Endophytic Microbes from Medicinal Plants in Fenghuang Mountain as a Source of Antibiotics.

One of the largest concerns with world health today is still antibiotic resistance, which is making it imperative to find efficient alternatives as soon as possible. It has been demonstrated that microbes are reliable sources for the creation of therapeutic antibiotics. This research intends to investigate the endophytic microorganisms from several medicinal plants in Fenghuang Mountain (Jiangsu Province, China) and to discover new antibiotics from their secondary metabolites. A total of 269 endophytic strains were isolated from nine distinct medicinal plants. Taxonomic analysis revealed that there were 20 distinct species among these endophytes, with Streptomyces being the most common genus. Three of the target strains were chosen for scale-up fermentation after preliminary screening of antibacterial activities and the metabolomics investigation using LC-MS. These strains were Penicillium sp. NX-S-6, Streptomyces sp. YHLB-L-2 and Streptomyces sp. ZLBB-S-6. Twenty-three secondary metabolites (1-23), including a new sorbicillin analogue (1), were produced as a result of antibacterial activity-guided isolation. Through spectroscopic analysis using MS and NMR, the structures of yield compounds were clarified. According to antibacterial data, S. aureus or B. subtilis were inhibited to varying degrees by sorrentanone (3), emodic acid (8), GKK1032 B (10), linoleic acid (14), toyocamycin (17) and quinomycin A (21). The most effective antimicrobial agent against S. aureus, B. subtilis, E. coli and A. baumannii was quinomycin A (21). In addition, quinomycin A showed strong antifungal activity against Aspergillus fumigatus, Cryptococcus neoformans, and two clinical isolated strains Aspergillus fumigatus #176 and #339, with MIC as 16, 4, 16 and 16 µg/mL, respectively. This is the first time that bioprospecting of actinobacteria and their secondary metabolites from medicinal plants in Fenghuang Mountain was reported. The finding demonstrates the potential of endophytic microbes in medical plants to produce a variety of natural products. Endophytic microbes will be an important source for new antibiotics.

Effects of the hypoxia-inducible factor-1 inhibitor echinomycin on vascular endothelial growth factor production and apoptosis in human ectopic endometriotic stromal cells.

Recent evidence points to a possible role for hypoxia-inducible factor (HIF)-1 in the pathogenesis and development of endometriosis. The objectives of this study were to investigate the critical role of HIF-1 in endometriosis and the effect of the HIF-1 inhibitor echinomycin on human ectopic endometriotic stromal cells (eESCs). Ectopic endometriotic tissues were obtained from 20 patients, who received an operation for ovarian endometriomas. We examined vascular endothelial growth factor (VEGF) and stromal cell-derived factor-1 (SDF-1) production, HIF-1 expression, cell proliferation and apoptosis of eESCs. Cobalt chloride (CoCl2) significantly induced expression of HIF-1α protein and VEGF production in a time-dependent manner in eESCs, but reduced SDF-1 production. VEGF production was significantly suppressed by treatment of 100 nM echinomycin without causing cell toxicity, but 0.1-10 nM echinomycin or 100 nM progestin had no significant effect. SDF-1 production was not affected by echinomycin treatment at any dose. Echinomycin inhibited cell proliferation and induced apoptotic cell death of the eESCs, and significantly inhibited expression of the anti-apoptotic proteins Bcl-2 and Bcl-xL. Echinomycin inhibits VEGF production and induces apoptosis of eESCs by suppression of Bcl-2 and Bcl-xL. These findings suggest the unique therapeutic potential for echinomycin as an inhibitor of HIF-1 activation for endometriosis treatment.

In vitro and in vivo activities of echinomycin against clinical isolates of Staphylococcus aureus.

