MCF-7/VD(R): a new vitamin D resistant cell line

BC-N102 suppress breast cancer tumorigenesis by interfering with cell cycle regulatory proteins and hormonal signaling, and induction of time-course arrest of cell cycle at G1/G0 phase

Mechanisms of breast cancer progression and invasion, often involve alteration of hormonal signaling, and upregulation and/or activation of signal transduction pathways that input to cell cycle regulation. Herein, we describe a rationally designed first-in-class novel small molecule inhibitor for targeting oncogenic and hormonal signaling in ER-positive breast cancer. BC-N102 treatment exhibits dose-dependent cytotoxic effects against ER+ breast cancer cell lines. BC-N102 exhibited time course- and dose-dependent cell cycle arrest via downregulation of the estrogen receptor (ER), progesterone receptor (PR), androgen receptor (AR), phosphatidylinositol 3-kinase (PI3K), phosphorylated (p)-extracellular signal-regulated kinase (ERK), p-Akt, CDK2, and CDK4 while increasing p38 mitogen-activated protein kinase (MAPK), and mineralocorticoid receptor (MR) signaling in breast cancer cell line. In addition, we found that BC-N102 suppressed breast cancer tumorigenesis in vivo and prolonged the survival of animals. Our results suggest that the proper application of BC-N102 may be a beneficial chemotherapeutic strategy for ER+ breast cancer patients.

Role of insulin-like growth factor binding protein-3 in 1, 25-dihydroxyvitamin-d 3 -induced breast cancer cell apoptosis

Insulin-like growth factor I (IGF-I) is implicated in breast cancer development and 1, 25-dihydroxyvitamin D₃ (1, 25-D₃) has been shown to attenuate prosurvival effects of IGF-I on breast cancer cells. In this study the role of IGF binding protein-3 (IGFBP-3) in 1, 25-D₃-induced apoptosis was investigated using parental MCF-7 breast cancer cells and MCF-7/VD^R cells, which are resistant to the growth inhibitory effects of 1, 25-D₃. Treatment with 1, 25-D₃ increased IGFBP-3 mRNA expression in both cell lines but increases in intracellular IGFBP-3 protein and its secretion were observed only in MCF-7. 1, 25-D₃-induced apoptosis was not associated with activation of any caspase but PARP-1 cleavage was detected in parental cells. IGFBP-3 treatment alone produced cleavage of caspases 7, 8, and 9 and PARP-1 in MCF-7 cells. IGFBP-3 failed to activate caspases in MCF-7/VD^R cells; however PARP-1 cleavage was detected. 1, 25-D₃ treatment inhibited IGF-I/Akt survival signalling in MCF-7 but not in MCF-7/VD^R cells. In contrast, IGFBP-3 treatment was effective in inhibiting IGF-I/Akt pathways in both breast cancer lines. These results suggest a role for IGFBP-3 in 1, 25-D₃ apoptotic signalling and that impaired secretion of IGFBP-3 may be involved in acquired resistance to vitamin D in breast cancer.

The immunomodulatory drug lenalidomide restores a vitamin D sensitive phenotype to the vitamin D resistant breast cancer cell line MDA-MB-231 through inhibition of BCL-2: potential for breast cancer therapeutics

1α,25-Dihydroxyvitamin D3, (1,25-D3) the biologically active form of vitamin-D, is well established as a cancer cell growth inhibitor in addition to maintaining bone mineralization. In breast cancer cells, inhibitory effects on angiogenesis, and metastasis have been observed together with enhancement of apoptosis and induction of cell cycle arrest. There is a correlation between vitamin-D receptor expression on breast cancer cells and patient survival. However vitamin-D resistance and hypercalcaemia are key limiting factors in clinical use. The IMiD(®) immunomodulatory drug lenalidomide, (Revlimid(®), CC-5013) used in myeloma, can also modulate apoptotic and growth signalling. We studied whether lenalidomide treated breast cancer cells would acquire sensitivity to 1,25-D3 with resulting growth inhibition. The cell lines MCF-12A, MCF-7 and MDA-MB-231, representing non-tumorogenic, tumorogenic, and vitamin-D resistant lines respectively were treated with lenalidomide and/or 1,25-D3(at 100 nM). Whereas lenalidomide alone had no effect on cell growth, a 50% inhibition of cell growth by 1,25-D3 was achieved with additional 1 μM lenalidomide in resistant cells. This effect was through apoptosis measured by PARP cleavage and annexin-V expression. An apoptosis protein array showed that the 1,25-D3 and lenalidomide combination increased pro-apoptotic proteins (phosphorylated p53) and decreased BCL-2 expression. BCL-2 inhibition is proposed as a mechanism of action for the combined drugs in the MDA-MB-231 cell line. In vitamin D resistant cell lines MCF-7VDR and HBL-100 where the combination does not affect BCL-2-no inhibitory effect is observed. These results demonstrate the potential for the combinatorial use of lenalidomide and 1,25-D3 for vitamin D refractory tumours.

