CYP24A1 is an independent prognostic marker of survival in patients with lung adenocarcinoma

Epigenetic regulation of vitamin D metabolism in human lung adenocarcinoma

INTRODUCTION

1α,25-Dihydroxyvitamin D3 (1,25-D3) is antiproliferative in preclinical models of lung cancer, but in tumor tissues, its efficacy may be limited by CYP24A1 expression. CYP24A1 is the rate limiting catabolic enzyme for 1,25-D3 and is overexpressed in human lung adenocarcinoma (AC) by unknown mechanisms.

METHODS

The DNA methylation status of CYP24A1 was determined by bisulfite DNA pyrosequencing in a panel of 30 lung cell lines and 90 surgically resected lung AC. The level of CYP24A1 methylation was correlated with CYP24A1 expression in lung AC cell lines and tumors. In addition, histone modifications were assessed by quantitative chromatin immunoprecipitation-polymerase chain reaction (ChIP-qPCR) in A549, NCI-H460, and SK-LU-1.

RESULTS

Bisulfite DNA pyrosequencing analysis revealed that CYP24A1 gene was heterogeneously methylated in lung AC. Expression of CYP24A1 was inversely correlated with promoter DNA methylation in lung AC cell lines and tumors. Treatment with 5-aza-2'-deoxycytidine (5-Aza) and trichostatin A (TSA) increased CYP24A1 expression in lung AC. We observed that CYP24A1 promoter hypermethylation decreased CYP24A1 enzyme activity in vitro, whereas treatment with 5-Aza and/or TSA increased CYP24A1 enzyme affinity for its substrate 1,25-D3. In addition, ChIP-qPCR analysis revealed specific histone modifications within the CYP24A1 promoter region. Treatment with TSA increased H3K4me2 and H3K9ac and simultaneously decreased H3K9me2 at the CYP24A1 promoter and treatment with 5-Aza and/or TSA increased the recruitment of vitamin D receptor (VDR) to vitamin D response elements (VDRE) of the CYP24A1 promoter.

CONCLUSIONS

The expression of CYP24A1 gene in human lung AC is in part epigenetically regulated by promoter DNA methylation and repressive histone modifications. These findings should be taken into consideration when targeting CYP24A1 to optimize antiproliferative effects of 1,25-D3 in lung AC.

Association of GWAS-identified lung cancer susceptibility loci with survival length in patients with small-cell lung cancer treated with platinum-based chemotherapy

Genetic variants have been shown to affect length of survival in cancer patients. This study explored the association between lung cancer susceptibility loci tagged by single-nucleotide polymorphisms (SNPs) identified in the genome-wide association studies and length of survival in small-cell lung cancer (SCLC). Eighteen SNPs were genotyped among 874 SCLC patients and Cox proportional hazards regression was used to examine the effects of genotype on survival length under an additive model with age, sex, smoking status and clinical stage as covariates. We identified 3 loci, 20q13.2 (rs4809957G >A), 22q12.2 (rs36600C >T) and 5p15.33 (rs401681C >T), significantly associated with the survival time of SCLC patients. The adjusted hazard ratio (HR) for patients with the rs4809957 GA or AA genotype was 0.80 (95% CI, 0.66–0.96; P = 0.0187) and 0.73 (95% CI, 0.55–0.96; P = 0.0263) compared with the GG genotype. Using the dominant model, the adjusted HR for patients carrying at least one T allele at rs36600 or rs401681 was 0.78 (95% CI, 0.63–0.96; P = 0.0199) and 1.29 (95% CI, 1.08–1.55; P = 0.0047), respectively, compared with the CC genotype. Stratification analyses showed that the significant associations of these 3 loci were only seen in smokers and male patients. The rs4809957 SNP was only significantly associated with length of survival of patients with extensive-stage but not limited-stage tumor. These results suggest that some of the lung cancer susceptibility loci might also affect the prognosis of SCLC.

CYP24A1 expression inversely correlates with melanoma progression: clinic-pathological studies

The major role of 24-hydroxylase (CYP24A1) is to maintain 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) homeostasis. Recently, it has been discovered that CYP24A1 also catalyses the hydroxylation of 20(OH)D3, producing dihydroxy-derivatives that show very effective antitumorigenic activities. Previously we showed a negative correlation of vitamin D receptor (VDR) and CYP27B1 expression with progression, aggressiveness and overall or disease-free survivals of skin melanomas. Therefore, we analyzed CYP24A1 expression in relation to clinicopathomorphological features of nevi, skin melanomas and metastases. In melanocytic tumors, the level of CYP24A1 was higher than in the normal epidermis. The statistically highest mean CYP24A1 level was found in nevi and early stage melanomas. With melanoma progression, CYP24A1 levels decreased and in advanced stages were comparable to the normal epidermis and metastases. Furthermore, the CYP24A1 expression positively correlated with VDR and CYP27B1, and negatively correlated with mitotic activity. Lower CYP24A1 levels correlated with the presence of ulceration, necrosis, nodular type and amelanotic phenotypes. Moreover, a lack of detectable CYP24A1 expression was related to shorter overall and disease-free survival. In conclusion, the local vitamin D endocrine system affects melanoma behavior and an elevated level of CYP24A1 appears to have an important impact on the formation of melanocytic nevi and melanomagenesis, or progression, at early stages of tumor development.