OBJECTIVES: To verify in vitro and in vivo activities of echinomycin against clinical isolates of Staphylococcus aureus, we compared antistaphylococcal activities of echinomycin with those of vancomycin. METHODS: In vitro activities (MICs and MBCs) of oxacillin, vancomycin and echinomycin against 18 isolates of methicillin-susceptible S. aureus (MSSA) and 118 isolates of methicillin-resistant S. aureus (MRSA) were compared. Using four representative isolates of S. aureus, time-kill assay and in vivo antistaphylococcal activities were assessed. Echinomycin and vancomycin were compared in an in vivo mouse infection model. RESULTS: Echinomycin demonstrated higher in vitro activities against MSSA and MRSA strains, exhibiting 2-fold lower MIC(90)s and 4-fold lower MBC(90)s than vancomycin. Additionally, time-kill assay indicated that echinomycin is more potent than vancomycin against MSSA and MRSA strains in the context of MICs and MBCs. Using an in vivo protection model, it was shown that the 50% effective doses of echinomycin were at least 7-fold lower than those of vancomycin. Therefore, echinomycin displayed excellent protection in mice against acute peritoneal infections caused by both MSSA and MRSA strains. CONCLUSIONS: Collectively, these data indicate that the activity of echinomycin against S. aureus strains is at least equivalent to that of vancomycin, regardless of the methicillin resistance of these strains. These promising activities of echinomycin might justify its potential use against infections with S. aureus strains resistant to vancomycin. This might be the first report to show that echinomycin possesses antipathogenic staphylococcal activity.

NMR investigation of echinomycin binding to d(ACGTTAACGT)2: Hoogsteen versus Watson-Crick A.T base pairing between echinomycin binding sites.

The structure of the echinomycin complex with the self-complementary DNA decamer d(ACGTTAACGT)2 has been investigated in solution by proton NMR spectroscopy. Echinomycin binds as a bisintercalator at the CpG steps. An analysis of the intermolecular NOE patterns defined the position and orientation of the bound drug molecule. The terminal A.T base pairs are Hoogsteen base-paired, whereas the central four A.T base pairs are clearly Watson-Crick base-paired. Thus, the presence of the extra A.T base pairs between the binding sites appears to prevent the formation of Hoogsteen base pairs immediately adjacent to the binding site. All four central A.T base pairs are destabilized relative to those in the free DNA. Because there is no evidence for unwinding of the DNA duplex in the complex relative to the free DNA, we conclude that the hypersensitivity to DNA cleavage reagents distal to echinomycin binding sites might be due to the destabilization of DNA structure induced by the drug binding.

Studies on antibiotic biosynthesis by protoplasts and resting cells of Streptomyces echinatus. Part II. Effect of chromophore precursors.

Washed cell and protoplast suspensions from Streptomyces echinatus A8331, which produces the quinoxaline antibiotic echinomycin, have been used to study the effects of analogues of the natural chromophore upon antibiotic biosynthesis. Addition of quinoline-2-carboxylic acid caused a decrease in the labelling of echinomycin from L-[methyl-14C]methionine and an increase in labelled chloroform-extractable material. Quinoxaline-2-carboxylic acid increased the incorporation of radioactivity into both fractions. Thieno[3,2-b]pyridine-5-carboxylic acid, 6-methylquinoline-2-carboxylic acid, and quinoline-2-carboxylic acid (also to a lesser extent 7-chloroquinoxaline-2-carboxylic acid) increased markedly the incorporation of radioactivity into chloroform-extractable material and virtually abolished echinomycin synthesis. Autoradiographs of extracts from suspensions supplemented with the latter four analogues revealed bis-substituted metabolites not found in unsupplemented cultures. When protoplast suspensions were incubated with L-[U-14C]serine, L-[U-14C]valine, or DL-[benzene ring-U-14C]tryptophan, quinoline-2-carboxylic acid, thieno[3,2-b]pyridine-5-carboxylic acid, and 6-methylquinoline-2-carboxylic acid directed the synthesis of antibiotically active bis derivatives at the expense of echinomycin. When analogues of quinoxaline-2-carboxylic acid previously found unsuitable for incorporation by growing cultures were tested in protoplast suspensions, only isoquinoline-3-carboxylic acid caused a large increase in the incorporation of radioactivity from L-[methyl-14C]methionine into chloroform-extractable material. With DL-[benzene ring-U-14C]tryptophan as the radiolabel, benzotriazoline-2-acetic acid and 6-bromoquinoxaline-2-carboxylic acid as well as isoquinoline-3-carboxylic acid sharply reduced the labelling of echinomycin.