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

The epidermis of chronic idiopathic lichen planus during topical treatment with the vitamin D3 analogue KH 1060

A parallel-group, double-blind, randomised study was performed to establish the effect of the vitamin D3 analogue KH 1060, in an ointment versus vehicle only, on the epidermal cell characteristics of chronic idiopathic lichen planus; KH 1060 also has marked immunosuppressive activity. A group of 10 patients were treated for 8 weeks with either KH 1060 ointment or vehicle only. In addition to the assessment of clinical scores, keratotome biopsies were taken before and after 8 weeks' treatment. Epidermal cell suspensions were prepared with trypsin and the suspensions incubated with TO-PRO-3 (DNA marker), RKSE 60 (marker for keratin 10-positive cells) and antivimentin (marker for all non-keratinocytes). In nine of the 10 patients, keratotome biopsies were obtained both before and after 8 weeks treatment. The vehicle alone had no significant effect on the clinical severity scores or epidermal cell characteristics. In contrast, the KH 1060 ointment resulted in a statistically significant reduction in the percentage of cells in S- and G2M phase and the percentage of vimentin-positive cells, but it did not affect the percentage of keratin 10-positive cells.

The vitamin D analog, KH1060, is rapidly degraded both in vivo and in vitro via several pathways: principal metabolites generated retain significant biological activity

Vitamin D analogs are valuable drugs with established and potential uses in hyperproliferative disorders. Lexacalcitol (KH1060) is over 100 times more active than 1alpha,25-dihydroxyvitamin D3 [1alpha,25-(OH)2D3], as judged by in vitro antiproliferative and cell differentiating assays. The underlying biochemical reasons for the increased biological activity of KH1060 are unknown, but are thought to include 1) metabolic considerations in addition to explanations based upon 2) enhanced stability of KH1060-liganded transcriptional complexes. In this study we explored the in vivo and in vitro metabolism of KH1060. We established by physicochemical techniques the existence of multiple side-chain hydroxylated metabolites of KH1060, including 24-, 24a-, 26-, and 26a-hydroxylated derivatives as well as side-chain truncated forms. KH1060 metabolism could be blocked by the cytochrome P450 inhibitor, ketoconazole. KH1060 was not an effective competitor of C24 oxidation of 1alpha,25-(OH)2D3. Certain hydroxylated metabolites of KH1060 retained significant biological activity in vitamin D-dependent reporter gene systems (chloramphenicol acetyltransferase). Likewise, those metabolites accumulating in the target cell culture models in metabolism studies, particularly 24a-hydroxy-KH1060 and 26-hydroxy-KH1060, retained biological activities superior to those of 1alpha,25-(OH)2D3 in native gene expression systems in vitamin D target cells (osteopontin and P450cc24). We conclude that KH1060 is rapidly metabolized by a variety of cytochrome P450-mediated enzyme systems to products, many of which retain significant biological activity in vitamin D-dependent assay systems. These results provide an explanation for the considerable biological activity advantage displayed by KH1060 compared with 1alpha,25-(OH)2D3 in various in vitro assay systems.

The role of vitamin D derivatives and retinoids in the differentiation of human leukaemia cells

The capabilities of 1alpha, 25-dihydroxyvitamin D3 (1,25(OH)2D3), and two novel vitamin D analogues, EB1089 and KH1060, to induce the differentiation of two established leukaemia cell lines, U937 and HL-60, were assessed alone or in combination with the retinoid compounds, 9-cis retinoic acid (9-cis RA) and all-trans retinoic acid (ATRA). The vitamin D derivatives acted to increase the differentiation of U937 and HL-60 cell cultures in a dose-dependent manner, as determined by nitroblue tetrazolium (NBT) reduction, with EB1089 and KH1060 being more effective than the native hormone. As an additional index of leukaemic cell differentiation, induction of expression of the phenotypic cell surface antigen, CD14, and the beta2-integrins, CD11b and CD18 by the vitamin D and retinoid compounds were monitored using fluorescence activated cell sorting (FACS) analyses. Following 96-hr treatment of U937 and HL-60 cells with 5 x 10(-10) M of the vitamin D derivatives, a striking increase in CD14 antigen expression was apparent, indicating the promotion by these compounds of a monocyte/macrophage lineage of cells. CD11b and CD18 antigen expression were also raised above control levels. In contrast, both retinoid compounds used at the higher concentration of 1 x 10(-8) M were not effective inducers of CD14 antigen expression. However, CD11b and CD18 were both readily increased in U937 and HL-60 cell cultures. Treatment of U937 cell cultures with the vitamin D compounds and the retinoids resulted in cooperative effects on induction of differentiation, with correlation by both NBT reduction and FACS analyses of CD14 antigen expression. The presence of 9-cis RA or ATRA appeared to contribute to the further increase of CD14 in these cells. HL-60 cell cotreatment with these compounds also displayed enhanced cooperative effects in phagocytic function by NBT reduction. However, analysis of CD14 revealed a dramatic diminution in HL-60 cells treated with the combinations of the vitamin D derivatives and the retinoids. Assessment of HL-60 cell morphology treated with these combinations demonstrated the presence of a mixed population of monocytes and granulocytes. CD11b and CD18 antigen expression was also enhanced in both cell lines with cotreatment. The ability of EB1089 and KH1060 to induce leukaemic cell differentiation may provide an additional option for therapeutic use alone or together with other differentiation agents such as 9-cis RA or ATRA.

Synergistic induction of HL60 cell differentiation by ketoconazole and 1-desoxy analogues of vitamin D3

BACKGROUND

The goal of differentiation therapy is to induce cancer cells to stop proliferating and to express characteristics of normal cells. Vitamin D analogues, such as the deltanoids, are being evaluated as differentiation agents in the treatment of several human cancers (e.g., myeloid leukemias); however, these compounds have a tendency to produce hypercalcemia in patients receiving therapy. A combination of a differentiation-inducing deltanoid with a compound that blocks entry of calcium into cells (e.g., ketoconazole) may offer a new approach to differentiation therapy and address the problem of hypercalcemia. We investigated whether various ketoconazole-deltanoid combinations would alter cellular differentiation or intracellular calcium homeostasis in comparison with deltanoids used alone.

METHODS

Cultured human leukemia HL60 cells were treated with ketoconazole-deltanoid combinations. Markers of differentiation (expression of CD11b and CD14 antigens and of non-specific esterase) were measured by flow cytometry and cytochemistry; cell cycle distribution was measured by flow cytometry of propidium iodide-stained cells. Expression of differentiation-related genes was assessed by northern blotting and immunoblotting, and changes in intracellular calcium homeostasis were monitored by fluorescence analysis of fura-2-containing cells.

