Synthetic molecular evolution of host cell-compatible, antimicrobial peptides effective against drug-resistant, biofilm-forming bacteria

Novel classes of antibiotics and new strategies to prevent and treat infections are urgently needed because the rapid rise in drugresistant bacterial infections in recent decades has been accompanied by a parallel decline in development of new antibiotics. Membrane permeabilizing antimicrobial peptides (AMPs) have long been considered a potentially promising, novel class of antibiotic, especially for wound protection and treatment to prevent the development of serious infections. Yet, despite thousands of known examples, AMPs have only infrequently proceeded as far as clinical trials, especially the chemically simple, linear examples. In part, this is due to impediments that often limit their applications in vivo. These can include low solubility, residual toxicity, susceptibility to proteolysis, and loss of activity due to host cell, tissue, and protein binding. Here we show how synthetic molecular evolution can be used to evolve potentially advantageous antimicrobial peptides that lack these impediments from parent peptides that have at least some of them. As an example of how the antibiotic discovery pipeline can be populated with more promising candidates, we evolved and optimized one family of linear AMPs into a new generation with high solubility, low cytotoxicity, potent broad-spectrum sterilizing activity against a panel of grampositive and gram-negative ESKAPE pathogens, and antibiofilm activity against gram-positive and gram-negative biofilms. The evolved peptides have these activities in vitro even in the presence of concentrated host cells and also in vivo in the complex, cell- and protein-rich environment of a purulent animal wound model infected with drug-resistant bacteria.