P03.04SENSITIZING GLIOBLASTOMA CELLS TO THERAPY BY TARGETING THE L-GLUTAMATE/L-CYSTINE ANTIPORTER SYSTEM XC-

Glutamate is the most prominent excitatory neurotransmitter of the brain. Due to its pivotal role, deregulations of the glutamate metabolism have been heavily implicated in various diseases of the CNS. System xc- (SXC), an L-cystine/L-Glutamate antiporter represents the primary non-vesicular route of glutamate release. SXC is upregulated under amino acid deprivation, xenobiotic exposure and oxidative stress. Since certain cancers seem to be unable to synthesise sufficient concentrations of L-cysteine, they depend on L-cystine influx by SXC activity, in order to uphold a sufficient Glutathione level. Glutathione is a neuroprotective peptide, known to be involved in removal of xenobiotics, such as chemotherapeutic drugs. L-cysteine is essential for its synthesis. SXC is highly expressed in Glioblastoma Multiforme (GBM), which is known to be the most common type of brain malignancy and also the most aggressive one, with a median survival of only 14 months. While the incidence only lays around 18.71 in 100.000, they do account for 2.3 % of all cancer-related deaths. Recurrence, due to resistant tumour cells, is one of the main reasons for the poor survival. Therefore, targeting SXC might sensitize the tumour to conventional therapy. In my project, I am investigating expression of SXC in GBM -in surgical specimen and patient derived cell lines- and the effect of Sulfasalazine (SSZ) on viability and SXC expression. SSZ is a FDA-approved SXC antagonist, commonly used in inflammatory bowel diseases. In order to analyse the expression of SXC, different methods were carried out, such as immunostaining, flow cytometry, western blotting and quantitative PCR. Since my results supported the evidence of expression of SXC, cell lines were treated in vitro with either SSZ or Temozolomide alone or concomitantly. Results showed that concomitant treatment resulted in a continuous decrease in viability over the course of 30 days. Survival was significantly decreased when compared to control, SSZ or TMZ alone, where a rescue effect could be observed. In conclusion, the evidence shows a strong correlation between prolonged survival and concomitant use of SSZ and TMZ, thusly strongly suggesting a heightened sensitivity towards therapeutic means conveyed by blocking of the system xc- antiporter. Thusly, pharmacokinetics of SSZ have been analysed in order to assess whether the drug or its metabolites successfully cross the blood brain barrier. In future work the efficacy of combined treatment with SSZ and temozolomide will be evaluated in vivo in order to indicate whether there would be any clinical utility.