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

The effects of KH 1060, a potent 20-epi analogue of the vitamin D3 hormone, on hairless mouse skin in vivo

Dermal effects of KH 1060, a novel, highly potent 20-epi analogue of 1 alpha,25-dihyroxyvitamin D3, were investigated in a hairless mouse model. During daily topical applications of a 0.4 microM solution of KH 1060 for 4 weeks, epidermal hyperplasia and an increase of dermal thickness and mass were observed. KH 1060 upregulated glycosaminoglycan and collagen synthesis in the skin, and increased glycosaminoglycan deposition in the subepidermal region. Reverse transcription-polymerase chain reaction amplification of the transforming growth factor (TGF) beta 1-specific mRNA revealed that KH 1060 stimulated expression of this growth factor in the epidermis, but not in the dermis. Changes observed after application of 1 alpha,25-dihydroxyvitamin D3 were much less pronounced but qualitatively similar to the effects of KH 1060, whereas structurally related but receptor inactive compounds, vitamin D3 and 1 beta,25-dihydroxyvitamin D3, did not produce any effects. Furthermore, we were unable to demonstrate the involvement of the non-genomic, receptor-independent vitamin D signalling in the skin, using a specific stimulator (Ro 24-2090) and a blocker (1 beta,25-dihydroxyvitamin D3) of this pathway. Our findings provide the first evidence that a strong vitamin D3 analogue triggers synthesis of skin connective tissue, possibly via vitamin D receptor activation and the paracrine action of epidermis-derived TGF-beta 1.

Distinct conformational changes induced by 20-epi analogues of 1 alpha,25-dihydroxyvitamin D3 are associated with enhanced activation of the vitamin D receptor

The relative affinities of the 1 alpha,25-dihydroxyvitamin D3 (1,25-D3) analogues 20-epi-1 alpha,25-dihydroxyvitamin D3 (IE) and 20-epi-22-oxa-24a,26a,27a-tri-homo-1 alpha,25-dihydroxyvitamin D3 (ID) to the nuclear vitamin D receptor (VDR) are similar to that of 1,25-D3, but their antiproliferative action is 1000-fold greater. We tested whether the greater antiproliferative effect of these analogues is due to a differential activation of the VDR. In ROS 17/2.8 cells, the effective doses required to produce 50% maximal stimulation (ED50) of transfected reporter genes driven by either the osteocalcin or the osteopontin vitamin D-response elements (VDRE) were 5 x 10(-9) M, 10(-10) M, and 10(-11) M for 1,25-D3, ID, and IE, respectively. Similar results were obtained when recombinant human VDR was cotransfected into CV-1 cells with an osteocalcin VDRE-reporter plasmid. We found that in vitro the sensitivity of 1,25-D3-induced and analogue-induced receptors to proteases was different. The ED50 for binding to VDRE, as determined by electrophoretic mobility shift assays, was significantly higher for 1,25-D3-induced than for analogue-induced VDR. The concentration of retinoid X receptor (RXR) was significantly lower in 1,25-D3-induced than analogue-induced VDR complexes with VDRE. We therefore conclude that IE and ID augment transcriptional activity of VDR more than 1,25-D3 does, by producing conformational changes that enhance dimerization of VDR with RXR. We suggest that these conformational changes are due to differences in the contact sites of the 20-epi analogues and 1,25-D3 with the VDR.

Characterization of the metabolic pathway of 1,25-dihydroxy-16-ene vitamin D3 in rat kidney by on-line high performance liquid chromatography-electrospray tandem mass spectrometry

1,25-Dihydroxy-16-ene vitamin D3 is a synthetic analog of 1,25-dihydroxyvitamin D3, the most physiologically active metabolite of vitamin D3. The renal metabolism of 1,25-dihydroxy-16-ene vitamin D3 had been studied previously using a perfused rat kidney system [Reddy et al., Bioorg Med Chem Lett 3: 1879-1884, 1993], and its C-24 oxidative metabolic pathway had been found to be different from that of 1,25-dihydroxyvitamin D3 by HPLC. To further delineate the differences between the C-24 oxidative metabolic pathways of 1,25-dihydroxyvitamin D3 and 1,25-dihydroxy-16-ene vitamin D3 in this present study we investigated the C-24 oxidation pathway of 1,25-dihydroxy-16-ene vitamin D3 using a novel detection approach based on on-line capillary liquid chromatography coupled to electrospray tandem mass spectrometry. Two types of tandem mass spectrometric detection were employed to characterize the metabolites in the kidney perfusate: (a) the preliminary screening of metabolites by parent scan, which led to the tentative discovery of the production of 1,23,25-trihydroxy-24-oxo-16-ene vitamin D3, a new metabolite of 1,25-dihydroxy-16-ene vitamin D3, and (b) the pharmacokinetic studies of the substrate, 1,25-dihydroxy-16-ene vitamin D3 and its metabolites by multiple reaction monitoring. In the latter, the mass spectrometric sensitivity for quantification was found to be about 20-fold better than UV detection. The current work concluded that the C-24 oxidative metabolic pathway of 1,25-dihydroxy-16-ene vitamin D3 closely mimicked that of its natural counterpart. Furthermore, the use of mass spectrometry permitted the clearance rate of the starting substrate to be studied at a more physiological level (ng/mL or submicromolar level), which had not been possible previously by HPLC-UV detection.

