Dynemicins, new antibiotics with the 1,5-diyn-3-ene and anthraquinone subunit. I. Production, isolation and physico-chemical properties

Micromonospora: A Prolific Source of Bioactive Secondary Metabolites with Therapeutic Potential

Micromonospora, one of the most important actinomycetes genera, is well-known as the treasure trove of bioactive secondary metabolites (SMs). Herein, together with an in-depth genomic analysis of the reported Micromonospora strains, all SMs from this genus are comprehensively summarized, containing structural features, bioactive properties, and mode of actions as well as their biosynthetic and chemical synthesis pathways. The perspective enables a detailed view of Micromonospora-derived SMs, which will enrich the chemical diversity of natural products and inspire new drug discovery in the pharmaceutical industry.

Discovery of Six Ramoplanin Family Gene Clusters and the Lipoglycodepsipeptide Chersinamycin*

Ramoplanins and enduracidins are peptidoglycan lipid intermediate II-binding lipodepsipeptides with broad-spectrum activity against methicillin- and vancomycin-resistant Gram-positive pathogens. Targeted genome mining using probes from conserved sequences within the ramoplanin/enduracidin biosynthetic gene clusters (BGCs) was used to identify six microorganisms with BGCs predicted to produce unique lipodepsipeptide congeners of ramoplanin and enduracidin. Fermentation of Micromonospora chersina yielded a novel lipoglycodepsipeptide, called chersinamycin, which exhibited good antibiotic activity against Gram-positive bacteria (1-2 μg/mL) similar to the ramoplanins and enduracidins. The covalent structure of chersinamycin was determined by NMR spectroscopy and tandem mass spectrometry in conjunction with chemical degradation studies. These six new BGCs and isolation of a new antimicrobial peptide provide much-needed tools to investigate the fundamental aspects of lipodepsipeptide biosynthesis and to facilitate efforts to produce novel antibiotics capable of combating antibiotic-resistant infections.

Self-delivery nanoparticles of an amphiphilic irinotecan–enediyne conjugate for cancer combination chemotherapy

An amphiphilic small molecular drug self-delivery system was designed by linking a hydrophilic topoisomerase I inhibitor irinotecan (Ir) with a lipophilic cytotoxic enediyne (EDY) antibiotic through an ester bond.

Molecular characterization and its antioxidant activity of a newly isolated Streptomyces coelicoflavus BC 01 from mangrove soil

OBJECTIVE

To isolate and identify the biologically active strain of Streptomyces species from mangrove soil of Visakhapatnam region.

MATERIALS AND METHODS

Actinomycetes are isolated by using starch casein agar media and four potential strains were selected to evaluate the antioxidant activity by using the standard methods DPPH, FRAP and total antioxidant capacity. Further, significant antioxidant activity strain characterized by morphological, physiological, biochemical and molecular characterization.

RESULTS

20 actinomycetes strains were isolated, among them four active isolates designated as BC 01, BC 02, BC 03 and BC 04 were studied for antioxidant activities. Of these four isolates, BC 01 showed a potent antioxidant activity when compared with other isolates. The morphological, biochemical and molecular characterization of the active isolate BC 01 belongs to the genus Streptomyces species. The phylogenetic tree was constructed and nucleotide blast in search indicated that the strain is 99.7% similarity with Streptomyces coelicoflavus.

CONCLUSION

The results of the present investigation proven that actinomycetes isolated from mangroves are potent source of antioxidants. The strain BC 01 exhibited a potential in vitro antioxidant activity; studies of actinomycetes from mangrove soil can be useful in discovery of novel species to get novel drugs.

in Silico analysis of Escherichia coli polyphosphate kinase (PPK) as a novel antimicrobial drug target and its high throughput virtual screening against PubChem library

Multiple drug resistance (MDR) in bacteria is a global health challenge that needs urgent attention. The 2011 outbreak caused by Escherichia coli O104:H4 in Europe has exposed the inability of present antibiotic arsenal to tackle the problem of antimicrobial infections. It has further posed a tremendous burden on entire pharmaceutical industry to find novel drugs and/or drug targets. Polyphosphate kinase (PPK) in bacteria plays a crucial role in helping latter to adapt to stringent conditions of low nutritional availability thus making it a good target for antibacterials. In spite of this critical role, to best of our knowledge no in-silico work has been carried out to develop PPK as an antibiotic target. In the present study, virtual screening of PPK was carried out against all the 3D compounds with pharmacological action present in PubChem database. Our screening results were further refined by interaction maps to eliminate the false positive data respectively. From our results, compound number 5281927 (PubChem ID) has been found to have significant affinity towards affinity towards PPK active ATP-binding site indicating its therapeutic relevance.

