Current progress in using vitamin D and its analogs for cancer prevention and treatment

Exploiting Vitamin D Receptor and Its Ligands to Target Squamous Cell Carcinomas of the Head and Neck

Vitamin D (VitD) and its receptor (VDR) have been intensively investigated in many cancers. As knowledge for head and neck cancer (HNC) is limited, we investigated the (pre)clinical and therapeutic relevance of the VDR/VitD-axis. We found that VDR was differentially expressed in HNC tumors, correlating to the patients' clinical parameters. Poorly differentiated tumors showed high VDR and Ki67 expression, whereas the VDR and Ki67 levels decreased from moderate to well-differentiated tumors. The VitD serum levels were lowest in patients with poorly differentiated cancers (4.1 ± 0.5 ng/mL), increasing from moderate (7.3 ± 4.3 ng/mL) to well-differentiated (13.2 ± 3.4 ng/mL) tumors. Notably, females showed higher VitD insufficiency compared to males, correlating with poor differentiation of the tumor. To mechanistically uncover VDR/VitD's pathophysiological relevance, we demonstrated that VitD induced VDR nuclear-translocation (VitD < 100 nM) in HNC cells. RNA sequencing and heat map analysis showed that various nuclear receptors were differentially expressed in cisplatin-resistant versus sensitive HNC cells including VDR and the VDR interaction partner retinoic acid receptor (RXR). However, RXR expression was not significantly correlated with the clinical parameters, and cotreatment with its ligand, retinoic acid, did not enhance the killing by cisplatin. Moreover, the Chou-Talalay algorithm uncovered that VitD/cisplatin combinations synergistically killed tumor cells (VitD < 100 nM) and also inhibited the PI3K/Akt/mTOR pathway. Importantly, these findings were confirmed in 3D-tumor-spheroid models mimicking the patients' tumor microarchitecture. Here, VitD already affected the 3D-tumor-spheroid formation, which was not seen in the 2D-cultures. We conclude that novel VDR/VitD-targeted drug combinations and nuclear receptors should also be intensely explored for HNC. Gender-specific VDR/VitD-effects may be correlated to socioeconomic differences and need to be considered during VitD (supplementation)-therapies.

Role of vitamin D3 in tumor aggressiveness and radiation response for hepatocellular carcinoma

Locoregional control is a significant prognostic factor for hepatocellular carcinoma (HCC). Historically, the use of radiotherapy (RT) for HCC was limited owing to the low radiotolerance of the liver and the need for high RT doses for disease control. We aimed to examine if 1α,25-dihydroxyvitamin D3 (calcitriol) has a role in the tumor inhibition and the radiation response of HCC in vitro and in vivo, and explore the underlying mechanisms. The human and murine liver cancer cell lines were selected for cellular and animal experiments to investigate the changes in tumor characteristics and the radiation response after calcitriol supplementation. The effects induced by calcitriol supplementation on interleukin-6 (IL-6) signaling and the tumor immune microenvironment following RT were also examined. Our data revealed that calcitriol supplementation attenuated tumor aggressive behavior, decrease IL-6 expression, and augmented radiation-induced tumor inhibition. The biological changes following calcitriol treatment included suppressed epithelial-mesenchymal transition, attenuated cancer stem cell-like properties and increased radiation-induced reactive oxygen species and cell death in vitro. Regarding immune microenvironment, calcitriol attenuated the recruitment of myeloid-derived suppressor cell (MDSC) recruitment and increased the infiltration of cytotoxic T cells in tumor following RT. Furthermore, When the primary liver tumor was irradiated with larger dose per fraction, calcitriol induced a smaller size of synchronous unirradiated tumor in mice, which linked with attenuated IL-6 signaling and MDSC recruitment. In conclusion, calcitriol treatment reduced tumor aggressiveness and enhanced the radiation response. The inhibited IL-6 signaling and subsequently enhanced antitumor immunity might be responsible to augment radiation-induced tumoricidal effect induced by calcitriol. Based on our results, we suggest that calcitriol could exert the antitumor and radiosensitization effects for HCC, especially for multifocal tumors.

Zinc, ω-3 polyunsaturated fatty acids and vitamin D: An essential combination for prevention and treatment of cancers

Zinc, ω-3 polyunsaturated fatty acids (PUFAs) and vitamin D are essential nutrients for health, maturation and general wellbeing. Extensive literature searches have revealed the widespread similarity in molecular biological properties of zinc, ω-3 PUFAs and vitamin D, and their similar anti-cancer properties, even though they have different modes of action. These three nutrients are separately essential for good health, especially in the aged. Zinc, ω-3 PUFAs and vitamin D are inexpensive and safe as they are fundamentally natural and have the properties of correcting and inhibiting undesirable actions without disturbing the normal functions of cells or their extracellular environment. This review of the anticancer properties of zinc, ω-3 PUFAs and vitamin D is made in the context of the hallmarks of cancer. The anticancer properties of zinc, ω-3 PUFAs and vitamin D can therefore be used beneficially through combined treatment or supplementation. It is proposed that sufficiency of zinc, ω-3 PUFAs and vitamin D is a necessary requirement during chemotherapy treatment and that clinical trials can have questionable integrity if this sufficiency is not checked and maintained during efficacy trials.

