2-aminoimidazoles potentiate ß-lactam antimicrobial activity against Mycobacterium tuberculosis by reducing ß-lactamase secretion and increasing cell envelope permeability

Abstract

There is an urgent need to develop new drug treatment strategies to control the global spread of drug-sensitive and multidrug-resistant Mycobacterium tuberculosis (M. tuberculosis). The ß-lactam class of antibiotics is among the safest and most widely prescribed antibiotics, but they are not effective against M. tuberculosis due to intrinsic resistance. This study shows that 2-aminoimidazole (2-AI)-based small molecules potentiate ß-lactam antibiotics against M. tuberculosis. Active 2-AI compounds significantly reduced the minimal inhibitory and bactericidal concentrations of ß-lactams by increasing M. tuberculosis cell envelope permeability and decreasing protein secretion including ß-lactamase. Metabolic labeling and transcriptional profiling experiments revealed that 2-AI compounds impair mycolic acid biosynthesis, export and linkage to the mycobacterial envelope, counteracting an important defense mechanism reducing permeability to external agents. Additionally, other important constituents of the M. tuberculosis outer membrane including sulfolipid-1 and polyacyltrehalose were also less abundant in 2-AI treated bacilli. As a consequence of 2-AI treatment, M. tuberculosis displayed increased sensitivity to SDS, increased permeability to nucleic acid staining dyes, and rapid binding of cell wall targeting antibiotics. Transcriptional profiling analysis further confirmed that 2-AI induces transcriptional regulators associated with cell envelope stress. 2-AI based small molecules potentiate the antimicrobial activity of ß-lactams by a mechanism that is distinct from specific inhibitors of ß-lactamase activity and therefore may have value as an adjunctive anti-TB treatment.

Novel Antimicrobials from Uncultured Bacteria Acting against Mycobacterium tuberculosis

“…A microtiter assay was used to determine the amount of β-lactamase in the culture filtrate (CF) and whole-cell lysate (WCL) by monitoring the hydrolysis of the chromogenic substrate nitrocefin over time. The cleavage of nitrocefin by β-lactamase results in a shift in the absorbance of nitrocefin from 490 nm to 390 nm ( 25 , 26 ). Here, we monitored the hydrolysis of nitrocefin by the ratio of the absorbance at 490 nm to the absorbance at 390 nm.…”

Oxidative Phosphorylation—an Update on a New, Essential Target Space for Drug Discovery in Mycobacterium tuberculosis

“…A wide range of compounds currently exists that target the PMF in bacteria, including rotenone which inhibits major proton pumps and protonophores (e.g., carbonyl cyanide m-chlorophenyl hydrazone, also known as CCCP), which translocate protons across the cell membranes [14] (Table 5). More specifically to mycobacteria, pyrazinoic acid, the active form of the first-line TB drug PZA, was demonstrated to decrease PMF and ATP levels in M. bovis BCG [185]. Several other compounds active against M. tb including SQ109, BDQ and CFZ were also found to be multi-targeting by behaving as uncouplers in addition to targeting enzymes [186].…”

“…Recently, 2-aminoimidazoles (2-AI), a class of molecules with anti-biofilm activity, was shown to revert drug tolerance in an in vitro M. tb biofilm model [184]. This class of compounds potentiate the activity of β-lactams by altering protein secretion and lipid export, suggesting that 2-AI may perturb membrane energization [185]. Derivative 2B8 rapidly depolarized the membrane potential of live M. smeg, and collapsed the ∆pH generated by M. smeg IMVs energized with NADH, similar to CCCP and other mycobacterial uncouplers.…”

Cell Surface Biosynthesis and Remodeling Pathways in Mycobacteria Reveal New Drug Targets

“…Therefore, the search for orally bioavailable carbapenems continues. The 2-aminoimidazoles (2-AIs) have recently been shown to potentiate the activity of b-lactams by decreasing Mtb protein secretion and also by increasing the CW permeability (Jeon et al, 2017). This was due to inhibition of the electron transport chain which resulted in impairment of protein secretion systems and MA biosynthesis (Jeon et al, 2019).…”