Will analogs of 1,25-dihydroxyvitamin D(3) (calcitriol) open a new era in cancer therapy?

Antiproliferative Activity of Non-Calcemic Vitamin D Analogs on Human Melanoma Lines in Relation to VDR and PDIA3 Receptors

Vitamin D is a precursor for secosteroidal hormones, which demonstrate pleiotropic biological activities, including the regulation of growth and the differentiation of normal and malignant cells. Our previous studies have indicated that the inhibition of melanoma proliferation by a short side-chain, low calcemic analog of vitamin D—21(OH)pD is not fully dependent on the expression of vitamin D receptor (VDR). We have examined the effects of classic vitamin D metabolites, 1,25(OH)₂D₃ and 25(OH)D₃, and two low calcemic vitamin D analogs, (21(OH)pD and calcipotriol), on proliferation, mRNA expression and vitamin D receptor (VDR) translocation in three human melanoma cell lines: WM98, A375 and SK-MEL-188b (subline b of SK-MEL-188, which lost responsiveness to 1,25(OH)₂D₃ and became VDR^−/−CYP27B1^−/−). All tested compounds efficiently inhibited the proliferation of WM98 and A375 melanoma cells except SK-MEL-188b, in which only the short side-chain vitamin D analog—21(OH)pD was effective. Overall, 21(OH)pD was the most potent compound in all three melanoma cell lines in the study. The lack of responsiveness of SK-MEL-188b to 1,25(OH)₂D₃, 25(OH)D₃ and calcipotriol is explained by a lack of characteristic transcripts for the VDR, its splicing variants as well as for vitamin D-activating enzyme CYP27B1. On the other hand, the expression of VDR and its splicing variants and other vitamin D related genes (RXR, PDIA3, CYP3A4, CYP2R1, CYP27B1, CYP24A1 and CYP11A1) was detected in WM98 and A375 melanomas with the transcript levels being modulated by vitamin D analogs. The expression of VDR isoforms in WM98 cells was stimulated strongly by calcipotriol. The antiproliferative activities of 21(OH)pD appear not to require VDR translocation to the nucleus, which explains the high efficacy of this noncalcemic pregnacalciferol analog in SK-MEL-188b melanoma, that is, VDR^−/−. Therefore, we propose that 21(OH)pD is a good candidate for melanoma therapy, although the mechanism of its action remains to be defined.

Vitamins and Melanoma

A tremendous amount of information was published over the past decades in relation to the role of vitamins in various neoplastic diseases. In particular, several studies showed an inverse relationship between selected vitamins intake and cancer risk. In this review we will focus on the role played by vitamins in melanoma with particular regard to vitamin A, D, K, E and C. Given that vitamin supplementation is easy, convenient, and readily accepted by patients, in the future the use of vitamins in chemoprevention and therapy of melanoma could be encouraged if supported by pre-clinical and clinical evidence.

Antitumor effects of vitamin D analogs on hamster and mouse melanoma cell lines in relation to melanin pigmentation

Deregulated melanogenesis is involved in melanomagenesis and melanoma progression and resistance to therapy. Vitamin D analogs have anti-melanoma activity. While the hypercalcaemic effect of the active form of Vitamin D (1,25(OH)₂D₃) limits its therapeutic use, novel Vitamin D analogs with a modified side chain demonstrate low calcaemic activity. We therefore examined the effect of secosteroidal analogs, both classic (1,25(OH)₂D₃ and 25(OH)D₃), and novel relatively non-calcemic ones (20(OH)D₃, calcipotriol, 21(OH)pD, pD and 20(OH)pL), on proliferation, colony formation in monolayer and soft-agar, and mRNA and protein expression by melanoma cells. Murine B16-F10 and hamster Bomirski Ab cell lines were shown to be effective models to study how melanogenesis affects anti-melanoma treatment. Novel Vitamin D analogs with a short side-chain and lumisterol-like 20(OH)pL efficiently inhibited rodent melanoma growth. Moderate pigmentation sensitized rodent melanoma cells towards Vitamin D analogs, and altered expression of key genes involved in Vitamin D signaling, which was opposite to the effect on heavily pigmented cells. Interestingly, melanogenesis inhibited ligand-induced Vitamin D receptor translocation and ligand-induced expression of VDR and CYP24A1 genes. These findings indicate that melanogenesis can affect the anti-melanoma activity of Vitamin D analogs in a complex manner.

