Senolytic D-retro-inverso peptide (Mitochondrial / Longevity Research — selective senolysis) Limited Human Data

FOXO4-DRI

Also Known As: FOXO4-D-Retro-Inverso, FOXO4 DRI, D-retro-inverso FOXO4 peptide, Proxofim (research-vendor catalog name only — NOT a regulatory INN)

FOXO4-DRI (FOXO4-D-Retro-Inverso) is a synthetic peptide of approximately 46 amino acids in D-retro-inverso configuration (all amino acids in D-form, sequence reversed) — not an L-peptide, not a natural sequence. It was first described in 2017 by Baar et al. in the laboratory of Peter L. J. de Keizer at Erasmus MC and the Buck Institute for Research on Aging (Cell 169(1):132-147.e16, PMID 28340339, DOI 10.1016/j.cell.2017.02.031). The construct comprises the D-retro-inverso forkhead-domain region of FOXO4 fused to a cationic, HIV-TAT-derived cell-penetrating peptide cargo (CPP cargo) plus a poly-Arg tail. Studies report in mouse models — chemotherapy-induced aging (doxorubicin), natural aging, and the XpdTTD/TTD progeroid model — restoration of fur density, fitness markers, renal function and "willingness to explore" after 5 mg/kg i.v. every other day × 3, with selective apoptosis of senescent cells confirmed by TUNEL staining and no thrombocytopenia or cardiac toxicity reported. The mechanistic core is competitive disruption of the FOXO4-p53 protein-protein interaction in senescent cells, leading to p53 nuclear exclusion and cell-intrinsic apoptosis via the BAX / cleaved caspase-3 mitochondrial pathway — a senolytic effect that spares healthy proliferating cells. A ClinicalTrials.gov v2 API audit on 2 May 2026 returned zero registered FOXO4-DRI human trials worldwide. FOXO4-DRI is not approved by FDA, EMA, MHRA, PMDA, Health Canada, TGA, NMPA, ANVISA or any other regulatory agency; no DrugBank monograph exists. "Proxofim" is a research-vendor catalog name, NOT a regulatory INN. ES-1 and ES2 are separate, shorter design peptides (Le Roy 2021 EBioMedicine, PMID 34689087) — NOT synonyms for FOXO4-DRI. Limited human data — preclinical reports only. Research use only.

Identity & Chemistry

PubChem 2D rendering of the FOXO4-DRI peptide (CID 167312269), a 46-residue D-retro-inverso peptide composed of the FOXO4 p53-binding region fused to a HIV-TAT-derived cationic cell-penetrating peptide cargo. Image-acquisition deferred — no canonical Wikimedia structure exists; PubChem fallback used pending in-house render.
Image credit: Structure data from PubChem CID 167312269, U.S. National Library of Medicine (image-acquisition deferred — no canonical Wikimedia file as of 2026-05-02) · Public Domain (U.S. Government work — National Library of Medicine)
Amino Acid Sequence
H-ltlrkepaseiaqsileaysqngwanrrsggkrppprrrqrrkkrg-OH (≈ 46 residues, lower-case denotes D-amino acids; D-retro-inverso of the FOXO4 p53-binding region fused to a HIV-TAT-derived cell-penetrating peptide cargo with a poly-Arg tail). The sequence corresponds to the construct described in Baar 2017 supplementary materials (PMID 28340339).
Molecular Formula
C₂₂₈H₃₈₈N₈₆O₆₄
Molecular Weight
5358.15 g·mol⁻¹ (≈ 5358.2 Da, free peptide; PubChem CID 167312269). Salt forms (TFA, acetate), CPP cargo variants and purity grades are preparation-specific and vary across vendor lots — the canonical figure above describes the Baar-2017 construct and may not match every commercial preparation.
CAS Number
2460055-10-9
PubChem CID
167312269
IUPAC Name
Full IUPAC peptide nomenclature is preparation-specific (varies with TFA / acetate counter-ion and exact CPP cargo variant); the systematic name computed for the canonical Baar-2017 construct is hosted at PubChem CID 167312269 but exceeds 350 characters and is not reproduced inline. ChemSpider 129428086.
Solubility
Water-soluble due to the high cationic charge of the poly-Arg cell-penetrating cargo; lyophilised peptide is typically reconstituted with sterile water or isotonic saline at the bench. Quantitative aqueous solubility data are not publicly disclosed at PubChem CID 167312269.
Storage
Lyophilised peptide: store at −20 °C or −80 °C protected from light (long-term stability per vendor guidance — not from peer-reviewed source). Reconstituted solutions: store at 2–8 °C, short-term. Vendor / supplier certificate of analysis governs; for research use only.

