Hypericin activated by an incoherent light source has photodynamic effects on esophageal cancer cells

Background and aims: Photodynamic therapy (PDT) is a new treatment modality for early esophageal neoplasia. With two absorption maxima in the visible light range (550 and 588 nm) hypericin is a very promising photosensitizer for PDT with incoherent light sources. We studied the effects of photosensitizing hypericin in both primary cell cultures and cell lines (squamous: Kyse-140 and adenocarcinoma: OE-33) of human esophageal cancer using an incoherent white light source. Materials and methods: Esophageal cancer cells were preincubated (4-24 h) with hypericin (10 nM-1 μM) and then irradiated with a light energy dose of 30 J/cm². Results: Hypericin showed strong phototoxic effects and induced apoptosis in a dose-dependent fashion. The IC₅₀ value of hypericin phototoxicity was approximately 30 nM in both squamous and adenocarcinoma cells. In the concentrations used nonphotoactivated hypericin showed no toxic or apoptotic potency. The phototoxicity of hypericin was compared to that of δ-aminolevulinic acid (5-ALA), which is already being used for photodynamic therapy of gastrointestinal cancer. 5-ALA produced similar phototoxic effects but at a much higher dose (IC₅₀ 182± 8 μM in Kyse-140 and 308±40 μM in OE-33 cells). Moreover, 5-ALA did not induce apoptosis to a relevant extent. Conclusion: Hypericin is a very promising new photosensitizer for innovative photodynamic therapy of esophageal cancer. Both the well known clinical safety of hypericin and the lower costs of broad band light sources argue in favor of clinical trials.