Studies on the subtype selectivity of CP-101,606: evidence for two classes of NR2B-selective NMDA receptor antagonists

The subtype-selectivity of racemic [H-3]CP-101,606, a novel high-affinity NMDA receptor radioligand was determined using defined recombinant NMDA receptor subunits expressed in HEK 293 cells. [H-3]CP-101,606 binds to adult rodent forebrain and NR1/NR2B receptors expressed in HEK 293 cells with K-D=4.2 nM and 6.0 nM, respectively. In contrast, no high affinity specific binding was detected to NR1, NR2A, NR2B subunits expressed alone or NR1/NR2A receptors. HEK 293 cells were transfected with NR1, NR2A and NR2B receptor subunits and complexes comprising all three subunits were isolated by anti-NR2A immunoaffinity chromatography. Based on immunoblotting with subunit-selective antibodies, the immunopurified material contained all three NMDA receptor subunit polypeptides. However, in contrast to parallel studies in which high affinity [H-3]Ro-25,6981 binding activity was observed, no high affinity [H-3]CP-101,606 binding sites were detected to the immunopurified material. This study provides further evidence for two distinct classes of NR2B-directed NMDA receptor antagonists, one which binds with high affinity irrespective whether another NR2 subunit type is present (Ro-25,6981) and a second class which is affected significantly by the presence of another NR2 subunit type within the receptor complex, exemplified by CP-101,606. (C) 2002 Elsevier Science Ltd. All rights reserved.