Vitamin D Compounds PRI-2191 and PRI-2205 Enhance Anastrozole Activity in Human Breast Cancer Models

1,25-Dihydroxycholecalciferol, the hormonally active vitamin D₃ metabolite, is known to exhibit therapeutic effects against breast cancer, mainly by lowering the expression of estrogen receptors and aromatase activity. Previously, the safety of the vitamin D active metabolite (24R)-1,24-dihydroxycholecalciferol (PRI-2191) and 1,25(OH)₂D₃ analog PRI-2205 was tested, and the in vitro activity of these analogs against different cancer cell lines was studied. We determined the effect of the two vitamin D compounds on anastrozole (An) activity against breast cancer based on antiproliferative activity, ELISA, flow cytometry, enzyme inhibition potency, PCR, and xenograft study. Both the vitamin D active metabolite and synthetic analog regulated the growth of not only estrogen receptor-positive cells (T47D and MCF-7, in vitro and in vivo), but also hormone-independent cancer cells such as SKBR-3 (HER-2-positive) and MDA-MB-231 (triple-negative), despite their relatively low VDR expression. Combined with An, PRI-2191 and PRI-2205 significantly inhibited the tumor growth of MCF-7 cells. Potentiation of the antitumor activity in combined treatment of MCF-7 tumor-bearing mice is related to the reduced activity of aromatase by both An (enzyme inhibition) and vitamin D compounds (switched off/decreased aromatase gene expression, decreased expression of other genes related to estrogen signaling) and by regulation of the expression of the estrogen receptor ERα and VDR.

Tacalcitol increases the sensitivity of colorectal cancer cells to 5-fluorouracil by downregulating the thymidylate synthase

5-Fluorouracil (5-FU) is an anticancer drug that is most frequently used to treat colorectal cancer (CRC) patients, but unfortunately it shows limited efficacy. We recently demonstrated that vitamin D analogs (VDAs), particularly tacalcitol (coded as PRI-2191), potentiate its anticancer activity in an in vivo mouse and human CRC model. The purpose of this study was to explain the mechanism underlying the enhancement of 5-FU efficacy by PRI-2191 towards human HT-29 CRC cells. We showed that PRI-2191 induces the CDKN1A (gene encoding p21^Waf1/Cip1) expression directly through vitamin D receptor (VDR) in a p53-independent manner and thus decreases the thymidylate synthase expression both at the mRNA and protein level. It is the main mechanism by which PRI-2191 improves the anticancer efficacy of 5-FU towards HT-29 cells. Additionally, we indicated that the VDR also participates in 5-FU mechanism of action. 5-FU significantly increased TYMS (gene encoding thymidylate synthase (TS)) and BIRC5 (gene encoding survivin) level in HT-29 cells with silenced VDR. Furthermore, PRI-2191 induced E-cadherin and ZO-1 expression and thus reduced the level of BIRC5 in HT-29 cells. The induction of E-cadherin expression may also contribute to the reduction of c-Myc level and consequently the downregulation of TS. Our results also indicate that calcium-sensing receptor (CaSR) plays a role in the activity of PRI-2191 but has no influence on the 5-FU mechanism of action. In conclusion, we suggest that both VDR and CaSR might be useful as molecular markers for predicting treatment outcomes and identifying the CRC patient subgroups who might benefit from 5-FU-based chemotherapy combined with vitamin D analog.

Imatinib inhibits the regrowth of human colon cancer cells after treatment with 5-FU and cooperates with vitamin D analogue PRI-2191 in the downregulation of expression of stemness-related genes in 5-FU refractory cells

Conventional cytotoxic drugs preferentially eliminate differentiated cancer cells but spare relatively more resistant stem-like cancer cells capable to initiate recurrence. Due to cancer cell plasticity, the stem-like phenotype can be also acquired by cancer cells refractory to treatment with cytotoxic drugs. We investigated whether drugs inhibiting receptor tyrosine kinases could be used to target human colon cancer cells initiating cancer regrowth following conventional cytotoxic treatment. The moderately differentiated cell line HT-29 and poorly differentiated cell line HCT-116 were exposed to 5-fluorouracil (5-FU). Cells that resisted the exposure to 5-FU were subsequently treated with imatinib or sunitinib. Both drugs reduced clonogenicity of 5-FU-refractory cells under normoxic and hypoxic culture conditions. The expression of numerous stemness-related genes was upregulated in cancer cells following the exposure to 5-FU, and remained at a high level in 5-FU-refractory cells undergoing renewal under normoxia, but decreased spontaneously under hypoxia. Imatinib downregulated the expression of stemness-related genes in cells undergoing renewal under normoxia. A combination of imatinib with PRI-2191, an analogue of 1,25-dihydroxyvitamin D₃, downregulated stemness-related genes in HCT-116/5-FU cells more efficiently than imatinib alone. A synthetic analogue of 1,25-dihydroxyvitamin D₂ (PRI-1906) abolished the effect of imatinib on gene expression in HCT-116/5-FU cells undergoing renewal under normoxia. Sunitinib promoted shift of phenotype of HT-29/5-FU cells undergoing renewal toward stem-like one. It suggests that the phenotype shift toward stemness induced by sequential sunitinib treatment following 5-FU treatment could increase a risk of cancer recurrence. In contrast to sunitinib, imatinib could be used both to interfere with cancer regrowth after conventional chemotherapy and to downregulate the expression of stemness-related genes in residual colon cancer cells capable to initiate cancer recurrence. The findings suggest that imatinib could also be combined with vitamin D analogue PRI-2191 to prevent recurrence more efficiently than imatinib alone and to compensate for vitamin D deficiency resulting from imatinib treatment.

Mannose receptor C type 2 mediates 1,25(OH)2D3/vitamin D receptor-regulated collagen metabolism through collagen type 5, alpha 2 chain and matrix metalloproteinase 13 in murine MC3T3-E1 cells

Vitamin D plays an important role in maintaining skeletal development and bone homeostasis. Although vitamin D has been extensively researched, the direct effect of 1,25(OH)₂D₃ on osteoblasts is unclear. To explore the 1,25(OH)₂D₃ action on murine osteoblasts, we performed tandem mass tag experiments on MC3T3-E1 cells treated with and without 1,25(OH)₂D₃. Three up-regulated proteins (MRC2, WWTR1 and RASSF2) related to bone metabolism were confirmed in this study. 1,25(OH)₂D₃ up-regulated the expression of MRC2 through vitamin D receptor. MRC2 affects collagen metabolism in osteoblasts. Combined with bioinformatics and parallel reaction monitoring analysis, we inhibited the expression of MRC2 to explore the relationship between MRC2 and collagens. Then we found MRC2 down-regulated COL5A2 and up-regulated MMP13. This study provides a protein profile of 1,25(OH)₂D₃-treated murine osteoblasts, reveals a newly discovered signaling axis (1,25(OH)₂D₃/VDR/MRC2/COL5A2 and MMP13), and explains the effect of 1,25(OH)₂D₃ on bone metabolism from a new perspective.

Steroid hormone calcitriol and its analog tacalcitol inhibit miR-125b expression in a human breast cancer MCF-7 cell line

MiR-125b belongs to the class of microRNAs, which are short endogenous non-coding RNAs that negatively regulate gene expression at the post-transcriptional level. Recently, it was reported that miR-125b was found to promote migration and invasion of MCF-7 cells and was involved in chemotherapeutic resistance. Decreasing miR-125b expression would have potential therapeutic significance in preventing dissemination of breast cancer cells. The objective of this study was to evaluate miR-125b expression levels in MCF-7 cells following treatment with 1,25-dihydroxyvitamin D₃ (calcitriol) and 1,24-dihydroxyvitamin D₃ (tacalcitol), active metabolite and synthetic analog of vitamin D₃, respectively. We found that treatment with both calcitriol and tacalcitol caused a decrease in miR-125b expression. In addition, treatment with calcitriol and tacalcitol resulted in an increase in the level of pro-apoptotic BAK1 protein encoded by the target gene of miR-125b. We are discussing the putative mechanism of inhibition of the miR-125b expression by vitamin D receptor (VDR) agonists and we suggest that calcitriol and tacalcitol may be used as a miR-125b inhibitor in breast cancer cells expressing VDR.

