Proline-rich antimicrobial peptides in the age of antibiotic-resistance: a new weapon to fight Klebsiella pneumoniae bloodstream infections

Bloodstream infections require rapid and effective intervention because of their high mortality risk. However, the number of antibiotics used to treat these conditions has been reduced dramatically due to the diffusion of antibiotic-resistant pathogens. Bloodstream infections caused by antibiotic resistant Klebsiella pneumoniae, with a worrisome mortality rate of between 40% and 50%, are representative of the current antibiotic crisis. The need for new antimicrobial drugs is evident. In this scenario, antimicrobial peptides (AMPs) gained interest as compounds to develop new anti-infectives. AMPs possess potent antimicrobial activity associated with low bacteria rate of resistance development. Unfortunately, most AMPs are also rather cytotoxic. The Proline-rich antimicrobial peptides (PrAMPs) are an exception. PrAMPs display specific and non-membranolytic antimicrobial mechanism of action. They kill bacteria by binding to the bacterial ribosomes and blocking protein synthesis. This makes PrAMPs selective for bacteria and generally well tolerated by eukaryotic cells. The aim of this project is to identify a lead compound from a group of selected PrAMPs suitable to fight antibiotic-resistant K. pneumoniae bloodstream infections. The project will identify the PrAMP that exhibits: i) the best in vitro antimicrobial activity against planktonic or sessile forms of multidrug-resistant clinical isolates of K. pneumoniae; ii) the best tolerability to human cells and possibly; iii) anti-inflammatory and LPS-inactivating properties. Experiments will be performed under conditions simulating the final use (e.g. in whole blood). Structure-activity relationship studies will help identify structural features of PrAMPs associated with desired biological activities. Finally, in vivo experiments in mouse models of a bloodstream K. pneumoniae infection and of LPS shock will determine the actual efficacy of the selected PrAMP as antimicrobial and/or immunomodulatory agent. The project, presented by three integrated and complementary units, will provide a robust preclinical evaluation of PrAMPs, that will show whether these compounds can address the urgent need of new drugs to combat antibiotic-resistant K. pneumoniae bloodstream infections. In addition, the project could pave the way for the development of other further optimized antimicrobial drugs based on PrAMPs.