Review
Equivalent anticancer activities of dietary vitamin D and calcitriol in an animal model of breast cancer: Importance of mammary CYP27B1 for treatment and prevention

https://doi.org/10.1016/j.jsbmb.2012.08.005Get rights and content

Abstract

Calcitriol [1,25(OH)2D3], the hormonally active form of vitamin D exerts anti-proliferative, pro-apoptotic, anti-inflammatory effects and other anticancer actions in breast cancer (BCa) cell cultures and animal models of BCa. Our research is focused on investigating the potential beneficial effects of dietary vitamin D3 compared to calcitriol and the underlying mechanisms in BCa treatment and chemoprevention. We recently found that dietary vitamin D3 exhibits significant tumor inhibitory effects in xenograft models of BCa that are equivalent to those elicited by the administration of the active hormone calcitriol. At the easily achievable dose tested in our studies, dietary vitamin D3 exhibited substantial tumor inhibitory activity and, unlike calcitriol, did not cause hypercalcemia demonstrating its relative safety. We found elevations in circulating calcitriol as well as increased CYP27B1 expression in the tumor and the intestine in tumor-bearing mice ingesting a vitamin D3-supplemented diet. We hypothesize that the elevation in circulating 25(OH)D induced by dietary vitamin D3 supplements stimulates local synthesis of calcitriol in the mammary tumor microenvironment and the ensuing paracrine/autocrine actions play a major role in the anticancer activity of dietary vitamin D3. Our findings suggest that the endocrine activity of calcitriol derived from tumor and other extra-renal sources such as the intestine, probably also plays a role in mediating the anticancer effects of dietary vitamin D3. Thus it appears that multiple sites of 1α-hydroxylation contribute to the anticancer effects of dietary vitamin D3. Our data strongly suggest that dietary vitamin D will be useful in the chemoprevention and treatment of BCa since it is a safe, economical and easily available nutritional agent that is equivalent to calcitriol in exerting anticancer effects, at least in mouse models. Furthermore, adequate vitamin D nutrition and avoidance of vitamin D deficiency appear to be important in reducing BCa risk. These findings warrant clinical trials in BCa patients and in women at high risk for BCa to evaluate the benefits of dietary vitamin D3 supplementation.

This article is part of a Special Issue entitled ‘Vitamin D Workshop’.

Highlights

▸ Dietary vitamin D3 and calcitriol exhibit equivalent tumor inhibition in mouse models of breast cancer. ▸ At moderate, achievable doses dietary vitamin D3 does not cause hypercalcemia, demonstrating safety. ▸ Tumor CYP27B1 and local calcitriol synthesis play a major role in the anticancer activity of vitamin D3. ▸ Endocrine activity of calcitriol derived from tumor and other extra-renal sources also contribute. ▸ Avoidance of vitamin D deficiency is important for reducing breast cancer risk.

Introduction

Vitamin D plays an important role in calcium homeostasis through its actions in intestine, kidney, parathyroid glands and bone [1]. When written without a subscript the D indicates either D2 or D3. Vitamin D is not really a vitamin but the precursor to the potent steroid hormone 1,25-dihydroxyvitamin D3 (1,25(OH)2D3 or calcitriol). Vitamin D derived from the diet or synthesized in the skin gets hydroxylated to 25(OH)D by liver 25-hydroxylase enzymes (CYP2R1 and CYP27A1) [1]. 25(OH)D, the circulating prohormone, is converted to 1,25(OH)2D3 by the kidney in a tightly controlled enzymatic step catalyzed by 1α-hydroxylase (CYP27B1) [1]. Calcitriol binds to the vitamin D receptor (VDR), a member of the steroid receptor superfamily to regulate gene expression in all tissues of the body. In addition to its actions on calcium and bone homeostasis, calcitriol also exhibits anti-proliferative and pro-differentiation activities indicating its potential use in the prevention and treatment of multiple cancers, including breast cancer (BCa) [2], [3], [4], [5], [6], [7], [8], [9].