Cellular and molecular effects of vitamin D on carcinogenesis

Epidemiologic data suggest that the incidence and severity of many types of cancer inversely correlates with indices of vitamin D status. The vitamin D receptor (VDR) is highly expressed in epithelial cells at risk for carcinogenesis including those resident in skin, breast, prostate and colon, providing a direct molecular link by which vitamin D status impacts on carcinogenesis. Consistent with this concept, activation of VDR by its ligand 1,25-dihydroxyvitamin D (1,25D) triggers comprehensive genomic changes in epithelial cells that contribute to maintenance of the differentiated phenotype, resistance to cellular stresses and protection of the genome. Many epithelial cells also express the vitamin D metabolizing enzyme CYP27B1 which enables autocrine generation of 1,25D from the circulating vitamin D metabolite 25-hydroxyvitamin D (25D), critically linking overall vitamin D status with cellular anti-tumor actions. Furthermore, pre-clinical studies in animal models has demonstrated that dietary supplementation with vitamin D or chronic treatment with VDR agonists decreases tumor development in skin, colon, prostate and breast. Conversely, deletion of the VDR gene in mice alters the balance between proliferation and apoptosis, increases oxidative DNA damage, and enhances susceptibility to carcinogenesis in these tissues. Because VDR expression is retained in many human tumors, vitamin D status may be an important modulator of cancer progression in persons living with cancer. Collectively, these observations have reinforced the need to further define the molecular actions of the VDR and the human requirement for vitamin D in relation to cancer development and progression.

Down-regulation of NF-kappaB signals is involved in loss of 1alpha,25-dihydroxyvitamin D3 responsiveness

Vitamin D anti-tumor effect is often found reduced in the late stages of cancer. To uncover vitamin D resistance mechanism, we established a vitamin D-resistant human prostate cancer LNCaP cell line, LNCaP-R, by chronic exposure of cells to 1alpha,25-dihydroxyvitamin D(3) (1,25-VD). The vitamin D receptor (VDR)-mediated transcriptional activity was reduced in LNCaP-R, whereas VDR expression level and DNA-binding capacity were similar compared to parental cells (LNCaP-P). The expressions of the key factors involved in VDR transactivity, including CYP24A1 and VDR-associated proteins are all increased in LNCaP-R cells, and yet treatment with ketoconazole, P450 enzymes inhibitor, as well as trichostatin A (TSA), a histone deacetylase inhibitor, did not sensitize LNCaP-R cells response to vitamin D, suggesting that neither a local 1,25-VD availability, nor VDR-associated proteins are responsible for the vitamin D resistance. Interestingly, nuclear factor-kappaB (NF-kappaB) signaling, which is critical for 1,25-VD/VDR activity was found reduced in LNCaP-R cells, thereby treatment with NF-kappaB activator, 12-O-tetradecanoylphorbol-13-acetate (TPA), can sensitize LNCaP-R vitamin D response. Together, we conclude that NF-kappaB signaling is critical for vitamin D sensitivity, and dysregulation of this pathway would result in vitamin D resistance and disease progression.

Human male gamete endocrinology: 1alpha, 25-dihydroxyvitamin D3 (1,25(OH)2D3) regulates different aspects of human sperm biology and metabolism

BACKGROUND

A wider biological role of 1alpha,25-Dihydroxyvitamin D3 (1,25(OH)2D3), the active metabolite of vitamin D3, in tissues not primarily related to mineral metabolism was suggested. Recently, we evidenced the ultrastructural localization the 1,25(OH)2D3 receptor in the human sperm. However, the 1,25(OH)2D3 action in human male reproduction has not yet been clarified.

