Effect of cationic drugs on suprahelical organization of DNA

Interaction of a minor groove-binding drug Hoechst-33258, and an intercalating drug, proflavin, with the PSI(+) form of DNA, was studied using CD spectroscopy. Both drugs are shown to relax the suprahelical organization of DNA, leading to the formation of a B-like structure, above a certain drug to phosphate ratio. However, unlike proflavin, Hoechst-33258 brings about further structural changes after formation of the B-like structure whereas proflavin does not. A reversal of the CD signal in the 300-450-nm spectral region is also observed with Hoechst-33258, indicating a change in the handedness of the suprahelical organization of DNA. To the best of our knowledge, drug-mediated changes as presented in this paper have not been reported so far.