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 IC50s 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.

Recently, it has been reported that 5-HT2 receptor agonists effectively reduce intraocular pressure (IOP) in a nonhuman primate model of glaucoma. Although 1-[(2S)-2-aminopropyl]indazol-6-ol (AL-34662) was shown to have good efficacy in this nonhuman primate model of ocular hypertension as well as a desirable physicochemical and permeability profile, subsequently identified cardiovascular side effects in multiple species precluded further clinical evaluation of this compound. Herein, we report selected structural modifications that resulted in the identification of (8R)-1-[(2S)-2-aminopropyl]-8,9-dihydro-7H-pyrano[2,3-g]indazol-8-ol (13), which displayed an acceptable profile to support advancement for further preclinical evaluation as a candidate for proof-of-concept studies in humans.

Although several classes of drugs, including FP-receptor prostaglandin agonist analogs, are available to treat elevated intraocular pressure (IOP) associated with glaucoma, novel pharmaceuticals to treat this potentially blinding disease are still being sought. With recent demonstration of potent IOP-lowering activity of serotonin-2 receptor agonists in conscious ocular hypertensive Cynomolgus monkey eyes, the prospects of this unexampled class of compounds yielding new drugs for the treatment of elevated IOP look bright. This article reviews the ocular serotonergic literature pertaining to elevated IOP in patients with ocular hypertension and glaucoma, the data on ocular hypotensive serotonin-2 agonists, and discusses their potential mechanism(s) of action at the cellular and whole-animal level.

AL-38022A is a novel synthetic serotonergic (5-HT) ligand that exhibited high affinity for each of the 5-HT2 receptor subtypes (K-i <= 2.2 nM), but a significantly lower (> 100-fold less) affinity for other 5-HT receptors. In addition, AL-38022A displayed a very low affinity for a broad array of other receptors, neurotransmitter transport sites, ion channels, and second messenger elements, making it a relatively selective agent. AL-38022A potently stimulated functional responses via native and cloned rat (EC50 range: 1.9-22.5 nM) and human (EC5o range: 0.5-2.2 nM) 5-HT2 receptor subtypes including [Ca2+](i) mobilization and tissue contractions with apparently similar potencies and intrinsic activities and was a full agonist at all 5-HT2 receptor subtypes. The CNS activity of AL-38022A was assessed by evaluating its discriminative stimulus effects in both a rat and a monkey drug discrimination paradigm using DOM as the training drug. AL-38022A fully generalized to the DOM stimulus in each of these Studies; in monkeys MDL 100907 antagonized both DOM and AL-38022A. The pharmacological profile of AL-38022A suggests that it could be a useful tool in defining 5-HT2 receptor signaling and receptor characterization where 5-HT may function as a neurotransmitter. (c) 2008 Elsevier Inc, All rights reserved.

A series of 8-substituted benzodifuran analogs was prepared and evaluated for 5-HT(2A) receptor binding and activation. Several compounds containing ether and ester functionality were found to be potent agonists. Topical ocular administration of 5, 18, and 25 effectively reduced intra-ocular pressure in the hypertensive cynomolgus monkey eye in the range of 25-37%.

Thieno[3,2-e]-1,2-thiazine-6-sulfonamide 1,1-dioxides, which have a quaternary ammonium moiety incorporated into their structures, were synthesized. All of the quaternary ammonium salts prepared in the present study are potent inhibitors of both human carbonic anhydrase-II and recombinant human carbonic anhydrase-IV; they are significantly more potent as inhibitors of these carbonic anhydrase isozymes than the previously reported inhibitor quaternary ammonium homosulfanilamide. By virtue of the permanent cationic charge on these compounds they are anticipated to be membrane-impermeable inhibitors of carbonic anhydrase. Spiro quaternary ammonium compounds, such as 15 and 16, when formed by intracellular cyclization following transport of a suitable precursor molecule, such as 14, may be selective prolonged inhibitors of cytosolic carbonic anhydrase due to intracellular entrapment.

Serotonin 5-HT(2) receptor agonists have been identified as a potential new class of agents for the treatment of ocular hypertension and glaucoma. The initially reported tryptamine analogues displayed either poor solution stability, potent central nervous system activity, or both of these undesirable characteristics and were unacceptable for clinical evaluation. A series of 1-(2-aminopropyl)-1H-indazole analogues was synthesized and evaluated for their suitability for consideration as clinical candidates. 1-((S)-2-Aminopropyl)-1H-indazol-6-ol (9) was identified as a peripherally acting potent 5-HT(2) receptor agonist (EC(50) = 42.7 nM, E(max) = 89%) with high selectivity for the 5-HT(2) receptors relative to other serotonergic receptor subtypes and other families of receptors and has significantly greater solution stability than alpha-methyl-5-hydroxytryptamine. Additionally, 9 potently lowers intraocular pressure in conscious ocular hypertensive monkeys (-13 mmHg, 33%); this reduction appears to be through a local rather than a centrally mediated effect. Compound 9 appears to be an excellent 5-HT(2) receptor agonist for conducting further studies directed toward a clinical proof-of-concept study for this class of ocular hypotensive agents.