20-epi-vitamin D3 analogues: a novel class of potent regulators of cell growth and immune responses

Vitamin D(3) analogs (MC 1288, KH 1060, EB 1089, GS 1558, and CB 1093): studies on their mechanism of action

Selected 20-epi and 20-normal vitamin D(3) analogs were studied. First, point mutations were introduced into human vitamin D receptor (VDR) to identify residues important for ligand binding. In helices three, four and five, His229, Asp232, Ser237 and Arg274 seem to have an important role in the binding of calcitriol. Surprisingly, the 20-epi analog MC 1288 did not bind to Ser237. Second, the effects of analogs on VDR degradation were studied. The transcriptionally active 20-epi analogs protected VDR against degradation more efficiently than the 20-normal analogs and calcitriol. With proteasome inhibitor MG-132 formation of Sug-1-RXRbeta-VDR-VDRE complex was detected. The 20-epi analogs effectively prevented its formation. Thus, the 20-epi analogs induce a VDR conformation, which prevents binding of factors mediating VDR degradation. Third, the analogs were found to be powerful regulators of cell cycle progression in MG-63 cells. They arrested cell cycle in the G0/G1 phase at lower concentrations and earlier time points than calcitriol. This was accompanied by hypophosphorylation of Rb followed by strong inhibition of Cdk2 activity. This correlated with increased levels of p27. Cdk2 and cyclin E levels were downregulated but those of p21 and cyclin D1 were not affected. Thus, a similar sequence of events with calcitriol and the analogs in inhibiting MG-63 cell growth was detected but the analogs had much longer lasting and stronger effects than calcitriol. A unifying scheme for the varying effects of vitamin D(3) analogs is presented.

Highly potent cell differentiation-inducing analogues of 1alpha,25-dihydroxyvitamin D3: synthesis and biological activity of 2-methyl-1,25-dihydroxyvitamin D3 with side-chain modifications

Eight 2-methyl substituted analogues of 20-epi-22R-methyl-1alpha,25-dihydroxyvitamin D3 (5) and 20-epi-24,26,27-trihomo-22-oxa-1alpha,25-dihydroxyvitamin D3 (6: KH-1060) were convergently synthesized. Preparation of the CD-ring portions with modified side chains of 5 and 6, followed by palladium-catalyzed cross-coupling with the A-ring enyne synthons (20a-d), (3S,4S,5R)-, (3S,4R,5R)-, (3S,4S,5S)- and (3R,4R,5S)-3,5-bis[(tert-butyldimethylsilyl)oxy]-4-methyloct-1-en-7-yne, afforded two sets of four A-ring stereoisomers of 20-epi-2,22-dimethyl-1,25-dihydroxyvitamin D3 (7a-d) and 20-epi-24,26,27-trihomo-2-methyl-22-oxa-1,25-dihydroxyvitamin D3 (8a-d). The biological profiles of the hybrid analogues were assessed in terms of affinity for vitamin D receptor (VDR) and HL-60 cell differentiation-inducing activity in comparison with the natural hormone. The combined modifications of the A-ring at the 2-position and the side chain yielded analogues with high potency.

Suppressive effect of 1,25-dihydroxyvitamin D3 and its analogues EB 1089 and KH 1060 on T lymphocyte proliferation in active ulcerative colitis

This study examined the effect exerted by 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] and two vitamin D analogues, EB 1089 and KH 1060, on the proliferation of T lymphocytes obtained from ulcerative colitis (UC) patients and healthy controls. The proliferative response of T lymphocytes to phytohaemagglutinin treatment was first analyzed on days three, five, and seven of culture. Cell proliferation was significantly lower in UC patients than that observed in healthy controls. The highest proliferation value, in either controls or patients, was registered on day five of culture. On day seven, a decrease in proliferation occurred, less evident in patients with respect to controls, whereas on day three, controls and patients showed the same proliferation value. The response of T lymphocytes of either healthy controls or UC patients to 1,25(OH)2D3, EB 1089, or KH 1060 was then investigated, treating the cells for three, five, and seven days with 10 nM vitamin D derivatives. In the presence of these compounds, cell proliferation was significantly inhibited in both groups, but on day seven, the inhibition of lymphocyte proliferation was remarkable in controls, whereas in patients it was similar to that registered on day five. The highest inhibition values were always obtained in the presence of KH 1060, and the time dependence was continuous in controls, but in the presence of EB 1089 only in patients. T lymphocytes prepared from healthy controls and UC patients were then cultured for five days in the presence of vitamin D derivatives at three different concentrations (0.1, 1, and 10 nM). In the two groups, a dose-dependent inhibition was registered in the presence of 1,25(OH)2D3 or EB 1089, while the inhibition of proliferation exerted by KH 1060 was not dose-dependent. The results obtained suggest an option for the use of the two non-hypercalcemic vitamin D analogues in the therapy of UC patients, perhaps in association with other immunosuppressive drugs.

Development of analogues of 1alpha,25-dihydroxyvitamin D3 with biased side chain orientation: methylated des-C,D-homo analogues

The discovery that 1alpha,25-dihydroxyvitamin D3 is effective in the inhibition of cellular proliferation and in the induction of cellular differentiation has led to a search for analogues in which these activities and the classical calcemic activity of this hormone are separated. In this context, the synthesis and biological evaluation are reported of the three stereoisomeric CD-ring modified structural analogues in order to enforce a particular and different orientation of the 25-hydroxylated side chain. Comparison of the results of the biological evaluation and conformational analysis of the side chain suggests one defined and "active" geometry.

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.

1alpha,25-dihydroxy-16-ene-23-yne-vitamin D3 and 1alpha,25-dihydroxy-16-ene-23-yne-20-epi-vitamin D3: analogs of 1alpha,25-dihydroxyvitamin D3 that resist metabolism through the C-24 oxidation pathway are metabolized through the C-3 epimerization pathway

The secosteroid hormone 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)2D3] is metabolized in its target tissues through modifications of both the side chain and the A-ring. The C-24 oxidation pathway, the previously well established main side chain modification pathway, is initiated by hydroxylation at C-24 of the side chain. The C-3 epimerization pathway, the newly discovered A-ring modification pathway, is initiated by epimerization of the hydroxyl group at C-3 of the A-ring. The end products of the metabolism of 1alpha,25(OH)2D3 through the C-24 oxidation and the C-3 epimerization pathways are calcitroic acid and 1alpha,25-dihydroxy-3-epi-vitamin-D3 respectively. During the past two decades, numerous noncalcemic analogs of 1alpha,25(OH)2D3 were synthesized. Several of the analogs have altered side chain structures and as a result some of these analogs have been shown to resist their metabolism through side chain modifications. For example, two of the analogs, namely, 1alpha,25-dihydroxy-16-ene-23-yne-vitamin D3 [1alpha,25(OH)2-16-ene-23-yne-D3] and 1alpha,25-dihydroxy-16-ene-23-yne-20-epi-vitamin D3 [1alpha,25(OH)2-16-ene-23-yne-20-epi-D3], have been shown to resist their metabolism through the C-24 oxidation pathway. However, the possibility of the metabolism of these two analogs through the C-3 epimerization pathway has not been studied. Therefore, in our present study, we investigated the metabolism of these two analogs in rat osteosarcoma cells (UMR 106) which are known to express the C-3 epimerization pathway. The results of our study indicate that both analogs [1alpha,25(OH)2-16-ene-23-yne-D3 and 1alpha,25(OH)2-16-ene-23-yne-20-epi-D3] are metabolized through the C-3 epimerization pathway in UMR 106 cells. The identity of the C-3 epimer of 1alpha,25(OH)2-16-ene-23-yne-D3 [1alpha,25(OH)2-16-ene-23-yne-3-epi-D3] was confirmed by GC/MS analysis and its comigration with synthetic 1alpha,25(OH)2-16-ene-23-yne-3-epi-D3 on both straight and reverse-phase HPLC systems. The identity of the C-3 epimer of 1alpha,25(OH)2-16-ene-23-yne-20-epi-D3 [1alpha,25(OH)2-16-ene-23-yne-20-epi-3-epi-D3] was confirmed by GC/MS and 1H NMR analysis. Thus, we indicate that vitamin D analogs which resist their metabolism through the C-24 oxidation pathway, have the potential to be metabolized through the C-3 epimerization pathway. In our present study, we also noted that the rate of C-3 epimerization of 1alpha,25(OH)2-16-ene-23-yne-20-epi-D3 is about 10 times greater than the rate of C-3 epimerization of 1alpha,25(OH)2-16-ene-23-yne-D3. Thus, we indicate for the first time that certain structural modifications of the side chain such as 20-epi modification can alter significantly the rate of C-3 epimerization of vitamin D compounds.