RESULTS

Ketoconazole strongly potentiated the differentiating activity of the deltanoids, which exhibited low potency when used alone. Ketoconazole-deltanoid combinations had little effect on HL60 cell-cycle distribution, although the cells did stop proliferating and they differentiated. Ketoconazole-deltanoid combinations produced only minor changes in intracellular calcium homeostasis compared with changes produced by 1,25-dihydroxyvitamin D3, either alone or in combination with ketoconazole.

CONCLUSION

These results suggest that ketoconazole may be useful in combination with vitamin D analogues in the differentiation therapy for myeloid leukemias.

Conformational studies of human vitamin-D receptor by antipeptide antibodies, partial proteolytic digestion and ligand binding

We have studied conformational changes of human vitamin-D receptor by using antipeptide antibodies, partial proteolytic digestion and binding of the natural ligand calcitriol or its synthetic analogs. Before exposing either [35S]methionine-labelled in vitro translated human vitamin-D receptor or a recombinant human vitamin-D receptor produced either in Escherichia coli or in Sf9 insect cells to limited proteolysis by trypsin or chymotrypsin, the proteins were treated with calcitriol or its synthetic analogs. The digestion products were analyzed by SDS/PAGE, immunoblotting with polyclonal antipeptide antibodies targeted against different domains of the receptor, and Edman N-terminal sequencing. After limited proteolysis with trypsin, two fragments of Mr 21,000 and Mr 34,000 could be localized into N-terminus and C-terminus of the receptor, respectively, by antipeptide antibodies. We found that treatment with calcitriol or its synthetic analogs leads to differential resistance of the ligand-binding domain of the recombinant receptor to partial proteolysis in vitro. We suggest that this is due to distinct conformational changes in the domain induced by the different ligands. The short N-terminal region and the Zn-finger domain form, however, a protease-resistant structure which is independent on the presence or absence of the ligand. When the C-terminal fragment of Mr 34,000 was further analyzed by Edman N-terminal sequencing, the major cleavage site in the receptor between amino acids Arg173 and His174 was revealed.

A new analog of 1,25-(OH)2D3, 19-NOR-1,25-(OH)2D2, suppresses serum PTH and parathyroid gland growth in uremic rats without elevation of intestinal vitamin D receptor content

We have previously reported that 19-nor-1,25-(OH)2D2, a new analog of 1,25-(OH)2D3, suppresses parathyroid hormone (PTH) secretion in uremic rats in the absence of hypercalcemia or hyperphosphatemia. In the current study, we examined the effect of 19-nor-1,25-(OH)2D2 on parathyroid gland growth and intestinal vitamin D receptor (VDR) content. After induction of uremia by 5/6 nephrectomy, rats were divided into five experimental groups and received intraperitoneal injections of vehicle, 1,25-(OH)2D3 (2 or 6 ng/rat), or 19-nor-1,25-(OH)2D2 (25 or 100 ng/rat) three times a week for 8 weeks. Twelve normal rats received vehicle and served as the normal control group. During the course of the study, rats were maintained on a 1.0% calcium and 0.8% phosphorus diet. The higher dose of 1,25-(OH)2D3, 6 ng, significantly decreased PTH from 52.7 +/- 10.2 pg/mL in the uremic control group to 25.7 +/- 6.7 pg/mL (P < 0.01). This dose of 1,25-(OH)2D3, however, increased serum levels of both ionized calcium (4.71 +/- 0.05 to 4.85 +/- 0.06 mg/dL; P < 0.05) and phosphorus (4.34 +/- 0.30 to 6.67 +/- 0.63 mg/dL; P < 0.01). Both doses of 19-nor-1,25-(OH)2D2 decreased serum PTH as effectively as 1,25-(OH)2D3 without changes in serum calcium or phosphorus. The 100-ng dose of 19-nor-1,25-(OH)2D2 decreased PTH to 20.7 +/- 3.1 pg/mL (P < 0.01) and suppressed parathyroid gland growth by more than 50%. Both doses of 19-nor-1,25-(OH)2D2 also decreased endogenous 1,25-(OH)2D3 levels compared with uremic control rats (25 ng:30.4 +/- 2.0, P < 0.05, and 100 ng:27.9 +/- 3.2, P < 0.01, v 48.4 +/- 6.6 pg/mL). The 6-ng dose of 1,25-(OH)2D3 elevated intestinal VDR content (138.5 +/- 20.0 fmol/mg protein) compared with animals receiving both doses of 19-nor-1,25-(OH)2D2 (25 ng:84.0 +/- 11.9, P < 0.05, and 100 ng:78.4 +/- 10.9, P < 0.01). This was probably attributable to the marked decrease in endogenous 1,25-(OH)2D3 levels caused by both doses of 19-nor-1,25-(OH)2D2 because intestinal VDR correlated directly with serum 1,25-(OH)2D3 (r = 0.963; P = 0.008). Thus, 19-nor-1,25-(OH)2D2 appears to exert a selective action on the parathyroid glands compared with the intestine. Its low calcemic and phosphatemic properties may result from the decreased endogenous 1,25-(OH)2D3 levels that lead to a reduction in intestinal VDR. This selectivity makes this analog ideal for the treatment of secondary hyperparathyroidism.

Effects of calcitriol and its analogues, calcipotriol (MC 903) and 20-epi-1alpha,25-dihydroxyvitamin D3 (MC 1288), on calcium influx and DNA synthesis in cultured muscle cells

The fast actions of the secosteroid hormone 1alpha,25-dihydroxyvitamin D3 [1,25(OH)2D3; calcitriol] and the synthetic analogues calcipotriol (MC 903) and 20-epi-1alpha,25(OH)2D3 (MC 1288) on cell calcium influx were compared in rat duodenum enterocytes as well as in cells from chick embryo skeletal muscle (myoblasts) and heart (myocytes), at various concentrations (10(-12) to 10(-8) M) and treatment intervals (1-10 min). In enterocytes, at a concentration of 10(-11) M, MC 1288 was significantly more active than 1,25(OH)2D3 in rapidly stimulating 45Ca2+ uptake by enterocytes (80 vs 38% above controls, respectively), whereas MC 903 was devoid of activity. However, calcipotriol increased Ca2+ influx in myocytes and myoblasts to a greater extent than the natural hormone, whereas MC 1288 was more active only in myoblasts. Analogously to 1,25(OH)2D3, the fast MC 903- and MC 1288-induced stimulation of 45Ca2+ uptake in enterocytes and muscle cells could be blocked by both verapamil and nifedipine. In addition, MC 903 and MC 1288 were more effective than 1,25(OH)2D3 in stimulating DNA synthesis in proliferating myoblasts and in inhibiting DNA synthesis in differentiating myoblasts. The results suggest, therefore, that modifications in the side-chain of the 1,25(OH)2D3 molecule increase its ability to modulate muscle cell Ca2+ metabolism and growth. These findings are potentially relevant for the development of analogues for the treatment of vitamin D-dependent myopathies.

