Biotransformation and protein binding of N-(4-hydroxyphenyl)retinamide in murine mammary epithelial cells

The biotransformation of N-(4-hydroxyphenyl)retinamide (HPR), and interactions of parent compound and/or metabolites with the cellular retinoid binding proteins (CRBPs) and cellular retinoic acid binding proteins (CRABPs) were examined in murine mammary tumor virus (MuMTV)-induced murine mammary tumor cells (GR-3A) grown in monolayer cell culture. Soluble fractions (cytosols) obtained from the extracts of GR-3A cells after high speed centrifugation were found to contain proteins of approx. 15,000 daltons which bound retinol and retinoic acid, but did not bind HPR or HPR metabolites. Moreover, HPLC analysis of GR-3A cell extracts demonstrated that [3H]retinol and [3H]retinoic acid were not detected in cells that had been exposed to [3H]HPR for 48 h. These findings, that under in vitro conditions there is no appreciable enzymatic hydrolysis of HPR to retinoic acid or conversion to retinol, suggests that the metabolism and cytological effects of HPR may be distinct from those of retinol or retinoic acid within murine mammary epithelial cells.