Compound screening and transcriptional profiling in human primary keratinocytes: a brief guideline

Cultured human primary keratinocytes constitute suitable targets for in-depth evaluation of the proliferative or differentiative potential of compounds. There is, however, a double-edged and intrinsically inseparable transition from biological activity to cytotoxicity for any agent under investigation. For that reason, we here first of all present an established protocol for the isolation, cultivation, and analysis of primary foreskin-derived keratinocytes. Taking calcitriol as example, we then reveal how a straightforward photometric cell culture assay can be exploited to assess overall cell viability in response to increasing compound doses. With predetermined cellular cytotoxicity at hand, physiologically meaningful (sub-toxic) compound concentrations for subsequent stimulation of cells can be readily selected, and, in doing so, differentially expressed genes with biological significance can be reliably identified.

The relevance of the vitamin D endocrine system (VDES) for tumorigenesis, prevention, and treatment of non-melanoma skin cancer (NMSC): Present concepts and future perspectives

Solar UV (UV)-B-radiation exerts both beneficial and adverse effects on human health. On the one hand, it is the most important environmental risk factor for the development of non-melanoma skin cancer [NMSC; most importantly basal (BCC) and squamous (SCC) cell carcinomas], that represent the most common malignancies in Caucasian populations. On the other hand, the human body's requirements of vitamin D are mainly achieved by UV-B-induced cutaneous photosynthesis. This dilemma represents a serious problem in many populations, for an association of vitamin D-deficiency and multiple independent diseases including various types of cancer has been convincingly demonstrated. In line with these findings, epidemiologic and laboratory investigations now indicate that vitamin D and its metabolites have a risk reducing effect for NMSC. Potential mechanisms of action include inhibition of the hedgehog signaling pathway (BCC) and modulation of p53-mediated DNA damage response (SCC). As a consequence of these new findings it can be concluded that UV-B-radiation exerts both beneficial and adverse effects on risk and prognosis of NMSC. It can be assumed that many independent factors, including frequency and dose of UV-B exposure, skin area exposed, and individual factors (such as skin type and genetic determinants of the skin`s vitamin D status and of signaling pathways that are involved in the tumorigenesis of NMSC) determine whether UV-B exposure promotes or inhibits tumorigenesis of NMSC. Moreover, these findings may help to explain many of the differential effects of UV-B radiation on risk of NMSC, including variation in the dose-dependent risk for development of SCC in situ (actinic keratosis, AK), invasive SCC, and BCC. In this review, we analyze the relevance of the vitamin D endocrine system (VDES) for tumorigenesis, prevention, and treatment of NMSC and give an overview of present concepts and future perspectives.

Vitamin D-insufficiency: An estimate of the situation in Germany

Background: Vitamin D insufficiency is increasingly recognized as an important risk factor in the pathogenesis of falls and fractures and may increase the risk of other diseases. The aim of this study was to obtain information about the vitamin D supply from a representative cohort of the German population.

 

Methods: 264 General practitioners participated in the DeViD-Trial (D-Vitamin in Deutschland) by taking blood samples from their consenting daily ambulant patients regardless of the actual reason for consultation. In these blood samples vitamin D [25(OH)D] and other related parameters were measured at a central laboratory. The patients filled in a simple questionnaire (i.e., age, sex, etc.). The trial was performed between February 26 and May 25, 2007.

Results: Laboratory and personal data were documented for 1,343 individuals (615 men, 728 women). The age distribution ranged from 20 to 99 y, the mean age of the whole cohort was 57.6 y (men 58.2, women 57.2). The mean 25-OH-D-value for the whole cohort was 16.2 ng/ml (range: 6.0 to 66.8, median 14.1 ng/ml). Ten percent of the patients had 25(OH)D-values below 7 ng/ml, 65% below 20 ng/ml and 92% showed values below 30 ng/ml.

