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

Abstract

Introduction: The 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 methods: We 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.

Results: Foslipos(®) 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 3h. No significant DNA damage was found for UMB-SCC 969.

Conclusion: Our data shows that the combinatorial application decrease photosensitizer toxicity, which can be advantageous in PDT treatments.