title: Optimization of chemical functionalities of indole-2-carboxamides to improve allosteric parameters for the cannabinoid receptor 1 (CB1).
abstract: 5-Chloro-3-ethyl-N-(4-(piperidin-1-yl)phenethyl)-1H-indole-2-carboxamide (1; ORG27569) is a prototypical allosteric modulator for the cannabinoid type 1 receptor (CB1). Here, we reveal key structural requirements of indole-2-carboxamides for allosteric modulation of CB1: a critical chain length at the C3-position, an electron withdrawing group at the C5-position, the length of the linker between the amide bond and the phenyl ring B, and the amino substituent on the phenyl ring B. These significantly impact the binding affinity (KB) and the binding cooperativity (α). A potent CB1 allosteric modulator 5-chloro-N-(4-(dimethylamino)phenethyl)-3-propyl-1H-indole-2-carboxamide (12d) was identified. It exhibited a KB of 259.3 nM with a strikingly high binding α of 24.5. We also identified 5-chloro-N-(4-(dimethylamino)phenethyl)-3-hexyl-1H-indole-2-carboxamide (12f) with a KB of 89.1 nM, which is among the lowest KB values obtained for any allosteric modulator of CB1. These positive allosteric modulators of orthosteric agonist binding nonetheless antagonized the agonist-induced G-protein coupling to the CB1 receptor, yet induced β-arrestin mediated ERK1/2 phosphorylation.
authors.affiliation: Department of Pharmaceutical Sciences, University of Connecticut , Storrs, Connecticut, United States.
authors.forename: Leepakshi
authors.initials: L
authors.lastname: Khurana
authors.forename: Hamed I
authors.initials: HI
authors.lastname: Ali
authors.forename: Teresa
authors.initials: T
authors.lastname: Olszewska
authors.forename: Kwang H
authors.initials: KH
authors.lastname: Ahn
authors.forename: Aparna
authors.initials: A
authors.lastname: Damaraju
authors.forename: Debra A
authors.initials: DA
authors.lastname: Kendall
authors.forename: Dai
authors.initials: D
authors.lastname: Lu
mesh_terms: D000494:Allosteric Regulation; D000814:Aniline Compounds / Q000737:chemistry* / Q000494:pharmacology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D015151:Immunoblotting; D007211:Indoles / Q000737:chemistry* / Q000494:pharmacology*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D008958:Models, Molecular; D015394:Molecular Structure; D010766:Phosphorylation / Q000187:drug effects; D010880:Piperidines / Q000737:chemistry*; D011485:Protein Binding; D011869:Radioligand Assay; D043884:Receptor, Cannabinoid, CB1 / Q000819:agonists* / Q000378:metabolism*; D013329:Structure-Activity Relationship
chemical_list: C572504:5-chloro-3-ethyl-1H-indole-2-carboxylic acid (2-(4-piperidin-1-yl-phenyl)ethyl)amide; C000589314:5-chloro-N-(4-(dimethylamino)phenethyl)-3-propyl-1H-indole-2-carboxamide; D000814:Aniline Compounds; D007211:Indoles; D010880:Piperidines; D043884:Receptor, Cannabinoid, CB1; D016244:Guanosine 5'-O-(3-Thiotriphosphate); C535150:MAPK1 protein, human; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3