Cell culture: Cell experiments were performed with the glioma cell line U-87 MG (ATCC HTB-14). Cells were grown in Eagle's Minimum Essential Medium (MEM, no glutamine and phenol red, Gibco™) supplemented with 10 % fetal calve serum (FCS), 1 % penicillin / streptomycin, 1 % L-glutamine and 1 % sodium pyruvate (all purchased from Gibco™). They were seeded with densities between 5000 cells/cm 2 and 20,000 cells/cm 2 and cultivated in glass-bottom cell culture dishes (Willco Wells, HBST-5040) for 24 h prior to further treatment. Cell culture dishes were equipped with glass coverslip bottoms of 170 µm thickness on average and coated with FCS to improve cell adherence. After 24 h, cells were mostly attached to the cell culture dish bottoms and used for hypericin incubation. Cultivation was accomplished at 37 °C and 5 % CO2 atmosphere.