihydroartemisinin alone, 0.36 ± 0.20 μM and 11 ± 5%; and with succinylacetone, >100 μM and 2 ± 5%).
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Marti F, Chadwick J, Amewu RK, Burrell-Saward H, Srivastava A, Ward SA, Sharma R, Berry N, O'Neill PM. Second generation analogues of RKA182: synthetic tetraoxanes with outstanding in vitro and in vivo antimalarial activities. MEDCHEMCOMM 2011. [DOI: 10.1039/c1md00102g] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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61
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Barton V, Fisher N, Biagini GA, Ward SA, O'Neill PM. Inhibiting Plasmodium cytochrome bc1: a complex issue. Curr Opin Chem Biol 2010; 14:440-6. [PMID: 20570550 DOI: 10.1016/j.cbpa.2010.05.005] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2010] [Revised: 05/03/2010] [Accepted: 05/03/2010] [Indexed: 11/19/2022]
Abstract
The cytochrome bc(1) complex is a key mitochondrial enzyme that catalyses transfer of electrons maintaining the membrane potential of mitochondria. Currently, atovaquone is the only drug in clinical use targeting the Plasmodium falciparum bc(1) complex. The rapid emergence of resistance to atovaquone resulted in a costly combination with proguanil (Malarone), limiting its widespread use in resource-poor disease-endemic areas. Cheaper alternatives that can overcome resistance are desperately required. Here we describe recent advances of bc(1)-targeted inhibitors that include hydroxynaphthoquinones (atovaquone analogues), pyridones (clodipol analogues), acridine related compounds (acridinediones and acridones) and quinolones. Significantly, many of these developmental compounds demonstrate little cross resistance with atovaquone-resistant parasite strains, and selected classes have excellent oral activity profiles in rodent models of malaria.
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62
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Biagini GA, Hill A, Mbekeani A, Shone A, Nixon G, Stocks P, Gibbons P, Amewu R, Hong DW, Barton V, Pidathala C, Chadwick J, Le Pensee L, Warman A, Sharma R, Fisher N, Berry NG, O'Neill PM, Ward SA. Development of a novel drug for uncomplicated malaria targeting the mitochondrial NADH:quinone oxidoreductase. Malar J 2010. [PMCID: PMC2963242 DOI: 10.1186/1475-2875-9-s2-o4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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63
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Ward SA, Fisher N, Hill A, Mbekeani A, Shone A, Nixon G, Stocks P, Gibbons P, Amewu R, Hong DW, Barton V, Pidathala C, Chadwick J, Le Pensee L, Warman A, Sharma R, Berry NG, O'Neill PM, Biagini GA. A novel drug for uncomplicated malaria: targeted high throughput screening (HTS) against the type II NADH:ubiquinone oxidoreductase (PfNdh2) of Plasmodium falciparum. Malar J 2010. [PMCID: PMC2963205 DOI: 10.1186/1475-2875-9-s2-i14] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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64
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O'Neill PM, Amewu RK, Nixon GL, Bousejra ElGarah F, Mungthin M, Chadwick J, Shone AE, Vivas L, Lander H, Barton V, Muangnoicharoen S, Bray PG, Davies J, Park BK, Wittlin S, Brun R, Preschel M, Zhang K, Ward SA. Identification of a 1,2,4,5-Tetraoxane Antimalarial Drug-Development Candidate (RKA 182) with Superior Properties to the Semisynthetic Artemisinins. Angew Chem Int Ed Engl 2010; 49:5693-7. [PMID: 20629058 DOI: 10.1002/anie.201001026] [Citation(s) in RCA: 100] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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65
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Barton V, Ward SA, Chadwick J, Hill A, O'Neill PM. Rationale design of biotinylated antimalarial endoperoxide carbon centered radical prodrugs for applications in proteomics. J Med Chem 2010; 53:4555-9. [PMID: 20476788 DOI: 10.1021/jm100201j] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The semisynthetic artemisinin derivatives such as artesunate and artemether, along with the fully synthetic endoperoxide antimalarials (e.g., OZ277, Nature 2004, 430, 900-904), are believed to mediate their antimalarial effects by iron-induced formation of carbon-centered radicals capable of alkylating heme and/or protein. Here, we describe the design and synthesis of a series of biotinylated endoperoxide probe molecules for use in proteomic studies. The target molecules include derivatives of the artemisinin and OZ families, and we demonstrate that these conjugates express nanomolar in vitro activity versus cultured strains of Plasmodium falciparum. We also describe the synthesis of chemically cleavable linked conjugates designed to enable mild elution of labeled proteins during target protein identification.
