Genome Mining and Metabolic Profiling Uncover Polycyclic Tetramate Macrolactams from Streptomyces koyangensis SCSIO 5802.

We have previously shown deep-sea-derived Streptomyces koyangensis SCSIO 5802 to produce two types of active secondary metabolites, abyssomicins and candicidins. Here, we report the complete genome sequence of S. koyangensis SCSIO 5802 employing bioinformatics to highlight its potential to produce at least 21 categories of natural products. In order to mine novel natural products, the production of two polycyclic tetramate macrolactams (PTMs), the known 10-epi-HSAF (1) and a new compound, koyanamide A (2), was stimulated via inactivation of the abyssomicin and candicidin biosynthetic machineries. Detailed bioinformatics analyses revealed a PKS/NRPS gene cluster, containing 6 open reading frames (ORFs) and spanning ~16 kb of contiguous genomic DNA, as the putative PTM biosynthetic gene cluster (BGC) (termed herein sko). We furthermore demonstrate, via gene disruption experiments, that the sko cluster encodes the biosynthesis of 10-epi-HSAF and koyanamide A. Finally, we propose a plausible biosynthetic pathway to 10-epi-HSAF and koyanamide A. In total, this study demonstrates an effective approach to cryptic BGC activation enabling the discovery of new bioactive metabolites; genome mining and metabolic profiling methods play key roles in this strategy.

Shunt products of aminoansamycins from aas1 overexpressed mutant strain of Streptomyces sp. S35.

Constitutively expression of the pathway-specific activators is an effective method to activate silent gene clusters and improve natural product production. In this study, nine shunt products of aminoansamycins (1-9) were identified from a recombinant mutant strain S35-LAL by overexpressed the large-ATP-binding regulator of the LuxR family (LAL) gene aas1 in Streptomyces sp. S35. All the compounds showed no anti-microbial, anti-T3SS and cytotoxic activities.

Spotlight on 17-AAG as an Hsp90 inhibitor for molecular targeted cancer treatment.

Hsp90 is a ubiquitous chaperone with important roles in the organization and maturation of client proteins that are involved in the progression and survival of cancer cells. Multiple oncogenic pathways can be affected by inhibition of Hsp90 function through degradation of its client proteins. That makes Hsp90 a therapeutic target for cancer treatment. 17-allylamino-17-demethoxy-geldanamycin (17-AAG) is a potent Hsp90 inhibitor that binds to Hsp90 and inhibits its chaperoning function, which results in the degradation of Hsp90's client proteins. There have been several preclinical studies of 17-AAG as a single agent or in combination with other anticancer agents for a wide range of human cancers. Data from various phases of clinical trials show that 17-AAG can be given safely at biologically active dosages with mild toxicity. Even though 17-AAG has suitable pharmacological potency, its low water solubility and high hepatotoxicity could significantly restrict its clinical use. Nanomaterials-based drug delivery carriers may overcome these drawbacks. In this paper, we review preclinical and clinical research on 17-AAG as a single agent and in combination with other anticancer agents. In addition, we highlight the potential of using nanocarriers and nanocombination therapy to improve therapeutic effects of 17-AAG.

Preparation and evaluation of 17-allyamino-17-demethoxygeldanamycin (17-AAG)-loaded poly(lactic acid-co-glycolic acid) nanoparticles.

In the present study, we developed the novel 17-allyamino-17-demethoxygeldanamycin (17-AAG)-loaded poly(lactic acid-co-glycolic acid) (PLGA) nanoparticles (NPs) using the combination of sodium lauryl sulfate and poloxamer 407 as the anionic and non-ionic surfactant for stabilization. The PLGA NPs were prepared by emulsification/solvent evaporation method. Both the drug/polymer ratio and phase ratio were 1:10 (w/w). The optimized formulation of 17-AAG-loaded PLGA NPs had a particle size and polydispersity index of 151.6 ± 2.0 and 0.152 ± 0.010 nm, respectively, which was further supported by TEM image. The encapsulation efficiency and drug loading capacity were 69.9 and 7.0%, respectively. In vitro release study showed sustained release. When in vitro release data were fitted to Korsmeyer-Peppas model, the n value was 0.468, which suggested that the drug was released by anomalous or non-Fickian diffusion. In addition, 17-AAG-loaded PLGA NPs in 72 h, displayed approximately 60% cell viability reduction at 10 µg/ml 17-AAG concentration, in MCF-7 cell lines, indicating sustained release from NPs. Therefore, our results demonstrated that incorporation of 17-AAG into PLGA NPs could provide a novel effective nanocarrier for the treatment of cancer.

Genome shuffling enhances biocontrol abilities of Streptomyces strains against two potato pathogens.

AIMS: To employ the genome shuffling technique for improving the phenotype of a biocontrol control agent of the genus Streptomyces. METHODS AND RESULTS: Two rounds of genome shuffling (GS) were carried out with Streptomyces melanosporofaciens EF-76, a geldanamycin producer. Six fusants that showed optimized in vitro antagonistic activity against Streptomyces scabies or Phytophthora infestans, two important pathogens of potato crops, were selected. All selected fusants retained the capacity to produce geldanamycin, but none overproduced this antibiotic. The higher antagonism ability appeared to result from a diversification of secreted metabolites. Seven or eight metabolites were detected in the HPLC profiles of parental strains, whereas 12-15 were detected in fusant strains. Biocontrol assays revealed that four of six fusants protected tubers more efficiently than parental strains. CONCLUSIONS: GS emerged as an elegant and rapid tool to optimize the antagonistic ability of Streptomyces strains. Optimization of the in vitro antagonistic activity against plant pathogens appears to be an effective approach to select for improved biocontrol agents. The enhanced phenotype did not depend on an overproduction of a specific antibiotic but rather on the secretion of a wider variety of secondary metabolites. SIGNIFICANCE AND IMPACT OF THE STUDY: Improved capacities of a biocontrol agent compensate for the lack of efficient chemical control of potato scab.

Antagonistic effect of divalent cations Ca2+ and Mg2+ on the morphological development of Streptomyces hygroscopicus var. geldanus.

Supplementation of the divalent cations calcium and magnesium to submerged cultures of Streptomyces hygroscopicus var. geldanus greatly influenced morphological development and secondary metabolite synthesis. The disparate response could be explained in terms of the differential effects of Ca2+ and Mg2+ ions on cell surface hydrophobicity. Cultures supplemented with calcium ions were found to be hydrophobic, which resulted in cell concentration-dependent aggregation. In contrast, those grown in a magnesium-rich medium were found to be hydrophilic with the organism growing as freely dispersed filaments that synthesised geldanamycin at an optimal rate in comparison to hydrophobic pellets.