FOXO4-DRI — Research Product Overview

**Disclaimer:** This product overview is provided strictly for in-vitro and preclinical research use. [FOXO4-DRI](/research/foxo4-dri-senolytic) is not approved by the FDA for human use, is not a drug, food, or cosmetic, and nothing in this document constitutes medical advice or a recommendation for human administration. Materials are sold to qualified research professionals for laboratory investigation only.

Overview

FOXO4-DRI is a synthetic D-retro-inverso (DRI) peptide designed to disrupt the protein-protein interaction between FOXO4 and p53, selectively inducing apoptosis in senescent cells while sparing healthy proliferating and quiescent cells. The peptide was developed by the Peter L.J. de Keizer laboratory and first described in a landmark 2017 paper in *Cell* (Baar et al.), in which it was shown to selectively eliminate senescent cells in vitro and to restore fur density, renal function, and physical fitness in naturally aged mice. FOXO4-DRI is one of the most well-characterized peptide-based senolytics in the literature and a frequent comparator in senolytic discovery work.

For a deeper treatment of senolytic biology see our FOXO4-DRI senolytic mechanisms article and the FOXO4-DRI senolytic aging research overview, which collects subsequent independent replication and indication-specific work.

Sequence and Structural Notes

• Sequence (D-retro-inverso form): ltlrkrrlrhnvwlarflv (lowercase indicates D-amino acids)
• Length: 19 residues
• Approximate molecular weight: ~2444 Da (varies slightly with salt form)
• Backbone: all D-amino acids in reverse sequence relative to the parent FOXO4 fragment, preserving side-chain topology while resisting proteolysis
• N-terminus: typically free amine
• C-terminus: typically free acid; some preparations supplied with C-terminal amidation
• Charge at pH 7: strongly cationic (~+5) due to multiple arginine and lysine residues

The D-retro-inverso design is the key engineering feature of this peptide. By using D-amino acids in reverse order, the side-chain spatial arrangement of the parent L-peptide is approximately preserved while protease recognition is abolished. This dramatically extends the in-vivo half-life relative to the L-form.

Mechanism of Action (Summary)

1. FOXO4-p53 interaction disruption — competes for the FOXO4 surface that normally tethers p53 in the nucleus of senescent cells.
2. p53 nuclear exclusion — released p53 redistributes to mitochondria and triggers cell-intrinsic apoptosis.
3. Selectivity for senescent cells — healthy cells do not depend on FOXO4-mediated p53 sequestration for survival, so they are largely unaffected.
4. Proteolysis resistance — the D-retro-inverso backbone confers extended in-vivo persistence relative to the L-peptide.

Preclinical Research Summary

The Baar et al. 2017 *Cell* paper demonstrated that FOXO4-DRI:

• Selectively killed senescent IMR90 fibroblasts and other senescent cell types in vitro
• Caused minimal toxicity in proliferating or quiescent control cells
• Restored fur density, renal marker normalization, and treadmill running endurance in 25-month-old wild-type mice when administered intraperitoneally on a 3-doses-over-5-days schedule, repeated every 2 weeks
• Reduced doxorubicin-induced premature aging phenotypes when administered after chemotherapy

Subsequent work has explored FOXO4-DRI in models of osteoarthritis (selective clearance of senescent chondrocytes), idiopathic pulmonary fibrosis, age-related testosterone insufficiency in Leydig cells, and intervertebral-disc degeneration. The peptide remains a standard tool compound in senolytic research, often used as a positive control alongside small-molecule senolytics such as the dasatinib + quercetin combination.

