In vitro Characterization of a small molecule inhibitor of the alanine serine cysteine transporter ‐1 (SLC7A10)

Abstract

NMDA receptor hypofunction is hypothesized to contribute to cognitive deficits associated with schizophrenia. Since direct activation of NMDA receptors is associated with serious adverse effects, modulation of the NMDA co-agonists, glycine or D-serine, represents a viable alternative therapeutic approach. Indeed, clinical trials with glycine and D-serine have shown positive results, although concerns over toxicity related to the high-doses required for efficacy remain. Synaptic concentrations of D-serine and glycine are regulated by the amino acid transporter alanine serine cysteine transporter-1 (asc-1). Inhibition of asc-1 would increase synaptic D-serine and possibly glycine, eliminating the need for high-dose Schizophrenia is a complex neuropsychiatric disorder characterized by positive symptoms, negative symptoms, and cognitive deficits (Brown et al. 2010). While current antipsychotic medications are effective at alleviating positive symptoms, treatment of negative symptoms and cognitive deficits remain an unmet medical need. Cognitive deficits are hypothesized to results from an under-activation or hypofunction of NMDA receptors. This hypothesis is based on data in human subjects, demonstrating that the pharmacological blockade of NMDA receptors produces cognitive deficits that parallel those seen in schizophrenia patients (Malhotra et al. 1996;Adler et al. 1999). These findings are supported by pre-clinical data demonstrating that inhibition of NMDA receptor function disrupts measures of cognition (Jentsch et al. 1997a,b;Stefani and Moghaddam 2005). Based on these data, development of newer medications has largely focused on improving NMDA receptor function. However, since direct pharmacological activation of NMDA receptors leads to over-excitation and seizures, indirect modulation of NMDA receptors at one of the many regulatory sites may provide an attractive alternative to addressing NMDA receptor hypofunction.Activation of NMDA receptors requires the binding of both glutamate as an agonist and either glycine or D-serine as a coagonist. Recent clinical trials have shown beneficial effects of adjunctive D-serine and glycine treatment on both cognitive and negative symptom domains of schizophrenia (Javitt et al. 1994;Heresco-Levy et al. 1996 Abbreviations used: NMDA, N-methyl-D-aspartate; asc-1, Na + -independent alanine-serine-cysteine transporter 1; ASCT-1 and -2, Na + -dependent alanine-serine-cysteine transporter 1 and 2; LAT-1 and 2, large amino acid transporter; AIB, a-aminoisobutyric acid.

2-Amino-4-bis(aryloxybenzyl)aminobutanoic acids: A novel scaffold for inhibition of ASCT2-mediated glutamine transport

“…14 Interestingly, other compounds in this series, (Table 1, Compounds 8, 10) demonstrated some preference for blocking glutamine transport in the rat cell line. Our most potent compound in the rat cell line (Table 1, Compound 5) also exhibited this preference and blocked ASCT2-mediated glutamine uptake in C6 cells with an IC 50 of 1.3 μM.…”

Iterative Focused Screening with Biological Fingerprints Identifies Selective Asc-1 Inhibitors Distinct from Traditional High Throughput Screening

“…(4) Several small molecule Asc-1-selective inhibitors have been developed with differing mechanisms of action, and recent studies have suggested that inhibition of Asc-1 may paradoxically result in reduced, rather than increased, levels of D-serine. (5)(6)(7) Asc-1 (encoded by SLC7A10 gene) is the "light unit" of a heterodimeric amino-acid transporter (where transport activity takes place), which also contains the "heavy unit" 4F2 cell-surface antigen heavy chain (4F2hc, encoded by the SLC3A2 gene). It is a Na + -independent amino acid transporter with homology to the system L transporter (LAT) family.…”

“…(12) We initially sought to identify selective inhibitors of Asc-1 by developing an assay that would support a screen of our full compound collection (~3 M compounds). Although radiolabelled amino acid uptake is a well-tested method for examining transporter function including Asc-1, (5)(6)(7) developing a cell line and an assay detection format robust enough for a miniaturized (1536-well plate based) approach was a significant challenge. We describe a radiotracer uptake screening strategy using whole cells (heterologously expressing Asc-1) adherent to scintillation proximity assay (SPA) beads with [ 35 S]-cysteine as a surrogate for D-serine.…”

A novel Na+‐Independent alanine‐serine‐cysteine transporter 1 inhibitor inhibits both influx and efflux of D‐Serine

“…The effective dose of D‐Ser was very high in both humans (30 mg/kg/day) and animals (0.8–1.0 g/kg), and the possibility of off‐target and D‐Ser‐related peripheral side effects are concerns. Thus, selective increases in the extracellular D‐Ser levels in the target brain region are desirable, in which one approach is to inhibit the uptake of D‐Ser into the cells in the brain (Thomsen et al, ; Brown et al, ).…”