Stage-specific inhibition of mammary carcinogenesis by 1alpha-hydroxyvitamin D5

Non-Musculoskeletal Benefits of Vitamin D beyond the Musculoskeletal System

Vitamin D, a fat-soluble prohormone, is endogenously synthesized in response to sunlight or taken from dietary supplements. Since vitamin D receptors are present in most tissues and cells in the body, the mounting understanding of the role of vitamin D in humans indicates that it does not only play an important role in the musculoskeletal system, but has beneficial effects elsewhere as well. This review summarizes the metabolism of vitamin D, the research regarding the possible risk factors leading to vitamin D deficiency, and the relationships between vitamin D deficiency and numerous illnesses, including rickets, osteoporosis and osteomalacia, muscle weakness and falls, autoimmune disorders, infectious diseases, cardiovascular diseases (CVDs), cancers, and neurological disorders. The system-wide effects of vitamin D and the mechanisms of the diseases are also discussed. Although accumulating evidence supports associations of vitamin D deficiency with physical and mental disorders and beneficial effects of vitamin D with health maintenance and disease prevention, there continue to be controversies over the beneficial effects of vitamin D. Thus, more well-designed and statistically powered trials are required to enable the assessment of vitamin D’s role in optimizing health and preventing disease.

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.

Vitamin D4 in mushrooms

An unknown vitamin D compound was observed in the HPLC-UV chromatogram of edible mushrooms in the course of analyzing vitamin D(2) as part of a food composition study and confirmed by liquid chromatography-mass spectrometry to be vitamin D(4) (22-dihydroergocalciferol). Vitamin D(4) was quantified by HPLC with UV detection, with vitamin [(3)H] itamin D(3) as an internal standard. White button, crimini, portabella, enoki, shiitake, maitake, oyster, morel, chanterelle, and UV-treated portabella mushrooms were analyzed, as four composites each of a total of 71 samples from U.S. retail suppliers and producers. Vitamin D(4) was present (>0.1 µg/100 g) in a total of 18 composites and in at least one composite of each mushroom type except white button. The level was highest in samples with known UV exposure: vitamin D enhanced portabella, and maitake mushrooms from one supplier (0.2-7.0 and 22.5-35.4 µg/100 g, respectively). Other mushrooms had detectable vitamin D(4) in some but not all samples. In one composite of oyster mushrooms the vitamin D(4) content was more than twice that of D(2) (6.29 vs. 2.59 µg/100 g). Vitamin D(4) exceeded 2 µg/100 g in the morel and chanterelle mushroom samples that contained D(4), but was undetectable in two morel samples. The vitamin D(4) precursor 22,23-dihydroergosterol was found in all composites (4.49-16.5 mg/100 g). Vitamin D(4) should be expected to occur in mushrooms exposed to UV light, such as commercially produced vitamin D enhanced products, wild grown mushrooms or other mushrooms receiving incidental exposure. Because vitamin D(4) coeluted with D(3) in the routine HPLC analysis of vitamin D(2) and an alternate mobile phase was necessary for resolution, researchers analyzing vitamin D(2) in mushrooms and using D(3) as an internal standard should verify that the system will resolve vitamins D(3) and D(4).

Vitamin D and cancer: a review of molecular mechanisms

The population-based association between low vitamin D status and increased cancer risk can be inconsistent, but it is now generally accepted. These relationships link low serum 25OHD (25-hydroxyvitamin D) levels to cancer, whereas cell-based studies show that the metabolite 1,25(OH)2D (1,25-dihydroxyvitamin D) is a biologically active metabolite that works through vitamin D receptor to regulate gene transcription. In the present review we discuss the literature relevant to the molecular events that may account for the beneficial impact of vitamin D on cancer prevention or treatment. These data show that although vitamin D-induced growth arrest and apoptosis of tumour cells or their non-neoplastic progenitors are plausible mechanisms, other chemoprotective mechanisms are also worthy of consideration. These alternative mechanisms include enhancing DNA repair, antioxidant protection and immunomodulation. In addition, other cell targets, such as the stromal cells, endothelial cells and cells of the immune system, may be regulated by 1,25(OH)2D and contribute to vitamin D-mediated cancer prevention.

