EB1089, a synthetic analogue of vitamin D, induces apoptosis in breast cancer cells in vivo and in vitro

Vitamin D in Cancer Prevention and Treatment: A Review of Epidemiological, Preclinical, and Cellular Studies

Inhibition of human carcinomas has previously been linked to vitamin D due to its effects on cancer cell proliferation, migration, angiogenesis, and apoptosis induction. The anticancer activity of vitamin D has been confirmed by several studies, which have shown that increased cancer incidence is associated with decreased vitamin D and that dietary supplementation of vitamin D slows down the growth of xenografted tumors in mice. Vitamin D inhibits the growth of cancer cells by the induction of apoptosis as well as by arresting the cells at the G0/G1 (or) G2/M phase of the cell cycle. Aim and Key Scientific Concepts of the Review: The purpose of this article is to thoroughly review the existing information and discuss and debate to conclude whether vitamin D could be used as an agent to prevent/treat cancers. The existing empirical data have demonstrated that vitamin D can also work in the absence of vitamin D receptors (VDRs), indicating the presence of multiple mechanisms of action for this sunshine vitamin. Polymorphism in the VDR is known to play a key role in tumor cell metastasis and drug resistance. Although there is evidence that vitamin D has both therapeutic and cancer-preventive properties, numerous uncertainties and concerns regarding its use in cancer treatment still exist. These include (a) increased calcium levels in individuals receiving therapeutic doses of vitamin D to suppress the growth of cancer cells; (b) hyperglycemia induction in certain vitamin D-treated study participants; (c) a dearth of evidence showing preventive or therapeutic benefits of cancer in clinical trials; (d) very weak support from proof-of-principle studies; and (e) the inability of vitamin D alone to treat advanced cancers. Addressing these concerns, more potent and less toxic vitamin D analogs have been created, and these are presently undergoing clinical trial evaluation. To provide key information regarding the functions of vitamin D and VDRs, this review provided details of significant advancements in the functional analysis of vitamin D and its analogs and VDR polymorphisms associated with cancers.

The vitamin D analog EB1089 sensitizes triple-negative breast cancer cells to the antiproliferative effects of antiestrogens

PURPOSE

Patients bearing estrogen receptor (ER)α-negative breast cancer tumors confront poor prognosis and are typically unresponsive to hormone therapy. Previous studies have shown that calcitriol, the active vitamin D metabolite, can induce ERα expression in ERα-negative cells. EB1089, a calcitriol analog with reduced calcemic effects, exhibits greater potency than calcitriol in inhibiting cancer cell growth. However, the impact of EB1089 on ERα expression in triple-negative breast cancer (TNBC) cells remains unexplored. This study aims to investigate whether EB1089 could induce functional ERα expression in TNBC cell lines, potentially enabling the antiproliferative effects of antiestrogens.

MATERIALS AND METHODS

TNBC cell lines HCC1806 and HCC1937 were treated with EB1089, and ERα expression was analyzed using real-time PCR and Western blots. The transcriptional activity of induced ERα was evaluated through a luciferase reporter assay. The antiproliferative effects of tamoxifen and fulvestrant antiestrogens were assessed using the sulforhodamine B assay in the EB1089-treated cells.

RESULTS

Our findings indicated that EB1089 significantly induced ERα mRNA and protein expression in TNBC cells. Moreover, EB1089-induced ERα exhibited transcriptional activity and effectively restored the inhibitory effects of antiestrogens, thereby suppressing cell proliferation in TNBC cells.

CONCLUSION

EB1089 induced the expression of functional ERα in TNBC cells, restoring the antiproliferative effects of antiestrogens. These results highlight the potential of using EB1089 as a promising strategy for re-establishment of the antiproliferative effect of antiestrogens as a possible management for TNBC. This research lays the foundation for potential advancements in TNBC treatment, offering new avenues for targeted and effective interventions.

The vitamin D receptor agonist EB1089 can exert its antiviral activity independently of the vitamin D receptor

Vitamin D has been shown to have antiviral activity in a number of different systems. However, few studies have investigated whether the antiviral activity is exerted through the vitamin D receptor (VDR). In this study, we investigated whether the antiviral activity of a vitamin D receptor agonist (EB1089) towards dengue virus (DENV) was modulated by VDR. To undertake this, VDR was successively overexpressed, knocked down and retargeted through mutation of the nuclear localization signal. In no case was an effect seen on the level of the antiviral activity induced by EB1089, strongly indicating that the antiviral activity of EB1089 is not exerted through VDR. To further explore the antiviral activity of EB1089 in a more biologically relevant system, human neural progenitor cells were differentiated from induced pluripotent stem cells, and infected with Zika virus (ZIKV). EB1089 exerted a significant antiviral effect, reducing virus titers by some 2Log10. In support of the results seen with DENV, no expression of VDR at the protein level was observed. Collectively, these results show that the vitamin D receptor agonist EB1089 exerts its antiviral activity independently of VDR.

Antitumoral effects of dovitinib in triple-negative breast cancer are synergized by calcitriol in vivo and in vitro

Chemotherapy is a standard therapeutic option for triple-negative breast cancer (TNBC); however, its effectiveness is often compromised by drug-related toxicity and resistance development. Herein, we aimed to evaluate whether an improved antineoplastic effect could be achieved in vitro and in vivo in TNBC by combining dovitinib, a multi-kinase inhibitor, with calcitriol, a natural anticancer hormone. In vitro, cell proliferation and cell-cycle distribution were studied by sulforhodamine B-assays and flow cytometry. In vivo, dovitinib/calcitriol effects on tumor growth, angiogenesis, and endothelium activation were evaluated in xenografted mice by caliper measures, Itgb3/VEGFR2-immunohistochemistry and ^99mTc-Ethylenediamine-N,N-diacetic acid/hydrazinonicotinamyl-Glu[cyclo(Arg-Gly-Asp-D-Phe-Lys)]₂ (^99mTc-RGD₂)-tumor uptake. The drug combination elicited a synergistically improved antiproliferative effect in TNBC-derived cells, which allowed a 7-fold and a 3.3-fold dovitinib dose-reduction in MBCDF-Tum and HCC-1806 cells, respectively. Mechanistically, the co-treatment induced a cell cycle profile suggestive of cell death and DNA damage (accumulation of cells in SubG1, S, and G2/M phases), increased the number of multinucleated cells and inhibited tumor growth to a greater extent than each compound alone. Tumor uptake of ^99mTc-RGD₂ was reduced by dovitinib, suggesting angiogenesis inhibition, which was corroborated by decreased endothelial cell growth, tumor-vessel density and VEGFR2 expression. In summary, calcitriol synergized dovitinib anticancer effects in vitro and in vivo, allowing for a significant dose-reduction of dovitinib while maintaining its antiproliferative potency. Our results suggest the beneficial convergence of independent antitumor mechanisms of dovitinib and calcitriol to inhibit TNBC-tumor growth.

Repurposing vitamin D for treatment of human malignancies via targeting tumor microenvironment

Tumor cells along with a small proportion of cancer stem cells exist in a stromal microenvironment consisting of vasculature, cancer-associated fibroblasts, immune cells and extracellular components. Recent epidemiological and clinical studies strongly support that vitamin D supplementation is associated with reduced cancer risk and favorable prognosis. Experimental results suggest that vitamin D not only suppresses cancer cells, but also regulates tumor microenvironment to facilitate tumor repression. In this review, we have outlined the current knowledge on epidemiological studies and clinical trials of vitamin D. Notably, we summarized and discussed the anticancer action of vitamin D in cancer cells, cancer stem cells and stroma cells in tumor microenvironment, providing a better understanding of the role of vitamin D in cancer. We presently re-propose vitamin D to be a novel and economical anticancer agent.

Vitamin D and K signaling pathways in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a primary liver malignancy, and is now the six most common in between malignancies. Early diagnosis of HCC with prompt treatment increases the opportunity of patients to survive. With the advances in understanding the molecular biology of HCC, new therapeutic strategies to treat HCC have emerged. There is a growing consensus that vitamins are important for the control of various cancers. Biochemical evidence clearly indicates that HCC cells are responsive to the inhibitory effect of vitamin D, vitamin D analogues and vitamin K. In this review, we summarize the mechanisms used by vitamin D and K to influence the development of HCC and the latest development of vitamin analogues for potential HCC therapy.