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66
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Pacorel B, Leung SC, Stachulski AV, Davies J, Vivas L, Lander H, Ward SA, Kaiser M, Brun R, O'Neill PM. Modular synthesis and in vitro and in vivo antimalarial assessment of C-10 pyrrole mannich base derivatives of artemisinin. J Med Chem 2010; 53:633-40. [PMID: 19957999 DOI: 10.1021/jm901216v] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In two steps from dihydroartemisinin, a small array of 16 semisynthetic C-10 pyrrole Mannich artemisinin derivatives (7a-p) have been prepared in moderate to excellent yield. In vitro analysis against both chloroquine sensitive and resistant strains has demonstrated that these analogues have nanomolar antimalarial activity, with several compounds being more than 3 times more potent than the natural product artemisinin. In addition to a potent antimalarial profile, these molecules also have very high in vitro therapeutic indices. Analysis of the optimal Mannich side chain substitution for in vitro and in vivo activity reveals that the morpholine and N-methylpiperazine Mannich side chains provide analogues with the best activity profiles, both in vitro and in vivo in the Peter's 4 day test.
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Amewu R, Gibbons P, Mukhtar A, Stachulski AV, Ward SA, Hall C, Rimmer K, Davies J, Vivas L, Bacsa J, Mercer AE, Nixon G, Stocks PA, O'Neill PM. Synthesis, in vitro and in vivo antimalarial assessment of sulfide, sulfone and vinyl amide-substituted 1,2,4-trioxanes prepared via thiol-olefin co-oxygenation (TOCO) of allylic alcohols. Org Biomol Chem 2010; 8:2068-77. [DOI: 10.1039/b924319d] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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68
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Jones M, Mercer AE, Stocks PA, La Pensée LJI, Cosstick R, Park BK, Kennedy ME, Piantanida I, Ward SA, Davies J, Bray PG, Rawe SL, Baird J, Charidza T, Janneh O, O'Neill PM. Antitumour and antimalarial activity of artemisinin-acridine hybrids. Bioorg Med Chem Lett 2009; 19:2033-7. [PMID: 19249201 DOI: 10.1016/j.bmcl.2009.02.028] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2008] [Revised: 02/05/2009] [Accepted: 02/06/2009] [Indexed: 11/29/2022]
Abstract
Artemisinin-acridine hybrids were prepared and evaluated for their in vitro activity against tumour cell lines and a chloroquine sensitive strain of Plasmodium falciparum. They showed a 2-4-fold increase in activity against HL60, MDA-MB-231 and MCF-7 cells in comparison with dihydroartemisinin (DHA) and moderate antimalarial activity. Strong evidence that the compounds induce apoptosis in HL60 cells was obtained by flow cytometry, which indicated accumulation of cells in the G1 phase of the cell cycle.
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Araújo NCP, Barton V, Jones M, Stocks PA, Ward SA, Davies J, Bray PG, Shone AE, Cristiano MLS, O'Neill PM. Semi-synthetic and synthetic 1,2,4-trioxaquines and 1,2,4-trioxolaquines: synthesis, preliminary SAR and comparison with acridine endoperoxide conjugates. Bioorg Med Chem Lett 2009; 19:2038-43. [PMID: 19251414 DOI: 10.1016/j.bmcl.2009.02.013] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2008] [Revised: 02/04/2009] [Accepted: 02/04/2009] [Indexed: 11/18/2022]
Abstract
A novel series of semi-synthetic trioxaquines and synthetic trioxolaquines were prepared, in moderate to good yields. Antimalarial activity was evaluated against both the chloroquine-sensitive 3D7 and resistant K1 strain of Plasmodium falciparum and both series of compounds were shown to be active in the low nanomolar range. For comparison the corresponding 9-amino acridine analogues were also prepared and shown to have low nanomolar activity like their quinoline counterparts.
