Biological characterization of ARRY-142886 (AZD6244), a potent, highly selective mitogen-activated protein kinase kinase 1/2 inhibitor

PURPOSE

The Ras-Raf-mitogen-activated protein kinase kinase (MEK) pathway is overactive in many human cancers and is thus a target for novel therapeutics. We have developed a highly potent and selective inhibitor of MEK1/2. The purpose of these studies has been to show the biological efficacy of ARRY-142886 (AZD6244) in enzymatic, cellular, and animal models.

EXPERIMENTAL DESIGN

The ability of ARRY-142886 to inhibit purified MEK1 as well as other kinases was evaluated. Its effects on extracellular signal-regulated kinase (ERK) phosphorylation and proliferation in several cell lines were also determined. Finally, the inhibitor was tested in HT-29 (colorectal) and BxPC3 (pancreatic) xenograft tumor models.

RESULTS

The IC(50) of ARRY-142886 was determined to be 14 nmol/L against purified MEK1. This activity is not competitive with ATP, which is consistent with the high specificity of compound for MEK1/2. Basal and epidermal growth factor-induced ERK1/2 phosphorylation was inhibited in several cell lines as well as 12-O-tetradecanoylphorbol-13-acetate-induced ERK1/2 phosphorylation in isolated peripheral blood mononuclear cells. Treatment with ARRY-142886 resulted in the growth inhibition of several cell lines containing B-Raf and Ras mutations but had no effect on a normal fibroblast cell line. When dosed orally, ARRY-142886 was capable of inhibiting both ERK1/2 phosphorylation and growth of HT-29 xenograft tumors in nude mice. Tumor regressions were also seen in a BxPC3 xenograft model. In addition, tumors remained responsive to growth inhibition after a 7-day dosing holiday.

CONCLUSIONS

ARRY-142886 is a potent and selective MEK1/2 inhibitor that is highly active in both in vitro and in vivo tumor models. This compound is currently being investigated in clinical studies.

7,8-Dihydroxy-4-methylcoumarin induces apoptosis of human lung adenocarcinoma cells by ROS-independent mitochondrial pathway through partial inhibition of ERK/MAPK signaling

Coumarins have attracted intense interest in recent years because they have been identified from natural sources, especially green plants and have diverse pharmacological properties. In this study, we investigated whether 7,8-dihydroxy-4-methylcoumarin (DHMC) caused apoptosis in A549 human non-small cell lung carcinoma cells (NSCLC) and, if so, by what mechanisms. Here, we show that, in A549 human NSCLC cells, DHMC induces apoptosis through mitochondria-mediated caspase-dependent pathway. Although an increase in the levels of reactive oxygen species (ROS) was observed, pre-treatment with antioxidant showed no protective effect against DHMC-induced apoptosis. In addition, our immunoblot data revealed that DHMC treatment led to down-regulation of Bcl-xl, Bax, p21, Cox-2, p53 and upregulation of c-Myc. Results in the present study for the first time suggest that DHMC induces apoptosis in human lung A549 cells through partial inhibition of ERK/MAPK signaling.

MEK-ERK inhibition corrects the defect in VLDL assembly in HepG2 cells: potential role of ERK in VLDL-ApoB100 particle assembly

OBJECTIVE

Hepatic VLDL assembly is defective in HepG2 cells, resulting in the secretion of immature triglyceride-poor LDL-sized apoB particles. We investigated the mechanisms underlying defective VLDL assembly in HepG2 and have obtained evidence implicating the MEK-ERK pathway.

