1alpha,25-dihydroxyvitamin D(3)-26,23-lactone analogs antagonize differentiation of human leukemia cells (HL-60 cells) but not of human acute promyelocytic leukemia cells (NB4 cells)

The Centennial Collection of VDR Ligands: Metabolites, Analogs, Hybrids and Non-Secosteroidal Ligands

Since the discovery of vitamin D a century ago, a great number of metabolites, analogs, hybrids and nonsteroidal VDR ligands have been developed. An enormous effort has been made to synthesize compounds which present beneficial properties while attaining lower calcium serum levels than calcitriol. This structural review covers VDR ligands published to date.

Inhibitors for the Vitamin D Receptor-Coregulator Interaction

The vitamin D receptor (VDR) belongs to the superfamily of nuclear receptors and is activated by the endogenous ligand 1,25-dihydroxyvitamin D3. The genomic effects mediated by VDR consist of the activation and repression of gene transcription, which includes the formation of multiprotein complexes with coregulator proteins. Coregulators bind many nuclear receptors and can be categorized according to their role as coactivators (gene activation) or corepressors (gene repression). Herein, different approaches to develop compounds that modulate the interaction between VDR and coregulators are summarized. This includes coregulator peptides that were identified by creating phage display libraries. Subsequent modification of these peptides including the introduction of a tether or nonhydrolyzable bonds resulted in the first direct VDR-coregulator inhibitors. Later, small molecules that inhibit VDR-coregulator inhibitors were identified using rational drug design and high-throughput screening. Early on, allosteric inhibition of VDR-coregulator interactions was achieved with VDR antagonists that change the conformation of VDR and modulate the interactions with coregulators. A detailed discussion of their dual agonist/antagonist effects is given as well as a summary of their biological effects in cell-based assays and in vivo studies.

Vitamin D receptor ligands: the impact of crystal structures

INTRODUCTION

In the past years, the biologically active form of vitamin D(3), 1α,25-dihydroxyvitamin D(3) (1α,25(OH)(2)D(3)), has received large appreciation due to the broad physiological impact of the hormone and its nuclear receptor, the transcription factor vitamin D receptor (VDR). Recently, the understanding of VDR actions has progressed greatly, due to VDR crystal structures with various ligands.

AREAS COVERED

This review will present and discuss new synthetic agonistic and antagonistic 1α,25(OH)(2)D(3) analogs in the context of the recent insights provided by VDR crystal structures.

EXPERT OPINION

During the last 5 years, a large number of new 1α,25(OH)(2)D(3) analogs, many of which have an interesting functional profile, have been patented. Moreover, for a surprisingly high number of 1α,25(OH)(2)D(3) analogs, the crystal structure data of their complex with the VDR is available. This structural information provides important insight into the functional potential of the VDR ligands and explains their agonistic and antagonistic action. However, so far, only for a few VDR ligands, a rational design, based on crystal structure information, has been applied. The design of future analogs may also take the specificity of co-factor interaction into account, in order to create selective VDR modulators.

Discovery of candidate serum proteomic and metabolomic biomarkers in ankylosing spondylitis

Ankylosing Spondylitis (AS) is a common inflammatory rheumatic disease with a predilection for the axial skeleton, affecting 0.2% of the population. Current diagnostic criteria rely on a composite of clinical and radiological changes, with a mean time to diagnosis of 5 to 10 years. In this study we employed nano liquid-chromatography mass spectrometry analysis to detect and quantify proteins and small compounds including endogenous peptides and metabolites in serum from 18 AS patients and nine healthy individuals. We identified a total of 316 proteins in serum, of which 22 showed significant up- or down-regulation (p < 0.05) in AS patients. Receiver operating characteristic analysis of combined levels of serum amyloid P component and inter-α-trypsin inhibitor heavy chain 1 revealed high diagnostic value for Ankylosing Spondylitis (area under the curve = 0.98). We also depleted individual sera of proteins to analyze endogenous peptides and metabolic compounds. We detected more than 7000 molecular features in patients and healthy individuals. Quantitative MS analysis revealed compound profiles that correlate with the clinical assessment of disease activity. One molecular feature identified as a Vitamin D3 metabolite—(23S,25R)-25-hydroxyvitamin D3 26,23-peroxylactone—was down-regulated in AS. The ratio of this vitamin D metabolite versus vitamin D binding protein serum levels was also altered in AS as compared with controls. These changes may contribute to pathological skeletal changes in AS. Our study is the first example of an integration of proteomic and metabolomic techniques to find new biomarker candidates for the diagnosis of Ankylosing Spondylitis.

Ultraviolet B and incidence rates of leukemia worldwide

BACKGROUND

Recent research has suggested a relationship between vitamin D deficiency and risk of leukemia.

PURPOSE

Using data from the UN cancer database, GLOBOCAN, this study will determine whether a relationship exists for latitude and ultraviolet B (UVB) irradiance with incidence rates of leukemia in 175 countries.

METHODS

Multiple regression was used to analyze the independent association between UVB and age-adjusted incidence rates of leukemia in 139 countries in 2002. This study controlled for dietary data on intake of energy from animal sources and per capita healthcare expenditures. The analyses were performed in 2009.

RESULTS

People residing in the highest-latitude countries had the highest rates of leukemia in both men (R(2)=0.34, p<0.0001) and women (R(2)=0.24, p<0.0001). In men, UVB was independently inversely associated with leukemia incidence rates (p≤0.001), whereas animal energy consumption (p=0.02) and per capita healthcare expenditures (p≤0.0001) were independently positively associated (R(2) for model=0.61, p≤0.0001). In women, UVB adjusted for cloud cover was independently inversely associated with leukemia incidence rates (p≤0.01), whereas animal energy consumption (p≤0.05) and per capita healthcare expenditures (p=0.0002) were independently positively associated (R(2) for model=0.51, p<0.0001).

