Anti-androgen flutamide suppresses hepatocellular carcinoma cell proliferation via the aryl hydrocarbon receptor mediated induction of transforming growth factor-β1

Abstract

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor and a member of the basic helix-loop-helix PER/ARNT/SIM family of chemosensors and developmental regulators. The AhR is widely known as a mediator of dioxin toxicity; however, it also suppresses cancer cell proliferation and recent findings have implicated its role as a tumor suppressor. We conducted a chemical library screen to identify nontoxic AhR ligands with anti-cancer effects and discovered flutamide (Eulexin) as a putative AhR ligand. Flutamide is an androgen receptor (AR) antagonist approved by the United States Food and Drug Administration for the treatment of prostate cancer. We found that flutamide inhibited the growth of several cancer cell lines independent of AR status, and that suppression of AhR expression reversed the anti-proliferative effects of flutamide. We investigated the AhR-dependent mechanism of action of flutamide in human hepatocellular carcinoma cells and identified that transforming growth factor-β1 (TGF-β1) is induced by flutamide in an AhR-dependent manner. In contrast, the potent AhR agonist 2,3,7,8-Tetrachlorodibenzo-p-dioxin had no effect on TGF-β1 expression, indicating the ligand specificity of AhR activation. We also determined that TGF-β1 induction is required for the AhR-dependent growth inhibitory effects of flutamide. Therefore, flutamide may be effective in AhR-positive cancers that are sensitive to TGF-β1 signaling, such as hepatocellular carcinoma.

The aryl hydrocarbon receptor is required for induction of p21cip1/waf1 expression and growth inhibition by SU5416 in hepatoma cells

“…The functional differences in AhR activation by TCDD and other AhR ligands [11, 27, 40–43] remains an important topic that continues to be investigated. Possibilities include modulation of the AhR in a ligand-selective manner to interact with distinct DNA-binding sequences, recruitment of new co-activator proteins, or induction of complementary cellular pathways that act in conjunction with the AhR signaling that result in AhR ligand-specific phenotypes.…”

The aryl hydrocarbon receptor (AhR) as a drug target for cancer chemotherapy

“…2) [55–58]. Flutamide, but not TCDD, induced TGFβ in liver cancer cells and this response was AhR-dependent [56]. Studies in this laboratory screened a panel of AhR-active pharmaceuticals, including 4-hydroxytamoxifen, flutamide, leflunomide, mexiletine, nimodiphine, omeprazole, sulindac and tranilast, in cell migration.…”

“…The results and mechanism of action were ligand-, tumor type-, response- and cell context-dependent. For example, in BT474 and MDA-MD-231 breast cancer cell lines, these compounds differentially induced CYP1A1 and CYP1B1 gene expression and, in ER-negative MDA-MB-468 cells, all of the AhR-active compounds except mexiletine and also TCDD inhibited migration [43,56,57]. In ER-negative MDA-MD-231 cells, TCDD and omeprazole, but not 4-hydroxytamoxifen, flutamide, leflunomide, mexiletine, nimodipine, sulindac and tranilast, inhibited migration and this was due, in part, to AhR-dependent downregulation of the pro-migration gene CXCR4 [43].…”

Androgen Receptor Could Be a Potential Therapeutic Target in Patients with Advanced Hepatocellular Carcinoma

“…AREs exist in the promoter region of vascular endothelial growth factor (VEGF) [8] and glucose-regulated protein 78 kDa (GRP78) [9], and they play a role in the growth of human hepatocytes. Transforming growth factor, beta 1 (TGF-β1) transcription is also activated by androgen and AR complex in hepatocytes [16,17]. This transcriptional activation function of AR is important in the normal sexual development of the male gender as well as the progression of cancer [8,14,18].…”