Inhibitors of PIM-1 kinase: a computational analysis of the binding free energies of a range of imidazo [1,2-b] pyridazines.

The binding of a selection of competitive imidazo [1,2-b] pyridazine inhibitors of PIM-1 kinase with nanomolar activity has been analyzed using computational methods. Molecular dynamics simulations using umbrella sampling to determine a potential of mean force have been used to accurately predict the relative free energies of binding of these inhibitors, from -4.3 to -9.5 kcal mol(-1), in excellent agreement with the trends observed in previous experimental assays. The relative activity of the inhibitors could not be accounted for by any single effect or interaction within the active site and could only be fully reproduced when the overall free energies were considered, including important contributions from interactions outside the hinge region and using explicit solvent in the active site. The potential of mean force for the displacement of the glycine-rich phosphate binding loop (P-loop) has also been estimated and shown to be an important feature in the binding of these ligands.