In vitro metabolism of calcipotriol (MC 903), a vitamin D analogue

Pharmacokinetics of intra-articular vitamin D analogue calcipotriol in sheep and metabolism in human synovial and mesenchymal stromal cells

Calcipotriol (MC903) is a side chain analogue of the biologically active 1,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃]. Due to its anti-inflammatory and anti-proliferative effects on stromal cells, calcipotriol is a promising candidate for the local treatment of arthritis. In this preliminary work, we studied the pharmacokinetics and safety of calcipotriol after an IV (0.1 mg/kg given to one sheep) and intra-articular dose (0.054 mg/kg, 0.216 mg/kg and 0.560 mg/kg given to three sheep). The terminal half-life of calcipotriol was approximately 1 h after an IV dose. After intra-articular dosing, the systemic absorption was between 1 and 13% during the observed 24 h. Hypercalcemia or other clinical adverse effects did not occur in any animal during the study, and no macroscopic or microscopic alterations were seen in the synovium of the calcipotriol-injected knees compared to the vehicle knees. The in vitro metabolism of calcipotriol was analyzed with LC-MS from human synovial and mesenchymal stromal cell cultures. Both cell types were able to metabolize calcipotriol with MC1080 and MC1046 as the main metabolites. CYP24A1 transcripts were strongly induced by a 48-hour calcipotriol exposure in mesenchymal stromal cells, but not consistently in synovial stromal cells, as determined by RT-qPCR. Calcipotriol proved to be safe after a single intra-articular dose with applied concentrations, and it is metabolized by the cells of the joint. Slow dissolution of calcipotriol crystals in the joint can extend the pharmaceutical impact on the synovium, cartilage and subcortical bone.

IL-1α, IL-6 and TNF-α in Cutaneous Lesions of Lupus Erythematosus are Inhibited by Topical Application of Calcipotriol

Lupus Erythematosus (LE) is an autoimmune disorder with an unknown etiology and pathogenesis. Skin lesions of LE express several cytokines which correlate to histological findings such as IL-1 and IL-6 which are mediators of epidermal growth and proliferation. Skin lesions of LE are generally treated with immunosuppressive agents such as oral or topically applied corticosteroids. Recently a new drug, calcipotriol, a vitamin D3 analogue has been useful in treatment of psoriasis with no ad verse effect on calcium metabolism. This drug shares immunomodulatory effects with vit. D3 by inhibiting several cytokines produced by keratinocytes.

In order to test the clinical effectiveness of calcipotriol in cutaneous lesions of LE we have investigated several proinflammatory cytokines such as: IL-1α, IL-1β, IL-4, IL-5, IL-6, IL-8, MCP-1, TNF-α. Using an avidin-biotin immunoperoxidase system we have found IL-1 in both forms, IL-6 and TNF-α in basal keratinocytes in patients affected with LE, after treatment they were reverted to normal. This inhibition is induced at a molecular level as demostrated by reduced IL-1, IL-6 and TNFα mRNA expression. This is the first report showing that calcipotriol is effective in cutaneous lesions of LE and suggesting that this action is due to an inhibition of protein synthesis and mRNA expression for IL-1α, IL-6 and TNFα.

Multifunctional and potent roles of the 3-hydroxypropoxy group provide eldecalcitol's benefit in osteoporosis treatment

Eldecalcitol (1α,25-dihydroxy-2β-(3-hydroxypropoxy)vitamin D3, [developing code: ED-71]), a new osteoporosis treatment drug that was recently approved in Japan, is a best-in-class drug in the class of calcitriol (1α,25-dihydroxyvitamin D3) and its prodrug alfacalcidol (1α-hydroxyvitamin D3), which have been used to treat osteoporosis for 30 years. In a comparative Phase III clinical study with alfacalcidol in osteoporosis patients, eldecalcitol demonstrated superior efficacy in the endpoints of increment of bone mineral density and reduction of bone fracture with equivalent safety to alfacalcidol. Eldecalcitol was discovered by searching synthetic analogs of calcitriol and alfacalcidol, and its main structural characteristic is having the 3-hydroxypropoxy group at the 2β-position. This review discusses why introducing the group leads to excellent efficacy and safety in osteoporosis treatment and elucidates the functional roles of the 3-hydroxypropoxy group. Briefly, the functional roles of the group are, first, realizing the metabolism switching in which eldecalcitol shows resistance to CYP24A1 and is metabolized in the liver; second, increasing the affinity to the serum carrier protein and prolonging the half-life to 53h; and third, stabilizing the eldecalcitol-receptor complex. Taken together, these functional roles of the 3-hydroxypropoxy group are beneficial in osteoporosis treatment. This review attempts to give a detailed account of the mode of action of eldecalcitol by clarifying these multifunctional roles of the 3-hydroxypropoxy group from the medicinal chemist's perspective.

