Caspase 8 is absent or low in many ex vivo gliomas

Better treatments are required urgently for patients with malignant glioma, which currently is incurable. Death ligands, such as tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), may offer promise for the treatment high-grade glioma if such ligands induce apoptotic signaling in vivo in glioma cells. Caspase 8 is required for death ligand signaling, and its levels may influence the sensitivity of glioma cells to death ligands. It also may act as a tumor suppressor protein. The authors analyzed caspase 8 expression levels in ex vivo glioma specimens and explored potential mechanisms of its regulation.

Eleven glioblastomas, 5 anaplastic astrocytomas, and 3 low-grade astrocytomas were studied. The levels of caspase 8, caspase 10, cellular FLICE inhibitory protein (c-FLIP), and signal transducer and activator of transcription (STAT)-1 were assayed using quantitative immunoblotting. Caspase 8 mRNA was measured by Northern blot analysis. The methylation status of the caspase 8 gene was determined by bisulfate modification of genomic DNA, cloning, and sequencing. Statistical analyses were performed using nonparametric (Spearman) correlations.

Some ex vivo glioma samples lacked detectable caspase 8, with many expressing barely detectable levels. No tumors expressed significant amounts of caspase 10 or c-FLIP. A strong association was found between caspase 8 mRNA and protein levels. Neither expression of the transcription factor STAT-1 nor caspase 8 gene methylation correlated with caspase 8 levels.

The absence of caspase 8 protein in many resected glioma samples implied that many patients with glioma may not benefit from death ligand-based treatments, unless caspase 8 (or caspase 10) protein expression can be elevated. Demethylating agents are unlikely to boost caspase 8 levels in glioma cells, but treatments that increase caspase 8 mRNA levels may up-regulate expression of the protein.