Interactions of Potential Anticancer Drug 4-chloro-6-(1H-imidazo[4,5-b]phenazine-2-yl)benzene-1,3-diol with Supercoiled and Linear Plasmid DNAs

Introduction: Does DNA superhelicity effect nucleic acid interactions with drugs? To test such a possibility, the interactions of the linear and superhelical forms of the pGEX-4T-2 plasmid have been investigated with a newly synthesized compound, 4-chloro-6-(1H-imidazo [4,5-b]phenazine-2-yl)benzene-1,3-diol, positively tested for the antiproliferative (cell growth-limiting) properties, important for the development of anticancer drugs. Methods: The accumulation of the compound, and its possible reorientation (phase transition) within the plasmid layer adsorbed on a Glassy Carbon (GC) electrode has been monitored in 5 min. intervals using alternatively two voltammetric methods—Differential Pulse (DP), showing redox properties and—Alternating Current (AC), reflecting both redox and structural properties (capacity/resistance change related to DNA condensation) of the DNA-drug layers. Results and Discussion: The accumulation plots of the compound in plasmid layers are different for superhelical and linear pGEX-4T-2 and also depend on the DNA coverage by the compound. The reorientation (phase transition) occurs at a compound concentration 2 µM for the superhelical plasmid and 1.5 µM for the linear one, as compared to 8 µM for the compound layer formed on bare GC, thus proving the existence of the DNA–compound interactions. Interestingly, the phase transition is redox-sensitive, e.g., AC redox signal II is visible for the linear, but not for the superhelical plasmid, thus reflecting different orientation of the compound in these two types of pGEX-4T-2 plasmid, related to the condensation in the DNA–compound layer and seen as a decrease in the C/R signal. Conclusions: The results suggest that the reorientation of the compound leading to plasmid condensation occurs differently in supercoiled and linear pGEX-4T-2 (redox specific accumulation and condensation).