ACD856

ACD856 is a triazinetrione derivative and the lead compound of AlzeCure Pharma's neurotrophin-modulator program ^[1][2]. It emerged from a screen of roughly 25,000 molecules that sought small molecules able to potentiate signaling of nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF); that effort identified the triazinetrione ACD855 and, subsequently, ACD856 as positive allosteric modulators of the Trk receptors ^[1]. As a pan-Trk modulator it acts across TrkA, TrkB, and TrkC ^[2].

In preclinical work ACD856 enhanced NGF-induced neurite outgrowth, raised levels of the synaptic protein SNAP25, and increased phosphorylation of TrkB and the downstream signaling kinase ERK1/2 ^[2]. It protected cultured neurons against amyloid-beta and energy-deprivation stress, increased BDNF in the brains of aged mice, and produced an antidepressant-like effect that persisted for several days after dosing ^[2]. It acted as a cognitive enhancer in a TrkB-dependent manner across behavioral models, and a single treatment was reported to restore age-related cognitive decline in old mice toward the performance of young animals, findings the developers interpret as pointing to both symptomatic and disease-modifying, neurorestorative effects ^[1][2].

ACD856 has advanced into early clinical testing. A microdose study and a Phase 1 single-ascending-dose trial in healthy volunteers found it well tolerated, with rapid absorption, near-complete oral bioavailability, and an elimination half-life of roughly 20 hours ^[4]. A subsequent multiple-ascending-dose study confirmed good tolerability, demonstrated central nervous system exposure in cerebrospinal fluid, and detected dose-dependent changes on quantitative electroencephalography consistent with central target engagement ^[3]. As an experimental agent it is not approved for any use and remains in clinical development rather than on the market ^[3][4].

Regulatory status: not approved as a medicine by any authority anywhere; ACD856 is an investigational compound at Phase 1/1b. It is nonetheless already sold by research-chemical suppliers including Everychem and Probechem, both of which label it for laboratory use only and not for human use.

WADA: ACD856 is not named individually on the Prohibited List, but as a pharmacological substance under clinical development with no approval from any governmental health authority for human therapeutic use, it falls squarely within category S0 (Non-Approved Substances), which is prohibited at all times, in and out of competition.

Observed adverse effects in humans are limited and mild. In the single-dose study there were no serious adverse events and no dose-related trend in adverse events, laboratory values, vital signs, ECG, physical examination or stool frequency; the most common event was headache, reported by 8 of 56 subjects on 11 occasions, and notably it occurred only in the 1 to 40 mg range and not at 75 or 150 mg, arguing against a drug effect. In the 7-day repeat-dose study there were again no serious adverse events; of the events judged possibly treatment-related, the two moderate ones were a transient, asymptomatic rise in lipase and amylase in one subject after the final dose, which normalised within 24 hours. That pancreatic enzyme signal is the only laboratory finding of note in the entire human record and it has not been followed up in any published study.

Mechanism-based risks that the sponsor anticipated from earlier drugs that stimulate NGF or BDNF signalling, and screened for, are altered gut motility (loose and more frequent stools), reduced appetite and weight loss, diffuse muscle pain, and eosinophilia; none of these was severe or serious in those earlier programmes and none was reported with ACD856, but the volunteer numbers are far too small to exclude them.

Major safety unknowns: total published human exposure is roughly 86 healthy volunteers with a maximum published treatment duration of 7 days, so there is no long-term safety data at all. Nothing is published on drug-drug interactions, use in older adults or in any patient group, abuse liability, tolerance or withdrawal, reproductive toxicity, or carcinogenicity.

The carcinogenicity gap deserves specific mention: NTRK gene fusions drive several human cancers and approved oncology drugs such as larotrectinib and entrectinib work by inhibiting Trk, so a compound designed to potentiate all three Trk receptors is acting in the opposite direction; no published data address whether this matters, and the absence of evidence is not evidence of safety. The qEEG changes reported as central target engagement (increased relative theta power, decreased fast alpha and beta, raised theta/beta ratio) are the sponsor's interpretation of a signal that is not an established marker of cognitive benefit; a higher theta/beta ratio is more usually described in attention deficit and in cognitive decline.

ACD856 is an investigational small-molecule positive allosteric modulator of tropomyosin receptor kinase (Trk) receptors developed by the Swedish biotech AlzeCure Pharma, which markets it under the NeuroRestore program for Alzheimer's disease, depression and other conditions of impaired cognition. The candidate emerged as a follow-up to an earlier compound, ACD855, which was shelved because its half-life in humans proved too long for practical dosing. To de-risk ACD856, AlzeCure ran an intravenous microdose phase 0 study in six healthy men before advancing to a randomized, double-blind phase 1 single-ascending-dose trial spanning 1 to 150 mg in 56 healthy subjects, with results reported around 2021 to 2024. It remains an early clinical-stage research compound rather than an approved drug.