Pharmacological characterization of a nonpeptide bradykinin B2 receptor antagonist, FR165649, and agonist, FR190997

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.

Tactical Approaches to Interconverting GPCR Agonists and Antagonists

There are many reported examples of small structural modifications to GPCR-targeted ligands leading to major changes in their functional activity, converting agonists into antagonists or vice versa. These shifts in functional activity are often accompanied by negligible changes in binding affinity. The current perspective focuses on outlining and analyzing various approaches that have been used to interconvert GPCR agonists, partial agonists, and antagonists in order to achieve the intended functional activity at a GPCR of therapeutic interest. An improved understanding of specific structural modifications that are likely to alter the functional activity of a GPCR ligand may be of use to researchers designing GPCR-targeted drugs and/or probe compounds, specifically in cases where a particular ligand exhibits good potency but not the preferred functional activity at the GPCR of choice.

Neuropeptides: metabolism to bioactive fragments and the pharmacology of their receptors

The proteolytic processing of neuropeptides has an important regulatory function and the peptide fragments resulting from the enzymatic degradation often exert essential physiological roles. The proteolytic processing generates, not only biologically inactive fragments, but also bioactive fragments that modulate or even counteract the response of their parent peptides. Frequently, these peptide fragments interact with receptors that are not recognized by the parent peptides. This review discusses tachykinins, opioid peptides, angiotensins, bradykinins, and neuropeptide Y that are present in the central nervous system and their processing to bioactive degradation products. These well-known neuropeptide systems have been selected since they provide illustrative examples that proteolytic degradation of parent peptides can lead to bioactive metabolites with different biological activities as compared to their parent peptides. For example, substance P, dynorphin A, angiotensin I and II, bradykinin, and neuropeptide Y are all degraded to bioactive fragments with pharmacological profiles that differ considerably from those of the parent peptides. The review discusses a selection of the large number of drug-like molecules that act as agonists or antagonists at receptors of neuropeptides. It focuses in particular on the efforts to identify selective drug-like agonists and antagonists mimicking the effects of the endogenous peptide fragments formed. As exemplified in this review, many common neuropeptides are degraded to a variety of smaller fragments but many of the fragments generated have not yet been examined in detail with regard to their potential biological activities. Since these bioactive fragments contain a small number of amino acid residues, they provide an ideal starting point for the development of drug-like substances with ability to mimic the effects of the degradation products. Thus, these substances could provide a rich source of new pharmaceuticals. However, as discussed herein relatively few examples have so far been disclosed of successful attempts to create bioavailable, drug-like agonists or antagonists, starting from the structure of endogenous peptide fragments and applying procedures relying on stepwise manipulations and simplifications of the peptide structures.

FR-190997, a nonpeptide bradykinin B2-receptor partial agonist, is a potent and efficacious intraocular pressure lowering agent in ocular hypertensive cynomolgus monkeys

Preclinical Research FR-190997 (8-[2,6-dichloro-3-[N-[(E)-4-(N-methylcarbamoyl) cinnaminoacetyl]-N-methylamino]benzyloxy]-2-methyl-4- (2-pyridylmethoxy) quinoline), a nonpeptide bradykinin (BK) B2-receptor-selective agonist, represents a novel class of ocular hypotensive agents. FR-190997 exhibited a high affinity for the human cloned B2-receptor (Ki = 9.8 nM) and a relatively high potency (EC50 = 155 nM) for mobilizing intracellular Ca(2+) ([Ca(2+)]i) in human ocular cells from nonpigmented ciliary epithelium; trabecular meshwork [h-TM]; ciliary muscle [h-CM] that are involved in regulating intraocular pressure (IOP). Unlike BK, FR-190997 behaved as a partial agonist (Emax = 38-80%) in these cells and its [Ca(2+)]i-mobilizing effects were blocked by the B2-receptor-selective antagonists (HOE-140, Ki = 0.8-7 nM; WIN-64338, Ki = 157-425 nM). FR-190997 stimulated the production of prostaglandins (PGs) in h-CM and h-TM cells (EC50 = 15-19 nM; Emax = 27-33%); an effect that was reduced by the cyclooxygenase-2 inhibitor bromfenac, and by HOE-140. FR-190997 also induced pro-matrix metalloproteinase (MMP)-1 and MMP-3 release from h-CM cells. FR-190997 significantly lowered IOP (37% [P < 0.001] with 30 μg, 24 h post-topical ocular dosing) in ocular hypertensive eyes of conscious Cynomolgus monkeys. This effect was reduced by bromfenac and completely blocked by a B2-antagonist. FR-190997 primarily stimulated uveoslceral outflow (UVSO) of aqueous humor (2.6 to 3.9-fold above baseline). In conclusion, FR-190997 is a B2-receptor selective partial agonist that activates phospholipase C, mobilizes [Ca(2+)]; induces PG and pro-MMP production, and that profoundly lowers IOP by promoting UVSO in ocular hypertensive Cynomolgus monkey eyes.