Vitamin D analogues: Potential use in cancer treatment

The vitamin D receptor (VDR) is a member of the thyroid-steroid family of nuclear transcription factors. Following binding of the active form of vitamin D, i.e., 1,25(OH)₂D3 (also known as calcitriol) and interaction with co-activators and co-repressors, VDR regulates the expression of several different genes. Although relatively little work has been carried out on VDR in human cancers, several epidemiological studies suggest that low circulating levels of vitamin D are associated with both an increased risk of developing specific cancer types and poor outcome in patients with specific diagnosed cancers. These associations apply especially in colorectal and breast cancer. Consistent with these findings, calcitriol as well as several of its synthetic analogues have been shown to inhibit tumor cell growth in vitro and in diverse animal model systems. Indeed, some of these vitamin D analogues with low calcemic inducing activity (e.g., EB1089, inecalcitol, paricalcitol) have progressed to clinical trials in patients with cancer. Preliminary results from these trials suggest that these vitamin D analogues have minimal toxicity, but clear evidence of efficacy remains to be shown. Although evidence of efficacy for mono-treatment with vitamin D analogues is currently lacking, several studies have reported that supplementation with calcitriol or the presence of high endogenous circulating levels of vitamin D enhances response to standard therapies.

Role of vitamin D in uterine fibroid biology

OBJECTIVE

To provide a detailed summary of current scientific knowledge on uterine fibroids (leiomyomas) in vitro and in in vivo animal models, as well as to postulate the potential role of vitamin D3 as an effective, inexpensive, safe, long-term treatment option for uterine fibroids.

DESIGN

PubMed search articles were used to identify the most relevant studies on uterine fibroids, as well as effects of vitamin D3 on uterine fibroid cells and fibroid tumor growth in in vivo animal models.

SETTING

University research laboratory.

PATIENT(S)

Not applicable.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Not applicable.

RESULT(S)

Despite numerous publications available on uterine fibroids, information about the role that vitamin D3 plays in the regulation of uterine fibroids is limited. Most of the recent vitamin D3-related studies on uterine fibroids were published from our group. Recent studies have demonstrated that vitamin D deficiency plays a significant role in the development of uterine fibroids. Our recent studies have demonstrated that vitamin D3 reduces leiomyoma cell proliferation in vitro and leiomyoma tumor growth in in vivo animal models. These results postulate the potential role of vitamin D3 for an effective, safe, nonsurgical medical treatment option for uterine fibroids.

CONCLUSION(S)

This article reviews human and animal studies and uncovers new possibilities for understanding the vitamin D-based therapeutic option for an effective, safe, long-term treatment of uterine fibroids. On the basis of these results, a clinical trial with vitamin D3 or a hypocalcemic analog, paricalcitol, may be warranted for nonsurgical medical treatment of uterine fibroids.

The human cytomegalovirus lytic cycle is induced by 1,25-dihydroxyvitamin D3 in peripheral blood monocytes and in the THP-1 monocytic cell line

Human cytomegalovirus (HCMV) resides in a latent form in hematopoietic progenitors and undifferentiated cells within the myeloid lineage. Maturation and differentiation along the myeloid lineage triggers lytic replication. Here, we used peripheral blood monocytes and the monocytic cell line THP-1 to investigate the effects of 1,25-dihydroxyvitamin D3 on HCMV replication. Interestingly, 1,25-dihydroxyvitamin D3 induces lytic replication marked by upregulation of HCMV gene expression and production of infectious virus. Moreover, we demonstrate that the effects of 1,25-dihydroxyvitamin D3 correlate with maturation/differentiation of the monocytes and not by directly stimulating the MIEP. These results are somewhat surprising as 1,25-dihydroxyvitamin D3 typically boosts immunity to bacteria and viruses rather than driving the infectious life cycle as it does for HCMV. Defining the signaling pathways kindled by 1,25-dihydroxyvitamin D3 will lead to a better understanding of the underlying molecular mechanisms that determine the fate of HCMV once it infects cells in the myeloid lineage.

Comparative regulation of gene expression by 1,25-dihydroxyvitamin D3 in cells derived from normal mammary tissue and breast cancer

Previous genomic profiling of immortalized, non-tumorigenic human breast epithelial cells identified a set of 1,25-dihydroxyvitamin D3 (1,25D) regulated genes with potential relevance to breast cancer prevention. In this report, we characterized the effect of 1,25D on a subset of these genes in six cell lines derived from mammary tissue and breast cancers. Non-tumorigenic cell lines included hTERT-HME1, HME and MCF10A cells which are often used to model normal breast epithelial cells. Breast cancer cell lines included MCF7 cells (a model of early stage, estrogen-dependent disease), DCIS.com cells (a derivative of MCF10A cells that models in situ breast cancer) and Hs578T cells (a model of metastatic disease). All of these cell lines express the vitamin D receptor (VDR) and exhibit anti-cancer responses to 1,25D such as changes in proliferation, apoptosis, metabolism, or invasion. Our comparative data demonstrate highly variable responses to 1,25D (100nM, 24h) between the cell lines. In both hTERT-HME1 and HME cell lines, CYP24A1, SLC1A1 and ITGB3 were up-regulated whereas KDR, GLUL and BIRC3 were down-regulated in response to 1,25D. In contrast, no changes in SLC1A1, ITGB3 or GLUL expression were detected in 1,25D treated MCF10A cells although KDR and BIRC3 were down-regulated by 1,25D. The effects of 1,25D on these genes in the breast cancer cell lines were blunted, with the DCIS.com cells exhibiting the most similar responses to the immortalized hTERT-HME1 and HME cells. The differences in cellular responses were not due to general impairment in VDR function as robust CYP24A1 induction was observed in all cell lines. Thus, our data indicate that the genomic changes induced by 1,25D are highly cell-type specific even in model cell lines derived from the same tissue. The implication of these findings is that genomic responses to changes in vitamin D status in vivo are likely to be distinct from individual to individual, particularly in neoplastic tissue. This article is part of a Special Issue entitled '17th Vitamin D Workshop'.

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.

A xenograft animal model of human arteriovenous malformations

Background

Arteriovenous malformations (AVMs) are a type of high-flow vascular malformations that most commonly occurs in the head and neck. They are present at birth but are usually clinically asymptomatic until later in life. The pathogenesis of AVMs remains unclear and therapeutic approaches to AVMs are unsatisfied. In order to provide a tool for studying the pathogenesis and therapies of this disease, we established and studied a xenograft animal model of human AVMs.

Methods

Fresh human AVMs specimens harvested from 4 patients were sectioned (5x5x5 mm) and xenografted subcutaneously in 5 immunologically naïve nude mice (Athymic Nude-Foxn1^nu). Each mouse had four pieces specimens in four quadrants along the back. The grafts were observed weekly for volume, color and texture. The grafts were harvested at every 30 days intervals for histologic examination. All grafts (n = 20) were sectioned and stained for hematoxylin and eosin (H&E). Comparative pathologic evaluation of the grafts and native AVMs were performed by two blinded pathologists. Immunohistochemical examination of human-specific nuclear antigen, vascular endothelial growth factor receptor-2 (VEGFR-2) and Ki-67 was performed.

Results

Clinical characteristics and pathologic diagnosis of native human derived AVMs were confirmed. 85% (n = 17) of AVM xenografts survived although the sizes decreased after implantation. Histological examination demonstrated numerous small and medium-size vessels and revealed structural characteristics matching the native AVMs tissue.76.5% (n = 13) of the surviving xenografts were positive for Ki-67 and human-specific nuclear antigen suggesting survival of the human derived tissue, 52.9% (n = 9) were positive for VEGFR-2.

Conclusions

This preliminary xenograft animal model suggests that AVMs can survive in the nude mouse. The presence of human-specific nuclear antigen, VEGFR-2, and Ki-67 demonstrates the stability of native tissue qualities within the xenografts.

