AL-3138 antagonizes FP prostanoid receptor-mediated inositol phosphates generation: comparison with some purported FP antagonists

Discovery to Launch of Anti-allergy (Emadine; Patanol/Pataday/Pazeo) and Anti-glaucoma (Travatan; Simbrinza) Ocular Drugs, and Generation of Novel Pharmacological Tools Such as AL-8810

The eye and eyesight are exquistly designed and are precious, and yet we often take them for granted. Good vision is critical for our long-term survival and for humanity's enduring progress. Unfortunately, since ocular diseases do not culminate in life-and-death scenarios, awareness of the plight of millions of people suffering from such eye ailments is not publicized as other diseases. However, losing eyesight or falling victim to visual impairment is a frightening outlook for most people. Glaucoma, a collection of chronic optic neuropathies, of which the most prevalent form, primary open-angle glaucoma (POAG), is the second leading cause of irreversible blindness. POAG currently afflicts >70 million people worldwide and is an insidious, progressive, silent thief of sight that is asymptomatic. On the other hand, allergic conjunctivitis (AC), and the associated rhinitis ("hay-fever"), frequently victimizes a huge number of people worldwide, especially during seasonal changes. While not life-threatening, sufferers of AC soon learn the value of drugs to treat their signs and symptoms of AC as they desire rapid relief to overcome the ocular itching/pain, redness, and tearing AC causes. Herein, I will describe the collective efforts of many researchers whose industrious, diligent, and dedicated team work resulted in the discovery, biochemical/pharmacological characterization, development and eventual launch of drugs to treat AC (e.g., olopatadine [Patanol/Pataday/Pazeo] and emedastine [Emedine]), and for treating ocular hypertension and POAG (e.g., travoprost [Travatan ] and Simbrinza). This represents a personal perspective.

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.

International Union of Basic and Clinical Pharmacology. LXXXIII: classification of prostanoid receptors, updating 15 years of progress

It is now more than 15 years since the molecular structures of the major prostanoid receptors were elucidated. Since then, substantial progress has been achieved with respect to distribution and function, signal transduction mechanisms, and the design of agonists and antagonists (http://www.iuphar-db.org/DATABASE/FamilyIntroductionForward?familyId=58). This review systematically details these advances. More recent developments in prostanoid receptor research are included. The DP(2) receptor, also termed CRTH2, has little structural resemblance to DP(1) and other receptors described in the original prostanoid receptor classification. DP(2) receptors are more closely related to chemoattractant receptors. Prostanoid receptors have also been found to heterodimerize with other prostanoid receptor subtypes and nonprostanoids. This may extend signal transduction pathways and create new ligand recognition sites: prostacyclin/thromboxane A(2) heterodimeric receptors for 8-epi-prostaglandin E(2), wild-type/alternative (alt4) heterodimers for the prostaglandin FP receptor for bimatoprost and the prostamides. It is anticipated that the 15 years of research progress described herein will lead to novel therapeutic entities.

PG F(2α) Receptor: A Promising Therapeutic Target for Cardiovascular Disease

Prostaglandins (PGs), a group of key lipid mediators, are involved in numerous physiological and pathological processes including inflammation and cardiovascular homeostasis. Each PG acts on its specific and distinct cell surface G protein-coupled receptors (GPCRs) or peroxisome proliferator-activated receptors (PPARs). Prostaglandin F(2α) receptor (FP) is required for female reproductive function such as luteolysis and parturition. It has recently been implicated in blood pressure regulation, atherosclerosis and other inflammation-related disorders. The emerging role of FP in cardiovascular diseases is highlighted and potential therapeutic translation is discussed in the current review.

