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

Abstract

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. Ten gastric cancer cell lines were treated with 5-aza-dC for 72h and their growth was analyzed by conducting WST assay. In vivo effect of the drugs was analyzed using xenografts of OCUM-2M/SN38 cells. Genome-wide expression and DNA methylation analyses were conducted using microarrays, and biological functions were identified through ingenuity pathway analysis. 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, 226.4nM to 32.91nM; 44As3, 128.2nM to 19.32nM; OCUM2M/SN38, 74.43nM to 16.47nM) and CDDP (TMK1, 5.05µM to 2.26µM; OCUM2M, 10.79µM to 2.77µM), 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 OCUM2M/SN38, treatment with 5-aza-dC before irinotecan showed markedly enhanced tumor suppression. Epigenetic priming with 5-aza-dC can improve the sensitivity of gastric cancer cells to SN38 and CDDP.