P21

Overview

P21 (also P021) is a small peptidergic compound — the tetrapeptide core Asp-Gly-Gly-Leu with an N-terminal acetyl and a C-terminal adamantylated glycine amide (Ac-DGGL(A)G-NH2) — derived from an active region (residues ~148–151) of human ciliary neurotrophic factor (CNTF). It was designed and characterized in the Khalid Iqbal laboratory at the New York State Institute for Basic Research in Developmental Disabilities (NYS IBR). It is an experimental, preclinical compound — NOT FDA-approved and NOT tested in humans in published trials. Distinct from the cyclin-dependent kinase inhibitor protein p21/CDKN1A/WAF1 (a completely different gene product; the two share only the name).

Mechanism of Action

Preclinical data (Iqbal group) suggest that P21 mimics the neurogenic/neurotrophic effect of CNTF by competitively antagonizing leukemia inhibitory factor (LIF) signaling at the gp130/LIFR complex, which de-inhibits hippocampal and subventricular-zone neurogenesis. Downstream, P21 increases BDNF expression, which activates TrkB → PI3K/Akt → inhibition of GSK-3β, reducing tau hyperphosphorylation in AD mouse models. The adamantyl modification is intended to improve oral bioavailability, BBB penetration, and resistance to exopeptidases.

Research Summary

Evidence is preclinical (rodent) only. Key publication: Kazim, Blanchard, Dai, Tung, LaFerla, Iqbal & Iqbal, Neurobiology of Disease 2014 (PMID 25046994) reported that chronic oral P021 rescued cognition, boosted dentate-gyrus neurogenesis, and reduced tau hyperphosphorylation in 3xTg-AD mice. Additional preclinical papers from the Iqbal group (and collaborators) have shown dendritic/synaptic rescue in AD and aging rodent models (e.g., Kazim et al., Alzheimer's Res Ther 2017). No Phase 1/2/3 human trials have been published; no human safety or pharmacokinetic data exist. Grey-market vendor material is unvalidated — purity, identity, and dosing are not verifiable.

Dosing Information

Reported Side Effects

• Unknown in humans; no published safety data
• In chronic rodent dosing (up to ~18 months) the Iqbal group reported no tumors, overt toxicity, weight loss, or pain behaviors — but this does not establish human safety

Research References

• Disease-modifying effect of chronic oral treatment with a neurotrophic peptidergic compound (P021) in a triple-transgenic mouse model of Alzheimer's disease (Kazim et al., Neurobiol Dis 2014) (2014)