Malignant brain tumors are devastating despite aggressive treatments such as surgical resection, chemotherapy and radiation therapy. The average life expectancy of patients with newly diagnosed glioblastoma is approximately ~18 months. It is clear that increased survival of brain tumor patients requires the design of new therapeutic modalities, especially those that enhance currently available treatments and/or limit tumor growth. One novel therapeutic arena is the metabolic dysregulation that results in an increased need for glucose in tumor cells. This phenomenon suggests that a reduction in tumor growth could be achieved by decreasing glucose availability, which can be accomplished through pharmacological means or through the use of a high-fat, low-carbohydrate ketogenic diet (KD). The KD, as the name implies, also provides increased blood ketones to support the energy needs of normal tissues. Preclinical work from a number of laboratories has shown that the KD does indeed reduce tumor growth in vivo. In addition, the KD has been shown to reduce angiogenesis, inflammation, peri-tumoral edema, migration and invasion. Furthermore, this diet can enhance the activity of radiation and chemotherapy in a mouse model of glioma, thus increasing survival. Additional studies in vitro have indicated that increasing ketones such asβ-hydroxybutyrate (βHB) in the absence of glucose reduction can also inhibit cell growth and potentiate the effects of chemotherapy and radiation. Thus, while we are only beginning to understand the pluripotent mechanisms through which the KD affects tumor growth and response to conventional therapies, the emerging data provide strong support for the use of a KD in the treatment of malignant gliomas. This has led to a limited number of clinical trials investigating the use of a KD in patients with primary and recurrent glioma.

The Ten Eleven Translocation (TET) enzymes have been found to be mutated in both diffuse large B-cell (DLBCL) and peripheral T-cell (PTCL) lymphomas resulting in DNA hypermethylation. Recent studies in embryonal stem cells showed that ascorbic acid (AA) is a cofactor for TET with a binding site at the catalytic domain, and enhances TET activity. We hypothesized that AA could potentially enhance TET activity in lymphoma cells to cause DNA demethylation, reactivate expression of tumor suppressor genes and enhance chemosensitivity. We demonstrate in vitro that AA treatment of DLBCL and PTCL cells using AA concentrations achievable intravenously increased TET activity leading to DNA demethylation. This epigenetic effect is independent of hydrogen peroxide. AA treatment increased the expression of SMAD1, a tumor suppressor gene known to be suppressed by methylation, and increased chemosensitivity of lymphoma cells. Twenty-nine percent (10/34) of unselected lymphoma patients had plasma AA levels that were deficient suggesting an additional clinical mechanism of TET hypofunction. These data indicate that AA has the potential to modify TET function in lymphoma and enhance chemosensitivity. In addition, the AA deficiency seen in some patients may further impair TET function and contribute to resistance. Clinical trials testing intravenous AA with chemotherapy are warranted.

Vitamin C is an essential dietary nutrient that has a variety of biological functions. Recent studies have provided promising evidence for its additional health benefits including anti-cancer activity. Vitamin B2, another essential dietary nutrient, is often coexisted with vitamin C in some fruits, vegetables or dietary supplements. The objective of the present study is to determine whether combination of vitamin C and B2 can achieve a synergistic anti-cancer activity. MDA-MB-231, MCF-7 and A549 cells were employed to evaluate the combinatory effects of vitamin C and B2. We found that combination of vitamin C and vitamin B2 resulted in a synergistic cell death induction in all cell lines tested. Further mechanistic investigations revealed that vitamin B2 sensitized cancer cells to vitamin C through inhibition of Akt and Bad phosphorylation. Our findings identified vitamin B2 as a promising sensitizer for improving the efficacy of vitamin C-based cancer chemoprevention and chemotherapy.