Comparator Peptides and Molecules

The senolytic field is structurally divided into peptide-based agents (of which FOXO4-DRI is the canonical example) and small-molecule agents. The most widely studied small-molecule comparator is the dasatinib + quercetin (D+Q) combination, an oral cocktail in which dasatinib (a tyrosine kinase inhibitor) targets ephrin-receptor-driven survival pathways in senescent fibroblasts and quercetin (a flavonoid) targets BCL-2/BCL-xL-driven survival in senescent endothelial cells. D+Q has reached human clinical trials in idiopathic pulmonary fibrosis and diabetic kidney disease, while FOXO4-DRI remains preclinical. Navitoclax (ABT-263) is a BH3-mimetic small-molecule senolytic with strong in-vitro activity but on-target hematological toxicity. Fisetin is a naturally occurring flavonoid with weaker but well-tolerated senolytic activity. UBX0101 is a clinical-stage MDM2 inhibitor that disrupts MDM2-p53 interaction; in conceptual contrast, FOXO4-DRI disrupts FOXO4-p53 interaction, achieving similar p53 release through a different protein-protein interface.

The peptide architecture itself has been compared to other DRI scaffolds. Protac-style and stapled-peptide alternatives have been published but have not displaced FOXO4-DRI as the standard tool compound. Researchers studying senescence-context tissue repair frequently combine FOXO4-DRI clearance with regenerative peptides such as BPC-157 or TB-500, or with metabolic adjuncts via NAD vs NMN vs NR. Telomere-axis comparators include Epitalon, which acts on hTERT rather than on senescent-cell killing — a complementary rather than competing mechanism. The sirtuin-NAD axis and mTOR pathway peptides provide adjacent longevity-axis context.

Deeper Preclinical Breakdown

Baar et al. 2017 (*Cell* 169, PMID 28340339) is the founding study and remains the single most-cited FOXO4-DRI reference. The protocol used 25-month-old wild-type C57BL/6 mice (equivalent to ~75-year-old humans). FOXO4-DRI was administered intraperitoneally at 5 mg/kg on a "3-doses-over-5-days" schedule (days 1, 3, 5), with the cycle repeated every 2 weeks. Endpoints included fur density (measured by image analysis), renal function (BUN, creatinine), and treadmill running endurance. After 7 weeks, treated animals showed significant restoration of fur, normalization of renal markers, and 30–40% improvement in running endurance. SA-β-gal+ cell counts in liver and kidney decreased by 50–80% in treated animals. The doxorubicin-induced premature aging arm of the same paper used 10 mg/kg doxorubicin followed by FOXO4-DRI at the same schedule, showing protection against fur loss and fitness decline. Limitations include the relatively short treatment window, the absence of long-term lifespan endpoints in the original paper, and the high dose (5 mg/kg) relative to typical peptide therapeutics.

Zhang et al. 2020 (PMID 32074083) extended the model to age-related Leydig cell dysfunction in 21-month-old mice. FOXO4-DRI at 5 mg/kg IP for 4 cycles selectively cleared senescent Leydig cells (identified by p16-positive immunostaining) and restored testosterone biosynthesis. The study demonstrated tissue-specificity of senescent-cell clearance: spermatogenesis was unaffected because germ cells lacked the FOXO4-p53 dependency.

Zhao et al. 2021 (*Front Bioeng Biotechnol*, PMID 33996785) evaluated FOXO4-DRI in expanded human chondrocyte cultures. Cells were passaged to senescence (P9), then treated with FOXO4-DRI at 25 µM for 24 hours. Senescent (SA-β-gal+) chondrocytes were selectively eliminated while proliferating chondrocytes were spared, validating use of the peptide in cartilage-engineering protocols. Limitations include the relatively narrow concentration range tested and lack of long-term phenotype tracking.

Formulation Considerations

FOXO4-DRI is supplied as a white-to-off-white lyophilized powder, typically 5 mg or 10 mg per vial. The D-retro-inverso architecture is the defining engineering feature, and chiral verification (Marfey's reagent or chiral HPLC) on the COA is non-negotiable for quality work. The peptide is moderately hydrophobic and aqueous solutions can become turbid above 5 mg/mL — visual inspection of reconstituted material is required. For in-vitro work, DMSO is commonly used to make a 10 mM stock, then diluted into culture medium so final DMSO concentration stays below 0.1% to avoid solvent toxicity. For in-vivo work, sterile saline or PBS at 1–5 mg/mL is typical, with the dose volume adjusted accordingly.

