Malignant melanoma is the deadliest form of skin cancer and highly chemoresistant. Melittin, an amphiphilic peptide containing 26 amino acid residues, is the major active ingredient from bee venom (BV). Although melittin is known to have several biological activities such as anti-inflammatory, antibacterial and anticancer effects, its antimelanoma effect and underlying molecular mechanism have not been fully elucidated. In the current study, we investigated the inhibitory effect and action mechanism of BV and melittin against various melanoma cells including B16F10, A375SM and SK-MEL-28. BV and melittin potently suppressed the growth, clonogenic survival, migration and invasion of melanoma cells. They also reduced the melanin formation in α-melanocyte-stimulating hormone (MSH)-stimulated melanoma cells. Furthermore, BV and melittin induced the apoptosis of melanoma cells by enhancing the activities of caspase-3 and -9. In addition, we demonstrated that the antimelanoma effect of BV and melittin is associated with the downregulation of PI3K/AKT/mTOR and MAPK signaling pathways. We also found that the combination of melittin with the chemotherapeutic agent temozolomide (TMZ) significantly increases the inhibition of growth as well as invasion in melanoma cells compared to melittin or TMZ alone. Taken together, these results suggest that melittin could be potentially applied for the prevention and treatment of malignant melanoma.

Streptomyces sp. VN1 was isolated from the coastal region of Phu Yen Province (central Viet Nam). Morphological, physiological, and whole genome phylogenetic analyses suggested that strain Streptomyces sp. VN1 belonged to genus Streptomyces. Whole genome sequencing analysis showed its genome was 8,341,703 base pairs in length with GC content of 72.5%. Diverse metabolites, including cinnamamide, spirotetronate antibiotic lobophorin A, diketopiperazines cyclo-L-proline-L-tyrosine, and a unique furan-type compound were isolated from Streptomyces sp. VN1. Structures of these compounds were studied by HR-Q-TOF ESI/MS/MS and 2D NMR analyses. Bioassay-guided purification yielded a furan-type compound which exhibited in vitro anticancer activity against AGS, HCT116, A375M, U87MG, and A549 cell lines with IC 50 values of 40.5, 123.7, 84.67, 50, and 58.64 µM, respectively. In silico genome analysis of the isolated Streptomyces sp. VN1 contained 34 gene clusters responsible for the biosynthesis of known and/or novel secondary metabolites, including different types of terpene, T1PKS, T2PKS, T3PKS, NRPS, and hybrid PKS-NRPS. Genome mining with HR-Q-TOF ESI/MS/MS analysis of the crude extract confirmed the biosynthesis of lobophorin analogs. This study indicates that Streptomyces sp. VN1 is a promising strain for biosynthesis of novel natural products. Natural products (NPs) have been starting points of drug discovery for several decades. Major antimicrobials and chemotherapeutics entering clinical trials are often based on NPs 1,2. Drugs with a natural origin can be produced as primary or secondary metabolites from versatile living organisms. Different microorganisms such as Streptomyces, myxobacteria and uncultured bacteria are major sources of such beneficial NPs 3,4. Moreover, different metabolic engineering approaches and sophisticated techniques employing systems biology or synthetic biology can assist in harnessing the full potential of these bacteria in terms of productivity or creating diverse products 5,6. Hence, there is renewed interest in mining microorganisms for new leads owing to the remarkable success of microbial metabolites as starting points for developing effective antibiotics, anticancer agents, and agrochemicals 7. Streptomyces are Gram-positive, aerobic bacteria in the order of Actinomycetales within the class of Actinobacteria. Genus Streptomyces was first proposed by Waksman and Henrici in 1943. It was classified into the family of Streptomycetaceae based on its morphology and cell wall chemotype 8. Previous studies have shown that more than 74% of current antibiotics are derived from the genus Streptomyces 9. Using integrated approaches of compound screening and drug development, Streptomyces arsenal has been found to be able to combat antibiotic resistance 5. Multiple approaches such as ribosome engineering 10 and genome mining 11 have been used to find new secondary metabolites in old Streptomyces strains. Besides the effort to work on old strains to explore novel biosynthetic gene clusters (BGCs),...

