In vitro and in vivo analysis in NIR-PDD combining multiphoton excitation and 5-ALA

Photodynamic Therapy (PDT) is one of the minimally invasive therapies for early stage of cancers. 5-Aminolevulinic acid (5-ALA) is a photosensitizer that is clinically used in PDT. In our country, 5-ALA has been approved and used as a photosensitizer for photodynamic diagnosis (PDD), but not for PDT. The conventional procedure of 5-ALA-PDT using visible light sources has problems with the spatial selectivity, specificity and penetration depth onto cancer cells in the tissue. To overcome this, we evaluated the phototoxicity in tumor cells under 5-ALA treatment by two-photon excitation for the indication expansion of PDD/PDT in in vitro condition. In this study, a gastric cancer cell line MKN74 treated with 5-ALA was microscopically irradiated with a near-infrared ultrafast pulse laser and assessed the cell viability. In the result, the florescence signal and cell death successfully occurred by two-photon excitation, but the photobleaching is significantly high in the areas where the cells survived. To improve the therapeutic efficiency, further optimization of laser parameters such as average power, pulse width, repetition rate, and the irradiation strategies in vitro and in vivo.