Inhibition of angiogenesis as a mechanism for inhibition by 1alpha-hydroxyvitamin D3 and 1,25-dihydroxyvitamin D3 of colon carcinogenesis induced by azoxymethane in Wistar rats

Vitamin D for Prevention and Treatment of Colorectal Cancer: What is the Evidence?

Vitamin D insufficiency is highly prevalent in the U.S., particularly among colorectal cancer (CRC) patients. These low levels of vitamin D are concerning in light of increasing evidence that vitamin D may have health benefits beyond skeletal outcomes. Prospective observational studies suggest that higher vitamin D levels are associated with lower risk of incident CRC as well as improved survival in patients with established CRC, and randomized clinical trials are desperately needed to establish causality. Moreover, there remains a great need to improve prognosis for patients with CRC, and investigating vitamin D as a potential therapeutic modality is an attractive option in regards to safety and cost, particularly in this era of expensive and often toxic anti-neoplastic agents. In this review, the available published evidence on vitamin D's activity in CRC will be summarized, spanning preclinical, epidemiological, and clinical studies, and future research directions will be discussed.

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.

[Vitamin D and breast cancer: physiopathology, biological and clinical implications]

There is a recent increase in interest of vitamin D and breast cancer, facing the number of publications on the subject. This increase have several reasons, on the one hand, vitamin D deficiency is more and more prevalent and, on the other hand, there are new data that highlights the extra-bone effects of vitamin D, especially in breast cancer, the vitamin D is involved in the breast cancer risk factor, the prognosis, and the interaction with breast cancer treatments. This combination between vitamin D deficiency and breast cancer is extremely usual, and combined with all cancer clinical parameters: the incidence, the tumour biology, the clinical presentation, the prognosis, and the antineoplastic treatment tolerance. This vitamin D deficiency is increased after adjuvant cancer treatments. And yet, this problem increases bone metabolism disruptions in breast cancer patients, inducing osteoporotic risk at long time, even though this population is curable. This problem is therefore serious in the adjuvant breast cancer treatment. Unfortunately, in this population, the current recommendations are clearly insufficient, and the current randomized clinical trial results would contribute to define the best way to correct the vitamin D deficiency, quickly and secure.

The association between plasma 25-hydroxyvitamin D and subgroups in age-related macular degeneration: a cross-sectional study

OBJECTIVES

To evaluate potential differences in plasma 25-hydroxyvitamin in subtypes of age-related macular degeneration (AMD), and in patients in Clinical Age-Related Maculopathy Staging (CARMS) group 5 with or without subretinal fibrosis.

METHODS

This single-center cross-sectional study included 178 participants during a period of 20 months. Ninety-five patients belonged to CARMS 5; twelve belonged to CARMS 4; twenty-two belonged to CARMS 2 or 3; and 49 individuals did not have AMD (CARMS 1). Following a structured interview, a detailed bilateral retinal examination was performed and participants were allocated to their respective subgroups in accordance with the Clinical Age-Related Maculopathy Staging system. Plasma 25-hydroxyvitamin D2 and D3 were analyzed using liquid chromatography-tandem mass spectrometry. Genomic DNA was extracted from leukocytes and genotyped for single nucleotide polymorphisms (SNPs) in the vitamin D metabolism. Differences in plasma 25-hydroxyvitamin D were determined in the subgroups as well as between patients in CARMS 5 with or without subretinal fibrosis.

RESULTS

Plasma 25-hydroxyvitamin D was comparable in patients across CARMS groups 1 to 5 (p = 0.83). In CARMS 5, the presence of subretinal fibrosis was associated with significantly lower concentrations of 25-hydroxyvitamin D as compared to the absence of subretinal fibrosis (47.2 versus 75.6 nmol/L, p<0.001). Patients in CARMS 5 with subretinal fibrosis were more likely to have insufficient levels of 25-hydroxyvitamin D compared to patients without subretinal fibrosis (p = 0.006). No association was found between the SNPs rs10877012, rs2228570, rs4588, or rs7041 and AMD subgroups or plasma 25-hydroxyvitamin levels.

CONCLUSIONS

This study suggests that the presence of subretinal fibrosis in patients belonging to CARMS 5 may be associated with a poor vitamin D status. Our observations warrant further investigation into the role of vitamin D in the development of subretinal fibrosis.

Vitamin D in thyroid tumorigenesis and development

Besides its classical role in bone and calcium homeostasis, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), the active form of vitamin D, has many non-classical effects; antiproliferative, anti-apoptotic and prodifferentiating effects of 1,25(OH)2D3 have been described in several tumour types in preclinical models. This review focuses on the insights gained in the elucidation of the role of 1,25(OH)2D3 in the normal thyroid and in the pathogenesis, progression and treatment of thyroid cancer, the most common endocrine malignancy. An increasing amount of observations points towards a role for impaired 1,25(OH)2D3-VDR signalling in the occurrence and progression of thyroid cancer, and a potential for structural analogues in the multimodal treatment of dedifferentiated iodine-resistant thyroid cancer. A role for vitamin D in thyroid-related autoimmunity is less convincing and needs further study. Altered 1,25(OH)2D3-VDR signalling does not influence normal thyroid development nor thyrocyte function, but does affect C-cell function, at least in rodents. If these findings also apply to humans deserves further study.

Relationships of uPA and VEGF expression in esophageal cancer and microvascular density with tumorous invasion and metastasis

OBJECTIVE

To investigate uPA and VEGF expression in esophageal cancer and relations with tumorous invasion and metastasis.

METHODS

Immunohistochemistry was used to detect uPA and VEGF expression in the normal epithelial tissue of esophageal mucosa and cancer tissue and detect CD34 labeled micrangium and analyze the relationships with clinical pathological features and tumor angiogenesis.

RESULTS

Positive rates for uPA and VEGF protein expression were significantly greater in esophageal cancer than normal epithelial tissue (P < 0.05), the two being linked (P <0.05). In addition, uPA and VEGF protein expression of the high microvessel density (MVD) group was significantly lower than in the low MVD group (P < 0.05), with relation to clinical pathological staging, differentiation and lymph node metastasis (P < 0.05).

CONCLUSION

In esophageal cancer tissue, uPA and VEGF proteins are overexpressed and promote tumor angiogenesis, indicative of a poor prognosis.

Role of androgen and vitamin D receptors in endothelial cells from benign and malignant human prostate

Forty years ago, Judah Folkman (Folkman. N Engl J Med 285: 1182-1186, 1971) proposed that tumor growth might be controlled by limiting formation of new blood vessels (angiogenesis) needed to supply a growing tumor with oxygen and nutrients. To this end, numerous "antiangiogenic" agents have been developed and tested for therapeutic efficacy in cancer patients, including prostate cancer (CaP) patients, with limited success. Despite the lack of clinical efficacy of lead anti-angiogenic therapeutics in CaP patients, recent published evidence continues to support the idea that prostate tumor vasculature provides a reasonable target for development of new therapeutics. Particularly relevant to antiangiogenic therapies targeted to the prostate is the observation that specific hormones can affect the survival and vascular function of prostate endothelial cells within normal and malignant prostate tissues. Here, we review the evidence demonstrating that both androgen(s) and vitamin D significantly impact the growth and survival of endothelial cells residing within prostate cancer and that systemic changes in circulating androgen or vitamin D drastically affect blood flow and vascularity of prostate tissue. Furthermore, recent evidence will be discussed about the expression of the receptors for both androgen and vitamin D in prostate endothelial cells that argues for direct effects of these hormone-activated receptors on the biology of endothelial cells. Based on this literature, we propose that prostate tumor vasculature represents an unexplored target for modulation of tumor growth. A better understanding of androgen and vitamin D effects on prostate endothelial cells will support development of more effective angiogenesis-targeting therapeutics for CaP patients.

Potent 19-norvitamin D analogs for prostate and liver cancer therapy

The active form of vitamin D(3), 1α,25(OH)(2)D(3) or calcitriol, is known to inhibit the proliferation and invasiveness of many types of cancer cells, including prostate and liver cancer cells. These findings support the use of 1α,25(OH)(2)D(3) for prostate and liver cancer therapy. However, 1α,25(OH)(2)D(3) can cause hypercalcemia, thus, analogs of 1α,25(OH)(2)D(3) that are less calcemic but exhibit potent antiproliferative activity would be attractive as therapeutic agents. We have developed 2α-functional group substituted 19-norvitamin D(3) analogs with and without 14-epimerization. Among them, 2α- and 2β-(3-hydroxypropyl)-1α,25-dihydroxy-19-norvitamin D(3) (MART-10 and -11, respectively) and 14-epi-2α- and 14-epi-2β-(3-hydroxypropyl)-1α,25-dihydroxy-19-norvitamin D(3) (14-epi-MART-10 and 14-epi-MART-11, respectively) were found to be the most promising. In this review, we discuss the synthesis of this unique class of vitamin D analogs, the molecular mechanism of anticancer actions of vitamin D, and the biological evaluation of these analogs for potential application to the prevention and treatment of prostate and liver cancer.