Comparative pharmacology of bombesin receptor subtype-3, nonpeptide agonist MK-5046, a universal peptide agonist, and peptide antagonist Bantag-1 for human bombesin receptors

Bombesin-receptor-subtype-3 (BRS-3) is an orphan G-protein-coupled receptor of the bombesin (Bn) family whose natural ligand is unknown and which does not bind any natural Bn-peptide with high affinity. It is present in the central nervous system, peripheral tissues, and tumors; however, its role in normal physiology/pathophysiology is largely unknown because of the lack of selective ligands. Recently, MK-5046 [(2S)-1,1,1-trifluoro-2-[4-(1H-pyrazol-1-yl)phenyl]-3-(4-{[1-(trifluoromethyl)cyclopropyl]methyl}-1H-imidazol-2-yl)propan-2-ol] and Bantag-1 [Boc-Phe-His-4-amino-5-cyclohexyl-2,4,5-trideoxypentonyl-Leu-(3-dimethylamino) benzylamide N-methylammonium trifluoroacetate], a nonpeptide agonist and a peptide antagonist, respectively, for BRS-3 have been described, but there have been limited studies on their pharmacology. We studied MK-5046 and Bantag-1 interactions with human Bn-receptors-human bombesin receptor subtype-3 (hBRS-3), gastrin-releasing peptide receptor (GRP-R), and neuromedin B receptor (NMB-R)-and compared them with the nonselective, peptide-agonist [d-Tyr6,βAla11,Phe13,Nle14]Bn-(6-14) (peptide #1). Receptor activation was detected by activation of phospholipase C (PLC), mitogen-activated protein kinase (MAPK), focal adhesion kinase (FAK), paxillin, and Akt. In hBRS-3 cells, the relative affinities were Bantag-1 (1.3 nM) > peptide #1 (2 nM) > MK-5046 (37-160 nM) > GRP, NMB (>10 μM), and the binding-dose-inhibition curves were broad (>4 logs), with Hill coefficients differing significantly from unity. Curve-fitting demonstrated high-affinity (MK-5046, Ki = 0.08 nM) and low-affinity (MK-5046, Ki = 11-29 nM) binding sites. For PLC activation in hBRS-3 cells, the relative potencies were MK-5046 (0.02 nM) > peptide #1 (6 nM) > GRP, NMB, Bantag-1 (>10 μM), and MK-5046 had a biphasic dose response, whereas peptide #1 was monophasic. Bantag-1 was a specific hBRS-3-antagonist. In hBRS-3 cells, MK-5046 was a full agonist for activation of MAPK, FAK, Akt, and paxillin; however, it was a partial agonist for phospholipase A2 (PLA2) activation. The kinetics of activation/duration of action for PLC/MAPK activation of MK-5046 and peptide #1 differed, with peptide #1 causing more rapid stimulation; however, MK-5046 had more prolonged activity. Our study finds that MK-5046 and Bantag-1 have high affinity/selectivity for hBRS-3. The nonpeptide MK-5046 and peptide #1 agonists differ markedly in their receptor coupling, ability to activate different signaling cascades, and kinetics/duration of action. These results show that their hBRS-3 receptor activation is not always concordant and could lead to markedly different cellular responses.

Hypothesized and found mechanisms for potentiation of bradykinin actions

Potentiation of hormone actions can occur by different mechanisms, including inhibition of degrading enzymes, interaction with the hormone receptor leading to stabilization of bioactive conformation or leading to receptor homo- and hetero-oligomerization, receptor phosphorylation and dephosphorylation or can occur by directly influencing the signal transduction and ion channels. In this review the potentiation of bradykinin actions in different systems by certain compounds will be reviewed. Despite many long years of experimental research and investigation the mechanisms of potentiating action remain not fully understood. One of the most contradictory findings are the distinct differences between the inhibition of the angiotensin I-converting enzyme and the potentiation of the bradykinin induced smooth muscle reaction. Contradictory findings and hypothesized mechanisms in the literature are discussed in this review and in some cases compared to own results. Investigation of potentiating actions was extended from hypotension, smooth muscle reaction and cellular actions to activation of immunocompetent cells. In our opinion the potentiation of bradykinin action can occur by different mechanisms, depending on the system and the applied potentiating factor used.

