Interaction of anticancer herbal drug berberine with DNA immobilized on the glassy carbon electrode

The interaction of anticancer herbal drug berberine with double-strand DNA (dsDNA) and single-strand DNA (ssDNA) in solution, dsDNA immobilized on the glassy carbon electrode prepared by Langmuir-Blodgett technique, were investigated by electrochemical techniques (cyclic voltammetry, differential pulse voltammetry) and UV spectroscopy. The presence of DNA results in a decrease of the currents and a negative shift of the electrode potentials from the DPV curves of berberine, indicating the dominance of electrostatic interactions. The spectroscopy data confirmed that the predominant interaction between berberine and DNA is electrostatic. The binding of berberine with DNA, when analyzed in terms of the cooperative Hill model, yields the binding constant K-a=2.2(+/- 0.2) x 10(4) M-1, corresponding to the dissociation equilibrium constant K-d=4.6(+/- 0.3) x 10(-5) M, which in the range of the applied concentrations, of DNA (bp) and berberine, and a Hill coefficient m = 1.82(+/- 0.08) in Britton-Robinson buffer solution (0.05 M, pH 5.72) at T=298 K (25 degrees C). Apparently, at least two molecules of berberine have to bind as a couple to cause, e.g., the "elementary event" of current change. The results are suggestive for further fruitful applications of this anticancer herbal drug and DNA-modified electrodes. (C) 2008 Elsevier B.V. All rights reserved.