Systems biology-based analysis implicates a novel role for vitamin D metabolism in the pathogenesis of age-related macular degeneration

Vitamin D has been shown to have anti-angiogenic properties and to play a protective role in several types of cancer, including breast, prostate and cutaneous melanoma. Similarly, vitamin D levels have been shown to be protective for risk of a number of conditions, including cardiovascular disease and chronic kidney disease, as well as numerous autoimmune disorders such as multiple sclerosis, inflammatory bowel diseases and type 1 diabetes mellitus. A study performed by Parekh et al. was the first to suggest a role for vitamin D in age-related macular degeneration (AMD) and showed a correlation between reduced serum vitamin D levels and risk for early AMD. Based on this study and the protective role of vitamin D in diseases with similar pathophysiology to AMD, we examined the role of vitamin D in a family-based cohort of 481 sibling pairs. Using extremely phenotypically discordant sibling pairs, initially we evaluated the association of neovascular AMD and vitamin D/sunlight-related epidemiological factors. After controlling for established AMD risk factors, including polymorphisms of the genes encoding complement factor H (CFH) and age-related maculopathy susceptibility 2/HtrA serine peptidase (ARMS2/HTRA1), and smoking history, we found that ultraviolet irradiance was protective for the development of neovascular AMD (p = 0.001). Although evaluation of serum vitamin D levels (25-hydroxyvitamin D [25(OH)D]) was higher in unaffected individuals than in their affected siblings, this finding did not reach statistical significance.

Based on the relationship between ultraviolet irradiance and vitamin D production, we employed a candidate gene approach for evaluating common variation in key vitamin D pathway genes (the genes encoding the vitamin D receptor [VDR]; cytochrome P450, family 27, subfamily B, polypeptide 1 [CYP27B1]; cytochrome P450, family 24, subfamily A, polypeptide 1 [CYP24A1]; and CYP27A1) in this same family-based cohort. Initial findings were then validated and replicated in the extended family cohort, an unrelated case-control cohort from central Greece and a prospective nested case-control population from the Nurse's Health Study and Health Professionals Follow-Up Studies, which included patients with all subtypes of AMD for a total of 2,528 individuals. Single point variants in CYP24A1 (the gene encoding the catabolising enzyme of the vitamin D pathway) were demonstrated to influence AMD risk after controlling for smoking history, sex and age in all populations, both separately and, more importantly, in a meta-analysis. This is the first report demonstrating a genetic association between vitamin D metabolism and AMD risk. These findings were also supplemented with expression data from human donor eyes and human retinal cell lines. These data not only extend previous biological studies in the AMD field, but further emphasise common antecedents between several disorders with an inflammatory/immunogenic component such as cardiovascular disease, cancer and AMD.

Prediagnostic 25-hydroxyvitamin D, VDR and CASR polymorphisms, and survival in patients with colorectal cancer in western European ppulations

BACKGROUND

Individuals with higher blood 25-hydroxyvitamin D [25(OH)D] levels have a lower risk of developing colorectal cancer (CRC), but the influence of 25(OH)D on mortality after CRC diagnosis is unknown.

METHODS

The association between prediagnostic 25(OH)D levels and CRC-specific (N = 444) and overall mortality (N = 541) was prospectively examined among 1,202 participants diagnosed with CRC between 1992 and 2003 in the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort. Multivariable Cox proportional hazards models were used to calculate HRs and corresponding 95% CIs according to 25(OH)D quintiles and genetic variation within the VDR and CASR genes. Potential dietary, lifestyle, and metabolic effect modifiers were also investigated.

RESULTS

There were 541 deaths, 444 (82%) due to CRC. Mean follow-up was 73 months. In multivariable analysis, higher 25(OH)D levels were associated with a statistically significant reduction in CRC-specific (P(trend) = 0.04) and overall mortality (P(trend) = 0.01). Participants with 25(OH)D levels in the highest quintile had an adjusted HR of 0.69 (95% CI: 0.50-0.93) for CRC-specific mortality and 0.67 (95% CI: 0.50-0.88) for overall mortality, compared with the lowest quintile. Except for a possible interaction by prediagnostic dietary calcium intake (P(interaction) = 0.01), no other potential modifying factors related to CRC survival were noted. The VDR (FokI and BsmI) and CASR (rs1801725) genotypes were not associated with survival.

CONCLUSIONS

High prediagnostic 25(OH)D levels are associated with improved survival of patients with CRC.

IMPACT

Our findings may stimulate further research directed at investigating the effects of blood vitamin D levels before, at, and after CRC diagnosis on outcomes in CRC patients.

Hepatocellular carcinoma and vitamin D: a review

The non-classical actions of vitamin D, namely antiproliferation, pro-differentiation, pro-apoptosis, anti-inflammation, and immune regulation, have received great attention during the past decade. Increasing evidence from epidemiological studies showing the inverse association between vitamin D status and incidence of many forms of cancer as well as biochemical studies has suggested that vitamin D deficiency may play a role in the cause and progression of these types of cancer. Recently, vitamin D and its analogs have been deemed as potential regimen to treat a variety of cancers alone or in combination with other drugs. Although, the epidemiologic evidence regarding the association of vitamin D and hepatocellular carcinoma (HCC) is still inconclusive, biochemical evidence clearly indicates that HCC cells are responsive to the inhibitory effect of vitamin D and its analogs. In this review, we discuss the current status of HCC and its treatment, the source, metabolism, functions, and the mechanism of actions of vitamin D, and the biochemical studies of vitamin D analogs and their implications in the prevention and treatment of HCC.

Circulating levels of vitamin D, vitamin D receptor polymorphisms, and colorectal adenoma: a meta-analysis

Growing evidence suggests an elevated risk for colorectal neoplasia among individuals with low levels of vitamin D, the biological actions of which are mediated by the vitamin D receptor (VDR). To investigate the association among vitamin D status, VDR polymorphisms (FokI, and BsmI), and colorectal adenoma, we conducted a meta-analysis of nine studies of circulating levels of 25-hydroxyvitamin D (25(OH)D) and five studies of FokI or BsmI polymorphisms in relation to colorectal adenomas. Study-specific relative risks (RRs) and 95% confidence intervals (CIs) were pooled using a random-effects model. A total of 3398 colorectal adenomas for 25(OH)D and 1754 colorectal adenomas for VDR were included in the meta-analysis. We identified a significant inverse association between colorectal adenoma (combined RR, 0.93; 95% CI, 0.87-0.98 per 10 ng/mL increase in 25(OH)D levels). When we examined FokI and BsmI polymorphisms in the meta-analysis, we found no association for either FokI (combined RR, 1.00; 95% CI, 0.95-1.06) or BsmI (combined RR, 0.99; 95% CI, 0.93-1.05) in the additive model. These data suggest an inverse association between circulating 25(OH)D levels and colorectal adenoma risk.

Emerging role of vitamin D in colorectal cancer

Colorectal cancer is a common cancer and the fourth leading cause of death in Korea. The incidence and mortality of colorectal cancer varies according to risk factors, such as age, family history, genetic history, food habits, and physical activities. Some studies have focused on the association between vitamin D and colorectal cancer. Today, there is growing evidence that high vitamin D intake and a plasma level of 25(OH)D₃ reduce the incidence of colorectal cancer by modifying cancer angiogenesis, cell apoptosis, differentiation, and proliferation. Taken together, these results suggest that vitamin D supplementation alone, or in combination with anti-cancer agents, might reduce the incidence of colorectal cancer. In this review, we discuss the function and mechanism of vitamin D including the effect of vitamin D on colorectal cancer.

Reconsidering the connection between vitamin D levels and age-related macular degeneration

PURPOSE

Recent evidence has suggested a correlation between reduced vitamin D levels and delayed angiogenesis and reduced inflammatory response, which are known to have a major role in the development and progression of age-related macular degeneration (AMD).

DESIGN

Cross-sectional study.

PARTICIPANTS

Members of the Maccabi Healthcare Services (MHS, one of the four largest Israeli Health Maintenance Organization) aged ≥60 years, whose vitamin D levels were taken as part of routine examinations between 2000 and 2008.