METHODS AND RESULTS

By RT-PCR, Western blot and Immunofluorescence techniques, we demonstrated that human sperm expresses the 1,25(OH)2D3 receptor (VDR). Besides, 25(OH)D3-1 alpha-hydroxylase, evidenced by Western blot analysis, indicated that in sperm 1,25(OH)2D3 is locally produced, highlighting the potential for autocrine-paracrine responses. 1,25(OH)2D3 through VDR, increased intracellular Ca2+ levels, motility and acrosin activity revealing an unexpected significance of this hormone in the acquisition of fertilizing ability. In sperm, 1,25(OH)2D3 through VDR, reduces triglycerides content concomitantly to the increase of lipase activity. Rapid responses stimulated by 1,25(OH)2D3 have been observed on Akt, MAPK and GSK3 implying that this secosteroid is involved in different sperm signalling pathways.

CONCLUSION

Our data extended the role of 1,25(OH)2D3 beyond its conventional physiological actions, paving the way for novel therapeutic opportunities in the treatment of the male reproduction disorders.

Anti-proliferative action of vitamin D in MCF7 is still active after siRNA-VDR knock-down

Background

The active form of Vitamin D, 1,25-dihydroxyvitamin D₃ (1,25D), has strong anti-proliferative effects, yet the molecular mechanisms underneath this effect remain unclear. In contrast, the molecular mechanism of 1,25D for the regulation of calcium homeostasis has principally been resolved, demonstrating a pivotal role for the vitamin D receptor (VDR).

Results

We first addressed the question whether the anti-proliferative effects of 1,25D are influenced by VDR. Knockdown of VDR by siRNA did not affect the anti-proliferative effects of 1,25D in MCF7 breast cancer cells. This unanticipated finding led us to take an alternative approach using genome wide screens to study the molecular mechanisms of 1,25D in proliferation. For that purpose, four independently developed and stable 1,25D resistant MCF7 cell lines were analyzed. Array CGH identified a copy number alteration in a region of 13.5 Mb at chromosome 11q13.4-14.1 common to all four 1,25D resistant cell lines. Expression arrays revealed that no single gene was differentially expressed between the sensitive and resistant cells, but multiple membrane receptor signaling pathways were altered in the 1,25D resistant cell lines. Importantly, in the genome wide experiments neither VDR, CYP24A1 nor other known vitamin D signaling pathway genes were associated with 1,25D resistance.

Conclusion

In conclusion, siRNA and genome wide studies both suggest that the anti-proliferative effects of 1,25D in MCF7 breast tumor cell lines do not rely on classical Vitamin D pathway per se.

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.

Increased Expression of Corepressors in Aggressive Androgen-Independent Prostate Cancer Cells Results in Loss of 1α,25-Dihydroxyvitamin D3 Responsiveness

Vitamin D has antiproliferative activity in prostate cancer; however, resistance to vitamin D-mediated growth inhibition occurs. To investigate the mechanisms of vitamin D resistance, we screened two prostate cancer sublines of CWR22rv1, CWR22R-1, and CWR22R-2, with differential sensitivity to vitamin D. CWR22R-2 showed less response to the antiproliferative effect of vitamin D than CWR22R-1. The vitamin D receptor (VDR)-mediated transcriptional activity was also decreased in CWR22R-2. We further showed that the DNA-binding ability of VDR was decreased and the amount of NCoR in VDR response element was increased in CWR22R-2. Analysis of VDR-associated protein profiles found higher expression of the corepressors, NCoR1 and SMRT, in CWR22R-2 cells. Treatment with the histone deacetylase inhibitor, trichostatin A, increased vitamin D/VDR transcriptional activity and promoted the antiproliferative effect of vitamin D in CWR22R-2 cells. Targeted down-regulation of NCoR1 and SMRT by small interference RNA was able to restore CWR22R-2 response to vitamin D. Together, we showed that increased NCoR1 and SMRT expression in CWR22R-2 cells resulted in reduced VDR-mediated transcriptional activity and attenuated antiproliferative response to vitamin D. Our data suggest that the integrity of the vitamin D/VDR-mediated signaling pathway is crucial in predicting vitamin D responsiveness and thus provide a rational design to improve vitamin D-based treatment efficacy based on molecular profiles of patients.

