P021 Research

P021 research began with a 2010 paper and has stayed preclinical ever since. The compound is a small synthetic molecule derived from ciliary neurotrophic factor, usually shortened to CNTF. Sixteen years of animal and cell studies now exist, and no human trial of any phase has ever been registered. Every primary study in the published record was produced by a group that includes the compound's patent holder. This article describes what those studies investigated and where the evidence stops.

What P021 is

P021 is also written P-21, and the 2010 origin paper calls it P21.^[1] Its CAS number is 1246751-68-7 and its PubChem entry is CID 56599151. The formula is C27H42N6O8, the molecular weight 578.67 g/mol, and the sequence Ac-DGGLAG-NH2.

The literature calls it a tetrapeptide, meaning four natural residues, Asp-Gly-Gly-Leu, copied from a short active region of human CNTF. That word is incomplete, because an acetyl cap sits at one end of the molecule and an adamantylated glycine at the other. The same string is also written Ac-DGGL(A)G-NH2, where the A marks the adamantyl group on the final glycine rather than an alanine residue. So the six letters denote five positions, not six residues. The adamantyl cage is the deliberate design feature. Its stated purposes are to raise lipophilicity, to aid blood-brain-barrier penetration and to resist enzymatic breakdown.

Several naming collisions matter here. p21, also called CDKN1A, is an unrelated cell cycle protein, and "P021" doubles as a genetic testing probemix code and a conference poster number. A raw PubMed search on P021 returns 45 records, of which only a minority concern this compound. CNTF itself is a separate entity, a protein of roughly 200 residues whose findings are not findings about this mimetic. Research-grade P021 is the small molecule described above.

How P021 is thought to work

The proposed mechanism is interference with CNTF-family receptor signaling, leading to increased BDNF expression. In cell culture the origin paper reported that P021 inhibited LIF-induced STAT3 phosphorylation, and in wild-type mice it reported improved learning and memory alongside increased neurogenesis.^[1] Several later animal studies from the Iqbal laboratory report a recurring trio of readouts: BDNF rises, GSK3-beta activity falls, and dentate gyrus neurogenesis markers increase.

That pattern is not uniform across the record. In 3xTg-AD mice treated from the first postnatal day, pro-BDNF, TrkB and CNTF were unchanged.^[2] In Cdkl5 knockout mice, chronic treatment in vivo did not raise BDNF levels.^[3]

Brain penetration is the weak point in this account, because raising it is one stated purpose of the adamantyl modification. Papers from the group state that P021 is blood-brain-barrier permeable.^[2][4] One of them attributes that permeability to testing carried out by a commercial service, and cites the 2010 origin paper for it.^[1][2] No study in this record publishes a measurement of how much P021 reaches brain tissue in any animal. Brain penetration is therefore asserted in this literature rather than documented by published data. What the animal data do cover is plasma and gut. Wei and colleagues report a plasma half-life above three hours, alongside high stability in artificial gastric and intestinal fluid.^[2]

P021 preclinical research

Every finding in this section comes from an animal model or from cultured cells.

One study treated female 3xTg-AD mice orally for twelve months, starting at nine to ten months of age.^[5] It reported reduced tau hyperphosphorylation, raised BDNF, lower GSK3-beta activity and rescued cognition, neurogenesis and synaptic plasticity. The amyloid result was narrower than the tau result. The significant fall in soluble amyloid-beta was recorded after six months of treatment and was not present after twelve. Insoluble amyloid-beta 40 and 42 were unmoved at both timepoints. The reduction in plaque load in the CA1 region was a trend that did not reach significance.^[5] Total tau was unchanged, and only phosphorylated tau moved. The Morris water maze probe trial showed a non-significant trend rather than a significant effect. The dentate gyrus GluA2/3 density deficit was not restored. Western blot showed no change in GluN1 or GluA2/3 protein.

A secondary prevention study began treatment in three-month-old female 3xTg-AD mice, before overt pathology appeared.^[6] It reported prevention of both amyloid and tau pathology, rescued episodic memory and a markedly reduced mortality rate. A companion paper under the same protocol reported prevention of dendritic and synaptic deficits and of cognitive impairment.^[7]

Two further studies treated 3xTg-AD mice during development. One gave P021 from the prenatal period into early postnatal life and reported prevention of Alzheimer-like behavior, with reduced tau hyperphosphorylation and reduced plaque load measured at twenty-two months.^[8] The other treated from the first postnatal day to four months of age and reported prevention of Alzheimer-like behavior and synaptic dysfunction.^[2] That second study reported no significant effect on Morris water maze escape latency or on target crossings. Only time in the target quadrant moved. It also reported no effect on pro-BDNF, TrkB or CNTF, and none on GluN2B or GluA1 messenger RNA.

