FOXO4-DRI is an experimental synthetic peptide designed to kill senescent cells, the damaged cells that stop dividing but do not die and that accumulate with age. It works by breaking the grip that the transcription factor FOXO4 keeps on the tumor-suppressor protein p53 inside those cells, which releases p53 and triggers the cell’s own suicide program. Compounds that do this are called senolytics.

It was first described in 2017 by a group at Erasmus University Medical Center in Rotterdam working with the Buck Institute, in a paper reporting improved fur density, activity and kidney function in prematurely aged and naturally aged mice (Baar et al., Cell 2017).

The single most important fact about FOXO4-DRI is that all of this evidence is preclinical. There are no published human trials, no registered clinical trials, and no approval by any medicines regulator. A 2026 review of the FOXO4 literature states plainly that FOXO4-DRI “has shown senolytic activity in preclinical models… but has not been clinically validated” (Mateescu et al., Antioxidants 2026). This page summarizes what the published laboratory and animal studies report. It is for education only and is not medical advice.

Property	Detail
Class	Cell-penetrating senolytic peptide; FOXO4-p53 interaction inhibitor
Also called	FOXO4 D-Retro-Inverso, FOXO4-p53 interfering peptide
Composition	Short peptide built almost entirely from D-amino acids in reversed sequence, fused to the HIV-TAT cell-entry sequence; formula C228H388N86O64, molecular weight ≈5,358 g/mol (PubChem CID 167312269)
Mechanism	Competes with endogenous FOXO4 for binding to the p53 transactivation domain, causing nuclear exclusion of active p53 and caspase-dependent apoptosis in senescent cells
Route in studies	Intravenous or intraperitoneal injection in rodents; direct addition to culture medium in vitro
Doses in animal studies	5 mg/kg, three injections given every other day (mice)
Human data	None. No published or registered clinical trials
Half-life	Not published. The original paper reports intracellular detection for at least 72 h after a single exposure in cell culture, which is not a plasma half-life
Regulatory status	Not approved by FDA or EMA; not named in 21 CFR 1308.13 (US Schedule III)
WADA status	Not named on the 2026 Prohibited List, but class S0 prohibits at all times any substance with no current approval for human therapeutic use

What it is

Senescent cells are cells that have permanently exited the cell cycle after damage. They survive for long periods and secrete a persistent mix of inflammatory and tissue-remodeling molecules known as the senescence-associated secretory phenotype, or SASP. That secretion is useful in wound healing but is thought to drive tissue decline when senescent cells accumulate (Baar et al., Cell 2017).

The 2017 Rotterdam work started from an unexpected observation in human IMR90 lung fibroblasts made senescent by ionizing radiation: the cells had switched on pro-apoptotic genes but were not dying. Screening transcription factors linked to apoptosis pointed to FOXO4, whose messenger RNA and protein rose progressively as senescence developed. Silencing FOXO4 with short hairpin RNA released cytochrome C from mitochondria and cleaved caspase-3, which showed that FOXO4 was acting as the brake on apoptosis.

Rather than silence the gene, the authors designed a peptide copy of the part of FOXO4 that binds p53, so that it would compete for p53 and act as a decoy. Three design choices define the molecule:

Design choice	Purpose
A FOXO4 region conserved in humans and mice but different from FOXO1 and FOXO3	FOXO1 and FOXO3 are essential for development and tumor suppression; FOXO4 is only marginally expressed in most tissues, and FOXO4 knockout mice have no striking phenotype
D-Retro-Inverso form: D-amino acids assembled in reverse order	A mirror-image peptide that keeps a similar shape but resists the enzymes that break down ordinary L-peptides. The same peptide in L-form had no effect on senescent cell viability
Fusion to the HIV-TAT sequence	A basic, hydrophilic stretch that carries cargo across the cell membrane without energy input

Nuclear magnetic resonance experiments showed that adding the peptide to a bound FOXO4-p53 complex reversed the chemical shifts of FOXO4 back toward the unbound state, meaning the peptide outcompetes FOXO4 for p53. A 2025 structural follow-up resolved the interaction in detail: both the FOXO4-derived part and the cationic cell-entry part contact the disordered p53 transactivation domain, and phosphorylation of p53 increases the affinity (Bourgeois et al., Nat Commun 2025).

