Cucurbitacin B exhibits antitumor effects on CD133+ HepG2 liver cancer stem cells by inhibiting JAK2/STAT3 signaling pathway

Cancer stem cells (CSCs), a crucial cancer cell subpopulation, possess stemness phenotypic characteristics. Cucurbitacin B (CuB), a tetracyclic triterpenoid isolated from Cucurbitaceae , exerts widely pharmacological activities in many diseases. The aim of this study was to enrich, identify liver CSCs and investigate antitumor effects of CuB as well as explore the underlying molecular mechanisms in these liver CSCs. HepG2 cell lines were used for the enrichment of liver CSCs by serum-free medium culture and magnetic-activated cell sorting. The CSC characteristics were analyzed by immunofluorescent staining, sphere-forming, western blot and xenograft tumorigenicity assay. CuB’ antitumor effects and underlying molecular mechanism were measured by cell counting kit-8, colony formation, sphere-forming, cell cycle, xenograft and western blot assay. Our results showed that we could enrich 97.29% CD133+ HepG2 cells, which possessed CSC characteristics including re-renewal capacity, proliferative ability, sorafenib resistance, overexpressed stemness-related molecules and enhanced tumorigenic potential. Furthermore, we also found that CuB inhibited cell viability, sphere formation, colony formation and arrested cell cycle at G2/M phase as well as sensitized CD133+ HepG2 cells to sorafenib in vitro and in vivo. Western blot assay indicated that CuB inhibited expression levels of cyclin B1, CDK1, CD133, p-JAK2 and p-STAT3. In conclusion, our findings indicated that CuB could exhibit antitumor effects on CD133+ HepG2 CSCs by inhibiting the Janus kinase 2/signal transducers and activators of transcription-3 signaling pathway, expanding basic and preclinical investigations on liver CSCs.