title: Lobeline esters as novel ligands for neuronal nicotinic acetylcholine receptors and neurotransmitter transporters.
abstract: Vesicular monoamine transporter-2 (VMAT2) is a viable target for development of pharmacotherapies for psychostimulant abuse. Lobeline (1) is a potent antagonist at alpha4beta2 * nicotinic acetylcholine receptors, has moderate affinity (K(i)=5.46microM) for VMAT2, and is being investigated currently as a clinical candidate for treatment of psychostimulant abuse. A series of carboxylic acid and sulfonic acid ester analogs 2-20 of lobeline were synthesized and evaluated for interaction with alpha4beta2 * and alpha7 * neuronal nicotinic acetylcholine receptors (nAChRs), the dopamine transporter (DAT), serotonin transporter (SERT) and VMAT2. Both carboxylic acid and sulfonic acid esters had low affinity at alpha7 * nAChRs. Similar to lobeline (K(i)=4nM), sulfonic acid esters had high affinity at alpha4beta2 * (K(i)=5-17nM). Aromatic carboxylic acid ester analogs of lobeline (2-4) were 100-1000-fold less potent than lobeline at alpha4beta2 * nAChRs, whereas aliphatic carboxylic acid ester analogs were 10-100-fold less potent than lobeline at alpha4beta2 *. Two representative lobeline esters, the 10-O-benzoate (2) and the 10-O-benzenesulfonate (10) were evaluated in the (36)Rb(+) efflux assay using rat thalamic synaptosomes, and were shown to be antagonists with IC(50) values of 0.85microM and 1.60microM, respectively. Both carboxylic and sulfonic acid esters exhibited a range of potencies (equipotent to 13-45-fold greater potency compared to lobeline) for inhibiting DAT and SERT, respectively, and like lobeline, had moderate affinity (K(i)=1.98-10.8microM) for VMAT2. One of the more interesting analogs, p-methoxybenzoic acid ester 4, had low affinity at alpha4beta2 * nAChRs (K(i)=19.3microM) and was equipotent with lobeline, at VMAT2 (K(i)=2.98microM), exhibiting a 6.5-fold selectivity for VMAT2 over alpha4beta2 nAChRs. Thus, esterification of the lobeline molecule may be a useful structural modification for the development of lobeline analogs with improved selectivity at VMAT2.
authors.affiliation: College of Pharmacy, University of Kentucky, Rose Street, Lexington, KY 40536-0082, USA.
authors.forename: Marhaba
authors.initials: M
authors.lastname: Hojahmat
authors.forename: David B
authors.initials: DB
authors.lastname: Horton
authors.forename: Seth D
authors.initials: SD
authors.lastname: Norrholm
authors.forename: Dennis K
authors.initials: DK
authors.lastname: Miller
authors.forename: Vladimir P
authors.initials: VP
authors.lastname: Grinevich
authors.forename: Agripina Gabriela
authors.initials: AG
authors.lastname: Deaciuc
authors.forename: Linda P
authors.initials: LP
authors.lastname: Dwoskin
authors.forename: Peter A
authors.initials: PA
authors.lastname: Crooks
mesh_terms: D000818:Animals; D004952:Esters / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D008024:Ligands; D008120:Lobeline / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D008297:Male; D015394:Molecular Structure; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D050479:Neurotransmitter Transport Proteins / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011978:Receptors, Nicotinic / Q000187:drug effects*; D013237:Stereoisomerism; D013329:Structure-Activity Relationship
chemical_list: D004952:Esters; D008024:Ligands; D050479:Neurotransmitter Transport Proteins; D011978:Receptors, Nicotinic; D008120:Lobeline