Identification of natural compound garcinone E as a novel autophagic flux inhibitor with anticancer effect in nasopharyngeal carcinoma cells

CONTEXT: Current chemotherapeutic drugs cannot meet the treatment needs of patients with nasopharyngeal carcinoma (NPC), so urgent action is needed to discover novel chemotherapeutic agents. Our previous study revealed that garcinone E (GE) inhibited the proliferation and metastasis of NPC, suggesting that the compound might display promising anticancer activity. OBJECTIVE: To examine the mechanism underlying the anti-NPC activity of GE for the first time. MATERIALS AND METHODS: For MTS assay, NPC cells were treated with 2.5-20 μmol/L GE or dimethyl sulfoxide for 24, 48, and 72 h. Colony formation capacity, cell cycle distribution, and in vivo xenograft experiment of GE were assessed. MDC staining, StubRFP-sensGFP-LC3 observation, LysoBrite Blue staining, and immunofluorescence examined the autophagy of NPC cells after GE exposure. Western blotting, RNA-sequencing, and RT-qPCR measured protein and mRNA levels. RESULTS: GE suppressed cell viability with an IC(50) of 7.64, 8.83 and 4.65 μmol/L for HK1, HONE1 and S18 cells. GE inhibited colony formation and cell cycle, increased autophagosome number, and inhibited the autophagic flux partially by blocking lysosome-autophagosome fusion, and repressed S18 xenograft growth. GE dysregulated the expression of autophagy- and cell cycle-related proteins such as Beclin-1, SQSTM1/p62, LC3, CDKs, and Cyclins. Bioinformatics GO and KEGG pathway enrichment analysis of RNA-seq showed that autophagy was enriched in differentially expressed genes upon GE treatment. DISCUSSION AND CONCLUSION: GE acts as an autophagic flux inhibitor, which may have potential chemotherapeutic use for NPC treatment and may have an application in basic research to explore the mechanisms of autophagy.