Epigenetic priming sensitizes gastric cancer cells to irinotecan and cisplatin by restoring multiple pathways.

ABSTRACT

BACKGROUND: Gastric cancer is heavily influenced by aberrant DNA methylation that alters multiple cancer-related pathways, and may respond to DNA demethylating agents, such as 5-aza-2'-deoxycytidine (5-aza-dC). Here, we aimed to analyze whether 5-aza-dC can sensitize gastric cancer cells to clinically used cytotoxic drugs. METHODS: Ten gastric cancer cell lines were treated with 5-aza-dC for 72 h and their growth was analyzed by conducting WST assay. In vivo effect of the drugs was analyzed using xenografts of OCUM-2 M/SN38 cells. Genome-wide expression and DNA methylation analyses were conducted using microarrays, and biological functions were identified through ingenuity pathway analysis. RESULTS: The cell lines most resistant to SN38 (an active metabolite of irinotecan), CDDP, PTX, and 5-FU, were identified. 5-Aza-dC pre-treatment of the resistant cell lines decreased the IC50 values for SN38 (TMK1, 226.4 nM to 32.91 nM; 44As3, 128.2 nM to 19.32 nM; OCUM2 M/SN38, 74.43 nM to 16.47 nM) and CDDP (TMK1, 5.05 µM to 2.26 µM; OCUM2 M, 10.79 µM to 2.77 µM), but not PTX and 5-FU. The reactivation of apoptosis-related genes, such as RUNX3, PYCARD, TNF, FAS, and FASLG, was induced by pre-treatment with 5-aza-dC, and the DNA demethylation of promoter CpG islands of RUNX3 and PYCARD was confirmed. In a xenograft model with OCUM2 M/SN38, treatment with 5-aza-dC before irinotecan showed markedly enhanced tumor suppression. CONCLUSION: Epigenetic priming with 5-aza-dC can improve the sensitivity of gastric cancer cells to SN38 and CDDP.