In the more recent literature, 25(OH)D values below 30 ng/ml are regarded as sub-optimal for bone, muscle and general health. Correspondingly it can be stated that in this representative population there is a high prevalence of moderate to severe vitamin D-insufficiency regardless of young or old age

Fundamental questions to sun protection: A continuous education symposium on vitamin D, immune system and sun protection at the University of Zürich

Since exposure to sunlight is a main factor in the development of non-melanoma skin cancer and there are associations between malignant melanoma and short-term intense ultraviolet (UV) exposure, particularly burning in childhood, strict protection from UV-radiation is recommended. However, up to 90% of all requisite vitamin D has to be formed within the skin through the action of the sun-a serious problem, for a connection between vitamin D deficiency, demonstrated in epidemiological studies, and various types of cancer and other diseases has been confirmed. A UVB-triggered skin autonomous vitamin D(3) synthesis pathway has recently been described, producing the active Vitamin D metabolite calcitriol. This cutaneous vitamin D(3) pathway is unique. Keratinocytes and dendritic cells can convert vitamin D to calcitriol. Cutaneous T cells activated in the presence of calcitriol express the chemokine receptor CCR10 attracting them to the chemokine CCL27 that keratinocytes express selectively in the epidermis, and migrate from dermal layers of the skin to the epidermis under UV radiation. Thus, calcitriol has endocrine roles beyond its calciotropic action, including cell growth and cancer prevention. Therefore, strict sun protection procedures to prevent skin cancer may induce the risk of vitamin D deficiency. As there is evidence that the protective effect of less intense solar radiation can outweigh its mutagenic effect, better balanced approaches to sun protection should be sought.

Translational research on rapid steroid actions

Translational research is a burgeoning science that shows potential to improve the transition of research from bench to bedside. This novel science explores all major aspects of preclinical and clinical issues which are relevant for the success of translational pharmaceutical or medical device/diagnostic innovations. This includes target risk assessment, biomarker evaluation and predictivity grading both for efficacy and toxicity, early human trial design adequate to guide stop/go decisions on grounds of biomarker panels, and biostatistical methods to analyze multiple readout situations and quantify risk projections. Representing a comparably novel science, rapid steroid actions have been recognized to carry potential clinical implications in various fields. Findings in this field have not yet been successfully translated into clinically relevant new medicines except for neurosteroids. A promising compound is the membrane estrogen receptor agonist STX, which may be applicable for estrogen withdrawal symptoms. Nongenomic vitamin D analogs may be useful as antiinflammatory, anticancer or diabetes preventing agents. Further the membrane thyroid receptor agonist tetrac may be useful in cancer treatment. Unfortunately lazaroids (membrane-only active glucocorticoids), which have been clinically tested as neuroprotective agents, had to be abandoned because of lacking clinical efficacy. Yet, the hierarchy of antirheumatic glucocorticoid action in regard to their clinical potency may better correlate with their membrane effects than their ability to bind to the classic glucocorticoid receptor. To improve the translational success of the rapid actions of steroids research, scientists should become familiar with major aspects of translational work and always seek for translational dimensions in their research.

Position paper: Rapid responses to steroids: current status and future prospects

Steroids exert their actions through several pathways. The classical genomic pathway, which involves binding of steroids to receptors and subsequent modulation of gene expression, is well characterized. Besides this, rapid actions of steroids have been shown to exist. Since 30 years, research on rapid actions of steroids is an emerging field of science. Today, rapid effects of steroids are well established, and are shown to exist for every type of steroid. The classical steroid receptors have been shown to be involved in rapid actions, but there is also strong evidence that unrelated structures mediate these rapid effects. Despite increasing knowledge about the mechanisms and structures which mediate these actions, there is still no unanimous acceptance of this category. This article briefly reviews the history of the field including current controversies and challenges. It is not meant as a broad review of literature, but should increase the awareness of the endocrinology society for rapid responses to steroids. As members of the organizing committee of the VI International Meeting on Rapid Responses to Steroid Hormones 2009, we propose a research agenda focusing on the identification of new receptoral structures and the identification of mechanisms of actions at physiological steroid concentrations. Additionally, efforts for the propagation of translational studies, which should finally lead to clinical benefit in the area of rapid steroid action research, should be intensified.

