title: CYP24A1 inhibition facilitates the anti-tumor effect of vitamin D3 on colorectal cancer cells.
abstract: OBJECTIVE
  The effects of vitamin D3 have been investigated on various tumors, including colorectal cancer (CRC). 25-hydroxyvitamin-D3-24-hydroxylase (CYP24A1), the enzyme that inactivates the active vitamin D3 metabolite 1,25-dihydroxyvitamin D3 (1,25-D3), is considered to be the main enzyme determining the biological half-life of 1,25-D3. During colorectal carcinogenesis, the expression and concentration of CYP24A1 increases significantly, suggesting that this phenomenon could be responsible for the proposed efficacy of 1,25-D3 in the treatment of CRC. The aim of this study was to investigate the anti-tumor effects of vitamin D3 on the human CRC cell line Caco-2 after inhibition of the cytochrome P450 component of CYP24A1 activity.
  
  
  METHODS
  We examined the expression of CYP24A1 mRNA and the effects of 1,25-D3 on the cell line Caco-2 after inhibition of CYP24A1. Cell viability and proliferation were determined by means of sulforhodamine-B staining and bromodeoxyuridine incorporation, respectively, while cytotoxicity was estimated via the lactate dehydrogenase content of the cell culture supernatant. CYP24A1 expression was measured by real-time reverse transcription polymerase chain reaction. A number of tetralone compounds were synthesized to investigate their CP24A1 inhibitory activity.
  
  
  RESULTS
  In response to 1,25-D3, CYP24A1 mRNA expression was enhanced significantly, in a time- and dose-dependent manner. Caco-2 cell viability and proliferation were not influenced by the administration of 1,25-D3 alone, but were markedly reduced by co-administration of 1,25-D3 and KD-35, a CYP24A1-inhibiting tetralone. Our data suggest that the mechanism of action of co-administered KD-35 and 1,25-D3 does not involve a direct cytotoxic effect, but rather the inhibition of cell proliferation.
  
  
  CONCLUSIONS
  These findings demonstrate that the selective inhibition of CYP24A1 by compounds such as KD-35 may be a new approach for enhancement of the anti-tumor effect of 1,25-D3 on CRC.
authors.affiliation: 1st Department of Internal Medicine, Semmelweis University, H-1083 Budapest, Hungary. jkosa@bel1.sote.hu
authors.forename: János P
authors.initials: JP
authors.lastname: Kósa
authors.forename: Péter
authors.initials: P
authors.lastname: Horváth
authors.forename: János
authors.initials: J
authors.lastname: Wölfling
authors.forename: Dóra
authors.initials: D
authors.lastname: Kovács
authors.forename: Bernadett
authors.initials: B
authors.lastname: Balla
authors.forename: Péter
authors.initials: P
authors.lastname: Mátyus
authors.forename: Evelin
authors.initials: E
authors.lastname: Horváth
authors.forename: Gábor
authors.initials: G
authors.lastname: Speer
authors.forename: István
authors.initials: I
authors.lastname: Takács
authors.forename: Zsolt
authors.initials: Z
authors.lastname: Nagy
authors.forename: Henrik
authors.initials: H
authors.lastname: Horváth
authors.forename: Péter
authors.initials: P
authors.lastname: Lakatos
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D018938:Caco-2 Cells; D002117:Calcitriol / Q000494:pharmacology*; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D015179:Colorectal Neoplasms / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D004305:Dose-Response Relationship, Drug; D004790:Enzyme Induction; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006801:Humans; D012333:RNA, Messenger / Q000096:biosynthesis; D013250:Steroid Hydroxylases / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000235:genetics; D044024:Tetralones / Q000494:pharmacology*; D013997:Time Factors; D065668:Vitamin D3 24-Hydroxylase
chemical_list: D000970:Antineoplastic Agents; D004791:Enzyme Inhibitors; D012333:RNA, Messenger; D044024:Tetralones; D013250:Steroid Hydroxylases; C585549:CYP24A1 protein, human; D065668:Vitamin D3 24-Hydroxylase; D002117:Calcitriol
keywords: CYP24A1 inhibition; Caco-2 cell culture; Colorectal cancer; Tetralone derivatives; Vitamin D3