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.     

Effects of a novel vitamin D analogue MC903 on cell proliferation and differentiation in vitro and on calcium metabolism in vivo

MC 903 is a novel vitamin D analogue which has been tested for its effects on cell differentiation and cell proliferation in vitro using the human histiocytic lymphoma cell line U937, and on calcium metabolism in rats in vivo. In the present investigation MC 903 was compared to the natural metabolite of vitamin D3, 1 alpha,25-dihydroxycholecalciferol [1,25(OH)2D3] and to its synthetic analogue 1 alpha-hydroxycholecalciferol [1 alpha (OH)D3]. MC 903 was found to be a potent inducer of cell differentiation and to inhibit cell proliferation and DNA-synthesis in concentrations comparable to those observed with 1,25(OH)2D3. 1 alpha (OH)D3, which is only active after metabolic conversion to 1,25(OH)2D3, was more than 100 times less potent. Oral or intraperitoneal administration of MC 903 to rats showed that the compound was at least 100 times less active than 1,25(OH)2D3 and 1 alpha (OH)D3 in causing hypercalciuria, hypercalcemia and bone calcium mobilisation. The low vitamin D activity of MC 903 was further confirmed by administration of the compound to rachitic rats. The strong direct effects of MC 903 on cell proliferation and cell differentiation, coupled with its decreased activity as a classical vitamin D makes this compound an interesting candidate for studies in human proliferative disorders such as psoriasis.     

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.     

Calcipotriol: A New Drug for Topical Psoriasis Treatment

Abstract: Vitamin D is best known for its role in the regulation of calcium and bone metabolism. The effects of the biologically active form of vitamin D, 1,25-dihydroxyvitamin D₃ (1,25 (OH)₂D₃), are mediated by binding to a specific intracellular vitamin D receptor, which is present in most tissues including the skin where it regulates the growth of epidermal cells. Calcipotriol is a synthetic analogue of 1,25(OH)₂D₃. In vitro the activity of calcipotriol is comparable to that of 1,25(OH)₂D₃. In vivo, however, the risk of calcipotriol changing calcium metabolism is greatly reduced. Animal studies have established that calcipotriol is 100–200 times less calcaemic than 1,25 (OH)₂-D₃. This low calcaemic activity is mainly due to the rapid metabolism of calcipotriol. This pharmacological profile makes calcipotriol an ideal candidate for topical treatment of hyperproliferative skin disorders, such as psoriasis. This paper reviews the clinical experience with calcipotriol in psoriasis patients.     

Comparison of Calcipotriol with Selected Metabolites and Analogues of Vitamin D3: Effects on Cell Growth Regulation in Vitro and Calcium Metabolism in Vivo

Abstract: 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 1α,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 1α,25(OH)₂D₃, these included the two physiologically occurring metabolites 25(OH)D₃ and 24,25(OH)₂D₃, and the two synthetic analogues 1α(OH)D₃ and 1α,24(OH)₂D₃. 25(OH)D₃ and 24,25(OH)₂D₃ were shown to be inactive both in vitro and in vivo. 1α(OH)D₃ was found to have a low biological activity in vitro, but was highly calcaemic in vivo after biotransformation to 1α,25(OH)₂D₃. Calcipotriol, 1α,24(OH)₂D₃ and 1α,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.     

The role of monocytes and T cells in 1,25-dihydroxyvitamin D3 mediated inhibition of B cell function in vitro

1,25-Dihydroxyvitamin D3 (1,25-(OH)2D3) inhibits immunoglobulin production by human mononuclear cells (MNC) in vitro. The present study was undertaken to evaluate the role of T cells and monocytes in 1,25-(OH)2D3 induced suppression of B cell functions. The synthetic vitamin D3 analogue MC 903 was examined in parallel. 1,25-(OH)2D3 and MC 903 showed a dose-related inhibition of IgM, IgG and IgA plaque-forming cells in poke-weed mitogen (PWM) activated cultures of MNC. This effect was most likely mediated through impairment of T cell and monocyte functions. First, the inhibitory effect was seen after PWM stimulation, but not after Epstein-Barr virus stimulation which activates B cells independently of T cells and monocytes. Second, 1,25-(OH)2D3 was not effective in T cell and monocyte-depleted cultures. Third, the effect of 1,25-(OH)2D3 on PWM driven MNC was reversed by addition of the recombinant monokines: interleukin (IL)-1 beta, tumour necrosis factor alpha (rTNF alpha), rIL-6, as well as the lymphokines: lymphotoxin (rLT) and rIL-2. This is consistent with the finding that 1,25-(OH)2D3 also inhibited IL-1 alpha, TNF alpha and LT production in these cultures. The assumption that B cells are not directly affected by 1,25-(OH)2D3 was further supported by the fact that 24 h of culture with 10(-8) M 1,25-(OH)2D3 failed to reduce immunoglobulin production by in vivo activated B cells.     

