gms | German Medical Science

Objective: ALA-PDT (delta-aminolevulinic acid supported photodynamic therapy) is a method under investigation for its benefit on survival in recurrent gliomas. Exact cellular mechanisms are not well understood so far. We investigated the mechanisms of damage and induction of apoptosis by photodynamic therapy in human ex-vivo samples and glioma cell-lines.

Methods: Samples of eight PDT treated glioblastoma patients were collected at the end of operation and paraffin-embedded for later investigation. Additionally, two glioma cell-lines, U373 and U87 were cultured to spheroids,treated by PDT and cut into frozen-sections. All cells were stained by HE (hematoxylin-eosin), for Ki67, caspase 3 and TUNEL (TdT-mediated dUTP-biotin nick end labeling) and evaluated by light and fluorescence microscopy. Additionally, survival data of patients included in this survey was analyzed.

Results: All in vivo samples were identified as glioblastoma tissue in HE and Ki67 staining; TUNEL staining was positive in all samples. 20 to 80 percent of cells were TUNEL positive indicating DNA-Fragmentation. ALA-PDT treated spheroids were highly TUNEL positive, whereas in native spheroids and those only treated with ALA without additional laser radiation only single cells were apoptotic. Caspase 3 remained negative in all investigated samples. At the time of this survey 5 out of 8 patients were still alive, 3 died with an average survival of 41.6 weeks after surgery.

Conclusions: DNA-Fragmentation seems to play a significant role in the mechanism of ALA-PDT. Whether this truly represents apoptosis remains to be clarified.