Effects of potent vitamin D3 analogs on clonal proliferation of human prostate cancer cell lines

BACKGROUND

Management of prostate cancer that has spread outside of the prostate capsule is a difficult problem. Innovative, non-toxic approaches to the disease are required. New, relatively non-toxic vitamin D3 analogs have recently been synthesized. We report that several of these compounds have marked antiproliferative effects on prostate cells.

METHODS

The clonal antiproliferative activity of five novel analogs of 1,25 dihydroxyvitamin D3 [1,25(OH)2D3, (cmpd C)] as well as 1,25(OH)2D3 itself was tested on three human prostate cancer cell lines (PC-3, LNCaP, and DU-145). The analogs were 20-epi-22oxa-24a,26a,27a-tri-homo-1 alpha,25(OH)2D3 (code name: KH 1060); 24a26a27a-tri-homo-22,24-diene-1 alpha,25(OH)2D3 (code name: EB 1089); 1,25(OH)2-16ene-D3 (code name: HM); 1,25(OH)2-16ene-23yne-D3 (code name: V); 1,25(OH)2-20-epi-D3 (code name: MC 1288)].

RESULTS

With the parent compound [1,25(OH)2D3], the effective dose that inhibited 50% clonogenic growth of PC-3 and LNCaP was 10(-8)M and 7 x 10(-9)M, respectively. For these prostate cancer cell lines, KH 1060 was the most potent analog by an order of 25- to 35-fold as compared to cmpd C. The second and third most potent analogs were HM and MC 1288. DU-145 was resistant to all the vitamin D3 analogs. The major side-effect of 1,25(OH)2D3 is the production of hypercalcemia. The relative inhibitory index (RII) was determined by comparing the antiproliferative activity of the analog to its ability to produce hypercalcemia in mice injected intraperitoneally every other day. The KH 1060 had the best RTI: 50- to 70-fold greater than 1,25(OH)2D3 for PC-3 and LNCaP, respectively.

CONCLUSIONS

A trial of one or more of these innovative compounds should be considered for treatment of minimal residual disease of prostate cancer.

A vitamin D analog, MC1288, inhibits adventitial inflammation and suppresses intimal lesions in rat aortic allografts

Certain analogs of vitamin D have been shown to prevent autoimmune diseases and prolong cardiac allograft survival. We transplanted aortic allografts from DA rats to WF rats to investigate the effect of a synthetic vitamin D analog, MC1288, and cyclosporine (CsA), alone or in combination, on acute and chronic rejection (allograft arteriosclerosis) and the mechanism of action of MC1288. The histological changes in the vascular wall were quantitated as point score units (psu). Adventitial inflammation linked with acute rejection at 1 month after transplantation decreased from 10.0+/-0.9 psu to 4.1+/-1.0 psu (P<0.01) when MC1288, 0.1 microg/kg/every other day, and CsA, 5 mg/kg/day, were combined. Intimal thickening decreased from 2.5+/-0.3 psu to 1.1+/-0.4 psu (P<0.05) at 3 months after transplantation. Proliferation of the adventitial lymphoid cells, detected by bromodeoxyuridine labeling, decreased from 140+/-36 to 20+/-19 labeled cells/cross-section. MC1288 alone suppressed interleukin 2 receptor-expressing cells from 156 to 90 positive cells/cross-section. Taken together, MC1288 with CsA effectively suppress T cell proliferation and activation and decrease intimal thickening.

Transitional cell carcinoma express vitamin D receptors

Recently, vitamin D analogues have shown antineoplastic effect in several diseases. Vitamin D analogues exert its effect by interacting with the vitamin D receptor (VDR). Studies of VDR in transitional cell carcinoma (TCC) have not been reported. The purpose of the present study was therefore to examine whether human bladder tumor cells express VDR. Tumor biopsies were obtained from 26 patients with TCC. Expression of VDR was examined by immunohistochemical experiments. All tumors expressed VDR. Biopsies from advanced disease contained more VDR positive cells than low stage disease (p < 0.05). Similarly, also tumor grade appeared to be related to the number of cells expressing the receptor. Normal urothlium also expressed VDR but only with low intensity. Our study shows that TCC cells possess the VDR receptor which may make them capable to respond to stimulation with vitamin D, but functional studies of vitamin D's effect on TCC cells in vitro are necessary before the efficacy of treatment with vitamin D analogues in TCC can be evaluated in patients.

The noncalcemic vitamin D analogues EB1089 and 22-oxacalcitriol interact with the vitamin D receptor and suppress parathyroid hormone-related peptide gene expression

Humoral hypercalcemia of malignancy, a frequent complication of squamous cell carcinomas of the lung, is mediated by the parathyroid hormone-related peptide (PTHrP). This study was undertaken to determine whether 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] and two nonhypercalcemic analogues. EB1089 and 22-oxa-1,25(OH)(2)D(3) (OCT), suppress PTHrP gene expression in a human lung squamous cancer cell line, NCI H520. All three compounds (1) decreased steady-state PTHrP mRNA and secreted peptide levels via a transcriptional mechanism; (2) modulated promoter activity of 1,25(OH)(2)D(3)-responsive DNA sequences; and (3) activated the vitamin D receptor (VDR) both in vitro and in vivo. Thus, EB1089 and OCT inhibit PTHrP gene expression in NCI H520 cells and modulate gene expression through the same mechanism as 1,25(OH)(2)D(3), namely, activation of the VDR. 1,25(OH)(2)D(3) is hypercalcemic in vivo. However, the noncalcemic analogues EB1089 and OCT have a therapeutic potential through suppression of PTHrP gene transcription.

Effects of 1,25-dihydroxyvitamin D3 and its 20-epi analogues (MC 1288, MC 1301, KH 1060), on clonal keratinocyte growth: evidence for differentiation of keratinocyte stem cells and analysis of the modulatory effects of cytokines

1. Keratinocytes are functionally divided into stem cells, transit amplifying cells and terminally differentiated cells. In a hyperproliferative skin disease, psoriasis, increased mitotic activity of the stem cells is chiefly responsible for epidermal hyperplasia. The effects of 1,25dihydroxyvitamin D3 (1,25(OH)2D3) and potent vitamin D3 analogues (MC 1288: 20-epi-1,25(OH)2D3, MC 1301: 20-epi-24a-homo-26,27-dimethyl-1,25(OH)2D3, KH 1060: 20-epi-22-oxa-24a-homo-26,27-dimethyl-1,25(OH)2D3) on the stem cells were investigated. 2. Stem cells were identified retrospectively as those giving rise to large keratinocyte colonies in culture (holoclones). 1,25(OH)2D3 (10(-8)-10(-6) M) suppressed formation of holoclones by stimulating the progenitor cell differentiation into the phenotype expressing differentiation markers (keratins K1/K10 and involucrin). 3. 20-Epi vitamin D3 analogues were more potent than 1,25(OH)2D3 in inhibiting the clonal keratinocyte growth. This activity correlated with the ability to induce cell differentiation (KH 1060 > MC 1301 > MC 1288 > 1,25(OH)2D3). 4. Cytokines modulated the effects of 1,25(OH)2D3 on clonal growth. One of the following cytokines (epidermal growth factor, transforming growth factor alpha, interleukin-1 alpha, interleukin-1 beta, interleukin-6, interleukin-8) was required for 1,25(OH)2D3 to suppress clonal growth and induce cell differentiation. In contrast, keratinocyte growth factor and insulin-like growth factor I attenuated the effects of 1,25(OH)2D3. 5. In conclusion, 1,25(OH)2D3 and 20-epi vitamin D3 analogues suppress clonal growth by directly inducing the differentiation of progenitor cells. It is conceivable that stimulation of stem cells differentiation is a major mechanism of action of vitamin D3 compounds in psoriasis. Balance between different types of cytokines in psoriatic epidermis may be an important factor determining the clinical effect of vitamin D-based therapy.