METHODS

All data for this study were obtained from MHS databases that include medical information on 1.8 million subscribers.

MAIN OUTCOME MEASURES

Serum 25-OH vitamin D levels.

RESULTS

The total study population comprised of 1045 members diagnosed as having AMD, and 8124 as non-AMD, for whom there was information on vitamin D levels. The mean±SD level of 25-OH vitamin D was 24.1±9.41  ng/ml (range 0.8-120) for the AMD patients and 24.13±9.50  ng/ml (range 0.0-120) for the controls (P=ns). One-third (33.6%) of the AMD patients and 32.86% of the controls had a 25-OH vitamin D level <16  ng/ml, and the proportions of tests in which the 25-OH vitamin D level was >74  ng/ml were 0.19 and 0.14%, respectively (P=ns).

CONCLUSIONS

No association was detected between vitamin D levels and the presence of AMD in this cross-sectional study. These results raise some doubt about an association between reduced vitamin D levels and the prevalence of AMD.

Calcium, vitamin D and colorectal cancer chemoprevention

Identifying modifiable risk factors, particularly dietary factors, which have been hypothesized to play an important role in colorectal carcinogenesis, remains crucial in developing primary prevention strategies. Calcium and vitamin D have been shown consistently in experimental studies to have anti-cancerous properties including but not limited to stimulating differentiation, reducing proliferation, and inducing apoptosis. The majority of epidemiologic studies consistently support an approximately 20-30% reduction in risk of colorectal cancer and adenomas comparing high to low intake categories of both calcium and vitamin D, although independent effects may not be adequately separated. Less consistency exists on the dose-response relation for both nutrients. Intake of calcium of not more than 1000 mg/d and intake of vitamin D of 1000-2000 IU/d, achieving a level of at least 30 ng/mL, appear important for colorectal cancer prevention. More study is warranted to determine the optimal intake levels and duration to reduce the colorectal cancer risk.

Vitamin D status in patients with stage IV colorectal cancer: findings from Intergroup trial N9741

PURPOSE

Previous studies have suggested that higher plasma 25-hydroxyvitamin D(3) [25(OH)D] levels are associated with decreased colorectal cancer risk and improved survival, but the prevalence of vitamin D deficiency in advanced colorectal cancer and its influence on outcomes are unknown.

PATIENTS AND METHODS

We prospectively measured plasma 25(OH)D levels in 515 patients with stage IV colorectal cancer participating in a randomized trial of chemotherapy. Vitamin D deficiency was defined as 25(OH)D lower than 20 ng/mL, insufficiency as 20 to 29 ng/mL, and sufficiency as ≥ 30 ng/mL. We examined the association between baseline 25(OH)D level and selected patient characteristics. Cox proportional hazards models were used to calculate hazard ratios (HR) for death, disease progression, and tumor response, adjusted for prognostic factors.

RESULTS

Among 515 eligible patients, 50% of the study population was vitamin D deficient, and 82% were vitamin D insufficient. Plasma 25(OH)D levels were lower in black patients compared to white patients and patients of other race (median, 10.7 v 21.1 v 19.3 ng/mL, respectively; P < .001), and females compared to males (median, 18.3 v 21.7 ng/mL, respectively; P = .0005). Baseline plasma 25(OH)D levels were not associated with patient outcome, although given the distribution of plasma levels in this cohort, statistical power for survival analyses were limited.

CONCLUSION

Vitamin D deficiency is highly prevalent among patients with stage IV colorectal cancer receiving first-line chemotherapy, particularly in black and female patients.

Circulating levels of vitamin D and colon and rectal cancer: the Physicians' Health Study and a meta-analysis of prospective studies

It remains unknown whether increased risk with low levels of vitamin D is present for colon and/or rectal cancer. To investigate the association between circulating vitamin D levels and colon and rectal cancer, we examined the associations between plasma levels of 25-hydroxyvitamin D [25(OH)D] and 1,25-dihydroxyvitamin D [1,25(OH)2D] and colon and rectal cancer in the Physicians' Health Study and then conducted a meta-analysis of eight prospective studies of circulating levels of 25(OH)D and colon and rectal cancers, including the Physicians' Health Study. Study-specific ORs and 95% CIs were pooled by using a random-effects model. A total of 1,822 colon and 868 rectal cancers were included in the meta-analysis. We observed a significant inverse association for colorectal cancer (OR = 0.66; 95% CI, 0.54-0.81), comparing top versus bottom quantiles of circulating 25(OH)D levels. The inverse association was stronger for rectal cancer (OR = 0.50 for top versus bottom quantiles; 95% CI, 0.28-0.88) than colon cancer (OR = 0.77; 95% CI, 0.56-1.07; P value for difference between colon and rectal cancer = 0.20). These data suggest an inverse association between circulating 25(OH)D levels and colorectal cancer, with a stronger association for rectal cancer.

Vitamin D homeostasis is compromised due to increased urinary excretion of the 25-hydroxycholecalciferol-vitamin D-binding protein complex in the Zucker diabetic fatty rat

Altered serum concentrations of the major circulating form of vitamin D [25-hydroxycholecalciferol (25D(3))] and its active hormone derivative [1,25-dihydroxycholecalciferol (1,25D(3))] have been linked to non-insulin-dependent diabetes mellitus (NIDDM). However, a mechanistic basis for this occurrence has not been fully elucidated. Normally, renal reabsorption of vitamin D-binding protein-bound 25D(3) absolutely requires receptor-mediated endocytosis via a receptor complex containing megalin, cubilin, and disabled-2 (Dab2), whereas an absence of megalin or its endocytic partners can lead to a marked urinary loss of 25D and severe vitamin D deficiency. Therefore, we hypothesized that reduced serum vitamin D status in NIDDM may be due to reduced expression of megalin and/or its endocytic partners and increased urinary excretion of protein-complexed 25D(3). In the present study, we utilized Zucker diabetic fatty Rats (ZDF) to demonstrate that renal reuptake of the 25D(3)-DBP complex was compromised in ZDF animals, which was reflected by a reduction in expression of megalin and Dab2. Moreover, serum levels of both 25D(3) and 1,25D(3) were reduced, and urinary 25D(3), 1,25D(3), and DBP excretion were elevated in the ZDF animals compared with their lean controls regardless of vitamin D levels in the diet. Taken together, these are the first reports to our knowledge that associate compromised renal reabsorption of the 25D(3)-DBP complex with expression of megalin and its endocytic partners in NIDDM, which in turn can lead to compromised vitamin D status.

CYP24A1 inhibition enhances the antitumor activity of calcitriol

High systemic exposures to calcitriol are necessary for optimal antitumor effects. Human prostate cancer PC3 cells are insensitive to calcitriol treatment. Therefore, we investigated whether the inhibition of 24-hydroxylase (CYP24A1), the major calcitriol inactivating enzyme, by ketoconazole (KTZ) or RC2204 modulates calcitriol serum pharmacokinetics and biologic effects. Dexamethasone (Dex) was added to minimize calcitriol-induced hypercalcemia and as a steroid replacement for the KTZ inhibition of steroid biosynthesis cytochrome P450 enzymes. KTZ effectively inhibited time-dependent calcitriol-inducible CYP24A1 protein expression and enzyme activity in PC3 cells and C3H/HeJ mouse kidney tissues. Systemic calcitriol exposure area under the curve was higher in mice treated with a combination of calcitriol and KTZ than with calcitriol alone. KTZ and Dex synergistically potentiated calcitriol-mediated antiproliferative effects in PC3 cells in vitro; this effect was associated with enhanced apoptosis. After treatment with calcitriol and KTZ/Dex, although caspase-9 and caspase-3 were not activated and cytochrome c was not released by mitochondria, caspase-8 was activated and the truncated Bid protein level was increased. Translocation of apoptosis-inducing factor to the nucleus was observed, indicating a role of the apoptosis-inducing factor-mediated and caspase-independent apoptotic pathways. Calcitriol and KTZ/Dex combination suppressed the clonogenic survival and enhanced the growth inhibition observed with calcitriol alone in PC3 human prostate cancer xenograft mouse model. Our results show that the administration of calcitriol in combination with CYP24A1 inhibitor enhances antiproliferative effects, increases systemic calcitriol exposure, and promotes the activation of caspase-independent apoptosis pathway.

Multivitamin use is not associated with cancer recurrence or survival in patients with stage III colon cancer: findings from CALGB 89803

PURPOSE

Multivitamin use is widespread in the United States, especially among patients with cancer. However, the influence of multivitamin supplementation on cancer recurrence and death after a curative resection of colon cancer is unknown.

