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Nigel Yarlett

Pace University, Department of Chemistry and Physical Sciences, Faculty Member

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I am a biochemical parasitologist working mainly with neglected diseases. In collaboration with Drugs for Neglected Diseases I was part of an International group that resulted in the discovery of oxaborole treatment for Human African Trypanosomiasis. I have developed an in vitro culture method for Cryptosporidium parvum utilizing a hollow fiber bioreactor that permits long term drug studies to be performed using the parasite.

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Papers by Nigel Yarlett

Genomic and virulence analysis of in vitro cultured Cryptosporidium parvum

PLOS pathogens, Feb 28, 2024

Recent advances in the in vitro cultivation of Cryptosporidium parvum using hollow fiber bioreact... more Recent advances in the in vitro cultivation of Cryptosporidium parvum using hollow fiber bioreactor technology (HFB) have permitted continuous growth of parasites that complete all life cycle stages. The method provides access to all stages of the parasite and provides a method for non-animal production of oocysts for use in clinical trials. Here we examined the effect of long-term (>20 months) in vitro culture on virulence-factors, genome conservation, and in vivo pathogenicity of the host by in vitro cultured parasites. We find low-level sequence variation that is consistent with that observed in calf-passaged parasites. Further using a calf model infection, oocysts obtained from the HFB caused diarrhea of the same volume, duration and oocyst shedding intensity as in vivo passaged parasites.

eLS, 2021

Hit to lead and lead optimization of novel small molecules for the treatment of human African trypanosomiasis

Identification of a Novel Potent and SelectiveAnti-Trichomonas vaginalis Agent among Libraries of Bisbenzimidazoles

Proceedings of 3rd International Electronic Conference on Medicinal Chemistry, 2017

MIC after 48 h under aerobic conditions T. vaginalis isolate C1: 9 ± 4 μM vs 18 ± 5 μM for metron... more MIC after 48 h under aerobic conditions T. vaginalis isolate C1: 9 ± 4 μM vs 18 ± 5 μM for metronidazole T. vaginalis isolate 085: 26 ± 7 μM vs 145 ± 12 μM for metronidazole Ability to cure a mouse model infection using T. vaginalis isolate 286 at 10 mg kg-1 day-1 for 4 days: 4/5 vs 5/5 for metronidazole T. vaginalis isolate 085 at 10 mg kg-1 day-1 for 4 days: 4/5 vs 0/5 for metronidazole Identification of a Novel Potent and Selective Anti-Trichomonas vaginalis Agent among Libraries of Bisbenzimidazoles

Nitroimidazole Reduction by Pyruvate: Ferredoxin Oxidoreductase from Trichomonas vaginalis

Journal of Eukaryotic Microbiology, 1983

Polyamines in chemotherapy for African trypanosomiasis

P-Glycoprotein–Mediated Efflux Reduces the In Vivo Efficacy of a Therapeutic Targeting the Gastrointestinal Parasite Cryptosporidium

The Journal of Infectious Diseases, 2019

Recent studies have illustrated the burden Cryptosporidium infection places on the lives of malno... more Recent studies have illustrated the burden Cryptosporidium infection places on the lives of malnourished children and immunocompromised individuals. Treatment options remain limited, and efforts to develop a new therapeutic are currently underway. However, there are unresolved questions about the ideal pharmacokinetic characteristics of new anti-Cryptosporidium therapeutics. Specifically, should drug developers optimize therapeutics and formulations to increase drug exposure in the gastrointestinal lumen, enterocytes, or systemic circulation? Furthermore, how should researchers interpret data suggesting their therapeutic is a drug efflux transporter substrate? In vivo drug transporter–mediated alterations in efficacy are well recognized in multiple disease areas, but the impact of intestinal transporters on therapeutic efficacy against enteric diseases has not been established. Using multiple in vitro models and a mouse model of Cryptosporidium infection, we characterized the effect...

