Pili are defined as virulence factors for many gram-negative bacterial pathogens in the human host. The initial contact between the host and pathogen is often mediated by pilus-associated adhesins. The assembly of a large family of pili is dependent on a periplasmic chaperone. PapD, from the Pap pilus system, is the best-characterized member of this large family of proteins. Details of the interaction between PapD and pilus subunits, studied through crystallography, revealed a conserved interaction along the G-l beta strand and at the base of the inter-domain chaperone cleft. Molecular modeling of this interaction using the VALIDATE ligand-receptor docking algorithm revealed a novel family of putative chaperone inhibitors. A novel and proprietary combinatorial, synthetic pathway for the production of these compounds has been developed by SIGA sponsored scientists. We have developed several chaperone-binding assays that are suitable for High-Throughput Screening and for testing a combinatorial library of putative inhibitors. These assays will be utilized to test novel compounds that inhibit chaperone function and to screen an iterative combinatorial chemistry library to identify a lead compound. The lead compounds, based on in vitro chaperone binding will be tested in in vivo assays for secondary screening of potential leads in bacteria.
Identification of a chaperone inhibitor should lead to the development of novel highly effective broad-spectrum anti-infectives that will have wide utility in the clinic. These novel agents will be effective against organisms resistant to the current armory of antibiotics and stem the tide of multiply resistant gram-negative pathogens. For example, E. coli is responsible for 6.5 million doctor visits per year for urinary tract infections and is the most common cause of all nosocomial infections and the most common source of bacteremia in the community. Together these complaints have a $3.0 billion annual cost. Therefore, the successful outcome of the proposed SBIR has a broad and far-reaching commercial potential.