Cutaneous vitamin D synthesis versus skin cancer development: The Janus faces of solar UV-radiation

In scientific and public communities, there is an ongoing discussion how to balance between positive and negative effects of solar UV-exposure. On the one hand, solar UV-radiation represents the most important environmental risk factor for the development of non-melanoma skin cancer. Consequently, UV protection is an important measure to prevent these malignancies, especially in risk groups. Otherwise, approximately 90% of all vitamin D needed by the human body has to be formed in the skin through the action of UV-radiation. This dilemma represents a serious problem, for an association of vitamin D-deficiency and multiple independent diseases including various types of cancer, bone diseases, autoimmune diseases, infectious diseases, cardiovascular diseases and hypertension has now been reported in a large number of investigative and epidemiologic studies. As a consequence, it has been assumed that for the general population in the US, Europe and other countries, the net effects of solar UV B-radiation on human health are beneficial at or near current levels. We and others have shown that strict sun protection causes vitamin D-deficiency/insufficiency and that detection and treatment of vitamin D-deficiency in sun deprived risk groups is of high importance. Although further work is necessary to define an adequate vitamin D-status and adequate guidelines for solar and artificial UV-exposure, it is at present mandatory that public health campaigns and sun protection recommendations to prevent skin cancer consider these facts. In this review, we analyze the present literature to help developing well-balanced recommendations on sun protection that ensure an adequate vitamin D-status. These recommendations will hopefully protect us against adverse effects of UV protection without significantly increasing the risk to develop UV-induced skin cancer.

Effect of a vitamin D(3) derivative (B3CD) with postulated anti-cancer activity in an ovarian cancer animal model

The objective of the present study was to test the hypothesis that Calcidiol derivative B3CD qualifies as a potential anti-cancer drug in vivo employing an ovarian cancer xenograft model in mice. In addition, the selectivity of B3CD on viability and proliferation of platinum-resistant human ovarian cancer cell lines in comparison to control cell lines was analyzed in vitro. B3CD displayed cell line-specific cytotoxicity screened against a panel of ovarian and other carcinoma cell lines, endothelial and control cells. B3CD, at sub-cytotoxic concentrations, revealed stronger effects on the proliferation of SKOV-3 ovarian cancer cells vs. primary fibroblasts as determined by BrdU incorporation analysis. Treatment with B3CD at 0.5 microM resulted in highly condensed chromatin and fragmented nuclei in SKOV-3 cells but not in primary fibroblasts. B3CD induced cell death at low drug concentrations (< or = 0.5 microM) in SKOV-3 ovarian cancer cells is mediated by the p38 MAPK signaling pathway: B3CD induced p38 MAPK expression and activation in SKOV-3 cells and inhibition of p38 signaling counteracted B3CD induced cell death in vitro. An ovarian cancer cell animal model (human SKOV-3 cell derived xenografts in nude mice) revealed that tumor growth in few B3CD treated mice accelerated while the majority of B3CD treated mice displayed delayed tumor growth or full tumor regression. B3CD possesses anti-ovarian cancer properties in vitro and in vivo. We propose the further development of non-calcemic bromoacetoxy derivatives of vitamin D(3) as potential anti-cancer therapeutics.

