A novel synthetic vitamin D3 analogue, 2-beta-(3-hydroxypropoxy)-calcitriol (ED-71): its biological activities and pharmacological effects on calcium metabolism

Eldecalcitol inhibits the progression of oral cancer by suppressing the expression of GPx-1

OBJECTIVES

This study aimed to investigate the role of eldecalcitol in the progression of oral squamous cell carcinoma and to explore the related mechanism.

MATERIALS AND METHODS

The effects of eldecalcitol on the proliferation, cell cycle, apoptosis, and migration of oral cancer cells (SCC-15 and CAL-27) were evaluated with cell counting kit-8, flow cytometry, quantitative real-time polymerase chain reaction, western blotting, and scratch assay. Mouse xenograft tumor model was established to further confirm the role of eldecalcitol in the progression of oral cancer. Immunohistochemistry, quantitative real-time polymerase chain reaction, and western blotting were used to detect glutathione peroxidase-1 expression in oral cancer tissue and cells treated with eldecalcitol.

RESULTS

Eldecalcitol was found to inhibit the proliferation and migration of SCC-15 and CAL-27 cells significantly, block the cell cycle in the G0/G1 phase, and enhance the apoptosis. In addition, glutathione peroxidase-1 was downregulated by eldecalcitol and acted as an important medium of eldecalcitol in inhibiting the proliferation and migration of SCC-15 and CAL-27 cells, as well as promoting their apoptosis.

CONCLUSIONS

Eldecalcitol may inhibit the progression of oral cancer by suppressing the expression of glutathione peroxidase-1, which may provide new insight into the application of eldecalcitol as a potential anti-cancer drug.

Effects of risedronate, alendronate, and minodronate alone or in combination with eldecalcitol on bone mineral density, quality, and strength in ovariectomized rats

Combination therapy of active vitamin D₃ with some bisphosphonates (BPs) has been reported to be clinically beneficial. However, combination therapy of eldecalcitol (ELD) with BP has to date not been validated as to whether it is beneficial in the clinical setting. Preclinical studies suggested that simultaneous treatment with ELD and some BPs is more effective than monotherapy. However, the relative potency of various BPs, when used in combination with ELD, is completely unknown. In this study, we examined and compared the effects of risedronate (RIS), alendronate (ALN), and minodronate (MIN) alone or in combination with ELD on bone mass, microarchitecture, strength, and material properties in ovariectomized Sprague-Dawley rats aged 13 weeks. RIS, ALN, MIN, and ELD were administered five times weekly for 16 weeks. Micro-computed tomography analysis, compression test, and Fourier transform infrared (FTIR) imaging analysis were performed 16 weeks after treatment initiation. Trabecular and cortical bone mineral density (BMD) in the fourth lumbar vertebra (L4) significantly increased in the RIS + ELD, ALN + ELD, and MIN + ELD groups compared with the vehicle group. Moreover, the bone microarchitecture of L4 in all the BP + ELD groups also significantly improved. On mechanical testing of L4, the maximum load was significantly increased in the RIS + ELD and ALN + ELD groups. FTIR analysis revealed that the mineral-to-collagen ratio of trabecular bone in L3 of all the BP + ELD groups was significantly increased compared with the vehicle group. By contrast, the carbonate-to-phosphate ratio, a parameter of mineral immaturity, was significantly decreased in the RIS + ELD and ALN + ELD groups. BP + ELD improved the BMD and structural properties of the bone to a similar extent. RIS + ELD and ALN + ELD also improved bone strength. Furthermore, treatment with BP + ELD improved the bone material. These results suggest that the combination therapy of BP and ELD is beneficial and warrants further clinical trials.

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Combination of bisphosphonates and eldecalcitol was superior to either monotherapy.

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Bone quality on FTIR imaging analysis correlated with bone strength.

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Combined bisphosphonate and eldecalcitol may be useful in the clinical setting.