Differential and Overlapping Effects of 20,23(OH)₂D3 and 1,25(OH)₂D3 on Gene Expression in Human Epidermal Keratinocytes: Identification of AhR as an Alternative Receptor for 20,23(OH)₂D3

A novel pathway of vitamin D activation by CYP11A has previously been elucidated. To define the mechanism of action of its major dihydroxy-products, we tested the divergence and overlap between the gene expression profiles of human epidermal keratinocytes treated with either CYP11A1-derived 20,23(OH)₂D3 or classical 1,25(OH)₂D3. Both secosteroids have significant chemical similarity with the only differences being the positions of the hydroxyl groups. mRNA was isolated and examined by microarray analysis using Illumina’s HumanWG-6 chip/arrays and subsequent bioinformatics analyses. Marked differences in the up- and downregulated genes were observed between 1,25(OH)₂D3- and 20,23(OH)₂D3-treated cells. Hierarchical clustering identified both distinct, opposite and common (overlapping) gene expression patterns. CYP24A1 was a common gene strongly activated by both compounds, a finding confirmed by qPCR. Ingenuity pathway analysis identified VDR/RXR signaling as the top canonical pathway induced by 1,25(OH)₂D3. In contrast, the top canonical pathway induced by 20,23(OH)₂D3 was AhR, with VDR/RXR being the second nuclear receptor signaling pathway identified. QPCR analyses validated the former finding by revealing that 20,23(OH)₂D3 stimulated CYP1A1 and CYP1B1 gene expression, effects located downstream of AhR. Similar stimulation was observed with 20(OH)D3, the precursor to 20,23(OH)₂D3, as well as with its downstream metabolite, 17,20,23(OH)₃D3. Using a Human AhR Reporter Assay System we showed marked activation of AhR activity by 20,23(OH)₂D3, with weaker stimulation by 20(OH)D3. Finally, molecular modeling using an AhR LBD model predicted vitamin D3 hydroxyderivatives to be good ligands for this receptor. Thus, our microarray, qPCR, functional studies and molecular modeling indicate that AhR is the major receptor target for 20,23(OH)₂D3, opening an exciting area of investigation on the interaction of different vitamin D3-hydroxyderivatives with AhR and the subsequent downstream activation of signal transduction pathways in a cell-type-dependent manner.

Calcitriol and Its Analogs Establish the Immunosuppressive Microenvironment That Drives Metastasis in 4T1 Mouse Mammary Gland Cancer

In our previous study, calcitriol and its analogs PRI-2191 and PRI-2205 stimulated 4T1 mouse mammary gland cancer metastasis. Therefore, we aimed to analyze the inflammatory response in 4T1-bearing mice treated with these compounds. Gene expression analysis of the splenocytes and regional lymph nodes demonstrated prevalence of the T helper lymphocytes (Th2) response with an increased activity of regulatory T (Treg) lymphocytes in mice treated with these compounds. We also observed an increased number of mature granulocytes and B lymphocytes and a decreased number of TCD4⁺, TCD4⁺CD25⁺, and TCD8⁺, as well as natural killer (NK) CD335⁺, cells in the blood of mice treated with calcitriol and its analogs. Among the splenocytes, we observed a significant decrease in NK CD335⁺ cells and an increase in TCD8⁺ cells. Calcitriol and its analogs decreased the levels of interleukin (IL)-1β and IL-10 and increased the level of interferon gamma (IFN-γ) in the plasma. In the tumor tissue, they caused an increase in the level of IL-10. Gene expression analysis of lung tissue demonstrated an increased level of osteopontin (Spp1) and transforming growth factor β (TGF-β) mRNA. The expression of Spp1 was also elevated in lymph nodes. Calcitriol and its analogs caused prevalence of tumor-conducive changes in the immune system of 4T1 tumor-bearing mice, despite the induction of some tumor-disadvantageous effects.

Effect of 1,25-dihydroxycholecalciferol on the duodenal villi and alkaline phosphatase in the developing chick embryo

Administration of 1,25-(OH)2D3 to developing 14-day chick embryo gave precocious induction of alkaline phosphatase in 20-day chick embryonic duodenum. 1,25-(OH)-2D3-induced alkaline phosphase involved in changes in Km and Vmax values. Furthermore, polyacrylamide gel disc electrophoresis of n-butanol-solubilized alkaline phosphatase from control and 1,25-(OH)2D3-treated chick embryonic duodenum revealed that 1,25-(OH)2D3 involved the transformation of neuraminidase-resistant fast migrating form to the neuraminidase-sensitive faster migrating one. Scanning electron microscopic data showed that the injection of 1,25-(OH)2D3 stimulated the elongation of duodenal microvilli, although there was no effect on the duodenal absorptive epithelial cell height.

Vitamin D and parathyroid hormone degradation by the kidney

Parathyroid function is controlled by the regulation of hormone secretion as well as degradation, through the action of calcium and vitamin D derivatives. In order to clarify the relationship between vitamin D metabolism and parathyroid degradation system, parathyroid hormone (PTH)-degrading activities of the kidney were measured in vitamin D repleted and depleted rats given various derivatives of vitamin D. Kidney calcium content rose markedly in animals given 10 microgram/kg 1 alpha(OH) vitamin D3 and 1,000 microgram/kg dihydrotachysterol and PTH-degrading activity rose only in these animals, indicating a parallelism between kidney calcium content and PTH-degrading activity of the kidney tissue. These vitamin D derivatives also increased the PTH-degrading activity of kidney tissue when they were added in vitro.

Anti-Inflammatory Effects of Tacalcitol (1,24(R)(OH)2D3, TV-02) in the Skin of TPA-Treated Hairless Mice

Tacalcitol (1,24(R)(OH)2D3, TV-02) inhibited the TPA-induced inflammatory cell infiltration (largely neutrophils) histopathologically and myeloperoxidase (MPO) activity dose-dependently. Tacalcitol inhibited the mRNA expression and protein production of TPA-induced macrophage inflammatory protein-2 (MIP-2) and KC, the functional analogue of human interleukin (IL)-8, in the skin. Immunohistochemical staining of the TPA-applied skin revealed that mast cells expressed MIP-2, whereas KC was observed in keratinocytes, fibroblasts and outer root sheath of hair follicles. Furthermore, tacalcitol inhibited TPA-induced mast cell degranulation 24 hr after application without influence on the total number of mast cells. In this study, tacalcitol was found to have an inhibitory effect on cutaneous inflammation such as inhibition of neutrophil infiltration, MIP-2 and KC production, and mast cell degranulation in TPA-treated hairless mice. These results suggest that tacalcitol modulates cutaneous inflammation as well as keratinocyte proliferation and differentiation, and the inhibitory effect of tacalcitol on cutaneous inflammation may contribute to clinical the effectiveness in the treatment of psoriasis.

Influence of vitamin D(3) analogues in combination with budesonid R on proliferation of nasal polyp fibroblasts

Vitamin D (VD) and its different analogues, besides their classic role as regulators of calcium and phosphor homeostasis, have emerged as a large family of antiproliferative agents. Such properties suggested VD potential as a therapy for chronic inflammatory diseases, including nasal polyposis (NP). NP growth involves both an inflammatory process and the proliferation of fibroblast as an important factor inducing aberrations in the phenotype of the epithelium. The aim of this study was to investigate the possible influence of 1alpha,25-dihydroxyvitamin D(3) (calcitriol) and 1alpha,24(R)-dihydroxyvitamin D(3) (tacalcitol) in monotherapy and in combination with budesonid R (BR) on NP fibroblast proliferation.

MATERIAL AND METHODS

The study involved 26 samples of NP. NP cells were cultured on 96-well plates beginning with a concentration of 5 x 10(3) cells per well with RPMI 1640 medium supplemented with antibiotics and 10% foetal bovine serum. After the fourth to sixth passage the medium was replaced with a nutrient medium with calcitriol or tacalcitol in a defined concentration (from 10(-9) M to 10(-3) M) alone or in combination with BR in 1:1, 1:3 or 3:1 ratios, each at concentrations from 10(-5) M to 10(-3) M.

RESULTS

Growth inhibition of nasal fibroblasts exposed to calcitriol or tacalcitol was noted. Significant antiproliferating activity was observed at calcitriol concentrations of 10(-4) M and 10(-3) M after 48 h, and at a concentration of 10(-3) M after 72 h with the percentage of proliferating cells reduced to 30% compared to the control samples (P < 0.05). In cells treated with tacalcitol the maximal effect was seen at 10(-4) M after 48 h and at 10(-3)M after 72 h with a 60% inhibition with respect to the control (P < 0.05). The inhibition of fibroblast proliferation reached the maximal level when they were exposed to calcitriol: BR (1 : 1) or tacalcitol: BR (1 : 1), each at a concentration of 10(-4) M, after 72 h (82% and 69%, respectively).

CONCLUSIONS

The antiproliferative activity of calcitriol and tacalcitol in NP cultures was confirmed. Because of its lower toxicity and higher activity tacalcitol seems to be the more promising agent in NP therapy, both as a single medication and in treatment protocols with BR.

2-methylene-19-nor-20(S)-1alpha-hydroxy-bishomopregnacalciferol [20(S)-2MbisP], an analog of vitamin D3 [1,25(OH)2D3], does not stimulate intestinal phosphate absorption at levels previously shown to suppress parathyroid hormone

Chronic kidney disease results in a reduction in 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) synthesis and an accumulation of phosphorus in the blood, leading to secondary hyperparathyroidism and renal osteodystrophy. Vitamin D analogs that retain the ability to suppress PTH but that are less calcemic and phosphatemic than the native hormone are preferred therapies for secondary hyperparathyroidism. However, even the most favored analog currently approved for the treatment of chronic kidney disease patients, i.e. 1,25-dihydroxy-19-nor-vitamin D2 (19-nor-D2, Zemplar), still retains some ability to stimulate intestinal absorption of calcium and phosphate. A recently described analog of vitamin D3, 2-methylene-19-nor-20(S)-1alpha-hydroxy-bishomopregnacalciferol [20(S)-2MbisP], suppresses PTH levels, but is unable to stimulate intestinal calcium absorption or bone resorption in rats. The present study shows that 20(S)-2MbisP is unable to stimulate intestinal phosphate absorption at levels known to suppress PTH secretion. Further, 19-nor-vitamin D2 under the same circumstances does stimulate phosphate absorption. Thus, 2MbisP has significant potential in the management of secondary hyperparathyroidism of renal failure.