The sum of many small changes: microRNAs are specifically and potentially globally altered by vitamin D3 metabolites

Vitamin D3 deficiency is rampant which may contribute to increased risk of many diseases including cancer, cardiovascular disease and autoimmune disorders. Genomic activity of the active metabolite 1,25-dihydroxyvitamin D (1,25D) mediates most vitamin D3's actions and many gene targets of 1,25D have been characterized. As the importance of non-coding RNAs has emerged, the ability of vitamin D3via 1,25D to regulate microRNAs (miRNAs) has been demonstrated in several cancer cell lines, patient tissue and sera. In vitamin D3 intervention patient trials, significant differences in miRNAs are observed between treatment groups and/or between baseline and followup. In patient sera from population studies, specific miRNA differences associate with serum levels of 25D. The findings thus far indicate that dietary vitamin D3 in patients and 1,25D in vitro not only regulate specific miRNA(s), but may also globally upregulate miRNA levels. This article is part of a Special Issue entitled 'Vitamin D Workshop'.

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

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'.

Evaluation of the potential therapeutic role of a new generation of vitamin D analog, MART-10, in human pancreatic cancer cells in vitro and in vivo

Pancreatic cancer is a lethal disease with no known effective chemotherapy and radiotherapy, and most patients are diagnosed in the late stage, making them unsuitable for surgery. Therefore, new therapeutic strategies are urgently needed. 1α,25-dihydroxyvitamin D3 [1α,25(OH)2D3] is known to possess antitumor actions in many cancer cells in vitro and in vivo models. However, its clinical use is hampered by hypercalcemia. In this study, we investigated the effectiveness and safety of a new generation, less calcemic analog of 1α,25(OH)2D3, 19-nor-2α-(3-hydroxypropyl)-1α,25-dihydroxyvitamin D3 (MART-10), in BxPC-3 human pancreatic carcinoma cells in vitro and in vivo. We demonstrate that MART-10 is at least 100-fold more potent than 1α,25(OH)2D3 in inhibiting BxPC-3 cell proliferation in a time- and dose-dependent manner, accompanied by a greater upregulation of cyclin-dependent kinase inhibitors p21 and p27 and a greater downregulation of cyclin D3 and cyclin-dependent kinases 4 and 5, leading to a greater increase in the fraction of cells in G0/G1 phase. No induction of apoptosis and no effect on Cdc25 phosphatases A and C were observed in the presence of either MART-10 or 1α,25(OH)2D3. In a xenograft mouse model, treatment with 0.3 µg/kg body weight of MART-10 twice/week for 3 weeks caused a greater suppression of BxPC-3 tumor growth than the same dose of 1α,25(OH)2D3 without inducing hypercalcemia and weight loss. In conclusion, MART-10 is a promising agent against pancreatic cancer growth. Further clinical trial is warranted.

Vitamin D analog EB1089 inhibits aromatase expression by dissociation of comodulator WSTF from the CYP19A1 promoter-a new regulatory pathway for aromatase

The enzyme aromatase, encoded by the CYP19A1 gene, catalyzes the production of estrogens and inhibition of aromatase has therefore become one of the key strategies in breast cancer treatment. We have studied the effects of the vitamin D analog EB1089 on aromatase gene expression and enzyme activity in breast cancer cells. We found that EB1089 was able to decrease the gene expression and enzyme activity as well as inhibit aromatase-dependent cell growth. Furthermore, a low dose of EB1089 combined with low doses of clinically used aromatase inhibitors such as anastrozole, letrozole and exemestane were able to effectively inhibit aromatase-dependent growth of breast cancer cells. The molecular mechanism for this effect of EB1089 on the aromatase gene expression was investigated and we found that it is mediated by the vitamin D receptor (VDR), vitamin D receptor interacting repressor (VDIR) and Williams syndrome transcription factor (WSTF). ChIP and Re-ChIP assays revealed that EB1089 mediates dissociation of WSTF from the CYP19A1 promoter and thereby decreases the gene expression. Regulation of aromatase via WSTF has not been reported previously. Furthermore, gene silencing of WSTF results in decreased gene expression of CYP19A1 and aromatase activity, showing that WSTF is an interesting drug target for development of new anti-cancer drugs. In summary, we report that the vitamin D analog EB1089 is able to decrease the gene expression and enzyme activity of aromatase via a novel regulatory pathway for aromatase and suggest that EB1089 may be a new treatment option for estrogen dependent breast cancer.

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.

1,25-dihydroxyvitamin D3 treatment shrinks uterine leiomyoma tumors in the Eker rat model

Uterine leiomyomas (fibroids) are the most common benign tumors in women of reproductive age. These tumors are three to four times more prevalent in African American women, who also have a 10 times higher incidence of hypovitaminosis D than white women. Recent studies have demonstrated the antitumor effects of 1,25-dihydroxyvitamin D3 on several cancers, but its effects on uterine leiomyomas are still unknown. To determine the antitumor and therapeutic effects of 1,25-dihydroxyvitamin D3 on uterine leiomyomas, female Eker rats (14-16 mo old) harboring uterine leiomyomas were randomized into control and experimental groups and were given vehicle versus 1,25-dihydroxyvitamin D3 (0.5 μg/kg per day) subcutaneously for 3 wk, respectively. At the end of the experiment, the rats were euthanized, and the leiomyoma tumors were analyzed. Treatment with 1,25-dihydroxyvitamin D3 significantly reduced leiomyoma tumor size in Eker rats. It also reduced leiomyoma size by suppressing cell growth and proliferation-related genes (Pcna, cyclin D1 [Ccnd1], Myc, Cdk1, Cdk2, and Cdk4), antiapoptotic genes (Bcl2 and Bcl2l1 [Bcl-x]), and estrogen and progesterone receptors. Additionally, immunohistochemistry revealed decreased expression of PCNA and MKI67 (a marker of proliferation) and increased expression of caspase 3 in 1,25-dihydroxyvitamin D3-treated Eker rat leiomyomas. Toxicity analyses using serum samples showed similar levels of SGOT, SGPT, calcium, and total bilirubin in 1,25-dihydroxyvitamin D3-treated and vehicle-treated control Eker rats. These results support that 1,25-dihydroxyvitamin D3 is an antitumor agent that may be a potential safe, nonsurgical therapeutic option for the treatment of uterine leiomyomas.

Does vitamin D protect against DNA damage?

Vitamin D is a secosteroid best known for its role in maintaining bone and muscle health. Adequate levels of vitamin D may also be beneficial in maintaining DNA integrity. This role of vitamin D can be divided into a primary function that prevents damage from DNA and a secondary function that regulates the growth rate of cells. The potential for vitamin D to reduce oxidative damage to DNA in a human has been suggested by clinical trial where vitamin D supplementation reduced 8-hydroxy-2'-deoxyguanosine, a marker of oxidative damage, in colorectal epithelial crypt cells. Studies in animal models and in different cell types have also shown marked reduction in oxidative stress damage and chromosomal aberrations, prevention of telomere shortening and inhibition of telomerase activity following treatment with vitamin D. The secondary function of vitamin D in preventing DNA damage includes regulation of the poly-ADP-ribose polymerase activity in the DNA damage response pathway involved in the detection of DNA lesions. It is also able to regulate the cell cycle to prevent the propagation of damaged DNA, and to regulate apoptosis to promote cell death. Vitamin D may contribute to prevention of human colorectal cancer, though there is little evidence to suggest that prevention of DNA damage mediates this effect, if real. Very limited human data mean that the intake of vitamin D required to minimise DNA damage remains uncertain.

MNU-induced mammary gland carcinogenesis: chemopreventive and therapeutic effects of vitamin D and Seocalcitol on selected regulatory vitamin D receptor pathways

The effects of administration of vitamin D₃ and Seocalcitol on MNU-induced carcinogenesis of mammary gland in Sprague-Dawley rats have been investigated. Administration of both substances in a weekly dose of 7 μg/kg caused prolonged latency of mammary gland tumors. The latency of tumors was markedly prolonged for 30-40 days by Seocalcitol. Using PET analysis, reduction in [¹⁸F]2-fluoro-2-deoxy-d-glucose (FDG) uptake or tumor volume in tumors chemopreventively treated with vitamin D₃ were detected in MNU-induced tumors, vitamin D₃ reduced expression of 25-hydroxylase (25OHase) (p<0.01) and 24-hydroxylase (24OHase) (p<0.01) and Seocalcitol 24OHase. Positive regulation of 25OHase mRNA level after the treatment with vitamin D₃ was observed in liver, while in kidney, vitamin D₃ and Seocalcitol induced expression of 24OHase was significant. Our observations indicate a cross talk between respective pathways of VDR, RARs/RXRs, TRs and ERs in carcinogenesis process.