Vitamin D Signaling in Inflammation and Cancer: Molecular Mechanisms and Therapeutic Implications

Vitamin D and its active metabolites are important nutrients for human skeletal health. UV irradiation of skin converts 7-dehydrocholesterol into vitamin D3, which metabolized in the liver and kidneys into its active form, 1α,25-dihydroxyvitamin D3. Apart from its classical role in calcium and phosphate regulation, scientists have shown that the vitamin D receptor is expressed in almost all tissues of the body, hence it has numerous biological effects. These includes fetal and adult homeostatic functions in development and differentiation of metabolic, epidermal, endocrine, neurological and immunological systems of the body. Moreover, the expression of vitamin D receptor in the majority of immune cells and the ability of these cells to actively metabolize 25(OH)D3 into its active form 1,25(OH)₂D3 reinforces the important role of vitamin D signaling in maintaining a healthy immune system. In addition, several studies have showed that vitamin D has important regulatory roles of mechanisms controlling proliferation, differentiation and growth. The administration of vitamin D analogues or the active metabolite of vitamin D activates apoptotic pathways, has antiproliferative effects and inhibits angiogenesis. This review aims to provide an up-to-date overview on the effects of vitamin D and its receptor (VDR) in regulating inflammation, different cell death modalities and cancer. It also aims to investigate the possible therapeutic benefits of vitamin D and its analogues as anticancer agents.

Synthesis of Gemini analogs of 19-norcalcitriol and their platinum(II) complexes

Hormonally active vitamin D₃ metabolite, calcitriol, plays an important role in calcium-phosphate homeostasis, immune system actions and cell differentiation. Although anticancer activity of calcitriol is well documented and thousands of its analogs have been synthesized, none has been approved as a potential drug against cancer. Therefore, we attempted to introduce the cytotoxic effect to the calcitriol molecule by its linking to cisplatin. Herein, we present the synthesis of vitamin D compounds, designed on the basis of molecular modeling and docking experiments to the vitamin D receptor, and characterized by the presence of significantly different two side chains attached to C-20. In this study, a new synthetic approach to Gemini analogs was developed. Preparation of the target 19-norcalcitriol compounds involved separate syntheses of several building blocks (the A-ring, C/D-rings and side-chain fragments). The convergent synthetic strategy was used to combine these components by the different coupling processes, the crucial one being Wittig-Horner reaction of the Grundmann ketone analog with the known 2-methylene A-ring phosphine oxide. Due to the nature of the constructed steroidal side chains (bidentate ligands), which allowed coordination of metal ions, the first conjugate-type platinum(II) complexes of the vitamin D analogs were also successfully prepared and characterized. The target vitamin D compounds, displaying significant affinity for a vitamin D receptor, were assessed in vitro for their anti-proliferative activities towards several cell lines.

Effects of an Omega-3 and Vitamin D Supplement on Fatty Acids and Vitamin D Serum Levels in Double-Blinded, Randomized, Controlled Trials in Healthy and Crohn's Disease Populations

Two trials separately measured the bioavailability and impact on inflammation of a supplement taken daily containing 510 mg Docosahexaenoic acid (DHA), 344 mg Eicosapentaenoic acid (EPA), and 1000 IU of vitamin D (25-hydroxyvitamin D; 25(OH)D), for healthy and Crohn’s disease (CD) populations. Both trials were double blinded, randomized, placebo-controlled with cross-over. Participants were randomly allocated to groups A (placebo then supplement) or B (supplement then placebo). Both included a washout. Fatty acid (N-3 PUFAs) and vitamin D serum levels, plasma C-reactive protein (CRP), and stool calprotectin were measured before and after each treatment period. Outcome measures were analyzed using generalized linear mixed models, including terms for treatment, period, and a treatment-by-period interaction. The supplement significantly increased serum levels in healthy and CD groups for EPA (p < 0.001 and p < 0.001, respectively), Docosapentaenoic acid (p < 0.001 and 0.005), DHA (p < 0.001 and 0.006), the omega-3 index (p < 0.001 and 0.001), and (vitamin D (p < 0.001 and 0.027). CRP and calprotectin measures showed no evidence of a treatment effect on inflammation; however, model estimation was imprecise for both outcomes, hence further research is required to elucidate potential inflammation effects. The nutrient supplement increased serum levels of key N-3 PUFAs and vitamin D in both populations, showing the preparation was readily bioavailable.

Role of vitamin D and vitamin D receptor (VDR) in oral cancer

Oral cancer is known as one of the most common cancers, with a poor prognosis, related to delayed clinical diagnosis, either due to the lack of particular biomarkers related to the disease or costly therapeutic alternatives. Vitamin D executes its functions by interacting with the vitamin D receptor (VDR), both in healthy and diseased individuals, including oral cancer. This review discusses the role of vitamin D and VDR on tumorigenesis, emphasizing on oral cancer. Furthermore, regulation of VDR expression, mechanisms of anticancer effects of calcitriol, oral cancer chemoresistance and its relation with VDR and polymorphisms of VDR gene will be discussed. The manuscript is prepared mainly using the information collected from PubMed and MEDLINE.

