BACKGROUND:Hypoxia inducible factor-1 alpha (HIF-1α) is thought to play a role in melanoma carcinogenesis. Posttranslational regulation of HIF-1α is dependent on Prolyl hydroxylase (PHD 1-3) and Factor Inhibiting HIF (FIH) hydroxylase enzymes, which require ascorbic acid as a co-factor for optimal function. Depleted intra-tumoral ascorbic acid may thus play a role in the loss of HIF-1α regulation in melanoma. These studies assess the ability of ascorbic acid to reduce HIF-1α protein and transcriptional activity in metastatic melanoma and reduce its invasive potential.

METHODS:HIF-1α protein was evaluated by western blot, while transcriptional activity was measured by HIF-1 HRE-luciferase reporter gene activity. Melanoma cells were treated with ascorbic acid (AA) and ascorbate 2-phosphate (A2P) to assess their ability to reduce HIF-1α accumulation and activity. siRNA was used to deplete cellular PHD2 in order to evaluate this effect on AA's ability to lower HIF-1α levels. A2P's effect on invasive activity was measured by the Matrigel invasion assay. Data was analyzed by One-way ANOVA with Tukey's multiple comparisons test, or Student-T test as appropriate, with p < .05 considered significant.

RESULTS:Supplementation with both AA and A2P antagonized normoxic as well as cobalt chloride- and PHD inhibitor ethyl 3, 4-dihydroxybenzoate induced HIF-1α protein stabilization and transcriptional activity. Knockdown of the PHD2 isoform with siRNA did not impede the ability of AA to reduce normoxic HIF-1α protein. Additionally, reducing HIF-1α levels with A2P resulted in a significant reduction in the ability of the melanoma cells to invade through Matrigel.

CONCLUSION:These studies suggest a positive role for AA in regulating HIF-1α in melanoma by demonstrating that supplementation with either AA, or its oxidation-resistant analog A2P, effectively reduces HIF-1α protein and transcriptional activity in metastatic melanoma cells. Our data, while supporting the function of AA as a necessary cofactor for PHD and likely FIH activity, also suggests a potential non-PHD/FIH role for AA in HIF-1α regulation by its continued ability to reduce HIF-1α in the presence of PHD inhibition. The use of the oxidation-resistant AA analog, A2P, to reduce the ability of HIF-1α to promote malignant progression in melanoma cells and enhance their response to therapy warrants further investigation.

INTRODUCTION:Accumulation of hypoxia inducible factor-1 alpha (HIF-1α) in malignant tissue is known to contribute to oncogenic progression and is inversely associated with patient survival. Ascorbic acid (AA) depletion in malignant tissue may contribute to aberrant normoxic activity of HIF-1α. While AA supplementation has been shown to attenuate HIF-1α function in malignant melanoma, the use of dehydroascorbic acid (DHA) as a therapeutic means to increase intracellular AA and modulate HIF-1α function is yet to be evaluated. Here we compared the ability of AA and DHA to increase intracellular vitamin C content and decrease the malignant potential of human melanoma by reducing the activity of HIF-1α.

METHODS:HIF-1α protein accumulation was evaluated by western blot and transcriptional activity was evaluated by reporter gene assay using a HIF-1 HRE-luciferase plasmid. Protein expressions and subcellular localizations of vitamin C transporters were evaluated by western blot and confocal imaging. Intracellularvitamin C content following AA, ascorbate 2-phosphate (A2P), or DHA supplementation was determined using a vitamin C assay. Malignant potential was accessed using a 3D spheroid Matrigel invasion assay. Data was analyzed by One or Two-way ANOVA with Tukey's multiple comparisons test as appropriate with p<0.05 considered significant.

RESULTS:Melanoma cells expressed both sodium dependent vitamin C (SVCT) and glucose (GLUT) transporters for AA and DHA transport respectively, however advanced melanomas responded favorably to AA, but not DHA. Physiological glucose conditions significantly impaired intracellular vitamin C accumulation following DHA treatment. Consequently, A2P and AA, but not DHA treated cells demonstrated lower HIF-1α protein expression and activity, and reduced malignant potential. The ability of AA to regulate HIF-1α was dependent on SVCT2 function and SVCT2 was not significantly inhibited at pH representative of the tumor microenvironment.

CONCLUSIONS:The use of ascorbic acid as an adjuvant cancer therapy remains under investigated. While AA and A2P were capable of modulating HIF-1α protein accumulation/activity, DHA supplementation resulted in minimal intracellular vitamin C activity with decreased ability to inhibit HIF-1α activity and malignant potential in advanced melanoma. Restoring AA dependent regulation of HIF-1α in malignant cells may prove beneficial in reducingchemotherapy resistance and improving treatment outcomes.

