Biological evaluation of epoxy analogs of 1 alpha,25-dihydroxyvitamin D3.
The biological activity of 16-epoxy side-chain analogs of 1 alpha,25-dihydroxyvitamin D3, (1 alpha,25(OH)2D3) was evaluated in vitro and in vivo. Compared to 1 alpha,25(0H)2D3, all analogs had lower affinities for the pig duodenal vitamin D receptor and also for the human serum vitamin D binding protein. The in vitro effects on cell proliferation or differentiation of human promyeloid leukemia (induction of superoxide production in HL-60 cells), human osteosarcoma MG-63 cells (osteocalcin secretion), or human breast cancer cells (incorporation of thymidine in MCF-7 cells), was markedly inhibited by several epoxy analogs, compared to 1 alpha,25(OH)2D3, but the rank order of their activity widely varied among different cancer cells. The most potent analogs (24S,25S-24-hydroxy-25,26-epoxy-22-ene-1 alpha-OHD3, 25,26-epoxy-23-yne-1 alpha-OHD3, and 25,26-epoxy-23-yne-20-epi-1 alpha-OHD3 or compounds, 16, 5, and 7, respectively) were equipotent (16 and 5) or 30-fold (compound 7 on MG-63 cells) to 40-fold (compound 7 on MCF-7 cells) more active than 1 alpha,25-(OH)2D3. These analogs were nevertheless poorly antirachitic (< 3%) when tested in vitamin D-deficient chicks (using serum and bone calcium, serum osteocalcin and duodenal calbindin D-28K, as end points). Compound 7 was also 100-fold more active than 1 alpha,25-(OH)2D3 in inhibition of proliferation of human foreskin keratinocytes. Some epoxy analogs of 1 alpha,25-(OH)2D3 thus display interesting dissociations between their receptor affinity and their potency to induce cell differentiation, whereas their effect on cell proliferation/differentiation exceed their calcemic effects more than 100- to 1000-fold.
Laboratory of Experimental Medicine and Endocrinology, Gasthuisberg, Katholieke Universiteit Leuven, Belgium.
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K
Allewaert
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Zhao
J
J
Zhao
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F
Glibert
D
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Branisteanu
P
P
De Clercq
M
M
Vandewalle
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Bouillon
D000818:Animals; D002117:Calcitriol / Q000031:analogs & derivatives*; D002118:Calcium / Q000097:blood; D002454:Cell Differentiation / Q000187:drug effects; D002645:Chickens; D004852:Epoxy Compounds / Q000138:chemical synthesis* / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D015603:Keratinocytes / Q000166:cytology / Q000187:drug effects; D013329:Structure-Activity Relationship; D014407:Tumor Cells, Cultured
D004852:Epoxy Compounds; D002117:Calcitriol; D002118:Calcium