Antibiotic Discovery Targeting Bacterial GroEL/GroES Chaperonin Systems

Abstract

The Centers for Disease Control (CDC) and World Health Organizations (WHO) have highlighted six species of highly drug-resistant bacteria, commonly termed the ESKAPE pathogens, that new antibacterials are urgently needed to treat). The ESKAPE pathogens account for over two-million infections and have healthcare costs upwards of $20 billion dollars annually. Over the past several decades, pharmaceutical companies have drastically reduced their research programs for developing new antibacterial agents. As well, bacteria are predisposed to rapidly generate resistance against these “me too” drugs, making this strategy a temporary stop-gap in our ability to fight these pathogens. This has left the burden to identify new antibiotics that function through fundamentally unique mechanisms of action to academia. Towards this goal, we are developing a unique antibacterial strategy that functions through targeting the bacterial GroEL chaperonin systems. GroEL is a molecular chaperone that helps fold proteins into their functional states. Being an essential protein, inhibiting GroEL activity leads to global aggregation and bacterial cell death. We previously reported a high-throughput screening effort that identified 235 GroEL inhibitors. A subsequent study with a subset of these inhibitors identified several that kill bacteria. To follow-up, we have synthesized 43 analogs of a hit-to-lead molecule, compound 1, containing systematic deletions of substituents and substructures to determine the essential parts of the scaffold for inhibiting GroEL and killing bacteria. Along with inhibiting GroEL, several compound 1 analogs exhibit >50-fold therapeutic windows between antibacterial efficacy and cytotoxicity to human liver and kidney cells in cell culture. Evaluation of two lead candidates (1 and 11) in a gain-of-resistance assay indicated that MRSA bacteria were not able to easily generate resistance to this compound class. Compound 1 also exhibited the ability to permeate through already established S. aureus biofilms and maintain its bactericidal effects, whereas vancomycin could not. Having established initial structure-activity relationships for the compound 1 substituents and substructures in this study, future efforts will focus on optimizing the antibacterial effects of lead candidates and reducing their off-target toxicity to human cells.