The discovery of N-1 substituted 2-aminobenzimidazoles as zinc-dependent S. aureus biofilm inhibitors

2-Aminoimidazoles Inhibit Mycobacterium abscessus Biofilms in a Zinc-Dependent Manner

Biofilm growth is thought to be a significant obstacle to the successful treatment of Mycobacterium abscessus infections. A search for agents capable of inhibiting M. abscessus biofilms led to our interest in 2-aminoimidazoles and related scaffolds, which have proven to display antibiofilm properties against a number of Gram-negative and Gram-positive bacteria, including Mycobacterium tuberculosis and Mycobacterium smegmatis. The screening of a library of 30 compounds led to the identification of a compound, AB-2-29, which inhibits the formation of M. abscessus biofilms with an IC₅₀ (the concentration required to inhibit 50% of biofilm formation) in the range of 12.5 to 25 μM. Interestingly, AB-2-29 appears to chelate zinc, and its antibiofilm activity is potentiated by the addition of zinc to the culture medium. Preliminary mechanistic studies indicate that AB-2-29 acts through a distinct mechanism from those reported to date for 2-aminoimidazole compounds.

Strategies and Approaches for Discovery of Small Molecule Disruptors of Biofilm Physiology

Biofilms, the predominant growth mode of microorganisms, pose a significant risk to human health. The protective biofilm matrix, typically composed of exopolysaccharides, proteins, nucleic acids, and lipids, combined with biofilm-grown bacteria’s heterogenous physiology, leads to enhanced fitness and tolerance to traditional methods for treatment. There is a need to identify biofilm inhibitors using diverse approaches and targeting different stages of biofilm formation. This review discusses discovery strategies that successfully identified a wide range of inhibitors and the processes used to characterize their inhibition mechanism and further improvement. Additionally, we examine the structure–activity relationship (SAR) for some of these inhibitors to optimize inhibitor activity.

PIA and rSesC Mixture Arisen Antibodies Could Inhibit the Biofilm-Formation in Staphylococcus aureus

BACKGROUND

Staphylococcus aureus as a causative agent of hospital-acquired infections has been considered as the primary concern in biomaterial-related infections (BAIs).

METHODS

Following the purification of polysaccharide intercellular adhesion (PIA) as an efficient macromolecule in biofilm formation in the native condition, recombinant S. epidermidis surface-exposed rSesC protein, with the most homology to clumping factor A (ClfA) in S. aureus was cloned and expressed in a prokaryotic host as well. Fourier transform infrared spectrometry (FTIR) and Western blotting procedure analyzed purified PIA and protein, respectively. Then, the immune response was evaluated by measuring total IgG titers. Moreover, the capacity of Anti-biofilm forming activity of arisen antibodies to a biofilm-forming S. aureus strains was assessed by the semi-quantitative micro-plate procedure.

RESULTS

Data showed that the total IgGs were boosted in mice immunized sera. By performing an inhibition assay, the biofilm inhibitory effect of secreted antibodies to test strain was observed. Arisen antibodies against the mixture significantly were more potent than PIA and rSesC, when comparing individual antigens in a biofilm inhibition assay.

CONCLUSION

immunization of mice with mentioned antigens especially a mixture of them, could eliminate the biofilm formation process in S. aureus. Hopefully, this study corresponds to the suggestion that the immunization of mice with PIA and rSesC candidate vaccines could protect against S. aureus infection.

Natural products as inspiration for the development of bacterial antibiofilm agents

Natural products have historically been a rich source of diverse chemical matter with numerous biological activities, and have played an important role in drug discovery in many areas including infectious disease. Synthetic and medicinal chemistry have been, and continue to be, important tools to realize the potential of natural products as therapeutics and as chemical probes. The formation of biofilms by bacteria in an infection setting is a significant factor in the recalcitrance of many bacterial infections, conferring increased tolerance to many antibiotics and to the host immune response, and as yet there are no approved therapeutics for combatting biofilm-based bacterial infections. Small molecules that interfere with the ability of bacteria to form and maintain biofilms can overcome antibiotic tolerance conferred by the biofilm phenotype, and have the potential to form combination therapies with conventional antibiotics. Many natural products with anti-biofilm activity have been identified from plants, microbes, and marine life, including: elligic acid glycosides, hamamelitannin, carolacton, skyllamycins, promysalin, phenazines, bromoageliferin, flustramine C, meridianin D, and brominated furanones. Total synthesis and medicinal chemistry programs have facilitated structure confirmation, identification of critical structural motifs, better understanding of mechanistic pathways, and the development of more potent, more accessible, or more pharmacologically favorable derivatives of anti-biofilm natural products.

Purification of PIA and rSesC as Putative Vaccine Candidates Against Staphylococcus aureus

BACKGROUND

Staphylococcus aureus is predominant at sites of biomaterial-associated infection (BAI) and frequently infects hospitalized individuals.

METHODS

The polysaccharide intercellular adhesin (PIA) and S. epidermidis rSesC protein, major macromolecules in biofilm formation, were purified under native conditions and cloned and expressed in a prokaryotic host.