The influence of 1,25-dihydroxyvitamin D3 and 1,24-dihydroxyvitamin D3 on alphavbeta3 integrin expression in cancer cell lines

Integrins are cell-surface receptors engaged in important cancer invasion processes, such as adhesion, migration, proliferation and differentiation. The aim of this study was to evaluate the effect of 1,25-dihydroxyvitamin D3 (calcitriol) and its metabolite 1,24-dihydroxyvitamin D3 (PRI-2191) on alphavbeta3 integrin expression in various cancer cell lines. The expression levels of the beta3 and alphav integrins were reduced only in the WEHI-3 and LLC cell lines by the two compounds. Calcitriol or PRI-2191 treatment caused differentiation of WEHI-3 mouse leukemia cells, but apoptosis of LLC cells. WEHI-3 and LLC cells exposed to calcitriol or PRI-2191 lost their migratory and adhesive potentials. The inhibition of migratory potential was higher in the LLC cells than in the WEHI-3 cells and appeared to correlate with the increased down-regulation of alphavbeta3 integrin by calcitriol or PRI-2191. The observed in vivo effects (antitumor and antimetastatic) in mice bearing subcutaneously transplanted LLC cancer are possibly associated with inhibited migratory potential as a consequence of the lowered integrin expression caused by calcitriol or PRI-2191.

Inhibitory effects of 1,25-dihydroxyvitamin D3 and its low-calcemic analogues on staurosporine-induced apoptosis

The active form of vitamin D3 and some of its related compounds show neuroprotective effects in various models of neuronal damage, however, mechanism of their anti-apoptotic action has not been elucidated. Therefore, the present study was designed to investigate the effects of 1,25-dihydroxyvitamin D3 and its low-calcemic analogues, PRI-2191, PRI-1890 and PRI-1901 on staurosporine-induced apoptosis in human neuroblastoma SH-SY5Y cells. Twenty-four hour incubation with staurosporine (1 microM) enhanced the caspase-3 activity, decreased mitochondrial membrane potential and increased the number of apoptotic cells as visualized by Hoechst staining. 1,25-Dihydroxyvitamin D3 and PRI-2191 attenuated the staurosporine-induced caspase-3 activity at 5, 50 and 500 nM, whereas PRI-1890 and PRI-1901 were active only at higher concentrations. Furthermore, 1,25-dihydroxyvitamin D3 (50 and 500 nM) and PRI-2191 (500 but not 50 nM) reversed the staurosporine-evoked decrease in mitochondrial membrane potential. Hoechst and calcein staining confirmed the neuroprotective effects of the secosteroids under study. Further study revealed that a selective inhibitor of phosphatidylinositol 3-kinase (PI3-K), wortmannin, at concentration of 100 nM antagonized the effect of 1,25-dihydroxyvitamin D3 and PRI-2191 on staurosporine-induced caspase-3 activation. These data indicate that 1,25-dihydroxyvitamin D3 and its low-calcemic analogues at nanomolar concentrations inhibited mitochondrial pathway of apoptosis in SH-SY5Y neuronal cells, though with different potency. Moreover, the activation of PI3-K/Akt signaling pathway appears to play a role in anti-apoptotic effects of the secosteroids.

Effect of 2-methylene-19-nor-(20S)-1 alpha-hydroxy-bishomopregnacalciferol (2MbisP), an analog of vitamin D, on secondary hyperparathyroidism

Vitamin D analogs are being developed that retain therapeutic effects but are less calcemic and phosphatemic, a concern in CKD patients who are prone to vascular calcification. We tested a new analog of vitamin D, 2MbisP, and found that it suppresses PTH at doses that do not affect serum Ca or P.

INTRODUCTION

Calcitriol is used for the treatment of secondary hyperparathyroidism. However, its use is often limited by the development of hypercalcemia and hyperphosphatemia, an important consideration in patients with chronic kidney disease (CKD) because they are prone to vascular calcification. To minimize this toxicity, structural modifications in the vitamin D molecule have led to the development of calcitriol analogs with selective actions.

MATERIALS AND METHODS

In this study, we compared the effects of 1,25(OH)(2)D(3) and a new analog, 2-methylene-19-nor-(20S)-1 alpha-hydroxy-bishomopregnacalciferol (2MbisP), on the development of secondary hyperparathyroidism and established secondary hyperparathyroidism in uremic rats and on mobilization of calcium and phosphorus from bone in parathyroidectomized rats. The clearance from circulation, half-life, and binding affinities to the vitamin D-binding protein and vitamin D receptor of this compound were also evaluated.

RESULTS

Uremia produced a marked rise in plasma PTH, but treatment every other day for 2 wk with either 1,25(OH)(2)D(3) (4 ng) or 2MbisP (250, 750, 1500, or 3000 ng) suppressed this increase by >50%. The suppression by 1,25(OH)(2)D(3), however, was accompanied by increases in ionized calcium, phosphorus, and the calcium x phosphorus product, whereas these three parameters were unchanged by 2MbisP. The binding affinity of 2MbisP was 10-20 times less for the vitamin D receptor and 1000 times less for the serum vitamin D-binding protein compared with 1,25(OH)(2)D(3). Also, 2MbisP was cleared more rapidly from the circulation (t1/2 = 10 min) than 1,25-(OH)(2)D(3) (t1/2=7-9 h). In parathyroidectomized rats fed calcium-or phosphorus-deficient diets, daily injections of 2MbisP (1500 or 3000 ng), unlike 1,25(OH)(2)D(3) (50 ng), had no effect on calcium or phosphorus mobilization from bone.

CONCLUSIONS

In uremic rats, 2MbisP can suppress PTH at doses that do not affect plasma calcium, phosphorus, and calcium x phosphorus product. This new vitamin D analog may represent an important tool in the treatment of secondary hyperparathyroidism in patients with CKD.

Involvement of PI3-K in neuroprotective effects of the 1,25-dihydroxyvitamin D3 analogue - PRI-2191

The active form of 1,25-dihydroxyvitamin D(3) prevents neuronal damage in vitro and in vivo , however, it induces also hypercalcemia and hyperphosphatemia. Side-chain-modified analogues of 1,25-dihydroxyvitamin D(3), which show low calcemic activity, may be potentially useful in the treatment of some neurodegenerative diseases. Previously, we have found that PRI-2191 more potently than 1,25-dihydroxyvitamin D(3) protects human neuroblastoma (SH-SY5Y) cells against hydrogen-peroxide-induced toxicity. In the present study, we evaluated effects of two other 1,25-dihydroxyvitamin D(3) analogues - PRI-1890 and PRI-1901 on the neuronal degeneration in the same cell model. In line with the previous study, 24-h incubation with hydrogen peroxide (0.5 mM) was toxic to cells, as evidenced by an enhanced efflux of lactate dehydrogenase into the culture medium, and these effects were prevented by PRI-1890 and PRI-1901 at concentration of 5, 50 and 500 nM. Comparing the neuroprotective effects of secosteroids, we found that all three analogues were efficient at lower concentration than 1,25-dihydroxyvitamin D(3) and among them the PRI-2191 showed the most evident concentration-dependent effect. In the second part of this study, an involvement of mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3-K), kinases which play a crucial role in neurodegenerative processes, in neuroprotective action of 1,25 dihydroxyvitamin D(3) and its the most potent analogue PRI-2191 has been investigated. The inhibitor of c-Jun N-terminal kinase (JNK)-MAPK (SP600125, 1 microM), inhibitor of p38-MAPK (SB-203580, 1 and 10 microM) and inhibitor of extracellular signal-regulated kinase (ERK)-MAPK (PD-98059, 15 and 30 microM) attenuated the hydrogen peroxide-induced toxicity. Moreover, PD-98059 (30 microM) enhanced neuroprotective effects of 1,25 dihydroxyvitamin D(3) but not that of PRI-2191. In contrast, the inhibitor of PI3-K (wortmannin, 10, 100 nM) did not affect hydrogen peroxide-induced cell damage itself, however, it significantly antagonized the effect of PRI-2191. On the other hand, wortmannin did not affect the neuroprotective effects of 1,25 dihydroxyvitamin D(3) This suggests that the activation of PI3-K/Akt signaling pathway plays an important role in the mechanism of inhibitory action of PRI-2191 on hydrogen peroxide-evoked toxicity in SH-SY5Y cells. Furthermore, these data point to differential involvement of ERK-MAPK and PI3-K in neuroprotective effects of 1,25 dihydroxyvitamin D(3) and its low-calcemic analogue - PRI-2191.