The peptide is covered by patent applications, and the Rotterdam and Graz groups disclose shares in and funding from Cleara Biotech, a company developing p53-binding compounds for senescence-linked disease (Bourgeois et al., Nat Commun 2025).

How it works in the body

In senescent fibroblasts, antibody staining against the HIV-TAT portion detected the peptide inside cells as early as 2–4 hours after it was added, and it remained detectable for at least 72 hours (Baar et al., Cell 2017). Once inside, the sequence of events reported is:

the peptide displaces FOXO4 from p53;
senescence-associated FOXO4 foci, PML bodies and 53BP1 DNA-SCARS break up;
p53 phosphorylated on serine 15 accumulates and is excluded from the nucleus;
caspase-3 and caspase-7 activate, and the cell dies by apoptosis.

Knocking down p53 or adding pan-caspase inhibitors blunted the effect, confirming that killing depends on p53 and on caspases rather than on general toxicity. An independent 2026 study in endothelial cells reported the same chain of events through BAX and cleaved caspase-3 (Hu et al., Front Bioeng Biotechnol 2026).

No absorption, distribution, metabolism or plasma half-life data have been published for FOXO4-DRI in any species. The 2026 Antioxidants review lists pharmacokinetic and delivery studies, long-term toxicology and explicit assessment of p53-dependent tumor surveillance as prerequisites that have not been met (Mateescu et al., Antioxidants 2026).

Regulatory status

No marketing approval. There is no FDA-approved product containing FOXO4-DRI; searches of the FDA drug label and Drugs@FDA databases return no record.
Not a controlled substance in the US. It is not named in the Schedule III list of anabolic steroids and related substances at 21 CFR 1308.13, nor in the other federal schedules.
Prohibited in sport. FOXO4-DRI is not listed by name, but class S0 of the WADA 2026 Prohibited List prohibits at all times “any pharmacological substance which is not addressed by any of the subsequent sections of the List and with no current approval by any governmental regulatory health authority for human therapeutic use,” which includes drugs in preclinical development.
Research-only supply. In the original paper, the peptide was manufactured to order for research use, and the authors state it is subject to patent applications and may be shared with research organizations under a material transfer agreement for research and educational purposes only.

What the research shows

All findings below come from cell culture or animal experiments. None has been tested in people.

Selectivity in cell culture

In human IMR90 fibroblasts, the peptide reduced the viability of senescent cells far more than of dividing control cells, with a reported selectivity index of 11.73-fold between the two EC50 values. Real-time density measurements showed the effect starting 24–36 hours after a 25 µmol/L exposure (Baar et al., Cell 2017).

Two comparisons in the same paper are worth noting:

Comparison compound	Result in senescent IMR90 cells
The same peptide in ordinary L-form	No effect on senescent cell viability
An unrelated DRI peptide based on FOXM1	No effect on senescent cell viability
Quercetin plus dasatinib	No selectivity for senescent cells in this assay
ABT-737 (a pan-BCL inhibitor)	Selective for senescent cells, but affected control cells already at low doses

Potency rose when the senescent cells were producing more SASP: pretreatment with interleukin-1α, interleukin-1β or LPS increased killing, while an interleukin-1 receptor antagonist or cortisol reduced it. In other words, the peptide was most active against the most inflammatory senescent cells.

Chemotherapy-induced senescence in mice

In mice given two intraperitoneal doses of 10 mg/kg doxorubicin, three intravenous injections of 5 mg/kg FOXO4-DRI on days 1, 3 and 5 reduced p16-driven senescence signal, lowered the number of liver cells with FOXO4 foci and interleukin-6 expression, blunted the doxorubicin-induced loss of body weight, and reduced the rise in plasma aspartate aminotransferase, a marker of liver injury. Clearing senescent cells genetically produced a comparable drop in aspartate aminotransferase, which supports senescence clearance as the mechanism (Baar et al., Cell 2017).

Accelerated and natural aging in mice

The headline experiments used two models: XpdTTD/TTD mice, which age prematurely, and naturally aged wild-type mice carrying a p16-luciferase senescence reporter.