METHODS AND RESULTS

HepG2 cells exhibited considerably higher levels of the ERK1/2 mass and activity compared with primary hepatocytes. Inhibition of ERK1/2 using the MEK1/MEK2 inhibitor, U0126 (but not the inactive analogue) led to a significant increase in apoB secretion. In the presence of oleic acid, ERK1/2 inhibition caused a major shift in the lipoprotein distribution with a majority of particles secreted as VLDL, an effect independent of insulin. In contrast, overexpression of constitutively active MEK1 decreased apoB and large VLDL secretion. MEK1/2 inhibition significantly increased both cellular and microsomal TG mass, and mRNA levels for DGAT-1 and DGAT-2. In contrast to ERK, modulation of the PI3-K pathway or inhibition of the p38 MAP kinase, had no effect on lipoprotein density profile. Modulation of the MEK-ERK pathway in primary hamster hepatocytes led to changes in apoB secretion and altered the density profile of apoB-containing lipoproteins.

CONCLUSIONS

Inhibition of the overactive ras-MEK-ERK pathway in HepG2 cells can correct the defect in VLDL assembly leading to the secretion of large, VLDL-sized particles, similar to primary hepatocytes, implicating the MEK-ERK cascade in VLDL assembly in the HepG2 model. Modulation of this pathway in primary hepatocytes also regulates apoB secretion and appears to alter the formation of VLDL-1 sized particles.

Regulation of Drosophila p38 activation by specific MAP2 kinase and MAP3 kinase in response to different stimuli

The p38 mitogen-activated protein kinase (MAPK) signaling pathway plays an important role in cellular responses to inflammatory stimuli and environmental stress. Activation of p38 is mediated through phosphorylation by upstream MAPKK, which in turn is activated by MAPKKK. However, the mechanism of how different upstream MAP2Ks and MAP3Ks specifically contribute to p38 activation in response to different stimuli is still not clearly understood. By using double-stranded RNA-mediated interference (RNAi) in Drosophila cells, we demonstrate that D-MKK3 is a major MAP2K responsible for D-p38 activation by UV, heat shock, NaCl or peptiodglycan (PGN). Stimulation of UV and PGN activates D-p38 through D-MEKK1, heat shock-induced activation of D-p38 signals through both D-MEKK1 and D-ASK1. On the other hand, maximal activation of D-p38 by NaCl requires the expression of four MAP3Ks.

Inhibitors of the mitogen-activated protein kinase kinase 1/2 signaling pathway clear prion-infected cells from PrPSc

Prions represent a unique class of infectious agents in which the normal cellular prion protein (PrPC) is converted to an abnormal isoform (PrPSc), which accumulates in the brain and constitutes the major, if not the only, component of the infectious particle. Factors that still remain to be identified may facilitate the conversion of PrPC to PrPSc. In the present study, we first demonstrated that a growth factor of the neurotrophin family, brain-derived neurotrophic factor (BDNF), stimulates the formation of PrPSc in a gonadotropin-releasing hormone-secreting neuronal cell line (GT1-1 cells) infected with the Rocky Mountain Laboratory (RML) strain of scrapie as determined by Western blot analysis. We then observed that the prion-infected cells can be cleared from PrPSc by treatment with three inhibitors of mitogen-activated protein kinase kinase 1/2 (MEK1/2) [1,4-diamino-2,3-dicyano-1,4-bis(o-aminophenylmercapto)butadiene and 2-(2-amino-3-methyoxyphenyl)-4H-1-benzopyran-4-one, as well as alpha-[amino[(4-aminophenyl)thio]methylene]-2-(trifluoromethyl) benzeneacetonitrile, which passes the blood-brain barrier], a component of one of the intracellular signaling pathways activated by BDNF. The MEK1/2 inhibitors were also efficient in clearing PrPSc from prion-infected GT1-1 cells stimulated to accumulate high levels of PrPSc by enhanced serum concentrations in the medium or by the use of a serum-free neuron-specific neurobasal medium. PrPSc did not reappear in the cultures within 5 weeks after completion of treatment. We conclude that inhibitors of the MEK1/2 pathway can efficiently and probably irreversibly clear PrP(Sc) from prion-infected cells. The MEK pathway may therefore be a suitable target for therapeutic intervention in prion diseases.