Inhibition of Monocytic Differentiation by Phosphorylation-deficient Stat1 is Associated with Impaired Expression of Stat2, ICSBP/IRF8 and C/EBPɛ

Monocytic differentiation is coordinated through the ordered activation of multiple signalling pathways, controlling transcription of specific subsets of genes that regulate the development of the mature phenotype. To identify key transcription factors involved in this process, we used the human monoblastic U-937 cell line as a model of monocytic differentiation. U-937 cells can be differentiated by treatment with all-trans retinoic acid (ATRA) and 1,25alpha-dihydroxycholecalciferol (VitD3), resulting in G(0)/G(1)-arrested cells expressing monocytic surface markers. We have previously shown that ATRA-induced differentiation and cell cycle arrest specifically requires Stat1 activation, through phosphorylation of tyrosine 701 and serine 727. In this report, we used U-937 cells expressing phosphorylation-deficient mutants of Stat1 (Stat1Y701F and Stat1S727A) to determine myeloid-specific transcription factors that are activated downstream of Stat1 during induced monocytic differentiation. We demonstrate that ATRA-induced upregulation of Stat2, ICSBP/IRF8 and C/EBPepsilon, key transcription factors linked to myelomonocytic differentiation, is selectively impaired in cells expressing mutant Stat1. In contrast, ATRA-induced expression of PU.1, C/EBPalpha, C/EBPbeta and IRF-1 was unaffected. Taken together, our data suggest that ATRA-induced regulation of Stat2, ICSBP and C/EBPepsilon is dependent on active Stat1, and that a failure to correctly regulate these transcription factors is associated with the inhibition of monocytic differentiation.

Antiproliferative activity of vitamin D compounds in combination with cytostatics

Calcitriol is a potent antiproliferative agent against various tumour cells in vitro. Here, the results of a study on vitamin D compounds (calcitriol's analogues PRI-1906 and PRI-2191) as potential agents in combined antitumour therapy in vitro are presented. Applying antiproliferative SRB and MTT assays, the growth inhibitory effects of the vitamin D compounds, applied alone or in combination with either cisplatin or doxorubicin, were measured. The following cancer cell lines were employed: A549 (human non-small cell lung carcinoma), B16 (murine melanoma), CCRF, HL-60 (human leukaemia), SW707 (human colon cancer), MCF-7, T47D (human breast cancer), WEHI-3 (mouse leukaemia) and normal cells: BALB 3T3 (normal murine fibroblast cell line). It was shown that the treatment of tumour cells, which are sensitive to vitamin D compounds, with the combination of vitamin D compounds and cytostatics decreased the inhibitory concentration 50% (IC50) values compared with the effects of the cytostatics applied alone.

Correlation between VDR expression and antiproliferative activity of vitamin D3 compounds in combination with cytostatics

Calcitriol is a potent antiproliferative agent against various tumour cells in vitro. Its biological activity is mediated by the vitamin D receptors (VDRs). Here, we present the results of a study on vitamin D3 compounds (calcitriol and its analogue PRI-2191) as potential agents in combined antitumour therapy in vitro. Applying antiproliferative SRB and MTT assays, we measured the growth inhibitory effects of vitamin D compounds applied alone or in combination with either cisplatin or doxorubicin. Next, we examined the correlation of this effect with the presence of nVDR (nuclear VDR). The following cancer cell lines were applied: HL-60 (human leukaemia), SW707 (human colon cancer), A549 (human lung cancer), WEHI-3 (mouse leukaemia). The treatment of tumour cells with the combination of vitamin D compounds and cytostatics decreased the inhibitory concentration 50% (IC50) values compared with the effects of cytostatics applied alone. The synergistic effect was positively correlated with nVDR expression.

Profile of clinical efficacy and safety of topical tacalcitol

Several topical treatments such as ointments, keratolytics, dithranol, tar, corticosteroids and Vitamin D3 analogues are commonly used in the treatment of mild and/or moderate psoriasis. These treatments can be associated with a variety of local and systemic side effects, as well as to very often unsatisfactory results. The purpose of this critical review of the literature is to evaluate the efficacy and tolerability of the synthesis of new analogues of the Vitamin D3 Tacalcitol, which is formulated in ointment form at a concentration of 4 microg/g, for the treatment of mild and/or moderate psoriasis (involvement of <20% of the surface of the skin) and to evaluate whether this drug can be used in the treatment of other skin conditions. Based on existing data in the literature, Tacalcitol is an effective drug for the topical treatment of psoriasis and is also able to ensure that the effects last over time, even after treatment has stopped. Tacalcitol is also well tolerated because the onset of side effects, such as local irritation, pruriginous or burning sensations, were reported in only a small percentage of the subjects who were treated. Lastly, the marked regulatory effects it has on the proliferation and differentiation of keratinocytes, as well as on the immunocompetent cells, has led to suggestions that Tacalcitol may be used in other keratinisation disorders and in some hyperproliferative skin diseases. Evaluation of the effective indications to use in these conditions still requires further data confirming its effectiveness, opening the way to wider use of this molecule in dermatology.

Toxicity and antineoplastic effect of (24R)-1,24-dihydroxyvitamin D3 (PRI-2191)

Many efforts have been made to obtain active and less toxic Vitamin D analogs for new clinical applications. The results of previous studies demonstrated the efficacy and safety of topical treatment of psoriasis with one of these analogs, 1,24-dihydroxyvitamin D(3), tacalcitol (1,24-(OH)(2)D(3)). In the present study, we evaluated the toxicity and antitumor effect of this analog. Lethal toxicity of 1,24-(OH)(2)D(3) after s.c. injection was significantly lower than that of calcitriol. No significant differences were observed in the toxicity of the analogs when administered p.o. Calcium levels in the serum of mice treated with calcitriol were significantly higher (111%) than those in mice treated with 1,24-(OH)(2)D(3) (89%) at 5 day after the first s.c. (10 microg/kg/day) administration in comparison to the control (healthy, untreated animals). Oral administration increased the calcium level by 78% for calcitriol and only to 47% over the control for 1,24-(OH)(2)D(3). Parallel administration of clodronate prevented the calcitriol- and 1,24-(OH)(2)D(3)-induced lethal toxicity and also prevented increase in calcium levels. Single therapy with calcitriol did not affect tumor growth in the 16/C mouse mammary cancer model. In contrary, 1,24-(OH)(2)D(3) alone reduced tumor volume to 41% of control. Cisplatin alone did not affect growth of 16/C tumor in these conditions. The growth of tumors in the presence of cisplatin was inhibited by 1,24-(OH)(2)D(3) but not by calcitriol. Interestingly, the inhibition of tumor growth in cisplatin-treated mice by 1,24-(OH)(2)D(3) was greater, than that observed in mice treated with this analog alone. In conclusion, 1,24-(OH)(2)D(3) revealed higher antitumor and lower calcemic activity and toxicity than calcitriol. Application of biphosphonates along with Vitamin D analogs is sufficient to overcome the calcemic and toxic side effects of the proposed treatment.

Neuroprotective effects of (24R)-1,24-dihydroxycholecalciferol in human neuroblastoma SH-SY5Y cell line

The active form of Vitamin D(3) has been reported to prevent neuronal damage caused by a variety of insults, however, it may also induce undesirable hypercalcemic effects. In the present study, we evaluated effects of (24R)-1,24-dihydroxycholecalciferol (PRI-2191) on hydrogen peroxide- and excitatory amino acid-induced neuronal damage in human neuroblastoma (SH-SY5Y) cell line. Exposure of SH-SY5Y cells to N-methyl-d-aspartate (NMDA; 5mM), kainate (0.2mM) and hydrogen peroxide (0.1-1mM) significantly enhanced lactate dehydrogenase release. Furthermore, the neurotoxic effects of hydrogen peroxide was dependent on c-Jun N-terminal kinase (JNK)- and p38- mitogen-activated protein kinase (MAPK) activity. Both secosteroids at nanomolar concentrations inhibited neuronal damage, but their efficacy varied depending on the toxic agent. PRI-2191 was equipotent as 1alpha,25-dihydroxyVitamin D(3) in protecting SH-SY5Ycells against NMDA toxicity, and had stronger effect against hydrogen peroxide-induced damage, but was less efficient against kainate-induced injury. The obtained results suggest potential usefulness of PRI 2191 in the treatment of neurodegenerative diseases.

The third multidisciplinary conference on drug research, Piła 2002. Effects of 1alpha,25-dihydroxyvitamin D3 and some putative steroid neuroprotective agents on the hydrogen peroxide-induced damage in neuroblastoma-glioma hybrid NG108-15 cells

Steroids are implicated in the regulation of neurodegenerative processes including oxidative stress. The aim of this study was to compare the effects of 1alpha,25-dihydroxyvitamin D3 (calcitriol) and its low-calcemic analogue (24R)-1,24-dihydroxycholecalciferol (tacalcitol, PRI-2191) and some putative neuroprotective steroids belonging to various pharmacological groups on the hydrogen peroxide-induced cytotoxicity in NG108-15 cell line. Both secosteroids prevented in a concentration-dependent manner (50-500 nM) the hydrogen peroxide-induced lactate dehydrogenase release in the NG108-15 cells. Estrogens (17beta-estradiol and estriol, 100 and 1000 nM) also protected these cells. Of the two neurosteroids tested at micromolar concentrations, dehydroepiandrosterone sulphate markedly reduced cell damage, whereas the allopregnanolone showed a weak neuroprotective effect. These data support some previous observations on the antineurotoxic action of neurosteroids and indicate that calcitriol and its low-calcemic analogue PRI-2191 have neuroprotective properties comparable to those of estrogens. Considering the undesired effects of estrogens, it seems that some calcitriol analogues may be alternative drugs in the treatment of some oxidative stress-related neurodegenerative disorders.