Mechanism of Action

Studies report that FOXO4-DRI competitively disrupts the FOXO4-p53 protein-protein interaction in senescent cells. Disruption causes phosphorylated p53 to be excluded from the nucleus, which in senescent cells — uniquely, due to their elevated p53-phosphorylation tone — triggers cell-intrinsic apoptosis via the BAX / cleaved caspase-3 mitochondrial pathway (selective senolysis). Healthy proliferating cells without that elevated p53-phosphorylation tone are spared. Observed in research settings.

In healthy cells, FOXO4 and p53 cooperatively regulate the cell cycle and apoptosis at modest levels (Bourgeois & Madl 2018, FEBS Lett, PMID 29683489). In senescent cells — which accumulate during aging, post-chemotherapy and at sites of fibrosis — FOXO4 is upregulated and forms persistent foci with phosphorylated p53. These foci sequester p53 in the nucleus and prevent it from triggering apoptosis, allowing senescent cells to persist and secrete pro-inflammatory SASP factors. FOXO4-DRI is the D-amino-acid retro-inverso version of the FOXO4 forkhead-domain p53-binding region, fused to a cationic cell-penetrating peptide cargo (HIV-TAT-derived cargo / poly-Arg). Once internalized, FOXO4-DRI competitively binds the disordered p53 transactivation domain (TAD2), displacing endogenous FOXO4 and releasing p53 from the foci. Released phosphorylated p53 is then exported from the nucleus, which in senescent cells (uniquely, due to their elevated p53-phosphorylation tone) triggers the BAX / cleaved caspase-3 mitochondrial apoptotic pathway. Healthy cells do not have the elevated p53-phospho tone, so the same exclusion does not trigger apoptosis in them — yielding selective senolysis. Reported in Baar 2017 (mechanism), Bourgeois 2025 (structure, Nat Commun), and Hu 2026 (BAX / cleaved caspase-3 readout). Important editorial scoping: statements about human pharmacology do not exist — zero registered FOXO4-DRI human trials per ClinicalTrials.gov v2 API audit 2026-05-02. Mechanism statements here are intentionally hedged — studies report, observed in research settings — and never framed as established human pharmacology. Research use only.

Molecular Targets

  • FOXO4 (Forkhead box O4 transcription factor) — the peptide mimics the FOXO4 forkhead-domain region that binds p53 (Baar 2017, PMID 28340339)
  • TP53 (p53) — the disordered p53 transactivation domain 2 (TAD2) is the primary FOXO4-DRI binding partner; Ser46 and Thr55 phosphorylation enhance affinity (Bourgeois 2025, Nat Commun, PMID 40593617)
  • BAX / cleaved caspase-3 (downstream pro-apoptotic cascade) — apoptotic readout in senescent endothelial, Leydig and fibroblast cells (Hu 2026, PMID 41625068; Zhang 2020, PMID 31959736)
  • p53 phospho-Ser15 / phospho-Ser46 / phospho-Thr55 — phosphorylation state modulates affinity for both FOXO4 and FOXO4-DRI (Bourgeois 2025)

Signaling Pathways

  • Competitive disruption of the FOXO4-p53 protein-protein interaction in senescent-cell foci → release of phosphorylated p53 → nuclear export → BAX / cleaved caspase-3 activation → selective senolysis (Baar 2017)
  • p53 nuclear exclusion in senescent cells — the distinct mechanism that spares healthy cells with lower p53-phosphorylation tone (Baar 2017; Bourgeois 2025)
  • SASP suppression (senescence-associated secretory phenotype) as a secondary effect after elimination of the senescent-cell fraction (Han 2022, PMID 35510614; Li 2024, PMID 39025385)
  • Structural refinement 2025: binding to the disordered p53-TAD2 with transient α-helical folding upon docking (Bourgeois 2025, PMID 40593617)

Research Applications

The published evidence base is exclusively preclinical (mouse in vivo plus human cells in vitro): the original Baar 2017 Cell paper (chemotherapy-aging, natural aging, XpdTTD progeria) plus independent extensions in aged Leydig cells / testosterone (Zhang 2020), human chondrocytes in vitro (Huang 2021), bleomycin pulmonary fibrosis (Han 2022), spermatogenesis (Li 2024), endothelial cells / vascular aging (Hu 2026) and the 2025 structural refinement of the p53-TAD2 binding site (Bourgeois 2025, Nat Commun). Unlike Khavinson-dominance for Epitalon, the FOXO4-DRI literature spans at least four institutions independent of the de Keizer founding lab — Sun Yat-sen University, U Pittsburgh, Tianjin / CAMS, Wenzhou Medical University — a multi-lab replication in tissue-specific aging models, but no human clinical replication. Observed in research settings.

