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Preclinical and clinical pharmacology of the GABAA receptor a5 subtype-selective inverse agonist a5IA

journal contribution
posted on 2023-06-08, 14:40 authored by John R Atack
a5IA is a triazolophthalazine that selectively attenuates the effects of GABA at GABAA receptors containing an a5 subunit. It enhances long-term potentiation in an in vitro model of mouse hippocampal synaptic plasticity, gives good in vivo receptor occupancy and improves cognitive performance in normal rats as measured using the delayed-matching-to-place version of the Morris water maze yet, importantly, it is without anxiogenic or proconvulsant liabilities. The hydroxymethyl isoxazole metabolite, which occurs both in vitro and in vivo, has a very low aqueous solubility (0.6 µg/mL) that resulted in renal toxicity (crystal formation) at very high doses in preclinical safety and toxicity studies. Although this precluded it from being dosed to humans over prolonged periods of time, a5IA is, nevertheless, well tolerated in young and elderly subjects up to a dose of 6 mg in multiple-dose studies and gives a plasma EC50 for a5IA occupancy measured using [11C]flumazenil PET of 10 ng/mL. The compound was evaluated in experimental studies and although in elderly subjects a5IA does not improve performance in a paired-associate learning task (a 4-mg dose actually impairs performance), it is able to reverse the ethanol-induced impairment in performance in healthy young normal volunteers. These data demonstrate that in man an a5-selective inverse agonist may be effective at increasing performance under certain conditions. Whether or not such a compound has efficacy in conditions associated with cognitive deficits, such as attention-deficit hyperactivity disorder, Alzheimer's disease or schizophrenia remains to be determined.

History

Publication status

  • Published

Journal

Pharmacology and Therapeutics

ISSN

0163-7258

Publisher

Elsevier

Issue

1

Volume

125

Page range

11-26

Department affiliated with

  • Biochemistry Publications

Full text available

  • No

Peer reviewed?

  • Yes

Legacy Posted Date

2013-04-09

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