Abstract 494: Tumor ascorbate content is associated with extended disease-free survival and decreased hypoxia-inducible factor-1 activation in patients with colorectal cancer

Abstract

Abstract Ascorbate (vitamin C) is a specific cofactor for a range of dioxygenase enzymes, including those involved in histone and DNA demethylation and also the enzymes that ‘switch off’ hypoxia-inducible factor (HIF)-1. These processes have to potential to influence tumor biology, where inadequate intracellular ascorbate levels may contribute to tumor progression and an over-active HIF-1 survival response. We previously demonstrated an association between low ascorbate levels and high HIF-1 activation in clinical samples from patients with endometrial cancer. In order to determine whether this is a universal phenomenon, we have now proceeded to a second cancer type, colorectal cancer. Clinical, pathological and follow-up data, as well as samples of tumor and adjacent normal tissue, were collected from 50 consenting colorectal cancer patients. Protein levels of HIF-1α and three pro-survival target gene products, Bcl-2/adenovirus E1B 19 kDa interacting protein 3 (BNIP3), glucose transporter 1 (GLUT-1) and VEGF, were measured by Western blot or ELISA and related to the tumor ascorbate content. HIF-1α, BNIP3 and VEGF protein levels were all elevated in tumor compared to adjacent normal tissue (p<0.01), while ascorbate levels were lower in tumor tissue (p<0.001). There was a significant inverse relationship between the tumor ascorbate content and HIF-1 pathway activation (p=0.002) and tumor size (p=0.018). High grade tumors had up to 40% less ascorbate than adjacent normal tissue and also compared to low grade tumors. Patients with tumors containing low ascorbate had significantly shorter disease-free survival than patients with high levels of ascorbate in their tumors (p=0.04). The ability of tumors to accumulate ascorbate, according to the ratio of ascorbate in tumor compared to paired normal tissue, also tended to be associated with disease-free survival (p=0.08). Levels of ascorbate in normal tissue were not associated with disease-free survival (p=0.614). This is the first report demonstrating a relationship between ascorbate levels in human tumors and patient survival. This relationship may rely on the ability of ascorbate to promote dioxygenase activity and dampen the HIF survival response, as this is the second tumor type where low cellular ascorbate levels were associated with increased HIF-1 activation. An intervention clinical trial is now warranted to determine if tumor levels of ascorbate can be manipulated. Citation Format: Caroline Kuiper, Gabi Dachs, Margaret Currie, John Pearson, Delwyn Munn, Margreet Vissers. Tumor ascorbate content is associated with extended disease-free survival and decreased hypoxia-inducible factor-1 activation in patients with colorectal cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 494. doi:10.1158/1538-7445.AM2014-494