Prostanoid receptor antagonists: development strategies and therapeutic applications

Identification of the primary products of cyclo-oxygenase (COX)/prostaglandin synthase(s), which occurred between 1958 and 1976, was followed by a classification system for prostanoid receptors (DP, EP(1), EP(2) ...) based mainly on the pharmacological actions of natural and synthetic agonists and a few antagonists. The design of potent selective antagonists was rapid for certain prostanoid receptors (EP(1), TP), slow for others (FP, IP) and has yet to be achieved in certain cases (EP(2)). While some antagonists are structurally related to the natural agonist, most recent compounds are 'non-prostanoid' (often acyl-sulphonamides) and have emerged from high-throughput screening of compound libraries, made possible by the development of (functional) assays involving single recombinant prostanoid receptors. Selective antagonists have been crucial to defining the roles of PGD(2) (acting on DP(1) and DP(2) receptors) and PGE(2) (on EP(1) and EP(4) receptors) in various inflammatory conditions; there are clear opportunities for therapeutic intervention. The vast endeavour on TP (thromboxane) antagonists is considered in relation to their limited pharmaceutical success in the cardiovascular area. Correspondingly, the clinical utility of IP (prostacyclin) antagonists is assessed in relation to the cloud hanging over the long-term safety of selective COX-2 inhibitors. Aspirin apart, COX inhibitors broadly suppress all prostanoid pathways, while high selectivity has been a major goal in receptor antagonist development; more targeted therapy may require an intermediate position with defined antagonist selectivity profiles. This review is intended to provide overviews of each antagonist class (including prostamide antagonists), covering major development strategies and current and potential clinical usage.

Synthetic FP-prostaglandin-induced contraction of rat uterus smooth muscle in vitro

Numerous synthetic FP-class prostaglandin (PG) analogs stimulated the contraction of isolated non-pregnant female rat uterus in a concentration-dependent manner with the following agonist potencies: bimatoprost acid (17-phenyl-trinor PGF(2alpha); EC(50)=0.68+/-0.06 nM)=cloprostenol (EC(50)=0.73+/-0.01 nM)>travoprost acid (EC(50)=1.3+/-0.07 nM)>latanoprost acid (EC(50)=2.7+/-0.08 nM)>PGF(2alpha) (EC(50)=52+/-11 nM)>unoprostone (UF-021; EC(50)=310+/-101 nM)>S-1033 (EC(50)=610+/-4 nM)>bimatoprost (EC(50)=1130+/-173 nM). The FP-receptor antagonist, AL-8810, antagonized the contractile effects of PGF(2alpha) (K(i)=2.9+/-0.2 microM), travoprost acid (K(i)=0.6+/-0.1 microM) and bimatoprost (K(i)=0.2+/-0.02 microM). Agonist and antagonist potencies for rat uterus contraction by these PGs compared well with their potencies for inducing/blocking functional responses in other systems (r=0.83-0.94) except with bovine iris sphincter (r=0.2; p<0.7). In conclusion, the rat uterus contains functionally active FP-receptors whose activation by a variety of free acid and an amide forms of synthetic PGs leads to the contraction of this tissue and which can be pharmacologically blocked by an FP-receptor antagonist, AL-8810.

Prostamides (prostaglandin-ethanolamides) and their pharmacology

The prostamides are part of a large and continually expanding series of pharmacologically unique neutral lipids. They are COX-2 derived oxidation products of the endocannabinoid/endovanniloid anandamide. Prostamide pharmacology is unique and, as in the case of the endocannabinoids anandamide and 2-arachidonylglycerol, bears little resemblance to that of the corresponding free acids. By virtue of its close relationship to the anti-glaucoma drug bimatoprost, prostamide F(2alpha) has received the greatest research attention. Prostamide F(2alpha) and bimatoprost effects appear independent of prostanoid FP receptor activation, according to a litany of agonist studies. Studies involving freshly isolated and separate feline iridial smooth muscle cells revealed that bimatoprost and FP receptor agonists stimulated different cells, without exception. This suggests the existence of receptors that preferentially recognize prostamide F(2alpha). The recent discovery of prostamide antagonists has provided further support for prostamide receptors as discrete entities. The prototypical prostamide antagonists, AGN 204396 and 7, blocked the effects of prostamide F(2alpha) and bimatoprost but not those of PGF(2alpha) and FP receptor agonists in the feline iris. Second generation more potent prostamide antagonists, such as AGN 211334, should allow the role of prostamides in health and disease to be elucidated. From the therapeutics standpoint, the prostamide F(2alpha) analogue bimatoprost is the most efficacious ocular hypotensive agent currently available for the treatment of glaucoma.