Common impurities visible on a quality COA include partial-L-amino-acid contamination (the most consequential, since L-residues at any position would expose protease-cleavage sites), oxidized variants of the tryptophan residue, and TFA counter-ion residue. Lyophilized stability is at least 24 months at -20 °C; reconstituted stability is up to 14 days at 2–8 °C in DMSO. See the peptide reconstitution guide, understanding peptide purity, and reading HPLC COA for protocol depth.

Research-Context Dosing Ranges

The most-cited rodent reference dose is 5 mg/kg IP on the "3-doses-over-5-days" schedule of Baar et al. 2017, repeated every 2 weeks. Subsequent work has used the same schedule across most aged-rodent indications (Leydig cells, IPF, IVD degeneration). In-vitro doses range from 1 µM to 25 µM in 24-hour exposures. Cell-killing selectivity (senescent vs proliferating) is typically tested across dose-response curves spanning 0.1–50 µM. No human dosing is implied or recommended.

Common Research Applications

• In-vitro senescent vs. proliferating cell killing assays (IMR90, BJ, MEF, primary chondrocytes)
• SA-β-galactosidase clearance assays in aged or stress-induced senescent cultures
• Naturally aged or chemotoxin-aged rodent models for senescent-cell burden
• Senolytic discovery screens as a benchmark positive control
• Combination studies with NAD+ precursors — see NAD vs NMN vs NR and the sirtuin-NAD axis

Handling, Reconstitution, and Storage

• Form supplied: white-to-off-white lyophilized powder, typically 5 mg or 10 mg per vial
• [Reconstitution](/research/peptide-reconstitution-guide): for in-vitro work, DMSO is commonly used to make a 10 mM stock, then diluted into culture medium so that final DMSO concentration is below 0.1%; for in-vivo work, sterile saline or phosphate-buffered saline at 1–5 mg/mL is typical
• Solubility note: the peptide is moderately hydrophobic; aqueous solutions can become turbid above 5 mg/mL — verify visually before use
• Lyophilized stability: ≥24 months at -20 °C, desiccated and protected from light
• Reconstituted stability: up to 14 days at 2–8 °C in DMSO; up to 7 days in aqueous buffer; aliquot and freeze at -20 °C or -80 °C for longer-term storage
• Avoid: prolonged exposure to oxidizing conditions; freeze-thaw beyond 3–4 cycles

See peptide reconstitution guide for general protocol guidance.

Lab Specifications

• HPLC purity target: ≥95.0% by RP-HPLC at 220 nm (≥98.0% available for high-grade research lots)
• Identity confirmation: ESI-MS or MALDI-TOF, observed mass within ±2 Da of theoretical
• D-amino acid verification: chiral HPLC or Marfey's reagent assay confirming D-stereochemistry of all 19 residues
• TFA / acetate counter-ion: typically <12% w/w
• Endotoxin: <5 EU/mg for cell-culture grade
• Water content: <8% by Karl Fischer

Because the D-retro-inverso architecture is the defining engineering feature, researchers should require chiral verification on the COA. See understanding peptide purity.

Cross-References

Related Viking Labs research:

• FOXO4-DRI senolytic mechanisms
• FOXO4-DRI senolytic aging research
• NAD vs NMN vs NR
• Sirtuin-NAD axis
• Product overview: Epitalon
• Peptides longevity research 2026

Summary

FOXO4-DRI is the canonical peptide senolytic tool compound in academic research. Its D-retro-inverso architecture, well-characterized FOXO4-p53 disruption mechanism, and reproducible activity in both cellular and naturally aged rodent models make it a frequent positive control in senolytic discovery work. Researchers should pay particular attention to chiral verification of the supplied material, to DMSO concentration in cell-culture experiments, and to the dosing schedule used in the original Baar et al. publication when designing comparative studies.

*This document is provided for research and educational purposes only. Viking Labs does not sell products intended for human consumption.*