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Sabbani S, Stocks PA, Ellis GL, Davies J, Hedenstrom E, Ward SA, O'Neill PM. Piperidine dispiro-1,2,4-trioxane analogues. Bioorg Med Chem Lett 2008; 18:5804-8. [PMID: 18845438 DOI: 10.1016/j.bmcl.2008.09.052] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2008] [Revised: 09/11/2008] [Accepted: 09/12/2008] [Indexed: 11/24/2022]
Abstract
Dispiro N-Boc-protected 1,2,4-trioxane 2 was synthesised via Mo(acac)(2) catalysed perhydrolysis of N-Boc spirooxirane followed by condensation of the resulting beta-hydroperoxy alcohol 10 with 2-adamantanone. N-Boc 1,2,4-trioxane 2 was converted to the amine 1,2,4-trioxane hydrochloride salt 3 which was subsequently used to prepare derivatives (4-7). Several of these novel 1,2,4-trioxanes had nanomolar antimalarial activity versus the 3D7 strain of Plasmodium falciparum. Amine intermediate 3 represents a versatile derivative for the preparation of achiral arrays of trioxane analogues with antimalarial activity.
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71
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Ellis GL, Amewu R, Sabbani S, Stocks PA, Shone A, Stanford D, Gibbons P, Davies J, Vivas L, Charnaud S, Bongard E, Hall C, Rimmer K, Lozanom S, Jesús M, Gargallo D, Ward SA, O'Neill PM. Two-step synthesis of achiral dispiro-1,2,4,5-tetraoxanes with outstanding antimalarial activity, low toxicity, and high-stability profiles. J Med Chem 2008; 51:2170-7. [PMID: 18341274 DOI: 10.1021/jm701435h] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A rapid, two-step synthesis of a range of dispiro-1,2,4,5-tetraoxanes with potent antimalarial activity both in vitro and in vivo has been achieved. These 1,2,4,5-tetraoxanes have been proven to be superior to 1,2,4-trioxolanes in terms of stability and to be superior to trioxane analogues in terms of both stability and activity. Selected analogues have in vitro nanomolar antimalarial activity and good oral activity and are nontoxic in screens for both cytotoxicity and genotoxicity. The synthesis of a fluorescent 7-nitrobenza-2-oxa-1,3-diazole (NBD) tagged tetraoxane probe and use of laser scanning confocal microscopy techniques have shown that tagged molecules accumulate selectively only in parasite infected erythrocytes and that intraparasitic formation of adducts could be inhibited by co-incubation with the iron chelator desferrioxamine (DFO).
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Biagini GA, Fisher N, Berry N, Stocks PA, Meunier B, Williams DP, Bonar-Law R, Bray PG, Owen A, O'Neill PM, Ward SA. Acridinediones: selective and potent inhibitors of the malaria parasite mitochondrial bc1 complex. Mol Pharmacol 2008; 73:1347-55. [PMID: 18319379 DOI: 10.1124/mol.108.045120] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The development of drug resistance to affordable drugs has contributed to a global increase in the number of deaths from malaria. This unacceptable situation has stimulated research for new drugs active against multidrug-resistant Plasmodium falciparum parasites. In this regard, we show here that deshydroxy-1-imino derivatives of acridine (i.e., dihydroacridinediones) are selective antimalarial drugs acting as potent (nanomolar K(i)) inhibitors of parasite mitochondrial bc(1) complex. Inhibition of the bc(1) complex led to a collapse of the mitochondrial membrane potential, resulting in cell death (IC(50) approximately 15 nM). The selectivity of one of the dihydroacridinediones against the parasite enzyme was some 5000-fold higher than for the human bc(1) complex, significantly higher ( approximately 200 fold) than that observed with atovaquone, a licensed bc(1)-specific antimalarial drug. Experiments performed with yeast manifesting mutations in the bc(1) complex reveal that binding is directed to the quinol oxidation site (Q(o)) of the bc(1) complex. This is supported by favorable binding energies for in silico docking of dihydroacridinediones to P. falciparum bc(1) Q(o). Dihydroacridinediones represent an entirely new class of bc(1) inhibitors and the potential of these compounds as novel antimalarial drugs is discussed.
