CASP3 and central nervous system cancer: Conversely, increases in the caspase-3, 8 and 9 enzyme activities were identified in H2O2-treated C6 glioma cells and that were then blocked by the addition of quercetin, which resulted in the blocking of phosphorylated extracellular signal-regulated protein kinase (ERK) and p53 protein expressions induced by H2O2.