Potentiation of bradykinin actions by analogues of the bradykinin potentiating nonapeptide BPP9alpha

Synthetic analogues of the bradykinin potentiating nonapeptide BPP9alpha indicate significantly different structural requirements for potentiation of the bradykinin (BK)-induced smooth muscle contraction (GPI) and the inhibition of isolated somatic angiotensin I-converting enzyme (ACE). The results disprove the ACE inhibition as the only single mechanism and also the direct interaction of potentiating peptides with the bradykinin receptors in transfected COS-7 cells as molecular mechanism of potentiation. Our results indicate a stimulation of inositol phosphates (IPn) formation independently from the B2 receptor. Furthermore, the results with La3+ support the role of extracellular Ca2+ and its influx through corresponding channels. The missing effect of calyculin on the GPI disproves the role of phosphatases in the potentiating action. These experimental studies should not only contribute to a better understanding of the potentiating mechanisms but also incorporate a shift in the research towards the immune system, in particular towards the immunocompetent polymorphonuclear leukocytes. The chemotaxis of these cells can be potentiated most likely by exclusive inhibition of the enzymatic degradation of bradykinin. Thus the obtained results give evidence that the potentiation of the bradykinin action can occur by different mechanisms, depending on the system and on the applied potentiating factor.

Putative roles of kinin receptors in the therapeutic effects of angiotensin 1-converting enzyme inhibitors in diabetes mellitus

The role of endogenous kinins and their receptors in diabetes mellitus is being confirmed with the recent developments of molecular and genetic animal models. Compelling evidence suggests that the kinin B(2) receptor is organ-protective and partakes to the therapeutic effects of angiotensin 1-converting enzyme inhibitors (ACEI) and angiotensin AT(1) receptor antagonists. Benefits derive primarily from vasodilatory, antihypertensive, antiproliferative, antihypertrophic, antifibrotic, antithrombotic and antioxidant properties of kinin B(2) receptor activation. Mechanisms include the formation of nitric oxide and prostacyclin and the inhibition of NAD(P)H oxidase activity involving classical and novel signalling pathways. Kinin B(2) receptor also ameliorates insulin resistance by increasing glucose uptake and supply, and by inducing glucose transporter-4 translocation either directly or through phosphorylation of insulin receptor. The kinin B(1) receptor, which is induced by the cytokine network, growth factors and hyperglycaemia, mediates hyperalgesia, vascular hyperpermeability and leukocytes infiltration in diabetic animals. However, emerging data highlight reno- and cardio-protective effects mediated by kinin B(1) receptor under chronic ACEI therapy in diabetes mellitus. Thus, the Janus-faced of kinin receptors needs to be taken into account in future drug development. For instance, locally acting kinin B(1)/B(2) receptor agonists if used in a safe therapeutic window may represent a more rationale strategy in the prevention and management of diabetic complications. Because kinin B(2) receptor antagonists may further increase insulin resistance, the persisting dogma that restricts the development of kinin receptor analogues to antagonists (that is still relevant to abrogate pain and inflammation) needs to be revisited.

Bradykinin B2 receptors mediate contraction in the normal and inflamed human gallbladder in vitro

BACKGROUND & AIMS

The components of the kinin system, including kinongens, kininogenases, and B(2) and B(1) receptors, are expressed and activated during inflammation. Here, we investigated the expression of the kinin B(2) receptor messenger RNA, kininogen and kallikrein immunoreactivity, and the ability of kinins to contract control and inflamed gallbladders in vitro.

METHODS

Human gallbladders, obtained from patients undergoing cholecystectomy either for acute cholecystitis secondary to gallstone disease or during elective gastro-entero-pancreatic surgery (controls), were processed for reverse-transcription polymerase chain reaction analysis, kallikrein and kininogen immunohistochemistry, binding studies, and in vitro contractility studies.

