Cheryl Loetscher: This Day in Drug Discovery – Wakix and H3 Receptor Inverse Agonism in Narcolepsy

Cheryl Loetscher, Founder, CEO of Quantum Biological Computing and AI Systems, shared a post on LinkedIn:

“What if wakefulness and cataplexy control could be restored without conventional stimulants by blocking the central nervous system’s presynaptic histamine off-switch? [1,2]

On October 13, 2020, regulatory approval was granted for an expanded indication of Wakix (pitolisant), a first-in-class histamine H3 receptor antagonist/inverse agonist developed by Harmony Biosciences and Bioprojet for the treatment of cataplexy in adult patients with narcolepsy [1,3].

By selectively engaging presynaptic H3 autoreceptors, Wakix releases constitutive inhibitory control and increases histaminergic output to manage both cataplexy and excessive daytime sleepiness without federal controlled-substance scheduling [2,4].

The Discovery Insight

Can wake-promoting histaminergic tone be increased by reducing constitutive inhibitory control at the H3 autoreceptor? [1,2]

Narcolepsy is a chronic neurological disorder driven by the loss of hypocretin/orexin neurons in the hypothalamus, resulting in profound daytime sleepiness and debilitating cataplexy (sudden loss of muscle tone) [2,3].

• Presynaptic Autoreceptor Braking: Histamine H3 receptors act as presynaptic autoreceptors coupled to Gi/o proteins, maintaining high constitutive inhibitory tone that restrains cAMP and limits the synaptic release of wake-promoting histamine [2,4].
• The Non-Scheduled Challenge: Established narcolepsy management traditionally relied on scheduled dopamine stimulants or GABA agonists with significant abuse liability; bypassing scheduled mechanisms required selectively mobilizing endogenous wake-promoting neurotransmission [1,3].

The Scientific Solution

Pitolisant antagonizes and inversely agonizes H3 receptors, reducing H3-mediated inhibitory tone and increasing histaminergic neuronal activity [1,2]:

• Selective H3 Engagement: Pitolisant binds with high affinity to presynaptic histamine H3 receptors, acting as both a competitive antagonist and an inverse agonist [2,4].
• Autoreceptor Inhibition Released: By suppressing Gi/o-mediated constitutive inhibitory signaling, pitolisant prevents the downregulation of cAMP and releases the intrinsic molecular brake on the presynaptic neuron [2,4].
• Histaminergic Output Increased: Relieving autoreceptor suppression triggers the synthesis and release of endogenous histamine from neuronal terminals across hypothalamic and cortical projections [2,4].
• Wakefulness and Cataplexy Control: Elevated histaminergic tone stimulates postsynaptic H1 receptors across central arousal networks, driving wakefulness and reducing the frequency of cataplectic episodes [1,3].

Translational and Clinical Legacy

• First-in-Class H3 Receptor Modulator: Pioneered the clinical validation of histamine H3 receptor inverse agonism as a distinct therapeutic modality in central nervous system disorders [1,2].
• Non-Scheduled Treatment Paradigm: Established the first non-scheduled (DEA non-controlled) treatment option in the United States approved for both excessive daytime sleepiness and cataplexy in adults with narcolepsy [1,3].
• Pivotal Phase 3 Proof: Validated in the Phase 3 HARMONY CTP trial, demonstrating statistically significant reductions in weekly cataplexy rates and improvements in daytime alertness [2,3].

The Synthetion Lab Take

Reduce H3 activity.

Increase histaminergic output.

Wakix demonstrated that by switching off the presynaptic H3 brake and reversing constitutive Gi/o signaling, researchers could harness the brain’s endogenous histamine pathways to restore wakefulness and suppress cataplexy [2,4].

WAKIX, you are the Wakefulness Wavemaker!

References:

[1] US Food and Drug Administration. FDA approves expanded use of Wakix (pitolisant) for cataplexy in adult patients with narcolepsy. Silver Spring (MD): FDA; 2020 Oct 13.

[2] Dauvilliers Y, Bassetti C, Lammers GJ, et al. Pitolisant versus placebo or modafinil in patients with narcolepsy: a double-blind, randomised, trial. Lancet Neurol. 2013;12(11):1068-75.

[3] Szakacs Z, Dauvilliers Y, Mikhaylov V, et al. Safety and efficacy of pitolisant on cataplexy in patients with narcolepsy: a randomised, double-blind, placebo-controlled trial. Lancet Neurol. 2017;16(3):200-7.

[4] Schwartz JC. The histamine H3 receptor: from discovery to clinical trials with pitolisant. Br J Pharmacol. 2011;163(4):713-21.”

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