The animal work extends beyond Alzheimer's models. In aged Fisher rats, one study reported that chronic oral P021 reduced age-related memory decline and restored neurogenesis and BDNF.^[9] The behavioral effect in that study was partial rather than complete. Morris water maze error bars overlapped the vehicle-treated old rats, and treated animals never reached young-rat performance. Magnetic resonance spectroscopy showed no change in hippocampal GABA, glutamate, NAA, NAA plus NAAG or glutamine.^[9] FDG-PET showed no effect on brain glucose uptake.^[9]

A later study in aged rats reported reduced total tau in cerebrospinal fluid.^[4] In brain tissue, total tau fell in the hippocampus and not in the cortex.^[4] Amyloid-beta and amyloid precursor protein in cerebrospinal fluid were elevated in those aged rats and were not reduced by treatment.^[4] Phosphorylated tau species were not evaluated in that study. In Ts65Dn mice, a Down syndrome model, early treatment rescued developmental delay and later memory deficits.^[10] One study in aged rats and 3xTg-AD mice reported reduced retinal changes resembling age-related macular degeneration.^[11] Rodents have no macula, and that study measured histopathology without any visual function testing.

A 2026 diffusion MRI study in female 3xTg-AD mice found partially normalized white matter microstructure, including increased fractional anisotropy in the corpus callosum.^[12] The fimbria showed no difference between treated and vehicle-treated transgenic mice, and many gray matter measures were unaffected.^[12] The authors state three limitations of their own: no histological validation, no behavioral testing, and a single timepoint.

Several of these studies measured large marker panels and reported a subset as changed. The prenatal study recorded no change in synapsin, synaptophysin, MAP2 or Iba1.^[8] The Ts65Dn study recorded no effect on PSD-95, TrkB, CNTF or CREB.^[10] The companion prevention paper recorded no change in MAP2 at nine months.^[7] At eighteen months the same paper recorded no change in cortical pCREB, CREB, synapsin 1 or GluA1, and none in hippocampal synaptophysin or GluA2/3.^[7]

P021 in CDKL5 deficiency disorder models

The clearest failure in the record comes from the study with the most external involvement. Mottolese and colleagues, working with Elisabetta Ciani's group in Bologna, tested P021 in models of CDKL5 deficiency disorder.^[3] Both arms of that study are preclinical, one in cultured cells and one in mice.

In cultured human neuronal cells lacking CDKL5, P021 restored proliferation, survival and maturation.^[3] In Cdkl5 knockout mice the same compound did not reproduce those results. The authors write that chronic treatment in vivo did not raise BDNF levels and did not improve neuroanatomical defects, giving limited behavioral benefit.^[3]

In those knockout mice, memory was not restored on the Morris water maze or on passive avoidance.^[3] Social behavior was not restored on marble burying or on nest building, and motor function was not restored on the rotarod.^[3] Survival of newborn DCX-positive dentate cells was not restored, and CA1 pyramidal neuron survival was unaffected.^[3] Dendritic spine and synapse maturation in those mice were also unaffected.^[3] One measure did improve: muscular rigidity on the catalepsy bar test.^[3] A trend toward reduced anxiety in the open field did not reach significance.^[3]

That failed in vivo experiment delivered P021 in the diet. The mouse work in that paper used male animals only, across a total of thirty-nine animals.^[3]

That is a clean dissociation between an in vitro success and an in vivo failure, and the central proposed mechanism did not engage in the living animal. The authors also ran a second in vivo experiment in older mice at a higher exposure, explicitly to test whether dose or age explained the result.^[3] It failed as well. Their conclusion leaves open whether starting prenatally or treating for longer would change the outcome.

Human research on P021

There is none. Not limited, and not mixed, but absent.

No P021 study is registered on ClinicalTrials.gov. P021 appears in no FDA drug approval record and on no FDA drug label. The only United States regulatory record is a substance registry identifier, UNII VV8CZC8PAS, which is not an approval, a designation, or evidence of a filing.

