gms | German Medical Science

Objective: Despite aggressive therapy patients with Glioblastoma multiforme have a poor prognosis. Deregulation of the PI3-Kinase (PI3K) survival pathway via different mechanisms has been reported in a significant proportion of glioblastoma tumor samples and correlates with poor prognosis. Therefore, modulation of the PI3-K pathway seems to be a promising approach to target therapy resistance of glioblastoma.

Methods: To reverse drug resistance we targeted PI3K by using a PI3K class I specific as well as a classical broad range PI3K family inhibitor. Glioblastoma cell lines (U87MG, U138MG and U118MG) as well as primary cultured cells isolated from patients with glioblastoma were used. While apoptosis was measured by FACs analysis of propidium iodide-stained nuclei, DNA damage/repair (yH2AX positivity and comet assay) were determined by fluorescence microscopy followed by computer analysis. For in vivo experiments U87MG cells were stereotactically implanted into the right striatum of CD1-nude mice.

Results: Inhibition of PI3K significantly sensitized glioblastoma cells for apoptosis by various anticancer drugs, such as temozolomide and the topoisomerase II inhibitors doxorubicin and etoposide in a time- and dose-dependent manner. Analysis of the underlying molecular mechanisms revealed a differential response in the cells´ DNA damage/repair pathways. In particular, the total number and duration of yH2AX-foci positive cells upon treatment with doxorubicin were increased by up to 20% in the presence of the PI3-K inhibitor. These findings were confirmed by detailed analysis of DNA damage by the comet assay, here an increase in damage of 38% (after 12hrs) and 54% (after 18hrs) was observed by combinatorial treatment. Furthermore, an orthotopic tumor model in mouse was established to investigate the in vivo relevance of our findings.

Conclusions: By demonstrating that PI3K inhibitors enhance treatment-induced apoptosis in glioblastoma cells by interfering with the cell´s DNA damage/repair response, our findings have important implications for novel strategies in glioblastoma treatment. PI3K inhibitors represent a promising new partner for combinatorial treatment in glioblastoma.