Vitamin D endocrine system and osteoclasts

Vitamin D was discovered as an anti-rachitic agent preventing a failure in bone mineralization, but it is now established that the active form of vitamin D3 (1α,25(OH)2D3) induces bone resorption. Discovery of the receptor activator of nuclear factor -κB ligand (RANKL) uncovered the molecular mechanism by which 1α,25(OH)2D3 stimulates bone resorption. Treating osteoblastic cells with 1α,25(OH)2D3 stimulates RANKL expression, which in turn induces osteoclastogenesis. Nevertheless, active vitamin D compounds such as calcitriol (1α,25(OH)2D3), alfacalcidol (1α(OH)D3) and eldecalcitol (1α,25-dihydroxy-2β-(3-hydroxypropoxy) vitamin D3) have been used as therapeutic drugs for osteoporosis, as they increase bone mineral density (BMD) in osteoporotic patients. Paradoxically, the increase in BMD is caused by the suppression of bone resorption. Several studies have been performed to elucidate the mechanism by which active vitamin D compounds suppress bone resorption in vivo. Our study showed that daily administration of eldecalcitol to mice suppressed neither the number of osteoclast precursors in the bone marrow nor the number of osteoclasts formed in ex vivo cultures. Eldecalcitol administration suppressed RANKL expression in osteoblasts. This review discusses how the difference between in vitro and in vivo effects of active vitamin D compounds on bone resorption is induced.

The role of the serum vitamin D binding protein in the actions of the vitamin D analog eldecalcitol (ED-71) on bone and mineral metabolism

The vitamin D analog ED-71 (eldecalcitol) has been shown to be superior to calcitriol and its precursor alfacalcidol in maintaining or increasing bone mass in women and animal models with osteoporosis. The mechanism for the greater effectiveness of ED-71 is unknown. In the present study, we tested the hypothesis that the higher activity of ED-71 is due to its higher affinity for the serum vitamin D binding protein (DBP) by comparing the activities of orally administered ED-71, calcitriol and 22-oxacalcitriol (OCT) in wild type (WT) and DBP-ablated (DBPko) mice. In 8-week-old male WT mice, the effects of the analogs on serum and urinary calcium and phosphate were ED-71 > calcitriol > OCT. The results in DBPko mice were identical to those of the WT mice for all parameters tested. In ovariectomized mice, ED-71 was more effective than calcitriol in increasing bone mineral density, but again, there were no differences in the responses of the WT versus DBPko OVX mice. This lack of an effect of DBP ablation on the activities of oral ED-71 occurred despite the finding that peak circulating levels of ED-71 were 100 times lower and disappeared quickly in the DBPko mice while the peak levels at 1 h in WT mice were maintained for at least 24 h. These findings indicate that although DBP has a major influence on circulating levels of vitamin D compounds, it is not responsible for the greater efficacy of ED-71 on bone and mineral metabolism.

Sphingosine-1-phosphate-mediated osteoclast precursor monocyte migration is a critical point of control in antibone-resorptive action of active vitamin D

The migration and positioning of osteoclast precursor monocytes are controlled by the blood-enriched lipid mediator sphingosine-1-phosphate (S1P) and have recently been shown to be critical points of control in osteoclastogenesis and bone homeostasis. Here, we show that calcitriol, which is the hormonally active form of vitamin D, and its therapeutically used analog, eldecalcitol, inhibit bone resorption by modulating this mechanism. Vitamin D analogs have been used clinically for treating osteoporosis, although the mode of its pharmacologic action remains to be fully elucidated. In this study, we found that active vitamin D reduced the expression of S1PR2, a chemorepulsive receptor for blood S1P, on circulating osteoclast precursor monocytes both in vitro and in vivo. Calcitriol- or eldecalcitol-treated monocytoid RAW264.7 cells, which display osteoclast precursor-like properties, migrated readily to S1P. Concordantly, the mobility of circulating CX3CR1(+) osteoclast precursor monocytes was significantly increased on systemic administration of active vitamin D. These results show a mechanism for active vitamin D in controlling the migratory behavior of circulating osteoclast precursors, and this action should be conducive to limiting osteoclastic bone resorption in vivo.

