FOXO4-DRI

01 · What it is

FOXO4-DRI has the best-defined molecular target of any compound in this project, confirmed at atomic resolution by three structural biology groups who do not work together — and the most alarming single animal result: in a model of pulmonary hypertension, clearing senescent cells made the disease worse.

FOXO4-DRI is a designed peptide, not a natural one. It is built from the region of the forkhead transcription factor FOXO4 that contacts the tumour suppressor p53, rebuilt in D-retro-inverso form — the sequence reversed and synthesised from D-amino acids, an arrangement that approximately preserves the topology of the side chains presented to a binding partner while making the molecule resistant to proteases, which cleave L-peptides and largely ignore D-ones. It carries a cell-penetrating segment to get it inside cells.

The logic behind it is worth stating carefully, because it is the clearest therapeutic rationale in this family.

Senescent cells accumulate with age. They stop dividing but do not die, and they secrete a mixture of inflammatory signals — the senescence-associated secretory phenotype — that damages the tissue around them. They persist because they are protected from apoptosis, and one of the mechanisms of that protection is that FOXO4 binds p53 in the nucleus and holds it there, preventing it from executing the cell death programme it would otherwise trigger in a cell this damaged.

In 2017 a group at Erasmus MC, working with Judith Campisi and Jan Hoeijmakers, designed a peptide to break that interaction. In senescent cells it caused selective p53 nuclear exclusion and cell-intrinsic apoptosis, and in mice it restored tissue homeostasis after chemotoxicity and in ageing ¹. The paper appeared in Cell.

The target has since been defined structurally, by people with no stake in the compound. A 2025 paper identified the disordered p53 transactivation domain as the target of both FOXO4 and FOXO4-DRI ¹⁷. A Prague group independently characterised the FOXO forkhead domain–p53 transactivation domain interaction and its structural plasticity ¹⁶, having earlier shown that FOXO4 binds the p53 transactivation and C-terminal regulatory domains and inhibits p53’s own DNA binding ⁷. A Korean group used NMR to map the dual binding surfaces ⁸ and then designed alternative peptide inhibitors against them ¹⁸.

Four laboratories, three countries, structural methods, converging on the same interaction. Nothing else in Family E has that.

And then there is the Circulation paper. In 2023, a group studying pulmonary hypertension cleared senescent cells four different ways — a p16-promoter-driven suicide gene, the senolytic ABT263, FOXO4-DRI, and p16 inactivation — and reported that eliminating senescent cells can promote pulmonary hypertension development and progression ⁹. The title is a statement of the finding. Senescent cells are not uniformly harmful, senolysis is not uniformly beneficial, and in at least one vascular disease the intervention runs the wrong way.

No human has been given this compound. Forty indexed records, not one of them a clinical trial.

02 · Evidence at a glance

Evidence grade

Preclinical — no human study of any kind is indexed

Structure

D-retro-inverso peptide derived from the FOXO4 p53-binding region, with a cell-penetrating segment

Why D-retro-inverso

Preserves side-chain presentation while resisting proteolysis

Molecular target

The disordered p53 transactivation domain, defined structurally ¹⁷

Independent structural confirmation

Three unaffiliated groups ^7,8,16,18

Mechanism

Disrupts FOXO4–p53 binding → p53 nuclear exclusion → apoptosis in senescent cells ^1,14

Founding paper

Cell, 2017 ¹

Principal safety finding

Senescent cell clearance, including by FOXO4-DRI, promoted pulmonary hypertension development and progression ⁹

Animal models with positive results

Aged Leydig cells and testosterone ⁴; spermatogenesis ¹³; pulmonary fibrosis ¹⁰; bronchopulmonary dysplasia ¹²

Human cell work

Chondrocytes ⁵; keloid fibroblasts ¹⁴; endothelial cells ¹⁹

Human trials

None

Human subjects to date

0

Indexed records

~40

Approval status

None, any jurisdiction

03 · Mechanism of action

The FOXO4–p53 interaction

p53 responds to cellular damage by driving either repair, arrest or apoptosis. In a senescent cell the damage is permanent, so the arrest becomes permanent too — and the cell survives, which under other circumstances p53 would not permit. FOXO4 is part of why. It binds p53 in the nucleus, sequestering it into foci and directing it toward transcription of p21, the arrest programme, and away from apoptosis ³.

FOXO4 expression is elevated in senescent cells ¹³, which is what makes the interaction a selective target: disrupting it should affect cells where it is abundant and leave others largely alone.

