Effects of hypericin and a chlorin based photosensitizer alone or in combination in squamous cell carcinoma cells in the dark

SummaryIntroductionThe toxic influence of photosensitizers in the dark is poorly investigated. In our study we used the photosensitizers liposomal meso-tetrahydroxyphenyl chlorin derivative (Foslipos®) and hypericin as well as their 1:1 combination on two different head and neck squamous cell carcinoma (HNSCC) cell lines (UMB-SCC 745 and UMB-SCC 969).Materials and methodsWe examined uptake, efflux and localization of the photosensitizers with confocal microscopy. Fluorescence quantification was measured with a micro-plate spectrometer. Special interest was given to effects on cell proliferation (BrdU proliferation assay), RNA quality (Bioanalyzer measurements) and DNA damage (comet assays) in the dark.ResultsFoslipos® uptake was linear over time and its efflux was not achieved even after 24 h while uptake of hypericin reached a plateau after 5 h and was almost eliminated after 24 h. Localization of Foslipos® was organelle-unspecific. Hypericin was found mainly at membranes and in trans-golgi network. Foslipos® treated cells showed cell toxicity for the highest concentration (10 μg/mL). In contrast, hypericin was toxic for all concentrations (10–0.6 μg/mL). The photosensitizer combination was non-toxic for all concentrations (10–0.6 μg/mL). No changes in RNA quality were monitored. Initial DNA damage was found only in hypericin treated UMB-SCC 745, which recovered after 3 h. No significant DNA damage was found for UMB-SCC 969.ConclusionOur data shows that the combinatorial application decrease photosensitizer toxicity, which can be advantageous in PDT treatments.