Chemotherapy-induced aging and natural aging — mice, in vivo

in vivo

Studies report that FOXO4-DRI 5 mg/kg i.v. every other day × 3 in chemo-aged and naturally aged mice (and in the XpdTTD/TTD progeroid model) restored fur density, fitness markers, renal function and "willingness to explore". Selective apoptosis of senescent cells was confirmed by TUNEL staining; no thrombocytopenia and no cardiac toxicity were reported — in contrast to small-molecule senolytics like dasatinib + quercetin.

— Baar et al. 2017, Cell 169(1):132-147.e16 (PMID 28340339, DOI 10.1016/j.cell.2017.02.031)

Aged Leydig cells / testosterone — naturally aged male mice (20–24 months), in vivo

in vivo

Studies report that FOXO4-DRI 5 mg/kg i.p. every other day × 3 in naturally aged male mice induced p53 nuclear exclusion and apoptosis in senescent Leydig cells, increased serum testosterone within 30 days, and upregulated the testosterone-synthesis proteins 3β-HSD and CYP11A1.

— Zhang et al. 2020, Aging (Albany NY) 12(2):1272-1284 (PMID 31959736)

Human chondrocyte expansion — in vitro (human cells)

in vitro

Studies report that FOXO4-DRI selectively eliminated > 50% of senescent cells in extensively expanded human chondrocytes (PDL9) while sparing minimally-expanded controls (PDL3); inflammatory factors were reduced but chondrogenic capacity was not restored.

— Huang et al. 2021, Front Bioeng Biotechnol 9:677576 (PMID 33996787)

Bleomycin-induced pulmonary fibrosis — mice, in vivo

in vivo

Studies report that FOXO4-DRI reduced senescent-cell burden, downregulated SASP factors and attenuated bleomycin-induced collagen deposition; myofibroblasts were preferentially targeted. Comparable efficacy to pirfenidone in the same model. No human translational evidence.

— Han et al. 2022, J Cell Mol Med 26(11):3269-3280 (PMID 35510614)

Structural characterization of the FOXO4-DRI : p53-TAD2 interaction — solution NMR / structural biology

in vitro

Studies report in 2025 in a solution-NMR study that the disordered p53-TAD2 region is the primary FOXO4-DRI binding interface; transient α-helical folding upon docking was confirmed; phospho-Ser46 and phospho-Thr55 enhance affinity. The structural refinement sharpens the mechanistic hypothesis from Baar 2017.

— Bourgeois et al. 2025, Nat Commun 16:5672 (PMID 40593617, DOI 10.1038/s41467-025-60844-9)

Endothelial cell senescence / vascular aging — mice in vivo + HUVEC in vitro

in vivo

Studies report that FOXO4-DRI suppressed aortic aging, improved vascular function, and acted via the p53 / BCL-2 / BAX / cleaved caspase-3 pathway in senescent endothelial cells. The findings reproduce the central senolysis hypothesis in a distinct tissue compartment.

— Hu et al. 2026, Front Bioeng Biotechnol 13:1729166 (PMID 41625068)

Clinical Status

Regulatory Status
FOXO4-DRI is NOT approved — by the FDA, EMA, MHRA, PMDA, Health Canada, TGA, NMPA or ANVISA — and does not appear in any Western or international pharmacopoeia as an active substance. A systematic ClinicalTrials.gov v2 API query on 2 May 2026 for "FOXO4-DRI", "FOXO4 DRI", "Proxofim", "ES-1 senolytic" and "Cleara Biotech" returned zero registered FOXO4-DRI human trials worldwide. A broader "FOXO4" query returns one hit (NCT07494565, "Celecoxib Plus R-CHOP vs R-CHOP in Newly Diagnosed Advanced CD5+ DLBCL"), in which FOXO4 is used as an exploratory biomarker and NOT as an intervention — that study is NOT a FOXO4-DRI trial and is editorially excluded. Cleara Biotech (Erasmus MC spin-out, de Keizer lab) is in preclinical development on FOXO4-p53-axis senolytics but per public records (including Fight Aging February 2026 commentary) has NOT advanced FOXO4-DRI itself to a registered human trial. "Proxofim" is a research-vendor catalog name — NOT a regulatory INN. ES-1 / ES2 are a separate, shorter design peptide (Le Roy 2021, EBioMedicine, PMID 34689087) — NOT a synonym. Anti-doping: FOXO4-DRI is not explicitly named on the WADA Prohibited List 2026, but falls under WADA Class S0 (Non-Approved Substances) by virtue of lacking approval from any regulator anywhere.
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Highest Trial Phase
Highest published phase: preclinical only (mouse in vivo + human cells in vitro). NO registered human Phase 1/2/3 trial as of audit date 2026-05-02.
Sponsor
Discovery: Peter L. J. de Keizer, Erasmus MC / Buck Institute for Research on Aging (Baar 2017). Affiliated commercial vehicle: Cleara Biotech (Erasmus MC spin-out; preclinical development of FOXO4-p53-axis senolytics; FOXO4-DRI itself not advanced to a registered human trial). Numeric Biotech is mentioned in the field; Oisin Biotechnologies works on a separate gene-therapy-based senolytic mechanism and is NOT developing FOXO4-DRI — do not conflate.
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Safety Profile