Vitamin D and prevention of breast cancer

Epidemiologic data have demonstrated that breast cancer incidence is inversely correlated with indices of vitamin D status, including ultraviolet exposure, which enhances epidermal vitamin D synthesis. The vitamin D receptor (VDR) is expressed in mammary epithelial cells, suggesting that vitamin D may directly influence sensitivity of the gland to transformation. Consistent with this concept, in vitro studies have demonstrated that the VDR ligand, 1,25-dihydroxyvitamin D (1, 25D), exerts negative growth regulatory effects on mammary epithelial cells that contribute to maintenance of the differentiated phenotype. Furthermore, deletion of the VDR gene in mice alters the balance between proliferation and apoptosis in the mammary gland, which ultimately enhances its susceptibility to carcinogenesis. In addition, dietary supplementation with vitamin D, or chronic treatment with synthetic VDR agonists, reduces the incidence of carcinogen-induced mammary tumors in rodents. Collectively, these observations have reinforced the need to further define the human requirement for vitamin D and the molecular actions of the VDR in relation to prevention of breast cancer.

Identification of VDR-responsive gene signatures in breast cancer cells

OBJECTIVES

Defining transcriptional profiles which predict cancer cell anti-proliferative responsiveness towards 1,25-dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)] is required to improve and tailor the chemotherapeutic application of this seco-steroid hormone to individual cancer patients.

METHODS

We undertook a transcriptomic approach with Affymetrix human U133 GeneChips to determine responsive and resistant gene signatures in MCF-7 breast cancer cells and 1alpha,25(OH)(2)D(3)-resistant MCF-7(Res) cells, respectively. Principal component and hierarchical clustering analyses demonstrated that the patterns of responsiveness between the 2 cell types differed clearly and were used to generate heat maps. Differentially regulated gene targets were validated with Q-RT-PCR and the biological impact upon proliferation measured.

RESULTS

In untreated MCF-7(Res) cells, 163 genes were up-regulated and 274 down-regulated (with a log(2) ratio of >0.5) compared to the MCF-7 controls. Using the same gene expression threshold, 1alpha,25(OH)(2)D(3) treatment (100 nM, 6 h) of MCF-7 cells up-regulated 91 genes and down-regulated 5, whereas in MCF-7(Res), despite their resistance to the anti-proliferative effects, 156 genes were modulated with 91 being down-regulated. Strikingly, CYP24 was the only induced gene that was common to the genetic profiles of the 2 sets of 1alpha,25(OH)(2)D(3)-treated cells. Heat map analyses defined 2 sub-clusters of genes: (1) basal expression patterns associated with insensitivity towards 1alpha,25(OH)(2)D(3) and (2) regulated expression patterns associated with 1alpha,25(OH)(2)D(3) sensitivity. This latter cluster contained BAX, GADD45alpha, IGFBP-3, EGFR, MAPK4 and TGF-beta(2). Time course studies confirmed the 1alpha,25(OH)(2)D(3) regulation of TGF-beta(2) in MCF-7 and non-tumourigenic MCF-12A cells but not in MCF-7(Res) cells. Co-treatment of MCF-7(Res) cells with exogenous TGF-beta(2) plus 1alpha,25(OH)(2)D(3) enhanced anti-proliferative and vitamin D receptor transcriptional effects.

CONCLUSIONS

Basal and regulated gene patterns can be used to predict and monitor the cellular response towards vitamin D(3) compounds and may possibly be applied as a further diagnostic tool.

Identification of novel mediators of Vitamin D signaling and 1,25(OH)2D3 resistance in mammary cells

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 demonstrated that the VDR ligand, 1,25(OH)(2)D(3), modulates key proteins involved in signaling proliferation, differentiation and survival of normal mammary epithelial cells. Anti-proliferative and pro-differentiating effects of 1,25(OH)(2)D(3) have also been observed in VDR positive breast cancer cells, indicating that transformation per se does not abolish Vitamin D signaling. However, many breast cancer cell lines are less sensitive to 1,25(OH)(2)D(3) than normal mammary epithelial cells. Reduced sensitivity to 1,25(OH)(2)D(3) has been linked to alterations in Vitamin D metabolizing enzymes as well as down regulation of VDR expression or function. In this report, we describe results from a proteomics screening approach used to search for proteins involved in dictating sensitivity or resistance to Vitamin D mediated apoptosis in breast cancer cells. Several proteins not previously linked to 1,25(OH)(2)D(3) signaling were identified with this approach, and a distinct subset of proteins was linked to 1,25(OH)(2)D(3) resistance. Follow-up studies to determine the relevance of these proteins to Vitamin D signaling in general are in progress.

Autocrine metabolism of vitamin D in normal and malignant breast tissue

PURPOSE

Vitamin D seems to exert a protective effect against common cancers, although this does not correlate with circulating levels of active 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], indicating a more localized activation of vitamin D. The aim of this study was to investigate the significance of this in breast cancer.

