Clotrimazole causes membrane depolarization and induces sub G0 cell cycle arrest in Leishmania donovani

Clotrimazole is an FDA approved drug and is widely used as an antifungal agent. An extensive body of research is available about its mechanism of action on various cell types but its mode of killing of Leishmania donovani parasites is unknown. L. donovani causes Visceral Leishmaniasis which is a public health problem with limited treatment options. Its present chemotherapy is expensive, has adverse effects and is plagued with drug resistance issues. In this study we have explored the possibility of repurposing clotrimazole as an antileishmanial drug. We have assessed its efficacy on the parasites and attempted to understand its mode of action. We found that it has a half-maximal inhibitory concentration (IC50) of 35.75 ± 1.06 μM, 12.75 ± 0.35 μM and 73 ± 1.41 μM in promastigotes, intracellular amastigotes and macrophages, respectively. Clotrimazole is 5.73 times more selective for the intracellular amastigotes as compared to the mammalian cell. Effect of clotrimazole was reduced by ergosterol supplementation. It leads to impaired parasite morphology. It alters plasma membrane permeability and disrupts plasma membrane potential. Mitochondrial function is compromised as is evident from increased ROS generation, depolarized mitochondrial membrane and decreased ATP levels. Cell cycle analysis of clotrimazole treated parasites shows arrest at sub-G0 phase suggesting apoptotic mode of cell death.

Pyridoxal kinase gene deletion leads to impaired growth, deranged redox metabolism and cell cycle arrest in Leishmania donovani

Pyridoxal kinase (PdxK) is a vitamin B6 salvage pathway enzyme which produces pyridoxal phosphate. We have investigated the impact of PdxK deletion in Leishmania donovani on parasite survivability, infectivity and cellular metabolism. LdPdxK mutants were generated by gene replacement strategy. All mutants showed significant reduction in growth in comparison to wild type. For PdxK mediated biochemical perturbations, only heterozygous mutants and complementation mutants were used as the growth of null mutants were compromised. Heterozygous mutant showed reduction invitro infectivity and higher cytosolic and mitochondrial ROS levels. Glutathione levels decreased significantly in heterozygous mutant indicating its involvement in cellular oxidative metabolism. Pyridoxal kinase gene deletion resulted in reduced ATP levels in parasites and arrest at G0/G1 phase of cell cycle. All these perturbations were rescued by PdxK gene complementation. This is the first report to confirm that LdPdxK plays an indispensable role in cell survival, pathogenicity, redox metabolism and cell cycle progression of L. donovani parasites. These results provide substantial evidence supporting PdxK as a therapeutic target for the development of specific antileishmanial drug candidates.

Leishmania donovani 6-phosphogluconolactonase: Crucial for growth and host infection?

The hexose monophosphate shunt is a crucial pathway in a variety of microorganisms owing to its vital metabolic products and intermediates such as NADPH, ribose 5-phosphate etc. The enzyme 6-phosphogluconolactonase catalyses the second step of this pathway, converting 6-phosphogluconolactone to 6-phosphogluconic acid. This enzyme has been known to have a significant involvement in growth, pathogenesis and sensitivity to oxidative stress in bacterial and protozoal pathogens. However, the functional role of kinetoplastid Leishmania donovani 6-phospohogluconolactonase (Ld6PGL) remains unexplored. L. donovani is the second largest parasitic killer and causative organism of life threatening visceral leishmaniasis. To understand its possible functional role in the parasite, the alleles of Ld6PGL were sequentially knocked-out followed by gene complementation. The Ld6PGL mutant cell lines showed decrease in transcriptional and translational expression as well as in the enzyme activity. In case of Ld6PGL null mutants, approximately 2-fold reduction was observed in growth. The null mutants also showed ∼38% decrease in infectivity, which recovered to ∼15% on complementation. Scanning electron microscopy showed a marked decrease in flagellar length in the knockout parasites. When treated with the standard drug miltefosine, the mutant strains had no significant change in the drug sensitivity. However, the Ld6PGL mutants were more susceptible to oxidative stress. Our findings suggest that 6PGL is required for parasite growth and infection but it is not essential.