Synthesis, biological evaluation, and conformational analysis of A-ring diastereomers of 2-methyl-1,25-dihydroxyvitamin D(3) and their 20-epimers: unique activity profiles depending on the stereochemistry of the A-ring and at C-20

All eight possible A-ring diastereomers of 2-methyl-1, 25-dihydroxyvitamin D(3) (2) and 2-methyl-20-epi-1, 25-dihydroxyvitamin D(3) (3) were convergently synthesized. The A-ring enyne synthons 19 were synthesized starting with methyl (S)-(+)- or (R)-(-)-3-hydroxy-2-methylpropionate (8). This was converted to the alcohol 14 as a 1:1 epimeric mixture in several steps. After having been separated by column chromatography, each isomer led to the requisite A-ring enyne synthons 19 again as 1:1 mixtures at C-1. Coupling of the resulting A-ring enynes 20a-h with the CD-ring portions 5a,b in the presence of a Pd catalyst afforded the 2-methyl analogues 2a-h and 3a-h in good yield. In this way, all possible A-ring diastereomers were synthesized. The synthesized analogues were biologically evaluated both in vitro and in vivo. The potency was highly dependent on the stereochemistry of each isomer. In particular, the alpha alpha beta-isomer 2g exhibited 4-fold higher potency than 1 alpha,25-dihydroxyvitamin D(3) (1) both in bovine thymus VDR binding and in elevation of rat serum calcium concentration and was twice as potent as the parent compound in HL-60 cell differentiation. Furthermore, its 20-epimer, that is, 20-epi-alpha alpha beta 3g, exhibited exceptionally high activities: 12-fold higher in VDR binding affinity, 7-fold higher in calcium mobilization, and 590-fold higher in HL-60 cell differentiation, as compared to 1 alpha,25-dihydroxyvitamin D(3) (1). Accordingly, the double modification of 2-methyl substitution and 20-epimerization resulted in unique activity profiles. Conformational analysis of the A-ring by (1)H NMR and an X-ray crystallographic analysis of the alpha alpha beta-isomer 2g are also described.

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.

Characterization of a novel analogue of 1alpha,25(OH)(2)-vitamin D(3) with two side chains: interaction with its nuclear receptor and cellular actions

The hormone 1alpha,25(OH)(2)-vitamin D(3) (125D) binds to its nuclear receptor (VDR) to stimulate gene transcription activity. Inversion of configuration at C-20 of the side chain to generate 20-epi-1alpha,25(OH)(2)D(3) (20E-125D) increases transcription 200-5000-fold over 125D with its 20-normal (20N) side chain. This enhancement has been attributed to the VDR ligand-binding domain (LBD) having different contact sites for 20N and 20E side chains that generate different VDR conformations. We synthesized 1alpha, 25-dihydroxy-21-(3-hydroxy-3-methylbutyl)vitamin D(3) (Gemini) with two six-carbon side chains (both 20N and 20E orientations). Energy minimization calculations indicate the Gemini side chain possesses significantly more energy minima than either 125D or 20E-125D (2346, 207, and 127 minima, respectively). We compared activities of 125D, 20E-125D, and Gemini, respectively, in several assays: binding to wild-type (100%, 147%, and 38%) and C-terminal-truncated mutant VDR; transcriptional activity (of the transfected osteopontin promoter in ROS 17/2.8 cells: ED(50) 10, 0.005, and 1.0 nM); mediation of conformational changes in VDR assessed by protease clipping (major trypsin-resistant fragment of 34, 34, and 28 kDa). For inhibition of cellular clonal growth of human leukemia (HL-60) and breast cancer (MCF7) cell lines, the ED(50)(125D)/ED(50)(Gem) was respectively 380 and 316. We conclude that while Gemini readily binds to the VDR and generates unique conformational changes, none of them is able to permit a superior gene transcription activity despite the presence of a 20E side chain.

Additive inhibitory effect of calcipotriol and anthralin on ribonuclease P activity

The effects of two antipsoriatic compounds, calcipotriol and anthralin, separately or in combination on ribonuclease P (RNase P), were investigated using a cell-free system from the slime mold Dictyostelium discoideum. RNase P is an ubiquitous and essential enzyme which endonucleolytically cleaves all tRNA precursors to produce the mature 5' end. The substrate for RNase P assays was an in vitro (32)P-labeled transcript of the Schizosaccharomyces pombe tRNA(Ser) gene supS1. Enzyme assays were carried out at 37 degrees in 20 microL 50 mM Tris-HCL 7.6 buffer, containing 10 mM NH(4)Cl, 5 mM MgCl(2), and 10% isopropanol. Calcipotriol or anthralin alone exerted a dose-dependent inhibitory effect on RNase P activity, with the former being more active than the latter in this respect. Simultaneous exposure of the enzyme to both drugs resulted in an enhancement of RNase P inhibition, which was additive. Considering the lack of structural similarities between the substrate (precursor tRNA) of RNase P and the tested drugs, it seems reasonable to suggest that their effects may be due to binding to allosteric inhibition sites of the enzyme. Although our in vitro findings cannot be directly extrapolated to the in vivo human condition, they do suggest that the inhibitory effects of calcipotriol and anthralin on tRNA biogenesis may be implicated in the mechanisms of their antipsoriatic action. Moreover, the additive inhibitory effect of these compounds on RNase P activity provides an experimental basis for their possible combined therapeutic application in the management of psoriasis.

Immunosuppressive drugs: the first 50 years and a glance forward

During the past 50 years, many immunosuppressive drugs have been described. Often their mechanisms of action were established long after their discovery. Eventually these mechanisms were found to fall into five groups: (i) regulators of gene expression; (ii) alkylating agents; (iii) inhibitors of de novo purine synthesis; (iv) inhibitors of de novo pyrimidine synthesis; and (v) inhibitors of kinases and phosphatases. Glucocorticoids exert immunosuppressive and anti-inflammatory activity mainly by inhibiting the expression of genes for interleukin-2 and other mediators. Cyclophosphamide metabolites alkylate DNA bases and preferentially suppress immune responses mediated by B-lymphocytes. Methotrexate and its polyglutamate derivatives suppress inflammatory responses through release of adenosine; they suppress immune responses by inducing the apoptosis of activated T-lymphocytes and inhibiting the synthesis of both purines and pyrimidines. Azathioprine metabolites inhibit several enzymes of purine synthesis. Mycophenolic acid and mizoribine inhibit inosine monophosphate dehydrogenase, thereby depleting guanosine nucleotides. Mycophenolic acid induces apoptosis of activated T-lymphocytes. A leflunomide metabolite and Brequinar inhibit dihydroorotate dehydrogenase, thereby suppressing pyrimidine nucleotide synthesis. Cyclosporine and FK-506 (Tacrolimus) inhibit the phosphatase activity of calcineurin, thereby suppressing the production of IL-2 and other cytokines. In addition, these compounds have recently been found to block the JNK and p38 signaling pathways triggered by antigen recognition in T-cells. In contrast, rapamycin inhibits kinases required for cell cycling and responses to IL-2. Rapamycin also induces apoptosis of activated T-lymphocytes. Immunosuppressive and anti-inflammatory compounds in development include inhibitors of p38 kinase and of the type IV isoform of cyclic AMP phosphodiesterase which is expressed in lymphocytes and monocytes.A promising future application of immunosuppressive drugs is their use in a regime to induce tolerance to allografts. The role of leukocytes in grafts, and the induction of apoptosis of clones of responding T-lymphocytes, is discussed.