PATIENTS AND METHODS

We conducted a prospective, observational study of 1,038 patients with stage III colon cancer enrolled in a randomized adjuvant chemotherapy trial. Patients reported on multivitamin use during and 6 months after adjuvant chemotherapy. Patients were observed until March 2009 for disease recurrence and death. To minimize bias by occult recurrence, we excluded patients who recurred or died within 90 days of their multivitamin assessment.

RESULTS

Among 1,038 patients, 518 (49.9%) reported multivitamin use during adjuvant chemotherapy. Compared with nonusers, the multivariate hazard ratio (HR) for disease-free survival was 0.94 (95% CI, 0.77 to 1.15) for patients who used multivitamins. Similarly, multivitamin use during adjuvant chemotherapy was not significantly associated with recurrence-free survival (multivariate HR, 0.93; 95% CI, 0.75 to 1.15) or overall survival (multivariate HR 0.92; 95% CI, 0.74 to 1.16). Multivitamin use reported 6 months after completion of adjuvant chemotherapy was also not associated with improved patient outcome, and consistent use both during and following adjuvant therapy conferred no benefit. Neither an increasing number of tablets nor increasing duration of use before cancer diagnosis was associated with cancer recurrence or mortality. Multivitamin use also did not improve the rates of grade 3 and higher GI toxicity.

CONCLUSION

Multivitamin use during and after adjuvant chemotherapy was not significantly associated with improved outcomes in patients with stage III colon cancer.

Epigenetic silencing of CYP24 in the tumor microenvironment

Calcitriol (1,25 dihydroxycholecalciferol) has significant anti-tumor activity in vitro and in vivo in a number of tumor model systems. We developed a system for isolation of fresh endothelial cells from tumors and Matrigel environments which demonstrate that CYP24, the catabolic enzyme involved in vitamin D signaling, is epigenetically silenced selectively in tumor-derived endothelial cells (TDEC). TDEC maintain phenotypic characteristics which are distinct from endothelial cells isolated from normal tissues and from Matrigel plugs (MDEC). In TDEC, calcitriol induces G(0)/G(1) arrest, modulates p27 and p21, and induces apoptotic cell death and decreases P-Erk and P-Akt. In contrast, endothelial cells isolated from normal tissues and MDEC are unresponsive to calcitriol-mediated anti-proliferative effects despite intact signaling through the vitamin D receptor (VDR). In TDEC, which are sensitive to calcitriol, the CYP24 promoter is hypermethylated in two CpG island regions located at the 5'end; this hypermethylation may contribute to gene silencing of CYP24. The extent of methylation in these two regions is significantly less in MDEC. Lastly, treatment of TDEC with a DNA methyltransferase inhibitor restores calcitriol-mediated induction of CYP24 and resistance to calcitriol. These data suggest that epigenetic silencing of CYP24 modulates cellular responses to calcitriol.

Genetic variation in the vitamin D receptor (VDR) and the vitamin D-binding protein (GC) and risk for colorectal cancer: results from the Colon Cancer Family Registry

Epidemiologic evidence supports a role for vitamin D in colorectal cancer (CRC) risk. Variants in vitamin D-related genes might modify the association between vitamin D levels and CRC risk. In this analysis, we did a comprehensive evaluation of common variants in the vitamin D receptor (VDR) and the vitamin D-binding protein (GC; group-specific component) genes using a population-based case-unaffected sibling control design that included 1,750 sibships recruited into the Colon Cancer Family Registry. We also evaluated whether any associations differed by calcium supplement use, family history of CRC, or tumor characteristics. Heterogeneity by calcium and vitamin D intake was evaluated for a subset of 585 cases and 837 sibling controls who completed a detailed food frequency questionnaire. Age- and sex-adjusted associations were estimated using conditional logistic regression. Overall, we did not find evidence for an association between any single-nucleotide polymorphism (SNP) in VDR or GC and risk for CRC (range of unadjusted P values 0.01-0.98 for VDR and 0.07-0.95 for GC). None of these associations was significant after adjustment for multiple comparisons. We also found no evidence that calcium or vitamin D intake (food and supplement) from the food frequency questionnaire modified the association estimates between VDR and GC SNPs and CRC. We did observe associations between SNPs in GC and microsatellite unstable CRC, although these results should be confirmed in additional studies. Overall, our results do not provide evidence for a role of common genetic variants in VDR or GC in susceptibility to CRC.

1 Alpha,25-dihydroxyvitamin D3 and its TX527 analog inhibit the growth of endothelial cells transformed by Kaposi sarcoma-associated herpes virus G protein-coupled receptor in vitro and in vivo

The Kaposi sarcoma-associated herpes virus-G protein-coupled receptor is a key molecule in the pathogenesis of Kaposi sarcoma, playing a central role in promoting vascular endothelial growth factor-driven angiogenesis and spindle cell proliferation. We studied the effects of 1 alpha,25-dihydroxyvitamin D(3) [1 alpha,25(OH)(2)D(3)] and the analog TX527 on the proliferation of endothelial cells (SVECs) and SVECs transformed by the viral G protein-coupled receptor (SVEC-vGPCR). 1 alpha,25(OH)(2)D(3) and TX527 decreased SVEC-vGPCR and SVEC numbers, the response being time dependent and similar in both cell lines. Vitamin D receptor (VDR) levels increased on treatment with 10 nm 1 alpha,25(OH)(2)D(3) or 1 nm TX527 in a time-dependent manner (1.5-24 h) in SVECs and SVEC-vGPCR. Basal VDR levels were increased in SVEC-vGPCR. The antiproliferative effects were accompanied by reduction in cyclin D1 and accumulation of p27 in SVECs but not SVEC-vGPCR. Induction of VDR was blocked by transfection of short hairpin RNA against VDR in SVEC-vGPCR and the antiproliferative effects of 1 alpha,25(OH)(2)D(3) and TX527 were decreased, involving the VDR genomic pathway in the hormone and analog mechanism of action. In vivo experiments showed that 1 alpha,25(OH)(2)D(3) and TX527 decreased SVEC-vGPCR tumor progression when the tumor cells were implanted in nude mice. In conclusion, we have demonstrated that 1 alpha,25(OH)(2)D(3) and its TX527 analog have antiproliferative effects on the growth of endothelial cells transformed by the vGPCR in vitro and in vivo, the vitamin D receptor being part of the inhibitory mechanism of action.

Vitamin D inhibits growth of human airway smooth muscle cells through growth factor-induced phosphorylation of retinoblastoma protein and checkpoint kinase 1

BACKGROUND AND PURPOSE

Airway remodelling in asthma is manifested, in part, as increased airway smooth muscle (ASM) mass, reflecting myocyte proliferation. We hypothesized that calcitriol, a secosteroidal vitamin D receptor (VDR) modulator, would inhibit growth factor-induced myocyte proliferation.

EXPERIMENTAL APPROACH

Human ASM cell cultures were derived from bronchial samples taken during surgery. ASM cells were treated with platelet-derived growth factor (PDGF) (10 ng.mL(-1)) for 24 h in the presence of calcitriol, dexamethasone or a checkpoint kinase 1 (Chk1) inhibitor (SB218078). The effects of calcitriol on PDGF-mediated cell proliferation were assessed by thymidine incorporation assay, propidium iodide-based cell cycle analysis, caspase-3 assay and immunoblotting for specific cell cycle modulators.

KEY RESULTS

Calcitriol, but not dexamethasone, inhibited PDGF-induced ASM DNA synthesis concentration dependently (IC(50)= 520 +/- 52 nM). These effects were associated with VDR-mediated expression of cytochrome CYP24A1 with no effects on ASM apoptosis. Calcitriol substantially inhibited (P < 0.01) PDGF-stimulated cell growth in ASM derived from both normal (59 +/- 8%) and asthmatic subjects (57 +/- 9%). Calcitriol inhibited PDGF-induced phosphorylation of retinoblastoma protein (Rb) and Chk1, with no effects on PDGF-mediated activation of extracellular signal-regulated kinases 1/2, PI3-kinase and S6 kinase, or expression of p21(Waf/Cip-1), p27(Kip1), cyclin D and E2F-1. Consistent with these observations, SB218078 also inhibited (IC(50)= 450 +/- 100 pM) PDGF-induced cell cycle progression.

CONCLUSIONS AND IMPLICATIONS

Calcitriol decreased PDGF-induced ASM cell growth by inhibiting Rb and Chk1 phosphorylation.

