ALX 5407: A potent, selective inhibitor of the hGIyT1 glycine transporter

High-affinity glycine transport in neurons and glial cells is a primary mea ns of inactivating synaptic glycine. We have synthesized a potent selective inhibitor of glycine transporter 1 (GlyT1), and characterized its activity using a quail fibroblast cell line (QT6). The glycine transporters GlyT1A, GlyT1B, GlyT1C, and GlyT2 were stably expressed in QT6 cells. The transpor ters expressed in these cells exhibited appropriate characteristics as desc ribed previously for these genes: Na+/ Cl- dependence, appropriate K-m valu es for glycine uptake, and appropriate pharmacology, as defined in part by the ability of N-methyl glycine (sarcosine) to competitively inhibit glycin e transport. Furthermore, the characteristics of the transporters in the ce ll lines recapitulate the characteristics of glycine trans-porters observed in tissue preparations. We developed a sarcosine derivative, (R)-(N-[3-(4' -fluorophenyl)-3-(4'-phenylphenoxy)propyl])sarcosine (ALX 5407), and examin ed its activity against the cloned glycine transporters. ALX 5407 completel y inhibited glycine transport in the GlyT1 cells, with an IC50 value of 3 n M, but had little or no activity at the human GlyT2 transporter, at other b inding sites for glycine, or at other neurotransmitter transporters. The in hibition of glycine transport was essentially irreversible, ALX 5407 repres ents a novel tool in the investigation of N-methyl-D-aspartate-receptor fun ction. This class of drug may lead to novel therapies in the treatment of s chizophrenia.