Evaluation of Alkanediamide-Linked Bisbenzamidines as Potential Antiparasitic Agents

Proceedings of 1st International Electronic Conference on Medicinal Chemistry, 2015

A series of 15 alkanediamide-linked bisbenzamidines and related analogs were synthesized and test... more A series of 15 alkanediamide-linked bisbenzamidines and related analogs were synthesized and tested in vitro against two Trypanosoma brucei (Tb) strains: T. b. brucei (Tbb) and T. b. rhodesiense (Tbr), two Plasmodium falciparum (Pf) strains: a chloroquine-sensitive strain (NF54) and a chloroquine-resistant strain (K1), Trypanosoma cruzi (Tc), and Leishmania donovani (Ld). The in vitro cytotoxicity was determined against rat myoblast cells (L6). Seven compounds (5, 6, 10, 11, 12, 14, 15) showed high potency toward both strains of Tb and Pf with the inhibitory concentrations for 50% (IC50) in the nanomolar range (IC50 = 1-96 nM). None of the tested derivatives was significantly active against Tc or Ld. Three of the more potent compounds (5, 6, 11) were evaluated in vivo in mice infected with the drug-sensitive (Lab 110 EATRO and KETRI 2002) or drug-resistant (KETRI 2538 and KETRI 1992) clinical isolates of T. brucei. Compounds 5 and 6 were highly effective in curing 100% mice infected with the drug-sensitive strains, including a drug-resistant strain KETRI 2538, but were ineffective against KETRI 1992. Thermal melting of DNA and molecular modeling studies indicate AT-rich DNA sequences in the minor grove as possible binding sites for these compounds. Several of the tested compounds are excellent leads for the development of improved antiparasitic agents.

Encyclopedia of Life Sciences, 2001

Lead optimization of novel boron-containing drug candidates for the treatment of human African trypanosomiasis

Human African Trypanosomiasis (HAT) represents a significant public health problem in sub-Saharan... more Human African Trypanosomiasis (HAT) represents a significant public health problem in sub-Saharan Africa affecting hundreds of thousands of individuals. An urgent need exists for the discovery and development of new, safe, and effective drugs to treat HAT, as existing therapies suffer from poor safety profiles, difficult treatment regimens, limited effectiveness, and a high cost of goods. From a collaborative effort between SCYNEXIS, Anacor Pharmaceuticals, Pace University, and DNDi, we report ongoing lead optimization efforts on a novel class of small molecule boron-containing compounds, exemplified by SCYX-6759. These compounds inhibit in vitro growth of T. brucei with IC 50 's ~100 nM, are not cytotoxic to mammalian cells, and exhibit good physiochemical and pharmacokinetic properties. In a murine model of CNS-stage disease utilizing the TREU667 strain of T.b.brucei, treatment with 50 mg/kg of SCYX-6759 BID for 14 days has demonstrated 100% efficacy, resulting in absence of blood parasites for >180 days. Development of a structure-activity relationship (SAR) profile for this chemical series and efforts to improve biological and pharmacokinetic profiles in the CNS-disease model through chemical modifications are reported herein.

In vitro pharmacodynamics and mechanism of action studies of oxaborole 6-carboxamides: a new class of compounds for the treatment of African trypanosomiasis

Human African Trypanosomiasis (HAT) is a fatal disease caused by Trypanosoma brucei spp. There is... more Human African Trypanosomiasis (HAT) is a fatal disease caused by Trypanosoma brucei spp. There is a need for new treatment for HAT because current treatments are costly, difficult to administer and frequently toxic. We have identified several oxaborole 6-carboxamides that demonstrate potent activity against T. brucei brucei in vitro and exhibit efficacy against both the acute and chronic CNS stages of HAT in mouse models. Exposure of T. b. brucei to oxaboroles leads to significant changes in shape, reduction in cellular size and detached flagella at the time of death. In vitro studies performed to characterize the relationship between killing of T. brucei and oxaborole exposure, demonstrate an early (6-9 hrs) onset of trypanocidal activity as shown by the inability of the parasites to generate ATP. Parasite commitment to death in vitro occurs with similar kinetics even when compound is washed out 2-3 hours following exposure. For mechanism of action studies, fluorescently tagged oxaborole analogues have been synthesized and incubated with T. brucei parasites to identify sub-cellular localization. In addition, representative compounds have been immobilized on agarose matrices for use in affinity capture of parasite target proteins which will be identified by mass spectrometry and data base searches. Collectively these studies which use AN3520 as a example will provide a better understanding of how oxaboroles exert their trypanocidal effects and enable us to develop valuable PK/PD models to ensure appropriate drug delivery for treatment of HAT.

