Transient induction of cytochromes P450 1A1 and 1B1 in MCF-7 human breast cancer cells by indirubin

• Published in: Biochemical pharmacology Vol. 66; no. 12; pp. 2313 - 2321
• Main Authors: Spink, Barbara C., Hussain, Mirza M., Katz, Barbara H., Eisele, Leslie, Spink, David C.
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 15-12-2003; Elsevier Science
• Subjects: Antibiotics, Antineoplastic - pharmacology; Aryl Hydrocarbon Hydroxylases - biosynthesis; Aryl hydrocarbon receptor; Biological and medical sciences; Breast Neoplasms - pathology; CYP1A1; CYP1B1; Cytochrome P-450 CYP1A1 - biosynthesis; Cytochrome P-450 CYP1B1; Cytochrome P450; Enzyme Induction - drug effects; Estrogens - metabolism; Female; Humans; Indirubin; Indoles - pharmacology; Medical sciences; Pharmacology. Drug treatments; Polychlorinated Dibenzodioxins - pharmacology; Promoter Regions, Genetic - drug effects; Real-time PCR; Receptors, Aryl Hydrocarbon - agonists; RNA, Messenger - biosynthesis; RNA, Messenger - drug effects; Tumor Cells, Cultured; EROD; OR; Indirubin; Cytochrome P450; TCDD; AhR; DMEM; Aryl hydrocarbon receptor; Real-time PCR; DRE; E 2; CYP1A1; MeOE 2; CYP1B1; SEM; CYP; HPLC; Human; Mammary gland diseases; Pharmacology; Breast cancer; Malignant tumor; Biological receptor
• ISSN: 0006-2952; 1873-2968
• DOI: 10.1016/j.bcp.2003.08.019

The aryl hydrocarbon receptor (AhR), when activated by exogenous ligands such as 2,3,7,8-tetrachlorodibenzo-
p-dioxin (TCDD), regulates expression of several phase I and phase II enzymes and is also involved in the regulation of cell proliferation. Several studies suggest that endogenous AhR ligand(s) may exist. One putative endogenous ligand is indirubin, which was recently identified in human urine and bovine serum. We determined the effect of indirubin in MCF-7 breast cancer cells on induction of the activities of cytochromes P450 (CYP) 1A1 and 1B1, as measured by estradiol and ethoxyresorufin metabolism, and on induction of the CYP1A1 and CYP1B1 mRNAs. With 4-hr exposure, the effects of indirubin and TCDD at 10
nM on CYP activity were comparable, but the effects of indirubin, unlike those of TCDD, were transitory. Indirubin-induced ethoxyresorufin-
O-deethylase activity was maximal by 6–9
hr post-exposure and had disappeared by 24
hr, whereas TCDD-induced activities remained elevated for at least 72
hr. The effects of indirubin on CYP mRNA induction were maximal at 3
hr. Indirubin was metabolized by microsomes containing cDNA-expressed human CYP1A1 or CYP1B1. The potency of indirubin was comparable to that of TCDD in a CYP1B1-promoter-driven luciferase assay, when MCF-7 cells were co-exposed to the AhR ligands together with the CYP inhibitor, ellipticine. Thus, if indirubin is an endogenous AhR ligand, then AhR-mediated signaling by indirubin is likely to be transient and tightly controlled by the ability of indirubin to induce CYP1A1 and CYP1B1, and hence its own metabolism.