Synthesis of novel nitroreductase enzyme-activated nitric oxide prodrugs to site-specifically kill bacteria

The developing antibiotic resistance crisis creates a serious need for new antimicrobial agents. In this work, novel nitroaromatic-protected piperazine diazeniumdiolate (nitric oxide donor) prodrugs are synthesized to release nitric oxide upon enzyme activation to kill bacteria. Antibacterial prodrugs could help reduce side effects due to antibiotics, only releasing the therapeutic where infections are concentrated. The nitroreductase enzyme, which is found almost exclusively in bacteria, reduces the nitroaromatic-protecting group of the synthesized compounds and catalyzes the release of nitric oxide. This paper shows that nitric oxide release from the synthesized compounds only occurs in the presence of a bacteria-derived nitroreductase enzyme, demonstrating the possibility of site-specific delivery of an antibacterial therapeutic. The amount of nitric oxide release is measured at concentrations of 0.01, 0.1, and 1 mM, and is well within antibacterial levels at concentrations of 0.1 and 1 mM. The antibacterial activity of the compounds is demonstrated after exposure of the compounds to Escherichia coli, a nitroreductase-producing bacterial species, leading to up to a 94% reduction in the number of viable bacteria after 24 h at 1 mM concentrations of the prodrug. This study is the first example of an antibacterial diazeniumdiolate prodrug activated by a nitroreductase enzyme, and further demonstrates the possibilities of antibacterial prodrugs.