Gi/o GPCRs drive the formation of actin-rich tunneling nanotubes in cancer cells via a Gβγ/PKCα/FARP1/Cdc42 axis

The functional association between stimulation of G-protein-coupled receptors (GPCRs) by eicosanoids and actin cytoskeleton reorganization remains largely unexplored. Using a model of human adrenocortical cancer cells, here we established that activation of the GPCR OXER1 by its natural agonist, the eicosanoid 5-oxo-eicosatetraenoic acid, leads to the formation of filopodia-like elongated projections connecting adjacent cells, known as tunneling nanotube (TNT)-like structures. This effect is reduced by pertussis toxin and GUE1654, a biased antagonist for the Gβγ pathway downstream of OXER1 activation. We also observed pertussis toxin-dependent TNT biogenesis in response to lysophosphatidic acid, indicative of a general response driven by Gi/o-coupled GPCRs. TNT generation by either 5-oxo-eicosatetraenoic acid or lysophosphatidic acid is partially dependent on the transactivation of the epidermal growth factor receptor and impaired by phosphoinositide 3-kinase inhibition. Subsequent signaling analysis reveals a strict requirement of phospholipase C β3 and its downstream effector protein kinase Cα. Consistent with the established role of Rho small GTPases in the formation of actin-rich projecting structures, we identified the phosphoinositide 3-kinase-regulated guanine nucleotide exchange factor FARP1 as a GPCR effector essential for TNT formation, acting via Cdc42. Altogether, our study pioneers a link between Gi/o-coupled GPCRs and TNT development and sheds light into the intricate signaling pathways governing the generation of specialized actin-rich elongated structures in response to bioactive signaling lipids.

Oxoeicosanoid receptor inhibition alleviates acute myocardial infarction through activation of BCAT1

5-Oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) is an arachidonic acid metabolite produced along with leukotrienes via the 5-lipoxygenase pathway. Metabolomics studies have shown that 5-oxo-ETE level is elevated in the serum in acute myocardial infarction (AMI). The actions of 5-oxo-ETE are mediated by the highly selective oxoeicosanoid receptor (OXE-R). Moreover, increased OXE-R content was verified in AMI patients and mice. However, the precise role of OXE-R in AMI is unclear. In the present study, we demonstrate that 5-oxo-ETE triggered myocardial injury in mice. Pathway enrichment analysis identified branched chain amino acid transaminase 1/2 (BCAT1/2) as potential mediators of this effect. Western blot and immunohistochemical analyses showed that BCAT1/BCAT2 expression was significantly reduced by AMI in vitro and in vivo, while pharmacologic inhibition of BCAT1/BCAT2 accelerated myocardial injury. Conversely, heart-specific overexpression of BCAT1/BCAT2 in mice protected against ischemic myocardial injury. Treatment with the selective OXE-R inhibitor Gue1654 alleviated coronary artery ligation-induced ischemic myocardial injury in mice and oxygen/glucose deprivation-induced injury in cardiomyocytes through activation of BCAT1, while inhibiting OXE-R suppressed protein kinase C-ε (PKC-ε)/nuclear factor κB (NF-κB) signaling and cardiomyocyte apoptosis. Overall, our study confirmed a novel target OXE-R for the treatment of AMI based on metabolomics, and targeting OXE-R may represent unrecognized therapeutic intervention for cardiovascular diseases through activation of BCAT1.

