Molecular Recognition between Anticancer Drug, Regorafenib and Human Serum Albumin: Interaction Revisited

The wet-lab techniques (fluorimetry and spectrophotometry), along with computational techniques (molecular docking and molecular dynamics (MD) simulation), were applied to re-examine the association of an anticancer drug, regorafenib (REG) with human serum albumin (HSA). The REG-induced protein fluorescence quenching was characterized as static quenching based on a decrement in the KSV (Stern-Volmer constant) with increasing temperature and hyperchromic effect in the absorption spectra. The REG-HSA complex (Ka = 0.63 - 1.17 x 105 M-1) was stabilized by hydrophobic and van der Waals interactions in combination with hydrogen bonds, as revealed by thermodynamic data (& UDelta;rS' = +17.17 J mol-1 K-1 and & UDelta;rH' = -23.00 kJ mol-1), and further supported by molecular docking assessment. Microenvironmental fluctuations around HSA fluorophores and better protein stability against thermal stress were evident due to REG-HSA complexation. Accessibility of both Sudlow's Sites I and II but priority for Site I of the protein for REG was inferred by the competitive ligand displacement and molecular docking assessments. MD simulation results supported the stability of the complex.