An unexpected negative inotropic effect of prostaglandin F2alpha in the rat heart

Prostaglandin F(2alpha) (PGF(2alpha)) is produced during myocardial inflammation and many of the insults that trigger contractile dysfunction also activate prostaglandin synthesis and production. However, although PGF(2alpha) plays a significant role in the cardiac response to inflammation, the effect of this particular compound on the heart was largely studied at the cellular level and probably no due attention was paid to the effect of PGF(2alpha) on the whole heart contractility. Therefore, in the present study we have investigated the effect of PGF(2alpha) on isolated right ventricle of the rat heart. PGF(2alpha) (1nM-1microM) induced concentration-dependent decrease of the amplitude of contractions of the ventricular muscle. Real time RT-PCR has revealed that prostaglandin FP receptors are expressed in the rat myocardium and the level of expression was similar to those of creatine kinase and adenylate kinase, which are proteins abundantly present in the heart. An antagonist of FP receptors, PGF(2alpha) dimetilamide (10nM), abolished negative inotropic effect induced by PGF(2alpha). To examine the possibility that PGF(2alpha) could activate non-FP prostaglandin receptor, we have measured the level of expression of all known prostaglandin receptors in the rat heart. These experiments have shown that the order of expression of prostaglandin receptors in the rat heart is FP>>EP1=TP>EP4>EP3>DP=IP. Based on the obtained results we conclude that PGF(2alpha) induces negative inotropic effect on rat heart by activating FP prostaglandin receptors. This effect of PGF(2alpha) could contribute to cardiac dysfunction in conditions of systemic and myocardial inflammation.

Ocular Hypotensive FP Prostaglandin (PG) Analogs: PG Receptor Subtype Binding Affinities and Selectivities, and Agonist Potencies at FP and Other PG Receptors in Cultured Cells

Natural prostaglandins (PGs) such as PGD2, PGE2, PGF2(2alpha), and PGI2 exhibited the highest affinity for their respective cognate receptors, but were the least selective agents when tested in receptor binding assays. Travoprost acid ([+]-fluprostenol) was the most FP-receptor-selective compound, exhibiting a high affinity (Ki = 35 +/- 5 nM) for the FP receptor, and minimal affinity for DP (Ki = 52,000 nM), EP1 (Ki = 9540 nM), EP3 (Ki = 3501 nM), EP4 (Ki = 41,000 nM), IP (Ki > 90,000 nM), and TP (Ki = 121,000 nM) receptors. Travoprost acid was the most potent PG analog tested in FP receptor functional phosphoinositide turnover assays in the following cell types: human ciliary muscle (EC50 = 1.4 nM), human trabecular meshwork (EC50 = 3.6 nM), and mouse fibroblasts and rat aortic smooth muscle cells (EC50 = 2.6 nM). Although latanoprost acid exhibited a relatively high affinity for the FP receptor (Ki = 98 nM), it had significant functional activity at FP (EC50 = 32-124 nM) and EP1 (EC50 = 119 nM) receptors. Bimatoprost acid was less selective, exhibiting a relatively high affinity for the FP (Ki = 83 nM), EP1 (Ki = 95 nM), and EP3 (Ki = 387 nM) receptors. Bimatoprost acid exhibited functional activity at the EP1 (EC50 = 2.7 nM) and FP (EC50 = 2.8-3.8 nM in most cells) receptors. Bimatoprost (nonhydrolyzed amide) also behaved as an FP agonist at the cloned human FP receptor (EC50 = 681 nM), in h-TM (EC50 = 3245 nM) and other cell types. Unoprostone and S-1033 bound with low affinity (Ki = 5.9 microM to > 22 microM) to the FP receptor, were not selective, but activated the FP receptor. In conclusion, travoprost acid has the highest affinity, the highest FP-receptor-selectivity, and the highest potency at the FP receptor as compared to the other ocular hypotensive PG analogs known so far, including free acids of latanoprost, bimatoprost, and unoprostone isopropyl ester.