Vitamin D analogs

Vitamin D has gone through a renaissance with the association of vitamin D deficiency with a wide array of common diseases including breast, colorectal and prostate cancers, cardio-vascular disease, autoimmune conditions and infections. Vitamin D analogs constitute a valuable group of compounds which can be used to regulate gene expression in functions as varied as calcium and phosphate homeostasis, as well as cell growth regulation and cell differentiation of a wide spectrum of cell types. This review will discuss the full range of vitamin D compounds currently available, some of their possible uses, and potential mechanisms of action.

Calcipotriol ointment. A review of its use in the management of psoriasis

Calcipotriol, a vitamin D3 analog, acts not only to inhibit cell proliferation and enhance cell differentiation in the skin of patients with psoriasis, but also appears to have effects on immunologic markers that are thought to play a role in the etiology of the disease. In several well designed, short term studies in adults, calcipotriol ointment 50 micrograms/g twice daily provided similar or superior efficacy to several other antipsoriatic agents in adult patients with mild to moderate psoriasis. In patients with nonscalp psoriasis, the drug provided superior efficacy to twice daily placebo (vehicle ointment), twice daily fluocinonide 500 micrograms/g, once daily tacalcitol 4 micrograms/g and twice daily coal tar 5% plus allantoin 2% and hydrocortisone 0.5%. Furthermore, calcipotriol therapy generally provided superior efficacy to twice daily betamethasone valerate 1 to 1.2 mg/g or once daily dithranol 1 to 20 mg/g, and similar efficacy to twice daily betamethasone dipropionate plus salicylic acid or once daily maxacalcitol 6 to 50 micrograms/g. Limited data indicated that calcipotriol ointment 50 micrograms/g also improved overall disease severity in children. In combination with other antipsoriatic agents [acitretin, cyclosporine, betamethasone valerate, halobetasol (ulobetasol)], ultraviolet B or psoralen ultraviolet A (PUVA) phototherapy, calcipotriol ointment 50 micrograms/g twice daily improved the beneficial effects of these drugs on overall disease severity in adult patients with moderate to severe psoriasis. Furthermore, in separate trials, calcipotriol combination therapy reduced the dosage of acitretin required to achieve clearance of psoriasis and the duration of PUVA and dosage of UVA phototherapy, potentially improving the benefit/risk ratio for these other antipsoriatic treatments. Calcipotriol was generally well tolerated in short and long term studies in adult patients, with the majority of adverse events being mild to moderate in intensity and transient. The most common adverse events associated with calcipotriol therapy were dermatologic in nature and included lesional or perilesional irritations, face and scalp irritations, worsening of psoriasis and miscellaneous dermatologic events. Notably, there have been very few reports of patients developing hypercalcemia or hypercalciuria during calcipotriol therapy, with most occurring in patients who exceeded the recommended dosage of 100 g/week. Although data in children are limited, the drug was well tolerated with the nature and incidence of adverse effects similar to those observed in adult patients.

CONCLUSIONS

Extensive clinical experience, along with several short and long term clinical trials, has shown calcipotriol ointment to be an effective and well tolerated topical agent in adult patients with psoriasis. In addition, calcipotriol ointment proved beneficial in combination with other topical, phototherapy or systemic antipsoriatic treatments, reducing the dosage and/or duration of some of these treatments and potentially improving their benefit/risk ratio. Calcipotriol ointment is valuable as a first- or second-line therapy option for the management of mild to moderate psoriasis and in combination with other antipsoriatic agents for more severe psoriasis.

