Synthetic low-calcaemic vitamin D3 analogues inhibit secretion of insulin-like growth factor II and stimulate production of insulin-like growth factor-binding protein-6 in conjunction with growth suppression of HT-29 colon cancer cells

Yoon S. Oh, Eun J. Kim, Beverly S. Schaffer, Young H. Kang, Lise Binderup, Richard G. MacDonald, Jung H.Y. Park

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Abstract

The aims of the present study were to compare the ability of various synthetic analogues of 1α,25-dihydroxyvitamin D3 [1α,25-(OH)2D3] to inhibit proliferation of HT-29 cells, a human colon adenocarcinoma cell line. HT-29 cells were incubated for 144 h with various concentrations (0-100 nM) of 1α,25-(OH)2D3, or the analogues EB1089, CB1093 or 1β,25-(OH)2D3. All these analogues except 1β,25-(OH)2D3 inhibited cell proliferation, but relative potencies and efficacies of EB1089 and CB1093 were much greater than that of the native vitamin. Cells grew in serum-free medium, reaching a plateau density at day 10 of culture, and addition of 10 nM 1α,25-(OH)2D3 or 1β,25-(OH)2D3 did not alter the long-term growth characteristics of HT-29 cells. However, cells treated with 10 nM EB1089 or CB1093 grew at a rate slower than control and reached final densities that were 53±1 and 36±2% lower than control, respectively. Immunoblot analysis of serum-free conditioned medium using a monoclonal anti-insulin-like growth factor-(IGF)-II antibody showed that both 10 nM EB1089 and CB1093 markedly inhibited secretion of both mature 7500 Mr and higher Mr forms of IGF-II. Ligand blot and immunoblot analyses of conditioned media revealed the presence of IGFBPs of Mr 24,000 (IGFBP-4), 30,000 (glycosylated IGFBP-4), 35,000 (IGFBP-2) and 32,000-34,000 (IGFBP-6). The level of IGFBP-2 was decreased by 42±8 and 49±7% by 10 nM EB 1089 and CB1093, respectively, compared to controls. IGFBP-6 was increased approximately twofold by EB1089 and CB1093, and exogenously added IGFBP-6 inhibited HT-29 cell proliferation. These results suggest that inhibition of HT-29 cell proliferation by EB1089 and CB1093 may be attributed, at least in part, to the decreased secretion of IGF-II. The increase in IGFBP-6 concentration coupled with its high affinity for IGF-II may also contribute to decreased cellular proliferation by an indirect mechanism involving sequestration of endogenously produced IGF-II.

Original languageEnglish (US)
Pages (from-to)141-149
Number of pages9
JournalMolecular and Cellular Endocrinology
Volume183
Issue number1-2
DOIs
StatePublished - Oct 25 2001

Keywords

  • 1α,25-Dihydroxyvitamin D3
  • CB1093
  • Colon cancer cells
  • EB1089
  • Insulin-like growth factor
  • Insulin-like growth factor binding proteins
  • Vitamin D

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Endocrinology

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