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.

A scaffold hopping strategy to generate new aryl-2-amino pyrimidine MRSA biofilm inhibitors

Infections that stem from bacterial biofilms are difficult to eradicate. Within a biofilm state, bacteria are upwards of 1000-fold more resistant to conventional antibiotics, necessitating the development of alternative approaches to treat biofilm-based infections. One such approach is the development of small molecule adjuvants that can inhibit/disrupt bacterial biofilms. When such molecules are paired with conventional antibiotics, these dual treatments present a combination approach to eradicate biofilm-based infections. Previously, we have demonstrated that small molecules containing either a 2-amino pyrimidine (2-AP) or a 2-aminoimidazole (2-AI) heterocycle are potent anti-biofilm agents. Herein, we now report a scaffold hopping strategy to generate new aryl 2-AP analogs that inhibit biofilm formation by methicillin-resistant Staphylococcus aureus (MRSA). These molecules also suppress colistin resistance in colistin resistant Klebsiella pneumoniae, lowering the minimum inhibitory concentration (MIC) by 32-fold.

Augmenting the Activity of Macrolide Adjuvants against Acinetobacter baumannii

Approximately 1.7 million Americans develop hospital associated infections each year, resulting in more than 98,000 deaths. One of the main contributors to such infections is the Gram-negative pathogen Acinetobacter baumannii. Recently, it was reported that aryl 2-aminoimidazole (2-AI) compounds potentiate macrolide antibiotics against a highly virulent strain of A. baumannii, AB5075. The two lead compounds in that report increased clarithromycin (CLR) potency against AB5075 by 16-fold, lowering the minimum inhibitory concentration (MIC) from 32 to 2 μg/mL at a concentration of 10 μM. Herein, we report a structure-activity relationship study of a panel of derivatives structurally inspired by the previously reported aryl 2-AI leads. Substitutions around the core phenyl ring yielded a lead that potentiates clarithromycin by 64- and 32-fold against AB5075 at 10 and 7.5 μM, exceeding the dose response of the original lead. Additional probing of the amide linker led to the discovery of two urea containing adjuvants that suppressed clarithromycin resistance in AB5075 by 64- and 128-fold at 7.5 μM. Finally, the originally reported adjuvant was tested for its ability to suppress the evolution of resistance to clarithromycin over the course of nine consecutive days. At 30 μM, the parent compound reduced the CLR MIC from 512 to 2 μg/mL, demonstrating that the original lead remained active against a more CLR resistant strain of AB5075.

Meridianin D analogues possess antibiofilm activity against Mycobacterium smegmatis

The formation of bacterial biofilms significantly decreases the efficacy of antibiotic treatments. Herein, we've investigated the antibiofilm properties of the natural product meridianin D and a library of analogues against Mycobacterium smegmatis. As a result, we discovered several analogues that both inhibit and disperse M. smegmatis biofilms.