Differential interaction of 1alpha,25-dihydroxyvitamin D3 analogues and their 20-epi homologues with the vitamin D receptor

An important focus of structure-function studies of synthetic ligands for the vitamin D receptor (VDR) concerns the chiral center at carbon 20 of the steroid side chain; 20-epi analogues are 100-10, 000 times more potent transcriptionally than the natural hormone 1alpha,25-dihydroxyvitamin D3 (1alpha,25-(OH)2D3). We have compared the binding properties of three pairs of analogues either with a natural (N) or 20-epi (E) orientation. In intact cells, 45-60% of VDR.N-analogue complexes, but only 5-20% of VDR.E-analogue complexes, dissociated over a 3-h interval. The two groups of ligands induced distinct changes in VDR conformation as revealed by protease clipping assays. Mapping of ligand-VDR binding activity by deletions indicated that amino acids 420-427 were important for high affinity of VDR.N-analogue complexes, but not for VDR.E-analogue complexes. Site-directed mutagenesis revealed that residues 421 and 422 were essential for 1alpha,25-(OH)2D3-induced conformational changes, high affinity of 1alpha,25-(OH)2D3 for VDR, and transcriptional activity, but not for binding of its 20-epi analogue. In contrast, deletion of residues 396-427 abolished binding of 1alpha,25-(OH)2D3, but binding of its 20-epi analogue was still detectable. The results suggest that the ligand-binding domain of VDR has multiple and different contact sites for the two families of side chain-modified ligands, resulting in VDR.ligand complexes with different half-lives and transcriptional activities.

Synergistic decrease of clonal proliferation, induction of differentiation, and apoptosis of acute promyelocytic leukemia cells after combined treatment with novel 20-epi vitamin D3 analogs and 9-cis retinoic acid

Patients with acute promyelocytic leukemia (APL) usually relapse after all-trans retinoic acid (RA) treatment because this therapy fails to eradicate the malignant clone. Our data showed that KH 1060 and other 20-epi vitamin D3 analogs alone were potent inhibitors of clonal growth of NB4 cells, an APL cell line (ED50, approximately 5 x 10(-11) M). The combination of KH 1060 and 9-cis-RA synergistically and irreversibly enhanced this effect. Neither KH 1060 nor 9-cis-RA (10(-6) M, 3 d) were strong inducers of differentiation of NB4 cells. However, 98% of the cells underwent differentiation to a mature phenotype with features of both granulocytes and monocytes after exposure to a combination of both compounds. Apoptosis only increased after incubation of NB4 cells with 9-cis-RA alone (28%) or with a combination of 9-cis-RA plus KH1060 (32%). Immunohistochemistry showed that the bcl-2 protein decreased from nearly 100% of the wild-type NB4 cells to 2% after incubation with a combination of KH 1060 and 9-cis-RA, and the bax protein increased from 50% of wild-type NB4 cells to 92% after culture with both analogs (5 x 10(-7) M, 3 d). Western blot analysis paralleled these results. Studies of APL cells from one untreated individual paralleled our results with NB4 cells. Taken together, the data demonstrated that nearly all of the NB4 cells can be irreversibly induced to differentiate terminally when exposed to the combination of KH 1060 and 9-cis-RA.

Proliferation and differentiation of cultured human keratinocytes is modulated by 1,25(OH)2D3 and synthetic vitamin D3 analogues in a cell density-, calcium- and serum-dependent manner

The natural form of vitamin D3, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) decreases proliferation and promotes terminal differentiation of cultured human epidermal keratinocytes. The purpose of this study was to find out to what extent the culture conditions determine the sensitivity of keratinocytes to 1,25(OH)2D3 and synthetic vitamin D analogues. Human keratinocytes were grown in microplates. Cell proliferation (MTT-assay) and differentiation (quantity of transglutaminase type I) were measured consecutively in the same monolayer. When vitamin D3 analogues were added to 50-60% confluent keratinocytes grown in serum-free keratinocyte growth medium with 0.09 mM Ca2+, stimulation of the proliferation was either minimal or non-existent, while differentiation was unaffected or slightly inhibited. There was no difference in the sensitivity to 1,25(OH)2D3 and the vitamin D3 analogues. When 1,25(OH)2D3 was added to less confluent keratinocytes (30%) a marked antiproliferative effect was observed. Addition of 3% charcoal stripped foetal calf serum further enhanced the antiproliferative effect of 1,25(OH)2D3, and a difference in the sensitivity of the vitamin D3 analogues was noted. If, finally, the Ca2+ concentration was raised to 0.3 mM, 1,25(OH)2D3 and the vitamin D3 analogues stimulated differentiation. Also, a biphasic effect on proliferation occurred: stimulation at low vitamin D concentrations and inhibition at higher concentrations. Furthermore, keratinocytes became more sensitive to the synthetic vitamin D3 analogues than to 1,25(OH)2D3: KH1060 > EB1089 > GS1500 > or = EB1213 > calcipotriol > 1,25(OH)2D3. For all compounds tested differentiation occurred at concentrations 10 to 30 times lower than for proliferation. These results indicate that the sensitivity to vitamin D3 analogues as well as the direction of the response to vitamin D3 analogues is dependent on the keratinocyte density, the availability of serum and Ca2+ concentrations.