An Effective Model of the Retinoic Acid Induced HL-60 Differentiation Program

In this study, we present an effective model All-Trans Retinoic Acid (ATRA)-induced differentiation of HL-60 cells. The model describes reinforcing feedback between an ATRA-inducible signalsome complex involving many proteins including Vav1, a guanine nucleotide exchange factor, and the activation of the mitogen activated protein kinase (MAPK) cascade. We decomposed the effective model into three modules; a signal initiation module that sensed and transformed an ATRA signal into program activation signals; a signal integration module that controlled the expression of upstream transcription factors; and a phenotype module which encoded the expression of functional differentiation markers from the ATRA-inducible transcription factors. We identified an ensemble of effective model parameters using measurements taken from ATRA-induced HL-60 cells. Using these parameters, model analysis predicted that MAPK activation was bistable as a function of ATRA exposure. Conformational experiments supported ATRA-induced bistability. Additionally, the model captured intermediate and phenotypic gene expression data. Knockout analysis suggested Gfi-1 and PPARg were critical to the ATRAinduced differentiation program. These findings, combined with other literature evidence, suggested that reinforcing feedback is central to hyperactive signaling in a diversity of cell fate programs.

BRAF signals to pro-apoptotic BIM to enhance AraC cytotoxicity induced in AML cells by Vitamin D-based differentiation agents

Vitamin D has so far not fulfilled its early promise as an antineoplastic agent, in spite of compelling in vitro data. With the aim of bringing vitamin D or its derivatives (VDDs) effectively to the clinic, we developed a two-pronged approach. First, by adding the plant-derived Carnosic Acid (CA) to a vitamin D2 derivative Doxercalciferol we increased its differentiation potency without increasing it hypercalcemic properties. Second, we added these two agents together to AML cells already treated with Cytarabine (AraC), the standard drug for the treatment of patients with AML. We now report that BRAF, a part of the MAPK signaling pathway, is required for the optimally increased cell death in this system and acts upstream of BIM, the regulator of the caspase cascade that leads to cell death by apoptosis. It is proposed that this therapeutic regimen should be tested in a clinical trial.

1α,25(OH) 2D3 Sensitive Cytosolic pH Regulation and Glycolytic Flux in Human Endometrial Ishikawa Cells

BACKGROUND/AIMS

Tumor cell proliferation is modified by 1,25-Dihydroxy-Vitamin D3 (1,25(OH)2D3), a steroid hormone predominantly known for its role in calcium and phosphorus metabolism. Key properties of tumor cells include enhanced glycolytic flux with excessive consumption of glucose and formation of lactate. As glycolysis is highly sensitive to cytosolic pH, maintenance of glycolysis requires export of H+ ions and lactate, which is in part accomplished by Na+/H+ exchangers, such as NHE1 and monocarboxylate transporters, such as MCT4. An effect of 1,25(OH)2D3 on those transport processes has, however, never been reported. As cytosolic pH impacts on apoptosis, the study further explored the effect of 1,25(OH)2D3 on apoptosis and on the apoptosis regulating kinase AKT, transcription factor Forkhead box O-3 (FOXO3A) and B-cell lymphoma protein BCL-2.

METHODS

In human endometrial adenocarcinoma (Ishikawa) cells, cytosolic pH (pHi) was determined utilizing (2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein [BCECF] fluorescence, Na+/H+ exchanger activity from Na+ dependent realkalinization after an ammonium pulse, NHE1 and MCT4 transcript levels using qRT-PCR, NHE1, MCT4, total & phospho AKT, total & phospho-FOXO3A and BCL-2 protein abundance by Western blotting, lactate concentration in the supernatant utilizing a colorimetric enzyme assay and cell death quantification using CytoTox 96®, Annexin V and Propidium Iodide staining.

RESULTS

A 24 hours treatment with 1,25(OH)2D3 (100 nM) significantly increased cytosolic pH (pHi), significantly decreased Na+/H+ exchanger activity, NHE1 and MCT4 transcript levels as well as protein abundance and significantly increased lactate concentration in the supernatant. Treatment of Ishikawa cells with 1,25(OH)2D3 (100 nM) further triggered apoptosis, an effect paralleled by decreased phosphorylation of AKT and FOXO3A as well as decreased abundance of BCL-2.

CONCLUSIONS

In Ishikawa cells 1,25(OH)2D3 is a powerful stimulator of glycolysis, an effect presumably due to cytosolic alkalinization. Despite stimulation of glycolysis, 1,25(OH)2D3 stimulates slightly but significantly suicidal cell death, an effect presumably in part due to decreased activation of AKT with decreased inhibition of pro-apoptotic transcription factor FOXO3A and downregulation of the anti-apoptotic protein BCL-2.

