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.

Considerable preclinical and epidemiologic data suggest that vitamin D may play a role in the pathogenesis, progression and therapy of cancer. Numerous epidemiologic studies support the hypothesis that individuals with lower serum vitamin D levels have a higher risk of a number of cancers. Measures of vitamin D level in such studies include both surrogate estimates of vitamin D level (residence in more northern latitudes, history of activity and sun exposure) as well as measured serum 25(OH) cholecalciferol levels. Perhaps the most robust of these epidemiologic studies is that of Giovannucci and colleagues who developed and validated an estimate of serum 25(OH) cholecalciferol level and reported that among more than 40,000 individuals in the Health professionals Study an increase in 25(OH) cholecalciferol level of 62.5ng/mL was associated with a reduction in the risk of head/neck, esophagus, pancreas cancers and acute leukemia by >50%. Unfortunately very limited data are available to indicate whether or not giving vitamin D supplements reduces the risk of cancer. Many preclinical studies indicate that exposing cancer cells -as well as vascular endothelial cells derived from tumors -to high concentrations of active metabolites of vitamin D halts progression through cell cycle, induces apoptosis and will slow or stop the growth of tumors in vivo. There are no data that one type of cancer is more or less susceptible to the effects of vitamin D. Vitamin D also potentiates the antitumor activity of a number of types of cytotoxic anticancer agents in in vivo preclinical models. Vitamin D analogues initiate signaling through a number of important pathways, but the pathway(s) essential to the antitumor activities of vitamin D are unclear. Clinical studies of vitamin D as an antitumor agent have been hampered by the lack of a suitable pharmaceutical preparation for clinical study. All commercially available formulations are inadequate because of the necessity to administer large numbers of caplets and the poor "bioavailability" of calcitriol (the most carefully studied analogue) at these high doses. Preclinical data suggest that very high exposures to calcitriol are necessary for the antitumor effects. Clinical data do indicate that very high doses of calcitriol (>100mcg weekly, intravenously and 0.15mcg/kg weekly orally) can be given safely. The maximum tolerated dose (MTD) of calcitriol is unclear. While a 250 patient trial in men with castration resistant prostate cancer (CRPC) comparing docetaxel (36mg/sqm weekly) +/-calcitriol 0.15mcg/kg indicated that calcitriol was very safe, may have reduced to death rate, an adequately powered (1000 patients) randomized study of weekly docetaxel + calcitriol vs q3 week docetaxel was negative. The limitations of this trial were the unequal chemotherapy arms compared in this study and the failure to use an optimal biologic dose or MTD of calcitriol. In view of the substantial preclinical and epidemiologic data supporting the potential role of vitamin D in cancer, careful s...

The acetylating enzyme, spermidine/spermine N 1 -acetyltransferase, participates in polyamine homeostasis by regulating polyamine export and catabolism. Previously, we reported that overexpression of the enzyme in cultured tumor cells and mice activates metabolic flux through the polyamine pathway and depletes the N 1 -acetyltransferase coenzyme and fatty acid precursor, acetyl-CoA. Here, we investigate this possibility in spermidine/spermine N 1 -acetyltransferase transgenic mice in which the enzyme is systemically overexpressed and in spermidine/spermine N 1 -acetyltransferase knock-out mice. Tissues of the former were characterized by increased N 1 -acetyltransferase activity, a marked elevation in tissue and urinary acetylated polyamines, a compensatory increase in polyamine biosynthetic enzyme activity, and an increase in metabolic flux through the polyamine pathway. These polyamine effects were accompanied by a decrease in white adipose acetyl-and malonyl-CoA pools, a major (20-fold) increase in glucose and palmitate oxidation, and a distinctly lean phenotype. In SSAT-ko mice, the opposite relationship between polyamine and fat metabolism was observed. In the absence of N 1 -acetylation of polyamines, there was a shift in urinary and tissue polyamines indicative of a decline in metabolic flux. This was accompanied by an increase in white adipose acetyl-and malonyl-CoA pools, a decrease in adipose palmitate and glucose oxidation, and an accumulation of body fat. The latter was further exaggerated under a high fat diet, where knock-out mice gained twice as much weight as wild-type mice. A model is proposed whereby the expression status of spermidine/spermine N 1 -acetyltransferase alters body fat accumulation by metabolically modulating tissue acetyl-and malonyl-CoA levels, thereby influencing fatty acid biosynthesis and oxidation.The polyamines putrescine (Put), 3 spermidine (Spd), and spermine (Spm) are known for their critical role in supporting cell proliferation, albeit in ways that have not yet been clearly defined. For the most part, polyamines do not incorporate into macromolecules but rather bind electrostatically to negatively charged molecules, such as DNA, RNA, and phospholipids. Thus, as metabolically distinct entities, homeostatic control of intracellular polyamines is critical to their role in supporting cell proliferation. This is achieved by effector systems that regulate biosynthesis, catabolism, uptake, and export of these molecules. The enzyme, spermidine/spermine N 1 -acetyltransferase (SSAT), catalyzes the transfer of acetyl groups from acetyl-CoA to the terminal amines of polyamines and, thus, readies the molecule for export or catabolism via polyamine oxidase. The enzyme is short lived, sensitively regulated by intracellular polyamine pools, and highly inducible by polyamine analogues and various cytotoxic agents (1, 2).Although most antiproliferative strategies targeting the polyamine pathway seek to deplete intracellular pools by inhibiting biosynthesis, we have been investigating t...

