Salivary Histatin-5 Holds Promising Applications in Oral Cancer Photodynamic Therapy

Objectives: Oral Squamous Cell Carcinoma (OSCC) is a common and aggressive type of head and neck cancer with a high death rate. Photodynamic therapy (PDT) is an encouraging method for treating cancer. PDT uses a photosensitizer (PS) that is activated by specific light wavelengths and leads to the production of reactive oxygen species (ROS), which in turn causes the death of cancer cells. The objective of this study is to examine if salivary peptides RR14 and DR9/2RR14, and histatin-5 (Hst5) protein, which is normally found in human saliva and has known antifungal properties, can improve the effectiveness of PDT against OSCC.
Methods: Human gingival fibroblasts (FGH) and squamous cell carcinoma (SCC-25) cells were subjected to treatment with toluidine blue O (TBO) and Hst5, both separately and together. Subsequently, they were exposed to red light in order to stimulate the production of ROS. Cell viability was determined by employing alamarBlue™ and MTT assays, while the potential effectiveness of the treatment was evaluated by monitoring ROS generation and TBO photobleaching.
Results: The findings indicated that the joint utilization of Hst5 and TBO substantially augmented the generation of ROS in comparison to the use of TBO alone. Nevertheless, the combined therapy resulted in decreased cell mortality, indicating that Hst5 has a dual function as both a pro-oxidant and an antioxidant. To confirm this dichotomy, experiments involving UV-C exposure have demonstrated that Hst5 has a protective effect against cell death caused by ROS.
Conclusions: Our findings ultimately suggest that Hst5 enhances ROS production in PDT, making it a suitable enhancer for photosensitizing agents utilized in antineoplastic PDT. Aditionally, Hst5 acts as a potent antioxidant in the presence of cancer cells, which holds promise for limiting the cytotoxicity of PDT to the adjacent healthy oral mucosal tissue during oral cancer photodynamic treatment.