Exploring the binding characteristics of bovine serum albumin with CDK4/6 inhibitors Ribociclib: Multi-spectral analysis and molecular simulation studies.

Ribociclib (RIB), a tyrosine kinase inhibitor, exhibits promising antitumor efficacy and controlled toxicity in HR+/HER2- breast cancer patients, which is closely related to the binding with plasma proteins. This study utilized a combination of spectroscopic techniques including UV spectroscopy, fluorescence spectroscopy, and circular dichroism (CD) as well as molecular docking and molecular dynamic simulation to clarify the binding mechanism between bovine serum albumin (BSA) and RIB. The findings demonstrated that RIB produced a 1:1 stoichiometric complex with BSA, which quenched BSA's fluorescence in the manner of the static quenching mechanism. Site labelling experiments pinpointed Site III on BSA as the primary binding site for RIB, a finding validated by molecular docking. Van der Waals forces and hydrogen bonding interactions as key drivers in the formation of RIB-BSA complexes, a conclusion supported by molecular docking. Molecular simulation studies suggested that the insertion of RIB into the hydrophobic cavity (Site III) of BSA induced subtle conformational changes in the BSA protein, and CD measurements confirmed alterations in BSA secondary structure content. Synchronous and three-dimensional fluorescence spectroscopy further demonstrated that RIB decreased the hydrophobicity of the microenvironment surrounding tyrosine and tryptophan residues. These findings offer valuable insights into the pharmacokinetics and structural modifications of RIB.