VDR primary targets by genome-wide transcriptional profiling

There is growing evidence that 1α,25-dihydroxyvitamin D3 (1α,25(OH)2D3) plays a role in breast cancer prevention and survival. It elicits a variety of antitumor activities like controlling cellular differentiation, proliferation and angiogenesis. Most of its biological effects are exerted via its nuclear receptor which acts as a transcriptional regulator. Here, we carried out a genome-wide investigation of the primary transcriptional targets of 1α,25(OH)2D3 in breast epithelial cancer cells using RNA-Seq technology. We identified early transcriptional targets of 1α,25(OH)2D3 involved in adhesion, growth regulation, angiogenesis, actin cytoskeleton regulation, hexose transport, inflammation and immunomodulation, apoptosis, endocytosis and signaling. Furthermore, we found several transcription factors to be regulated by 1α,25(OH)2D3 that subsequently amplify and diversify the transcriptional output driven by 1α,25(OH)2D3 leading finally to a growth arrest of the cells. Moreover, we could show that 1α,25(OH)2D3 elevates the trimethylation of histone H3 lysine 4 at several target gene promoters. Our present transcriptomic analysis of differential expression after 1α,25(OH)2D3 treatment provides a resource of primary 1α,25(OH)2D3 targets that might drive the antiproliferative action in breast cancer epithelial cells.

Increased CYP24A1 expression is associated with BRAF(V600E) mutation and advanced stages in papillary thyroid carcinoma

OBJECTIVE

1α, 25(OH)2 D3 (calcitriol), the active form of vitamin D, has been shown to exert antiproliferative effects in many cancers. Overexpression of CYP24A1, the primary vitamin D-inactivating enzyme, is also observed in a variety of human cancers, thus potentially neutralizing the antitumour effect of 1α, 25(OH)2 D3. This study investigates the expression of CYP24A1 and the effect of BRAF(V600E) on its expression in thyroid cancer.

METHODS

We investigated 60 papillary thyroid carcinoma (PTC) specimens for CYP24A1 expression and its association with BRAF mutation and disease progression. CYP24A1 expression was measured by real-time RT-PCR, and BRAF(V600E) mutation was detected by PCR-DNA sequencing analysis. The interaction between BRAF(V600E) and CYP24A1 expression was determined by Western blot analysis and real-time RT-PCR.

RESULTS

CYP24A1 expression was increased in PTC as compared to benign multinodular goitre. The expression was further increased in stage III and IV tumours. There is a strong correlation between CYP24A1 overexpression and BRAF(V600E) mutation (P < 0·01). In thyroid cancer cell lines expressing BRAF(V600E) , CYP24A1 expression was significantly higher when compared to those without BRAF(V600E) expression. BRAF(V600E) transgene expression in CAL62 cell line can induce CYP24A1 expression. Furthermore, BRAF(V600E) inhibitor PLX4720 can significantly down-regulate CYP24A1 expression and enhance the antiproliferative effects of calcitriol in thyroid cancer cell lines.

CONCLUSION

CYP24A1 overexpression is a poor prognostic indicator for PTC and may reflect BRAF(V600E) mutation and MARK activation. The crosstalk between vitamin D and MAPK signalling pathways results in resistance to calcitriol-mediated antitumour effects, and the resistance can be reversed by BRAF(V600E) inhibitor PLX4720.

Role of Vitamin D Metabolism and Activity on Carcinogenesis

The vitamin D endocrine system regulates a broad variety of independent biological processes, and its deficiency is associated with rickets, bone diseases, diabetes, cardiovascular diseases, and tuberculosis. Cellular and molecular studies have also shown that it is implicated in the suppression of cancer cell invasion, angiogenesis, and metastasis. Sunlight exposure and consequent increased circulating levels of vitamin D are associated with reduced occurrence and a reduced mortality in different histological types of cancer, including those resident in the skin, prostate, breast, colon, ovary, kidney, and bladder. The vitamin D receptor (VDR) as a steroid hormone superfamily of nuclear receptors is highly expressed in epithelial cells at risk for carcinogenesis, providing a direct molecular link by which vitamin D status impacts on carcinogenesis. 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. The aim of this review is to highlight the relationship between vitamin D, VDR, and cancer, summarizing several mechanisms proposed to explain the potential protective effect of vitamin D against the development and progression of cancer.

Cell-type specific features of circular RNA expression

Thousands of loci in the human and mouse genomes give rise to circular RNA transcripts; at many of these loci, the predominant RNA isoform is a circle. Using an improved computational approach for circular RNA identification, we found widespread circular RNA expression in Drosophila melanogaster and estimate that in humans, circular RNA may account for 1% as many molecules as poly(A) RNA. Analysis of data from the ENCODE consortium revealed that the repertoire of genes expressing circular RNA, the ratio of circular to linear transcripts for each gene, and even the pattern of splice isoforms of circular RNAs from each gene were cell-type specific. These results suggest that biogenesis of circular RNA is an integral, conserved, and regulated feature of the gene expression program.

Vitamin D deficiency and the lung: disease initiator or disease modifier?

