Vitamin C as an Epigenetic Therapeutic for Acute Myeloid Leukaemia

Acute myeloid leukaemia (AML) is a deadly disease characterised by the abnormal proliferation of immature blood cells in the bone marrow with a block in haematopoietic differentiation. The disease is heterogeneous, and genetic analysis has identified at least 11 different subgroups. Mutations in epigenetic enzymes occur commonly in AML and we now understand that epigenetic dysregulation is strongly implicated in the pathogenesis of the disease. For example, deletions and loss-of-function mutations in the epigenetic demethylase TET2 arise in approximately 10% of de novo AML cases. The discovery of mutations in epigenetic enzymes as drivers of AML opens a window of opportunity for the identification of small molecule therapeutics to reverse epigenetic dysfunction. Recent evidence has cast a spotlight on vitamin C as one potential epigenetic therapeutic through its action as a co-factor for the TET and histone lysine demethylase enzymes. I examined the epigenetic effects of vitamin C in AML, by using a SKM-1 myeloid leukaemia cell model characterised by a heterozygous loss-of-function mutation in TET2. Treatment with vitamin C decreased SKM-1 proliferation in vitro and promoted differentiation towards a more mature cell phenotype. Unexpectedly, vitamin C also inhibited the proliferation of NB4 and K562 cells, both leukaemia cell lines without TET2 mutations. My research shows that vitamin C can act via at least two separate mechanisms to decrease the proliferation of leukaemia cells in vitro. One mechanism likely involves the generation of hydrogen peroxide causing cell death, and in the SKM-1 cells this mechanism was inhibited by catalase or by the substitution of ascorbate with phosphoascorbate, a redox stable alternative. The second mechanism was independent of hydrogen peroxide and caused decreased cellular proliferation. The increased activity of TET2 following vitamin C administration may play a role in the decrease in SKM-1 cell growth. This is because the changes in cellular surface antigen expression observed after treatment with vitamin C reflect the pattern observed in other studies following TET2 reactivation. Combination treatments are the cornerstone for successful therapy in AML. Thus, vitamin C is likely to be most effective in AML as an adjunct therapy. For this reason, it is important to understand how vitamin C affects the activity of other therapeutics such as the anti-cancer drug Prima-1Met. Prima-1Met is a novel compound with the potential to reactivate mutant p53 and cause cancer cell death through oxidative stress mechanisms. The drug’s mechanisms of action are significant given that TP53 mutations are associated with a dismal prognosis in AML. I show that vitamin C does not appear to counteract the effects of Prima-1Met in the SKM-1 model. These results support the growing body of literature highlighting vitamin C’s potential as an epigenetic therapeutic in AML