Tissue distribution and activity studies of 1,24-dihydroxyvitamin D2, a metabolite of vitamin D2 with low calcemic activity in vivo

The active vitamin D compound 1alpha,24(S)-dihydroxyvitamin D(2) (1,24(OH)(2)D(2)) is under development as a therapy for disorders including cancer and secondary hyperparathyroidism. 1,24(OH)(2)D(2) is a potent inhibitor of cell proliferation in vitro and, relative to calcitriol (1,25(OH)(2)D(3)), has reduced calcemic activity in vivo. To examine the mechanisms underlying this reduced calcemic activity, we studied the tissue distribution in rats of radiolabeled 1,24(OH)(2)D(2) or 1,25(OH)(2)D(3) over 24h. Serum levels of 1,24(OH)(2)D(2) were lower than those of 1,25(OH)(2)D(3) at all time points; however, tissue levels of radiolabeled compounds followed different patterns. In duodenum and kidney, 1,24(OH)(2)D(2) and 1,25(OH)(2)D(3) rose to similar levels at early time points; 1,24(OH)(2)D(2) levels then declined more rapidly. In bone marrow, 1,24(OH)(2)D(2) and 1,25(OH)(2)D(3) were present at similar levels at all time points. In liver, 1,24(OH)(2)D(2) levels were two-fold higher than 1,25(OH)(2)D(3) at 1h post-injection, declining to similar levels by 8h. In vitamin D-deficient rats, doses of 1,24(OH)(2)D(2) 30-fold higher than 1,25(OH)(2)D(3) were required to produce equal stimulation of intestinal calcium absorption. In the same deficient animals, 1,24(OH)(2)D(2) and 1,25(OH)(2)D(3) were nearly equipotent at stimulating bone calcium mobilization. In cultured bone cells, 1,24(OH)(2)D(2) and 1,25(OH)(2)D(3) were equipotent at stimulating osteoclast formation and bone resorption. In summary, the reduced calcemic activity of 1,24(OH)(2)D(2) may result from altered pharmacokinetics relative to 1,25(OH)(2)D(3), resulting in relatively rapid decreases in 1,24(OH)(2)D(2) levels and activity in target organs such as intestine. Further studies will be necessary to confirm these findings and to confirm the clinical utility of 1,24(OH)(2)D(2).     

Antitumor effect of 22-oxa-1 alpha,25-dihydroxyvitamin D3, a potent angiogenesis inhibitor, on rat mammary tumors induced by 7,12-dimethylbenz[a]anthracene.

The effect of 22-oxa-1 alpha,25-dihydroxyvitamin D3 (22-oxa-1,25(OH)2D3) on the growth of autochthonous rat mammary tumors induced by 7,12-dimethylbenz[a]anthracene (DMBA) was examined on the basis of our previous finding that this synthetic vitamin D3 analog has a potent angiogenesis inhibitory effect. Two doses of 22-oxa-1,25(OH)2D3, 0.1 and 1 microgram/kg of body weight, due to the limited amount of the compound available, were used. The daily administration of 22-oxa-1,25(OH)2D3 at the dose of 1 microgram/kg/day resulted in significant inhibition of the growth of these mammary tumors at 1, 2 and 3 weeks after the administration of this agent, although the agent caused little or no regression of the tumors. After daily administration for 3 weeks, a significant antitumor effect was also observed in the group treated with 0.1 microgram/kg/day. Treatment with 22-oxa-1,25(OH)2D3 did not affect the serum calcium levels in the treated rats. The lower dose of 22-oxa-1,25(OH)2D3 neither affected weight gain nor caused a decrease in body weight, while the higher dose, although having some effect on weight gain, did not induce a decrease in body weight. There were no significant differences in the weights of adrenals, uteri and ovaries between the treated groups and controls. These results suggest that 22-oxa-1,25(OH)2D3 has a significant growth inhibitory effect on DMBA-induced autochthonous mammary tumors in rats, without producing severe side effects, including hypercalcemic activity.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of 1,25-dihydroxyvitamin D3 analogue 1,24(OH)2-22-ene-24-cyclopropyl D3 on proliferation and differentiation of a human megakaryoblastic leukemia cell line.

