Disappointing results in the treatment of glioblastoma multiforme with surgery, radiation, and chemotherapy have fueled a search for new treatment modalities. Here we present the biologic effects of a glutathione-S transferase fusion protein of melanoma differentiation associated gene-7 (mda-7), GST-MDA-7 (1 nM; 30 nM), on cell survival and cell signaling in primary human glioma cells in vitro. GST-MDA-7, in a dose- and time-dependent fashion killed glioma cells with diverse genetic characteristics; 1 nM caused arrest without death whereas 30 nM caused arrest and killing after exposure. Combined inhibition of ERK1/2 and AKT function was required to enhance 1 nM GST-MDA-7 lethality in all cell types whereas combined activation of MEK1 and AKT was required to suppress 30 nM GST-MDA-7 lethality; both effects mediated in part by modulating JNK1-3 activity. The geldanamycin 17AAG inhibited AKT and ERK1/2 in GBM cells and enhanced GST-MDA-7 lethality. JNK1-3 signaling promoted BAX activation and mitochondrial dysfunction. In GBM6 cells GST-MDA-7 (30 nM) transiently activated p38 MAPK which was modestly protective against JNK1-3 -induced toxicity, whereas GST-MDA-7 (300 nM) caused prolonged intense p38 MAPK activation which promoted cell death. In GBM12 cells that express full length mutant activated ERBB1 inhibition of ERBB1 did not modify GST-MDA-7 lethality, however, in U118 established glioma cells, stable over-expression of wild type ERBB1 and/or truncated active ERBB1 vIII suppressed GST-MDA-7 lethality. Our data argue that combined inhibition of ERK1/2 and AKT function, regardless of genetic background, promotes MDA-7 lethality in human primary human glioma cells via JNK1-3 signaling and is likely to represent a more ubiquitous approach to enhancing MDA-7 toxicity in this cell type than inhibition of ERBB1 function.
99th AACR Annual Meeting-- Apr 12-16, 2008; San Diego, CA