P21 (P021)

P21 (also written P021) is a small synthetic peptide derived from the active region of ciliary neurotrophic factor (CNTF). Developed in Khalid Iqbal's laboratory at the New York State Institute for Basic Research, it was engineered to keep the neurogenic and neurotrophic activity of CNTF while being blood-brain-barrier permeable, orally bioavailable and metabolically stable. The published evidence is entirely preclinical, drawn from rodent models of Alzheimer-type disease, Down syndrome and ageing.

What it is

P021 is an acetylated, C-terminally amidated tetrapeptide built on the sequence Ac-DGGLAG-NH2, whose core Asp-Gly-Gly-Leu (DGGL) motif corresponds to the active fragment of human CNTF identified by epitope mapping. The terminal residue is an unnatural adamantane-based amino acid: a glycine bearing a tricyclic adamantane cage that raises lipophilicity and, in turn, blood-brain-barrier penetrance. This design grew out of efforts to reduce the neurotrophic activity of the porcine-brain preparation Cerebrolysin down to a single small, defined and drug-like molecule.

The compound has the molecular formula C27H42N6O8, a molecular weight of about 578.7 g/mol, and CAS number 1246751-68-7 (also catalogued as GLXC-21260). Because it is a single defined synthetic sequence rather than a mixture, it can be characterised by standard HPLC and mass spectrometry. It sits in the class of small-molecule neurotrophic-factor mimetic peptides. Supplied strictly for laboratory research use only, not for human or veterinary use.

How it works

The proposed mechanism centres on the leukemia inhibitory factor (LIF) and BDNF axes. P021 is reported to competitively inhibit LIF within the JAK-STAT3 signalling pathway; because LIF signalling restrains the formation of neural progenitor cells, this disinhibition is proposed to favour neurogenesis. In parallel, P021 increases CREB activity and the transcription and expression of brain-derived neurotrophic factor (BDNF). Newly expressed BDNF then binds its receptor tropomyosin receptor kinase B (TrkB), activating the PI3-kinase/Akt pathway.

Downstream of PI3K/Akt, inhibitory phosphorylation of glycogen synthase kinase 3 beta (GSK-3β) at Ser9 reduces the kinase's activity. Since GSK-3β is a principal tau kinase, its inhibition is proposed to limit the abnormal hyperphosphorylation of tau and the resulting neurofibrillary pathology. Across the rodent literature this BDNF/TrkB/PI3K/Akt/GSK-3β cascade is invoked to explain the reported gains in hippocampal neurogenesis, dendritic and synaptic integrity, and spatial memory.

What the research shows

P021 has been studied only in animals and cell systems; there is no human clinical outcome data. The most quantitative reports come from the Ts65Dn mouse model of Down syndrome and from 3xTg-AD mice and aged rats. In the Ts65Dn work, treatment given to pregnant dams from embryonic day 8 through postnatal day 21 roughly doubled BDNF, raised inhibitory Ser9 phosphorylation of GSK-3β, increased the phospho-CREB/CREB ratio, and improved novel-object discrimination, with spatial memory in the Morris water maze restored to wild-type-comparable levels. In 3xTg-AD mice and aged rats, chronic dietary or gavage dosing rescued dendritic and synaptic deficits, increased neurogenesis, reduced tau and amyloid pathology, and blunted microgliosis and astrogliosis.

Side Effects

The safety picture for P021 (also written P21) is drawn entirely from preclinical work in rodents, including transgenic Alzheimer's disease mouse models. There are no published human trials, so no human side-effect profile exists. P021 was deliberately engineered as a small, orally bioavailable, blood-brain-barrier-penetrant tetrapeptide mimetic of ciliary neurotrophic factor (CNTF), specifically to avoid the poor pharmacokinetics and systemic adverse effects that limited native CNTF. What follows summarizes what the animal literature reports, not what is established in people.

In short, P021 has a favorable tolerability record only in rodents, and its designers frame that as evidence it sidesteps the problems of native CNTF rather than proof of human safety. No human safety data exist, so the side-effect profile in people is entirely uncharacterized.

At a glance

Dosing

All documented P21 (P021) doses come from preclinical rodent studies in Alzheimer's and related models, mainly from the Iqbal and Kazim laboratory. There is no established human dose, and P021 has not been tested in human clinical trials. The figures below are rodent research doses expressed as the study authors reported them, typically in nanomoles per gram of feed or nanomoles per kilogram of body weight. They are shown for educational context only and are not instructions for use in humans.

These are rodent-study doses only. No human dose for P21 exists, and no validated animal-to-human dose conversion has been established for this peptide. P21 is offered strictly for laboratory research use, and the information above is educational, not medical or dosing advice.

Preparing it

P021 is supplied as a lyophilised powder and is reconstituted with bacteriostatic or sterile water before use. See the reconstitution guide for step-by-step handling and the concentration guide for calculating volume per unit of peptide. Reconstituted solution is typically kept refrigerated at 2-8 C and shielded from light. This handling note is provided for laboratory research use only.

Compared with Cerebrolysin

P021 traces directly to the neurotrophic-mimetic programme that also produced the interest in Cerebrolysin. Where Cerebrolysin is an undefined mixture of porcine-brain peptides given by injection, P021 is a single, fully defined small molecule intended to reproduce a comparable BDNF-linked neurotrophic signal with better oral bioavailability and blood-brain-barrier access. That reductionist design is the main pharmacological argument for studying P021, though its evidence base remains far smaller and entirely preclinical.

Where to go next

Last updated on July 3, 2026