Chaetoglobosin E inhibits tumor growth and promotes the anti-tumor efficacy of cytotoxic drugs in esophageal squamous cell carcinoma by targeting PLK1

BACKGROUND: Currently, there is no satisfactory treatment available for esophageal squamous cell carcinoma (ESCC), and thus, there is a pressing need to develop effective drugs. Chaetoglobosin E, a cytochalasan alkaloid derived from metabolites of Chaetomium madrasense 375, is a chaetoglobosin with intense anti-tumor activity. Therefore, revealing its anti-tumor mechanism for the application of cytochalasans is crucial. METHODS: The cytotoxic effect of chaetoglobosin E and cisplatin on esophageal cancer KYSE-30, KYSE-150, and TE-1 cells was detected using cell viability or colony formation assays. The cell cycle, apoptosis, autophagy, invasion, and metastasis were assayed by flow cytometry or western blot. The potential target of chaetoglobosin E was assayed by RNA sequencing (RNA-seq) and large loop prediction software analysis and was assessed by western blot and real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR). The effect of its target on cell pyroptosis was assayed using overexpression and silence experiments. RESULTS: Chaetoglobosin E significantly inhibited the proliferation of KYSE-30, KYSE-150, and TE-1 cells, especially KYSE-30 cells. Our results showed that chaetoglobosin E induced the G2/M phase arrest of KYSE-30 cells, followed by the down-regulation of cyclinB1, CDC2, and p-CDC2, and up-regulation of p21. Moreover, chaetoglobosin E also decreased the anti-apoptotic protein expression of Bcl-2, increased apoptotic expression of Bax, increased autophagy protein expressions of beclin1 and LC3, decreased invasion and metastasis protein expression of E-cadherin, and increased expression of vimentin. The RNA-seq and large loop prediction software analysis results indicated that its potential target might be polo-like kinase 1 (PLK1). Moreover, results also showed that chaetoglobosin E can reverse the PLK1 overexpression plasmid-induced up-regulation of the PLK1 protein. Furthermore, we found that chaetoglobosin E induced pyroptosis via the activation of the gasdermin E (GSDME) protein. Further studies showed that the high expression of PLK1 inactivated the GSDME protein, while the knockdown of PLK1 expression activated the GSDME protein, indicating that chaetoglobosin E induced cell pyroptosis by inhibiting PLK1. CONCLUSIONS: This study suggested that chaetoglobosin E may be a novel lead compound to the treatment of ESCC patients by targeting PLK1, and elucidated for the first time that PLK1 was involved in a new pyroptosis mechanism.