CONCLUSIONS

Countries with low UVB had higher age-adjusted incidence rates of leukemia. This suggests the possibility that low serum 25-hydroxyvitamin D status, because of lower levels of UVB, somehow might predict the development of leukemia.

3D-QSAR Studies on C24-Monoalkylated Vitamin D3 26,23-Lactones and their C2α-Modified Derivatives with Inhibitory Activity to Vitamin D Receptor

The ligand-based three-dimensional quantitative structure-activity relationship (3D-QSAR) for 82 inhibitors of 25-dehydro-1α-hydroxyvitamin D3 -26,23-lactone analogs has been studied by using comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) models. The established CoMFA model in training set gives a cross-validated q(2) value of 0.516 and a non-cross-validated rncv (2) value of 0.667, while the CoMSIA model results in q(2) =0.517 and rncv (2) =0.632. In general, the predictive ability of the CoMFA model is superior to that of the CoMSIA model, with rpred (2) =0.639 for the CoMFA and rpred (2) =0.619 for the CoMSIA model. Based on the CoMFA contour maps, some key structural characters of vitamin D3 analogs responsible for inhibitory activity are identified, and some new C2α-modified 24-alkylvitamin D3 lactone analogs with high predicted pIC50 values are designed. The ligand functional group mutations by FEP simulation and docking studies reveal the rationality of the molecular design.

Vitamin D3-driven signals for myeloid cell differentiation--implications for differentiation therapy

Primitive myeloid leukemic cell lines can be driven to differentiate to monocyte-like cells by 1alpha,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), and, therefore, 1,25(OH)(2)D(3) may be useful in differentiation therapy of myeloid leukemia and myelodysplastic syndromes (MDS). Recent studies have provided important insights into the mechanism of 1,25(OH)(2)D(3)-stimulated differentiation. For myeloid progenitors to complete monocytic differentiation a complex network of intracellular signals has to be activated and/or inactivated in a precise temporal and spatial pattern. 1,25(OH)(2)D(3) achieves this change to the 'signaling landscape' by (i) direct genomic modulation of the level of expression of key regulators of cell signaling and differentiation pathways, and (ii) activation of intracellular signaling pathways. An improved understanding of the mode of action of 1,25(OH)(2)D(3) is facilitating the development of new therapeutic regimens.

On the mechanism underlying (23S)-25-dehydro-1alpha(OH)-vitamin D3-26,23-lactone antagonism of hVDRwt gene activation and its switch to a superagonist

(23S)-25-Dehydro-1alpha(OH)-vitamin D(3)-26,23-lactone (MK) is an antagonist of the 1alpha,25(OH)(2)-vitamin D(3) (1,25D)/human nuclear vitamin D receptor (hVDR) transcription initiation complex, where the activation helix (i.e. helix-12) is closed. To study the mode of antagonism of MK an hVDR mutant library was designed to alter the free molecular volume in the region of the hVDR ligand binding pocket occupied by the ligand side-chain atoms (i.e. proximal to helix-12). The 1,25D-hVDR structure-function studies demonstrate that 1) van der Waals contacts between helix-12 residues Leu-414 and Val-418 and 1,25D enhance the stability of the closed helix-12 conformer and 2) removal of the side-chain H-bonds to His-305(F) and/or His-397(F) have no effect on 1,25D transactivation, even though they reduce the binding affinity of 1,25D. The MK structure-function results demonstrate that the His-305, Leu-404, Leu-414, and Val-418 mutations, which increase the free volume of the hVDR ligand binding pocket, significantly enhance MK antagonist potency. Surprisingly, the H305F and H305F/H397F mutations turn MK into a VDR superagonist (EC(50) approximately 0.05 nm) but do not concomitantly alter MK binding affinity. Molecular modeling studies demonstrate that MK antagonism stems from its side chain energetically preferring a pose in the VDR ligand binding pocket where its terminal C26-methylene atom is far removed from helix-12. MK superagonism results from an energetically favored increase in interaction between Leu-404/Val-418 and C26, resulting in an increase in the stability and population of the closed, helix-12 conformer. Finally, the results/model generated, coupled with application of a VDR ensemble allosterics model, provide an understanding for the species specificity of MK.

The vitamin D sterol-vitamin D receptor ensemble model offers unique insights into both genomic and rapid-response signaling

Steroid hormones serve as chemical messengers in a wide number of species and target tissues by transmitting signals that result in both genomic and nongenomic responses. Genomic responses are mediated by the formation of a ligand-receptor complex with its cognate steroid hormone nuclear receptor (NR). Nongenomic responses can be mediated at the plasma membrane by a membrane-localized NR. The focus of this Review is on the structural attributes and molecular mechanisms underlying vitamin D sterol (VDS)-vitamin D receptor (VDR) selective and stereospecific regulation of nongenomic and genomic signaling. The VDS-VDR conformational ensemble model describes how VDSs can selectively initiate or block either nongenomic or genomic biological responses by interacting with two VDR ligand-binding pockets, one kinetically favored by 1alpha,25(OH)(2)D(3) (1,25D) and the other thermodynamically favored. We describe the variables that affect the three major elements of the model: the conformational flexibility of the unliganded (apo) protein, the flexibility of the VDS, and the physicochemical selectivity of the VDR genomic pocket (VDR-GP) and alternative pocket (VDR-AP). We also discuss how these three factors collectively provide a rational explanation for the complexities of VDS regulation of cell biology and highlight the current limitations of the model.