EXPERIMENTAL DESIGN

Quantitative reverse transcription-PCR analysis of mRNA expression was carried out for the vitamin D-activating enzyme 1alpha-hydroxylase, the catabolic enzyme 24-hydroxylase, and the vitamin D receptor in 41 tumors and paired nonneoplastic tissue as well as breast cancer cell lines. Immunohistochemistry was used to assess 1alpha-hydroxylase protein expression, and enzyme assays were used to quantify vitamin D metabolism.

RESULTS

Expression of mRNA for 1alpha-hydroxylase (27-fold; P < 5 x 10(-11)), vitamin D receptor (7-fold; P < 1.5 x 10(-8)), and 24-hydroxylase (4-fold; P < 0.02) was higher in breast tumors. 1alpha-Hydroxylase enzyme activity was also higher in tumors (44.3 +/- 11.4 versus 12.4 +/- 4.8 fmol/h/mg protein in nonneoplastic tissue; P < 0.05). However, production of inactive 1,24,25-trihydroxyvitamin D3 was also significantly higher in tumors (84.8 +/- 11.7 versus 33.6 +/- 8.5 fmol/h/mg protein; P < 0.01). Antisense inhibition of 24-hydroxylase in vitro increased antiproliferative responses to 1,25(OH)2D3.

CONCLUSION

These data indicate that the vitamin D-activating enzyme 1alpha-hydroxylase is up-regulated in breast tumors. However, dysregulated expression of 24-hydroxylase seems to abrogate the effects of local 1,25(OH)2D3 production in tumors by catalyzing catabolism to less active vitamin D metabolites. The enzymes involved in autocrine metabolism of vitamin D in breast tissue may therefore provide important targets for both the prevention and treatment of breast cancer.

Molecular activity of 1,25-dihydroxyvitamin D3 in primary cultures of human prostatic epithelial cells revealed by cDNA microarray analysis

1,25-Dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] exerts anti-proliferative, differentiating and apoptotic effects on prostatic cells. These activities, in addition to epidemiologic findings that link Vitamin D to prostate cancer risk, support the use of 1,25(OH)(2)D(3) for prevention or therapy of prostate cancer. The molecular mechanisms by which 1,25(OH)(2)D(3) exerts antitumor effects on prostatic cells are not well-defined. In addition, there is heterogeneity among the responses of various prostate cell lines and primary cultures to 1,25(OH)(2)D(3) with regard to growth inhibition, differentiation and apoptosis. To understand the basis of these differential responses and to develop a better model of Vitamin D action in the prostate, we performed cDNA microarray analyses of primary cultures of normal and malignant human prostatic epithelial cells, treated with 50 nM of 1,25(OH)(2)D(3) for 6 and 24 h. CYP24 (25-hydroxyvitamin D(3)-24-hydroxylase) was the most highly upregulated gene. Significant and early upregulation of dual specificity phosphatase 10 (DUSP10), validated in five additional primary cultures, points to inhibition of members of the mitogen-activated protein kinase (MAPK) superfamily as a key event mediating activity of 1,25(OH)(2)D(3) in prostatic epithelial cells. The functions of other regulated genes suggest protection by 1,25(OH)(2)D(3) from oxidative stress. Overall, these results provide new insights into the molecular basis of antitumor activities of Vitamin D in prostate cells.

Antiproliferative role of vitamin D and its analogs--a brief overview

The active metabolite of vitamin D, 1alpha, 25-dihydroxyvitamin D3 [1,25(OH)2D3]--a seco-steroid hormone is a pivotal regulator of cellular proliferation and differentiation those are independent of its classical function of calcium homeostasis and bone mineralization. The existence of the nuclear vitamin D receptor (VDR) has been found in numerous tissues in different organs, which are the so-called 'non-classical' targets of this seco-steroid hormone. Vitamin D has been documented as a potent antiproliferative agent in different tissues and cells. Epidemiological studies reveal a negative correlation between physiological level of vitamin and cancer risk. Studies using animal models clearly demonstrate protective role of vitamin D in different cancer types by the reduction in tumor progression and by monitoring biochemical parameters. Experiments with cultured human and animal cancer cell lines show similar antiproliferative role of vitamin D manifested by up or down regulations of crucial genes leading to inhibition of cellular growth. Hypercalcemia hinders broad-spectrum therapeutic uses of vitamin D in cancer chemotherapy. Application of vitamin D analogs having similar chemical structures or other compounds having vitamin D like actions but lacking calcemic adverse effects are getting significant attention towards rational therapeutics to treat cancer. The current review focuses on the application of vitamin D and its analogs in different forms of cancer and on the molecular mechanism involved in vitamin D mediated inhibition in cellular proliferation, cell cycle, induction of apoptosis and tumor suppression, which may eventually evolve as a meaningful cancer therapy.

