FOXO4-DRI

Mechanism

In senescent cells p53 is phosphorylated at serine 15 (p53-pS15) and sequestered in nuclear bodies. FOXO4 localises alongside it and prevents its nuclear exclusion, so the cell escapes the intrinsic apoptotic pathway it would otherwise run. FOXO4-DRI is an antagonist of that interaction.

Baar and colleagues demonstrated the competition directly by NMR: adding the peptide to a FOXO4–p53 complex reverted the chemical-shift perturbations to the unbound state, indicating that FOXO4-DRI competes with FOXO4 for p53 binding. Displacing FOXO4 releases active p53 from the nucleus, which is recruited to mitochondria and initiates caspase-dependent, cell-intrinsic apoptosis. Knockdown of p53 reduced the peptide's effect on senescent cells, and pan-caspase inhibition blocked it — evidence that the effect runs through p53 and caspases rather than through non-specific toxicity.

Selectivity is attributed to dependency rather than to a cell-surface target: senescent cells rely on FOXO4-mediated p53 sequestration for survival, whereas non-senescent cells have redundant anti-apoptotic mechanisms. That is the proposed reason FOXO4-DRI behaves as a senolytic rather than as a general cytotoxic agent.

Evidence base

The primary evidence is a single preclinical study. Baar et al. (2017) reported that FOXO4-DRI reduced the viability of senescent IMR90 fibroblasts selectively, with an approximately 11.7-fold difference between senescent and control cells; the same sequence in the L-isoform, and an unrelated DRI peptide, had no effect. In naturally aged mice the peptide reduced senescent-cell burden and was reported to improve kidney function, fur density and measures of physical performance; in a doxorubicin chemotoxicity model it partially reversed the metabolic ageing phenotype.

Subsequent work has been in vitro. FOXO4-DRI removed senescent cells from cultures of human chondrocytes while sparing non-senescent cells, with reduced senescence-associated β-galactosidase staining; in keloid-derived fibroblasts and organ cultures it promoted apoptosis and reduced the G0/G1 fraction alongside changes in p53-serine15 phosphorylation. Both lines of work are laboratory studies, and neither provides human clinical data.

The gaps are the ones that matter clinically: no human trial, no dose-finding, no safety or tolerability data, and no independent replication in a whole-animal model beyond the original laboratory. Reports that DRI peptides have reached clinical development for other sequences are not evidence about this compound. Evidence grade: Limited — the mechanism is well characterised in vitro, the in vivo record is one mouse study, and the human column is empty. That is stated here rather than implied.

Protocols

There is no human research protocol for FOXO4-DRI, and none is offered here. The published in vivo work was conducted in mice under an experimental protocol described in the primary paper; the in vitro work used cultured human and murine cells. Any laboratory use of this compound as a research material is subject to institutional approvals and to local law. Peptide Data does not provide protocols for human use, and this profile contains no guidance on human administration.

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UK legal status

FOXO4-DRI has no UK marketing authorisation and is not a licensed medicine. Under the Medicines Act 1968 and the Human Medicines Regulations 2012, a product is a medicine if it is presented as having properties for treating or preventing disease in human beings, or if it may be administered to human beings with a view to making a medical diagnosis or to restoring, correcting or modifying physiological functions. The MHRA determines that classification case by case.

Two consequences follow for this compound. First, a supplier that markets FOXO4-DRI with claims about anti-ageing, disease or physiological effects moves the product across the medicines boundary, and an unauthorised medicine may not be sold or supplied in the UK. Second, the MHRA has stated that it disregards claims that a product is 'for research purposes' where it is clear those claims are being used as an attempt to avoid medicines regulation. A research-use-only label describes intended use; it is not an exemption.

FOXO4-DRI is therefore a research compound. This profile describes the published research and does not describe, approve or facilitate human use.