Siderophore-gold(I) conjugates : a Trojan horse strategy against pathogenic Gram-negative bacteria – RHEINGOLD

Pathogenic bacteria are a permanent threat for Humanity even the discovery of antibiotics led to the fade-out of mass epidemies. Nevertheless, human being faces more and more antibiotic-resistant bacterial strains. Thus, the constant development of innovative antibiotics is crucial, especially against Gram-negative bacteria found in many lethal infections. The current antibiotic arsenal is mainly composed of organic compounds when organometallic derivatives appear to be reserved principally to cancer. However, the toxicity profiles of current last resort antibiotics make now organometallic derivatives competitive. More particularly, gold(I) complexes have shown impressive bactericidal properties on Gram-positive pathogens, but these chemical entities poorly cross the bacterial envelope of Gram-negative bacteria. Bacterial iron uptake systems are gates through the envelope. Siderophores are small iron(III) chelating molecules secreted by bacteria to promote iron acquisition. Siderophores are able to use bacterial iron uptake systems to cross bacterial membrane reaching therefore bacterial inner space. Siderophores could be thus used as vectors to promote accumulation of bactericidal metals into Gram-negative bacteria using a so-called Trojan horse strategy. In our approach gold(I) complexes will be conjugated to siderophore vectors through linkers. The recognition of the ferric-siderophores by specific outer membrane transporters will lead to the uptake of the whole conjugate inside the bacterium. This approach will, at one and at the same time, increase the penetration of organometallic species and reduce the peripheral toxicity of gold(I) for host cells. Vectors to be used in our approach will be analogues of enterobactin, desferrioxamin B (DFOB), pyoverdine and pyochelin, four siderophores used by Gram-negative pathogens and P. aeruginosa more particularly. These vectors will be synthesized in the team of partner 1 (Dr. Gaëtan MISLIN, UMR7242 BSC, Illkirch) and will be generated with alkyne or azide functions. These functions will be used for the conjugation of gold(I) complexes by azide-alkyne cycloaddition (CAA, click chemistry). These gold(I) complexes will be prepared by partner 2 (Dr. Sylvain GAILLARD, UMR6507 LCMT, Caen) in the form of N-heterocyclic carbene (NHC). The conjugates synthesized in the present project will be tested by Partner 3 (Pr Katy JEANNOT, UMR6249 Besançon), primarily on P. aeruginosa. This screening will be then extended to other pathogenic bacteria with a specific focus on critical Gram-negative pathogens from a collection of resistant clinical isolates. ADME-Tox study will be performed on the more promising conjugates in order to assess the therapeutic potential of our approach. The emergence of resistance is a crucial consideration in the development of new antimicrobial compounds with longer shelf life. Our study aims also to assess the potential of our conjugates to induce resistance, both to themselves and to commercially available antimicrobials (cross-resistance). Additionally, we will characterize the mechanisms of resistance developed and evaluate the susceptibility of our compounds against previously identified mechanisms, as well as strains exhibiting reduced susceptibility or resistance to cefiderocol (the sole Trojan Horse antibiotic marketed so far). The structure of the project, the methodologies used and the expertise of the partners should allow the production of conjugates siderophores-gold(I) that are both effective against Gram-negative bacteria and have a toxicity compatible with use in humans.