Fighting infections with non-proteinogenic amino acids – biphenyl derivatives

Abstract

Background: The emergence of multidrug-resistant (MDR) bacterial pathogens is a global problem for medicine despite the vast number of available antimicrobials. Novel effective antimicrobials and various approaches are required to overcome this challenge. The non-proteinogenic amino acids and biphenyl-containing compounds are widely used in drug design. The incorporation of the biphenyl group into amino acid side chains appears to be a promising approach for developing effective antimicrobials. Bacterial extracellular proteases are virulent factors that can be detrimental, destroying host tissue and compromising the immune system during infection. The treatment of infectious diseases with protease inhibitors, in combination with antibiotics, has shown promising results. 

Objective: To reveal the effective antimicrobial compounds, the influence of biphenyl-containing amino acids on the growth of antibiotic-resistant bacteria, and the activity of bacterial proteases involved in the progression of infections were studied.

Methods: Susceptibility of the strains was assessed by serial dilutions in the presence of the studied compound in a broth at final concentrations ranging from 0.005 mM to 0.5 mM.  The optical density of bacterial cultures was measured. The MIC was determined as the lowest concentration of the compound that prevented visible bacterial growth after incubation. Proteinase activity was measured by the method of free amino groups determined by the OPA reagent.

Results: The non-proteinogenic amino acids containing biphenyl groups in the side chain were tested on their ability to inhibit the growth of antibiotic-resistant P. aeruginosa 80 (clinical isolate), K.pneumonia 63 (clinical isolate), E.coli ESBL 64 (clinical isolate), S.maltophilia MDC 9288, S. aureus MDC 5233 strains, and bacterial protease activities. According to the results obtained, (S)-3-([1,1'-biphenyl]-4-yl)-2-aminopropanoic acid and (S)-3-([1,1':4',1''-terphenyl]-4-yl)-2-aminopropanoic acid demonstrate antibacterial activity against Gram-negative Enterobacteriaceae strains and Gram-positive S. aureus MDC 5233 strain with MIC values ranging from ≤ 0.5mg/L to 14.4 mg/l.  The non-proteinogenic amino acid (S)-3-([1,1':4',1''-terphenyl]-4-yl)-2-aminopropanoic acid inhibits proteinase K activity.

Conclusions: This study demonstrated that (S)-3-([1,1'-biphenyl]-4-yl)-2-aminopropanoic acid and (S)-3-([1,1':4',1''-terphenyl]-4-yl)-2-aminopropanoic acid showed a high level of antibacterial activity against Gram-negative Enterobacteriaceae strains and Gram-positive S. aureus MDC 5233 strain. Thus, these non-proteinogenic amino acids can be considered novel, promising antimicrobials and recommended for the treatment of infections. Novel inhibitor of Proteinase K and collagenase activity - (S)-3-([1,1':4',1''-terphenyl]-4-yl)-2-aminopropanoic acid was revealed.

Novelty:  Novel non-proteinogenic amino acids – biphenyl derivatives possessing antibacterial activity towards antibiotic-resistant strains have been revealed in this study. According to the results obtained, (S)-3-([1,1':4',1''-terphenyl]-4-yl)-2-aminopropanoic acid is a novel inhibitor of proteinase K and clostridial collagenase.

Keywords: multi-drug resistance, biphenyl derivatives, antimicrobials, virulence factors, protease inhibitors.