22-oxa-1,25-dihydroxyvitamin D3 efficiently inhibits tumor growth in inoculated mice and primary histoculture of cholangiocarcinoma

BACKGROUND

It is well known that 1α,25-Dihydroxyvitamin D3 (1,25[OH]2 D3) restrains cell proliferation and induces differentiation and apoptosis in normal and tumor cells. The authors of this report recently demonstrated that 1,25(OH)2 D3 effectively inhibits the proliferation of cholangiocarcinoma (CCA) cell lines. The antitumor activity and the underlying mechanism of 22-oxa-D3, an analog of vitamin D, in mice and in tissue cultures from patients with CCA were further explored in the current study.

METHODS

Cell growth and cell cycle distribution were examined in CCA cells by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and flow cytometry. Mice were injected subcutaneously with 4×10(6) CCA cells at both flank sides and intraperitoneal injections with phosphate-buffered saline or 22-oxa-D3 (15 μg/kg/day) for 17 days thereafter. Tumors were removed the next day. The expression levels of cyclin D1 and the cyclin-dependent kinase inhibitor p21 were determined by Western blot analysis and immunohistochemistry. Growth inhibition of 22-oxa-D3 in fresh tissue samples from patients with CCA was analyzed by using a histodrug response assay.

RESULTS

22-oxa-D3 effectively suppressed the growth of CCA cell lines in a time-dependent and dose-dependent manner. 22-oxa-D3 arrested CCA cells at G1 phase to S phase by the suppression of cyclin D1 expression and the up-regulation of p21. Supplementation of 22-oxa-D3 to CCA-inoculated mice significantly inhibited tumor growth without hypercalcemia or serious side effects. The treatment also induced cellular apoptosis in tissue samples from patients with CCA.

CONCLUSIONS

22-oxa-D3 effectively suppressed tumor growth in CCA-inoculated mice and induced cellular apoptosis in tissue samples from patients with CCA. The current data encourage further investigation of 1,25(OH)2 D3 or its analogues as therapeutic agents in the treatment of patients with CCA.

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

These studies focus on identification of vitamin D regulated pathways that impact development or progression of breast cancer. In mouse experiments, we assessed genomic profiles of glandular tissue and established tumors from MMTV-neu mice fed adequate (250 IU/kg) or high (5000 IU/kg) vitamin D (cholecalciferol). Genomic profiles were also obtained in murine mammary cells that differentially express VDR that were cultured in vitro with 100 nM 1,25-dihydroxyvitamin D (1,25D). Ten candidate genes were identified that were commonly regulated in murine cells treated with 1,25D in vitro and in mammary gland of mice fed high dietary vitamin D. In complementary studies, the vitamin D pathway was evaluated in human mammary epithelial cells as a function of transformation. Genes regulated by 1,25D in human mammary epithelial cells included those involved in innate immunity (CD14), differentiation (Bmp6), extracellular matrix remodeling (Plau) and cell survival (Birc3). Transformation reduced VDR content and blunted the induction of some, but not all, target genes by 1,25D in human mammary cells. Collectively, these in vivo and in vitro data demonstrate that vitamin D signaling impacts on common pathways that drive differentiation, alter metabolism, remodel the extracellular matrix and trigger innate immunity in mammary tissue.

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 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.

Mechanism of UV-related carcinogenesis and its contribution to nevi/melanoma

Melanoma consists 4-5 % of all skin cancers, but it contributes to 71-80 % of skin cancers deaths. UV light affects cell and tissue homeostasis due to its damaging effects on DNA integrity and modification of expression of a plethora of genes. DNA repair systems protect cells from UV-induced lesions. Several animal models of melanoma have been developed (Xiphophorus, Opossum Monodelphis domestica, mouse models and human skin engrafts into other animals). This review discusses possible links between UV and genes significantly related to melanoma but does not discuss melanoma genetics. These include oncogenes, tumor suppressor genes, genes related to melanocyte-keratinocyte and melanocyte-matrix interaction, growth factors and their receptors, CRH, ACTH, α-MSH, glucocorticoids, ID1, NF-kappaB and vitamin D3.

Preadministration of high-dose salicylates, suppressors of NF-kappaB activation, may increase the chemosensitivity of many cancers: an example of proapoptotic signal modulation therapy

NF-kappaB activity is elevated in a high proportion of cancers, particularly advanced cancers that have been treated previously. Cytotoxic treatment selects for such up-regulation inasmuch as NF-kappaB promotes transcription of a large number of proteins that inhibit both the intrinsic and extrinsic pathways of apoptosis; NF-kappaB also boosts expression of mdr1, which expels many drugs from cells. Indeed, high NF-kappaB activity appears to be largely responsible for the chemo- and radioresistance of many cancers. Thus, agents that suppress NF-kappaB activity should be useful as adjuvants to cytotoxic cancer therapy. Of the compounds that are known to be NF-kappaB antagonists, the most practical for current use may be the nonsteroidal anti-inflammatory drugs aspirin, salicylic acid, and sulindac, each of which binds to and inhibits Ikappa kinase- beta, a central mediator of NF-kappa activation; the low millimolar plasma concentrations of salicylate required for effective inhibition of this kinase in vivo can be achieved with high-dose regimens traditionally used to manage rheumatic disorders. The gastrointestinal toxicity of such regimens could be minimized by using salsalate or enteric-coated sodium salicy-late or by administering misoprostol in conjunction with aspirin therapy. Presumably, best results would be seen if these agents were administered for several days prior to a course of chemo- or radiotherapy, continuing throughout the course. This concept should first be tested in nude mice bearing xenografts of chemoresistant human tumors known to have elevated NF-kappa activity. Ultimately, more complex adjuvant regimens can be envisioned in which salicylates are used in conjunction with other NF-kappa antagonists and/or agents that target other mediators of down-regulated apoptosis in cancer, such as Stat3; coadministration of salicylate and organic selenium may have intriguing potential in this regard. These strategies may also have potential as adjuvants to metronomic chemotherapy, which seeks to suppress angio-genesis by targeting cycling endothelial cells in tumors.

25-Hydroxyvitamin D3 1alpha-hydroxylase expression in breast cancer and use of non-1alpha-hydroxylated vitamin D analogue

Introduction

The cytochrome P450 mitochondrial enzyme 25-hydroxyvitamin D₃ 1α-hydroxylase (1α-hydroxylase) of renal tubule cells hydroxylates the major circulating form of vitamin D (25(OH)D₃) to the active systemic hormone 1,25(OH)₂D₃. Local production of 1,25(OH)₂D₃ appears to occur also at other sites where 1α-hydroxylase is expressed for autocrine/paracrine regulation. To reduce risks of hypercalcemia during treatment with vitamin D, we have previously suggested use of non-1α-hydroxylated vitamin D analogues to target tissues where 1α-hydroxylase is expressed, including the parathyroid glands in secondary hyperparathyroidism. The present study was undertaken to examine expression of 1α-hydroxylase in breast cancer and to investigate whether a non-1α-hydroxylated vitamin D analogue displayed biological function. In addition, expression of the 25-hydroxyvitamin D₃ 24-hydroxylase (24-hydroxylase) and the vitamin D receptor (VDR) was investigated.

Methods

The expression of 1α-hydroxylase, 24-hydroxylase and VDR was investigated in breast cancer specimens (n = 19) and normal breast tissues (n = 10) by immunohistochemistry and/or RT-PCR. Consecutive cryosections of 6 μm essentially free of immune cells were used in the analyses. The effect of vitamin D analogues on transcriptional activation was analyzed in transiently transfected MCF-7 breast cancer cells.