Pharmacokinetic studies of vitamin D analogues: relationship to vitamin D binding protein (DBP)

Vitamin D(3), 25-hydroxyvitamin D(3) (25OHD(3)) and 1α,25-dihydroxyvitamin D(3) (1α,25(OH)(2)D(3)) bind to the vitamin D binding protein (DBP) in the serum. During the development of synthetic vitamin D analogues, it has been shown that the majority of analogues bind to DBP with a low affinity. This modifies their biological activitiesin vitro compared to 1α,25(OH)(2)D(3), since binding to DBP decreases the cellular uptake and access to the vitamin D receptor. It is therefore important to elucidate the possible role played by the binding or lack of binding to DBPin vivo. We have investigated the relationship between the binding affinity for human DBP and the serum level and serum half-life (t(1/2)) in rats of a series of new vitamin D analogues. The binding affinity for DBP was determined by displacement of(3)H-1,25(OH)(2)D(3) from DBP attached to Affi-Gel 10. The serum levels in rats following a single intravenous dose were assessed by HPLC and the serum half-life was determined for each analogue. In the group of vitamin D analogues which showed a low or no affinity for DBP, we have identified compounds with a short t(1/2) and compounds with a long t(1/2), all characterized by low initial serum levels. Compounds with a long t(1/2) were also found in the group with a high affinity for DBP, and they were easily identifiable by their high initial serum level. These results showed that the initial serum level of vitamin D analogues correlated with the affinity for DBP, but that there seemed to be no correlation with the metabolic rate as reflected by measurement of the serum half-life of the analogues.

Biological evaluation of epoxy analogs of 1 alpha,25-dihydroxyvitamin D3

The biological activity of 16-epoxy side-chain analogs of 1 alpha,25-dihydroxyvitamin D3, (1 alpha,25(OH)2D3) was evaluated in vitro and in vivo. Compared to 1 alpha,25(0H)2D3, all analogs had lower affinities for the pig duodenal vitamin D receptor and also for the human serum vitamin D binding protein. The in vitro effects on cell proliferation or differentiation of human promyeloid leukemia (induction of superoxide production in HL-60 cells), human osteosarcoma MG-63 cells (osteocalcin secretion), or human breast cancer cells (incorporation of thymidine in MCF-7 cells), was markedly inhibited by several epoxy analogs, compared to 1 alpha,25(OH)2D3, but the rank order of their activity widely varied among different cancer cells. The most potent analogs (24S,25S-24-hydroxy-25,26-epoxy-22-ene-1 alpha-OHD3, 25,26-epoxy-23-yne-1 alpha-OHD3, and 25,26-epoxy-23-yne-20-epi-1 alpha-OHD3 or compounds, 16, 5, and 7, respectively) were equipotent (16 and 5) or 30-fold (compound 7 on MG-63 cells) to 40-fold (compound 7 on MCF-7 cells) more active than 1 alpha,25-(OH)2D3. These analogs were nevertheless poorly antirachitic (< 3%) when tested in vitamin D-deficient chicks (using serum and bone calcium, serum osteocalcin and duodenal calbindin D-28K, as end points). Compound 7 was also 100-fold more active than 1 alpha,25-(OH)2D3 in inhibition of proliferation of human foreskin keratinocytes. Some epoxy analogs of 1 alpha,25-(OH)2D3 thus display interesting dissociations between their receptor affinity and their potency to induce cell differentiation, whereas their effect on cell proliferation/differentiation exceed their calcemic effects more than 100- to 1000-fold.

Stimulation of epidermal proliferation in mice with 1 alpha, 25-dihydroxyvitamin D3 and receptor-active 20-EPI analogues of 1 alpha, 25-dihydroxyvitamin D3

The effects of 1 alpha, 25-dihydroxyvitamin D3 (1 alpha, 25-(OH)2D3) and receptor-active 20-epi vitamin D analogues (MC 1288, 20-epi-1 alpha, 25-(OH)2D3; MC 1301, 20-epi-24a-homo-26,27-dimethyl-1 alpha, 25-(OH)2D3, and KH 1060: 20-epi-22-oxa-24a-homo-26,27-dimethyl-1 alpha, 25-(OH)2D3) on epidermal proliferation in mice were studied in vivo. Single topical applications of all compounds induced epidermal proliferation in a dose-dependent manner. The relative potencies in vivo (KH 1060 > MC1301 > MC1288 > 1 alpha, 25-(OH)2D3) correlated well with the known activities of these compounds to inhibit U 937 cell proliferation in vitro. Vitamin D3 and 1 beta, 25-(OH)2D3, two compounds that do not bind the vitamin D receptor, did not affect epidermal proliferation. Our study shows that vitamin D3 compounds that bind to the vitamin D receptor stimulate epidermal proliferation in mice.

Calcipotriol inhibits rectal epithelial cell proliferation in ulcerative proctocolitis

Vitamin D3 reduces human rectal crypt cell production rate (CCPR) and may thereby protect against colorectal cancer. Cell turnover is increased in ulcerative proctocolitis, which might therefore respond to vitamin D3 metabolites. This study investigated the effect of calcipotriol, a synthetic vitamin D3 analogue that avoids hypercalcaemia, on human rectal CCPR in ulcerative proctocolitis. Paired rectal biopsy specimens from seven patients with severe disease were established in organ culture with or without calcipotriol (1 x 10(-6) M). After 15 hours, vincristine (0.6 microgram/ml) was added to induce metaphase arrest, and CCPR was determined by linear regression analysis of accumulated metaphases. Compared with values in 17 controls with incidental anal conditions, median rectal CCPR was 28% higher in ulcerative proctocolitis: 5.90 (5.00-9.50) v 4.80 (2.85-7.07) cells/crypt/hour (p < 0.01). Calcipotriol reduced CCPR by 62% in patients with ulcerative proctocolitis, from 5.90 (5.00-9.50) to 2.21 (0.81-3.22) cells/crypt/hour (median with range) p < 0.01. Thus calcipotriol can dampen the hyperproliferative state in ulcerative proctocolitis and could have a therapeutic role in the control of this inflammatory condition.