One claim in circulation reads the other way. A secondary report on P021 lists the compound as in clinical development by Phanes Biotech, and states two lines away that no clinical trials of it exist. A company license to develop a compound is not a registered trial. Phanes Biotech is also not Phanes Therapeutics, an unrelated oncology company in San Diego whose registered trials involve other compounds.

Safety in humans has therefore never been assessed. No human dose, no human pharmacokinetic measurement and no human adverse event record exists for this compound.

An approved CNTF product does exist, and it is not P021. Revakinagene taroretcel, an encapsulated cell gene therapy delivering full-length CNTF protein, is FDA-approved for adults with idiopathic macular telangiectasia type 2. The same cell therapy also holds FDA orphan drug designation for retinitis pigmentosa. Both of those standings belong to the CNTF protein product. P021 holds no regulatory standing in eye disease or in any other indication.

The parent protein's own human record is a failure record, and it is not evidence about P021. In a randomized placebo-controlled trial in 730 people with amyotrophic lateral sclerosis, recombinant human CNTF showed no significant effect on the primary muscle strength endpoint.^[13] Treated patients showed a statistically significant early decrease in strength. Mortality was similar across all three arms, and no secondary measure reached significance. Reported side effects included anorexia, weight loss and cough.^[13] Those side effects were sufficient to limit dosing in many patients in that trial.^[13] A recombinant CNTF variant later produced more weight loss than placebo over twelve weeks in obese adults.^[14] Its clinical development was then halted on peripheral side effects and the emergence of CNTF antibodies.^[15]

Those human findings belong to CNTF proteins rather than to this small molecule. The safety case made for P021 is written against that record. The only harm signal recorded for P021 itself comes from an independent narrative review.^[16] That review notes a theoretical risk of anti-P021 antibody formation, with no immune reaction observed to date.^[16]

Independence, disclosure and the retraction question

Sixteen primary research and review records on PubMed have P021 as their subject and Khalid Iqbal as an author. No primary study of P021 has been published by a group that does not include him. The only Iqbal-free publication in the record is the independent narrative review, and it reports no new data.^[16] Iqbal holds United States patents covering P021 and its precursor peptide. He is also co-founder and Chief Scientific Officer of Phanes Biotech, which holds the worldwide license to develop it. Two apparently external groups, in Bologna and at the Medical University of South Carolina, list him as a co-author. Those are collaborations rather than independent verification.

Disclosure across that corpus is inconsistent. Mottolese 2024 and Falangola 2026 state the patents and the company role in full.^[3][12] Kazim 2017 discloses the patents alone.^[10] The companion Baazaoui 2017 paper and Wei 2020 each state that the authors declare no competing interests.^[7][8] Liu 2019 carries both a disclosure naming the P021 patent and boilerplate declaring an absence of commercial relationships.^[11] Those two statements contradict each other inside one article.

No P021 paper has been retracted, and none carries an expression of concern. One paper in the adjacent precursor program was retracted in June 2026.^[17][18] That study compared CNTF-derived peptides against cerebrolysin in amyloid transgenic mice, and it tested Peptide 6 and Peptide 6A, the eleven-residue CNTF precursors, which are different compounds from P021.

That retracted paper was a collaboration rather than one laboratory's work. It was led from the University of California, San Diego, and its thirteen authors include Khalid Iqbal and other members of the P021 team.^[17] Three of the co-authors were with EVER Neuro Pharma, which manufactures cerebrolysin, the comparator drug in that study's own title and design.^[17]

The retraction notice records two different kinds of image problem. Three panels are described as highly similar to figures in a 2010 paper by Crews, Rockenstein and Masliah.^[18][19] That earlier paper concerns amyloid transgenic modeling and contains no CNTF peptide work. A fourth panel is described as containing in-image modifications, including duplications and cloned sections.^[18] The notice traces that fourth item to no other publication, so it sits inside the retracted paper itself. The three reused panels trace to the histology contribution of the San Diego group. PubMed returns thirty-two records for that group's senior author, Eliezer Masliah, carrying a retraction or expression-of-concern publication type.

A separate correction sits on the most recent P021 paper. A published erratum to the 2026 diffusion MRI study appeared later the same year, and it locates the correction to one page of that paper.^[20]

Conclusion

P021 has a sixteen-year preclinical dataset in animals and cells. It has never been independently replicated and never been given to a human. Its reported positives sit alongside repeated null results inside the same studies. It also contains one clear in vivo failure, in its most externally conducted study.