Outcome	Reported effect of FOXO4-DRI
p16-driven senescence signal (whole body imaging)	Reduced in both fast-aging and naturally aged mice
Fur density	Improved in both models; abdominal surface temperature, used as a proxy for fur loss, fell
Responsiveness to gentle physical stimuli	Improved in both models
Voluntary running-wheel activity	Increased over time in most fast-aging mice; variation in naturally aged mice was too large to analyze
Kidney tubular cells lacking lamin B1 (a senescence marker)	Normalized in fast-aging mice; lamin-B1-positive cells increased in naturally aged mice
Kidney interleukin-6	Reduced in both models
Plasma urea	Elevation reversed in both models
Plasma creatinine	Reduced in naturally aged mice
Platelet count at 30 days	Not noticeably changed

Untreated fast-aging mice ran 1.37 ± 0.54 km/day on average, against 9.37 ± 1.1 km/day for wild-type littermates, which is the baseline frailty the treatment was measured against. Plasma urea and creatinine are markers of kidney filtration; both fell as much with the peptide as with genetic removal of senescent cells, which again points to senescence clearance as the mechanism rather than a direct effect on the kidney.

Testes and testosterone in aged mice

Two studies from Sun Yat-sen University are the reason this compound is discussed in a hormone context. In human testis tissue, FOXO4 was found specifically in Leydig cells, the cells that make testosterone, and it sat in the cytoplasm in men under 30 but in the nucleus in men aged 65 and older, where it tracked with lower expression of the testosterone-synthesizing enzyme 3β-HSD (Zhang et al., Aging 2020).

In mouse TM3 Leydig cells made senescent with hydrogen peroxide, the peptide pushed phosphorylated p53 out of the nucleus and raised the apoptosis rate from 10% to 27%, while leaving normal Leydig cells unaffected. In naturally aged male mice (20–24 months), three intraperitoneal injections of 5 mg/kg given every other day raised serum testosterone measured 30 days later, raised testicular 3β-HSD and CYP11A1 protein, and lowered testicular p53, p21, p16 and the SASP factors interleukin-1β, interleukin-6 and TGF-β, with no change in body weight or testis weight (n = 6 per group).

The authors are explicit about the limits: they did not show directly that senescent Leydig cells were eliminated in the live animals, did not establish when the testosterone rise began, and did not test how long it lasted. A follow-up study in aged mice reported improved sperm quality and spermatogenesis, attributed to less SASP secretion from Leydig cells (Li et al., Exp Gerontol 2024).

These are rodent results at a single dose level. No study has measured testosterone in humans given this peptide.

Other animal and tissue models

Model	Design	Reported result
Bleomycin-induced lung fibrosis in mice	5 mg/kg intraperitoneally on days 14, 16 and 18 after bleomycin	Fewer senescent cells, less SASP, less collagen deposition, comparable to the approved drug pirfenidone (Han et al., J Cell Mol Med 2022)
Bleomycin-induced lung fibrosis in mice	Therapeutic dosing after bleomycin	Milder lung pathology, less collagen, redistribution of nuclear p53, lower total extracellular matrix protein (Liu et al., Naunyn Schmiedebergs Arch Pharmacol 2023)
Non-small-cell lung cancer with radiotherapy, in vitro and in mice	Peptide targeted senescence-like cancer-associated fibroblasts	Radiosensitized tumors and reduced radiation-induced lung fibrosis (Meng et al., JCI Insight 2021)
Human chondrocytes expanded in culture	Peptide applied to cells at population doubling level 9	Removed more than half the cells and lowered senescence markers, with no effect on minimally expanded cells; did not improve cartilage-forming capacity (Huang et al., Front Bioeng Biotechnol 2021)
Keloid scar fibroblasts and keloid organ culture	25 µmol/L for 3 days in a serum-limitation senescence model	Apoptosis of senescent keloid fibroblasts with nuclear exclusion of serine-15-phosphorylated p53; no effect on non-senescent fibroblasts (Kong et al., Commun Biol 2025)
Hyperoxic bronchopulmonary dysplasia in rat pups	Peptide given intraperitoneally on postnatal days 4, 6, 8 and 10	Less cellular senescence and improved alveolar structure, similar to two other agents tested (Jing et al., Am J Respir Cell Mol Biol 2024)
Aorta of naturally aged and progeroid mice	Injection	Suppressed aortic aging markers and improved aortic function; apoptosis of senescent endothelial cells via p53, BAX and caspase-3 (Hu et al., Front Bioeng Biotechnol 2026)

A 2026 narrative review collects animal reports of effects on cerebral blood flow, blood-brain barrier integrity and memory in aging and Alzheimer’s disease models (Alameen et al., Naunyn Schmiedebergs Arch Pharmacol 2026). These are animal data summarized by reviewers, not human findings, and the same review notes that the human work on this axis involves other compounds, such as high-dose fisetin, rather than FOXO4-DRI itself.