Targeting the OXE receptor as a potential novel therapy for asthma

5-Oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) is an arachidonic acid metabolite formed by oxidation of the 5-lipoxygenase (5-LO) product 5S-hydroxy-6,8,11,14-eicosatetraenoic acid (5S-HETE) by the NADP+-dependent enzyme 5-hydroxyeicosanoid dehydrogenase. It is the only 5-LO product with appreciable chemoattractant activity for human eosinophils. Its actions are mediated by the selective OXE receptor, which is highly expressed on eosinophils, basophils, neutrophils and monocytes. Orthologs of the OXER1 gene, which encodes this receptor, are found in many species except for rodents. Intradermal injection of 5-oxo-ETE into humans and monkeys elicits eosinophil infiltration into the skin, raising the possibility that it may play a pathophysiological role in eosinophilic diseases. To investigate this and possibly identify a novel therapy we sought to prepare synthetic antagonists that could selectively block the OXE receptor. We synthesized a series of indole-based compounds bearing substituents that mimic the regions of 5-oxo-ETE that are required for biological activity, which we modified to reduce metabolism. The most potent of these OXE receptor antagonists is S-Y048, which is a potent inhibitor of 5-oxo-ETE-induced calcium mobilization (IC50, 20 pM) and has a long half-life following oral administration. S-Y048 inhibited allergen-induced eosinophil infiltration into the skin of rhesus monkeys that had been experimentally sensitized to house dust mite and inhibited pulmonary inflammation resulting from challenge with aerosolized allergen. These data provide the first evidence for a pathophysiological role for 5-oxo-ETE in mammals and suggest that potent and selective OXE receptor antagonists such as S-Y048 may be useful therapeutic agents in asthma and other eosinophilic diseases.

Inhibition of allergen-induced dermal eosinophilia by an oxoeicosanoid receptor antagonist in non-human primates

BACKGROUND AND PURPOSE

5-Oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE), acting via the OXE receptor, is unique among 5-lipoxygenase products in its ability to directly induce human eosinophil migration, suggesting its involvement in eosinophilic diseases. To address this hypothesis, we synthesized selective indole-based OXE receptor antagonists. Because rodents lack an OXE receptor orthologue, we sought to determine whether these antagonists could attenuate allergen-induced skin eosinophilia in sensitized monkeys.

EXPERIMENTAL APPROACH

In a pilot study, cynomolgus monkeys with environmentally acquired sensitivity to Ascaris suum were treated orally with the "first-generation" OXE antagonist 230 prior to intradermal injection of 5-oxo-ETE or Ascaris extract. Eosinophils were evaluated in punch biopsy samples taken 6 or 24 hr later. We subsequently treated captive-bred rhesus monkeys sensitized to house dust mite (HDM) allergen with a more recently developed OXE antagonist, S-Y048, and evaluated its effects on dermal eosinophilia induced by either 5-oxo-ETE or HDM.

KEY RESULTS

In a pilot experiment, both 5-oxo-ETE and Ascaris extract induced dermal eosinophilia in cynomolgus monkeys, which appeared to be reduced by 230. Subsequently, we found that the related OXE antagonist S-Y048 is a highly potent inhibitor of 5-oxo-ETE-induced activation of rhesus monkey eosinophils in vitro and has a half-life in plasma of about 6 hr after oral administration. S-Y048 significantly inhibited eosinophil infiltration into the skin in response to both intradermally administered 5-oxo-ETE and HDM.

CONCLUSIONS AND IMPLICATIONS

5-Oxo-ETE may play an important role in allergen-induced eosinophilia. Blocking its effects with S-Y048 may provide a novel therapeutic approach for eosinophilic diseases.

Novel highly potent OXE receptor antagonists with prolonged plasma lifetimes that are converted to active metabolites in vivo in monkeys

BACKGROUND AND PURPOSE

The 5-lipoxygenase product 5-oxo-6E,8Z,11Z,14Z-eicosatetraenoic acid (5-oxo-ETE), acting through the OXE receptor, is a potent eosinophil chemoattractant that may be an important proinflammatory mediator in eosinophilic diseases such as asthma. We previously identified a series of indole-based OXE receptor antagonists that rapidly appear in the blood following oral administration but have limited lifetimes. The objective of this study was to increase the potency and plasma half-lives of these compounds and thereby identify the optimal candidate for future preclinical studies in monkeys, as rodents do not have an OXE receptor orthologue.