Polyamine Metabolism

Biochemistry and Molecular Biology of Parasites, 1995

Publisher Summary Polyamines are low-molecular-weight molecules that are found in both prokaryote... more Publisher Summary Polyamines are low-molecular-weight molecules that are found in both prokaryotes and eukaryotes, and which fulfil essential needs for growth, division, and differentiation. This chapter explains that polyamine metabolism by parasites differs in several ways from the mammalian host, these include, enzyme half-life, turnover, substrate specificity, types and quantities of polyamines produced. Polyamines are positively charged and associate with negatively charged molecules, such as phospholipids and nucleic acids through electrostatic interactions. Spermidine and spermine interact with DNA and also with tRNA. This binding is responsible in part for maintaining the conformation of these molecules. The interaction of polyamines with macromolecules makes the estimation of intracellular bound and unbound pool sizes difficult since disruption of cells frequently destroys cell compartments, promoting reassociation of amines. The production of the novel bis glutathionyl spermidine adduct by trypanosomatids, its role as an anti-oxidant and the protein structure of trypanothione reductase is discussed with respect to the more conventional glutathione reductase system. The role of S-adenosylmethionine and decarboxylated S-adenosylmethionine as critical precursors in the biosynthesis of the higher polyamines is explored with respect to differences in the function and control of the pathway by various parasites. The chapter concludes that polyamine biosynthesis in parasites is different from that of the host to afford multiple opportunities for drug development, these may aim at circumventing polyamine biosynthesis or at inhibiting precursors necessary for polyamine synthesis. ..

Chapter 3. Antiparasitic Drug Discovery for the Polyamine Pathway

Drug Discovery, 2011

Diseases caused by parasitic organisms are a significant component of global morbidity and repres... more Diseases caused by parasitic organisms are a significant component of global morbidity and represent a serious challenge for drug discovery and development. Because polyamines are absolutely required for growth, survival and cellular homeostasis in parasitic organisms, polyamine metabolism is an important target for the discovery of antiparasitic agents. The rational design of antiparasitic agents that target the polyamine pathway relies on the fact that there are significant differences between human and parasitic polyamine metabolism. However, polyamine metabolism in these parasitic organisms is as diverse as the parasites themselves. As a result, a thorough understanding of polyamine metabolism in each organism, and of the structural differences in enzymes involved in this pathway, greatly facilitates the drug discovery process. In this chapter, the current understanding of polyamine metabolism in various organisms is described. In addition, recent efforts to specifically target parasitic enzymes involved in polyamine metabolism, or to modulate parasitic metabolic processes that are not found in humans, are described.

Inducible Resistance to Oxidant Stress in the Protozoan Leishmania chagasi

Journal of Biological Chemistry, 2000

Leishmania sp. protozoa are introduced into a mammalian skin by a sandfly vector, whereupon they ... more Leishmania sp. protozoa are introduced into a mammalian skin by a sandfly vector, whereupon they encounter increased temperature and toxic oxidants generated during phagocytosis. We studied the effects of 37°C "heat shock" or sublethal menadione, which generates superoxide and hydrogen peroxide, on Leishmania chagasi virulence. Both heat and menadione caused parasites to become more resistant to H 2 O 2-mediated toxicity. Peroxide resistance was also induced as promastigotes developed in culture from logarithmic to their virulent stationary phase form. Peroxide resistance was not associated with an increase in reduced thiols (trypanothione and glutathione) or increased activity of ornithine decarboxylase, which is rate-limiting in trypanothione synthesis. Membrane lipophosphoglycan increased in size as parasites developed to stationary phase but not after environmental exposures. Instead, parasites underwent a heat shock response upon exposure to heat or sublethal menadione, detected by increased levels of HSP70. Transfection of promastigotes with L. chagasi HSP70 caused a heat-inducible increase in resistance to peroxide, implying it is involved in antioxidant defense. We conclude that leishmania have redundant mechanisms for resisting toxic oxidants. Some are induced during developmental change and others are induced in response to environmental stress.