The novel analogue of 1,25-dihydroxyvitamin D3 (1,25(OH)2 D3), 1,24(OH)2-22-ene-24-cyclopropyl D3 (calcipotriol, MC903), exhibits similar effects on cell proliferation and cell differentiation in a newly established human megakaryoblastic leukemia cell line (HIMeg). MC903 was found to inhibit cell proliferation and induce cell differentiation in a liquid culture system at concentrations comparable to those of 1,25(OH)2 D3. Colony formation assay showed that MC903 or 1,25(OH)2 D3 markedly diminished the colony-forming ability of HIMeg cells at concentrations of 10(-6) M to 10(-10) M. Cell cycle analysis demonstrated that, as seen with 1,25(OH)2 D3, MC903 also altered the cell cycle distribution; the fraction of cells in G0 + G1 increased while those in S and G2 + M decreased. It can be concluded from these findings that 1,25(OH)2 D3 and its analogue MC903 have approximately equipotent effects on cells of megakaryoblastic lineage and are potentially useful in studying the cellular processes that are responsible for megakaryocytopoiesis.     

In vivo and in vitro pharmacokinetics and metabolism studies of 26,26,26,27,27,27-F6-1,25(OH)2 vitamin D3 (Falecalcitriol) in rat: induction of vitamin D3-24-hydroxylase (CYP24) responsible for 23S-hydroxylation in target tissues and the drop in serum levels.

1. 26,26,26,27,27,27-F6,-1,25(OH)2 vitamin D3, Falecalcitriol, the hexafluorinated analogue of 1,25(OH)2 vitamin D3, has been reported to be several times more potent than the parent compound regarding some vitamin D actions. The reason for enhanced biological activity appears related to F6-1,25(OH)2 vitamin D3 metabolism to F6-1,23S,25(OH)3 vitamin D3, a bioactive 23S-hydroxylated form which is resistant to further metabolism. 2. In the present in vivo studies, the repeated oral administration of [3H]F6-1,25(OH)2 vitamin D3 to rat resulted in a significant reduction of the radioactivity and the F6-1,25(OH)2 vitamin D3 concentrations in serum, especially at the 2 h maximum point after each dosing. Additionally, F6-1,23S,25(OH)3 vitamin D3 in the serum and small intestine was increased by the prior administration of F6-1,25(OH)2 vitamin D3. 3. Further in vitro investigation showed [3H]F6-1,25(OH)2 vitamin D3 to be metabolized to F6-1,23S,25(OH)3 vitamin D3 by kidney and small intestine homogenates of rat, the reaction being increased by the prior administration of F6-1,25(OH)2 vitamin D3. Moreover, this latter treatment was associated with a marked increase of CYP24 mRNA in the small intestine within 4 h after dosing. 4. The results indicate that in vivo metabolism of F6-1,25(OH)2 vitamin D3 to F6-1,23S,25(OH)3 vitamin D3 is catalysed by CYP24, the enzyme being induced by prior substrate exposure.     

Synthesis and Crystal Structure of Anhydrous Analog of 1,25-Dihydroxyvitamin D3

As predicted by single crystal X-ray crystallography, and contrary to the reported suggestions, the anhydrous form of calcipotriol, a therapeutically important vitamin D analog, was found stable enough to be used as an active pharmaceutical ingredient. The crystal and molecular structure of calcipotriol anhydrate was solved and refined using single crystal X-ray diffraction. The analog was obtained by a novel convergent synthesis from the vitamin D C-22 sulfone, as an advanced intermediate and a side-chain fragment. The homo-chiral side-chain aldehyde was obtained from cyclopropanecarboxyaldehyde by the chromatographic separation of the intermediate diastereomeric salts with (S)-naproxen. Calcipotriol anhydrate showed a single peak in differential scanning calorimetry and the absence of a peak from a water molecule, typical for the monohydrate. Calcipotriol anhydrate, as the only 1,25-dihydroxylated analog of vitamin D₃, exists as a mixture of both α- and β-forms of the A-ring, present in the asymmetric part of the unit cell of the crystal lattice. The intermolecular hydrogen bonding between both conformers in the crystal lattice indicated that the stability of calcipotriol anhydrate might be at least the same as for the known monohydrate. The usefulness of calcipotriol anhydrate as an active pharmaceutical ingredient was confirmed by the stability study in the standard conditions used for the storage of vitamin D analogs.     