Serum vitamin D3 levels are not associated with thyroid cancer prevalence in euthyroid subjects without autoimmune thyroid disease

BACKGROUND/AIMS

Previous studies have suggested that elevated serum vitamin D levels might protect against thyroid cancer. Elevated serum thyroid stimulating hormone levels and autoimmune thyroid disease (AITD) are suggested to be thyroid cancer promoting factors but have not been well controlled in previous studies. We designed the present study to evaluate whether serum vitamin D levels are associated with thyroid cancer in euthyroid patients with no clinical evidence of AITD.

METHODS

This cross-sectional study included subjects who underwent routine health check-ups, including serum 25-hydroxy vitamin D3 (25(OH)D3) levels, anti-thyroid peroxidase antibody (TPO-Ab), and thyroid ultrasonography (US). Inclusion criteria were euthyroid, negative TPO-Ab, and no evidence of AITD by US findings. Thyroid cancer diagnoses were based on fine needle aspiration cytology and/or postsurgical histopathological findings.

RESULTS

We enrolled 5,186 subjects (64% male, 37% female) in this study, including 53 patients (1%) with a diagnosis of thyroid cancer (33 males, 20 females). Mean 25(OH)D3 levels were similar between the thyroid cancer and control groups (p = 0.20). Subgroup analysis according to sex or seasonal variation also revealed no differences in 25(OH)D3 levels between the two groups. Based on the levels of 25(OH)D3, there was no significant difference in the prevalence of thyroid cancer; the prevalence was 0.71%, 0.94%, 1.40%, and 0.82% in the deficient, insufficient, sufficient, and excess groups, respectively (p = 0.64).

CONCLUSIONS

The levels of serum 25(OH)D3 are not associated with thyroid cancer prevalence in euthyroid subjects with no clinical evidence of AITD.

The conformational dynamics of H2-H3n and S2-H6 in gating ligand entry into the buried binding cavity of vitamin D receptor

Crystal structures of holo vitamin D receptor (VDR) revealed a canonical conformation in which the ligand is entrapped in a hydrophobic cavity buried in the ligand-binding domain (LBD). The mousetrap model postulates that helix 12 is positioned away from the domain to expose the interior cavity. However, the extended form of helix 12 is likely due to artifacts during crystallization. In this study, we set out to investigate conformational dynamics of apo VDR using molecular dynamics simulation on microsecond timescale. Here we show the neighboring backbones of helix 2-helix 3n and beta strand 2-helix 6 of LBD, instead of the helix 12, undergo large-scale motion, possibly gating the entrance of ligand to the ligand binding domain. Docking analysis to the simulated open structure of VDR with the estimated free energy of -37.0 kJ/mol, would emphasise the role of H2-H3n and S2-H6 in facilitating the entrance of calcitriol to the LBD of VDR.

Prodifferentiation Activity of Novel Vitamin D₂ Analogs PRI-1916 and PRI-1917 and Their Combinations with a Plant Polyphenol in Acute Myeloid Leukemia Cells

1α,25-dihydroxyvitamin D₃ (1,25D3) is a powerful differentiation inducer for acute myeloid leukemia (AML) cells. However, 1,25D3 doses required for differentiation of AML cells may cause lethal hypercalcemia in vivo. There is evidence that vitamin D₂ is less toxic than vitamin D₃ in animals. Here, we determined the differentiation effects of novel analogs of 1α,25-dihydroxyvitamin D₂ (1,25D2), PRI-1916 and PRI-1917, in which the extended side chains of their previously reported precursors (PRI-1906 and PRI-1907, respectively) underwent further 24Z (24-cis) modification. Using four human AML cell lines representing different stages of myeloid maturation (KG-1a, HL60, U937, and MOLM-13), we found that the potency of PRI-1916 was slightly higher or equal to that of PRI-1906 while PRI-1917 was significantly less potent than PRI-1907. We also demonstrated that 1,25D2 was a less effective differentiation agent than 1,25D3 in these cell lines. Irrespective of their differentiation potency, all the vitamin D₂ derivatives tested were less potent than 1,25D3 in transactivating the DR3-type vitamin D response elements. However, similar to 1,25D3, both 1,25D2 and its analogs could strongly cooperate with the plant polyphenol carnosic acid in inducing cell differentiation and inhibition of G1–S cell cycle transition. These results indicate that the 24Z modification has contrasting effects on the differentiation ability of PRI-1906 and PRI-1907 and that the addition of a plant polyphenol could result in a similar extent of cell differentiation induced by different vitamin D compounds. The enhanced antileukemic effects of the tested combinations may constitute the basis for the development of novel approaches for differentiation therapy of AML.

The role of vitamin D in cancer prevention

Vitamin D, also known as cholecalciferol, is the precursor to the active steroid hormone 1, 25-dihydroxyvitamin D3 (calcitriol; 1, 25(OH)2D3). The main physiological role for 1, 25(OH)2D3 is to regulate calcium and inorganic phosphate homeostasis for bone health. More recently, vitamin D has been investigated for its effects in the prevention and treatment of a variety of diseases such as cancer, autoimmune disorders, and cardiovascular disease. Preclinical data strongly support a role for vitamin D in the prevention of cancer through its anti-proliferative, pro-apoptotic, and anti-angiogenic effects on cells. Epidemiologic and clinical studies have shown mixed data on the correlation between serum vitamin D levels and cancer risk. This report seeks to outline results from the most recent preclinical and clinical studies investigating the potential role of vitamin D in cancer prevention.

