Multitargeting of selected prostanoid receptors provides agents with enhanced anti-inflammatory activity in macrophages

Neuroaxonal and cellular damage/protection by prostanoid receptor ligands, fatty acid derivatives and associated enzyme inhibitors

Cellular and mitochondrial membrane phospholipids provide the substrate for synthesis and release of prostaglandins in response to certain chemical, mechanical, noxious and other stimuli. Prostaglandin D₂, prostaglandin E₂, prostaglandin F_2α, prostaglandin I₂ and thromboxane-A₂ interact with five major receptors (and their sub-types) to elicit specific downstream cellular and tissue actions. In general, prostaglandins have been associated with pain, inflammation, and edema when they are present at high local concentrations and involved on a chronic basis. However, in acute settings, certain endogenous and exogenous prostaglandins have beneficial effects ranging from mediating muscle contraction/relaxation, providing cellular protection, regulating sleep, and enhancing blood flow, to lowering intraocular pressure to prevent the development of glaucoma, a blinding disease. Several classes of prostaglandins are implicated (or are considered beneficial) in certain central nervous system dysfunctions (e.g., Alzheimer’s, Parkinson’s, and Huntington’s diseases; amyotrophic lateral sclerosis and multiple sclerosis; stroke, traumatic brain injuries and pain) and in ocular disorders (e.g., ocular hypertension and glaucoma; allergy and inflammation; edematous retinal disorders). This review endeavors to address the physiological/pathological roles of prostaglandins in the central nervous system and ocular function in health and disease, and provides insights towards the therapeutic utility of some prostaglandin agonists and antagonists, polyunsaturated fatty acids, and cyclooxygenase inhibitors.

A Second Generation Prostanoid Receptor Antagonist Acting at Multiple Receptor Subtypes

It has previously been reported that a prototypical compound (AGN 211377), which blocks pro-inflammatory prostanoid receptors (DP₁, DP₂, EP₁, EP_4, FP, TP) and leaves open IP and EP₂ receptors so that their anti-inflammatory properties could be exerted, produced superior inhibitory effects on cytokine release from human macrophages compared to cyclooxygenase (COX) inhibitors. This favorable activity profile translated into animal studies, with AGN 211377 exceeding the level of inhibition afforded by COX inhibition. AGN 211377 was not, however, a practical drug candidate, having poor bioavailability and cost of goods concerns. Compound 1 (designated AGN 225660) represents a second-generation compound with an entirely different "druggable" core structure. Such a dramatic change in chemical scaffold created uncertainty with respect to matching the effects of AGN 211377. AGN 225660 inhibited RANTES, IL-8, and MCP-1 secretion by at least 50%, from TNFα activated human macrophages. Although AGN 225660 reduced TNFα-evoked MCP-1 release from human monocyte-derived macrophages, it increased LPS-induced MCP-1 secretion (up to 2-fold) from human monocyte-derived dendritic cells. However, AGN 225660 inhibited the release of IL12p 70 and IL-23 from human monocyte-derived dendritic cells stimulated by LPS by more than 70%. This effect of AGN 225660 was reproduced in part by the prototype compound AGN 211377 and a combination of selective DP₁, EP₁, EP₄, FP, and TP antagonists. These findings suggest important effects on T cell skewing and disease modification by this class of therapeutic agents. AGN 225660 exhibited good ocular bioavailability and was active in reducing ocular inflammation associated with phacoemulsification surgery, LPS, and arachidonic acid induced uveitis.

Antiglaucoma EP2 Agonists: A Long Road That Led Somewhere

For >2 decades, EP₂ agonists have been the subject of antiglaucoma research and development by scientists in industry and academia around the world. The road has led to the recent approval of the first drug of this class. This article reviews the development of EP₂ agonists from conception to clinical approval, discussing pharmacology, structure, biodistribution, therapeutics, and drug delivery. An extensive list of source references is provided for the reader's benefit.