1alpha,25-Dihydroxyvitamin D(3)-26,23-lactam analogues function as vitamin D receptor antagonists in human and rodent cells

(23S,25S)-N-Benzyl-1alpha,25-dihydroxyvitamin D(3)-26,23-lactam ((23S,25S)-N-benzyl-1alpha,25-(OH)(2)D(3)-26,23-lactam, (23S,25S)-DLAM-1P) antagonizes nuclear vitamin D receptor (VDR)-mediated differentiation of human promyelocytic leukemia (HL-60) cells [Y. Kato, Y. Nakano, H. Sano, A. Tanatani, H. Kobayashi, R. Shimazawa, H. Koshino, Y. Hashimoto, K. Nagasawa, Synthesis of 1alpha,25-dihydroxy vitamin D(3)-26,23-lactams (DLAMs), a novel series of 1alpha,25-dihydroxy vitamin D(3) antagonist, Bioorg. Med. Chem. Lett. 14 (2004) 2579-2583]. To enhance its VDR antagonistic actions, we synthesized multiple analogues of 1alpha,25-(OH)(2)D(3)-26,23-lactam. Among these analogues, (23S,25S)-N-phenetyl-1alpha,25-(OH)(2)D(3)-26,23-lactam, ((23S,25S)-DLAM-2P) had the strongest VDR binding affinity, which was 3 times higher than that of (23S,25S)-DLAM-1P. The 1alpha,25-(OH)(2)D(3)-26,23-lactam analogues never induced HL-60 cell differentiation even at 10(-6)M, but (23S,25S)-DLAM-1P and (23S,25S)-DLAM-2P significantly and dose-dependently inhibited HL-60 differentiation induced by 10(-8)M 1alpha,25-dihydroxyvitamin D(3) (1alpha,25-(OH)(2)D(3)). These compounds also inhibited human and mouse cultures of osteoclast formation by marrow cells treated with 1alpha,25-(OH)(2)D(3). Moreover, the 1alpha,25-(OH)(2)D(3)-26,23-lactam analogues minimally induced 25-hydroxyvitamin D(3)-24-hydroxylase gene expression in HL-60 cells and human and mouse osteoblastic cells, but 10(-6)M (23S,25S)-DLAM-1P or (23S,25S)-DLAM-2P significantly blocked 24-hydroxylase gene expression induced by 10(-8)M 1alpha,25-(OH)(2)D(3). (23S,25S)-DLAM-2P was 5-12 times more potent as a vitamin D antagonist than (23S,25S)-DLAM-1P in HL-60 cells, human and mouse bone marrow cultures. These results demonstrate that (23S,25S)-DLAM-1P and (23S,25S)-DLAM-2P antagonize HL-60 cell differentiation and osteoclast formation by human and mouse osteoclast precursors induced by 1alpha,25-(OH)(2)D(3) through blocking VDR-mediated gene transcription. In contrast, (23S)-25-deoxy-1alpha-hydroxyvitamin D(3)-26,23-lactone, which only blocks human VDR, these vitamin D antagonists can block VDR in human cells and rodent cells.

[Creation of highly potent vitamin D receptor antagonists]

Vitamin D receptor antagonist has attracted significant level of interests because of its potential utility in the treatment of Paget's disease, which is known as the most flagrant example of disordered bone remodeling and the second most common bone disease after osteoporosis in Anglo-Saxons. Recent studies on Paget's disease suggested a specific increase in osteoclasts sensitivity to the differentiation activity of active vitamin D(3) as the principal mechanism for abnormal bone formation. We set out to conduct a structure-activity relationship study on the first VDR antagonists of TEI-9647 and TEI-9648 (25-dehydro-1alpha-hydroxyvitamin D(3)-26,23-lactone) toward improved VDR antagonistic activity. Given that both potent agonists and antagonists must have high affinity for the VDR, we hoped that our accumulated knowledge in VDR agonists would help us identify potent antagonists. First, 2alpha-modified TEI-9647 analogs were synthesized, and then, 24-substitution was next investigated to stabilize its lactone structure under the physiological conditions. Finally, 2alpha-modified 24-methyl-, 24,24-dimethyl-25-dehydro-1alpha-hydroxyvitamin D(3)-26,23-lactone analogs were synthesized. It was found that 2alpha,24,24-trimethyl-TEI-9647 was found to possess approximately 90-fold improved antagonistic activity (IC(50) 0.093 nM) over the original TEI-9647 (IC(50) 8.3 nM).

Further Synthetic and Biological Studies on Vitamin D Hormone Antagonists Based on C24-Alkylation and C2α-Functionalization of 25-Dehydro-1α-hydroxyvitamin D3-26,23-lactones

An efficient synthesis and the biological evaluation of 80 novel analogs of 25-dehydro-1alpha-hydroxyvitamin D3-26,23S-lactone 2 (TEI-9647) and its 23R epimer (3) in which the lactone ring was systematically functionalized by introduction of a C1 to C4 primary alkyl group at the C24 position (5 sets of 4 diastereomers), together with their C2alpha-methyl, 3-hydroxypropyl, and 3-hydroxypropoxy-substituted derivatives were described. The triene structure of the vitamin D3 was constructed using palladium-catalyzed alkenylative cyclization of the A-ring precursor enyne with the CD-ring counterpart bromoolefin having the C24-alkylated lactone moiety on the side chain. The CD-ring precursors having 23,24-cis lactones were prepared by using a chromium-mediated syn-selective allylation-lactonization process, and the 23,24-trans lactone derivatives were derived from these via inversion of the C23 stereochemistry. The biological evaluation revealed that both binding affinity for chick vitamin D hormone receptor and antagonistic activity (inhibition of vitamin D hormone induced HL-60 cell differentiation) were affected by the orientation and chain-length of the primary alkyl group on the lactone ring. Furthermore, the C2alpha-functionalization of the C24-alkylated vitamin D3 lactones dramatically enhanced their biological activities. The most potent compound to emerge, (23S,24S)-2alpha-(3-hydroxypropoxy)-24-propyl exhibited almost 1000-fold stronger antagonistic activity (IC50=7.4 pM) than 2 (IC50=6.3 nM).

