The Engineered Lysin, CF-370, is Active Against Antibiotic-Resistant Gram-Negative Pathogens In vitro and Synergizes with Meropenem in Experimental Pseudomonas aeruginosa Pneumonia.

ABSTRACT

BACKGROUND: Lysins (cell wall hydrolases) targeting Gram-negative organisms require engineering to permeabilize the outer membrane and access subjacent peptidoglycan to facilitate killing. In the current study, the potential clinical utility for engineered lysin, CF-370, was examined in vitro and in vivo against Gram-negative pathogens important in human infections. METHODS: MICs and bactericidal activity were determined using standard methods. An in vivo proof-of-concept efficacy study was conducted using a rabbit acute pneumonia model caused by Pseudomonas aeruginosa. RESULTS: CF-370 exhibited potent antimicrobial activity, with MIC50/90 values (in µg/mL) for P. aeruginosa, 1/2; Acinetobacter baumannii, 1/1; Escherichia coli, 0.25/1; Klebsiella pneumoniae, 2/4; Enterobacter cloacae 1/4; and Stenotrophomonas maltophilia 2/8. CF-370 furthermore demonstrated i) bactericidal activity; (ii) activity in serum; iii) a low propensity for resistance; iv) anti-biofilm activity; and v) synergy with antibiotics. In the pneumonia model, CF-370 alone decreased bacterial densities in lungs, kidneys and spleen vs. vehicle control, and demonstrated significantly increased efficacy when combined with meropenem (vs either agent alone). CONCLUSIONS: CF-370 is the first engineered lysin described with potent broad spectrum in vitro activity against multiple clinically-relevant Gram-negative pathogens, as well as potent in vivo efficacy in an animal model of severe invasive multi-system infection.