Binding of 8-methoxypsoralen to DNA in vitro: Monitoring by spectroscopic and chemometrics approaches

8-Methoxypsoralen (8-MOP) is a naturally occurring furanocoumarin with a variety of biological and pharmacological activities. The binding mechanism of 8-MOP to calf thymus DNA (ctDNA) at physiological pH was investigated by multi-spectroscopic techniques including UV-vis absorption, fluorescence, circular dichroism (CD) and Fourier transform infrared (FT-IR) spectroscopy along with DNA melting studies and viscosity measurements. The multivariate curve resolution-alternating least squares (MCR-ALS) chemometrics approach was introduced to resolve the expanded UV-vis spectral data matrix, and both the pure spectra and the equilibrium concentration profiles for the components (8-MOP, ctDNA and 8-MOP-ctDNA complex) in the system were successfully obtained to monitor the 8-MOP-ctDNA interaction. The results suggested that 8-MOP could bind to ctDNA via intercalation binding as evidenced by significant increases in melting and relative viscosity of ctDNA and competitive study using acridine orange (AO) as a fluorescence probe. The positive values of enthalpy and entropy change suggested that hydrogen bonds and van der Waals forces played a predominant role in the binding process. Further, FT-IR and CD spectra analysis indicated that 8-MOP preferentially bound to A-T base pairs with no major perturbation in ctDNA double helix conformation. Moreover, molecular docking was employed to exhibit the specific binding mode of 8-MOP to ctDNA intuitively.