LC separation of calcipotriol from its photodegradation products and protection possibilities using adjuvants

Mobile phase optimization and reversed-phase column characteristics were used to separate photodegradation products from the parent compound, 24-cyclopropyl-9-,10-secochola-5,7,10(19),22-tetraene-1alpha,3beta,24-triol (calcipotriol). Separation between calcipotriol and its degradation products was obtained with an acetonitrile/water (53:47, v/v) mobile phase on a C(18) Hypersil ODS column (250 mm length, 4.6 mm id, 5 microm particle size) and a flow rate of 1 ml/min. Using this system, the influence of commonly used solvents in dermatology on degradation was studied. The addition of a UV filter in two concentrations was also evaluated for its possible protective effect to light exposure. Propylene glycol and polyethylene glycol 400 decreased the speed of degradation. The sunscreen 2-hydroxy-4-methoxybenzophenone affords a protection proportional to the filter concentration used in the study.

Double bond in the side chain of 1alpha,25-dihydroxy-22-ene-vitamin D(3) is reduced during its metabolism: studies in chronic myeloid leukemia (RWLeu-4) cells and rat kidney

1alpha,25-Dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)] is mainly metabolized via the C-24 oxidation pathway and undergoes several side chain modifications which include C-24 hydroxylation, C-24 ketonization, C-23 hydroxylation and side chain cleavage between C-23 and C-24 to form the final product, calcitroic acid. In a recent study we reported that 1alpha,25-dihydroxyvitamin D(2) [1alpha,25(OH)(2)D(2)] like 1alpha,25(OH)(2)D(3), is also converted into the same final product, calcitroic acid. This finding indicated that 1alpha,25(OH)(2)D(2) also undergoes side chain cleavage between C-23 and C-24. As the side chain of 1alpha,25(OH)(2)D(2) when compared to the side chain of 1alpha,25(OH)(2)D(3), has a double bond between C-22 and C-23 and an extra methyl group at C-24 position, it opens the possibility for both (a) double bond reduction and (b) demethylation to occur during the metabolism of 1alpha,25(OH)(2)D(2). We undertook the present study to establish firmly the possibility of double bond reduction in the metabolism of vitamin D(2) related compounds. We compared the metabolism of 1alpha,25-dihydroxy-22-ene-vitamin D(3) [1alpha,25(OH)(2)-22-ene-D(3)], a synthetic vitamin D analog whose side chain differs from that of 1alpha,25(OH)(2)D(3) only through a single modification namely the presence of a double bond between C-22 and C-23. Metabolism studies were performed in the chronic myeloid leukemic cell line (RWLeu-4) and in the isolated perfused rat kidney. Our results indicate that both 1alpha,25(OH)(2)-22-ene-D(3) and 1alpha,25(OH)(2)D(3) are converted into common metabolites namely, 1alpha,24(R),25-trihydroxyvitamin D(3) [1alpha,24(R),25(OH)(3)D(3)], 1alpha,25-dihydroxy-24-oxovitamin D(3) [1alpha,25(OH)(2)-24-oxo-D(3)], 1alpha,23(S),25-trihydroxy-24-oxovitamin D(3) and 1alpha,23-dihydroxy-24,25,26,27-tetranorvitamin D(3). This finding indicates that the double bond in the side chain of 1alpha,25(OH)(2)-22-ene-D(3) is reduced during its metabolism. Along with the aforementioned metabolites, 1alpha,25(OH)(2)-22-ene-D(3) is also converted into two additional metabolites namely, 1alpha,24,25(OH)(3)-22-ene-D(3) and 1alpha,25(OH)(2)-24-oxo-22-ene-D(3). Furthermore, we did not observe direct conversion of 1alpha,25(OH)(2)-22-ene-D(3) into 1alpha,25(OH)(2)D(3). These findings indicate that 1alpha,25(OH)(2)-22-ene-D(3) is first converted into 1alpha,24,25(OH)(3)-22-ene-D(3) and 1alpha,25(OH)(2)-24-oxo-22-ene-D(3). Then the double bonds in the side chains of 1alpha,24,25(OH)(3)-22-ene-D(3) and 1alpha,25(OH)(2)-24-oxo-22-ene-D(3) undergo reduction to form 1alpha,24(R),25(OH)(3)D(3) and 1alpha,25(OH)(2)-24-oxo-D(3), respectively. Thus, our study indicates that the double bond in 1alpha,25(OH)(2)-22-ene-D(3) is reduced during its metabolism. Furthermore, it appears that the double bond reduction occurs only during the second or the third step of 1alpha,25(OH)(2)-22-ene-D(3) metabolism indicating that prior C-24 hydroxylation of 1alpha,25(OH)(2)-22-ene-D(3) is required for the double bond reduction to occur.

