5-Aminolevulinic Acid-Mediated Photodynamic Therapy Induces Ferroptosis in Oral Leukoplakia and Oral Squamous Cell Carcinoma

5-Aminolevulinic acid (ALA)-mediated photodynamic therapy (PDT) is one of the treatment modalities for oral leukoplakia (OLK) and oral squamous cell carcinoma (OSCC). However, the role of ferroptosis in ALA-PDT for OLK and OSCC remains unclear. Therefore, this study aimed to investigate whether ALA-PDT can induce ferroptosis in OLK and OSCC. We detected relative cellular dehydrogenase activity (CCK-8 assay), long-term proliferative viability, reactive oxygen species (ROS) generation, glutathione levels, and mitochondrial morphology after ALA-PDT. The expression of ferroptosis-related proteins was detected using Western blot. A tongue OSCC model was established in male BalB/c nude mice, and then ALA-PDT was performed. Immunohistochemical staining of Ki67, GPX4 and FTH1 was conducted to evaluate the effect of ALA-PDT. Subsequently, OLK and OSCC cells were pre-treated with ferrostatin-1 (Fer-1) before ALA-PDT. Relative cellular dehydrogenase activity, ROS generation, lipid peroxidation, Fe2+ levels, and ferroptosis-related protein expression were measured. Finally, OLK and OSCC cells were treated with a combination of ALA-PDT and erastin, and mitochondrial function was evaluated. In vitro study showed that ALA-PDT increased ROS generation and decreased GSH/GSSG ratio in OLK and OSCC cells. After ALA-PDT, mitochondrial morphology exhibited typical characteristics of ferroptosis. In vivo experiments showed that immunohistochemistry (IHC) scores of Ki67, GPX4 and FTH1 in the tissues decreased after ALA-PDT. Moreover, pre-treatment with Fer-1 could reverse ROS levels, lipid peroxidation and intracellular Fe2+ accumulation in OLK and OSCC cells after ALA-PDT. Additionally, Fer-1 pre-treatment reversed the changes in protein expression induced by ALA-PDT. The combination of ALA-PDT and erastin significantly reduced mitochondrial O2•− production and decreased mitochondrial membrane potential. Above all, ALA-PDT can induce ferroptosis in OLK and OSCC. The use of ferroptosis agonists may enhance the therapeutic efficacy of ALA-PDT for OLK and OSCC.