Androgen Receptor regulation of Vitamin D receptor in response of castration-resistant prostate cancer cells to 1α-Hydroxyvitamin D5 - a calcitriol analog

Calcitriol (1,25(OH)(2)D3) is cytostatic for prostate cancer (CaP), but had limited therapeutic utility due to hypercalcemia-related toxicities, leading to the development of low-calcemic calcitriol analogs. We show that one analog, 1-α-Hydroxyvitamin-D5 (1α(OH)D5), induced apoptosis in castration-sensitive LNCaP prostate cancer cells, but unlike calcitriol, did not increase androgen receptor (AR) transcriptional activity. LNCaP-AI, a castrate-resistant (CRCaP) LNCaP subline, was resistant to 1α(OH)D5 in the presence of androgens; however, androgen withdrawal (AWD), although ineffective by itself, sensitized LNCaP-AI cells to 1α(OH)D5. Investigation of the mechanism revealed that the vitamin D receptor (VDR), which mediates the effects of 1α(OH)D5, is downregulated in LNCaP-AI cells compared to LNCaP in the presence of androgens, whereas AWD restored VDR expression. Since LNCaP-AI cells expressed higher AR compared to LNCaP and AWD decreased AR, this indicated an inverse relationship between VDR and AR. Further, AR stimulation (by increased androgen) suppressed VDR, while AR downregulation (by ARsiRNA) stimulated VDR levels and sensitized LNCaP-AI cells to 1α(OH)D5 similar to AWD. Another cell line, pRNS-1-1, although isolated from a normal prostate, had lost AR expression in culture and adapted to androgen-independent growth. These cells expressed the VDR and were sensitive to 1α(OH)D5, but restoration of AR expression suppressed VDR levels and induced resistance to 1α(OH)D5 treatment. Taken together, these results demonstrate negative regulation of VDR by AR in CRCaP cells. This effect is likely mediated by prohibitin (PHB), which was inhibited by AR transcriptional activity and stimulated VDR in CRCaP, but not castrate-sensitive cells. Therefore, in castration sensitive cells, although the AR negatively regulates PHB, this does not affect VDR expression, whereas in CRCaP cells, negative regulation of PHB by the AR results in concomitant negative regulation of the VDR by the AR. These data demonstrate a novel mechanism by which 1α(OH)D5 prolong the effectiveness of AWD in CaP cells.

Antiproliferative action of menadione and 1,25(OH)2D3 on breast cancer cells

Calcitriol or 1,25(OH)(2)D(3) is a negative growth regulator of MCF-7 breast cancer cells. The growth arrest is due to apoptosis activation, which involves mitochondrial disruption. This effect is blunted in vitamin D resistant cells (MCF-7(DRes) cells). Menadione (MEN), a glutathione (GSH)-depleting compound, may potentiate antitumoral effects of anticancer drugs. The aim of this study was to investigate whether MEN enhances cellular responsiveness of MCF-7 cells to 1,25(OH)(2)D(3). Cells were cultured and treated with different concentrations of 1,25(OH)(2)D(3)+/-MEN or vehicle for 96 h. GSH levels and the activity of antioxidant enzymes were determined by spectrophotometry and ROS production by flow cytometry. Both drugs decreased growth and enhanced ROS in MCF-7 cells, obtaining the maximal effects when 1,25(OH)(2)D(3) was combined with MEN (P<0.01 vs. Control and vs. each compound alone). MCF-7(DRes) cells were not responsive to 1,25(OH)(2)D(3), but the cell proliferation was slightly inhibited by the combined treatment. Calcitriol and MEN separately enhanced antioxidant enzyme activities, but when they were used in combination, the effect was more pronounced (P<0.05 vs. Control and vs. each compound alone). MEN, calcitriol and the combined treatment decreased GSH levels (P<0.05 vs. Control). The data indicate that MEN potentiates the effect of 1,25(OH)(2)D(3) on growth arrest in MCF-7 cells by oxidative stress and increases the activities of antioxidant enzymes, probably as a compensatory mechanism.

25-Hydroxyvitamin D3 is a natural chemopreventive agent against carcinogen induced precancerous lesions in mouse mammary gland organ culture