Vitamin D deficiency is a global public health problem and has been associated with an increased incidence and severity of many diseases including diseases of the respiratory system. These associations have largely been demonstrated epidemiologically and have formed the basis of the justification for a large number of clinical supplementation trials with a view to improving disease outcomes. However, the trials that have been completed to date and the ongoing experimental studies that have attempted to demonstrate a mechanistic link between vitamin D deficiency and lung disease have been disappointing. This observation raises many questions regarding whether vitamin D deficiency is truly associated with disease pathogenesis, is only important in the exacerbation of disease or is simply an indirect biomarker of other disease mechanisms? In this review, we will briefly summarize our current understanding of the role of vitamin D in these processes with a focus on lung disease.

24-Hydroxylase in cancer: impact on vitamin D-based anticancer therapeutics

The active vitamin D hormone 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) plays a major role in regulating calcium homeostasis and bone mineralization. 1,25(OH)2D3 also modulates cellular proliferation and differentiation in a variety of cell types. 24-Hydroxylase, encoded by the CYP24A1 gene, is the key enzyme which converts 1,25(OH)2D3 to less active calcitroic acid. Nearly all cell types express 24-hydroxylase, the highest activity being observed in the kidney. There is increasing evidence linking the incidence and prognosis of certain cancers to low serum 25(OH)D3 levels and high expression of vitamin D 24-hydroxylase, supporting the idea that elevated CYP24A1 expression may stimulate degradation of vitamin D metabolites including 25(OH)D3 and 1,25(OH)2D3. The over expression of CYP24A1 in cancer cells may be a factor affecting 1,25(OH)2D3 bioavailability and anti-proliferative activity pre-clinically and clinically. The combination of 1,25(OH)2D3 with CYP24A1 inhibitors enhances 1,25(OH)2D3 mediated signaling and anti-proliferative effects and may be useful in overcoming effects of aberrant CYP24A1 expression. This article is part of a Special Issue entitled 'Vitamin D Workshop'.

Differential response to 1α,25-dihydroxyvitamin D3 (1α,25(OH)2D3) in non-small cell lung cancer cells with distinct oncogene mutations

We previously demonstrated that non-small cell lung cancer (NSCLC) cells and primary human lung tumors aberrantly express the vitamin D3-catabolizing enzyme, CYP24, and that CYP24 restricts transcriptional regulation and growth control by 1α,25-dihydroxyvitamin D3 (1,25(OH)2D3) in NSCLC cells. To ascertain the basis for CYP24 dysregulation, we assembled a panel of cell lines that represent distinct molecular classes of lung cancer: cell lines were selected which harbored mutually exclusive mutations in either the K-ras or the Epidermal Growth Factor Receptor (EGFR) genes. We observed that K-ras mutant lines displayed a basal vitamin D receptor (VDR)(low)CYP24(high) phenotype, whereas EGFR mutant lines had a VDR(high)CYP24(low) phenotype. A mutation-associated difference in CYP24 expression was also observed in clinical specimens. Specifically, K-ras mutation was associated with a median 4.2-fold increase in CYP24 mRNA expression (p=4.8×10(-7)) compared to EGFR mutation in a series of 147 primary lung adenocarcinoma cases. Because of their differential basal expression of VDR and CYP24, we hypothesized that NSCLC cells with an EGFR mutation would be more responsive to 1,25(OH)2D3 treatment than those with a K-ras mutation. To test this, we measured the ability of 1,25(OH)2D3 to increase reporter gene activity, induce transcription of endogenous target genes, and suppress colony formation. In each assay, the extent of 1,25(OH)2D3 response was greater in EGFR mutation-positive HCC827 and H1975 cells than in K-ras mutation-positive A549 and 128.88T cells. We subsequently examined the effect of combining 1,25(OH)2D3 with erlotinib, which is used clinically in the treatment of EGFR mutation-positive NSCLC. 1,25(OH)2D3/erlotinib combination resulted in significantly greater growth inhibition than either single agent in both the erlotinib-sensitive HCC827 cell line and the erlotinib-resistant H1975 cell line. These data are the first to suggest that EGFR mutations may identify a lung cancer subset which remains responsive to and is likely to benefit from 1,25(OH)2D3 administration. This article is part of a Special Issue entitled 'Vitamin D Workshop'.

Extrahepatic 25-Hydroxylation of Vitamin D3 in an Engineered Osteoblast Precursor Cell Line Exploring the Influence on Cellular Proliferation and Matrix Maturation during Bone Development

Osteoblastic precursors experience distinct stages during differentiation and bone development, which include proliferation, extracellular matrix (ECM) maturation, and ECM mineralization. It is well known that vitamin D plays a large role in the regulation of bone mineralization and homeostasis via the endocrine system. The activation of vitamin D requires two sequential hydroxylation steps, first in the kidney and then in the liver, in order to carry out its role in calcium homeostasis. Recent research has demonstrated that human-derived mesenchymal stem cells (MSCs) and osteoblasts can metabolize the immediate vitamin D precursor 25-dihydroxyvitamin D3 (25OHD3) to the active steroid lα,25-dihydroxyvitamin D3 (1,25OH2D3) and elicit an osteogenic response. However, reports of extrahepatic metabolism of vitamin D3, the parental vitamin D precursor, have been limited. In this study, we investigated whether osteoblast precursors have the capacity to convert vitamin D3 to 1,25OH2D3 and examined the potential of vitamin D3 to induce 1,25OH2D3 associated biological activities in osteoblast precursors. It was demonstrated that the engineered osteoblast precursor derived from human marrow (OPC1) is capable of metabolizing vitamin D3 to 1,25OH2D3 in a dose-dependent manner. It was also demonstrated that administration of vitamin D3 leads to the increase in alkaline phosphatase (ALP) activity associated with osteoblast ECM maturation and calcium deposits and a decrease in cellular proliferation in both osteoblast precursor cell lines 0PC1 andOMC3T3-E1. These findings provide a two-dimensional culture foundation for future three-dimensional engineered tissue studies using the OPC1 cell line.

