Inhibition of VMAT2 by β2-adrenergic agonists, antagonists, and the atypical antipsychotic ziprasidone

Abstract

Vesicular monoamine transporter 2 (VMAT2) is responsible for packing monoamine neurotransmitters into synaptic vesicles for storage and subsequent neurotransmission. VMAT2 inhibitors are approved for symptomatic treatment of tardive dyskinesia and Huntington’s chorea, but despite being much-studied inhibitors their exact binding site and mechanism behind binding and inhibition of monoamine transport are not known. Here we report the identification of several approved drugs, notably β2-adrenergic agonists salmeterol, vilanterol and formoterol, β2-adrenergic antagonist carvedilol and the atypical antipsychotic ziprasidone as inhibitors of rat VMAT2. Further, plausible binding modes of the established VMAT2 inhibitors reserpine and tetrabenazine and hit compounds salmeterol and ziprasidone were identified using molecular dynamics simulations and functional assays using VMAT2 wild-type and mutants. Our findings show VMAT2 as a potential off-target of treatments with several approved drugs in use today and can also provide important first steps in both drug repurposing and therapy development targeting VMAT2 function.

Transport and inhibition mechanism for VMAT2-mediated synaptic loading of monoamines

“…3F). In particular, the substitution of V232L caused the utmost loss of binding affinity, consistent with previous notion that Val232 contributes the most favorable enthalpy for TBZ-VMAT2 association (6). In our structure, Val232 points to the TBZ isobutyl group (Fig.…”

“…Serotonin (5-HT), dopamine (DA), and norepinephrine (NE) are major monoamine neurotransmitters that play critical roles in a variety of physiological, emotional and behavioral functions( 1–3 ). Dysregulated monoaminergic neurotransmission is involved in the pathogenesis of several neurological and psychiatric disorders( 4 ), such as depression, Huntington’s disease, Parkinson’s disease (PD), Alzheimer’s disease (AD), attention-deficit hyperactivity disorder (ADHD), and schizophrenia( 5 , 6 ). Despite their divergent biosynthesis routes, the uptake into the presynaptic vesicles of these monoamines converge by the action of VMAT2 driven by proton gradient, which regulates the essential monoaminergic signaling in nerve system( 4 ).…”

Structural mechanisms for VMAT2 inhibition by tetrabenazine

“…Our model of the VMAT2-TBZ complex allowed us to pinpoint two residues which contribute to the specificity of TBZ to VMAT2 over VMAT1. Previous studies have highlighted V232 51 , which is a leucine in VMAT1, as being putatively involved in conferring differences in affinity, and our model shows that V232 is positioned closely to the isobutyl of TBZ which is wedged into a small hydrophobic pocket (ED Fig. 5a).…”

“…Our binding and transport studies further confirm this as the mutation of E312 to glutamine greatly reduces serotonin transport and DTBZ binding (Fig 4f, g). Moreover, mutation of E312 to an alanine has long been known to completely negate all TBZ binding and transport activities 30,31,44 again highlighting the requirement of hydrogen bond pairing with TBZ.…”

“…7). Because E312 was previously shown to be necessary for substrate transport and inhibitor binding, we first selected this residue for mutagenesis to probe its importance in TBZ binding 31,51 . We performed radiolabeled binding experiments to assess the effect of mutating residues in the TBZ binding site by measuring binding of 3 H-labeled DTBZ (Fig.…”