FOXO4

Classification

Designed retro-inverso senolytic peptide; striking mouse data, no human data at all

Structure and chemistry

FOXO4-DRI stands for FOXO4 D-Retro-Inverso. It is a designed peptide derived from the forkhead domain of the FOXO4 transcription factor, built using a retro-inverso strategy: the amino acid sequence is reversed and every residue is a D-amino acid rather than the natural L form. That combination preserves the three-dimensional arrangement of side chains needed for binding while making the peptide highly resistant to proteolytic degradation. It also carries a cationic cell-penetrating segment derived from HIV-TAT, which is what gets it inside cells.

What the published research shows

The research is preclinical and it is high quality — published in Cell and Nature Communications, with independent groups extending the work into fibrosis, cartilage, vascular and brain aging models. What does not exist is any human data. No clinical trial has characterized its safety, dosing or pharmacokinetics in people, at any phase.

Mechanism of action

Senescent cells accumulate with age and resist dying. Part of why they survive is that FOXO4 binds p53 and holds it in the nucleus, preventing p53 from reaching the mitochondria where it would trigger apoptosis. FOXO4-DRI competes for that interaction: displacing p53 from FOXO4 allows it to relocate to the mitochondria and initiate caspase-dependent cell death. The selectivity argument is that FOXO4 is only meaningfully expressed in a small fraction of non-senescent adult cells, so healthy tissue is largely unaffected. Structural work published in 2025 used NMR to show that FOXO4-DRI binds the disordered p53 transactivation domain forming a transiently folded complex, with both the FOXO4-derived region and the cationic cell-permeability segment contributing to the interaction.

Development history

Designed rather than discovered. Marjolein Baar, Peter L.J. de Keizer and colleagues built it as a targeted competitor of a specific protein-protein interaction, and published it in Cell in 2017. The peptide and the associated mouse models were made subject to patent applications and shared with research organizations under material transfer agreements for research and educational use.

Current regulatory status

FOXO4-DRI is not approved anywhere, has never been tested in humans, and is not an established compounding substance. One safety consideration deserves emphasis, and it follows directly from the mechanism: the entire safety case rests on selectivity. If FOXO4-p53 sequestration turns out to be less exclusive to senescent cells in humans than in mice, the consequence is triggering p53-driven apoptosis in cells that were not meant to die. That is a hypothesis that has not been tested in a person.

Analytical testing

Retro-inverso peptides present a specific analytical problem: a D-amino-acid peptide and its L-amino-acid counterpart have identical molecular masses. Mass spectrometry alone therefore cannot confirm that the material is actually the retro-inverso form rather than an ordinary L-peptide of the same composition — and the L version would be rapidly degraded and functionally different. Meaningful verification requires chiral analysis or an orthogonal method, which most commercial COAs do not include.

Ordering from Great Falls

MontanaPep, also known as Montana Peptides, is an independently owned supplier based at 715 13th Ave S, Great Falls, Montana. Local pickup is available by arrangement, and we ship to research addresses across Montana including Billings, Missoula, Bozeman, Helena, Butte, Kalispell and Havre. Call (406) 799-0812 or email customerservice@montanapep.com.

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