Isolation and characterization of bioactive metabolites from Xylaria psidii, an endophytic fungus of the medicinal plant Aegle marmelos and their role in mitochondrial dependent apoptosis against pancreatic cancer cells

Background: The genus Xylaria has been reported as a rich source of biologically active secondary metabolites. In the present study, an endophytic fungus Xylaria psidii has been isolated from the leaf sample of Aegle marmelos (L.) Corr., characterized on the basis of its morphological features and sequence data for the ITS region (KU291350) of the nuclear ribosomal DNA. Biological screening of ethyl acetate extract of Xylaria psidii displayed a potential therapeutic effect on pancreatic cancer cells.

Hypothesis: This study was designed systematically to explore Xylaria psidii, an endophytic fungus for the identification of biologically active secondary metabolites against pancreatic cancer cells.

Methods: While exploring the bioactive secondary metabolites, a sensitive and reliable LC-MS based dereplication approach was applied to identify four compounds A-D from fungal extract. Further bioactivity guided isolation of fungal extract yielded two major metabolites 1 and 2. The structures of 1 and 2 have been determined by detailed spectroscopic analysis including MS, NMR, IR and UV data and similarity with published data. Xylarione A (1) is new whereas (-) 5-methylmellein (2) is reported for the first time from X. psidii. Both the isolated compounds were screened for their effect on the viability and proliferation against a panel of cancer cell lines (MCF-7, MIA-Pa-Ca-2, NCI-H226, HepG2 and DU145) of different tissue origin.

Results: Compounds 1 and 2 exhibited cytotoxicity against pancreatic cancer (MIA-Pa-Ca-2) cells with IC₅₀ values of 16.0 and 19.0 µm, respectively. The cell cycle distribution in MIA-Pa-Ca-2 cells, confirmed a cell cycle arrest at the sub-G1 phase. Cell death induced by 1 and 2 displayed features characteristic of apoptosis. Flow cytometry based analysis of 1 and 2 using Rhodamine-123 displayed substantial loss of mitochondrial membrane potential in a concentration dependent manner by both the compounds.

Conclusion: Results conclude that the isolated compounds 1 and 2 are responsible for the activity shown by crude ethyl acetate extract and may act as potential leads for medicinal chemists for designing more potent analogs.