EXPERIMENTAL APPROACH

We synthesized a series of substituted phenylalkyl indoles and compared their antagonist potencies, pharmacokinetics, and metabolism to those of our earlier compounds. The potencies of some of their metabolites were also investigated.

KEY RESULTS

Among the compounds tested, the S-enantiomer of the m-chlorophenyl compound (S-Y048) was the most potent, with an pIC50 of about 10.8 for inhibition of 5-oxo-ETE-induced calcium mobilization in human neutrophils. When administered orally to cynomolgus monkeys, S-Y048 rapidly appeared in the blood and had a half-life in plasma of over 7 hr, considerably longer than any of the other OXE analogues tested. A major hydroxylated metabolite, with a potency close to that of its precursor, was identified in plasma.

CONCLUSION AND IMPLICATIONS

Because of its highly potent antagonist activity and its long lifetime in vivo, S-Y048 may be a useful anti-inflammatory agent for the treatment of eosinophilic diseases such as asthma, allergic rhinitis, and atopic dermatitis.

Metabolism and pharmacokinetics of a potent N-acylindole antagonist of the OXE receptor for the eosinophil chemoattractant 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) in rats and monkeys

We previously identified the indole 264 as a potent in vitro antagonist of the human OXE receptor that mediates the actions of the powerful eosinophil chemoattractant 5-oxo-ETE. No antagonists of this receptor are currently commercially available or are being tested in clinical studies. The lack of a rodent ortholog of the OXE receptor has hampered progress in this area because of the unavailability of commonly used mouse or rat animal models. In the present study, we examined the feasibility of using the cynomolgus monkey as an animal model to investigate the efficacy of orally administered 264 in future in vivo studies. We first confirmed that 264 is active in monkeys by showing that it is a potent inhibitor of 5-oxo-ETE-induced actin polymerization and chemotaxis in granulocytes. The major microsomal metabolites of 264 were identified by cochromatography with authentic chemically synthesized standards and LC-MS/MS as its ω2-hydroxy and ω2-oxo derivatives, formed by ω2-oxidation of its hexyl side chain. Small amounts of ω1-oxidation products were also identified. None of these metabolites have substantial antagonist potency. High levels of 264 appeared rapidly in the blood following oral administration to both rats and monkeys, and declined to low levels by 24 h. As with microsomes, its major plasma metabolites in monkeys were ω2-oxidation products. We conclude that the monkey is a suitable animal model to investigate potential therapeutic effects of 264. This, or a related compound with diminished susceptibility to ω2-oxidation, could be a useful therapeutic agent in eosinophilic disorders such as asthma.

Expression and function of OXE receptor, an eicosanoid receptor, in steroidogenic cells

Hormonal regulation of steroidogenesis involves arachidonic acid (AA) metabolism through the 5-lipoxygenase pathway. One of the products, 5-hydroperoxy-eicosatetraenoic acid (5-HpETE), acts as a modulator of the activity of the steroidogenic acute regulatory (StAR) protein promoter. Besides, an oxoeicosanoid receptor of the leukotriene receptor family named OXE-R is a membrane protein with high affinity and response to 5-HpETE, among other AA derivatives. The aim of our work was to elucidate whether this receptor may be involved in steroidogenesis. RT-PCR and western blot analysis demonstrated the presence of the mRNA and protein of the receptor in human H295R adrenocortical cells. The treatment of H295R or MA-10 cells (murine Leydig cell line) with 8Br-cAMP together with docosahexaenoic acid (DHA, an antagonist of the receptor) partially reduced StAR induction and steroidogenesis. On the contrary, 5-oxo-ETE - the prototypical agonist, with higher affinity and potency on the receptor - increased cAMP-dependent steroid production, StAR mRNA and protein levels. These results lead us to conclude that AA might modulate StAR induction and steroidogenesis, at least in part, through 5-HpETE production and activation of a membrane receptor, such as the OXE-R.

