Spectroscopic analysis of the binding of doxorubicin to human .alpha.-1 acid glycoprotein

The binding of the anticancer drug doxorubicin (DOX) to human α-1 acid glycoprotein (AGP) is investigated using absorbance and fluorescence spectroscopies. Steady-state fluorescence and UV-vis absorbance measurements produced evidence of the formation of a 1:1 complex between DOX and AGP. Scatchard analysis indicated the presence of one major binding site for the drug on the protein, and estimated complex formation constants using both spectroscopic methods ranged from 104 to 105 M-1. Fluorescence lifetime and polarization measurements provided further evidence of complexation and indicated a "loose" binding of DOX to its binding site on AGP. Stern-Volmer fluorescence quenching analysis showed reduced accessibility of bound DOX to an anionic quencher, suggesting that the binding site for DOX on AGP is hydrophobic in nature.