Comparative effects of 1,25(OH)2D3 and EB1089 on cell cycle kinetics and apoptosis in MCF-7 breast cancer cells

1,25-dihydroxyvitamin D3 [1,25(OH)2D3], the active metabolite of vitamin D2 inhibits breast cancer cell growth both in vivo and in vitro. In addition to its anti-proliferative effects, 1,25(OH)2D3 induces morphological and biochemical markers of apoptosis in MCF-7 cells. In the studies reported here, we compared the effects of 1,25(OH)2D3 and EB1089, a low calcemic vitamin D analog, on cell cycle kinetics and apoptosis in MCF-7 cells. Both vitamin D compounds reduced viable MCF-7 cell number in a time and dose dependent manner, with EB1089 approximately 50 fold more potent than 1,25(OH)2D3. Flow cytometric analysis indicated that both agents induced cell cycle arrest in G, G1 which was associated with accumulation of the hypophosphorylated form of the retinoblastoma (Rb) protein. MCF-7 cells treated with either 1,25(OH)2D3 or EB1089 for 48 h exhibited characteristics of apoptosis, including cytoplasmic condensation, pyknotic nuclei, condensed chromatin and DNA fragmentation. Cells treated with either agent exhibited up regulation of proteins associated with mammary gland regression (clusterin and cathepsin B) and down regulation of the anti-apoptotic protein bcl-2. These studies demonstrate that, despite its lower calcemic activity in vivo, the vitamin D analog EB1089 induces effects that are indistinguishable from those of 1,25(OH)2D3 on cell number, cell cycle and indices of apoptosis in MCF-7 cells in vitro. In addition, since both agents rapidly down regulate estrogen receptor, disruption of estrogen dependent signalling may play a role in the induction of apoptosis by vitamin D compounds in MCF-7 cells.

A 20-epi side chain restores growth-regulatory and transcriptional activities of an A ring-modified hybrid analog of 1 alpha, 25-dihydroxyvitamin D3 without increasing its affinity to the vitamin D receptor

1 alpha-hydroxymethyl-25-hydroxyvitamin D3 and 1 beta-hydroxymethyl -3 alpha,25-hydroxyvitamin D3, two analogs with modifications restricted to the A ring, bind poorly to vitamin D receptor (VDR). The effective doses required for 50% of maximal binding activity (ED50) are 7 x 10(-7) M for the former and 8 x 10(-8) M for the latter, and the ED50 for their growth-inhibitory activities is greater than 10(-6) M. Unexpectedly, a hybrid analog with 20-epi configuration at its side chain and a 1 beta-hydroxymethyl group but not a 1 alpha-hydroxymethyl group inhibits malignant cell growth with an ED50 of 7 x 10(-9) M. To determine if the restored biological activity of the hybrid analog is associated with better binding to VDR, we performed competitive binding assays in vitro with calf thymus VDR and in vivo with recombinant human VDR. We found that the 20 epi side chain reduced the affinity of the 1 beta- and the 1 alpha-hydroxymethyl hybrid analogs for VDR in vitro and in vivo fourfold to tenfold. To determine whether the 1 beta-hydroxymethyl analogs induced a VDR-mediated transcription, we tested the induction of reporter gene expression through the osteocalcin vitamin D response element (VDRE) in ROS 17/2.8 cells and the induction of binding activity of VDR to VDRE in COS-1 cells. We found that the ED50 for transcriptional activity of 1 beta-hydroxymethyl-3 alpha,25-hydroxyvitamin D3 was greater than 10(-6) M, but its 1 alpha diastereomer had barely detectable transcriptional activity. The 20-epi side chain preferentially increased the transcriptional activity of the 1 beta-hydroxymethyl hybrid analog to an ED50 of 10(-8) M, but the 1 alpha-hydroxymethyl hybrid analog remained inactive. To confirm that this transcriptional activity was dependent on the VDR, we repeated the assay in VDR-negative CV-1 cells and compared ligand-dependent expression of the VDRE/growth hormone reporter in the presence of either wild-type or transcriptionally inactive mutant VDR expression vectors. Transcription was induced by the 1 beta-hydroxymethyl compounds only in the presence of wild-type VDR. Thus, we conclude that it is possible, by adding a 20 epi side chain, to restore growth-inhibitory and VDR-mediated transcriptional activities without increasing binding to the VDR of A ring-modified analogs.

Potent gene regulatory and antiproliferative activities of 20-methyl analogues of 1,25 dihydroxyvitamin D3

The biological active form of vitamin D3, 1,25-dihydroxyvitamin D3 (VD), regulates cellular growth and differentiation. This provides the hormone with an interesting therapeutic potential. However, hypercalcemia is a side effect, which is caused by VD's classical action, the regulation of calcium homeostasis. This made the need for VD analogues with selectively increased cell regulatory properties. Studies with 20-epi analogues pointed out the importance of the carbon-20 position and led to the development of 20-methyl derivatives of VD. In this report the biological properties of the compounds ZK161422 and ZK157202, which are 20-methyl- and 20-methyl-23-eneanalogues, respectively, have been analyzed in comparison with VD. Both compounds show about 2-fold lower affinity to the VD receptor (VDR) than VD. However, compared to VD, their antiproliferative effect is up to 30-fold higher on human peripheral blood mononuclear cells and even up to 300-fold higher on human breast cancer MCF-7 cells. Whereas the hypercalcemic effect for ZK157202 is also increased 10-fold, ZK161422 has the same calcium-mobilizing potency as VD. Moreover, ZK161422, but not ZK157202, showed preference for gene activation from a promoter carrying a VD response element with a palindromic arrangement of two hexameric receptor binding sites spaced by 9 nucleotides (IP9) rather than for activation from a response element formed by a direct repeat spaced by 3 nucleotides (DR3). This observation supports a model, in which promoter selectivity reflects the selectively increased antiproliferative effect of VD analogues.

Conformational change and enhanced stabilization of the vitamin D receptor by the 1,25-dihydroxyvitamin D3 analog KH1060

The 1,25-dihydroxyvitamin D3 [1,25-(OH)2vitamin D3] analog KH1060 exerts very potent effects on cell proliferation and cell differentiation via the vitamin D receptor (VDR). However, the activities of KH1060 are not associated with an increased affinity for the VDR. We now show that increased stabilization of the VDR-KH1060 complex could be an explanation for its high potencies. VDR half-life studies performed with cycloheximide-translational blocked rat osteoblast-like ROS 17/2.8 cells demonstrated that, in the absence of ligand, VDR levels rapidly decreased. After 2 hr, less than 10% of the initial VDR level could be measured. In the presence of 1,25-(OH)2vitamin D3, the VDR half-life was 15 hr. After 24 hr. less than 20% of the initial VDR content was detectable, whereas, at this time-point, when the cells were incubated with KH1060 80% of the VDR was still present. Differences in 1,25-(OH)2vitamin D3- and KH1060-induced conformational changes of the VDR could underlie the increased VDR stability. As assessed by limited proteolytic digestion analysis, both 1,25-(OH)2vitamin D3 and KH1060 caused a specific conformational change of the VDR. Compared with 1,25-(OH)2vitamin D3, KH1060 induced a conformational change that led to a far more dramatic protection of the VDR against proteolytic degradation. In conclusion, the altered VDR stability and the possibly underlying change in VDR conformation caused by KH1060 could be an explanation for its enhanced bioactivity.