Cytochrome P450-mediated metabolism of vitamin D

The vitamin D signal transduction system involves a series of cytochrome P450-containing sterol hydroxylases to generate and degrade the active hormone, 1α,25-dihydroxyvitamin D3, which serves as a ligand for the vitamin D receptor-mediated transcriptional gene expression described in companion articles in this review series. This review updates our current knowledge of the specific anabolic cytochrome P450s involved in 25- and 1α-hydroxylation, as well as the catabolic cytochrome P450 involved in 24- and 23-hydroxylation steps, which are believed to initiate inactivation of the vitamin D molecule. We focus on the biochemical properties of these enzymes; key residues in their active sites derived from crystal structures and mutagenesis studies; the physiological roles of these enzymes as determined by animal knockout studies and human genetic diseases; and the regulation of these different cytochrome P450s by extracellular ions and peptide modulators. We highlight the importance of these cytochrome P450s in the pathogenesis of kidney disease, metabolic bone disease, and hyperproliferative diseases, such as psoriasis and cancer; as well as explore potential future developments in the field.

Increased copy-number and not DNA hypomethylation causes overexpression of the candidate proto-oncogene CYP24A1 in colorectal cancer

In colorectal cancer (CRC) the vitamin D catabolizing enzyme 1,25-dihydroxyvitamin D 24-hydroxylase (CYP24A1) is overexpressed with a potentially significant, positive impact on the catabolism of 1,25-dihydroxyvitamin D₃ (1,25-D₃). However, the underlying mechanism of CYP24A1 overexpression is poorly understood. In the present study, we investigated possible causes including hypomethylation of the CYP24A1 promoter, amplification of the CYP24A1 gene locus (20q13.2), and altered expression of CYP24A1-specific transcription factors. We quantified CYP24A1 gene copy-number, performed bisulfite sequencing of the CYP24A1 promoter to assess DNA methylation, and measured mRNA expression of CYP24A1, 25-hydroxyvitamin D 1α-hydroxylase (CYP27B1), vitamin D receptor (VDR) and retinoid X receptor (RXR). We found that 77 (60%) out of 127 colorectal tumors showed increased CYP24A1 gene copy-number and that more than 6 copies of CYP24A1 correlated positively with CYP24A1 mRNA expression suggestive of a causal relationship. No differences in CYP24A1 promoter methylation were found between tumor tissue and adjacent mucosa from the same patient or between tissues with high or low mRNA expression, thus excluding DNA hypomethylation as a possible cause of CYP24A1 overexpression in CRC. Furthermore, mRNA expression of several factors involved in replication licensing positively correlated with CYP24A1 mRNA expression, raising the possibility that CYP24A1 overexpression might favor increased proliferation in tumors by suppressing local 1,25-D₃ levels. We conclude that high copy-number gain is a key determinant of CYP24A1 overexpression in CRC. Other postulated causes of CYP24A1 overexpression including promoter hypomethylation and enhanced VDR and/or RXR expression do not appear to be involved.

What’s new?

Recently, it has been suggested that the association between colorectal cancer and reduced levels of circulating vitamin D may be related to overexpression of the vitamin D-catabolizing enzyme, CYP24A1 in the tumor. In this search for a mechanistic explanation, increased CYP24A1 gene copy number was associated with the enzyme’s overexpression in 60 percent of colorectal tumors, and expression was correlated strongly with proliferation markers. The findings suggest that CYP24A1 overexpression is likely to deplete tumor calcitriol (1,25-dihydroxyvitamin D₃) levels, possibly increasing the proliferative potential of the tumors.

Dysregulation of vitamin D3 synthesis leads to enhanced cholangiocarcinoma growth

BACKGROUND

Cholangiocarcinoma is a deadly biliary tumour with limited treatment strategies. Vitamin (1,25(OH)2D) has anti-proliferative effects on several cancers. Vitamin D3 is synthesized by the enzyme, CYP27B1, and signals via the nuclear vitamin D3 receptor. The enzyme, CYP24A1, degrades vitamin D3.

AIMS

(i) Measure the expression of CYP27B1, CYP24A1, and vitamin D3 receptor in human nonmalignant and cholangiocarcinoma lines and biopsy control or tumour samples; and (ii) evaluate the effects of vitamin D3 on vitamin D3 synthesis and cholangiocarcinoma growth.

METHODS

In vitro studies were performed in malignant and nonmalignant cholangiocytes. Vitamin D3 receptor, CYP24 and CYP27 expression was measured in cell lines and biopsy samples. Cell lines were stimulated with vehicle or vitamin D3 from 30min to 48h. Cell viability was assessed by MTS assays and BrdU incorporation. Vitamin D3 receptor, CYP24A1 and CYP27B1 expression was measured in cholangiocarcinoma cells stimulated with vehicle or vitamin D3.

