Clobazam and Its Active Metabolite N-desmethylclobazam Display Significantly Greater Affinities for α2- versus α1-GABAA–Receptor Complexes

Abstract

Clobazam (CLB), a 1,5-benzodiazepine (BZD), was FDA-approved in October 2011 for the adjunctive treatment of seizures associated with Lennox-Gastaut syndrome (LGS) in patients 2 years and older. BZDs exert various CNS effects through allosteric modulation of GABAA receptors. The structurally distinct, 1,4-BZD clonazepam (CLN) is also approved to treat LGS. The precise mechanisms of action and clinical efficacy of both are unknown. Data show that the GABAA α1-subunit–selective compound zolpidem [ZOL] exhibits hypnotic/sedative effects. Conversely, data from knock-in mice carrying BZD binding site mutations suggest that the α2 subunit mediates anticonvulsant effects, without sedative actions. Hence, the specific pattern of interactions across the GABAA receptor complexes of BZDs might be reflected in their clinical efficacies and adverse effect profiles. In this study, GABAA-receptor binding affinities of CLB, N-desmethylclobazam (N-CLB, the major metabolite of CLB), CLN, and ZOL were characterized with native receptors from rat-brain homogenates and on cloned receptors from HEK293 cells transfected with combinations of α (α1, α2, α3, or α5), β2, and γ2 subtypes. Our results demonstrate that CLB and N-CLB have significantly greater binding affinities for α2- vs. α1-receptor complexes, a difference not observed for CLN, for which no distinction between α2 and α1 receptors was observed. Our experiments with ZOL confirmed the high preference for α1 receptors. These results provide potential clues to a new understanding of the pharmacologic modes of action of CLB and N-CLB.

GABAergic modulation in central sensitization in humans

“…The smaller sedative effect of CBZ is consistent with a recent report that compared the affinities of CBZ, NDMC, and zolpidem to a1GABA A Rs and a2GABA A Rs. 18 According to this study, CBZ and NDMC have higher affinities to a2GABA A Rs than to a1GABA A Rs, whereas CLN has similar affinities to both subtypes, and zolpidem binds a1GABA A Rs with higher affinity than a2GABA A Rs. Therefore, CBZ seemed to be a suitable tool compound to further study the role of GABA A receptors in human pain pathways.…”

“…26 At subsaturating concentrations, NDMC may exert even stronger effects on spinal GABA A Rs than CBZ, as NDMC's affinity to a2GABA A Rs, which predominate in the spinal cord, 31 is higher than that of CBZ. 18 In this study, the duration of secondary hyperalgesia was too short to verify the contribution of NDMC to antihyperalgesia because NDMC plasma levels rose only slowly and reached maximum values only after 23.5 (62.4) hours when ASH was no longer detectable. Future studies should be designed to specifically assess the contribution of NDMC to antihyperalgesic and sedative effects in humans.…”

“…It exerted less cognitive and psychomotor side effects compared with CLN and lorazepam in a wide range of pharmacodynamic tests in healthy volunteers and patients. 14,29,38 According to recent work, CBZ displays significantly higher affinity for a2GABA A R than for a1GABA A R. 18 We previously demonstrated its antihyperalgesic effect in mice, 6 and a recent exploratory study in healthy volunteers has suggested an antihyperalgesic effect in capsaicin-induced hyperalgesia. 41 Hence, CBZ seems to be a suitable compound to test the antihyperalgesic effect of GABA A receptor modulators in humans.…”

Coadministered cannabidiol and clobazam: Preclinical evidence for both pharmacodynamic and pharmacokinetic interactions

“…[34][35][36] Because Na V 1.1 channels are expressed predominantly on GABAergic interneurons, loss-of-function SCN1A mutations found in Dravet syndrome patients impair interneuron function leading to neuronal hyperexcitability. [34][35][36] Because Na V 1.1 channels are expressed predominantly on GABAergic interneurons, loss-of-function SCN1A mutations found in Dravet syndrome patients impair interneuron function leading to neuronal hyperexcitability.…”

Deconstructing tolerance with clobazam

“…This apparent pattern of binding selectivity differentiates this agent from other classic benzodiazepines such as clonazepam. 27 These properties may allow clobazam to retain efficacy as antiepileptic agent while displaying a relatively low risk for the development of tolerance with long-term treatment. 17–19 …”