An epigenetic perspective on pharmacologic ascorbate in colon cancer

Abstract

AimThere is growing interest in pharmacologic ascorbate (Asc) and its therapeutic properties (Levine et al. Adv Nutr 2011;2:78). We examined cell viability, histone deacetylase (HDAC) expression, and related protein modifications in cancer versus noncancer colon epithelial cells following exposure to Asc.MethodsMTT assays were conducted in HCT116 colon cancer and CCD841 non‐transformed colonic epithelial cells treated with 0.25 to 16 mM Asc or ascorbate‐2‐phosphate (AAp), in the presence and absence of catalase (CAT, 280 U/mg), or with 5 to 160 μM H2O2. Cell lysates obtained 6 h and 24 h post‐treatment were immunoblotted as reported by Rajendran et al. Mol Cancer 2011;10:68.ResultsIn MTT assays, IC50 data were as follows: 8 mM Asc (CCD841); 3 mM Asc (HCT116), >;50mM AAp (HCT116), and 65 μM H2O2 (HCT116). CAT protected against both Asc‐ and H2O2‐ induced cytotoxicity. At 6 h, Asc and H2O2 altered the expression of HDACs (HDAC4, HDAC6, SIRT3) and enhanced the acetylation of histone (H3, H4) and non‐histone proteins (tubulin, p53).ConclusionsAsc was more cytotoxic to colon cancer cells than non‐cancer cells. Findings with the non‐H2O2 producing compound AAp, and with CAT, implicated H2O2 in Asc‐induced cytotoxicity. Asc was shown, for the first time, to alter epigenetic end‐points related to HDAC changes in colon cancer cells.Grant Funding Source: CA090890, CA090890, AT002034