Cure of murine Trypanosoma brucei rhodesiense infections with an S-adenosylmethionine decarboxylase inhibitor

Antimicrobial Agents and Chemotherapy, 1992

The compound 5'-([(Z)-4-amino-2-butenyl]methylamino)-5'-deoxyadenosine (MDL73811), a pote... more The compound 5'-([(Z)-4-amino-2-butenyl]methylamino)-5'-deoxyadenosine (MDL73811), a potent inhibitor of S-adenosylmethionine decarboxylase, was effective in mice against six of eight clinical isolates of Trypanosoma brucei rhodesiense, the causative agent of East African sleeping sickness. In combination with the ornithine decarboxylase inhibitor DL-alpha-difluoromethylornithine (DFMO; Ornidyl), MDL73811 acted synergistically to cure seven of eight infections. MDL73811 was effective when given singly at 50 to 100 mg/kg of body weight per day for 7 days (osmotic pumps). In combination with subcurative DFMO levels (0.25 to 1.0% in drinking water for 7 days), the curative MDL73811 dose could be lowered to 25 or 50 mg/kg, depending on the isolate. Oral administration of the MDL73811-DFMO combination was also effective in an acute infection and in a long-term central nervous system model of Trypansoma brucei brucei infection. These data indicate that MDL73811 may be effective th...

5'-Alkyl-substituted analogs of 5'-methylthioadenosine as trypanocides

Antimicrobial Agents and Chemotherapy, 1991

5'-Deoxy-5'-(methylthio)adenosine (MTA) is a by-product of polyamine metabolism and is ph... more 5'-Deoxy-5'-(methylthio)adenosine (MTA) is a by-product of polyamine metabolism and is phosphoryolytically cleaved to adenine and 5-deoxy-5-(methylthio)ribose-1-phosphate (MTR-1-P) by MTA phosphorylase. In eukaryotes, adenine is subsequently salvaged and converted to nucleotides, while MTR-1-P is converted to methionine. We examined 5'-deoxy-5'-substituted analogs of MTA for trypanocidal activity in vitro and in vivo. 5'-Deoxy-5'-(hydroxyethyl)thioadenosine (HETA) and its 5'-bromo,5'-chloro and 5'-fluoro derivatives were cleaved by extracts of the African trypanosome Trypanosoma brucei brucei (Km for MTA, 11.5 microM; Km for HETA, 13.2 microM) in a phosphate-dependent reaction. HETA and the three halo analogs were 50% inhibitory to growth at 0.5 to 5.0 microM in vitro. Inhibition of growth was reversible by exogenous methionine and 2-keto-4-methylthiobutyric acid, an intermediate in methionine synthesis from MTR-1-P. HETA was selected for further ...

In Memoriam: Michael Levandowsky (1935-2016)

Journal of Eukaryotic Microbiology, 2017

MIKE Levandowsky, a microbiologist and aquatic ecologist passed away December 23, 2016. Mike was ... more MIKE Levandowsky, a microbiologist and aquatic ecologist passed away December 23, 2016. Mike was truly a man for all seasons with deep knowledge in several fields, and was as quick to fill up the blackboard with differential equations, as he was to wax poetic about some dinoflagellate behavior he had just seen under the microscope. He

Stage 2 Human African Trypanosomiasis

Pharmacokinetics and pharmacodynamics utilizing unbound target tissue exposure as part of a dispo... more

This article cites 32 articles, 8 of which can be accessed free at:

Oxygen levels are key to understanding “Anaerobic” protozoan pathogens with micro-aerophilic lifestyles

Advances in Microbial Physiology

Publications abound on the physiology, biochemistry and molecular biology of "anaerobic&quot... more Publications abound on the physiology, biochemistry and molecular biology of "anaerobic" protozoal parasites as usually grown under "anaerobic" culture conditions. The media routinely used are poised at low redox potentials using techniques that remove O2 to "undetectable" levels in sealed containers. However there is growing understanding that these culture conditions do not faithfully resemble the O2 environments these organisms inhabit. Here we review for protists lacking oxidative energy metabolism, the oxygen cascade from atmospheric to intracellular concentrations and relevant methods of measurements of O2, some well-studied parasitic or symbiotic protozoan lifestyles, their homeodynamic metabolic and redox balances, organism-drug-oxygen interactions, and the present and future prospects for improved drugs and treatment regimes.

