No abstract

In view of the nonavailability of complete X-ray structure of carbamates cocrystallized with AChE enzyme, the 3D-QSAR model development based on cocrystallized conformer (CCBA) as well as docked conformer-based alignment (DCBA) is not feasible. Therefore, the only two alternatives viz. pharmacophore and maximum common substructure-based alignments are left for the 3D-QSAR comparative molecular field analyses (CoMFA) and comparative molecular similarity indices analyses (CoMSIA) model development. So, in the present study, the 3D-QSAR models have been developed using both alignment methods, where CoMFA and CoMSIA models based on pharmacophore-based alignment were in good agreement with each other and demonstrated significant superiority over MCS-based alignment in terms of leave-one-out (LOO) cross-validated q(2) values of 0.573 and 0.723 and the r(2) values of 0.972 and 0.950, respectively. The validation of the best CoMFA and CoMSIA models based on pharmacophore (Hip-Hop)-based alignment on a test set of 17 compounds provided significant predictive r(2) [r(2)(pred(test))] of 0.614 and 0.788, respectively. The contour map analyses revealed the relative importance of steric, electrostatic, and hydrophobicity for AChE inhibition activity. However, hydrophobic factor plays a major contribution to the AChE inhibitory activity modulation which is in strong agreement with the fact that the AChE is having a wide active site gorge (approximately 20 A) occupied by a large number of hydrophobic amino acid residues.

Background and purpose: New antileishmanials from natural products are urgently needed due to the emergence of drug resistance complicated by severe cytotoxic effects. 16a-Hydroxycleroda-3,13 (14)Z-dien-15,16-olide (Compound 1) from Polyalthia longifolia was found to be a potential antileishmanial and non-cytotoxic, as evidenced by long-term survival (>6 months) of treated animals. This prompted us to determine its target and, using molecular modelling, identify the interactions responsible for its specific antileishmanial activity. Experimental approach: In vitro activity of compound was assessed using intracellular transgenic green fluorescent proteinstably expressed Leishmania donovani parasites. In vivo activity and survival of animals post-treatment were evaluated in L. donovani-infected hamsters. Known property of clerodane diterpenes as potent human DNA topoisomerase inhibitors led us to evaluate the inhibition of recombinant L. donovani topoisomerase I using relaxation assay. Mode of cell death induced by Compound 1 was assessed by phosphotidylserine exposure post-treatment. Molecular modelling studies were conducted with DNA topoisomerase I to identify the binding interactions responsible for its activity. Key results: Bioassay-guided fractionation led to isolation of Compound 1 as a non-cytotoxic, orally active antileishmanial. Compound 1 inhibited recombinant DNA topoisomerase I which, ultimately, induced apoptosis. Molecular docking studies indicated that five strong hydrogen-bonding interactions and hydrophobic interactions of Compound 1 with L. donovani DNA-topoisomerase are responsible for its antileishmanial activity. Conclusions and implications:The data reveal Compound 1 is a potent and safe antileishmanial. The study further exploited the structural determinants responsible for its non-cytotoxic and potent activity, to raise the feasibility of specifically targeting the target enzyme responsible for its activity through rational drug design.

A systematic virtual screening (VS) experiment, consisting of the development of 3D-pharmacophore, screening of virtual library, synthesis, and pharmacology, is reported. The predictive pharmacophore model (correlation = 0.955) with one H-bond donor and three hydrophobic features was developed using HypoGen on a training set of 24 carbamates as AChE inhibitors. The model was validated on a test set of 40 carbamates (correlation = 0.844). The pharmacophore-based VS of virtual library led to the identification of novel carbamates as potent AChE inhibitors. The synthesis and pharmacological evaluation of nine carbamates against three diverse assay systems, namely (i) in vitro Ellman method, (ii) in vivo passive avoidance test, and (iii) aldicarb-sensitivity assay, led to the discovery of orally active novel AChE inhibitors which improved scopolamine-induce cognition impairment in Swiss male mice. Finally, two novel lead compounds 85 and 86 are selected as candidate molecules for further optimization.

Hsp90 (Heat shock protein 90) is an important therapeutic target for the treatment of cancer. To identify important chemical features for Hsp90 inhibitory activity, a 3D-QSAR pharmacophore model was developed using a set of 61 inhibitors (a training set of 31 and a test set of 30 compounds) belonging to a series of 2-amino-6-halopurine and 7'-substituted benzothiazolothio- and pyridinothiazolothio-purines. The best HypoGen model consisted of five pharmacophoric features: one hydrogen bond acceptor (HBA), one hydrogen bond donor (HBD) and three hydrophobic (HY) groups. It showed a high correlation coefficient (r = 0.943) and low root mean square deviation (RMSD = 0.751). This model was validated against 30 known Hsp90 inhibitors, where it showed a high predictive value for R(2)pred = 0.805], thus confirming that HY, HBA and HBD features are essential for Hsp90 inhibition. The validated pharmacophore model (Hypo-1) was used as a 3D query for virtual screening to retrieve potential inhibitors from the Maybridge and National Cancer Institute (NCI) databases. The hit compounds were subsequently subjected to molecular docking studies and, finally, five hits were prioritized as potential leads based on GoldScore function.