Results

1α-hydroxylase protein was demonstrated in 79% and 100% of breast cancer specimens and normal breast, respectively. The overall relative mRNA levels of 1α-hydroxylase and 24-hydroxylase in normal breast compared to breast tumors were: 1α-hydroxylase, 1 ± 0.07 versus 0.7 ± 0.05, respectively (p < 0.001); 24-hydroxylase, 1 ± 0.08 verus 2.1 ± 0.2, respectively (p < 0.001). The VDR was expressed in 95% of the tumors as expected, with mRNA levels of 1 ± 0.09 and 1.4 ± 0.12 (p < 0.05) in breast cancer and normal breast, respectively. The ketoconazole-sensitive transcription activation potential of the non-1α-hydroxylated vitamin D analogue prodrug of EB1089 (EB1285) was demonstrated in MCF-7 cells, which express 1α-hydroxylase. The activity of EB1285 was about 20% of 1,25(OH)₂D₃.

Conclusion

These results demonstrate nearly normal expression levels of 1α-hydroxylase, 24-hydroxylase and VDR in the majority of investigated breast cancer specimens. A non-1α-hydroxylated vitamin D analogue displayed activity in breast cancer cells. Such analogues may present future therapeutic options for proliferative disorders where 1α-hydroxylase is expressed.

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.

Inhibition of proliferation and induction of apoptosis by 25-hydroxyvitamin D3-3beta-(2)-Bromoacetate, a nontoxic and vitamin D receptor-alkylating analog of 25-hydroxyvitamin D3 in prostate cancer cells

The 25-hydroxyvitamin D(3) (25-OH-D(3)) is a nontoxic and low-affinity vitamin D receptor (VDR)-binding metabolic precursor of 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)]. We hypothesized that covalent attachment of a 25-OH-D(3) analog to the hormone-binding pocket of VDR might convert the latter into transcriptionally active holo-form, making 25-OH-D(3) biologically active. Furthermore, it might be possible to translate the nontoxic nature of 25-OH-D(3) into its analog. We showed earlier that 25-hydroxyvitamin D(3)-3-bromoacetate (25-OH-D(3)-3-BE) alkylated the hormone-binding pocket of VDR. In this communication we describe that 10(-6) mol/L of 25-OH-D(3)-3-BE inhibited the growth of keratinocytes, LNCaP, and LAPC-4 androgen-sensitive and PC-3 and DU145 androgen-refractory prostate cancer cells, and PZ-HPV-7 immortalized normal prostate cells with similar or stronger efficacy as 1,25(OH)(2)D(3). But its effect was strongest in LNCaP, PC-3, LAPC-4, and DU145 cells. Furthermore, 25-OH-D(3)-3-BE was toxic to these prostate cancer cells and caused these cells to undergo apoptosis as shown by DNA-fragmentation and caspase-activation assays. In a reporter assay with COS-7 cells, transfected with a 1alpha,25-dihydroxyvitamin D(3)-24-hydroxylase (24-OHase)-construct and VDR-expression vector, 25-OH-D(3)-3-BE induced 24-OHase promoter activity. In a "pull down assay" with PC-3 cells, 25-OH-D(3)-3-BE induced strong interaction between VDR and general transcription factors, retinoid X receptor, and GRIP-1. Collectively, these results strongly suggested that the cellular effects of 25-OH-D(3)-3-BE were manifested via 1,25(OH)(2)D(3)/VDR signaling pathway. A toxicity study in CD-1 mice showed that 166 microg/kg of 25-OH-D(3)-3-BE did not raise serum-calcium beyond vehicle control. Collectively, these results strongly suggested that 25-OH-D(3)-3-BE has a strong potential as a therapeutic agent for androgen-sensitive and androgen-refractory prostate cancer.

Differential regulation of survivin expression and apoptosis by vitamin D3 compounds in two isogenic MCF-7 breast cancer cell sublines

Although both the antiapoptotic function of survivin and vitamin D3 (VD3)-mediated cell growth inhibition and apoptosis have been extensively studied, it is not known whether survivin plays a role in VD3 compound-mediated cell growth inhibition and apoptosis induction. Using an isogenic model of MCF-7 breast adenocarcinoma cells (MCF-7E and MCF-7L sublines that are sensitive and resistant to VD3 compounds), we found that VD3 compounds effectively downregulated survivin in VD3-sensitive MCF-7E cells, which was associated with VD3-induced apoptosis. In contrast, VD3 compounds failed to downregulate survivin in VD3-resistant MCF-7L cells, which showed resistant to VD3-induced apoptosis. However, inhibition of survivin expression by small interfering RNA (siRNA) induced cell death per se and further sensitized VD3-induced apoptosis in MCF-7L cells, indicating that the inability of these cells to respond to VD3 is due to the failure to downregulate survivin. Forced expression of survivin not only blocked VD3-mediated G1 cell accumulation but also increased S and G2/M cell populations. VD3 treatment rapidly triggered the activation of p38 MAPK signaling in MCF-7E cells but not in MCF-7L cells. Moreover, inhibition of p38 activation diminished VD3-mediated survivin inhibition and partially rescued VD3-induced cell death. We further showed that VD3 increased the expression of TGF(beta)1 and TGF(beta) receptor 2, and that blocking the function of TGF(beta) receptor 2 diminished VD3 compound-mediated survivin downregulation. Thus, we propose that the VD3 compound-induced growth inhibition and apoptosis induction are at least partially dependent on survivin downregulation via VD3-induced TGFbeta signaling and the activation of p38 MAPK pathway. Targeting survivin through these pathways may lead to novel applications for cancer therapeutics.

22-Oxa-1alpha,25-dihydroxyvitamin D3 inhibits metastasis and angiogenesis in lung cancer

1alpha,25-Dihydroxyvitamin D(3) (1alpha,25-D(3)) has potent antiproliferative and anti-invasive properties in vitro in cancer cells. However, its calcemic effect in vivo limits its therapeutic applications. Here, we report the efficacy of 22-oxa-1alpha,25-dihydroxyvitamin D(3) (22-oxa-1alpha,25-D(3)), a low calcemic analog of vitamin D, against the development of metastatic lung carcinoma after an intravenous injection of green fluorescent protein-transfected Lewis lung carcinoma (LLC-GFP) cells in C57BL/6 mice. The mice injected with tumor cells were implanted simultaneously with osmotic minipumps containing either 1alpha,25-D(3), 22-oxa-1alpha,25-D(3) or vehicle. The 1alpha,25-D(3) treatment group had been hypercalcemic, but the 22-oxa-1alpha,25-D(3) and vehicle treatment groups remained normocalcemic for the duration of the experiment. The total number of lung metastases, lung weight and the expression of GFP mRNA in the lung were markedly decreased in 1alpha,25-D(3) and 22-oxa-1alpha,25-D(3)-treated mice. In the in vitro experiment, 1alpha,25-D(3) and 22-oxa-1alpha,25-D(3) reduced the expression of matrix metalloproteinase (MMP)-2, MMP-9, vascular endothelial growth factor and parathyroid hormone-related protein in LLC-GFP cells. Furthermore, in the angiogenesis assay, the number of tumor cells or basic fibroblast growth factor-induced angiogenesis was reduced in 1alpha,25-D(3) and 22-oxa-1alpha,25-D(3)-treated mice. Moreover, using a new experimental model of vitamin D receptor (VDR) null mutant (VDR(-/-)) mice with corrected hypocalcemia and hypervitaminosis D, we examine the anti-cancer effect of 22-oxa-1alpha,25-D(3) without other functions induced by 22-oxa-1alpha,25-D(3) in the host. In the VDR(-/-) mice, 22-oxa-1alpha,25-D(3) directly inhibited the metastatic activity of LLC-GFP cells in a dose-dependent manner without exerting a direct influence on the calcemic activity or other actions regulated by 22-oxa-1alpha,25-D(3) in the host. These results indicate that the inhibition of metastasis and angiogenesis-inducing activity in cancer cells seemed to be a major mechanism responsible for the anti-cancer effects of 22-oxa-1alpha,25-D(3). Our findings show that 22-oxa-1alpha,25-D(3) is beneficial for the prevention of metastasis in lung carcinoma.

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.

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.