Genomic and virulence analysis of in vitro cultured Cryptosporidium parvum

PLOS pathogens, Feb 28, 2024

Recent advances in the in vitro cultivation of Cryptosporidium parvum using hollow fiber bioreact... more Recent advances in the in vitro cultivation of Cryptosporidium parvum using hollow fiber bioreactor technology (HFB) have permitted continuous growth of parasites that complete all life cycle stages. The method provides access to all stages of the parasite and provides a method for non-animal production of oocysts for use in clinical trials. Here we examined the effect of long-term (>20 months) in vitro culture on virulence-factors, genome conservation, and in vivo pathogenicity of the host by in vitro cultured parasites. We find low-level sequence variation that is consistent with that observed in calf-passaged parasites. Further using a calf model infection, oocysts obtained from the HFB caused diarrhea of the same volume, duration and oocyst shedding intensity as in vivo passaged parasites.

eLS, 2021

Hit to lead and lead optimization of novel small molecules for the treatment of human African trypanosomiasis

Identification of a Novel Potent and SelectiveAnti-Trichomonas vaginalis Agent among Libraries of Bisbenzimidazoles

Proceedings of 3rd International Electronic Conference on Medicinal Chemistry, 2017

MIC after 48 h under aerobic conditions T. vaginalis isolate C1: 9 ± 4 μM vs 18 ± 5 μM for metron... more MIC after 48 h under aerobic conditions T. vaginalis isolate C1: 9 ± 4 μM vs 18 ± 5 μM for metronidazole T. vaginalis isolate 085: 26 ± 7 μM vs 145 ± 12 μM for metronidazole Ability to cure a mouse model infection using T. vaginalis isolate 286 at 10 mg kg-1 day-1 for 4 days: 4/5 vs 5/5 for metronidazole T. vaginalis isolate 085 at 10 mg kg-1 day-1 for 4 days: 4/5 vs 0/5 for metronidazole Identification of a Novel Potent and Selective Anti-Trichomonas vaginalis Agent among Libraries of Bisbenzimidazoles

Nitroimidazole Reduction by Pyruvate: Ferredoxin Oxidoreductase from Trichomonas vaginalis

Journal of Eukaryotic Microbiology, 1983

Polyamines in chemotherapy for African trypanosomiasis

P-Glycoprotein–Mediated Efflux Reduces the In Vivo Efficacy of a Therapeutic Targeting the Gastrointestinal Parasite Cryptosporidium

The Journal of Infectious Diseases, 2019

Recent studies have illustrated the burden Cryptosporidium infection places on the lives of malno... more Recent studies have illustrated the burden Cryptosporidium infection places on the lives of malnourished children and immunocompromised individuals. Treatment options remain limited, and efforts to develop a new therapeutic are currently underway. However, there are unresolved questions about the ideal pharmacokinetic characteristics of new anti-Cryptosporidium therapeutics. Specifically, should drug developers optimize therapeutics and formulations to increase drug exposure in the gastrointestinal lumen, enterocytes, or systemic circulation? Furthermore, how should researchers interpret data suggesting their therapeutic is a drug efflux transporter substrate? In vivo drug transporter–mediated alterations in efficacy are well recognized in multiple disease areas, but the impact of intestinal transporters on therapeutic efficacy against enteric diseases has not been established. Using multiple in vitro models and a mouse model of Cryptosporidium infection, we characterized the effect...

