Development of Novel Drugs for Smoking Cessation Pharmacotherapy

Zaveri, Nurulain

Abstract

The overall goal of this SBIR Phase I project is to identify at least two suitable, efficacious preclinical candidates from our novel series of very potent and highly selective ?3?4 nicotinic acetylcholine receptor (nAChR) ligands, for further translational development into smoking cessation medications. The promising in vivo efficacy of the highly selective ?3?4 nAChR antagonist compound from this series in significant blocking nicotine self-administration in rats, at low doses, with no effect on food responding, strongly supports our hypothesis that '?3?4 nAChR antagonism'is a promising new pharmacological mechanism for smoking cessation pharmacotherapy, and supports the proposed preclinical ADME assessment and efficacy studies to identify two suitable preclinical candidates from this series for further development. Although there is evidence that success rates for quitting smoking, are 2-3 times higher when pharmacotherapy is used than when no treatments are used, the repertoire of current pharmacotherapies is extremely limited. With the enormous health and economic burdens that smoking has on our society, and notwithstanding the limited efficacy and emerging side-effects of the few currently available smoking cessation medications, development of new medications for smoking cessation, particularly against new pharmacological targets, is a critical need, to decrease the impact of smoking on health and mortality. Although it is known that the reinforcing and addictive effects of nicotine are due to is actions on the nicotinic acetylcholine receptors, a major barrier in the field has been the identification of the various nAChR subtypes that play a role in the various aspects of nicotine dependence, and their validation as drug targets. This has been exacerbated by lack of subtype-selective nAChR ligands that can be used as tools or developed as therapeutics. Several recent studies suggest that the ?3?4 subtype of the nAChR is important for several aspects of nicotine dependence. Recent genetic association studies show that single nucleotide polymorphisms (SNPs) in the gene cluster CHRNA5/A3/B4, encoding for the ?3, ?5 and ?4 nAChR subunits are associated with increased risk for heavy smoking, inability to quit, and increased sensitivity to nicotine. Furthermore, the ?4 nAChR subunit has been shown to be necessary for nicotine withdrawal. The promising in vivo efficacy of our highly selective ?3?4 nAChR antagonist suggests that ?3?4 antagonism may be a promising target for smoking cessation and appears to be consistent with the recent genetic studies on the role of the ?3?4 subtype. Based on these results, we propose, in this application, a preclinical development program to evaluate this compound series in in vitro ADME studies and in vivo biovailability and blood-brain penetration assays (Aim 1), to select two candidate compounds for full efficacy evaluation in animal models of nicotine self-administration and reinstatement (a model of drug relapse) (Aim 2). Lead optimization to improve the drug-like suitability of the initial series of compounds is also proposed (Aim 3).
Our Specific Aims are designed as a first step toward the preclinical development of this promising class of compounds as pharmacotherapies for tobacco dependence.

Public Health Relevance

The overall goal of the proposed research is to develop our novel ?3?4 nAChR antagonists as smoking cessation medications against a new target, the ?3?4 nAChRs, which have been recently implicated in several genetic studies, to be involved in smoking behaviors and withdrawal. Our exciting preliminary data shows that our lead compound dramatically inhibits nicotine self-administration in laboratory animal models. It is our ultimate goal to take this promising series of compounds into the clinic, and to provide a new, safe therapeutic option to assist smokers who wish to quit. Successful completion of this project will be the first step in this clinical translation of our promising discoveries, for the development of pharmacotherapies for smoking cessation.