Synthesis and biological activity of novel vitamin D analogues: 24,24-difluoro-25-hydroxy-26,27-dimethylvitamin D3 and 24,24-difluoro-1 alpha,25-dihydroxy-26,27-dimethylvitamin D3

We synthesized 24,24-difluoro-25-hydroxy-26,27-dimethylvitamin D3 (16), and 24,24-difluoro-1 alpha, 25-dihydroxy-26,27-dimethylvitamin D3 (21), from 3 beta-hydroxy-22,23-dinorcholenic acid 3-acetate. Compound 16 was found to be a highly potent vitamin D analogue with bioactivity similar to that of 25-hydroxyvitamin D3 in vivo. Compound 16 was bound by vitamin D binding protein with an affinity slightly less than that of 25-hydroxyvitamin D3. It was bound to the intestinal cytosol receptor for 1,25-dihydroxyvitamin D3 with approximately the same affinity as that of 25-hydroxyvitamin D3. In the organ-culture duodenum, 16 induced the synthesis of calcium binding protein with a potency approximately 1/20 that of 1,25-dihydroxyvitamin D3. Compound 21 was also noted to be a highly potent vitamin D analogue with bioactivity in vivo similar to that of 1,25-dihydroxyvitamin D3. It was bound to vitamin D binding protein with an affinity considerably less than that of 1,25-dihydroxyvitamin D3. It was bound to the intestinal cytosol receptor for 1,25-dihydroxyvitamin D3 with an affinity slightly less than that of the native hormone. In the organ-culture duodenum, 21 was noted to be about 3 times more active than 1,25-dihydroxyvitamin D3 in the induction of calcium binding protein. The introduction of fluorines at C-24 and extension of the sterol side chain at C-26 and C-27 by methylene groups results in vitamin D analogues that have biological activity in vivo similar to those of the respective nonfluorinated natural sterols.     

Calcipotriol. A review of its pharmacological properties and therapeutic use in psoriasis vulgaris.

Calcipotriol (calcipotriene) is a vitamin D3 analogue which inhibits epidermal cell proliferation and enhances cell differentiation. In patients with chronic plaque psoriasis involved in short term studies of 6 to 8 weeks' duration, calcipotriol ointment applied twice daily was significantly more effective than betamethasone valerate and dithranol (anthralin). Pooled data from clinical trials show that calcipotriol is well tolerated, with the majority of adverse events being mild and transient local reactions. Topically applied calcipotriol has low hypercalcaemic potential and, in contrast to topical corticosteroids, oral retinoids and orally administered calcitriol, methotrexate and cyclosporin, calcipotriol does not appear to be associated with a risk of serious adverse events. Thus, at this early stage in its clinical development, calcipotriol appears to be an effective and well tolerated topical therapy for the management of psoriasis; if promising preliminary clinical findings are confirmed, calcipotriol will represent a major advance in this difficult area of therapeutics.     

Paricalcitol capsules for the control of secondary hyperparathyroidism in chronic kidney disease

Secondary hyperparathyroidism is a common complication of patients with chronic kidney disease. Treatment with calcitriol, the active form of vitamin D, reduces parathyroid hormone levels, but may result in elevations in serum calcium and phosphorus. New vitamin D analogues have been developed to reduce parathyroid hormone secretion without concomitant hypercalcaemia and hyperphosphataemia. Recent data from studies with paricalcitol capsules, the oral formulation of 19-nor-1,25(OH)2D2, show a significant reduction in parathyroid hormone levels with no change in calcium and phosphorus levels when compared with placebo. Paricalcitol also compares favourably to other oral vitamin D analogues, effectively decreasing parathyroid secretion with less hypercalcaemia and hypercalciuria than other agents.     

Regulation of sodium, calcium and vitamin D metabolism in Dahl rats on a high-salt/low-potassium diet: genetic and neural influences

