Comprehending binding features between ibrutinib and Human Alpha-1 acid glycoprotein: Combined experimental...

Human alpha-1 acidic glycoprotein (HAG) is one of the proteins widely present in the blood, and the level of HAG in patients with cancer and inflammation is significantly increased. As one of transport proteins in the blood, the ability of HAG to bind with a drug, especially alkaline drugs, affects significantly the drug content at the target site, which in turn affects the efficacy of the drug. In this study, the interaction mechanism between HAG and the first generation Bruton's tyrosine kinase (BTK) inhibitor namely ibrutinib was explored by a combination of multi-spectroscopic techniques and theoretical calculations. The findings revealed that the quenching and binding constants of the HAG-ibrutinib system both reduced as the temperature rose, demonstrating that ibrutinib quenched the intrinsic fluorescence of HAG in a static manner. It was confirmed that HAG and ibrutinib formed a 1:1 complex with moderate affinity due to the binding constant of around 10⁵ M^-1 and accompanied by Förster resonance energy transfer. It was verified by thermodynamic parameter analysis and competition assays as well as molecular simulation that the existence of hydrogen bonds, van der Waals forces, and hydrophobic forces in the complexation of HAG and ibrutinib.The findings from theoretical calculations including molecular docking and theoretical calculation simulation confirmed that ibrutinib bound to the barrel hydrophobic pocket of HAG with a binding energy of -41.9 kJ∙mol^-1, and the the binding constant of around 10⁵ M^-1 and the contribution of each residue in the complexation of ibrutinib and HAG. Additionally, it can be confirmed that metal ions affected the binding interaction of ibrutinib with HAG, among them, some promoted binding while others inhibited it.