The genus Streptomyces is one of the most important sources producing a huge amount of secondary metabolites applied in the pharmaceutical industry nowadays, especially in cancer treatment. In this study, the anticancer effect of Streptomyces sp. SS162 isolated from marine corals was investigated utilizing a 3-(4,5-dimethylthazol-2yl)-2,5-diphenyl tetrazolium-bromide cytotoxicity assay. The results showed that the SS162-cultured medium caused a significant inhibitory effect (64.63%) on the A549 lung carcinoma cell line among various cancer cell lines while being less toxic to normal fibroblasts. The effect of the SS162-cultured medium was in a time-dependent manner. After 24 hours of treatment, A549 cells shrank, expressed round morphology, and lost adhesion to the culture surface, leading to the deceleration of cell proliferation that has not been reported in other works. Regarding cytotoxic mechanism, SS162-cultured medium inhibited A549 cancer cell growth via the 2.75-fold downregulation of microtubule-associated TPX2 mRNA level and the 2.78-fold upregulation of cyclin-dependent-kinase-inhibitor CDKN1B expression. Notably, the antiproliferative capacity of Streptomyces sp. via the downregulation of TPX2 level was reported here for the first time. After the extraction of SS162-cultured medium by ethyl acetate solvent, the crude extract could also suppress the proliferation of A549 cells with an IC50 value of 407.38 μg/ml and a selectivity index greater than 2.5 implying a specific effect on cancer cells. These findings proved the effect of Streptomyces sp. SS162 against lung cancer and simultaneously provided a suggestion that SS162-cultured medium could be potential for discovering novel anticancer agents.
Key words: anticancer, cytotoxicity, human lung adenocarcinoma cell line A549, Streptomyces sp. SS162, crude extract.
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