In vitro characterization of a novel, potent and selective M3 antagonist

J-104129, a novel muscarinic M3 receptor antagonist with high selectivity for M3 over M2 receptors

A new class of 4-acetamidopiperidine derivatives has been synthesized and investigated for human muscarinic receptor subtype selectivity. Introduction of a hydrocarbon chain of appropriate length into the piperidine nitrogen of the racemic N-(piperidin-4-yl)-2-cyclobutyl-2-hydroxy-2-phenylacetamide platform conferred up to 70-fold selectivity for human muscarinic M3 receptors over M2 receptors. Subsequent synthetic derivatizations resulted in highly potent M3 receptor antagonists with selectivity greater than two orders of magnitude for M3 over M2 receptors, from which the analogue 4r was selected. Preparation of both enantiomers of 4r led to the identification of (2R)-N-[1-(4-methyl-3-pentenyl)piperidin-4-yl]-2-cyclopentyl-2-hyd roxy-2-phenylacetamide (J-104129, (R)-4r), which exhibited 120-fold selectivity for M3 receptors (Ki = 4.2 nM) over M2 receptors (Ki = 490 nM). In isolated rat trachea, (R)-4r potently and specifically antagonized acetylcholine (ACh)-induced responses with a K(B) value of 3.3 nM. The highly subtype-selective profile was also seen in isolated rat tissue assays (50-fold) and in anesthetized rats (> 250-fold). Oral administration of J-104129 ((R)-4r) antagonized ACh-induced bronchoconstriction with an ED50 value of 0.58 mg/kg in rats. Thus, J-104129 ((R)-4r) may effectively facilitate bronchodilation in the treatment of obstructive airway disease.

Constitutive muscarinic receptors are involved in the growth and differentiation of friend erythroleukemia cells

Binding experiments with the specific muscarinic ligand [3H]N-methylscopolamine (3H-NMS) have shown the presence of constitutive muscarinic acetylcholine receptors (mAChR) on Friend murine erythroleukemia cells (MELC). Competition experiments with a panel of specific antagonists indicated that the mAChR were predominantly of the M3 subtype. This was confirmed by the rt-PCR analysis of mRNA levels for M1-M5 AChR. Uninduced MELC expressed approximately 2,100 and 1,200 binding sites per cell of growing and resting populations, respectively. The dissociation constant (K(D)) for 3H-NMS was in the picomolar range. The modulation of mAChR upon induction suggested that MELC growth and maturation might be under control of a cholinergic system since mAChR were markedly decreased or virtually absent in MELC induced to terminal division by dimethyl sulfoxide (DMSO) or hexamethylene bisacetamide (HMBA), respectively. In turn, the number of mAChR on MELC committed to polyploidization by colcemid was either increased over or maintained at the control levels when receptor densities were expressed per cell or surface unit (square micrometers), respectively. Moreover, the muscarinic agonist carbachol was found to inhibit MELC differentiation by decreasing by approximately 35% the amount of benzidine-positive (B+) cells in HMBA-induced cultures and, to a lesser degree, also AChE levels. The carbachol effect on erythroid differentiation was reverted by atropine that was found to restore the original amount of B+ cells, while it reduced acetylcholinesterase (AChE) to levels of approximately 66% of control. Such a selective atropine-mediated inhibition of AChE expression was observed also in HMBA-induced MELC supplemented with the antagonist. These results have suggested that mAChR on MELC are functional and might play a role in modulating the expression of either the erythroid or megakaryocytic traits of these cells.