What the peptide does

FOXO4-DRI competes for the interaction. The consequence reported in the founding paper is p53 nuclear exclusion followed by cell-intrinsic apoptosis, occurring selectively in senescent cells ¹. In keloid fibroblasts the same sequence was observed with a specific modification tracked: nuclear exclusion of p53 phosphorylated at serine 15 ¹⁴. In endothelial cells, FOXO4-DRI’s effect on senescence was traced through the p53 signalling pathway ¹⁹.

The structural work, and why it matters here

Most compounds in this project have a proposed mechanism supported by phenotype. This one has a mechanism supported by structure, characterised by groups with no involvement in developing it.

The p53 transactivation domain is intrinsically disordered — it has no fixed structure until it binds something — which makes it a difficult target and an interesting one. A 2025 paper identified this disordered region as the target of both native FOXO4 and the peptide ¹⁷. A Prague group mapped the FOXO forkhead domain–p53 transactivation domain interaction and reported its structural plasticity ¹⁶, having previously shown that FOXO4 engages both the transactivation and C-terminal regulatory domains of p53 and inhibits p53 binding to DNA ⁷. A Korean group characterised the dual binding surfaces biophysically ⁸ and used that map to design alternative peptide inhibitors inducing apoptosis selectively in senescent cancer cells ¹⁸.

Independent structural convergence on a target is the strongest form of mechanistic evidence available short of a clinical result, and this compound has it. It says the peptide binds what it is supposed to bind. It says nothing about whether binding it helps.

Alternative delivery

The peptide is not the only way to hit FOXO4. Self-assembled DNA nanotubes carrying an antisense approach against FOXO4 selectively eliminated cigarette-smoke-induced senescent lung fibroblasts ¹¹, which is an independent test of the target rather than of the molecule.

04 · Key research findings

The founding result. FOXO4 was identified as a pivot in senescent cell viability. A designed peptide perturbing the FOXO4–p53 interaction caused selective p53 nuclear exclusion and cell-intrinsic apoptosis in senescent cells, and restored tissue homeostasis in mice in response to chemotoxicity and to ageing ¹.

A high-profile paper, in a major journal, with a mechanism and an in vivo readout. It is the reason this compound exists commercially, and it remains the only study reporting whole-organism benefit from ageing itself.

The result that cuts the other way. Senescent cell clearance was achieved by four independent methods — a p16-promoter-driven suicide gene in p16-ATTAC mice, the senolytic ABT263, cell-permeable FOXO4-DRI, and p16 inactivation — and the finding was that eliminating senescent cells can promote pulmonary hypertension development and progression ⁹.

Four clearance methods converging on harm is a much harder result to dismiss than a single compound’s off-target effect. It says the biology, not the molecule, is the problem in that tissue — and it was published in Circulation in 2023, six years after the founding paper, by a group with no connection to it.

Reproductive ageing in mice. FOXO4-DRI alleviated age-related testosterone secretion insufficiency by targeting senescent Leydig cells in aged mice, with selective p53 nuclear exclusion and apoptosis in those cells ⁴. The same group later reported improved spermatogenesis in aged mice through reduced senescence-associated secretory phenotype secretion from Leydig cells ¹³.

Two studies, one group, one tissue, consistent direction. The second explains the first mechanistically, which is a stronger pattern than two independent positive results at the same level.

Lung. FOXO4-DRI reduced extracellular matrix production in fibroblasts and ameliorated bleomycin-induced pulmonary fibrosis in mice, with redistribution of intranuclear p53 ¹⁰. In a hyperoxic bronchopulmonary dysplasia model, Foxo4-DRI was one of three agents administered intraperitoneally in the protocol used in that study — alongside an antioxidant peptide and an ER-stress agent — to test the contribution of cellular senescence to disease progression ¹².

The lung findings sit awkwardly against the pulmonary hypertension result ⁹, since all three concern senescence in lung tissue and two point one way while one points the other. No paper reconciles them.

Human cells. FOXO4-DRI selectively removed senescent cells from in vitro expanded human chondrocytes, work from a Pittsburgh group with no connection to the originators ⁵. It induced apoptosis and decreased the G0/G1 fraction in pro-senescence models of keloid organ cultures and fibroblasts, with p53-serine 15 nuclear exclusion ¹⁴. It affected endothelial cell senescence through p53 signalling ¹⁹.

Three independent human cell systems, three positive results for the selective-killing phenotype. This is genuine replication of the cellular effect.

Reviews and framing. The FOXO4–p53 axis in cellular senescence has been reviewed by structural biologists working on it ³, within the broader p53 senescence-modulator literature ⁶, in the context of senescence in kidney disease ², across FOXO roles in neurological disorders ¹⁵, and in 2026 as a strategy for brain ageing and cognitive decline ²⁰.

The 2026 brain-ageing review is a proposal about where the compound might go, not a report of it having gone there.

