ALX 5407: a potent, selective inhibitor of the hGlyT1 glycine transporter

High-affinity glycine transport in neurons and glial cells is a primary means 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 transporters expressed in these cells exhibited appropriate characteristics as described previously for these genes: Na(+)/Cl(-) dependence, appropriate K(m) values for glycine uptake, and appropriate pharmacology, as defined in part by the ability of N-methyl glycine (sarcosine) to competitively inhibit glycine transport. Furthermore, the characteristics of the transporters in the cell lines recapitulate the characteristics of glycine transporters observed in tissue preparations. We developed a sarcosine derivative, (R)-(N-[3-(4'-fluorophenyl)-3-(4'-phenylphenoxy)propyl])sarcosine (ALX 5407), and examined its activity against the cloned glycine transporters. ALX 5407 completely inhibited glycine transport in the GlyT1 cells, with an IC(50) value of 3 nM, but had little or no activity at the human GlyT2 transporter, at other binding sites for glycine, or at other neurotransmitter transporters. The inhibition of glycine transport was essentially irreversible. ALX 5407 represents a novel tool in the investigation of N-methyl-D-aspartate-receptor function. This class of drug may lead to novel therapies in the treatment of schizophrenia.