Natural product piperlongumine inhibits proliferation of oral squamous carcinoma cells by inducing ferroptosis and inhibiting intracellular antioxidant capacity.

Background: As a new form of cell death, ferroptosis has been shown to have inhibitory effects on a variety of tumor cells except oral squamous cell carcinoma (OSCC). There were few investigations on the effects and molecular mechanisms of piperlongumine (PL, a ferroptosis inducer) and CB-839 (a GLS1 inhibitor which promotes ferroptosis) on OSCC cells. This article assesses the anticancer effect and mechanism of PL as well as combined with CB-839. Methods: OSCC cells were treated with specified concentration of PL alone or with ferroptosis inhibitor Ferrostatin-1 (Fer-1) and antioxidant N-Acetylcysteine (NAC) to assess their effects on biological characteristics such as cell proliferation, cell death and intracellular ferroptosis related pathways. Also, cells were treated with PL combined with CB-839 to evaluate the synergistic effect of CB-839 on PL's anticancer effects. Results: The results showed that the proliferation rate of PL-treated OSCC cells were decreased in a dose- and time-dependent manner. PL can induce OSCC cells apoptosis. Lipid peroxidation (LPO) and intracellular reactive oxygen species (ROS) were accumulated after PL treatment. We found some protein changes significantly such as the expression of DMT1 increased, and the expression of FTH1, SLC7A11 and GPX4 decreased. In addition, the anti-proliferation effect of PL can be reversed by Fer-1 and NAC and the level of LPO and ROS was decreased accordingly. Importantly, we found that PL and CB-839 in combination could decrease the cell viability and the LPO level synergistically, accompanied by a large consumption of glutathione (GSH). These evidences prove that PL can induce ferroptosis of OSCC cells, which can be enhanced by CB-839. Conclusions: Our study suggested that the nature product PL can induce the ferroptotic death of OSCC cells, which is further enhanced when combined with CB-839. The synergistic anticancer effect of these two may prove new strategy for OSCC treatment.