1 alpha-hydroxyvitamin D3, hypercalcemia, and growth suppression of 7,12-dimethylbenz[a]anthracene-induced rat mammary tumors

Vitamin D as a Potential Preventive Agent For Young Women's Breast Cancer

Clinical studies backed by research in animal models suggest that vitamin D may protect against the development of breast cancer, implicating vitamin D as a promising candidate for breast cancer prevention. However, despite clear preclinical evidence showing protective roles for vitamin D, broadly targeted clinical trials of vitamin D supplementation have yielded conflicting findings, highlighting the complexity of translating preclinical data to efficacy in humans. While vitamin D supplementation targeted to high-risk populations is a strategy anticipated to increase prevention efficacy, a complimentary approach is to target transient, developmental windows of elevated breast cancer risk. Postpartum mammary gland involution represents a developmental window of increased breast cancer promotion that may be poised for vitamin D supplementation. Targeting the window of involution with short-term vitamin D intervention may offer a simple, cost-effective approach for the prevention of breast cancers that develop postpartum. In this review, we highlight epidemiologic and preclinical studies linking vitamin D deficiency with breast cancer development. We discuss the underlying mechanisms through which vitamin D deficiency contributes to cancer development, with an emphasis on the anti-inflammatory activity of vitamin D. We also discuss current evidence for vitamin D as an immunotherapeutic agent and the potential for vitamin D as a preventative strategy for young woman's breast cancer.

Vitamin D in cancer chemoprevention

CONTEXT

There is increasing evidence that Vitamin D (Vit D) and its metabolites, besides their well-known calcium-related functions, may also exert antiproliferative, pro-differentiating, and immune modulatory effects on tumor cells in vitro and may also delay tumor growth in vivo.

OBJECTIVE

The aim of this review is to provide fresh insight into the most recent advances on the role of Vit D and its analogues as chemopreventive drugs in cancer therapy.

METHODS

A systematic review of experimental and clinical studies on Vit D and cancer was undertaken by using the major electronic health database including ISI Web of Science, Medline, PubMed, Scopus and Google Scholar.

RESULTS AND CONCLUSION

Experimental and clinical observations suggest that Vit D and its analogues may be effective in preventing the malignant transformation and/or the progression of various types of human tumors including breast cancer, prostate cancer, colorectal cancer, and some hematological malignances. These findings suggest the possibility of the clinical use of these molecules as novel potential chemopreventive and anticancer agents.

The future of vitamin D analogs

The active form of vitamin D₃, 1,25-dihydroxyvitamin D₃, is a major regulator of bone and calcium homeostasis. In addition, this hormone also inhibits the proliferation and stimulates the differentiation of normal as well as malignant cells. Supraphysiological doses of 1,25-dihydroxyvitamin D₃ are required to reduce cancer cell proliferation. However, these doses will lead in vivo to calcemic side effects such as hypercalcemia and hypercalciuria. During the last 25 years, many structural analogs of 1,25-dihydroxyvitamin D₃ have been synthesized by the introduction of chemical modifications in the A-ring, central CD-ring region or side chain of 1,25-dihydroxyvitamin D₃ in the hope to find molecules with a clear dissociation between the beneficial antiproliferative effects and adverse calcemic side effects. One example of such an analog with a good dissociation ratio is calcipotriol (Daivonex®), which is clinically used to treat the hyperproliferative skin disease psoriasis. Other vitamin D analogs were clinically approved for the treatment of osteoporosis or secondary hyperparathyroidism. No vitamin D analog is currently used in the clinic for the treatment of cancer although several analogs have been shown to be potent drugs in animal models of cancer. Transcriptomics studies as well as in vitro cell biological experiments unraveled basic mechanisms involved in the antineoplastic effects of vitamin D and its analogs. 1,25-dihydroxyvitamin D₃ and analogs act in a cell type- and tissue-specific manner. Moreover, a blockade in the transition of the G0/1 toward S phase of the cell cycle, induction of apoptosis, inhibition of migration and invasion of tumor cells together with effects on angiogenesis and inflammation have been implicated in the pleiotropic effects of 1,25-dihydroxyvitamin D₃ and its analogs. In this review we will give an overview of the action of vitamin D analogs in tumor cells and look forward how these compounds could be introduced in the clinical practice.