Highly Potent Vitamin D Receptor Antagonists: Design, Synthesis, and Biological Evaluation

Vitamin D receptor (VDR) antagonists have attracted significant levels of interest because of their potential utility in the treatment of Paget's disease, which is known as the most flagrant example of disordered bone remodeling and the second most common bone disease after osteoporosis in Anglo-Saxons. Recent studies on Paget's disease suggested a specific increase in osteoclasts' sensitivity to the differentiation activity of active vitamin D(3) as the principal mechanism for abnormal bone formation. We set out to conduct a structure-activity relationship study on the first VDR antagonists, TEI-9647 and TEI-9648 (25-dehydro-1alpha-hydroxyvitamin D(3)-26,23-lactone), with the goal of improved VDR antagonistic activity. Given that both potent agonists and antagonists must have high affinity for the VDR, we hoped that our accumulated knowledge in the field of VDR agonists would help us identify potent antagonists. First 2alpha-modified TEI-9647 analogues were synthesized, and then 24-substitution to stabilize the lactone structure under physiological conditions was investigated. Finally, 2alpha-modified 24-methyl-, 24,24-dimethyl-, and 24,24-ethano-25-dehydro-1alpha-hydroxyvitamin D(3)-26,23-lactone analogues were synthesized. The synthesis of the 24,24-ethano-TEI lactone was accomplished through Ru-catalyzed intermolecular enyne metathesis of the alkynone CD-ring side chain with ethylene to give a dienone, followed by regioselective cyclopropanation. It was found that 2alpha,24,24-trimethyl-TEI-9647 (39) possessed an antagonistic activity (IC(50)=0.093 nM) approximately 90 times that of the original TEI-9647 (IC(50)=8.3 nM).

1Alpha,25-dihydroxyvitamin D3-mediated stimulation of steroid sulphatase activity in myeloid leukaemic cell lines requires VDRnuc-mediated activation of the RAS/RAF/ERK-MAP kinase signalling pathway

1Alpha,25-dihydroxyvitamin D(3) (1alpha,25(OH)(2)D(3)) stimulates the activity of steroid sulphatase (STS) in myeloid cells [Hughes et al., 2001, 2005]. This was attenuated by inhibitors of phospholipase D (PLD) (n-butanol, 2,3-diphosphoglyceric acid, C(2)-ceramide) and phosphatidate phosphohydrolase (PAP) (propranolol and chlorpromazine), but was unaffected by inhibitors of phospholipase C. The 1alpha,25(OH)(2)D(3)-induced STS activity was also attenuated by inhibitors of protein kinase Calpha and protein kinase Cdelta (Go 6976, HBDDE and rottlerin), but not by an inhibitor of protein kinase Cbeta (LY379196). Additionally, 1alpha,25(OH)(2)D(3)-induced STS activity was attenuated by inhibitors of RAS (manumycin A), RAF (GW5074), MEK (PD098059 and U1026) and JNK (SP600125), but not p38 (PD169316). 1alpha,25(OH)(2)D(3) produced a rapid and long lasting stimulation of the ERK-MAP kinase signalling cascade in HL60 myeloid leukaemic cells. This 'non-genomic' effect of 1alpha,25(OH)(2)D(3) blocked by pharmacological antagonists of nuclear vitamin D receptors (VDR(nuc)) and does not appear to require hetero-dimerisation with the retinoid-X receptor (RXR). Inhibitors of the Src tyrosine kinase (PP1), RAS (manumycin A), RAS-RAF interactions (sulindac sulphide and RAS inhibitory peptide), RAF (GW5074 or chloroquine), and protein kinase Calpha (HBDDE) abrogated the 1alpha,25(OH)(2)D(3)-stimulated increase in ERK-MAP kinase activity. Taken together, these results show that 1alpha,25(OH)(2)D(3)/VDR(nuc) activation of the RAS/RAF/ERK-MAP kinase signalling pathway plays an important role in augmenting STS activity in human myeloid leukaemic cell lines.

In silico studies using Radial Distribution Function approach for predicting affinity of 1 alpha,25-dihydroxyvitamin D(3) analogues for Vitamin D receptor

The Radial Distribution Function (RDF) approach has been applied to the study of the chick intestinal VDR affinity of 49 Vitamin D analogues. A model able to describe more than 77.5% of the variance in the experimental activity was developed with the use of the mentioned approach. In contrast, none of four different approaches, including the use of Topological, BCUT, Randić molecular profiles and Geometrical descriptors were able to explain more than 55% of the variance in the mentioned property, with the same number of variables in the equation.

A perspective on how the Vitamin D sterol/Vitamin D receptor (VDR) conformational ensemble model can potentially be used to understand the structure-function results of A-ring modified Vitamin D sterols

