P021
Ac-DGGL-Am, P-21, CNTF(148-151) mimetic, adamantylated CNTF peptide
P021 is a small peptide mimetic derived from a four-residue active region of ciliary neurotrophic factor, with an adamantane cage attached at the C-terminus to make it lipophilic, orally absorbable and brain-penetrant. It was developed at the New York State Institute for Basic Research in Developmental Disabilities specifically to capture CNTF's pro-neurogenic activity without the severe appetite suppression that ended CNTF's own clinical development. It has an unusually coherent animal literature and no human data at all. Note that P021 and the earlier compound P21 are not the same molecule, although the names are often used interchangeably online.
Mechanism
Ciliary neurotrophic factor promotes neurogenesis and neuronal survival through the gp130/LIFR receptor complex and JAK/STAT signalling, but is unusable as a drug: it does not cross the blood-brain barrier, and systemic administration causes profound anorexia and weight loss through hypothalamic STAT3 activation. P021 was designed around this problem. It reproduces only the short biologically active stretch of CNTF (residues 148 to 151, Asp-Gly-Gly-Leu), acetylated at the N-terminus and joined at the C-terminus through an amide bond to a carbamoyl-substituted adamantane cage. The adamantane does two jobs: it raises lipophilicity enough for oral absorption and blood-brain barrier transit, and it sterically shields the C-terminus from carboxypeptidase attack. It is worth being precise about naming, because sources conflate two compounds: the earlier hexapeptide amide Ac-DGGLAG-NH2 is designated P21, whereas P021 is the adamantylated tetrapeptide derivative, CAS 1246751-68-7, formula C27H42N6O8, molar mass 578.7 Da. Both identifiers were checked against PubChem for this monograph.
Functionally, P021 is reported to act as a competitive antagonist of leukaemia inhibitory factor signalling. LIF, acting through the same gp130/LIFR machinery, restrains the transition of neural stem cells to neural progenitors; blocking that restraint releases progenitor formation and increases neurogenesis. Downstream, chronic P021 treatment in rodents is associated with increased BDNF expression, enhanced dendritic and synaptic markers, and (the finding that has attracted most attention) reduced abnormal tau hyperphosphorylation, apparently through inhibition of protein phosphatase-2A-regulated kinase activity. It is worth being clear that this is a mechanism inferred from downstream effects in whole animals rather than from a defined binding constant at a purified receptor.
What the research shows
For a compound with no human data, the animal literature around P021 and its immediate predecessors is unusually broad, sustained and internally consistent. In normal adult mice, the peptidergic compound of this series enhanced learning, short-term memory and spatial reference memory alongside increased neurogenesis and maturation of newborn neurons. In aged rats it reduced elevated cerebrospinal fluid tau, and in aged mice it rescued cognitive ageing. In the 3xTg-AD triple transgenic mouse, chronic oral treatment reduced abnormal tau hyperphosphorylation and accumulation and rescued deficits in cognition, neurogenesis and synaptic plasticity. Subsequent work extended this to prevention rather than treatment: early administration prevented dendritic and synaptic deficits and cognitive impairment; treatment initiated in the prenatal-to-early-postnatal window prevented Alzheimer-like behaviour and pathology; and in the Ts65Dn mouse model of Down syndrome, early neurotrophic pharmacotherapy rescued developmental delay and Alzheimer-like memory deficits.
One caveat about that literature is nomenclatural and matters for anyone tracing the primary sources. The 2010 FEBS Letters paper that is routinely cited as the founding P021 study in fact reports the hexapeptide Ac-DGGLAG-NH2, which the authors call P21; the adamantylated compound P021 is a later derivative from the same programme. The two are chemically distinct, and citing the 2010 result as direct evidence for P021 is an error that has propagated widely.
The second qualification is the familiar one, and it is decisive. Essentially this entire body of work comes from one laboratory (Khalid Iqbal's group and its collaborators), and there is no substantial independent replication by an unaffiliated team. More fundamentally, P021 has never entered human study: no Phase 1 trial, no registered study, no published human exposure. Transgenic mouse models of Alzheimer's disease have an exceptionally poor record of predicting clinical benefit; many compounds have cleared amyloid, reduced tau and rescued memory in these models and then failed comprehensively in people. A compound that looks excellent in 3xTg-AD mice has demonstrated something real about mouse biology and almost nothing about human dementia.
Evidence assessment
Preclinical only
There is no human data of any kind (no Phase 1, no registered trial, no published exposure), and the substantial animal literature derives almost entirely from the single laboratory that developed the compound.
Tiers are applied consistently across the library and re-checked when new trials read out. Read the grading method.
