Evaluation of the efficacy of the hypocretin/orexin receptor agonists TAK‐925 and ARN‐776 in narcoleptic orexin/tTA; TetO‐DTA mice

Abstract

SummaryThe sleep disorder narcolepsy, a hypocretin deficiency disorder thought to be due to degeneration of hypothalamic hypocretin/orexin neurons, is currently treated symptomatically. We evaluated the efficacy of two small molecule hypocretin/orexin receptor‐2 (HCRTR2) agonists in narcoleptic male orexin/tTA; TetO‐DTA mice. TAK‐925 (1–10 mg/kg, s.c.) and ARN‐776 (1–10 mg/kg, i.p.) were injected 15 min before dark onset in a repeated measures design. EEG, EMG, subcutaneous temperature (Tsc) and activity were recorded by telemetry; recordings for the first 6 h of the dark period were scored for sleep/wake and cataplexy. At all doses tested, TAK‐925 and ARN‐776 caused continuous wakefulness and eliminated sleep for the first hour. Both TAK‐925 and ARN‐776 caused dose‐related delays in NREM sleep onset. All doses of TAK‐925 and all but the lowest dose of ARN‐776 eliminated cataplexy during the first hour after treatment; the anti‐cataplectic effect of TAK‐925 persisted into the second hour for the highest dose. TAK‐925 and ARN‐776 also reduced the cumulative amount of cataplexy during the 6 h post‐dosing period. The acute increase in wakefulness produced by both HCRTR2 agonists was characterised by increased spectral power in the gamma EEG band. Although neither compound provoked a NREM sleep rebound, both compounds affected NREM EEG during the second hour post‐dosing. TAK‐925 and ARN‐776 also increased gross motor activity, running wheel activity, and Tsc, suggesting that the wake‐promoting and sleep‐suppressing activities of these compounds could be a consequence of hyperactivity. Nonetheless, the anti‐cataplectic activity of TAK‐925 and ARN‐776 is encouraging for the development of HCRTR2 agonists.