Tuberculosis (TB) causes millions of deaths every year, ranking as one of the most dangerous infectious diseases worldwide. Because several pathogenic strains of M. tuberculosis (Mtb) have developed resistance against most of the established anti-TB drugs, new therapeutic options are urgently needed. An attractive target for the development of new anti-TB agents is the salicylate synthase MbtI, the first enzyme of the mycobacterial siderophore biochemical machinery, absent in human cells. In this work, a set of analogues of 5-(3-cyanophenyl)furan-2-carboxylic acid (I), the most potent MbtI inhibitor identified to date, was synthesized, characterized, and tested to further elucidate the structural requirements for achieving an efficient MbtI inhibition and potent antitubercular activity. The structure–activity relationships (SAR) discussed herein evidenced the importance of the side chain linked to the phenyl moiety to improve the in vitro antimycobacterial activity. In detail, 1f emerged as the most effective analogue against the pathogen, acting without cytotoxicity issues. To deepen the understanding of its mechanism of action, we established a fluorescence-based screening test to quantify the pathogen infectivity within host cells, using MPI-2 murine cells, a robust surrogate for alveolar macrophages. The set-up of the new assay demonstrates significant potential to accelerate the discovery of new anti-TB drugs.

The constant demand of silver nanoparticles (AgNPs) for different applications requires a new selection of solvents and reagents for their synthesis, to make them less toxic to living organisms and the environment. Among the alternative technologies that can be used to exclude the use of toxic products, green chemistry is based on the employment of biomolecules derived from plants or microorganisms to achieve NPs. Therefore, with the aim of applying the principles of circular economy, the waste deriving from the production of olive oil represents a useful source of polyphenols to be used as reduction agents to obtain AgNPs. In our work, we employed the Olive Mill Wastewater (OMWW), the so-called vegetation water typical of the Mediterranean geographical area, to achieve two sizes of AgNPs, i.e., 50 nm and 30 nm. These NPs were tested on the human monocytic cell line (THP-1) using two concentrations (3 µM and 5 µM) to understand their ability to trigger or not the inflammatory response. This was undertaken following IL-6, IL-8, IL-5 and TNF-α secretion and the NF-kB translocation. We concluded that the AgNPs did not induce strong activation of these pathways, especially when the cells were treated with higher dimensional NPs. Consequently, the application of these NPs in vivo for therapeutic purpose could be significant.

Targeting pathogenic mechanisms, rather than essential processes, represents a very attractive approach for the development of new antimycobacterial drugs. In this context, iron acquisition routes have recently emerged as potentially druggable pathways. However, the importance of siderophore biosynthesis in the virulence and pathogenicity of M. abscessus (Mab) is still poorly understood. In this study, we investigated the Salicylate Synthase (SaS) of Mab as an innovative molecular target for the development of inhibitors of siderophore production. Notably, Mab-SaS does not have any counterpart in human cells, making it an interesting candidate for drug discovery. Starting from the analysis of the binding of a series of furan-based derivatives, previously identified by our group as inhibitors of MbtI from M. tuberculosis (Mtb), we successfully selected the lead compound 1, exhibiting a strong activity against Mab-SaS (IC50 ≈ 5 µM). Computational studies characterized the key interactions between 1 and the enzyme, highlighting the important roles of Y387, G421, and K207, the latter being one of the residues involved in the first step of the catalytic reaction. These results support the hypothesis that 5-phenylfuran-2-carboxylic acids are also a promising class of Mab-SaS inhibitors, paving the way for the optimization and rational design of more potent derivatives.