Evaluation of potential drugs against leishmaniasis targeting catalytic subunit of Leishmania donovani nuclear DNA primase using ligand based virtual screening, docking and molecular dynamics approaches.

Leishmania donovani, causes leishmaniasis, a global health trouble with around 89 different countries and its population under its risk. Replication initiation events have been instrumental in regulating the DNA duplication and as the small subunit of L. donovani nuclear DNA primase (Ld-PriS) inherits the catalytic site, it plays a vital role in DNA replication. In this study we have aimed Ld-PriS for the first time as a prospective target for the application of drug against Leishmania parasite. 3-D structures of Ld-PriS were built and ligand-based virtual screening was performed using hybrid similarity recognition techniques. Ligands from the ZINC database were used for the screening purposes based on known DNA primase inhibitor Sphingosine as a query. Top 150 ligands were taken into consideration for molecular docking against the query protein (Ld-PriS) using PyRx and iGEMDOCK softwares. Top five compounds with the best docking score were selected for pharmacokinetic investigation and molecular dynamic simulation. These top five screened inhibitors showed very poor binding affinity toward the catalytic subunit of human primase indicating their safety toward the host normal replication mechanism. The top five compounds showed good pharmacokinetic profiles and ADMET predictions revealed good absorption, solubility, permeability, uniform distribution, proper metabolism, minimal toxicity and good bioavailability. Simulation studies upto 50 ns revealed the three leads ZINC000009219046, ZINC000025998119 and ZINC000004677901 bind with Ld-PriS throughout the simulation and there were no huge variations in their backbone suggesting that these three may play as potential lead compounds for developing new drug against leishmaniasis.Communicated by Ramaswamy H. Sarma.

Magnolol Inhibits LPS-induced NF-kappaB/Rel Activation by Blocking p38 Kinase in Murine Macrophages

This study demonstrates the ability of magnolol, a hydroxylated biphenyl compound isolated from Magnolia officinalis, to inhibit LPS-induced expression of iNOS gene and activation of NF-kappaB/Rel in RAW 264.7 cells. Immunohisto-chemical staining of iNOS and Western blot analysis showed magnolol to inhibit iNOS gene expression. Reporter gene assay and electrophoretic mobility shift assay showed that magnolol inhibited NF-kappaB/Rel transcriptional activation and DNA binding, respectively. Since p38 is important in the regulation of iNOS gene expression, we investigated the possibility that magnolol to target p38 for its anti-inflammatory effects. A molecular modeling study proposed a binding position for magnolol that targets the ATP binding site of p38 kinase (3GC7). Direct interaction of magnolol and p38 was further confirmed by pull down assay using magnolol conjugated to Sepharose 4B beads. The specific p38 inhibitor SB203580 abrogated the LPS-induced NF-kappaB/Rel activation, whereas the selective MEK-1 inhibitor PD98059 did not affect the NF-kappaB/Rel. Collectively, the results of the series of experiments indicate that magnolol inhibits iNOS gene expression by blocking NF-kappaB/Rel and p38 kinase signaling.