05 · Evidence overview

06 · Safety profile

Animal data. No formal toxicology programme is identified. The mouse studies report efficacy endpoints ^1,4,10,12,13 and are not designed to find a toxic dose.

The most important safety information in this file is not a toxicology study but a disease-model result. Clearing senescent cells — by suicide gene, by ABT263, by FOXO4-DRI, or by p16 inactivation — promoted the development and progression of pulmonary hypertension ⁹. That is a finding about the consequences of the intended pharmacology working as designed, which is a different and more serious category of risk than an off-target effect.

Human data. None exists. There is no reported human exposure to FOXO4-DRI in the peer-reviewed literature at any dose, by any route, for any duration.

What is genuinely unknown. Whether senescent cells are safe to remove in any given tissue: the pulmonary hypertension result ⁹ establishes that the answer is not always yes, and senescence has recognised beneficial roles in wound healing and in restraining fibrosis that the reviews in this file acknowledge ². Pharmacokinetics, absent for any species — the D-retro-inverso design is intended to extend half-life, and nobody has published what half-life it achieves. Tissue distribution, and therefore which senescent cell populations are actually reached. Immunogenicity, which is unstudied and specifically relevant here: a peptide built from D-amino acids is cleared slowly and processed differently by antigen-presenting cells, and long persistence of a non-natural polymer is a plausible immunological concern that no paper addresses. Whether disrupting FOXO4–p53 binding in non-senescent cells with high FOXO4 has consequences. Whether transiently freeing p53 from sequestration affects tumour biology in either direction — the Korean work shows the axis can be targeted to kill senescent cancer cells ¹⁸, which cuts both ways. Repeat-dose toxicology, genotoxicity, reproductive toxicology and carcinogenicity: none performed — and reproductive toxicology is a specific gap given that two of the positive animal studies concern the testis ^4,13. And the identity and stereochemical purity of any commercial preparation: a D-retro-inverso peptide requires every residue to be the correct enantiomer, and a synthesis shortcut produces a molecule with different properties. No published analysis has examined any product sold under this name.

07 · US regulatory status

Current as of 6 September 2026. FOXO4-DRI is not approved as a drug in the United States or any other jurisdiction and is not a controlled substance.

No marketing authorisation has been sought or granted anywhere. No investigational new drug programme appears in the peer-reviewed record. Nine years after a Cell paper with a defined mechanism and an in vivo result ¹, the compound has not entered clinical development — while other senolytic approaches have. That gap is a fact about the field’s own assessment of this molecule, and the pulmonary hypertension result ⁹ is one plausible part of the explanation.

Under the World Anti-Doping Code, peptide hormones and growth factors are prohibited at all times, and substances not approved for human therapeutic use by any governmental regulatory health authority fall within class S0. Competitors should consult the current Prohibited List directly rather than rely on secondary summaries, including this one.

08 · Limitations of the evidence

1. There is no human evidence of any kind. No indexed study reports administration of FOXO4-DRI to a person. Every claim in this guide describes mice or cultured cells.

1. The central concern is not that the compound fails but that it may succeed in the wrong tissue. Four independent methods of clearing senescent cells promoted pulmonary hypertension development and progression ⁹. Senolysis is not a uniformly beneficial intervention, and no framework exists for predicting which tissues benefit and which do not.

1. The lung literature contradicts itself. Senescent cell clearance worsened pulmonary hypertension ⁹; FOXO4-DRI ameliorated bleomycin-induced pulmonary fibrosis ¹⁰; senescence contributed to bronchopulmonary dysplasia progression ¹². Three lung studies, two directions, no reconciliation.

1. Strong structural evidence is not clinical evidence, and the two are easily conflated for this compound. Four laboratories agreeing on where the peptide binds ^7,8,16,17,18 establishes the mechanism and nothing about outcomes.

1. Animal-to-human translation is untested, and senescent cell burden differs enormously between a laboratory mouse and a human of any age. A short-lived animal in a pathogen-free facility is not a model of a seventy-year-old’s senescent cell landscape.

1. The positive in vivo results cluster in a small number of tissues and groups. Testis, twice, from one group ^4,13. Lung, three times, disagreeing ^9,10,12. The founding paper remains the only report of benefit in ageing itself ¹.

1. Pharmacokinetics are entirely absent. The D-retro-inverso design exists to solve a pharmacokinetic problem and no study reports whether it does.

1. Immunogenicity of a D-amino acid peptide is unstudied and is a foreseeable issue. Slow clearance of a non-natural polymer is a standard concern, and nothing in this record addresses it.

1. No randomised controlled trial exists in any species for any endpoint.

1. Stereochemical identity of commercial material is unverifiable from the literature. A D-retro-inverso peptide is defined by the chirality of every residue. No published analysis has examined any product sold as FOXO4-DRI, and a preparation containing L-residues would be a different and shorter-lived molecule.