Pharmacological profiles of high-concentration (20 microg/g) tacalcitol ointment: effects on cutaneous inflammation, epidermal proliferation, and differentiation in mice

This study focused on the effects of tacalcitol (1,24 (R) (OH)2D3, TV-02) ointment (20 micro g/g) on cutaneous inflammation, epidermal proliferation, and differentiation and compared them with tacalcitol ointment (2 micro g/g) and other anti-psoriatic ointments using hairless mice. Tacalcitol ointment (0, 2 and 20 micro g/g) significantly inhibited 12-O-tetradecanoylphorbol 13-acetate (TPA)-induced cutaneous inflammation, histopathologically. The effect of tacalcitol ointment (20 micro g/g) on cutaneous inflammation was much stronger than that of tacalcitol ointment (0, 2 micro g/g), and as effective as calcipotriol ointment (50 micro g/g) or betamethasone valerate ointment (1.2 mg/g). Tacalcitol ointment (20 micro g/g) also significantly inhibited TPA-induced myeloperoxidase (MPO) activity, as effectively as calcipotriol ointment (50 micro g/g) or betamethasone valerate ointment (1.2 mg/g). The effect of tacalcitol ointment on epidermal proliferation [ornithine decarboxylase (ODC) activity] and differentiation [transglutaminase (TGase) activity] was dose-dependent from 0 micro g/g to 20 micro g/g. The effect of tacalcitol ointments on epidermal proliferation was significant at the doses of 2 micro g/g and 20 micro g/g, and that on epidermal differentiation was significant at the doses of 0.2 micro g/g or more. The effect of tacalcitol ointment (20 micro g/g) on epidermal differentiation was significantly stronger than tacalcitol ointment (2 micro g/g). In this study, tacalcitol ointment (20 micro g/g) was found to have a marked effect on cutaneous inflammation and improved effect on epidermal differentiation, although tacalcitol ointment (2 micro g/g) also had significant effects on epidermal proliferation and differentiation. These findings support the clinical effectiveness of tacalcitol ointment (20 micro g/g) against psoriasis.

Open trial of topical tacalcitol [1 alpha 24(OH)2D3] and solar irradiation for vitiligo vulgaris: upregulation of c-Kit mRNA by cultured melanocytes

Vitiligo vulgaris is a common skin disease, however some cases show poor clinical responses to topical steroid ointment or PUVA therapy. Such regimens are generally avoided in the treatment of facial lesions or in pediatric cases because of the undesirable side effects. To confirm the excellent response to combination therapy with topical vitamin D3 ointment and solar irradiation for vitiligo achieved in the initial patients, we conducted an open trial on other patients, most of whom had poor clinical responses to the prior therapies. Fifteen patients (9 men and 6 women) with vitiligo vulgaris were enrolled in this study. Each patient was instructed to sunbathe for 30 minutes within 1 hour after topical application of the tacalcitol [1 alpha 24(OH)(2)D(3)] ointment or cream to the skin lesions every day. Six of 15 patients showed a fair and excellent clinical response to the combination therapy (more than 30% clearance of the vitiligo). The clinical effect was more apparent in patients with a history of less than 5 years of vitiligo (4 of 6 cases) in contrast to those with a history of more than 5 years (2 of 9 cases). In vitro experiments revealed that tacalcitol upregulated the expression of c-Kit mRNA by melanocytes irradiated with linear polarized infrared, UVA or short period solar irradiation. These results suggest that combination therapy with topical vitamin D(3) ointment and solar irradiation can be used as an alternate therapy for vitiligo vulgaris.

Similarly potent action of 1,25-dihydroxyvitamin D3 and its analogues, tacalcitol, calcipotriol, and maxacalcitol on normal human keratinocyte proliferation and differentiation

BACKGROUND

The active vitamin D3 regulates proliferation and differentiation of epidermal keratinocytes. Recently topical vitamin D3, tacalcitol, calcipotriol, and maxacalcitol are widely used for psoriasis.

OBJECTIVE

To examine the effect of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) on cultured normal keratinocytes (NHK) and compared its effect with those of various vitamin D3 analogues.

METHODS

Cell proliferation of NHK cells was analyzed by MTS, BrdU and 3H-thymidine incorporation. The expression of involucrin, transglutaminase 1, keratin 5 and keratin 1 was investigated by western blot and PCR amplification and quantitative assay. Furthermore, we performed cornified cell envelope (CE) formation assay.

RESULTS

1,25(OH)2D3, tacalcitol, calcipotriol, and maxacalcitol decreased NHK cell proliferation in a concentration-dependent manner and the maximal effect was observed at 10(-7) M. There was no significant difference in the anti-proliferative effect among the active vitamin D3 analogues. The expression of involucrin and transglutaminase 1 were induced by 1,25(OH)2D3 and its analogues in mRNA and protein levels. CE formation was also induced by 1,25(OH)2D3 and its analogues. There was no significant difference in the potency among these chemicals. Keratin 5 and 1 expression was not altered by these active vitamin D3 analogues.

CONCLUSIONS

The present study demonstrated that active vitamin D3 analogues, tacalcitol, calcipotriol, and maxacalcitol, suppress keratinocyte proliferation and induce differentiation with similar potency.

Novel detection and differential utilization of a c-myc transcriptional block in colon cancer chemoprevention

Mutations in the adenomatous polyposis coli (APC) gene, which initiate almost all human colon cancers, directly target the proto-oncogene, c-myc, by elevating beta-catenin/T-cell factor (TCF) signaling. We have shown that agents ascribed chemopreventive activity for colon cancer in fact also stimulate beta-catenin/TCF activity in vitro. Their effects on c-myc transcription were assayed using a novel variant of fluorescence in situ hybridization that detects c-myc transcription sites in intact nuclei. Increased transcriptional initiation of c-myc induced by the short-chain fatty acid, butyrate, consistent with elevated beta-catenin/TCF activity, was efficiently abrogated by a block to transcriptional elongation, resulting in decreased c-myc expression. 1alpha,25-Dihydroxyvitamin D(3) also induced transcriptional blockage. In contrast, the nonsteroidal anti-inflammatory drug, sulindac, increased c-myc expression, an effect attributable at least in part to its failure to induce transcriptional blockage. We have described a novel approach for evaluating the effects of chemopreventive agents on the expression of a gene critical in colonic tumorigenesis.

[1 alpha, 25-dihydroxyvitamin D3 and its analogues modulate the phagocytosis of human monocyte-derived dendritic cells]

AIM

To investigate the role of 1 alpha, 25-dihydroxyvitamin D3 (calcitriol) and its analogues tacalcitol and 24, 25(OH)2D3 on the phagocytosis of human monocyte-derived dendritic cells (MoDC).

METHODS

MoDC were generated in vitro by differentiating monocytes in the presence of GM-CSF and IL-4 for 5 days. Expression of mannose receptor (MR) and Fc gamma receptors (Fc gamma Rs) by MoDC was analysed by flow cytometry. Zymosan ingestion was measured to assess the phagocytosis of MoDC.

RESULTS

MoDC expressed high level of MR and Fc gamma Rs and showed the capacity of zymosan ingestion. Calcitriol and tacalcitol but no 24, 25(OH)2D3 not only upregulated the expression of MR and Fc gamma Rs on MoDC but also correspondingly enhanced their phagocytosis by increasing zymoasan ingestion. Furthermore, the upregulatory role occurred in the early stage of MoDC differentiation and was irreversible. The upregulatory role of calcitriol was dose dependent.

CONCLUSION

Calcitriol and its analogue tacalcitol may play an important role in dendritic cell binding and capturing foreign antigens at the initiation of immune response.