Vitamin D and urological cancers

Introduction

Vitamin D controls calcium and phosphate homeostasis. Additionally, it has been proven that vitamin D is an important modulator of cellular differentiation and proliferation in a number of normal and malignant cells. Vitamin D can regulate proliferation, apoptosis, and cell adhesion at the tumor cell level. It also modifies tumor angiogenesis, invasion, and metastasis and also decreases oxidative DNA damage.

Material and methods

The Medline and Web of Science databases were searched without time limit on October 2015 using the terms ‘vitamin D’ in conjunction with ‘kidney cancer’, ‘bladder cancer’, ‘prostate cancer’, and ‘testis cancer’. Autoalerts in Medline were also run and reference lists of original articles, review articles, and book chapters were searched for further eligible articles.

Results

In recent years, vitamin D has received vast attention due to suggestions that it may have a crucial role in the prevention and therapy of various cancers. Many epidemiologic studies have reported the impact of VD3 on preventing several cancers and other pathologies. Assuming that vitamin D status changes cancer risk, enough vitamin D supply would be an easy, economical, and safe cancer incidence and mortality reduction method. However, despite numerous researches, the role of vitamin D in cancer incidence and therapy remains unclear.

Conclusions

The impact of vitamin D is well described in breast, colon, and prostate cancer; yet, there is only little published about other malignancies.

Total synthesis of biologically active 20S-hydroxyvitamin D3

A total synthetic strategy of 20S-hydroxyvitamin D3 [20S-(OH)D3] involving modified synthesis of key intermediates 7 and 12, Grignard reaction to stereoselectively generate 20S-OH and Wittig-Horner coupling to establish D3 framework, was completed in 16 steps with an overall yield of 0.4%. The synthetic 20S-(OH)D3 activated vitamin D receptor (VDR) and initiated the expression of downstream genes. In addition, 20S-(OH)D3 showed similar inhibitory potency as calcitriol [1,25(OH)2D3] on proliferation of melanoma cells.

Induced myelomonocytic differentiation in leukemia cells is accompanied by noncanonical transcription factor expression

Transcription factors that drive non-neoplastic myelomonocytic differentiation are well characterized but have not been systematically analyzed in the leukemic context. We investigated widely used, patient-derived myeloid leukemia cell lines with proclivity for differentiation into granulocytes by retinoic acid (RA) and/or monocytes by 1,25-dihyrdroxyvitamin D3 (D3). Using K562 (FAB M1), HL60 (FAB M2), RA-resistant HL60 sublines, NB4 (FAB M3), and U937 (FAB M5), we correlated nuclear transcription factor expression to immunophenotype, G1/G0 cell cycle arrest and functional inducible oxidative metabolism. We found that myelomonocytic transcription factors are aberrantly expressed in these cell lines. Monocytic-lineage factor EGR1 was not induced by D3 (the monocytic inducer) but instead by RA (the granulocytic inducer) in lineage bipotent myeloblastic HL60. In promyelocytic NB4 cells, EGR1 levels were increased by D3, while Gfi-1 expression (which promotes the granulocytic lineage) was upregulated during D3-induced monocytic differentiation in HL60, and by RA treatment in monocytic U937 cells. Furthermore, RARα and VDR expression were not strongly correlated to differentiation. In response to different differentiation inducers, U937 exhibited the most distinct transcription factor expression profile, while similarly mature NB4 and HL60 were better coupled. Overall, the differentiation induction agents RA and D3 elicited cell-specific responses across these common FAB M1-M5 cell lines.

1α,25-Dihydroxyvitamin D3 Inhibits Esophageal Squamous Cell Carcinoma Progression by Reducing IL6 Signaling

The aim of this study was to highlight the role of 1α,25-dihydroxyvitamin D3 (calcitriol) in esophageal squamous cell carcinoma (SCC). The human esophageal SCC cell lines CE81T and TE2 were selected for cellular and animal experiments to investigate the changes in tumor behavior after calcitriol supplementation and the underlying mechanisms. Moreover, we evaluated the relationship between calcitriol supplementation, myeloid-derived suppressor cell (MDSC) recruitment, IL6 levels, and tumor progression by a 4-nitroquinoline 1-oxide (4-NQO)-induced esophageal tumor animal model. In this study, we demonstrated that calcitriol supplementation inhibited aggressive tumor behavior both in vitro and in vivo. The underlying changes included increased cell death, a lower degree of epithelial-mesenchymal transition, and inhibited IL6 signaling. In the 4-NQO-induced esophageal tumor animal model, increased IL6 and MDSC recruitment were linked with invasive esophageal tumors. Supplementation with calcitriol attenuated the level of IL6, the induction of MDSCs, and the incidence of 4-NQO-induced invasive tumors. Moreover, the IL6-induced changes in C57 mice, including augmented MDSC recruitment, increased levels of ROS and p-Stat3 in MDSCs, and higher suppressive function of MDSCs in T-cell proliferation, which were abrogated by calcitriol supplementation. On the basis of our results, we concluded that calcitriol abrogated the IL6-induced aggressive tumor behavior and MDSC recruitment to inhibit esophageal tumor promotion. Therefore, we suggest that supplementation with vitamin D3 may be a promising strategy for the prevention and treatment of esophageal SCC.