Section snippets

Vitamin D and breast cancer

Recent meta-analyses of epidemiological data support a protective role for vitamin D in BCa development [10], [11]. An analysis of pooled data from observational studies suggests that serum 25(OH)D levels of 52 ng/ml or more are associated with 50% reduction in BCa risk [12]. Although the recent report by the Institute of Medicine (IOM) [13] concluded that further evidence is required to establish a cause–effect relationship between vitamin D levels and cancer prevention, the IOM committee

Mechanisms of the anticancer actions of calcitriol in BCa cell cultures

The active hormone calcitriol inhibits the growth of both estrogen receptor-positive (ER+) and ER-negative human BCa cell lines by regulating many molecular pathways (reviewed in [5], [6], [9]). These regulatory actions include the induction of cell cycle arrest [16], [17], [18] and apoptosis [3], [19], [20] and promoting differentiation [21], [22], [23]. In addition, calcitriol reduces the invasive and metastatic potential of several BCa cells [24], [25], [26]. Calcitriol also exhibits potent

Studies of calcitriol efficacy in animal models of BCa

The anticancer effects of calcitriol in cell culture models have been observed at high concentrations of the hormone. Achievement of adequate concentrations of calcitriol to demonstrate anticancer effects in vivo runs the risk of causing hypercalcemia and hypercalciuria leading to renal stone formation. The following alternate approaches have been used to minimize the toxicity: (1) Several academic investigators and pharmaceutical companies have focused their efforts on designing calcitriol

Dietary vitamin D supplementation as a therapeutic approach in BCa

Ongoing studies in our laboratory are investigating the potential benefit of dietary vitamin D3 in the treatment and chemoprevention of BCa. Our rationale is based on studies that have demonstrated the presence of the enzyme CYP27B1 in normal and malignant mammary tissue [9], [15], [50], [51], which converts the circulating prohormone 25(OH)D3 to the active hormone calcitriol locally within the breast. Recent studies show that breast adipocytes also express CYP27B1 [52]. These observations

Dietary vitamin D3 exhibits anticancer activity equivalent to calcitriol

Our recent study [57] demonstrated significant tumor shrinkage (>50%) in female nude mice bearing MCF-7 xenografts following ingestion of a vitamin D3-supplemented diet (5000 IU/kg) compared to the standard diet (1000 IU vitamin D3/kg) (Fig. 1). Reduction in tumor growth was noticed within one week of starting the supplemented diet and by 4 weeks the tumors were reduced to less than half the size of tumors in mice fed the control diet. In parallel the effects of graded concentrations of

Importance of tumor CYP27B1 expression

We and others have shown that supplementation of the mouse diet to increase vitamin D content 5-fold over the standard diet resulted in an elevation in the levels of circulating 25(OH)D as expected [48], [57]. Interestingly, comparison of mice receiving a dietary vitamin D supplement to mice on the standard diet revealed the following two unexpected findings that warrant discussion: (1) an increase in the expression of CYP27B1 mRNA in the tumors (Fig. 2A) and (2) a significant elevation in

Rise in circulating concentrations of calcitriol following dietary supplementation with vitamin D3

In spite of the elevations in serum 25(OH)D levels following dietary vitamin D3 ingestion, we did not expect an increase in circulating calcitriol levels because of the tight regulation of renal CYP27B1 by PTH and serum calcium that restricts renal 25(OH)D conversion to calcitriol [1]. Since extra-renal CYP27B1 is not regulated by PTH [56], we hypothesized that the extent of 25(OH)D conversion to calcitriol in the tumors would not be restricted and would be proportional to the dietary levels of

Safety of dietary vitamin D intervention

Another interesting observation from our studies was that the ingestion of dietary vitamin D3 at 5000 IU/kg did not increase serum calcium levels, in spite of the elevations detected in the serum calcitriol concentration. Interestingly, the elevated serum calcitriol levels assayed in blood of mice receiving calcitriol, drawn 14 h after the final calcitriol injections, were lower than the concentrations in mice receiving the vitamin D3-supplemented diet. However, the time-point of the blood draw

Summary and conclusions

Numerous studies in various cell culture and animal models of BCa demonstrate the anticancer effects of calcitriol. Our recent studies in mouse tumor models highlight the potential utility of dietary vitamin D3 in BCa treatment and chemoprevention. We have shown that dietary vitamin D3 exhibits significant tumor inhibitory effects in xenograft models of BCa, which are equivalent to the anticancer benefits mediated by the active hormone calcitriol. At moderate, achievable doses dietary vitamin D3

Acknowledgments

This work was supported by NCI grant CA13099, Komen Foundation grant 070101 and CBCRPgrant # 17OB-0071 to D.F.