1alpha,25-dihydroxyvitamin D(3) (calcitriol) and its analogue, 19-nor-1alpha,25(OH)(2)D(2), potentiate the effects of ionising radiation on human prostate cancer cells

Radiotherapy with external beam radiation or brachytherapy is an established therapeutic modality for prostate cancer. Approximately 30% of patients with localised prostate cancer relapse at the irradiated site. Secondary effects of ionising radiation (IR), for example, bowel and bladder complications, are common. Thus, the search for biological response modifiers that could potentiate the therapeutic effects of radiation and limit the occurrence of serious side effects is an important task in prostate cancer therapy. 1alpha,25-Dihydroxyvitamin D(3) (calcitriol), the active metabolite of vitamin D, and its analogues are under investigation for the treatment of several malignancies including prostate cancer. Here, we report that 1alpha,25-dihydroxyvitamin D(3) and its less calcaemic analogue 19-nor-1alpha,25-(OH)(2)D(2) (Zemplar) act synergistically with IR to inhibit the growth of the human prostate cancer cells in vitro. 1alpha,25-dihydroxyvitamin D(3) potentiated IR-induced apoptosis of LNCaP cells, and nanomolar doses of 1alpha,25-dihydroxyvitamin D(3) and 19-nor-1alpha,25-(OH)(2)D(2) showed synergistic inhibition of growth of LNCaP cells at radiobiologically relevant doses of IR (1-2 Gy). At higher doses of IR, the combination of 1alpha,25-dihydroxyvitamin D(3) and IR or 19-nor-1alpha,25-(OH)(2)D(2) and IR resulted in moderate antagonism. The synergistic effect at radiobiologically relevant doses of radiation suggests that a combination of 1alpha,25-dihydroxyvitamin D(3) or 19-nor-1alpha,25-(OH)(2)D(2) with IR could permit a reduction in the dose of radiation given clinically and thus potentially reduce treatment-related morbidity.

New insights regarding pharmacologic approaches for ovarian cancer prevention

The pathogenesis of epithelial ovarian cancer is not completely understood, but it commonly is believed that the process of recurrent ovulation (incessant ovulation) causes genetic damage in ovarian epithelial cells and that sufficient genetic damage can lead to ovarian cancer in susceptible individuals. Under this model, it has been suggested that reproductive and hormonal factors, such as pregnancy and oral contraceptive use, decrease ovarian cancer risk mainly via their inhibitory effects on ovulation. There is mounting evidence that the ovarian epithelium is a hormonally responsive target organ whose biology can be impacted strongly by the local hormonal environment. Progestin-mediated apoptotic effects may be a major mechanism underlying the ovarian cancer protective effects of pregnancy (a high progestin state) and oral contraceptive pill use. Similarly, retinoids, vitamin D, and non-steroidal anti-inflammatory drugs may have biologic effects on the ovarian epithelium that are cancer preventive, whereas androgens may have stimulatory effects on the ovarian epithelium, leading to an increased ovarian cancer risk.

Effects of Seocalcitol (EB1089) on Nitrosomethyl Urea-Induced Rat Mammary Tumors

Although 1,25-dihydroxyvitamin D3 is a potent cell-differentiating agent, its use in cancer prevention or therapy is precluded because it induces hypercalcemia. Synthetic analogs have been developed which inhibit tumor progression in animal models of breast cancer. One analog, Seocalcitol (EB1089) has been shown to be effective in causing regression of N-methyl-nitrosourea-induced rat mammary tumors. However, at the most effective oral dose, a significant increase in serum and urinary calcium levels were observed. In order to compare the efficacy of different dosing schedules of Seocalcitol, rats were treated either 6 times weekly (1 microg/kg) or by intermittent dosing to achieve the same total weekly dose. All dosing schedules of Seocalcitol were effective in inhibiting tumor progression. Once daily dosing was significantly more effective than intermittent dosing but was associated with a greater rise in serum calcium concentration. In order to evaluate alternative treatment strategies to limit calcemic effects, we assessed the efficacy of limiting vitamin D-induced hypercalcemia using bisphosphonates. Seocalcitol (2.5 microg/kg daily p.o. for 4 weeks) alone and in combination with pamidronate (APD 0.4 mg/kg per day s.c.) or the same dose of the bisphosphonate EB 1053 caused substantial tumor regression. No statistically significant difference was seen between combination treatment and Seocalcitol treatment alone. Co-treatment with APD or EB 1053 did not limit the rise in serum calcium induced by Seocalcitol alone. Cessation of treatment or administration of a lower dose (1microg/kg twice weekly) reversed hypercalcemia, hypercalciuria and weight loss induced by high dose Seocalcitol. However, reduction in tumor volume was maintained in the majority of animals.

A phase II study of the vitamin D analogue Seocalcitol in patients with inoperable hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a common malignant tumour, which has a poor prognosis. Surgical resection can be curative but most patients are inoperable and most chemotherapy agents have minimal activity in this disease. Seocalcitol, a vitamin D analogue, induces differentiation and inhibits growth in cancer cell lines and in vivo. The vitamin D receptor is expressed in hepatocytes and more abundantly in HCC cells. In total, 56 patients with inoperable advanced HCC were included in an uncontrolled study of oral Seocalcitol treatment for up to 1 year (with possible extension for responders). The dose was titrated according to serum calcium levels. The treatment effect was evaluated by regular CT scans. Out of 33 patients evaluable for tumour response, two had complete response (CR), 12 stable disease and 19 progressive disease. The CRs appeared after 6 and 24 months of treatment, and lasted for 29 and at least 36 months (patient still in remission when data censored). Seocalcitol was well tolerated; the most frequent toxicity was hypercalcaemia and related symptoms. Most patients tolerated a daily dose of 10 micro g of Seocalcitol. This is the first study showing activity, by reduction in tumour dimensions, of a differentiating agent in patients with an advanced bulky, solid tumour. Seocalcitol may have an effect in the treatment of HCC, especially in early disease when a prolonged treatment can be instituted. The survival benefit with or without tumour response should be determined in controlled studies.

(Patho)physiological implications of the novel epithelial Ca2+ channels TRPV5 and TRPV6

The epithelial Ca(2+) channels TRPV5 and TRPV6 constitute the apical Ca(2+) entry mechanism in active Ca(2+) (re)absorption. These two members of the superfamily of transient receptor potential (TRP) channels were cloned from the vitamin-D-responsive epithelia of kidney and small intestine and subsequently identified in other tissues such as bone, pancreas and prostate. These channels are regulated by vitamin D as exemplified in animal models of vitamin-D-deficiency rickets. In addition, the epithelial Ca(2+) channels might be involved in the multifactorial pathogenesis of disorders ranging from idiopathic hypercalciuria, stone disease and postmenopausal osteoporosis. This review highlights the emerging (patho)physiological implications of these epithelial Ca(2+) channels.

Efficacy of Vitamin D compounds to modulate estrogen receptor negative breast cancer growth and invasion

In estrogen receptor (ER) positive breast cancer cells such as MCF-7 cells, the anti-tumor effects of 1,25(OH)(2)D(3) (1,25D(3)) may be secondary to disruption of estrogen mediated survival signals. If so, then sensitivity to 1,25D(3) mediated growth arrest could be reduced in estrogen independent breast cancer cells. The aim of these studies was to determine the effects of 1,25D(3) and EB1089 on the ER negative, invasive human breast cancer cell line SUM-159PT. 1,25D(3) and EB1089 reduced SUM-159PT cell growth subsequent to elevation of p27 and p21 levels. 1,25D(3) mediated apoptosis of SUM-159PT cells was associated with an enrichment of membrane bound bax, a redistribution of cytochome c from the mitochondria to the cytosol and PARP cleavage. 1,25D(3) and EB1089 also inhibited SUM-159PT cell invasion through an 8 microM Matrigel membrane. In pre-clinical studies, EB1089 dramatically reduced the growth of SUM-159PT xenografts in nude mice. The decreased size of tumors from EB1089 treated mice was associated with decreased proliferation and increased DNA fragmentation. Our data support the concept that Vitamin D(3) compounds trigger apoptosis by mechanisms independent of estrogen signaling. These studies indicate that Vitamin D(3) based therapeutics may be beneficial, alone or in conjunction with other agents, for the treatment of estrogen independent breast cancer.