Effects of vitamin D3 stimulation of thioredoxin-interacting protein in hepatocellular carcinoma

AIM

Thioredoxin-interacting protein (TXNIP) promotes oxidative stress by inactivating thioredoxin (TXN). This protein is involved in diverse disease processes, including insulin resistance, atherosclerosis and carcinogenesis. The aim of the present study was to measure the expression and function of TXNIP in in vitro models of liver disease, as well as in primary human hepatocellular carcinoma (HCC) tissue specimens. In addition, we wanted to determine the effects of vitamin D3-induced TXNIP stimulation in HCC-derived cell lines.

METHODS

TXNIP expression was measured by quantitative reverse transcription polymerase chain reaction and western blots. TXNIP expression was stimulated by vitamin D exposure and by transfection. Cell proliferation, apoptosis and reactive oxygen species were determined by standard assays.

RESULTS

TXNIP expression levels were low in HCC cell lines, and vitamin D3 stimulated TXNIP expression in vitro. In HCC cells transfected with a TXNIP expression vector or treated with exogenous vitamin D3, there was a reduction in cell proliferation and an increase in apoptosis. Cells expressing TXNIP were markedly susceptible to oxidative injury induced by cobalt chloride or bacterial lipopolysaccharide. TXNIP expression was reduced or absent in a majority of primary human HCC specimens relative to matching, non-cancerous liver tissue.

CONCLUSION

TXNIP expression is low or absent in human HCC specimens and HCC-derived cell lines. Vitamin D3 stimulates TXNIP expression, resulting in diminished proliferation and enhanced apoptosis. Liver cells expressing TXNIP are primed for oxidative injury. These findings suggest that stimulation of TXNIP expression, by factors such as vitamin D3, may attenuate carcinogenesis in patients with chronic liver disease.

Pharmacological effects of vitamin D and its analogs: recent developments

Calcitriol, the hormonally active form of vitamin D, is well known for its diverse pharmacological activities, including modulation of cell growth, neuromuscular and immune function and reduction of inflammation. Calcitriol and its analogs exert potent effects on cellular differentiation and proliferation, regulate apoptosis and produce immunomodulatory effects. The purpose of this review is to provide information on various physiological and pharmacological activities of calcitriol and its newly discovered analogs. Special emphasis is given to skin diseases, cancer, diabetes and multiple sclerosis. A discussion is raised on the mechanisms of action of calcitriol and its analogs in various diseases, as well as on possible methods of delivery and targeting.

Retinoic acid therapy resistance progresses from unilineage to bilineage in HL-60 leukemic blasts

Emergent resistance can be progressive and driven by global signaling aberrations. All-trans retinoic acid (RA) is the standard therapeutic agent for acute promyelocytic leukemia, but 10-20% of patients are not responsive, and initially responsive patients relapse and develop retinoic acid resistance. The patient-derived, lineage-bipotent acute myeloblastic leukemia (FAB M2) HL-60 cell line is a potent tool for characterizing differentiation-induction therapy responsiveness and resistance in t(15;17)-negative cells. Wild-type (WT) HL-60 cells undergo RA-induced granulocytic differentiation, or monocytic differentiation in response to 1,25-dihydroxyvitamin D3 (D3). Two sequentially emergent RA-resistant HL-60 cell lines, R38+ and R38-, distinguishable by RA-inducible CD38 expression, do not arrest in G1/G0 and fail to upregulate CD11b and the myeloid-associated signaling factors Vav1, c-Cbl, Lyn, Fgr, and c-Raf after RA treatment. Here, we show that the R38+ and R38- HL-60 cell lines display a progressive reduced response to D3-induced differentiation therapy. Exploiting the biphasic dynamic of induced HL-60 differentiation, we examined if resistance-related defects occurred during the first 24 h (the early or "precommitment" phase) or subsequently (the late or "lineage-commitment" phase). HL-60 were treated with RA or D3 for 24 h, washed and retreated with either the same, different, or no differentiation agent. Using flow cytometry, D3 was able to induce CD38, CD11b and CD14 expression, and G1/G0 arrest when present during the lineage-commitment stage in R38+ cells, and to a lesser degree in R38- cells. Clustering analysis of cytometry and quantified Western blot data indicated that WT, R38+ and R38- HL-60 cells exhibited decreasing correlation between phenotypic markers and signaling factor expression. Thus differentiation induction therapy resistance can develop in stages, with initial partial RA resistance and moderate vitamin D3 responsiveness (unilineage maturation block), followed by bilineage maturation block and progressive signaling defects, notably the reduced expression of Vav1, Fgr, and c-Raf.

