Investigation of Aryl 2-Aminoimidazoles as Antibiotic Adjuvants Against Gram-Negative Bacteria

Antimicrobial resistance (AMR) is one of the leading global health and development threats to date, being responsible for an estimated 1.27 million deaths worldwide in 2019. Since the COVID-19 pandemic there have been setbacks in combatting AMR. While COVID-19 is caused by a virus, 80% of patients that were hospitalized with COVID-19 between March and October 2020 were prescribed antibiotics. This over prescribing of antibiotics caused a 20% increase in hospital-acquired antibiotic resistant bacterial infections. In addition to the rise in antibiotic resistant infections, the antibiotic development pipeline has seen a very low return, signifying a need for different approaches to overcome AMR. One approach to combat this critical threat to human health is the use of small molecule adjuvants. Adjuvants are non-microbiocidal compounds that allow for continued use of current antibiotics. Adjuvants can help recover efficacy that is diminished due to resistance, as well as expand the spectrum of activity of antibiotics to include bacteria that are intrinsically resistant. Initial efforts described in this document include a structure activity relationship (SAR) study on a library of aryl 2-aminoimidazole (2-AI) adjuvants, that have previously been shown to sensitize gram-negative bacteria to gram-positive selective antibiotics, as adjuvants for aminoglycoside antibiotics. Detailed discussions outline the discovery and SAR investigation of compounds containing a 2-AI moiety as adjuvants for the aminoglycoside class of antibiotics. The SAR study led to the identification of several compounds that resensitize Acinetobacter baumannii, as well as Klebsiella pneumoniae, to aminoglycoside antibiotics, notably tobramycin, with reductions in minimum inhibitory concentrations (MICs) as high as 64-fold. Lastly, this document details the use of small molecule adjuvants that augment the activity of gram-positive selective antibiotics against gram-negative bacteria, thus expanding the spectrum of activity. Comprehensive discussions outline the SAR investigation of new generation compounds containing a 2-AI moiety to reveal lead clarithromycin adjuvants. A lead 2-AI adjuvant lowers the clarithromycin MIC 2048- and 1024-fold against two strains of A. baumannii. In addition, activity for these adjuvants is seen across a variety of A. baumannii clinical isolates. Furthermore, cytotoxicity studies revealed reduced cytotoxicity towards HepG2 cells by new generation 2-AI analogs, displaying a therapeutic index (TI) up to six-fold higher than the parent 2-AIs.