title: Glycine transporter (GlyT1) inhibitors with reduced residence time increase prepulse inhibition without inducing hyperlocomotion in DBA/2 mice.
abstract: Inhibition of the glycine transporter type 1 (GlyT1) leading to potentiation of the glycine site (GlyB) on the N-methyl-d-aspartate (NMDA) receptor has been proposed as a novel therapeutic approach for schizophrenia. However, sarcosine-based GlyT1 inhibitors produce undesirable side effects including compulsive walking and respiratory distress. The influence of specific biochemical properties of GlyT1 inhibitors, such as mode of inhibition and residence time, on adverse effects is unknown. Two GlyT1 inhibitors that contain a sarcosine moiety, sarcosine and ALX-5407, and two compounds that do not contain a sarcosine moiety, Roche-7 and Merck (S)-13h, were evaluated for their potency, mode of inhibition, and target residence times in vitro, and modulation of prepulse inhibition (PPI) and locomotor activity in vivo. (S)-13h and sarcosine were competitive inhibitors while ALX-5407 and Roche-7 demonstrated mixed noncompetitive inhibition. Potency of GlyT1 inhibition (ALX-5407>(S)-13h>Roche-7≫sarcosine) did not correlate with residence time on GlyT1 (sarcosine=Roche-7≪(S)-13h<ALX-5407). ALX-5407 and (S)-13h induced compulsive walking, termed obstinate progression (OP), at doses that increased PPI in DBA/2 mice, demonstrating that OP was not a function of mode of inhibition or inhibitor chemotype. Sarcosine and Roche-7 increased PPI without inducing OP, suggesting that compounds with decreased GlyT1 residence time were efficacious without adverse effects. Direct activation of the GlyB site by d-serine did not produce OP. However, OP induced by (S)-13h was blocked by strychnine, a glycine receptor (GlyA) antagonist, suggesting that OP induced by GlyT1 inhibition was mediated by GlyA. Thus, GlyT1 inhibitors with short residence times demonstrated efficacy without mechanism-based adverse effects.
authors.affiliation: Cephalon, Inc., West Chester, PA 19380, USA. kkopec@cephalon.com
authors.forename: Karla
authors.initials: K
authors.lastname: Kopec
authors.forename: Dorothy G
authors.initials: DG
authors.lastname: Flood
authors.forename: Maciej
authors.initials: M
authors.lastname: Gasior
authors.forename: Beth Ann W
authors.initials: BA
authors.lastname: McKenna
authors.forename: Eva
authors.initials: E
authors.lastname: Zuvich
authors.forename: Justin
authors.initials: J
authors.lastname: Schreiber
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Salvino
authors.forename: John T
authors.initials: JT
authors.lastname: Durkin
authors.forename: Mark A
authors.initials: MA
authors.lastname: Ator
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Marino
mesh_terms: D000818:Animals; D005998:Glycine / Q000378:metabolism; D050487:Glycine Plasma Membrane Transport Proteins / Q000037:antagonists & inhibitors* / Q000502:physiology; D008297:Male; D051379:Mice; D008811:Mice, Inbred DBA; D009043:Motor Activity / Q000187:drug effects*; D009433:Neural Inhibition / Q000187:drug effects*; D012521:Sarcosine / Q000031:analogs & derivatives / Q000494:pharmacology; D012694:Serine / Q000494:pharmacology; D013331:Strychnine / Q000494:pharmacology; D013997:Time Factors
chemical_list: C510369:(R)-(N-(3-(4'-fluorophenyl)-3-(4'-phenylphenoxy)propyl))sarcosine; D050487:Glycine Plasma Membrane Transport Proteins; C493267:Slc6a9 protein, mouse; D012694:Serine; D013331:Strychnine; D005998:Glycine; D012521:Sarcosine