RESULTS

In cholangiocarcinoma lines and biopsy samples, vitamin D3 receptor and CYP24A1 expression increased compared to controls, whereas CYP27B1 expression was decreased or unchanged. Vitamin D3 induced nuclear translocation of vitamin D3 receptor in cholangiocarcinoma and decreased cholangiocarcinoma growth.

CONCLUSION

Treatment with vitamin D3 decreased CYP24A1, whereas CYP27B1 expression increased. Modulation of vitamin D3 synthesis may be important in the management of cholangiocarcinoma.

A phase I/II pharmacokinetic and pharmacogenomic study of calcitriol in combination with cisplatin and docetaxel in advanced non-small-cell lung cancer

BACKGROUND

Preclinical studies demonstrated antiproliferative synergy of 1,25-D3 (calcitriol) with cisplatin. The goals of this phase I/II study were to determine the recommended phase II dose (RP2D) of 1,25-D3 with cisplatin and docetaxel and its efficacy in metastatic non-small-cell lung cancer.

METHODS

Patients were ≥18 years, PS 0-1 with normal organ function. In the phase I portion, patients received escalating doses of 1,25-D3 intravenously every 21 days prior to docetaxel 75 mg/m(2) and cisplatin 75 mg/m(2) using standard 3 + 3 design, targeting dose-limiting toxicity (DLT) rate <33 %. Dose levels of 1,25-D3 were 30, 45, 60, and 80 mcg/m(2). A two-stage design was employed for phase II portion. We correlated CYP24A1 tagSNPs with clinical outcome and 1,25-D3 pharmacokinetics (PK).

RESULTS

34 patients were enrolled. At 80 mcg/m(2), 2/4 patients had DLTs of grade 4 neutropenia. Hypercalcemia was not observed. The RP2D of 1,25-D3 was 60 mcg/m(2). Among 20 evaluable phase II patients, there were 2 confirmed, 4 unconfirmed partial responses (PR), and 9 stable disease (SD). Median time to progression was 5.8 months (95 % CI 3.4, 6.5), and median overall survival 8.7 months (95 % CI 7.6, 39.4). CYP24A1 SNP rs3787554 (C > T) correlated with disease progression (P = 0.03) and CYP24A1 SNP rs2762939 (C > G) trended toward PR/SD (P = 0.08). There was no association between 1,25-D3 PK and CYP24A1 SNPs.

CONCLUSIONS

The RP2D of 1,25-D3 with docetaxel and cisplatin was 60 mcg/m(2) every 21 days. Pre-specified endpoint of 50 % confirmed RR was not met in the phase II study. Functional SNPs in CYP24A1 may inform future studies individualizing 1,25-D3.

Vitamin D: metabolism, molecular mechanisms, and mutations to malignancies

The potential protective effects of vitamin D against cutaneous carcinogenesis are still poorly understood. The inhibition, by vitamin D, of various cancers in in vitro and in vivo models has triggered detailed investigation of vitamin D effects on neoplastic behavior. Recent studies highlight that such neoplastic features as the tumor microenvironment, angiogenesis, DNA mutagenesis, and apoptosis are all connected to vitamin D metabolic pathways. This review discusses these connections. Vitamin D modulation of the cell cycle, DNA repair and apoptosis via its receptors (VDRs) may have a suppressive effect on skin cancer as some studies suggest. The regulation of multiple tumor signaling pathways by vitamin D may have an implication in cutaneous carcinogenesis and tumor progression to malignancy.

Inhibition of protein kinase CK2 reduces Cyp24a1 expression and enhances 1,25-dihydroxyvitamin D(3) antitumor activity in human prostate cancer cells

Vitamin D has broad range of physiological functions and antitumor effects. 24-Hydroxylase, encoded by the CYP24A1 gene, is the key enzyme for degrading many forms of vitamin D including the most active form, 1,25D(3). Inhibition of CYP24A1 enhances 1,25D(3) antitumor activity. To isolate regulators of CYP24A1 expression in prostate cancer cells, we established a stable prostate cancer cell line PC3 with CYP24A1 promoter driving luciferase expression to screen a small molecular library for compounds that inhibit CYP24A1 promoter activity. From this screening, we identified, 4,5,6,7-tetrabromobenzimidazole (TBBz), a protein kinase CK2 selective inhibitor as a disruptor of CYP24A1 promoter activity. We show that TBBz inhibits CYP24A1 promoter activity induced by 1,25D(3) in prostate cancer cells. In addition, TBBz downregulates endogenous CYP24A1 mRNA level in TBBz-treated PC3 cells. Furthermore, siRNA-mediated CK2 knockdown reduces 1,25D(3)-induced CYP24A1 mRNA expression in PC3 cells. These results suggest that CK2 contributes to 1,25D(3)-mediated target gene expression. Finally, inhibition of CK2 by TBBz or CK2 siRNA significantly enhances 1,25D(3)-mediated antiproliferative effect in vitro and in vivo in a xenograft model. In summary, our findings reveal that protein kinase CK2 is involved in the regulation of CYP24A1 expression by 1,25D(3) and CK2 inhibitor enhances 1,25D(3)-mediated antitumor effect.