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Stocks PA, Bray PG, Barton VE, Al-Helal M, Jones M, Araujo NC, Gibbons P, Ward SA, Hughes RH, Biagini GA, Davies J, Amewu R, Mercer AE, Ellis G, O'Neill PM. Evidence for a Common Non-Heme Chelatable-Iron-Dependent Activation Mechanism for Semisynthetic and Synthetic Endoperoxide Antimalarial Drugs. Angew Chem Int Ed Engl 2007; 46:6278-83. [PMID: 17640025 DOI: 10.1002/anie.200604697] [Citation(s) in RCA: 105] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Mercer AE, Maggs JL, Sun XM, Cohen GM, Chadwick J, O'Neill PM, Park BK. Evidence for the involvement of carbon-centered radicals in the induction of apoptotic cell death by artemisinin compounds. J Biol Chem 2007; 282:9372-9382. [PMID: 17227762 DOI: 10.1074/jbc.m610375200] [Citation(s) in RCA: 144] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Artemisinin and its derivatives are currently recommended as first-line antimalarials in regions where Plasmodium falciparum is resistant to traditional drugs. The cytotoxic activity of these endoperoxides toward rapidly dividing human carcinoma cells and cell lines has been reported, and it is hypothesized that activation of the endoperoxide bridge by an iron(II) species, to form C-centered radicals, is essential for cytotoxicity. The studies described here have utilized artemisinin derivatives, dihydroartemisinin, 10beta-(p-bromophenoxy)dihydroartemisinin, and 10beta-(p-fluorophenoxy)dihydroartemisinin, to determine the chemistry of endoperoxide bridge activation to reactive intermediates responsible for initiating cell death and to elucidate the molecular mechanism of cell death. These studies have demonstrated the selective cytotoxic activity of the endoperoxides toward leukemia cell lines (HL-60 and Jurkat) over quiescent peripheral blood mononuclear cells. Deoxy-10beta-(p-fluorophenoxy)dihydroartemisinin, which lacks the endoperoxide bridge, was 50- and 130-fold less active in HL-60 and Jurkat cells, respectively, confirming the importance of this functional group for cytotoxicity. We have shown that chemical activation is responsible for cytotoxicity by using liquid chromatography-mass spectrometry analysis to monitor endoperoxide activation by measurement of a stable rearrangement product of endoperoxide-derived radicals, which was formed in sensitive HL-60 cells but not in insensitive peripheral blood mononuclear cells. In HL-60 cells the endoperoxides induce caspase-dependent apoptotic cell death characterized by concentration- and time-dependent mitochondrial membrane depolarization, activation of caspases-3 and -7, sub-G(0)/G(1) DNA formation, and attenuation by benzyloxycarbonyl-VAD-fluoromethyl ketone, a caspase inhibitor. Overall, these results indicate that endoperoxide-induced cell death is a consequence of activation of the endoperoxide bridge to radical species, which triggers caspase-dependent apoptosis.
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Amewu R, Stachulski AV, Berry NG, Ward SA, Davies J, Labat G, Rossignol JF, O'Neill PM. Synthesis of 1,2,4-trioxepanes via application of thiol-olefin Co-oxygenation methodology. Bioorg Med Chem Lett 2006; 16:6124-30. [PMID: 16978862 DOI: 10.1016/j.bmcl.2006.08.098] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2006] [Revised: 08/24/2006] [Accepted: 08/25/2006] [Indexed: 11/28/2022]
Abstract
Thiol-olefin co-oxygenation (TOCO) of substituted allylic alcohols generates beta-hydroxy peroxides that can be condensed in situ with various ketones, to afford a series of functionalised 1,2,4-trioxepanes in good yields. Manipulation of the phenylsulfenyl group in 8a-8c allows for convenient modification to the spiro-trioxepane substituents. Surprisingly, and in contrast to the 1,2,4-trioxanes examined, 1,2,4-trioxepanes are inactive as antimalarials up to 1000 nM and we rationalize this observation based on the inherent stability of these systems to ferrous mediated degradation. FMO calculations clearly show that the sigma* orbital of the peroxide moiety of 1,2,4-trioxane derivatives 4a and 14b are lower in energy and more accessible to attack by Fe(II) compared to their trioxepane analogues 8b and 9b.
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