The biological activity of 23-oxa-, 23-oxa-24-oxo-, and 23-thia-dihydroxyvitamin D3

Three analogs of 1 alpha,25-(OH)2D3 with an oxygen or another heteroatom at position 23 were synthesized in search of separating the cell-differentiating from the calcemic effects of the vitamin D hormone. Their ability to induce superoxide production in human myeloid leukemia cells (HL-60) was 1 alpha,25-(OH)2D3 > 23-oxa-24-oxo-1 alpha,25-(OH)2D3 > 23-thia-1 alpha,25-(OH)2D3 > 23-oxa-1 alpha, 25-(OH)2D3. 23-oxa-24-oxo-1 alpha, 25(OH)2D3 was slightly more potent than 1 alpha,25-(OH)2D3 in inhibiting cell proliferation in MCF-7 cells and 23-thia- and 23-oxa-1 alpha,25(OH)2D3 were less potent. Their in vitro potency to produce osteocalcin in MG-63 cells was 1 alpha,25-(OH)2D3 > 23-oxa-24-oxo-1 alpha,25-(OH)2D3 > 23-thia-1 alpha,25-(OH)2D3 = 23-oxa-1 alpha,25-(OH)2D3. All three analogs had reduced receptor and DBP affinity compared to 1 alpha,25-(OH)2D3. When these analogs were injected in rachitic chicks, only little calcemic effects were observed. The introduction of a heteroatom in carbon 23 of 1 alpha,25-(OH)2D3 thus creates analogs with dissociated action on cell differentiation and calcium homeostasis.

MC 1288--a vitamin D analogue with immunosuppressive effects on heart and small bowel grafts

The vitamin D analogue MC 1288 (20-epi-1 alpha,25-dihydroxycholecalciferol) was tested here for its possible immunosuppressive properties in vivo using different rat transplantation models. MC 1288, in a dose of 0.1 microgram/kg daily, administered intraperitoneally for 10 days, was found to be effective in prolonging cardiac allograft survival. Untreated recipients rejected their grafts around day 8 while MC 1288 treatment delayed rejection until day 22 (P < 0.001). Addition of the immunostimulatory drug LS-2616 (Linomide) reduced the immunosuppressive effect of MC 1288 and rejection occurred around day 11. The immunosuppressive effect of MC 1288 on rejection following small bowel transplantation was determined by measuring the amounts of hyaluronan (HA) secreted into the intestinal lumen. On day 6 post-transplantation the amounts of intraluminal HA in untreated animals was 29.2 +/- 5.3 ng/min and cm, while in MC 1288-treated animals it was just 5.0 +/- 1.6 ng/min and cm (P < 0.01). We conclude that MC 1288 has immunosuppressive effects that may make it suitable for the prevention of graft rejection.

The 1,25-dihydroxyvitamin D3 (VD) analogues MC903, EB1089 and KH1060 activate the VD receptor: homodimers show higher ligand sensitivity than heterodimers with retinoid X receptors

The nuclear receptor for 1,25-dihydroxyvitamin D3 (VD), VDR, belongs to the nuclear receptor superfamily. This ligand-inducible transcription factor mediates the genomic VD signalling pathways by binding to specific response elements in the promoter region of VD regulated genes. Two types of natural VD response elements are used as models for the VDR-mediated transcriptional activation: one is bound by VDR-homodimers and is found in the human osteocalcin gene promoter, and the other is bound by heterodimers of VDR with retinoid X receptors (RXRs) as in the mouse osteopontin promoter. Here, we demonstrate that the VD analogues MC903, EB1089 and KH1060, previously shown to be potent regulators of proliferation and differentiation, are able to act as ligands for VDR and replace VD as a ligand in both nuclear signalling pathways. We found that they have different potency and sensitivity in their ability to stimulate the hormone-dependent promoter element. MC903 and EB1089 provide about 20% higher induction of gene activity than VD in a gene reporter system, whereas KH1060 was more sensitive, inducing transcription at about 100-fold lower doses than VD. Interestingly, VD and its analogues induce VDR homodimer-mediated gene activity at a 3- to 4-fold lower concentration than that of VDR-RXR heterodimers. This suggests that the ligand concentration is an additional regulatory level in the discrimination between signalling pathways involving homo- and heterodimeric hormone receptors.

Inhibition of glucocorticoid-induced epidermal and dermal atrophy with KH 1060--a potent 20-epi analogue of 1,25-dihydroxyvitamin D3

1. The possibility of preventing and treating glucocorticoid-induced skin atrophy with KH 1060 (the potent 20-epi-22-oxa-24a-homo-26,27-dimethyl analogue of 1,25-dihydroxyvitamin D3) was examined in a hairless mouse model. 2. KH 1060 (0.625-6.25 pmol cm-2 of skin) applied topically for 7 days together with 2.5 nmol cm-2 betamethasone-17-valerate prevented, in a concentration-dependent manner, the development of epidermal, dermal and total skin thinning caused by the glucocorticoid. The effect of KH 1060 on the epidermis occurred at a lower dose than on the dermis, and at doses above 1.25 pmol cm-2 KH 1060 caused epidermal hyperplasia. 3. KH 1060 (2.5 pmol cm-2) prevented the development of betamethasone-associated skin atrophy in mice during a long-term (4 weeks) treatment, and reversed established cutaneous glucocorticoid atrophy. 4. Radiolabelling experiments with [35S]-sulphate and [3H]-proline in vivo revealed that KH 1060 stimulated the synthesis of sulphated glycosaminoglycans and hydroxyproline in skin treated with betamethasone. 5. These findings strongly suggest that KH 1060 prevents and reverses glucocorticoid-induced skin atrophy by stimulating epidermal proliferation and enhancing synthesis of extracellular matrix in the dermis.