The vitamin D analog ED-71 is a potent regulator of intestinal phosphate absorption and NaPi-IIb

The vitamin D analog ED-71 [1α,25-dihydroxy-2β-(3-hydroxypropyloxy)vitamin D(3)] has been approved for treatment of osteoporosis in Japan, but its effects on mineral metabolism have not been fully explored. We investigated the actions of ED-71 on phosphate (Pi) absorption and induction of the intestinal sodium/phosphate cotransporters. Oral treatment of vitamin D-deficient rats with ED-71 (20 pmol every other day for 8 d) produced a maximal 8-fold increase in duodenal Pi absorption, measured by the in situ loop method, whereas 1,25-dihyroxyvitamin D(3) [1,25(OH)(2)D(3]), at doses up to 150 pmol, had no effect. This action of ED-71 was attributable to a dramatic 24-fold induction of sodium-dependent Pi transporter type IIb (NaPi-IIb) mRNA in the duodenum; Pit-1 and Pit-2 mRNA levels were not increased. In vitamin D-replete rats, ED-71 treatment (50 pmol) at 72 and 24 h before death increased NaPi-IIb mRNA in the duodenum and jejunum, but not the ileum, whereas 1,25(OH)(2)D(3) at 1000 pmol was ineffective in all segments. Single oral doses of ED-71 increased mouse intestinal NaPi-IIb mRNA and protein between 6 and 24 h. Surprisingly, rat lung NaPi-IIb was not increased by ED-71, despite its coexpression with the vitamin D receptor in alveolar type II cells. However, ED-71 did not induce intestinal NaPi-IIb in vitamin D receptor-ablated mice. The greater potency of ED-71 than 1,25(OH)(2)D(3) on NaPi-IIb appears to be due to much higher and more prolonged levels of ED-71 in the circulation. In summary, ED-71, due to its disparate pharmacokinetics, is a much more potent inducer of intestinal Pi absorption and NaPi-IIb than 1,25(OH)(2)D(3), suggesting a role for this analog in the treatment of Pi-wasting disorders.

Bone effects of vitamin D - Discrepancies between in vivo and in vitro studies

Vitamin D was discovered as an anti-rachitic agent, but even at present, there is no direct evidence to support the concept that vitamin D directly stimulates osteoblastic bone formation and mineralization. It appears to be paradoxical, but vitamin D functions in the process of osteoclastic bone resorption. In 1952, Carlsson reported that administration of vitamin D(3) to rats fed a vitamin D-deficient, low calcium diet raised serum calcium levels. Since the diet did not contain appreciable amounts of calcium, the rise in serum calcium was considered to be derived from bone. Since then, this assay has been used as a standard bioassay for vitamin D compounds. Osteoclasts, the cells responsible for bone resorption, develop from hematopoietic cells of the monocyte-macrophage lineage. Several lines of evidence have shown that the active form of vitamin D(3), 1α,25-dihydroxyvitamin D(3) [1α,25(OH)(2)D(3)] is one of the most potent inducers of receptor activator of NF-κB ligand (RANKL), a key molecule for osteoclastogenesis, in vitro. In fact, 1α,25(OH)(2)D(3) strongly induced osteoclast formation and bone resorption in vitro. Nevertheless, 1α,25(OH)(2)D(3) and its prodrug, Alfacalcidol (1α-hydroxyvitamin D(3)) have been used as therapeutic agents for osteoporosis since 1983, because they increase bone mineral density and reduce the incidence of bone fracture in vivo. Furthermore, a new vitamin D analog, Eldecalcitol [2β-(3-hydroxypropoxy)-1α,25(OH)(2)D(3)], has been approved as a new drug for osteoporosis in Japan in January 2011. Interestingly, these beneficial effects of in vivo administration of vitamin D compounds are caused by the suppression of osteoclastic bone resorption. The present review article describes the mechanism of the discrepancy of vitamin D compounds in osteoclastic bone resorption between in vivo and in vitro.

