Epileptic
seizures are among the presenting clinical signs of
malignant glioma patients, frequently necessitating treatment with
antiepileptic drugs (AEDs). The efficacy of 5-aminolevulinic
acid (5-ALA)-based intraoperative fluorescence-guided surgery and
photodynamic therapy (
PDT) in
glioblastoma multiforme (GBM) patients depends on the specific accumulation and total amount of intracellularly synthesized
protoporphyrin IX (
PpIX) in tumour cells. In this study, we investigated the effect of the AEDs
phenytoin (PHY) and
levetiracetam (LEVE) on 5-ALA-induced
PpIX accumulation in two
glioma cell lines (U373 MG and U-87 MG) and primary GBM cells isolated from a human biopsy.
After treatment with PHY and LEVE for three days cells were incubated with 1 mM: 5-ALA for 4 h and
PpIX accumulation was determined by fluorescence measurement. We observed a decrease in
PpIX synthesis of up to 55 ± 12 % in primary GBM cells after incubation with
phenytoin. This reduction was dose-dependent for all tested cell lines and primary GBM cells. LEVE on the other hand did not alter
PpIX concentration in GBM cells.
PDT was performed in vitro by irradiating the GBM cells with light doses from 0.5 to 10 J cm(-2) at 627 nm after AED and 5-ALA treatment. Although less
PpIX accumulated in PHY-treated cells, efficacy of
PDT was not affected. We assume that damage to the mitochondrial membrane by PHY inhibits
PpIX synthesis in vitro, because we showed
mitochondrial dysfunction as a result of reduced mitochondrial membrane potential in PHY-treated cells. No change in
glutathione status was observed. To evaluate further the effect of PHY on
PpIX fluorescence, and to establish its significance in clinical practice, animal and clinical studies are required, because the results presented here imply PHY may reduce intracellular accumulation of
PpIX in patients with high-grade
gliomas.