Objective: The loss of caspase-8 expression correlates with unfavorable survival outcomes in neuroblastoma (NB). Caspase-8 gene inactivation is caused by methylation. This study aimed to explore the effect of the demethylation agent 5-azacytidine on caspase-8 expression and whether 5-azacytidine can increase the sensitivity of chemotherapy drug doxorubicin to NB cells.
Methods: Caspase-8 mRNA expression in NB cell lines (SH-SY5Y cells) was examined by RT-PCR before and after 5-azacytidine treatment. Survival rates of SH-SY5Y cells were detected using MTT analysis and compared among the doxorubicin alone treatment, 5-azacytidine along with doxorubicin treatment, and caspase-8 inhibitor+5-azacytidine+doxorubicin treatment groups.
Results: Caspase-8 mRNA was not expressed in untreated SH-SY5Y cell lines. Caspase-8 mRNA expression in SH-SY5Y cells was detectable 3 days after 5-azacytidine treatment, and increased significantly 5 days after 5-azacytidine treatment (P < 0.05). Survival rates of SH-SY5Y cells treated with 5-azacytidine along with different concentrations of doxorubicin (0.05, 0.1,0.25, 0.5 microg/mL) were (77.61 +/- 7.30)%, (57.35 +/- 6.64)%, (46.25 +/- 4.46)% and (35.59 +/- 5.12)%, respectively, which were significantly lower than those treated with doxorubicin alone (94.89 +/- 4.15%, 80.60 +/- 8.50%, 64.48 +/- 4.92% and 52.32 +/- 6.71%) (P < 0.01). Caspase-8 inhibitor pretreatment resulted in an increased survival rate of SH-SY5Y cells (92.95 +/- 3.48%, 78.39 +/- 4.28 %, 62.31 +/- 6.50% and 49.92 +/- 5.77%) compared with the 5-azacytidine+doxorubicin treatment group.
Conclusions: 5-azacytidine may enhance anti-tumor efficacy of doxorubicin to NB cell lines, possibly through an up-regulation of caspase-8 mRNA expression.