The potent anti-proliferative effect of 20-epi analogues of 1,25 dihydroxyvitamin D3 in human breast-cancer MCF-7 cells is related to promoter selectivity

The hormone 1,25-dihydroxyvitamin D3 (VD) has a potential use as an anti-tumor agent, but its clinical applications are restricted by its strong calcemic activity. This has led to the development of VD analogues with selectively increased growth-inhibitory activity. One of the most potent analogues is KH1060, which is a 20-epi-22-oxa-derivative of VD. In human breast cancer MCF-7 cells, we studied the growth-inhibitory activities of a set of 8 analogues that cover conservative structural changes from 20-epi-VD (MC1288) to KH1060. In the same cellular system, we analyzed the potential of these 8 analogues to stimulate reporter gene activity driven by a recently discovered novel-type VD response element. We found that this VD response element is more appropriate than classical VD response elements to correlate anti-proliferative effects of VD analogues with their gene-regulatory properties.

High-affinity nuclear receptor binding of 20-epi analogues of 1,25-dihydroxyvitamin D3 correlates well with gene activation

The hormone 1,25-dihydroxyvitamin D3 (VD) has the potential for clinical use in several diseases, such as cancer, osteoporosis, and psoriasis. The action of VD is mediated by primary responding genes that contain in their promoter region a binding site for the transcription factor VDR. Most of the known VD response elements are formed by a direct repeat of two hexameric core binding motifs spaced by three nucleotides (DR3) bound by a heterodimer of VDR and the retinoid X receptor (RXR). Various VD analogues have been developed in order to optimize the therapeutic profile of VD. This report presents a novel experimental system that may help in the understanding of the structural basis for the high potency of a VD analogue like KH1060, which is a 20-epi-22-oxa-derivative of VD. In human breast cancer cells, MCF-7, the half-maximal gene activation values for KH1060 and seven of its structural precursors were determined on a DR3-type VD response element. These eight analogues cover conservative structural changes from 20-epi-VD (MC1288) to KH1060. With a modified version of the limited protease digestion assay the functional affinity of the analogues to VDR was measured. The functional receptor affinity of the eight analogues was found to be directly proportional to their potency in VDR-RXR-mediated gene activity.

Calcitriol and lexicalcitol (KH1060) inhibit the growth of human breast adenocarcinoma cells by enhancing transforming growth factor-beta production

The mechanisms involved in the antiproliferative action of calcitriol (1 alpha, 25(OH)2D3) were investigated using human breast carcinoma epithelial cells (the MCF-7 cell line). Calcitriol and KH1060, a synthetic analog, inhibited cell growth in a time-and dose-dependent way. The substances similarly stimulated total TGF-beta secretion after 24 hours, and Northern blot analyses showed that mRNA levels for TGF-beta 1 were increased, as well. When MCF-7 cells were co-incubated with calcitriol and a neutralizing anti TGF-beta 1, beta 2, beta 3 antibody, growth inhibition was completely abrogated. With KH1060, the antibody could only partly block growth inhibition. This study shows that TGF-beta is involved in the growth response to calcitriol and KH1060 in MCF-7 cells.

Conformationally restricted analogs of 1 alpha, 25-dihydroxyvitamin D3 and its 20-epimer: compounds for study of the three-dimensional structure of vitamin D responsible for binding to the receptor

Two proteins play important roles in the expression of vitamin D function: the specific nuclear receptor protein (vitamin D receptor, VDR) and the transport protein (vitamin D binding protein, DBP). This study was conducted to clarify the conformation of vitamin D responsible for binding to those proteins. For the purpose, the side chain mobility of 1,25(OH)2D3 (1) and its 20-epimer, 20-epi-1,25(OH)2D3 (2), was analyzed by a systematic conformational search. The results were depicted as a three-dimensional dot map, which indicates that the side chains of the two vitamins (1 and 2) occupy different spatial regions that are separated in two areas. We denoted these areas as A and G for 1 and EA and EG for 2. Four analogs, the diastereomers at C(20) and C(22) (3-6) of 22-methylated 1,25(OH)2D3 whose side chains were confined to occupy G, A, EA, and EG, respectively, were designed. These analogs (3-6) were synthesized efficiently by a stereoselective conjugate addition of organocuprate to steroidal E- and Z-22-en-24-ones as the key step. In binding to the VDR the affinities of the analogs (3-6) relative to 1,25-(OH)2D3 (1) were 1/60, 1/3, 20, and 1/100, respectively. These results indicate that the A region is responsible for binding of 1 to VDR and the EA region for binding of 2. Only isomer 4 showed significant affinity for DBP, indicating only the A region is responsible for binding to DBP. Thus, 5 showed clear separation of binding affinities for two proteins, VDR and DBP. Having the highest known VDR affinity, (22R)-22-methyl-20-epi-1,25(OH)2D3 (5) has potential both as a therapeutic agent and as a tool to study the molecular mechanism of vitamin D-mediated gene transcription.

Effects of 1,25 dihydroxyvitamin D3 and its analogues on induction of apoptosis in breast cancer cells

Vitamin D derivatives have been shown both to inhibit the proliferation of cultured breast cancer cells and to cause regression of experimental mammary tumours in vivo. We have investigated the ability of several vitamin D analogues to promote the regression of experimental rat mammary tumours. Our results revealed that one vitamin D compound in particular, EB1089 (1(S),3(R)-dihydroxy-20(R)-5'-ethyl- 5'-hydroxy-hepta-1'(E),3'(E)-dien-1'-yl)-9,10-secopregna-5(Z ),7(E) ,10(19)-triene), was highly effective at inhibiting tumour progression, without causing a significant rise in serum calcium concentration. Tumour regression occurs when the rate of cell death is greater than the rate of cell proliferation. Apoptosis (programmed or active cell death) is an active, energy-dependent process in which a distinct series of biochemical and molecular events leads to the death of cells by specific signals. We have examined effects of 1,25-dihydroxyvitamin D3 (1,25(OH)2(D)3) and the synthetic vitamin D analogue EB1089 on indices of apoptosis in cultured human breast cancer cells. The effects of the vitamin D compounds on the expression of two oncoproteins which may regulate apoptosis, bcl-2 and p53 were examined by Western analysis. In MCF-7 cell cultures treated for six days with 1,25(OH)2(D)3 or EB1089 (1 x 10(-8) M), bcl-2 protein was reduced in comparison to control levels, whereas p53 protein was increased. In addition, the p21 protein, whose gene WAF-1 is induced by wild type p53, was also increased by both vitamin D compounds. Using Northern analysis, it was observed that 24-h treatment of MCF-7 cells with 1 x 10(-8) M 1,25(OH)2(D)3 or EB1089 resulted in an induction of TRPM-2 (clusterin) mRNA, a gene associated with onset of apoptosis in the involuting prostate. Fragmentation of genomic DNA is a characteristic feature of apoptosis. With the terminal deoxynucleotidyl transferase (TdT) assay, 3'-OH DNA breaks indicative of DNA fragmentation were detected histochemically in MCF-7 cells treated with 1 x 10(-8) M 1,25(OH)2(D)3 or EB1089 for four days prior to fixation and TdT reaction. Further evidence of apoptosis was obtained following six days treatment of MCF-7 cell cultures with 5 x 10(-8) M 1,25(OH)2(D)3 or EB1089, utilizing a cell death ELISA assay, which measures the presence of histone-associated oligonucleosome complexes generated from DNA fragmentation. Taken together our findings indicate that vitamin D derivatives may play a role in regulating the expression of genes and protein products implicated in apoptosis.

