title: Screening and characterisation of antimicrobial properties of semisynthetic betulin derivatives.
abstract: Betulin (lup-20(29)-ene-3β, 28-diol) is a naturally occurring triterpene, which is found in substantial amounts from the outer bark of birch trees. A library of 51 structurally diverse semisynthetic betulin derivatives was screened against five bacterial strains, Enterobacter aerogenes, Escherichia coli, Enterococcus faecalis, Pseudomonas aeruginosa, Staphylococcus aureus and a fungal strain Candida albicans, using broth microdilution assays. Primary antimicrobial screening at 50 µM concentration led to the identification of five compounds showing antimicrobial properties (inhibition of growth by >70% against one or more microbial strains). According to the dose-response results, 28-O-(N-acetylanthraniloyl)betulin (compound 5) was the most active, showing MIC90 of 6.25 µM against two Gram-positive bacteria, E. faecalis and S. aureus. However, the activity of this compound was affected by albumin binding, which was demonstrated by the loss of activity in a host-pathogen co-culture assay as well as in the antibacterial assay in the presence of increased concentration of albumin. Furthermore, the effects on mammalian cells were evaluated by cytotoxicity assessment on hepatocyte cell culture after 24 h exposure to the compounds. Betulinic aldehyde (18), betulin-28-oxime (31) and hetero cycloadduct with acetoxy groups at carbon atoms 3 and 28 and ethyl substituent at the triazolo ring (43) displayed cytotoxicity towards hepatocytes, with IC50 values of 47, 25 and 16 µM, respectively. The IC50 value for 28-O-(N-acetylanthraniloyl)betulin (5) was 56 µM. The current study presents an insight into using betulin scaffold for developing derivatives with antibacterial potential, and furthermore the necessity of in-depth analysis of found actives through selectivity profiling and follow-up studies including in silico ADMET predictions.
authors.affiliation: Centre for Drug Research (CDR), Faculty of Pharmacy, University of Helsinki, Helsinki, Finland.
authors.forename: Shafiul
authors.initials: S
authors.lastname: Haque
authors.affiliation: Centre for Drug Research (CDR), Faculty of Pharmacy, University of Helsinki, Helsinki, Finland.
authors.forename: Dorota A
authors.initials: DA
authors.lastname: Nawrot
authors.affiliation: Division of Pharmaceutical Chemistry, Faculty of Pharmacy, University of Helsinki, Helsinki, Finland; VTT Technical Research Centre of Finland, Espoo, Finland.
authors.forename: Sami
authors.initials: S
authors.lastname: Alakurtti
authors.affiliation: Centre for Drug Research (CDR), Faculty of Pharmacy, University of Helsinki, Helsinki, Finland.
authors.forename: Leo
authors.initials: L
authors.lastname: Ghemtio
authors.affiliation: Division of Pharmaceutical Chemistry, Faculty of Pharmacy, University of Helsinki, Helsinki, Finland.
authors.forename: Jari
authors.initials: J
authors.lastname: Yli-Kauhaluoma
authors.affiliation: Centre for Drug Research (CDR), Faculty of Pharmacy, University of Helsinki, Helsinki, Finland.
authors.forename: Päivi
authors.initials: P
authors.lastname: Tammela
mesh_terms: D000418:Albumins / Q000494:pharmacology; D000890:Anti-Infective Agents / Q000494:pharmacology*; D002176:Candida albicans / Q000187:drug effects*; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D006090:Gram-Negative Bacteria / Q000187:drug effects*; D006094:Gram-Positive Bacteria / Q000187:drug effects*; D006801:Humans; D008826:Microbial Sensitivity Tests; D010936:Plant Extracts / Q000494:pharmacology; D013329:Structure-Activity Relationship; D014315:Triterpenes / Q000009:adverse effects / Q000737:chemistry / Q000494:pharmacology*; D000094062:Betulinic Acid
chemical_list: D000418:Albumins; D000890:Anti-Infective Agents; D010936:Plant Extracts; D014315:Triterpenes; C002503:betulin; D000094062:Betulinic Acid