Sensitization of Gram-Negative Bacteria to Aminoglycosides with 2-Aminoimidazole Adjuvants.

In 2019, five million deaths associated with antimicrobial resistance were reported by The Centers for Disease Control and Prevention (CDC). Acinetobacter baumannii, a Gram-negative bacterial pathogen, is among the list of urgent threats. Previously, we reported 2-aminoimidazole (2-AI) adjuvants that potentiate macrolide activity against A. baumannii. In this study, we identify several of these adjuvants that sensitize A. baumannii to aminoglycoside antibiotics. Lead compounds 1 and 7 lower the tobramycin (TOB) minimum inhibitory concentration (MIC) against the TOB-resistant strain AB5075 from 128 µg/mL to 2 µg/mL at 30 µM. In addition, the lead compounds lower the TOB MIC against the TOB-susceptible strain AB19606 from 4 µg/mL to 1 µg/mL and 0.5 µg/mL, respectively, at 30 µM and 15 µM. The evolution of resistance to TOB and 1 in AB5075 revealed mutations in genes related to protein synthesis, the survival of bacteria under environmental stressors, bacteriophages, and proteins containing Ig-like domains.

Dimeric 2-aminoimidazoles are highly active adjuvants for gram-positive selective antibiotics against Acinetobacter baumannii.

The Centers for Disease Control and Prevention (CDC) reports that hospital acquired infections have increased by 65% since 2019. One of the main contributors is the gram-negative bacterium Acinetobacter baumannii. Previously, we reported aryl 2-aminoimidazole (2-AI) adjuvants that potentiate macrolide antibiotics against A. baumannii. Macrolide antibiotics are typically used to treat infections caused by gram-positive bacteria, but are ineffective against most gram-negative bacteria. We describe a new class of dimeric 2-AIs that are highly active macrolide adjuvants, with lead compounds lowering minimum inhibitory concentrations (MICs) to or below the gram-positive breakpoint level against A. baumannii. The parent dimer lowers the clarithromycin (CLR) MIC against A. baumannii 5075 from 32 µg/mL to 1 µg/mL at 7.5 µM (3.4 µg/mL), and a subsequent structure activity relationship (SAR) study identified several compounds with increased activity. The lead compound lowers the CLR MIC to 2 µg/mL at 1.5 µM (0.72 µg/mL), far exceeding the activity of both the parent dimer and the previous lead aryl 2-AI. Furthermore, these dimeric 2-AIs exhibit considerably reduced mammalian cell toxicity compared to aryl-2AI adjuvants, with IC50s of the two lead compounds against HepG2 cells of >200 µg/mL, giving therapeutic indices of >250.

Structure-Function Studies on IMD-0354 Identifies Highly Active Colistin Adjuvants.

Infections caused by multidrug-resistant (MDR) bacteria, particularly Gram-negative bacteria, are an escalating global health threat. Often clinicians are forced to administer the last-resort antibiotic colistin; however, colistin resistance is becoming increasingly prevalent, giving rise to the potential for a situation in which there are no treatment options for MDR Gram-negative infections. The development of adjuvants that circumvent bacterial resistance mechanisms is a promising orthogonal approach to the development of new antibiotics. We recently disclosed that the known IKK-ß inhibitor IMD-0354 potently suppresses colistin resistance in several Gram-negative strains. In this study, we explore the structure-activity relationship (SAR) between the IMD-0354 scaffold and colistin resistance suppression, and identify several compounds with more potent activity than the parent against highly colistin-resistant strains of Acinetobacter baumannii and Klebsiella pneumoniae.