No human data

A search of ClinicalTrials.gov for FOXO4-DRI returns no registered study, and no clinical publication exists. Everything claimed for this peptide in humans is extrapolation from rodents and cell culture.

Side effects and risks

The honest summary

There is no human safety data of any kind: no dose-finding study, no reported adverse-event profile, no information on immune reactions to a foreign peptide, and no long-term follow-up in any species. The original authors wrote only that “as far as tested here” the peptide appeared well tolerated, and called a more thorough analysis necessary (Baar et al., Cell 2017).

Reassuring signals in rodents, and their limits

Over 30 days of treatment the 2017 study found no noticeable change in platelet counts or other whole-blood values, and no deleterious effect on the heart as far as tested. Platelets matter here because the main senolytic alternative in that era, the pan-BCL inhibitors ABT-263 and ABT-737, cause severe thrombocytopenia (a drop in platelets). The peptide also did not make healthy cells more sensitive to subsequent DNA damage. These are short observations in small groups of mice, not a toxicology program.

A clear negative finding

Clearing senescent cells is not uniformly beneficial. A 2023 study in Circulation used several senolytic approaches, including FOXO4-DRI, in rodent models of pulmonary hypertension. Senescent pulmonary endothelial cells made up about 30% of lung senescent cells in normal mice, and removing them worsened pulmonary hemodynamics: right ventricular systolic pressure and hypertrophy rose, vessel remodeling increased, and pulmonary endothelial cells were markedly depleted. The authors concluded that senolytic interventions “may worsen pulmonary hemodynamics” (Born et al., Circulation 2023).

Theoretical concerns raised in the literature

p53 and tumor surveillance. The peptide works by displacing p53, the central tumor-suppressor protein. The 2026 Antioxidants review names explicit assessment of p53-dependent tumor surveillance as an unmet requirement before clinical translation (Mateescu et al., Antioxidants 2026).
Tissue distribution of the target. The authors of the Leydig cell study noted that in humans FOXO4 protein is reported in testis, placenta and muscle, and argued that muscle damage and cardiotoxicity would need particular attention during any treatment (Zhang et al., Aging 2020).
Chronic FOXO4 loss is not the same as blocking one interaction. FOXO proteins participate in DNA-damage repair, and Foxo4-null mice are susceptible to acute damage, which is why the authors pursued a peptide that blocks a single protein-protein interaction rather than a FOXO4 inhibitor (Baar et al., Cell 2017).

Quality and identity of material sold outside research

Because no approved product exists, any material offered outside a research supply chain has no regulatory oversight of identity, purity, sterility or endotoxin content. The peptide used in the founding study was made to order at over 95% purity and stored as dry 1 mg aliquots specifically to avoid freeze-thaw artifacts, which indicates how sensitive the handling is. No published analysis has examined the content of material sold under this name.

Key takeaways

A designed decoy, not a hormone. FOXO4-DRI is a mirror-image peptide that competes with FOXO4 for binding to p53, which pushes active p53 out of the nucleus and makes senescent cells kill themselves through caspases.
Selective in the dish. In human fibroblasts it was about 12 times more potent against senescent than dividing cells, and the effect disappeared when the same peptide was made in ordinary L-form.
Encouraging but narrow animal data. Three injections of 5 mg/kg improved fur, activity, kidney filtration markers and, in separate work, serum testosterone in aged mice. Group sizes were small and only one dose level was tested.
Zero human evidence. No published or registered clinical trial exists, no pharmacokinetic data exist in any species, and a 2026 review states the compound has not been clinically validated. The half-life of 4 hours listed in some compound databases is not supported by any published measurement.
Removing senescent cells can backfire. In rodent pulmonary hypertension models, senolytic treatment including this peptide worsened pulmonary pressures and depleted lung endothelial cells.
No approval, and prohibited in sport. It is not approved by FDA or EMA and is not a US controlled substance, but WADA class S0 bans any non-approved pharmacological substance at all times.

