doi:10.1016/j.heliyon.2024.e27982engGalano-Frutos, Juan JoséMaity, RitwikIguarbe, VerónicaAínsa, José AntonioVelázquez-Campoy, AdriánSchaible, Ulrich E.Mamat, UweSancho, JavierL-Thyroxine and L-thyroxine-based antimicrobials against Streptococcus pneumoniae and other Gram-positive bacteriaART-2024-138072Objectives: The rise of antibiotic-resistant Streptococcus pneumoniae (Sp) poses a significant global health threat, urging the quest for novel antimicrobial solutions. We have discovered that the human hormone l-thyroxine has antibacterial properties. In order to explore its drugability we perform here the characterization of a series of l-thyroxine analogues and describe the structural determinants influencing their antibacterial efficacy. Method: We performed a high-throughput screening of a library of compounds approved for use in humans, complemented with ITC assays on purified Sp-flavodoxin, to pinpoint molecules binding to this protein. Antimicrobial in vitro susceptibility assays of the hit compound (l-thyroxine) as well as of 13 l-thyroxine analogues were done against a panel of Gram-positive and Gram-negative bacteria. Toxicity of compounds on HepG2 cells was also assessed. A combined structure-activity and computational docking analysis was carried out to uncover functional groups crucial for the antimicrobial potency of these compounds. Results: Human l-thyroxine binds to Sp-flavodoxin, forming a 1:1 complex of low micromolar Kd. While l-thyroxine specifically inhibited Sp growth, some derivatives displayed activity against other Gram-positive bacteria like Staphylococcus aureus and Enterococcus faecalis, while remaining inactive against Gram-negative pathogens. Neither l-thyroxine nor some selected derivatives exhibited toxicity to HepG2 cells. Conclusions: l-thyroxine derivatives targeting bacterial flavodoxins represent a new and promising class of antimicrobials.2024http://zaguan.unizar.es/record/13338110.1016/j.heliyon.2024.e27982http://zaguan.unizar.es/record/133381oai:zaguan.unizar.es:133381info:eu-repo/grantAgreement/ES/DGA/E45-23Rinfo:eu-repo/grantAgreement/ES/MICINN/PID2019-107293GB-I00info:eu-repo/grantAgreement/ES/MICINN/PID2022-141068NB-I00Heliyon 10, 7 (2024), e27982 [11 pp.]by-nc-ndhttps://creativecommons.org/licenses/by-nc-nd/4.0/deed.esinfo:eu-repo/semantics/openAccess