Protective role of fish oil (Maxepa) on early events of rat mammary carcinogenesis by modulation of DNA-protein crosslinks, cell proliferation and p53 expression

BACKGROUND

Fish oil is known to protect from many types of cancers of the colon, liver, breast, prostate and lung 123. The objective of the present study was to evaluate the role of fish oil [Maxepa, supplemented at a dose of 0.5 ml is equivalent to 90 mg eicosapentaenoic acid (EPA) and 60 mg docosahexaenoic acid (DHA)] on cell proliferation, expression of p53 tumor suppressor protein and DNA protein crosslinks (DPCs) in a defined model of chemical rat mammary carcinogenesis. Mammary carcinogenesis was initiated by a single, intravenous (i.v.) tail vein injection of 7,12 dimethylbenz(alpha)anthracene (DMBA) at a dose of 5 mg DMBA/2 ml corn oil/kg body weight in female Sprague-Dawley rats at 7 weeks of age. Fish oil supplementation was started daily, 2 weeks prior to DMBA injection and continued for 24 (31 weeks of animal age) weeks and 35 (42 weeks of animal age) weeks of post DMBA injection, for histopathological and immunohistochemical and for morphological studies, respectively.

RESULTS

Our results indicate the chemopreventive effect of fish oil (Maxepa) on DMBA-induced rat mammary carcinogenesis. Administration of fish oil further showed a prominent reduction of cell proliferation (24.34%, P = 0.001); DPCs (25%, P < 0.001) and an increased expression of p53 protein (4.636 +/- 0.19, P < 0.001) in preneoplastic mammary tissue when compared to carcinogen control counterpart. Histopathological and morphological analyses were carried out as end-point biomarkers.

CONCLUSION

Our study thus provides evidence for the anticarcinogenic effect of fish oil (Maxepa) in limiting mammary preneoplasia in Sprague-Dawley rats.

Suppression of cell proliferation, induction of apoptosis and cell cycle arrest: chemopreventive activity of vanadium in vivo and in vitro

In the present study, the authors evaluated the anticancer mechanism of vanadium, a dietary micronutrient and an important pharmacological agent, on a defined model of chemically induced rat mammary carcinogenesis in vivo and on human breast cancer cell line MCF7 in vitro. Female Sprague-Dawley rats were treated with 7,12-dimethylbenz(alpha)anthracene (0.5 mg/100 g body weight) by a single tail vein injection in an oil emulsion to induce mammary preneoplasia. Vanadium (ammonium monovanadate) at a concentration of 0.5 ppm (4.27 micromol/l) was supplemented in drinking water and given ad libitum to the experimental groups for 24 weeks. Histological finding showed substantial repair of hyperplastic lesions. There was a significant reduction in incidence, multiplicity (34%, p < 0.01), size of palpable mammary tumors and delay in mean latency period of tumor appearance. Immunohistochemical analysis in vivo indicated a decrease in cell proliferation (24.68% p < 0.05) and an increase among the TUNEL-positive apoptotic cells along with strong expressions of p53 and Bax, and downregulation of Bcl2 proteins in the mammary tissue of vanadium-treated animals. Further, MCF7 cells were cultured in minimal essential medium and were treated with 100, 175 and 250 microM of vanadium (ammonium monovanadate) for 36 hr. Exposure of MCF7 cells to vanadium led to induction of apoptosis in a dose-dependent manner. It was found further that vanadium treatment brought about a prominent cell cycle arrest and chromosomal condensation, leading to apoptosis (42.62%, p < 0.05). Results of both the in vivo and in vitro study demonstrate that vanadium has the potential to be developed into an anti-breast cancer drug in the near future.

Protective role of vanadium on the early process of rat mammary carcinogenesis by influencing expression of metallothionein, GGT-positive foci and DNA fragmentation

