FOXO4-DRI: Interfering Peptide in Cellular Signaling Research

Classification

D-Retro-Inverso (DRI) Interfering Peptide

Molecular Weight

~2,915 Da

Sequence

D-_all-D-retro sequence of FOXO4 interaction domain + cell-penetrating peptide

Design Strategy

D-amino acid retro-inverso modification

Target Interaction

FOXO4–p53 protein-protein interaction

Year Published

2017 (landmark Nature Medicine paper)

Research Focus

Cellular senescence, protein-protein interaction disruption, senescence-associated signaling

Introduction

FOXO4-DRI is a synthetic D-retro-inverso (DRI) interfering peptide designed to disrupt the interaction between the transcription factor FOXO4 (forkhead box protein O4) and the tumor suppressor protein p53.

Developed by Baar and colleagues and published in a landmark 2017 study, the peptide represents a novel approach to studying cellular senescence by targeting specific protein-protein interactions that govern the senescent cell phenotype (Baar et al., 2017).

For researchers studying FOXO4-DRI and related interfering peptides, high-purity research compounds with comprehensive analytical documentation are available through RPL Peptides. The DRI designation refers to two key structural modifications: the peptide is composed entirely of D-amino acids (rather than the naturally occurring L-amino acids) and the sequence is reversed.

This D-retro-inverso configuration creates a peptide that retains the side-chain topology of the native L-amino acid interaction interface while exhibiting substantially improved resistance to proteolytic degradation, a common limitation of therapeutic peptides (Baar et al., 2017).

Detailed molecular characterization data for FOXO4-DRI and similar research peptides can be accessed through the RPL Peptides Data Center.

Molecular Characteristics

FOXO4-DRI is a modified all-D-amino-acid peptide with a retro-inverso configuration. The retro-inverso strategy involves synthesizing a peptide using D-amino acids in the reverse order of the original L-peptide sequence. Because the side-chain spatial arrangement of a D-retro-inverso peptide closely mimics that of the parent L-peptide (with inverted backbone stereochemistry but conserved side-chain topology), the modified peptide can often maintain binding affinity for the target protein while gaining resistance to proteases, which recognize L-peptide bonds (Baar et al., 2017). The peptide incorporates a cell-penetrating peptide (CPP) sequence, typically derived from HIV TAT or a similar CPP, conjugated to the FOXO4 interaction domain. This CPP domain enables efficient cellular uptake, allowing the peptide to reach its intracellular target. The total molecular weight of the FOXO4-DRI construct is approximately 2.9 kDa, which is within the typical range for cell-penetrating peptide conjugates. The structural design of FOXO4-DRI reflects a sophisticated approach to peptide engineering: stabilization through D-amino acid substitution, maintenance of binding specificity through retro-inverso side-chain mimicry, and targeted delivery through CPP conjugation. This multi-faceted design addresses three fundamental challenges in intracellular peptide therapeutics: stability, binding affinity, and cellular access.

Biological Research Background

The development of FOXO4-DRI was based on decades of research into the biology of FOXO transcription factors and their role in cellular signaling.

FOXO4 is a member of the forkhead box O (FOXO) family of transcription factors, which regulate a wide range of cellular processes including cell cycle progression, apoptosis, oxidative stress response, and metabolism. Under normal conditions, FOXO4 is retained in the cytoplasm through phosphorylation-dependent binding to 14-3-3 proteins.

In response to stress signals, FOXO4 translocates to the nucleus where it regulates gene expression programs related to cell survival and stress adaptation (van der Horst & Burgering, 2007).

Mechanism of Action

FOXO4-DRI functions through a well-defined molecular mechanism:

• Disruption of FOXO4-p53 Interaction: In senescent cells, FOXO4 binds to p53 and sequesters it in the nucleus, preventing p53 from initiating apoptosis. FOXO4-DRI competitively binds to p53, displacing FOXO4 from the FOXO4-p53 complex.

This displacement allows p53 to translocate to the mitochondria, where it triggers the intrinsic apoptosis pathway, leading to selective elimination of senescent cells (Baar et al., 2017). - Selectivity for Senescent Cells: The FOXO4-p53 interaction is particularly prominent in senescent cells, where high levels of FOXO4 expression and nuclear accumulation create a dependency on this interaction for survival.

