Neeloo Singh

Publications

• 4.80

  Impact points

  In silico screening, structure-activity relationship, and biologic evaluation of selective pteridine reductase inhibitors targeting visceral leishmaniasis.

  Jaspreet Kaur, Pranav Kumar, Sargam Tyagi, Richa Pathak, Sanjay Batra, Prashant Singh, Neeloo Singh

  Antimicrobial agents and chemotherapy. 02/2011; 55(2):659-66.

  In this study we utilized the concept of rational drug design to identify novel compounds with optimal selectivity, efficacy and safety, which would bind to the target enzyme pteridine reductase 1 (PTR1) in Leishmania parasites. Twelve compounds afforded from Baylis-Hillman chemistry were docked by ... [more] In this study we utilized the concept of rational drug design to identify novel compounds with optimal selectivity, efficacy and safety, which would bind to the target enzyme pteridine reductase 1 (PTR1) in Leishmania parasites. Twelve compounds afforded from Baylis-Hillman chemistry were docked by using the QUANTUM program into the active site of Leishmania donovani PTR1 homology model. The biological activity for these compounds was estimated in green fluorescent protein-transfected L. donovani promastigotes, and the most potential analogue was further investigated in intracellular amastigotes. Structure-activity relationship based on homology model drawn on our recombinant enzyme was substantiated by recombinant enzyme inhibition assay and growth of the cell culture. Flow cytometry results indicated that 7-(4-chlorobenzyl)-3-methyl-4-(4-trifluoromethyl-phenyl)-3,4,6,7,8,9-hexahydro-pyrimido[1,2-a]pyrimidin-2-one (compound 7) was 10 times more active on L. donovani amastigotes (50% inhibitory concentration [IC(50)] = 3 μM) than on promastigotes (IC(50) = 29 μM). Compound 7 exhibited a K(i) value of 0.72 μM in a recombinant enzyme inhibition assay. We discovered that novel pyrimido[1,2-a]pyrimidin-2-one systems generated from the allyl amines afforded from the Baylis-Hillman acetates could have potential as a valuable pharmacological tool against the neglected disease visceral leishmaniasis.

• Bioinformatic Analysis of Leishmania donovani Long-Chain Fatty Acid-CoA Ligase as a Novel Drug Target.

  Jaspreet Kaur, Rameshwar Tiwari, Arun Kumar, Neeloo Singh

  Molecular biology international. 01/2011; 2011:278051.

  Fatty acyl-CoA synthetase (fatty acid: CoA ligase, AMP-forming; (EC 6.2.1.3)) catalyzes the formation of fatty acyl-CoA by a two-step process that proceeds through the hydrolysis of pyrophosphate. Fatty acyl-CoA represents bioactive compounds that are involved in protein transport, enzyme activation... [more] Fatty acyl-CoA synthetase (fatty acid: CoA ligase, AMP-forming; (EC 6.2.1.3)) catalyzes the formation of fatty acyl-CoA by a two-step process that proceeds through the hydrolysis of pyrophosphate. Fatty acyl-CoA represents bioactive compounds that are involved in protein transport, enzyme activation, protein acylation, cell signaling, and transcriptional control in addition to serving as substrates for beta oxidation and phospholipid biosynthesis. Fatty acyl-CoA synthetase occupies a pivotal role in cellular homeostasis, particularly in lipid metabolism. Our interest in fatty acyl-CoA synthetase stems from the identification of this enzyme, long-chain fatty acyl-CoA ligase (LCFA) by microarray analysis. We found this enzyme to be differentially expressed by Leishmania donovani amastigotes resistant to antimonial treatment. In the present study, we confirm the presence of long-chain fatty acyl-CoA ligase gene in the genome of clinical isolates of Leishmania donovani collected from the disease endemic area in India. We predict a molecular model for this enzyme for in silico docking studies using chemical library available in our institute. On the basis of the data presented in this work, we propose that long-chain fatty acyl-CoA ligase enzyme serves as an important protein and a potential target candidate for development of selective inhibitors against leishmaniasis.

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• 2.94

  Impact points

  Elevated levels of tryparedoxin peroxidase in antimony unresponsive Leishmania donovani field isolates.

