FOXO4-DRI

FOXO4-DRI is a synthetic 45-residue peptide (sequence LTLRKEPASEIAQSILEAYSQNGWANRRSGGKRPPPRRRQRRKKRG) corresponding to the reversed, all-D-amino-acid (D-retro-inverso) version of the FOXO4 segment that contacts the tumor-suppressor protein p53, fused to an arginine-rich cell-penetrating segment. It does not occur naturally; it is laboratory-synthesized. The peptide was introduced by Baar et al. (Cell, 2017) from work at Erasmus University Medical Center as a tool to disrupt the FOXO4–p53 interaction in cellular-senescence research. The D-retro-inverso design — reversing the sequence and substituting every residue with its mirror-image D-enantiomer — is a peptide-engineering strategy intended to raise resistance to proteolytic breakdown while preserving the spatial arrangement of side chains.

The mechanistic premise comes from the FOXO4–p53 axis. Baar et al. (2017) described FOXO4 as interacting with p53 and influencing its subcellular localization in senescent cells, with the DRI peptide studied as a competitive disruptor of that interaction. A review by Bourgeois and Madl (FEBS Letters, 2018) surveys the FOXO4–p53 axis, framing both as transcription factors that converge on the regulation of cellular senescence and the senescence-associated gene p21. The wider FOXO/p53 transcription-factor biology has been examined in cell-cycle, apoptosis, and DNA-damage-response contexts.

A substantial structural literature has mapped how FOXO4 and p53 engage one another and where the DRI peptide binds. Kim et al. (FEBS Journal, 2022) used NMR spectroscopy to describe dual binding surfaces between the FOXO4 forkhead domain and the p53 transactivation domain, and between FOXO4's C-terminal region and the p53 DNA-binding domain. Mandal et al. (Protein Science, 2022) characterized how FOXO4 contacts the p53 transactivation domain and C-terminal regulatory domain and reported that complex formation can block p53 binding to DNA. Kohoutova et al. (Nature Communications, 2025) used NMR-data-driven simulations to describe the structural plasticity of the FOXO-DBD:p53-TAD interaction and multiple binding modes. Bourgeois et al. (Nature Communications, 2025) solved solution-NMR structural models of the p53 transactivation domain in complex with both the FOXO4 forkhead domain and FOXO4-DRI, reporting that the disordered peptide binds the disordered p53 transactivation domain in a transiently folded complex and that p53 phosphorylation modulates the measured affinity.

FOXO4-DRI is studied within the broader senolytics field, which examines tools that selectively induce apoptosis in senescent cells. Reviews place it in this landscape alongside small-molecule senolytics (Gorgoulis et al., Cell, 2019; Chaib, Tchkonia & Kirkland, Nature Medicine, 2022). Le et al. (eBioMedicine, 2021) used molecular modelling of the FOXO4–p53 interface to design a series of rationally engineered peptides — including one designated ES2 — and examined disruption of FOXO4–p53 nuclear foci and p53-mediated apoptosis endpoints in senescent human cancer-cell cultures and orthotopic mouse models.

Independent groups have examined the peptide across several model systems, measuring senescent-cell viability, apoptosis, and p53 localization endpoints. Huang et al. (Frontiers in Bioengineering and Biotechnology, 2021) examined in-vitro-expanded human chondrocyte cultures, comparing effects on viability between higher- and lower-passage cells. Zhang et al. (Aging, 2020) studied senescent Leydig-cell populations in a naturally aged mouse model, measuring p53 nuclear exclusion and apoptosis endpoints. Han et al. (Journal of Cellular and Molecular Medicine, 2022) examined a bleomycin-induced rodent pulmonary-fibrosis model with attention to fibroblast and extracellular-matrix endpoints. A keloid-fibroblast study (Communications Biology, 2025) measured apoptosis and cell-cycle distribution alongside p53-serine-15 phosphorylation and nuclear-exclusion endpoints. A later endothelial-cell study (Frontiers in Bioengineering and Biotechnology, 2026) examined senescent endothelial cultures with reference to the p53/BCL-2/Caspase-3 pathway.

Background context comes from FOXO transcription-factor biology more broadly. FOXO4 is a forkhead-box transcription factor whose DNA-binding (forkhead) domain and transactivation regions have been characterized by NMR; work on FOXO4–DNA recognition (Communications Biology, 2024) examined how the forkhead domain discriminates target from non-target DNA sequences. This literature establishes the domain architecture that the DRI peptide is designed to mimic and the structural framework within which the FOXO4–p53 interaction is interpreted.