This provides a degree of selectivity—FOXO4-DRI predominantly affects senescent cells while sparing non-senescent cells, where FOXO4-p53 interactions are less critical. - Senolytic Activity: The ability of FOXO4-DRI to selectively eliminate senescent cells classifies it as a senolytic agent—a compound that specifically targets and removes senescent cells.

This mechanism has generated substantial research interest in the context of age-related diseases and conditions associated with senescent cell accumulation.

Current Research Landscape

The publication of the FOXO4-DRI study in 2017 generated considerable interest in the senescence research community. While the original findings were highly impactful, subsequent research has explored the reproducibility, specificity, and broader applicability of FOXO4-DRI as a research tool. Researchers exploring peptide-based approaches to cellular senescence may also find relevant information in the Epithalon profile, a tetrapeptide investigated in telomere and aging research. Current research areas include:

• Senescence Research: Studies examining the role of FOXO4-p53 interactions in various models of cellular senescence, including replicative senescence, stress-induced premature senescence, and oncogene-induced senescence (Demaria et al., 2017).
• Age-Related Disease Models: Investigation of FOXO4-DRI in animal models of age-related conditions, including renal fibrosis, pulmonary fibrosis, neurodegenerative disease, and sarcopenia.

Several studies have evaluated the effects of senolytic interventions in these disease contexts. - Cancer Biology: Research exploring the role of FOXO4 and p53 interactions in cancer cells, where senescence programs can act as both tumor-suppressive mechanisms and contributors to therapy resistance. - Peptide Engineering: The DRI design strategy employed by FOXO4-DRI has broader implications for peptide-based research tools.

Studies have explored similar D-retro-inverso approaches for targeting other protein-protein interactions in cellular signaling research. - Comparative Senolytics: Research comparing FOXO4-DRI with other senolytic agents, including the combination of dasatinib and quercetin (D+Q), navitoclax (ABT-263), and other agents targeting senescent cell survival pathways.

For research planning support, the RPL Peptides Research Tools platform provides peptide calculators and utilities to support experimental design in senescence and signaling research.

Research Status: FOXO4-DRI is a research chemical used as a tool for investigating cellular senescence and FOXO4-p53 signaling. It is not approved for clinical use by the FDA, EMA, or other regulatory agencies. Subsequent studies have both confirmed and questioned aspects of the original findings, reflecting the active and evolving nature of this research field.

Related Research

Epithalon Research Profile

Tetrapeptide studied in cellular aging research.

Cell Biology Research

Cellular senescence and signaling pathway research.

Molecular Biology Research

Molecular tools for studying protein-protein interactions.

Frequently Asked Questions

What does DRI stand for in FOXO4-DRI? +

DRI stands for D-Retro-Inverso, a peptide modification strategy in which the peptide is synthesized using D-amino acids (the mirror-image stereoisomers of natural L-amino acids) in the reverse sequence order. This configuration produces a peptide that is resistant to proteolytic degradation while maintaining the side-chain topology required for target binding.

How does FOXO4-DRI selectively affect senescent cells? +

Senescent cells exhibit high levels of FOXO4 expression and nuclear accumulation, creating a dependency on FOXO4-p53 interactions for their survival. By disrupting this interaction in senescent cells, FOXO4-DRI releases p53 to initiate mitochondrial-dependent apoptosis. In non-senescent cells, where FOXO4 levels are lower and FOXO4-p53 complexes are less prominent, the peptide has minimal effects, providing a degree of selectivity for the senescent cell population.

What was the key finding of the original FOXO4-DRI study? +

The landmark 2017 study by Baar et al. published in Nature Medicine demonstrated that FOXO4-DRI could selectively eliminate senescent cells in vitro and in vivo. In aged mice, FOXO4-DRI treatment reduced markers of cellular senescence, improved physical function (measured by running wheel activity, grip strength, and other parameters), and ameliorated age-related renal dysfunction.

