Possible Mechanisms of Resistance Development to Photodynamic Therapy (PDT) In Vulvar Cancer Cells

Photodynamic therapy (PDT) is a low-invasive treatment method that can be used to treat VIN patients. A photosensitizer (PS) applied to a patient is activated with use of the appropriate wavelength of light, which in an oxygen environment leads to the formation of a reactive oxygen species (ROS) that destroys the tumor. However, cells can protect themselves against these cytotoxic products by increasing their antioxidant mechanisms and repair capacity. Changes in the cytoskeleton may also influence resistance to PDT. Our results revealed that PDT-resistant cells changed the amount of ROS. Cells resistant to PDT A-431 exhibited a decreased ROS level and showed higher viability after oxidizing agent treatment. Resistant Cal-39 cells exhibited a decreased O₂^- level but increased other ROS. This provides protection from PDT but not from other oxidizing agents. Moreover, PDT leads to alterations in the cytoskeleton that may result in an epithelial-mesenchymal transition (EMT) or increased adhesion. Both EMT and cell adhesion may activate signaling pathways involved in survival. This means that resistance to PDT in vulvar cancer may be at least in part a result of changes in ROS level and alterations in the cytoskeleton.