Vitamin D and Breast Cancer

Vitamin D regulates calcium and phosphorus blood levels and bone metabolism via effects on intestine, kidney, and bone. Vitamin D is formed from 7-dehydrocholesterol in the skin by ultraviolet irradiation or is taken up from dietary sources. Vitamin D must be metabolically altered successively in the liver and kidney to form the biologically most active compound, 1,25-dihydroxyvitamin D3. This active compound acts through binding to a specific receptor, the vitamin D receptor, which is a member of the steroid hormone receptor family. During the last fifteen years, it has become apparent that the active form of vitamin D exerts effects on a variety of tissues apparently unrelated to calcium homeostasis. 1,25-Dihydroxyvitamin D3 has been shown to promote cellular differentiation and inhibit proliferation of haematopoietic cells, cancer cells, and keratinocytes. In addition, studies with animal models for cancer have shown that 1,25-dihydroxyvitamin D3 administration can prolong the survival of leukaemic mice and suppress the growth of tumours of different origin, including breast, colon, skin, and lung. This thesis focuses on a possible role of vitamin D in the treatment of breast cancer

Inhibition of insulin- and insulin-like growth factor-I-stimulated growth of human breast cancer cells by 1,25-dihydroxyvitamin D3 and the vitamin D3 analogue EB1089

1, 25 Dihydroxyvitamin D3 (1,25-(OH)2D3) and a number of synthetic vitamin D3 analogues with low calcaemic activity, have been shown to inhibit breast cancer cell growth in vitro as well as in vivo. The purpose of the present study was to investigate a possible interaction of 1, 25-(OH)2D3 and the vitamin D3 analogue EB1089 with the insulin-IGF-I regulatory system. The oestrogen receptor-positive MCF-7 human breast cancer cells used in this study are able to grow autonomously and their growth is stimulated by insulin. In order to avoid interference of IGF-binding proteins (IGF-BPs), we used an analogue of IGF-I, long R3 IGF-I, which stimulated MCF-7 cell growth similar to insulin. The growth stimulation by insulin and by long R3 IGF-I was completely inhibited by 1,25-(OH)2D3 and EB1089. Autonomous growth was also inhibited by 1,25-(OH)2D3 and EB1089. The analogue EB1089 was active at 50 times lower concentrations than 1,25-(OH)2D3. It was shown that growth inhibition was not achieved through downregulation of insulin and IGF-I binding after 48 h. Paradoxically, after prolonged treatment (8 days), an upregulation of insulin and IGF-I binding was observed. Two possible intracellular mediators of the insulin-IGF mitogenic signal are C-FOS and mitogen-activated protein (MAP) kinase. Insulin-induced C-FOS mRNA was inhibited by 1,25-(OH)2D3, suggesting that it could be involved in the growth inhibition by 1,25-(OH)2D3. MAP kinase activation appeared not to be involved in growth stimulation by both insulin and IGF-I. Together, the present study demonstrates that vitamin D3 compounds can block the mitogenic activity of insulin and IGF-I, which may contribute to their tumour suppressive activity observed in vivo. Copyrigh

Breast cancer chemoprevention: beyond tamoxifen

A large number of new potential chemoprevention agents are available that target molecular abnormalities found in estrogen receptor (ER)-negative and/or ER-positive precancerous breast tissue and have side effect profiles that differ from tamoxifen. Classes of agents currently undergoing evaluation in clinical prevention trials or those for which testing is planned in the near future include new selective ER modulators, aromatase inactivators/inhibitors, gonadotrophin-releasing hormone agonists, monoterpenes, isoflavones, retinoids, rexinoids, vitamin D derivatives, and inhibitors of tyrosine kinase, cyclooxygenase-2, and polyamine synthesis. New clinical testing models will use morphological and molecular biomarkers to select candidates at highest short-term risk, to predict the response to a particular class of agent, and to assess the response in phase II prevention trials. If validated, morphological and molecular markers could eventually replace cancer incidence as an indicator of efficacy in future phase III trials

Regulation of 1,25-dihydroxyvitamin D3 receptor gene expression by parathyroid hormone and cAMP-agonists

We studied the effect of parathyroid hormone (PTH) and activation of the cAMP signal pathway on vitamin D receptor (VDR) mRNA levels in the phenotypically osteoblast cell line UMR 106. PTH caused a time- and dose-dependent increase of the VDR mRNA content with a maximum after 2 h. After 24 h the VDR mRNA level in PTH-treated cells returned to control level. In contrast, the 1,25-dihydroxyvitamin D3 (1,25(OH)2D3)-induced increase in VDR mRNA did not decline after 24 h. Inhibition of transcription with actinomycin D (10 μg/ml) completely abolished the PTH-induced increase of VDR mRNA and inhibition of translation with cycloheximide (1 μg/ml) resulted in superinduction of VDR mRNA. The role of cAMP in the induction of VDR mRNA was studied with several agents acting via the cAMP pathway. Incubation for 2 and 4 h with forskolin, Bt2cAMP, PTHrP or prostaglandin E2 caused an increase in the level of VDR mRNA comparable to that caused by PTH. The calcium ionophore A23187 did not affect VDR mRNA level. The present study demonstrates that PTH and activation of the cAMP signal pathway cause up-regulation of VDR via induction of VDR gene expression. The effect of cAMP on the VDR gene is suggestive for a cAMP responsive element in the VDR gene

Transforming growth factor β-induced dissociation between vitamin D receptor level and 1,25-dihydroxyvitamin D3 action in osteoblast-like cells

In the present study the interaction between a locally produced factor in bone, transforming growth factor β (TGFβ) and a systemic regulator of bone metabolism, 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) was investigated. In rat (UMR 106, ROS 17/2.8) and human (MG-63) osteoblastic cell lines and in isolated fetal rat osteoblasts TGFβ caused a comparable increase in vitamin D receptor (VDR) level. A maximum was observed after 6 h at 1 ng/ml TGFβ. Scatchard analysis revealed that up-regulation of VDR is due to an increase in receptor number and not to a change in affinity. This was supported by Northern blot analysis which showed a dose- and time-dependent increase in VDR mRNA by TGFβ. To assess the significance of the TGFβ-induced increase in VDR level for l,25-(OH)2D3 effects cells were preincubated with TGF for 4 h (causing a 2–3-fold increase of the VDR level) and subsequently incubated with l,25-(OH)2D3 for 4 h and 24 h. TGFβ preincubation potently inhibited subsequent l,25-(OH)2D3 stimulation of osteocalcin production in both ROS 17/2.8 and MG-63 cells on protein as well as mRNA level. A similar inhibition by TGFβ was observed on the 1,25-(OH)2D3-induced increase in osteopontin mRNA. The current study demonstrates dissociation between regulation of VDR level and modulation of two l,25-(OH)2D3 biological responses by TGFβ in osteoblast-like cell lines of different origin. This dissociation shows that, besides interaction at VDR level also at other levels in the cell interaction(s) exist between TGFβ and 1,25-(OH)2D3. Besides, these data emphasize the potential importance of the interplay of locally produced factors and systemic calciotrophic hormones in the regulation of bone metabolism