Novel ring A stereoisomers of 2-methyl-1alpha,25-dihydroxyvitamin D(3) and 2-methyl-20-epi-1alpha,25-dihydroxyvitamin D(3): transactivation of target genes and modulation of differentiation in human promyelocytic leukemia (HL-60) cells

We evaluated the biological activity of two sets of ring A stereoisomers of 2-methyl-1alpha,25-dihydroxyvitamin D(3) (2-methyl-1alpha,25(OH)(2)D(3)) and 2-methyl-20-epi-1alpha, 25-dihydroxyvitamin D(3) (2-methyl-20-epi-1alpha,25(OH)(2)D(3)) in terms of the following: transactivation of a rat 25-hydroxyvitamin D(3)-24-hydroxylase gene promoter including two vitamin D response elements (VDREs) and a human osteocalcin gene promoter including a VDRE in transfected human osteosarcoma (MG-63) cells; a vitamin D receptor (VDR)-mediated response using a VDR-GAL4 one-hybrid luciferase reporter system and a retinoid X receptor alpha (RXRalpha)-mediated response using an expressed VDR/RXRalpha-GAL4 modified two-hybrid luciferase reporter system in transfected human epitheloid carcinoma, cervix (HeLa) cells; and modulation of cell surface CD11b antigen expression in human leukemia (HL-60) cells. All the diastereomers of both analogues exhibited unique biological activity profiles depending upon the configurations of the C-1 and C-3 hydroxyl groups, the C-2 methyl group in ring A, and the C-20 methyl group in the side chain. Of the eight possible diastereomers of the 2-methyl analogues, 2alpha-methyl-1alpha,25(OH)(2)D(3) was the most potent and exhibited comparable or even greater biological potency than 1alpha,25(OH)(2)D(3). Of the eight possible diastereomers of the 2-methyl-20-epi analogues, 2alpha-methyl-20-epi-1alpha,25(OH)(2)D(3) was the most potent and exhibited 100- to 200-fold higher transcriptional potencies than 1alpha,25(OH)(2)D(3) and exceptionally high cell regulatory activities. 2beta-methyl-20-epi-1alpha,25(OH)(2)D(3) was nearly as potent as its 2-epimer, 2alpha-methyl-20-epi-1alpha,25(OH)(2)D(3), whereas its 20-epimer, 2beta-methyl-1alpha,25(OH)(2)D(3), was almost completely biologically inactive. In these respects, it can be postulated that the double modification of 2-methyl substitution and 20-epimerization to 1alpha,25(OH)(2)D(3) induces remarkable changes in a VDR/RXRalpha/VDRE-mediated signaling response and greatly enhances biological activity. The other striking finding was that 2beta-methyl-20-epi-3-epi-1beta,25(OH)(2)D(3) is transcriptionally more active than 1alpha,25(OH)(2)D(3) despite lacking the 1alpha-hydroxyl group, which was believed to be essential for expressing VDR-mediated gene transcription. Since the C-20 natural counterpart, 2beta-methyl-3-epi-1beta,25(OH)(2)D(3), was almost completely biologically inactive, 20-epimerization is probably responsible for activation of gene expression. Although earlier extensive structure-activity studies of vitamin D analogues showed stereochemistry at the C-1, C-3, and C-20 of 1alpha,25(OH)(2)D(3) to be the key structural motif for vitamin D action, our results clearly demonstrated that stereochemistry at the C-2 is also an important structural motif for vitamin D action and imply that 2-methyl substitution possibly induces conformational changes in ring A depending upon the combinations of configurations of the C-1 and C-3 hydroxyl groups with C-20 stereochemistry. Consequently, several of these analogues exhibit exceptionally high or unexpected biological activities at the molecular and cellular levels. These results suggest that 2-methyl substitution together with alterations of stereochemistry in both ring A and the side chain of 1alpha, 25(OH)(2)D(3) will provide useful analogues for structure-activity studies and development of therapeutic agents with unique biological activity profiles.

Contribution of several metabolites of the vitamin D analog 20-epi-22-oxa-24a,26a,27a-tri-homo-1,25-(OH)(2) vitamin D(3) (KH 1060) to the overall biological activity of KH1060 by a shared mechanism of action

The synthetic 1,25-dihydroxyvitamin D(3) (1,25-(OH)(2)D(3)) analog 20-epi-22-oxa-24a,26a,27a-tri-homo-1,25-(OH)(2)vitamin D(3) (KH1060) is considerably more potent than its cognate hormone. The mechanism of action of KH1060 includes interaction with the vitamin D receptor (VDR). We previously showed that KH1060 increases VDR stability in ROS 17/2.8 osteoblastic cells by inducing a specific conformational change in the VDR. KH1060 is metabolized, both in vivo and in vitro, into several stable products. In the present study, we investigated whether these metabolites might contribute to the increased biological activity of KH1060. We found that the potencies of two of these metabolites, 24a-OH-KH1060 and 26-OH-KH1060, were similar to that of 1,25-(OH)(2)D(3) in inducing osteocalcin production by the osteoblast cell line ROS 17/2.8. This report further showed that these metabolites had the same effects as KH1060 on VDR: they increased VDR stability in ROS 17/2.8 cells, while limited proteolytic analysis revealed that they caused a conformational change in the VDR, resulting in an increased resistance against proteolytic cleavage. Furthermore, as shown in gel mobility shift assays, both compounds clearly induced VDR binding to vitamin D response elements. Together, these results show that the potent in vitro activity of KH1060 is not only directed by the effects on the VDR conformation/stabilization of the analog itself, but also by certain of its long-lived metabolites, and emphasizes the importance of detailed knowledge of the metabolism of synthetic hormonal analogs.

Modulation of ribonuclease P activity by calcipotriol

The effects of cholesterol, 7-dehydrocholesterol, vitamin D3 and several synthetic vitamin D3 analogs on ribonuclease P (RNase P) were investigated using a cell-free system from the slime mold Dictyostelium discoideum. RNase P is an ubiquitous and essential enzyme that endonucleolytically cleaves all tRNA precursors to produce the mature 5' end. Among the compounds tested, only calcipotriol was capable of affecting RNase P activity, and revealed a bimodal action at the kinetic phase of the reaction. Depending on the concentration of the drug, both activation and inhibition of tRNA maturation were observed, indicating that calcipotriol may have a direct effect on tRNA biogenesis, possibly associated with the presence of a highly reactive small ring on the side chain of its molecule.

Induction of tissue plasminogen activator secretion from rat heart microvascular cells by fM 1,25(OH)(2)D(3)

We investigated the effects of 1,25-dihydroxyvitamin D(3) [25(OH)(2)D(3)] on tissue plasminogen activator (tPA) secretion from primary cultures of rat heart microvascular cells. After an initial 5-day culture period, cells were treated for 24 h with 1,25(OH)(2)D(3) and several of its analogs. The results showed that 1,25(OH)(2)D(3) induced tPA secretion at 10(-10) to 10(-16) M. A less calcemic analog, Ro-25-8272, and an analog that binds the vitamin D receptor but is ineffective at perturbing Ca(2+) channels, Ro-24-5531, were approximately 10% as active as 1,25(OH)(2)D(3). An analog that binds the vitamin D receptor poorly but is an effective Ca(2+) channel agonist, Ro-24-2287, required approximately 10(-13) M to induce tPA secretion. Combinations of Ro-24-5531 and Ro-24-2287 were approximately as potent as 1,25(OH)(2)D(3). Treatment of the cells with BAY K 8644 or thapsigargin also increased tPA secretion, suggesting that increased cytosolic calcium concentration ([Ca(2+)]) induces tPA secretion. The results suggested that the sensitivity of the tPA secretory response of microvascular cells to 1,25(OH)(2)D(3) was due in part to generation of a vitamin D-depleted state in vitro and in part to synergistic effects of 1,25(OH)(2)D(3) on two different induction pathways of tPA release.

Biological activity of CD-ring modified 1alpha,25-dihydroxyvitamin D analogues: C-ring and five-membered D-ring analogues

Nonsteroidal analogues of 1alpha,25(OH)2D3, lacking either the full five-membered D ring (C-ring analogues) or the full six-membered C ring (D-ring analogues) are more potent inhibitors of cell proliferation or inducers of cell differentiation than is 1alpha,25(OH)2D3. Maximal superagonistic activity was seen for the C-ring analogue with a 24(R)-hydroxyl group in the side chain [30- to 60-fold the activity of 1alpha,25(OH)2D3]. The 19-nor-16-ene-26,27-bishomo C-ring analogue showed the best ratio of antiproliferative to calcemic effects (1275-fold better than 1alpha,25(OH)2D3 and severalfold better than all vitamin D analogues so far described). The analogues are able to stimulate specific vitamin D-dependent genes and are active in transfection assays using an osteocalcin promoter VDRE. Low binding affinity to the vitamin D binding protein, differences in metabolism, or affinity for the vitamin D receptor (VDR) are not the most important explanations for the enhanced intrinsic activity. However, the analogues are able to induce conformational changes in the VDR, which makes the VDR-ligand complex more resistant against protease digestion than is 1alpha,25(OH)2D3. In contrast to 20-epimer steroidal vitamin D analogues, 20-epimer C-ring analogues were less potent than analogues with a natural C-20 configuration. In conclusion, several nonsteroidal vitamin D analogues are superagonists of 1alpha,25(OH)2D3 despite lower receptor affinity and, for the C-ring analogues, higher flexibility of the side chain; moreover, they have a better selectivity profile than all analogues yet published.