Anti-proliferative and pro-apoptotic properties of 3-bromoacetoxy calcidiol in high-risk neuroblastoma

The cytotoxic, anti-proliferative and apoptotic effects of 3-Bromoacetoxy Calcidiol (B3CD), a derivative of vitamin D3 precursor calcidiol, on human neuroblastoma (NB) cells were examined. NB, predominantly a tumor of early childhood, is the most common extracranial solid tumor. Despite aggressive treatments, survival for advanced stages remains low and novel treatment strategies are needed. B3CD-induced apoptosis in various neuroblastic cells via caspases-3 and -9 activation. B3CD upregulated mitochondrial pro-apoptotic Bax and anti-apoptotic Bcl-2 expression, caused cytochrome c release, downregulated N-Myc expression and activated pro-survival marker Akt. Accordingly, B3CD treatment dose dependently reduced the viability of NB cells with IC50 values between 1 and 3 microm. The cytotoxicity of B3CD was significantly higher than for the calcemic parent-compound vitamin D3 (IC50 between 10 and 30 microm). Further studies revealed that B3CD treatment inhibits the proliferation of NB cells at low concentrations (IC50 between 30 and 100 nm). Cell cycle analysis showed a dramatic increase in the apoptotic sub-diploidal population along with a cell cycle block. In summary, the present study shows that B3CD is toxic to NB cells via suppression of cell proliferation and cell viability by caspase activation and regulation of survival signals. These results suggest that B3CD could be developed as a treatment for NB.

Calcitriol sensitizes colon cancer cells to H2O2-induced cytotoxicity while inhibiting caspase activation

The anti-cancer activity of calcitriol, the active metabolite of Vitamin D, in the colon is usually attributed to its anti-proliferative and pro-differentiative actions. The levels of reactive oxygen species (ROS) are high in colon carcinomas due to increased aerobic metabolism and exposure to various anti-cancer modalities. We examined whether calcitriol modulates the response of colon cancer cells to the cytotoxic action of the common mediator of ROS injury, H2O2. Pretreatment with calcitriol (100 nM, 48 h) sensitized HT-29 colon cancer cells to cell death induced by acute exposure to H2O2 or chronic exposure to the H2O2 generating system, glucose/glucose-oxidase. Although the morphological features of H2O2-induced HT-29 cell death are consistent with apoptosis, we detected no executioner caspase activation in response to cytotoxic concentrations of H2O2 and treatment with a pan-caspase inhibitor did not affect H2O2-induced cytotoxicity nor its enhancement by calcitriol. Conversely, exposure of HT-29 cells to sub-toxic concentrations of H2O2 resulted in low executioner caspase activation that was inhibited by pretreatment with calcitriol. The sensitization of colon cancer cells to ROS-induced cytotoxicity may contribute to its assumed action as a chemopreventive agent and to its therapeutic potential alone or in combination with other anti-cancer modalities.

E-cadherin and vitamin D receptor regulation by SNAIL and ZEB1 in colon cancer: clinicopathological correlations

E-cadherin (CDH1) gene expression is strictly regulated. The transcriptional factors SNAIL and ZEB1 are involved in its repression, whereas activation of vitamin D receptor (VDR) by vitamin D induces its transcription. We study the expression and functional correlation of SNAIL, CDH1, VDR and ZEB1 genes and examine their possible involvement in colon cancer. The expression of these four genes was measured by real time-PCR in 114 patients with colorectal cancer, and tumor characteristics were analyzed in each patient. SNAIL expression was associated with downregulation of CDH1 (P < 0.001) and VDR (P < 0.001) gene products. We also found a positive correlation between CDH1 and VDR expressions. However, the association between SNAIL and CDH1 was not found in patients with high expression of ZEB1. We observed a correlation between downregulation of: a) ZEB1 and presence of polyps in surgical resections; b) VDR and poor differentiation and c) CDH1 and poor differentiation, vascular invasion, presence of lymph node metastases and advanced stages; as well as a trend toward a correlation between SNAIL expression in tumors and vascular invasion. The correlations between SNAIL, CDH1, VDR and ZEB1 and the association between reduced expression of CDH1 and VDR and aggressive tumor characteristics emphasize the value of analyzing these genes in colon cancer patients for prognostic purposes and for predicting response to possible therapies with vitamin D or its analogs.