  Susan Wyllie, Goutam Mandal, Neeloo Singh, Shyam Sundar, Alan H Fairlamb, Mitali Chatterjee

  Molecular and biochemical parasitology. 10/2010; 173(2):162-4.

  Enhancement of the anti-oxidant metabolism of Leishmania parasites, dependent upon the unique dithiol trypanothione, has been implicated in laboratory-generated antimony resistance. Here, the role of the trypanothione-dependent anti-oxidant pathway is studied in antimony-resistant clinical isolates.... [more] Enhancement of the anti-oxidant metabolism of Leishmania parasites, dependent upon the unique dithiol trypanothione, has been implicated in laboratory-generated antimony resistance. Here, the role of the trypanothione-dependent anti-oxidant pathway is studied in antimony-resistant clinical isolates. Elevated levels of tryparedoxin and tryparedoxin peroxidase, key enzymes in hydroperoxide detoxification, were observed in antimonial resistant parasites resulting in an increased metabolism of peroxides. These data suggest that enhanced anti-oxidant defences may play a significant role in clinical resistance to antimonials.
• 4.35

  Impact points

  Molecular docking, structure-activity relationship and biological evaluation of the anticancer drug monastrol as a pteridine reductase inhibitor in a clinical isolate of Leishmania donovani.

  Jaspreet Kaur, Shyam Sundar, Neeloo Singh

  The Journal of antimicrobial chemotherapy. 08/2010; 65(8):1742-8.

  Using the pteridine reductase (PTR1) enzyme of Leishmania as the target, the objective of our study was to find a drug candidate that can enter the clinical development process after being evaluated for safety and efficacy in animals. Monastrol (R) and (S) enantiomers were docked using the QUANTUM p... [more] Using the pteridine reductase (PTR1) enzyme of Leishmania as the target, the objective of our study was to find a drug candidate that can enter the clinical development process after being evaluated for safety and efficacy in animals. Monastrol (R) and (S) enantiomers were docked using the QUANTUM program into the active site of a Leishmania donovani PTR1 (LdPTR1) homology model. A structure-activity relationship based on a homology model of a recombinant enzyme was substantiated by a recombinant enzyme inhibition assay. We adapted an L. donovani (transfected with green fluorescent protein) intramacrophage amastigote screening assay as a cellular model for leishmaniasis. Furthermore, since the clinicopathological features and immunopathological mechanisms of visceral leishmaniasis (VL) in a hamster model are remarkably similar to those of human disease, systemic infection of hamsters with L. donovani was utilized to collect in vivo data for monastrol. Both monastrol (R) and (S) enantiomers fit well in the ligand-binding pocket of LdPTR1. Monastrol exhibits a K(i) value of 0.428 microM in the recombinant enzyme inhibition assay. We confirm monastrol as a potent inhibitor of PTR1 in Leishmania; it inhibits proliferation of amastigotes with an IC(50) (50% inhibitory concentration) of 10 microM in macrophage cultures infected with an L. donovani clinical isolate, with no host cytotoxicity. We also show that in experimental animals, oral administration of a 5 mg/kg dose of monastrol on two alternate days inhibits 50% of parasite growth, giving therapeutic backing to the use of monastrol as a potent antileishmanial in human VL cases. To our knowledge, this is the first report presenting monastrol as a potent oral antileishmanial.
• 1.60

  Impact points

  Leishmania donovani: oral therapy with glycosyl 1,4-dihydropyridine analogue showing apoptosis like phenotypes targeting pteridine reductase 1 in intracellular amastigotes.

  Jaspreet Kaur, Nasib Singh, Biswajit Kumar Singh, Anuradha Dube, Rama Pati Tripathi, Prashant Singh, Neeloo Singh

  Experimental parasitology. 02/2010; 125(3):310-4.