Angiotensin II Elevates Nitric Oxide Synthase 3 Expression and Nitric Oxide Production Via a Mitogen-Activated Protein Kinase Cascade in Ovine Fetoplacental Artery Endothelial Cells1

Normal pregnancy is associated with high angiotensin II (ANG II) concentrations in the maternal and fetal circulation. These high levels of ANG II may promote production vasodilators such as nitric oxide (NO). ANG II receptors are expressed in ovine fetoplacental artery endothelial (OFPAE) cells and mediate ANG II-stimulated OFPAE cell proliferation. Herein, we tested whether ANG II stimulated NO synthase 3 (NOS3, also known as eNOS) expression and total NO (NO(x)) production via activation of mitogen-activated protein kinase 3/1 (MAPK3/1, also known as ERK1/2) in OFPAE cells. ANG II elevated (P < 0.05) eNOS protein, but not mRNA levels with a maximum effect at 10 nM. ANG II also dose dependently increased (P < 0.05) NO(x) production with a maximal effect at doses of 1-100 nM. Activation of ERK1/2 by ANG II was determined by immunocytochemistry and Western blot analysis. ANG II rapidly induced positive staining for phosphorylated ERK1/2, appearing in cytosol after 1-5 min of ANG II treatment, accumulating in nuclei after 10 min, and disappearing at 15 min. ANG II increased (P < 0.05) phosphorylated ERK1/2 protein levels. Activation of ERK1/2 was confirmed by an immunocomplex kinase assay using ELK1 as a substrate. PD98059 significantly inhibited ANG II-induced ERK1/2 activation, and the ANG II-elevated eNOS protein levels but only partially reduced ANG II-increased NO(x) production. Thus, in OFPAE cells, the ANG II increased NO(x) production is associated with elevated eNOS protein expression, which is mediated at least in part via activation of the mitogen-activated protein kinase kinase1 and kinase2 (MAP2K1 and MAP2K2, known also as MEK1/2)/ERK1/2 cascade. Together with our previous observation that ANG II stimulates OFPAE cell proliferation, these data suggest that ANG II is a key regulator for both vasodilation and angiogenesis in the ovine fetoplacenta.

Activation of hypothalamic ATP-sensitive K+ channels by the aminoguanidine carboxylate BVT.12777

Derivatives of 3-guanidinopropionic acid, such as leptin, reduce body weight in obese, diabetic mice. We have assessed whether one of these analogues, BVT.12777 activates intracellular signalling pathways in the arcuate nucleus in a manner analogous to leptin and insulin. In addition, because these hormones have been shown to activate K(ATP) channels in a subset of arcuate neurones, we examined whether this channel is also a functional endpoint for BVT.12777 in the arcuate nucleus. BVT.12777 transiently increased phosphorylation of MAPK, STAT3, PKB and GSK3, in a manner identical to that observed for leptin and insulin. BVT.12777 also hyperpolarized glucose-responsive neurones by increasing the activity of K(ATP) channels. The increase in K(ATP) activity driven by BVT.12777 was PI3-kinase independent, unlike leptin and insulin activation of this channel, and could also be elicited in isolated patches. However, K(ATP) activity induced by BVT.12777 was dependent on actin filament dynamics, both in intact neurones and isolated patches. Thus, BVT.12777 modulates arcuate neurone K(ATP) activity by re-organization of the cytoskeleton, a mechanism that has also been ascribed to leptin and insulin. Consequently, BVT.12777 appears to act as a leptin and insulin mimetic with respect to at least some elements of arcuate neurone intracellular signalling and the activation of K(ATP) channels. Resistance to leptin and insulin, associated with obesity has, at least in part, been postulated to be due to aberrant intracellular signalling in arcuate neurones. The data presented here indicate that it may be possible to develop drugs, which by-pass up-stream signalling components associated with adiposity hormone resistance, such as PI3-kinase, but can still induce functional outputs from arcuate neurones by targeting downstream components of the leptin and insulin signalling cascades.