The role of vitamin D in reducing cancer risk and progression

Vitamin D is not really a vitamin but the precursor to the potent steroid hormone calcitriol, which has widespread actions throughout the body. Calcitriol regulates numerous cellular pathways that could have a role in determining cancer risk and prognosis. Although epidemiological and early clinical trials are inconsistent, and randomized control trials in humans do not yet exist to conclusively support a beneficial role for vitamin D, accumulating results from preclinical and some clinical studies strongly suggest that vitamin D deficiency increases the risk of developing cancer and that avoiding deficiency and adding vitamin D supplements might be an economical and safe way to reduce cancer incidence and improve cancer prognosis and outcome.

1α,25-Dihydroxyvitamin D₃ inhibits the human H295R cell proliferation by cell cycle arrest: a model for a protective role of vitamin D receptor against adrenocortical cancer

Using the human H295R adrenocortical carcinoma cell line as a model, we analyzed the role of 1α,25-dihydroxyvitamin D₃ [1α,25(OH)₂D₃)]--vitamin D receptor (VDR) axis in the growth of adrenocortical cancer (ACC). The presence of VDR in various adrenocortical tissues, including ACC, was also investigated. DNA synthesis was evaluated by [³H]thymidine cell incorporation after treatment with 1α,25(OH)₂D₃ at increasing doses. The effect of 1α,25(OH)₂D₃ on cell cycle and apoptosis was analyzed with a flow cytometer. Cyclin-dependent kinase 4 (CDK4) expression, a molecular marker of G1-S cell cycle transition phase, was evaluated in cells treated with 1α,25(OH)₂D₃ before and after VDR gene silencing. 1α,25(OH)₂D₃ treatment inhibited cell proliferation by 20% at a dose of 1 nM, in parallel with steroid secretion decrease. A cell cycle arrest in G1, with no change in apoptotic cell proportion, was observed after 10 nM 1α,25(OH)₂D₃ cell exposure. CDK4 activation was reduced by 10 nM 1α,25(OH)₂D₃ but was not affected by 1α,25(OH)₂D₃ after VDR gene silencing. Expression of VDR mRNA was lower in ACC than in benign adrenocortical tumors. VDR immunostaining was evident in benign tumors but it was weak in ACC tissues.

CONCLUSIONS

Slightly supra-physiological concentrations of 1α,25(OH)₂D₃ have a moderate anti-proliferative effect on H295R cells. Anti-proliferative effect was due to cell cycle arrest in G1 phase, without inducing apoptosis. The low mRNA expression levels at qRT-PCR as well as the weak immunohistochemical expression of VDR in ACC, suggests a protective role of VDR against malignant adrenocortical growth.

Phytoagents for cancer management: regulation of nucleic acid oxidation, ROS, and related mechanisms

Accumulation of oxidized nucleic acids causes genomic instability leading to senescence, apoptosis, and tumorigenesis. Phytoagents are known to reduce the risk of cancer development; whether such effects are through regulating the extent of nucleic acid oxidation remains unclear. Here, we outlined the role of reactive oxygen species in nucleic acid oxidation as a driving force in cancer progression. The consequential relationship between genome instability and cancer progression highlights the importance of modulation of cellular redox level in cancer management. Current epidemiological and experimental evidence demonstrate the effects and modes of action of phytoagents in nucleic acid oxidation and provide rationales for the use of phytoagents as chemopreventive or therapeutic agents. Vitamins and various phytoagents antagonize carcinogen-triggered oxidative stress by scavenging free radicals and/or activating endogenous defence systems such as Nrf2-regulated antioxidant genes or pathways. Moreover, metal ion chelation by phytoagents helps to attenuate oxidative DNA damage caused by transition metal ions. Besides, the prooxidant effects of some phytoagents pose selective cytotoxicity on cancer cells and shed light on a new strategy of cancer therapy. The “double-edged sword” role of phytoagents as redox regulators in nucleic acid oxidation and their possible roles in cancer prevention or therapy are discussed in this review.

Evaluating and adapting the Mediterranean diet for non-Mediterranean populations: a critical appraisal

This review outlines the limitations of current techniques for evaluating the Mediterranean diet in Mediterranean versus non-Mediterranean populations. Differences between the two populations with regard to the foods that are available, food processing and preparation techniques, and eating and lifestyle habits may influence the implementation and effects of a Mediterranean diet in non-Mediterranean regions. For example, the composition of food groups may vary significantly, due to differences in the specific foods within a food group and to differences in aspects of food production and preparation. Notable differences between the diets of Mediterranean versus non-Mediterranean populations include the source of monounsaturated fatty acids (olive oil versus meat), the amount of vegetables consumed and their manner of preparation, the source of alcohol (wine versus other) and the pattern of intake, and the types of meat and dairy products consumed. Lifestyle factors such as meal patterns and exposure to sunlight may also act as confounding factors when the overall benefits of a Mediterranean diet are assessed. Improving the calculation of Mediterranean diet scores and measuring plasma nutrient levels may help mitigate the effects of confounders. These considerations could have important health implications when a Mediterranean diet is implemented by non-Mediterranean populations.

