Oligomycin F, a new immunosuppressive homologue of oligomycin A

Antimicrobial spiroketal macrolides and dichloro-diketopiperazine from Micromonospora sp. FIMYZ51

Four compounds (1-4) featuring with an L-rhodinose and spiroketal, possess uncommon continuous hydroxy groups in the macrolide skeleton, and a dichloro-diketopiperazine (5) were isolated from a marine derived Micromonospora sp. FIMYZ51. The determination of the relative and absolute configurations of all isolates was achieved by extensive spectroscopic analyses, single-crystal X-ray diffraction analysis, and ECD calculations. According to structural characteristic and genomic sequences, a plausible biosynthetic pathway for compound 1-4 was proposed and a spirocyclase was inferred to be responsible for the formation of the rare spirocyclic moiety. Compounds 1-4 exhibited potent antifungal activities which is equal to itraconazole against Aspergillus niger. Compounds 1-5 exhibited different degree of inhibitory activities against opportunistic pathogenic bacteria of endocarditis (Micrococcus luteus) with MIC values ranging from 0.0625 μg/mL to 32 μg/mL. Compounds 2 and 3 showed moderate cytotoxicity against drug-resistant tumor cell lines (Namalwa and U266). The result not only provides active lead-compounds, but also reveal the potential of the spirocyclase gene resources from Micromonospora sp., which highlights the promising potential of the strain for biomedical applications.

Structures, Biosynthesis, and Bioactivity of Oligomycins from the Marine-Derived Streptomyces sp. FXY-T5

Oligomycins are potent antifungal and antitumor agents. Mass spectrometry (MS)- and nuclear magnetic resonance (NMR)-based metabolomic fingerprinting analysis of marine-derived actinomycetes in our in-house library provided an oligomycin-producing strain, Streptomyces sp. FXY-T5. Chemical investigation led to the discovery of five new oligomycins, 24-lumooligomycin B (1), 4-lumooligomycin B (2), 6-lumooligomycin B (3), 40-homooligomycin B (4), and 15-hydroxy-oligomycin B (5), together with seven biosynthetically related known derivatives. Their structures were assigned by MS, NMR, electronic circular dichroism (ECD), and single-crystal X-ray diffraction analyses. The biosynthesis pathway of oligomycins was first proposed based on the analysis of a type I modular polyketide synthase (PKS) system and targeted gene disruption. As expected, the isolated oligomycins showed significant antiagricultural fungal pathogen activity and antiproliferative properties from which the possible structure-activity relationships were first suggested. More importantly, oligomycins induced significant G1-phase cell cycle arrest on cancer cells and significantly attenuated their Cyclin D1 and PCNA expression through a β-catenin signaling pathway.

Oligomycins inhibit Magnaporthe oryzae Triticum and suppress wheat blast disease

Oligomycins are macrolide antibiotics, produced by Streptomyces spp. that show antagonistic effects against several microorganisms such as bacteria, fungi, nematodes and the oomycete Plasmopara viticola. Conidiogenesis, germination of conidia and formation of appressoria are determining factors pertaining to pathogenicity and successful diseases cycles of filamentous fungal phytopathogens. The goal of this research was to evaluate the in vitro suppressive effects of two oligomycins, oligomycin B and F along with a commercial fungicide Nativo® 75WG on hyphal growth, conidiogenesis, conidial germination, and appressorial formation of the wheat blast fungus, Magnaporthe oryzae Triticum (MoT) pathotype. We also determined the efficacy of these two oligomycins and the fungicide product in vivo in suppressing wheat blast with a detached leaf assay. Both oligomycins suppressed the growth of MoT mycelium in a dose dependent manner. Between the two natural products, oligomycin F provided higher inhibition of MoT hyphal growth compared to oligomycin B with a minimum inhibitory concentration of 0.005 and 0.05 μg/disk, respectively. The application of the compounds completely halted conidial formation of the MoT mycelium in agar medium. Further bioassays showed that these compounds significantly inhibited MoT conidia germination and induced lysis. The compounds also caused abnormal germ tube formation and suppressed appressorial formation of germinated spores. Interestingly, the application of these macrolides significantly inhibited wheat blast on detached leaves of wheat. This is the first report on the inhibition of mycelial growth, conidiogenesis, germination of conidia, deleterious morphological changes in germinated conidia, and suppression of blast disease of wheat by oligomycins from Streptomyces spp. Further study is needed to unravel the precise mode of action of these natural compounds and consider them as biopesticides for controlling wheat blast.

Inhibition of Pro-Inflammatory Cytokines by Metabolites of Streptomycetes-A Potential Alternative to Current Anti-Inflammatory Drugs?

Current treatment of chronic diseases includes, among others, application of cytokines, monoclonal antibodies, cellular therapies, and immunostimulants. As all the underlying mechanisms of a particular diseases are not always fully clarified, treatment can be inefficient and associated with various, sometimes serious, side effects. Small secondary metabolites produced by various microbes represent an attractive alternative as future anti-inflammatory drug leads. Compared to current drugs, they are cheaper, can often be administered orally, but still can keep a high target-specificity. Some compounds produced by actinomycetes or fungi have already been used as immunomodulators—tacrolimus, sirolimus, and cyclosporine. This work documents strong anti-inflammatory features of another secondary metabolite of streptomycetes—manumycin-type polyketides. We compared the effect of four related compounds: manumycin A, manumycin B, asukamycin, and colabomycin E on activation and survival of human monocyte/macrophage cell line THP-1. The anti-cancer effect of manucycine A has been demonstrated; the immunomodulatory capacities of manumycin A are obvious when using micromolar concentrations. The application of all four compounds in 0.25–5 μM concentrations leads to efficient, concentration-dependent inhibition of IL-1β and TNF expression in THP-1 upon LPS stimulation, while the three latter compounds show a significantly lower pro-apoptotic effect than manumycin A. We have demonstrated the anti-inflammatory capacity of selected manumycin-type polyketides.

