Antineoplastic agents target the 25-hydroxyvitamin D3 24-hydroxylase messenger RNA for degradation: implications in anticancer activity

The Non-Genomic Actions of Vitamin D

Since its discovery in 1920, a great deal of effort has gone into investigating the physiological actions of vitamin D and the impact its deficiency has on human health. Despite this intense interest, there is still disagreement on what constitutes the lower boundary of adequacy and on the Recommended Dietary Allowance. There has also been a major push to elucidate the biochemistry of vitamin D, its metabolic pathways and the mechanisms that mediate its action. Originally thought to act by altering the expression of target genes, it was realized in the mid-1980s that some of the actions of vitamin D were too rapid to be accounted for by changes at the genomic level. These rapid non-genomic actions have attracted as much interest as the genomic actions and they have spawned additional questions in an already busy field. This mini-review attempts to summarise the in vitro and in vivo work that has been conducted to characterise the rapid non-genomic actions, the mechanisms that give rise to these properties and the roles that these play in the overall action of vitamin D at the cellular level. Understanding the effects of vitamin D at the cellular level should enable the design of elegant human studies to extract the full potential of vitamin D to benefit human health.

26,26,26,27,27,27-Hexadeuterated-1,25-Dihydroxyvitamin D3 (1,25D-d6) As Adjuvant of Chemotherapy in Breast Cancer Cell Lines

It has been demonstrated that 1,25-dihydroxyvitamin D₃ (1,25D) and some of its analogues have antitumor activity. 1,25D labeled with deuterium (26,26,26,27,27,27-hexadeuterated 1α,25-dihydroxyvitamin D₃, or 1,25D-d₆) is commonly used as internal standard for 1,25D liquid chromatography-mass spectrometry (LC-MS) quantification. In the present study using human breast cancer cell lines, the biological activity of 1,25D-d₆ administered alone and in combination with two commonly used antineoplastic agents, 5-fluorouracil and etoposide, was evaluated. Using an MTT assay, flow cytometry, and western blots, our data demonstrated that 1,25D-d₆ has effects similar to the natural hormone on cell proliferation, cell cycle, and apoptosis. Furthermore, the combination of 1,25D-d₆ and etoposide enhances the antitumoral effects of both compounds. Interestingly, the antitumoral effect is higher in the more aggressive MDA-MB-231 breast cancer cell line. Our data indicate that 1,25D-d₆ administered alone or in combination with chemotherapy could be a good experimental method for accurately quantifying active 1,25D levels in cultures or in biological fluids, on both in vitro breast cancer cell lines and in vivo animal experimental models.

[The role of vitamin D in the prevention and the additional therapy of cancers]

The active metabolite of vitamin D apart from a crucial role in maintaining mineral homeostasis and skeletal functions, has antiproliferative, apoptosis and differentiation inducing as well as immunomodulatory effects in cancer. It is well known that with increasing sunshine exposure the incidence of breast, prostate and colorectal cancer is decreasing. A number of in vitro and in vivo experiments documented the effects of vitamin D in the inhibition of the tumorigenesis. In studying the role of vitamin D in cancer, it is imperative to examine the potential pathways that control local tissue levels of vitamin D. The enzyme 24-hydroxylase converts the active vitamin D to inactive metabolite. Extra-renal production of this enzyme is observed and has been increasingly recognized as present in cancer cells. This enzyme is rate limiting for the amount of local vitamin D in cancer tissues and elevated expression is associated with an adverse prognosis. 24-hydroxylase may be a predictive marker of vitamin D efficacy in patients with cancer as an adjunctive therapy. There are many vitamin D analogs with no pronounced hypercalcemizing effects. Some analogs are in phase 1 and 2 clinical test, and they might have a role in the therapy of several types of cancer. At present our main task is to make an effort to decrease the vitamin D deficiency in Hungary. Speer G. The D-day. The role of vitamin D in the prevention and the additional therapy of cancers.

The candidate oncogene CYP24A1: A potential biomarker for colorectal tumorigenesis

The main autocrine/paracrine role of the active metabolite of vitamin D(3), 1alpha,25-dihydroxyvitamin D(3) (1,25-D(3)), is inhibition of cell growth and induction of cell differentiation and/or apoptosis. Synthesis and degradation of the secosteroid occurs not only in the kidney but also in normal tissue or malignant extrarenal tissues such as the colon. Because 25-hydroxyvitamin D(3) 24-hydroxylase (CYP24A1) is considered to be the main enzyme determining the biological half-life of 1,25-D(3), we have examined expression of the CYP24A1 mRNA (by real-time RT-PCR) and protein (by immunohistochemistry) in normal human colon mucosa, colorectal adenomas, and adenocarcinomas in 111 patients. Although 76% of the normal and benign colonic tissue was either completely devoid of or expressed very low levels of CYP24A1, in the majority of the adenocarcinomas (69%), the enzyme was present at high concentrations. A parallel increased expression of the proliferation marker Ki-67 in the same samples suggests that overexpression of CYP24A1 reduced local 1,25-D(3) availability, decreasing its antiproliferative effect.

A novel SNP in a vitamin D response element of the CYP24A1 promoter reduces protein binding, transactivation, and gene expression

The active form of vitamin D (1alpha,25(OH)(2)D(3)) is known to have antiproliferative effects and has been implicated in cancers of the colon, breast, and prostate. These cancers occur more frequently among African Americans than Caucasians, and individuals with African ancestry are known to have approximately twofold lower levels of serum vitamin D (25(OH)D) compared with individuals of European ancestry. However, epidemiological studies of the vitamin D receptor (VDR) have shown inconsistent associations with cancer risk, suggesting that differences in other genes in the pathway may be important. We sought to identify functionally significant polymorphic variants in CYP24A1, a gene that is highly inducible by 1alpha,25(OH)(2)D(3) and that encodes the primary catabolic enzyme in the pathway. Here we report the identification of six novel SNPs in the human CYP24A1 promoter, including one at nucleotide -279 occurring within the distal vitamin D response element (VDRE2). Our experiments demonstrate that the VDRE2 variant results in decreased protein binding and transactivation in vitro, and reduced expression of CYP24A1 in cultured primary human lymphocytes provides evidence for an effect in vivo. This variant was only observed in our African American population, and represents a first step toward understanding differences in disease risk among racial/ethnic groups.