Apoptosis‐inducing effect of diketopiperazine disulfides produced by Aspergillus sp. KMD 901 isolated from marine sediment on HCT116 colon cancer cell lines

Aims: Research is to identify the bioactive secondary metabolites produced by Aspergillus sp. KMD 901 isolated from marine sediment and to assess their apoptosis‐inducing effects. Methods and Results: Aspergillus sp. KMD 901 was isolated from marine sediment obtained from the East Sea of Korea. An ethyl acetate extract of KMD 901 exhibited potent cytotoxic activity towards five cancer cell lines (HCT116, AGS, A549, MCF‐7 and HepG2). Sequencing of the internal transcribed spacer (ITS) region in this strain allowed us to identify KMD 901 as a strain of Aspergillus versicolor. The cytotoxic compounds from Aspergillus sp. KMD 901 were purified by reversed‐phase high‐performance liquid chromatography and identified as diketopiperazine disulfides through spectroscopic analyses including extensive 2D NMR and mass spectrometry. The diketopiperazine disulfides were found to induce apoptosis in HCT116 cells based on cell morphology, DNA fragmentation observed by agarose gel electrophoresis, Annexin‐V/PI staining using a flow cytometer and cleavage of poly (ADP‐ribose) polymerase (PARP), caspase‐3, caspase‐8, caspase‐9 and Bcl‐2 family proteins (Bcl‐2, Bcl‐xL and Bax) using Western blotting analysis. Further study using an in vivo xenograft model showed inhibitory effects of acetylapoaranotin (2) on tumour proliferation. Conclusion: A new diketopiperazine disulfide, deoxyapoaranotin (3), along with previously described acetylaranotin (1) and acetylapoaranotin (2) was separated from Aspergillus sp. KMD 901 and found to have direct cytotoxic and apoptosis‐inducing effects towards HCT116 colon cancer cell lines. Significance and Impact of the Study: These results suggest that the diketopiperazine disulfides produced from Aspergillus sp., KMD 901, could be candidates for the development of apoptosis‐inducing antitumour agents. Also, this study indicates that marine natural products as potential source of pharmaceuticals.