Long-pulse dye laser for photodynamic therapy: investigations in vitro andin vivo

Background and Objective: Continuous wave lasers or incoherent lamps are us ed effectively for photodynamic therapy (PDT). As the mechanism of action o f pulsed lasers in PDT is not known, we investigated the efficacy of PDT wi th B-aminolevulinic acid (ALA) using a long-pulse (1.5 ms) tunable flashlam p-pumped pulsed dye laser (LPDL) in vitro and in vivo. Study Design/Materials and Methods: HaCaT human keratinocytes were incubate d with ALA (3 mmol/l) and irradiated (0-50 J/cm(2)) using the LPDL at 585 n m, 595 nm, or 600 nm vs. an incoherent light source (580-740 nm). Topical A LA-PDT was performed on 24 patients with actinic keratoses (AK) on the head (n = 200) after incubation with a 20% ALA emulsion and irradiation by eith er an incoherent light source (160 mW/cm(2), 60-160 J/cm(2)) or the LPDL (5 85 nm, 18 J/cm(2)). Results: Maximal cytotoxic effects in vitro were achieved using the LPDL at 585 nm or the incoherent lamp (50 J/cm(2)). Sodium azide, a quencher of si nglet oxygen, significantly reduced cell killing, suggesting that the cytot oxic effects are mainly mediated by singlet oxygen. This is supported by an increase of lipid peroxides as determined by malondialdehyde after adding D2O, Complete remission was achieved in 79% of 100 AK treated by ALA and th e LPDL and in 84% of 100 AK treated by ALA and the incoherent lamp. Pain du ring light treatment was significantly reduced by using the LPDL. Control l esions (LPDL without ALA) did not clear. Conclusion: These results show the in vitro and in vivo efficacy of ALA-PDT using a pulsed light source mediated by singlet oxygen. Lasers Surg. Med. 25:51-59, 1999. (C) 1999 Wiley-Liss, Inc.