A "Core-Linker-Polyamine (CLP)" strategy enabling rapid discovery of antileishmanial aminoalkyl-quinoline-carboxamides that target oxidative stress mechanism

A "Core-Linker-Polyamine (CLP)" strategy has been exploited to develop new antileishmanial agents. It involves the linker-based assembly of alkyl-polyamine side chain as a potential pharmacophore motif with a privileged heterocyclic motif, 4-arylquinoline. A series of aminoalkyl 4-arylquinoline-2-carboxamides and their analogs were synthesized and tested against L. donovani promastigotes. Among all synthesized derivatives, 10 compounds showed significant antipromastigote activities with more efficacy (IC 50 : 4.75-8 µ M) than an antileishmanial oral drug Miltefosine (IC 50 : 8.9±1.55 µ M). Most active compounds 9a and 9b , displayed negligible cytotoxicity towards human monocytic (THP-1) macrophages. The compounds show antileishmanial activity by generating mitochondrial superoxide radicals. However, they did not show interference with trypanothione reductase, a redox enzyme of Leishmania. Significant change in the morphology of the L. donovani promastigote by the compounds was observed. The Structure-activity relationship analysis suggest the pharmacophoric importance of alkylpolyamine and carboxamide motifs.  In silico evaluation  indicated that the investigated active molecules 9a and 9b possess important drug-likeness, physicochemical and pharmacokinetic-relevant properties.

Identification of 2-arylquinazolines with alkyl-polyamine motifs as potent antileishmanial agents: synthesis and biological evaluation studies

2-Arylquinazolines with a range of alkyl polyamines as side chain/ring functional motifs at the 4th-position were considered for antileishmanial study with the rationale that related heterocyclic scaffolds and polyamine functionalities are present in drugs, clinical trial agents, natural products and anti-parasitic/leishmanial agents. Synthesis involves construction of the 2-arylquinazolin-4-one ring and deoxyamination via deoxychlorination followed by SNAr-based amination or a methodology of SNAr-deoxyamination driven by BOP-mediated hydroxyl-activation. Various alkyl-polyamines important for activities were incorporated. A total of 26 compounds were prepared and screened against Leishmania donovani (Ld) promastigote cells using the MTT assay. Most of the investigated series of compounds showed characteristic leishmanicidal properties. Several compounds showed pronounced leishmanicidal activities (IC50: 5-6.5 μM) with higher efficiency than the antileishmanial drug miltefosine (IC50: 10.5 μM), and relatively less cytotoxicity to macrophage host cells (SI: 9.27-13.5) compared to miltefosine (SI: 3.42). Important pharmacophoric skeletons were identified.

Exploring Leishmania donovani 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) as a potential drug target by biochemical, biophysical and inhibition studies

3-Hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase (HMGR), an NADPH dependant enzyme catalyzes the synthesis of mevalonic acid from HMG-CoA required for isoprenoid biosynthesis. The HMGR gene from Leishmania donovani was cloned and expressed. Genome analysis of L. donovani revealed that HMGR gene having an open reading frame of 1305 bp encodes a putative protein of 434 amino acids. LdHMGR showed optimal activity at pH 7.2 and temperature 37 °C. Kinetic analysis of this enzyme revealed Km values of 35.7 ± 2.5 μM for (R,S)-HMG-CoA and 70 ± 7.9 μM for the cofactor NADPH. On tryptophan fluorescence quenching, the Stern Volmer constant (Ksv), binding constant (Ka) and protein:cofactor stoichiometry for interaction of NADPH cofactor with the enzyme were found to be 6.0 ± 0.7 M(-1), 0.17 μM and 0.72 respectively. Polyclonal anti-rat HMGR antibody detected a band of ∼45 kDa in all phases of promastigote growth. Biophysical analysis of the secondary structure of LdHMGR confirmed the presence of 25.7 ± 0.35% alpha helicity. Thermal denaturation studies showed extreme stability of the enzyme with 60% helical structure retained at 90 °C. Statins (simvastatin and atorvastatin) and non-statin (resveratrol) effectively inhibited the growth of L. donovani promastigotes as well as the catalytic activity of the recombinant LdHMGR. Atorvastatin was found to be most potent antileishmanial inhibitor with an IC50 value of 19.4 ± 3.07 μM and a very lower concentration of 315.5 ± 2.1 nM was enough to cause 50% recombinant LdHMGR enzyme inhibition suggesting direct interaction with the rate limiting enzyme of the ergosterol biosynthetic pathway. Exogenous supplementation of ergosterol in case of atorvastatin and resveratrol treated cells caused complete reversal of growth inhibition whereas simvastatin was found to be ergosterol refractory. Cholesterol supplementation however, failed to overcome growth inhibition in all the cases. Overall our study emphasizes on exploring LdHMGR as a potential drug target for the development of novel antileishmanial agents.

