Preclinical analysis of sodium valproate for the treatment of pediatric diffuse intrinsic pontine glioma and adult glioblastoma

Epigenetic dysregulation is evident in high grade glioma, particularly diffuse intrinsic pontine glioma (DIPG), which often present with histone mutations and 46% of adult glioblastomas (GBM) harbour at least one mutation of an epigenetic regulator. Cell viability assays were used to investigate the effects of sodium valproate (VPA) on five ex vivo DIPG cell lines, three commercial glioblastoma cell lines and two ex vivo GBM cell lines and determine the IC50 dose. Cytotoxic IC50s range from 1.8-10mM after a 72 hour drug exposure. To examine the mechanism of cell death caused by VPA, Annexin V and 7-AAD positivity was analysed by flow cytometry. In DIPG cells, sodium valproate induced apoptosis, further confirmed by the presence of cleaved caspase 3 and PARP as determined by western blotting. Clonogenic capacity of glioma cells post VPA treatment was assessed by colony formation assays using one GBM and one DIPG cell line. According to published data, 15% of VPA serum levels can be achieved in the brain by systemic delivery. Therefore, to achieve significant glioma cytotoxicity clinically, other methods of drug delivery may be required. As such, ongoing preclinical in vivo work is underway to assess the effects of VPA when delivered directly to the brain of Wistar rats by convection enhanced delivery (CED). To summarise, the histone deacetylase inhibitor sodium valproate, causes glioma cytotoxicity in both pediatric DIPG cells and adult glioblastoma stem cell lines in vitro. DIPG cell death was a result of apoptosis and VPA reduced the long-term proliferation of both DIPG and GBM cells. Initial, in vivo work has demonstrated that VPA can feasibly be delivered by CED to the brain of Wistar rats at high concentration. Further work is needed to determine the efficacy of sodium valproate when delivered by CED to a relevant orthotopic glioma model.