09 · References

1. Baar MP, Brandt RMC, Putavet DA, et al. Targeted apoptosis of senescent cells restores tissue homeostasis in response to chemotoxicity and aging. Cell. 2017 Mar 23;169(1):132–147.e16.

   PMID 28340339 ↗

2. Valentijn FA, Falke LL, Nguyen TQ, Goldschmeding R. Cellular senescence in the aging and diseased kidney. J Cell Commun Signal. 2018 Mar;12(1):69–82.

   PMID 29260442 ↗

3. Bourgeois B, Madl T. Regulation of cellular senescence via the FOXO4-p53 axis. FEBS Lett. 2018 Jun;592(12):2083–2097.

   PMID 29683489 ↗

4. 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 Jan 20;12(2):1272–1284.

   PMID 31959736 ↗

5. 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 Apr 29;9:677576.

   PMID 33996787 ↗

6. Pawge G, Khatik GL. p53 regulated senescence mechanism and role of its modulators in age-related disorders. Biochem Pharmacol. 2021 Aug;190:114651.

   PMID 34118220 ↗

7. Mandal R, Kohoutova K, Petrvalska O, Horvath M, Srb P, Veverka V, Obsilova V, Obsil T. FOXO4 interacts with p53 TAD and CRD and inhibits its binding to DNA. Protein Sci. 2022 May;31(5):e4287.

   PMID 35481640 ↗

8. Kim J, Ahn D, Park CJ. Biophysical investigation of the dual binding surfaces of human transcription factors FOXO4 and p53. FEBS J. 2022 Jun;289(11):3163–3182.

   PMID 34954873 ↗

9. Born E, Lipskaia L, Breau M, et al. Eliminating senescent cells can promote pulmonary hypertension development and progression. Circulation. 2023 Feb 21;147(8):650–666.

   PMID 36515093 ↗

10. Liu Y, Hou Q, Wang R, Liu Y, Cheng Z. FOXO4-D-Retro-Inverso targets extracellular matrix production in fibroblasts and ameliorates bleomycin-induced pulmonary fibrosis in mice. Naunyn Schmiedebergs Arch Pharmacol. 2023 Oct;396(10):2393–2403.

    PMID 37074394 ↗

11. Han Y, Wu Y, He B, Wu D, Hua J, Qian H, Zhang J. DNA nanoparticles targeting FOXO4 selectively eliminate cigarette smoke-induced senescent lung fibroblasts. Nanoscale Adv. 2023 Oct 5;5(21):5965–5973.

    PMID 37881696 ↗

12. 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 Feb;70(2):94–109.

    PMID 37874230 ↗

13. 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 Oct 1;195:112522.

    PMID 39025385 ↗

14. Kong YX, Li ZS, Liu YB, Pan B, Fu X, Xiao R, Yan L. FOXO4-DRI induces keloid senescent fibroblast apoptosis by promoting nuclear exclusion of upregulated p53-serine 15 phosphorylation. Commun Biol. 2025 Feb 24;8(1):299.

    PMID 39994346 ↗

15. Asadi Y, Moundounga RK, Chakroborty A, Pokokiri A, Wang H. FOXOs and their roles in acute and chronic neurological disorders. Front Mol Biosci. 2025 Apr 7;12:1538472.

    PMID 40260403 ↗

16. Kohoutova K, Srb P, Obsilova V, Veverka V, Obsil T. Structural plasticity of the FOXO-DBD:p53-TAD interaction. Nat Commun. 2025 May 27;16(1):4907.

    PMID 40425537 ↗

17. Bourgeois B, Spreitzer E, Platero-Rochart D, Paar M, Zhou Q, Usluer S, de Keizer PLJ, Burgering BMT, Sánchez-Murcia PA, Madl T. The disordered p53 transactivation domain is the target of FOXO4 and the senolytic compound FOXO4-DRI. Nat Commun. 2025 Jul 1;16(1):5672.

    PMID 40593617 ↗

18. Kang D, Lim Y, Ahn D, Lee J, Park CJ. Peptide inhibitors targeting FOXO4-p53 interactions and inducing senescent cancer cell-specific apoptosis. J Med Chem. 2025 Aug 14;68(15):15683–15694.

    PMID 40739602 ↗

19. Hu Z, Li F, Hu C, et al. FOXO4-DRI regulates endothelial cell senescence via the P53 signaling pathway. Front Bioeng Biotechnol. 2026 Jan 15;13:1729166.

    PMID 41625068 ↗

20. 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 Jul;399(10):14659–14676.

    PMID 42024235 ↗