Can vitamin C reduce metastasis in a mouse model of breast cancer?

Abstract

Ascorbate supplementation has been shown to reduce the aggressiveness of tumours in ascorbate-dependent Gulo-/- mice using both melanoma and lung cancer models. To date there is limited information on breast cancer growth and metastasis with ascorbate supplementation in these mice. Breast cancer is a major health concern worldwide. Metastatic disease is associated with poor prognosis therefore improved treatments are required. Ascorbate is a known co factor for the iron and 2-oxoglutarate dependant dioxygenases, such as prolyl hydroxylase domain, ten-eleven translocation and jumonji enzymes. These enzymes are involved in a number of cellular processes that reduce cancer growth, including control of hypoxia inducible factor (HIF)-1α stability and epigenetic modifications resulting in a global affect on gene expression. The tumour microenvironment enhances expression of tumour promoting genes, whereas ascorbate may dampen this response via increasing dioxygenase activity. It is therefore thought that ascorbate may be useful in normalising the tumour microenvironment leading to a less aggressive tumour phenotype. The aim of this study was to explore the relationship between ascorbate supplementation and metastasis using the Gulo-/- mouse model. Mice were implanted with EO771 mouse breast cancer cells, either orthotopically or subcutaneously (SC), and assigned to treatment groups; Control (200mg/L ascorbate), diet (3300mg/L ascorbate) or high dose vitamin C (1g/kg ascorbate IP injection). Ascorbate concentrations in plasma and tissues were measured using reverse phase high performance liquid chromatography. Hypoxia, HIF-1α, metalloproteinase-2 and N-cadherin were analysed in tumour and metastatic lesions using immunohistochemistry. Ascorbate supplementation had no affect on the exponential growth of tumours or the development of metastases in this model. Ascorbate concentration in tissues could be manipulated by both oral supplementation and injected ascorbate. IHC analysis showed no relationship between ascorbate supplementation and extent of hypoxia in tumour and metastasis tissue. SC implantation resulted in a higher incidence of metastasis compared to orthotopic implantation. Incidence of metastasis appeared to increase the longer cells were removed from growth media prior to implantation. The data from this study is different from previous studies which have shown that ascorbate supplementation slowed tumour growth, reduced tumour hypoxia and decreased HIF-1α protein. As a strong HIF response was not evident in the EO771 model, this model may not respond to ascorbate in the same way these other models do. This study suggests that a HIF response may be required for the benefit of ascorbate supplementation to be seen.