Observed in research settings

Limited human data — preclinical reports only. In published mouse studies (Baar 2017; Zhang 2020; Han 2022; Li 2024; Hu 2026), FOXO4-DRI at 5 mg/kg i.v. or i.p. every other day for three doses was reported as "well tolerated in vivo" without systematic adverse-event collection. No human safety dataset exists; vendor-driven self-administration anecdotes do NOT constitute peer-reviewed safety evidence. Observed in research settings; for research use only.

Adverse Events Reported in Studies

  • Mouse studies: no thrombocytopenia (in contrast to small-molecule senolytics dasatinib + quercetin) reported — Baar 2017
  • Mouse studies: no cardiac toxicity in tissues examined — Baar 2017
  • Human studies: ZERO — no systematically captured adverse events from human studies exist because no registered human FOXO4-DRI trial exists worldwide (ClinicalTrials.gov v2 API audit 2026-05-02)

Serious Adverse Events

  • Human data gap: ZERO independent long-term pharmacovigilance dataset for FOXO4-DRI exists — multi-month or multi-year human safety data have not been published. Safety statements should be tagged exclusively as "limited human data — preclinical reports only"
  • Theoretical concern (mechanism-derived, not observed): off-target apoptosis of healthy cells with elevated baseline p53-phospho tone (e.g. stress-exposed tissues) — currently not quantified
  • Theoretical immunogenicity concern: a 46-residue D-retro-inverso peptide with HIV-TAT-derived cargo — D-amino acids generally reduce immunogenicity, but human data are absent
  • Vendor-market caveat: FOXO4-DRI is widely sold by research-peptide vendors (Tauret Labs, Power Peptides, Nu Science, Core Peptides, PharmaLab Global, vPeptide, and others); biotech-longevity forums circulate vendor copy that overstates the evidence ("pulmonary fibrosis breakthrough", "anti-aging therapy", "testosterone restoration"). Vendor copy is NOT a citation source and is NOT validated by Triscience editorial. Anti-doping: WADA Class S0 (Non-Approved Substances)

References

  1. Baar MP, Brandt RMC, Putavet DA, Klein JDD, Derks KWJ, Bourgeois BRM, Stryeck S, Rijksen Y, van Willigenburg H, Feijtel DA, van der Pluijm I, Essers J, van Cappellen WA, van IJcken WF, Houtsmuller AB, Pothof J, de Bruin RWF, Madl T, Hoeijmakers JHJ, Campisi J, de Keizer PLJ Targeted Apoptosis of Senescent Cells Restores Tissue Homeostasis in Response to Chemotoxicity and Aging Cell 2017;169(1):132-147.e16. 2017 .

    DOI: 10.1016/j.cell.2017.02.031 PMID: 28340339 View Source

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

    DOI: 10.1002/1873-3468.13057 PMID: 29683489 View Source

  3. Zhang C, Xie Y, Chen H, Lv L, Yao J, Zhang M, Xia K, Feng X, Li Y, Liang X, Sun X, Deng C, Liu G FOXO4-DRI alleviates age-related testosterone secretion insufficiency by targeting senescent Leydig cells in aged mice Aging (Albany NY) 2020;12(2):1272-1284. 2020 .

    DOI: 10.18632/aging.102682 PMID: 31959736 View Source

  4. Huang Y, He Y, Makarcyzk MJ, Lin H Senolytic Peptide FOXO4-DRI Selectively Removes Senescent Cells From in vitro Expanded Human Chondrocytes Frontiers in Bioengineering and Biotechnology 2021;9:677576. 2021 .

