title: New alkaloid antibiotics that target the DNA topoisomerase I of Streptococcus pneumoniae.
abstract: Streptococcus pneumoniae has two type II DNA-topoisomerases (DNA-gyrase and DNA topoisomerase IV) and a single type I enzyme (DNA-topoisomerase I, TopA), as demonstrated here. Although fluoroquinolones target type II enzymes, antibiotics efficiently targeting TopA have not yet been reported. Eighteen alkaloids (seven aporphine and 11 phenanthrenes) were semisynthesized from boldine and used to test inhibition both of TopA activity and of cell growth. Two phenanthrenes (seconeolitsine and N-methyl-seconeolitsine) effectively inhibited both TopA activity and cell growth at equivalent concentrations (∼17 μM). Evidence for in vivo TopA targeting by seconeolitsine was provided by the protection of growth inhibition in a S. pneumoniae culture in which the enzyme was overproduced. Additionally, hypernegative supercoiling was observed in an internal plasmid after drug treatment. Furthermore, a model of pneumococcal TopA was made based on the crystal structure of Escherichia coli TopA. Docking calculations indicated strong interactions of the alkaloids with the nucleotide-binding site in the closed protein conformation, which correlated with their inhibitory effect. Finally, although seconeolitsine and N-methyl-seconeolitsine inhibited TopA and bacterial growth, they did not affect human cell viability. Therefore, these new alkaloids can be envisaged as new therapeutic candidates for the treatment of S. pneumoniae infections resistant to other antibiotics.
authors.affiliation: Unidad de Genética Bacteriana, Centro Nacional de Microbiología and CIBER Enfermedades Respiratorias, Instituto de Salud Carlos III, 28220 Majadahonda, Madrid, Spain.
authors.forename: María Teresa
authors.initials: MT
authors.lastname: García
authors.forename: María Amparo
authors.initials: MA
authors.lastname: Blázquez
authors.forename: María José
authors.initials: MJ
authors.lastname: Ferrándiz
authors.forename: María Jesús
authors.initials: MJ
authors.lastname: Sanz
authors.forename: Noella
authors.initials: N
authors.lastname: Silva-Martín
authors.forename: Juan A
authors.initials: JA
authors.lastname: Hermoso
authors.forename: Adela G
authors.initials: AG
authors.lastname: de la Campa
mesh_terms: D000470:Alkaloids / Q000737:chemistry / Q000494:pharmacology; D000900:Anti-Bacterial Agents / Q000737:chemistry / Q000494:pharmacology; D001426:Bacterial Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D004264:DNA Topoisomerases, Type I / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D006801:Humans; D008958:Models, Molecular; D010616:Phenanthrenes / Q000737:chemistry / Q000494:pharmacology; D017434:Protein Structure, Tertiary; D013296:Streptococcus pneumoniae / Q000201:enzymology* / Q000254:growth & development; D059004:Topoisomerase I Inhibitors / Q000737:chemistry / Q000494:pharmacology
chemical_list: D000470:Alkaloids; D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D010616:Phenanthrenes; D059004:Topoisomerase I Inhibitors; D004264:DNA Topoisomerases, Type I