  Glycosyl 1,4-dihydropyridine analogue (2,6-dimethyl-4-(3-O-benzyl-1,2-O-isopropylidene-beta-l-threo pentofuranos-4-yl)-1-phenyl-1,4-dihydro-pyridine-3,5-dicarboxylic acid diethyl ester) synthesized in our laboratory, inhibited Leishmania donovani infection in vitro and in hamsters (Mesocricetus aura... [more] Glycosyl 1,4-dihydropyridine analogue (2,6-dimethyl-4-(3-O-benzyl-1,2-O-isopropylidene-beta-l-threo pentofuranos-4-yl)-1-phenyl-1,4-dihydro-pyridine-3,5-dicarboxylic acid diethyl ester) synthesized in our laboratory, inhibited Leishmania donovani infection in vitro and in hamsters (Mesocricetus auratus) when administered orally. This analogue is nontoxic, cell-permeable and orally effective. This glycosyl dihydropyridine analogue functioned through arrest of cells in sub-G0/G1-phase, triggering mitochondrial membrane depolarization-mediated programmed cell death of the intracellular amastigotes.
• 1.51

  Impact points

  An orally effective dihydropyrimidone (DHPM) analogue induces apoptosis-like cell death in clinical isolates of Leishmania donovani overexpressing pteridine reductase 1.

  Neeloo Singh, Jaspreet Kaur, Pranav Kumar, Swati Gupta, Nasib Singh, Angana Ghosal, Avijit Dutta, Ashutosh Kumar, RamaPati Tripathi, Mohammad Siddiqi, Chitra Mandal, Anuradha Dube

  Parasitology research. 08/2009;

  The protozoan parasite Leishmania donovani is the causative agent of visceral leishmaniasis. The enzyme pteridine reductase 1 (PTR1) of L. donovani acts as a metabolic bypass for drugs targeting dihydrofolate reductase (DHFR); therefore, for successful antifolate chemotherapy to be developed against... [more] The protozoan parasite Leishmania donovani is the causative agent of visceral leishmaniasis. The enzyme pteridine reductase 1 (PTR1) of L. donovani acts as a metabolic bypass for drugs targeting dihydrofolate reductase (DHFR); therefore, for successful antifolate chemotherapy to be developed against Leishmania, it must target both enzyme activities. Leishmania cells overexpressing PTR1 tagged at the N-terminal with green fluorescent protein were established to screen for proprietary dihydropyrimidone (DHPM) derivatives of DHFR specificity synthesised in our laboratory. A cell-permeable molecule with impressive antileishmanial in vitro and in vivo oral activity was identified. Structure activity relationship based on homology model drawn on our recombinant enzyme established the highly selective inhibition of the enzyme by this analogue. It was seen that the leishmanicidal effect of this analogue is triggered by programmed cell death mediated by the loss of plasma membrane integrity as detected by binding of annexin V and propidium iodide (PI), loss of mitochondrial membrane potential culminating in cell cycle arrest at the sub-G0/G1 phase and oligonucleosomal DNA fragmentation. Hence, this DHPM analogue [(4-fluoro-phenyl)-6-methyl-2-thioxo-1, 2, 3, 4-tetrahydropyrimidine-5-carboxylic acid ethyl ester] is a potent antileishmanial agent that merits further pharmacological investigation.
• 1.60

  Impact points

  Leishmania donovani: A glycosyl dihydropyridine analogue induces apoptosis like cell death via targeting pteridine reductase 1 in promastigotes.

  Jaspreet Kaur, Biswajit Kumar Singh, Rama Pati Tripathi, Prashant Singh, Neeloo Singh

  Experimental parasitology. 08/2009;

  Targeting of pteridine reductase1 (PTR1) in Leishmania is essential for development of successful antifolate chemotherapy. In search for specific inhibitors of PTR1 we have previously reported phenyl 1, 4-dihydropyridine ring as the lead structure showing antileishmanial efficacy in vitro and by the... [more] Targeting of pteridine reductase1 (PTR1) in Leishmania is essential for development of successful antifolate chemotherapy. In search for specific inhibitors of PTR1 we have previously reported phenyl 1, 4-dihydropyridine ring as the lead structure showing antileishmanial efficacy in vitro and by the oral route in vivo. In this study we present programmed cell death inducing potential of this glycosyl dihydropyridine analogue (2, 6-dimethyl-4-(3-O-benzyl-1, 2-O-isopropylidene-beta-L-threo-pentofuranos-4-yl)-1-phenyl-1, 4-dihydro-pyridine-3, 5-dicarboxylic acid diethyl ester). Flow cytometric analysis revealed that this analogue induces cell cycle arrest at G2/M phase with subsequent increase in sub-G1 peak. Incubation of Leishmania promastigotes with this analogue causes exposure of phosphatidylserine to the outer leaflet of plasma membrane, formation of reactive oxygen species, depolarization of mitochondrial membrane potential and concomitant nuclear alterations that included DNA fragmentation. The results from this study on promastigotes give important lead to investigate further in intracellular amastigotes, the biologically relevant parasite stage in host macrophages.
• 1.60

