Simultaneous Two-photon Excitation of Photofrin in Relation to Photodynamic Therapy

Abstract Photodynamic therapy (PDT), the use of light-activated drugs (photosensitizers), is an emerging treatment modality for tumors as well as various nononcologic conditions. Single-photon (1-γ) PDT is limited by low specificity of the photosensitizer, leading to damage to healthy tissue adjacent to the diseased target tissue. One solution is to use simultaneous two-photon (2-γ) excitation with ultrafast pulses of near-IR light. Due to the nonlinear interaction mechanism, 2-γ excitation with a focused beam is localized in three dimensions, allowing treatment volumes on the order of femtoliters. We propose that this will be valuable in PDT of age-related macular degeneration (AMD), which causes blindness due to abnormal choroidal neovasculature and which is currently treated by 1-γ PDT. Here, Photofrin has been used as the photosensitizer to demonstrate proof-of-principle of 2-γ killing of vascular endothelial cells in vitro. The 2-γ absorption properties of Photofrin were investigated in the 750–900 n...