Role of calcium, vitamin D, and the extrarenal vitamin D hydroxylases in carcinogenesis

Vitamin D deficiency and low calcium intake are considered risk factors for several cancers. Vitamin D, synthesized in the skin or ingested through the diet, is transformed through two hydroxylation steps to the active metabolite, 1α,25-dihydroxyvitamin D3 (1,25-D3). 25-hydroxylases in the liver are responsible for the first hydroxylation step. The ultimate activation is performed by the renal 25-hydroxyvitamin D 1α-hydroxylase (CYP27B1), while the 1,25-dihydroxyvitamin D 24-hydroxylase (CYP24A1) in the kidneys degrades the active metabolite. These two renal vitamin D hydroxylases control the endocrine serum 1,25-D3 levels, and are responsible for maintaining mineral homeostasis. In addition, the active vitamin D hormone 1,25-D3 regulates cellular proliferation, differentiation, and apoptosis in multiple tissues in a paracrine/autocrine manner. Interestingly, it is the low serum level of the precursor 25- hydroxyvitamin D3 (25-D3) that predisposes to numerous cancers and other chronic diseases, and not the serum concentration of the active vitamin D hormone. The extra-renal autocrine/paracrine vitamin D system is able to synthesize and degrade locally the active 1,25- D3 necessary to maintain normal cell growth and to counteract mitogenic stimuli. Thus, vitamin D hydroxylases play a prominent role in this process. The present review describes the role of the vitamin D hydroxylases in cancer pathogenesis and the cross-talk between the extra-renal autocrine/paracrine vitamin D system and calcium in cancer prevention.

Genetic sequence variants in vitamin D metabolism pathway genes, serum vitamin D level and outcome in head and neck cancer patients

Although some studies have reported associations between serum vitamin D level and prognosis in several cancers, others have found associations between genetic sequence variants (GSVs) in the vitamin D metabolism pathway genes and outcomes in various cancers including head and neck cancer (HNC). We comprehensively evaluated the association and interaction of GSVs in vitamin D metabolism pathway genes and their regulatory effects on circulatory serum vitamin D level in HNC outcome. We systemically evaluated the association of 89 tagging and candidate-based GSVs in six major vitamin D metabolism pathway genes (VDR, GC, CYP24A1, CYP27A1, CYP27B1 and CYP2R1) and the circulating serum vitamin D level with overall survival (OS) and second primary cancer (SPC) in 522 Stages I-II radiation-treated patients with HNC. For OS: median follow-up time was 8 years; for SPC, 4.4 years. The most common subsite was the larynx (84%). Three hundred and twelve patients were alive at the end of follow-up for OS. SPCs were diagnosed in 108 patients and were primarily of lung (46%). Serum vitamin D levels were significantly lower in patients carrying the minor alleles of GC:rs4588 and CYP2R1:rs10500804. CYP24A1:rs2296241 was significantly associated with OS and CYP2R1:rs1993116 was with SPC. These two GSVs remained significantly associated after adjusting for serum vitamin D level and important clinical factors. GSVs in the vitamin D metabolism pathway genes were associated with disease outcomes in HNC patients; however, these GSVs are different from those affecting serum vitamin D levels.

Serum 25-hydroxyvitamin D, vitamin A, and lung cancer mortality in the US population: a potential nutrient-nutrient interaction

OBJECTIVE

Excess vitamin A may interrupt vitamin D-mediated transcription of target genes. This study investigated whether serum 25-hydroxyvitamin D [25(OH)D] concentrations were associated with lung cancer mortality, and whether this association varied by excess circulating vitamin A and vitamin A/β-carotene supplement use.

METHOD

We analyzed 16,693 men and women in the Third National Health and Nutrition Examination Survey (NHANES III), 1988-1994. Lung cancer mortality (n = 258, 104 were former smokers and 23 were never smokers) were identified through National Death Index as of 2006. Serum 25(OH)D was measured by a radioimmunoassay. Vitamin A biomarkers including serum retinol, β-carotene, and retinyl esters were measured by HPLC. Supplement use for the past month was obtained by self-report. Multivariate-adjusted hazard ratios (HR) were estimated by Cox proportional hazard models.

RESULTS

There was no association of serum 25(OH)D with overall lung cancer mortality. Among nonsmokers, ≥44 vs. <44 nmol/L of serum 25(OH)D was associated with a decreased risk (HR = 0.53, 95 % CI = 0.31-0.92, former/never smokers and HR = 0.31, 95 % CI = 0.13-0.77, distant-former [quit ≥20 years]/never smokers). The associations were not observed among participants with excess circulating vitamin A (serum retinyl esters ≥7.0 μg/dL or the ratio of retinyl esters to retinol ≥0.08) or vitamin A/β-carotene supplement users. However, statistical evidence to support effect modification of vitamin A was less clear.

CONCLUSIONS

Serum 25(OH)D concentrations were inversely associated with lung cancer mortality in nonsmokers. The beneficial association was diminished among those with excess circulating vitamin A or vitamin A/β-carotene supplement users.

