P21 (P021)

A synthetic, orally active ciliary neurotrophic factor peptide mimetic (Ac-DGGLAG-NH2) from Khalid Iqbal's laboratory, studied only in rodent models of Alzheimer's disease, aging and Down syndrome, with no human trials and no regulatory approval.

Also referenced as: P021, P-21, P-021, Peptide 021

Also appears in: Neuroprotection

What is P21 (P021)?

P021 is a small synthetic peptide mimetic of ciliary neurotrophic factor (CNTF), written as Ac-DGGLAG-NH2 (C27H42N6O8, molecular weight about 578.7). The core is the four-residue sequence Asp-Gly-Gly-Leu, which corresponds to amino acids 148–151 of human CNTF; the trailing “AG” in the written sequence denotes a single adamantane-based glycine residue, added at the C-terminus so that the acetylated, amidated molecule is more lipophilic and more resistant to exopeptidases than the bare fragment. That is why the originating laboratory calls it a tetrapeptide even though the shorthand contains six letters.

The compound was designed in the laboratory of Khalid Iqbal and the late Inge Grundke-Iqbal at the New York State Institute for Basic Research in Developmental Disabilities on Staten Island, and was first reported in 2010 under the name P21 (Li et al., FEBS Letters, 2010;584(15):3359–3365). It is a truncated, stabilized successor to Peptide 6, an 11-residue fragment spanning CNTF residues 146–156 that the same group had studied earlier. Every later paper uses the name P021. It appears in the research-peptide market on the strength of rodent findings on hippocampal neurogenesis, brain-derived neurotrophic factor (BDNF) and memory; the company developing it, Phanes Biotech of Malvern, Pennsylvania, describes it as a preclinical Alzheimer’s disease candidate.

How it works

• Competitive inhibition of leukemia inhibitory factor (LIF) signaling. Full-length CNTF signals through a receptor complex shared with LIF. The parent fragment, Peptide 6, was characterized as acting by competitively inhibiting LIF signaling (Chohan et al., Neurobiology of Aging, 2011;32(8):1420–1434), and P021 reduced LIF-induced STAT3 phosphorylation in cell culture (Li et al., FEBS Letters, 2010;584(15):3359–3365). Because LIF signaling holds neural progenitors in an undifferentiated state, dampening it is proposed to free progenitors in the dentate gyrus to mature into neurons (Kazim and Iqbal, Molecular Neurodegeneration, 2016;11(1):50).
• Increased BDNF expression with downstream CREB activation. Chronic oral P021 raised BDNF in 3xTg-AD mice (Kazim et al., Neurobiology of Disease, 2014;71:110–130), in aged rats alongside TrkB and phosphorylated CREB (Bolognin et al., Neurobiology of Aging, 2014;35(9):2134–2146), and in Ts65Dn mice (Kazim et al., Scientific Reports, 2017;7:45561). Treatment from birth in 3xTg-AD mice increased pCREB and BDNF and engaged PLC/PKC, MEK/ERK and PI3K/Akt cascades with restoration of synaptic proteins (Wei et al., Journal of Alzheimer’s Disease, 2021;82(2):631–646).
• BDNF-dependent inhibition of GSK-3β and reduced tau hyperphosphorylation. In 3xTg-AD mice, P021 increased Ser9-phosphorylated (inactive) GSK-3β and reduced tau phosphorylation at AT8, PHF-1 and 12E8 epitopes without changing total tau; the authors attribute the tau effect to BDNF–TrkB–Akt signaling rather than direct kinase inhibition (Kazim et al., Neurobiology of Disease, 2014;71:110–130). Reductions in soluble Aβ were interpreted as reduced generation rather than clearance.
• Dentate gyrus neurogenesis and synaptic plasticity. P021 increased BrdU-labeled newborn cells and their maturation into neurons in the dentate gyrus of normal adult mice (Li et al., FEBS Letters, 2010) and roughly quadrupled doublecortin- and Ki-67-positive counts in 3xTg-AD mice treated from three months of age, with increases in PSD-95, MAP2 and glutamate-receptor subunits (Baazaoui and Iqbal, Alzheimer’s Research & Therapy, 2017;9(1):45).

Two caveats sit over the whole list. Nearly every mechanistic paper comes from the laboratory that designed the compound, whose head is a named inventor on the patents covering it (assigned to the Research Foundation for Mental Hygiene) and is co-founder and chief scientific officer of the company developing it. And although Khatoon et al. (Journal of Alzheimer’s Disease, 2015;47(3):557–564) reported P021 as blood-brain-barrier permeable, the Alzheimer’s Drug Discovery Foundation’s May 12, 2025 review lists brain penetration as not documented and notes that no study has directly measured how much P021 reaches the brain after oral dosing.

