Identification of novel deoxyribofuranosyl indole antimicrobial agents

Abstract

Three novel deoxyribofuranosyl indole derivatives, FG050227 (1), FG050223 (2) and FG050204 (3), were identified as antimicrobial agents effective against Gram-positive bacterial strains and some fungi. The MIC values of (1), (2) and (3) against methicillin-resistant Staphylococcus aureus were 3.0, 6.0 and 13 lg ml À1 , respectively. Compounds 1 and 3 had bactericidal activity against exponentially growing S. aureus and inhibited biosynthesis of peptidoglycan, protein, RNA and DNA. Compound 2 was bacteriostatic and inhibited the biosynthesis of protein and RNA. The results indicated that deoxyribofuranosyl indole derivatives could be potential lead compounds for the development of antimicrobial agents. The Journal of Antibiotics (2012) 65, 53-57; doi:10.1038/ja.2011; published online 14 December 2011Keywords: bactericidal; macromolecule synthesis; MRSA; novel antimicrobial; VRE INTRODUCTIONThe emergence of resistant strains against antimicrobial agents is a serious problem in the clinical field. Staphylococcus aureus strains resistant to penicillin 1 and methicillin 2 were identified as early as 2 years after their initial use. Vancomycin-resistant enterococcus (VRE) emerged in 1987, 3 a few years after vancomycin began to be used worldwide. 4 S. aureus that is resistant to relatively intermediate concentrations of vancomycin was first reported in 1997 in Japan. 5 Linezolide and daptomycin, the antibiotics effective against methicillin-resistant Staphylococcus aures (MRSA) and VRE, became ineffective within 1 6 and 2 7,8 years after approval by Food and Drug Administration in the USA, respectively. Therefore, the discovery of novel antimicrobial agents effective against multi-drug resistant bacteria is crucial. Toward this aim, we screened chemical compounds against S. aureus. Here, we report the identification of three novel deoxyribofuranosyl indole compounds as potential antimicrobial agents against Gram-positive bacteria, including MRSA and VRE, and some fungi. MATERIALS AND METHODS Microbial strains and culture conditionsThe bacterial and fungal strains used in this study are summarized in Table 1. Bacterial cultures were prepared in either Luria Bertani (LB) medium (tryptone 10 g l À1 , yeast extract 5 g l À1 , NaCl 10 g l À1 ) or Muller-Hinton Broth (MHB) (DIFCO, Franklin Lakes, NJ, USA). For antimicrobial susceptibility tests, cation-adjusted MHB was used. Fungal suspensions were prepared in Roswell Park Memorial Institute medium (Sigma Aldrich, St Louis, MO, USA). Chemicals and antibioticsVancomycin, daptomycin and norfloxacin were purchased from Wako Pure Chemicals (Osaka, Japan), Sequoia Research Products (Pangbourne, UK), and Sigma Aldrich, respectively. Rifampicin and chloramphenicol were obtained from Nacalai Tesque (Kyoto, Japan). Radiolabelled Chemical library and screening methodOur chemical library contains intermediates of several natural product synthesis projects, (for example, K252a, 9 ecteinascidin 743, 10 kainic acid, 11 etc). The compounds were screened based on MIC values against meth...

Advantages of the Silkworm As an Animal Model for Developing Novel Antimicrobial Agents

“…Purification based on in vitro activity alone may miss to identify therapeutically effective compounds. Furthermore, our previous experience of selecting the hits from a chemical library using minimum inhibitory concentrations (MIC) as an indicator showed that these compounds had no therapeutic activity (Paudel et al, 2012, 2013). Therefore, we chose to evaluate the therapeutic activity using the silkworm infection model to purify therapeutically effective compounds.…”

Induction of Virulence Gene Expression in Staphylococcus aureus by Pulmonary Surfactant

“…Moreover, some of these resistant strains, community-associated methicillin-resistant S. aureus (CA-MRSA), have acquired higher virulence potentials than those of hospital-associated methicillin-resistant S. aureus (HA-MRSA) (4,5). Our research group has investigated various aspects of the virulence mechanisms of S. aureus, e.g., identification and characterization of novel virulence genes (6); investigation of the involvement of the staphylococcal cassette chromosome mec element (SCCmec), a mobile genetic element that provides methicillin resistance, in pathogenesis (7,8); analysis of activation mechanisms of innate immunity by use of insects as animal models (9-13); and searching for new antibiotics with novel chemical structures (14,15). These studies have provided some insights into sepsis and have contributed to the establishment of some drug therapies.…”

A Novel Spiro-Heterocyclic Compound Identified by the Silkworm Infection Model Inhibits Transcription in Staphylococcus aureus

“…The sources of the strains are indicated by asterisks .* Hamamoto et al, 2015 ,** Suzuki et al, 2011 ,*** Paudel et al, 2012 .…”

“…The amount of incorporated radiolabeled precursors was measured as previously described (Maki et al, 2001; Paudel et al, 2012, 2013). S. aureus RN4220 was grown to exponential phase and used for the assay in the presence of 25 μci [ 3 H] N -acetyl-glucosamine (American Radiolabeled Chemicals, St. Louis, MO, USA) or 2 μci/mL of either [ 3 H] uridine (Moravek Biochemical, Brea, CA, USA), [ 3 H] thymidine (Moravek Biochemical), or [ 35 S] methionine (Institute of Isotopes, Budapest, Hungary).…”