  Impact points

  Flow cytometric determination of intracellular non-protein thiols in Leishmania promastigotes using 5-chloromethyl fluorescein diacetate.

  Avijit Sarkar, Goutam Mandal, Neeloo Singh, Shyam Sundar, Mitali Chatterjee

  Experimental parasitology. 05/2009;

  Leishmania parasites lack catalase and therefore, their anti-oxidant system hinges primarily upon non protein thiols; accordingly, depletion of thiols could potentially serve as an effective drug target. We have developed a flow cytometry based assay using 5-chloromethyl fluorescein diacetate based ... [more] Leishmania parasites lack catalase and therefore, their anti-oxidant system hinges primarily upon non protein thiols; accordingly, depletion of thiols could potentially serve as an effective drug target. We have developed a flow cytometry based assay using 5-chloromethyl fluorescein diacetate based upon its selective staining of non protein thiols. Its specificity was confirmed using buthionine sulphoximine (a gamma glutamyl cysteine synthetase inhibitor), diamide (an oxidizing agent of intracellular thiols) and N-ethylmaleimide (a covalent modifier of cysteine residues) as evidenced by reduction in fluorescence; furthermore, restoration of fluorescence by N-acetyl cysteine corroborated specificity of 5-chloromethyl fluorescein diacetate to measure non protein thiols. Differences in basal level of thiols in antimony sensitive and antimony resistant Leishmania field isolates were detected. The depletion of non protein thiols by conventional antileishmanial drugs e.g. antimony and miltefosine was demonstrated. Furthermore, fluorescence was unaffected by depletion of ATP in majority of the strains studied, indicating that 5-chloromethyl fluorescein diacetate is not a substrate for the pump operative in most Leishmania donovani strains. Taken together, measurement of 5-chloromethyl fluorescein diacetate fluorescence is an effective method for monitoring non protein thiols in Leishmania promastigotes.
• 0.57

  Impact points

  Functionality of drug efflux pumps in antimonial resistant Leishmania donovani field isolates.

  Goutam Mandal, Avijit Sarkar, Piu Saha, Neeloo Singh, Shyam Sundar, Mitali Chatterjee

  Indian journal of biochemistry & biophysics. 03/2009; 46(1):86-92.

  The recent upsurge of antimony (Sb) resistance is a major impediment to successful chemotherapy of visceral leishmaniasis (VL). Mechanisms involved in antimony resistance have demonstrated an upregulation of drug efflux pumps; however, the biological role drug efflux pumps in clinical isolates remai... [more] The recent upsurge of antimony (Sb) resistance is a major impediment to successful chemotherapy of visceral leishmaniasis (VL). Mechanisms involved in antimony resistance have demonstrated an upregulation of drug efflux pumps; however, the biological role drug efflux pumps in clinical isolates remains to be substantiated. Thus, in this study, the functionality of drug efflux pumps was measured in promastigotes and axenic amastigotes isolated from VL patients, who were either Sb-sensitive (AG83, 2001 and MC9) or resistant (NS2, 41 and GE1) using rhodamine123 as a substrate for multidrug resistant (MDR) pumps and calcein as a substrate for multidrug resistance-associated proteins (MRP) respectively; their specificity was confirmed using established blockers. Sb-resistant (Sb-R) isolates accumulated higher amounts of R123, as compared to Sb-sensitive (Sb-S) isolates. Verapamil, a MDR inhibitor failed to alter R123 accumulation, suggesting absence of classical MDR activity. In Sb-R isolates, both promastigotes and axenic amastigotes accumulated significantly lower amounts of calcein than Sb-S isolates and probenecid, an established pan MRP blocker, marginally increased calcein accumulation. Depletion of ATP dramatically increased calcein accumulation primarily in Sb-R isolates, indicating existence of a MRP-like pump, which was more active in Sb-R isolates. In conclusion, our data suggested that overfunctioning of a MRP-like pump contributed towards generation of Sb-R phenotype in L. donovani field isolates.
• 3.93

  Impact points

  Discovery of novel vaccine candidates and drug targets against visceral leishmaniasis using proteomics and transcriptomics.

