Characterization of SSR103800, a selective inhibitor of the glycine transporter-1 in models predictive of therapeutic activity in schizophrenia.

On native human, rat and mouse glycine transporter-1(GlyT1), SSR130800 behaves as a selective inhibitor with IC50 values of 1.9, 5.3 and 6.8 nM, respectively. It reversibly blocked glycine uptake in mouse brain cortical homogenates, increased extracellular levels of glycine in the rat prefrontal cortex, and potentiated NMDA-mediated excitatory postsynaptic currents in rat hippocampal slices. SSR103800 (30 mg/kg, p.o.) decreased MK-801- and PCP-induced locomotor hyperactivity in rodents. SSR103800 (1 and 10 mg/kg, p.o.) attenuated social recognition deficit in adult rats induced by neonatal injections of PCP (10 mg/kg, s.c., on post-natal day 7, 9 and 11). SSR103800 (3 mg/kg, p.o.) counteracted the deficit in short-term visual episodic-like memory induced by a low challenge dose of PCP (1 mg/kg, i.p.), in PCP-sensitized rats (10 mg/kg, i.p.). SSR103800 (30 mg/kg, i.p.) increased the prepulse inhibition of the startle reflex in DBA/1J mice. SSR103800 decreased defensive- and despair-related behaviors in the tonic immobility test in gerbils (10 and 30 mg/kg, p.o.) and in the forced-swimming procedure in rats (1 and 3 mg/kg, p.o.), respectively. These findings suggest that SSR103800 may have a therapeutic potential in the management of the core symptoms of schizophrenia and comorbid depression states.

Neurochemical, electrophysiological and pharmacological profiles of the selective inhibitor of the glycine transporter-1 SSR504734, a potential new type of antipsychotic.

Noncompetitive N-methyl-D-aspartate (NMDA) blockers induce schizophrenic-like symptoms in humans, presumably by impairing glutamatergic transmission. Therefore, a compound potentiating this neurotransmission, by increasing extracellular levels of glycine (a requisite co-agonist of glutamate), could possess antipsychotic activity. Blocking the glycine transporter-1 (GlyT1) should, by increasing extracellular glycine levels, potentiate glutamatergic neurotransmission. SSR504734, a selective and reversible inhibitor of human, rat, and mouse GlyT1 (IC50=18, 15, and 38 nM, respectively), blocked reversibly the ex vivo uptake of glycine (mouse cortical homogenates: ID50: 5 mg/kg i.p.), rapidly and for a long duration. In vivo, it increased (minimal efficacious dose (MED): 3 mg/kg i.p.) extracellular levels of glycine in the rat prefrontal cortex (PFC). This resulted in an enhanced glutamatergic neurotransmission, as SSR504734 potentiated NMDA-mediated excitatory postsynaptic currents (EPSCs) in rat hippocampal slices (minimal efficacious concentration (MEC): 0.5 microM) and intrastriatal glycine-induced rotations in mice (MED: 1 mg/kg i.p.). It normalized activity in rat models of hippocampal and PFC hypofunctioning (through activation of presynaptic CB1 receptors): it reversed the decrease in electrically evoked [3H]acetylcholine release in hippocampal slices (MEC: 10 nM) and the reduction of PFC neurons firing (MED: 0.3 mg/kg i.v.). SSR504734 prevented ketamine-induced metabolic activation in mice limbic areas and reversed MK-801-induced hyperactivity and increase in EEG spectral energy in mice and rats, respectively (MED: 10-30 mg/kg i.p.). In schizophrenia models, it normalized a spontaneous prepulse inhibition deficit in DBA/2 mice (MED: 15 mg/kg i.p.), and reversed hypersensitivity to locomotor effects of d-amphetamine and selective attention deficits (MED: 1-3 mg/kg i.p.) in adult rats treated neonatally with phencyclidine. Finally, it increased extracellular dopamine in rat PFC (MED: 10 mg/kg i.p.). The compound showed additional activity in depression/anxiety models, such as the chronic mild stress in mice (10 mg/kg i.p.), ultrasonic distress calls in rat pups separated from their mother (MED: 1 mg/kg s.c.), and the increased latency of paradoxical sleep in rats (MED: 30 mg/kg i.p.). In conclusion, SSR504734 is a potent and selective GlyT1 inhibitor, exhibiting activity in schizophrenia, anxiety and depression models. By targeting one of the primary causes of schizophrenia (hypoglutamatergy), it is expected to be efficacious not only against positive but also negative symptoms, cognitive deficits, and comorbid depression/anxiety states.