Cathepsin K is a lysosomal cysteine protease that is highly and selectively expressed in osteoclasts, the cells which degrade bone during the continuous cycle of bone degradation and formation. Inhibition of cathepsin K represents a potential therapeutic approach for diseases characterized by excessive bone resorption such as osteoporosis. In order to elucidate the essential structural features for cathepsin K, a three-dimensional pharmacophore hypotheses were built on the basis of a set of known cathepsin K inhibitors selected from the literature using catalyst program. Several methods are used in validation of pharmacophore hypothesis were presented, and the fourth hypothesis (Hypo4) was considered to be the best pharmacophore hypothesis which has a correlation coefficient of 0.944 with training set and has high prediction of activity for a set of 30 test molecules with correlation of 0.909. The model (Hypo4) was then employed as 3D search query to screen the Maybridge database containing 59,000 compounds, to discover novel and highly potent ligands. For analyzing intermolecular interactions between protein and ligand, all the molecules were docked using Glide software. The result showed that the type and spatial location of chemical features encoded in the pharmacophore are in full agreement with the enzyme inhibitor interaction pattern identified from molecular docking.

Adenosine receptor A2B (ADoR A2B) is an important G protein-coupled receptor (GPCR) of the rhodopsin family, and plays a pivotal role in gastrointestinal, neurological and hypersensitive disorders. QSAR and pharmacophore studies were carried out using 63 ADoR A2B inhibitor molecules to characterize molecular features and structural requirements for biological interaction. QSAR modelling using genetic algorithm- partial least squares (G/PLS) method identified molecular shape, size electrophilicity and conformational flexibility as important descriptors for these compounds affinity to the receptor. Further analysis of pharmacophore model revealed hydrogen bond acceptor (HBA), hydrogen bond donor (HBD), hydrophobic aliphatic (HY-ala) and hydrophobic aromatic (HY-aro) as the crucial molecular features that predict binding affinity of these compounds to ADoR A2B. These observations provide important insights to the rationale development of novel and potent compounds against ADoR A2B.