Understanding the genetic architecture of cancer pathways that distinguishes subsets of human cancer is critical to developing new therapies that better target tumors based on their molecular expression profiles. In this study, we identify an integrated gene signature from multiple transgenic models of epithelial cancers intrinsic to the functions of the Simian virus 40 T/t-antigens that is associated with the biological behavior and prognosis for several human epithelial tumors. This genetic signature, composed primarily of genes regulating cell replication, proliferation, DNA repair, and apoptosis, is not a general cancer signature. Rather, it is uniquely activated primarily in tumors with aberrant p53, Rb, or BRCA1 expression but not in tumors initiated through the overexpression of myc, ras, her2/neu, or polyoma middle T oncogenes. Importantly, human breast, lung, and prostate tumors expressing this set of genes represent subsets of tumors with the most aggressive phenotype and with poor prognosis. The T/t-antigen signature is highly predictive of human breast cancer prognosis. Because this class of epithelial tumors is generally intractable to currently existing standard therapies, this genetic signature identifies potential targets for novel therapies directed against these lethal forms of cancer. Because these genetic targets have been discovered using mammary, prostate, and lung T/t-antigen mouse cancer models, these models are rationale candidates for use in preclinical testing of therapies focused on these biologically important targets. [Cancer Res 2007;67(17):8065-80]

Calcitriol, a regulator of calcium homeostasis with antitumor properties, is degraded by the product of the CYP24A1 gene, which is downregulated in human prostate cancer by unknown mechanisms. We found that CYP24A1 expression is inversely correlated with promoter DNA methylation in prostate cancer cell lines. Treatment with the DNA methyltransferase inhibitor 5-aza-2′-deoxycytidine (DAC) activates CYP24A1 expression in prostate cancer cells. In vitro methylation of the CYP24A1 promoter represses its promoter activity. Furthermore, inhibition of histone deacetylases by trichostatin A (TSA) enhances the expression of CYP24A1 in prostate cancer cells. Quantitative chromatin immunoprecipitation-PCR (ChIP-qPCR) reveals that specific histone modifications are associated with the CYP24A1 promoter region. Treatment with TSA increases H3K9ac and H3K4me2 and simultaneously decreases H3K9me2 at the CYP24A1 promoter. ChIP-qPCR assay reveals that treatment with DAC and TSA increases the recruitment of vitamin D receptor to the CYP24A1 promoter. Reverse transcriptase-PCR analysis of paired human prostate samples revealed that CYP24A1 expression is downregulated in prostate malignant lesions compared with adjacent histologically benign lesions. Bisulfite pyrosequencing shows that CYP24A1 gene is hypermethylated in malignant lesions compared with matched benign lesions. Our findings indicate that repression of CYP24A1 gene expression in human prostate cancer cells is mediated in part by promoter DNA methylation and repressive histone modifications.