The association between plasma 25-hydroxyvitamin D and subgroups in age-related macular degeneration: a cross-sectional study

OBJECTIVES

To evaluate potential differences in plasma 25-hydroxyvitamin in subtypes of age-related macular degeneration (AMD), and in patients in Clinical Age-Related Maculopathy Staging (CARMS) group 5 with or without subretinal fibrosis.

METHODS

This single-center cross-sectional study included 178 participants during a period of 20 months. Ninety-five patients belonged to CARMS 5; twelve belonged to CARMS 4; twenty-two belonged to CARMS 2 or 3; and 49 individuals did not have AMD (CARMS 1). Following a structured interview, a detailed bilateral retinal examination was performed and participants were allocated to their respective subgroups in accordance with the Clinical Age-Related Maculopathy Staging system. Plasma 25-hydroxyvitamin D2 and D3 were analyzed using liquid chromatography-tandem mass spectrometry. Genomic DNA was extracted from leukocytes and genotyped for single nucleotide polymorphisms (SNPs) in the vitamin D metabolism. Differences in plasma 25-hydroxyvitamin D were determined in the subgroups as well as between patients in CARMS 5 with or without subretinal fibrosis.

RESULTS

Plasma 25-hydroxyvitamin D was comparable in patients across CARMS groups 1 to 5 (p = 0.83). In CARMS 5, the presence of subretinal fibrosis was associated with significantly lower concentrations of 25-hydroxyvitamin D as compared to the absence of subretinal fibrosis (47.2 versus 75.6 nmol/L, p<0.001). Patients in CARMS 5 with subretinal fibrosis were more likely to have insufficient levels of 25-hydroxyvitamin D compared to patients without subretinal fibrosis (p = 0.006). No association was found between the SNPs rs10877012, rs2228570, rs4588, or rs7041 and AMD subgroups or plasma 25-hydroxyvitamin levels.

CONCLUSIONS

This study suggests that the presence of subretinal fibrosis in patients belonging to CARMS 5 may be associated with a poor vitamin D status. Our observations warrant further investigation into the role of vitamin D in the development of subretinal fibrosis.

Progesterone enhances calcitriol antitumor activity by upregulating vitamin D receptor expression and promoting apoptosis in endometrial cancer cells

Human studies suggest that progesterone and calcitriol may prove beneficial in preventing or inhibiting oncogenesis, but the underlying mechanism is not fully understood. The current study investigates the effects of progesterone, calcitriol, and their combination on immortalized human endometrial epithelial cells and endometrial cancer cells and identifies their targets of action. Combination treatment with both agents enhanced vitamin D receptor expression and inhibited cell proliferation through caspase-3 activation and induction of G0-G1 cell-cycle arrest with associated downregulation of cyclins D1 and D3 and p27 induction. We used mass spectrometry-based proteomics to measure protein abundance differences between calcitriol-, progesterone-, or combination-exposed endometrial cells. A total of 117 proteins showed differential expression among these three treatments. Four proteins were then selected for validation studies: histone H1.4 (HIST1H1E), histidine triad nucleotide-binding protein 2 (HINT2), IFN-induced, double-stranded RNA-activated protein kinase (EIF2AK2), and Bcl-2-associated X protein (BAX). Abundance levels of selected candidates were low in endometrial cancer cell lines versus the immortalized endometrial epithelial cell line. All four proteins displayed elevated expression in cancer cells upon exposure to calcitriol, progesterone, or the combination. Further BAX analysis through gain- or loss-of-function experiments revealed that upregulation of BAX decreased cell proliferation by changing the BAX:BCL-2 ratio. Knockdown of BAX attenuated progesterone- and calcitriol-induced cell growth inhibition. Our results showed that progesterone and calcitriol upregulate the expression of BAX along with other apoptosis-related proteins, which induce inhibition of endometrial cancer cell growth by apoptosis and cell-cycle arrest.

Vitamin D and breast cancer: emerging concepts

The benefit of vitamin D in cancer prevention and to certain extent therapy has been well recognized. The active form of vitamin D, 1,25-dihydroxycholecalciferol (1,25(OH)2 D3) is a natural ligand for vitamin D receptor (VDR). Since 1,25(OH)2D3 exerts toxic effects at a concentration that is beneficial, nearly 1500 analogs of vitamin D have been synthesized and evaluated for their efficacy in a variety of carcinogenesis and human cancer models both in vitro and in vivo. Among these only a handful of them have been approved for evaluation in clinical trials for leukemia, breast, prostate and colon cancers. The mechanism of vitamin D action is mediated by the nuclear VDR and the signaling cascade for its action is extensively reported. In this review we focus on the newer concepts for vitamin D action. These include (1) differential effects of vitamin D in maintaining cell proliferation when the cells are under stress but suppressing cell growth when the cells are transformed; (2) functional significance of VDR polymorphism in potential vitamin D responsiveness; (3) regulation of constitutive splicing of vitamin D target gene, CYP24a, by the hormone and its significance; and (4) regulation of microRNA by vitamin D in breast cancer. It is anticipated that the new work in these selective areas would expand the understanding of vitamin D in breast cancer prevention and therapy.