PD98059 Is an Equipotent Antagonist of the Aryl Hydrocarbon Receptor and Inhibitor of Mitogen-Activated Protein Kinase Kinase

Abstract

PD98059 [2-(2'-amino-3'-methoxyphenyl)-oxanaphthalen-4-one] is a flavonoid and a potent inhibitor of mitogen-activated protein kinase kinase (MEK). Concentrations of PD98059 of </=20 muM were not cytotoxic to cultures of the immortalized human breast epithelial cell line MCF10A. The agent was weakly cytostatic at concentrations of >/=10 microM. In vivo exposure of cultures to </=20 microM PD98059 for 2-22 hr did not affect overall extracellular signal-regulated kinase contents; however, exposure to PD98059 resulted in a rapid loss (>95%) of the dually phosphorylated forms of extracellular signal-regulated kinase (IC50 = 1 muM). Treatment of cultures with PD98059 of >/=1 muM either at the time of addition or up to 48 hr before the addition of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) suppressed in a concentration-dependent manner the accumulation of induced steady state CYP1A1, CYP1B1, and NQO1 mRNAs. The addition of PD98059 to rat liver cytosol just before the addition of TCDD suppressed TCDD binding (IC50 = 4 muM) and aryl hydrocarbon receptor (AHR) transformation (IC50 = 1 muM), as measured by sucrose gradient centrifugation and electrophoretic mobility shift assays. Flavone and flavanone, two closely related structural analogs of PD98059, inhibited AHR transformation by TCDD with IC50 values similar to that obtained with PD98059. However, neither analog was as potent as PD98059 in inhibiting MEK (IC50 approximately 190 muM for both). These results suggest that PD98059 is a ligand for the AHR and functions as an AHR antagonist at concentrations commonly used to inhibit MEK and signaling processes that entail MEK activation.

ERK Kinase Inhibition Stabilizes the Aryl Hydrocarbon Receptor

“…However, the underlying mechanisms linking kinase control and Ah receptor directed gene transcription are blurred by findings that most kinase inhibitors also inhibit ligand binding to the Ah receptor (23,24). For example, PD98059, an Erk kinase inhibitor with structural similarity to Ah receptor inhibitory flavonoids (25), directly interferes with TCDD binding to the Ah receptor (24). Similar findings have been observed with the pyridinyl imidazole compounds that are used as tools to inhibit p38 MAP kinase.…”

“…1B). This can be explained in part because PD98059 is a competitive inhibitor of the Ah receptor (24). However, treatment with U0126 did not block B[a]P-7,8-dihydodiol-induced apoptosis, as determined by DNA fragmentation and PARP-1 cleavage (Fig.…”

“…PD98059 blocks apoptosis, but this can be explained by the findings that PD98059 is a competitive antagonist of the Ah receptor and through this mechanism inhibits Cyp1a1 induction. Although U0126 completely inhibits BPDE-2 induced apoptosis, it has no ability to prevent cell death when cells are treated with (24). Because PD98059 is unable to activate the cytosolic Ah receptor, it is considered an antagonist, whereas ␤-naphthoflavone and TCDF are known agonists.…”

“…Recent evidence has also demonstrated that pyridinyl imidazole compounds, inhibitors of p38 MAP kinase activity, weakly inhibit histone acetyltransferase activity, potentially inhibiting TCDD induction of Cyp1a1 transcription (22). However, the underlying mechanisms linking kinase control and Ah receptor directed gene transcription are blurred by findings that most kinase inhibitors also inhibit ligand binding to the Ah receptor (23,24). For example, PD98059, an Erk kinase inhibitor with structural similarity to Ah receptor inhibitory flavonoids (25), directly interferes with TCDD binding to the Ah receptor (24).…”

Variable apoptotic response of NSCLC cells to inhibition of the MEK/ERK pathway by small molecules or dominant negative mutants

“…Although there are no published data on effects of U0126 on substrates outside the MAPK family, PD98059 has equipotent effects on inhibiting MEK, cyclooxygenase (COX) 1 and 2, and the aryl hydrocarbon receptor. 24,25 Inhibition of COX-2 by MEK inhibitors is unlikely to explain the cytostatic effects of the MEK inhibitors, however, because other investigators have shown that COX-2 inhibitors are cytotoxic to NSCLC cells, with and without chemotherapy. 26,27 In contrast to PD98059, nonspecific effects of DNMs toward inhibition of other targets have not been described.…”