Association analyses identify multiple new lung cancer susceptibility loci and their interactions with smoking in the Chinese population

To find additional susceptibility loci for lung cancer, we tested promising associations from our previous genome-wide association study (GWAS) of lung cancer in the Chinese population in an extended validation sample size of 7,436 individuals with lung cancer (cases) and 7,483 controls. We found genome-wide significant (P < 5.0 × 10(-8)) evidence for three additional lung cancer susceptibility loci at 10p14 (rs1663689, close to GATA3, P = 2.84 × 10(-10)), 5q32 (rs2895680 in PPP2R2B-STK32A-DPYSL3, P = 6.60 × 10(-9)) and 20q13.2 (rs4809957 in CYP24A1, P = 1.20 × 10(-8)). We also found consistent associations for rs247008 at 5q31.1 (IL3-CSF2-P4HA2, P = 7.68 × 10(-8)) and rs9439519 at 1p36.32 (AJAP1-NPHP4, P = 3.65 × 10(-6)). Four of these loci showed evidence for interactions with smoking dose (P = 1.72 × 10(-10), P = 5.07 × 10(-3), P = 6.77 × 10(-3) and P = 4.49 × 10(-2) for rs2895680, rs4809957, rs247008 and rs9439519, respectively). These results advance our understanding of lung cancer susceptibility and highlight potential pathways that integrate genetic variants and smoking in the development of lung cancer.

Polymorphisms related to the serum 25-hydroxyvitamin D level and risk of myocardial infarction, diabetes, cancer and mortality. The Tromsø Study

OBJECTIVE

Low serum 25(OH)D levels are associated with cardiovascular risk factors, and also predict future myocardial infarction (MI), type 2 diabetes (T2DM), cancer and all-cause mortality. Recently several single nucleotide polymorphisms (SNPs) associated with serum 25-hydroxyvitamin D (25(OH)D) level have been identified. If these relations are causal one would expect a similar association between these SNPs and health.

METHODS

DNA was prepared from subjects who participated in the fourth survey of the Tromsø Study in 1994-1995 and who were registered with the endpoints MI, T2DM, cancer or death as well as a randomly selected control group. The endpoint registers were complete up to 2007-2010. Genotyping was performed for 17 SNPs related to the serum 25(OH)D level.

RESULTS

A total of 9528 subjects were selected for genetic analyses which were successfully performed for at least one SNP in 9471 subjects. Among these, 2025 were registered with MI, 1092 with T2DM, 2924 with cancer and 3828 had died. The mean differences in serum 25(OH)D levels between SNP genotypes with the lowest and highest serum 25(OH)D levels varied from 0.1 to 7.8 nmol/L. A genotype score based on weighted risk alleles regarding low serum 25(OH)D levels was established. There was no consistent association between the genotype score or individuals SNPs and MI, T2DM, cancer, mortality or risk factors for disease. However, for rs6013897 genotypes (located at the 24-hydroxylase gene (CYP24A1)) there was a significant association with breast cancer (P<0.05).

CONCLUSION

Our results do not support nor exclude a causal relationship between serum 25(OH)D levels and MI, T2DM, cancer or mortality, and our observation on breast cancer needs confirmation. Further genetic studies are warranted, particularly in populations with vitamin D deficiency.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01395303.

CYP24 inhibition preserves 1α,25-dihydroxyvitamin D(3) anti-proliferative signaling in lung cancer cells

Human lung tumors aberrantly express the 1α,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3))-catabolizing enzyme, CYP24. We hypothesized that CYP24 reduces 1,25(OH)(2)D(3)-mediated transcription and allows lung cancer cells to escape its growth-inhibitory action. To test this, H292 lung cancer cells and the CYP24-selective inhibitor CTA091 were utilized. In H292 cells, CTA091 reduces 1,25(OH)(2)D(3) catabolism, significantly increases 1,25(OH)(2)D(3)-mediated growth inhibition, and increases 1,25(OH)(2)D(3) effects on induced and repressed genes in gene expression profiling studies. Pathway mapping of repressed genes uncovered cell cycle as a predominant 1,25(OH)(2)D(3) target. In H292 cells, 1,25(OH)(2)D(3) significantly decreases cyclin E2 levels and induces G(0)/G(1) arrest. A broader set of cyclins is down-regulated when 1,25(OH)(2)D(3) is combined with CTA091, and cell cycle arrest further increases. Effects of CTA091 on 1,25(OH)(2)D(3) signaling are vitamin D receptor-dependent. These data provide evidence that CYP24 limits 1,25(OH)(2)D(3) anti-proliferative signaling in cancer cells, and suggest that CTA091 may be beneficial in preserving 1,25(OH)(2)D(3) action in lung cancer.

Characterization of vitamin D receptor (VDR) in lung adenocarcinoma

PURPOSE

The anti-proliferative effects of 1α,25-dihydroxyvitamin D(3) (1,25-D(3), calcitriol, the active form of vitamin D) are mediated by the nuclear vitamin D receptor (VDR). In the present study, we characterized VDR expression in lung adenocarcinoma (AC).

EXPERIMENTAL DESIGN

We examined VDR mRNA expression using a quantitative real-time PCR (qRT-PCR) in 100 patients who underwent surgery for lung AC. In a subset of these patients (n=89), we examined VDR protein expression using immunohistochemistry. We also examined the association of VDR protein expression with circulating serum levels of 25-hydroxyvitamin D(3) (25-D(3)) and 1,25-D(3). The antiproliferative effects and cell cycle arrest of 1,25-D(3) were examined using lung cancer cell lines with high (SKLU-1) as well as low (A549) expression of VDR mRNA.