Vitamin D receptor binding and biological effects of cholecalciferol analogues in rat thyroid cells

The cholecalciferol analogues 1(S),3(R)-dihydroxy-20(R)-[3'(S)-cyclopropyl-3'-hydroxyprop-1'(E)- enyl]-9,10-secopregna-5(Z),7(E),10(19)-triene (calcipotriol, MC 903), 1(S),3(R)-dihydroxy-20(R)-[3'-ethyl-3'-hydroxy- pentoxy]-9,10-secopregna-5(Z),7(E),10(19)-triene (KH 1060) and 1(S),3(R)-dihydroxy-20(R)-[5'-ethyl-5'-hydroxy-hepta- 1',3'(E)-diene-1'-yl]-9,10-secopregna-5(Z),7(E),10(19)-triene (EB 1089) have been modified in the side chain to increase their effects on cell differentiation and proliferation and to reduce the risk of inducing hypercalcemia. The effects of these analogues were tested on FRTL-5 cells, a strain of continuously growing and well-differentiated rat thyroid cells. FRTL-5 cells express a normal vitamin D receptor (VDR), and 1,25-(OH)2D3 potently attenuates the thyrotropin (TSH) stimulated production of the intracellular signalling molecule 3',5'-cyclic adenosine monophosphate (cAMP), iodide uptake and cell growth of these cells. These effects were also induced by the cholecalciferol analogues after 4 days of incubation. KH 1060 was the biologically most potent of the analogues and, compared to KH 1060, the IC50 values were 1.2-, 2.7- and 14-fold higher when 1,25-(OH)2D3, EB 1089 and MC 903, respectively, were used for the displacement of receptor bound [3H]1,25-(OH)2D3. As indicated by their VDR binding, 1,25-(OH)2D3 and EB 1089 were equipotent inhibitors of the TSH stimulated adenylyl cyclase activity, iodide uptake and FRTL-5 cell growth. The analogue MC 903 was the second most potent inhibitor of cell growth in spite of expressing the lowest affinity for the VDR and the weakest inhibition of TSH-stimulated adenylyl cyclase activity and iodide uptake. In conclusion, the biological effects of these cholecalciferol analogues in rat thyroid FRTL-5 cells seem to be mainly determined by their binding affinity for the VDR, although non-genomic effects can not be excluded.

Vitamin D stimulates DNA synthesis in alveolar type-II cells

Alveolar type-II cells are responsible for alveolar epithelial cell proliferation during growth and development and in response to lung injury. Based on the observation of abnormal lung development in rachitic rat pups and the expression of receptors for vitamin D by fetal alveolar epithelial cells, the present study examined the influence of 1,25-dihydroxy vitamin D (DHD) on the proliferation of primary cultures of fetal, neonatal and adult alveolar epithelial cells. The ontogony of vitamin D responsiveness was examined, using fetal (days 18, 19 and 22 = term), neonatal (days 7 and 18) alveolar epithelial cells as well as adult alveolar type-II cells. Maximal stimulation of [3H]thymidine incorporation occurred in neonatal d18 cells: (250 +/- 4.8%, n = 4, P < 0.05). Incubation of adult type-II cells, in the presence of 10(-9) M DHD increased thymidine incorporation into DNA (149.1 +/- 33.2%, mean +/- S.E., n = 3, P < 0.001) compared to control cells maintained in basal medium. Exposure to DHD also increased thymidine incorporation after stimulation with a mixture of conventional progression factors (insulin (10 micrograms/ml) (I), cholera toxin (10 micrograms/ml) (C) and EGF (20 ng/ml) (E)) (349.4 +/- 42.9% vs. 213.5 +/- 23.6%, n = 6, P < 0.005). Autoradiographic labeling indices of adult type-II cells increased from 3.1 +/- 0.6% for cells cultured in basal medium to 7.2 +/- 1.7% in cells exposed to DHD from the time of plating and I, C, E from 20-68 h in culture (n = 4, P < 0.05). Although no increase in the number of adult type-II cells was observed in these experiments, flow cytometric analysis of nuclear DNA content revealed an increased proportion of cells in the S and G2 phases of the cell cycle (basal: S = 2.6%, G2/M = 3.0%, DHD+GF: S = 4.7%, G2/M = 5.6%, P < 0.05 for each comparison). These data demonstrate that vitamin D3 is a growth factor for alveolar type-II cells and suggest the possibility that local elaboration of vitamin D may provide a novel mechanism of modulation of epithelial proliferation in the context of lung development and repair.

Increased biological activity of 20-epi-1,25-dihydroxyvitamin D3 is due to reduced catabolism and altered protein binding

The 20-epi series of vitamin D3 analogs has been shown to be made up of more potent inducers of cell differentiation than calcitriol in vitro. Using 20-epi-1 alpha,25-dihydroxyvitamin D3 (MC 1288), we attempted to rationalize this increased biological activity by examining several parameters including the binding affinity of the analog for the plasma binding globulin (DBP) and the target cell vitamin D receptor (VDR), as well as attempting to measure the rate at which MC 1288 is metabolized. MC 1288 was found to be metabolized 36 times more slowly than its epimer 1,25-dihydroxy vitamin D3 (1,25-(OH)2D3), forming several metabolites which were analogous to metabolites of 1,25-(OH)2D3 formed in the side chain oxidation pathway. Bovine thymus VDR bound MC 1288 with five times greater affinity than calcitriol, while rat plasma DBP did not bind MC 1288 even at a concentration of 50 microM, 5000 times the B50 of 25-OH-D3, the ligand used in the assay. Using a vitamin D-inducible growth hormone gene reporter system we were able to demonstrate that MC 1288 induces human growth hormone (hGH) activity 30-fold more efficiently than 1,25-(OH)2D3 in the presence of fetal calf serum (FCS), while the analog is only 10 times more efficient than 1,25-(OH)2D3 in the absence of FCS. We therefore conclude that MC 1288 is more biologically active than calcitriol in vitro due to a combination of factors: the increased VDR binding affinity, the decreased DBP binding affinity, and the decreased rate of metabolism. As with other analogs of vitamin D, the altered protein binding and decreased catabolism of MC 1288 may be important in pharmaceutical applications such as a topical treatment for psoriasis or skin cancer.

