SL-327

SL-327 is a selective inhibitor of MEK1 and MEK2 with IC50 values of 0.18 and 0.22μM,  respectively.
MEK1 and MEK2 (ERK) are a kinase enzyme which phosphorylate mitogen-activated protein kinase (MAPK). Extracellular signal-regulated kinase (ERK) activity is essential for the acquisition of associative learning tasks.
In adult male CD-1 mice, SL-327 inhibited Pp-ERK immunostaining in the nuclei of the cells induced by cocaine. SL-327 pretreatment inhibited c-Fos expression in nuclear and inhibited activation of ERK within all the amygdala, namely LA, BLA, BMP, Ce and MePD [1]. In morphine-pretreated rats, SL-327 increased (58%) the expression of morphine-induced psychomotor sensitization (SW3) and fully prevented the upregulation of p-PEA-15, p-FADD, and p-Akt1 at SW3 [2]. In adult male DBA/2J mice, SL-327 significantly reduced pERK levels by 40% in both the motor cortex and dorsal striatum [3]. In rat model, SL-327 inhibited MAPK/ERK cascade, which prevented LTP-dependent gene induction and CREB and Elk-1 phosphorylation, resulting in rapidly decaying LTP [4].
References:
[1]. Radwanska K, Caboche J, Kaczmarek L. Extracellular signal-regulated kinases (ERKs) modulate cocaine-induced gene expression in the mouse amygdala. Eur J Neurosci, 2005, 22(4): 939-948.
[2]. Ramos-Miguel A, Esteban S, García-Sevilla JA. The time course of unconditioned morphine-induced psychomotor sensitization mirrors the phosphorylation of FADD and MEK/ERK in rat striatum: role of PEA-15 as a FADD-ERK binding partner in striatal plasticity. Eur Neuropsychopharmacol, 2010, 20(1): 49-64.
[3]. Groblewski PA, Franken FH, Cunningham CL. Inhibition of extracellular signal-regulated kinase (ERK) activity with SL327 does not prevent acquisition, expression, and extinction of ethanol-seeking behavior in mice. Behav Brain Res, 2011, 217(2): 399-407.
[4]. Davis S, Vanhoutte P, Pages C, et al. The MAPK/ERK cascade targets both Elk-1 and cAMP response element-binding protein to control long-term potentiation-dependent gene expression in the dentate gyrus in vivo. J Neurosci, 2000, 20(12): 4563-4572.

Effects of the MEK inhibitor, SL-327, on rewarding, motor- and cellular-activating effects of D-amphetamine and SKF-82958, and their augmentation by food restriction in rat.[Pubmed:18766328]

Psychopharmacology (Berl). 2009 Jan;201(4):495-506.

RATIONALE: Food restriction (FR) enhances learned and unlearned behavioral responses to drugs of abuse and increases D-1 dopamine (DA) receptor-mediated activation of extracellular signal-regulated kinases (ERK) 1/2 MAP kinase in nucleus accumbens (NAc). While a role has been established for ERK signaling in drug-mediated associative learning, it is not clear whether ERK regulates unconditioned behavioral effects of abused drugs. OBJECTIVES: The purpose of this study was to determine whether blockade of ERK signaling, using the brain-penetrant MEK inhibitor, SL-327, decreases behavioral or NAc cellular responses to acute drug treatment and their augmentation by FR. MATERIALS AND METHODS: Separate experiments assessed the effects of SL-327 (50 mg/kg, intraperitoneally) on (1) the reward-potentiating effect of D-amphetamine in an intracranial self-stimulation protocol, (2) the locomotor-activating effect of the D-1 agonist, SKF-82958, and (3) Fos-immunostaining induced in the NAc by SKF-82958. RESULTS: FR rats displayed enhanced responses to drug treatment on all measures. SL-327 had no effect on sensitivity to rewarding brain stimulation or the reward-potentiating effect of D-amphetamine. The MEK inhibitor, U0126, microinjected into the NAc was also without effect. The locomotor-activating effect of SKF-82958 was unaffected by SL-327. In contrast, SL-327 decreased NAc Fos-immunostaining and abolished the difference between feeding groups. CONCLUSIONS: These results support the conclusion that ERK signaling does not mediate unlearned behavioral responses to drug treatment. However, the upregulation of ERK and downstream transcriptional responses to acute drug treatment may underlie the reported enhancement of reward-related learning in FR subjects.

Significant neuroprotection against ischemic brain injury by inhibition of the MEK1 protein kinase in mice: exploration of potential mechanism associated with apoptosis.[Pubmed:12490588]

J Pharmacol Exp Ther. 2003 Jan;304(1):172-8.

