Spectroscopic studies on the interaction between erlotinib hydrochloride and bovine serum albumin

Background and the purpose of the study: The binding ability of a drug to serum albumin has influence on the pharmacokinetics of a drug. In the present study, the mutual interaction of anticancer drug erlotinib hydrochloride with bovine serum albumin (BSA) using fluorescence and UV/vis spectroscopy was investigated. The BSA solution (0.1 mM) was prepared daily in Tris buffer (0.05 mol l-1, pH =7.4) and treated at final concentration of 1.67×10-5 M with different amounts of erlotinib hydrochloride to obtain final concentrations of 0, 0.2, 0.4, 0.8, 1, 2, 4, 6, 8, 20 and 42 μM receptively. The mixture was allowed to stand for 5 min and the fluorescence quenching spectra were recorded at 298, 303, 308 and 313 K. It was found that erlotinib hydrochloride caused the fluorescence quenching of BSA by the formation of a BSA-erlotinib hydrochloride complex. The mechanism of the complex formation was then analyzed by determination of the number of binding sites, apparent binding constant Ka, and calculation of the corresponding thermodynamic parameters such as the free energy (ΔG), enthalpy (ΔH) and entropy changes (ΔS) at different temperatures. Results showed that binding of erlotinib hydrochloride to BSA was spontaneous, and the hydrophobic forces played a major role in the complex formation. The distance, r, between donor (BSA) and acceptor (erlotinib hydrochloride) was found to be less than 8 nm suggesting the occurrence of non-radiative energy transferring and static quenching between these two molecules. The results provided preliminary information on the binding of erlotinib hydrochloride to BSA and the presence of a single binding site on BSA and Ka values for the association of BSA with erlotinib hydrochloride increased by the increase in temperature.