Research status

No human trials. ClinicalTrials.gov holds no study of P021, Peptide 021 or Phanes Biotech as of November 2026, and the Alzheimer’s Drug Discovery Foundation’s Cognitive Vitality report, last updated May 12, 2025, records no human or observational data of any kind. Phanes Biotech, founded in 2020 with Khalid Iqbal as co-founder and chief scientific officer, listed P021 as “Pre Clinical” when it presented at the BIO International Convention on June 7, 2023, and was seeking partners and investors; no investigational new drug application, first-in-human study or regulatory designation for P021 has been announced since. The compound has never been approved by the FDA or any other regulator.

Lineage: Peptide 6 and Peptide 6c. The program began with Peptide 6, an 11-mer corresponding to CNTF residues 146–156, delivered by subcutaneous slow-release pellets. It increased dentate gyrus neurogenesis and improved reference memory in normal mice, with a reported plasma half-life over six hours (Chohan et al., Neurobiology of Aging, 2011;32(8):1420–1434). In 3xTg-AD mice it restored cognition and plasticity but had no detectable effect on Aβ or tau pathology at nine months (Blanchard et al., Acta Neuropathologica, 2010;120(5):605–621). It also rescued cognitive deficits in an adeno-associated-virus rat model of sporadic Alzheimer’s disease (Bolognin et al., Acta Neuropathologica, 2012;123(1):133–151) and improved memory after controlled cortical impact in mice (Chohan et al., Neurosurgery, 2015;76(2):201–214). A tetrapeptide fragment, Peptide 6c, reproduced the neurogenic and memory effects without weight loss (Blanchard et al., Journal of Alzheimer’s Disease, 2010;21(4):1185–1195). One paper in this lineage, a comparison of Peptides 6 and 6A with cerebrolysin in AβPP transgenic mice (Rockenstein et al., Journal of Alzheimer’s Disease, 2011;27(4):743–752), was retracted in June 2026; it did not study P021 itself.

P021 in Alzheimer’s-type models. The design paper showed that P21 given by subcutaneous depot for 35 days improved short-term and spatial reference memory and increased neurogenesis in normal adult C57BL/6 mice (Li et al., FEBS Letters, 2010;584(15):3359–3365). The central disease study treated female 3xTg-AD mice with P021 in the diet for 12 months starting at 9–10 months of age: alongside the tau and BDNF effects described above, soluble Aβ40 and Aβ42 fell at the six-month timepoint but not at twelve, insoluble Aβ was unchanged, and deficits in object recognition, water-maze learning, neurogenesis and synaptic markers were rescued; treated mice also gained weight without eating more (Kazim et al., Neurobiology of Disease, 2014;71:110–130). Two companion studies started dietary treatment at three months, before overt pathology, and continued to 21 months. One reported rescue of dendritic and synaptic deficits, a roughly four-fold rise in neurogenesis and reversal of spatial memory impairment (Baazaoui and Iqbal, Alzheimer’s Research & Therapy, 2017;9(1):45); the other reported less Fluoro-Jade C neurodegeneration, roughly 50% less tau hyperphosphorylation and partial reduction of plaque load at 18 months, together with survival of 87% versus 41% at week 71 (Baazaoui and Iqbal, Journal of Alzheimer’s Disease, 2017;58(1):215–230). Later work pushed the start earlier still: dietary treatment from embryonic day 8 to postnatal day 21 was associated with better cognition at 4 months and less tau and plaque pathology at 22 months (Wei et al., Alzheimer’s Research & Therapy, 2020;12(1):102), and treatment from birth to postnatal day 120 prevented cognitive impairment at 4 months (Wei et al., Journal of Alzheimer’s Disease, 2021;82(2):631–646). A diffusion MRI study from the Medical University of South Carolina, with Iqbal as co-author, reported brain microstructure changes after early treatment in the same model (Falangola et al., Magnetic Resonance Imaging, 2026;129:110641).

Aging. In 22- to 24-month-old Fischer rats, 88 days of oral gavage reduced the age-related decline in water-maze performance, restored neurogenesis and BDNF, and lowered hippocampal myo-inositol on magnetic resonance spectroscopy, although treated old rats did not reach the performance of young rats and FDG-PET glucose uptake was unchanged (Bolognin et al., Neurobiology of Aging, 2014;35(9):2134–2146). A follow-up reported lower hippocampal and cerebrospinal-fluid total tau, no change in CSF Aβ, and no detectable immune reaction to the peptide (Khatoon et al., Journal of Alzheimer’s Disease, 2015;47(3):557–564).

