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HTL0018318 A selective M1 partial agonist from Heptares that improved memory and attention in healthy volunteers and Alzheimer's patients, and was halted in 2018 over a tumour finding in monkeys rather than anything seen in people.
- selective M1 activation with no detectable M2 or M3 agonism
- improved working memory and learning in healthy volunteers
- improved attention and episodic memory on top of donepezil
- no pharmacokinetic interaction with donepezil
- well characterised, dose proportional pharmacokinetics
- hyperhidrosis and cold sweats
- nausea and abdominal discomfort
- modest rises in blood pressure and pulse rate
- headache
- development halted after a primate tumour finding
Overview
The cleanest M1 agonist ever taken into humans, and a genuinely frustrating loss. It did what M1 agonists are supposed to do and mostly avoided what they usually do wrong; the cholinergic side effects were mild and faded with repeated dosing. It was stopped by a preclinical toxicology result at doses no patient was ever given, with no human signal at all. Nothing about the clinical data argues against the mechanism.
- The compound improved working memory and learning in healthy volunteers, which is unusual; most pro-cognitive candidates only show anything in impaired populations, and the healthy volunteer result came with moderate to large effect sizes.
- It worked on top of donepezil rather than instead of it, improving attention and episodic memory in Alzheimer's patients already taking a full 10 mg daily dose, with no pharmacokinetic interaction between the two.
- The finding that ended it was a single rare tumour type in a nine month primate study at doses above the clinical range; about 310 humans had been dosed by then with no serious safety signal.
Mechanism
HTL0018318 is an orthosteric M1 partial that came out of structure based design against a stabilised M1 receptor. The clinical papers describe it as highly selective for M1, with an EC50 of roughly 100 nM, about twofold selectivity for M1 over M4, and no detectable functional agonist activity at human M2 or M3 [2]. In healthy younger and older volunteers, ten days of dosing at 15 to 35 mg daily produced significant improvements on short term working memory (n-back) and learning (Milner maze) with moderate to large effect sizes [2].
In 60 patients with mild to moderate Alzheimer's disease already stable on donepezil 10 mg daily, four weeks of HTL0018318 improved specific attention and episodic memory endpoints on top of the cholinesterase inhibitor, which matters because it suggests the two mechanisms add rather than overlap [4]. A dedicated interaction study found no meaningful pharmacokinetic or pharmacodynamic interference between HTL0018318 and donepezil [3].
receptor fingerprint
M1 (CHRM1)Partial agonist
M4 (CHRM4)Partial agonist
M2 (CHRM2)No detectable functional agonism
M3 (CHRM3)No detectable functional agonism
Safetyrisks and cautions, not medical advice
In humans the profile was mild and recognisably cholinergic: hyperhidrosis, nausea, chills, cold sweats and feeling cold, plus increases in systolic blood pressure of up to about 10 to 12 mmHg after single doses that tended to attenuate with repeated dosing [1]. In the Alzheimer's study headache was the most common event at 7 to 21 percent, cholinergic events were reported by 0 to 13 percent, and two patients stopped because of adverse events [4]. Roughly 310 people were exposed across the programme without a serious safety signal. What stopped the drug was not a human finding. In a nine month animal toxicology study in non human primates, at doses and durations exceeding anything given to people, a rare neoplastic tumour was observed, and Allergan and Sosei voluntarily suspended all clinical development in September 2018 pending investigation.
History
HTL0018318 was designed at Heptares Therapeutics in Cambridge, the drug discovery arm of Japan's Sosei Group, and licensed to Allergan in 2016 as part of a portfolio of subtype selective muscarinic agonists. It ran phase 1 studies in the United Kingdom, the Netherlands and Japan, completed a phase 1b in Alzheimer's patients in Europe, and had a phase 2 in dementia with Lewy bodies planned; that Lewy body study (NCT03592862) was withdrawn without enrolling a single participant after the September 2018 suspension. AbbVie, which had acquired Allergan, terminated the licence effective 4 January 2021 and returned all rights, assets and data to Sosei Heptares, which now trades as Nxera Pharma. No restart of HTL0018318 has been publicly announced since, and its current status is best described as shelved rather than formally killed.
Reputation
Held in high regard by researchers who work on muscarinic cognition, and cited as evidence that a selective M1 agonist can be both tolerable and pro-cognitive in real patients. It is also the standard example of a programme ended by a preclinical finding at supra clinical doses with nothing wrong in the clinic, which is a different and less common way for a drug to die than the usual efficacy miss.
Subjective profileweighing the evidence above
The cleanest M1 agonist ever taken into humans, and a genuinely frustrating loss. It did what M1 agonists are supposed to do and mostly avoided what they usually do wrong; the cholinergic side effects were mild and faded with repeated dosing. It was stopped by a preclinical toxicology result at doses no patient was ever given, with no human signal at all. Nothing about the clinical data argues against the mechanism.
Resources
This entry is here for reference.
Research
- 1.First-in-man study to investigate safety, pharmacokinetics and exploratory pharmacodynamics of HTL0018318, a novel M1-receptor partial agonist for the treatment of dementias.
- 2.Safety, pharmacokinetics and exploratory pro-cognitive effects of HTL0018318, a selective M1 receptor agonist, in healthy younger adult and elderly subjects: a multiple ascending dose study.
- 3.Safety and Pharmacokinetics of HTL0018318, a Novel M1 Receptor Agonist, Given in Combination with Donepezil at Steady State: A Randomized Trial in Healthy Elderly Subjects.
- 4.A phase 1b/2a multicenter study of the safety and preliminary pharmacodynamic effects of selective muscarinic M1 receptor agonist HTL0018318 in patients with mild-to-moderate Alzheimer's disease.
4 listed here; entry last updated July 2026
Reviews
My notesprivate to this device
FAQ
Why was it stopped if nothing went wrong in people?
A nine month toxicology study in non human primates, run at doses and durations well above anything a person received, turned up a rare neoplastic tumour. Allergan and Sosei suspended clinical work in September 2018 to investigate. No safety signal had been seen in the roughly 310 humans dosed by that point, but a tumour finding in a long primate study is the kind of result that halts a chronic use drug regardless.
Is it still in development?
Not visibly. AbbVie handed all rights back to Sosei Heptares, now Nxera Pharma, effective 4 January 2021, and no clinical study of HTL0018318 has been announced since. The company has continued with other muscarinic agonists, including M4 and M1 preferring compounds partnered with Neurocrine Biosciences, but those are different molecules.
How is it different from xanomeline?
It is far more selective. Xanomeline binds all five muscarinic subtypes at similar affinity and only prefers M1 and M4 in what it does after binding. HTL0018318 is a designed M1 partial agonist with no detectable functional agonism at M2 or M3, which is why its cholinergic side effects were mild enough to dose without a peripheral blocker.
Could I get hold of it?
No. It was never approved anywhere, no trials are running, and no human dose is established for use outside a trial.
Adverse effects
- hyperhidrosis and cold sweats
- nausea and abdominal discomfort
- modest rises in blood pressure and pulse rate
- headache
- development halted after a primate tumour finding