Key studies
Neurotrophic peptides incorporating adamantane improve learning and memory, promote neurogenesis and synaptic plasticity in mice Preclinical only
The compound highlighted in this paper is Ac-DGGLAG-NH2, which the authors name P21. It enhanced learning and both short-term and spatial reference memory in normal adult mice and increased neurogenesis and maturation of newly born neurons in the dentate gyrus.
Disease modifying effect of chronic oral treatment with a neurotrophic peptidergic compound in a triple transgenic mouse model of Alzheimer's disease Preclinical only
Reduced abnormal tau hyperphosphorylation and accumulation and rescued deficits in cognition, neurogenesis and synaptic plasticity.
Rescue of cognitive-aging by administration of a neurogenic and/or neurotrophic compound Preclinical only
Administration of the neurotrophic compound rescued age-related cognitive decline with associated neurogenic effects.
Elevated Tau Level in Aged Rat Cerebrospinal Fluid Reduced by Treatment with a Neurotrophic Compound Preclinical only
Treatment reduced elevated cerebrospinal fluid tau in aged rats, providing a biomarker-level readout.
Prevention of dendritic and synaptic deficits and cognitive impairment with a neurotrophic compound Preclinical only
Early treatment prevented dendritic and synaptic deficits and associated cognitive impairment.
Early neurotrophic pharmacotherapy rescues developmental delay and Alzheimer's-like memory deficits in the Ts65Dn mouse model of Down syndrome Preclinical only
Early P021 treatment rescued developmental delay and Alzheimer-like memory deficits in this model.
Prenatal to early postnatal neurotrophic treatment prevents Alzheimer-like behavior and pathology in mice Preclinical only
Treatment across the prenatal to early postnatal window prevented Alzheimer-like behaviour and pathology.
Neurotrophic factor small-molecule mimetics mediated neuroregeneration and synaptic repair: emerging therapeutic modality for Alzheimer's disease Preclinical only
Places P021 within the broader class of neurotrophic mimetics and sets out the rationale for targeting neuroregeneration in Alzheimer's disease.
Safety
No human safety data exists. The animal studies report chronic oral dosing over months without the anorexia and weight loss that ended CNTF's development, which was the explicit design goal and appears to have been achieved in rodents. That is a meaningful preclinical result, but it is not a safety profile. There is no published formal toxicology package, no genotoxicity or carcinogenicity assessment in the public domain, no reproductive toxicity data despite the striking emphasis in the literature on prenatal and early postnatal dosing, and no human pharmacokinetics. Material sold to consumers is not manufactured under pharmaceutical GMP and its identity and purity are not independently verified, a particular problem here, since the P21 and P021 names are used interchangeably in the grey market for two chemically different molecules. Anyone treating this compound as characterised is mistaking a well-executed animal programme for clinical evidence.
Regulatory status
| Jurisdiction | Status |
|---|---|
| United Kingdom | No UK marketing authorisation. Not a controlled drug, but as an unlicensed medicinal product it may not lawfully be sold, supplied or advertised for human use under the Human Medicines Regulations 2012. |
| United States | Not FDA-approved for any indication and never studied in a registered human trial. It is sold in the US only as an unapproved substance under a "research use only" label. |
| WADA (sport) | Not named on the WADA Prohibited List. As a neurotrophic factor mimetic without regulatory approval for human therapeutic use it would fall within the scope of category S0 (non-approved substances), and athletes should treat its status as unresolved rather than permitted. |
Questions
No. There is no Phase 1 trial, no registered study, and no published human exposure data. Every finding comes from mice and rats.
No, although the names are used interchangeably almost everywhere. P21 is the hexapeptide amide Ac-DGGLAG-NH2 reported in the 2010 FEBS Letters paper. P021 is the adamantylated tetrapeptide Ac-DGGL-Am, CAS 1246751-68-7, formula C27H42N6O8. They come from the same programme and the same laboratory, but they are different molecules, and results obtained with one are not automatically evidence for the other.
Both descriptions appear in the literature and they are compatible. P021 reproduces a four-residue active region of ciliary neurotrophic factor and is reported to act by competitively antagonising leukaemia inhibitory factor signalling at the shared gp130/LIFR complex, releasing the brake LIF places on neural progenitor formation.
CNTF causes severe anorexia through hypothalamic STAT3 activation, which is what ended its clinical development. P021 reproduces only a short active fragment rather than the whole protein, and in rodent studies chronic dosing did not produce the weight loss seen with CNTF. Whether that holds in humans is untested.
Not reliably. Transgenic mouse models have repeatedly shown clearance of amyloid, reduction of tau and rescue of memory for compounds that then failed in human trials. The mouse result is real; its predictive value for human dementia is poor.