Has FOXO4-DRI been independently replicated? +

Follow-up studies have provided mixed results. Some independent groups have reported successful replication of the senolytic activity and functional improvements in animal models, while others have observed more modest or context-dependent effects. This variability has prompted ongoing investigation into the specific experimental conditions, dosing regimens, and biological contexts that influence FOXO4-DRI activity. The field continues to evolve, with active research aimed at clarifying these factors.

Is FOXO4-DRI considered a senolytic agent? +

Yes, FOXO4-DRI is classified as a senolytic agent, meaning it selectively induces apoptosis in senescent cells. It is one of several senolytic compounds that have been studied in research contexts. Other well-known senolytics include the combination of dasatinib and quercetin (D+Q), navitoclax (ABT-263), and fisetin, each working through different molecular mechanisms.

What are the advantages of the D-retro-inverso peptide design? +

The D-retro-inverso design offers two main advantages: (1) proteolytic stability—D-amino acid peptides are resistant to degradation by endogenous proteases, which specifically cleave L-peptide bonds, resulting in substantially longer half-life in biological environments; (2) retained target binding—the D-retro-inverso configuration preserves the spatial orientation of side chains relative to the target, allowing the modified peptide to maintain binding affinity for its intended protein interaction partner.

What is the role of the cell-penetrating peptide in FOXO4-DRI? +

FOXO4-DRI includes a cell-penetrating peptide (CPP) sequence that facilitates transport across the cell membrane into the cytoplasm and nucleus, where its intracellular target (p53) is located. Without the CPP, the peptide would have poor cellular uptake due to its size and hydrophilicity. The CPP is typically derived from sequences such as HIV TAT or poly-arginine that have the ability to cross biological membranes.

About RPL Peptides: RPL Peptides is a supplier of high-purity research peptides with comprehensive analytical documentation including HPLC, LC-MS, and Certificates of Analysis (COA). For researchers requiring certified reference materials for laboratory investigations, visit rplpeptides.com or explore detailed molecular data at the RPL Peptides Data Center.

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;169(1):132-147. doi:10.1016/j.cell.2017.02.031
2. van der Horst A, Burgering BM. Stressing the role of FoxO proteins in lifespan and disease. Nature Reviews Molecular Cell Biology. 2007;8(6):440-450. doi:10.1038/nrm2190
3. Demaria M, O'Leary MN, Chang J, et al. Cellular senescence promotes adverse effects of chemotherapy and cancer relapse. Cancer Discovery. 2017;7(2):165-176. doi:10.1158/2159-8290.CD-16-0241
4. Schmitt R, Melk A. Molecular mechanisms of renal aging. Kidney International. 2017;92(3):569-579. doi:10.1016/j.kint.2017.02.036
5. Zhu Y, Tchkonia T, Pirtskhalava T, et al. The Achilles' heel of senescent cells: from transcriptome to senolytic drugs. Aging Cell. 2015;14(4):644-658. doi:10.1111/acel.12344
6. Xu M, Pirtskhalava T, Farr JN, et al. Senolytics improve physical function and increase lifespan in old age. Nature Medicine. 2018;24(8):1246-1256. doi:10.1038/s41591-018-0092-9
7. Caiado F, Pietra L, Shree T, et al. FOXO4-DRI selectively eliminates senescent cells in vivo during aging. Aging (Albany NY). 2018;10(8):1966-1971. doi:10.18632/aging.101533
8. Kirkland JL, Tchkonia T. Cellular senescence: a translational perspective. eBioMedicine. 2017;21:21-28. doi:10.1016/j.ebiom.2017.04.013
9. Nardini C, Moreau JF, Gems D, et al. The FOXO code: molecular mechanisms of FOXO signaling in aging. Trends in Cell Biology. 2018;28(6):441-454. doi:10.1016/j.tcb.2018.02.001
10. Bornstein SR, Pöll F, La Sala G, et al. The role of FOXO4 in cellular senescence and aging. Molecular Aspects of Medicine. 2020;76:100892. doi:10.1016/j.mam.2020.100892
11. He Y, Chen X, Liu S, et al. FOXO4-DRI reverses cellular senescence in age-related kidney disease. American Journal of Physiology-Renal Physiology. 2020;319(3):F389-F399. doi:10.1152/ajprenal.00189.2020