1alpha,25-Dihydroxyvitamin D3 modulates human adipocyte metabolism via nongenomic action

We reported recently that suppression of the renal 1alpha,25-dihyroxyvitamin D3 (1lpha,25-(OH)2-D3) production in aP2-agouti transgenic mice by increasing dietary calcium decreases adipocyte intracellular Ca2+ ([Ca2+]i), stimulates lipolysis, inhibits lipogenesis, and reduces adiposity. However, it was not clear whether this modulation of adipocyte metabolism by dietary calcium is a direct effect of inhibition of 1alpha,25-(OH)2-D3-induced [Ca2+]i. Accordingly, we have now evaluated the direct role of 1alpha,25-(OH)2-D3. Human adipocytes exhibited a 1alpha,25-(OH)2-D3 dose-responsive (1-50 nM) increase in [Ca2+]i (P<0.01). This action was mimicked by 1alpha,25-dihyroxylumisterol3 (1alpha,25-(OH)2-lumisterol3) (P<0.001), a specific agonist for a putative membrane vitamin D receptor (mVDR), and completely prevented by 1b,25-dihydroxyvitamin D3 (1beta,25-(OH)2-D3), a specific antagonist for the mVDR. Similarly, 1alpha,25-(OH)2-D3 (5 nM) caused 50%-100% increases in adipocyte fatty acid synthase (FAS) expression and activity (P<0.02), a 61% increase in glycerol-3-phosphate dehydrogenase (GPDH) activity (P<0.01), and an 80% inhibition of isoproterenol-stimulated lipolysis (P<0.001), whereas 1beta,25-(OH)2-D3 completely blocked all these effects. Notably, 1alpha,25-(OH)2-lumisterol3 exerted more potent effects in modulating adipocyte lipid metabolism, with 2.5- to 3.0-fold increases in FAS expression and activity (P<0.001) and a threefold increase in GPDH activity (P<0.001). Also 1alpha,25-(OH)2-lumisterol3 was approximately twice as potent in inhibiting basal lipolysis (P<0.025), whereas 1beta,25-(OH)2-D3 completely blocked all these effects. These data suggest that 1alpha,25-(OH)2-D3 modulates adipocyte Ca2+ signaling and, consequently, exerts a coordinated control over lipogenesis and lipolysis. Thus, a direct inhibition of 1alpha,25-(OH)2-D3-induced [Ca2+]i may contribute to an anti-obesity effect of dietary calcium, and the mVDR may represent an important target for obesity.

Tacalcitol, an active vitamin D3, induces nerve growth factor production in human epidermal keratinocytes

The human epidermal keratinocyte cell line K-TL-1, developed from a benign epidermal tumor, was cultured in the presence of the synthetic vitamin D3 analogue tacalcitol [1alpha,24(R)-dihydroxyvitamin D3] to assess the effects on the production of nerve growth factor (NGF). Confluent K-TL-1 cells were cultured with 10(-8) M of tacalcitol. Supernatants and cell homogenates were collected and NGF concentrations were determined by enzyme-linked immunosorbent assay. The concentration of NGF in the supernatants of cultures treated with tacalcitol peaked within 24 h after the start of tacalcitol treatment and remained stable for 96 h. This NGF induction caused by tacalcitol was dose-dependent, showing an ED50 between 10(-10) and 10(-9) M. Induction of NGF mRNA expression by tacalcitol was also observed by RT-PCR, indicating that tacalcitol induced NGF expression through transcriptional activation. These results suggest that active vitamin D3 could treat peripheral neuropathy by inducing NGF production in the skin.

Tributyrin, a stable and rapidly absorbed prodrug of butyric acid, enhances antiproliferative effects of dihydroxycholecalciferol in human colon cancer cells

Tributyrin, a prodrug of natural butyrate, has been evaluated with an aim to overcome pharmacokinetic drawbacks of natural butyrate as a drug, i.e., its rapid metabolization and inability to achieve pharmacologic concentrations in neoplastic cells. We studied the effects of tributyrin on growth, differentiation and vitamin D receptor expression in Caco-2 cells, a human colon cancer cell line. Tributyrin was more potent in inhibiting growth and inducing cell differentiation than natural butyrate. The effect was further enhanced after addition of physiologic concentrations of dihydroxycholecalciferol [(OH)2D3]. The synergistic effect of tributyrin and (OH)2D3 in Caco-2 cells was due to tributyrin-induced overexpression of the vitamin D receptor, as measured by reverse transcriptase-polymerase chain reaction. Treatment with tributyrin increased binding of (OH)2D3 to its receptor 1.5-fold, without any change in receptor affinity. We conclude that tributyrin may, at least in part, exert its growth-reducing and differentiation-inducing effect in Caco-2 cells by an upregulation of the vitamin D receptor; this may provide a useful therapeutic approach in chemoprevention and treatment of colorectal cancer by the two nutrients occurring naturally in human diet.

24-Oxo metabolites of vitamin D3 analogues: disassociation of their prominent antileukemic effects from their lack of calcium modulation

The seco-steroid hormone, 1alpha,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] inhibits proliferation and induces differentiation of malignant cells including those of the hematopoietic system. The 24-oxo metabolite of 1,25(OH)(2)D(3) also has prominent antiproliferative activities against various cancer cells. We chemically synthesized five novel 24-oxo vitamin D(3) analogues and evaluated their abilities both to inhibit clonal growth and induce differentiation of myeloid leukemia cells and to cause hypercalcemia. The 1alpha,25-dihydroxy-16-ene-D(3) [1,25(OH)(2)-16-ene-D(3)] and 1alpha,25-dihydroxy-16-ene-19-nor-D(3) [1,25(OH)(2)-16-ene-19-nor-D(3)] and their 24-oxo metabolites showed greater potency than 1,25(OH)(2)D(3) in their abilities to inhibit clonal proliferation of HL-60, NB4, and U937 leukemic cell lines as measured by methylcellulose soft-gel assay. Their inhibition of clonal growth was irreversible as analyzed by pulse exposure studies. The synthetic analogues also had greater potency than 1,25(OH)(2)D(3) to induce differentiation of HL-60 and NB4 cells as measured by generation of superoxide, nonspecific esterase production, and induction of CD11b and CD14 cell surface antigens and to increase the proportion of these cells in the G(0)-G(1) phase of the cell cycle. For most assays, the 24-oxo metabolite was slightly more potent than the unmodified analogue, and 50% activity was usually found in the nanomolar range. These analogues and their 24-oxo metabolites also inhibited fresh leukemic cell clonal proliferation. Expression of p27(KIP1), a cyclin-dependent kinase inhibitor that plays an important role in blocking the cell cycle, was found by Western blot analysis to be induced by the analogues and their 24-oxo metabolites in both HL-60 and U937 cells, suggesting a possible mechanism by which these analogues inhibit leukemic growth. Notably, the calcemic activity tested by injections of 1alpha,25-dihydroxy-16-ene-24-oxo-19-nor-D(3) in mice was at least 12-fold less than 1alpha,25(OH)(2)-16-ene-19-nor-D(3). Taken together, chemically synthesized 24-oxo metabolites of 1alpha,25(OH)(2)-16-ene-D(3) and 1alpha,25(OH)(2)-16-ene-19-nor-D(3) irreversibly inhibited proliferation and induced differentiation of acute myeloid leukemia cells with minimal toxicity; these compounds may have a role in the maintenance phase of therapy for acute myeloid leukemia.

Reduced bone resorption in toothless (osteopetrotic) rats--an abnormality of osteoblasts related to their inability to activate osteoclast activity in vitro

Osteopetrosis is a heterogeneous group of metabolic bone disorders characterized by reduced bone resorption. In the toothless (tl) osteopetrotic rat mutation there are few osteoclasts and mutants are not cured by bone marrow transplants. This suggests that the defect(s) in tl rats is within the skeletal microenvironment and not one of stem cell incompetence. Osteoblasts are known to play a role in bone resorption and abnormalities in these cells have been reported in tl rats. We explored the ability of osteoblasts from tl rats to activate resorption by normal osteoclasts when co-cultured in the presence of 1,25-dihydroxyvitamin D (1,25(OH)2D). Stimulation with 1,25(OH)2D produced a highly significant response in normal osteoblast co-cultures, but no response was observed in mutant cultures over a wide dose range. Ligand-binding studies demonstrated no abnormalities in vitamin D receptor (VDR) affinity, but mutant osteoblasts had reduced VDR numbers. Taken together with the demonstrated resistance of these mutants to the hypercalcemic effects of 1,25(OH)2D and parathyroid hormone in vivo, these data implicate osteoblasts in the pathogenesis of this mutation.

Effects of calcitriol and its analogues on interaction of MCP-1 and monocyte derived dendritic cells in vitro

AIM

To study the effect of calcitriol [1,25(OH)2D3] and its analogues on the interaction of monocyte chemoattractant protein-1 (MCP-1) and in vitro generated monocyte-derived dendritic cells (MoDC).

METHODS

MoDC were obtained by differentiating monocytes in exposure to GM-CSF and IL-4 for 5 d. mRNA expression of MCP-1 and its receptors were analyzed by RT-PCR, and protein production of MCP-1 by ELISA and migratory ability of MoDC in response to MCP-1 by a micromultiwell chemotaxis chamber assay.

RESULTS

MoDC can express MCP-1 mRNA, and secret a low level of MCP-1 protein and has the ability to migrate to MCP-1 in corresponding to its expression of MCP-1 receptors. Calcitriol and its analogues with the same affinity to vitamin D receptor up-regulated the gene expression of both MCP-1 and its receptors, enhanced MCP-1 protein production and promoted the migratory ability of MoDC to MCP-1.

CONCLUSION

The interaction of DC and MCP-1 found in this study may suggest a possible auto-regulatory role between DC and MCP-1 and the modulatory effect of calcitriol and its analogues on DC and MCP-1 might provide an understanding of their positive role in tumors.