Vanadium, a dietary micronutrient, is now proving to be a promising anti-tumour agent. The present study was conducted to ascertain its anti-neoplastic potential against an experimental mammary carcinogenesis. Female Sprague-Dawley rats at 50 days of age were treated with 7,12-dimethylbenz(alpha)anthracene (DMBA; 0.5 mg per 100 g body weight) by a single tail vein injection in an oil emulsion. Vanadium (ammonium monovanadate) at a concentration of 0.5 p.p.m. was supplemented in the drinking water and given ad libitum to the experimental group immediately after the carcinogen treatment and it continued until the termination of the study (24 weeks for histological, immunological and biochemical observations and 35 weeks for morphological findings). It was found that vanadium treatment brought about substantial protection against DMBA-induced mammary carcinogenesis. This was evident from histological findings that showed substantial repair of hyperplastic lesions following supplementation of vanadium alone. There was a significant reduction in incidence (P<0.05), total number, multiplicity (P<0.01), size of palpable mammary tumours and delay in mean latency period of tumour appearance (P<0.001) following vanadium supplementation compared to the DMBA control. The immunohistochemical localization of metallothionein (a prognostic marker for breast cancer) showed reduced expression with vanadium treatment. Further, DNA fragmentation in the mammary tissue of the vanadium-treated group indicated apoptosis. In this group, vanadium also caused a significant decrease in the number (P<0.002) and focal area (P<0.05) of gamma-glutaminetranspeptidase-positive hepatic foci. The results clearly show the anti-neoplastic potential of vanadium.

Suppression of cell proliferation, DNA protein cross-links, and induction of apoptosis by vanadium in chemical rat mammary carcinogenesis

Vanadium, a dietary micronutrient, has recently been considered as an important pharmacological agent. The present investigation was carried out to ascertain its anticarcinogenic potential against an experimental rat mammary carcinogenesis. Female Sprague-Dawley rats were treated with 7,12dimethylbenz(alpha)anthracene (DMBA) (0.5 mg/100 g body weight) by a single tail vein injection in an oil emulsion. Vanadium (ammonium monovanadate) at a concentration of 0.5 ppm (4.27 micromol/L) was supplemented in drinking water and given ad libitum to the experimental group. The present study was an attempt to assess the effect of vanadium (ammonium monovanadate) on cell proliferation, apoptosis and histopathology in the mammary tissue. We also have examined DNA fragmentation and DNA protein cross-links (DPC) in the liver of rats as well. Immunohistochemical analysis indicated that early neoplasia in mammary tissue proceeds by a decrease in apoptotic cell death (ACD), which was also examined with TUNEL assay, rather than an increase in cell proliferation (P<0.01). DPC in liver were reduced by vanadium treatment (ANOVA, F=13.7, P<0.01). Agarose gel electrophoresis revealed DNA fragmentation in the vanadium-treated group, confirming apoptosis further. Results of the study indicate that the mammary preneoplasia is sensitive to vanadium intervention whereas normal proliferating cells are not.

Melatonin and vitamin D3 increase TGF-beta1 release and induce growth inhibition in breast cancer cell cultures

BACKGROUND

Evidence has accumulated that 1,25-dihydroxyvitamin D(3) [1,25-(OH)(2)D(3)] is involved in the regulation of the proliferation of breast tumor cells. For complete tumor suppression high hypercalcemic doses of 1,25-(OH)(2)D(3) are needed. The aim of this study was to assess the effect of combined treatment of 1,25-(OH)(2)D(3) at low doses and melatonin (MEL) on the proliferation of estrogen-responsive rat breast cancer cell line RM4.

MATERIALS AND METHODS

RM4 cell proliferation was assessed by [3H]thymidine uptake. The presence of TGF-beta(1) in serum-free conditioned medium was determined by inhibition antibody binding assay.

RESULTS

In 17-betaE cultured RM4 cells both MEL and 1,25-(OH)(2)D(3) alone and in combination significantly reduced [3H]thymidine incorporation in a dose-related fashion. MEL by itself was ineffective in inhibiting the FCS-cultured RM4 cells, while 1,25-(OH)(2)D(3) strongly inhibited [3H]thymidine incorporation. Meanwhile, MEL increased the sensitivity of the FCS-cultured RM4 cells to 1,25-(OH)(2)D(3) in the combined regimen, from 20- to 100-fold. MEL significantly enhanced the TGF-beta(1) secretion from RM4 cells and vitamin D(3) increased the TGF-beta(1) secretion in a dose-dependent manner, from 2- to 7-fold. Moreover, a further enhancement of the TGF-beta(1) release was obtained with the combined treatment, but only for low 1,25-(OH)(2)D(3) concentrations. The addition of monoclonal anti-TGF-beta(1) antibody to the medium of RM4 cells exposed to vitamin D(3) alone or in combination with MEL increased the [3H]thymidine uptake compared to the correspondent cells cultured without antibody.