Vitamin D receptor expression is associated with PIK3CA and KRAS mutations in colorectal cancer

Vitamin D is associated with decreased risks of various cancers, including colon cancer. The vitamin D receptor (VDR) is a transcription factor, which plays an important role in cellular differentiation and inhibition of proliferation. A link between VDR and the RAS-mitogen-activated protein kinase (MAPK) or phosphatidylinositol 3-kinase (PI3K)-AKT pathway has been suggested. However, the prognostic role of VDR expression or its relationship with PIK3CA or KRAS mutation remains uncertain. Among 619 colorectal cancers in two prospective cohort studies, 233 (38%) tumors showed VDR overexpression by immunohistochemistry. We analyzed for PIK3CA and KRAS mutations and LINE-1 methylation by Pyrosequencing, microsatellite instability (MSI), and DNA methylation (epigenetic changes) in eight CpG island methylator phenotype (CIMP)-specific promoters [CACNA1G, CDKN2A (p16), CRABP1, IGF2, MLH1, NEUROG1, RUNX3, and SOCS1] by MethyLight (real-time PCR). VDR overexpression was significantly associated with KRAS mutation (odds ratio, 1.55; 95% confidence interval, 1.11-2.16) and PIK3CA mutation (odds ratio, 2.17; 95% confidence interval, 1.36-3.47), both of which persisted in multivariate logistic regression analysis. VDR was not independently associated with body mass index, family history of colorectal cancer, tumor location (colon versus rectum), stage, tumor grade, signet ring cells, CIMP, MSI, LINE-1 hypomethylation, BRAF, p53, p21, beta-catenin, or cyclooxygenase-2. VDR expression was not significantly related with patient survival, prognosis, or clinical outcome. In conclusion, VDR overexpression in colorectal cancer is independently associated with PIK3CA and KRAS mutations. Our data support potential interactions between the VDR, RAS-MAPK and PI3K-AKT pathways, and possible influence by KRAS or PIK3CA mutation on therapy or chemoprevention targeting VDR.

Prospective study of predictors of vitamin D status and survival in patients with colorectal cancer

BACKGROUND

In an earlier study, a 25-hydroxyvitamin D(3) (25(OH)D) score calculated from known predictors of vitamin D status significantly predicted plasma levels of 25(OH)D and the risk of colorectal cancer, but the influence of the 25(OH)D score on survival after diagnosis is unknown.

MATERIALS AND METHODS

We prospectively examined the influence of post-diagnosis predicted 25(OH)D levels on mortality among 1017 participants in the Nurses' Health Study and Health Professionals Follow-Up Study who were diagnosed with colorectal cancer from 1986 to 2004. Colorectal cancer-specific and overall mortality according to quintiles of predicted 25(OH)D levels were assessed. Cox proportional hazards models were used to calculate hazard ratios (HRs) adjusted for other risk factors of survival.

RESULTS

Higher predicted 25(OH)D levels were associated with a significant reduction in colorectal cancer-specific (P trend=0.02) and overall mortality (P trend=0.002). Compared with levels in the lowest quintile, participants with predicted 25(OH)D levels in the highest quintile had an adjusted HR of 0.50 (95% CI, 0.26-0.95) for cancer-specific mortality and 0.62 (95% CI, 0.42-0.93) for overall mortality.

CONCLUSION

Higher predicted 25(OH)D levels after a diagnosis of colorectal cancer may be associated with improved survival. Further study of the vitamin D pathway in colorectal cancer is warranted.

Vitamin D for the prevention and treatment of pancreatic cancer

Pancreatic cancer is ranked fifth among cancer-related deaths worldwide with a 5-year survival rate of less than 5%. Currently, surgery is the only effective therapy. However, most patients are diagnosed in the late stage and are not suitable for receiving curative surgery. Moreover, pancreatic cancer doesn’t respond well to traditional chemotherapy and radiotherapy, leaving little effective treatment for advanced pancreatic cancer cases. 1α,25-dihydroxyvitamin D₃ [1α,25(OH)₂D₃], the biologically active form of vitamin D₃, was originally identified during studies of calcium and bone metabolism, though it is now recognized that it exerts biological effects in almost every tissue in the body. Abundant evidence has shown that 1α,25(OH)₂D₃ has antiproliferative, apoptotic, pro-differentiation and antiangiogensis effects in many types of cancer cells in vivo and in vitro, including breast, prostate, and colon. Similarly, the antitumor growth effect of 1α,25(OH)₂D₃ on pancreatic cells has been demonstrated. The clinical use of 1α,25(OH)₂D₃ is impeded by the lethal side effects of hypercalcemia and hypercalciuria. Therefore, 1α,25(OH)₂D₃ analogs, which are either equipotent or more potent than 1α,25(OH)₂D₃ in inhibiting tumor cell growth but with fewer hypercalcemic and hypercalciuric side effects, have been developed for the treatment of different cancers. Recently, a pre-clinical study demonstrated that a less calcemic analog of 1α,25(OH)₂D₃, 19-nor-1α,25(OH)₂D₂ (Paricalcitol), is effective in inhibiting tumor growth in vitro and in vivo, via upregulation of p21 and p27 tumor suppressor genes. Studies on the anti-tumor effects of a more potent analog of Paricalcitol are underway. 1α,25(OH)₂D₃ and its analogs are potentially attractive novel therapies for pancreatic cancer.

Phase II study of calcitriol-enhanced docetaxel in patients with previously untreated metastatic or locally advanced pancreatic cancer

PURPOSE

To determine the safety and efficacy of weekly high-dose oral calcitriol and docetaxel, given to patients with non-resectable, incurable pancreatic cancer.

PATIENTS AND METHODS

Twenty-five patients were enrolled onto this phase II study. Patients were treated with oral calcitriol 0.5 microg/kg on day 1, followed by docetaxel 36 mg/m(2) IV on day 2, administered weekly for three consecutive weeks, followed by 1 week without treatment. Patients followed a low-calcium diet and increased their hydration. The primary end-point of the trial was time-to-progression.

RESULTS

Three of 25 patients attained a partial response (12%, 95% CI 3 to 31) and seven (28%) achieved stable disease. Median time-to-progression was 15 weeks, and median overall survival was 24 weeks. Toxicities observed (hyperglycemia, fatigue) were mostly attributable to the docetaxel or its pre-treatment.

CONCLUSIONS

This regimen of high-dose calcitriol with docetaxel may have activity in incurable pancreatic cancer, with a modest increase in TTP when compared to historical findings using single-agent docetaxel. However, results do not appear superior to those seen with gemcitabine, with or without erlotinib.

Circulating 25-hydroxyvitamin d levels and survival in patients with colorectal cancer

PURPOSE

Higher plasma 25-hydroxyvitamin D(3) (25(OH)D) levels are associated with a decreased incidence of colorectal cancer, but the influence of plasma 25(OH)D on the outcome of patients with established colorectal cancer is unknown.

PATIENTS AND METHODS

We prospectively examined the association between prediagnosis 25(OH)D levels and mortality among 304 participants in the Nurses' Health Study (NHS) and the Health Professionals Follow-Up Study (HPFS) who were diagnosed with colorectal cancer from 1991 to 2002. Participants diagnosed within 2 years of blood collection were excluded. Patients were observed until death, June 2005 (NHS), or January 2005 (HPFS), whichever came first. The primary end point was overall mortality. Cox proportional hazards models were used to calculate hazard ratios (HR) adjusted for other risk factors for cancer survival.

RESULTS

Higher plasma 25(OH)D levels were associated with a significant reduction in overall mortality (P for trend = .02). Compared with the lowest quartile, participants in the highest quartile had an adjusted HR of 0.52 (95% CI, 0.29 to 0.94) for overall mortality. A trend toward improved colorectal cancer-specific mortality was also seen (HR = 0.61; 95% CI, 0.31 to 1.19). The results remained unchanged after excluding patients diagnosed within 5 years of blood collection (P for trend = .04); the multivariate HR for overall mortality comparing extreme quartiles was 0.45 (95% CI, 0.19 to 1.09).

CONCLUSION

Among patients with colorectal cancer, higher prediagnosis plasma 25(OH)D levels were associated with a significant improvement in overall survival. Further study of the vitamin D pathway and its influence on colorectal carcinogenesis and cancer progression is warranted.