The vitamin D analog 1α,25-Dihydroxy-2β-(3-Hydroxypropyloxy) vitamin D(3) (Eldecalcitol) is a potent regulator of calcium and phosphate metabolism

The vitamin D analog 1α,25-dihydroxy-2β-(3-hydroxypropyloxy)vitamin D(3) (ED-71 or eldecalcitol) has been developed for treatment of osteoporosis, but its effects on mineral metabolism have not been investigated in detail. In the present study, we compared the effects of eldecalcitol and calcitriol on calcium (Ca) and phosphate (Pi) handling in rats. Oral administration of eldecalcitol (0, 7.5, 20, or 50 pmol) q.o.d. for 2 weeks dose-dependently increased ionized Ca, intestinal Ca absorption, and urinary Ca excretion, while these doses of calcitriol had no significant effects. The highest dose of eldecalcitol did not alter serum Pi but stimulated both intestinal Pi absorption and urinary Pi excretion; the latter was attributable, in part, to increased serum FGF-23. The effects of high-dose eldecalcitol on Ca and Pi absorption and urinary excretion and FGF-23 persisted for several days following cessation of treatment. The higher potency of eldecalcitol on Ca and Pi handling was also observed in parathyroidectomized rats infused with PTH, excluding a role for differential regulation of PTH. Direct measurement of duodenal Ca absorption by the in situ loop method confirmed the higher potency of eldecalcitol in this segment via induction of TRPV6. These studies indicated that with chronic administration eldecalcitol is more potent than calcitriol at stimulating intestinal absorption of Ca and Pi, as well as FGF-23. The mechanisms responsible for the higher potency of eldecalcitol are speculated to be its higher vitamin D-binding protein (DBP) affinity and resistance to metabolism.

Comparison of the effects of eldecalcitol and alfacalcidol on bone and calcium metabolism

Eldecalcitol [ED-71, 2beta-(3-hydroxypropyloxy)-1,25-dihydroxyvitamin D3] increases lumbar and hip bone mineral density (BMD) in a dose-dependent manner in osteoporotic patients with vitamin D supplementation. However, there has been no head-to-head comparison of the effects of eldecalcitol with alfacalcidol on bone and calcium metabolism in human subjects. Therefore, a randomized open-label clinical trial was conducted to compare the effect of eldecalcitol on bone turnover markers and calcium metabolism in 59 Japanese postmenopausal women. Subjects were randomly assigned to receive 1.0 microg alfacalcidol, 0.5 or 1.0 microg eldecalcitol once a day for 12 weeks. There was almost no increase in serum calcium (Ca) throughout the study period. Eldecalcitol from 0.5 to 1.0 microg increased daily urinary Ca excretion in a dose-dependent manner, and 1.0 microg eldecalcitol increased urinary Ca to a similar extent to 1.0 microg alfacalcidol. Both 0.5 and 1.0 microg eldecalcitol suppressed urinary NTX stronger than 1.0 microg alfacalcidol (-6, -30 and -35% in 1.0 microg alfacalcidol, 0.5 and 1.0 microg eldecalcitol-treated groups, respectively, at 12 weeks). In contrast, changes in serum BALP were similar among the three groups (-22, -22 and -29% in 1.0 microg alfacalcidol, 0.5 and 1.0 microg eldecalcitol-treated groups, respectively, at 12 weeks). These results demonstrate that 0.5-1.0 microg eldecalcitol can effectively inhibit bone resorption stronger than alfacalcidol with a similar effect on bone formation and a comparable effect on urinary Ca excretion, and suggest that eldecalcitol may have a better osteoprotective effect than alfacalcidol.