Accessibility to bacterial nucleic acids of the intercalating drug aliphatic amino acid-ellipticinium derivatives in Escherichia coli and Salmonella typhimurium

Abstract

The fluorescence of the aliphatic (amino acido)-N2-methyl-9-hydroxyellipticinium (AA-NMHE) derivatives dehydroglycino-NMHE, dehydroalanino-NMHE, dehydrovalino-NMHE, and dehydroleucino-NMHE was characterized. The changes in the fluorescence properties of the drugs, including increase in quantum yields, increase in fluorescence lifetimes, and ocurrence of energy transfer upon binding to DNA in vitro, were further investigated. The measurement of the fluorescence increment of AA-NMHE when bound to fluorescent sites inside intact bacteria was found to be suitable for the determination of the accessibility of the drugs to bacterial nucleic acids according to the method of Lambert and Le Pecq. With this methodology, the kinetics of drug uptake, the ability of the drug to reach the bacterial nucleic acids at equilibrium, and the nature of the ligand binding model were determined in 2 AA-NMHE-sensitive strains, E. coli BL 101 and S. typhimurium TA 98. At nonsaturating concentrations, each AA-NMHE exhibits a marked difference in its ability to reach the bacterial nucleic acids. This parameter seems to be correlated with the antibacterial efficiency of the drugs. The accessibility of AA-NMHE to the bacterial nucleic acids appears to be under the control of the hydrophobic character of the drugs on the 1 hand and the phenotype of the bacteria on the other hand. It is suggested that the increase in the accessibilty to bacterial nucleic acids resulting either from a hydrophobic effect or from mutation is related to the ability of the drugs to reach a class of binding sites likely organized in a nucleosome-like structure.