Efficient synthesis and biological evaluation of all A-ring diastereomers of 1alpha,25-dihydroxyvitamin D3 and its 20-epimer

An improved synthesis of the diastereomers of 1alpha,25-dihydroxyvitamin D3 (1) was accomplished utilizing our practical route to the A-ring synthon. We applied this procedure to synthesize for the first time all possible A-ring diastereomers of 20-epi-1alpha,25-dihydroxyvitamin D3 (2). Ten-step conversion of 1-(4-methoxyphenoxy)but-3-ene (6), including enantiomeric introduction of the C-3 hydroxyl group to the olefin by the Sharpless asymmetric dihydroxylation, provided all four possible stereoisomers of A-ring enynes (3). i.e., (3R,5R)-, (3R,5S)-, (3S,5R)- and (3S,5S)-bis[(tert-butyldimethylsilyl)oxy]oct-1-en-7-yne, in good overall yield. Palladium-catalyzed cross-coupling of the A-ring synthon with the 20-epi CD-ring portion (5), (E)-(20S)-de-A,B-8-(bromomethylene)cholestan-25-ol, followed by deprotection, afforded the requisite diastereomers of 20-epi-1alpha,25-dihydroxyvitamin D3 (2). The biological profiles of the synthesized stereoisomers were assessed in terms of affinities for vitamin D receptor (VDR) and vitamin D binding protein (DBP). HL-60 cell differentiation-inducing activity and in vivo calcium-regulating potency in comparison with the natural hormone.

Isolation and identification of 1alpha-hydroxy-24-oxovitamin D3 and 1alpha,23-dihydroxy-24-oxovitamin D3: metabolites of 1alpha,24(R)-dihydroxyvitamin D3 produced in rat kidney

1alpha,24(R)-Dihydroxyvitamin D3 [1alpha,24(R)(OH)2D3], a synthetic vitamin D3 analog, has been developed as a drug for topical use in the treatment of psoriasis. At present, the target tissue metabolism of 1alpha,24(R)(OH)2D3 is not understood completely. In our present study, we investigated the metabolism of 1alpha,24(R)(OH)2D3 in the isolated perfused rat kidney. The results indicated that 1alpha,24(R)(OH)2D3 is metabolized in rat kidney into several metabolites, of which 1alpha,24(R),25-trihydroxyvitamin D3, 1alpha,25-dihydroxy-24-oxovitamin D3, 1alpha,23(S),25-trihydroxy-24-oxovitamin D3, and 1alpha,23-dihydroxy-24,25,26,27-tetranorvitamin D3 are similar to the previously known metabolites of 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)2D3]. In addition to these aforementioned metabolites, we also identified two new metabolites, namely 1alpha-hydroxy-24-oxovitamin D3 and 1alpha,23-dihydroxy-24-oxovitamin D3. The two new metabolites do not possess the C-25 hydroxyl group. Thus, the metabolism of 1alpha,24(R)(OH)2D3 into both 25-hydroxylated and non-25-hydroxylated metabolites suggests that 1alpha,24(R)(OH)2D3 is metabolized in the rat kidney through two pathways. The first pathway is initiated by C-25 hydroxylation and proceeds further via the C-24 oxidation pathway. The second pathway directly proceeds via the C-24 oxidation pathway without prior hydroxylation at the C-25 position. Furthermore, we demonstrated that rat kidney did not convert 1alpha-hydroxyvitamin D3 [1alpha(OH)D3] into 1alpha,25(OH)2D3. This finding indicates that the rat kidney does not possess the classical vitamin D3-25-hydroxylase (CYP27) activity. However, from our present study it is apparent that prior hydroxylation of 1alpha(OH)D3 at the C-24 position in the 'R' orientation allows 25-hydroxylation to occur. At present, the enzyme responsible for the C-25 hydroxylation of 1alpha,24(R)(OH)2D3 is unknown. Our observation that the side chain of 1alpha,24(R)(OH)2D3 underwent 24-ketonization and 23-hydroxylation even in the absence of the C-25 hydroxyl group suggests that 1alpha,25(OH)2D3-24-hydroxylase (CYP24) can perform some steps of the C-24 oxidation pathway without prior C-25 hydroxylation. Thus, we speculate that CYP24 may be playing a dual role in the metabolism of 1alpha,24(R)(OH)2D3.

Enhanced biological activity of 1alpha,25-dihydroxy-20-epi-vitamin D3, the C-20 epimer of 1alpha,25-dihydroxyvitamin D3, is in part due to its metabolism into stable intermediary metabolites with significant biological activity

1alpha,25-dihydroxy-20-epi-vitamin D3 (1alpha,25(OH)2-20-epi-D3), the C-20 epimer of the natural hormone 1alpha,25(OH)2D3, is several fold more potent than the natural hormone in inhibiting cell growth and inducing cell differentiation. At present, the various mechanisms responsible for the enhanced biological activities of this unique vitamin D3 analog are not fully understood. In our present study we compared the target tissue metabolism of 1alpha,25(OH)2D3 with that of 1alpha,25(OH)2-20-epi-D3 using the technique of isolated perfused rat kidney. The results indicated that the C-24 oxidation pathway plays a major role in the metabolism of both compounds in the rat kidney. However, it was noted that the concentrations of two of the intermediary metabolites of 1alpha,25(OH)2-20-epi-D3, namely, 1alpha,24(R),25(OH)3-20-epi-D3 and 1alpha,25(OH)2-24-oxo-20-epi-D3 in the kidney perfusate, exceeded the concentrations of the corresponding intermediary metabolites of 1alpha,25(OH)2D3. Furthermore, 1alpha,25(OH)2-24-oxo-20-epi-D3 induces the conformation of the vitamin D receptor similar to that induced by its parent analog and is nearly as potent as its parent in inducing transactivation of a gene construct containing the human osteocalcin vitamin D-responsive element. We conclude that 1alpha,25(OH)2-20-epi-D3 by itself is not metabolically stable when compared to 1alpha,25(OH)2D3, but it acquires its metabolic stability because of the reduced rate of catabolism of its intermediary metabolites. Furthermore, 1alpha,25(OH)2-24-oxo-20-epi-D3, the stable bioactive intermediary metabolite plays a significant role in generating the enhanced biological activities ascribed to 1alpha,25(OH)2-20-epi-D3.

Vitamin D analogs, 20-Epi-22-oxa-24a,26a,27a,-trihomo-1alpha,25(OH)2-vitamin D3, 1,24(OH)2-22-ene-24-cyclopropyl-vitamin D3 and 1alpha,25(OH)2-lumisterol3 prime NB4 leukemia cells for monocytic differentiation via nongenomic signaling pathways, involving calcium and calpain

Side-chain modified vitamin D analogs including 20-Epi-22-oxa-24a,26a,27a-trihomo-1alpha,2 5-dihydroxyvitamin D3 (KH1060), and 1,24-dihydroxy-22-ene-24-cyclopropyl-vitamin D3 (MC903) were originally designed to aid in the treatment of hyperproliferative disorders including psoriasis and cancer. Here we demonstrate that these analogs, as well as the 6-cis-locked conformer, 1alpha,25-dihydroxy-lumisterol3 (JN) prime NB4 cells for monocytic differentiation. Previously, the action of MC903 and KH1060 was presumed to be mediated by the nuclear vitamin D receptor (VDRnuc). Differentiation in response to all analogs was shown to be inhibited by 1beta,25-dihydroxyvitamin D3 (HL), the antagonist to the nongenomic activities of 1,25D3. These data suggest that although MC903 and KH1060 may bind the VDRnuc, that the differentiative activities of these agents requires nongenomic signaling pathways. Here we show that 1alpha,25(OH)2-d5-previtamin D3 (HF), JN, KH1060, and MC903 induce expression of PKC alpha and PKC delta and translocation of both isoforms to the particulate fraction, and PKC alpha to the nuclear fraction. The full differentiation response with combinations of analogs and TPA was inhibited 50% by the membrane permeable Ca2+ chelator, 1,2-bis(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid (BAPTA-AM) or calpain inhibitor I. These data demonstrate that intracellular free calcium and the calcium-dependent protease, calpain play critical roles in monocytic differentiation. Intracellular calcium appears to be most critical in the 1,25D3-priming stage of differentiation, while calpain is essential in the TPA maturation response.