MEK1/2 is a serine/threonine protein kinase that phosphorylates and activates extracellular signal-responsive kinase (ERK)1/2. In the present study we explored the role of MEK1/2 in ischemic brain injury using a selective MEK1/2 inhibitor, SL327, in mice. C57BL/6 mice were subjected to a 30-min occlusion of the middle cerebral artery (MCAO) followed by reperfusion. Western blot analysis demonstrated the immediate activation of MEK/ERK after reperfusion (within the first 10 min) in the ischemic brain; this activation was dose dependently blocked by SL327 (10-100 mg/kg, i.p.). A single dose of SL327 (100 mg/kg) administered 15 min before or 25 min after the onset of ischemia resulted in 63.6% (n = 18, p < 0.001) and 50.7% (n = 18, p < 0.01) reduction in infarct size, respectively, compared with vehicle-treated mice. Similarly, SL327 significantly reduced neurological deficits 1 to 3 days after reperfusion (n = 12, p < 0.01). The salutary effect of SL327-induced neuroprotection was independent of mitochondrial cytochrome c release or caspase-8-mediated apoptosis; however, SL327 markedly suppressed the levels of active caspase-3 and DNA fragmentation (as a measure of apoptosis) after ischemia/reperfusion. Our data suggest that the inhibition of MEK1/2 results in neuroprotection from reperfusion injury and that this protection may be associated with the reduction in apoptosis.

The MAPK/ERK cascade targets both Elk-1 and cAMP response element-binding protein to control long-term potentiation-dependent gene expression in the dentate gyrus in vivo.[Pubmed:10844026]

J Neurosci. 2000 Jun 15;20(12):4563-72.

The mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) signaling cascade contributes to synaptic plasticity and to long-term memory formation, yet whether MAPK/ERK controls activity-dependent gene expression critical for long-lasting changes at the synapse and what the events underlying transduction of the signal are remain uncertain. Here we show that induction of long-term potentiation (LTP) in the dentate gyrus in vivo leads to rapid phosphorylation and nuclear translocation of MAPK/ERK. Following a similar time course, the two downstream transcriptional targets of MAPK/ERK, cAMP response element-binding protein (CREB) and the ternary complex factor Elk-1, a key transcriptional-regulator of serum response element (SRE)-driven gene expression, were hyperphosphorylated and the immediate early gene zif268 was upregulated. The mRNA encoding MAP kinase phosphatase MKP-1 was upregulated at the time point when MAPK/ERK phosphorylation had returned to basal levels, suggesting a negative feedback loop to regulate deactivation of MAPK/ERK. We also show that inhibition of the MAPK/ERK cascade by the MAPK kinase MEK inhibitor SL327 prevented CREB and Elk-1 phosphorylation, and LTP-dependent gene induction, resulting in rapidly decaying LTP. In conclusion, we suggest that Elk-1 forms an important link in the MAP kinase pathway to transduce signals from the cell surface to the nucleus to activate the genetic machinery necessary for the maintenance of synaptic plasticity in the dentate gyrus. Thus, MAPK/ERK activation is required for LTP-dependent transcriptional regulation and we suggest this is regulated by two parallel signaling pathways, the MAPK/ERK-Elk-1 pathway targeting SRE and the MAPK/ERK-CREB pathway targeting CRE.

Regulation of cyclooxygenase-2 induction in the mouse uterus during decidualization. An event of early pregnancy.[Pubmed:10969080]

J Biol Chem. 2000 Nov 24;275(47):37086-92.

The infertility phenotype of cyclooxygenase-2 (Cox-2)-deficient female mice establishes the important role of Cox-2 in pregnancy. Cox-2 deficiency results in defective ovulation, fertilization, implantation, and decidualization; the latter of which can be restored in part by the prostacyclin analog carbaprostacyclin. Uterine Cox-2 expression during early pregnancy shows distinct localization and kinetics in the uterine luminal epithelium and underlying stromal cells, suggesting that expression is tightly regulated. Several intracellular signaling cascades including ERK, p38, and JNK are implicated in vitro as critical components of regulated Cox-2 expression in response to mitogens, growth factors, and cytokines. We investigated the involvement of these signaling pathways during Cox-2 induction in vivo by monitoring uterine kinase activity after intraluminal application of a deciduogenic stimulus. Our results show that the ERK and p38 pathways are activated in uterine preparations as early as 5-min post-stimulation. ERK activation was sustained for several hours with a return to baseline levels by 4 h. p38 activation was rapid with a peak at 5-min post-stimulation and returned to near baseline levels after 45 min. Systemic administration of a MEK inhibitor completely inhibited ERK activation, but did not affect early (2 h) luminal epithelial or late (24 h) stromal Cox-2 expression and only modestly affected decidualization. In contrast, administration of a p38 inhibitor modestly inhibited early Cox-2 expression in the luminal epithelium, while dramatically diminishing late stromal expression. In parallel, induced stromal peroxisomal proliferator activated receptor-delta (PPARdelta) expression is blunted by p38 inhibition. p38 inhibition also significantly inhibited decidualization. These results suggest that p38, but not ERK, activation is required for induced Cox-2 and PPARdelta expression during decidualization. In addition, inhibition of p38 led to decreased decidualization suggesting that an intracrine prostanoid pathway consisting of Cox-2, prostacyclin, and PPARdelta is required for maintenance of early pregnancy.