title: The immunosuppressive drug azathioprine inhibits biosynthesis of the bacterial signal molecule cyclic-di-GMP by interfering with intracellular nucleotide pool availability.
abstract: In Gram-negative bacteria, production of the signal molecule c-di-GMP by diguanylate cyclases (DGCs) is a key trigger for biofilm formation, which, in turn, is often required for the development of chronic bacterial infections. Thus, DGCs represent interesting targets for new chemotherapeutic drugs with anti-biofilm activity. We searched for inhibitors of the WspR protein, a Pseudomonas aeruginosa DGC involved in biofilm formation and production of virulence factors, using a set of microbiological assays developed in an Escherichia coli strain expressing the wspR gene. We found that azathioprine, an immunosuppressive drug used in the treatment of Crohn's disease, was able to inhibit WspR-dependent c-di-GMP biosynthesis in bacterial cells. However, in vitro enzymatic assays ruled out direct inhibition of WspR DGC activity either by azathioprine or by its metabolic derivative 2-amino-6-mercapto-purine riboside. Azathioprine is an inhibitor of 5-aminoimidazole-4-carboxamide ribotide (AICAR) transformylase, an enzyme involved in purine biosynthesis, which suggests that inhibition of c-di-GMP biosynthesis by azathioprine may be due to perturbation of intracellular nucleotide pools. Consistent with this hypothesis, WspR activity is abolished in an E. coli purH mutant strain, unable to produce AICAR transformylase. Despite its effect on WspR, azathioprine failed to prevent biofilm formation by P. aeruginosa; however, it affected production of extracellular structures in E. coli clinical isolates, suggesting efficient inhibition of c-di-GMP biosynthesis in this bacterium. Our results indicate that azathioprine can prevent biofilm formation in E. coli through inhibition of c-di-GMP biosynthesis and suggest that such inhibition might contribute to its anti-inflammatory activity in Crohn's disease.
authors.affiliation: Department of Biosciences, Università degli Studi di Milano, Via Celoria 26, 20133 Milan, Italy.
authors.forename: Davide
authors.initials: D
authors.lastname: Antoniani
authors.forename: Elio
authors.initials: E
authors.lastname: Rossi
authors.forename: Serena
authors.initials: S
authors.lastname: Rinaldo
authors.forename: Paola
authors.initials: P
authors.lastname: Bocci
authors.forename: Marco
authors.initials: M
authors.lastname: Lolicato
authors.forename: Alessandro
authors.initials: A
authors.lastname: Paiardini
authors.forename: Nadia
authors.initials: N
authors.lastname: Raffaelli
authors.forename: Francesca
authors.initials: F
authors.lastname: Cutruzzolà
authors.forename: Paolo
authors.initials: P
authors.lastname: Landini
mesh_terms: D000900:Anti-Bacterial Agents / Q000378:metabolism; D001379:Azathioprine / Q000378:metabolism*; D018441:Biofilms / Q000187:drug effects / Q000254:growth & development; D006152:Cyclic GMP / Q000031:analogs & derivatives* / Q000096:biosynthesis; D004926:Escherichia coli / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D009711:Nucleotides / Q000037:antagonists & inhibitors*; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology
chemical_list: D000900:Anti-Bacterial Agents; D009711:Nucleotides; C062025:bis(3',5')-cyclic diguanylic acid; D006152:Cyclic GMP; D001379:Azathioprine