Synthesis, biological activity, and conformational analysis of four seco-D-15,19-bisnor-1alpha,25-dihydroxyvitamin D analogues, diastereomeric at C17 and C20

The synthesis of four CD-ring-modified 19-nor-1alpha, 25-dihydroxyvitamin D(3) derivatives lacking C15, referred to as 6C analogues, and diastereomeric at C17 and C20 is described. The synthesis involves an Ireland-Claisen rearrangement of a 3-methyl-substituted ester of (1R)-3-methyl-2-cyclohexen-1-ol as the key step, followed by elaboration of the side chain, transformation into a C8 cyclohexanone derivative, and final Wittig-Horner coupling with the 19-nor A-ring phosphine oxide. Despite possessing a more flexible side chain than the parent hormone, biological evaluation showed an unexpected superagonistic antiproliferative and prodifferentiating activity (10-50 times higher as compared to that of 1alpha,25(OH)(2)D(3)) for the diastereomer with the "natural" configuration at C17 and C20. The other diastereomers exhibit a 25-90% decrease in activity. All four analogues show a decreased binding affinity (45% or less), and their calcemic activity is 4-400 times less than that of 1alpha,25(OH)(2)D(3). The conformational behavior of their side chain was studied using molecular mechanics calculations, and the result is presented as volume maps. A relative activity volume was determined by subtraction of the volume map of the least active analogue from the volume map of the most active one. This shows three regions corresponding to preferred orientations in space of the side chain of the active analogue. One of these regions was found to overlap with the region that is preferentially occupied by the most active of the four diastereomeric 22-methyl-substituted 1alpha,25(OH)(2)D(3) analogues.

In colorectal carcinoma patients, serum vitamin D levels vary according to stage of the carcinoma

BACKGROUND

Epidemiologic studies have demonstrated an inverse correlation between dietary calcium and vitamin D intake and the incidence of colorectal carcinoma. Elevated serum levels of 25-hydroxyvitamin D3 (25-OH-D3) are associated with a major reduction in the incidence of this neoplasm. The reduction in tumor size and number induced by calcium supplements in an experimental carcinogenesis model was neutralized by vitamin D3 deficiency. To the authors' knowledge, vitamin D serum levels have never been determined previously in colorectal carcinoma patients. They compared serum 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), 25-OH-D3, and parathyroid hormone (PTH) levels of colorectal carcinoma patients with those of healthy controls.

METHODS

Serum 1,25(OH)2D3, 25-OH-D3, and PTH levels were determined in 84 colorectal carcinoma patients (10 with Stage I, 29 with Stage II, 25 with Stage III, and 20 with Stage IV) and 30 healthy controls, all of whom were normocalcemic and not taking calcium or vitamin D supplements.

RESULTS

25-OH-D3 serum levels were higher in cancer patients than controls, irrespective of stage. Serum 1,25(OH)2D3 decreased with advancing stage: 73 +/- 18, 48 +/- 16, 39 +/- 12, 34 +/- 13, and 75 +/- 20 pg/mL in Stages I, II, III, IV, and controls, respectively. There was a corresponding increase in serum PTH levels: 58.0 +/- 9.4, 73.7 +/- 14.4, 79.0 +/- 21.3, 100.4 +/- 30.9, and 51.2 +/- 3.9 pg/mL in Stages I, II, III, IV, and controls, respectively. Serum vitamin D metabolite levels did not correlate with gender, age, tumor localization, or histologic grade.

CONCLUSIONS

An inverse correlation between serum levels of the active metabolite of vitamin D and colorectal carcinoma stage has been demonstrated for the first time, to the authors' knowledge, in colorectal carcinoma patients. Because 1,25(OH)2D3 has been shown to inhibit proliferation of colonic epithelial cells, decreased serum levels may facilitate the growth of colorectal carcinoma and influence its biologic behavior.

Novel 20-epi-vitamin D3 analog combined with 9-cis-retinoic acid markedly inhibits colony growth of prostate cancer cells

BACKGROUND

1,25 dihydroxyvitamin D3 (1,25D) and retinoids may play an important role in preventing progression of prostate cancer.

METHODS

We examined the ability of four novel 20-epi-vitamin D3 analogs (CB1093, KH1060, KH1266, and CB1267), either alone or in combination with 9-cis retinoic acid (RA) to inhibit colony growth of a human prostate cancer cell line, LNCaP, using soft agar as well as bone marrow stroma. Also, the effect of these analogs on the cell cycle and expression of Ki-67, p21(waf-1), and p27(kip1) in LNCaP cells was examined.

RESULTS

The analog CB1267 was the most potent, with 8 x 10(-10) M of the analog inhibiting 50% colony growth (ED50) of LNCaP. 9-cis-RA also inhibited colony growth of LNCaP (ED50, 5 x 10(-7) M). Combined, CB1267 and 9-cis-RA synergistically inhibited colony growth and significantly increased the number of LNCaP cells in G0/G1 phase. Cell cycle arrest was associated with increased levels of p21(waf-1) and p27(kip1) and decreased expression of Ki-67 protein. Pulse-exposure to this combination (5 x 10(-8) M) irreversibly inhibited colony growth, both in soft agar and on normal human bone marrow stroma.

CONCLUSIONS

Combination of a new vitamin D3 analog (CB1267) and a retinoid (9-cis-RA) potently inhibited colony formation of LNCaP prostate cancer cells in vitro, suggesting further studies in animal models. This combination may afford an interesting therapeutic approach to low-burden prostate cancer.

20-Epi analogues of 1,25-dihydroxyvitamin D3 are highly potent inducers of DRIP coactivator complex binding to the vitamin D3 receptor

1,25-Dihydroxyvitamin D3 (1,25(OH)2D3) plays a major role in the stimulation of bone growth, mineralization, and intestinal calcium and phosphate absorption; it also acts as a general inhibitor of cellular proliferation. Several new, clinically relevant compounds dissociate antiproliferative and calcemic activities of 1,25(OH)2D3, but the molecular basis for this has not been clearly elucidated. Here, we tested whether the potency of one class of compounds, 20-epi analogues, to induce myeloid cell differentiation, is because of direct molecular effects on vitamin D receptor (VDR). We report that two 20-epi analogues, MC1627 and MC1288, induced differentiation and transcription of p21(Waf1,Cip1), a key VDR target gene involved in growth inhibition, at a concentration 100-fold lower than that of 1,25(OH)2D3. We compared this sensitivity to analogue effects on VDR interacting proteins: RXR, GRIP-1, and DRIP205, a subunit of the DRIP coactivator complex. Compared with the interaction of VDR with RXR or GRIP-1, the differentiation dose-response most closely correlated to the ligand-dependent recruitment of the DRIP coactivator complex to VDR and to the ability of the receptor to activate transcription in a cell-free system. These results provide compelling links between the efficiency of the 20-epi analogue in inducing VDR/DRIP interactions, transactivation in vitro, and its enhanced ability to induce cellular differentiation.