CONCLUSIONS

Our data point to a potential benefit of combination therapy with 1,25-(OH)(2)D(3) and MEL in the treatment of breast cancer and suggest that the growth inhibition could be related, at least in part, to the enhanced TGF-beta(1) secretion.

Two novel metabolic pathways of 22-oxacalcitriol (OCT). C-25 dehydration and C-3 epimerization and biological activities of novel OCT metabolites

22-Oxacalcitriol (OCT) is an analog of calcitriol, characterized by potent differentiation-inducing activity and low calcemic liability. The metabolism of OCT has been studied and its polar metabolites, such as 24/26-hydroxylated-OCT and hexanor-1 alpha,20-dihydroxyvitamin D(3) (1 alpha,20(OH)(2)D(3)), have been identified. In contrast, little is known about the less polar metabolites of OCT, which have been found in relatively large amounts. In this study, the in vitro metabolism of OCT was studied in UMR 106, Caco-2, and LLC-PK(1) cells to identify the less polar metabolites and to assess their biological activity. OCT was initially metabolized to three less polar metabolites, 3-epi-OCT and two dehydrates, 25-dehydroxy- 25-ene-22-oxa-1 alpha(OH)D(3) (25-ene-22-oxa-1 alpha(OH)D(3)) and 25-dehydroxy-24-ene-22-oxa-1 alpha(OH)D(3) (24-ene-22-oxa-1 alpha(OH)D(3)). We also observed further metabolites, the two C-3 epimers of the C-25 dehydrates, 25-ene-3-epi-22-oxa-1 alpha(OH)D(3) and 24-ene-3-epi-22-oxa-1 alpha(OH)D(3). The structures of these metabolites were successfully assigned by (1)H NMR and LC-MS analyses. The three cell lines differ in their ability to metabolize OCT through the C-3 epimerization or the C-25 dehydration pathway. The biological activity of the OCT metabolites assessed by a luciferase reporter gene transcriptional activation system, binding assays for the vitamin D receptor (VDR) and vitamin D-binding protein (DBP), and assays for regulatory activities of cell differentiation and proliferation was found to be lower than that of OCT. Thus, both the C-3 epimerization and C-25 dehydration may work to reduce the biological activity of OCT.

Sunlight and mortality from breast, ovarian, colon, prostate, and non-melanoma skin cancer: a composite death certificate based case-control study

OBJECTIVES

To explore whether mortality from female breast, ovarian, colon, and prostate cancer were negatively associated with exposure to sunlight.

METHODS

A death certificate based case-control study of mortality was conducted into five cancers: female breast, ovarian, colon, prostate, and non-melanoma skin cancer (as a positive control) to examine associations with residential and occupational exposure to sunlight. Cases were all deaths from these cancers between 1984 and 1995 in 24 states of the United States. Controls, which were age frequency matched to a series of cases, excluded deaths from cancer and certain neurological diseases. Multiple logistic regression was used in a model that included age, sex, race, residential exposure to sunlight (based on region), and socioeconomic status, occupational exposure to sunlight, and physical activity (the last three based on usual occupation).

RESULTS

Residential exposure to sunlight was negatively and significantly associated with mortality from female breast, ovarian, prostate, and colon cancer. Only female breast and colon cancer, however, also showed significant negative associations with jobs with the highest occupational exposure to sunlight (odds ratio (OR) 0.82 (95% confidence interval (95% CI) 0.70 to 0.97) for female breast cancer; OR 0.90 (95% CI 0.86 to 0.94) for colon cancer). For both cancers, the negative association with occupational sunlight was greatest in the geographical region of highest exposure to sunlight and was independent of physical activity on the job. Non-melanoma skin cancer, as expected, was positively associated with both residential and occupational sunlight.

CONCLUSIONS

In this exploratory study, unlike mortality from non-melanoma skin cancer, mortality from female breast cancer and colon cancer were negatively associated with both residential and occupational sunlight.