The steroid hormone 1alpha,25(OH)(2)-Vitamin D(3) (1,25D) activates both genomic and non-genomic intracellular signaling cascades. It is also well recognized that co-incubation of 1,25D with its C-1 epimer, 1beta,25D (HL), suppresses the efficiency of the non-genomic signal activated by 1,25D alone and that its C-3 epimer, 3alpha-1,25D (HJ) is nearly as potent as 1,25D in suppressing PTH secretion, believed to be propagated by 1,25D's genomic signaling. Both these sterols lack the hypercalcemic effect induced by pharmacological doses of 1,25D and have reduced VDR affinity compared to 1,25D, as measured in a steroid competition assay. Recent functional studies suggest that the VDR is required for both non-genomic and genomic signaling. Along these lines we have recently proposed a Vitamin D sterol/VDR conformational ensemble model that posits the VDR contains two distinct, yet overlapping ligand binding sites, and that the potential differential stabilities of 1,25D and HL in these two pockets can be used to explain their different non-genomic signaling properties. The overlapping region is predominantly occupied by the sterol's A-ring when it is bound to either the genomic ligand binding pocket (G-pocket), defined by X-ray crystallography, or the alternative ligand binding pocket (A-pocket), discovered using in silico techniques (directed docking). Therefore, to gain further insight into the potential application of this model we docked the other A-ring diastereomer [(1beta,3alpha)=HH] of 1,25D and its 1- and 3-deoxy forms (25D and CF, respectively) to the A- and G-pockets to assess their potential stabilities in the pockets, relative to 1,25D. The models were then used to provide putative mechanistic arguments for their known structure-function experimental results. This model may provide new insights into how Vitamin D sterols that uncouple the unwanted hypercalcemic effect from attractive growth inhibitory/differentiation properties can do so by differentially stabilizing different subpopulations of VDR conformational ensemble members.

Nongenotropic, Anti-Apoptotic Signaling of 1α,25(OH)2-Vitamin D3 and Analogs through the Ligand Binding Domain of the Vitamin D Receptor in Osteoblasts and Osteocytes

Because sex steroids regulate the life span of bone cells by modulating cytoplasmic kinase activity via a nongenotropic action of their classical receptors, we have explored the possibility that the vitamin D nuclear receptor (VDR) might exhibit similar nongenotropic actions. We report that the conformationally flexible full VDR agonist, 1alpha,25(OH)2-vitamin D3 (1alpha,25(OH)2D3), and the 6-s-cis-locked 1alpha,25(OH)2-lumisterol3 (JN) analog, also acting through the VDR but with poor transcriptional activity, protected murine osteoblastic or osteocytic cells from apoptosis. This effect was reproduced in HeLa cells transiently transfected with either wild type VDR or a mutant consisting of only the VDR ligand binding domain. The VDR ligand binding domain bound [3H]1alpha,25(OH)2D3 as effectively as wild type VDR but did not induce vitamin D response element-mediated transcription. The anti-apoptotic effects of 1alpha,25(OH)2D3 and the 6-s-cis-locked 1alpha,25(OH)2-lumisterol3 analog in calvaria cells were blocked by three cytoplasmic kinase inhibitors: Src kinase inhibitor 4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP1), phosphatidylinositol 3 kinase inhibitor Wortmannin, and the JNK kinase inhibitor SP600125. However, inhibition of p38 with SB203580 or ERK with either U0126 or a transfected dominant negative MEK did not interfere with these anti-apoptotic actions. Further, 1alpha,25(OH)2D3 induced rapid (5 min) association of VDR with Src kinase in OB-6 cells. Finally, actinomycin D or cycloheximide prevented the anti-apoptotic effect of 1alpha,25(OH)2D3, indicating that transcriptional events are also required. These findings suggest that nongenotropic modulation of kinase activity is also a general property of the VDR and that ligands that activate nongenotropic signals, but lack transcriptional activity, display different biological profiles from the steroid hormone 1alpha,25(OH)2D3.

The antagonism between 2-methyl-1,25-dihydroxyvitamin D3 and 2-methyl-20-epi-1,25-dihydroxyvitamin D3 in non-genomic pathway-mediated biological responses induced by 1alpha,25-dihydroxyvitamin D3 assessed by NB4 cell differentiation

We synthesized all eight possible A-ring diastereomers of 2-methyl substituted analogs of 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)2D3] and also all eight A-ring diastereomers of 2-methyl-20-epi-1alpha,25(OH)2D3. Their biological activities, especially the antagonistic effect on non-genomic pathway-mediated responses induced by 1alpha,25(OH)2D3 or its 6-s-cis-conformer analog, 1alpha,25(OH)2-lumisterol3, were assessed using an NB4 cell differentiation system. Antagonistic activity was observed for the 1beta-hydroxyl diastereomers, including 2beta-methyl-1beta,25(OH)2D3 and 2beta-methyl-3-epi-1beta,25(OH)2D3. Very interestingly, 2beta-methyl-3-epi-1alpha,25(OH)2D3 also antagonized the non-genomic pathway, despite its 1alpha-hydroxyl group. Other 1alpha-hydroxyl diastereomers did not show antagonistic activity. 20-epimerization diminished the antagonistic effect of all of these analogs on the non-genomic pathway. These findings suggested that the combination of the 2-methyl substitution of the A-ring and 20-epimerization of the side chain could alter the biological activities in terms of antagonism of non-genomic pathway-mediated biological response. Based on a previous report, 2-methyl substitution alters the equilibrium of the A-ring conformation between the alpha- and beta-chair conformers. The 2beta-methyl diastereomers, which exhibited antagonism on non-genomic pathway-mediated response, were considered to prefer the beta-conformer. Further examination to elucidate the relationship between the altered ligand shape and receptors interaction will be important for molecular level understanding of the mechanism of antagonism of the non-genomic pathway.

A structural basis for the species-specific antagonism of 26,23-lactones on vitamin D signaling

The 26,23-lactone derivative of 1alpha,25-dihydroxyvitamin D3, TEI-9647, is a partial antagonist of the of human vitamin D receptor (VDR). However, we found that TEI-9647 in rat cells behaves as a weak VDR agonist. This behavior could be mimicked in human cells by the double mutagenesis of human VDR (specifically C403S and C410N). The increased agonistic action of TEI-9647 correlates to a gain in the interaction of the VDR with coactivator protein and a decreased stabilization of the antagonistic conformation of the receptor. Molecular dynamics simulations indicated that TEI-9647 acts as antagonist of human VDR by reducing the stability of helix 12 of the ligand binding domain. In contrast, N410 of the rat VDR stabilized, via backbone contacts, the interaction between helices 11 and 12. This results in TEI-9647 becoming a weak agonist in this organism.