Antagonistic action of novel 1alpha,25-dihydroxyvitamin D3-26, 23-lactone analogs on differentiation of human leukemia cells (HL-60) induced by 1alpha,25-dihydroxyvitamin D3

We examined the effects of two novel 1alpha,25-dihydroxyvitamin D3-26,23-lactone (1alpha,25-lactone) analogues on human promyelocytic leukemia cell (HL-60) differentiation using the evaluation system of the vitamin D nuclear receptor (VDR)/vitamin D-responsive element (DRE)-mediated genomic action stimulated by 1alpha,25-dihydroxyvitamin D3 (1alpha,25(OH)2D3) and its analogues. We found that the 1alpha,25-lactone analogues (23S)-25-dehydro-1alpha-hydroxyvitamin-D3-26,23-lactone (TEI-9647), and (23R)-25-dehydro-1alpha-hydroxyvitamin-D3-26,23-lactone (TEI-9648) bound much more strongly to the VDR than the natural (23S, 25R)-1alpha,25(OH)2D3-26,23-lactone, but did not induce cell differentiation even at high concentrations (10(-6) M). Intriguingly, the differentiation of HL-60 cells induced by 1alpha,25(OH)2D3 was inhibited by either TEI-9647 or TEI-9648 but not by the natural lactone. In contrast, retinoic acid or 12-O-tetradecanoylphorbol-13-acetate-induced HL-60 cell differentiation was not blocked by TEI-9647 or TEI-9648. In separate studies, TEI-9647 (10(-7) M) was found to be an effective antagonist of both 1alpha,25(OH)2D3 (10(-8) M) mediated induction of p21(WAF1, CIP1) in HL-60 cells and activation of the luciferase reporter assay in COS-7 cells transfected with cDNA containing the DRE of the rat 25(OH)D3-24-hydroxylase gene and cDNA of the human VDR. Collectively the results strongly suggest that our novel 1alpha,25-lactone analogues, TEI-9647 and TEI-9648, are specific antagonists of 1alpha, 25(OH)2D3 action, specifically VDR/DRE-mediated genomic action. As such, they represent the first examples of antagonists, which act on the nuclear VDR.

New Synthetic Strategies to Vitamin D Analogues Modified at the Side Chain and D Ring. Synthesis of 1alpha,25-Dihydroxy-16-ene-vitamin D(3) and C-20 Analogues(1)

Two efficient synthetic routes to 1alpha,25-dihydroxy-16-ene-vitamin D(3) (4a) and their C-20 analogues (3 and 4) have been developed. Key features common to both routes A and B are the introduction of side chains functionalized at C20 (17, 21, 19, and 25). In route A the CD side chain fragments 5 and 6 are prepared by S(N)2' syn displacement of allylic carbamates 8 and 9 (X = OCONHPh) by Li(2)Cu(3)R(5). The triene unit is then constructed by assembling the latter fragments with the A-ring fragment using the Wittig-Horner method (average yield of vitamin D analogue 35%, 11-13 steps from ketone 11). In route B, the S(N)2' syn displacement of the carbamate moiety by Li(2)Cu(3)R(5) is carried out on intermediates 12 and 13, both of which bear the vitamin D triene unit (average yield of vitamin D analogue 27%, 13-15 steps from ketone 11). The latter route is particularly attractive as an approach to diverse C-20 vitamin D analogues for biological screening.

Three-dimensional structure-function relationship of vitamin D: side chain location and various activities

The various biological activities of side-chain mobility restricted analogs, four diastereomers at C(20) and C(22) of 22-methyl-1alpha,25-dihydroxyvitamin D3, were evaluated. The relationship between structure and the various activities of the analogs was discussed in terms of the active space region concept that we previously suggested.

Rapid actions of calcitriol and its side chain analogues CB1093 and GS1500 on intracellular calcium levels in skeletal muscle cells: a comparative study

1. The ability of synthetic analogues of the secosteroid hormone 1alpha,25-dihydroxy-vitamin-D3 [calcitriol, CT; 1,25(OH)2D3] to exert non-genomic (rapid) effects on target cells has been scarcely studied. To evaluate the pharmacological potential of the CT side-chain analogues CB1093 and GS1500, we compared their fast effects on intracellular calcium concentration ([Ca2+]i) in chick skeletal muscle cells with those elicited by the natural hormone. 2. Both analogues, similarly to CT, specifically induced rapid (30-60 s) and sustained rises in [Ca2+]i levels. CB1093 and GS1500 were more potent than the natural hormone at concentrations as low as 10(-13) M (4.5 fold stimulation) and 10(-12) M (2.5 fold), respectively, whereas higher concentrations (10(-9)- 10(-8) M) of CT were more effective than the analogues in elevating [Ca2+]i. Cyclic AMP was markedly increased by both analogues pointing for a role of this messenger in the fast actions of the synthetic compounds. 3. In Ca2+ free medium CT and analogues elicited a transient elevation in [Ca2+]i. The PLC inhibitors U73122 (2 microM) and neomycin (0.5 mM), as well as depletion of intracellular stores with thapsigargin (1 microM), completely prevented CB1093/GS1500-dependent changes in [Ca2+]i suggesting that, similarly to CT, these analogues mobilized Ca2+ from an IP3/thapsigargin-sensitive store. 4. The voltage-dependent calcium channel (VDCC) blocker nifedipine (2 microM) reduced by 50-60% the influx phase of the [Ca2+]i response to CB1093 and GS1500, indicating that VDCC contributed partially to Ca2+ entry. The Ca2+ readdition protocol suggested that analogue-dependent activation of a SOC entry pathway accounted, to the same extent as for CT, for the remaining non-VDCC mediated Ca2+ influx.

Differential effects of 20-epi vitamin D analogs on the vitamin D receptor homodimer

Vitamin D analogs have received increased attention because of their possible therapeutic benefits in treating osteoporosis and various proliferative disorders. Several analogs were examined for their effects on DNA binding of the vitamin D receptor (VDR) homodimer complex with the murine osteopontin vitamin D response element. All of the tested analogs increased complex binding by recombinant human VDR in the electrophoretic mobility shift assay and notable differences in mobility of these complexes were observed. A panel of C-terminal anti-VDR antisera were screened for their ability to interact with analog-bound VDR homodimer complexes or as a heterodimer complex with recombinant human retinoid X receptor alpha (rhRXR alpha). Like calcitriol, analog-bound heterodimer complexes were largely resistant to interaction with these antisera; however, striking differences were observed with the various antisera in an analogous homodimer binding experiment. KH1060 and CB1093, analogs with 20-epi conformations, produced homodimer complexes that were 3- to 6-fold more resistant to supershifting with Ab180 compared with the hormone or EB1089. Chymotrypsin digestion in combination with Western blotting using a C-terminal anti-VDR antiserum revealed similar digestion patterns for all ligands. However, KH1060- and CB1093-bound VDR complexes were more resistant to digestion than either calcitriol or EB1089. Finally, the ability of these compounds to yield stable homodimer complexes was assessed by challenging preformed homodimer with the exogenous addition of rhRXR alpha extracts. Although new heterodimer complexes appeared in a time-dependent fashion, the preformed homodimer complexes exhibited stable binding throughout the time course of the experiment. The results indicate that VDR homodimers are targets of vitamin D analogs with differential effects on C-terminal protein conformation that may partially explain the varied biological responses of these compounds.

Metabolism of 1alpha,25(OH)2D3 and its 20-epi analog integrates clonal expansion, maturation and apoptosis during HL-60 cell differentiation

Induction of growth arrest and monocyte differentiation of HL-60 leukemia cells by 1alpha,25 dihydroxyvitamin D3 (1alpha,25(OH)2D3) is well established. By contrast, we have observed, that 1alpha,25(OH)2D3 and its metabolites play separate roles in clonal expansion and survival of differentiating HL-60 cells. Cells that had differentiated by 48 h (CD14 positive) grew slower than control cells, whereas CD14 negative cells were growing faster at this time point. Inhibiting 1alpha,25(OH)2D3 or 1alpha,25(OH)2-20-epi-D3 metabolism, by the 25(OH)D3-24-hydroxylase inhibitor ketoconazole, abolished hyperproliferation of CD14 negative cells. Instead, both the onset of differentiation and subsequent apoptosis were enhanced. These events were associated with immediate up-regulation of the cyclin-dependent kinase inhibitor p21(waf1) and a lack of sustained expression, respectively. Stimulation and inhibition of growth by vitamin D3-related compounds was observed to be concentration and metabolite specific. Low amounts of 1alpha,25(OH)2-20-epi-D3 and 1alpha,24,25(OH)3-20-epi-D3 stimulated HL-60 cell growth. At higher concentrations, 1alpha,25(OH)2-20-epi-D3 was a more potent inducer than 1alpha,24,25(OH)3-20-epi-D3 of HL-60 differentiation; 1alpha,25(OH)2-20-epi-24-oxo-D3 was exclusively pro-differentiative at all concentrations. 1alpha,25(OH)2-20-epi-D3 and 1alpha,24,25(OH)3-20-epi-D3 stimulated proliferation of KG-1a leukemia cells, but neither of these compounds nor 1alpha,25(OH)3-20-epi-24-oxo-D3 exerted pro-differentiative effects on these cells. These findings shed new light on the pro- and anti-proliferative effects of 1alpha,25(OH)2D3 and lead to the postulate that metabolism of 1alpha,25(OH)2D3 and its 20-epi analog regulates different subsets of genes so as to co-ordinate population expansion and the differentiation process. Furthermore, 1alpha,25(OH)2D3 metabolism and/or sensitivity to the effects of metabolites may be altered in transformed cells to derive a clonal advantage.