Sources

Baar MP, Brandt RMC, Putavet DA, et al. Targeted apoptosis of senescent cells restores tissue homeostasis in response to chemotoxicity and aging. Cell. 2017;169(1):132–147.e16. PubMed; PMC.
Bourgeois B, Spreitzer E, Platero-Rochart D, et al. The disordered p53 transactivation domain is the target of FOXO4 and the senolytic compound FOXO4-DRI. Nat Commun. 2025;16(1):5672. PubMed.
Mateescu DM, Gavrilescu DM, Marinescu AR, et al. FOXO4 as a redox-sensitive regulator of antioxidant defense and cellular senescence: cysteine-based signaling, p53 interaction, and therapeutic targeting. Antioxidants (Basel). 2026;15(7):842. PubMed.
Zhang C, Xie Y, Chen H, et al. FOXO4-DRI alleviates age-related testosterone secretion insufficiency by targeting senescent Leydig cells in aged mice. Aging (Albany NY). 2020;12(2):1272–1284. PubMed; PMC.
Li Y, Zhang C, Cheng H, et al. FOXO4-DRI improves spermatogenesis in aged mice through reducing senescence-associated secretory phenotype secretion from Leydig cells. Exp Gerontol. 2024;195:112522. PubMed.
Born E, Lipskaia L, Breau M, et al. Eliminating senescent cells can promote pulmonary hypertension development and progression. Circulation. 2023;147(8):650–666. PubMed.
Hu Z, Li F, Hu C, et al. FOXO4-DRI regulates endothelial cell senescence via the P53 signaling pathway. Front Bioeng Biotechnol. 2026;13:1729166. PubMed.
Huang Y, He Y, Makarcyzk MJ, Lin H. Senolytic peptide FOXO4-DRI selectively removes senescent cells from in vitro expanded human chondrocytes. Front Bioeng Biotechnol. 2021;9:677576. PubMed.
Kong YX, Li ZS, Liu YB, et al. FOXO4-DRI induces keloid senescent fibroblast apoptosis by promoting nuclear exclusion of upregulated p53-serine 15 phosphorylation. Commun Biol. 2025;8(1):299. PubMed.
Han X, Yuan T, Zhang J, et al. FOXO4 peptide targets myofibroblast ameliorates bleomycin-induced pulmonary fibrosis in mice through ECM-receptor interaction pathway. J Cell Mol Med. 2022;26(11):3269–3280. PubMed.
Liu Y, Hou Q, Wang R, et al. FOXO4-D-Retro-Inverso targets extracellular matrix production in fibroblasts and ameliorates bleomycin-induced pulmonary fibrosis in mice. Naunyn Schmiedebergs Arch Pharmacol. 2023;396(10):2393–2403. PubMed.
Meng J, Li Y, Wan C, et al. Targeting senescence-like fibroblasts radiosensitizes non-small cell lung cancer and reduces radiation-induced pulmonary fibrosis. JCI Insight. 2021;6(23):e146334. PubMed.
Jing X, Jia S, Teng M, et al. Cellular senescence contributes to the progression of hyperoxic bronchopulmonary dysplasia. Am J Respir Cell Mol Biol. 2024;70(2):94–109. PubMed.
Alameen AAM, Al-Kuraishy HM, Fawzy MN, Batiha GE. Targeting the FOXO4-p53 axis by retro-inverso peptide senolytic agents: a pharmacological strategy to mitigate brain aging and cognitive decline. Naunyn Schmiedebergs Arch Pharmacol. 2026;399(10):14659–14676. PubMed.
National Center for Biotechnology Information. PubChem compound summary for CID 167312269, FOXO4-DRI. PubChem.
World Anti-Doping Agency. The 2026 Prohibited List, in effect 1 January 2026. WADA 2026 Prohibited List.
Drug Enforcement Administration. Schedule III controlled substances. 21 CFR 1308.13. 21 CFR 1308.13.

FOX04 DRI