FOXO4-DRI storage and stability start from its design. It is a retro-inverso all-D peptide, so proteases barely touch it, but chemistry still does. Keep the sealed powder cold, dark and desiccated, and warm the vial before opening. Moisture and adsorption to glass cause most of the losses.
- FOXO4-DRI is a retro-inverso all-D peptide, which confers protease resistance and no protection at all against hydrolysis, deamidation or oxidation.
- Gross vial weight commonly overstates peptide mass by ten to twenty-five percent because of trifluoroacetate counterion and bound water.
- The strongly cationic sequence adsorbs to glass and untreated plastic, producing apparent potency loss that no HPLC trace of the powder will reveal.
- Condensation on a cold vial opened straight from the freezer is the most common avoidable handling error and leaves no visible trace.
- No regulator has approved FOXO4-DRI; the compound is unscheduled in the United States, which says nothing about lawful use in people.
What is FOXO4-DRI, and why does that change the storage question?
FOXO4-DRI is a retro-inverso peptide. The sequence runs in reverse and every residue is the D enantiomer, an arrangement that approximately preserves the spatial presentation of the side chains while giving a backbone that mammalian proteases largely ignore. Baar and colleagues described the construct in Cell in 2017 as a tool for interfering with the FOXO4 interaction with p53 in senescent cells, and most material in circulation traces back to that design.
It is a long peptide by solid-phase synthesis standards, in the region of forty to fifty residues, and it carries a strongly basic segment that gives the molecule its cell entry behavior and a high net positive charge at neutral pH. Suppliers do not all sell an identical construct. Some list a free acid C-terminus, some an amide; some append or truncate the import segment. Read the sequence printed on the certificate of analysis and check it against what your protocol assumes before you plan anything else around it.
The protease resistance is the part that gets over-read. Stability toward enzymatic cleavage is a statement about enzymes. It says nothing about hydrolysis, deamidation, oxidation or moisture uptake, none of which have any preference for one enantiomer over the other. A damp vial of FOXO4-DRI degrades on much the same schedule as an L-peptide of comparable composition.
- Moisture — condensation on a cold vial, plus a hygroscopic TFA counterion
- Adsorption — cationic sequence against anionic glass, worst when dilute
- Counterion mass — gross weight is not peptide weight
- Oxygen and light — Met and Trp, if your construct has them
- Deamidation at Asn-Gly, driven by water and warmth
Which degradation routes do D-amino acids leave untouched?
Non-enzymatic degradation of peptides is well mapped, and the routes that matter for a given sequence follow from the residues it contains. Butreddy and colleagues surveyed the stresses and mechanisms for lyophilized peptide and protein material in 2020; that review is still a serviceable map. What follows applies the general picture to the features FOXO4-DRI actually has.
| Route | Driver | Sequence feature at risk | Control |
|---|---|---|---|
| Backbone hydrolysis | Water activity, temperature, extremes of pH in solution | Any amide bond; Asp-Pro and Asp-Gly are faster | Keep the solid dry and sealed against desiccant |
| Deamidation and isoaspartate formation | Water, temperature, pH above roughly 6 | Asn and Gln, with Asn-Gly the fastest motif | Dry storage; cold |
| Oxidation | Headspace oxygen, light, trace iron and copper | Met, Trp, Cys if present in your construct | Dark storage, minimal headspace, metal-free water |
| Disulfide scrambling | Oxygen, neutral to alkaline pH | Only constructs containing Cys | Check the certificate; if Cys is present, treat pH and air as variables |
| Moisture uptake | Ambient humidity, cold surfaces, hygroscopic counterion | The whole cake | Equilibrate before opening; reseal fast |
| Surface adsorption | Contact with borosilicate glass and untreated plastic | Arg and Lys side chains against anionic surfaces | Low-binding polypropylene; document container choice |
Aggregation sits lower on this list than it does for a lipidated peptide. Strong net positive charge keeps monomers repelling each other in dilute aqueous solution, which is helpful. It also means the peptide sticks to almost everything else, which is the subject of a later section.
Nothing on that table is switched off by D-stereochemistry. The first entry in a scan of your own sequence should be for Asn-Gly, Met and Trp, because those three tell you whether deamidation and oxidation are theoretical concerns or live ones for the exact material in the vial.