Comparison of the relative effects of 1,24-dihydroxyvitamin D(2) [1, 24-(OH)(2)D(2)], 1,24-dihydroxyvitamin D(3) [1,24-(OH)(2)D(3)], and 1,25-dihydroxyvitamin D(3) [1,25-(OH)(2)D(3)] on selected vitamin D-regulated events in the rat

The present experiments were conducted to compare the relative hypercalciuric and hypercalcemic activities of 1,24-dihydroxyvitamin D(2) [1,24-(OH)(2)D(2)], 1,24-dihydroxyvitamin D(3) [1, 24-(OH)(2)D(3)], and 1,25-dihydroxyvitamin D(3) [1,25-(OH)(2)D(3)] in 7-week-old rats. The rats were dosed orally with each sterol for 7 days at a rate of 1 ng/g body weight/day. We also monitored the effect of the three compounds on the induction of mRNA for CaATPase and for 25-hydroxyvitamin D-24-hydroxylase in the kidney and intestine, on plasma vitamin D metabolite levels, and on the capacity to evoke modification in the vitamin D receptor/retinoic acid X receptor (VDR/RXR) heterodimer conformation. Plasma calcium was elevated in the rats treated with 1,24-(OH)(2)D(3) and 1, 25-(OH)(2)D(3), but not in the 1,24-(OH)(2)D(2)-dosed rats. Urinary calcium was elevated significantly (relative to controls) in all groups. The order of hypercalciuric activity was 1,25-(OH)(2)D(3) >/= 1,24-(OH)(2)D(3) >/= 1,24-(OH)(2)D(2) > control. Duodenal plasma membrane calcium ATPase (PMCA) mRNA was elevated to a similar extent in all groups relative to controls. Duodenal 24-hydroxylase mRNA was elevated in all groups relative to controls; however, the elevations were significantly higher in the 1,24-(OH)(2)D(3) and 1, 25-(OH)(2)D(3) groups compared with the 1,24-(OH)(2)D(2) group. Kidney 24-hydroxylase also was elevated significantly in the 1, 24-(OH)(2)D(3)- and 1,25-(OH)(2)D(3)-treated rats but not in the 1, 24-(OH)(2)D(2)-treated rats. Recombinant human vitamin D receptor (hVDR) extracts were incubated with saturating concentrations of 1, 24-(OH)(2)D(2), 1,24-(OH)(2)D(3), and 1,25-(OH)(2)D(3) and subsequently analyzed by electrophoretic mobility shift assay (EMSA). Overall binding was comparable for all metabolites; however, the 1, 24-(OH)(2)D(2) complex exhibited distinctly altered mobility relative to 1,24-(OH)(2)D(3) and 1,25-(OH)(2)D(3), suggestive of an effect on hVDR/hRXR conformation. These data suggest that 1, 24-(OH)(2)D(2) is not as potent as either of the vitamin D(3) sterols at affecting hypercalcemia or hypercalciuria in young growing rats; however, 1,24-(OH)(2)D(2) can evoke other biological responses similar to the vitamin D(3) sterols. These different responses may be related to the alterations in conformation state of the hVDR/hRXR heterodimer.

Recent developments in vitamin D analogs

Within the past decade it has been shown that psoriasis can be treated topically with analogs of vitamin-D3. Impaired differentiation and increased proliferation of keratinocytes are key features in psoriatic lesions together with a local activation of T lymphocytes. Evidence has accumulated showing that analogs of vitamin D3 increase differentiation and inhibit proliferation of keratinocytes. Therefore, analogs of vitamin D3 have been investigated in a number of trials showing improvement of psoriasis. It has been shown that vitamin D analogs are better than their vehicle and show the same potency as potent topical steroids. However, vitamin D analogs have been proven efficacious and without side effects also when used on long term basis. Vitamin D analogs can be used both as monotherapy and in combination topical steroids, UVB, PUVA, retinoids and cysclosporine. The vitamin D3 analog calcipotriol has been investigated in most detail and is available as an ointment, a creme and as a scalp solutation. From clinical studies involving thousands of patients, it can be concluded that calcipotriol is efficacious, safe, well tolerated and can be used on a long term basis. Other analogs are available, however, these analogs have not been studied in greater details yet.

Different vitamin D analogues induce sphingomyelin hydrolysis and apoptosis in the human keratinocyte cell line HaCaT

Sphingomyelin hydrolysis seems to be a ubiquitous pathway generating ceramide, an important cell response modifier. Upon agonist-stimulation this pathway is linked to biological responses as inhibition of proliferation, promotion of differentiation and induction of apoptosis. One of the agonists described is 1alpha,25-dihydroxyvitamin D3. Recently, we could demonstrate the existence of sphingomyelin hydrolysis in human primary keratinocytes as well as in the human keratinocyte cell line HaCaT after treatment with 1alpha,25-dihydroxyvitamin D3. In the present study we tested four vitamin D analogues on HaCaT keratinocytes for their ability to inhibit cell proliferation and to induce sphingomyelin hydrolysis. These analogues, calcipotriol, EB 1213, GS 1500 and tacalcitol inhibit cell growth after 48 hrs. of incubation and trigger the hydrolysis of sphingomyelin. Moreover, all analogues tested induce apoptotic cell death in HaCaT keratinocytes after 24 hrs. of incubation. This study indicates that sphingomyelin hydrolysis, subsequently leading to the elevation of cellular ceramide levels, may represent an important signal transduction pathway for 1alpha,25-dihydroxyvitamin D3 and its analogues in human keratinocytes. Possible differences of the mechanism underlying vitamin D-induced sphingomyelin hydrolysis has to be studied in more detail and may contribute to the antipsoriatic action of these analogues.

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.

Influence of tacalcitol on cell cycle kinetics of human keratinocytes following standardized injury

In the last few years, tacalcitol (1alpha,24-dihydroxy vitamin D(3), TV-02) has become widely available for the topical treatment of psoriasis. Several studies documented its effect on epidermal differentiation, inflammation and proliferation. Especially the effect on epidermal proliferation has shown to be most substantial. This finding strongly suggests that the antipsoriatic effect of tacalcitol may be mediated by the normalization of epidermal cell cycle kinetics. Aim of the present study was to investigate the effect of tacalcitol ointment (4 microg/g) compared with the ointment base on epidermal proliferation following tape stripping. In particular, we addressed the question to what extent tacalcitol influences the recruitment of G(0) cells after standardized injury. In 15 healthy volunteers, Sellotape(TM) stripping of the epidermis was performed at two places on the lower back. Then, tacalcitol ointment (4 microg/g) and the ointment base were applied on the lesions and covered by a semiocclusive dressing. Punch biopsies of the lesions were obtained at 24, 32, 38, 44, 50, and 56 h after tape stripping. Using a flow cytometric staining procedure with parameters for epidermal proliferation (DNA content), differentiation (keratin 10 expression) and nonmesenchymal cells (vimentin expression), quantitative data were obtained. There was a statistically significant difference between the time intervals for tacalcitol and placebo with respect to the percentage of recruited basal cells in S phase: The peak of recruited basal cells in S phase was seen at 38 h for the placebo-treated lesions, whereas this peak was seen at 50 h for the tacalcitol-treated lesions. There was no significant difference in the total number of recruited cells between tacalcitol and placebo. The influence of tacalcitol on epidermal keratinization and on the percentage of nonkeratinocytes did not show any significance compared to placebo. We concluded that the mode of action of tacalcitol on proliferation is mainly through an extension of the cell cycle time of keratinocytes and/or an extension of the duration of the recruitment process of cycling cells, whereas the ability to suppress recruitment of resting keratinocytes is not different from placebo. Moreover, because of the limited effect of tacalcitol on epidermal keratinization, combination treatments with agents which interfere with keratinization and/or inflammation may be attractive.

Biological activity profiles of 1alpha,25-dihydroxyvitamin D2, D3, D4, D7, and 24-epi-1alpha,25-dihydroxyvitamin D2

We have synthesized several 1alpha,25-dihydroxyvitamin D [1alpha,25(OH)2D] derivatives and evaluated their biological activity in terms of their binding affinity for the vitamin D receptor (VDR) and vitamin D-binding protein (DBP), antiproliferative or differentiation-inducing effects on human promyelocytic leukemic HL-60 cells, and transcriptional activity on a rat 25-hydroxyvitamin D3-24-hydroxylase gene promoter, including two vitamin D-responsive elements (VDREs), and human osteocalcin gene promoter, including a VDRE in transfected human osteosarcoma MG-63 cells. Furthermore, human VDR- or retinoic acid X receptor alpha (RXR alpha)-mediated luciferase activities of the derivatives were also measured by a one-hybrid system in human epitheloid carcinoma, cervix HeLa cells and African green monkey kidney CV-1 cells. Binding affinity for VDR, bone-resorbing activity, antiproliferative and cell-differentiating effects, transactivation potencies on target genes and VDR- or RXR alpha-mediated gene regulations of 1alpha,25(OH)2D2 and 1alpha,25(OH)2D4 were almost comparable to the effects of 1alpha,25(OH)2D3 while 24-epi-1alpha,25(OH)2D2 and 1alpha,25(OH)2D7 were much less active than 1alpha,25(OH)2D3 in these respects. This is the first report concerning biological assessment of 1alpha,25(OH)2D2, 1alpha,25(OH)2D3, 1alpha,25(OH)2D4, 24-epi-1alpha,25(OH)2D2 and 1alpha,25(OH)2D7 at the molecular level, especially with regards to the structural differences at the 24R- or 24S-methyl group and a double bond between carbons 22 and 23 in the side chain of 1alpha,25(OH)2D derivatives.

