Head and neck squamous cell carcinoma (HNSCC) often presents a therapeutic challenge due to the presence of hypoxic tumor regions that resist traditional treatments. While photodynamic therapy (PDT) is an established modality, the precise molecular mechanisms governing its efficacy under low-oxygen conditions remain incompletely understood. This study investigates the role of temoporfin-based PDT (mTHPC-PDT) in inducing ferroptosis, a regulated form of iron-dependent cell death, and evaluates its impact on HNSCC viability in both normoxic and hypoxic environments.

We utilized HNSCC cell lines to perform mTHPC-PDT experiments under controlled atmospheric conditions (21% and 1% O2). Ferroptosis induction was validated through the assessment of lipid peroxidation, glutathione (GSH) depletion, and the regulatory activity of GPX4. Pharmacological inhibitors, such as ferrostatin-1, were employed to confirm the specificity of the death pathway. Furthermore, mitochondrial morphology and intracellular reactive oxygen species (ROS) levels were monitored to map the stress response.

Our data reveal that temoporfin (Foscan®)-mediated PDT robustly triggers ferroptosis in HNSCC cells. Under normoxia, mTHPC-PDT caused a rapid accumulation of lipid hydroperoxides and a significant decline in GPX4 expression. Crucially, while hypoxia typically confers resistance to oxidative stress, we observed that ferroptosis remained a significant regulator of cell death, albeit with altered kinetics compared to normoxic conditions. The inhibition of ferroptosis partially rescued cell viability, highlighting its role as a primary cytotoxic mechanism. These findings suggest that PDT can bypass conventional apoptotic resistance by engaging the ferroptotic machinery.

This research identifies ferroptosis as a pivotal cell death pathway in mTHPC-PDT treated HNSCC. The ability of temoporfin to maintain efficacy across different oxygen tensions underscores its potential as a versatile clinical tool. Strategic modulation of ferroptotic sensitivity may further enhance the therapeutic outcomes of PDT in patients with advanced or hypoxic head and neck tumors.

This study was supported by Ministry of Science and Technology (MOST), and China Medical University, Taiwan. We acknowledge the core facilities for their assistance with flow cytometry and imaging.