FOXO4-DRI (Proxofim)
FOXO4-DRI is a synthetic peptide designed as a retro-inverso analog of the FOXO4 transcription factor, in which natural L-amino acids are replaced with their D-enantiomers. This engineering significantly enhances half-life and proteolytic resistance, extending biological activity in vivo. The key mechanism consists of competitive interference with the binding between endogenous FOXO4 and the p53 protein—a main regulator of the cell cycle and apoptosis. The FOXO4–p53 interaction is essential to maintain the vitality of senescent cells; by inhibiting it, FOXO4-DRI reactivates apoptosis in non-proliferative cells, allowing their selective elimination without damaging healthy tissue. [1]
Preclinical Results: Removal of Senescence and Functional Restoration
In animal models, the administration of FOXO4-DRI has produced a significant reduction of the senescent cell load in treated tissues, accompanied by the restoration of functional integrity in organs such as the kidneys, liver, and skin. In aged mice, “youthful” phenotypic traits reappeared: greater physical activity, improved cognitive performance, and increased fur density. These outcomes, although not necessarily implying an increase in lifespan, are associated with an extension of the healthspan, defined as the period of life spent in good health. [1]
Further experiments indicate that the peptide suppresses pro-inflammatory and fibrogenic factors characteristic of the senescence-associated secretory phenotype (SASP), helping to recondition the damaged tissue microenvironment. In models of pathological scarring (e.g., keloids), FOXO4-DRI promoted apoptosis of resistant senescent fibroblasts and reduced proliferation in G0/G1, demonstrating senolytic potential useful in dermatology, regenerative medicine, and other degenerative conditions. [2]
Retro-inverso (DRI) Peptides: Definition and Limits
Retro-inverso peptides (or DRI) have a reversed sequence and are composed of D-amino acids, mirror images of natural L-amino acids. This architecture “mimics” the spatial conformation of the native peptide but offers greater enzymatic resistance, prolonged activity, and often lower immunogenicity. They are promising candidates when the target is a protein–protein interaction. However, the retro-inverso approach may not faithfully reproduce biological function in helical structures (e.g., p53 or HIV-1 proteins); nonetheless, there are exceptions (e.g., D-peptides derived from p53 active on MDM2) that show how accurate design can maintain affinity and function in specific contexts. [3]
FOXO4-DRI, Aging, and Cellular Senescence
The relationship between FOXO4 and aging is complex, but evidence indicates a key role in the control of longevity, stress resistance, and genomic integrity. FOXO4 belongs to the FOXO family (FOXO1/3/4/6), conserved through evolution and long associated with aging pathways. A crucial aspect is its involvement in the insulin/IGF pathway, which regulates metabolism, cell cycle, and apoptosis. In C. elegans, different FOXO isoforms, especially DAF-16A, extend lifespan by modulating genes such as gst-20 and srr-4, linked to pro-longevity mechanisms. [4]
FOXO4 affects not only lifespan but also the quality of aging through its interaction with p53, the “guardian of the genome.” This dialogue determines whether a cell remains in a senescent, metabolically active state or undergoes apoptosis. Senolytics such as FOXO4-DRI selectively disrupt the FOXO4–p53 interaction, enabling the targeted elimination of dysfunctional cells. The “therapeutic rejuvenation” thus induced improves tissue homeostasis and opens prospects for extending healthspan and preventing age-related diseases. [5][6]
Insulin Signaling and Metabolic Homeostasis
FOXO factors (FOXO1/3/4/6) are central mediators of insulin/IGF signals and participate in the regulation of metabolism, growth/differentiation, oxidative stress response, autophagy, and senescence. Genetic or expression alterations in FOXO are associated with type 2 diabetes, insulin resistance, cancer, and neurodegeneration. Among these, FOXO6 stands out for tissue-specific expression (liver, muscle, CNS) and relation to fasting hyperglycemia and hyperlipidemia. In this context, selective modulation strategies of FOXO—including peptide analogs such as FOXO4-DRI—appear promising for correcting downstream pathways and alleviating metabolic complications. [7]
Heart, Proteostasis, and Age-Related Decline
With aging, the myocardium shows a decline in proteasomal activity, favoring the accumulation of oxidized/ubiquitinated proteins and increasing vulnerability to cardiovascular diseases. Mouse and rat models show a reduction in the 20S proteasome with alterations in quantity and composition. FOXO factors, including FOXO4, regulate autophagy and the proteasome: their increase is associated with greater cellular “housekeeping” and less accumulation of damaged proteins. Modulating the FOXO4–p53 axis and senescence with FOXO4-DRI could theoretically support cardiac proteostasis and mitigate functional decline. [8][9]
Neurodegeneration: Proteostasis and the Role of FOXO
In cognitive aging, malfunction of the ubiquitin–proteasome system is often involved: dysfunctions have been detected in Alzheimer’s, Parkinson’s, Huntington’s, prion diseases, and ALS. Whether this is cause or effect remains open, but reduced proteasomal activity promotes toxic protein aggregation and damage progression. FOXO factors, subject to multiple post-translational modifications (phosphorylation, acetylation, ubiquitination, etc.), can have neuroprotective or, if deregulated, detrimental effects. The experimental use of exogenous forms such as FOXO4-DRI is being explored as a potential means to slow the progression of neurodegenerative diseases, complementing approaches that restore proteostasis, reduce oxidative stress, and limit glial senescence. [10][11]
Format and Research Use
FOXO4-DRI is supplied as a peptide for research use only. Applications concern the study of senescence, SASP, tissue regeneration, metabolism, cardiovascular, and neurodegeneration. Any use is limited to experimental contexts; it is not intended for diagnosis, treatment, or human/animal consumption. Handling, solubilization, and storage must follow internal procedures and regulatory standards applicable to research materials.
Scientific References
- [1] Baar MP, et al. Targeted apoptosis of senescent cells restores tissue homeostasis in response to chemotoxicity and aging. Cell. 2017;169(1):132–147.e16.
- [2] Kong YX, et al. FOXO4-DRI induces keloid senescent fibroblast apoptosis. 2025.
- [3] Li C, et al. Limitations of peptide retro-inverso isomerization in molecular mimicry. J Biol Chem. 2010;285(25):19572–19581.
- [4] Chen AT-Y, et al. Longevity genes revealed by integrative analysis of isoform-specific daf-16/FoxO mutants of C. elegans. Genetics. 2015;201(2):613–629.
- [5] Krimpenfort P, Berns A. Rejuvenation by therapeutic elimination of senescent cells. Cell. 2017;169(1):3–5.
- [6] Senescence and aging: causes, consequences, and therapeutic avenues. J Cell Biol. 2018;217(1):65–77.
- [7] Lee S, Dong HH. FoxO integration of insulin signaling with glucose and lipid metabolism. J Endocrinol. 2017;233(2):R67–R79.
- [8] Bulteau A-L, Szweda LI, Friguet B. Age-dependent declines in proteasome activity in the heart. Arch Biochem Biophys. 2002;397(2):298–304.
- [9] Murtaza G, et al. FOXO transcriptional factors and long-term living. Oxid Med Cell Longev. 2017.
- [10] Ciechanover A, Brundin P. The ubiquitin-proteasome system in neurodegenerative diseases. Neuron. 2003;40(2):427–446.
- [11] Hu W, et al. Roles of FoxO transcription factors in neurodegenerative diseases. Prog Neurobiol. 2019;181:101645.