RESULTS

LPurification of the macromolecules was confirmed by FTIR and Western blotting.

CONCLUSION

The S. epidermidis SesC protein and PIA were uccessfully purified. Both are considered as vaccine candidates.

Anti-biofilm activity of quinazoline derivatives against Mycobacterium smegmatis

Bacteria employ a number of mechanisms to resist the effects of antibiotics, including the formation of biofilms. We explored the anti-biofilm capabilities of a library of compounds based upon a 2-aminoquinazoline (2-AQ) scaffold against Mycobacterium smegmatis. This study resulted in the identification of 2-AQ derivatives with biofilm inhibition activity against M. smegmatis.

Using 2-aminobenzimidazole derivatives to inhibit Mycobacterium smegmatis biofilm formation

Biofilm formation by mycobacteria can lead to enhanced antibiotic tolerance. Herein, we report on the identification of a series of 2-aminobenzimidazole (2-ABI) derivatives that potently inhibit biofilm formation by Mycobacterium smegmatis.

Using Small-Molecule Adjuvants to Repurpose Azithromycin for Use against Pseudomonas aeruginosa

A major contributor to fatalities in cystic fibrosis (CF) patients stems from infection with opportunistic bacterium Pseudomonas aeruginosa. As a result of the CF patient's vulnerability to bacterial infections, one of the main treatment focuses is antibiotic therapy. However, the highly adaptive nature of P. aeruginosa, in addition to the intrinsic resistance to many antibiotics exhibited by most Gram-negative bacteria, means that multi-drug-resistant (MDR) strains are increasingly prevalent. This makes the eradication of pseudomonal lung infections nearly impossible once the infection becomes chronic. New methods to treat pseudomonal infections are greatly needed in order to eradicate MDR bacteria found within the respiratory tract, and ultimately better the quality of life for CF patients. Herein, we describe a novel approach to combatting pseudomonal infections through the use of bis-2-aminoimidazole adjuvants that can potentiate the activity of a macrolide antibiotic commonly prescribed to CF patients as an anti-inflammatory agent. Our lead bis-2-AI exhibits a 1024-fold reduction in the minimum inhibitory concentration of azithromycin in vitro and displays activity in a Galleria mellonella model of infection.

Synthetic small molecules as anti-biofilm agents in the struggle against antibiotic resistance

Biofilm formation significantly contributes to microbial survival in hostile environments and it is currently considered a key virulence factor for pathogens responsible for serious chronic infections. In the last decade many efforts have been made to identify new agents able to modulate bacterial biofilm life cycle, and many compounds have shown interesting activities in inhibiting biofilm formation or in dispersing pre-formed biofilms. However, only a few of these compounds were tested using in vivo models for their clinical significance. Contrary to conventional antibiotics, most of the anti-biofilm compounds act as anti-virulence agents as they do not affect bacterial growth. In this review we selected the most relevant literature of the last decade, focusing on the development of synthetic small molecules able to prevent bacterial biofilm formation or to eradicate pre-existing biofilms of clinically relevant Gram-positive and Gram-negative pathogens. In addition, we provide a comprehensive list of the possible targets to counteract biofilm formation and development, as well as a detailed discussion the advantages and disadvantages of the different current biofilm-targeting strategies.

2-Aminobenzimidazoles as antibiofilm agents against Salmonella enterica serovar Typhimurium

Serovars within the species Salmonella enterica are some of the most common food and water-borne pathogens worldwide. Some S. enterica serovars have shown a remarkable ability to persist both inside and outside the human body. Salmonella enterica serovar Typhi can cause chronic, asymptomatic infection of the human gallbladder. This organism's ability to survive inside the gallbladder centers around its ability to form biofilms on gallstone surfaces. Currently, chronic carriage of S. Typhi is treated by invasive methods, which are not well suited to areas where Salmonella carriage is prevalent. Herein, we report 2-aminobenzimidazoles that inhibit S. enterica serovar Typhimurium (a surrogate for S. Typhi) biofilm formation in low micromolar concentrations. Modifications to the head, tail, and linker regions of the original hit compound elucidated new, more effective analogues that inhibit S. Typhimurium biofilm formation while being non-toxic to planktonic bacterial growth.

Meridianin D Analogues Display Antibiofilm Activity against MRSA and Increase Colistin Efficacy in Gram-Negative Bacteria

In the last 30 years, development of new classes of antibiotics has slowed, increasing the necessity for new options to treat multidrug resistant bacterial infections. Development of antibiotic adjuvants that increase the effectiveness of currently available antibiotics is a promising alternative approach to classical antibiotic development. Reports of the ability of the natural product meridianin D to modulate bacterial behavior have been rare. Herein, we describe the ability of meridianin D to inhibit biofilm formation of methicillin-resistant Staphylococcus aureus (MRSA) and to increase the potency of colistin against colistin-resistant and sensitive Gram-negative bacteria. Analogues were identified that are capable of inhibiting and dispersing MRSA biofilms and lowering the colistin MIC to below the CLSI breakpoint against Acinetobacter baumannii, Klebsiella pneumoniae, and Escherichia coli.

