Background::
Xanthones are a class of heterocyclic natural products, which are promising sources of anticancer leads. Phomoxanthone B（PXB）and Phomoxanthone A（PXA）are xanthone dimers. PXA is well studied as an anti-cancer agent, but PXB is not. In our study, PXB was isolated from the endophytic fungus Phomopsis sp. By254.
Objective::
The purpose of this study was to identify the underlying anti-tumor mechanisms of PXB in breast cancer MCF7 cell line.
Methods::
Apoptosis, cell cycle, proliferation, invasion and migration assays were used to assess the antitumor activity of PXB. RNA sequencing was used to analyze the effect of PXB treatment on gene expression in MCF7 cells.
Results::
PXB showed cytotoxicity toward a variety of tumor cells, especially MCF7 cells. PXB inhibited the migration and invasion, arrested cell cycle at G2/M phase and induced apoptosis associated with caspase-3 activation in MCF7 cells. The detailed transcriptome analysis revealed that PXB affected several pathways related to tumorigenesis, metabolisms-, and oxidative phosphorylation in MCF7 cells. KEGG transcriptome analysis revealed that PXB upregulated pro-survival signal pathways such as MAPK, PI3K-AKT and STAT3 pathways. We found that PXB also significantly upregulated the expression of IL24, DDIT3 and XAF1, which may contribute to PXB-induced apoptosis. We further found that PXB may downregulate oxidative phosphorylation by decreasing the expression of electron transport chain genes, especially MT-ND1, which is a potential unfavorable prognostic marker for ER-positive breast cancer.
Conclusion::
PXB exerts strong cytotoxicity against human tumor cells and has a potential for ER-positive breast cancer treatment.
The combination of methylsulfonylmethane and tamoxifen inhibits the Jak2/STAT5b pathway and synergistically inhibits tumor growth and metastasis in ER-positive breast cancer xenografts