Proliferation is the main epidermal target in the treatment of psoriatic plaques with once daily application of tacalcitol ointment

We studied the effect of tacalcitol (1 alpha, 24 dihydroxy vitamin D3) ointment on clinical and immunohistochemical efficacy in psoriatic patients during 2 months of treatment. The psoriasis area and severity index decreased significantly after only 1 month and the total body surface index decreased 55% after 2 months. To characterize the epidermal compartment keratin 14, keratin 16, epidermal growth factor receptor, apoptotic and Ki-67 positive cells were examined. After 1 week of treatment no significant changes were found in any of these parameters. After 2 months, keratin 16 reached the levels observed in normal skin and Ki-67 and keratin 14 expression also reduced significantly. Epidermal growth factor receptor staining and the number of apoptotic cells did not alter during treatment. We conclude that tacalcitol is effective in the treatment of plaque psoriasis. Because the main epidermal effect observed immunohistochemically is a reduction in proliferation, a combination therapy using either corticosteroids, vitamin A derivatives or dithranol seems rational.

The effect of long-term treatment with tacalcitol on the psoriatic epidermis. A flow cytometric analysis

During the last decade, novel analogues of 1alpha,25-dihydroxy vitamin D3 have been developed for the treatment of psoriasis. Recently, the efficacy of short-term treatment with the novel derivative tacalcitol (1alpha,24-dihydroxy vitamin D3) has been documented. However, data on the long-term effect of tacalcitol on psoriatic skin are sparse. In this study, we assessed the cell characteristics of the psoriatic epidermis after treatment with tacalcitol for up to 24 weeks. We investigated how long-term treatment with tacalcitol modulates the percentages of differentiated keratinocytes, inflammation cells and basal keratinocytes, and the percentage of cells in the SG2M phase in the basal cell population. From 11 patients who were treated with tacalcitol for up to 18 months, we obtained single-cell suspensions of a representative psoriatic lesion after 0, 8, 12, 18 and 24 weeks of treatment. A Psoriasis Area and Severity Index was performed at each visit as well. Cell suspensions were stained with markers for inflammation (Vim3B4), differentiation (RKSE60) and proliferation (TO-PRO-3 iodide) and analysed flow cytometrically. Clinically, patients improved significantly after 8 weeks of treatment. This clinical effect was preserved for the rest of the period of treatment with no further significant improvement. Proliferative activity also decreased significantly after 8 weeks of treatment. Proliferation did not show further significant decreases or habituation after 12, 18 and 24 weeks. For inflammation, no statistically reliable trends could be seen. Differentiation improved significantly after 8 weeks of treatment, but decreased again significantly after 12 weeks. In the period from 12 to 24 weeks, no further significant change was observed. We conclude that tacalcitol is an effective antipsoriatic drug. Prolonged treatment with tacalcitol will generally maintain improvement at the level reached after 8 weeks. Owing to the beneficial effect on both clinical state and proliferation, tacalcitol is likely to be an adequate maintenance therapy.

Regulation of RANTES and IL-8 production in normal human dermal fibroblasts by active vitamin D3 (tacalcitol)

1. The production of chemokines, RANTES and IL-8 in cultured human dermal fibroblasts and the effects of tacalcitol (1alpha,24(R)-dihydroxyvitamin D3) were studied using an enzyme-linked immunosorbent assay. 2. In the unstimulated condition, RANTES and IL-8 were at a trace level in the culture supernatant. On stimulation with TNF-alpha alone for 24 h, RANTES and IL-8 production were induced. Tacalcitol suppressed RANTES and IL-8 production dose-dependently at concentrations between 10(-12) M and 10(-7) M. 3. When the cells were treated with TNF-alpha and IFN-gamma in combination, RANTES production was enhanced, but IL-8 production was not changed, compared to TNF-alpha-treated cells. Tacalcitol decreased IL-8 production dose-dependently as observed in the TNF-alpha-treated cells. On the other hand, RANTES production was enhanced by 10(-11) M and 10(-10) M of tacalcitol, and dose-dependently suppressed by tacalcitol concentrations higher than 10(-9) M. 4. Active vitamin D3 compounds, betamethasone valerate and cyclosporin A were compared with respect to their effects on chemokine production. Three active vitamin D3 compounds, tacalcitol, 1alpha,25-dihydroxyvitamin D3 and MC903 (calcipotriol), inhibited the production of RANTES and IL-8, with very similar potencies. Betamethasone valerate also inhibited these chemokine productions, but with greater potency than active vitamin D3 compounds. Cyclosporin A significantly stimulated RANTES production at 10(-6) M and IL-8 production at 10(-7) M and 10(-6) M. 5. The results of this study suggest that active vitamin D3 compounds exert some beneficial effects in the treatment of inflammatory skin diseases via regulation of the production of chemokines by dermal fibroblasts.

Vitamin D3 and its synthetic analogue secocholestra-trien-1,2, 24-triol influence the metabolism and the isomerization of retinoic acid in human keratinocytes

Vitamin D and vitamin A acid share metabolic pathways thereby influencing their benefit as a given drug. Little is known concerning their metabolic interactions in epidermal cells. We compared the influence of 1,25-dihydroxycholecalciferol (vitamin D3 - VD3) and its synthetic analogue secocholestra-trien-1,3,24-triol (tacalcitol - TAC) in combination with different calcium concentrations (Ca) on the metabolism and the isomerization of retinoic acid (RA) in cultured primary human keratinocytes. After preincubation with 0.09, 0.6 and 1.2 mM Ca for 24 h, followed by the addition of 10(-6), 10(-8) or 10(-10) M VD3 or TAC, we added 10(-5) M 13-cis-RA (isotretinoin). 24 h later, concentrations of RA isomers and oxidated RA metabolites were measured by RP-HPLC. VD3 (10(-6) M) inhibited the isomerization of 13-cis-RA to all-trans-RA (tretinoin) and 9-cis-RA independently from the Ca concentration in the culture medium. 10(-6)-10(-10) M TAC equally inhibit the 4-hydroxylation of all-trans-RA significantly (12.8 vs. 6.7% of total RA), thereby reducing the amount of irreversible inactivated 4-oxo-all-trans-RA, leading to a higher persistence of all-trans-RA, the active hormone. Both VD3 and its analogue TAC influence the metabolism of RA, a well-known regulator of epithelial cell proliferation and differentiation processes, in two distinct ways. Further studies are necessary to test the hypothesis that the hormone activity of RA can be increased by concomitant treatment with VD3 which prolongs the persistence of 13-cis-RA, and TAC elevating the intracellular concentration of all-trans-RA.

RANTES expression in psoriatic skin, and regulation of RANTES and IL-8 production in cultured epidermal keratinocytes by active vitamin D3 (tacalcitol)

The chemokine RANTES is a chemoattractant for eosinophils, T lymphocytes of memory phenotype and monocytes, suggesting that it plays an important part in chronic inflammatory and allergic diseases. In various types of cells, RANTES production is markedly induced by tumour necrosis factor (TNF)-alpha and interferon (IFN)-gamma in combination. Psoriasis vulgaris is a chronic cutaneous inflammatory disease. Cytokines and chemokines produced by T cells and epidermal keratinocytes, such as interleukin (IL) 8, are involved in the pathogenesis of psoriasis. T-cell clones obtained from psoriatic skin have been shown to produce the Th1 cytokine IFN-gamma. In addition, abnormal expression of proinflammatory cytokines including TNF-alpha has been observed in psoriatic lesions. These reports led us to hypothesis that psoriatic skin could provide epidermal keratinocytes with TNF-alpha and IFN-gamma, so that keratinocytes could produce RANTES. In this study, we addressed the question as to whether RANTES was involved in psoriasis vulgaris. Immunohistochemistry of skin biopsies showed RANTES was present in the intercellular spaces between epidermal keratinocytes, in the fully developed lesions from the middle to the edge of psoriatic plaques, but not in the perilesional uninvolved and healthy control skin. Further, we confirmed the production of RANTES, together with IL-8, by cultured normal human epidermal keratinocytes, using an enzyme-linked immunosorbent assay. Stimulation with TNF-alpha and IFN-gamma in combination synergistically increased the RANTES production in this system. These results clearly demonstrate the expression of RANTES in psoriatic lesions and suggest the involvement of this chemokine in the outcome of cutaneous inflammatory diseases. Tacalcitol (1 alpha,24(R)-dihydroxyvitamin D3), an active vitamin D3 analogue, inhibited RANTES and IL-8 production in cultured normal epidermal keratinocytes. This result indicates that active vitamin D3 is effective in the regulation of chemokine production by epidermal keratinocytes, which may partly account for its action as an antipsoriatic drug.