Design of Novel Melatonin Analogs for the Reduction of Intraocular Pressure in Normotensive Rabbits Pilar Alarma-Estrany, Ana Guzman-Aranguez, Fernando Huete, Assumpta Peral, Robert Plourde, Jr., Teresa Pelaez, Benjamin Yerxa, and Jesu ´ s Pintor Departamento Bioquimica (P.A.-E., A.G.-A., F.H., T.P., J.P.) and Optica (A.P.), Escuela Universitaria de O ´ ptica, Universidad Complutense de Madrid, Madrid, Spain; and Inspire Pharmaceuticals, Inc., Durham, North Carolina (R.P., B.Y.) Received December 16, 2010; accepted March 1, 2011 ABSTRACT Melatonin, the MT 2 melatonin receptor agonist IIK7 [N-butanoyl- 2-(2-methoxy-6H-isoindolo[2,1-a]indol-11-yl)ethanamine], and the putative MT 3 melatonin receptor agonist 5-MCA-NAT [5- methoxycarbonylamino-N-acetyltryptamine] have previously been shown to reduce intraocular pressure (IOP) in ocular normo- tensive rabbits. To gain a better understanding of the structure- activity relationship of compounds that activate MT 2 and MT 3 receptors mediating reductions in IOP, novel melatonin analogs with rationally varied substitutions were synthesized and tested for their effects on IOP in ocular normotensive rabbits (n = 160). All synthesized melatonin analogs reduced IOP. The best-effect low- ering IOP was obtained with the analogs INS48848 [methyl-1- methylene-2,3,4,9-tetrahydro-1H-carbazol-6-ylcarbamate], INS48862 [methyl-2-bromo-3-(2-ethanamidoethyl)-1H-indol-5- ylcarbamate], and INS48852 [(E)-N-(2-(5-methoxy-1H-indol-3- yl)ethyl)-3-phenylprop-2-enamide]. These compounds produced dose-dependent decreases in IOP that were maximal at 0.1 mM (total dose of 0.259 g for INS48848, 0.354 g for INS48862, and 0.320 g for INS48852) and 1 mM (total dose of 2.59 g for INS48848, 3.54 g for INS48862, and 3.20 g for INS48852), with maximal reductions of 36.0  4.0, 24.0  1.5, and 30.0  1.5% for INS48848, INS48862, and INS48852, respectively. Studies using melatonin receptor antagonists (luzindole, prazosin, and DH97 [N-pentanoyl-2-benzyltryptamine]) indicated that INS48862 and INS48852 activate preferentially a MT 2 melatonin receptor and suggest that INS48848 may act mainly via a MT 3 receptor. The most effective compounds were also well tolerated in a battery of standard ocular surface irritation studies. The implication of these findings to the design of novel drugs to treat ocular hypertension is discussed. Introduction Glaucoma is a group of diseases characterized by retinal and optic neuropathy and progressive visual field loss. The most prevalent type, open angle glaucoma, is estimated to account for approximately 15% blindness worldwide (Thylefors and Ne ´grel, 1994). The pathology of this type is secondary to elevated intra- ocular pressure (IOP), and reduction of IOP is the most common treatment modality. In the normal eye, a balance of formation and outflow of aqueous humor regulates IOP, maintaining a mean IOP of approximately 16 mm Hg. In open angle glaucoma, normal aqueous humor outflow through the trabecular meshwork is impeded, and there is a consequential rise in IOP to values higher than 21 mm Hg (Schottenstein, 1996). Circadian fluctuation of IOP is well established, and the relationship between melatonin and IOP has been explored in view of the involvement of pineal melatonin in the regulation of This work was supported by grants from Ministerio de Ciencia e Inno- vacio ´n [SAF2007-60835, SAF2010-16024]; RETIC Red de Patología Ocular del Envejecimiento, Calidad Visual y Calidad de Vida [RD07/0062/0004]; NEUROTRANS CM [S-SAL 0253-2006]; and BSCH-UCM [GR58/08]. Article, publication date, and citation information can be found at http://jpet.aspetjournals.org. doi:10.1124/jpet.110.178319. ABBREVIATIONS: IOP, intraocular pressure; 5-MCA-NAT, 5-methoxycarbonylamino-N-acetyltryptamine; IIK7, N-butanoyl-2-(2-methoxy-6H- isoindolo[2,1-a]indol-11-yl)ethanamine; DH97, N-pentanoyl-2-benzyltryptamine; EA, electron affinity; FOSA, hydrophobic solvent-accessible surface area; DMSO, dimethyl sulfoxide; INS48848, methyl-1-methylene-2,3,4,9-tetrahydro-1H-carbazol-6-ylcarbamate; INS48862, methyl-2- bromo-3-(2-ethanamidoethyl)-1H-indol-5-ylcarbamate; INS48852, (E)-N-(2-(5-methoxy-1H-indol-3-yl)ethyl)-3-phenylprop-2-enamide; INS48864, S-(butylperoxy)-N-((5-methoxy-1H-indol-3-yl)methyl)thiohydroxylamine; INS48879, diphenyl (5-methoxy-1H-indol-3-yl)methylphosphoramidate; INS48476, methyl-3-(propanamidomethyl)-1H-indol-5-ylcarbamate; INS48793, methyl-2-bromo-3-(ethanamidomethyl)-1H-indol-5-ylcarbamate; INS48834, methyl-3-(ethanamidomethyl)-2-methyl-1H-indol-5-ylcarbamate; INS48497, allyl-3-(ethanamidomethyl)-1H-indol-5-ylcarbamate; INS48838, N-((5-methoxy-1H-indol-3-yl)methyl)propanamide; INS48853, N-((5-methoxy-1H-indol-3-yl)methyl)-2-methylpropanamide; INS48836, N-((5-methoxy-1H-indol-3-yl)methyl)benzamide; INS48882, 1-((5-methoxy-1H-indol-3-yl)methyl)-6-oxopiperidine-2-carboxylic acid; INS48887, methyl-3-(ethanamidomethyl)-1H-indol-5-ylcarbamate; INS48863, N-((5-methoxy-1H-indol-3-yl)methyl)methanesulfonamide; INS48803, methyl- 3-(2-ethanamidoethyl)-1-methyl-1H-indol-5-yl(methyl)carbamate. 0022-3565/11/3373-703–709$25.00 THE JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS Vol. 337, No. 3 Copyright © 2011 by The American Society for Pharmacology and Experimental Therapeutics 178319/3687322 JPET 337:703–709, 2011 Printed in U.S.A. 703 at ASPET Journals on March 24, 2017 jpet.aspetjournals.org Downloaded from