Des (1-3) IGF-I-stimulated growth of human stromal BPH cells is inhibited by a vitamin D3 analogue

Prostate growth and differentiation is under the control of androgens not only during fetal life and childhood but also in adulthood, and it has been proposed that increased prostatic concentration of androgens, or increased androgen responsiveness, causes benign prostatic hyperplasia (BPH). However, different androgen ablation strategies such as treatment with GnRH agonists and finasteride resulted in a modest decrease of the hyperplastic prostate volume. In the last few years it became evident that both androgen-dependent and androgen-independent growth factors promote prostate enlargement by inducing cell proliferation or reducing apoptosis. Therefore, new therapeutic strategies, aimed at reducing intraprostatic growth factor signaling, are under investigation. In this study, we report further evidence that a non hypercalcemic-analogue of vitamin D(3), analogue (V) decreases growth factor-induced human BPH cell proliferation and survival. We found that Des (1-3) insulin-like growth factor [Des (1-3) IGF-I], an IGF-I analogue, which does not bind to IGF-binding proteins, is a potent mitogen for BPH stromal cells via a dual mechanism: stimulation of cell growth and inhibition of apoptosis. Similar results were previously reported for another growth factor for BPH cells, keratinocyte growth factor (KGF). Accordingly, we speculate that both KGF and IGF might be involved in the pathogenesis of BPH. We also found analogue (V) not only inhibits the mitogenic activity of growth factors on BPH cells, but even decreased the basal expression of bcl-2, and induced apoptosis. Therefore, vitamin D(3) analogues might be considered for the medical treatment of BPH.

[Analysis of molecular mechanism of cancer cell differentiation and apoptosis induced by vitamin D3 analogs on the basis of molecular recognition of vitamin D receptor ligand binding domain]

1 alpha,25-Dihydroxyvitamin D3 [1 alpha,25 (OH)2D3] has antiproliferative, differentiation and apoptosis-inducing effects on many malignant cells. These properties have raised the possibility of its use as a therapeutic agent in cancer. Our recent studies using stereoisomers of the A-ring of monohydroxylated 19-nor or 2-methyl substituted 1 alpha,25 (OH)2D3 have clearly demonstrated that the A-ring analogs that contain 1 alpha-hydroxy or 3 beta-hydroxy group are potent inducers of HL-60 cell differentiation. In contrast, the A-ring analogs that contain 1 beta-hydroxy or 3 alpha-hydroxy group are potent stimulators of HL-60 cell apoptosis. It was interesting to note that the analogs could induce differentiation or apoptosis of HL-60 cells on the basis of the stereochemistry of both hydroxy groups at positions 1 and 3 of the A-ring. To further elucidate the possible roles of both the hydroxy groups in regulating cell differentiation and apoptosis, we have synthesized all possible diastereomers of the A-ring of 1 alpha,25 (OH)2D3 and examined their molecular mechanism of differentiation and apoptosis-inducing actions of HL-60 cells in vitro. This study shows that differentiation and apoptosis of HL-60 cells are strictly controlled by the stereochemistry of both hydroxy groups at positions 1 and 3 of the A-ring of 1 alpha,25 (OH)2D3, and the proteins responsible for the regulation of cell cycle and mitochondrial membrane potential are the major targets of 1 alpha,25 (OH)2D3 analogs. These findings provide useful information not only for structure-function studies of 1 alpha,25 (OH)2D3 analogs but also for the development of therapeutic agents for the treatment of cancer.

Vitamin D and cancer

Vitamin D, a steroid hormone and exerts its biological effects through its active metabolite 1alpha, 25 dihydroxyvitamin D3 [1,25(OH)2D3]. Like steroid hormones, 1,25(OH)2D3 is efficacious at very low concentrations and serves as a ligand for vitamin D receptors (VDR), associating with VDR very high affinity. Despite its potent property as a differentiating agent, its use in the clinical practice is hampered by the induction of hypercalcemia at a concentration required to suppress cancer cell proliferation. Therefore nearly 400 structural analogs of vitamin D3 have been synthesized and evaluated for their efficacy and toxicity. Among these analogs, relatively less toxic but highly efficacious analogs, EB1089, RO24-5531, 1alpha-hydroxyvitamin D5 and a few others have been evaluated in a preclinical toxicity and in Phase I clinical trials for dose tolerance in advanced cancer patients. Clinical trials using vitamin D analogs for prevention or therapy of cancer patients are still in their infancy. Vitamin D mediates its action by two independent pathways. Genomic pathway involves nuclear VDR and induces biological effects by interactions with hormone response elements and modulation of differential gene expressions. Evidence also suggests that vitamin D analogs also interact with steroid hormone(s) inducible genes. The non-genomic pathway is characterized by rapid actions of vitamin D. It involves interactions with membrane-VDR interactions and its interactions with protein kinase C and by altering intracellular calcium channels. Thus, the development of nontoxic analogs of vitamin D analogs and understanding of their molecular mechanism(s) of action are of significant importance in the prevention and treatment of cancer by vitamin D.

Antiproliferative action of vitamin D

During the past few years, it has become apparent that vitamin D may play an important role in malignant transformation. Epidemiological studies suggest that low vitamin D serum concentration increases especially the risk of hormone-related cancers. Experimentally, vitamin D suppresses the proliferation of normal and malignant cells and induces differentiation and apoptosis. In the present review we discuss the mechanisms whereby vitamin D regulates cell proliferation and whether it could be used in prevention and treatment of hyperproliferative disorders like cancers.

A phase II trial of the vitamin D analogue Seocalcitol (EB1089) in patients with inoperable pancreatic cancer

Inoperable cancer of the exocrine pancreas responds poorly to most conventional anti-cancer agents, and new agents are required to palliate this disease. Seocalcitol (EB1089), a vitamin D analogue, can inhibit growth, induce differentiation and induce apoptosis of cancer cell lines in vitro and can also inhibit growth of pancreatic cancer xenografts in vivo. Thirty-six patients with advanced pancreatic cancer received once daily oral treatment with seocalcitol with dose escalation every 2 weeks until hypercalcaemia occurred, following which patients continued with maintenance therapy. The most frequent toxicity was the anticipated dose-dependent hypercalcaemia, with most patients tolerating a dose of 10-15 microg per day in chronic administration. Fourteen patients completed at least 8 weeks of treatment and were evaluable for efficacy, whereas 22 patients were withdrawn prior to completing 8 weeks' treatment and in 20 of these patients withdrawal was due to clinical deterioration as a result of disease progression. No objective responses were observed, with five of 14 patients having stable disease in whom the duration of stable disease was 82-532 days (median=168 days). The time to treatment failure (n=36) ranged from 22 to 847 days, and with a median survival of approximately 100 days. Seocalcitol is well tolerated in pancreatic cancer but has no objective anti-tumour activity in advanced disease. Further studies are necessary to determine if this agent has any cytostatic activity in this malignancy in minimal disease states.

Autocrine TGFbeta signaling mediates vitamin D3 analog-induced growth inhibition in breast cells

In this study, we address whether TGFbeta signaling mediates vitamin D3 analog-induced growth inhibition in nonmalignant and malignant breast cells. Normal mammary epithelial cells (184), immortalized nonmalignant mammary epithelial cells (184A1 and MCF10A), and breast cancer cells (early passage MCF7: MCF7E) were sensitive to the inhibitory effects of vitamin D3 analogs (EB1089 and MC1288) while late passage MCF7 breast cancer (MCF7L) cells were relatively resistant. A similar pattern of sensitivity to TGFbeta was observed with these cells. Thus, the sensitivity to the vitamin D3 analogs correlated with the sensitivity to TGFbeta. MCF7L TGFbetaRII-transfected cells, which have autocrine TGFbeta activity, were more sensitive to EB1089 than MCF7L cells. TGFbeta neutralizing antibody was found to block the inhibitory effects of these analogs. These results are consistent with the idea that autocrine TGFbeta signaling mediates the anti-proliferative effects of the vitamin D3 analogs in these cells. The expression of TGFbeta isoforms and/or TGFbeta receptors was induced by the analogs in the vitamin D3 and TGFbeta sensitive cells. Vitamin D3 analogs did not induce TGFbeta or TGFbeta receptor expression in the resistant MCF7L cells. Therefore, EB1089 induces autocrine TGFbeta activity through increasing expression of TGFbeta isoforms and/or TGFbeta receptors. In addition, EB1089 induced nuclear VDR protein levels in the sensitive 184A1 cells but not in the resistant MCF7L cells. 184A1 cells were more sensitive to EB1089-induced VDR-dependent transactivation than MCF7L cells as measured by a luciferase reporter construct containing the VDRE, indicating a defect of VDR signaling in MCF7L cells. Smad3, a TGFbeta signaling mediator, coactivated VDR-dependent transactivation in 184A1 cells but not in MCF7L cells. These results indicate that Smad3 coactivates VDR to further enhance TGFbeta signaling and vitamin D3 signaling in the sensitive 184A1 cells. The results also indicate that Smad3 is not of itself sufficient to coactivate VDR in TGFbeta/vitamin D3 resistant MCF7L cells and other factors are required. We found that the PI 3-kinase pathway inhibitor LY29004 inhibited the synergy of TGFbeta and EB1089 on VDR-dependent transactivation activity. This indicates that the crosstalk between TGFbeta and vitamin D signaling is also PI 3-kinase pathway dependent.

