FoxO4-DRI

FoxO4-DRI was developed by Marco Demaria, Peter de Keizer, and colleagues at Erasmus University Medical Center in Rotterdam and first described in a 2017 Cell paper (Baar et al., PMID 28340339) titled "Targeted Apoptosis of Senescent Cells Restores Tissue Homeostasis in Response to Chemotoxicity and Aging." At Verified Peptides, we consider it one of the most mechanistically distinctive compounds in our catalog because it was engineered, not discovered — designed from the outset as a peptide mimic intended to interfere with a specific, previously characterized protein-protein interaction rather than isolated from a natural source or identified through a broad screening effort.

The peptide is a 46-amino-acid, all-D-amino-acid construct (CAS 2460055-10-9, PubChem CID 167312269, molecular formula C228H388N86O64, molecular weight approximately 5,358.05 g/mol). It combines two functional segments: a D-retro-inverso mimic of the C-terminal transactivation domain of the transcription factor FOXO4 — the region responsible for FOXO4's interaction with p53 — fused to an HIV-TAT-derived cell-penetrating sequence (RRRQRRKKRG) that allows the peptide to cross the cell membrane and reach its intracellular target.

"D-retro-inverso" describes a specific peptide-engineering technique: the amino acid sequence is reversed and built entirely from D-amino acids (mirror-image stereoisomers of the naturally occurring L-amino acids), which produces a molecule whose side chains project in roughly the same three-dimensional orientation as the original L-peptide, preserving its ability to bind the same target, while making the peptide backbone resistant to enzymatic degradation by the proteases that normally break down natural L-peptides. This resistance to degradation is central to why FoxO4-DRI can function as a stable research tool rather than being rapidly cleaved apart once inside a cell.

At Verified Peptides, we point researchers first to the foundational 2017 Cell paper (Baar et al., PMID 28340339), which reported that FoxO4-DRI selectively induced apoptosis in senescent cells in vitro and, in aged and chemotherapy-treated mice, restored fitness, fur density, and renal function while reducing markers of senescence in kidney tissue — all without evident toxicity to non-senescent, healthy tissue in the reported experiments. This paper established FoxO4-DRI as one of the earliest and most cited demonstrations of a targeted, mechanism-specific senolytic peptide, distinct from the broader small-molecule senolytic combinations being developed around the same period.

Follow-up preclinical research has extended these findings into additional tissue contexts. A 2021 study published in Frontiers in Bioengineering and Biotechnology (Huang et al., PMID 33996787) found that FoxO4-DRI selectively removed senescent cells from in vitro expanded human chondrocytes — cartilage-forming cells that are prone to senescence during the expansion process required for cell-based cartilage repair procedures — without depleting the healthy chondrocyte population, a finding relevant to regenerative-medicine research seeking to improve the quality of expanded cell populations used in cartilage repair. Separate research has examined FoxO4-DRI in the context of Leydig cell senescence and spermatogenesis in aged mice, reporting reduced senescence-associated secretory phenotype (SASP) output and improved measures of spermatogenic function, and additional published work has examined FoxO4-DRI's effects on endothelial cell senescence via the p53 signaling pathway.

We want to be direct with researchers about the current evidence boundary: as of 2026, FoxO4-DRI remains an exclusively preclinical compound. No human clinical trial has been registered on ClinicalTrials.gov, and no peer-reviewed publication has reported human trial data for the peptide. This stands in contrast to the small-molecule senolytic combination dasatinib-plus-quercetin (D+Q), which has already progressed through several completed human clinical trials with published efficacy and safety data — a meaningful distinction for researchers comparing the maturity of different senolytic research approaches. FoxO4-DRI's research program, while mechanistically well-characterized and actively continuing (including the 2025 structural refinement of its p53-binding mode and continued 2026 publications on endothelial senescence), has not yet reached the human-trial stage that some competing senolytic strategies have.

It is worth distinguishing FoxO4-DRI's academic development path from a separate, unrelated senolytic that did reach human trials and failed: UBX0101, developed by Unity Biotechnology as a small-molecule p53/MDM2 interaction inhibitor (a different mechanism and a different molecule entirely, despite both ultimately converging on p53 biology), was tested as a single intra-articular injection in a Phase 2 trial for painful knee osteoarthritis. Announced in August 2020, the trial found no statistically significant difference between any UBX0101 dose arm and placebo at the 12-week primary endpoint, a result the company attributed partly to an unusually strong placebo response, and Unity subsequently discontinued the program. We think this distinction matters for researchers evaluating the senolytic field broadly: a single senolytic candidate's clinical setback does not necessarily generalize to mechanistically unrelated senolytic peptides such as FoxO4-DRI, which has followed an entirely separate, still-preclinical academic research track rather than a company-sponsored clinical development program.