Intracellular free calcium and growth changes in single human keratinocytes in response to vitamin D and five 20-epi-analogues

Vitamin D, 1,25(OH)2D3, decreases proliferation and promotes differentiation of keratinocytes, and other keratinocyte differentiation stimuli have been associated with an early rise in intracellular free calcium, [Ca2+]i. We therefore investigated the effect of 1,25(OH)2D3, its precursor D3 and five 20-epi-analogues (EB1089, KH1060, KH1139, MC1288, MC1301) on growth and [Ca2+]i levels of normal human keratinocytes. Cells were cultured in medium MCDB153 with an extracellular calcium concentration of 70 microM or 1 mM. All the analogues were more potent than 1,25(OH)2D3 at inducing the morphological changes of differentiation, but D3 was inactive. At concentrations down to 10(-8) M 1,25(OH)2D3, caused significant inhibition of growth, as assessed by counting cells and measurement of thymidine labelling. At 5 days 50% inhibition of growth occurred with 64 nM 1,25(OH)2D3 and 3330 nM D3. All the analogues were more potent than 1,25(OH)2D3, and KH1060 inhibited growth at 10(-10) M. In single keratinocytes [Ca2+]i was measured by microspectrofluorimetric techniques using the dye fura-2. No immediate rise in [Ca2+]i was observed following addition of 1,25(OH)2D3 or the analogues up to 10(-6) M. However 10(-7) M 1,25(OH)2D3 or the analogues induced a gradual increase in [Ca2+]i, significant at 4 h (P < 0.001), which increased further over 2-3 days. D3 had no effect on [Ca2+]i. Increases in [Ca2+]i following the differentiation stimuli of either 2 mM extracellular calcium or 1,25(OH)2D3 were similar at 48 h, increasing from 100 +/- 3 nM (mean +/- SEM) in control cells to 150 +/- 3 nM with 2 mM calcium and 144 +/- 6 nM with 10(-7) M 1,25(OH)2D3. The effect of extracellular calcium in raising [Ca2+]i within minutes was more rapid than 1,25(OH)2D3, but in combination the two were not additive.

The in vivo effect of a new, in vitro, extremely potent vitamin D3 analog KH1060 on the suppression of renal allograft rejection in the rat

KH1060 is a new 20-epi-vitamin D3 analog, which has exerted a considerable immunosuppressive potency in vitro. We have tested in vivo the effect of KH1060 on the suppression of renal allograft rejection in the rat. Allogenic kidney transplantation from DA donor rats to Lewis recipient rats treated intraperitoneally with KH1060 in doses from 0.2 to 6 micrograms/kg/day, or saline (placebo group), or CyA 10 mg/kg/day for 10 days (positive control group), was performed. Median graft survival time in KH1060-treated groups was 7-9 days, in the placebo group 6 days, whereas CyA led to long-term graft survival, 34 days in 50% of rats and > 100 days in 50% of rats. In vivo, KH1060 failed to prolong renal allograft survival considerably, and led to development of hypercalcemia. Our results stress the existence of a large discrepancy between the in vitro and in vivo immunoregulatory effects of this vitamin D analog.

Vitamin D3 and calcipotriol decrease extracellular plasminogen activator activity in cultured keratinocytes

Vitamin D3, 1 alpha,25(OH)2D3, and its metabolites regulate the growth and differentiation of several cell types. Vitamin D3 and its analogue, calcipotriol (MC 903), inhibit the proliferation of cultured human and mouse keratinocytes and induce keratinocyte differentiation. Calcipotriol is effective in the treatment of psoriasis in which increased plasminogen activator activity has been reported. We analyzed therefore the effects of calcipotriol and vitamin D3 on the production of plasminogen activator (PA) activity in human keratinocytes and a mouse keratinocyte cell line. Caseinolysis-in-agarose assays indicated that vitamin D3 decreases total PA activity in both keratinocyte culture systems. Zymographic analyses of the medium indicated that the secreted activator was of the urokinase type (u-PA). A decrease was observed also in extracellular matrix and membrane-associated u-PA activity of vitamin D3 and calcipotriol treated cells. Immunoblotting analysis of the conditioned medium from human keratinocytes revealed a decrease in the u-PA protein levels. Accordingly, Northern hybridization analysis of the respective mRNAs indicated a rapid decrease in urokinase mRNA levels. Calcipotriol decreased u-PA activity also in the presence of inducers of u-PA activity like transforming growth factor-beta, epidermal growth factor, and phorbol-12-myristate-13-acetate. Calcipotriol also caused a decrease in tissue type PA (t-PA) activity of the keratinocytes. Most t-PA activity was associated with the extracellular matrices and cell membranes as revealed by zymographic analysis. Paradoxically, the secretion and deposition of the matrix of plasminogen activator inhibitor type 1 decreased in calcipotriol-treated cells. The results indicate that a major effect of vitamin D3 on cultured keratinocytes is a decrease of plasminogen activator activity.