Vitamin D analogs: therapeutic applications and mechanisms for selectivity

The vitamin D endocrine system plays a central role in mineral ion homeostasis through the actions of the vitamin D hormone, 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)], on the intestine, bone, parathyroid gland, and kidney. The main function of 1,25(OH)(2)D(3) is to promote the dietary absorption of calcium and phosphate, but effects on bone, kidney and the parathyroids fine-tune the mineral levels. In addition to these classical actions, 1,25(OH)(2)D(3) exerts pleiotropic effects in a wide variety of target tissues and cell types, often in an autocrine/paracrine fashion. These biological activities of 1,25(OH)(2)D(3) have suggested a multitude of potential therapeutic applications of the vitamin D hormone for the treatment of hyperproliferative disorders (e.g. cancer and psoriasis), immune dysfunction (autoimmune diseases), and endocrine disorders (e.g. hyperparathyroidism). Unfortunately, the effective therapeutic doses required to treat these disorders can produce substantial hypercalcemia. This limitation of 1,25(OH)(2)D(3) therapy has spurred the development of vitamin D analogs that retain the therapeutically important properties of 1,25(OH)(2)D(3), but with reduced calcemic activity. Analogs with improved therapeutic indices are now available for treatment of psoriasis and secondary hyperparathyroidism in chronic kidney disease, and research on newer analogs for these indications continues. Other analogs are under development and in clinical trials for treatment of various types of cancer, autoimmune disorders, and many other diseases. Although many new analogs show tremendous promise in cell-based models, this article will limit it focus on the development of analogs currently in use and those that have demonstrated efficacy in animal models or in clinical trials.

Chemopreventive effect of a vitamin D(3) analog, alfacalcidol, on colorectal carcinogenesis in mice with ulcerative colitis

An increased incidence of colorectal carcinoma is known to occur in patients with ulcerative colitis (UC), which displays a cycle of recurrence-remission in the colorectal mucosa. Repeated oral doses of 3% dextran sulfate sodium subsequent to a single intraperitoneal injection of azoxymethane induced a chronic UC resulting in an increased incidence of high-grade dysplasia and submucosal-invasive adenocarcinomas in the mouse colorectum. The active form of vitamin D(3) is a calcium-regulating hormone that increases serum calcium levels and intestinal calcium absorption. It has been reported that there is an inverse correlation between serum levels of the active metabolite of vitamin D and colorectal carcinoma stage. The features of the colitis induced in this animal model are very similar to the UC in patients in terms of both clinical and histological characteristics. Treatment with a vitamin D(3) analog, alfacalcidol, in mice prevented colitis and carcinogenesis; this is shown by inhibition of the decrease in colorectal length and inhibition of the increased incidence of colorectal dysplasia, with a reduction in the mRNA expression of the DNA-synthesizing enzyme, thymidine kinase, in colorectal tissues.

Epidemiological evidence for vitamin D and colorectal cancer

Since Garland and Garland formulated the hypothesis that vitamin D may protect against colorectal cancer in 1980, various epidemiological approaches have been undertaken to evaluate this hypothesis. These approaches include studies based on regional solar UVB radiation, plasma- or serum-based studies, dietary studies, and those examining multiple factors that influence vitamin D status. Studies over the past several decades have tended to support that higher levels of vitamin D may decrease risk of colorectal cancer. An important implication is that current recommended dietary intakes such as 200-400 IU/d may be too low to exert appreciable benefits. To substantially reduce risk, higher levels of vitamin D associated with sunshine exposure or considerably higher intakes may be required. Recent studies also suggest a potential benefit of vitamin D on other digestive system cancers. One study suggested that a better vitamin D status at the time of diagnosis and treatment, as indicated by season of diagnosis, may improve survival from colorectal cancer. Darker-skinned individuals who tend to make less vitamin D may be at particularly high risk for digestive system cancer. The strong biological evidence for a protective role of vitamin D supports the epidemiological data. More study is needed to determine the optimal levels and intakes of this vitamin to optimally reduce colorectal cancer risk.

Differential antiproliferative effects of calcitriol on tumor-derived and matrigel-derived endothelial cells

The most active metabolite of vitamin D, calcitriol, is growth inhibitory for various tumor types in vitro and in vivo and inhibits the growth of endothelial cells freshly isolated from tumors [tumor-derived endothelial cells (TDEC)]. We compared the effects of calcitriol on Matrigel-derived endothelial cells (MDEC) and TDEC isolated from Matrigel plugs and squamous cell carcinoma tumors, respectively. TDEC and MDEC expressed vitamin D receptor (VDR) and responded to calcitriol by increasing VDR protein expression. Although no mutations were found in VDR from either cell type, Scatchard plot analysis revealed a higher ligand-binding affinity in TDEC (K(d), 0.26 nmol/L) than MDEC (K(d), 0.65 nmol/L). The VDR signaling axis in both cells was intact as shown using nuclear translocation and 24-hydroxylase promoter-luciferase reporter assays. However, unlike TDEC, MDEC were resistant to calcitriol-induced growth inhibition. Calcitriol (10 nmol/L) resulted in a 12.3% growth inhibition of MDEC compared with 47% in TDEC. In TDEC, calcitriol resulted in induction of G(0)/G(1) arrest (10.75%) and reduction of S-phase cells (6.8%) with induction of p27 and down-regulation of p21 protein expression. Apoptotic effects, determined by Annexin V staining were also observed in calcitriol-treated TDEC (38.6%). Calcitriol caused reduced expression of p-Erk and p-Akt and an increase of poly(ADP-ribose) polymerase and caspase-3 cleavage in TDEC. By contrast, none of these effects on cell cycle or apoptosis were seen in calcitriol-treated MDEC. These results show that TDEC were more sensitive than MDEC to the antiproliferative effects of calcitriol despite apparently normal VDR content and structure of signaling axis in both cell types.

Vitamin D signalling pathways in cancer: potential for anticancer therapeutics

Epidemiological studies indicate that vitamin D insufficiency could have an aetiological role in various human cancers. Preclinical research indicates that the active metabolite of vitamin D, 1alpha,25(OH)2D3, also known as calcitriol, or vitamin D analogues might have potential as anticancer agents because their administration has antiproliferative effects, can activate apoptotic pathways and inhibit angiogenesis. In addition, 1alpha,25(OH)2D3 potentiates the anticancer effects of many cytotoxic and antiproliferative anticancer agents. Here, we outline the epidemiological, preclinical and clinical studies that support the development of 1alpha,25(OH)2D3 and vitamin D analogues as preventative and therapeutic anticancer agents.

1alpha,25-dihydroxyvitamin D3 (Calcitriol) inhibits hypoxia-inducible factor-1/vascular endothelial growth factor pathway in human cancer cells

In vitro and in vivo studies have shown that 1alpha,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] inhibits angiogenesis in cancer. We now examined whether the antiangiogenic effects of 1,25(OH)(2)D(3) are mediated by the hypoxia-inducible factor (HIF)-1 pathway. Our results showed that 1,25(OH)(2)D(3) reduces the protein expression of both the regulated HIF-1alpha subunit and the vascular endothelial growth factor (VEGF) in various human cancer cells. 1,25(OH)(2)D(3) also inhibited HIF-1 transcriptional activity (measured by reporter gene assay) as well as HIF-1 target genes, including VEGF, ET-1, and Glut-1. We also showed that 1,25(OH)(2)D(3) inhibits cell proliferation under hypoxia. Using HIF-1alpha knockout colon cancer cells, we show that the inhibition of the hypoxia-induced VEGF by 1,25(OH)(2)D(3) is mediated through a HIF-dependent pathway. Because HIF-1 is a major positive contributor in human tumorigenesis and angiogenesis, we believe that its inhibition by 1,25(OH)(2)D(3) strengthens the rationale to use vitamin D and its low-calcemic analogues in cancer chemoprevention and therapy.

