Rapid Identification of Novel Inhibitors of the Human Aquaporin-1 Water Channel.

Aquaporins (AQPs) are a family of membrane proteins that function as channels facilitating water transport in response to osmotic gradients. These play critical roles in several normal physiological and pathological states and are targets for drug discovery. Selective inhibition of the AQP1 water channel may provide a new approach for the treatment of several disorders including ocular hypertension/glaucoma, congestive heart failure, brain swelling associated with a stroke, corneal and macular edema, pulmonary edema, and otic disorders such as hearing loss and vertigo. We developed a high-throughput assay to screen a library of compounds as potential AQP1 modulators by monitoring the fluorescence dequenching of entrapped calcein in a confluent layer of AQP1-overexpressing CHO cells that were exposed to a hypotonic shock. Promising candidates were tested in a Xenopus oocyte-swelling assay, which confirmed the identification of two lead classes of compounds belonging to aromatic sulfonamides and dihydrobenzofurans with IC50 s in the low micromolar range. These selected compounds directly inhibited water transport in AQP1-enriched stripped erythrocyte ghosts and in proteoliposomes reconstituted with purified AQP1. Validation of these lead compounds, by the three independent assays, establishes a set of attractive AQP1 blockers for developing novel, small-molecule functional modulators of human AQP1.

Preclinical pharmacology, ocular tolerability and ocular hypotensive efficacy of a novel non-peptide bradykinin mimetic small molecule.

We sought to characterize the ocular pharmacology, tolerability and intraocular pressure (IOP)-lowering efficacy of FR-190997, a non-peptidic bradykinin (BK) B2-receptor agonist. FR-190997 possessed a relatively high receptor binding affinity (Ki = 27 nM) and a high in vitro potency (EC50 = 18.3 ± 4.4 nM) for inositol-1-phosphate generation via human cloned B2-receptors expressed in host cells with mimimal activity at B1-receptors. It also mobilized intracellular Ca2+ in isolated human trabecular meshwork (h-TM), ciliary muscle (h-CM), and in immortalized non-pigmented ciliary epithelial (h-iNPE) cells (EC50s = 167-384 nM; Emax = 32-86% of BK-induced response). HOE-140, a selective B2-receptor antagonist, potently blocked the latter effects of FR-190997 (e.g., IC50 = 7.3 ± 0.6 nM in h-CM cells). FR-190997 also stimulated the release of prostaglandins (PGs) from h-TM and h-CM cells (EC50s = 60-84 nM; Emax = 29-44% relative to max. BK-induced effects). FR-190997 (0.3-300 µg t.o.) did not activate cat corneal polymodal nociceptors and did not cause ocular discomfort in Dutch-Belted rabbits, but it was not well tolerated in New Zealand albino rabbits and Hartley guinea pigs. A single topical ocular (t.o.) dose of 1% FR-190997 in Dutch-Belted rabbits and mixed breed cats did not lower IOP. However, FR-190997 efficaciously lowered IOP of conscious ocular hypertensive cynomolgus monkey eyes (e.g., 34.5 ± 7.5% decrease; 6 h post-dose of 30 µg t.o.; n = 8). Thus, FR-190997 is an unexampled efficacious ocular hypotensive B2-receptor non-peptide BK agonist that activates multiple signaling pathways to cause IOP reduction.

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.

Human non-pigmented ciliary epithelium bradykinin B2-receptors: receptor localization, pharmacological characterization of intracellular Ca(2+) mobilization, and prostaglandin secretion.