At Verified Peptides, we sell research-grade FoxO4-DRI exclusively for laboratory and preclinical research use, consistent with its current, entirely investigational status.

FoxO4-DRI occupies an unusual place among research peptides because it was rationally designed as a peptide-based competitive inhibitor of a specific, previously mapped protein-protein interaction, rather than discovered in nature or found through untargeted screening. This "designed-to-order" origin is relatively rare among the compounds in this catalog and reflects a broader trend in peptide therapeutics toward engineering peptides against structurally characterized targets rather than relying solely on natural peptide discovery.

The peptide's cell-penetrating capability comes from a well-established biological tool rather than a novel discovery: the HIV-TAT-derived sequence (RRRQRRKKRG) fused to its C-terminus is the same class of cell-penetrating peptide sequence, derived from the HIV-1 transactivator of transcription (TAT) protein, widely used across peptide and protein research to help otherwise membrane-impermeable cargo cross into cells. Its inclusion in FoxO4-DRI is a practical engineering solution to a common problem in peptide-based research tools: getting a peptide designed to act on an intracellular target actually into the cell.

FoxO4-DRI's "selectivity" for senescent cells is not absolute in the sense of the peptide recognizing senescent cells directly — it does not distinguish cell types on contact. Instead, its selectivity is a consequence of the FOXO4-p53 sequestration mechanism itself being specific to senescent cells; because non-senescent cells do not have the same FOXO4-p53 dependency propping up their survival, releasing p53 in those cells has comparatively little effect. This distinction matters for researchers designing experiments, since the peptide's behavior in a given tissue depends heavily on the local proportion and biology of senescent versus non-senescent cells present.

Despite substantial preclinical research momentum since 2017 — spanning cartilage, reproductive, and endothelial tissue research contexts, and a 2025 structural refinement of its p53-binding mechanism — FoxO4-DRI has not been picked up for human clinical development in the same way the dasatinib-plus-quercetin small-molecule combination has, illustrating how a well-characterized, mechanistically elegant peptide does not automatically translate into a faster path to clinical trials than a less targeted, small-molecule alternative.

At Verified Peptides, we require independent third-party HPLC purity testing and mass spectrometry identity confirmation for every batch of research-grade FoxO4-DRI we offer, with a Certificate of Analysis (COA) available for each lot. As a 46-residue, all-D-amino-acid peptide, FoxO4-DRI is considerably more complex to synthesize than most standard L-amino-acid research peptides, and rigorous purity verification is correspondingly more important for ensuring consistent, reproducible experimental results.

We source exclusively from manufacturers operating under Good Manufacturing Practice (GMP)-aligned quality systems, and every lot is independently verified before being offered for sale rather than relying solely on a supplier's own internal documentation. Given the peptide's unusual D-retro-inverso construction, researchers should pay particular attention to confirming stereochemical identity via mass spectrometry, not simply overall amino acid composition, since a peptide with the correct composition but incorrect D/L stereochemistry would not be expected to retain the intended FOXO4-mimicking activity.

Researchers should always request and review the specific COA for the lot they receive, checking confirmed purity percentage and verified molecular identity, before use in any experimental protocol involving senescent-cell research models.

Lyophilized FoxO4-DRI is stable when stored at -20°C, protected from light and moisture, and researchers can generally expect the unreconstituted peptide to maintain integrity over an extended period under these conditions. At Verified Peptides, we ship lyophilized peptide with appropriate cold-chain packaging to preserve stability in transit.

Once reconstituted with sterile water or an appropriate diluent, FoxO4-DRI solution should be stored refrigerated at 2–8°C and used within the timeframe indicated on the product's documentation. Notably, the peptide's D-retro-inverso construction confers meaningfully greater resistance to enzymatic protease degradation than a comparable L-amino-acid peptide of similar length, which is one of the specific design advantages of the retro-inverso approach — but this protease resistance does not eliminate ordinary physical and chemical degradation risks from heat, light, or repeated freeze-thaw cycling.

Researchers should avoid repeated freeze-thaw cycles of reconstituted material and should aliquot solutions where practical to minimize how many times any single vial is thawed. Following the specific storage guidance provided with each lot's documentation remains the most reliable way to preserve a sample's research validity.