Calcium channel alpha2-delta type 1 subunit is the major binding protein for pregabalin in neocortex, hippocampus, amygdala, and spinal cord: An ex vivo autoradiographic study in alpha2-delta type 1 genetically modified mice

Pregabalin is a synthetic amino acid compound effective in clinical trials for the treatment of post-herpetic neuralgia, diabetic peripheral neuropathy, generalized anxiety disorder and adjunctive therapy for partial seizures of epilepsy. However, the mechanisms by which pregabalin exerts its therapeutic effects are not yet completely understood. In vitro studies have shown that pregabalin binds with high affinity to the alpha2-delta (α2-δ) subunits (Type 1 and 2) of voltage-gated calcium channels. To assess whether α2-δ Type 1 is the major central nervous system (CNS) binding protein for pregabalin in vivo, a mutant mouse with an arginine-to-alanine mutation at amino acid 217 of the α2-δ Type 1 protein (R217A mutation) was generated. Previous site-directed mutagenesis studies revealed that the R217A mutation dramatically reduces α2-δ 1 binding to pregabalin in vitro. In this autoradiographic analysis of R217A mice, we show that the mutation to α2-δ Type 1 substantially reduces specific pregabalin binding in CNS regions that are known to preferentially express the α2-δ Type 1 protein, notably the neocortex, hippocampus, basolateral amygdala and spinal cord. In mutant mice, pregabalin binding was robust throughout regions where the α2-δ Type 2 subunit mRNA is abundant, such as cerebellum. These findings, in conjunction with prior in vitro binding data, provide evidence that the α2-δ Type 1 subunit of voltage-gated calcium channels is the major binding protein for pregabalin in CNS. Moreover, the distinct localization of α2-δ Type 1 and mutation-resistant binding (assumed to be α2-δ Type 2) in brain areas subserving different functions suggests that identification of subunit-specific ligands could further enhance pharmacologic specificity.