DIFFERENTIATION-RELATED PATHWAYS OF 1-ALPHA,25-DIHYDROXYCHOLECALCIFEROL METABOLISM IN HUMAN COLON ADENOCARCINOMA-DERIVED CACO-2 CELLS - PRODUCTION OF 1-ALPHA,25-DIHYDROXY-3EPI-CHOLECALCIFEROL

We used the human colon adenocarcinoma-derived cell line Caco-2, which spontaneously differentiates in vitro, as a model system to investiga te the metabolism of 1 alpha,25-dihycaroxycholecalciferol in colon can cer cells. Subconfluent proliferating and conauent differentiating cel ls were incubated with 1 mu M,25-dihydroxycholecalciferol for a period of 24 to 48 h. HPLC analysis of the lipid extract of both cells and m edia was performed to isolate and identify the various metabolites of 1 alpha,25-dihydroxycholecalciferol. Undifferentiated, highly prolifer ating Caco-2 cells metabolized 1 alpha,25-dihydroxycholecalciferol int o several side chain modified metabolites formed through the C-24 oxid ation pathway. In contrast, no metabolites of the C-24 oxidation pathw ay were identified in differentiated Caco-2 cells. However, differenti ated cells produced significant amounts of a metabolite which was less polar than 1 alpha,25-dihydroxycholecalciferol on a straight phase HP LC system. This metabolite was identified as 1 alpha,25-dihydroxy-3 al pha-cholecaleiferol by comigration with a synthetic standard on two di fferent HPLC systems and gas chromatography-mass spectrometry. Thus, w e were able to demonstrate that the state of differentiation has a pro found influence on 1 alpha,25-dihydroxycholecalciferol metabolism in c olon cancer cells. (C) 1998 Academic Press.