Hydrolysis of 4-HPR to atRA occurs in vivo but is not required for retinamide-induced apoptosis

• Published in: Archives of biochemistry and biophysics Vol. 419; no. 2; pp. 234 - 243
• Main Authors: Chapman, Jason S, Weiss, Kevin L, Curley, Robert W, Highland, Margaret A, Clagett-Dame, Margaret
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15.11.2003
• Subjects: 4-HBR; 4-HPR; Administration, Oral; Animals; Apoptosis; Apoptosis - drug effects; Apoptosis - physiology; Body Weight - drug effects; Body Weight - physiology; Breast cancer; Breast Neoplasms - pathology; Breast Neoplasms - physiopathology; Cell Line, Tumor; Cell Survival - drug effects; CYP26B1; Dose-Response Relationship, Drug; Fenretinide - administration & dosage; HPLC; Humans; Hydrolysis; Male; Metabolism; Rats; Rats, Sprague-Dawley; Reporter assay; Retinoic acid; Tretinoin - administration & dosage; Tretinoin - analogs & derivatives; Tretinoin - blood; Vitamin A; Vitamin A - administration & dosage; Vitamin A - analogs & derivatives; Vitamin A Deficiency - drug therapy; Vitamin A Deficiency - physiopathology; Vitamin A; CYP26B1; 4-HPR; Reporter assay; Breast cancer; Metabolism; Retinoic acid; 4-HBR; HPLC; Apoptosis
• ISSN: 0003-9861; 1096-0384
• DOI: 10.1016/j.abb.2003.09.001

The retinamide, N-(4-hydroxyphenyl)retinamide (4-HPR), has shown promising anti-tumor activity, but it is unclear whether this compound is hydrolyzed to all- trans retinoic acid (atRA) and if so, whether this plays any role in its chemotherapeutic activity. To address this issue, the ability of 4-hydroxybenzylretinone (4-HBR), a carbon-linked analog of 4-HPR, to support growth in vitamin A-deficient (VAD) animals and to activate an atRA-responsive gene in vivo was compared to 4-HPR and atRA. Further, the non-hydrolyzable 4-HBR analog was used to determine whether the presence of the labile amide linkage in 4-HPR is essential for the induction of apoptosis in cultured MCF-7 breast cancer cells. Studies in VAD rats showed that 4-HPR, like atRA, supports animal growth and induces CYP26B1 mRNA expression in lung whereas 4-HBR does not. Analysis of plasma from 4-HPR- and atRA-treated VAD animals revealed the presence of atRA whereas it was not detected in plasma from animals given 4-HBR. To determine whether hydrolysis to atRA is necessary for apoptosis induced by 4-HPR in MCF-7 breast cancer cells, morphological and biochemical assays for apoptosis were performed. 4-HBR, like 4-HPR, induced apoptosis in MCF-7 cells. Apoptosis was not induced even at high concentrations of atRA, showing that 4-HPR and 4-HBR act in cells via a distinct signaling pathway. These results show that although limited hydrolysis of 4-HPR occurs in vivo, the ability to liberate atRA is not required for these 4-hydroxyphenyl retinoids to induce apoptosis in MCF-7 breast cancer cells. Thus the non-hydrolyzable analog, 4-HBR, may have significant therapeutic advantage over 4-HPR because it does not liberate atRA that can contribute to the adverse side effects of drug administration in vivo.