Oligomycins as inhibitors of K-Ras plasma membrane localisation

Frequently present in pancreatic, colorectal and non-small cell lung carcinomas, oncogenic mutant K-Ras must be localised to the plasma membrane (PM) to be functional. Inhibitors of K-Ras PM localisation are therefore putative cancer chemotherapeutics. By screening a microbial extract library in a high content cell-based assay we detected the rare oligomycin class of Streptomyces polyketides as inhibitors of K-Ras PM localisation. Cultivation and fractionation of three unique oligomycin producing Streptomyces strains yielded oligomycins A-E (1-5) and 21-hydroxy-oligomycin A (6), together with the new 21-hydroxy-oligomycin C (7) and 40-hydroxy-oligomycin B (8). Structures for 1-8 were assigned by detailed spectroscopic analysis. Cancer cell viability screening confirmed 1-8 were cytotoxic to human colorectal carcinoma cells (IC50 > 3 μM), and were inhibitors of the ABC transporter efflux pump P-glycoprotein (P-gp), with 5 being comparable in potency to the positive control verapamil. Significantly, oligomycins 1-8 proved to be exceptionally potent inhibitors of K-Ras PM localisation (Emax 0.67-0.75 with an IC50 ~ 1.5-14 nM).

Neomaclafungins A-I: oligomycin-class macrolides from a marine-derived actinomycete

Nine new 26-membered macrolides of the oligomycin subfamily, neomaclafungins A-I, were isolated from the fermentation broth of Actinoalloteichus sp. NPS702, which was isolated from marine sediment collected from Usa Bay, Kochi Prefecture, Japan. Their structures were identified through mass spectrometry and NMR experiments. They belong to the oligomycin class and have several distinct features including the presence of alkane or alkanol branches. Neomaclafungins A-I exhibited significant antifungal activity in vitro against Trichophyton mentagrophytes (ATCC 9533), showing MIC values between 1 and 3 μg/mL.

Structure and absolute stereochemistry of 21-hydroxyoligomycin A

21-Hydroxyoligomycin A (1) was isolated from Streptomyces cyaneogriseus ssp. noncyanogenus (LL-F28249) and fully characterized by NMR and single-crystal X-ray diffraction methods. The complete 1H and 13C NMR chemical shift assignments for 1 were made using 2D NMR experiments, and the chirality at C-21 was deduced to be R from a J-based configuration analysis. The absolute configuration at C-21 and at the other 18 chiral centers in the molecule were independently confirmed by anomalous dispersion measurements on a crystal of the chloroform methanol solvate of 21-hydroxyoligomycin A (1).

A Spirodiepoxide-Based Strategy to the A−B Ring System of Pectenotoxin 4

[reaction: see text] A synthesis of a pectenotoxin 4 C1-C15 segment is reported. Suitable C1-C7 and C8-C15 segments were prepared, coupled, converted to I and the C3-hydroxy variant, and then cyclized. Key findings include the stereoselective conversion of the allene to the corresponding spirodiepoxide, oxidative cleavage of the p-methoxybenzyl ether, and cyclization of the spirodiepoxide to spiroketal II.

Enhancement and selective production of oligomycin through inactivation of avermectin's starter unit in Streptomyces avermitilis

Oligomycin and its analogues, produced by Streptomyces avermitilis and other actinomycetes, are of interest for their potent and selective biological activities. PCR-mediated gene replacement, targeting bkdF, one of avermectin's starter unit encoding genes in S. avermitilis, was performed to yield an oligomycin producer, BIB0423. The engineered strain produced oligomycin A at 2.3 mg/ml compared to the wild type strain at 0.1 mg/ml. This resulting mutant was genetically stable and should be useful for the industrial production of oligomycin.

Ushikulides A and B, immunosuppressants produced by a strain of Streptomyces sp

Novel immunosuppressants, ushikulides A and B, were isolated from the culture broth of Streptomyces sp. IUK-102. Ushikulides A and B both have the same molecular formula, determined as C40H68O10. The structures of both compounds were elucidated to be novel 22-membered macrolides. Both compounds showed immunosuppressive activity for murine splenocyte proliferation in vitro.

Recent advances in immunosuppressants

In recent years, a large number of structurally diverse immunosuppressants have been discovered that are effective for the treatment of organ transplantation. Some of them are undergoing clinical trials and may soon enter into routine clinical practice. These compounds are either chemical entities obtained from natural sources/synthetic means or biomaterials such as monoclonal antibodies/gene products/proteins. They have been found to interfere at different stages of T cell activation and proliferation, and can be identified as inhibitors of nucleotide synthesis, growth factor signal transduction and differentiation. Newer strategies involving combination of new agents with traditional immunosuppressants, monoclonal antibodies and gene therapy offer enormous potential, not only for the investigation of mechanisms pertaining to graft rejection, but also for its therapeutic prevention.