Calcipotriol toxicity in a dog

A six-month-old Labrador retriever was presented for investigation of acute polyuria, polydipsia and haematemesis six hours following ingestion of a tube of the topical antipsoriatic vitamin D analogue, calcipotriol. Transient hypercalcaemia, azotaemia, proteinuria, thrombocytopenia and ventricular arrhythmias ensued. Abdominal ultrasonography and echocardiography revealed evidence of diffuse soft tissue mineralisation. Despite 13 days of intensive supportive care, the dog was euthanased due to continued haematemesis and anorexia. Necropsy confirmed mineralisation and necrosis of multiple organ systems consistent with vitamin D toxicity.

In vitro metabolism of the vitamin D analog, 22-oxacalcitriol, using cultured osteosarcoma, hepatoma, and keratinocyte cell lines

Using four cultured cell models representing liver, keratinocyte, and osteoblast, we have demonstrated that the vitamin D analog, 22-oxacalcitriol is degraded into a variety of hydroxylated and side chain truncated metabolites. Four of these metabolic products have been rigorously identified by high pressure liquid chromatography, diode array spectrophotometry, and gas chromatography-mass spectrometry analysis as 24-hydroxylated and 26-hydroxylated derivatives as well as the cleaved molecules, hexanor-1alpha,20-dihydroxyvitamin D3 and hexanor-20-oxo-1alpha-hydroxyvitamin D3. Comparison with chemically synthesized standards has revealed the stereochemistry of the biological products. Although differences exist in the amounts of products formed with the different cell types, it is apparent that 22-oxacalcitriol is subject to metabolism by both vitamin D-inducible and noninducible enzymes. Time course studies suggest that the truncated 20-alcohol is derived from a side chain hydroxylated molecule via a hemiacetal intermediate and the 20-oxo derivative is likely formed from the 20-alcohol. Biological activity measurements of the metabolites identified in our studies are consistent with the view that these are catabolites and that the biological activity of 22-oxacalcitriol is due to the parent compound. These results are also consistent with recent findings of others that the biliary excretory form of 22-oxacalcitriol is a glucuronide ester of the truncated 20-alcohol.

Different mechanisms of hydroxylation site selection by liver and kidney cytochrome P450 species (CYP27 and CYP24) involved in vitamin D metabolism

A series of homologated 1 alpha-hydroxyvitamin D3 and 1,25-dihydroxyvitamin D3 molecules with one to three extra carbons in the side chain were used to examine the substrate preferences and hydroxylation site selection mechanisms of the liver vitamin D3-25-hydroxylase (CYP27) and the target cell 25-hydroxyvitamin D3-24-hydroxylase (CYP24). Cultured and transfected cell models, used as sources of these hydroxylases, gave 23-, 24-, 25-, and 27-hydroxylated metabolites which were identified by their high performance liquid chromatography and GC-MS characteristics. Lengthening the side chain is tolerated by each cytochrome P450 isoform such that 25-hydroxylation or 24-hydroxylation continues to occur at the same rate as in the native side chain, while the site of hydroxylation remains the same for the liver enzyme in that CYP27 continues to hydroxylate at C-25 and C-27 (minor) despite the two-carbon-atom extension. Somewhat surprising is the finding that C-24 and C-23 (minor) hydroxylations also do not change as the side chain is extended by as much as three carbons. We conclude that CYP24 must be directed to its hydroxylation site(s) by the distance of carbon 24 from the vitamin D ring structure and not as in CYP27 by the distance of the hydroxylation site from the end of the side chain.

