Ascorbate availability affects tumor implantation-take rate and increases tumor rejection in Gulo–/– mice

Abstract

In solid tumors, HIF1 upregulates the expression of hundreds of genes involved in cell survival, tumor growth, and adaptation to the hypoxic microenvironment. HIF1 stabilization and activity are suppressed by prolyl and asparagine hydroxylases, which require oxygen as a substrate and ascorbate as a cofactor. This has led us to hypothesize that intracellular ascorbate availability could modify the hypoxic HIF1 response and influence tumor growth. In this study, we investigated the effect of variable intracellular ascorbate levels on HIF1 induction in cancer cells in vitro, and on tumor-take rate and growth in the Gulo−/− mouse. These mice depend on dietary ascorbate, and were supplemented with 3,300 mg/L, 330 mg/L, or 33 mg/L ascorbate in their drinking water, resulting in saturating, medium, or low plasma and tissue ascorbate levels, respectively. In Lewis lung carcinoma cells (LL/2) in culture, optimal ascorbate supplementation reduced HIF1 accumulation under physiological but not pathological hypoxia. LL/2, B16-F10 melanoma, or CMT-93 colorectal cancer cells were implanted subcutaneously into Gulo−/− mice at a range of cell inocula. Establishment of B16-F10 tumors in mice supplemented with 3,300 mg/L ascorbate required an increased number of cancer cells to initiate tumor growth compared with the number of cells required in mice on suboptimal ascorbate intake. Elevated ascorbate intake was also associated with decreased tumor ascorbate levels and a reduction in HIF1α expression and transcriptional activity. Following initial growth, all CMT-93 tumors regressed spontaneously, but mice supplemented with 33 mg/L ascorbate had lower plasma ascorbate levels and grew larger tumors than optimally supplemented mice. The data from this study indicate that improved ascorbate intake is consistent with increased intracellular ascorbate levels, reduced HIF1 activity and reduced tumor initiation and growth, and this may be advantageous in the management of cancer.

Potential Mechanisms of Action for Vitamin C in Cancer: Reviewing the Evidence

“…The co-factor role is specific to ascorbate ( Myllyla et al, 1978 ), which is structurally specific for the hydroxylase active site ( Kaczmarek et al, 2009 ). When cells are deficient in ascorbate, HIF hydroxylase activity is compromised and HIF transcription activity is increased, particularly in response to conditions of mild or moderate hypoxia ( Knowles et al, 2003 ; Vissers et al, 2007 ; Kuiper et al, 2014a ; Campbell et al, 2016a ). These observations have led to the hypothesis that increasing ascorbate supply to cancer cells could stimulate the activity of the HIF hydroxylases and decrease the activation of the HIFs, thereby slowing tumor growth rates.…”

“…There is a growing body of evidence consistent with this hypothesis. Investigations with the vitamin C-dependent Gulo -/- mouse have indicated a strong association between tumor ascorbate content, HIF activation and tumor growth in vivo following variable dietary intake or intra-peritoneal injection of pharmacological ascorbate ( Campbell et al, 2015 , 2016a ). The daily administration of high dose vitamin C to tumor-bearing Gulo -/- mice indicated that HIF-1 transcriptional activity was depressed in association with ascorbate uptake.…”

Intravenous Vitamin C for Cancer Therapy – Identifying the Current Gaps in Our Knowledge

“…Because of the pleiotropic functions of vitamin C, optimizing its levels in the body through diet and supplementation is likely to be of benefit to oncology patients. In support of this premise, studies in a vitamin C-requiring mouse model indicate that oral vitamin C supplementation of these animals can impair the development of tumors and can also increase the rejection rate of implanted tumor cells ( Campbell et al, 2016a ; Cha et al, 2016 ). This suggests an important role for vitamin C in host defense against cancer.…”

Ascorbic acid induces global epigenetic reprogramming to promote meiotic maturation and developmental competence of porcine oocytes

“…Subgroup III, the Jumonji C (JmjC) domain containing histone lysine demethylases (JmjC-KDMs), erases the methyl group on lysine residues of histones 12 . Subgroup IV, the hypoxia-inducible factor (HIF) hydroxylases, catalyzes hydroxylation on specific proline and asparagine residues of the transcription factor HIF-1α 13 . Studies confirmed that ascorbic acid regulates Tet, JmjC domain containing enzymes and HIF hydroxylases, to modulate dynamically the epigenetic status of DNA/histone methylation and HIF-1α activity 6 , 9 , 12 – 14 .…”