Identification and characterization of a novel Ribose 5-phosphate isomerase B from Leishmania donovani

Leishmaniasis is a group of tropical diseases caused by protozoan parasites of the genus Leishmania. Due to the emergence of resistance to the available antileishmanial drugs there is an immediate need to identify molecular targets on which to base future treatment strategies. Ribose 5-phosphate isomerase (Rpi; EC 5.3.1.6) is a key enzyme of the pentose phosphate pathway (PPP) which catalyses the reversible aldose-ketose isomerization between Ribose 5-phosphate (R5P) and Ribulose 5-phosphate (Ru5P). It exists in two isoforms A and B. These two are completely unrelated enzymes catalyzing the same reaction. Analysis of the Leishmania infantum genome revealed that though the RpiB gene is present, RpiA homologs are completely absent. An absence of RpiBs in the genomes of higher animals makes this enzyme a possible target for the chemotherapy of Leishmaniasis. In this paper, we report for the first time the presence of B isoform of the Rpi enzyme in Leishmania donovani (LdRpiB) by cloning and molecular characterization of the enzyme. An amplified L. donovani RpiB gene is 519 bp and encodes for a putative 172 amino acid protein with a molecular mass of ∼19 kDa. An ∼19 kDa protein with poly-His tag at the C-terminal end was obtained by heterologous expression of LdRpiB in Escherichia coli. The recombinant form of RpiB was obtained in soluble and active form. The LdRpiB exists as a dimer of dimers i.e. the tetramer form. The polyclonal antibody against Trypanosoma cruzi RpiB could detect a band of ∼19 kDa with the purified recombinant RpiB as well as native RpiB from the L. donovani promastigotes. Recombinant RpiB obeys the classical Michaelis-Menten kinetics utilizing R5P as the substrate with a K(m) value of 2.4±0.6 mM and K(cat) value of 30±5.2 s(-1). Our study confirms the presence of Ribose 5-phosphate isomerase B in L. donovani and provides functional characterization of RpiB for further validating it as a potential drug target.

Study of sugarcane pieces as yeast supports for ethanol production from sugarcane juice and molasses using newly isolated yeast from toddy sap

A repeated batch fermentation system was used to produce ethanol using Saccharomyces cerevisiae strain (NCIM 3640) immobilized on sugarcane (Saccharum officinarum L.) pieces. For comparison free cells were also used to produce ethanol by repeated batch fermentation. Scanning electron microscopy evidently showed that cell immobilization resulted in firm adsorption of the yeast cells within subsurface cavities, capillary flow through the vessels of the vascular bundle structure, and attachment of the yeast to the surface of the sugarcane pieces. Repeated batch fermentations using sugarcane supported biocatalyst were successfully carried out for at least ten times without any significant loss in ethanol production from sugarcane juice and molasses. The number of cells attached to the support increased during the fermentation process, and fewer yeast cells leaked into fermentation broth. Ethanol concentrations (about 72.65~76.28 g/L in an average value) and ethanol productivities (about 2.27~2.36 g/L/hr in an average value) were high and stable, and residual sugar concentrations were low in all fermentations (0.9~3.25 g/L) with conversions ranging from 98.03~99.43%, showing efficiency 91.57~95.43 and operational stability of biocatalyst for ethanol fermentation. The results of the work pertaining to the use of sugarcane as immobilized yeast support could be promising for industrial fermentations.

Development of patient support devices for execution of clinical radiotherapy for cancer patients: A preliminary report

The present paper illustrates our attempt to design and test the reproducibility of low-cost patient positioning devices prepared in-house in our radiotherapy department. Rigid thermocole boards with angulations, scales and support were designed as breast, pelvis and head positioning devices. Reproducibility and accuracy were tested by serial electronic portal imaging detector imaging.

The positioning devices (with or without superimposed moulds) showed variations within 2-3 mm on serial treatment days which were within acceptable limits.

It is therefore concluded that low-cost patient positioning devices for head, breast and pelvis (the common sites of treatments in radiotherapy) can be fabricated from available materials in-house. These have been shown to be resulting in accurate immobilization, can be customized for particular techniques and are considerably cheaper than commercially available solutions.