Targeting alpha7 nAChR for Therapeutic Effects

大脑中有两种主要的尼古丁受体。一种刺激，a7

There are two main types of nicotine receptors in the brain. Stimulation of one type, the a7 receptor, improves learning, memory, and attention; can suppress the auditory hallucinations of schizophrenics; and may also slow the progression of Alzheimer's disease. Stimulation of the other type of nicotine receptors can cause addiction. Therefore, the a7 nicotinic receptor is being energetically pursued as a drug target by more than a dozen drug companies. Much of that work has been guided by our previous studies. For example, until recently there was no systematic analysis that established the basic principles that underlie the selective activation of a7. We have now demonstrated that there are at least three distinct structural motifs which can be used to modify a core agonist structure to achieve a7 selectivity. Many a7-selective drugs have either anabaseine or quinuclidine as their core structure, modified by the addition of a large hydrophobic side group such as a benzene ring. The precise chemical structure of the hydrophobic side group determines efficacy and potency. Another key feature distinguishing the a7-selective agonists from one another is a varying ability to produce relatively stable desensitization following a transient phase of activation. The desensitization is due to prolonged binding to the receptor, and the desensitizing properties of specific agents are likely to impact their therapeutic utility. We have generated models for how the various a7-agonists dock in the ligand-binding domain of the a7 receptor and have identified amino acids which we hypothesize will have point-to-point interactions with substituents on the benzylidene groups of either quinuclidine or anabaseine-based agonists. We will investigate the potential importance of hydrogen bonding and hydrophobic interactions on the binding, gating, and desensitizing properties of the specific receptor/ligand combinations. We will test our hypotheses with site-directed mutations, as well as with novel a7-selective ligands that will be restricted in their ability to form specific point-to-point interactions, for example, agents which are only able to be H-bond donors or acceptors. Wild-type and mutant receptors will be expressed in either Xenopus oocytes or transiently transfected mammalian cells, and either whole-cell or single-channel currents will be measured. We will use the Type 2 positive allosteric modulator PNU-120596 to measure the desensitizing properties of specific ligands and overcome the intrinsically limited open probability of a7 receptors, making their single-channel currents more amenable to study. We will further manipulate open probability with tkP3BzPB, a novel a7selective noncompetitive antagonist that is use-independent, highly selective, potent, and slowly reversible. We will also test hypotheses derived from our models related to which subdomains of the receptor recognize the three different a7-selectivity motifs. Together these studies will provide important advancements leading to the future design of a7 agonists with optimized profiles of pharmacological properties.