Regulation of inflammation in cancer by eicosanoids

Inflammation in the tumor microenvironment is now recognized as one of the hallmarks of cancer. Endogenously produced lipid autacoids, locally acting small molecule lipid mediators, play a central role in inflammation and tissue homeostasis, and have recently been implicated in cancer. A well-studied group of autacoid mediators that are the products of arachidonic acid metabolism include: the prostaglandins, leukotrienes, lipoxins and cytochrome P450 (CYP) derived bioactive products. These lipid mediators are collectively referred to as eicosanoids and are generated by distinct enzymatic systems initiated by cyclooxygenases (COX 1 and 2), lipoxygenases (5-LOX, 12-LOX, 15-LOXa, 15-LOXb), and cytochrome P450s, respectively. These pathways are the target of approved drugs for the treatment of inflammation, pain, asthma, allergies, and cardiovascular disorders. Beyond their potent anti-inflammatory and anti-cancer effects, non-steroidal anti-inflammatory drugs (NSAIDs) and COX-2 specific inhibitors have been evaluated in both preclinical tumor models and clinical trials. Eicosanoid biosynthesis and actions can also be directly influenced by nutrients in the diet, as evidenced by the emerging role of omega-3 fatty acids in cancer prevention and treatment. Most research dedicated to using eicosanoids to inhibit tumor-associated inflammation has focused on the COX and LOX pathways. Novel experimental approaches that demonstrate the anti-tumor effects of inhibiting cancer-associated inflammation currently include: eicosanoid receptor antagonism, overexpression of eicosanoid metabolizing enzymes, and the use of endogenous anti-inflammatory lipid mediators. Here we review the actions of eicosanoids on inflammation in the context of tumorigenesis. Eicosanoids may represent a missing link between inflammation and cancer and thus could serve as therapeutic target(s) for inhibiting tumor growth.

Roles of affinity and lipophilicity in the slow kinetics of prostanoid receptor antagonists on isolated smooth muscle preparations

BACKGROUND AND PURPOSE

The highly lipophilic acyl-sulphonamides L-798106 and L-826266 showed surprisingly slow antagonism of the prostanoid EP₃ receptor system in guinea-pig aorta. Roles of affinity and lipophilicity in the onset kinetics of these and other prostanoid ligands were investigated.

EXPERIMENTAL APPROACH

Antagonist selectivity was assessed using a panel of human recombinant prostanoid receptor-fluorimetric imaging plate reader assays. Potencies/affinities and onset half-times of agonists and antagonists were obtained on guinea-pig-isolated aorta and vas deferens. n-Octanol-water partition coefficients were predicted.

KEY RESULTS

L-798106, L-826266 and the less lipophilic congener (DG)-3ap appear to behave as selective, competitive-reversible EP₃ antagonists. For ligands of low to moderate lipophilicity, potency increments for EP₃ and TP (thromboxane-like) agonism on guinea-pig aorta (above pEC₅₀ of 8.0) were associated with progressively longer onset half-times; similar trends were found for TP and histamine H₁ antagonism above a pA₂ limit of 8.0. In contrast, L-798106 (EP₃), L-826266 (EP₃, TP) and the lipophilic H₁ antagonists astemizole and terfenadine exhibited very slow onset rates despite their moderate affinities; (DG)-3ap (EP₃) had a faster onset. Agonism and antagonism on the vas deferens EP₃ system were overall much faster, although trends were similar.

CONCLUSIONS AND IMPLICATIONS

High affinity and high liphophilicity may contribute to the slow onsets of prostanoid ligands in some isolated smooth muscle preparations. Both relationships are explicable by tissue disposition under the limited diffusion model. EP₃ antagonists used as research tools should have moderate lipophilicity. The influence of lipophilicity on the potential clinical use of EP₃ antagonists is discussed.

