Methamphetamine (METH) abuse continues to escalate and effective treatments are not yet available. METH interacts with the vesicular monoamine transporter (VMAT2), promoting both dopamine (DA) release into the cytosol and reversal of the DA transporter (DAT) to increase extracellular DA concentrations, which is thought to be associated with its abuse liability. Importantly, progress on the current project has shown that ?-lobeline (LOB) has high affinity for the [3H]dihydrotetrabenazine binding site on VMAT2 and potently inhibits [3H]DA uptake into synaptic vesicles. We have also shown that LOB inhibits METH-evoked DA release in vitro and METH self-administration in rats. Thus, LOB has potential as a new therapeutic agent for the treatment of METH abuse, and has recently successfully completed Phase 1a clinical trials. However, LOB has been shown to interact with many different CNS targets (i.e. it is a relatively nonselective or “dirty” drug), including ?4?2*, ?6?2* and ?3?4* nicotinic acetylcholine receptors. In the current proposal, we aim to develop LOB analogs with high affinity and selectivity for VMAT2, which we believe will have increased benefits over LOB as therapeutic candidates for the treatment of METH abuse. We chose VMAT2 as the target as it is a key point of regulation in DA synaptic transmission, due to the high affinity of LOB for VMAT2, and due to METH’s interaction with VMAT2, which results in increased extracellular DA that is associated with its reward and abuse. Thus, our hypothesis focuses on VMAT2 as a novel therapeutic target for the treatment of METH abuse. Development of selective, high affinity VMAT2 inhibitors will allow us to test the hypothesis that selective inhibition of VMAT2 decreases METH reward. Preliminary structure-activity relationships (SAR), aimed at selectively targeting VMAT2 initially identified N-methyl-2,6-di- (cis-phenylethenyl)piperidine (meso-transdiene, MTD) as a lead analog due to its low affinity for ?4?2* and ?7* nAChRs, and thus, its greater selectivity for VMAT2 and DAT, compared with LOB. However, MTD also inhibits ?6?2* and ?3?4* nAChRs mediating nicotine (NIC)-evoked DA and NE release, respectively. Thus, although we did find that MTD decreases METH SA, MTD is not selective for VMAT2. SAR also identified N-methyl-2,6-di-(cis-phenylethyl)piperidine (lobelane), in which the trans-double bonds in MTD are replaced with saturated C-C bonds. Lobelane has negligible affinity for ?4?2*, ?7* and in addition does not inhibit ?6?2* nAChRs. Lobelane also has a relatively higher affinity for VMAT2 and DAT compared to MTD and LOB. Moreover, lobelane showed greater specificity in decreasing METH SA compared to MTD. Preliminary SAR for lobelane also revealed that aromatic substituted lobelane analogs have enhanced affinity for VMAT2, while having no affinity for ?4?2* and ?7* nAChRs. In this competitive renewal, the focus will be on the SAR of lobelane analogs in order to identify more potent and selective inhibitors of VMAT2. Analog interaction with nAChRs, DAT and NET will be evaluated to continue to direct the SAR towards greater selectivity for VMAT2. The VMAT2 pharmacophore will continue to be refined. Lobelane analogs with high affinity for VMAT2 which potently inhibit METH-evoked DA release in vitro and which do not interact at nAChRs will be assessed for their ability to specifically decrease METH SA in rats. Thus, we predict that lobelane analogs with high affinity and selectivity for VMAT2 will be the best candidates for the treatment of METH abuse. The long-term goal is to develop novel lobelane analogs and pioneer the development of a novel class of therapeutic agents which selectively target VMAT2 and have potential as efficacious treatments for METH abuse.

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