Nibha Mishra

Development of selective and reversible pyrazoline based MAO-A inhibitors: Synthesis, biological evaluation and docking studies.

3,5-Diaryl pyrazolines analogs were synthesized and evaluated for their monoamine oxidase (MAO) inhibitory activity. The compounds were found reversible and selective towards MAO-A with selectivity index in the magnitude of 10(3)-10(5). The docking studies were carried out to gain further structural insights of the binding mode and possible interactions with the active site of MAO-A. Interestingly, the theoretical (K(i)) values obtained by molecular docking studies were in congruence with their experimental (K(i)) values.

Development of selective and reversible pyrazoline based MAO-B inhibitors: virtual screening, synthesis and biological evaluation.

In an effort to develop selective MAO (monoamine oxidase) B inhibitors, structure based virtual screening was initiated on an in-house library. Top 10 HITS were synthesized and evaluated for MAO (A and B) inhibitory activity, both against human and rat enzymes. All the compounds were found selective, reversible and active in nM range (100 times more potent than selegeline) towards MAO-B. Outstanding co-relation between predicted and experimental K(i) values were observed.

Development of CoMFA and CoMSIA models of cytotoxicity data of anti-HIV-1-phenylamino-1H-imidazole derivatives

3D-QSAR models of 1-Phenylamino-1H-imidazole derivatives with cytotoxic potential have been developed using CoMFA and CoMSIA. Models were built keeping both 10% and 25% of molecules in test set. The Database and Field-Fit alignments were used for CoMFA model development. The best QSAR model was obtained from CoMFA analysis using Database alignment and employing 25% molecules in the test set (r(pred)(2) of 0.91 and r(m)(2) of 0.652). Database alignment with different fields such as Steric (S), Electrostatic (E), Acceptor (A), Donor (D) and Hydrophobic (H) was employed for CoMSIA model development. The best CoMSIA model was obtained by using the SHE fields and employing 25% molecules in the test set (r(pred)(2) of 0.789 and r(m)(2) of 0.410).

Synthesis and Ribonucleotide reductase inhibitory activity of thiosemicarbazones

Ribonucleotide reductase (RR) is an important therapeutic target for anticancer drugs. The structure of human RR features a 1:1 complex of two homodimeric subunits, hRRM1 and hRRM2. Prokaryotically expressed and highly purified recombinant human RR subunits, hRRM1 and hRRM2, were used for holoenzyme-based [(3)H]CDP reduction in vitro assay. Ten new thiosemicarbazones (7-16) were synthesized and screened for their RR inhibitory activity. Two thiosemicarbazones derived from p-hydroxy benzaldehyde (9 and 10) were found to be active but less potent than the standard, Hydroxyurea (HU). Guided by the activity of compounds 9 and 10, 11 new thiosemicarbazones (17-27) derived from p-hydroxy benzaldehyde were prepared and screened for their RR inhibitory activity. All the 11 compounds were more potent than HU.

Anticonvulsant activity of Benkara malabarica (Linn.) root extract: In vitro and in vivo investigation

AIM OF THE STUDY To systematically investigate the anticonvulsant activity of methanol extract of Benkara malabarica roots and to provide a biochemical basis elucidating its mode of action. METHODS The median lethal dose (LD(50)) of Benkara malabarica extract was determined. The anticonvulsant activity of the extract was assessed in strychnine-induced and isoniazide-induced convulsion models; phenytoin (20mg/kg) and diazepam (1mg/kg) were used as standards, respectively. Percentage protection provided by the drug was accounted as decrease in the number of convulsions within 8h of observation. Mechanism of action was studied by performing GABA transaminase (GABA-T) assay, isolated from rat brain. Active constituent was isolated and characterized from the plant extract. RESULTS The median lethal dose (LD50) of Benkara malabarica was found to be more than 500 mg/kg. It demonstrated 30% and 35% protection against strychnine-induced convulsions and 60% and 80% protection against isoniazide-induced convulsions, at doses of 25mg/kg and 50mg/kg, respectively. Enzyme assay results revealed that Benkara malabarica extract possesses GABA-T inhibitory activity (IC50=0.721 mg/ml). Scopoletin which was identified as the major constituent of the extract was found to be an inhibitor of GABA-T (IC50=10.57 microM). CONCLUSIONS The anticonvulsant activity of the plant extract is predominantly GABA mediated and may be due to the action of scopoletin alone or is a result of synergy of different compounds in the extract in which scopoletin is the major constituent.