Evaluation of Alkanediamide-Linked Bisbenzamidines as Potential Antiparasitic Agents

Proceedings of 1st International Electronic Conference on Medicinal Chemistry, 2015

A series of 15 alkanediamide-linked bisbenzamidines and related analogs were synthesized and test... more A series of 15 alkanediamide-linked bisbenzamidines and related analogs were synthesized and tested in vitro against two Trypanosoma brucei (Tb) strains: T. b. brucei (Tbb) and T. b. rhodesiense (Tbr), two Plasmodium falciparum (Pf) strains: a chloroquine-sensitive strain (NF54) and a chloroquine-resistant strain (K1), Trypanosoma cruzi (Tc), and Leishmania donovani (Ld). The in vitro cytotoxicity was determined against rat myoblast cells (L6). Seven compounds (5, 6, 10, 11, 12, 14, 15) showed high potency toward both strains of Tb and Pf with the inhibitory concentrations for 50% (IC50) in the nanomolar range (IC50 = 1-96 nM). None of the tested derivatives was significantly active against Tc or Ld. Three of the more potent compounds (5, 6, 11) were evaluated in vivo in mice infected with the drug-sensitive (Lab 110 EATRO and KETRI 2002) or drug-resistant (KETRI 2538 and KETRI 1992) clinical isolates of T. brucei. Compounds 5 and 6 were highly effective in curing 100% mice infected with the drug-sensitive strains, including a drug-resistant strain KETRI 2538, but were ineffective against KETRI 1992. Thermal melting of DNA and molecular modeling studies indicate AT-rich DNA sequences in the minor grove as possible binding sites for these compounds. Several of the tested compounds are excellent leads for the development of improved antiparasitic agents.

Encyclopedia of Life Sciences, 2001

Lead optimization of novel boron-containing drug candidates for the treatment of human African trypanosomiasis

Human African Trypanosomiasis (HAT) represents a significant public health problem in sub-Saharan... more Human African Trypanosomiasis (HAT) represents a significant public health problem in sub-Saharan Africa affecting hundreds of thousands of individuals. An urgent need exists for the discovery and development of new, safe, and effective drugs to treat HAT, as existing therapies suffer from poor safety profiles, difficult treatment regimens, limited effectiveness, and a high cost of goods. From a collaborative effort between SCYNEXIS, Anacor Pharmaceuticals, Pace University, and DNDi, we report ongoing lead optimization efforts on a novel class of small molecule boron-containing compounds, exemplified by SCYX-6759. These compounds inhibit in vitro growth of T. brucei with IC 50 's ~100 nM, are not cytotoxic to mammalian cells, and exhibit good physiochemical and pharmacokinetic properties. In a murine model of CNS-stage disease utilizing the TREU667 strain of T.b.brucei, treatment with 50 mg/kg of SCYX-6759 BID for 14 days has demonstrated 100% efficacy, resulting in absence of blood parasites for >180 days. Development of a structure-activity relationship (SAR) profile for this chemical series and efforts to improve biological and pharmacokinetic profiles in the CNS-disease model through chemical modifications are reported herein.

In vitro pharmacodynamics and mechanism of action studies of oxaborole 6-carboxamides: a new class of compounds for the treatment of African trypanosomiasis

Human African Trypanosomiasis (HAT) is a fatal disease caused by Trypanosoma brucei spp. There is... more Human African Trypanosomiasis (HAT) is a fatal disease caused by Trypanosoma brucei spp. There is a need for new treatment for HAT because current treatments are costly, difficult to administer and frequently toxic. We have identified several oxaborole 6-carboxamides that demonstrate potent activity against T. brucei brucei in vitro and exhibit efficacy against both the acute and chronic CNS stages of HAT in mouse models. Exposure of T. b. brucei to oxaboroles leads to significant changes in shape, reduction in cellular size and detached flagella at the time of death. In vitro studies performed to characterize the relationship between killing of T. brucei and oxaborole exposure, demonstrate an early (6-9 hrs) onset of trypanocidal activity as shown by the inability of the parasites to generate ATP. Parasite commitment to death in vitro occurs with similar kinetics even when compound is washed out 2-3 hours following exposure. For mechanism of action studies, fluorescently tagged oxaborole analogues have been synthesized and incubated with T. brucei parasites to identify sub-cellular localization. In addition, representative compounds have been immobilized on agarose matrices for use in affinity capture of parasite target proteins which will be identified by mass spectrometry and data base searches. Collectively these studies which use AN3520 as a example will provide a better understanding of how oxaboroles exert their trypanocidal effects and enable us to develop valuable PK/PD models to ensure appropriate drug delivery for treatment of HAT.