Bradykinin-induced, endothelium-dependent responses in porcine coronary arteries: involvement of potassium channel activation and epoxyeicosatrienoic acids

In coronary arteries, bradykinin opens endothelial intermediate- and small-conductance Ca2+-sensitive K+ channels (IK(Ca) and SK(Ca)) and, additionally, releases epoxyeicosatrienoic acids (EETs) from the endothelium. To clarify the involvement of these pathways in endothelium-dependent myocyte hyperpolarization, bradykinin-induced electrical changes in endothelial cells and myocytes of porcine coronary arteries (following nitric oxide (NO) synthase and cyclooxygenase inhibition) were measured using sharp microelectrodes. Hyperpolarization of endothelial cells by bradykinin (27.0 +/- 0.9 mV, n = 4) was partially inhibited (74%) by blockade of IK(Ca) and SK(Ca) channels using 10 microM TRAM-39 (2-(2-chlorophenyl)-2,2-diphenylacetonitrile) plus 100 nM apamin (leaving an iberiotoxin-sensitive component), whereas the response to substance P was abolished. After gap junction blockade with HEPES, (N-(2-hydroxyethyl)piperazine-N'-(2-ethanesulphonic acid)) hyperpolarization of the endothelium by 100 nM bradykinin was abolished by TRAM-39 plus apamin, whereas myocyte hyperpolarization still occurred (12.9 +/- 1.0 mV, n=4). The residual hyperpolarizations to 100 nM bradykinin were antagonized by the EET antagonist, 14,15-EEZE (14,15-epoxyeicosa-5(Z)-enoic acid) (10 microM), and abolished by iberiotoxin. Bradykinin-induced myocyte hyperpolarizations were also reduced by 14,15-EEZE-mSI (14,15-EEZE-methylsulfonylimide) (5,6- and 14,15-EET antagonist), whereas those to exogenous 11,12-EET were unaffected. These data show that bradykinin-induced hyperpolarization of endothelial cells (due to the opening of IK(Ca) and SK(Ca) channels) is electrotonically transferred to the myocytes via gap junctions. Bradykinin (but not substance P) also hyperpolarizes myocytes by a mechanism (independent of endothelial cell hyperpolarization) which involves endothelial cell production of EETs (most likely 14,15- and/or 11,12-EET). These open endothelial IK(Ca) and SK(Ca) channels and also activate large-conductance calcium-sensitive K+ channels (BK(Ca)) on the surrounding myocytes.

Studies of synergistic and antagonistic combinations of conventional cytotoxic agents with the multiple eicosanoid pathway modulator LY 293111

The arachidonic acid metabolic pathway is currently under active investigation as a promoter of malignancy and several molecules have been synthesized to block either the cyclooxygenase or lipoxygenase branches. LY 293111 is an oral agent known to be a leukotriene B4 antagonist, a 5-lipoxygenase inhibitor and a peroxisome proliferator-activated receptor (PPAR)-gamma agonist with cytotoxic properties in cell lines. We have studied this agent with classical chemotherapeutic agents in a 72-h culture with cell lines using median-effect analysis as a measure of antagonism or synergy. LY 293111 displays global synergy with the active metabolite of irinotecan, SN-38, in the majority of cell lines, synergistic to additive effects with gemcitabine in bladder cancer cell lines, and synergism with 5'-DFUR (the active metabolite of capecitabine) in two breast cancer and one sarcoma cell line. These effects occur at clinically attainable concentrations. The addition of a proteosome inhibitor to the LY 293111 and SN-38 combination markedly enhanced the cytotoxic effects in the sarcoma cell line. As the toxicity of LY 293111 in man is not hematological, this agent may have a role in combination therapy of selected malignancies.

Effects of eicosanoids on parameters in isolated rat hepatocytes and isolated rat hepatocyte couplets: protective effects of eicosanoid receptor antagonists

A number of eicosanoids caused plasma membrane blebbing in hepatocytes and this could be inhibited in a dose-dependent fashion by the receptor antagonists AH6809 and ICI 192605. The pattern of effectiveness of eicosanoids interfering with canalicular vacuole accumulation in hepatocyte couplets differed from that causing blebbing; the two most effective eicosanoids here were PGD2 and PGF2 alpha.