Efficacy of ultra short sub-30 minute incubation of 5-aminolevulinic acid photodynamic therapy in vitro

BACKGROUND AND OBJECTIVE The estimated incidence of cutaneous squamous cell carcinoma (SCC) is 700,000 cases per year. In the US, SCC incidence is highest among fair skinned adults older than 50 years of age. Thus, as the population ages, the reported number of SCCs will likely increase in the future. Photodynamic therapy (PDT) is an FDA approved therapy for treatment of actinic keratoses (AKs), a precursor to cutaneous SCC lesions. The FDA approved incubation time of the photosensitizing agent 5-aminolevulinic acid (ALA) is 14-18 hours. Recent studies have investigated short ALA incubation times of 1-3 hours with ALA and PDT demonstrating treatment success. Therefore, the question exists whether ALA incubation periods of less than 30 minutes are efficacious. Herein, we evaluate the efficacy of short ALA incubation periods by measuring apoptosis after 10, 15, and 20 minutes of ALA incubation. STUDY DESIGN/MATERIALS AND METHODS AG13145 normal human dermal fibroblasts HDFs were incubated with 10, 15, or 20 minute of ALA at various concentrations (0, 0.05, 0.075, 0.1, 0.25, 0.375, 0.5, 1, and 2 mM). After ALA incubation, samples were treated with 1,000 seconds (16 minutes 40 seconds) of Blu-U fluorescent blue light (417 ± 5 nm) for a fluence of 10 J/cm2 . Immediately following treatment with blue light, samples were collected and stained for apoptosis and necrosis with annexin-V and 7-aminoactinomycin D (7-AAD), and then analyzed by flow cytometry. RESULTS HDFs incubated with ALA for 10 minute at 36 °C followed by 10 J/cm2 of blue light had no statistically significant changes in apoptosis. HDFs incubated with ALA for 15 or 20 minutes at 36 °C followed by 10 J/cm2 of blue light had statistically significant increases in the percentages of cells positive for apoptosis in the 0.5, 1.0, and 2.0 mM ALA doses (P