Identification of novel CA IX inhibitor: Pharmacophore modeling, docking, DFT, and dynamic simulation.

Human Carbonic anhydrase IX (hCA IX) is found to be an essential biomarker for the treatment of hypoxic tumors in both the early and metastatic stages of cancer. Due to its active function in maintaining pH levels and overexpression in hypoxic conditions, hCA IX inhibitors can be a potential candidate specifically designed to target cancer development at various stages. In search of selective hCA IX inhibitors, we developed a pharmacophore model from the existing natural product inhibitors with IC50 values less than 50 nm. The identified hit molecules were then investigated on protein-ligand interactions using molecular docking experiments followed by molecular dynamics simulations. Among the zinc database 186 hits with an RMSD value less than 1 were obtained, indicating good contact with key residues HIS94, HIS96, HIS119, THR199, and ZN301 required for optimum activity. The top three compounds were subjected to molecular dynamics simulations for 100 ns to know the protein-ligand complex stability. Based on the obtained MD simulation results, binding free energies are calculated. Density Functional Theory (DFT) studies confirmed the energy variation between the Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO). The current study has led to the discovery of lead compounds that show considerable promise as hCA IX inhibitors and suggests that three compounds with special molecular features are more likely to be better-inhibiting hCA IX. Compound S35, characterized by a higher stability margin and a smaller energy gap in quantum studies, is an ideal candidate for selective inhibition of CA IX.

Ligand based pharmacophore modelling and integrated computational approaches in the quest for small molecule inhibitors against hCA IX.

Carbonic anhydrase IX is an important biomarker to fight hypoxic tumours in both initial and metastatic stages of many forms of cancer. Overexpression of hCA IX in the hypoxic environment, has an active role in pH maintenance and makes the hCA IX a better target for the inhibitors targeting specific types of cancer stages. Being a member of the carbonic anhydrase family and having sixteen isoforms, it is important to have a selective inhibition of hCA IX to limit the disruption in the biological and metabolic pathways where other isoforms of hCA are localised and to avoid the other toxicity and adverse effects we try to find selective hCA IX inhibitors from a natural derivative. In the process of finding selective hCA inhibitors we developed a pharmacophore model based on existing inhibitors with IC50 values of less than 50 nm, which is then validated with the external decoy set and used for database searching followed by virtual screening to identify the hits based on the pharmacophore fit score and RMSD. Molecular docking studies were performed to identify protein ligand interaction and molecular dynamics simulation studies to analyse the stability of the complex and DFT studies were carried out. The initial screening yielded 43 hits with the RMSD value less than 1, which when subjected to docking exhibited very good interaction with key residues ZN301, HIS94, HIS96 and HIS119. The top 4 compounds in the molecular dynamics simulation studies for 100 ns provided useful insights on the stability of the complex and the DFT studies confirmed the energy variation between HOMO and LUMO is within an acceptable range. An average binding score of -7.8 Kcal mol-1 for the lead compounds and high stability margin in the dynamics study concludes that these lead compounds demonstrated outstanding potential for hCA IX inhibitory action theoretically and that further experimental studies for selective inhibition are inevitable.