Molecular interactions of AL3818 (anlotinib) to human serum albumin as revealed by spectroscopic and molecular docking studies

Anlotinib (ANB) is a novel member of the tyrosine kinase inhibitors approved for different types of cancer, its binding to human serum albumin (HSA) is of significant pharmacological importance. Hence, this study was devoted to understand the nature of the binding between ANB and HSA via the use of a set of conventional spectroscopic tools supplemented by molecular docking analysis. Fluorescence spectral measurements revealed a clear quenching effect of ANB on the HSA intrinsic fluorescence, which was shown to follow the static quenching type via the formation of a non-fluorescent complex. Analyses of this fluorescence data using the Stern–Volmer, Lineweaver-Burk and double-log relations showed that ANB-HSA binding constants ranged from 0.96 to 1.15 × 105 M−1 as resulted from the different relations in three different experimental temperatures. Further interpretation of the data using thermodynamic equations reveled spontaneous reaction between ANB and HSA with negative enthalpy and positive entropy values that propose the contribution of electrostatic forces possibly accompanied by hydrogen bonding. Docking studies confirmed the ANB-HSA complex formation with the ANB bound to Site I on the HSA structure mainly with the amino acid residues LYS 199, ARG 222, LEU 238 and ALA 291.