Human Papilloma Virus (HPV) is associated in most instances with cervical cancer. The HPV oncoproteins target P53 protein for degradation, leading to deregulation of cell cycle. We investigated whether stabilization of P53 in cervical cancer cells, by downregulating HPV transcription would restore the apoptotic ability of these cells. Our findings show that vitamin C downregulates the redox sensitive transcription factor AP-1 and decreases one of its transcription targets HPV E6, and stabilizes P53. This was associated with an increase in Bax and decrease in Bcl-2 and telomerase activity. Accumulation of P53 and its target gene bax then sensitized HeLa cells to cell-cycle arrest, cell death/apoptosis induced by cisplatin, and etoposide. Increasing drug sensitivity of cervical carcinoma cells by stabilizing P53 using vitamin C is a novel approach and has potential clinical relevance.

In recent years the use of natural dietary antioxidants to minimize the cytotoxicity and the damage induced in normal tissues by antitumor agents is gaining consideration. In literature, it is reported that vitamin C exhibits some degree of antineoplastic activity whereas Mitoxantrone (MTZ) is a synthetic anti-cancer drug with significant clinical effectiveness in the treatment of human malignancies but with severe side effects. Therefore, we have investigated the effect of vitamin C alone or combined with MTZ on MDA-MB231 and MCF7 human breast cancer cell lines to analyze their dose-effect on the tumor cellular growth, cellular death, cell cycle and cell signaling. Our results have evidenced that there is a dose-dependence on the inhibition of the breast carcinoma cell lines, MCF7 and MDA-MB231, treated with vitamin C and MTZ. Moreover, their combination induces: i) a cytotoxic effect by apoptotic death, ii) a mild G2/M elongation and iii) H2AX and mild PI3K activation. Hence, the formulation of vitamin C with MTZ induces a higher cytotoxicity level on tumor cells compared to a disjointed treatment. We have also found that the vitamin C enhances the MTZ effect allowing the utilization of lower chemotherapic concentrations in comparison to the single treatments.

Bromodomain and extra-terminal inhibitors (BETi) are promising cancer therapies, yet prominent side effects of BETi at effective doses have been reported in Phase I clinical trials. Here we screened a panel of small molecules targeting epigenetic modulators against human metastatic melanoma cells. Cells were pretreated with or without ascorbate (vitamin C), which promotes DNA demethylation and subsequently changes the sensitivity to drugs. Top hits were structurally unrelated BETi including JQ1, I-BET151, CPI-203, and BI-2536. Ascorbate enhanced the efficacy of BETi by decreasing acetylation of histone H4, but not H3, while exerting no effect on the expression of BRD proteins. Histone acetyltransferase 1 (HAT1), which catalyzes H4K5ac and H4K12ac, was downregulated by ascorbate mainly via the TET-mediated DNA hydroxymethylation pathway. Loss of H4ac, especially H4K5ac and H4K12ac, disrupted the interaction between BRD4 and H4 by which ascorbate and BETi blocked the binding of BRD4 to acetylated histones. Co-treatment with ascorbate and JQ1 induced apoptosis and inhibited proliferation of cultured melanoma cells. Ascorbate deficiency as modeled in Gulo-/- mice diminished the treatment outcome of JQ1 for melanoma tumorgraft. In contrast, ascorbate supplementation lowered the effective dose of JQ1 needed to successfully inhibit melanoma tumors in mice. Based on our findings, future clinical trials with BETi should consider ascorbate levels in patients. Furthermore, ascorbate supplementation might help reduce the severe side effects that arise from BETi therapy by reducing the dosage necessary for treatment.

This review is directed to the redox-modulating properties and anticancer effect of vitamin K. The concept is focused on two aspects: (i) redox-cycle of vitamin K and its effect on the calcium homeostasis,"oncogenic"and"onco-suppressive"reactive oxygen species and the specific induction of oxidative stress in cancer; (ii) vitamin K plus C as a powerful redox-system, which forms a bypass between mitochondrial complexes II and III and thus prevents mitochondrial dysfunction, restores oxidative phosphorylation and aerobic glycolysis, modulates the redox-state of endogenous redox-pairs, eliminates the hypoxic environment of cancer cells and induces cell death. The analyzed data suggest that vitamin C&K can sensitize cancer cells to conventional chemotherapy, which allows achievement of a lower effective dose of the drug and minimizing the harmful side-effects. The review is intended for a wide audience of readers - from students to specialists in the field.