Human Ciliary Muscle Cell Responses to FP-Class Prostaglandin Analogs: Phosphoinositide Hydrolysis, Intracellular Ca2+ Mobilization and MAP Kinase Activation

Phospholipase C induced phosphoinositide (PI) turnover, intracellular Ca(2+) ([Ca(2+)](i)) mobilization and mitogen-activated protein (MAP) kinase activation by FP-class prostaglandin analogs was studied in normal human ciliary muscle (h-CM) cells. Agonist potencies obtained in the PI turnover assays were: travoprost acid ((+)-fluprostenol; EC(50) = 2.6 +/- 0.8 nM) > bimatoprost acid (EC(50) = 3.6 +/- 1.2 nM) > (+/-)-fluprostenol (EC(50) = 4.3 +/- 1.3 nM) >> prostaglandin F(2 alpha) (PGF(2 alpha)) (EC(50) = 134 +/- 17 nM) > latanoprost acid (EC(50) = 198 +/- 83 nM) > S-1033 (EC(50) = 2930 +/- 1420 nM) > unoprostone (EC(50) = 5590 +/- 1490 nM) > bimatoprost (EC(50) = 9600 +/- 1100 nM). Agonist potencies in h-CM cells correlated well with those previously obtained for the cloned human ciliary body-derived FP receptor (r = 0.96, p< 0.001) and that present on h-TM cells (r = 0.94, p< 0.0001). Travoprost acid, PGF(2 alpha) and unoprostone also stimulated [Ca(2+)](i) mobilization in h-CM cells with travoprost acid being the most potent agonist. MAP kinase activity was stimulated in the h-CM cells with the following rank order of activity (at 100 nM): travoprost acid > PGF(2 alpha) > latanoprost acid > PGD(2) > bimatoprost > latanoprost = bimatoprost acid = fluprostenol > PGE(2) = S-1033 > unoprostone > PGI(2). The PI turnover, [Ca(2+)](i) mobilization and MAP kinase activation induced by several of these agonists was blocked by the FP receptor antagonist, AL-8810 (11 beta-fluoro-15-epiindanyl PGF(2 alpha)) (e.g. K(i) = 5.7 microM versus PI turnover). These studies have characterized the biochemical and pharmacological properties of the native FP prostaglandin receptor present on h-CM cells using three signal transduction mechanism assays and a broad panel of FP-class agonist analogs (including free acids of bimatoprost, travoprost and latanoprost) and the FP receptor antagonist, AL-8810.

Bimatoprost (Lumigan((R))) is an agonist at the cloned human ocular FP prostaglandin receptor: real-time FLIPR-based intracellular Ca(2+) mobilization studies

Bimatoprost is the ethyl amide derivative of 17-phenyl-trinor prostaglandin F(2alpha). Here, we show that bimatoprost (K(i)=9250+/-846nM) and bimatoprost free acid (17-phenyl-trinor prostaglandin F(2alpha); K(i)=59+/-6nM) bind to the FP receptor and displace [(3)H]-travoprost acid, a selective FP agonist. Bimatoprost (EC(50)=3070+/-1330nM), Lumigan((R)) (bimatoprost 0.03% ophthalmic solution; EC(50)=1150+/-93nM) and bimatoprost acid (EC(50)=15+/-3nM) mobilized intracellular Ca(2+) ([Ca(2+)](i)) in <5s in HEK-293 cells expressing the cloned human ciliary body FP receptor on a fluorometric imaging plate reader (FLIPR). Furthermore, agonist effects of bimatoprost and bimatoprost acid were blocked by AL-8810 (11beta-fluoro-15-epi-15-indanyl prostaglandin F(2alpha); K(i)=0.7-2.1 MicroM), an FP receptor-selective antagonist. Therefore, the prodrug bimatoprost and its hydrolytic product, bimatoprost free acid, bind to and activate the human ocular FP prostaglandin receptor to mobilize [Ca(2+)](i), thus behaving as FP receptor agonists.