Antiproliferative effects of 1,25-dihydroxyvitamin D3 on breast cells: a mini review

The hormone 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3), the active form of vitamin D3, is an important regulator of calcium homeostasis, exerts antiproliferative effects on various cell systems and can induce differentiation in some kinds of hematopoietic cells. These effects are triggered by its receptor, vitamin D receptor (VDR), a phosphoprotein member of the nuclear receptor superfamily, which functions as a transcriptional factor. VDR binds as a heterodimer with retinoid X receptor (R X R) to hexameric repeats, characterized as vitamin D-responsive elements present in the regulatory region of target genes such as osteocalcin, osteopontin, calbindin-D28K, calbindin-D9K, p21WAF1/CIP1, TGF-beta2 and vitamin D 24-hydroxylase. Many factors such as glucocorticoids, estrogens, retinoids, proliferation rate and cell transformation can modulate VDR levels. VDR is expressed in mammary tissue and breast cancer cells, which are potential targets to hormone action. Besides having antiproliferative properties, vitamin D might also reduce the invasiveness of cancer cells and act as an anti-angiogenesis agent. All of these antitumoral features suggest that the properties of vitamin D could be explored for chemopreventive and therapeutic purposes in cancer. However, hypercalcemia is an undesirable side effect associated with pharmacological doses of 1,25-(OH)2D3. Some promising 1,25-(OH)2D3 analogs have been developed, which are less hypercalcemic in spite of being potent antiproliferative agents. They represent a new field of investigation.

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.

1 alpha,25-Dihydroxyvitamin D3 inhibits the invasive potential of human breast cancer cells in vitro

Using the Boyden chamber invasion assay, the effect of 1 alpha,25-dihydroxyvitamin D3 [1 apha,25(OH)2D3] on the invasiveness of the highly invasive, oestrogen receptor-negative human breast cancer cell line MDA-MB-231 was examined. The MDA-MB-231 cells were shown to contain high-affinity receptors for 1 alpha,25(OH)2D3 with a Kd of 1.5 x 10(-11) M. When the cells were treated with 1 alpha,25(OH)2D3 for 4 days before the assay was performed, a dose-dependent inhibition of their invasive potential was demonstrated. Fifty per cent inhibition of invasion was obtained with a concentration of 13 pM of 1 alpha,25(OH)2D3. However, when the cells were treated for only 6 h during the assay, no inhibitory effect was seen. The process of migration was also affected by treatment with 1 alpha,25(OH)2D3 for 4 days, although the inhibition was not of the same magnitude as seen for the invasion. Fifty per cent inhibition of migration occurred at a concentration of 3.2 nM of 1 alpha,25(OH)2D3 (250 times higher than in the invasion assay). Inhibition of invasion and migration was not due to the known anti-proliferative effect of 1 alpha,25(OH)2D3, as no growth reduction could be demonstrated with treatment up to 5 days. Based on the present investigation it can therefore be concluded that 1 alpha,25(OH)2D3 is able to inhibit tumour cell invasiveness by a mechanism which is not exclusively based on its anti-proliferative and anti-migrative effects.

Combined effects of 1,25-dihydroxyvitamin D3 and tamoxifen on the growth of MCF-7 and ZR-75-1 human breast cancer cells

In the present study we assessed the effect of combined treatment with 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) and tamoxifen (TAM) on the growth of estrogen-responsive (MCF-7) and estrogen-dependent (ZR-75-1) human breast cancer cells. Both basal and 17 beta-estradiol (17 beta-E2)-stimulated growth were studied. 1,25-(OH)2D3 (10(-10)-10(-7) M) time- and dose-dependently inhibited basal growth of MCF-7 cells, with growth arrest at 10(-7) M. Also, 17 beta-E2-stimulated growth of MCF-7 and ZR-75-1 cells was inhibited by 1,25(OH)2D3 in a time- and dose-dependent manner. TAM inhibited 17 beta-E2-stimulated growth of both cell lines and at high concentration (10(-6) M) it also inhibited basal growth of MCF-7 cells. 10(-6) M TAM together with 1,25-(OH)2D3 resulted n a further inhibition of basal (MCF-7 cells) as well as 17 beta-E2-stimulated proliferation (MCF-7 and ZR-75-1 cells) compared to the inhibition by these agents alone. TAM in combination with 10(-7) M 1,25-(OH)2D3 resulted in growth arrest of 17 beta-E2-stimulated growth of MCF-7 cells. The inhibition of basal and 17 beta-E2-stimulated growth of MCF-7 cells was additive at early time points (4 days), but less than additive at later time points (8-10 days). It was demonstrated that with co-treatment of MCF-7 cells an equipotent inhibition of basal growth could be reached with lower concentrations of 1,25-(OH)2D3, compared to treatment with 1,25-(OH)2D3 alone.(ABSTRACT TRUNCATED AT 250 WORDS)