  Shraddha Kumari, Awanish Kumar, Mukesh Samant, Neeloo Singh, Anuradha Dube

  Current drug targets. 12/2008; 9(11):938-47.

  Among the three clinical forms (cutaneous, mucosal and visceral) of leishmaniasis visceral (VL) one is the most devastating type caused by the invasion of the reticuloendothelial system of human by Leishmania donovani, L. infantum and L. chagasi. India and Sudan account for about half the world'... [more] Among the three clinical forms (cutaneous, mucosal and visceral) of leishmaniasis visceral (VL) one is the most devastating type caused by the invasion of the reticuloendothelial system of human by Leishmania donovani, L. infantum and L. chagasi. India and Sudan account for about half the world's burden of VL. Current control strategy is based on chemotherapy, which is difficult to administer, expensive and becoming ineffective due to the emergence of drug resistance. An understanding of resistance mechanism(s) operating in clinical isolates might provide additional leads for the development of new drugs. Further, due to the lack of fully effective treatment the search for novel immune targets is also needed. So far, no vaccine exists for VL despite indications of naturally developing immunity. Therefore, an urgent need for new and effective leishmanicidal agents and for this identification of novel drug and vaccine targets is imperative. The availability of the complete genome sequence of Leishmania has revolutionised many areas of leishmanial research and facilitated functional genomic studies as well as provided a wide range of novel targets for drug designing. Most notably, proteomics and transcriptomics have become important tools in gaining increased understanding of the biology of Leishmania to be explored on a global scale, thus accelerating the pace of discovery of vaccine/drug targets. In addition, these approaches provide the information regarding genes and proteins that are expressed and under which conditions. This review provides a comprehensive view about those proteins/genes identified using proteomics and transcriptomic tools for the development of vaccine/drug against VL.
• 1.60

  Impact points

  Leishmania donovani pteridine reductase 1: Biochemical properties and structure-modeling studies.

  Pranav Kumar, Ashutosh Kumar, Shyam Sundar Verma, Namrata Dwivedi, Nasib Singh, Mohammad Imran Siddiqi, Rama Pati Tripathi, Anuradha Dube, Neeloo Singh

  Experimental parasitology. 07/2008;

  Pteridine reductase 1 (PTR1, EC 1.5.1.33) is a NADPH dependent short-chain reductase (SDR) responsible for the salvage of pterins in the protozoan parasite Leishmania. This enzyme acts as a metabolic bypass for drugs targeting dihydrofolate reductase, therefore, for successful antifolate chemotherap... [more] Pteridine reductase 1 (PTR1, EC 1.5.1.33) is a NADPH dependent short-chain reductase (SDR) responsible for the salvage of pterins in the protozoan parasite Leishmania. This enzyme acts as a metabolic bypass for drugs targeting dihydrofolate reductase, therefore, for successful antifolate chemotherapy to be developed against Leishmania, it must target both enzyme activities. Based on homology model drawn on recombinant pteridine reductase isolated from a clinical isolate of L. donovani, we carried out molecular modeling and docking studies with two compounds of dihydrofolate reductase specificity showing promising antileishmanial activity in vitro. Both the inhibitors appeared to fit well in the active pocket revealing the tight binding of the carboxylic acid ethyl ester group of pyridine moiety to pteridine reductase and identify the important interactions necessary to assist the structure based development of novel pteridine reductase inhibitors.
• 1.88

  Impact points

  Proteomic approaches for discovery of new targets for vaccine and therapeutics against visceral leishmaniasis.