Vitamin D compounds in leukemia

The biologically active form of vitamin D, 1,25-dihydroxyvitamin D3 [1,25(OH)(2)D3,] possess in vitro multiple anti-cancer activities including growth arrest, induction of apoptosis and differentiation of a variety of different types of malignant cells. However, its use as a therapeutic agent is hindered by its calcemic effects. Analogs of 1,25(OH)(2)D3 have enhanced anti-tumor activity, with reduced calcemic effects. However, limited clinical studies using vitamin D compounds have not yet achieved major clinical success. Nevertheless, pre-clinical studies suggest that the combination of either 1,25(OH)(2)D3 or its analogs with other agents can have additive or synergistic anti-cancer activities, suggesting future clinical studies.

Vitamin D sensitizes breast cancer cells to the action of H2O2: mitochondria as a convergence point in the death pathway

Calcitriol, the hormonal form of vitamin D3, sensitizes breast cancer cells to reactive oxygen species (ROS)-dependent cytotoxicity induced by various anticancer modalities. This effect could be due to increased generation of ROS and/ or to increased sensitivity of the target cells to ROS. This work examined the effect of calcitriol on the damage inflicted on breast cancer cells by the direct action of ROS represented by H2O2. Treatment of MCF-7 cells with H2O2 resulted in activation of caspase 7 as well as induction of caspase-independent cell death. Both were enhanced by 48-72 h of pretreatment with calcitriol. This effect was not due to modulation of H2O2 degradation or to a specific effect on *OH-mediated cytotoxicity. The H2O2-induced drop in mitochondrial membrane potential and release of cytochrome c were enhanced by calcitriol. These findings indicate that calcitriol sensitizes breast cancer cells to ROS-induced death by affecting event(s) common to both caspase-dependent and -independent modes of cell death upstream to mitochondrial damage.

Differential biological effects of 1,25-dihydroxyVitamin D3 on melanoma cell lines in vitro

1,25-DihydroxyVitamin D(3) and analogs have been shown to inhibit proliferation and to induce differentiation in different cell types, including human melanocytes. However, various tumor cell lines that fail to respond to the antiproliferative effects of Vitamin D analogs have also been reported. Using real-time PCR (LightCycler), we have compared mRNA expression of Vitamin D receptor (VDR), Vitamin D-25-hydroxylase (25-OHase), 25-hydroxyVitamin D-1alpha-hydroxylase (1alpha-OHase), and 1,25-dihydroxyVitamin D-24-hydroxylase (24-OHase) in a melanoma cell line that responds to antiproliferative effects of Vitamin D (MeWo) with a non-responsive melanoma cell line (SkMel5). Additionally, modulation of cell proliferation by calpain inhibitors, as well as regulation of mRNA expression of VDR, 1alpha-OHase, and 24-OHase genes by Vitamin D analogs were assessed in melanoma cell lines in vitro using a WST-1 based colorimetric assay and real-time PCR, respectively. RNA for VDR, 25-OHase, 1alpha-OHase, and 24-OHase was detected in melanoma cell lines. In contrast to SkMel5 cells, treatment of MeWo cells with calcitriol resulted in a dose-dependent increase in mRNA for VDR and 24-OHase as well as in a suppression of cell proliferation (up to approximately 50%). Our findings demonstrate that local synthesis or metabolism of Vitamin D metabolites may be of importance for growth regulation of MM and melanoma cell lines. Additionally, metastasizing MM represents a promising target for palliative treatment with new Vitamin D analogs that exert little calcemic side effects or for pharmacological modulation of calcitriol synthesis/metabolism in these tumors.