Polyamine Metabolism

Biochemistry and Molecular Biology of Parasites, 1995

Publisher Summary Polyamines are low-molecular-weight molecules that are found in both prokaryote... more Publisher Summary Polyamines are low-molecular-weight molecules that are found in both prokaryotes and eukaryotes, and which fulfil essential needs for growth, division, and differentiation. This chapter explains that polyamine metabolism by parasites differs in several ways from the mammalian host, these include, enzyme half-life, turnover, substrate specificity, types and quantities of polyamines produced. Polyamines are positively charged and associate with negatively charged molecules, such as phospholipids and nucleic acids through electrostatic interactions. Spermidine and spermine interact with DNA and also with tRNA. This binding is responsible in part for maintaining the conformation of these molecules. The interaction of polyamines with macromolecules makes the estimation of intracellular bound and unbound pool sizes difficult since disruption of cells frequently destroys cell compartments, promoting reassociation of amines. The production of the novel bis glutathionyl spermidine adduct by trypanosomatids, its role as an anti-oxidant and the protein structure of trypanothione reductase is discussed with respect to the more conventional glutathione reductase system. The role of S-adenosylmethionine and decarboxylated S-adenosylmethionine as critical precursors in the biosynthesis of the higher polyamines is explored with respect to differences in the function and control of the pathway by various parasites. The chapter concludes that polyamine biosynthesis in parasites is different from that of the host to afford multiple opportunities for drug development, these may aim at circumventing polyamine biosynthesis or at inhibiting precursors necessary for polyamine synthesis. ..

Chapter 3. Antiparasitic Drug Discovery for the Polyamine Pathway

Drug Discovery, 2011

Diseases caused by parasitic organisms are a significant component of global morbidity and repres... more Diseases caused by parasitic organisms are a significant component of global morbidity and represent a serious challenge for drug discovery and development. Because polyamines are absolutely required for growth, survival and cellular homeostasis in parasitic organisms, polyamine metabolism is an important target for the discovery of antiparasitic agents. The rational design of antiparasitic agents that target the polyamine pathway relies on the fact that there are significant differences between human and parasitic polyamine metabolism. However, polyamine metabolism in these parasitic organisms is as diverse as the parasites themselves. As a result, a thorough understanding of polyamine metabolism in each organism, and of the structural differences in enzymes involved in this pathway, greatly facilitates the drug discovery process. In this chapter, the current understanding of polyamine metabolism in various organisms is described. In addition, recent efforts to specifically target parasitic enzymes involved in polyamine metabolism, or to modulate parasitic metabolic processes that are not found in humans, are described.

Inducible Resistance to Oxidant Stress in the Protozoan Leishmania chagasi

Journal of Biological Chemistry, 2000

Leishmania sp. protozoa are introduced into a mammalian skin by a sandfly vector, whereupon they ... more Leishmania sp. protozoa are introduced into a mammalian skin by a sandfly vector, whereupon they encounter increased temperature and toxic oxidants generated during phagocytosis. We studied the effects of 37°C "heat shock" or sublethal menadione, which generates superoxide and hydrogen peroxide, on Leishmania chagasi virulence. Both heat and menadione caused parasites to become more resistant to H 2 O 2-mediated toxicity. Peroxide resistance was also induced as promastigotes developed in culture from logarithmic to their virulent stationary phase form. Peroxide resistance was not associated with an increase in reduced thiols (trypanothione and glutathione) or increased activity of ornithine decarboxylase, which is rate-limiting in trypanothione synthesis. Membrane lipophosphoglycan increased in size as parasites developed to stationary phase but not after environmental exposures. Instead, parasites underwent a heat shock response upon exposure to heat or sublethal menadione, detected by increased levels of HSP70. Transfection of promastigotes with L. chagasi HSP70 caused a heat-inducible increase in resistance to peroxide, implying it is involved in antioxidant defense. We conclude that leishmania have redundant mechanisms for resisting toxic oxidants. Some are induced during developmental change and others are induced in response to environmental stress.