Ras activation is associated with vitamin D receptor mRNA instability in HC11 mammary cells

HC11, a spontaneously immortalized murine mammary lineage maintains features of normal cells while HC11 H-ras transformed cells (HC11 ras) are tumorigenic. Ras transformation is associated with a lower Vitamin D receptor (VDR) mRNA content. Our goal was to investigate the mechanism underlying VDR mRNA differences between these cells. Although the VDR transcriptional rate measured by run-on assays did not differ between the cells, our data suggested a pos transcriptional mechanism involving higher VDR mRNA degradation in HC11 ras cells which was not due to mutations in its 3'-UTR region since sequences of mRNA obtained from HC11 and HC11 ras cells were identical. Treatment of HC11 ras cells with a farnesyltransferase inhibitor, which prevents ras activation, causing an enhancement of VDR mRNA levels, indicating an association between the ras signaling pathway and VDR mRNA instability. The present work suggests that the decreased mRNA levels in HC11 ras cells might in part be due to an early loss of stability.

Sequential versus combined treatment of human breast cancer cells with antiestrogens and the vitamin D analogue EB1089 and evaluation of predictive markers for vitamin D treatment

Development of resistance to antihormonal therapy is a major problem in the treatment of breast cancer patients. Metastatic tumors, which progress after a period of response to treatment, often respond to second line endocrine treatment, but eventually develop estrogen independent growth. Vitamin D analogues are promising new drugs, using alternative mechanisms to inhibit growth of breast cancer cells. The sensitivity to antiestrogens and vitamin D analogues has been proposed to be inverse, indicating that the sensitivity to vitamin D analogues might increase after development of antiestrogen resistance and vice versa. In this study, the inverse sensitivity between antiestrogens and the vitamin D analogue EB1089 was examined in antiestrogen and vitamin D resistant breast cancer cell lines. The majority of the investigated antiestrogen resistant cell lines had increased sensitivity to treatment with the vitamin D analogue EB1089. In addition, growth of a vitamin D resistant cell line was more inhibited by the pure antiestrogen ICI 182,780 than the growth of the parental cells, indicating that the compounds may be used sequentially. An association between the expression level of the vitamin D receptor (VDR) and EB1089 sensitivity was observed, suggesting that VDR is a possible predictive marker for response to vitamin D treatment. Valuation of Bcl-2 gene expression may be useful in combination with VDR to predict the outcome of treatment with EB1089. Furthermore, we observed a synergistic growth inhibition and an abrogated development of resistance upon combined treatment with ICI 182,780 and EB1089. Therefore, antiestrogens and vitamin D analogues may also be used as combined treatment for breast cancer patients in the future.

Relevance of breast cancer cell lines as models for breast tumours: an update

The number of available breast cancer cell (BCC) lines is small, and only a very few of them have been extensively studied. Whether they are representative of the tumours from which they originated remains a matter of debate. Whether their diversity mirrors the well-known inter-tumoural heterogeneity is another essential question. While numerous similarities have long been found between cell lines and tumours, recent technical advances, including the use of micro-arrays and comparative genetic analysis, have brought new data to the discussion. This paper presents most of the BCC lines that have been described in some detail to date. It evaluates the accuracy of the few of them widely used (MCF-7, T-47D, BT-474, SK-BR-3, MDA-MB-231, Hs578T) as tumour models. It is concluded that BCC lines are likely to reflect, to a large extent, the features of cancer cells in vivo. The importance of oestrogen receptor-alpha (gene ESR1 ) and Her-2/ neu ( ERBB2 ) as classifiers for cell lines and tumours is underlined. The recourse to a larger set of cell lines is suggested since the exact origin of some of the widely used lines remains ambiguous. Investigations on additional specific lines are expected to improve our knowledge of BCC and of the dialogue that these maintain with their surrounding normal cells in vivo.

