Animal pharmacological effects of 24R,25-dihydroxyvitamin D3 one of the endogenous substances regulating calcium metabolism

24R,25-Dihydroxyvitamin D3 regulates breast cancer cells in vitro and in vivo

BACKGROUND

Epidemiological studies indicate high serum 25(OH)D₃ is associated with increased survival in breast cancer patients. Pre-clinical studies attributed this to anti-tumorigenic properties of its metabolite 1α,25(OH)₂D₃. However, 1α,25(OH)₂D₃ is highly calcemic and thus has a narrow therapeutic window. Here we propose another metabolite, 24R,25(OH)₂D₃, as an alternative non-calcemic vitamin D₃ supplement.

METHODS

NOD-SCID-IL2γR null female mice with MCF7 breast cancer xenografts in the mammary fat pad were treated with 24R,25(OH)₂D₃ and changes in tumor burden and metastases were assessed. ERα66+ MCF7 and T47D cells, and ERα66- HCC38 cells were treated with 24R,25(OH)₂D₃in vitro to assess effects on proliferation and apoptosis. Effects on migration and metastatic markers were assessed in MCF7.

RESULTS

24R,25(OH)₂D₃ reduced MCF7 tumor growth and metastasis in vivo. In vitro results indicate that this was not due to an anti-proliferative effect; 24R,25(OH)₂D₃ stimulated DNA synthesis in MCF7 and T47D. In contrast, markers of invasion and metastasis were decreased. 24R,25(OH)₂D₃ caused dose-dependent increases in apoptosis in MCF7 and T47D, but not HCC38 cells. Inhibitors to palmitoylation, caveolae integrity, phospholipase-D, and estrogen receptors (ER) demonstrate that 24R,25(OH)₂D₃ acts on MCF7 cells through caveolae-associated, phospholipase D-dependent mechanisms via cross-talk with ERs.

CONCLUSION

These results indicate that 24R,25(OH)₂D₃ shows promise in treatment of breast cancer by stimulating tumor apoptosis and reducing metastasis.

GENERAL SIGNIFICANCE

24R,25(OH)₂D₃ regulates breast cancer cell survival through ER-associated mechanisms similar to 24R,25(OH)₂D₃ effects on chondrocytes. Thus, 24R,25(OH)₂D₃ may modulate cell survival in other estrogen-responsive cell types, and its therapeutic potential should be investigated in ER-associated pathologies.

Vitamin D receptor in endometrial carcinoma and the differentiation-inducing effect of 1,25-dihydroxyvitamin D3 on endometrial carcinoma cell lines

In view of the potential of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] as a cell-differentiation-inducing agent in endometrial cancer, the localization of the vitamin D receptor (VDR) was examined immunohistochemically in 21 endometrial adenocarcinoma specimens, and the effect of 1,25(OH)2D3 on cell growth, as well as the phenotypic changes for cell maturation after treatment with 1,25(OH)2D3, was investigated in 2 endometrial carcinoma cell lines (AMEC-1, RL95-2). The VDR was detected in 14 of the 21 endometrial carcinoma specimens. The growth of RL95-2 cells expressing VDR was inhibited to 44% when cultured with 50 nM 1,25(OH)2D3 for 6 days. In contrast, the growth of AMEC-1 cells not expressing VDR was completely uninhibited even when cultured with 100 nM 1,25(OH)2D3 for 6 days. The RL95-2 cells exposed to 50 nM 1,25(OH)2D3 for 6 days had an increasing expression for 52.5 kD or 45 kD cytokeratin polypeptide, and they became columnar with pronounced polarity and formed gland-like structures when cultured in collagen gel. These results suggest that endometrial adenocarcinoma is a target for 1,25(OH)2D3, which appears to function as a cell-differentiation-inducing agent for the treatment of endometrial cancer.