Vitamin D receptor expression in colorectal cancer

AIMS

To determine whether the vitamin D receptor is expressed in colorectal cancer, and its relation to stage of disease.

METHODS

Paraffin embedded sections of colorectal cancer from 30 patients who had undergone surgery were studied. Immunohistochemistry using the specific monoclonal antibody 9A7 gamma directed against the nuclear vitamin D receptor was used to identify receptors for the active metabolite of vitamin D3 (1,25-dihydroxyvitamin D3).

RESULTS

Microscopically normal human colorectal epithelium showed vitamin D receptor expression predominantly in the mid and upper crypts. All the colorectal cancer tissue studied showed vitamin D receptor expression, with a median of 25.3 (range 10.1 to 43.7) cells/graticule field (x 400). Although vitamin D receptor staining was heterogeneous within the individual cancers, neither Dukes stage nor the degree of differentiation appeared to influence expression of the receptor.

CONCLUSIONS

Colorectal cancer tissue expresses the nuclear vitamin D receptor and this could act as a potential therapeutic target for synthetic vitamin D3 differentiating agents.

Combined effect of vitamin D3 analogs and paclitaxel on the growth of MCF-7 breast cancer cells in vivo

Vitamin D3 analogs and paclitaxel (Taxol) are able to inhibit the in vitro growth of a variety of malignant cells including breast cancer cells. These two compounds decrease growth by different mechanisms and they have nonoverlapping toxicities. We examined the abilities of three vitamin D3 compounds to inhibit growth of a human mammary cancer (MCF-7) in BNX triple immunodeficient mice either alone or with Taxol. Vitamin D3 analogs were 1,25(OH)2D3 (code name, Compound C), 1,25(OH)2-16-ene-23-yne-19-nor-26,27-F6-D3 (Compound LH), and 24a,26a,27a,-trihomo-22,24-diene-1,25(OH)2D3 (EB1089). At the doses chosen, the antitumor effect of vitamin D3 analogs alone was greater than that of Taxol alone, and an additive effect was observed when a vitamin D3 analog and Taxol were administered together. EB1089 was the most potent compound, and the EB1089 plus Taxol was the most active combination, decreasing the tumor mass nearly 4-fold compared to controls. Weight-gain in each of the experimental cohorts at the end of the study was less than the control group, but the gain was significantly less in only two experimental groups (those receiving either EB1089 or Compound C plus Taxol). None of the animals became hypercalcemic, and their complete blood counts, serum electrolyte analyses, and liver and renal functions were all fairly similar and within the normal range. In summary, this combination of a vitamin D3 analog and Taxol has the potential to be a therapy for breast cancer.

Leukemia cell differentiation: cellular and molecular interactions of retinoids and vitamin D

1. The conventional approach to treatment of acute myeloid leukemia has been the use of chemotherapy, which although being cytotoxic to malignant clones, is also cytodestructive to normal cells. In addition, some leukemia cells develop resistance to chemotherapy and are therefore difficult to eradicate. 2. Differentiation therapy, whereby immature cells are induced to attain a mature phenotype by differentiation agents, has provided an alternative strategy in the treatment of hyperproliferative disorders. This has been highlighted by the use of all-trans retinoic acid (ATRA) in the treatment of acute promyelocytic leukemia (APL). 3. Another differentiation agent, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), directs monocytic maturation of normal and leukemic cells. Cellular studies have revealed that combinations of vitamin D derivatives and retinoids such as ATRA and 9-cis retinoic acid (9-cis RA) exhibit cooperative effects on differentiation in established leukemia cell lines such as HL-60, U937, and NB4. Furthermore, vitamin D compounds, although not able to induce apoptosis when used alone, potentiate apoptosis induced by 9-cis RA in HL-60 cells and differentially regulate the expression of the apoptosis-related gene products bcl-2 and bax. The molecular mechanisms involved in regulating differentiation and apoptosis by these agents are mediated through the interactions of the nuclear receptors for vitamin D (VDR), ATRA (RAR), and 9-cis RA (RXR), which are able to form homo- or heterodimeric complexes and transcriptionally activate or repress target gene expression. 4. There is evidence to suggest that nitric oxide may also play a role in leukemic cell differentiation and that 1,25(OH)2D3 may influence endogenous nitric oxide production either by directly increasing tumor necrosis factor-alpha (TNF-alpha) or through a secondary mediator such as the C-type lectin CD23.

New 1alpha,25-dihydroxy-19-norvitamin D3 compounds of high biological activity: synthesis and biological evaluation of 2-hydroxymethyl, 2-methyl, and 2-methylene analogues

New highly active isomers of the natural hormone 1alpha, 25-dihydroxyvitamin D3 possessing an exomethylene group at the 2-position were prepared in a convergent manner, starting with (-)-quinic acid and the corresponding (20R)- and (20S)-25-hydroxy Grundmann ketones. These 2-methylene-19-norvitamins were efficiently converted to the 2-methyl and 2-hydroxymethyl derivatives, some of which exhibited pronounced in vivo biological activity. Configurations of the A-ring substituents were determined by 1H NOE difference spectroscopy as well as by spin decoupling experiments. It was established that the bulky methyl and hydroxymethyl substituents at C-2, due to their large conformational free energies, occupy mainly equatorial positions. Additionally, hydroxylation of the C(10)-C(19) double bond in 1alpha,25-(OH)2D3 was performed, resulting in 1alpha,19,25-trihydroxy-10,19-dihydrovitamin D3 derivatives in which the hydroxymethyl substituent at C-10, for steric reasons, is forced to occupy an axial position. In consequence, the vitamin D3 analogues were synthesized in which the 1alpha-hydroxy group, required for biological activity, is almost exclusively axially or equatorially oriented because of stabilization of the single A-ring chair conformations. The relative ability of the synthesized analogues to bind the porcine intestinal vitamin D receptor was assessed and compared with that of the natural hormone. It was established that vitamins possessing the axial orientation of the 1alpha-hydroxy substituent exhibit a significantly increased receptor binding affinity. Compounds with a 2-methylene substituent showed selective calcemic activity profiles, being extremely effective on bone calcium mobilization. 2alpha-Methyl-substituted vitamins proved to be much more active in vivo than the corresponding epimers with 2beta-configuration. All of the 2-substituted vitamins exhibited pronounced HL-60 differentiating activity, those 2alpha-substituted in the 20S-series being especially potent. The present studies imply that the axial orientation of the 1alpha-hydroxy group is necessary for biological activity of vitamin D compounds.

A vitamin D analogue (MC 1288) has immunomodulatory properties and suppresses collagen-induced arthritis (CIA) without causing hypercalcaemia

The immunomodulatory properties of the vitamin D analogue MC 1288 (20-epi-1alpha,25-dihydroxycholecalciferol) were investigated in CIA in rats. The analogue was administered systemically at three different time points; (i) for 10 consecutive days before collagen (CII) immunization; (ii) for 10 consecutive days after CII immunization; or (iii) for 7 consecutive days from disease onset. Treatment initiated either 10 days before CII immunization or at the day of collagen immunization effectively suppressed the development of arthritis. Treatment initiated at the day of the onset of arthritis reduced the severity of joint inflammation. Significantly, doses which did not induce hypercalcaemia decreased the incidence and severity of arthritis. In vivo treatment with the 20-epi analogue of 1alpha,25-dihydroxycholecalciferol diminished the serum levels of antibodies to rat CII. Similarly, mitogen-induced proliferation of lymph node cells from rat CII-immunized animals was reduced. The experiments demonstrate that the vitamin D analogue MC 1288 has the ability to prevent, and furthermore to suppress, already established CIA by its immunomodulatory properties without inducing hypercalcaemia.