Despite the role of vitamin D(3) endocrine system in prevention of mammary gland transformation in animal models, use of 1,25(OH)(2)D(3 )in clinical settings is precluded due to its toxicity in vivo. Therefore much effort has been placed in developing relatively non-toxic vitamin D analogs. Recently, with the discovery of the expression of 25-hydroxy vitamin D(3) 1alpha-hydroxylase (CYP27B1) in multiple extrarenal organs, the functional role of prohormone, 25-hydroxyvitamin D(3) [25(OH)D(3)], has been redefined. Since 25(OH)D(3) does not cause hypercalcemia and maintains relative high concentration in serum, it is possible that the prohormone can be converted to active hormone in mammary epithelial cells to provide chemopreventive effects. In the present study, we evaluated its functional significance using mouse mammary organ culture (MMOC) system. We first showed that 25(OH)D(3) 1alpha-hydroxylase is extensively expressed in mammary ductal epithelial cells at both protein and mRNA levels, which is a prerequisite for 25(OH)D(3) to function in an autocrine/paracrine manner. However, we also observed that clotrimazol (1alpha-hydroxylase inhibitor) enhanced 25(OH)D(3) -induced CYP24 expression in breast cancer cells. In mammary glands derived from 1alpha-hydroxylase knockout mice, 25(OH)D(3) treatment in organ culture significantly induced CYP24 expression, indicating a potential direct effect of 25(OH)D(3). In MMOC, 100-250 nM 25(OH)D(3) suppressed both ovarian hormone-dependent and -independent mammary precancerous lesions (induced by DMBA) by more than 50%, while the active hormone 1,25(OH)(2)D(3) (positive control) at 100 nM suppressed alveolar lesions by more than 80%. The inactive vitamin D(3) (negative control) at 100 nM suppressed alveolar lesions by only 20% (P>0.05). We found that 25(OH)D(3) inhibits DMBA-induced mammary alveolar lesions (MAL) in a stage-specific manner: 25(OH)D(3) mainly inhibits the promotion stage of lesion formation. We conclude that 25(OH)D(3) could serve as a non-toxic natural chemopreventive agent for further development for breast cancer prevention.

Targets of vitamin D receptor signaling in the mammary gland

Since the discovery of the vitamin D receptor (VDR) in mammary cells, the role of the vitamin D signaling pathway in normal glandular function and in breast cancer has been extensively explored. In vitro studies have shown that the VDR ligand, 1,25-dihydroxyvitamin D (1,25D), modulates key proteins involved in signaling proliferation, differentiation, and survival of normal mammary epithelial cells. Similar anti-proliferative and pro-differentiating effects of 1,25D have been observed in VDR-positive breast cancer cells, indicating that transformation per se does not abolish vitamin D signaling. However, many transformed breast cancer lose sensitivity to 1,25D secondary to alterations in vitamin D metabolizing enzymes or downregulation of VDR function. Over the years, our laboratory has focused on three general areas: (1) defining mechanisms of vitamin D-mediated apoptosis in breast cancer cells, (2) examining changes in the vitamin D signaling pathway during transformation, including the development of vitamin D resistance, and (3) using mouse models to study the impact of the VDR on growth regulatory pathways in the context of development and tumorigenesis in vivo. Recent developments include detection of megalin-mediated uptake of vitamin D-binding protein (DBP) and identification of CYP27B1 and CYP24 metabolizing enzymes in mammary cells, demonstration of precocious mammary gland development in VDR-null mice, and identification of novel pathways triggered by 1,25D during apoptosis. Our preclinical studies have been complemented by emerging data from other groups suggesting that human breast cancer may be influenced by VDR genotype and vitamin D status. Collectively, these studies have reinforced the need to further define the regulation and function of the vitamin D pathway in cells in relation to prevention and treatment of breast cancer.

Prohibitin is a novel target gene of vitamin D involved in its antiproliferative action in breast cancer cells

Previously, we showed that N-methyl-N-nitrosourea-transformed MCF12F breast epithelial cells exhibited differential expression of several genes, including up-regulation of prohibitin and elevated sensitivity to a relatively noncalcemic vitamin D analogue, 1alpha-hydroxyvitamin D5 [1alpha(OH)D5]. In this report, we evaluated the functional significance of prohibitin in relation to the cellular response to vitamin D. The in silico screening for putative transcription factor binding sites identified two vitamin D receptor (VDR)/retinoid X receptor binding sites in the 1-kb promoter region of prohibitin. Prohibitin up-regulation by 1alpha(OH)D5 treatment at both transcriptional and translational levels was confirmed by real-time reverse transcription-PCR and Western blot analysis in breast cancer cells, identifying prohibitin as a vitamin D target gene. Confocal microscopic analysis showed that prohibitin was localized in the nuclei of MCF-7 cells and a portion of prohibitin was colocalized with VDR, but direct physical interaction between VDR and prohibitin in cell lysates was not detectable. In MCF-7 cells expressing tetracycline-inducible prohibitin (Tet-On model), the overexpression of prohibitin inhibited cell proliferation and enhanced vitamin D-induced antiproliferative activity. Knockdown of prohibitin was accompanied by increased number of cells incorporating bromodeoxyuridine in the whole population and increased cell distribution in the S phase of cell cycle. In addition, prohibitin level had no significant effect on the vitamin D-induced transactivation of CYP24, a VDR target gene. This is the first report to suggest that prohibitin serves as a novel vitamin D target gene, which is involved in the antiproliferative action of vitamin D without affecting CYP24 transactivation in breast cancer cells.

