Studies on Radiosensitization with mycosporine-like amino acids and aromatic amino acids

Abstract

Mycosporine-like amino acids (MAAs) is a generic name for compounds with cyclohexenone or cycloheximine rings. MAAs absorb UV radiation and dissipate it as heat; thus, they exhibit antioxidant activity. Radiodynamic therapy (RDT) is a treatment modality that combines radiotherapy with a sensitizer to augment therapeutic effects. RDT is based on chemicals that produce reactive oxygen species (ROS) under X-ray irradiation. Recently, several radiosensitizers are being developed and characterized as producers of ROS under UV irradiation. Therefore, in this study, we focused on MAAs as radiosensitizers, and evaluated ROS production from MAAs and aromatic amino acids under X-ray and UV irradiation. Aromatic amino acids were selected because they have structures similar to those of MAAs. MAAs showed radical scavenging abilities but did not produce ROS under X-ray and UV irradiation. The fact that MAAs did not function as ROS producers under X-ray irradiation indicates that they are not suitable for RDT applications; however, because they did not produce ROS under UV irradiation, they might be important for application in the production of cosmetics. Surprisingly, histidine produced hydroxyl radicals and superoxide anions under UV and X-ray irradiations. Thus, the present study provides a paradigm for identifying compounds that can effectively enhance RDT.