P021 from Purepeptides is a research compound, supplied for laboratory research use only.

Frequently Asked Questions

Has P021 ever been tested in humans? No human study of P021 exists. No P021 study is registered on ClinicalTrials.gov, and P021 appears in no FDA drug approval record and on no FDA drug label. The only United States regulatory record is a substance registry identifier, which is not an approval or a designation. Safety in humans has therefore never been assessed.

Are P21 and P021 the same compound? Yes. P21, P021 and P-21 all name the same molecule, and the 2010 origin paper uses P21.^[1] It is unrelated to p21, also called CDKN1A, which is a cell cycle protein.

Has any P021 finding been replicated by an independent group? Not in the published record. Sixteen primary research and review records have P021 as their subject and Khalid Iqbal as an author. Two apparently external groups list him as a co-author, which makes those collaborations rather than independent verification.

Has any P021 research been retracted? No P021 paper has been retracted, and none carries an expression of concern. One paper in the adjacent precursor program was retracted in June 2026, a University of California, San Diego led collaboration that tested Peptide 6 and Peptide 6A rather than P021.^[17][18] The notice records three panels as highly similar to figures in a separate 2010 paper from that San Diego group, which contains no CNTF peptide work.^[18][19] It records a fourth panel as containing in-image modifications, and traces that item to no other publication.^[18]

References

1. 1

   Li B, Wanka L, Blanchard J, Liu F, Chohan MO, Iqbal K, Grundke-Iqbal I. Neurotrophic peptides incorporating adamantane improve learning and memory, promote neurogenesis and synaptic plasticity in mice. FEBS Lett. 2010;584(15):3359-3365. doi:10.1016/j.febslet.2010.06.025. PMID 20600002.
2. 2

   Wei W, Liu Y, Dai CL, Baazaoui N, Tung YC, Liu F, Iqbal K. Neurotrophic treatment initiated during early postnatal development prevents the Alzheimer-like behavior and synaptic dysfunction. J Alzheimers Dis. 2021;82(2):631-646. doi:10.3233/JAD-201599. PMID 34057082.
3. 3

   Mottolese N, Loi M, Trazzi S, Tassinari M, Uguagliati B, Candini G, Iqbal K, Medici G, Ciani E. Effects of a ciliary neurotrophic factor (CNTF) small-molecule peptide mimetic in an in vitro and in vivo model of CDKL5 deficiency disorder. J Neurodev Disord. 2024;16(1):65. doi:10.1186/s11689-024-09583-4. PMID 39592934.
4. 4

   Khatoon S, Chalbot S, Bolognin S, Puoliväli J, Iqbal K. Elevated tau level in aged rat cerebrospinal fluid reduced by treatment with a neurotrophic compound. J Alzheimers Dis. 2015;47(3):557-564. doi:10.3233/JAD-142799. PMID 26401692.
5. 5

   Kazim SF, Blanchard J, Dai CL, Tung YC, LaFerla FM, Iqbal IG, Iqbal K. Disease modifying effect of chronic oral treatment with a neurotrophic peptidergic compound in a triple transgenic mouse model of Alzheimer's disease. Neurobiol Dis. 2014;71:110-130. doi:10.1016/j.nbd.2014.07.001. PMID 25046994.
6. 6

   Baazaoui N, Iqbal K. Prevention of amyloid-beta and tau pathologies, associated neurodegeneration, and cognitive deficit by early treatment with a neurotrophic compound. J Alzheimers Dis. 2017;58(1):215-230. doi:10.3233/JAD-170075. PMID 28387677.
7. 7

   Baazaoui N, Iqbal K. Prevention of dendritic and synaptic deficits and cognitive impairment with a neurotrophic compound. Alzheimers Res Ther. 2017;9(1):45. doi:10.1186/s13195-017-0273-7. PMID 28655344.
8. 8

   Wei W, Wang Y, Liu Y, Dai CL, Tung YC, Liu F, Iqbal K. Prenatal to early postnatal neurotrophic treatment prevents Alzheimer-like behavior and pathology in mice. Alzheimers Res Ther. 2020;12(1):102. doi:10.1186/s13195-020-00666-7. PMID 32854771.
9. 9

