Fig. 1

Pretreatment with 5-azanucleosides enhances the cytotoxicity of topoisomerase inhibitors in CRC cells. a Treatment scheme for short-term experiments. b Cell viability of HCT116, DLD-1, and HT-29 cells after exposure to 1 μM 5-aza-dC (n ≥ 14) or 4 μM 5-aza-C (n ≥ 8) alone. c Cell viability of HCT116 and DLD-1 cells after sequential treatments with 5-azanucleosides (1 μM 5-aza-dC or 4 μM 5-aza-C) and topoisomerase inhibitors (5–75 μM irinotecan or 5–50 μM etoposide). Data are presented as means ± SD normalized to untreated control. *P < 0.05 compared with DNA demethylating agent treatment group and topoisomerase inhibitor treatment group. Irin - irinotecan, eto - etoposide, dox - doxorubicin, mit - mitoxantrone