Temperature-dependent impact of thermal aminolaevulinic acid photodynamic therapy on apoptosis and reactive oxygen species generation in human dermal fibroblasts

Summary Background Actinic keratoses (AKs) are generally accepted as common precursor lesions to invasive squamous cell carcinoma. Photodynamic therapy (PDT) is a common, in‐office, field therapy modality used in the treatment of AKs. Clinical and laboratory observations have demonstrated that temperature modulation can affect PDT efficacy. Objectives To demonstrate thermal PDT increases apoptotic cell death, and to investigate the mechanistic role of reactive oxygen species (ROS) free radicals in an in vitro human skin fibroblast model. Methods This study was completed using commercially available primary human skin fibroblasts treated with aminolaevulinic acid (ALA) at specific concentrations and controlled temperatures. Cell death, apoptosis and superoxide ROS levels were quantified. Results We found that thermal PDT with 0·5 mmol L−1 ALA resulted in significant temperature‐dependent increases in total apoptosis and superoxide ROS generation between 33 °C and 42 °C. Conclusions Our results indicate that thermal PDT significantly increases apoptotic cell death through increased generation of superoxide ROS in a temperature‐dependent manner. What's already known about this topic? Actinic keratoses (AKs) are generally accepted as common precursor lesions to invasive squamous cell carcinoma. Photodynamic therapy (PDT) is a common field therapy modality used in the treatment of AKs. Clinical and laboratory observations have demonstrated that thermal modulation can affect PDT efficacy. The underlying mechanism and cellular effects of thermal PDT are not well characterized from a temporal and biochemical perspective. What does this study add? Our findings demonstrate that thermal PDT increases, in a temperature‐dependent manner, superoxide reactive oxygen species generation and percentage of apoptosis‐positive cells. Temperature‐modulated PDT may represent an enhanced and cost‐effective modality to improve patient compliance and outcomes. Further in vitro, animal and clinical studies are needed to optimize treatment parameters. What is the translational message? We demonstrate that thermal PDT increases superoxide reactive oxygen species generation and percentage of apoptosis‐positive cells in a temperature‐dependent manner. Temperature‐modulated PDT may represent an enhanced and cost‐effective modality to improve patient compliance and outcomes. Clinical studies are needed to optimize dosing, incubation period and clinical outcomes. We hypothesize that our fi