Ropanicant (SUVN-911), an α4β2 nicotinic acetylcholine receptor antagonist intended for the treatment of depressive disorders: pharmacological, behavioral, and neurochemical characterization

Discovery of a Novel Class of Benzimidazole-Based Nicotinic Acetylcholine Receptor Modulators: Positive and Negative Modulation Arising from Overlapping Allosteric Sites

Here, we present the discovery of a novel class of benzimidazole-based allosteric modulators of nicotinic acetylcholine receptors (nAChRs). The modulators were developed based on a compound (1) exhibiting positive modulatory activity at α4β2 nAChR in a compound library screening by functional characterization of 100 analogues of 1 at nAChRs. Two distinct series of positive and negative allosteric modulators (PAMs and NAMs, respectively) comprising benzimidazole as a shared structural moiety emerged from this SAR study. The PAMs mediated weak modulation of α4β2 and α6β2β3, whereas the NAMs exhibited essentially equipotent inhibition of α4β2, α6β2β3, α6β4β3, and α3β4 nAChRs, with analogue 9j [2-(2,4-dichlorophenoxy)-1,3-dimethyl-1-H-benzo[d]imidazole-3-ium] displaying high-nanomolar and low-micromolar IC50 values at the β2- and β4-containing receptor subtypes, respectively. We propose that the PAMs and NAMs act through overlapping sites in the nAChR, and these findings thus underline the heterogenous modes of modulation that can arise from a shared allosteric site in the receptor.

Advances in small molecule selective ligands for heteromeric nicotinic acetylcholine receptors

The study of nicotinic acetylcholine receptors (nAChRs) has significantly progressed in the last decade, due to a) the improved techniques available for structural studies; b) the identification of ligands interacting at orthosteric and allosteric recognition sites on the nAChR proteins, able to tune channel conformational states; c) the better functional characterization of receptor subtypes/subunits and their therapeutic potential; d) the availability of novel pharmacological agents able to activate or block nicotinic-mediated cholinergic responses with subtype or stoichiometry selectivity. The copious literature on nAChRs is related to the pharmacological profile of new, promising subtype selective derivatives as well as the encouraging preclinical and early clinical evaluation of known ligands. However, recently approved therapeutic derivatives are still missing, and examples of ligands discontinued in advanced CNS clinical trials include drug candidates acting at both neuronal homomeric and heteromeric receptors. In this review, we have selected heteromeric nAChRs as the target and comment on literature reports of the past five years dealing with the discovery of new small molecule ligands or the advanced pharmacological/preclinical investigation of more promising compounds. The results obtained with bifunctional nicotinic ligands and a light-activated ligand as well as the applications of promising radiopharmaceuticals for heteromeric subtypes are also discussed.

Pathophysiology of nAChRs: limbic circuits and related disorders

Human epidemiological studies have identified links between nicotine intake and stress disorders, including anxiety, depression and PTSD. Here we review the clinical evidence for activation and desensitization of nicotinic acetylcholine receptors (nAChRs) relevant to affective disorders. We go on to describe clinical and preclinical pharmacological studies suggesting that nAChR function may be involved in the etiology of anxiety and depressive disorders, may be relevant targets for medication development, and may contribute to the antidepressant efficacy of non-nicotinic therapeutics. We then review what is known about nAChR function in a subset of limbic system areas (amygdala, hippocampus and prefrontal cortex), and how this contributes to stress-relevant behaviors in preclinical models that may be relevant to human affective disorders. Taken together, the preclinical and clinical literature point to a clear role for ACh signaling through nAChRs in regulation of behavioral responses to stress. Disruption of nAChR homeostasis is likely to contribute to the psychopathology observed in anxiety and depressive disorders. Targeting specific nAChRs may therefore be a strategy for medication development to treat these disorders or to augment the efficacy of current therapeutics.

Safety, Tolerability, and Pharmacokinetics of Ropanicant (SUVN-911), a Novel Alpha4 Beta2 Nicotinic Acetylcholine Receptor (α4β2 nAChR) Antagonist, in Healthy Adult and Elderly Subjects

BACKGROUND AND OBJECTIVES

Ropanicant hydrochloride (previously known as SUVN-911, hereinafter referred to as ropanicant) is a novel alpha4 beta2 nicotinic acetylcholine receptor (α4β2 nAchR) antagonist being developed for the treatment of major depressive disorder. The objectives of the present studies were to evaluate the safety, tolerability, and pharmacokinetics of ropanicant after single and multiple ascending doses and to evaluate the effect of food, sex, and age on its pharmacokinetics in healthy subjects.

METHODS

Two phase I studies have been conducted for ropanicant. Study 1 is a randomized, double-blind, placebo-controlled, first-in-human study to evaluate the safety, tolerability, and pharmacokinetics of single ascending doses (0.5, 6, 15, 30, and 60 mg) and multiple ascending doses (15, 30, and 45 mg) of ropanicant administered orally for 14 days to healthy male subjects. In Study 2, the effect of food, sex, and age on ropanicant pharmacokinetics was evaluated following a single 30-mg oral dose.

RESULTS

Ropanicant at single doses up to 60 mg and multiple doses up to 45 mg once daily was found to be safe and well tolerated in healthy subjects. The most frequently reported adverse events were headache and nausea. Ropanicant exposures were more than dose proportional following single and multiple administrations. Urinary excretion of unchanged ropanicant was low across the doses. Upon multiple dosing, 1.5- to 2.5-fold higher exposures for maximum concentration and 1.6- to 4.0-fold higher exposures for area under the concentration-time curve from time 0-24 h were observed on day 14 as compared with day 1. Sex had an effect on the pharmacokinetics of ropanicant as a 64% higher area under the concentration-time curve from time 0 to 24 h and a 26% higher maximum concentration was observed in female adults when compared with male adults. Plasma exposures were comparable in fasted versus fed conditions and in adult versus elderly subjects.

CONCLUSIONS

Ropanicant was found to be safe and well tolerated following single and multiple oral administrations in healthy subjects. Ropanicant showed nonlinear pharmacokinetics and accumulation following multiple dosing. Urinary excretion represents an insignificant elimination pathway for ropanicant. Ropanicant pharmacokinetics were sex dependent, and food and age had no effect on its pharmacokinetics.

CLINICAL TRIAL REGISTRATION

NCT03155503 and NCT03551288.