Cure of murine Trypanosoma brucei rhodesiense infections with an S-adenosylmethionine decarboxylase inhibitor

Antimicrobial Agents and Chemotherapy, 1992

The compound 5'-([(Z)-4-amino-2-butenyl]methylamino)-5'-deoxyadenosine (MDL73811), a pote... more The compound 5'-([(Z)-4-amino-2-butenyl]methylamino)-5'-deoxyadenosine (MDL73811), a potent inhibitor of S-adenosylmethionine decarboxylase, was effective in mice against six of eight clinical isolates of Trypanosoma brucei rhodesiense, the causative agent of East African sleeping sickness. In combination with the ornithine decarboxylase inhibitor DL-alpha-difluoromethylornithine (DFMO; Ornidyl), MDL73811 acted synergistically to cure seven of eight infections. MDL73811 was effective when given singly at 50 to 100 mg/kg of body weight per day for 7 days (osmotic pumps). In combination with subcurative DFMO levels (0.25 to 1.0% in drinking water for 7 days), the curative MDL73811 dose could be lowered to 25 or 50 mg/kg, depending on the isolate. Oral administration of the MDL73811-DFMO combination was also effective in an acute infection and in a long-term central nervous system model of Trypansoma brucei brucei infection. These data indicate that MDL73811 may be effective th...

5'-Alkyl-substituted analogs of 5'-methylthioadenosine as trypanocides

Antimicrobial Agents and Chemotherapy, 1991

5'-Deoxy-5'-(methylthio)adenosine (MTA) is a by-product of polyamine metabolism and is ph... more 5'-Deoxy-5'-(methylthio)adenosine (MTA) is a by-product of polyamine metabolism and is phosphoryolytically cleaved to adenine and 5-deoxy-5-(methylthio)ribose-1-phosphate (MTR-1-P) by MTA phosphorylase. In eukaryotes, adenine is subsequently salvaged and converted to nucleotides, while MTR-1-P is converted to methionine. We examined 5'-deoxy-5'-substituted analogs of MTA for trypanocidal activity in vitro and in vivo. 5'-Deoxy-5'-(hydroxyethyl)thioadenosine (HETA) and its 5'-bromo,5'-chloro and 5'-fluoro derivatives were cleaved by extracts of the African trypanosome Trypanosoma brucei brucei (Km for MTA, 11.5 microM; Km for HETA, 13.2 microM) in a phosphate-dependent reaction. HETA and the three halo analogs were 50% inhibitory to growth at 0.5 to 5.0 microM in vitro. Inhibition of growth was reversible by exogenous methionine and 2-keto-4-methylthiobutyric acid, an intermediate in methionine synthesis from MTR-1-P. HETA was selected for further ...

In Memoriam: Michael Levandowsky (1935-2016)

Journal of Eukaryotic Microbiology, 2017

MIKE Levandowsky, a microbiologist and aquatic ecologist passed away December 23, 2016. Mike was ... more MIKE Levandowsky, a microbiologist and aquatic ecologist passed away December 23, 2016. Mike was truly a man for all seasons with deep knowledge in several fields, and was as quick to fill up the blackboard with differential equations, as he was to wax poetic about some dinoflagellate behavior he had just seen under the microscope. He

Stage 2 Human African Trypanosomiasis

Pharmacokinetics and pharmacodynamics utilizing unbound target tissue exposure as part of a dispo... more

This article cites 32 articles, 8 of which can be accessed free at:

Oxygen levels are key to understanding “Anaerobic” protozoan pathogens with micro-aerophilic lifestyles

Advances in Microbial Physiology

Publications abound on the physiology, biochemistry and molecular biology of "anaerobic&quot... more Publications abound on the physiology, biochemistry and molecular biology of "anaerobic" protozoal parasites as usually grown under "anaerobic" culture conditions. The media routinely used are poised at low redox potentials using techniques that remove O2 to "undetectable" levels in sealed containers. However there is growing understanding that these culture conditions do not faithfully resemble the O2 environments these organisms inhabit. Here we review for protists lacking oxidative energy metabolism, the oxygen cascade from atmospheric to intracellular concentrations and relevant methods of measurements of O2, some well-studied parasitic or symbiotic protozoan lifestyles, their homeodynamic metabolic and redox balances, organism-drug-oxygen interactions, and the present and future prospects for improved drugs and treatment regimes.