What do counterion and net peptide content mean for the gross weight?
FOXO4-DRI is purified by reversed-phase HPLC in trifluoroacetic acid, and trifluoroacetate ends up paired with every protonated basic side chain. For an arginine-rich sequence that is a substantial fraction of what you weigh. Between the counterion and bound water, gross vial mass commonly overstates peptide mass by ten to twenty-five percent, occasionally more on a poorly dried lot.
A certificate that reports only chromatographic purity has not told you this. Purity by RP-HPLC at 214 nm is a statement about how much of the peptide-absorbing material in the sample is the target; net peptide content is a statement about how much of the powder is peptide at all. They are different numbers and a competent supplier reports both, with net content determined by amino acid analysis or nitrogen determination rather than assumed.
Residual TFA has a second consequence. It is hygroscopic, so a high-TFA lot picks up atmospheric water faster than a well-exchanged one. It is also documented to affect cell viability and proliferation in culture at residual levels that occur in ordinary synthesis-grade material, which is why acetate or hydrochloride salt exchange is offered for cell-based work. If your assay is cellular and your controls are behaving oddly, the counterion is worth ruling out before the peptide is.
How should FOXO4-DRI storage change by physical state?
| State | Temperature | Light | Relative horizon | Reasoning |
|---|---|---|---|---|
| Sealed powder, archive stock | Minus 80 °C, desiccated | Dark | Longest | All chemical routes slowed; water excluded |
| Sealed powder, working vial | Minus 20 °C, desiccated | Dark | Long | Adequate where openings are few and controlled |
| Powder in transit | Ambient, insulated | Dark | Days | Dry solid tolerates short excursions; solution does not |
| DMSO stock | Minus 20 °C, tightly capped | Dark | Variable | DMSO is hygroscopic; water ingress restarts hydrolysis |
The horizons are relative on purpose. Putting a month count against a research powder requires a stability study on that lot, in that container, under those conditions, which is what ICH Q1A(R2) sets out for regulated material and what almost no research supplier has done. Where a certificate carries a date, that date is the one to honor. Where it does not, the honest record says the window is unestablished and the material is monitored by re-analysis rather than by calendar.
Why is opening a cold vial where most material is lost?
A vial pulled from a minus twenty freezer into a room at 22 °C and moderate humidity is far below the dew point. Water condenses on the glass, and the moment the seal is broken it condenses inside as well. A lyophilized cake takes that water up on contact, and a cake sitting on a trifluoroacetate salt takes it up eagerly.
Nothing about this is visible. A slightly damp cake looks like a dry one, the vial goes back to the freezer with water now sealed inside it, and the next person repeats the cycle. Three or four rounds of that will do more to a peptide than a year of properly desiccated storage at any temperature you choose.
The control is dull and works. Let the sealed vial reach room temperature on the bench before breaking the seal, every time. Twenty to thirty minutes suits a small vial. Weigh promptly, reseal with the desiccant, and if your protocol logs excursions, log this one too. Where a vial is opened repeatedly, dispensing the whole contents into single-use portions on the first opening is better practice than returning to the same vial six times.
How does adsorption pass for a failed experiment?
Borosilicate glass presents a negatively charged silanol surface. A peptide carrying a run of arginines carries the complementary charge. At low micromolar concentrations and below, a meaningful fraction of the peptide can end up on the wall of the tube rather than staying in solution, and the effect is worst in exactly the dilute conditions where quantification matters most.
The symptom is not degradation. It is a dose-response curve that shifts between operators, a signal that seems weaker than expected, or a result that fails to reproduce when someone switches tube brands. None of that shows up on an HPLC trace of the original powder, because the powder was fine.
What should the record say?
A storage practice that is not written down cannot be reproduced by anyone else, including yourself in six months. The minimum record for a vial of FOXO4-DRI carries the source lot identifier, the certificate's purity and net peptide content figures, the container material, the date received and the initials of the person who checked it.
The reason is diagnostic rather than administrative. When a result comes out wrong, the first question is whether the material was what the protocol assumed it was. A chain that runs from sample to vial to lot to certificate answers that in a minute. A chain with a gap in it means repeating the experiment, and there is a reasonable chance of repeating the same error. What a certificate should contain, and how to read one that is thin, is covered in the quality standard.