Molecular mechanism of the vitamin D antagonistic actions of (23S)-25-dehydro-1alpha-hydroxyvitamin D3-26,23-lactone depends on the primary structure of the carboxyl-terminal region of the vitamin d receptor

We reported that (23S)-25-dehydro-1alpha-hydroxyvitamin D(3)-26,23-lactone (TEI-9647) antagonizes vitamin D receptor (VDR)-mediated genomic actions of 1alpha,25-dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)] in human cells but is agonistic in rodent cells. Human and rat VDR ligand-binding domains are similar, but differences in the C-terminal region are important for ligand binding and transactivation and might determine the agonistic/antagonistic effects of TEI-9647. We tested TEI-9647 on 1alpha,25(OH)(2)D(3) transactivation using SaOS-2 cells (human osteosarcoma) or ROS 24/1 cells (rat osteosarcoma) cotransfected with human or rodent VDR and a reporter. In both cell lines, TEI-9647 was antagonistic with wild-type human (h)VDR, but agonistic with overexpressed wild-type rat (r)VDR. VDR chimeras substituting the hVDR C-terminal region (activation function 2 domain) with corresponding rVDR residues diminished antagonism and increased agonism of TEI-9647. However, substitution of 25 C-terminal rVDR residues with corresponding hVDR residues diminished agonism and increased antagonism of TEI-9647. hVDR mutants (C403S, C410N) demonstrated that Cys403 and/or 410 was necessary for TEI-9647 antagonism of 1alpha,25(OH)(2)D(3) transactivation. These results suggest that species specificity of VDR, especially in the C-terminal region, determines the agonistic/antagonistic effects of TEI-9647 that determine, in part, VDR interactions with coactivators and emphasize the critical interaction between TEI-9647 and the two C-terminal hVDR Cys residues to mediate the antagonistic effect of TEI-9647.

1?,25-dihydroxyvitamin D3 stimulates steroid sulphatase activity in HL60 and NB4 acute myeloid leukaemia cell lines by different receptor-mediated mechanisms

Steroid sulphatase is a key enzyme in the biosynthesis of bioactive estrogens and androgens from highly abundant inactive circulating sulphated steroid precursors. Little is known about how the expression/activity of this enzyme is regulated. In this article, we show that of 1alpha,25(OH)2D3 stimulates an increase steroid sulphatase activity in the HL60 myeloid leukaemic cell line that is inhibited by a specific nuclear VDR (VDRnuc) antagonist and unaffected by plasma membrane-associated vitamin D receptor (VDRmem) agonists and antagonists. 1alpha,25(OH)2D3-mediated up-regulation of steroid sulphatase activity in HL60 cells was augmented by RXR agonists, blocked by RXR-specific antagonists, and RAR specific agonists and antagonists had no effect. In contrast, the 1alpha,25(OH)2D3-mediated up-regulation of steroid sulphatase activity in the NB4 myeloid leukaemic cell line was unaffected by the specific VDRnuc and RXR antagonists, but was blocked by a VDRmem-specific antagonist and was increased by VDRmem-specific agonists. The findings reveal that VDRnuc-RXR-heterodimers play a key role in the 1alpha,25(OH)2D3-mediated up-regulation of steroid sulphatase activity in HL60 cells. However, in NB4 cells, VDRnuc-derived signals do not play an obligatory role, and non-genomic VDRmem-derived signals are important.

Ligand structure-function relationships in the vitamin D endocrine system from the perspective of drug development (including cancer treatment)

It has become readily apparent to many scientists and pharmaceutical companies that the vitamin D endocrine system offers a wide array of drug development opportunities. There are already successes, as noted by 1alpha,25(OH)2D3 (Roche, and Abbott) for renal osteodystrophy and osteoporosis and 1alpha(OH)D3 (Leo, Chugai, Teijin) for renal osteodystrophy and (in Japan) osteoporosis, 1alpha,24(OH)2-24-cyclopropyl-D3 (Dovonex) and 1alpha,24(OH)2D3 (Teijin) for psoriasis, and 19-nor-1alpha,25(OH)2D2 (Abbott) for renal osteodystrophy, as well as drugs under active development. Yet there are still many important and challenging drug development frontiers, particularly in the area of cancer treatment and immune system disorders where exploration is only in the initial early stages. In addition, the application of vitamin D-related drugs in neurology and brain pathology should not be overlooked. It is to be hoped that the cellular and molecular basis for the vexing problem of analog-induced hypercalcemia will be elucidated. Given that there are believed to be over 2000 analogs of 1alpha,25(OH)2D3 already available for consideration, it is to be expected that over the next decade a significant number of new vitamin D structure-function drug development projects will be brought to conclusion.

Dramatic Enhancement of Antagonistic Activity on Vitamin D Receptor: A Double Functionalization of 1α-Hydroxyvitamin D3 26,23-Lactones

The synthesis of novel vitamin D receptor antagonists, 24-methyl-1alpha-hydroxyvitamin D(3) 26,23-lactones, is reported. We found that the biological activities of the vitamin D(3) lactones were affected by the structure of the lactone part. Furthermore, introduction of a 2alpha-methyl group into the 24-methylvitamin D(3) lactones dramatically enhanced their anti-vitamin D activity. [reaction: see text]

Remarkable effect of 2α-modification on the VDR antagonistic activity of 1α-hydroxyvitamin D3-26,23-lactones

Novel 2[small alpha]-methyl-, 2[small alpha]-(3-hydroxypropyl)- and 2[small alpha]-(3-hydroxypropoxy)-substituted 25-dehydro-1[small alpha]-hydroxyvitamin D-26,23-lactone derivatives were efficiently synthesized Reformatsky type allylation and palladium-catalyzed alkenylative cyclization processes, and their biological activities were evaluated. Introducing functional groups into the 2[small alpha]-position of the vitamin D-26,23-lactones resulted in remarkable enhancement of their antagonistic activity on vitamin D receptor (VDR).