Structure based virtual screening of GSK-3β: Importance of protein flexibility and induced fit

GSK-3beta, one of the vital enzymes responsible for various phosphorylation catalysis. Induced fit mechanism and the presence of conserved water molecule(s) in the active site poses complexity during the process of virtual screening. The present investigation reveals the practical strategy to handle the induced fit mechanism of GSK-3beta though flexible docking protocol. This protocol provides an enrichment of 70% in top 1% of the dataset with a rank correlation of >0.9 and found better in comparison to earlier reported protocols.

Effect of scopoletin on monoamine oxidases and brain amines

Naturally, occurring compounds with MAO inhibitory property may provide promising lead molecules against neurodegenerative disorders. We report MAO inhibitory activity of a naturally occurring coumarin (validated chemical scaffold as MAO inhibitors), scopoletin. It selectively (and reversibly) inhibits human (Ki = 20.7 μM) and mouse (Ki = 22 μM) MAO-B, ∼3.5 times more selective towards MAO-B than MAO-A. Docking studies revealed its molecular recognition and explained the selectivity mechanism towards MAO isoforms. Scopoletin occupied the hydrophobic aromatic pockets showing favorable interactions for MAO-B; experimental Ki agreed with the predicted Ki. In vivo, scopoletin (80 mg/kg, i.p.) treatment significantly increases dopamine level and decreases its metabolite DOPAC in striatum. Overall, scopoletin is a partially selective MAO-B inhibitor that increases brain dopamine level.

Exploring Different Virtual Screening Strategies for Acetylcholinesterase Inhibitors

The virtual screening problems associated with acetylcholinesterase (AChE) inhibitors were explored using multiple shape, and structure-based modeling strategies. The employed strategies include molecular docking, similarity search, and pharmacophore modeling. A subset from directory of useful decoys (DUD) related to AChE inhibitors was considered, which consists of 105 known inhibitors and 3732 decoys. Statistical quality of the models was evaluated by enrichment factor (EF) metrics and receiver operating curve (ROC) analysis. The results revealed that electrostatic similarity search protocol using EON (ET_combo) outperformed all other protocols with outstanding enrichment of >95% in top 1% and 2% of the dataset with an AUC of 0.958. Satisfactory performance was also observed for shape-based similarity search protocol using ROCS and PHASE. In contrast, the molecular docking protocol performed poorly with enrichment factors <30% in all cases. The shape- and electrostatic-based similarity search protocol emerged as a plausible solution for virtual screening of AChE inhibitors.

Additional acetyl cholinesterase inhibitory property of diaryl pyrazoline derivatives.

MAO-B and AChE are the two validated targets for Alzheimers disease. In pursuit of a single molecule hitting both the targets, we explored a set of previously reported extremely potent MAO-B selective inhibitors, for their additional AChE inhibitory activity. We performed molecular docking studies that formed the basis for in vitro enzyme assay, and provided necessary insights into their binding mode. Most of the compounds were found active at nano molar range, and are consistent with the docking results. The identified dual acting lead molecules may provide the basis for further exploring these chemical moieties.

Memory enhancement by Tamoxifen on amyloidosis mouse model

Tamoxifen (TMX) is a selective estrogen receptor modulator (SERM) used in the treatment of breast cancer. Earlier studies show its neuroprotection via regulating apoptosis, microglial functions, and synaptic plasticity. TMX also showed memory enhancement in ovariectomized mice, and protection from amyloid induced damage in hippocampal cell line. These reports encouraged us to explore the role of TMX in relevance to Alzheimers disease (AD). We report here, the effect of TMX treatment a) on memory, and b) levels of neurotransmitters (acetylcholine (ACh) and dopamine (DA)) in breeding-retired-female mice injected with beta amyloid1-42 (Aβ1-42). Mice were treated with TMX (10mg/kg, i.p.) for 15 days. In Morris water maze test, the TMX treated mice escape latency decreased during training trials. They also spent longer time in the platform quadrant on probe trial, compared to controls. In Passive avoidance test, TMX treated mice avoided stepping on the shock chamber. This suggests that TMX protects memory from Aβ induced toxicity. In frontal cortex, ACh was moderately increased, with TMX treatment. In striatum, dopamine was significantly increased, 3,4-dihydroxyphenylacetic acid (DOPAC) level and DOPAC/DA ratio was decreased post TMX treatment. Therefore, TMX enhances spatial and contextual memory by reducing dopamine metabolism and increasing ACh level in Aβ1-42 injected-breeding-retired-female mice.