EB 1089, a novel vitamin D analogue, has strong antiproliferative and differentiation inducing effects on cancer cells

EB 1089 is a novel vitamin D analogue which in vitro strongly inhibits the proliferation of U937 histiocytic lymphoma cells and MCF-7 breast cancer cells, with a potency of 50 to 100 times that of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]. Studies of c-myc and c-fos expression in MCF-7 cells and of differentiation markers in U937 cells show that growth inhibition by EB 1089 is accompanied by induction of differentiation. The ability of EB 1089 to affect calcium metabolism in vivo in rats is decreased, compared to 1,25(OH)2D3. This low calcemic effect combined with the strong biological effect on cancer cells in vitro, makes EB 1089 an interesting candidate for treatment of cancer.

Parathyroid hormone dependent T cell proliferation in uremic rats

Chronic renal failure (CRF) is combined with an impairment of the immune system. The T cell may be a target for the action of parathyroid hormone (PTH). Rats with CRF have high blood levels of PTH. Therefore, the present investigation examined some aspects of the T cell function in both normal and CRF rats before and after parathyroidectomy and after an isogenic kidney transplantation. The T cell proliferative response to phytohemagglutinin (PHA) stimulation was significantly higher in peripheral blood mononuclear cell (PBMC) cultures obtained from CRF rats than from normal rats. After parathyroidectomy the T cells of normal as well as of uremic rats could still be significantly stimulated by PHA, but now no significant difference was seen. When CRF was reversed after an isogenic kidney transplantation and PTH reversed to levels in the normal range, the T cell proliferative response to PHA was normalized. Rat PTH 1-84 stimulated in vitro the PHA-induced proliferation of T cells in a dose dependent manner. This effect was significant in CRF rat lymphocytes, but not in lymphocytes obtained from normal rats. Based upon the present results it is suggested that the secondary hyperparathyroidism in chronic uremia is responsible for the enhanced proliferative response to PHA of T cells from CRF rats.

Modulation of cell proliferation and cell cycle, and inhibition of cytokinesis by 1,25-dihydroxyvitamin D3 in C3H/10T1/2 fibroblasts

The growth-modulating effects of 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] were studied on three mouse embryo fibroblast cell lines. Concentrations ranging from 0.1 to 100 nM inhibited dose-dependently proliferation in the non-tumorigenic C3H/10T1/2 Cl 8 (10T1/2) and the chemically transformed C3H/10T1/2 Cl 16 (Cl 16) cells. The hormone had a biphasic effect on the transformed cell line C3H/10T1/2 TPA 482 (TPA 482) in which growth was stimulated by low concentrations. Exposure to 10 nM 1,25-(OH)2D3 for 5 days resulted in a 90% growth inhibition of 10T1/2 cells, and the hormone was 10 and 100 times less potent in Cl 16 and TPA 482 cells, respectively. The inhibition of cell replication was fully reversible on removal of the hormone. Treatment of 10T1/2 and Cl 16 cells with 10 nM 1,25-(OH)2D3 reduced the saturation density to 30 and 37% that of controls, respectively, suggesting an enhancement of cell-cell contact mediated growth inhibition. 1,25-(OH)2D3 inhibited cytokinesis in 10T1/2 cells, inducing the formation of binucleated cells. Flow cytometric studies showed that 1,25-(OH)2D3-treated cells accumulated in the Go/G1 phase while the number of cells in S phase decreased. This in vitro model system seems to be useful for studies of the molecular mechanisms of the growth modulating effect of 1,25-(OH)2D3.

1,25-Dihydroxyvitamin D3 and the vitamin D analogue KH1060 induce hyperproliferation in normal mouse epidermis. A BrdUrd/DNA flow cytometric study

1,25-dihydroxyvitamin D3 (calcitriol) affects differentiation and proliferation of epidermal keratinocytes in vitro and in vivo. We have studied the topical effects of calcitriol (0.08-2.0 micrograms/ml) and of a new vitamin D analogue, the epi-20-analogue KH1060 (0.4-2.0 micrograms/ml) on epidermal proliferation in normal hairless mice. Epidermis was examined at intervals from 4 h to 8 days after a single-dose application. The mitotic rate was assessed by the stathmokinetic method and hyperplasia was scored in histological sections. Cell cycle parameters were measured by bivariate bromodeoxyuridine (BrdUrd)/DNA flow cytometry on isolated epidermal basal cells after pulse-labelling with BrdUrd. Both calcitriol and KH1060 induced a dose- and time-dependent increase in the mitotic rate and in hyperplasia, the latter drug being the most effective. Calcitriol and KH1060 induced changes in the cell cycle traverse compatible with the regenerative reaction seen after other hyperplasiogens, but with an additionally increased accumulation of cells in the G2 phase. This is similar to that seen after topical application of retinoic acid to mouse skin. Our results are thus in contrast to the anti-proliferative effects of calcitriol observed in vitro and following treatment of the hyperproliferative disease psoriasis with calcitriol as well as other vitamin D analogues.

Comparison of calcipotriol with selected metabolites and analogues of vitamin D3: effects on cell growth regulation in vitro and calcium metabolism in vivo

Calcipotriol is a novel vitamin D3 analogue developed for topical treatment of psoriasis. Calcipotriol is believed to act via regulation of cell proliferation and differentiation. In this respect calcipotriol is as potent as 1 alpha, 25(OH)2D3, the physiologically active form of vitamin D3, but its calcaemic activity in vivo is 100 to 200 times lower. In the present investigation, the effects of calcipotriol on cell growth regulation in vitro and on calcium metabolism in vivo were compared to those exerted by a number of metabolites and analogues of vitamin D3. Besides 1 alpha, 25(OH)2D3, these included the two physiologically occurring metabolites 25(OH)D3 and 24,25(OH)2D3, and the two synthetic analogues 1 alpha (OH)D3 and 1 alpha, 24(OH)2D3. 25(OH)D3 and 24,25(OH)2D3 were shown to be inactive both in vitro and in vivo. 1 alpha (OH)D3 was found to have a low biological activity in vitro, but was highly calcaemic in vivo after biotransformation to 1 alpha, 25(OH)2D3. Calcipotriol, 1 alpha, 24(OH)2D3 and 1 alpha, 25(OH)2D3 were all three potent regulators of cell proliferation and differentiation in vitro. In vivo, only calcipotriol showed a greatly reduced calcaemic activity after both oral and intravenous administration. It is concluded that calcipotriol, with a reduced risk of inducing calcaemic side-effects upon absorption from the skin, possesses a favourable therapeutic profile for topical treatment of hyperproliferative diseases.

