Pyropheophorbide-α methyl ester-mediated photodynamic therapy triggers pyroptosis in osteosarcoma cells via the ROS/caspase-3/GSDME pathway.

Background: Pyropheophorbide-α methyl ester-mediated photodynamic therapy(MPPa-PDT) is a candidate treatment for solid tumors, including osteosarcoma. Pyroptosis has garnered significant attention in cancer research due to its pro-inflammatory and immunomodulatory nature. This study investigated the mechanism and role of MPPa-PDT-induced pyroptosis in osteosarcoma cells.

Methods: We treated human osteosarcoma 143b and HOS cells with MPPa at concentrations of 0.5 μM and 0.25 μM, respectively, then irradiated the cells with LED light at 630 nm wavelength with an energy density of 4.8 J/cm. Cell viability and apoptosis ratio were detected using CCK-8 and Annexin V-Propidium Iodide staining, respectively. Intracellular reactive oxygen species (ROS) levels and mitochondrial membrane potential (MtΔψ) were assessed using 2',7'-Dichlorofluorescin diacetate, and JC-1 staining kits, respectively. Scanning Electron Microscopy (SEM) was utilized to examine cell ultrastructure. The morphological changes of the cells were observed by an inverted microscope. Western blotting analysis was conducted to measure protein levels. To elucidate the mechanism and role, we re-evaluated relevant parameters after pretreating with NAC,Si caspase-3, and Si GSDME.

Results: MPPa-PDT inhibited the activity of osteosarcoma 143b and HOS cells and induced pyroptosis with mitochondrial damage, ROS aggregation, and activation of Caspase-3 and GSDME. The effects of MPPa-PDT on the activity and apoptosis of osteosarcoma cells were partially reversed after pretreating with Si GSDME. After NAC pretreatment, the activation of pyroptosis and Caspase-3 induced by MPPa-PDT was partially reversed. After Si Caspase-3 pretreatment, the pyroptosis induced by MPPa-PDT was partially reversed.

Conclusion: MPPa-PDT can induce pyroptosis in osteosarcoma cells, which has the effect of enhancing apoptotic processes. Mitochondrial damage and ROS/caspase-3/GSDME pathway are the possible mechanisms of pyroptosis induced by MPPa-PDT.