  Shraddha Kumari, Awanish Kumar, Mukesh Samant, Shyam Sundar, Neeloo Singh, Anuradha Dube

  Proteomics. Clinical applications. 03/2008; 2(3):372-86.

  Visceral leishmaniasis (VL) is the most devastating type caused by Leishmania donovani, Leishmania infantum, and Leishmania chagasi. The therapeutic mainstay is still based on the antiquated pentavalent antimonial against which resistance is now increasing. Unfortunately, due to the digenetic life c... [more] Visceral leishmaniasis (VL) is the most devastating type caused by Leishmania donovani, Leishmania infantum, and Leishmania chagasi. The therapeutic mainstay is still based on the antiquated pentavalent antimonial against which resistance is now increasing. Unfortunately, due to the digenetic life cycle of parasite, there is significant antigenic diversity. There is an urgent need to develop novel drug/vaccine targets against VL for which the primary goal should be to identify and characterize the structural and functional proteins. Proteomics, being widely employed in the study of Leishmania seems to be a suitable strategy as the availability of annotated sequenced genome of Leishmania major has opened the door for dissection of both protein expression/regulation and function. Advances in clinical proteomic technologies have enable to enhance our mechanistic understanding of virulence/pathogenicity/host-pathogen interactions, drug resistance thereby defining novel therapeutic/vaccine targets. Expression proteomics exploits the differential expression of leishmanial proteins as biomarkers for application towards early diagnosis. Further using immunoproteomics efforts were also focused on evaluating responses to define parasite T-cell epitopes as vaccine/diagnostic targets. This review has highlighted some of the relevant developments in the rapidly emerging field of leishmanial proteomics and focus on its future applications in drug and vaccine discovery against VL.
• 1.60

  Impact points

  Degradation of pteridine reductase 1 (PTR1) enzyme during growth phase in the protozoan parasite Leishmania donovani.

  Pranav Kumar, Shyam Sundar, Neeloo Singh

  Experimental parasitology. 07/2007; 116(2):182-9.

  Pteridine reductase 1 (PTR1) is an essential enzyme of pterin and folate metabolism in the protozoan parasite Leishmania. The present work is focused on the degradation of PTR1 during growth phase in Leishmania donovani. Western blot analysis with PTR1-GFP transfected promastigotes revealed that PTR... [more] Pteridine reductase 1 (PTR1) is an essential enzyme of pterin and folate metabolism in the protozoan parasite Leishmania. The present work is focused on the degradation of PTR1 during growth phase in Leishmania donovani. Western blot analysis with PTR1-GFP transfected promastigotes revealed that PTR1 protein was degraded in the stationary phase of growth at the time when the parasites were undergoing metacyclogenesis. Fluorescence microscopy revealed cytoplasmic localization of GFP tagged protein extending to the flagellum in these stationary phase promastigotes, implying that degradation of the protein was not by the usual multivesicular tubule lysosome (MVT) pathway. A probable destruction box of nine amino acids Q63ADLSNVAK71 and possible lysine residue K156 was identified in L. donovani PTR1 to be the site for ubiquitin conjugation. This suggests that PTR1 degradation during the stationary phase of growth is mediated by the proteasome. This leads to lower levels of H4-biopterin, which favors metacyclogenesis, and subsequently results in a highly infective stage of the parasite. Therefore, this finding has importance to identify new target molecule like the proteasome for therapeutic intervention.
• 1.78

  Impact points

  Possibility of membrane modification as a mechanism of antimony resistance in Leishmania donovani.

  Hema Kothari, Pranav Kumar, Shyam Sundar, Neeloo Singh

  Parasitology international. 04/2007; 56(1):77-80.

  Resistance to antimonials has become a clinical threat in the treatment of visceral leishmaniasis (VL). Unravelling the resistance mechanism needs attention to circumvent the problem of drug resistance. In one of the resistant isolates, we earlier identified a gene (PG1) implicated in antimony resis... [more] Resistance to antimonials has become a clinical threat in the treatment of visceral leishmaniasis (VL). Unravelling the resistance mechanism needs attention to circumvent the problem of drug resistance. In one of the resistant isolates, we earlier identified a gene (PG1) implicated in antimony resistance whose localization in the present study was confirmed on the pellicular plasma membrane of the parasite thereby indicating towards membrane modification as a mechanism of resistance in this resistant isolate.
• 1.51

  Impact points

  Translation of open reading frame in kinetoplast DNA minicircles of clinical isolates of L. donovani.