Calcitriol (1,25-Dihydroxycholecalciferol) Selectively Inhibits Proliferation of Freshly Isolated Tumor-Derived Endothelial Cells and Induces Apoptosis

Calcitriol (1,25-dihydroxycholecalciferol) has antiproliferative and/or proapoptotic effects on many cell types and the glucocorticoid dexamethasone enhances these effects. We have shown that calcitriol modulates several key signaling proteins involved in differentiation, proliferation and apoptosis in tumor-derived murine endothelial cells (TDEC) and that these effects were not seen with endothelial cells isolated similarly from normal tissues. In the present study, TDEC and mouse embryonic yolk sac endothelial cells (MYSEC) were treated with calcitriol and followed over time for an effect. MYSEC were utilized as 'normal' control endothelial cells because they were more primitive, being isolated from a highly neovascular tissue, and had a similar morphology without the stimulus of the tumor microenvironment. The vitamin D receptor (VDR) is present in TDEC and MYSEC, and was upregulated in calcitriol-treated TDEC and MYSEC; dexamethasone further increased VDR expression following 48 h of treatment. The modulatory effects on signaling proteins were maximal by treatment for 48 h; phospho-Erk, phospho-Akt, p21 and bcl-2 were decreased in treated TDEC with the induction of p27 but there were no effects on MYSEC. After 48 h increased apoptosis was seen in treated TDEC by annexin V labeling with caspase-3 cleavage and decreased levels of poly(ADP-ribose) polymerase, but no effects were seen in MYSEC. Cell cycle analysis showed increased G(0)/G(1) arrest and an increase in the apoptotic sub-G(1) peak in treated TDEC but similar effects were not seen in MYSEC following 48-hour treatment. Proliferation assays were utilized and TDEC demonstrated decreased proliferation compared to normal endothelial cells at 48 h. To determine whether or not the VDR signaling was impaired in MYSEC, we performed the 24-hydroxylase (CYP24) promoter-luciferase reporter assay. CYP24 is a key enzyme involved in the breakdown of vitamin D. VDR signaling was intact in both cell types and calcitriol induced CYP24 mRNA expression in MYSEC but not in TDEC. Taken together, despite similar levels of VDR expression and intact signaling in both cell types, calcitriol selectively inhibits proliferation and induces apoptosis in TDEC with no effect on MYSEC. Thus calcitriol exerts differential effects on TDEC compared to normal cells.

Vitamin D and cancer

1,25-dihydroxy Vitamin D [1,25-(OH)(2)D] exerts its effects via the vitamin D receptor (VDR) that belongs to the steroid/thyroid hormone receptor superfamily leading to gene regulation which results in various biological responses. Within the last two decades, the receptor has been shown to be present not only in classical target tissues such as bone, kidney and intestine but also in many other non-classical tissues. Besides the almost universal presence of VDRs, some cell types (e.g. keratinocytes, monocytes, bone, placenta) are capable of metabolizing 25-hydroxyvitamin D to 1,25(OH)(2)D by the enzyme 1alpha-hydroxylase (CYP27B1). The combined presence of 25(OH)D-1alpha-hydroxylase as well as the specific receptor in several tissues introduced the idea of a paracrine role for 1,25(OH)(2)D. Moreover, it has been demonstrated that 1,25(OH)(2)D can induce differentiation and inhibit proliferation of a wide variety of cell types. The molecular mechanisms behind this antiproliferative action is thoroughly explored but the whole picture is still difficult to understand. Important cell cycle regulators are involved such as cyclins, cyclin dependent kinases and their corresponding inhibitors as well as E2F transcription factors and accompanying pocket proteins. However the precise hierarchical structure of this wide diversity of actions of 1,25(OH)(2)D on genes influencing cell cycle progression is not firmly established nor do we understand which pathways are essential and which redundant. The antiproliferative action makes 1,25-(OH)(2)D and its analogs a possible therapeutic tool to treat hyperproliferative disorders, among which different types of cancer. This review focuses on the effects of 1,25(OH)(2)D and its analogs on cell proliferation, the results in in vivo experiments in Vitamin D deficient or resistant animals to cancer and the current epidemiological and intervention studies linking Vitamin D status or treatment and human cancer.

The role of vitamin D in cancer prevention

Vitamin D status differs by latitude and race, with residents of the northeastern United States and individuals with more skin pigmentation being at increased risk of deficiency. A PubMed database search yielded 63 observational studies of vitamin D status in relation to cancer risk, including 30 of colon, 13 of breast, 26 of prostate, and 7 of ovarian cancer, and several that assessed the association of vitamin D receptor genotype with cancer risk. The majority of studies found a protective relationship between sufficient vitamin D status and lower risk of cancer. The evidence suggests that efforts to improve vitamin D status, for example by vitamin D supplementation, could reduce cancer incidence and mortality at low cost, with few or no adverse effects.

1alpha,25-Dihydroxyvitamin D3 regulates the expression of Id1 and Id2 genes and the angiogenic phenotype of human colon carcinoma cells

1alpha,25-Dihydroxyvitamin D3 (1alpha,25(OH)2D3) has antitumor activity in addition to its classical action on calcium metabolism and bone tissue biology. It is thought to regulate the expression of multiple target genes and thus modulate processes critical for tumor growth and metastases. Here we show that 1alpha,25(OH)2D3 differentially regulates the expression of Id1 and Id2 genes, members of a family of transcriptional regulators of cell proliferation and differentiation. 1alpha,25(OH)2D3 induced epithelial differentiation in SW480-ADH human colon carcinoma cell line by promoting expression of the proteins implicated in adherent junction formation, including E-cadherin, and by inhibiting beta-catenin transcriptional activity. 1alpha,25(OH)2D3 activated the human Id1 gene promoter and rapidly induced Id1 RNA and protein. Ectopic overexpression of Id1 was not sufficient to induce E-cadherin, which was critical for the morphological changes induced by 1alpha,25(OH)2D3 in SW480-ADH cells. Conversely, Id2 transcription rate, RNA and protein levels were decreased by 1alpha,25(OH)2D3. Id2 downregulation by 1alpha,25(OH)2D3 mediated the antiproliferative effect of 1alpha,25(OH)2D3 on SW480-ADH cells. In addition, we showed that 1alpha,25(OH)2D3 changed the levels of the inducer of angiogenesis, vascular endothelial growth factor and the potent antiangiogenic factor thrombospondin-1, leading to a balanced change in the angiogenic potential of SW480-ADH human colon carcinoma cells.

Vitamin D and prevention of colorectal cancer

BACKGROUND

Inadequate photosynthesis or oral intake of Vitamin D are associated with high incidence rates of colorectal cancer, but the dose-response relationship has not been adequately studied.

METHODS

Dose-response gradients from observational studies of Vitamin D intake and serum 25-hydroxyvitamin D were plotted as trend lines. The point on each linear trend line corresponding to an odds ratio of 0.50 provided the prediagnostic Vitamin D intake or 25-hydroxyvitamin D concentration associated with 50% lower risk compared to <100IU/day Vitamin D or <13ng/ml serum 25-hydroxyvitamin D. Medians of these values were determined.

RESULTS

Overall, individuals with >or=1000IU/day oral Vitamin D (p<0.0001) or >or=33ng/ml (82nmol/l) serum 25-hydroxyvitamin D (p<0.01) had 50% lower incidence of colorectal cancer compared to reference values.

CONCLUSIONS

Intake of 1000IU/day of Vitamin D, half the safe upper intake established by the National Academy of Sciences, was associated with 50% lower risk. Serum 25-hydroxyvitamin D of 33ng/ml, which is known to be safe, also was associated with 50% lower risk. Prompt public health action is needed to increase intake of Vitamin D(3) to 1000IU/day, and to raise 25-hydroxyvitamin D by encouraging a modest duration of sunlight exposure.

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.

Vitamin D and colon carcinogenesis

Colorectal cancer is the third most commonly occurring cancer in the United States and accounts for approximately 11% of cancer deaths. Many epidemiological studies have shown an association between dietary factors, including calcium and vitamin D, and the incidence of colon cancer. Recently the Calcium Polyp Prevention Study demonstrated that calcium supplementation can reduce the recurrence of colon polyps, but the effect depends on serum vitamin D levels. We used the Apc(min) mouse model of intestinal cancer to investigate the effects of vitamin D treatment and calcium intake independently on polyp formation. We found that 1,25-dihydroxycholecaliferol was potent in inhibiting tumor load; however, the dose used to achieve this antiproliferative effect led to deleterious effects on serum calcium homeostasis. These effects were minimized by use of a synthetic analogue with reduced toxicity. Additionally, we tested the effect of a modified-calcium diet in Apc(min) mice but did not find a protective effect, perhaps because of a reduction in circulating levels of 25-hydroxycholecaliferol with increasing levels of dietary calcium. A number of other studies that use rodent models with vitamin D supplementation or deficiency illustrate the efficacy of vitamin D in colon cancer prevention. The mechanisms of direct action of vitamin D on colonic epithelium include regulation of growth factor and cytokine synthesis and signaling, as well as modulation of the cell cycle, apoptosis, and differentiation. Because of the apparent synergistic effect of vitamin D and calcium, cosupplementation of both nutrients in cancer prevention programs may be advised.

