25-Hydroxyvitamin D3 1alpha-hydroxylase expression in breast cancer and use of non-1alpha-hydroxylated vitamin D analogue

Breast Cancer Res. 2005;7(6):R980-6. doi: 10.1186/bcr1332. Epub 2005 Oct 6.


Introduction: The cytochrome P450 mitochondrial enzyme 25-hydroxyvitamin D3 1alpha-hydroxylase (1alpha-hydroxylase) of renal tubule cells hydroxylates the major circulating form of vitamin D (25(OH)D3) to the active systemic hormone 1,25(OH)2D3. Local production of 1,25(OH)2D3 appears to occur also at other sites where 1alpha-hydroxylase is expressed for autocrine/paracrine regulation. To reduce risks of hypercalcemia during treatment with vitamin D, we have previously suggested use of non-1alpha-hydroxylated vitamin D analogues to target tissues where 1alpha-hydroxylase is expressed, including the parathyroid glands in secondary hyperparathyroidism. The present study was undertaken to examine expression of 1alpha-hydroxylase in breast cancer and to investigate whether a non-1alpha-hydroxylated vitamin D analogue displayed biological function. In addition, expression of the 25-hydroxyvitamin D3 24-hydroxylase (24-hydroxylase) and the vitamin D receptor (VDR) was investigated.

Methods: The expression of 1alpha-hydroxylase, 24-hydroxylase and VDR was investigated in breast cancer specimens (n = 19) and normal breast tissues (n = 10) by immunohistochemistry and/or RT-PCR. Consecutive cryosections of 6 mum essentially free of immune cells were used in the analyses. The effect of vitamin D analogues on transcriptional activation was analyzed in transiently transfected MCF-7 breast cancer cells.

Results: 1alpha-hydroxylase protein was demonstrated in 79% and 100% of breast cancer specimens and normal breast, respectively. The overall relative mRNA levels of 1alpha-hydroxylase and 24-hydroxylase in normal breast compared to breast tumors were: 1alpha-hydroxylase, 1 +/- 0.07 versus 0.7 +/- 0.05, respectively (p < 0.001); 24-hydroxylase, 1 +/- 0.08 verus 2.1 +/- 0.2, respectively (p < 0.001). The VDR was expressed in 95% of the tumors as expected, with mRNA levels of 1 +/- 0.09 and 1.4 +/- 0.12 (p < 0.05) in breast cancer and normal breast, respectively. The ketoconazole-sensitive transcription activation potential of the non-1alpha-hydroxylated vitamin D analogue prodrug of EB1089 (EB1285) was demonstrated in MCF-7 cells, which express 1alpha-hydroxylase. The activity of EB1285 was about 20% of 1,25(OH)2D3.

Conclusion: These results demonstrate nearly normal expression levels of 1alpha-hydroxylase, 24-hydroxylase and VDR in the majority of investigated breast cancer specimens. A non-1alpha-hydroxylated vitamin D analogue displayed activity in breast cancer cells. Such analogues may present future therapeutic options for proliferative disorders where 1alpha-hydroxylase is expressed.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 25-Hydroxyvitamin D3 1-alpha-Hydroxylase / biosynthesis*
  • Breast Neoplasms / genetics*
  • Breast Neoplasms / pathology
  • Cell Proliferation
  • Female
  • Gene Expression Profiling
  • Humans
  • Immunohistochemistry
  • Receptors, Calcitriol / biosynthesis
  • Reverse Transcriptase Polymerase Chain Reaction
  • Steroid Hydroxylases / biosynthesis
  • Tumor Cells, Cultured
  • Vitamin D / analogs & derivatives*
  • Vitamin D3 24-Hydroxylase


  • Receptors, Calcitriol
  • Vitamin D
  • Steroid Hydroxylases
  • Vitamin D3 24-Hydroxylase
  • 25-Hydroxyvitamin D3 1-alpha-Hydroxylase