Vitamin D and cancer

The impact of dietary intake upon cell and tissue physiology, as well as pathophysiology, has emerged as being highly significant to the etiology of a number of high-profile malignancies. The vitamin D receptor (VDR) is a member of a large transcription factor family of nuclear receptors and responds specifically to a hormonal micronutrient (1α25(OH)₂D₃). A central endocrine role for this receptor in bone health was established at the beginning of the 20th century. An alternative role has been established over the last 25 years for the VDR to regulate cell growth and division, and promote differentiation through autocrine and paracrine mechanisms. These findings from in vitro and in vivo experiments have generated considerable interest in the potential to target the VDR in either chemoprevention or chemotherapy cancer settings. As with many potential cancer therapeutics, it has become equally clear that cancer cells display de novo and acquired mechanisms of resistance to these actions. Consequently, researchers are developing a range of experimental and clinical options to bring about more targeted actions, overcome resistance and enhance the efficacy of VDR-centered therapeutics.

Growth inhibition of carcinogen-transformed MCF-12F breast epithelial cells and hormone-sensitive BT-474 breast cancer cells by 1alpha-hydroxyvitamin D5

Several studies have established the active form of vitamin D(3) as an effective tumor-suppressing agent; however, its antitumor activity is achieved at doses that are hypercalcemic in vivo. Therefore, less calcemic vitamin D(3) analog, 1alpha-hydroxy-24-ethyl-cholecalciferol (1alpha[OH]D5), was evaluated for its potential use in breast cancer chemoprevention. Previously, 1alpha(OH)D5 showed anticarcinogenic activity in several in vivo and in vitro models. However, its effects on growth of normal tissue were not known. The present study was conducted to determine the effects of 1alpha(OH)D5 on the growth of normal mouse mammary gland and normal-like human breast epithelial MCF-12F cells and to compare these effects with carcinogen-transformed MCF-12F and breast cancer cells. No significant difference was observed in the growth or morphology of cultured mouse mammary gland and MCF-12F cells in the presence of 1alpha(OH)D5. However, the transformed MCF-12F cells underwent growth inhibition (40-60%, P < 0.05) upon 1alpha(OH)D5 treatment as determined by cell viability assays. Cell cycle analysis showed marked increase (50%) in G-1 phase for cells treated with 1alpha(OH)D5 compared with the controls. Moreover, the percentage of cells in the synthesis (S) phase of cell cycle was decreased by 70% in transformed MCF-12F, BT-474 and MCF-7 cells. The growth arrest was preceded by an increase in expression of cell cycle regulatory proteins p21(Waf-1) and p27(Kip-1). In addition, differential expression studies of parent and transformed MCF-12F cell lines using microarrays showed that prohibitin mRNA was increased 4-fold in the transformed cells. These results indicate that the growth inhibitory effect of 1alpha(OH)D5 was achieved in both carcinogen-transformed MCF-12F and breast cancer cells at a dose that was non-inhibitory in normal-like breast epithelial cells.

Clinical Trials Involving Vitamin D Analogs in Prostate Cancer

Vitamin D shows significant potential as a therapy for prostate cancer. However, its use in clinical trials has been hampered by its induction of hypercalcemia at serum concentrations required to suppress cancer cell proliferation. This has spurred the development of less calcemic analogs of vitamin D. In this article, we review the clinical trials and consider the future directions of the use of vitamin D and its analogs in the treatment or chemoprevention of prostate cancer. First, we summarize the epidemiological evidence leading to the hypothesis that vitamin D has anticancer activity. We then review the clinical trials using vitamin D analogs that involve patients with prostate cancer and conclude with a brief overview of our planned study with vitamin D5, [1alpha(OH)D5], which will begin shortly. Data for this review were identified by searches of PubMed, the Cochrane Library, Biosis, and references from relevant articles, using the search terms "vitamin D," "prostate cancer," "chemoprevention" and "vitamin D analog." Abstracts from recent international meetings were also reviewed but were only included when they were the only known reference to the clinical trial or the research mentioned. Only papers published in English were included.