Vitamin C promotes decitabine or azacytidine induced DNA hydroxymethylation and subsequent reactivation of the epigenetically silenced tumour suppressor CDKN1A in colon cancer cells

Abstract

Epigenetic silencing of tumour suppressor genes is a key hallmark of colorectal carcinogenesis. Despite this, the therapeutic potential of epigenetic agents capable of reactivating these silenced genes remains relatively unexplored. Evidence has shown the dietary antioxidant vitamin C (ascorbate) acts as an inducer of the ten-eleven translocation (TET) dioxygenases, an enzyme family that catalyses a recently described mechanism of DNA demethylation linked to gene re-expression. In this study, we set out to determine whether vitamin C can enhance the known anti-neoplastic actions of the DNA-demethylating agents decitabine (DAC) and azacytidine (AZA) in colorectal cancer cells. Administration of vitamin C alone significantly enhanced global levels of 5-hydroxymethyl-2’-deoxycytidine (5-hmdC), without altering 5-methyl-2’-deoxycytidine (5-mdC), as would be expected upon the activation of TET dioxygenases. Concomitant treatment of vitamin C with either AZA or DAC resulted in an unexpectedly high increase of global 5-hmdC levels, one that administration of any these compounds alone could not achieve. Notably, this was also accompanied by increased expression of the tumour suppressor p21 (CDKN1A), and a significant increase in apoptotic cell induction. Our in vitro data leads us to hypothesize that the reactivation of genes in colorectal cancer cells by AZA or DAC can be improved when the 5-hmdC levels are simultaneously increased by the TET activator vitamin C. The dual administration of demethylating agents and vitamin C to colorectal cancer patients, a demographic in which vitamin C deficiencies are common, may improve responses to epigenetic therapies.

Vitamin C in combination with inhibition of mutant IDH1 synergistically activates TET enzymes and epigenetically modulates gene silencing in colon cancer cells

“…The IDH1 +/+ cells exhibited increased 5-hmdC/dC levels after 48 h treatment with VC in a concentration-dependent manner. Differences were significant at 10 µM VC and reached maximal at 1 mM VC (Figure 3(a)), which is consistent with a previous report [36]. However, in IDH1 R132H/+ cells VC incubation only slightly increased 5-hmdC/dC levels, but not in a significant manner.…”

“…For these tumours, IDH mutations have become a target for novel therapeutic approaches including the use of hypomethylating agentsi.e., DNMT inhibitors or enhancers of TET enzyme activityand inhibitors of mutant IDH enzymes [36,37]. Although the hypomethylating agents like decitabine or 5-azacytidine were originally developed as cytostatic agents for leukaemia chemotherapy, their epigenetic properties have since been revealed to play an important role in their anti-cancer activity [38][39][40][41][42].…”

Dietary antioxidants remodel DNA methylation patterns in chronic disease

“…A positive correlation between plasma concentration of vitamin C and hydroxymethylation of leukocyte DNA was further observed in patients with inflammatory bowel disease, adenomatous polyps and colorectal cancer (Starczak et al, ). Additionally, vitamin C was found to increase the efficacy of DNA demethylating agents, such as decitabine (DAC) and azacytidine (AZA), that work through inhibition of DNMTs (Gerecke et al, ). Combination treatment of vitamin C with these DNMT inhibitors (DNMTi) reactivated tumour suppressor genes, for example, p21 in colon cancer and hepatocellular carcinoma (HCC) cells, through targeting both DNA methylation and demethylation mechanisms (Gerecke et al, ).…”

“…Additionally, vitamin C was found to increase the efficacy of DNA demethylating agents, such as decitabine (DAC) and azacytidine (AZA), that work through inhibition of DNMTs (Gerecke et al, ). Combination treatment of vitamin C with these DNMT inhibitors (DNMTi) reactivated tumour suppressor genes, for example, p21 in colon cancer and hepatocellular carcinoma (HCC) cells, through targeting both DNA methylation and demethylation mechanisms (Gerecke et al, ).…”

“…azacytidine (AZA), that work through inhibition of DNMTs (Gerecke et al, 2018). Combination treatment of vitamin C with these DNMT inhibitors (DNMTi) reactivated tumour suppressor genes, for example,…”