Current understanding of the molecular actions of vitamin D

The important reactions that occur to the vitamin D molecule and the important reactions involved in the expression of the final active form of vitamin D are reviewed in a critical manner. After an overview of the metabolism of vitamin D to its active form and to its metabolic degradation products, the molecular understanding of the 1alpha-hydroxylation reaction and the 24-hydroxylation reaction of the vitamin D hormone is presented. Furthermore, the role of vitamin D in maintenance of serum calcium is reviewed at the physiological level and at the molecular level whenever possible. Of particular importance is the regulation of the parathyroid gland by the vitamin D hormone. A third section describes the known molecular events involved in the action of 1alpha,25-dihydroxyvitamin D3 on its target cells. This includes reviewing what is now known concerning the overall mechanism of transcriptional regulation by vitamin D. It describes the vitamin D receptors that have been cloned and identified and describes the coactivators and retinoid X receptors required for the function of vitamin D in its genomic actions. The presence of receptor in previously uncharted target organs of vitamin D action has led to a study of the possible function of vitamin D in these organs. A good example of a new function described for 1alpha,25-dihydroxyvitamin D3 is that found in the parathyroid gland. This is also true for the role of vitamin D hormone in skin, the immune system, a possible role in the pancreas, i.e., in the islet cells, and a possible role in female reproduction. This review also raises the intriguing question of whether vitamin D plays an important role in embryonic development, since vitamin D deficiency does not prohibit development, nor does vitamin D receptor knockout. The final section reviews some interesting analogs of the vitamin D hormone and their possible uses. The review ends with possible ideas with regard to future directions of vitamin D drug design.

Inhibition of proliferation and induction of differentiation of osteoblastic cells by a novel 1,25-dihydroxyvitamin D3 analog with an extensively modified side chain (CB1093)

1,25-Dihydroxyvitamin D3 (1,25D) is involved in the regulation of proliferation and differentiation of a variety of cell types including cancer cells. In recent years, numerous new vitamin D3 analogs have been developed in order to obtain favorable therapeutic properties. The effects of a new 20-epi analog, CB1093 (20-epi-22-ethoxy-23-yne-24a,26a,27a-trihomo+ ++-1alpha,25(OH)2D3), on the proliferation and differentiation of human MG-63 osteosarcoma cell line were compared here with those of the parent compound 1,25D. Proliferation of the MG-63 cells was inhibited similarly by 22%, 50% and 59% after treatment with 0.1 microM 1,25D or CB1093 for 48 h, 96 h, and 144 h, respectively. In transfection experiments, the compounds were equipotent in stimulating reporter gene activity under the control of human osteocalcin gene promoter. In cell culture experiments, however, CB1093 was more potent than 1,25D at low concentrations and more effective for a longer period of time in activating the osteocalcin gene expression at mRNA and protein levels. Also, a 6-h pretreatment and subsequent culture for up to 120 h without 1,25D or CB1093 yielded higher osteocalcin mRNA and protein levels with analog-treated cells than with 1,25D-treated cells. The electrophoretic mobility shift assay (EMSA) revealed stronger VDR-VDRE binding with analog-treated MG-63 cells than with 1,25D-treated cells. The differences in the DNA binding of 1,25D-bound vs. analog-bound VDR, however, largely disappeared when the binding reactions were performed with recombinant hVDR and hRXRbeta proteins. These results demonstrate that the new analog CB1093 was equally or even more effective than 1,25D in regulating all human osteosarcoma cell functions ranging from growth inhibition to marker gene expression and that the differences in effectivity most probably resulted from interactions of the hVDR:hRXRbeta-complex with additional nuclear proteins.

Synthesis and biological activity of 2-methyl-20-epi analogues of 1 alpha,25-dihydroxyvitamin D3

Synthesis and biological evaluation of all eight possible A-ring diastereomers of 2-methyl-20-epi-1,25-dihydroxyvitamin D3 are described. Among the analogues synthesized. 2 alpha-methyl-20-epi-1 alpha,25-dihydroxyvitamin D3 exhibited exceptionally high potency. The double modification of 2-methyl substitution and 20-epimerization yielded analogues with unique activity profiles.

On the use of volume maps in the conformational analysis of vitamin D analogs

Dot maps used to represent the calculated conformations of the side chain of vitamin D derivatives are improved by replacing dots by coloured balls to create volume maps and to identify particular energy windows. Two procedures to define a relative activity volume, based on a pair of analogs with distinctly different biological activity and conformational behaviour, are presented.

Conformation-function relationship of vitamin D: conformational analysis predicts potential side-chain structure

In previous studies, we have grouped regions in space occupied by the vitamin D side chain into four: A, G, EA, and EG. We showed that the receptor (VDR) affinity of 1alpha,25-dihydroxyvitamin D3 derivatives increases, in terms of side-chain region, in the order EG, G, A, and EA. We called this the active space group concept. In the present study, we used this active space group concept to analyze the conformation-activity relationship of about 40 representative potent 1alpha,25-dihydroxyvitamin D3 analogues. We initially listed structural modifications in the side chain of potent vitamin D analogues and estimated their potency factor. Possible side-chain conformations of representative analogues were calculated by the molecular mechanics method and plotted on a dot map compared with the regions A, G, EA, and EG. The cell-differentiating potency of the analogues was correlated with our active space group concept with few exceptions. Among potent analogues with a natural configuration at C(20), the side chains of those with a 22-oxa, 22-ene, 16-ene, or a 18-nor modification were located in front of region EA (termed F). The side chains of the most potent 20-epi-22-oxa-24-homovitamin D analogues were concentrated at the left side of the EA region (L-EA). Thus, the side chains of almost all potent analogues were distributed around the EA region, and potency increased in the order A, F, EA, and L-EA.

The biological activity of nonsteroidal vitamin D hormone analogs lacking both the C- and D-rings

1alpha,25-dihydroxyvitamin D is a key calcium-regulating hormone but also displays potent differentiating and antiproliferative activities on many cell types. The structural requirements of this secosteroid hormone have been extensively studied for the A-ring and side chain, whereas relatively little is known about the requirements of the natural CD-ring structure for the vitamin D-like biological activity. We have embarked on a vast program in which derivatives were synthesized and evaluated characterized by profound structural changes in the central C/D-region. This first series of nonsteroidal analogs consists of (1R,3S)-5-((Z,2E)-4-((1S,3S)-3-(4-hydroxy-4-methylpentyl)-1,2,2-++ +trimethylcyclopentyl)-2-butenylidene)-4-methylenecyclohexan e-1,3-diol (KS 176) and derivatives thereof. These analogs are characterized by the absence of normal C- and D-rings and by the presence of an unnatural five-membered ring which we call the E-ring. KS 176 with the otherwise natural side chain structure of 1alpha,25(OH)2D3 has between 10 and 30% of the biological activity of 1alpha,25(OH)2D3 when tested in vitro (prodifferentiating effects on HL-60 and MG-63; antiproliferating activity on MCF-7 and keratinocytes) but has minimal in vivo calcemic effects. Introduction of several side chain modifications created analogs with increased intrinsic noncalcemic biological properties, whereas their calcemic potency remains very low. These data demonstrate that the full CD-rings are not mandatory for the biological activity of 1alpha,25(OH)2D3 since they can be replaced by a new ring structure which generates an appropriate spacing of the A-seco B-rings in relation to the side chain. The biological activity of these nonsteroidal analogs probably involves a classical genomic activation since they are also active in transfection assays using an osteocalcin vitamin D responsive element coupled to a human growth hormone reporter gene.

TGF-beta and calcitriol

Vitamin D3 and transforming growth factor-beta (TGF-beta) are molecules from unrelated families that share identical actions on cell growth and differentiation. The active metabolite of vitamin D3, calcitriol (1alpha,25-dihydroxyvitamin D3), induces an inhibitory effect on the growth of various cell types, and the expression of different markers of cell differentiation. As the receptor of vitamin D3 is ubiquitous, these effects are widespread in the organism. TGF-beta is a growth factor produced by many cell types, and is a known inhibitor of the proliferation of epithelial cells. Because of the similarity in their actions, many studies have been aimed at defining some interactions between the two substances. The purpose of this article is to illustrate the nature of the interactions, and two examples are developed. In normal or transformed epithelial cells, it has been demonstrated that the inhibitory effect of calcitriol on cell growth could be related to an induction of TGF-beta synthesis, and of a paracrine/autocrine loop. In bone, where both compounds play a very important role on the mechanisms controlling bone formation and remodeling, the interplay is more complex, and even includes the receptors of the two substances. Interest in this topic is growing and will surely lead to the establishment of new links between those two compounds.