  Hema Kothari, Pranav Kumar, Rohit Saluja, Shyam Sundar, Neeloo Singh

  Parasitology research. 04/2007; 100(4):893-7.

  Till today, it remains an enigma whether the open reading frames said to be transcribed in minicircle sequences are indeed translated into protein products or not. We establish a protein-coding gene in minicircle variable region of kinetoplast DNA from clinical isolates of Leishmania donovani. The p... [more] Till today, it remains an enigma whether the open reading frames said to be transcribed in minicircle sequences are indeed translated into protein products or not. We establish a protein-coding gene in minicircle variable region of kinetoplast DNA from clinical isolates of Leishmania donovani. The protein was expressed as an N-tagged green fluorescent protein (GFP) fusion protein in leishmanial expression system. Fluorescence microscopy of the transfectants carrying recombinant GFP construct showed the protein to be localized on the plasmalemma of the parasite. This shows that the minicircle transcript is indeed translated into a protein product in the parasite cell and further points toward probable biological function of minicircles in kinetoplastids.
• 1.83

  Impact points

  Drug resistance mechanisms in clinical isolates of Leishmania donovani.

  Neeloo Singh

  The Indian journal of medical research. 04/2006; 123(3):411-22.

  Leishmania are protozoan parasites distributed worldwide. About 1.5-2.0 million cases are reported in the world annually from this disease and the death toll is estimated to be 57,000. Along with Brazil, Sudan and Bangladesh, India contributes to 90 per cent of the global burden of visceral leishman... [more] Leishmania are protozoan parasites distributed worldwide. About 1.5-2.0 million cases are reported in the world annually from this disease and the death toll is estimated to be 57,000. Along with Brazil, Sudan and Bangladesh, India contributes to 90 per cent of the global burden of visceral leishmaniasis (VL). The absence of effective vaccines and vector control programmes, makes chemotherapy the most widely used tool against leishmaniasis. Chemotherapy based on pentavalent antimonials has been used for more than 50 years and remains the mainstay for treatment of leishmaniasis. Clinical resistance to pentavalent antimonials, in the form of sodium antimony gluconate (SAG), has become a major problem in the treatment of kala-azar (visceral leishmaniasis) in India. The mechanism of resistance is unclear in these clinical isolates although a lot of work has been carried out with Leishmania mutants selected in vitro by step-wise increasing drug concentration using the antimony related metal arsenic and more recently sodium antimony gluconate. We for the first time, investigated the molecular aspect of drug resistance in clinically confirmed sodium antimony gluconate resistant field isolates and found that the parasite evaded cytotoxic effects of therapy by enhanced efflux of drugs through overexpressed membrane proteins belonging to the superfamily of ABC (ATP-binding cassette) transporters. Additionally, our study also points towards cell surface changes in resistant isolates.
• 1.56

  Impact points

  Prokaryotic expression, purification, and polyclonal antibody production against a novel drug resistance gene of Leishmania donovani clinical isolate.

  Hema Kothari, Pranav Kumar, Neeloo Singh

  Protein expression and purification. 02/2006; 45(1):15-21.

  Diseases produced by protozoan parasites are one of the main causes of morbidity and mortality around the world, affecting millions of people. Among these, leishmaniasis has become the second most common cause of death and the problem is further complicated by the expansion of parasite resistance to... [more] Diseases produced by protozoan parasites are one of the main causes of morbidity and mortality around the world, affecting millions of people. Among these, leishmaniasis has become the second most common cause of death and the problem is further complicated by the expansion of parasite resistance to the conventional drugs. The high rate of therapeutic failure thus calls for new rational approaches to develop alternative drugs. Understanding resistance mechanisms may help identify new targets for drug development. So we present here the cloning, expression, purification, and antibody production of a gene implicated in imparting resistance to pentavalent antimony (SbV) in clinical isolates of kala azar with a view to gain insight into the novel mechanism of its drug resistance.
• 1.51

  Impact points

  Refractoriness to the treatment of sodium stibogluconate in Indian kala-azar field isolates persist in in vitro and in vivo experimental models.