RESULTS

Tissue expression of B(2) receptor messenger RNA and specific binding of [(3)H]-bradykinin increased significantly in acute cholecystitis compared to controls. Kallikrein immunoreactivity was detected in the epithelium and infiltrating leukocytes, whereas kininogen immunoreactivity in the lumen of blood vessels and interstitial space. Bradykinin contracted isolated strips of control and acute cholecystitis gallbladders. In acute cholecystitis tissue, efficacy of bradykinin was higher than that of control gallbladders and similar to that of cholecystokinin. The contraction induced by bradykinin was significantly attenuated by B(2) receptor antagonism but not by cyclooxygenase inhibition and B(1), muscarinic, or tachykinin receptor antagonism.

CONCLUSIONS

All the components of the kinin system are expressed in the human gallbladder. Bradykinin is a powerful spasmogen via B(2) receptor activation in the normal and, especially, in the inflamed human gallbladder.

Beneficial effects of combined blockade of ACE and AT1 receptor on intimal hyperplasia in balloon-injured rat artery

OBJECTIVE

The present study was undertaken to elucidate the effect of the ACE inhibitor and the angiotensin II type 1 (AT1) receptor antagonist in combination on neointimal hyperplasia after balloon injury.

METHODS AND RESULTS

Temocapril (an ACE inhibitor), CS-866 (an AT1 receptor antagonist), or their combination was given orally to rats, and their effects were compared on vascular hyperplasia induced by balloon injury. The maximal preventive effect of temocapril and CS-866 alone on neointimal thickening after balloon injury was obtained at a dose of 20 and 10 mg/kg per day, respectively. However, compared with either agent alone, combined temocapril and CS-866 (20 and 10 mg/kg per day, respectively) prevented intimal thickening to a larger extent. Furthermore, compared with either agent alone, combined temocapril and CS-866 prevented vascular smooth muscle cell proliferation in the intima more potently. The increase in platelet-derived growth factor receptor tyrosyl phosphorylation was reduced more potently by the combination of both agents compared with either agent alone. The nonpeptide bradykinin B2 receptor antagonist or the NO synthase inhibitor reduced the prevention of intimal thickening by combined temocapril and CS-866.

CONCLUSIONS

Compared with either agent alone, the combination of an ACE inhibitor and an AT1 receptor antagonist is more effective in the prevention of vascular hyperplasia due to bradykinin or NO.

Proinflammatory characteristics of a nonpeptide bradykinin mimic, FR190997, in vivo

1. Proinflammatory potency of the nonpeptide bradykinin (BK) B(2) receptor agonist FR190997 (8-[2,6-dichloro-3-[N-[(E)-4-(N-methylcarbamoyl)cinnamidoacetyl]-N-methylamino]benzyloxy]-2-methyl-4-(2-pyridylmethoxy)quinoline) was investigated. 2. Intradermal injection of FR190997 (0.03 - 3 nmol site(-1)) into dorsal skin of rats increased vascular permeability in a dose-dependent manner. The effect was less than that of BK, but it was long-acting and was inhibited by treatment with FR173657 (3 mg kg(-1), p.o.). Captopril (10 mg kg(-1), i.p.) did not enhance the plasma extravasation by FR190997 (0.3 nmol site(-1)) in the presence of soybean trypsin inhibitor (SBTI, 30 microg site(-1)). 3. Subcutaneous injection of FR190997 (3 nmol site(-1)) into the hindpaw of mice markedly induced paw swelling. The oedema lasted up to 3 h after the injection. Administration of indomethacin or NS-398 (10 mg kg(-1), i.p.) significantly reduced it at 3 h after the injection. 4. Simultaneous i.p. injection of prostaglandin (PG) E(2) (1 nmol site(-1)) or beraprost sodium (0.5 nmol site(-1)) with FR190997 (5 nmol site(-1)) greatly enhanced frequency of writhing reactions in mice. 5. FR190997 (0.3 - 30 nmol kg(-1), i.v.) showed less increase in airway opening pressure (Pao) in the guinea-pig after i.v. injection. Furthermore, FR190997 (0.03 - 30 nmol) resulted in a very weak contraction of tracheal ring strips and lung parenchymal sections in vitro. 6. In mice sponge implants, topical application of FR190997 increased angiogenesis and granulation with enhanced expressions of basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) mRNAs. 7. These results indicate that FR190997 has proinflammatory long-lasting characteristics and it might be 'a stable tool' for studying the role of BK B(2) receptor in vivo.