   Bolognin S, Buffelli M, Puoliväli J, Iqbal K. Rescue of cognitive-aging by administration of a neurogenic and/or neurotrophic compound. Neurobiol Aging. 2014;35(9):2134-2146. doi:10.1016/j.neurobiolaging.2014.02.017. PMID 24702821.
10. 10

    Kazim SF, Blanchard J, Bianchi R, Iqbal K. Early neurotrophic pharmacotherapy rescues developmental delay and Alzheimer's-like memory deficits in the Ts65Dn mouse model of Down syndrome. Sci Rep. 2017;7:45561. doi:10.1038/srep45561. PMID 28368015.
11. 11

    Liu Y, Wei W, Baazaoui N, Liu F, Iqbal K. Inhibition of AMD-like pathology with a neurotrophic compound in aged rats and 3xTg-AD mice. Front Aging Neurosci. 2019;11:309. doi:10.3389/fnagi.2019.00309. PMID 31803044.
12. 12

    Falangola MF, Voltin J, Cole M, Nietert PJ, Liu F, Iqbal K, Jensen JH. Diffusion MRI measures detect brain microstructure changes due to early treatment with neurotrophic peptide mimetic P021 in the 3xTg-AD mouse model of Alzheimer's disease. Magn Reson Imaging. 2026;129:110641. doi:10.1016/j.mri.2026.110641. PMID 41740658.
13. 13

    ALS CNTF Treatment Study Group. A double-blind placebo-controlled clinical trial of subcutaneous recombinant human ciliary neurotrophic factor (rHCNTF) in amyotrophic lateral sclerosis. Neurology. 1996;46(5):1244-1249. doi:10.1212/wnl.46.5.1244. PMID 8628460.
14. 14

    Ettinger MP, Littlejohn TW, Schwartz SL, Weiss SR, McIlwain HH, Heymsfield SB, et al. Recombinant variant of ciliary neurotrophic factor for weight loss in obese adults: a randomized, dose-ranging study. JAMA. 2003;289(14):1826-1832. doi:10.1001/jama.289.14.1826. PMID 12684362.
15. 15

    Rafii P, Cruz PR, Ettich J, Seibel C, Padrini G, Wittich C, et al. Engineered interleukin-6-derived cytokines recruit artificial receptor complexes and disclose CNTF signaling via the OSMR. J Biol Chem. 2024;300(5):107251. doi:10.1016/j.jbc.2024.107251. PMID 38569939.
16. 16

    Lozupone M, Dibello V, Sardone R, Castellana F, Zupo R, Lampignano L, et al. The development of peptide- and oligonucleotide-based drugs to prevent the formation of abnormal tau in tauopathies. Expert Opin Drug Discov. 2023;18(5):515-526. doi:10.1080/17460441.2023.2200245. PMID 37042028.
17. 17

    Rockenstein E, Ubhi K, Doppler E, Novak P, Moessler H, Li B, Blanchard J, Grundke-Iqbal I, Iqbal K, Mante M, Adame A, Crews L, Masliah E. Regional comparison of the neurogenic effects of CNTF-derived peptides and cerebrolysin in AbetaPP transgenic mice. J Alzheimers Dis. 2011;27(4):743-752. doi:10.3233/JAD-2011-110914. PMID 21860085. RETRACTED.
18. 18

    Retraction: Regional comparison of the neurogenic effects of CNTF-derived peptides and cerebrolysin in AbetaPP transgenic mice. J Alzheimers Dis. 2026;111(4):1893. doi:10.1177/13872877261442048. PMID 42015030.
19. 19

    Crews L, Rockenstein E, Masliah E. APP transgenic modeling of Alzheimer's disease: mechanisms of neurodegeneration and aberrant neurogenesis. Brain Struct Funct. 2010;214(2-3):111-126. doi:10.1007/s00429-009-0232-6. PMID 20091183.
20. 20

    Falangola MF, Voltin J, Cole M, Nietert PJ, Liu F, Iqbal K, Jensen JH. Corrigendum to diffusion MRI measures detect brain microstructure changes due to early treatment with neurotrophic peptide mimetic P021 in the 3xTg-AD mouse model of Alzheimer's disease. Magn Reson Imaging. 2026;130:110677. doi:10.1016/j.mri.2026.110677. PMID 41945082.