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

The active metabolite of vitamin D3, 1,25-dihydroxyvitamin D3 (1,25(OH)D3), has been recognized for over 2 decades as a modulator of cell proliferation and differentiation in many cell types, including breast cancer. However, any potential anti-tumour properties displayed by 1,25(OH)D3 are limited by the tendency to cause hypercalcaemia when administered at high doses. Because of this, synthetic vitamin D analogues have been developed that retain the anti-tumour effects seen with 1,25(OH)D3 but which have reduced calcaemic activity. However, it is still unclear as to how 1,25(OH)D3 and its synthetic analogues act within breast cancer cells to elicit the effects on cellular proliferation and differentiation. In this chapter we review the advances that have been made in trying to answer this question. It has been found so far that 1,25(OH)D3 has an effect on the expression of certain cell cycle regulators and in this way can bring about G1 arrest. Evidence has also emerged that vitamin D compounds can also affect the growth-promoting pathways initiated by two important factors involved in breast cancer cell promotion; namely the insulin-like growth factor I (IGF-I) and oestrogen-receptor (ER) pathways. Vitamin D compounds have also been implicated in promotion of apoptosis in breast cancer cells and evidence suggests that 1,25(OH)D3 and its synthetic analogues may potentiate responsiveness of breast cancer cells to conventional cytotoxic agents. Although much remains to be learned about the associated underlying mechanisms, ongoing research suggests that vitamin D analogues are a new class of compounds with potential in breast cancer treatment and prevention.

Vitamin D growth inhibition of breast cancer cells: gene expression patterns assessed by cDNA microarray

1,25-Dihydroxyvitamin D3 [1,25(OH)2D3], the active metabolite of vitamin D, is a potent inhibitor of breast cancer cell growth. Although it is evident that 1,25(OH)2D3 inhibits growth of both estrogen receptor alpha-positive [ER alpha(+)] and -negative [ER alpha(-)] breast cancer cells, the cellular pathways contributing to these effects remain unclear. We studied the gene expression patterns in ER alpha(+) MCF-7 and ER alpha(-) MDA MB 231 human breast cancer cells following 1,25(OH)2D3 treatment, using cDNA expression arrays. Both cell lines showed a significant induction of the 1,25(OH)2D3-dependent 24-hydroxylase gene, a marker for the actions of 1,25(OH)2D3. In MCF-7 cells, 51 genes were up-regulated and 19 genes were down-regulated. The up-regulated genes encoded cell adhesion molecules, growth factors/modulators, steroid receptors/co-activators, cytokines, kinases and transcription factors. Of the up-regulated genes, 40% were implicated in cell cycle regulation and apoptosis and included cyclin G1 and cyclin I, p21-activated kinase-1 (PAK-1), p53, retinoblastoma like-2 [Rb2 (p130)], insulin-like growth factor binding protein-5 (IGFBP5) and caspases. Among the down-regulated genes were ER alpha, growth factors, cytokines and several kinases. Some of these results were confirmed by real-time PCR. In MDA MB 231 cells, 20 genes were up-regulated and 13 genes were down-regulated. Very few genes directly implicated in cell cycle regulation were up-regulated. The matrix metalloproteinases formed a major class of genes that were down-regulated in the MDA MB 231 cells. Seven genes were commonly up-regulated in both cell lines and these included transforming growth factor (TGFbeta2) and Rb2 (p130). In conclusion, the gene expression profiles of the two cell lines studied were different with a few overlapping genes suggesting that different cellular pathways might be regulated by 1,25(OH)2D3 to exert its growth inhibitory effects in ER alpha(+) and ER alpha(-) cells.

Characterization of mammary tumor cell lines from wild type and vitamin D3 receptor knockout mice

