GET73 increases rat extracellular hippocampal CA1 GABA levels through a possible involvement of local mGlu5 receptor

Abstract

N-[(4-trifluoromethyl) benzyl] 4-methoxybutyramide (GET73) is a newly synthesized compound displaying anti-alcohol and anxiolytic properties. In light of the importance of the hippocampal CA1 subregion in alcohol addiction and anxiety-like behaviors-this in vivo microdialysis study characterized the effect of GET73 on extracellular GABA levels in the hippocampal CA1 region of the freely moving rat-including a possible role for mGlu5 receptor in mediating this effect. Both intraperitoneal administration (2-10 mg/kg) and local intra-hippocampal CA1 perfusion with GET73 (50-1000 nM) were associated with a transient, step-wise increase in dialysate hippocampal CA1 GABA levels. The GET73 (10 mg/kg)-induced increase in GABA levels was not affected by intra-CA1 perfusion with either the GABA reuptake inhibitor SKF89976A (0.5 mM) or by local GABAA (bicuculline; 1μM) and GABAB (CGP35348; 500 μM) receptor antagonists. On the contrary, the GET73-induced increase in GABA levels was partially counteracted by the intra-CA1 perfusion with the mGlu5 receptor negative allosteric modulator MPEP (300 µM). Interestingly, GET73 at the lowest (2 mg/kg) dose tested, by itself ineffective, fully counteracted the increase in GABA levels induced by the mGlu5 receptor agonist CHPG (1000 µM). Taken together, these findings suggest that the GET73-induced increase in hippocampal CA1 GABA levels operates independently of local GABA reuptake and/or GABAA or GABAB receptors. Furthermore, the present data lead to hypothesize a possible interaction between GET73 and mGluR5-mediated regulation of hippocampal CA1 GABA transmission, an effect which may be relevant to the ability of GET73 to reduce alcohol intake in an alcohol-preferring rat strain.

A Phase I randomized clinical trial testing the safety, tolerability and preliminary pharmacokinetics of the mGluR5 negative allosteric modulator GET 73 following single and repeated doses in healthy volunteers

“…GET 73 seems to partially act like a mGluR5 antagonist or negative allosteric modulator (Beggiato et al, 2013; Ferraro et al, 2011). GET 73 has been proposed as a potential novel pharmacotherapy for AUD and/or obesity.…”

In Vitro Functional Characterization of GET73 as Possible Negative Allosteric Modulator of Metabotropic Glutamate Receptor 5

“…Specifically, low nanomolar GET73 concentrations seemed to exert a negative modulation at mGluR5, and a possible amplification of MPEP-induced effects. On the other hand, the effects of higher (i.e., μM) GET73 concentrations were counteracted by MPEP, suggesting that the compound might also exert a positive modulation at mGluR5 ( Ferraro et al, 2011 , 2013 ; Beggiato et al, 2013 ). Relevantly, the postulated ability of GET73 to negatively modulate mGluR5 may likewise explain, at least partially, its efficacy in reducing rat alcohol intake, as shown for several other compounds acting as NAM at mGluR5 ( Olive, 2009 ; Duncan and Lawrence, 2012 ; Ferraro et al, 2013 ; Holmes et al, 2013 ; Mihov and Hasler, 2016 ; Goodwani et al, 2017 ).…”

“…Specifically, low nM concentrations exerted a negative modulation at mGluR5, and a possible amplification of MPEP-induced effects. On the other hand, the GET73-induced increase in glutamate and GABA signaling, exerted at higher μM concentrations, were counteracted by MPEP, suggesting that GET73 might also exert a positive modulation at mGluR5, at least in the model employed for those studies ( Ferraro et al, 2011 , 2013 ; Beggiato et al, 2013 ). However, the above studies only indirectly suggested the existence of a possible interaction between GET73 and mGluR5.…”

“…The mechanism of action of GET73 is still under study. This compound did not show affinity for a series of biological targets involved in drug addiction and alcohol dependence, including dopamine, serotonin, GABA, ionotropic glutamate receptors, along with dopamine and serotonin reuptake systems ( Loche et al, 2012 ); despite this negligible binding profile, the compound affected GABA and glutamate neurotransmission in the rat hippocampus ( Ferraro et al, 2011 ; Beggiato et al, 2013 ). Based on these data, additional studies were addressed to explore the possibility that GET73 could modulate metabotropic glutamate receptor (mGluR) functions, and specifically mGluR5.…”

“…In preclinical studies this compound has shown the ability to reduce alcohol intake along with anxiolytic-like properties ( Loche et al, 2012 ; Ferraro et al, 2013 ). Its possible mechanism of action has been related to the modulation of glutamate neurotransmission through the metabotropic glutamate subtype 5 receptor (mGluR5) ( Ferraro et al, 2011 , 2013 ; Beggiato et al, 2013 ), a promising target for the development of pharmacological alcohol dependence treatments ( Olive, 2009 ; Duncan and Lawrence, 2012 ; Holmes et al, 2013 ; Goodwani et al, 2017 ), and for many other psychiatric conditions, such as anxiety and depressive states ( Tatarczynska et al, 2001 ). The results of several Phase 1 clinical studies indicate that GET73 is safe and well-tolerated both in healthy volunteers ( Haass-Koffler et al, 2017a , b ), and in alcohol-dependent patients (ongoing study NCT01842503) 1 .…”