Studies On The Antitumor Activity Of The Secondary Metabolites Of Bacteria Isolated From Red Sea

It is well known that tumors have been a severe threat to human health for a long time. Medication is the main strategy for the treatment of tumors. However, up to now most of the antitumor drugs can only alleviate the state of illness but can’t cure it completely. Therefore it is very important for us to develop new antitumor drugs. Marine organisms account for about80%of the creatures on the Earth and they have abundant metabolic pathways. It is reported that marine organisms can produce large amounts of metabolites with novel structure and excellent bioactivity. In recent years, more and more researches developing the antitumor compounds have been focused on marine microbes, due to they are abundant, renewable and easy to be reproduced to large scale. As high salinity and temperature, the Red Sea has a special ecological environment, which leads to the unique and various metabolic pathways. It should be a good source of the active compounds with novel structures.In this thesis, we studied the antitumor activity of the marine microbes isolated from Red Sea. The anti-tumor activities of the isolates were screened based on the growth inhibition effect against liver cancer7721cell and cervical cancer HeLa cell. A highly active strain No.212was found. After the optimization of culture condition and enlargement of the cultivation, the antitumor substances were isolated from its metabolites.In detail,153microbial isolates, including141bacteria and12actinomycetes, were isolated from the Red Sea water samples. Through the anti-tumor active screening,13isolates (12bacteria, and1actinomycete) were active, accounting for8.5%of total isolates. The isolate No,212showed stable and lasting suppresses activity, whose inhibitive rates at the concentration of100μg/ml against Hela cell and7721cell were49.38%,47.92%, respectively. Therefore, the strain212was further studied. Based on the morphology and the16S rDNA sequence, strain212is identified as Micrococcus sp. It was found that the optimal growth condition of this stain was at pH7.8, NaCl0.3mol·L-1,28℃with4days cultivation. Strain212was then subcultured in large scale to about20L, from which5.0g crude extract by ethyl acetate were obtained. After that, the crude extracts were partitioned with hexane and trichloromethane. Both hexane and trichloromethane phases showed significant antitumor activity with inhibitive rate of40.74%,32.69%(hexane phase) and65.82%,56.25%(trichloromethane phase) against HeLa and7721cell respectively. The results indicated that the active substances should be lipid-soluble compounds with low or moderate polarity. Silica gel column chromatography and reverse phase highly performance liquid chromatography were also used for further separation of trichloromethane phase extracts and3active subfractions were obtained. We identified the active substances by GC-MS, the results indicated that the active fraction mainly consist of dipeptides and cyclic dipeptides. We suppose dipeptides and cyclic dipeptides might be the antitumor substances in the secondary metabolite of strain212(Micrococcus sp.). The separation and purification of the active subfrations will be further conducted.