1,25-Dihydroxyvitamin D(3) (1,25D(3)), the active metabolite of vitamin D(3), inhibits breast cancer cell growth in vivo and in vitro. To examine mechanisms of 1,25D(3) induced growth arrest and apoptosis, cell lines were established from DMBA induced mammary tumors derived from vitamin D(3) receptor knockout (VDRKO) and wild type (WT) mice. Two VDRKO (KO240, KO288) and two WT (WT145, WT276) cell lines were selected and characterized. All four cell lines express cytokeratins indicative of an epithelial origin, as well as vimentin, which is expressed in many transformed cell lines. The tumorigenicity of the cells was confirmed in vivo as all four cell lines form estrogen responsive tumors in nude mice. Both WT cell lines express the VDR protein and are sensitive to growth inhibition by 1,25D(3) at doses as low as 1 nM. Flow cytometric analysis indicated that 1,25D(3) induces G(0)/G(1) arrest and apoptosis in the WT cell lines. In contrast, both cell lines established from tumors that developed in VDRKO mice lack VDR mRNA and protein. Cells from WT mice exhibit 1,25D(3) inducible transcriptional activity, as measured by reporter gene assays, but cells from VDRKO mice do not. Cells from VDRKO mice are also completely resistant to 1,25D(3) mediated growth arrest and apoptosis over the range of 0.01-100 nM 1,25D(3). VDRKO cells are also resistant to the synthetic vitamin D(3) analogs EB1089 and CB1093 that are more potent growth inhibitors than 1,25D(3) in WT cells. This data conclusively demonstrate that the induction of cell cycle arrest and apoptosis in breast cancer cells by 1,25D(3), EB1089 and CB1093 is dependent on the nuclear VDR. Cells lacking VDR remain sensitive to growth arrest mediated by 9-cis retinoic acid, a ligand for the retinoid x receptor which can heterodimerize with the VDR. Sensitivity to apoptosis induced by the DNA damaging agent etoposide is not altered in VDRKO cells, indicating that VDR ablation does not impair apoptotic pathways in general. All four cell lines display equal sensitivity to tamoxifen induced growth arrest. These estrogen responsive, transformed cell lines which differentially express the VDR provide a novel model system for identification of the mechanisms by which 1,25D(3) regulates proliferation and apoptosis in breast cancer cells.

Impact of the Vitamin D3 receptor on growth-regulatory pathways in mammary gland and breast cancer

1,25-Dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) interacts with the Vitamin D(3) receptor (VDR) to modulate proliferation and apoptosis in a variety of cell types, including breast cancer cells. In this review, we discuss three issues related to the role of the VDR in growth control: first, whether mammary glands lacking VDR exhibit abnormal growth; second, whether the VDR is essential for induction of apoptosis by 1,25(OH)(2)D(3); and third, whether VDR up-regulation can sensitize cells to 1,25(OH)(2)D(3). Studies from our laboratory have demonstrated that mammary glands from VDR knockout (VDR KO) mice exhibit accelerated growth and branching during puberty, pregnancy and lactation as compared to wild-type (WT) mice. In addition, involution after weaning, a process driven by epithelial cell apoptosis, proceeds at a slower rate in VDR KO mice compared to WT mice. Using cells isolated from VDR KO and WT mice, we report that both normal and transformed mammary cells derived from WT mice are growth inhibited by 1,25(OH)(2)D(3), however, cells derived from VDR KO mice are completely unresponsive to 1,25(OH)(2)D(3). In human breast cancer cells, we have identified a variety of agents, including steroid hormones, phytoestrogens and growth factors, that up-regulate VDR expression and enhance sensitivity to 1,25(OH)(2)D(3)-mediated growth inhibition. Collectively, these studies support a role for 1,25(OH)(2)D(3) and the VDR in negative growth regulation of both normal mammary gland and breast cancer cells.

Sensitivity to growth suppression by 1alpha,25-dihydroxyvitamin D(3) among MCF-7 clones correlates with Vitamin D receptor protein induction

The antiproliferative effect of 1alpha,25-dihydroxyvitamin D(3) (1alpha,25(OH)(2)D(3)) has been studied for a decade in diverse model systems, but the signalling pathways linking 1alpha,25(OH)(2)D(3) to cell cycle arrest remains unclear. In our attempt to establish a model system which would allow further identification of important players in the process of the 1alpha,25(OH)(2)D(3) imposed cell cycle arrest, we have isolated derivatives of the human breast cancer cell line MCF-7 and chosen two nearly 1alpha,25(OH)(2)D(3) resistant and two hypersensitive sub-clones. Investigation of cell cycle proteins regulated by 1alpha,25(OH)(2)D(3) in these clones indicates that activation of one component/pathway is responsible for the linkage between 1alpha,25(OH)(2)D(3) and growth arrest. Protein levels of the Vitamin D receptor (VDR) were elevated in sensitive cells upon 1alpha,25(OH)(2)D(3) treatment, whereas resistant clones were unable to induce VDR upon 1alpha,25(OH)(2)D(3) treatment. Our data show that VDR protein levels and the ability of a cell to induce VDR upon 1alpha,25(OH)(2)D(3) treatment correlate with the antiproliferative effects of 1alpha,25(OH)(2)D(3), and suggest that the level of VDR in cancer cells might serve as a prognostic marker for treatment of cancer with 1alpha,25(OH)(2)D(3) analogues.