title: N-(4-hydroxyphenyl)retinamide (4-HPR)-mediated biological actions involve retinoid receptor-independent pathways in human breast carcinoma.
abstract: Retinoid response pathways involve retinoic acid receptors (RARs) and retinoid X receptors. N-(4-hydroxyphenyl) retinamide (4-HPR), a derivative of all-trans-retinoic acid (RA) is currently in clinical trials as a chemopreventive agent for breast cancer. The issue whether 4-HPR mediates its biological actions via classical retinoid receptor pathways remains to be investigated. In this study, we provide several lines of evidence that 4-HPR mediates its biological actions via a novel pathway(s) that does not involve the classical retinoid receptor pathways. For example, 4-HPR was more potent than RA as an antiproliferative agent and inhibited growth of otherwise RA-resistant human breast carcinoma cells. Exposure to 4-HPR resulted in the generation of DNA fragmentation with subsequent cell death in both RA-positive estrogen receptor (ER)-positive as well as RA-refractory ER-negative breast carcinoma cell lines. N-(4-Methoxyphenyl)retinamide (4-MPR), which is the major 4-HPR metabolite in circulation, was biologically inert in this system. 4-HPR and 4-MPR bound poorly to the RAR alpha, beta and gamma in vitro and only minimally activated the retinoic acid receptor element (RARE) and retinoid X receptor response elements (RXREs) in human breast carcinoma cells. Neither 4-HPR nor 4-MPR are metabolized to any of the known conventional retinoids. In addition, 4-HPR or 4-MPR transactivation of RAREs or RXREs transfected into MCF-7 and MDA-MB-231 cells was not noted at 48 h. Nevertheless 4-HPR-mediated cell death was observed at 48 h, further suggesting that neither 4-HPR nor 4-MPR are metabolized to retinoids which activate the RAREs or RXREs in breast carcinoma cells. Furthermore, unlike RA, which exhibited anti-AP1 activity, 4-HPR inhibition of growth did not involve anti-AP1 activity. These results suggest that 4-HPR acts by a unique pathway that is not mediated by retinoid receptors.
authors.affiliation: Department of Medicine, University of Maryland Cancer Center, USA.
authors.forename: M S
authors.initials: MS
authors.lastname: Sheikh
authors.forename: Z M
authors.initials: ZM
authors.lastname: Shao
authors.forename: X S
authors.initials: XS
authors.lastname: Li
authors.forename: J V
authors.initials: JV
authors.lastname: Ordonez
authors.forename: B A
authors.initials: BA
authors.lastname: Conley
authors.forename: S
authors.initials: S
authors.lastname: Wu
authors.forename: M I
authors.initials: MI
authors.lastname: Dawson
authors.forename: Q X
authors.initials: QX
authors.lastname: Han
authors.forename: W R
authors.initials: WR
authors.lastname: Chao
authors.forename: T
authors.initials: T
authors.lastname: Quick
mesh_terms: D016588:Anticarcinogenic Agents / Q000494:pharmacology*; D001943:Breast Neoplasms; D002455:Cell Division / Q000187:drug effects*; D002460:Cell Line; D019008:Drug Resistance, Neoplasm; D005260:Female; D017313:Fenretinide / Q000494:pharmacology*; D006801:Humans; D007700:Kinetics; D018168:Receptors, Retinoic Acid / Q000502:physiology*; D047488:Retinoid X Receptors; D014157:Transcription Factors / Q000502:physiology; D014212:Tretinoin / Q000031:analogs & derivatives / Q000494:pharmacology; D014407:Tumor Cells, Cultured
chemical_list: D016588:Anticarcinogenic Agents; D018168:Receptors, Retinoic Acid; D047488:Retinoid X Receptors; D014157:Transcription Factors; D017313:Fenretinide; D014212:Tretinoin; C058346:N-(4-methoxyphenyl)retinamide