FOXO4-DRI
FOXO4 D-Retro-Inverso peptide, FOXO4-p53 interfering peptide, FOX04-DRI
FOXO4-DRI is a senolytic peptide designed to kill senescent cells by breaking the interaction between the transcription factor FOXO4 and the tumour suppressor p53. It produced striking results in aged and progeroid mice in a 2017 Cell paper. It has never been given to a human being in a registered trial, and subsequent work has both refined its mechanism and shown that clearing senescent cells is not universally beneficial.
Mechanism
Senescent cells are damaged cells that have exited the cell cycle permanently but refuse to die. They accumulate with age and secrete a cocktail of inflammatory cytokines, proteases and growth factors known as the senescence-associated secretory phenotype, which degrades the tissue around them. Why they resist apoptosis despite carrying substantial DNA damage is the question FOXO4-DRI was built around.
The answer proposed by de Keizer's group is that in senescent cells the transcription factor FOXO4 is upregulated and binds p53, holding it in nuclear foci where it can drive cell-cycle arrest but cannot trigger apoptosis. FOXO4-DRI is a competitive inhibitor of that interaction. It reproduces the FOXO4 segment that contacts p53, fused to a cationic cell-penetrating import sequence, and is built as a D-retro-inverso peptide: every residue is the D-enantiomer and the sequence is reversed, which reconstructs the side-chain topology of the natural L-peptide while making the backbone essentially invisible to proteases. The result is a competitor that survives in plasma far longer than the L-form would.
Displacing p53 from FOXO4 allows it to leave the nuclear foci, accumulate in the cytoplasm and reach the mitochondria, where it triggers cytochrome c release and caspase-dependent apoptosis. The selectivity comes from the fact that non-senescent cells do not depend on the FOXO4-p53 complex for survival. A 2025 Nature Communications NMR study refined this picture, identifying the disordered p53 transactivation domain (p53TAD2) as the actual binding target of both FOXO4 and the peptide, showing that the two disordered partners form a transiently folded complex, and finding that the cationic cell-permeability segment itself contributes to the binding rather than merely ferrying the peptide across the membrane. p53 phosphorylation increased affinity for both. This sharpens the mechanism rather than overturning it.
What the research shows
The 2017 Cell paper is genuinely impressive within its own terms. In fast-ageing Xpd progeroid mice and in naturally aged mice, intraperitoneal FOXO4-DRI given on an intermittent schedule restored fur density, reversed loss of renal function as measured by blood urea nitrogen and creatinine, and increased spontaneous running-wheel activity. In mice given doxorubicin, it reduced chemotherapy-induced toxicity. Critically, the peptide was selectively toxic to senescent cells in culture while sparing proliferating and quiescent cells. Follow-up work has extended the model, showing that targeting senescent Leydig cells in aged mice partially restored testosterone secretion.
The honest framing is that all of this is mouse and cell work, published nine years ago in the case of the original paper, and no human trial has followed. There is no registered interventional study of FOXO4-DRI on ClinicalTrials.gov. There is no published human pharmacokinetic, toxicology or dose-finding data, and no measured half-life in any species. For a molecule of this profile, that gap is informative rather than incidental: senolytics as a field have moved into human trials with other agents, and the absence of a FOXO4-DRI programme suggests barriers that have not been publicly resolved.
The field has also produced a genuinely cautionary result, and it is one in which FOXO4-DRI itself was used. A 2023 Circulation study cleared senescent cells by three independent routes, a genetic suicide-gene construct, the senolytic drug ABT263, and FOXO4-DRI, across mouse and rat models of pulmonary hypertension, and found that clearance promoted rather than prevented the development and progression of the disease. Senescent cells participate in wound healing, tissue repair and tumour suppression, and removing them indiscriminately is not obviously a good idea. Any account of FOXO4-DRI that presents senolysis as uniformly rejuvenating is not describing the current literature.
Evidence assessment
Preclinical only
Evidence is confined to cell culture and rodent models; no human trial has been registered or published, and no human pharmacokinetic or toxicology data exist.
Tiers are applied consistently across the library and re-checked when new trials read out. Read the grading method.
Key studies
Targeted Apoptosis of Senescent Cells Restores Tissue Homeostasis in Response to Chemotoxicity and Aging Preclinical only
FOXO4-DRI selectively induced apoptosis in senescent cells and restored fur density, renal function and running-wheel activity in aged and progeroid mice.
The disordered p53 transactivation domain is the target of FOXO4 and the senolytic compound FOXO4-DRI Preclinical only
Identified the disordered p53 transactivation domain (p53TAD2) as the binding site for both FOXO4 and FOXO4-DRI, forming a transiently folded complex; the cationic cell-permeability segment contributes to binding, and p53 phosphorylation increases affinity for both.
FOXO4-DRI alleviates age-related testosterone secretion insufficiency by targeting senescent Leydig cells in aged mice Preclinical only
FOXO4-DRI cleared senescent Leydig cells and partially restored age-related decline in testosterone secretion.
Eliminating Senescent Cells Can Promote Pulmonary Hypertension Development and Progression Preclinical only
Senescent cell clearance promoted rather than prevented development and progression of pulmonary hypertension, demonstrating that senolysis is context-dependent and can be harmful.
Safety
No human safety data of any kind. Rodent studies reported tolerability on intermittent dosing schedules, but a compound whose entire purpose is to trigger apoptosis raises specific concerns that have not been resolved: off-target killing of non-senescent cells under conditions of stress, acute release of cellular contents if a large senescent burden is cleared at once, and the demonstrated possibility that removing senescent cells worsens disease in some tissues. Senescent cells also contribute to tumour suppression and wound repair. The 2023 pulmonary hypertension finding used FOXO4-DRI itself as one of three clearance methods, so it should be read as direct mechanism-linked evidence of risk for this compound, not as an isolated anomaly in an adjacent field.
Regulatory status
| Jurisdiction | Status |
|---|---|
| United Kingdom | No MHRA authorisation. Supply for human use would engage the Human Medicines Regulations 2012 regardless of a 'research use only' designation. |
| United States | Not approved by the FDA, not under investigational new drug status in any public registry, and not the subject of any registered clinical trial. Available only through research-chemical suppliers. |
| WADA (sport) | Not individually named on the Prohibited List but captured by section S0 (non-approved substances), which prohibits at all times any substance not approved by a government health authority for human therapeutic use. |
Questions
No. There is no registered clinical trial on ClinicalTrials.gov and no published human pharmacokinetic, toxicology or dose-finding data. Every result in circulation comes from cell culture or mice, and the foundational study was published in 2017.
The peptide is built from D-amino acids, the mirror images of the natural L-forms, and the sequence order is reversed. Together these two changes reconstruct the original side-chain arrangement while making the backbone unrecognisable to the proteases that would normally chew a peptide up within minutes.
No, and this is one of the more important qualifications in the field. A 2023 Circulation study found that eliminating senescent cells promoted pulmonary hypertension, and FOXO4-DRI was one of the three clearance methods used. Senescent cells also contribute to wound healing and tumour suppression, so indiscriminate clearance carries mechanism-linked risk.
Senescent cells depend on FOXO4 binding p53 to keep p53 sequestered in the nucleus and unable to trigger apoptosis. The peptide competes for that interaction, releasing p53 to reach the mitochondria and initiate cell death. Structural work in 2025 localised the contact to the disordered transactivation domain of p53.