OBJECTIVE: Glycine transporter 1 (GlyT-1) is one of the most attractive therapeutic targets for schizophrenia. There is great interest in developing radioligands for in vivo imaging of GlyT-1 in the brain using positron emission tomography. Here, we report the properties of three novel non-sarcosine-based radioligands [11C]CHIBA-3007, [11C]CHIBA-3009, and [11C]CHIBA-3011, for GlyT-1 imaging in the mouse brain in vivo. METHODS: The three radioligands were synthesized by N-[11C] methylation of the corresponding desmethyl precursor. A pharmacological characterization of these radioligands for in vivo imaging of GlyT-1 in the brain was conducted using male ddY mice. RESULTS: [11C]CHIBA-3009 and [11C]CHIBA-3011 were scarcely incorporated into the brain, whereas [11C]CHIBA-3007 showed slight but considerable brain uptake. Regional brain uptake of [11C]CHIBA-3007 (medulla oblongata>cerebellum>cortex) was similar to the distribution of the GlyT-1 protein. However, pretreatment with CHIBA-3007 (1 mg/kg) or the GlyT-1 selective inhibitor ALX5407 (N-[(3R)-3-([1,1'-Biphenyl]-4-yloxy)-3-(4-fluorophenyl)propyl]-N-methylglycine) (30 mg/kg) did not significantly decrease brain uptake of [11C]CHIBA-3007, suggesting low specific binding to GlyT-1. Pretreatment with cyclosporin A significantly increased brain uptake of [11C]CHIBA-3009 and [11C]CHIBA-3011, suggesting a role for P-glycoprotein in the brain uptake of these ligands. All three radioligands were rapidly degraded intact forms were 3-18% in plasma and 15-74% in the brain at 15 min after injection. CONCLUSION: The results suggest that these three radioligands are not suitable for in vivo imaging of GlyT-1 in the brain because of low brain uptake and rapid metabolism. Further structural refinement is necessary to enhance brain uptake.
Animals ; Brain ; Cyclosporine ; Glycine ; Glycine Plasma Membrane Transport Proteins ; Humans ; Ligands ; Male ; Methylation ; Mice ; Niacinamide ; P-Glycoprotein ; Plasma ; Positron-Emission Tomography ; Schizophrenia ; Thiophenes

Familial hyperekplexia, also called startle disease, is a rare neurological disorder characterized by excessive startle responses to noise or touch. It can be associated with serious injury from frequent falls, apnea spells, and aspiration pneumonia. Familial hyperekplexia has a heterogeneous genetic background with several identified causative genes; it demonstrates both dominant and recessive inheritance in the α1 subunit of the glycine receptor (GLRA1), the β subunit of the glycine receptor and the presynaptic sodium and chloride-dependent glycine transporter 2 genes. Clonazepam is an effective medical treatment for hyperekplexia. Here, we report genetically confirmed familial hyperekplexia patients presenting early adult cautious gait. Additionally, we review clinical features, mode of inheritance, ethnicity and the types and locations of mutations of previously reported hyperekplexia cases with a GLRA1 gene mutation.
Accidental Falls ; Adult ; Apnea ; Clonazepam ; Gait* ; Genetic Background ; Glycine Plasma Membrane Transport Proteins ; Humans ; Nervous System Diseases ; Noise ; Phenotype* ; Pneumonia, Aspiration ; Receptors, Glycine ; Reflex, Startle ; Sodium ; Stiff-Person Syndrome* ; Wills