No evidence for amplification of 25-hydroxyvitamin D-1alpha-OHase (1alpha-OHase) or 1,25-dihydroxyvitamin D-24-OHase (24-OHase) genes in malignant melanoma (MM)

Increasing evidence points at an important function of Vitamin D metabolites for growth regulation in various tissues, including MM. Using array CGH, amplification of 24-OHase was recently detected as a likely target oncogene of the amplification unit 20q13.2 in breast cancer cell lines and tumors. Additionally, amplification of 1alpha-OHase has been reported in human malignant glioma. Using immunohistochemistry, we have now detected nuclear Vitamin D receptor (VDR) immunoreactivity in primary cutaneous malignant melanoma (MM), indicating that Vitamin D metabolites may be of importance for the growth regulation in these tumors. Using Southern analysis, we have analyzed MM and metastases for evidence of amplification of 1alpha-OHase or 24-OHase genes. Our results do not support the hypothesis that amplification of 1alpha-OHase or 24-OHase genes may be of importance for pathogenesis or progression of MM.

Analysis of the vitamin D system in cutaneous malignancies

1,25-dihydroxyvitamin D3, the biological active metabolite of vitamin D, has great impact on keratinocyte growth and differentiation, and consequently has already been successfully used in the therapy of hyperproliferative skin disorders. We have now characterized the key components of the vitamin D system (VDR, 1alpha-OHase, 24-OHase and 25-OHase) in cutaneous basal cell carcinomas (BCC) and squamous cell carcinomas (SCC), using immunohistochemical and quantitative real-time PCR techniques. Additionally, proliferative activity (Ki-67 expression), differentiation status (cytokeratin 10 and transglutaminase K expression), rate of apoptosis (TUNEL assay) and the abundance of the main heterodimerization partners of VDR (RXRs) was determined for these tumours and correlated with the components of the Vitamin D system. Our findings indicate that the Vitamin D system may be of high importance for the growth behaviour of BCCs and SCCs and that new vitamin D analogues that exert less calcaemic side effects may be effective in the prevention or treatment of these tumours.

The role of reactive oxygen species in the anticancer activity of vitamin D

Calcitriol, the hormonal form of vitamin D, enhances the anticancer activity of the immune cytokine tumor necrosis factor, interleukin 1 and interleukin 6 in human breast and renal cell carcinoma cells without affecting the cytotoxic action of interferon-alpha or killer lymphocytes. It also enhances cytotoxicity induced by the anticancer drug doxorubicin, by the redox cycling quinone menadione, and by the reactive oxygen species hydrogen peroxide. The synergistic interaction was accompanied by increased oxidative stress, as manifested by glutathione depletion and was abolished by exposure to the thiol antioxidant N-acetylcysteine. The hormone on its own brought about an increase in the cellular redox state as reflected in the ratio between oxidized and reduced glutathione and glyceraldehyde-3-phosphate dehydrogenase, and a reduction in the expression of the antioxidant enzyme Cu/Zn superoxide dismutase. These results support the notion that the interplay between active vitamin D derivatives and other anticancer agents such as immune cytokines and anticancer drugs plays a role in the in vivo anticancer activity of vitamin D and that reactive oxygen species are involved in the anticancer activity of vitamin D on its own and in its cross-talk with other anticancer modalities.

Modulation of X-ray-induced apoptosis in human keratinocytes (HaCaT) by 1,25-dihydroxyvitamin D3

Possible effects of 1,25-dihydoxyvitamin D3 (vitamin D) on ionizing radiation-induced cell damage have been unknown until now. The task of the present study was to analyze, in a human keratinocyte cell line (HaCaT), the effects of a preincubation with vitamin D on the X-ray-induced mRNA expression of different genes related to apoptosis (gene array). The first results show that ionizing radiation leads to a down-regulation of various apoptosis-relevant genes in HaCaT cells pretreated with vitamin D. Therefore it can be speculated that vitamin D could prove to be a promising radioprotective substance.

A novel vitamin D-regulated immediate-early gene, IEX-1, alters cellular growth and apoptosis

1alpha,25-Dihydroxyvitamin D3 (1alpha,25(OH)2D3) inhibits the expression of an immediate-early gene, IEX-1, which is involved in the regulation of cellular growth and apoptosis in a variety of cells. 1alpha,25(OH)2D3 alters the subcellular localization of IEX-1 by causing an efflux of IEX-1 from the nucleus, and the sterol decreases the expression of IEX-1 messenger RNA in cells via a novel DR3 repeat-type DNA response element.