BackgroundUmbelliferone, also known as 7-hydroxycoumarin, is a phenolic metabolite found in many familiar plants. Its derivatives have been shown to have various pharmacological and chemo-preventive effects on human health. A uridine diphosphate glycosyltransferase YjiC from Bacillus licheniformis DSM 13, a cytochrome P450BM3 (CYP450 BM3) variant namely mutant 13 (M13) from Bacillus megaterium, and an O-methyltransferase from Streptomyces avermitilis (SaOMT2) were used for modifications of umbelliferone.ResultsThree umbelliferone derivatives (esculetin, skimmin, and herniarin) were generated through enzymatic and whole cell catalysis. To improve the efficiencies of biotransformation, different media, incubation time and concentration of substrate were optimized and the production was scaled up using a 3-L fermentor. The maximum yields of esculetin, skimmin, and herniarin were 337.10 μM (67.62%), 995.43 μM (99.54%), and 37.13 μM (37.13%), respectively. The water solubility of esculetin and skimmin were 1.28-folds and 3.98-folds as high as umbelliferone, respectively, whereas herniarin was 1.89-folds less soluble than umbelliferone. Moreover, the antibacterial and anticancer activities of herniarin showed higher than umbelliferone, esculetin and skimmin.ConclusionsThis study proves that both native and engineered enzymes could be employed for the production of precious compounds via whole cell biocatalysis. We successfully produced three molecules herniarin, esculetin and skimmin in practical amounts and their antibacterial and anticancer properties were accessed. One of the newly synthesized molecules the present research suggests that the combinatorial biosynthesis of different biosynthetic enzymes could rapidly promote to a novel secondary metabolite.Electronic supplementary materialThe online version of this article (doi:10.1186/s13036-017-0056-5) contains supplementary material, which is available to authorized users.

Specific inhibition of angiogenesis has been considered a powerful strategy for the treatment of cancer and other angiogenesis-related human diseases. Hovenia dulcis Thunb., Japanese raisin tree or Oriental raisin tree, is a hardy tree found in Asia, Eastern China and Korea and has been known to possess various biological activities, including antifatigue, antidiabetic, neuroprotective and hepatoprotective activity. In the present study, for the first time, we evaluated whether a 100% ethanol extract of Hovenia dulcis Thunb. (HDT) inhibits the angiogenesis of human umbilical vein endothelial cells (HUVECs) using in vitro angiogenesis assays. HDT suppressed vascular endothelial growth factor (VEGF)-induced proliferation, migration, invasion and tube formation of HUVECs at subtoxic doses. In addition, HDT significantly inhibited in vivo angiogenesis of the chorioallantoic membrane from growing chick embryos without exhibiting cytotoxicity. Furthermore, HDT downregulated not only VEGF receptor 2 (VEGFR2) signaling in HUVECs, but also hypoxia-inducible factor (HIF)-1α expression in hepatocarcinoma cell line HepG2. Ampelopsin is a bioactive flavanonol found in Hovenia dulcis Thunb. Our data showed that ampelopsin inhibited angiogenesis with no cytotoxicity by suppressing both VEGFR2 signaling and HIF-1α expression. These results suggest that Hovenia dulcis Thunb. and its active compound ampelopsin exhibit potent antiangiogenic activities and therefore could be valuable for the prevention and treatment of angiogenesis-related diseases including cancer.

Nargenicin A1 is major secondary metabolite produced by Nocardia sp. CS682, with an effective antibacterial activity against various Gram-positive bacteria. Most Nocardia spp. have metabolic ability to produce compounds of diverse nature, so one-strain-many-compounds (OSMAC) approach can be applied for obtaining versatile compounds from these strains. In this study, we characterized a novel 1, 3, 6, 8-tetrahydroxynaphthalene (THN) derivative by metabolic engineering approach leading to the inactivation of nargenicin A1 biosynthesis. By using genome mining, metabolite profiling, and bioinformatics, the biosynthetic gene cluster and biosynthetic mechanism were elucidated. Further, the antibacterial, anticancer, melanin formation, and UV protective properties for isolated THN compound were performed. The compound did not exhibit significant antibacterial and cytotoxic activities, but it exhibited promising UV protection effects. Thus, metabolic engineering is an effective strategy for discovering novel bioactive molecules.

Melanoma is the most serious type of skin cancer and remains highly drug-resistant. Therefore, the discovery of novel effective agents against melanoma is in high demand. Herein, we investigated the cytotoxic activities in melanoma cells and underlying molecular mechanisms of beauvericin (BEA) and its analogue beauvericin G 1 (BEA G 1 ), which are cyclohexadepsipeptides isolated from fungi. BEA and BEA G 1 significantly suppressed the growth, clonogenicity, migration, and invasion of A375SM human melanoma cells and promoted caspase-dependent apoptosis through upregulation of death receptors, as well as modulation of pro-and anti-apoptotic Bcl-2 family members. Furthermore, the effects of BEA and BEA G 1 were associated with the suppression of multiple molecular targets that play crucial roles in melanoma oncogenesis, including ERK, JNK, p38, NF-κB, STAT3, and MITF. Notably, the cytotoxic efficacy of BEA G 1 against A375SM cells was stronger than that of BEA. These findings suggest that BEA and BEA G 1 can be further investigated as potent cytotoxic natural compounds for the suppression of melanoma progression.