This page stops at the sealed vial.
How do you handle a vial, step by step?
- Keep archive stock as sealed powder at minus 80 °C, desiccated and dark. A working vial can sit at minus 20 °C where openings are few and controlled.
- Let the sealed vial reach room temperature on the bench before breaking the seal. Twenty to thirty minutes suits a small vial.
- Work promptly once it is open, then reseal with the desiccant.
- If the vial will be opened repeatedly, dispense the whole contents into single-use portions on the first opening.
- Record the lot, net peptide content, container, date and initials.
What is the regulatory position?
FOXO4-DRI has no marketing authorization from the FDA, the EMA or any comparable regulator. It has not been through human clinical trials as a licensed product, and published work with the construct is preclinical, principally the 2017 Cell report and subsequent laboratory studies building on it. There is no approved formulation, no established human exposure record, and no pharmaceutical quality system behind research-grade supply.
The material is not a controlled substance in the United States, which is a statement about scheduling and nothing more. Unscheduled and unapproved are compatible; the absence of a control listing carries no implication about safety or lawful use in people. Research-grade FOXO4-DRI is supplied for in-vitro laboratory work under a certificate of analysis covering identity and purity, which is a narrower claim than any medicine's label makes.
Status verified 26 August 2026.
FOR LABORATORY AND IN-VITRO RESEARCH USE ONLY. NOT FOR HUMAN OR ANIMAL CONSUMPTION. NOT FOR PERSONAL, MEDICAL, DIAGNOSTIC, THERAPEUTIC, OR RECREATIONAL USE.
Bottom line
FOXO4-DRI storage starts from one fact. The all-D backbone resists proteases and gives no protection against hydrolysis, deamidation or oxidation. Keep the powder cold, dark and desiccated, and warm the vial before opening it.
What is FOXO4-DRI studied for?
Published research on FOXO4-DRI investigates the areas below, which is a different question from what FOXO4-DRI will do for anyone, a claim about a living system that nothing on this site is sold for.
What it is. A D-retro-inverso peptide: a cell-penetrating peptide built from D-amino acids in reversed sequence order, designed to resist proteolysis while preserving the side-chain topology of the native FOXO4 sequence.
What the research looks at. Senescent cell clearance, doxorubicin-induced chemotoxicity, and fast-ageing and naturally aged mouse models.
How it is thought to work. Perturbs the interaction between FOXO4 and p53. In senescent cells this causes p53 nuclear exclusion and cell-intrinsic apoptosis — a senolytic mechanism that exploits how senescent cells specifically avoid dying.
What is not established. No human data, no approved product. The published in vivo work is explicitly qualified as being conducted under conditions where the peptide was well tolerated, which is itself a statement about a therapeutic window.
The full record, including the certificate for the lot in stock, is on the FOXO4-DRI product page.
Common questions
How should FOXO4-DRI be stored?
Does the all-D backbone make FOXO4-DRI more stable in storage?
Should FOXO4-DRI be stored at minus 20 or minus 80?
What should the certificate of analysis include for this compound?
More handling guides
Sources
- Baar et al., Cell, 2017. Original report of the FOXO4 D-retro-inverso peptide and its interference with the FOXO4–p53 interaction in senescent cells; supports the description of the construct, its all-D retro-inverso design and its preclinical status.
- Butreddy et al., International Journal of Biological Macromolecules, 2020. Review of stresses, degradation mechanisms and stabilization strategies for lyophilized peptide and protein material; supports the degradation-route table and the primacy of solid-state, desiccated storage.
- ICH Q1A(R2), Stability Testing of New Drug Substances and Products. Defines what a stability study must establish before a shelf life can be assigned; supports the position that undated research powder has an unestablished storage window.
- Cornish and colleagues. Trifluoroacetate, a contaminant in purified proteins, inhibits proliferation of osteoblasts and chondrocytes. American Journal of Physiology . Basis for treating residual trifluoroacetate as a real variable rather than an accounting detail: this paper measures inhibition of cell proliferation at trifluoroacetate concentrations that ride along with ordinary peptide salts.