Orchestration of multiple arrays of signal cross-talk and combinatorial interactions for maturation and cell death: another vision of t(15;17) preleukemic blast and APL-cell maturation

Despite intensive molecular biology investigations over the past 10 years, and an important breakthrough on how PML-RARalpha, the fusion protein resulting from t(15;17), can alter RARalpha and PML functions, no definitive views on how leukemia is generated and by what mechanism(s) the normal phenotype is restored, are yet available. 'Resistances' to pharmacological levels of all-trans-retinoic acid (ATRA) have been observed in experimental in vivo and in vitro models. In this review, we emphasize the key role played by signal cross-talk for both normal and neoplastic hemopoiesis. After an overview of reported experimental data on APL-cell maturation and apoptosis, we apply our current knowledge on signaling pathways to underline those which might generate signal cross-talks. The design of biological models suitable to decipher the integration of signal cross-talks at the transcriptional level should be our first priority today, to generate some realistic therapeutic approaches After 'Ten Years of Molecular APL', we still know very little about how the disease develops and how effective medicines work.

(23S)- and (23R)-25-dehydro-1alpha-hydroxyvitamin D(3)-26,23-lactone function as antagonists of vitamin D receptor-mediated genomic actions of 1alpha,25-dihydroxyvitamin D(3)

We synthesized various analogues of 1alpha,25-(OH)(2)D(3)-26,23-lactone and examined the effects of them on HL-60 cell differentiation using the evaluation system of the genomic action of 1alpha,25-(OH)(2)D(3). We found that (23S)- and (23R)-25-dehydro-1alpha-OH-D(3)-26,23-lactone (TEI-9647 and TEI-9648) strongly bound to the VDR, but did not induce HL-60 cell differentiation. Intriguingly, TEI-9647 and TEI-9648 did inhibit that induced by 1alpha,25-(OH)(2)D(3), whereas they did not suppress that caused by retinoic acid or TPA. On the contrary, the similar 25-dehydrated 24-dehydro analogues, TEI-D1807 and TEI-D1808, weakly but significantly induced HL-60 cell differentiation, never showing inhibitory effect on HL-60 cell differentiation induced by 1alpha,25-(OH)(2)D(3). In other experiments, TEI-9647 and TEI-9648 markedly suppressed 25-OH-D(3)-24-hydroxylase gene expression induced by 1alpha,25-(OH)(2)D(3) in HL-60 cells. TEI-9647 also inhibited the heterodimer formation between VDR and RXRalpha, and the VDR interaction with co-activator SRC-1 according to the results obtained from the mammalian two-hybrid system in Saos-2 cells. Taking all these results into consideration, we reached a manifest conclusion that TEI-9647 and TEI-9648 are the specific and first antagonists of 1alpha,25-(OH)(2)D(3) action, specifically VDR-VDRE mediated genomic action.

Different shapes of the steroid hormone 1alpha,25(OH)(2)-vitamin D(3) act as agonists for two different receptors in the vitamin D endocrine system to mediate genomic and rapid responses

Vitamin D(3) produces biologic responses as a consequence of its metabolism into 1alpha,25(OH)(2)-vitamin D(3) [1alpha,25(OH)(2)D(3)] and 24R,25(OH)(2)-vitamin D(3). The metabolic production of these two seco steroids and their generation of the plethora of biologic actions that are attributable to the parent vitamin D(3) are orchestrated via the integrated operation of the vitamin D endocrine system. This system is very similar in its organization to that of classic endocrine systems and is characterized by an endocrine gland (the kidney, the source of the two steroid hormones), target cells which possess receptors for the steroid hormones, and a feed-back loop involving changes in serum Ca(2+) that alter the secretion of parathyroid hormone (a stimulator of the renal 1-hydroxylase) which modulates the output by the kidney of the steroid hormones. There are, however, at least two unique aspects to the vitamin D endocrine system. (a) The chemical structures of vitamin D and its steroid hormones dictate that these be highly conformationally flexible molecules present a wide variety of shapes to their biologic environments. (b) It is now believed that 1alpha,25(OH)(2)D(3) produces biologic responses through two distinct receptors which recognize totally different shapes of the conformationally flexible 1alpha,25(OH)(2)D(3). Thus, the classic actions of 1alpha,25(OH)(2)D(3) to regulate gene transcription occur as a consequence of the stereospecific interaction of a modified 6-s-trans bowl-shape of 1alpha,25(OH)(2)D(3) with its nuclear receptor (VDR(nuc)). The ability of 1alpha,25(OH)(2)D(3) to generate a variety of rapid (seconds to minutes) biologic responses (opening of chloride channels, activation of PKC and MAP kinases) requires a planar 6-s-cis ligand shape which is recognized by a putative plasma membrane receptor (VDR(mem)) to initiate appropriate signal transduction pathways. This report summarizes the evidence for the specificity of different ligand shapes and the operation of the two receptor families for 1alpha,25(OH)(2)D(3).