    DOI: 10.3389/fbioe.2021.677576 PMID: 33996787 View Source

  5. Han X, Yuan T, Zhang J, Shi Y, Li D, Dong Y, Fan S FOXO4 peptide targets myofibroblast ameliorates bleomycin-induced pulmonary fibrosis in mice through ECM-receptor interaction pathway Journal of Cellular and Molecular Medicine 2022;26(11):3269-3280. 2022 .

    DOI: 10.1111/jcmm.17333 PMID: 35510614 View Source

  6. Li Y, Zhang C, Cheng H, Lv L, Zhu X, Ma M, Xu Z, He J, Xie Y, Yang X, Liang X, Deng C, Liu G FOXO4-DRI improves spermatogenesis in aged mice through reducing senescence-associated secretory phenotype secretion from Leydig cells Experimental Gerontology 2024;195:112522. 2024 .

    DOI: 10.1016/j.exger.2024.112522 PMID: 39025385 View Source

  7. 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 Nature Communications 2025;16:5672. 2025 .

    DOI: 10.1038/s41467-025-60844-9 PMID: 40593617 View Source

  8. Hu Z, Li F, Hu C, Shan Q, Tang Z, Jiang M, Yi X, Chen X, Jin L, Wang X, Wang Y FOXO4-DRI regulates endothelial cell senescence via the P53 signaling pathway Frontiers in Bioengineering and Biotechnology 2026;13:1729166. 2026 .

    DOI: 10.3389/fbioe.2025.1729166 PMID: 41625068 View Source

Frequently Asked Questions

Is FOXO4-DRI FDA-approved?
No. FOXO4-DRI is NOT approved by the FDA, EMA, MHRA, PMDA, Health Canada, TGA, NMPA, ANVISA or any other regulatory agency anywhere in the world as of audit date 2 May 2026. It is an investigational research peptide intended for laboratory use only and is not approved for human consumption.
Has FOXO4-DRI been tested in humans?
No registered human clinical trial of FOXO4-DRI exists as of 2 May 2026. A ClinicalTrials.gov v2 API audit on that date returned zero matching studies for "FOXO4-DRI", "FOXO4 DRI", "Proxofim" or "ES-1 senolytic". All published evidence comes from mouse models and in-vitro experiments on human cells.
Are "Proxofim", "ES-1" and "ES2" synonyms for FOXO4-DRI?
"Proxofim" is a research-vendor catalog name — NOT a regulatory INN; using the name implies NO regulatory approval. "ES-1" and "ES2" are a separate, shorter design peptide (Le Roy 2021, EBioMedicine, PMID 34689087) that outperformed FOXO4-DRI for FOXO4 affinity in melanoma modelling work — ES2 is NOT a synonym, it is a related design peptide. Do not equate these terms with FOXO4-DRI itself.
How is FOXO4-DRI different from senolytics like dasatinib + quercetin?
FOXO4-DRI is a 46-residue D-retro-inverso peptide that targets the FOXO4-p53 protein-protein interaction directly. Dasatinib + quercetin (D+Q) are oral small molecules that target tyrosine-kinase pro-survival pathways (Bcl-2, PI3K/AKT) and act as broad-spectrum senolytics. The mechanisms are distinct, the delivery routes differ (peptide injection vs. oral small molecule), and unlike D+Q (which has been in early-phase human trials for IPF and CKD) FOXO4-DRI has not entered registered human trials.
What were the main preclinical findings?
Studies report in Baar 2017 that FOXO4-DRI 5 mg/kg i.v. every other day × 3 in chemo-aged and naturally aged mice restored fur density, fitness, willingness to explore and renal function. Subsequent groups have reported senolytic effects in aged Leydig cells with testosterone restoration (Zhang 2020; Li 2024), human chondrocytes in vitro (Huang 2021), bleomycin-induced pulmonary fibrosis (Han 2022), keloid senescent fibroblasts (Comm Biol 2025) and aged endothelial cells with improved vascular function (Hu 2026). Observed in research settings — no human translational replication.
What are the risks of FOXO4-DRI?
There is no human safety dataset. Mouse studies have reported "well tolerated in vivo" without systematic adverse-event collection — this is NOT a safety endorsement for human use. Theoretical concerns include off-target apoptosis in tissues with elevated baseline p53-phospho tone, unknown immunogenicity, and unknown long-term effects of chronic senolytic dosing on tissue regenerative capacity. Use outside a properly-conducted clinical trial is unsupported by any regulatory framework.

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