  Anuradha Dube, Nasib Singh, Shyam Sundar, Neeloo Singh

  Parasitology research. 07/2005; 96(4):216-23.

  Ever since their discovery about 60 years ago as therapeutic agent for visceral leishmaniasis (VL) or kala-azar, pentavalent antimonials (Sb(v)) have remained the first line treatment of choice all over the world including India. But recently, the number of kala-azar patients unresponsive to sodium ... [more] Ever since their discovery about 60 years ago as therapeutic agent for visceral leishmaniasis (VL) or kala-azar, pentavalent antimonials (Sb(v)) have remained the first line treatment of choice all over the world including India. But recently, the number of kala-azar patients unresponsive to sodium stibogluconate (SSG) therapy, is steadily increasing in India. In this study, three clinical isolates, of which two were from SSG unresponsive and one from SSG responsive patients were evaluated for their infectivity and for their chemotherapeutic responses in vitro (macrophage-amastigote system) and in vivo (in hamsters). Persistence of SSG resistance was also checked by repeated passages in vitro as well as in vivo. The drug resistant strains (2039 and 2041) did not respond to SSG therapy both in vitro as well as in vivo but strains 2001 and Dd8 showed full sensitivity to SSG treatment. All the four strains responded well to amphotericin B and miltefosine treatment both in macrophages and in hamsters. The specific chemotherapeutic responses of all the strains to SSG were consistently persistent after repeated passages in cultures and in vivo, which indicates that these isolates are truly refractory to SSG treatment in field conditions. Two isolates were also transfected with green fluorescent protein (GFP) for the development of in vitro assay for studying antileishmanial activities of new and reference drugs in macrophages by flow cytometry.
• 1.56

  Impact points

  Overexpression in Escherichia coli and purification of pteridine reductase (PTR1) from a clinical isolate of Leishmania donovani.

  Pranav Kumar, Hema Kothari, Neeloo Singh

  Protein expression and purification. 01/2005; 38(2):228-36.

  Pteridine reductase 1 (PTR1) is part of a novel metabolic pathway in Leishmania associated with folate metabolism. Its main function is to salvage pterins but a second one is to reduce folates. The novelty and possible uniqueness of the pathway in which PTR1 is involved opens the possibility of deve... [more] Pteridine reductase 1 (PTR1) is part of a novel metabolic pathway in Leishmania associated with folate metabolism. Its main function is to salvage pterins but a second one is to reduce folates. The novelty and possible uniqueness of the pathway in which PTR1 is involved opens the possibility of developing specific inhibitors, which in combination with dihydrofolate reductase inhibitors could be highly effective against Leishmania. In order to increase our understanding of this putative important chemotherapeutic target, we present here the cloning, overexpression and purification of this enzyme from a clinical isolate of Leishmania donovani causing kala azar in India. This recombinant enzyme will set the basis for inhibition studies as well as for structure-function relationships.
• 2.80

  Impact points

  Short report: fluorescent Leishmania: application to anti-leishmanial drug testing.

  Neeloo Singh, Anuradha Dube

  The American journal of tropical medicine and hygiene. 11/2004; 71(4):400-2.

  Classic techniques for detecting the susceptibility of Leishmania to different drugs are time-consuming, laborious, and require the use of macrophages. The use of flow cytometry for monitoring Leishmania susceptibility to drugs is beginning to be implemented. Using green fluorescent protein (GFP), w... [more] Classic techniques for detecting the susceptibility of Leishmania to different drugs are time-consuming, laborious, and require the use of macrophages. The use of flow cytometry for monitoring Leishmania susceptibility to drugs is beginning to be implemented. Using green fluorescent protein (GFP), we have improved and simplified the screening procedure. We introduced a GFP marker into field strains of Leishmania causing kala-azar (visceral leishmaniasis) and explored the suitability of transgenic L. donovani promastigotes that constitutively express GFP in their cytoplasm as target cells for in vitro screening of anti-leishmanial drugs.