Ligands for the vitamin D endocrine system: different shapes function as agonists and antagonists for genomic and rapid response receptors or as a ligand for the plasma vitamin D binding protein

The integrated operation of the vitamin D endocrine system which produces the steroid hormone 1alpha,25(OH)(2)-vitamin D(3) (1alpha,25(OH)(2)D(3)) is dependent on four classes of proteins each of which have inherent in their secondary and tertiary structure a ligand binding domain (LBD) that allows the stereospecific binding of 1alpha,25(OH)(2)D(3) or related analogs as a substrate or ligand. These LBDs include: (a) the cytochrome P450 enzymes in the liver, kidney, and other tissues which metabolize vitamin D(3) into biologically active metabolites; (b) the plasma vitamin D binding protein (DBP) which selectively transports these hydrophobic molecules to the various target organs of the vitamin D endocrine system; (c) the nuclear receptor VDR(nuc) that is involved in regulation of gene transcription in over 30 cell types which possess this receptor; and (d) a plasma membrane receptor, VDR(mem), that is involved in initiation of signal transduction pathways which generate rapid biological responses. This article reviews the evidence that supports the conclusions that the LBD of the DBP, VDR(mem) and VDR(nuc) each select as their preferred ligand a unique shape of the conformationally flexible 1alpha,25(OH)(2)D(3). Two critical aspects of the conformationally flexible 1alpha,25(OH)(2)D(3) molecule which defines the optimum ligand shape are (a) the orientation and relative rigidity of the flexible 8 carbon side chain and (b) the position of the A ring in relation to the C/D rings as determined by the extent of rotation around the 6,7 single carbon bond of the seco B ring. These conclusions are based on consideration of structure-function studies of over 300 analogs of 1alpha,25(OH)(2)D(3), of these, 22 analogs are highlighted in this presentation.

25-Dehydro-1alpha-hydroxyvitamin D3-26,23S-lactone antagonizes the nuclear vitamin D receptor by mediating a unique noncovalent conformational change

(23S)-25-dehydro-1alpha-Dihydroxyvitamin D3-26,23-lactone (TEI-9647; MK) has been reported to antagonize the 1alpha,25-dihydroxyvitamin D3 nuclear receptor (VDR)- mediated increase in transcriptional activity. Using a transient transfection system incorporating the osteocalcin VDRE (vitamin D response element) in Cos-1 cells, we found that 20 nM MK antagonizes VDR-mediated transcription by 50% when driven by 1 nM 1alpha,25(OH)2D3. Four analogs of 1alpha,25(OH)2D3, also at 1 nM, were antagonized 25 to 39% by 20 nM MK. However, analogs with 16-ene/23-yne or 20-epi modifications, which have a significantly lower agonist ED50 for the VDR than 1alpha,25(OH)2D3, were antagonized by 20 nM MK only at 100 pM or 10 pM, respectively. One possible mechanism for antagonism is that the 25-dehydro alkene of MK might covalently bind the ligand-binding site of the VDR rendering it inactive. Utilization of a ligand exchange assay, however, demonstrated that MK bound to VDR is freely exchanged with 1alpha,25(OH)2D3 in vitro. These data support the apparent correlation between VDR transcriptional activation by agonists and the effective range of MK antagonism by competition. Furthermore, protease sensitivity analysis of MK bound to VDR indicates the presence of a unique conformational change in the VDR ligand-binding domain, showing a novel doublet of VDR fragments centered at 34 kDa, whereas 1alpha,25(OH)2D3 as a ligand produces only a single 34-kDa fragment. In comparison, the natural metabolite 1alpha,25-dihydroxyvitamin D3-26,23-lactone yields only the 30-kDa fragment that is produced by all ligands to varying degrees. Collectively, these results support that MK is a potent partial antagonist of the VDR for 1alpha,25(OH)2D3 and its analogs when in appropriate excess of the agonist.

Antagonistic action of novel 1alpha,25-dihydroxyvitamin D(3)-26, 23-lactone analogs on 25-hydroxyvitamin-D(3)-24-hydroxylase gene expression induced by 1alpha,25-dihydroxy-vitamin D(3) in human promyelocytic leukemia (HL-60) cells

We have demonstrated that 1alpha,25-dihydroxyvitamin D(3)-26, 23-lactone analogs, (23S)- and (23R)-25-dehydro-1alpha-hydroxyvitamin D(3)-26,23-lactone (TEI-9647, TEI-9648, respectively), inhibit HL-60 cell differentiation induced by 1alpha,25-dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)], but not differentiation caused by all-trans retinoic acid (D. Miura et al., 1999, J. Biol. Chem. 274, 16392). To assess whether the antagonistic actions of TEI-9647 and TEI-9648 in HL-60 cells are related to 1alpha,25(OH)(2)D(3) breakdown, we investigated their effects on catabolism of 1alpha,25(OH)(2)D(3). In HL-60 cells, the C-24 but not the C-23 side-chain oxidation pathway of 1alpha,25(OH)(2)D(3) has been reported. Here we demonstrate that 1alpha,25(OH)(2)D(3) was metabolized both to 24,25,26,27-tetranor-1alpha,23-(OH)(2)D(3) and 1alpha,25(OH)(2)D(3)-26,23-lactone; thus HL-60 cells constitutively possess both the 24- and the 23-hydroxylases. Metabolism of 1alpha, 25(OH)(2)D(3) was strongly suppressed by 10(-7) M TEI-9647 or 10(-6) M TEI-9648. 1alpha,25(OH)(2)D(3) alone slightly induced 24-hydroxylase gene expression by 8 h with full enhancement by 24-48 h; this induction was inhibited by 10(-6) M TEI-9647 and 10(-6) M TEI-9648 (86.2 and 31.9%, respectively) 24 h after treatment. However, analogs of TEI-9647 and TEI-9648 without the 25-dehydro functionality induced 24-hydroxylase gene expression. These results indicate that TEI-9647 and TEI-9648 clearly mediate their stereoselective antagonistic actions independent of their actions to block the catabolism of 1alpha,25(OH)(2)D(3). Therefore, TEI-9647 and TEI-9648 appear to be the first antagonists specific for the nuclear 1alpha,25(OH)(2)D(3) receptor-mediated genomic actions of 1alpha,25(OH)(2)D(3) in HL-60 cells.