Increased stringency of the 1,25-dihydroxyvitamin D3-induced G1 to S phase block in polyploid HL60 cells

Treatment of mammalian cells with 1,25-dihydroxyvitamin D3 (1,25D3) produces a G1 to S (G1/S) phase cell cycle block. In addition, it has been noted that a smaller proportion of cells accumulates in the G2/M compartment in 1,25D3-treated cultures. Since cyclins have a major influence on the regulation of cell cycle progression, we determined the expression of cyclins A and B as markers of the G2 phase and of cyclin E as the marker of G1/S transition. No increase in the steady-state levels of cyclin A or cyclin B mRNA was detected in the total cell population or in the cyclin B1 protein in the G2/M cell cycle compartment. In contrast, immunodetectable cyclin E protein was increased in cell cultures as a whole and specifically in the G2/M compartment cells. Determination of BrdU incorporation into DNA by flow cytometry showed marked inhibition of DNA replication in cells with DNA content higher than 4C, and autoradiography of 3H-TdR-pulsed cells showed that polynucleated cells did not replicate DNA after 96 h of treatment with 1,25D3 or analogs. Taken together, these experiments show that at least a portion of the G2/M compartment in 1,25D3-arrested cultures of HL60 cells represents G1 cells at a higher ploidy level, which are blocked from entering the high ploidy S phase.

Synthetic 20-epi analogs of calcitriol are potent inducers of target-gene activation in osteoblastic cells

We have compared the actions of calcitriol and its three synthetic analogs, 20-epi-22-oxa-24a,26a,27a-trihomo-1 alpha,25-dihydroxyvitamin D3 (KH 1060), 1 alpha,24S-(OH)2-22-ene-26,27-cyclopropyl vitamin D3 (MC 903) and 20-epi-1 alpha,25-dihydroxyvitamin D3 (MC 1288), on the expression of two marker genes of differentiated osteoblasts, namely alkaline phosphatase and osteocalcin, using human MG-63 osteosarcoma cells. Calcitriol and the analogs had qualitatively similar stimulatory effects on target-gene activation. Quantitatively, MC 903 behaved in most experiments essentially as the parent compound calcitriol. In vitamin D receptor/DNA complex formation MC 903, however, was more potent than calcitriol. In contrast, the 20-epi analogs, KH 1060 and MC 1288, were much more potent even at lower concentrations, than calcitriol and MC 903 in stimulating alkaline phosphatase activity, osteocalcin mRNA synthesis and osteocalcin secretion. The stimulation occurred to a greater degree and for a longer period than with calcitriol. This effect was apparently mediated by stronger and longer lasting binding of the vitamin D receptor to the osteocalcin vitamin D responsive element by the 20-epi analogs. After a 6-h treatment and during subsequent culture without hormone, the effects of the 20-epi analogs were also stronger and lasted longer than those with calcitriol or MC 903. Collectively, at comparable and lower concentrations, the 20-epi analogs, KH 1060 and MC 1288, mediate much stronger and longer lasting stimulatory effects than calcitriol or its analog MC 903 on target-gene expression associated with the differentiated phenotype of the MG-63 human osteosarcoma cells.

Vitamin D3 analogs inhibit growth and induce differentiation in LA-N-5 human neuroblastoma cells

The physiologically active metabolite of vitamin D3, 1,25-dihydroxycholecalciferol (D3), plays an important role in embryonic development and cell differentiation. Previously, we have demonstrated that D3 significantly induces differentiation and inhibits growth of LA-N-5 human neuroblastoma cells at concentrations of 24 nm and higher. In this study, we compared two D3 analogs, 20-epi-22oxa-25a,26a,27a-tri-homo-1,25-D3 (KH 1060) and 1,25-dihydroxy-22,24-diene, 24,26,27-trihomo (EB 1089), with D3 with respect to their effects on differentiation and growth inhibition. We report an inhibition of growth by 45-55% in cells treated with 0.24 nm EB 1089 and 0.24 nM KH 1060, similar to that seen in cells treated with 24 nM D3. At these concentrations, both EB 1089 and KH 1060 stimulate the differentiation of LA-N-5 neuroblastoma cells as shown by increased neurite outgrowth, decreased N-myc expression and decreased invasiveness in vitro. An increase in acetylcholinesterase activity, a functional measure of differentiation, was also exhibited. Previous reports have shown that treatment doses needed to achieve 24 nM serum concentrations of D3 in patients would result in hypercalcemia. EB 1089 and KH 1060 can cause the same in vitro effects on LA-N-5 human neuroblastoma cells at 1/100 of the concentration required of D3. These data suggest a potential clinical efficacy of EB 1089 and KH 1060 as biological response modifiers.

Immunohistochemical detection of 1,25-dihydroxyvitamin D3 receptors (VDR) in human skin. A comparison of five antibodies

Increasing evidence suggests an important regulatory function for 1 alpha,25-dihydroxyvitamin D3 in the growth control of epidermal cells and in skin immunology. Using immunohistochemical techniques we investigated the in situ expression of 1,25-dihydroxyvitamin D3 receptors (VDR) in normal human skin with one monoclonal rat antibody and four monospecific polyclonal rat antibodies to the VDR. Polyclonal rabbit antibodies have been raised against synthetic peptides corresponding to different amino acid residues of the human VDR, including regions close to the DNA binding domain and the hormone-binding domain. All antibodies revealed positive immunoreactivity in normal human skin. The antibodies showed differences in subcellular immunoreactivity and staining-intensity. Differences in subcellular distribution of VDR immunoreactivity are caused by the different epitopes recognized by the antibodies and not by the affinity of the antibodies for VDR. It seems that the antibodies may recognize different functional modifications of the receptor molecule (i.e.: hormone bound vs. hormone free; DNA bound vs. non-DNA bound; VDR vs. VDR/retinoid-X receptor [RXR] heterodimers). Using these newly raised antibodies future studies will be carried out to analyse subcellular distribution of VDR immunoreactivity in skin pathology.

