Pretreatment with 5-azacytidine increases global 5-hmC levels and platinum sensitivity. A, 5-hmC immunoblot and quantification of 5-hmC levels in A2780Res, CaOV3, OVCAR4, OVSAHO tumor lines treated for 72 hours with 5-azacytidine (5-aza). Methylene blue staining was used as a DNA loading control. Pretreatment with 5-aza significantly increases 5-hmC levels at all concentrations when compared with untreated (NT) controls in the tested cancer cell lines (*, P < 0.05; **, P < 0.01; ***, P < 0.001). B, The platinum sensitivity of ovarian cancer cell lines increases following pretreatment with 5-aza as shown by MTT analysis. Tumor lines, which were treated for 72 hours with 5, 10, or 20 μmol/L 5-aza followed by CDDP therapy, show statistically significant increases in CDDP IC50 values (*, P < 0.05; **, P < 0.01; ***, P < 0.001).