RESULTS

Higher VDR expression correlates with longer survival after adjusting for age, sex, disease stage and tumor grade (HR 0.73, 95% CI 0.58-0.91). In addition, there was a positive correlation (r=0.38) between serum 1,25-D(3) and tumor VDR protein expression. A greater anti-proliferative effect of 1,25-D(3) was observed in high compared to low VDR-expressing cell lines; these effects corresponded to G1 cell cycle arrest; this was associated with a decline in cyclin D1, S-phase kinase protein 2 (Skp2), retinoblastoma (Rb) and minichromosome maintenance 2 (MCM2) proteins involved in S-phase entry.

CONCLUSIONS

Increased VDR expression in lung AC is associated with improved survival. This may relate to a lower proliferative status and G1 arrest in high VDR-expressing tumors.

Hershberger P. A local effect of CYP24 inhibition on lung tumor xenograft exposure to 1,25-dihydroxyvitamin D(3) is revealed using a novel LC-MS/MS assay

The vitamin D(3) catabolizing enzyme, CYP24, is frequently over-expressed in tumors, where it may support proliferation by eliminating the growth suppressive effects of 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)). However, the impact of CYP24 expression in tumors or consequence of CYP24 inhibition on tumor levels of 1,25(OH)(2)D(3)in vivo has not been studied due to the lack of a suitable quantitative method. To address this need, an LC-MS/MS assay that permits absolute quantitation of 1,25(OH)(2)D(3) in plasma and tumor was developed. We applied this assay to the H292 lung tumor xenograft model: H292 cells eliminate 1,25(OH)(2)D(3) by a CYP24-dependent process in vitro, and 1,25(OH)(2)D(3) rapidly induces CYP24 expression in H292 cells in vivo. In tumor-bearing mice, plasma and tumor concentrations of 1,25(OH)(2)D(3) reached a maximum of 21.6 and 1.70ng/mL, respectively, following intraperitoneal dosing (20μg/kg 1,25(OH)(2)D(3)). When co-administered with the CYP24 selective inhibitor CTA091 (250μg/kg), 1,25(OH)(2)D(3) plasma levels increased 1.6-fold, and tumor levels increased 2.6-fold. The tumor/plasma ratio of 1,25(OH)(2)D(3) AUC was increased 1.7-fold by CTA091, suggesting that the inhibitor increased the tumor concentrations of 1,25(OH)(2)D(3) independent of its effects on plasma disposition. Compartmental modeling of 1,25(OH)(2)D(3) concentration versus time data confirmed that: 1,25(OH)(2)D(3) was eliminated from plasma and tumor; CTA091 reduced the elimination from both compartments; and that the effect of CTA091 on tumor exposure was greater than its effect on plasma. These results provide evidence that CYP24-expressing lung tumors eliminate 1,25(OH)(2)D(3) by a CYP24-dependent process in vivo and that CTA091 administration represents a feasible approach to increase tumor exposure to 1,25(OH)(2)D(3).

25-Hydroxyvitamin D-24-hydroxylase (CYP24A1): its important role in the degradation of vitamin D

CYP24A1 is the cytochrome P450 component of the 25-hydroxyvitamin D(3)-24-hydroxylase enzyme that catalyzes the conversion of 25-hydroxyvitamin D(3) (25-OH-D(3)) and 1,25-dihydroxyvitamin D(3) (1,25-(OH)(2)D(3)) into 24-hydroxylated products, which constitute the degradation of the vitamin D molecule. This review focuses on recent data in the CYP24A1 field, including biochemical, physiological and clinical developments. Notable among these are: the first crystal structure for rat CYP24A1; mutagenesis studies which change the regioselectivity of the enzyme; and the finding that natural inactivating mutations of CYP24A1 cause the genetic disease idiopathic infantile hypercalcemia (IIH). The review also discusses the emerging correlation between rising serum phosphate/FGF-23 levels and increased CYP24A1 expression in chronic kidney disease, which in turn underlies accelerated degradation of both serum 25-OH-D(3) and 1,25-(OH)(2)D(3) in this condition. This review concludes by evaluating the potential clinical utility of blocking this enzyme with CYP24A1 inhibitors in various disease states.

Short-term and long-term consequences and concerns regarding valid assessment of vitamin D deficiency: comparison of recent food supplementation and clinical guidance reports

PURPOSE OF REVIEW

The function and use of vitamin D supplementation has become very controversial. This review attempts to provide a balanced perspective with respect to the experimental findings published in the past 18 months.

RECENT FINDINGS

The recent contrasts between the Institute of Medicine (IOM) report and the Endocrine Societies report have caused great confusion with respect to the dietary requirement for vitamin D as well as the amount of circulating 25-hydroxyvitamin D that is desirable. Much recent data contradict the suggestions of the IOM report with respect to vitamin D's role in chronic disease such as cancer, cardiovascular function, immune function and autoimmune ailments such as multiple sclerosis.

SUMMARY

Controversy regarding supplementation with vitamin D is fueled by the different purposes of the IOM (guidance for food fortification and not to individualized patient care) and the Endocrine Societies (patient care) reports. Healthcare providers should formulate their own opinions with respect to vitamin D as it pertains to the care of their patient.