Real-time intracellular Ca2+ mobilization by travoprost acid, bimatoprost, unoprostone, and other analogs via endogenous mouse, rat, and cloned human FP prostaglandin receptors

The ability of a number of prostaglandin F 2 alpha (PGF 2 alpha) analogs to mobilize intracellular Ca2+[Ca2+]iand to compete for [3H]PGF 2 alpha binding to prostaglandin F 2 alpha receptors (FP) was evaluated. Radioligand binding studies measuring displacement of [3H]PGF 2 alpha by a variety of FP prostaglandin analogs yielded the following rank order of affinities: travoprost acid [(+)-16-m-trifluorophenoxy tetranor PGF 2 alpha; (+)-fluprostenol] > bimatoprost acid (17-phenyl-trinor PGF 2 alpha) >> unoprostone (13,14-dihydro-15-keto-20-ethyl PGF 2 alpha) = bimatoprost (17-phenyl-trinor PGF 2 alpha ethyl amide) > or = Lumigan (bimatoprost ophthalmic solution). In FP functional studies, travoprost acid (EC50= 17.5-37 nM, n = 13), bimatoprost acid (EC50= 23.3-49.0 nM, n = 6-12), unoprostone (EC50= 306-1270 nM, n = 4-8), bimatoprost (EC50= 3070- 3940 nM, n = 4-9), and Lumigan (EC50= 1470-3190 nM, n = 5-9) concentration dependently stimulated [Ca2+]imobilization via the rat (A7r5 cells), mouse (3T3 cells), and cloned human ocular FP prostanoid receptors. The rank order of potency of these compounds at the FP receptor of the three species was similar and in good agreement with the determined binding affinities. The agonist effects of these compounds were concentration dependently blocked by the FP receptor-selective antagonist, AL-8810 (11beta-fluoro-15-epi-15-indanyl-tetranor PGF 2 alpha) (Ki= 0.6-1.3 microM). These studies have demonstrated that bimatoprost, unoprostone, and bimatoprost acid possess direct agonist activities at the rat, mouse, and human FP prostanoid receptor and that travoprost acid is the most potent of the synthetic FP prostaglandin analogs tested.

Agonist activity of bimatoprost, travoprost, latanoprost, unoprostone isopropyl ester and other prostaglandin analogs at the cloned human ciliary body FP prostaglandin receptor

We have determined the agonist activity of a number of natural prostaglandins and prostaglandin analogs at the FP prostaglandin receptor cloned from a human ciliary body cDNA library using phosphoinositide (PI) turnover assays. Travoprost acid (EC50 = 3.2 +/- 0.6 nM) was the most potent agonist in these cells followed by bimatoprost free acid (17-phenyl-trinor PGF2alpha; EC50 = 5.8 +/- 2.6 nM), fluprostenol (EC50 = 6.1 +/- 1.5 nM), and latanoprost free acid (PHXA85; EC50 = 54.6 +/- 12.4 nM) which was 17-fold weaker (p < 0.001) than travoprost acid. Unoprostone and S-1033 were significantly (p < 0.001) weaker than travoprost acid. The amide prodrug, bimatoprost (EC50 = 694 +/- 293 nM), activated this FP receptor with an intermediate potency. The isopropyl ester prodrugs, travoprost (EC50 = 42.3 +/- 6.7 nM), latanoprost (EC50 = 126 +/- 347 nM) and unoprostone isopropyl ester (EC50 = 9,100 +/- 2,870 nM), also exhibited FP agonist activity. However, other compounds such as PGI2, bradykinin, histamine, and serotonin were inactive. The agonist activities of bimatoprost, unoprostone (UF-021), fluprostenol and acids of travoprost and latanoprost were antagonized by AL-8810 (11beta-fluoro- 15-epi-15-indanyl-PGF2alpha), an FP-receptor-selective antagonist (Ki = 1.0 - 2.1 microM; n = 3). These studies have demonstrated, for the first time, agonist activities of the currently known and marketed ocular hypotensive prostaglandin analogs at the cloned human ciliary body FP prostaglandin receptor.