Targeting the mycobactin biosynthesis pathway in M. tuberculosis: a step towards the improvement of the anti-virulence activity of MbtI inhibitors

The COVID-19 pandemic has left many countries struggling to ensure an adequate medical support to the population. The difficulties of the healthcare systems have had particularly devastating consequences on the diagnosis and treatment of tuberculosis (TB) infections, especially in the poorest communities. Hence, the development of antitubercular agents is vital, now more than ever. In this context, the design of anti-virulence compounds, i.e., molecules targeting pathways involved in the pathogenesis of M. tuberculosis but not essential for its survival, is emerging as a promising strategy. This innovative approach has several advantages, the principal being the prevention of resistance phenomena. Iron uptake constitutes a notable example of such pathways. Its suppression can be achieved by the inhibition of a mycobacterium-specific enzyme, namely the salicylate synthase MbtI, which is involved in the biosynthesis of high-affinity iron chelators. Starting from a structure-based virtual screening, our group developed a new class of potent furan-based inhibitors of MbtI. Co-crystallization studies led to the definition of their unexpected binding mode and, incidentally, shed light on the catalytical mechanism of the enzyme. Considering the modest, albeit promising, antimycobacterial effect of the lead compound, we explored the possibility of introducing modifications on its scaffold to enhance the crossing of the mycobacterial cell wall. Inspired by the crystallographic data, we designed new derivatives bearing different lipophilic moieties to increase their permeability, without disrupting the interaction with the enzyme. Based on our encouraging results, the best compounds were tested on infected macrophages to verify their protective effect against the pathogen. The preliminary results of our tests will be presented to support the potentialities of this novel antitubercular strategy.