Intracellular localisation of hypericin in human glioblastoma and carcinoma cell lines

Hypericin, a natural polycyclic quinone extracted from Hypericum perforatum, has been recently shown to be a powerful sensitiser for photodynamic therapy (PDT). However, its intracellular localisation remains unclear and contradictory. In the present work we compared the intracellular localisation of hypericin in three cultured cell lines (adenocarcinoma cells WiDr, carcinoma cells NHIK 3025 and glioblastoma cells D54Mg) with the distribution of fluorescent probes specific to lysosomes (LysoTracker Blue DND-22), mitochondria (MitoTracker Green FM) and endoplasmic reticulum (ERTracker Blue-White DPX). It was shown that the hypericin staining pattern was different compared to the intracellular distribution of mitochondria or lysosomes. Hypericin was concentrated in the perinucleolar cytoplasmic area mainly on one side of the nucleus--the region rich in endoplasmic reticulum and Golgi. Sometimes nuclear envelope was also stained. Plasma membrane was not stained but the dye was often accumulated in the intercellular space between the tightly contacting WiDr cells in colonies. Hypericin concentrations of 10 microM or less were not toxic for WiDr cells in the dark. Orange light (lambda max approximately 600 nm; 6 mW/cm2) killed the cells stained with 1 microM hypericin with LD50 approximately 1 J/cm2.