PURPOSE: To characterize the bradykinin (BK) receptor system in human non-pigmented ciliary epithelium (NPCE) using immunohistochemistry and functional cell-based techniques. METHODS: B2-receptor protein expression was studied in sections of human donor eyes and in Cynomolgus monkey eyes using immunohistochemical methods. The pharmacological characteristics of intracellular Ca(2+) ([Ca(2+)]i) mobilization in response to BK and related peptides, and blockade by two antagonists, was studied in primary human (p-h-NPCE) and in immortalized human NPCE (imh-NPCE) cells. Prostaglandins (PGs) release induced by BK was also studied in both cell-types using ELISA assays. Limited studies on primary human ciliary muscle (h-CM) cells and human trabecular meshwork (h-TM) cells and Chinese hamster ovary cells expressing human cloned B2-receptors (CHO-B2) were performed to compare with responses in both the NPCE cell-types. RESULTS: B2-receptor immunoreactivity was observed on human and Cynomolgus monkey NPCE cells on eye sections from both species. BK and related analog peptides differentially activated signaling mechanisms in NPCE cells by mobilizing [Ca(2+)]i, and the BK-evoked responses were blocked by B2-receptor-selective antagonists, HOE-140 and (S)-WIN-64338. Relative agonist potencies (EC50, nM) in p-h-NPCE cells [and in imh-NPCE cells] were: BK=3.4 ± 0.4 [6.3 nM]; Hyp(3)-BK EC50=1.7 ± 0.2 [6.0 nM], Lys-BK EC50=7.0 ± 0.3 [19.8 nM]; Met-Lys-BK EC50=106 ± 57.8 [125 nM]; Des-Arg(9)-BK EC50=>10,000 [16 µM]. The antagonist potencies for attenuating BK-induced mobilization of [Ca(2+)]i in these cells were: HOE-140 (Ki=7.9 ± 1.8 nM, n=4) and (S)-WIN-64338 (Ki=451 ± 44 nM, n=4). These NPCE cell data correlated well with those obtained for h-CM and h-TM cells, and with B2-receptor binding (r=0.99, p<0.0001). However, BK failed to stimulate total PGs production in both NPCE cell-types even though 10% bovine serum increased PG release (by 4.9-fold above baseline), and even though BK stimulated PG release from h-CM, h-TM and in CHO-B2 cells. BK (1 µM) also failed to increase nitric oxide (NO) levels in NPCE cells even though sodium nitropruside increased NO production by 3-fold. CONCLUSIONS: Human and monkey NPCE express immunoreactive B2-receptor proteins. These proteins were functionally active, since BK and related peptides potently stimulated mobilization of [Ca(2+)]i in p-h-NPCE and imNPCE cells that was blocked by two B2-selective antagonists. Down-stream signaling from B2-receptor activation did not appear to involve PG synthesis/release (or NO production) in NPCE cell-types under the present conditions, even though h-CM, h-TM and CHO-B2 cells exhibited robust PG synthesis and release in response to BK.

Trabecular meshwork bradykinin receptors: mRNA levels, immunohistochemical visualization, signaling processes pharmacology, and linkage to IOP reduction.

PURPOSE: To localize mRNA and protein of bradykinin (BK) receptors, BK precursor polypeptide (kininogen) mRNA, and to study functional biochemical pharmacology of the signal transduction processes mediated by B2-receptors in isolated human trabecular meshwork (h-TM) cells. Intraocular pressure (IOP) lowering effects of 2 kinins were also investigated. METHODS: Previously documented procedures were utilized throughout these studies. RESULTS: Kinninogen mRNA was most abundant in TM, ciliary body (CB), and optic nerve head and appeared elevated in glaucomatous h-TM tissue. High levels of B2-receptor mRNA were found in the sclera, iris, TM, and CB. B2-receptor subtype protein was localized in cells of the monkey and h-TM, and the treatment of isolated h-TM cells with transforming growth factor-ß2 (5 ng/mL) caused significant (P<0.04) downregulation of B2-receptor mRNA. In isolated primary h-TM cells, BK (EC50=0.8±0.2 nM; n=19) and Met-Lys-BK (EC50=6.5±1.5 nM) mobilized intracellular Ca(2+) and induced the release of prostaglandins (PGs) that was blocked by 2 B2-receptor antagonists [HOE-140; (S)-WIN-64338]. The cyclooxygenase inhibitor, bromfenac, abolished BK-induced PGs production. BK concentration dependently increased cell impedance, and it significantly (P<0.05) decreased h-TM cell volume in vitro. Intravitreal (ivt) administration of BK (50 µg), but not a B1-agonist (Sar-[D-Phe(9)]-Des-Arg(9)-BK; also at 50 µg), efficaciously lowered IOP (22.9% to 37% from baseline) of Dutch-Belted rabbits that naturally have high IOPs (27-28 mmHg). CONCLUSIONS: BK activates multiple signal transduction pathways in h-TM cells via B2-receptors that also mediate IOP reduction as observed in rabbits following ivt administration of BK. These ocular hypotensive effects of BK may be physiologically important and suggest a novel therapeutic potential of BK-related B2-agonists.

Protein expression, biochemical pharmacology of signal transduction, and relation to intraocular pressure modulation by bradykinin B2 receptors in ciliary muscle.