Suppression of Staphylococcus aureus biofilm formation and virulence by a benzimidazole derivative, UM-C162

Staphylococcus aureus is a major cause of nosocomial infections and secretes a diverse spectrum of virulence determinants as well as forms biofilm. The emergence of antibiotic-resistant S. aureus highlights the need for alternative forms of therapeutics other than conventional antibiotics. One route to meet this need is screening small molecule derivatives for potential anti-infective activity. Using a previously optimized C. elegans – S. aureus small molecule screen, we identified a benzimidazole derivative, UM-C162, which rescued nematodes from a S. aureus infection. UM-C162 prevented the formation of biofilm in a dose-dependent manner without interfering with bacterial viability. To examine the effect of UM-C162 on the expression of S. aureus virulence genes, a genome-wide transcriptome analysis was performed on UM-C162-treated pathogen. Our data indicated that the genes associated with biofilm formation, particularly those involved in bacterial attachment, were suppressed in UM-C162-treated bacteria. Additionally, a set of genes encoding vital S. aureus virulence factors were also down-regulated in the presence of UM-C162. Further biochemical analysis validated that UM-C162-mediated disruption of S. aureus hemolysins, proteases and clumping factors production. Collectively, our findings propose that UM-C162 is a promising compound that can be further developed as an anti-virulence agent to control S. aureus infections.

Natural Products as Platforms To Overcome Antibiotic Resistance

Natural products have served as powerful therapeutics against pathogenic bacteria since the golden age of antibiotics of the mid-20th century. However, the increasing frequency of antibiotic-resistant infections clearly demonstrates that new antibiotics are critical for modern medicine. Because combinatorial approaches have not yielded effective drugs, we propose that the development of new antibiotics around proven natural scaffolds is the best short-term solution to the rising crisis of antibiotic resistance. We analyze herein synthetic approaches aiming to reengineer natural products into potent antibiotics. Furthermore, we discuss approaches in modulating quorum sensing and biofilm formation as a nonlethal method, as well as narrow-spectrum pathogen-specific antibiotics, which are of interest given new insights into the implications of disrupting the microbiome.

The Discovery of 2-Aminobenzimidazoles That Sensitize Mycobacterium smegmatis and M. tuberculosis to β-Lactam Antibiotics in a Pattern Distinct from β-Lactamase Inhibitors

A library of 2-aminobenzimidazole derivatives was screened for the ability to suppress β-lactam resistance in Mycobacterium smegmatis. Several non-bactericidal compounds were identified that reversed intrinsic resistance to β-lactam antibiotics in a manner distinct from β-lactamase inhibitors. Activity also translates to M. tuberculosis, with a lead compound from this study potently suppressing carbenicillin resistance in multiple M. tuberculosis strains (including multidrug-resistant strains). Preliminary mechanistic studies revealed that the lead compounds act through a mechanism distinct from that of traditional β-lactamase inhibitors.

Agents that inhibit bacterial biofilm formation

In the biofilm form, bacteria are more resistant to various antimicrobial treatments. Bacteria in a biofilm can also survive harsh conditions and withstand the host's immune system. Therefore, there is a need for new treatment options to treat biofilm-associated infections. Currently, research is focused on the development of antibiofilm agents that are nontoxic, as it is believed that such molecules will not lead to future drug resistance. In this review, we discuss recent discoveries of antibiofilm agents and different approaches to inhibit/disperse biofilms. These new antibiofilm agents, which contain moieties such as imidazole, phenols, indole, triazole, sulfide, furanone, bromopyrrole, peptides, etc. have the potential to disperse bacterial biofilms in vivo and could positively impact human medicine in the future.

Reversal of Mycobacterium tuberculosis phenotypic drug resistance by 2-aminoimidazole-based small molecules

The expression of phenotypic drug resistance or drug tolerance serves as a strategy for Mycobacterium tuberculosis to survive in vivo antimicrobial drug treatment; however, the mechanisms are poorly understood. Progress toward a more in depth understanding of in vivo drug tolerance and the discovery of new therapeutic strategies designed specifically to treat drug-tolerant M. tuberculosis are hampered by the lack of appropriate in vitro assays. A library of 2-aminoimidazole-based small molecules combined with the antituberculosis drug isoniazid was screened against M. tuberculosis expressing in vitro drug tolerance as microbial communities attached to an extracellular matrix derived from lysed leukocytes. Based on the ability of nine of ten 2-aminoimidazole compounds to inhibit Mycobacterium smegmatis biofilm formation and three of ten molecules capable of dispersing established biofilms, two active candidates and one inactive control were tested against drug-tolerant M. tuberculosis. The two active compounds restored isoniazid susceptibility as well as reduced the in vitro minimum inhibitory concentrations of isoniazid in a dose-dependent manner. The dispersion of drug-tolerant M. tuberculosis with 2-aminoimidazole-based small molecules as an adjunct to antimicrobial treatment has the potential to be an effective antituberculosis treatment strategy designed specifically to eradicate drug-tolerant M. tuberculosis.