Biochem/physiol Actions

Tasimelteon is a Dual Melatonin Receptor Agonist (DMRA) recently approved (Hetlioz) for the treatment of Non-24-hour sleep–wake disorder, a disorder primarily found in the totally blind, where a lack of normal synchronization between the 24-hour light–dark cycle and the endogenous circadian rhythm causes it to drift out of alignment with conventional sleep–wake schedules. The endogenous rhythm of the circadian pacemaker in the suprachiasmatic nuclei (SCN) is typically slightly longer than 24 h and therefore must be synchronized to the 24-hour day, normally by light, but exogenous melatonin can also phase-shift circadian rhythms. Tasimelteon is a selective agonist for the SCN melatonin receptors MT1 and MT2 with greater affinity for the MT2 receptor thought to be more important in mediating circadian rhythm phase-shifting. EC50 values are 0.75 nM for MT1 and 0.1 nM for MT2 measured by inhibition of forskolin-stimulated cAMP accumulation in NIH-3T3 cells expressing human MT1 and MT2.