Mario Rivera photoMario Rivera
Professor, Department of Chemistry
The University of Kansas

Probes to disrupt iron homeostasis in Pseudomonas aeruginosa (2012-2014)

Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen which is primarily a nosocomial infection, and is particularly serious for patients hospitalized with burns, cancer, and cystic fibrosis where the fatality rate is ~50%. P. aeruginosa infection is the fourth most common in U.S. hospitals with an incidence of ~10% of all nosocomial infections, and is associated with a low susceptibility to antibiotic treatment largely due to multidrug efflux pumps associated with antibiotic resistance genes.

Given the severity and incidence of P. aeruginosa infection, new means of treatment that are not subject to antibiotic efflux would be valuable additions to current therapy. This application describes studies to explore a new and innovative direction for the development of antimicrobials by exploiting the vulnerability represented by bacterial iron homeostasis when pathogens are confronted with the host immune system. Our studies are based on unique results demonstrating that (1) the function of bacterioferritin (BfrB) is required for P. aeruginosa growth in cystic fibrosis sputum, (2) the function of BfrB in bacterial iron homeostasis requires binding and electron delivery by a ferredoxin Bfd, (3) the crucial BfrB-Bfd interface, recently defined by our X-ray crystallographic work, is highly complementary, and (4) small molecule probes (fragments) interact with BfrB at the BfrB-Bfd interface.

Consequently, we propose to develop probes that by inhibiting the BfrB-Bfd association inhibit bacterial iron homeostasis and impair P. aeruginosa growth. We have shown that fragment based drug discovery (FBDD) is a viable way to identify small molecules that block the BfrB-Bfd interface and inhibit the release of iron from BfrB. Our objective will be achieved by integrating the following activities in an iterative fashion:

  1. Carry out a fragment-based approach to discover inhibitors of the P. aeruginosa BfrB-Bfd protein-protein interface by the systematic combination of NMR methods, surface plasmon resonance spectroscopy, functional assays, in silico methods and X-ray crystallography.
  2. Utilize medicinal chemistry to drive iterative rounds of structure activity relationship development by parallel synthesis utilizing the following criteria: (i) in vitro binding to BfrB, (ii) inhibition of the interaction of BfrB with Bfd, (iii) inhibition of the release of iron from BfrB, (iv) inhibition of P. aeruginosa in a zone-killing assay.

The work has the potential to produce the first-ever chemical probes of the critical BfrB-Bfd interface, which are expected to provide critical insight as to the in vitro and in vivo function of BfrB, a promising target for the treatment of P. aeruginosa infection. Our long-term goal is to convert from a target validation to a drug discovery program, to discover and develop new therapeutics for the treatment of P. aeruginosa infection.