The metabotropic glutamate receptor 7 allosteric modulator AMN082: a monoaminergic agent in disguise?

Metabotropic glutamate receptor 7 (mGluR7) remains the most elusive of the eight known mGluRs primarily because of the limited availability of tool compounds to interrogate its potential therapeutic utility. The discovery of N,N'-dibenzhydrylethane-1,2-diamine dihydrochloride (AMN082) as the first orally active, brain-penetrable, mGluR7-selective allosteric agonist by Mitsukawa and colleagues (Proc Natl Acad Sci USA 102:18712-18717, 2005) provides a means to investigate this receptor system directly. AMN082 demonstrates mGluR7 agonist activity in vitro and interestingly has a behavioral profile that supports utility across a broad spectrum of psychiatric disorders including anxiety and depression. The present studies were conducted to extend the in vitro and in vivo characterization of AMN082 by evaluating its pharmacokinetic and metabolite profile. Profiling of AMN082 in rat liver microsomes revealed rapid metabolism (t(1/2) < 1 min) to a major metabolite, N-benzhydrylethane-1,2-diamine (Met-1). In vitro selectivity profiling of Met-1 demonstrated physiologically relevant transporter binding affinity at serotonin transporter (SERT), dopamine transporter (DAT), and norepinephrine transporter (NET) (323, 3020, and 3410 nM, respectively); whereas the parent compound AMN082 had appreciable affinity at NET (1385 nM). AMN082 produced antidepressant-like activity and receptor occupancy at SERT up to 4 h postdose, a time point at which AMN082 is significantly reduced in brain and plasma while the concentration of Met-1 continues to increase in brain. Acute Met-1 administration produced antidepressant-like activity as would be expected from its in vitro profile as a mixed SERT, NET, DAT inhibitor. Taken together, these data suggest that the reported in vivo actions of AMN082 should be interpreted with caution, because they may involve other mechanisms in addition to mGluR7.

Desvenlafaxine for major depressive disorder: incremental clinical benefits from a second-generation serotonin-norepinephrine reuptake inhibitor.

IMPORTANCE OF THE FIELD: genetic and pharmacologically-driven variations in common mechanisms involved in the disposition of antidepressant medications may contribute to variable interpatient response. This review describes the pharmacological properties underlying the safety and efficacy of desvenlafaxine, a second-generation serotonin-norepinephrine reuptake inhibitor (SNRI). AREAS COVERED IN THIS REVIEW: literature published between January 2006 and September 2010 evaluating desvenlafaxine was reviewed. WHAT WILL THE READER GAIN: Desvenlafaxine therapy is initiated at the therapeutic dose (50 mg/day) without a need for dose titration. Desvenlafaxine metabolism and distribution are not appreciably affected by altered function of cytochrome P450 (CYP) enzymes or permeability glycoprotein (P-gp). Desvenlafaxine has clinically insignificant effects on the activity of CYP and P-gp. The efficacy of desvenlafaxine in treating major depressive disorder has been established. Adverse events are characteristic of the SNRI class. Notably, the rate of discontinuation due to adverse events with the 50 mg/day recommended therapeutic dose is comparable to that seen with placebo. TAKE HOME MESSAGE: incremental benefits with desvenlafaxine, derived from straight-forward dosing, a simple metabolic profile and lack of interaction with active transporter P-gp and CYP enzymes may contribute to more consistent response, good tolerability and lower incidence of drug-drug interactions with concomitant medications.