BACKGROUND:Cells adapt to hypoxia by transcriptional induction of genes that participate in regulation of angiogenesis, glucose metabolism and cell proliferation. The primary factors mediating cell response to low oxygen tension are hypoxia inducible factors (HIFs), oxygen-dependent transcription activators. The stability and activity of theα subunits of HIFs are controlled by hydroxylation reactions that require ascorbate as a cofactor. Therefore, deficiency of intracellular vitamin C could contribute to HIFs overactivation. In this study, we investigated whether vitamin C content of human thyroid lesions is associated with HIF-1α and HIF-2α protein levels.

METHODS:Expression of HIF-1α and HIF-2α as well as vitamin C content was analyzed in thyroid lesions and cultured thyroid carcinoma cell lines (FTC-133 and 8305c) treated with hypoxia-mimetic agent (cobalt chloride) and ascorbic acid. The expression of HIFs and hypoxia-induced glucose transporters were determined by Westernblots while quantitative real-time PCR (qRT-PCR) was performed to detect HIFs mRNA levels. Ascorbate and dehydroascorbate levels were measured by HPLC method.

RESULTS:We found an inverse correlation between vitamin C level and HIF-1α but not HIF-2α expression in thyroid lesions. These results agree with our in vitro study showing that vitamin C induced a dose - dependent decrease of HIF-1α but not HIF-2α protein level in thyroid cancer cells FTC-133 and 8305C. The decreased HIF-1α expression was correlated with reduced expression of hypoxia-related glucose transporter 1 (GLUT1) in thyroid cancer cells.

CONCLUSION:The results demonstrate that HIF-1α activation is associated with vitamin C content in thyroid lesions. Our study suggests that high tumor tissue ascorbate level could limit the expression of HIF-1α and its targets in thyroid lesions.

We examined the antileukemic effects of high concentrations of L-ascorbic acid (high AA) on human leukemic cells. In vitro, high AA markedly induced apoptosis in various leukemic cell lines by generating hydrogen peroxide (H2O2) but not in normal hematopoietic stem/progenitor cells. High AA significantly repressed leukemic cell proliferation as well as neoangiogenesis in immunodeficient mice. We then noted that in leukemic cells, HIF-1α transcription was strongly suppressed by high AA and correlated with the transcription of VEGF. Our data indicate that exposure to high AA markedly increased the intracellular AA content of leukemic cells and inhibited the nuclear translocation of NF-κB, which mediates expression of HIF-1α. Wenext generated K562 cells that overexpressed HIF-1α (K562-HIF1α cells) and assessed the mechanistic relationship between inhibition of HIF-1α transcription and the antileukemic effect of high AA. The ability of high AA to induce apoptosis was significantly lower in K562-HIF1α cells than in K562cells in vitro. We found that expression of HIF-1α-regulated antiapoptotic proteins of the Bcl-2 family, such as Mcl-1, Bcl-xL, and Bcl-2, was significantly suppressed by high AA in K562 cells, but was sustained at higher levels in K562-HIF1α cells, regardless of high AA exposure. Moreover, repression of cell proliferation and neoangiogenesis by high AA was completely abrogated in mice receiving transplants of K562-HIF1α cells. These results indicate that, along with H2O2 generation, downregulation of HIF-1α transcription plays a crucial role in growth inhibition of human leukemic cells byhigh AA.

Nimustine (ACNU) has antitumor activities in patients with malignant glioma. Hyperbaric oxygen (HBO) may enhance the efficacy of certain therapies that are hampered by the hypoxic microenvironment. We examined the combined effects of ACNU and HBO in a GFP transgenic nude mice bearing human glioma model. Mice inoculated with human glioma cells SU3 were randomly divided into the four groups: (A) the control group, (B) the HBOT (HBO therapy) group, (C) the ACNU group, and (D) the HBOT+ACNU group. Tumor size was measured at the indicated time intervals with a caliper; mice were sacrificed 28 days after treatment, and immunohistochemistry staining and western blot analysis were carried out. By the end of the trial, the tumor weights of groups A, B, C, and D were (P < 0.05), 6.03 ± 1.47, 4.13 ± 1.82 (P < 0.05), 2.39 ± 0.25 (P < 0.05), and 1.43 ± 0.38 (P < 0.01), respectively. The expressions of TNF-α, MMP9, HIF-α, VEGF, NF-κB, and IL-1β were associated with the infiltration of inflammatory cells and the inhibition rate of tumor cells. Hyperbaric oxygen therapy (HBOT) could inhibit glioma cell proliferation and inflammatory cell infiltration, and exert a sensitizing effect on ACNU therapy partially through enhancing oxygen pressure (PO2 ) in tumor tissues and lower expression levels of HIF-1α, TNF-α, IL-1β, VEGF, MMP9, and NF-κB.