References (62)

  • J. Welsh

    Vitamin D actions in mammary gland and breast cancer

  • A.V. Krishnan et al.

    Vitamin D and breast cancer: inhibition of estrogen synthesis and signaling

    The Journal of Steroid Biochemistry and Molecular Biology

    (2010)
  • L.L. Ooi et al.

    Vitamin D deficiency promotes growth of MCF-7 human breast cancer in a rodent model of osteosclerotic bone metastasis

    Bone

    (2010)
  • G. Murillo et al.

    Chemoprevention of chemically-induced mammary and colon carcinogenesis by 1alpha-hydroxyvitamin D5

    The Journal of Steroid Biochemistry and Molecular Biology

    (2005)
  • D. Matthews et al.

    Genomic vitamin D signaling in breast cancer: insights from animal models and human cells

    The Journal of Steroid Biochemistry and Molecular Biology

    (2010)
  • E.L. Milliken et al.

    EB1089, a vitamin D receptor agonist, reduces proliferation and decreases tumor growth rate in a mouse model of hormone-induced mammary cancer

    Cancer Letters

    (2005)
  • M. Hewison et al.

    Extrarenal 1a-hydroxylase

  • C.M. Kemmis et al.

    Human mammary epithelial cells express CYP27B1 and are growth inhibited by 25-hydroxyvitamin D-3, the major circulating form of vitamin D-3

    Journal of Nutrition

    (2006)
  • W.R. Wecksler et al.

    Studies on the mode of action of vitamin D–XIV. Quantitative assessment of the structural requirements for the interaction of 1 alpha, 25-dihydroxyvitamin D3 with its chick intestinal mucosa receptor system

    Journal of Steroid Biochemistry

    (1978)
  • M.J. Rowling et al.

    High dietary vitamin D prevents hypocalcemia and osteomalacia in CYP27B1 knockout mice

    Journal of Nutrition

    (2007)
  • J.C. Fleet et al.

    Serum metabolite profiles and target tissue gene expression define the effect of cholecalciferol intake on calcium metabolism in rats and mice

    Journal of Nutrition

    (2008)
  • D. Feldman et al.

    Vitamin D: biology, action and clinical implications

  • T.M. Beer et al.

    Calcitriol in cancer treatment: from the lab to the clinic

    Molecular Cancer Therapeutics

    (2004)
  • K.W. Colston et al.

    Mechanisms implicated in the growth regulatory effects of vitamin D in breast cancer

    Endocrine-Related Cancer

    (2002)
  • K.K. Deeb et al.

    Vitamin D signalling pathways in cancer: potential for anticancer therapeutics

    Nature Reviews Cancer

    (2007)
  • A.V. Krishnan et al.

    Mechanisms of the anti-cancer and anti-inflammatory actions of vitamin D

    Annual Review of Pharmacology and Toxicology

    (2011)
  • F. Pereira et al.

    Vitamin D and colon cancer

    Endocrine-Related Cancer

    (2012)
  • P. Chen et al.

    Meta-analysis of vitamin D, calcium and the prevention of breast cancer

    Breast Cancer Research and Treatment

    (2010)
  • Institute of Medicine

    Dietary Reference Intakes for Calcium and Vitamin D

    (2011)
  • C.J. Rosen et al.

    The nonskeletal effects of vitamin D: an endocrine society scientific statement

    Endocrine Reviews

    (2012)
  • K. Townsend et al.

    Autocrine metabolism of vitamin D in normal and malignant breast tissue

    Clinical Cancer Research

    (2005)

    • Cited by (0)

    View full text
    Copyright © 2012 Elsevier Ltd. All rights reserved.