The biosynthetic genes encoding for the production of the dynemicin enediyne core in Micromonospora chersina ATCC53710

Dynemicin is a novel anthraquinone-fused member of the 10-membered enediyne antitumor antibiotic family. The development of a genetic system for the dynemicin producer Micromonospora chersina confirmed, for the first time, the requirement of the putative enediyne core biosynthetic genes (dynE8, U14 and U15) and a tailoring oxidase gene (orf23) for dynemicin production. Cloning and sequence analysis of a 76 kb of genomic sequence region containing dynE8 revealed a variety of genes conserved among known enediyne loci. Surprisingly, this fragment and flanking chromosomal DNA lacked any obvious genes encoding for the biosynthesis of the anthraquinone, suggesting that the location of genes encoding for the biosynthesis of the dynemicin enediyne core and the dynemicin anthraquinone are chromosomally distinct. The demonstrated trace production of a shunt product from mutant strain QGD23 (Deltaorf23) also sets the stage for subsequent studies to delineate the key steps in enediyne core biosynthesis and tailoring.

Enzymatic activation of DNA cleavage by dynemicin A and synthetic analogs

Dynemicin A (1), a member of the enediyne family of natural products, binds to double-stranded DNA (K(B) approximately 10(4) M(-1)) and in the presence of millimolar concentrations of a reducing cofactor such as NADPH or GSH reacts to cleave DNA. In this work, we show that the two flavin-based enzymes ferredoxin-NADP+ reductase and xanthine oxidase catalyze the reductive activation of 1 by NADPH and NADH, respectively. The enzyme-catalyzed reductive activation of 1 leads to more rapid and efficient cleavage of DNA, even with 10-20-fold lower concentrations of the stoichiometric reductant. Significantly, the enzymatic systems are also found to activate the tight-binding (K(B) > or = 10(6) M(-1)) synthetic dynemicin analogs 3 and 5 toward DNA cleavage. These same analogs do not undergo reductive activation with NADPH or NADH alone, where evidence has been obtained to support the proposal that the DNA-bound drugs are protected from reductive activation. The new enzymatic activation processes described may have important implications for chemistry occurring with 1 and synthetic analogs in vivo, as well as for the future development of dynemicin-based anticancer agents.

Enediyne-mediated cleavage of RNA

RNA cleavage by enediyne anticancer antibiotics was shown to occur with no apparent sequence selectivity, but RNA structure appears to be important in those substrates where cleavage was observed. Neocarzinostatin (NCS) cleaved a wider variety of RNA substrates than either esperamicin (ESP) or calicheamicin (CAL), and dynemicin (DYN) has yet to cleave any RNA substrate tried. NCS, ESP, and CAL were all observed to cleave RNA substrates near the 5'-end, and all three compounds exhibited cleavage in single-stranded loop regions of the RNA substrates. NCS required no thiol for activation and subsequent cleavage, but ESP and CAL required addition of thiol, as expected, for cleavage to occur. An RNA hairpin substrate containing a UCCU sequence, equivalent to the TCCT sequence preferred by CAL in double-stranded DNA substrates, was cleaved by CAL, but no retention of selectivity for the UCCU site was retained by CAL in this RNA substrate. This study confirms an earlier observation that RNA is a substrate for enediyne cleavage, and indicates that nucleic acid cleaving compounds such as the enediynes could be useful probes of RNA three-dimensional structure.

Novel bioactive compounds from Actinomycetes: a short review (1988-1992)

Novel secondary metabolites continue to be isolated from Actinomycetes. Their biological activities and chemical structures show a wide range of diversity. This short review provides information on the compounds isolated between 1988 and 1992, and highlights interesting substances discovered during screening.