Innovative zinc-binding inhibitors of Legionella pneumophila ProA reduce collagen and flagellin degradation, TLR5 evasion, and human lung tissue inflammation

Legionnaires' disease is a severe pneumonia caused by the aquatic bacterium Legionella pneumophila. In recent years, the number of cases has continuously increased according to the distribution of aerosol-producing technologies, global warming, and demographic ageing, which elevates bacterial transmission, environmental cell counts and host susceptibility. Despite the availability of an antibiotic therapy, this treatment cannot eradicate the risk of irreversible symptoms or high mortality rates. The bacterial zinc metalloprotease ProA significantly contributes to life-threatening tissue damage in patients and hence promotes progression of the disease. We hypothesize that additional application of an inhibitory agent against this protease may reduce serious complications and the risk of respiratory failure until successful bacterial clearance. Here we present a newly designed set of zinc-binding compounds and evaluated their inhibitory effects on the versatile physiological activity of ProA during infection. We identified a potent phosphonate inhibitor, which reduces ProA-dependent cleavage of host collagen IV and bacterial flagellin, immune evasion from the TLR5-NF-κB pathway and PMN-mediated inflammation in human lung tissue explants (HLTEs). Based on efficacy at the biochemical, cellular and tissue levels and the results of ProA co-crystallizations, we conclude that the selected inhibitors represent promising lead structures for the future development of clinically applicable pathoblockers against Legionnaires' disease.