FOXO4-DRI

Overview

FOXO4-DRI is an experimental senolytic peptide — a compound intended to selectively eliminate senescent cells ("zombie" cells that have stopped dividing but resist death and secrete inflammatory factors). It is a cell-penetrating, D-retro-inverso peptide: built from all-D amino acids in a reversed sequence, a design meant to resist enzymatic breakdown.

It was introduced by Baar et al., Cell 2017 (PMID 28340339). The stated rationale is that, in senescent cells, the transcription factor FOXO4 binds and sequesters the tumour-suppressor p53, blocking the cell's own death program. FOXO4-DRI is designed to competitively disrupt the FOXO4–p53 interaction, freeing p53 and pushing senescent cells into apoptosis while largely sparing normal proliferating cells.

The honest evidence picture is strictly preclinical. In-body efficacy data come from mice; the only "human" data are in vitro, on cultured human cells. There are no human clinical trials of any kind and no FDA or EMA approval. FOXO4-DRI is a laboratory research reagent, not an approved medicine.

Chemistry and structure

FOXO4-DRI is a large peptide combining the FOXO4 p53-binding region with a poly-arginine (TAT-like) cell-penetrating import sequence, synthesised as an all-D, retro-inverso construct.

A few caveats matter. The CAS number above is only vendor/aggregator-sourced and was not confirmed on the primary PubChem record. The exact amino-acid sequence comes from secondary vendor pages and was not verified against the PubChem isomeric record or the Baar 2017 supplementary methods. PubChem lists a molecular weight of 5358 for CID 167312269 (free base); an acetate salt form (CID 167312268) may differ, and this value was not independently re-computed from the formula here.

Mechanism of action

• Perturbs the FOXO4–p53 interaction. [In vitro] The peptide was designed against the FOXO4 region that binds p53, and blocks FOXO4 from sequestering p53 in senescent cells. (Baar et al., Cell 2017, PMID 28340339)
• Releases and excludes p53 from the nucleus, triggering apoptosis in senescent cells. [In vitro] Loss of FOXO4–p53 tethering leads to p53 nuclear exclusion and cell-intrinsic (mitochondrial) apoptosis, selectively in senescent versus proliferating cells. (Baar et al., Cell 2017, PMID 28340339)
• Reduces senescent-cell burden and restores tissue function in vivo. [Animal] In doxorubicin-treated, fast-aging XpdTTD/TTD, and naturally aged mice, it neutralised chemotoxicity and restored fitness, fur density, and renal function. (Baar et al., Cell 2017, PMID 28340339)
• Selectively removes senescent human chondrocytes in culture. [In vitro] 25 µM over 5 days removed more than half of heavily-expanded (senescent-rich, PDL9) human chondrocytes while sparing minimally-expanded (PDL3) cells — but it did not enhance cartilage-formation capacity. (Frontiers Bioeng Biotechnol 2021, PMC8116695)
• D-retro-inverso design confers protease resistance / longer half-life. [Hypothesis] This is the general design rationale for D-retro-inverso peptides (all-D amino acids, reversed sequence resist enzymatic degradation), asserted by the design rationale rather than a dedicated PK study verified here. (Design rationale, Baar et al. 2017)

Research and evidence

Human evidence. There are no well-established human clinical trials — none registered or completed were identified (safety, pharmacokinetics, dose, or efficacy). The only data on human cells are in vitro (senescent human chondrocytes), which is not the same as human dosing. In-body efficacy evidence is limited to mice.

Status and regulation

• Not approved by the FDA, EMA, or any other regulator for any indication. There is no approved label and no marketing authorisation.
• No registered or completed human clinical trial was identified.
• It exists only as a laboratory research reagent / preclinical tool compound, sold by chemical suppliers as "for research use only."
• Intended human use would render it an unauthorised/unlicensed medicine. This is a regulatory-status statement, not permission for human use, and not medical or legal advice — verify current status in your own jurisdiction (dated 2026-07-08).

Safety

• Human safety is not established. There are no human trials, so safety, therapeutic window, and toxicology in humans are unknown.
• Beyond the tolerability noted in the mouse work of Baar et al. (2017), animal and human safety, therapeutic window, and toxicology are not established.
• The compound acts by pushing cells into apoptosis via p53 — a mechanism with obvious potential for off-target effects, none of which has been characterised in humans.
• Research-grade material sold "for research use only" is not manufactured, purity-tested, or overseen to pharmaceutical standards.

Legal status

FOXO4-DRI has no approved medical status anywhere identified in the sources. It is classified and sold only as a research reagent ("for research use only"). Being unscheduled or lacking a "specific ban" is not affirmative permission to take it: a compound becomes an unauthorised/unlicensed medicine the moment it is intended for human use. No WADA sport-prohibition classification is asserted by any source — WADA status is not established and is a separate axis from legality; nothing is inferred here. Legal status is jurisdiction-specific and can change; this is not legal advice — check the rules in your own jurisdiction (dated 2026-07-08).

How it compares

FOXO4-DRI sits in the longevity and mitochondrial research space alongside other compounds studied for aging biology, but its mechanism is distinct — it is a senolytic (kills senescent cells) rather than a metabolic or membrane-targeting agent.

• SS-31 (elamipretide) is a mitochondria-targeting peptide that stabilises the inner membrane; unlike FOXO4-DRI, it has a substantial human trial program and one narrow regulatory approval.
• MOTS-c is a mitochondrial-derived metabolic regulator studied mostly in animals; like FOXO4-DRI, it has no approval, but it works by an entirely different mechanism.
• Epitalon is studied for telomere/pineal signaling in aging; also preclinical and unapproved, and mechanistically unrelated to senolysis.

The key distinction: FOXO4-DRI's evidence is preclinical only (mouse + cell culture), with no human trials at all — a lower human-evidence tier than SS-31.

Common misconceptions

• "FOXO4-DRI is a proven anti-aging drug." No. All efficacy data are preclinical (mice and cultured cells). There are no human trials and no approval.
• "It's been shown to work in humans." The only human-cell data are in vitro (senescent chondrocytes) — that is not human dosing, and it did not even improve cartilage formation in that study.
• "Proxofim is the same thing, verified." Material sometimes sold as "Proxofim" may correspond to FOXO4-DRI, but whether it is chemically identical to the Baar 2017 peptide is not independently verified.
• "The CAS number and sequence are confirmed." The CAS (2460055-10-9) is vendor-sourced and not confirmed on PubChem; the exact residue order is from secondary vendor pages and unverified against a primary record.
• "Unapproved means it's automatically WADA-banned." No source asserts a WADA class for FOXO4-DRI; WADA status is not established and is not inferred from lack of approval.