Upregulation of lymphocyte apoptosis as a strategy for preventing and treating autoimmune disorders: a role for whole-food vegan diets, fish oil and dopamine agonists

Induced apoptosis of autoreactive T-lymphocyte precursors in the thymus is crucial for the prevention of autoimmune disorders. IGF-I and prolactin, which are lymphocyte growth factors, may have the potential to suppress apoptosis in thymocytes and thus encourage autoimmunity; conversely, dietary fish oil rich in omega-3 fats appears to upregulate apoptosis in lymphocytes. Since whole-food vegan diets may downregulate systemic IGF-I activity, it is proposed that such a diet, in conjunction with fish oil supplementation and treatment with dopamine agonists capable of suppressing prolactin secretion, may have utility for treating and preventing autoimmune disorders. This prediction is consistent with the extreme rarity of autoimmune disorders among sub-Saharan black Africans as long as they followed their traditional quasi-vegan lifestyles, and with recent ecologic studies correlating risks for IDDM and for multiple sclerosis mortality with animal product and/or saturated fat consumption. Moreover, there is evidence that vegan or quasi-vegan diets are useful in the management of rheumatoid arthritis, multiple sclerosis, and possibly SLE. The dopamine agonist bromocryptine exerts anti-inflammatory effects in rodent models of autoimmunity, and there is preliminary evidence that this drug may be clinically useful in several human autoimmune diseases; better tolerated D2-specific agonists such as cabergoline may prove to be more practical for use in therapy. The moderate clinical utility of supplemental fish oil in rheumatoid arthritis and certain other autoimmune disorders is documented. It is not unlikely that extra-thymic anti-inflammatory effects contribute importantly to the clinical utility of vegan diets, bromocryptine, and fish oil in autoimmunity. The favorable impact of low latitude or high altitude on autoimmune risk may be mediated by superior vitamin D status, which is associated with decreased secretion of parathyroid hormone; there are theoretical grounds for suspecting that parathyroid hormone may inhibit apoptosis in thymocytes. Androgens appear to up-regulate thymocyte apoptosis, may be largely responsible for the relative protection from autoimmunity enjoyed by men, and merit further evaluation for the management of autoimmunity in women. It will probably prove more practical to prevent autoimmune disorders than to reverse them once established; a whole-food vegan diet, coupled with fish oil and vitamin D supplementation, may represent a practical strategy for achieving this prevention, while concurrently lowering risk for many other life-threatening 'Western' diseases.

Inhibitory effects of 1alpha,25-dihydroxyvitamin D(3) on the G(1)-S phase-controlling machinery

The nuclear hormone 1alpha,25-dihydroxyvitamin D(3) induces cell cycle arrest, differentiation, or apoptosis depending on target cell type and state. Although the antiproliferative effect of 1alpha,25-dihydroxyvitamin D(3) has been known for years, the molecular basis of the cell cycle blockade by 1alpha,25-dihydroxyvitamin D(3) remains largely unknown. Here we have investigated the mechanisms underlying the G(1) arrest induced upon 1alpha,25-dihydroxyvitamin D(3) treatment of the human breast cancer cell line MCF-7. Twenty-four-hour exposure of exponentially growing MCF-7 cells to 1alpha,25-dihydroxyvitamin D(3) impeded proliferation by preventing S phase entry, an effect that correlated with appearance of the growth-suppressing, hypophosphorylated form of the retinoblastoma protein (pRb), and modulation of cyclin-dependent kinase (cdk) activities of cdk-4, -6, and -2. Time course immunochemical and biochemical analyses of the cellular and molecular effects of 1alpha,25-dihydroxyvitamin D(3) treatment for up to 6 d revealed a dynamic chain of events, preventing activation of cyclin D1/cdk4, and loss of cyclin D3, which collectively lead to repression of the E2F transcription factors and thus negatively affected cyclin A protein expression. While the observed 10-fold inhibition of cyclin D1/cdk 4-associated kinase activity appeared independent of cdk inhibitors, the activity of cdk 2 decreased about 20-fold, reflecting joint effects of the lower abundance of its cyclin partners and a significant increase of the cdk inhibitor p21(CIP1/WAF1), which blocked the remaining cyclin A(E)/cdk 2 complexes. Together with a rapid down-modulation of the c-Myc oncoprotein in response to 1alpha,25-dihydroxyvitamin D(3), these results demonstrate that 1alpha,25-dihydroxyvitamin D(3) inhibits cell proliferation by targeting several key regulators governing the G(1)/S transition.

Vitamin D(3)-induced apoptosis of murine squamous cell carcinoma cells. Selective induction of caspase-dependent MEK cleavage and up-regulation of MEKK-1

Vitamin D(3) inhibits cell growth and induces apoptosis in several human cancer lines in vitro and in vivo. However, little is known about the molecular events involved in vitamin D(3)-induced apoptosis. Here, we demonstrate that the growth-promoting/pro-survival signaling molecule mitogen-activated protein kinase kinase (MEK) is cleaved in a caspase-dependent manner in murine squamous cell carcinoma (SCC) cells induced to undergo apoptosis by treatment with vitamin D(3). Cleavage resulted in nearly complete loss of full-length MEK and ERK1/2 phosphorylation. ERK1/2 expression was affected only slightly. The phosphorylation and expression of Akt, a kinase regulating a second cell survival pathway, was also inhibited after treatment with vitamin D(3). However, the pro-apoptotic signaling molecule MEKK-1 was up-regulated in both apoptotic and non-apoptotic cells with greater induction and partial N-terminal proteolysis of MEKK-1 observed in apoptotic cells. In contrast to vitamin D(3), cisplatin and etoposide down-regulated Akt levels only modestly, did not promote significant loss of MEK expression, and did not up-regulate MEKK-1. We propose that vitamin D(3) induces apoptosis in SCC cells by a unique mechanism involving selective caspase-dependent MEK cleavage and up-regulation of MEKK-1. Additional evidence is provided that vitamin D(3)-induced apoptosis may be mediated via p38 MAPK.

Vitamin D receptor gene polymorphisms are associated with breast cancer risk in a UK Caucasian population

There is increasing evidence that vitamin D can protect against breast cancer. The actions of vitamin D are mediated via the vitamin D receptor (VDR). We have investigated whether polymorphisms in the VDR gene are associated with altered breast cancer risk in a UK Caucasian population. We recruited 241 women following a negative screening mammogram and 181 women with known breast cancer. The VDR polymorphism Bsm I, an intronic 3' gene variant, was significantly associated with increased breast cancer risk: odds ratio bb vs BB genotype = 2.32 (95% CI, 1.23-4.39). The Bsm I polymorphism was in linkage disequilibrium with a candidate translational control site, the variable length poly (A) sequence in the 3' untranslated region. Thus, the 'L' poly (A) variant was also associated with a similar breast cancer risk. A 5' VDR gene variant, Fok I, was not associated with breast cancer risk. Further investigations into the mechanisms of interactions of the VDR with other environmental and/or genetic influences to alter breast cancer risk may lead to a new understanding of the role of vitamin D in the control of cellular and developmental pathways.