Origins of cell selectivity of cationic steroid antibiotics.

A key factor in the potential clinical utility of membrane-active antibiotics is their cell selectivity (i.e., prokaryote over eukaryote). Cationic steroid antibiotics were developed to mimic the lipid A binding character of polymyxin B and are shown to bind lipid A derivatives with affinity greater than that of polymyxin B. The outer membranes of Gram-negative bacteria are comprised primarily of lipid A, and a fluorophore-appended cationic steroid antibiotic displays very high selectivity for Gram-negative bacterial membranes over Gram-positive bacteria and eukaryotic cell membranes. This cell selectivity of cationic steroid antibiotics may be due, in part, to the affinity of these compounds for lipid A. Copyright 2004 American Chemical Society