Institute of Chemical Sciences and Technologies ''Giulio Natta'' (SCITEC) - CNR, Largo Francesco Vito 1, 00168, Rome, Italy; Biocomputation and Complex Systems Physics Institute (BIFI)-Joint Units: BIFI-IQFR (CSIC) and GBsC-CSIC, University of Zaragoza, Zaragoza 50018, Spain; Departamento de Bioquímica y Biología Molecular y Celular, Facultad de Ciencias, University of Zaragoza, Zaragoza 50009, Spain
Ritwik Maity
Biocomputation and Complex Systems Physics Institute (BIFI)-Joint Units: BIFI-IQFR (CSIC) and GBsC-CSIC, University of Zaragoza, Zaragoza 50018, Spain; Departamento de Bioquímica y Biología Molecular y Celular, Facultad de Ciencias, University of Zaragoza, Zaragoza 50009, Spain
Verónica Iguarbe
Biocomputation and Complex Systems Physics Institute (BIFI)-Joint Units: BIFI-IQFR (CSIC) and GBsC-CSIC, University of Zaragoza, Zaragoza 50018, Spain; Departamento de Bioquímica y Biología Molecular y Celular, Facultad de Ciencias, University of Zaragoza, Zaragoza 50009, Spain
José Antonio Aínsa
Biocomputation and Complex Systems Physics Institute (BIFI)-Joint Units: BIFI-IQFR (CSIC) and GBsC-CSIC, University of Zaragoza, Zaragoza 50018, Spain; Departamento de Microbiología, Pediatría, Radiología y Salud Pública, Facultad de Medicina, University of Zaragoza, Zaragoza 50009, Spain; CIBER de Enfermedades Respiratorias–CIBERES, Instituto de Salud Carlos III, Madrid 28029, Spain
Adrián Velázquez-Campoy
Biocomputation and Complex Systems Physics Institute (BIFI)-Joint Units: BIFI-IQFR (CSIC) and GBsC-CSIC, University of Zaragoza, Zaragoza 50018, Spain; Departamento de Bioquímica y Biología Molecular y Celular, Facultad de Ciencias, University of Zaragoza, Zaragoza 50009, Spain; Aragon Health Research Institute (IIS Aragón), Zaragoza 50009, Spain; CIBER de Enfermedades Hepáticas y Digestivas CIBERehd, Instituto de Salud Carlos III, Madrid 28029, Spain
Ulrich E. Schaible
Cellular Microbiology, Priority Research Area Infections, Research Center Borstel, Leibniz Lung Center, & Leibniz Research Alliance INFECTIONS, Borstel, Germany; Biochemical Microbiology & Immunochemistry, University of Lübeck, Lübeck, Germany; German Center for Infection Research (DZIF), Partner Site Hamburg-Lübeck-Borstel-Riems, Borstel Germany
Uwe Mamat
Cellular Microbiology, Priority Research Area Infections, Research Center Borstel, Leibniz Lung Center, & Leibniz Research Alliance INFECTIONS, Borstel, Germany
Javier Sancho
Biocomputation and Complex Systems Physics Institute (BIFI)-Joint Units: BIFI-IQFR (CSIC) and GBsC-CSIC, University of Zaragoza, Zaragoza 50018, Spain; Departamento de Bioquímica y Biología Molecular y Celular, Facultad de Ciencias, University of Zaragoza, Zaragoza 50009, Spain; Aragon Health Research Institute (IIS Aragón), Zaragoza 50009, Spain; Corresponding author. Biocomputation and Complex Systems Physics Institute (BIFI)-Joint Unit: GBsC-CSIC, University of Zaragoza, Zaragoza 50018, Spain.
Objectives: 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.