Two novel vitamin D analogues, KH 1060 and CB 966, prolong skin allograft survival in mice

KH 1060 and CB 966, two novel analogues of 1,25-dihydroxyvitamin D3(1,25(OH)2D3), were found to significantly delay the rejection of allogeneic skin grafts in CBA (H-2k) recipient mice, transplanted with skin from C57Bl/6 (H-2b) donor mice. Graft survival was assessed in mice treated with KH 1060 or CB 966 until the day of rejection, in comparison to mice treated with vehicle, 1,25(OH)2D3 or cyclosporin A (CsA). The mean graft survival time in days was found to be: 16.6 +/- 0.5 (CsA, 20 mg/kg/day orally (p.o.); 13.9 +/- 0.6 and 15.5 +/- 0.6 (1,25(OH)2D3, 0.2 and 0.4 microgram/kg/day intraperitoneally (i.p.)); 14.3 +/- 0.2 and 18.7 +/- 0.5 (CB 966, 0.2 and 0.4 microgram/kg/day i.p.); 13.7 +/- 0.8, 15.7 +/- 1.7, 18.2 +/- 2.7 and 24.5 +/- 0.5 (KH 1060, 0.02, 0.1, 0.2 and 0.4 microgram/kg/day i.p.). Mean graft survival in days for control mice was: 10.3 +/- 0.2 (vehicle for injection, i.p.) and 11.5 +/- 0.2 (olive oil, p.o.). Serum calcium levels, measured on the day of rejection, rose moderately after treatment with either KH 1060 or CB 966. Combination of CsA (20 mg/kg/day p.o.) with KH 1060 (0.1 microgram/kg/day i.p.) resulted in an additive or synergistic effect: 23.4 +/- 1.1 days of skin allograft survival, compared to 15.7 +/- 1.7 days with KH 1060 alone, and 15.1 +/- 1.9 days with CsA alone. KH 1060 was the most active of the tested compounds and can therefore be regarded as a potent immunosuppressor in transplantation; it can be used in combination with CsA and is effective at doses which only marginally affect serum calcium levels.

Toxicity of vitamin D analogues in rats fed diets with standard or low calcium contents

Sprague-Dawley rats were fed either a standard diet with 0.9/0.7% Ca/P or a semisynthetic low-calcium diet with 0.5/0.4% Ca/P and treated orally for 28 days with 1 alpha-hydroxycholecalciferol [1 alpha (OH)D3], a synthetic analogue of the physiologically active form of vitamin D3, 1 alpha,25-dihydroxycholecalciferol [1 alpha,25(OH)2D3], at dose levels of 0.2 and 2.0 micrograms kg/day. The high dose caused severe hypercalcaemia with retarded growth, nephrosis, and structural bone changes in rats fed the standard diet. The same dose caused only slight hypercalcaemia without growth retardation or bone changes, and only minimally affected the kidneys in rats fed the low-calcium diet. Hypercalcaemia with less pronounced pathological changes was found in the standard diet low-dose rats, whereas no hypercalcemia or pathological changes were found in the low-calcium diet low-dose group. The rats fed the low-calcium diet tolerated 1 alpha(OH)D3 at dose levels up to 10 times higher than rats on the standard diet. The use of diets low in calcium and low in phosphorus will thus allow the administration of higher dosages of vitamin D compounds without causing hypercalcaemia. This may permit a better evaluation of the pharmacologic and toxic effects not directly associated with the calcium-regulating properties of vitamin D metabolites and analogues.

Induction of leukotriene C4 synthase activity in differentiating human erythroleukemia cells

Leukotriene (LT)C4 synthase is a membrane-bound, specific glutathione transferase which catalyzes the transformation of LTA4 to LTC4. It was originally shown to be present in rodent mastocytoma and basophilic leukemia cells as well as in macrophages. Recently, expression of human LTC4 synthase was demonstrated in platelets (Söderström, M., et al. (1992) Arch. Biochem. Biophys. 294, 70-74). The present report describes the induction of LTC4 synthase activity during differentiation of human erythroleukemia (HEL) cells by the protein kinase C stimulator 12-O-tetradecanoyl phorbol 13-acetate (TPA), ligands of the steroid-thyroid hormone receptor superfamily: all-trans-retinoic acid (RA) and 1 alpha, 25-dihydroxy-vitamin D3 and in addition dimethylsulfoxide (DMSO). TPA was the most powerful inducer of enzyme activity followed by 1 alpha, 25-dihydroxy-vitamin D3 and DMSO. RA did not induce LTC4 synthase activity.

EB1089: a new vitamin D analogue that inhibits the growth of breast cancer cells in vivo and in vitro

EB1089 is a novel vitamin D analogue which has been tested for its effects on breast cancer cell growth in vitro, using the established human breast cancer cell line MCF-7, and in vivo on the growth of established rat mammary tumours. Both EB1089 and 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) inhibited MCF-7 cell proliferation with the synthetic analogue being at least an order of magnitude more potent than the native hormone. In vivo anti-tumour effects were investigated using the N-methyl-nitrosourea-induced rat mammary tumour model. Oral treatment with EB1089 was tested at three doses. With the lower dose, significant inhibition of tumour growth was seen in the absence of a rise in serum calcium. The same dose of 1,25-(OH)2D3 had no effect on tumour growth but caused hypercalcaemia. With the higher dose of EB1089, striking tumour regression was seen although serum calcium rose. This report demonstrates that EB1089 possess enhanced anti-tumour activity coupled with reduced calcaemic effects relative to 1,25-(OH)2D3 and thus may have therapeutic potential as an anti-tumour agent.