1. A dietary combination of high salt and low potassium (HSLK) exacerbates hypertension in Dahl salt-sensitive (DS) rats and renders previously normotensive Dahl salt-resistant (DR) rats hypertensive. In both strains, the severity of hypertension correlates with urinary calcium loss. However, the magnitude of excretory calcium losses is significantly greater in DS rats and is potentiated by chemical sympathectomy in both strains. 2. We hypothesized that a defect in vitamin D metabolism may underlie the observed strain-dependent differences in calcium balance. 3. Arterial blood pressure (ABP), water and mineral balance and serum concentrations of 1,25-dihydroxyvitamin D3 (1,25(OH)2 D3) and 25-hydroxyvitamin D3 (25(OH)D3) were measured in intact and chemically sympathectomized (6-hydroxydopamine; 6-OHDA) DS and DR rats after 8 weeks on a HSLK diet. 4. Chronic ingestion of this diet resulted in marked and moderate levels of hypertension in DS and DR rats, respectively. The hypertension was abated and eliminated by 6-OHDA in the DS and DR strains, respectively. Independent of treatment, DS rats had significantly higher urinary excretion of calcium and reduced intestinal absorption of the ion compared with DR rats. The DS rats had significantly higher serum levels of 1,25(OH)2 D3 and markedly lower serum levels of 25(OH)D3 than DR rats. Chemical sympathectomy tended to increase 1,25(OH)2 D3 and to decrease 25(OH)D3 levels in both strains. 5. These data indicate a genetic difference in vitamin D metabolism between DS and DR rats. The abnormally elevated levels of 1,25(OH)2 D3 in DS rats may be an appropriate compensatory response to excessive excretory calcium loss and reduced target organ sensitivity to the hormone and may, maladaptively, directly contribute to hypertension, by stimulating vascular smooth muscle contractility.     

Treatment with vitamin 24,25 (OH)2D3 does not change serum levels of 1,25 (OH)2D or urinary calcium excretion rate in man

40 healthy early postmenopausal women participated in a controlled therapeutic trial with the aim of examining whether treatment with 24,25 vitamin D3 changed the serum concentration of either 1,25 (OH)2D and/or the 24-hour urinary calcium excretion rate. The 40 women were randomized to treatment with either 24R,25 (OH)2D3 (10 micrograms daily) or placebo. Serum concentrations of calcium, 25 (OH) D, 1,25 (OH)2D, 24,25 (OH)2D3 and 24-hour urinary calcium excretion rate were measured before (t0) and after (t1) 6 months of treatment. In the 24,25 (OH)2D3 treated group there was a highly significant increase in the mean serum 24,25 (OH)2D3 concentration, whereas serum 25 (OH) D and 1,25 (OH)2D and serum and urinary calcium were unchanged during the trial. In the placebo group all values were similar before and after the trial. We conclude that treatment with 24,25 (OH)2D3 is not an alternative to conventional treatment of renal hypercalciuria.     

Toxicity of Vitamin D Analogues in Rats Fed Diets with Standard or Low Calcium Contents

Abstract: 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 1α-hydroxycholecalciferon [lα(OH)D₃], a synthetic analogue of the physiologically active form of vitamin D₃, lα,25-dihydroxycholecalciferol [1α,25(OH)₂D₃], at dose levels of 0.2 and 2.0 μg/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 1α(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.     

Vitamin D and the digestive system

Target tissues of in vivo receptor binding and deposition of 1,25(OH)2 vitamin D3 and its oxygen analog OCT are reviewed in rats, mice, hamsters and zebra finch, identified with high-resolution microscopic autoradiography. Throughout the digestive system numerous sites with nuclear receptor binding of 3H-1,25(OH)2 vitamin D3 and 3H-OCT exist: in the oral region, epithelial cells of the oral cavity, tongue and gingiva, teeth odontoblast and ameloblast precursor pulp and stratum intermedium cells; in the parotid, submandibular and sublingual salivary glands, epithelial cells of striated ducts and granular convoluted tubules, intercalated ducts and acinar cells, as well as myoepithelial cells; in the stomach, neck mucous cells of gastric glands, endocrine cells of the antrum, and muscle cells of the pyloric sphincter; in the small and large intestine, absorptive and crypt epithelial cells; in the pancreas, predominantly islet B-cells. Perisinusoidal stellate (Ito) cells in the liver concentrate and retain variable amounts of radiolabeled compound in regions of their cytoplasm after administration of 3H-I,25(OH)2 vitamin D3 and 3H-25(OH) vitamin D3, probably sites of specific storage, similar to vitamin A. Submucosa in stomach and intestine also retain variable amounts of radiolabel, however unspecific with all compounds studied. In pilot studies with 3H-25(OH)2 vitamin D3 and 3H-24,25(OH)2 vitamin D3, no nuclear concentration was detectable. The reviewed data for vitamin D and its oxygen analogue OCT indicate genomic effects on multiple target tissues of the digestive system that involve cell proliferation and differentiation, endo- and exocrine secretion, digestion and absorption for maintaining optimal functions, with potentials for health prophylaxis and therapies.