TitleThe aryl hydrocarbon receptor mediates leflunomide-induced growth inhibition of melanoma cells.
Publication TypeJournal Article
Year of Publication2012
AuthorsO'Donnell, EF, Kopparapu, PRao, Koch, DC, Jang, HSang, Phillips, JLynne, Tanguay, RL, Kerkvliet, NI, Kolluri, SKumar
JournalPLoS One
Date Published2012
KeywordsAniline Compounds, Cell Line, Tumor, Cell Proliferation, Cyclin-Dependent Kinase Inhibitor p21, Fluoresceins, Gene Knockdown Techniques, Humans, Hydroxybutyrates, Isoxazoles, Leflunomide, Melanoma, Oxidoreductases Acting on CH-CH Group Donors, Proto-Oncogene Proteins c-myc, Receptors, Aryl Hydrocarbon, Signal Transduction, Succinimides, Uridine

A novel role of the dihydroorotatedehydrogenase (DHODH) inhibitor leflunomide as a potential anti-melanoma therapy was recently reported (Nature 471:518-22, 2011). We previously reported that leflunomide strongly activates the transcriptional activity of the Aryl Hydrocarbon Receptor (AhR). We therefore tested whether the AhR regulates the anti-proliferative effects of leflunomide in melanoma. We first evaluated the expression of AhR in melanoma cells and found that AhR is highly expressed in A375 melanoma as well as in several other cancer cell types. To evaluate whether AhR plays a role in regulating the growth inhibitory effects of leflunomide in A375 cells, we generated a stable cell line from parental A375 cells expressing a doxycycline (DOX) inducible AhR shRNA. Using these cells in the absence or presence of DOX (normal AhR levels or AhR-knockdown, respectively) we found that the anti-proliferative effects of leflunomide, but not its metabolite A771726, were strongly dependent upon AhR expression. It has been well established that supplementation of cells with exogenous uridine completely rescues the anti-proliferative effects due to DHODH inhibition. Thus, we performed uridine rescue experiments in A375 cells to determine whether the anti-proliferative effects of leflunomide are solely due to DHODH inhibition as previously reported. Interestingly, saturating levels of uridine only modestly rescued A375 cells from the anti-proliferative effects of both leflunomide and A771726, indicating additional mechanism(s), apart from DHODH inhibition are responsible for the anti-proliferative effects of leflunomide in melanoma cells. Uridine also did not rescue MDA-MB-435S melanoma cell proliferation after leflunomide treatment. Our results reveal that the AhR is a molecular target of leflunomide and support the feasibility of the clinical application of leflunomide for treating melanoma. Furthermore, analysis of expression data from 967 cancer cell lines revealed that AhR is expressed in multiple different cancer types supporting the intriguing possibility of targeting the AhR for therapy in a number of cancers.

Alternate JournalPLoS ONE
PubMed ID22815870
PubMed Central IDPMC3398955
Grant ListES019000 / ES / NIEHS NIH HHS / United States
F31CA144571 / CA / NCI NIH HHS / United States
P30 ES00210 / ES / NIEHS NIH HHS / United States
R21 ES019000 / ES / NIEHS NIH HHS / United States
R01 ES016651 / ES / NIEHS NIH HHS / United States
ES016651 / ES / NIEHS NIH HHS / United States
T32ES07060 / ES / NIEHS NIH HHS / United States
F31 CA144571 / CA / NCI NIH HHS / United States
T32 ES007060 / ES / NIEHS NIH HHS / United States
P30 ES000210 / ES / NIEHS NIH HHS / United States