Studies On Secondary Metabolites Of Two Marine-derived Actinomycetes And Their Anti-tumor Activities

Actinomycetes are an important source of bioactive substances. Different from the terrestrial, marine environment possess the characteristic of high salinity, high pressure, low-temperature and low-nutrition. Marine-derived actinomycetes possess unique biosynthetic pathway in the long-term of adaptation to unique environment, resulting in broaden diversity of their secondary metabolites in chemical structures and bioactivities. In order to search for new secondary metabolites with antitumor activity from marine-derived actinomycetes,108 actinomycete strains were isolated from 20 marine-drived samples,17 bioactive strains were chosen by antitumor bioassay screening. Combined with bioactivity and chemical analysis, two strains Streptomyces sp. THS-55 and Streptomyces sp. HDN10-293 were selected for their significant cytotoxicity against P388 cells from the active srains and the activity strains library in our lab.Two targeted strains were incubated on a rotary shaker at 28℃ for 7 days, respectively. After 7 days of cultivation, whole broth was extracted three times with EtOAc and concentrated to extract in vacuo. The organic extract was fractionated to yield 30 pure compounds by column chromatography including silica gel, LH-20 column, MPLC and HPLC with C18 semi-preparative column and chiral-phase column. From Streptomyces sp. THS-55,19 compounds (1-19) were isolated; from Streptomyces sp. HDN 10-293,11 compounds (20-30) were isolated. Their structures were determined by physico-chemical properties and extensive spectroscopic analysis (UV, IR, MS, NMR, CD, X-ray). Among them there were 13 antimycins (1-13),5 nanaomycins (25-29),5 S-bridged dimeric PNQs (20-24),2 cyclic dipeptides (16-17) and other structural type compounds.The cytotoxic activities of 1-13 were evaluated by the SRB method using the HeLa (human cervical cancer cell line) and the MTT method using HL-60 (human promyelocytic leukemia cell line) and K562 (human erythroleukemic cell line) with ADM as positive control. All of compounds 1-13 exhibited significant cytotoxicity in vitro against HeLa cells with IC50 values ranged from 0.02 to 0.58 μM. But compounds 1-13 showed weak cytotoxicity against HL-60 and K562 cell lines. The evaluations of cytotoxic activities on the rest of the compounds are still in progress.In conclusion,30 compounds including 8 new compounds and 6 new natural products were isolated from the strains of THS-55 and HDN 10-293. To the best of our knowledge, compounds 1-6 are the first antimycins possesing 3-acetamido-2-hydroxybenzamide group linked to 3’-NH and compounds 7-10 which contain a 3-amino-2-hydroxybenzamide were firstly isolated from a natural source. Thus far, only four S-bridged dimeric PNQs have been reported from the natural source. In this paper five S-bridged dimeric PNQs were isolated from the strain of HDN 10-293. Although compound 20 shared the same planner structure with the reported compound BE-52440A, they didn’t have the identical absolute configurations. Compound 22 represent a new skeleton with the S-bridged dimeric PNQs fused with a rare unsaturated hexuronic acid. All 1-13 exhibited significant cytotoxicity in vitro against HeLa cell line. The assay for cytotoxic activities of S-bridged dimeric PNQs which have been reported to show significant cytotoxicity against a variety of cell lines is ongoing. All these studies provide novel structures for marine natural product chemistry and new lead compounds for the development of antitumor drugs. These results also suggested that the marine derived actinomycetes had the ability to produce metabolites with novel structures and significant bioactivities and the marine derived actinomycetes as pharmaceutical microbial resources have great value for further research.