**4.1 Hypericin differentiating neurons and glioma cell lines in vitro**

For selective PDT it would be advantageous when the PS enriches in the malignant cells more compared to neurons or glial cells. In 2005 we investigated eight human glioma cell lines (L; LN-18,LN-229, U87MG, U373MG, D247MG, U251MG, U251MG,T98G) and twelve primary human glioma cell cultures (P) and compared the hypericin uptake with human astrocytes (AC; SV-FHAS) and cerebellar granule neurons (N) prepared from 8-day-old Sprague-Dawley rat pups (Charles River, Sulzfeld, Germany). Long term glioma cell lines and primary human glioma cell cultures showed significant higher hypericin uptake compared to neurons. Hypericin uptake in astrocytes was higher compared to glioma cells and to neurons.(Ritz et al. 2005) Another investigation done by fluorescence microscopy showed that hypericin was predominately localized in the glial envelope surrounding the neuron in a model with crayfish neuron and surrounding glia. Uzdensky et al. found a minor fraction of hypericin in the neuron compared to the glia in this model.(Uzdensky et al. 2003)