PURPOSE: To examine the bradykinin (BK) B2-receptor system in human and monkey ciliary muscle (CM) using immunohistochemical techniques, and to pharmacologically characterize the associated biochemical signal transduction systems in human CM (h-CM) cells. BK-induced modulation of intraocular pressure (IOP) in pigmented Dutch-Belt rabbits and cynomolgus monkeys was also studied. METHODS: Previously published procedures were used throughout these studies. RESULTS: The human and monkey ciliary bodies expressed high levels of B2-receptor protein immunoreactivity. Various kinins differentially stimulated [Ca²âº](i) mobilization in primary h-CM cells (BK EC50=2.4±0.2 nM > Hyp³,ß-(2-thienyl)-Ala5,Tyr(Me)8-(®)-Arg9-BK (RMP-7) > Des-Arg9-BK EC50=4.2 µM [n=3-6]), and this was blocked by B2-selective antagonists, HOE-140 (IC50=1.4±0.1 nM) and WIN-63448 (IC50=174 nM). A phospholipase C inhibitor (U73122; 10-30 µM) and ethylene glycol tetraacetic acid (1-2 mM) abolished the BK-induced [Ca²âº](i) mobilization. Total prostaglandin (primarily PGE2) secretion stimulated by BK and other kinins in h-CM cells was attenuated by the cyclooxygenase inhibitors bromfenac and flurbiprofen, and by the B2-antagonists. BK and RMP-7 (100 nM) induced a twofold increase in extracellular signal-regulated kinase-1/2 phosphorylation, and BK (0.1-1 µM; at 24 h) caused a 1.4-3.1-fold increase in promatrix metalloproteinases-1-3 release. Topical ocular BK (100 µg) failed to alter IOP in cynomolgus monkeys. However, intravitreal injection of 50 µg of BK, but not Des-Arg9-BK, lowered IOP in rabbit eyes (22.9±7.3% and 37.0±5.6% at 5 h and 8 h post-injection; n=7-10). CONCLUSIONS: These studies have provided evidence of a functional endogenously expressed B2-receptor system in the CM that appears to be involved in modulating IOP.

Human conjunctival epithelial cell responses to platelet-activating factor (PAF): signal transduction and release of proinflammatory cytokines.

PURPOSE: The aims of the study were to characterize the signal transduction responses to platelet-activating factor (PAF) and to monitor the downstream effects of PAF on the production of proinflammatory cytokines in human conjunctival epithelial cells (HCECs). METHODS: The generation of inositol phosphates ([(3)H]IPs) from [(3)H]phosphoinositide (PI) hydrolysis and the mobilization of intracellular calcium ([Ca(2+)](i)) were evaluated using ion exchange chromatography and Fura-2 fluorescence techniques, respectively. The production of the cytokines (interleukin-6 [IL-6], interleukin-8 [IL-8], and granulocyte macrophage colony-stimulating factor [GM-CSF]) from PAF-stimulated HCECs was quantified using specific ELISA assays. Specific PAF antagonists were used to study the pharmacological aspects of PAF actions in HCECs. RESULTS: PAF (100 nM) maximally stimulated PI turnover in HCECs by 2.3+/-0.02 fold (n=21) above basal levels and with a potency (EC(50)) of 5.9+/-1.7 nM (n=4). PAF or its stabilized analog, methyl carbamyl (mc)PAF (EC(50)=0.8 nM), rapidly mobilized [Ca(2+)](i), which peaked within 30-60 s and remained elevated for 3 min. PAF (10 nM-1 microM) stimulated the release of the proinflammatory cytokines, IL-6, IL-8, and GM-CSF, 1.4-3.5 fold above basal levels. The effects of PAF (100 nM) on PI turnover and [Ca(2+)](i) were potently antagonized by the PAF antagonists, 1-o-hexadecyl-2-o-acetyl-sn-glycero-3-phospho (N,N,N-trimethyl) hexanolamine (IC(50)=0.69 microM; K(i)=38 nM), methyl 2-(phenylthio)ethyl-1,4-dihydro-2,4,6-trimethyl-pyridine-3,5-dicsrboxylate (PCA-42481; IC(50)=0.89 microM; K(i)=50 nM), rac-3-(N-octadecylcarbomoyl)-2-methoxy) propyl-(2-thiazolioethyl) phosphate (CV-3988; IC(50)=13 microM; K(i)=771 nM), and (+/-)-cis-3,5-dimethyl-2-(3-pyridyl)thiazolidin-4-one HCl (SM-10661; IC(50)=14 microM; K(i)=789 nM [n=3 for each antagonist]). PAF-induced production of IL-6, IL-8, and GM-CSF from HCECs was also blocked by these PAF antagonists (IC(50)=4.6- 8.6 microM). CONCLUSIONS: HCECs respond to PAF by generating IPs, mobilizing [Ca(2+)](i), and then secreting cytokines into the extracellular medium. These results suggest that HCECs may be key target cells for the PAF released from conjunctival mast cells following ocular allergic reactions. Therefore, HCECs in culture represent suitable in vitro models for the investigation of the role of PAF in human ocular allergic and inflammatory diseases and for the discovery of therapeutically useful PAF antagonists.

Preclinical pharmacology of AL-12182, a new ocular hypotensive 11-oxa prostaglandin analog.