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.

A comparative study of calcipotriol ointment and tar in chronic plaque psoriasis

The antipsoriatic efficacy, tolerability and safety of calcipotriol ointment was compared with tar in a prospective, right/left randomized, investigator-blinded controlled study. Calcipotriol ointment 50 micrograms/g twice daily was applied to one-half of the body. On the opposite side, white soft paraffin was applied in the morning, and coal tar solution BP 15% v/w in aqueous cream in the evening. Thirty patients with stable chronic plaque-type psoriasis were recruited. Assessments were made at 2, 4 and 6 weeks. Three patients were withdrawn from the study. A decrease in PASI score was seen on both sides at 2, 4 and 6 weeks. The differences from baseline between the two treatments were statistically significant in favour of calcipotriol. Improvement with calcipotriol was rapid in the first 2 weeks of treatment. With tar, significant improvement occurred only after 4 weeks of treatment. The differences in the scores for erythema, induration and desquamation from baseline between the two treatments were also statistically significantly in favour of calcipotriol at all evaluation points. Seven patients developed irritation on the calcipotriol-treated side, but there were no adverse effects on the tar-treated side. In two patients, itching associated with psoriasis was reduced by the calcipotriol. Although the mean serum calcium and phosphate levels remained within the normal ranges after 6 weeks' treatment, there were significant changes in their values compared with baseline.

A dialogue on analogues Newer vitamin-D drugs for use in bone disease, psoriasis, and cancer

Many new analogues of the vitamin-D hormone, 1 alpha,25-dihydroxy-vitamin D(3) [1 alpha,25-(OH)(2)D(3); calcitriol], have emerged that can mimic its various actions in classic calcium transport systems and/or in the regulation of cell proliferation and cell differentiation. Though some of these analogues have accentuated activity in cell differentiation assays in vitro, they lack appreciable "calcemic" activity in vivo, leading to the name "noncalcemic analogues." Several of these analogues are promising candidates for use in treatment of psoriasis and in tumor suppression, one of them, calcipotriol, being already widely approved for the former indication. New generations of calcemic analogues with altered pharmacokinetics are appearing for use in secondary hyperparathyroidism and osteoporosis. We believe that the selective properties of both types of analogues stem from altered receptor binding, blood protein binding, and rate of catabolism.

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.

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.

Efficacy and safety of calcipotriol (MC 903) ointment in psoriasis vulgaris. A randomized, double-blind, right/left comparative, vehicle-controlled study

BACKGROUND

The biologically active form of vitamin D3, calcitriol, may offer a new therapeutic approach to psoriasis. Calcipotriol, a new vitamin D3 analogue, is at least 100 times less calcemic than calcitriol.

OBJECTIVE

Our purpose was to study the efficacy and safety of calcipotriol in the treatment of psoriasis vulgaris.

METHODS

In a right/left comparative, double-blind study, treatment with calcipotriol ointment (50 micrograms/gm) twice daily and placebo was given for 4 weeks. The preferred treatment was continued, without opening the code, for another 4 weeks. Efficacy, as measured by the Psoriasis Area and Severity Index and by the investigator's and patient's global assessment, and safety were assessed every 2 weeks.

RESULTS

The mean Psoriasis Area and Severity Index fell in 4 weeks from 14.2 to 6.3 with calcipotriol and from 14.1 to 9.2 with placebo (p < 0.001; 95% confidence interval for difference: 1.78-->3.94). Local side effects were equally common with calcipotriol and placebo. The mean serum calcium remained unchanged.

CONCLUSION

Topical application of up to 50 gm of calcipotriol ointment per week was found to be an effective and safe treatment of psoriasis vulgaris.

