Polymyxin B combinations with FDA-approved non-antibiotic phenothiazine drugs targeting multi-drug resistance of Gram-negative pathogens

Maytham Hussein; Xiaohan Hu; Olivia K A Paulin; Simon Crawford; Qi Tony Zhou; Mark Baker; Elena K Schneider-Futschik; Yan Zhu; Jian Li; Tony Velkov

doi:10.1016/j.csbj.2020.08.008

Polymyxin B combinations with FDA-approved non-antibiotic phenothiazine drugs targeting multi-drug resistance of Gram-negative pathogens

Comput Struct Biotechnol J. 2020 Aug 21:18:2247-2258. doi: 10.1016/j.csbj.2020.08.008. eCollection 2020.

Authors

Affiliations

¹ Department of Pharmacology & Therapeutics, School of Biomedical Sciences, Faculty of Medicine, Dentistry and Health Sciences, The University of Melbourne, Parkville, VIC 3010, Australia.
² The Monash Ramaciotti Centre for Cryo-Electron Microscopy, Monash University, Clayton, Victoria 3800, Australia.
³ Department of Industrial and Physical Pharmacy, College of Pharmacy, Purdue University, West Lafayette, IN 47907-2091, USA.
⁴ Discipline of Biological Sciences, Priority Research Centre in Reproductive Biology, Faculty of Science and IT, University of Newcastle, University Drive, Callaghan NSW, 2308, Australia.
⁵ Monash Biomedicine Discovery Institute, Department of Microbiology, Monash University, Clayton, Victoria 3800, Australia.

Abstract

The status quo for combating uprising antibacterial resistance is to employ synergistic combinations of antibiotics. Nevertheless, the currently available combination therapies are fast becoming untenable. Combining antibiotics with various FDA-approved non-antibiotic drugs has emerged as a novel strategy against otherwise untreatable multi-drug resistant (MDR) pathogens. The apex of this study was to investigate the mechanisms of antibacterial synergy of the combination of polymyxin B with the phenothiazines against the MDR Gram-negative pathogens Acinetobacter baumannii, Klebsiella pneumoniae and Pseudomonas aeruginosa. The synergistic antibacterial effects were tested using checkerboard and static time-kill assays. Electron microscopy (EM) and untargeted metabolomics were used to ascertain the mechanism(s) of the antibacterial synergy. The combination of polymyxin B and the phenothiazines showed synergistic antibacterial activity in checkerboard and static time-kill assays at clinically relevant concentrations against both polymyxin-susceptible and polymyxin-resistant isolates. EM revealed that the polymyxin B-prochlorperazine combination resulted in greater damage to the bacterial cell compared to each drug monotherapy. In metabolomics, at 0.5 h, polymyxin B monotherapy and the combination (to a greatest extent) disorganised the bacterial cell envelope as manifested by a major perturbation in bacterial membrane lipids (glycerophospholipids and fatty acids), peptidoglycan and lipopolysaccharide (LPS) biosynthesis. At the late time exposure (4 h), the aforementioned effects (except LPS biosynthesis) perpetuated mainly with the combination therapy, indicating the disorganising bacterial membrane biogenesis is potentially behind the mechanisms of antibacterial synergy. In conclusion, the study highlights the potential usefulness of the combination of polymyxin B with phenothiazines for the treatment of polymyxin-resistant Gram-negative infections (e.g. CNS infections).

Keywords: Antimicrobial peptides; Antimicrobial resistance; Gram-negative; MDR; Metabolomics; Phenothiazines.