Enhancement of antiproliferative activity of 1alpha,25-dihydroxyvitamin D3 (analogs) by cytochrome P450 enzyme inhibitors is compound- and cell-type specific

Ketoconazole (keto) or liarozole (liaro), inhibitors of the cytochrome P450 enzymes that mediate vitamin D and A hydroxylations, could potentiate the antiproliferative effects of 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)2D3] and its analogs. Proliferation of MCF-7 and T47-D human breast cancer cells, MG-63 human osteosarcoma cells and HL-60 human promyeloid leukemia cells was concentration dependently inhibited by 1alpha,25(OH)2D3. The vitamin D analogs KH 1060 [20-epi-22-oxa-24,26,27-trihomo-1alpha,25(OH)2D3], RO 23-6010 [16-ene-23-yne-26-trifluoro-1,25(OH)2D2D3], ZXY 835 [20-epi-23-yne-25,26-epoxy-1alpha(OH)D3], and CD 99 [11alpha-methyl-1alpha,25(OH)2D3] were 150-,58-,16- and 7-fold more potent than 1alpha,25(OH)2D3 in inhibiting the proliferation of MCF-7 cells, respectively. A similar rank order of potency was observed in other cell lines. The antiproliferative effects of the vitamin D hormone and analogs was enhanced in MCF-7 cells when coincubated with 1 microM keto (7-, 10-, 5-, 25- and 1.3-fold more potent than in the absence of keto), respectively. The antiproliferative effect was less enhanced when 1alpha,25(OH)2D3 or its analogs KH 1060, ZXY 835 and RO 23-6010 were combined with liaro (3-, 7-, 2- and 3-fold, respectively). Keto and liaro did not markedly potentiate the activity of 1alpha,25(OH)2D3 or its analogs in MG-63 or HL-60 cells. These results suggest that differences in cellular metabolism can at least partially explain the different potency of vitamin D analogs. Moreover, the metabolism of vitamin D analogs is cell-type specific.

Differential effects of 1,25-dihydroxyvitamin D3-analogs on osteoblast-like cells and on in vitro bone resorption

Although numerous studies have shown potent antiproliferative and differentiation-inducing effects of 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) and its analogs on cells not directly related to bone metabolism, only few reports focussed on the effects of these analogs on bone. We compared the action of several recently developed analogs with that of 1,25-(OH)2D3 on human (MG-63) and rat (ROS 17/2.8) osteoblast-like cells and on in vitro bone resorption. In MG-63 cells the analogs EB1089 and KH1060 were about 166,000 and 14,000 times more potent than 1,25-(OH)2D3 in stimulating type I procollagen and 100 and 6,000 times more potent in stimulating osteocalcin production, respectively. Also in ROS 17/2.8 cells EB1089 and KH1060 were most potent in inducing osteocalcin synthesis. In vitro bone resorption was 2.3 and 17.5 times more potently stimulated by EB1089 and KH1060, respectively. In MG-63 cells, 1,25-(OH)2D3 and the analogs inhibited cell proliferation, whereas both 1,25-(OH)2D3 and the analogs stimulated the growth of ROS 17/2.8 cells. Differences in potency could neither be explained by affinity for the vitamin D receptor nor by a differential involvement of protein kinase C in the action of the analogs. Together, these data show that also in bone the analogs EB1089 and KH1060 are more potent than 1,25-(OH)2D3 but that the potency of the analogs compared to 1,25-(OH)2D3 is dependent on the biological response. On the basis of these observations it can be concluded that the reported reduced calcemic effect in vivo is not the result of a decreased responsiveness of bone to these analogs. Lastly, in view of eventual clinical application of 1,25-(OH)2D3-analogs, the observed stimulation of in vitro bone resorption and growth of an osteosarcoma cell line warrant in vivo studies to further examine these effects.

Studies on two new vitamin D analogs, EB 1089 and KH 1060: effects on bone resorption and osteoclast recruitment in vitro

We have investigated the effects on bone resorption of two new potent antiproliferative vitamin D3 analogs, EB 1089 and KH 1060, by studying recruitment of osteoclasts in murine bone marrow cultures and 45Ca release from prelabeled neonatal mouse calvarial bones. Binding studies to vitamin D receptor protein, from human osteosarcoma MG-63 cells, demonstrated kd values of 8.5 x 10(-11) for 1 alpha,25(OH)2D3, 6.5 x 10(-11) for KH 1060, and 2.7 x 10(-10) for EB 1089. 1 alpha,25(OH)2D3 and EB 1089 were equipotent stimulators of osteoclast recruitment in murine bone marrow cultures, with EC50 at 10(-10) mol/L, whereas KH 1060 was about tenfold more potent with an EC50 at 10(-11) mol/L. In serum-free media, 1 alpha,25(OH)2D3 enhanced 45Ca release from neonatal mouse calvarial bones with EC50 at 10(-11) mol/L, but in the presence of 10% fetal calf serum (FCS) the stimulatory effect was significantly diminished, with a threshold value at 10(-10) mol/L. EB 1089 stimulated bone resorption with an estimated EC50 at 3 x 10(-11) mol/L, whereas KH 1060 was about tenfold more potent than 1 alpha,25(OH)2D3, and stimulated bone resorption with an EC50 at 10(-12) mol/L. The effects of EB 1089 and KH 1060 on 45Ca release were not significantly affected by the addition of 10% FCS. Addition of vitamin D binding protein to serum-free incubations of neonatal mouse calvarial bones, significantly inhibited the bone resorbing effect of 1 alpha,25(OH)2D3, but did not affect EB 1089 and KH 1060 induced 45Ca release.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of combined treatment with the novel vitamin D analogue MC 1288 and cyclosporine A on cardiac allograft survival

The efficacy of combined treatment with the novel vitamin D analogue MC 1288 (20-epi-1 alpha,25-dihydroxycholecalciferol) and cyclosporine A (CyA) in preventing rejection following organ transplantation was evaluated in the heterotopic cardiac allograft model. Wistar/Kyoto rats received hearts from PVG donors and were subsequently treated with MC 1288 and CyA in various dose combinations. Administration of MC 1288 0.1 microgram/kg together with CyA 5 mg/kg produced significantly prolonged graft survival times as compared with single therapy with MC 1288 0.1 microgram/kg (p < 0.01) or CyA 5 mg/kg (p < 0.001). MC 1288 and CyA were tested also in combination with the immunomodulating drug LS-2616, which, in several laboratories, is used as a model for the evaluation of new combinations of immunosuppressive drugs. LS-2616 abolishes the immunosuppressive effect of CyA and the transplanted hearts are thus rejected at the same time as grafts of untreated recipients, i.e. on day 8. The immunosuppressive effect of MC 1288 is also counteracted by LS-2616, but the effect is not absolute and the median graft survival time is 11.0 days. Combined treatment with MC 1288 and CyA in the presence of LS-2616 resulted in a median graft survival time of 14.0 days. The results obtained in our experiments indicate at least an additive effect of MC 1288 and CyA thus suggesting that in the future MC 1288, or other vitamin D analogues, might be used to control rejection, either alone, in combination with CyA or in combination with other immunosuppressive drugs with other mechanisms of action.