Project summary:

    The discovery of penicillin followed by the use of antibiotics for the therapy of infectious diseases since the 1940s represented one of the most important moments in the evolution of modern medicine. However, a good number of pathogens have developed resistance to antibiotics, raising serious doubts about their efficiency in use. At present, antibiotic resistance of pathogenic microorganisms is a major concern of mankind, posing a serious threat to human health and economic development worldwide. The alarming spread of resistance along with the reduction of new developed antibiotics significantly decreased therapeutic possibilities, leading to increased mortality and morbidity. Finding effective new molecules to keep pace with antibiotic resistance is an important goal of current biomedical research.
In this context, the TriSflav project aimed to validate tricyclic synthetic flavonoids as effective antimicrobial agents. During the project, four flavonoids having I, Br, Cl and F as halogenated substituents at the benzopyran core were synthesized and characterized. The synthetic flavonoids were tested against bacterial (Staphylococcus aureus, Streptococcus pneumoniae, Acinetobacter baumannii, Enterococcus faecium and Escherichia coli, etc.) and fungal (Candida albicans, C. krusei and C. parapsilosis) clinically isolated strains, with different antibiotic resistance profiles. The obtained results showed that the tested synthetic flavonoids have important bactericidal and fungicidal properties, the antimicrobial activity being more important compared to antimicrobials such as penicillin, gentamicin or fluconazole. Antimicrobial effects are due to the fact that flavonoids target the cytoplasmic membrane, affecting its integrity and causing cell death. Furthermore, the proposed flavonoids influence some factors involved in antibiotic resistance or virulence. Thus, they show an important anti-biofilm activity, inhibiting the formation of biofilms or destroying mature microbial biofilms at low concentrations. The synthetic flavonoids have a reduced cytotoxicity at concentrations lower than 13.16 µg/ml and possess a pro-inflammatory effect.
Finally, the project proposed the flavonoid BrCl as an antimicrobial agent, with potential practical applications as an antibiotic and antiseptic (against some resistant strains of S. aureus, S. pneumoniae, A. baumannii and E. coli); disinfectant, against a wide spectrum of pathogenic microorganisms (including ESKAPE group pathogens and Candida species) resistant to antibiotics/antifungals.

Background

The desperate need for new antimicrobials. The discovery of penicillin in the 1940s was a turning point in human history, revolutionizing medicine and saving countless lives (Davies and Davies 2010). However, the discovery of efficient antibiotics provided a false sense of security to humankind due to the emergence of multidrug resistant bacteria (MDR) very soon after. Increasing resistance of microbial pathogens against many available antibiotics is a medical problem of major concern all over the world (Orhan et al. 2010). The discovery of new and more efficient antimicrobial drugs is therefore a matter of high priority among scientists and clinicians worldwide. Ideally, antibacterial agents should belong to new classes, since the structural alteration of drugs to which resistance has already developed, rarely provides a major solution (Cushnie and Lamb 2011).

Flavonoids as antimicrobials. Flavonoids, a group of heterocyclic organic compounds present in plants and related products, are a source of potentially good candidates for developing antimicrobial agents. Flavonoids have been used for a long time to treat and prevent various infectious diseases such as respiratory, gastrointestinal, urinary and skin infections (Seleem et al. 2017). In the past few years the subject of antibacterial research was focused on semisynthetic and synthetic flavonoids, some of these compounds being more active than the natural flavonoids.

Tricyclic 1,3-dithiolium flavonoids - new weapons to fight AMR. Our research group synthetized and characterized several novel tricyclic 1,3-dithiolium flavonoids (TSFl) with completely new structures, unrelated to any known natural compound (Bahrin et al. 2012). After an initial evaluation, we successfully demonstrated that these compounds displayed very potent antibacterial properties, inhibiting and also killing bacterial cells at very low concentrations (Lungu et al. 2013; Bahrin et al. 2014; Babii et al. 2016; Bahrin et al. 2016; Babii et al. 2018). One compound in particular – 4b (Figure 1), a TSFl with a bromine substituent at the benzopyran core (TSBrFl), displayed very potent antibacterial properties with low MIC values, as our preliminary results showed: 0.24 μg/ml against Staphylococcus aureus and 3.9 μg/ml against Escherichia coli (Babii et al. 2016).