Plasma Vitamin D Metabolites and Risk of Colorectal Cancer in Women

Objective: Experimental evidence suggests that 1,25-dihydroxyvitamin D and its precursor, 25-hydroxyvitamin D [25(OH)D], may aid in the prevention of colorectal cancer. We therefore examined risk in relation to plasma concentrations of these vitamin D metabolites. Methods: In a nested case-control study among women in the Nurses' Health Study, we identified 193 colorectal cancer cases, ages 46 to 78 years, diagnosed up to 11 years after blood collection. Two controls were matched per case on year of birth and month of blood draw. Odds ratios (OR) for risk of colorectal cancer were calculated using conditional logistic regression adjusted for body mass index, physical activity, smoking, family history, use of hormone replacement therapy, aspirin use, and dietary intakes. Results: We found a significant inverse linear association between plasma 25(OH)D and risk of colorectal cancer (P = 0.02). Among women in the highest quintile, the OR (95% confidence interval) was 0.53 (0.27–1.04). This inverse association remained strong when limited to women ≥60 years at blood collection (P = 0.006) but was not apparent among the younger women (P = 0.70). Benefit from higher 25(OH)D concentrations was observed for cancers at the distal colon and rectum (P = 0.02) but was not evident for those at the proximal colon (P = 0.81). In contrast to 25(OH)D, we did not observe an association between 1,25-dihydroxyvitamin D and colorectal cancer, although risk was elevated among the women in the highest quintile if they were also in the lower half of the 25(OH)D distribution (OR, 2.52; 95% confidence interval, 1.04–6.11). Conclusion: From these results and supporting evidence from previous studies, we conclude that higher plasma levels of 25(OH)D are associated with a lower risk of colorectal cancer in older women, particularly for cancers at the distal colon and rectum.

1alpha,25-dihydroxycholecalciferol increases the expression of vascular endothelial growth factor in C3H10T1/2 mouse embryo fibroblasts

Evidence suggests that biologically active vitamin D, 1,25-dihydroxycholecalciferol [1,25(OH)(2)D(3)], may inhibit carcinogenesis. Because angiogenesis is crucial to carcinogenesis, 1,25(OH)(2)D(3) regulation of proangiogenic vascular endothelial growth factor (VEGF) secretion was investigated in cellular models for multistage carcinogenesis. Conditioned media from 1,25(OH)(2)D(3)-treated C3H10T(1/2) mouse fibroblasts and their Harvey ras-oncogene transfected counterparts (rasneo11a cells) induced human umbilical vein endothelial cell (HUVEC) proliferation (1.3 and 0.3 times, respectively, P < 0.05), suggesting that 1,25(OH)(2)D(3) altered the angiogenic phenotype of the cells. Although rasneo11a cells secreted less VEGF than C3H10T(1/2) cells (97%, P < 0.005), 1,25(OH)(2)D(3) induced C3H10T(1/2) and rasneo11a cells to secrete 2 and 3 times, respectively, more VEGF than controls (P < 0.05). Similar effects on VEGF release occurred after 1,25(OH)(2)D(3) treatment of MCF10A and MCF10Aras cells, a human breast epithelial cell model for multistage carcinogenesis. In C3H10T(1/2) cells, 1,25(OH)(2)D(3) activated the VEGF promoter in a dose-dependent (5-100 nmol/L) manner (maximum 60%) and all doses induced VEGF secretion (P < 0.05). 1,25(OH)(2)D(3) induced VEGF mRNA expression ( approximately 50%) from 2 through 24 h; VEGF release was significantly increased at 8 h and sustained for 24 h. VEGF mRNA expression and release declined as C3H10T(1/2) cells grew more confluent, whereas the magnitude of 1,25(OH)(2)D(3)-stimulated changes in VEGF was greater in confluent (3.3 times RNA; 3.5 times release) than in subconfluent (50% RNA; 100% release) cultures (P < 0.05). Thus, 1,25(OH)(2)D(3) increases VEGF secretion, and in C3H10T(1/2) cells, this is likely through activation of the VEGF promoter and induction of gene expression. These data contribute to understanding the role 1,25(OH)(2)D(3) plays in regulation of angiogenesis in normal compared with disease states.

A moderately low phosphate intake may provide health benefits analogous to those conferred by UV light - a further advantage of vegan diets

Although exposure to ultraviolet light is often viewed as pathogenic owing to its role in the genesis of skin cancer and skin aging, there is growing epidemiological evidence that such exposure may decrease risk for a number of more serious cancers, may have a favorable impact on blood pressure and vascular health, and may help to prevent certain autoimmune disorders - in addition to its well-known influence on bone density. Most likely, these health benefits are reflective of improved vitamin D status. Increased synthesis or intake of vitamin D can be expected to down-regulate parathyroid hormone (PTH), and to increase autocrine synthesis of its active metabolite calcitriol in certain tissues; these effects, in turn, may impact cancer risk, vascular health, immune regulation, and bone density through a variety of mechanisms. Presumably, a truly adequate supplemental intake of vitamin D - manyfold higher than the grossly inadequate current RDA - could replicate the benefits of optimal UV exposure, without however damaging the skin. Diets moderately low in bioavailable phosphate - like many vegan diets - might be expected to have a complementary impact on disease risks, inasmuch as serum phosphate suppresses renal calcitriol synthesis while up-regulating that of PTH. A proviso is that the impact of dietary phosphorus on bone health is more equivocal than that of vitamin D. Increased intakes of calcium, on the other hand, down-regulate the production of both PTH and calcitriol - the latter effect may explain why the impact of dietary calcium on cancer risk (excepting colon cancer), hypertension, and autoimmunity is not clearly positive. An overview suggests that a vegan diet supplemented with high-dose vitamin D should increase both systemic and autocrine calcitriol production while suppressing PTH secretion, and thus should represent a highly effective way to achieve the wide-ranging health protection conferred by optimal UV exposure.

Vitamin D and prostate cancer

Vitamin D and its metabolites are best known for their actions in calcium and bone metabolism. However, epidemiological studies have suggested that an increased prostate cancer risk is associated with decreased production of vitamin D. In vitro and in vivo studies have shown that the biologically active form of vitamin D, 1alpha,25-dihydroxyvitamin D3 (1,25D), inhibits proliferation of cancer cells derived from multiple tissues, including the prostate. Although the mechanisms underlying the growth inhibitory effects of 1,25D have not been fully elucidated, in prostate cancer cells 1,25D reduces cell growth via a number of cellular pathways, including cell cycle arrest, induction of apoptosis, and altered activation of growth factor signaling. The hypercalcemia induced by 1,25D in vivo limits its use clinically as a therapeutic agent. However, several 1,25D analogs have been developed that reduce prostate tumor growth in rodent xenograft models without causing hypercalcemia. Additional studies are required in order to determine whether these 1,25D analogs will be useful therapeutic agents for the treatment of prostate cancer.

Antiproliferative effects of 1alpha,25-dihydroxyvitamin D(3) and vitamin D analogs on tumor-derived endothelial cells

Although there is abundant evidence that 1alpha,25-dihydroxyvitamin D(3) [1,25-(OH)(2)D(3)] inhibits the growth of several cancer cell types, inhibition of angiogenesis may also play a role in mediating the antitumor effects of 1,25-(OH)(2)D(3.) We examined the ability of 1,25-(OH)(2)D(3) to inhibit the growth of tumor-derived endothelial cells (TDECs) and normal endothelial cells and to modulate angiogenic signaling. 1,25-(OH)(2)D(3) inhibited the growth of TDECs from two tumor models at nanomolar concentrations, but was less potent against normal aortic or yolk sac endothelial cells. The vitamin D analogs Ro-25-6760, EB1089, and ILX23-7553 were also potent inhibitors of TDEC proliferation. Furthermore, the combination of 1,25-(OH)(2)D(3) and dexamethasone had greater activity than either agent alone. 1,25-(OH)(2)D(3) increased vitamin D receptor and p27(Kip1) protein levels in TDECs, whereas phospho-ERK1/2 and phospho-Akt levels were reduced. These changes were not observed in normal aortic endothelial cells. In squamous cell carcinoma and radiation-induced fibrosarcoma-1 cells, 1,25-(OH)(2)D(3) treatment caused a reduction in the angiogenic signaling molecule, angiopoietin-2. In conclusion, 1,25-(OH)(2)D(3) and its analogs directly inhibit TDEC proliferation at concentrations comparable to those required to inhibit tumor cells. Further, 1,25-(OH)(2)D(3) modulates cell cycle and survival signaling in TDECs and affects angiogenic signaling in cancer cells. Thus, our work supports the hypothesis that angiogenesis inhibition plays a role in the antitumor effects of 1,25-(OH)(2)D(3).