Cytotoxic secondary metabolites isolated from Penicillium sp. YT2019-3321, an endophytic fungus derived from Lonicera Japonica

Abstract

Introduction: Endophytic fungi associated with medicinal plants have proven to possess a high potential to produce structurally diverse metabolites, some of which are valuable for medicinal applications. In this study, Penicillium sp. YT2019-3321, an endophytic fungus derived from traditional Chinese medicine Lonicera japonica, was chemically studied.

Methods: The chemical structures of the isolated compounds were established by a correlative interpretation of HRESIMS and NMR spectroscopic data. The optical resolution of (±)-1 by chiral HPLC yielded individual enantiomers (+)-1 and (-)-1, and their stereochemistry were solved by X-ray diffraction crystallography, respectively.

Results and discussion: Eight structurally diversified secondary metabolites, including two previously unreported polyketides, named (±)-chrysoalide B (1) and penicidone E (2), were isolated and identified from Penicillium sp. YT2019-3321. Compound 2 possessed the γ-pyridone nucleus, which is rarely found in natural products. Cytotoxic assay revealed that the new compound 2 demonstrated a dose-dependent cytotoxicity against the human pancreatic tumor cells PATU8988T with the IC₅₀ value of 11.4 μM. Further studies indicated that 2 significantly induced apoptosis of PATU8988T cell lines, characterized by the morphologies abnormity, the reduction of cell number, the upregulation of proportion of apoptotic cells, and the ratio of Bcl-2 to Bax. Our study demonstrates that fungal secondary metabolites may have important significance in the discovery of drug leads.

Keywords: Penicillium; cytotoxic activity; endophytic fungus; polyketides; secondary metabolites.

FIGURE 1

Structures of the isolated compounds 1-8.

FIGURE 2

Key COSY and HMBC correlations for 1 and 2.

FIGURE 3

Molecular structures of (+)-1 and (–)-1 from single-crystal X-ray diffractometry.

FIGURE 4

Compound 2 (Cpd 2) induced human pancreatic cancer cells apoptosis. (A) Cytotoxic effect of Cpd 2 on PATU8988T measured by CCK-8. Cells were treated with Cpd 2 at the gradient concentrations from 1 to 50 μM for 24 and 48 h, respectively. (B) Morphological results of PATU8988T treated with Cpd 2. (C) Annexin V/PI double staining with flow cytometry analysis was used for the detection of cell apoptosis. (D) Western blotting of Bcl-2 and Bax.