Treatment of psoriasis with calcipotriol and other vitamin D analogues

The discovery of a high-affinity receptor for the bioactive form of vitamin D3, 1,25-dihydroxyvitamin D3 (1,25[OH]D3), in most skin cells has led to the finding of previously unknown effects of vitamin D on epidermal growth and on the skin immune system. 1,25(OH)2D3 inhibits epidermal proliferation and promotes epidermal differentiation. These properties provided the rationale for introducing 1,25(OH)2D3 in the treatment of psoriasis vulgaris. In addition to 1,25(OH)2D3, the synthetic vitamin D3 analogues 1 alpha(OH)D3, 1,24(OH)2D3, and calcipotriol have undergone clinical evaluation. Calcipotriol has been studied most extensively. Compared with 1,25(OH)2D3, calcipotriol is about 200 times less potent in its effects on calcium metabolism, although similar in receptor affinity. In double-blind, placebo-controlled, randomized studies, topical calcipotriol (50 micrograms/gm, up to 100 gm weekly) has been shown to be efficacious and safe for the treatment of psoriasis. A similar therapeutic profile has been seen in long-term studies. In comparative studies topical calcipotriol is slightly more efficacious than betamethasone 17-valerate and dithranol. The mode of action of calcipotriol and other vitamin D3 analogues in psoriasis is not known. Although vitamin D3 analogues affect epidermal growth, their immunosuppressive properties may be equally important for their antipsoriatic effect.

Vitamin D analogues and psoriasis

Topical vitamin D analogues offer a new, effective, more convenient and generally well-tolerated option for the treatment of psoriasis. Only psoriasis vulgaris has been intensively studied, but other forms of the disease may also respond. Both calcitriol and calcipotriol have been shown to be effective in numerous clinical trials, and the latter has compared well with betamethasone valerate and short-contact dithranol in controlled studies. Their mechanism of action is not yet fully understood and may prove complex. The most important effect may be a direct regulation of keratinocyte proliferation and differentiation. However, these compounds also have potent immunological properties, and may act by inhibition of cytokine production by keratinocytes or lymphocytes. Topical application of vitamin D analogues appears generally to be remarkably safe, but hypercalcaemia and hypercalciuria may develop if large quantities are used.

Immunological properties of vitamin D analogues and metabolites

This commentary has attempted to describe some of the new aspects of our knowledge of the immunological properties of 1 alpha,25(OH)2D3, the physiologically active metabolite of vitamin D3, and its new analogues. These analogues will, in the future, serve as tools to increase our understanding of the role of vitamin D in immunobiology, not only in basal research but also, hopefully, in the therapy of immune-mediated diseases.

Single and combined effects of the vitamin D analogue KH1060 and cyclosporin A on mercuric-chloride-induced autoimmune disease in the BN rat

Mercuric chloride induces in BN rats a self-limiting systemic autoimmune disease characterized by proliferation of autoreactive CD4+ T lymphocytes, polyclonal activation of B lymphocytes, and the development of an anti-glomerular basement membrane (GBM) nephritis with concomitant nephrotic range proteinuria. We have used this model of autoimmune disease to test the immunosuppressive ability of a novel vitamin D3 analogue KH1060. This compound prevents autoimmune manifestations including proteinuria, serum IgE, and serum anti-laminin antibodies in a dose-dependent manner, as does cyclosporin A (CyA). When dosages of KH1060 capable of partial reduction of proteinuria without causing significant hypercalcaemia are combined with small dosages of CyA also capable of partial prevention of proteinuria, an additive effect is seen, leading to complete prevention of proteinuria and substantial reductions in serum IgE and anti-laminin levels. Possible mechanisms of action are discussed and it is suggested that KH1060 could prove useful as an immunosuppressive agent in the treatment of autoimmune diseases.

Vitamin D3 and skin diseases

The physiologically active metabolite of vitamin D3, 1 alpha,25-dihydroxycolicalciferol [1,25(OH)2D3, calcitriol] has achieved the status of a hormone. It is believed to mediate its effects by binding to a specific receptor which belongs to the family of nuclear receptors for glucocorticoids, estrogens, thyroxine, and retinoid acid. It has been discovered that 1,25(OH)2D3 has the ability to regulate growth and differentiation in many cell types, including cancer cells, epidermal keratinocytes, and activated lymphocytes. This has set the stage for the development of a new class of compounds with potential usefulness in hyperproliferative and immune-mediated diseases. Ideally, such agents should possess potent effects as regulators of cell proliferation and differentiation at concentrations well below those that may induce side effects related to the classical vitamin D activity on calcium absorption and bone mineralization. In addition to 1,25(OH)2D3, the synthetic vitamin D3 analogues 1 alpha-OH-D3, 1,24(OH)2D3, and calcipotriol have undergone clinical evaluation. Calcipotriol has been studied most extensively. Compared with 1,25(OH)2D3, calcipotriol is about 200 times less potent in its effect on calcium metabolism although similar in receptor affinity. In double-blind, placebo-controlled multicenter studies, topical calcipotriol has been shown to be both efficacious and safe for the short- and long-term treatment of plaque-type psoriasis. Because some of the novel vitamin D analogues are potent regulators of cell growth and immune responses, they may be of potential interest in the treatment of ichthyoses, cancer, and autoimmune diseases.