Peptide and non-peptide bradykinin B2 receptor agonists and antagonists: a reappraisal of their pharmacology in the guinea-pig ileum

We have compared the pharmacology of different antagonists, Icatibant (H-DArg-Arg-Pro-Hyp-Gly-Thi-Ser-DTic-Oic-Arg-OH), MEN 11270 (H-DArg-Arg-Pro-Hyp-Gly-Thi-c(Dab-DTic-Oic-Arg)c(7 gamma-10 alpha)), and FR173657 ((E)-3-(6-acetamido-3-pyridyl)-N-[N-[2, 4-dichloro-3-[(2-methyl-8-quinolinyl)oxymethyl]phenyl]-N-methyl aminocarbonylmethyl]acrylamide) at bradykinin B2 receptors expressed in the guinea-pig ileum by using bradykinin and the non-peptide FR190997 ((8-[2,6-dichloro-3-[N-[(E)-4-(N-methylcarbamoyl)cinnamidoacety l]-N -methylamino]benzyloxy]-2-methyl-4-(2-pyridylmethoxy)quinoline) as agonists. In organ bath experiments, Icatibant and FR173657 exerted a non-competitive antagonism (pKB 9.5 and 9.2, respectively) of the contractile response to bradykinin, whereas MEN 11270 showed competitive antagonism (pKB 8.3, slope -0.90). The profile of action and apparent affinities of the three antagonists did not change if contact time was prolonged. The inhibition by the three antagonists of the contractile response to bradykinin was differently reverted by washout (MEN 11270 <30 min, Icatibant <60 min, FR173657 >60 min). The non-peptide ligand FR190997 acted as partial agonist if applied cumulatively to the bath (pD2 8.06, Emax 43% of maximal contractility), but as a full agonist when a maximally effective concentration was added (Emax 83%). FR173657 produced non-competitive antagonism of the response to FR190997 with apparent affinity similar to that measured toward bradykinin. On the contrary, Icatibant and MEN 11270 (300 nM both) competitively antagonized the contractile activity exerted by FR190997 with lower apparent pA2 value (6.9 and 7.2, respectively). In radioligand binding experiments, MEN 11270 and Icatibant displaced the [3H]bradykinin binding with pKi of 10.2 and 10.5 (Hill slope not different from unity), respectively. The non-peptide ligands displaced the [3H]bradykinin binding with similar affinity, their pKi being 8.7 and 8.6 for FR173657 and FR190997, respectively (both Hill slopes <1). The present study indicates the difference in the antagonism type (competitive vs. non-competitive) by Icatibant, MEN 11270, and FR173657, as mainly ascribable to their different reversibility from the bradykinin B2 receptor, and affected by the kinetic of the response induced by the different agonists. Results are discussed in view of a different interaction of peptide and non-peptide agonist at the receptor.

The agonist SR 146131 and the antagonist SR 27897 occupy different sites on the human CCK(1) receptor

1-[2-(4-(2-Chlorophenyl)thiazol-2-yl) aminocarbonyl indoyl] acetic acid (SR 27897) is an effective CCK(1) receptor antagonist, while the structurally related molecule 2-[4-(4-chloro-2, 5-dimethoxyphenyl)-5-(2-cyclohexyl-ethyl)-thiazol-2-ylcarbamoyl ]-5, 7-dimethyl-indol-1-yl-1-acetic acid (SR 146131) is a highly potent and specific agonist for the same receptor. To discover how the two molecules interact with the human cholecystokinin (CCK) CCK(1) receptor, we have carried out binding and activity studies with 33-point mutated receptors. Only six mutants showed altered [3H]SR 27897 binding properties, Lys(115), Lys(187), Phe(198), Trp(209), Leu(214) and Asn(333). In contrast, numerous mutations throughout the receptor either reduced SR 146131 agonist potency, Phe(97), Gly(122), Phe(198), Trp(209), Ile(229), Asn(333), Arg(336) and Leu(356) or increased it, Tyr(48), Cys(94), Asn(98), Leu(217) and Ser(359). Only mutations of Phe(198), Trp(209) and Asn(333) affected both SR 27897 and SR 146131 binding or activity. The collated information was used to construct molecular models of SR 27897 and SR 146131 bound to the human CCK(1) receptor. The clear difference in the binding sites of SR 27897 and SR 146131 offers a molecular explanation for their contrasting pharmacological characteristics.