FAAH-Catalyzed C-C Bond Cleavage of a New Multitarget Analgesic Drug

The discovery of extended catalytic versatilities is of great importance in both the chemistry and biotechnology fields. Fatty acid amide hydrolase (FAAH) belongs to the amidase signature superfamily and is a major endocannabinoid inactivating enzyme using an atypical catalytic mechanism involving hydrolysis of amide and occasionally ester bonds. FAAH inhibitors are efficacious in experimental models of neuropathic pain, inflammation, and anxiety, among others. We report a new multitarget drug, AGN220653, containing a carboxyamide-4-oxazole moiety and endowed with efficacious analgesic and anti-inflammatory activities, which are partly due to its capability of achieving inhibition of FAAH, and subsequently increasing the tissue concentrations of the endocannabinoid anandamide. This inhibitor behaves as a noncompetitive, slowly reversible inhibitor. Autoradiography of purified FAAH incubated with AGN220653, opportunely radiolabeled, indicated covalent binding followed by fragmentation of the molecule. Molecular docking suggested a possible nucleophilic attack by FAAH-Ser241 on the carbonyl group of the carboxyamide-4-oxazole moiety, resulting in the cleavage of the C-C bond between the oxazole and the carboxyamide moieties, instead of either of the two available amide bonds. MRM-MS analyses only detected the Ser241-assisted formation of the carbamate intermediate, thus confirming the cleavage of the aforementioned C-C bond. Quantum mechanics calculations were fully consistent with this mechanism. The study exemplifies how FAAH structural features and mechanism of action may override the binding and reactivity propensities of substrates. This unpredicted mechanism could pave the way to the future development of a completely new class of amidase inhibitors, of potential use against pain, inflammation, and mood disorders.

The affinity, intrinsic activity and selectivity of a structurally novel EP2 receptor agonist at human prostanoid receptors

BACKGROUND AND PURPOSE

Prostanoid EP₂ receptor agonists exhibit several activities including ocular hypotension, tocolysis and anti-inflammatory activity. This report describes the affinity and selectivity of a structurally novel, non-prostanoid EP₂ receptor agonist, PGN-9856, and its therapeutic potential.

EXPERIMENTAL APPROACH

The pharmacology of a series of non-prostanoid EP₂ receptor agonists was determined according to functional and radioligand binding studies, mostly using human recombinant prostanoid receptor transfectants. The selectivity of PGN-9856, as the preferred compound, was subsequently determined by using a diverse variety of non-prostanoid target proteins. The therapeutic potential of PGN-9856 was addressed by determining its activity in relevant primate cell, tissue and disease models.

KEY RESULTS

PGN-9856 was a selective and high affinity (pKi ≥ 8.3) ligand at human recombinant EP₂ receptors. In addition to high affinity binding, it was a potent and full EP₂ receptor agonist with a high level of selectivity at EP₁ , EP₃ , EP₄ , DP, FP, IP and TP receptors. In cells overexpressing human recombinant EP₂ receptors, PGN-9856 displayed a potency (pEC₅₀ ≥ 8.5) and a maximal response (increase in cAMP) comparable to that of the endogenous agonist PGE₂ . PGN-9856 exhibited no appreciable affinity (up 10 μM) for a range of 53 other receptors, ion channels and enzymes. Finally, PGN-9856 exhibited tocolytic, anti-inflammatory and long-acting ocular hypotensive properties consistent with its potent EP₂ receptor agonist properties.

CONCLUSIONS AND IMPLICATIONS

PGN-9856 is a potent, selective and efficacious prostanoid EP₂ receptor agonist with diverse potential therapeutic applications: tocolytic, anti-inflammatory and notably anti-glaucoma.

