Polyphyllin II Triggers Pyroptosis in Hepatocellular Carcinoma via Modulation of the ROS/NLRP3/Caspase-1/GSDMD Axis

Pyroptosis is a type of programmed cell death (PCD) with pro-inflammatory properties, which is characterized by the swelling with bubbles and the release of LDH and inflammatory cell cytokines. Polyphyllin II (PPII) is the main active ingredient of the Chinese herb Rhizoma Paridis and has been proven to exert high efficacy against a variety of malignant tumors. At present, the anti-tumor research on PPII mainly focuses on apoptosis that is an anti-inflammatory type of PCD, but other potential modes of death cell death and mechanisms of PPII remain to be discovered. Here, we first found that PPII could effectively inhibit the growth of hepatocellular carcinoma (HCC) cells via pyroptosis. After treatment with PPII, the morphology of swelling with bubbles and the formation of pores in the cell membrane in HCC cells were observed, and LDH and cell cytokines (IL-1β, IL-18, IL-6, TNF-α, IFN-β, and IFN-γ) were released. Furthermore, the flow cytometry results showed that PPII could activate oxidative stress by increasing Ca2+ influx, thereby promoting the production of ROS to exert anti-tumor effects. RNA sequencing revealed that pyroptosis is closely linked to several signaling pathways, including the MAPK, TNF, Rap1, mTOR, and FoxO pathways, as well as the PD-L1 expression and PD-1 checkpoint pathway. An in vivo study demonstrated that PPII treatment suppressed liver tumor growth in mice by pyroptosis in a dose-dependent manner, and it showed no obvious side effects within a certain range. The Western blot results of tumor tissues revealed that the pyroptosis effect of PPII on liver cancer was associated with the activation of the NLRP3/Caspase1/GSDMD pathway, which upregulates the expression of NLRP3, Cleaved-Caspase 1, GSDMD-N, IL-1β, and IL-18 proteins and downregulates the expression of pro-Caspase 1 and GSDMD proteins. In summary, our findings revealed the pyroptosis effect and mechanism of PPII in HCC cells in vitro and in vivo, suggesting that PPII may be used as a potential pyroptosis inducer for HCC treatment in the future.