Potentiation of the vascular response to kinins by inhibition of myocardial kininases

Inhibitors of angiotensin I-converting enzyme (ACE) are very efficacious in the potentiation of the actions of bradykinin (BK) and are able to provoke a B(2) receptor-mediated vasodilation even after desensitization of this receptor. Because this activity cannot be easily explained only by an inhibition of kinin degradation, direct interactions of ACE inhibitors with the B(2) receptor or its signal transduction have been hypothesized. To clarify the significance of degradation-independent potentiation, we studied the vasodilatory effects of BK and 2 degradation-resistant B(2) receptor agonists in the isolated rat heart, a model in which ACE and aminopeptidase P (APP) contribute equally to the degradation of BK. Coronary vasodilation to BK and to a peptidic (B6014) and a nonpeptidic (FR190997) degradation-resistant B(2) agonist was assessed in the presence or absence of the ACE inhibitor ramiprilat, the APP inhibitor mercaptoethanol, or both. Ramiprilat or mercaptoethanol induced leftward shifts in the BK dose-response curve (EC(50)=3.4 nmol/L) by a factor of 4.6 or 4.9, respectively. Combined inhibition of ACE and APP reduced the EC(50) of BK to 0.18 nmol/L (ie, by a factor of 19) but potentiated the activity of B6014 (EC(50)=1.9 nmol/L) only weakly without altering that of FR190997 (EC(50)=0.34 nmol/L). Desensitization of B(2) receptors was induced by the administration of BK (0.2 micromol/L) or FR190997 (0.1 micromol/L) for 30 minutes; the vascular reactivity to ramiprilat or increasing doses of BK was tested thereafter. After desensitization with BK, but not FR190997, an additional application of ramiprilat provoked a B(2) receptor-mediated vasodilation. High BK concentrations were still effective at the desensitized receptor. The process of desensitization was not altered by ramiprilat. These results show that in this model, all potentiating actions of ACE inhibitors on kinin-induced vasodilation are exclusively related to the reduction in BK breakdown and are equivalently provoked by APP inhibition. The desensitization of B(2) receptors is overcome by increasing BK concentrations, either directly or through the inhibition of ACE. These observations do not suggest any direct interactions of ACE inhibitors with the B(2) receptor or its signal transduction but point to a very high activity of BK degradation in the vicinity of the B(2) receptor in combination with a stimulation-dependent reduction in receptor affinity.

A nonpeptide mimic of bradykinin blunts the development of hypertension in young spontaneously hypertensive rats

We tested whether FR190997, a nonpeptide B(2) agonist, prevented the development of hypertension in young spontaneously hypertensive rats (SHR), which secrete less kallikrein into the urine than do Wistar-Kyoto rats. An intra-arterial (IA) injection of FR190997 (0.3 to 30 nmol/kg) caused dose-dependent hypotension in conscious Sprague-Dawley rats. Although the maximum hypotensive potency of FR190997 equaled that of bradykinin, its action lasted approximately 10 times as long. Hoe140 (100 nmol/kg IA) significantly blocked the hypotensive response induced by FR190997 (10 nmol/kg). Atropine (100 nmol/kg IA) did not affect this response. A selective infusion of FR190997 into the renal artery induced natriuresis and diuresis in anesthetized rabbits. A continuous infusion (2 nmol. 10 mL(-1). h(-1) per rat) of FR190997 into the abdominal aorta of young SHR (6 weeks old, n=6) for 6 days significantly (P<0.05) reduced mean blood pressure to 114+/-6 (day 2) and 110+/-6 (day 5) mm Hg, from 149+/-7 and 162+/-6 mm Hg, respectively, in vehicle-infused rats (n=6). At 8 days after continuous infusion (day 14), mean blood pressure (148+/-5 mm Hg) in FR190997-infused rats remained significantly (P<0. 05) lower than that in vehicle-infused rats (190+/-6 mm Hg), almost the peak value. The mesenteric artery isolated from FR190997-treated rats (day 14) had lower contractile sensitivity to norepinephrine than that from vehicle-treated rats. These results suggested that the continuous infusion of a nonpeptide B(2) agonist may prevent hypertension if performed in the critical phase.