Prostaglandin FP receptor antagonists: discovery, pharmacological characterization and therapeutic utility

In contrast to the availability of potent and selective antagonists of several prostaglandin receptor types (including DP₁ , DP₂ , EP and TP receptors), there has been a paucity of well-characterized, selective FP receptor antagonists. The earliest ones included dimethyl amide and dimethyl amine derivatives of PGF_2α , but these have failed to gain prominence. The fluorinated PGF_2α analogues, AL-8810 and AL-3138, were subsequently discovered as competitive and non-competitive FP receptor antagonists respectively. Non-prostanoid structures, such as the thiazolidinone AS604872, the D-amino acid-based oligopeptide PDC31 and its peptidomimic analogue PDC113.824 came next, but the latter two are allosteric inhibitors of FP receptor signalling. AL-8810 has a sub-micromolar in vitro potency and ≥2 log unit selectivity against most other PG receptors when tested in several cell- and tissue-based functional assays. Additionally, AL-8810 has demonstrated therapeutic efficacy as an FP receptor antagonist in animal models of stroke, traumatic brain injury, multiple sclerosis, allodynia and endometriosis. Consequently, it appears that AL-8810 has become the FP receptor antagonist of choice. LINKED ARTICLES: This article is part of a themed section on Eicosanoids 35 years from the 1982 Nobel: where are we now? To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.8/issuetoc.

Prostaglandins D2 and E2 have opposite effects on alveolar macrophages infected with Histoplasma capsulatum

Prostaglandin E₂ (PGE₂) suppresses macrophage effector mechanisms; however, little is known about the function of PGD₂ in infected alveolar macrophages (AMs). Using serum-opsonized Histoplasma capsulatum (Ops-H. capsulatum) in vitro, we demonstrated that AMs produced PGE₂ and PGD₂ in a time-dependent manner, with PGE₂ levels exceeding those of PGD₂ by 48 h postinfection. Comparison of the effects of both exogenous PGs on AMs revealed that PGD₂ increased phagocytosis and killing through the chemoattractant receptor-homologous molecule expressed on Th2 lymphocytes receptor, whereas PGE₂ had opposite effects, through E prostanoid (EP) receptor 2 (EP2)/EP4-dependent mechanisms. Moreover, PGD₂ inhibited phospholipase C-γ (PLC-γ) phosphorylation, reduced IL-10 production, and increased leukotriene B4 receptor expression. In contrast, exogenous PGE₂ treatment reduced PLC-γ phosphorylation, p38 and nuclear factor κB activation, TNF-α, H₂O₂, and leukotriene B₄, but increased IL-1β production. Using specific compounds to inhibit the synthesis of each PG in vitro and in vivo, we found that endogenous PGD₂ contributed to fungicidal mechanisms and controlled inflammation, whereas endogenous PGE₂ decreased phagocytosis and killing of the fungus and induced inflammation. These findings demonstrate that, although PGD₂ acts as an immunostimulatory mediator to control H. capsulatum infection, PGE₂ has immunosuppressive effects, and the balance between these two PGs may limit collateral immune damage at the expense of microbial containment.

A Prostacyclin Analog, Cicaprost, Exhibits Potent Anti-Inflammatory Activity in Human Primary Immune Cells and a Uveitis Model

PURPOSE

To investigate the therapeutic potential of a prostacyclin (IP) receptor agonist for ocular inflammation and the effect on immune cells.

METHODS

The anti-inflammatory activities of cicaprost were determined in primary human monocyte-derived macrophages and human monocyte-derived dendritic cells (MoDC), as well as a lipopolysaccharides (LPS)-induced rat uveitis model. Multiple cytokine release was measured by utilizing Luminex Technology. Prostacyclin (IP) Receptor expression was detected by reverse transcription-polymerase chain receptor. Leukocyte infiltration and protein exudation in the rat uveitis model were measured using a hemocytometer and protein concentration by a NanoDrop instrument.

RESULTS

Cicapost, an IP receptor agonist, potently inhibits proinflammatory chemokines/cytokine production not only from LPS- or TNFα (tumor necrosis factor-alpha)-induced primary human monocyte-derived macrophages, but also from LPS-stimulated MoDC. While constitutively expressed in macrophages, the IP receptor was inducible by LPS stimulation in MoDCs. In a LPS-induced rat uveitis model, cicaprost efficaciously prevents ocular inflammatory cell and protein leakage, as well as inflammatory cytokine release.

CONCLUSION

The IP receptor agonist cicaprost is a potent anti-inflammatory agent, implicating that the tightly controlled PGI₂/IP signaling pathway is important in regulating inflammation. This response could be harnessed in ocular inflammatory disease where steroids are currently the standard of care.