Effects of synthetic vitamin D analogues on breast cancer cell proliferation in vivo and in vitro

Calcipotriol (MC903) is a novel vitamin D analogue which effects cellular differentiation and proliferation in vitro and has reduced effects on calcium metabolism in vivo. In the present study its in vitro activity was evaluated using the MCF-7 breast cancer cell line, and its effects on calcium metabolism and mammary tumour growth were measured in vivo in adult female rats. Calcipotriol was compared to the natural metabolite of vitamin D3, 1 alpha,25-dihydroxycholecalciferol [1,25(OH)2D3] and its synthetic analogue 1 alpha hydroxycholecalciferol [1 alpha(OH)D3]. Both calcipotriol and 1,25(OH)2D3 produced significant inhibition of MCF-7 cell proliferation at a concentration of 5 x 10(-11) M. Intraperitoneal administration of calcipotriol to normal female rats showed that the analogue was 100-200 times less active than 1,25(OH)2D3 in raising serum calcium concentration and urinary calcium excretion. Anti-tumour activity of the vitamin D analogues was investigated in vivo using the nitrosomethylurea-induced rat mammary tumor model. Rats, maintained on a low calcium diet, were treated with 1 alpha(OH)D3 (0.25 and 1.25 micrograms/kg). Both doses produced a response rate of 25% but hypercalcaemia developed. Treatment with calcipotriol (50 micrograms/kg) of rats maintained on a normal laboratory diet caused inhibition of tumour progression (response rate 17%) without the development of severe hypercalcaemia. This study supports the concept that vitamin D derivatives may inhibit breast cancer cell proliferation in vivo.

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.

Actions of calcipotriol (MC 903), a novel vitamin D3 analog, on human bone-derived cells: comparison with 1,25-dihydroxyvitamin D3

The actions of a novel vitamin D3 analog calcipotriol (MC 903), on human bone-derived cells were compared to those of 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]. Both calcipotriol and 1,25-(OH)2D3 inhibited the proliferation of human osteoblast-like cells in a dose-dependent manner (10(-10)-10(-6) M), an effect observed at different cell densities. Lower concentrations of either agent exerted no marked effect on the growth of the cells compared to untreated cultures. Calcipotriol and 1,25-(OH)2D3 were equipotent in stimulating the activity of alkaline phosphatase and the synthesis of osteocalcin in human osteoblast-like cells. The stimulation of alkaline phosphatase activity and osteocalcin synthesis by both compounds was evident by 24 h and was increased progressively up to 96 h in a dose-dependent manner over the concentration range of 10(-10)-10(-6) M. The increment in both proteins was dependent on cell density and was attenuated at higher cell densities. In contrast to these actions, neither calcipotriol nor 1,25-(OH)2D3 (10(-14)-10(-6) M) affected the synthesis of prostaglandin E2. These studies indicate that calcipotriol and 1,25-(OH)2D3 exhibit a similar spectrum of activity on human osteoblast-like cells in vitro.

Nonhypercalcemic 1,25-(OH)2D3 analogs potently induce the human osteocalcin gene promoter stably transfected into rat osteosarcoma cells (ROSCO-2)

1,25-Dihydroxyvitamin D3 [1,25-(OH)2D3] is the active hormonal form of vitamin D3 and has potent effects on bone and calcium regulation. Over the past decade it has become apparent that 1,25-(OH)2D3 has other effects on cellular proliferation that potentially could be developed for therapy in human malignancy. Since the hypercalcemic effects of 1,25-(OH)2D3 have limited that use in the human, novel nonhypercalcemic analogs of 1,25-(OH)2D3 have been synthesized. The molecular mechanism of this divergence in these antiproliferative and calcium-regulating actions is unexplained. We have previously examined the human bone-specific gene osteocalcin as a model of the molecular mechanisms of vitamin D action in bone and have shown that induction of the osteocalcin gene by 1,25-(OH)2D3 is mediated through an unique and complex palindromic region of the promoter similar to but distinct from those of other steroid hormone-responsive elements. Using an osteosarcoma cell line permanently transfected with the vitamin D-responsive promoter of the human osteocalcin gene linked to a "reporter" gene, we have shown that there is a dose-dependent induction of CAT activity by 1,25-(OH)2D3 and that the potencies of vitamin D metabolites and analogs are comparable to those found in other vitamin D bioassays. Furthermore, vitamin D analogs, including MC-903, 22-oxa-1,25-(OH)2D3, and delta 22-1,25S,26-trihydroxyvitamin D3, which effect cellular differentiation but lack hypercalcemic activity in vivo, exhibit osteocalcin promoter inductive actions virtually identical to those of 1,25-(OH)2D3. Consideration of these and other data support the hypothesis that the divergent effects of such analogs on differentiation and calcium homeostasis reflect pharmacokinetic differences in vivo rather than distinct 1,25-(OH)2D3-sensitive pathways.

