Structural insight into epothilones antitumor activity based on the conformational preferences and tubulin binding...

Molecular dynamics simulations were employed to analyze the conformational preferences and binding modes of epothilones A and B as a source of structural information regarding the antitumor properties of these species. Our results suggest that the conformation of free and tubulin-bound epothilones is strongly influenced by the presence of a methyl group at C12 and that epothilones A and B exploit the binding cavity in a unique and different way. The binding sites of epothilones A and B share a common region of association (Leu215, Leu217, His227, Leu228, Ala231, Phe270, Gly360, and Leu361), but lead to different ligand-residue interactions. Average interaction energies predict a larger stabilization for the epothilone B-tubulin complex, which is mainly driven by the enhancement of the electrostatic component of ligand-residue interactions compared to the epothilone A-tubulin complex. These structural and energetic results can be useful to account for the activity difference between epothilones A and B, and to design more active and potent analogs that resemble the mechanism of action of epothilones against cancer cells.