title: Pharmacokinetic and anti-cancer properties of high dose ascorbate in solid tumours of ascorbate-dependent mice.
abstract: Despite recent evidence for an anti-tumour role for high-dose ascorbate, potential mechanisms of action are still unclear. At mM concentrations that are achieved with high-dose intravenous administration, autoxidation of ascorbate can generate cytotoxic levels of H2O2. Ascorbate is also a required co-factor for the hydroxylases that suppress the transcription factor hypoxia-inducible factor (HIF-1). HIF-1 supports an aggressive tumour phenotype and is associated with poor prognosis, and previous studies have shown that optimizing intracellular ascorbate levels down-regulates HIF-1 activation. In this study we have simultaneously measured ascorbate concentrations and the HIF-1 pathway activity in tumour tissue following high dose ascorbate administration, and have studied tumour growth and physiology. Gulo-/-mice, a model of the human ascorbate dependency condition, were implanted with syngeneic Lewis lung tumours, 1g/kg ascorbate was administered into the peritoneum, and ascorbate concentrations were monitored in plasma, liver and tumours. Ascorbate levels peaked within 30min, and although plasma and liver ascorbate returned to baseline within 16h, tumour levels remained elevated for 48h, possibly reflecting increased stability in the hypoxic tumour environment. The expression of HIF-1 and its target proteins was down-regulated with tumour ascorbate uptake. Elevated tumour ascorbate levels could be maintained with daily administration, and HIF-1 and vascular endothelial growth factor protein levels were reduced in these conditions. Increased tumour ascorbate was associated with slowed tumour growth, reduced tumour microvessel density and decreased hypoxia. Alternate day administration of ascorbate resulted in lower tumour levels and did not consistently decrease HIF-1 pathway activity. Levels of sodium-dependent vitamin C transporters 1 and 2 were not clearly associated with ascorbate accumulation by murine tumour cells in vitro or in vivo. Our results support the suppression of the hypoxic response by ascorbate as a plausible mechanism of action of its anti-tumour activity, and this may be useful in a clinical setting.
authors: Mackenzie Cancer Research Group, Department of Pathology, University of Otago, Christchurch 8011, New Zealand.
authors: Elizabeth J
authors: EJ
authors: Campbell
authors: Centre for Free Radical Research, Department of Pathology, University of Otago, Christchurch 8011, New Zealand.
authors: Margreet C M
authors: MCM
authors: Vissers
authors: Mackenzie Cancer Research Group, Department of Pathology, University of Otago, Christchurch 8011, New Zealand.
authors: Christina
authors: C
authors: Wohlrab
authors: Auckland Cancer Society Research Centre, University of Auckland, Auckland 1142, New Zealand.
authors: Kevin O
authors: KO
authors: Hicks
authors: Canterbury Regional Cancer and Haematology Service, Canterbury District Health Board, Christchurch 8011, New Zealand.
authors: R Matthew
authors: RM
authors: Strother
authors: Centre for Free Radical Research, Department of Pathology, University of Otago, Christchurch 8011, New Zealand.
authors: Stephanie M
authors: SM
authors: Bozonet
authors: Mackenzie Cancer Research Group, Department of Pathology, University of Otago, Christchurch 8011, New Zealand; Canterbury Regional Cancer and Haematology Service, Canterbury District Health Board, Christchurch 8011, New Zealand; Department of Medicine, University of Otago, Christchurch 8011, New Zealand.
authors: Bridget A
authors: BA
authors: Robinson
authors: Mackenzie Cancer Research Group, Department of Pathology, University of Otago, Christchurch 8011, New Zealand. Electronic address: gabi.dachs@otago.ac.nz.
authors: Gabi U
authors: GU
authors: Dachs
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000097:blood / Q000493:pharmacokinetics* / Q000494:pharmacology; D000975:Antioxidants / Q000378:metabolism / Q000493:pharmacokinetics* / Q000494:pharmacology; D001205:Ascorbic Acid / Q000097:blood / Q000493:pharmacokinetics* / Q000494:pharmacology; D018827:Carcinoma, Lewis Lung / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D004334:Drug Administration Schedule; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D007274:Injections, Intraperitoneal; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D015398:Signal Transduction; D060347:Sodium-Coupled Vitamin C Transporters / Q000235:genetics / Q000378:metabolism; D042461:Vascular Endothelial Growth Factor A / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D000975:Antioxidants; C497443:Hif1a protein, mouse; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D007527:Isoenzymes; D060347:Sodium-Coupled Vitamin C Transporters; D042461:Vascular Endothelial Growth Factor A; C467480:vascular endothelial growth factor A, mouse; D001205:Ascorbic Acid
keywords: Hypoxia-inducible factor-1; Lewis lung carcinoma; Mouse model; Pharmacokinetics; Vitamin C