Receptors for 1,25-dihydroxyvitamin D3 in gynecologic neoplasms

To determine if gynecologic malignancies are candidates for 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) therapy we measured vitamin D receptor (VDR) levels in 11 tumor specimens using a radiolabeled ligand-binding assay. VDR was demonstrated in 3 of 6 ovarian tumors and 1 of 1 uterine sarcomas, but not in endometrial tumors (2), cervical tumors (1), or Krukenberg tumors (1). Scatchard plots revealed that [3H]1,25(OH)2D3 was bound to a single class of high-affinity (Kd = 0.3 to 0.6 nM), saturable sites characteristic of authentic 1,25(OH)2D3 receptors. Specificity of binding activity for 1,25(OH)2D3, the active vitamin D3 metabolite, was demonstrated by failure of 25-hydroxy- and 24,25-dihydroxyvitamin D3 to compete effectively against 1,25(OH)2D3 binding in total cellular tumor extracts. The ovarian carcinoma cell line NIH:OVCAR3 was shown to possess VDR (binding capacity = 137 fmol/mg protein, Kd = 0.48 nM). A 3-day incubation of NIH:OVCAR3 cells with 100 nM 1,25(OH)2D3 resulted in 49% inhibition of cell growth. The growth inhibition of an ovarian carcinoma line and the observation that 36% of gynecologic tumors assayed were shown to be VDR-positive suggest that further study is warranted to delineate the mechanism and possible therapeutic aspects of 1,25(OH)2D3 action in gynecologic tumors.

Osteonal remodeling and mechanical properties of the femoral cortex in rabbits treated with 24R,25(OH)2D3

The increase of bone mass by therapeutics does not always mean the enhancement of bone quality. The purpose of this study is to clarify the changes of osteonal remodeling and the mechanical properties of femoral cortex in rabbits treated with 24R,25(OH)2D3. Fifteen NZW rabbits (3 kg B.W.) were divided into three groups of 5 animals each. Groups 1, 2, and 3 were given vehicle, 10 micrograms/kg, and 100 micrograms/kg 24R,25(OH)2D3, respectively, daily for 8 weeks. At the end of the experiment, the left femur was removed and bone mineral content (BMC) was measured with single photon absorptiometry. Serum 24,25(OH)2D concentrations reached levels of approximately 15 and 200 times that of the controls in groups 2 and 3, respectively. Neither 25(OH)D nor 1,25(OH)2D level showed any significant change in either group. Group 3 showed significant increase in mineral content and density in the epimetaphyseal regions, but the increase at the diaphyseal region did not reach a statistically significant level. Mechanical test for torsion was conducted for mid-cortical regions. After the test, bone pieces were bonded together with adhesive to reconstruct the original form, and undecalcified cross-sectional sections were made at the diaphyses. Fluorescent microscopy disclosed a marked reduction of remodeling in secondary osteonal bone area. The numbers for double-labeled osteons for groups 1, 2, and 3 were 2.47 +/- 0.819, 1.14 +/- 1.02* and 0.137 +/- 0.307* N/mm2, respectively, and the numbers for osteons with resorption lacunae were 1.37 +/- 0.721, 0.412 +/- 0.370* and 0.268 +/- 0.339** N/mm2, respectively. However, neither structural stiffness nor strength correlated with the indices of osteonal remodeling; instead, they were significantly correlated with bone mineral contents.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of vitamin D3 metabolites in ovariectomized rats

The effects of two vitamin D3 metabolites, 24R,25-dihydroxyvitamin D3 and 1 alpha,25-dihydroxyvitamin D3, were investigated in ovariectomized rats. The amount of ash in the femur on a defatted dry weight basis was significantly greater in rats treated with 1 microgram/kg 24R,25-dihydroxyvitamin D3, or 0.01 or 0.1 microgram/kg 1 alpha,25-dihydroxyvitamin D3 than in the controls. The concentration of bone gla protein in serum and amounts in the femur were significantly greater in rats treated with 1 or 10 micrograms/kg 24R,25-dihydroxyvitamin D3, but not those given 1 alpha,25-dihydroxyvitamin D3 compared with the controls. These results suggest that 24R,25-dihydroxyvitamin D3 increased bone mass probably through the stimulation of bone formation.