Down syndrome. In the Ts65Dn trisomy model, P021 given through the mother’s diet from embryonic day 8 to postnatal day 21 rescued delayed developmental milestones in pups and hippocampus-dependent memory deficits in adults, doubled BDNF, lowered GSK-3β activity and raised phosphorylated CREB, without changes in body weight, anxiety-like behavior or activity (Kazim et al., Scientific Reports, 2017;7:45561).

Retina. Treatment of aged rats and 3xTg-AD mice was reported to prevent retinal changes resembling age-related macular degeneration (Liu et al., Frontiers in Aging Neuroscience, 2019;11:309); rodents have no macula and no visual-function testing was performed.

A negative in vivo result. One of the few P021 studies led outside the originating laboratory, from the University of Bologna with Iqbal as co-author, tested P021 in CDKL5 deficiency disorder models. It restored proliferation, survival and maturation in a human CDKL5-knockout neuronal line, but chronic in vivo treatment of Cdkl5-knockout mice failed to raise BDNF, did not correct neuroanatomical defects and produced only limited behavioral benefit (Mottolese et al., Journal of Neurodevelopmental Disorders, 2024;16(1):65).

Reviews. The preclinical program is summarized by its authors in Kazim and Iqbal (Molecular Neurodegeneration, 2016;11(1):50) and Baazaoui and Iqbal (Biomolecules, 2022;12(10):1409). An independent review of peptide-based tau therapeutics discusses P021 and raises anti-drug antibody formation as a theoretical risk that has not yet been observed (Lozupone et al., Expert Opinion on Drug Discovery, 2023;18(5):515–526).

Common dosage forms

• Lyophilized powder in research vials, at milligram scale, labeled for laboratory use only. This is the only presentation in which P021 exists; there is no pharmaceutical product, compounded preparation or human formulation anywhere.
• Formulated rodent chow is the presentation used in nearly every disease-model study, with the peptide custom-milled into the diet of the animals or, in the prenatal studies, of their mothers.
• Oral gavage solution in saline was used in the aged-rat studies.
• Subcutaneous extended-release depot pellets were used in the 2010 design paper and in the earlier Peptide 6 work, and have not appeared in later P021 studies.
• No injectable solution, nasal spray, capsule or tablet of P021 has ever been manufactured to a pharmaceutical standard or administered to a person.

Key considerations

• Regulatory status. The Research Market status reflects the absence of any US approval, any registered clinical trial and any announced investigational new drug application for P021 as of November 2026, with the compound available only as a laboratory reagent. The company developing it described it as preclinical in June 2023, and nothing published since changes that stage. Orphan, fast-track or other designations have not been granted.
• The evidence is entirely preclinical and almost entirely from one laboratory. Every efficacy claim rests on rodents, most of them female 3xTg-AD mice, and most studies began treatment before any pathology existed or before birth. Those are prevention paradigms in genetically engineered animals and do not model treatment of a person with established disease. The designers are the named inventors on the patents and lead the science of the company developing the compound; the one in vivo efficacy study led by another group was largely negative. Independent replication of the core Alzheimer’s findings does not exist.
• Safety has never been assessed in humans. Across rodent studies lasting up to 18 months the literature reports no weight loss, tumors or pain behaviors, and weight gain rather than loss. That matters because full-length CNTF caused anorexia, muscle loss, cramps, hyperalgesia and neutralizing antibodies in human trials in the 1990s and 2000s; the claim that the mimetic avoids those effects by sparing the alternative IL-6 receptor pathway is plausible but has only rodent support, and antibody formation against the peptide remains an untested possibility in people.
• P021 is not p21. The cell-cycle regulator p21 (CDKN1A, also WAF1 or Cip1) is an unrelated protein that appears in thousands of cancer and senescence papers, and “p21” also names the Ras p21 GTPase and the p21-activated kinases. Literature searches on “P21 peptide” return large volumes of material about those proteins. The CNTF mimetic is unambiguous only under the names P021 or Peptide 021.
• Other naming traps. Peptide 6 (the 11-mer), Peptide 6A and Peptide 6c are earlier related fragments, not synonyms for P021, and one Peptide 6 comparison paper has been retracted. The written sequence Ac-DGGLAG-NH2 is sometimes misread as a six-residue peptide. Comparisons with cerebrolysin, a porcine brain-derived peptide mixture, describe a mechanistic analogy and do not make P021 a cerebrolysin fragment.