Repurposing Acitretin as an Antipseudomonal Agent Targeting the Iron-Regulated Heme Oxygenase.

Iron is an essential micronutrient for the survival and virulence of the bacterial pathogen . To overcome iron withholding and successfully colonize a host, uses a variety of mechanisms to acquire iron, including the secretion of high-affinity iron chelators (siderophores) or the uptake and utilization of heme. heme oxygenase (HemO) plays pivotal roles in heme sensing, uptake, and utilization and has emerged as a therapeutic target for the development of antipseudomonal agents. Using a high-throughput fluorescence quenching assay combined with minimum inhibitory concentration measurements, we screened the Selleck Bioactive collection of 2100 compounds and identified acitretin, a Food and Drug Administration-approved oral retinoid, as a potent and selective inhibitor of HemO. Acitretin binds to HemO with a value of 0.10 ± 0.02 μM and inhibits the growth of PAO1 with an IC of 70 ± 18 μg/mL. In addition, acitretin showed good selectivity for HemO, which uniquely generates BVIXβ/δ, over human heme oxygenase (hHO1) and other BVIXα-producing homologues such as the heme oxygenases from (nmHO) and (abHO). The binding of acitretin within the HemO active site was confirmed by H-N heteronuclear single-quantum coherence nuclear magnetic resonance, and molecular modeling provided further insight into potential interactions of acitretin with residues specific for orienting heme in the β/δ selective HemO. Moreover, at 20 μM, acitretin inhibited the enzymatic activity of HemO in cells by >60% and effectively blocked the ability of to sense and acquire heme as demonstrated in the β-galactosidase transcriptional reporter assay.