Nonpeptide mimic of bradykinin with long-acting properties

Kinins, members of a family of peptides released from kininogens by the action of kallikreins, have been implicated in a variety of biological activities including vasodilation, increased vascular permeability, contraction of smooth muscle cells and activation of sensory neurons. However, investigation of the physiological actions of kinins have been greatly hampered because its effects are curtailed by rapid proteolytic degradation. We examined the pharmacological characteristics of the first nonpeptide bradykinin receptor agonist 8-[2,6-dichloro-3-[N-[(E)-4-(N-methylcarbamoyl)cinnamidoacetyl+ ++]-N-methylamino]benzyloxy]-2-methyl-4-(2-pyridylmethoxy)quinolin e (FR190997). FR190997, whose structure is quite different from the natural peptide ligand, but is similar to the nonpeptide antagonists FR165649, FR167344 and FR173657, potently and selectively interacts with the human B2 receptor and markedly stimulates inositol phosphate formation in transfected Chinese hamster ovary (CHO) cells. FR190997 induces concentration-dependent contraction of isolated guinea pig ileum. In vivo, FR190997 mimics the biological action of bradykinin and induces hypotensive responses in rats with prolonged duration, presumably as a consequence of its resistance to proteolytic degradation. Therefore, FR190997 is a highly potent and subtype-selective nonpeptide agonist which displays high intrinsic activity at the bradykinin B2 receptor. This compound represents a powerful tool for further investigation of the physiology and pathophysiology of bradykinin receptors.

Structural requirements for B2-agonists with improved degradation stability

Studies on bradykinin (BK) have been impeded by the fact that this peptide is rapidly degraded by various kininases. Modifications enacted to stabilize the BK sequence have usually resulted in a loss of agonistic activity. In this study, new structural modifications were investigated with the aim to identify degradation-resistant agonists on the bradykinin B2-receptor. The efficacy and degradation stability of several potentially agonistic derivatives were examined using a B2-receptor model (FURA-stained rat fibroblasts) and rat serum kininases. Modifications of the investigated BK analogues included amino-terminal (D-Arg) or carboxy-terminal (Ile-Tyr) prolongation, various substitutions at positions 2, 5, 7, 8 (tetrahydroisoquinoline-3-carboxylic acid, octahydroindole-2-carboxylic acid, hydroxy-proline, beta-2-thienylalanine, 2,3-dehydro-phenylalanine, erythro-beta-phenylserine, erythro-alpha-amino-beta-phenyl-butyric acid, N-methyl-phenylalanine), or intramolecular cyclization via lactam bridges. Kinin inactivation was investigated in rat serum, where the activities of angiotensin I-converting enzyme (ACE), carboxypeptidase N (CPN), aminopeptidase P (APP) and aminopeptidase M (APM) could be differentiated by selective inhibitors. Analogues derived from phyllokinin (BK-Ile-Tyr-SO4) and cyclic peptides had no receptor affinity. Useful modifications compatible with agonistic activity included D-Arg0 (protects against APP), D-N-methyl-Phe7 and dehydro-Phe5 (protect against ACE), and erythro-phenylserine or erythro-amino-phenyl-butyric acid at position 8 (protect against ACE and CPN). Finally, the kinin derivatives D-Arg0-[Hyp3, Thi5, epsilonSer(betaPh)8]-BK and D-Arg0-[Hyp3, Thi5, epsilonAbu(betaPh)8]-BK proved to be potent B2-agonists with extensive stability against rat serum kininases.

Discovery of orally active nonpeptide bradykinin B2 receptor antagonists

Orally active nonpeptide bradykinin (BK) B2 receptor antagonists have been discovered by using directed random screening and chemical modification. These compounds displaced [3H]BK binding to B2 receptors in guinea-pig ileum membranes, rat uterus membranes and human lung fibroblasts with nanomolar IC50s. They did not inhibit different specific radio-ligand bindings to other receptor sites including B2 receptors. In isolated guinea-pig ileum preparations, these compounds had no agonistic effect on smooth muscle contraction at 10(-6) M, and caused parallel rightward shifts of the concentration-response curves to BK on contraction with higher p A2 values. They also blocked human B2 receptor-mediated phosphatidylinositol hydrolysis without agonistic effect. In vivo, the oral administrations of these antagonists potently inhibited BK-induced bronchoconstriction in guinea-pigs. They also reduced carrageenin-induced paw edema and caerulein-induced pancreatitis in rats. Moreover, these compounds alleviated kaolin-induced pain in mice by oral administration. These results show that our compounds are potent, selective, and orally active BK B2 receptor antagonists and that they may have therapeutic potential against inflammatory diseases and pain.