PURPOSE: The aim of this study was to determine selected in vivo ocular properties of AL-12182 (5,6-dihydro-4,5-didehydro-11-deoxy-11-oxa-16-(3-chlorophenoxy)-omega-tetranor-PGF(2alpha) isopropyl ester) and the in vitro profile of its free acid, AL-12180. METHODS: Previously documented radioligand binding and functional assays involving human ciliary muscle cells (h-CM), human trabecular meshwork (h-TM) and other cells, and porcine ocular arteries were utilized. For in vivo procedures, we utilized rabbits, cats, and nonhuman primates to measure hyperemia, pupil diameter, and intraocular pressure (IOP), respectively. RESULTS: AL-12180 exhibited the highest affinity for the FP-receptor (K(i) = 143 +/- 36 nM) and much lower affinity for DP-, EP(3)-, IP-, and TP-receptors, and for several nonprostanoid receptors, enzymes, neurotransmitter uptake sites, ion channels, and other regulatory sites. AL-12180 activated phospholipase C-mediated phosphoinositide hydrolysis (potency, EC(50) = 13.7-42.7 nM) through the FP-receptor in a variety of cells, such as h-CM, h-TM cells, human embryonic kidney cells expressing the cloned human ciliary body FP-receptor (HEK-FP), mouse 3T3 cells, and rat vascular smooth muscle cells. AL-8810, an FP-antagonist, blocked the effects of AL-12180 in h-CM cells (IC(50) = 8.7 microM). AL-12180 also stimulated the mobilization of intracellular Ca(2+) ([Ca(2+)](i)) in h-TM cells (EC(50) = 111 +/- 36 nM), h-CM cells (EC(50) = 11 nM), and in host cells expressing the cloned human ciliary body FP-receptor (EC(50) = 5.9 +/- 3.1 nM). AL-12180 lacked significant agonist activity at DP-, EP(2)-, EP(4)-, IP-, and TP-receptors in cell-based assays. However, AL-12180 contracted porcine central retinal and short posterior ciliary arteries in vitro with micromolar potencies that appeared to involve TP-receptor activation. in vivo, AL-12182 elicited dose-related hyperemia in the rabbit eye, miosis in the cat eye, and ocular hypotension in the nonhuman primate eye. CONCLUSIONS: AL-12180 is a relatively potent and selective FP-receptor agonist whose isopropyl ester prodrug (AL-12182) lowers IOP by as much as 40% following topical ocular dosing in a laser-induced nonhuman primate model of ocular hypertension.

Molecular pharmacology of the DP/EP2 class prostaglandin AL-6598 and quantitative autoradiographic visualization of DP and EP2 receptor sites in human eyes.

DP-class prostaglandins and prostaglandin analogs (collectively, prostaglandins or PGs) such as PGD2, BW245C, ZK110841, and ZK118182, lower intraocular pressure (IOP) in animal models of ocular hypertension. A new analog of ZK118182 (AL-6556; 13,14-dihydro-ZK118182) was synthesized, and the isopropyl ester of AL-6556 (AL-6598) was shown recently to lower IOP in the ocular hypertensive cynomolgus monkey model of glaucoma and in human subjects. AL-6556 and AL-6598 had an affinity (Ki) of 2.66-4.43 microM for DP receptors but a much lower affinity (K(i)s = 38-103 microM) for EP3, FP, IP, and TP receptors (n = 3-5). In addition, AL-6556 and AL-6598 exhibited K(i)s > 100 microM for 19 nonprostanoid receptors. Both PGs stimulated cAMP production (EC50 = 1.07 +/- 0.1 microM and EC50 = 2.64 +/- 0.84 microM; n = 3) by way of DP receptors in embryonic bovine tracheal fibroblasts. While AL-6556 and AL-6598 were partial agonists (EC(50)s = 0.47-0.69 microM; E(max) = 35%-46%) at EP2 receptors in human nonpigmented epithelial cells, neither had any agonist activity at EP4, IP, or FP receptors. The DP antagonist, BWA868C, effectively antagonized the effects of AL-6556 with a high potency (IC50 = 22.8 +/- 3.9 nM; n = 3). DP receptors radiolabeled with [3H]BWA868C on human eye sections by quantitative autoradiography were highly concentrated in the ciliary process (CP), longitudinal (LCM) and circular (CCM) ciliary muscles, and iris with much lower specific binding in the cornea (CN), lens (LNS), and retina (RET). EP2 receptors labeled with [3H]PGE2 were concentrated in the LCM, CM, RET, and iris. In conclusion, AL-6598 and AL-6556 are relatively DP-receptor-selective PGs with full agonist activity at the DP and partial agonist activity at the EP2 receptor. The IOP-lowering activities of these compounds may involve both the inflow and outflow mechanisms, as DP and EP2 receptors were visualized in human ocular tissues involved in such aqueous humor dynamics.