The effects of MC903 on 1,25-(OH)2D3 receptor binding, 24-hydroxylase activity and in vitro bone resorption

MC903, a new vitamin D analog has been shown to exert potent effects on cell proliferation and differentiation, while in vivo a decreased activity on calcium metabolism has been observed. In the osteoblast-like cell line UMR-106, MC903 displaces tritiated 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) from its receptor at least as efficiently as 1,25-(OH)2D3. The effect of MC903 on 1,25-(OH)2D3 receptor up-regulation in UMR-106 cells and on bone resorption in fetal mouse radii/ulnae was comparable to that of 1,25-(OH)2D3. MC903 was about 50% less effective in inducing 24-hydroxylase activity and the subsequent C24-side chain oxidation of 25-(OH)D3 compared to 1,25-(OH)2D3. Ketoconazole did not potentiate MC903-induced 1,25-(OH)2D3 receptor up-regulation as was found with 1,25-(OH)2D3 which suggests that the C24-oxidation plays a minor role in the inactivation of MC903. Nevertheless, the comparable effects of MC903 and 1,25-(OH)2D3 on in vitro bone resorption indicate that the lower effectivity of MC903 on bone calcium mobilization in vivo has to be due to a higher metabolic clearance rate.

Calcipotriol (MC 903): pharmacokinetics in rats and biological activities of metabolites. A comparative study with 1,25(OH)2D3

Calcipotriol (MC 903) is a novel analogue of the physiologically active metabolite of vitamin D3, 1 alpha,25-dihydroxycholecalciferol [1,25(OH)2D3]. MC 903 and 1,25(OH)2D3 have similar effects on cell proliferation and cell differentiation in vitro using the human histiocytic lymphoma cell line U 937, but in vivo MC903 has 100-200 times less effect on calcium metabolism. To elucidate this difference, the pharmacokinetic profiles after a single intravenous dose (50 micrograms/kg) of the two compounds to rats were compared. The area under the serum level/time curve (AUC) was more than 100 times higher for 1,25(OH)2D3 than for MC903 and the rate of clearance was more than 100 times higher for MC903 than for 1,25(OH)D3. Serum from MC903 or 1,25(OH)2D3 dosed rats (i.v. 10 micrograms/kg) was investigated for biological activities by incubation of U 937 cells with serum collected 0-24 hr after drug administration. Serum from MC903 dosed rats had an effect only when collected shortly after dosing, whereas serum from 1,25(OH)2D3 dosed rats had an effect when collected up to 4 hr after dosing. The biological effects on the U937 cells of the two major metabolites of MC903 (MC 1046 and MC 1080) were investigated. The metabolites had effects that were more than 100 times weaker than those of the parent compound. The effect of MC903 on proliferative disorders, its fast elimination and the formation of inactive metabolites makes MC903 suitable for topical treatment of psoriasis.

Metabolism of a cyclopropane-ring-containing analog of 1 alpha-hydroxyvitamin D3 in a hepatocyte cell model. Identification of 24-oxidized metabolites

MC969 is an analog of the calcemic drug 1 alpha-hydroxyvitamin D3 (1 alpha-OH-D3) in which carbons 25,26, and 27 in the side chain are incorporated into a cyclopropane ring. Metabolites of MC 969 were generated in an in vitro human hepatocyte cell model, Hep 3B. The identity of the metabolites was established by comigration on HPLC with authentic standards, and by mass spectrometry of native and chemically modified metabolites. Unequivocal identification of the 24-keto- and the two epimeric 24-alcohol metabolites is provided. No 25-hydroxylated metabolites were detected. In competition studies, MC 969 was able to inhibit 25-hydroxylation of tritiated vitamin D3 more effectively than 1 alpha-OH-D3 itself, indicating that the vitamin D3-25-hydroxylase may be responsible for generation of one or more of the metabolites observed.