Pharmacological profile of LF 16-0687, a new potent non-peptide bradykinin B2 receptor antagonist

LF 16-0687 (1-[[2,4-dichloro-3-[[(2,4-dimethylquinolin-8-yl)oxy] methyl]phenyl]sulfonyl]-N-[3-[[4-(aminoimethyl) phenyl] carbonylamino]propyl]-2(S)-pyrrolidinecarboxamide) has been selected from a large-scale medicinal chemistry program for further development. In competition binding studies using [3H]bradykinin (BK), LF 16-0687 bound to the human, rat and guinea-pig recombinant B2 receptor expressed in CHO cells giving K(i) values of 0.67 nM, 1.74 nM and 1.37 nM, respectively. It also bound to the native BK B2 receptor from human umbilical vein (HUV), rat uterus (RU) and guinea-pig ileum (GPI) giving K(i) values of 0.89 nM, 0.28 nM and 0.98 nM, respectively. It inhibited BK-induced IP1, IP2 and IP3 formation in INT407 cells yielding pK(B) values of 8.5, 8.6 and 8.7, respectively. In isolated organs experiments, LF 16-0687 behaved as a competitive antagonist of BK-mediated contractions giving pA2 values of 9.1 in HUV, 7.7 in RU and 9.1 in GPI. Binding and functional studies performed over 40 different receptors revealed that LF 16-0687 was selective for the BK B2 receptor. A continuous intravenous infusion of LF 16-0687 antagonized in a dose-dependent manner and with a rapid onset of action BK-induced hypotensive response. Subcutaneous administration of LF 16-0687 at 1.1 micromol/kg to rats markedly reduced BK-induced edema of the stomach (- 69%), duodenum (-65%) and pancreas (-56%).

Nonpeptidic ligands for peptide and protein receptors

The first potent nonpeptidic ligands for somatostatin, luteinizing hormone-releasing hormone, glucagon and bradykinin receptors have been reported. Nonpeptidic clinical candidates have been identified or are currently under study for substance P, bradykinin, endothelin, growth hormone secretagogue, angiotensin, vasopressin, motilin and cholecystokinin. Design, screening, combinatorial chemistry and classical medicinal chemistry all played important roles in these advances.

Pharmacology and cardiovascular implications of the kinin-kallikrein system

Kinins are peptide hormones that can exert a significant influence on the regulation of blood pressure and vascular tone due to their vasodilatatory, natriuretic and growth modulating activity. Their cardiovascular involvement in physiological and pathophysiological situations has been studied intensively since inhibitors for angiotensin I-converting enzyme and selective receptor antagonists have become available for pharmacologically potentiating or inhibiting kinin-mediated reactions. Molecular biological analysis and the establishment of genetically modified animal models have also allowed newer information to be acquired on this subject. In this review, the components and cardiovascularly relevant mechanisms of the kinin-kallikrein system shall be described. Organ-specific effects concerning the kidneys, the vascular system, the heart and nervous tissue shall also be illustrated. On this issue, the physiological functions and pathophysiological implications of the kinin-kallikrein system should be clearly distinguished from the many, mostly endothelium-mediated protective effects which occur during ACE inhibition due to the potentiation of kinin effects. Finally, a view shall also be cast upon newly discovered targets of action, which could be exploited for therapeutically altering the kinin-kallikrein system.

Nonpeptide antagonists for kinin receptors

Kinins are a family of small peptides acting as mediators of inflammation and pain in the peripheral and central nervous system. The two main 'kinins' in mammals are the nonapeptide bradykinin (BK, Arg1-Pro2-Pro3-Gly4-Phe5-Ser6-Pro7-Phe8-Arg9) and the decapeptide kallidin (KD, [Lys0]-BK, Lys1-Arg2-Pro3-Pro4-Gly5-Phe6-Ser7-Pro8-Phe9- Arg10). Their biological actions are mediated by two distinct receptors, termed B1 and B2. Kinin B and B2 receptor antagonists may be useful drugs endowed with analgesic and anti-inflammatory properties, with potential use in asthma, allergic rhinitis and other diseases. The first nonpeptide kinin B2 receptor antagonist, WIN 64338, was reported in 1993. Despite its low selectivity, the compound provided a reference for pharmacological and modeling studies. Several quinoline and imidazo[1,2-a]pyridine derivatives have been shown by Fujisawa to possess high affinity and selectivity for kinin B2 receptors. Among them, FR 173657 displayed excellent in vitro and in vivo antagonistic activity, while FR 190997 emerged as the first nonpeptide agonist for B2 receptor. Two structurally related Fournier compounds were recently published. Other kinin B2 receptor ligands were obtained by rational design, through library screening or from natural sources. The only example of a nonpeptide kinin B1 receptor ligand has been reported in a patent by Sanofi.