{"id":68,"slug":"68-foxo4-dri-fragment-truncation-retain-only-the-foxo4-cr3-mimetic-n-term","title":"FOXO4-DRI fragment: minimal CR3 helix (1-23) without CPP tail to test core p53 engagement","status":"PENDING","fold_verdict":"DISCARDED","discard_reason":null,"peptide":{"name":"FOXO4-DRI","class":"LONGEVITY","sequence":"LTLRKEPASEIAQSILEAYSQNGWANRRSGGKRPPPRRRQRRKKRG","modified_sequence":"LTLRKEPASEIAQSILEAYSQNG","modification_description":"Fragment/truncation: retain only the FOXO4 CR3-mimetic N-terminal helix (residues 1-23, LTLRKEPASEIAQSILEAYSQNG) and remove the entire C-terminal cationic CPP tail (residues 24-46) plus the GG linker, yielding a clean 23-residue helix-only peptide for evaluating the intrinsic p53-binding interface."},"target":{"protein":"Cellular tumor antigen p53","uniprot_id":"P04637","chembl_id":"CHEMBL4096","gene_symbol":"TP53"},"rationale":{"hypothesis":"We hypothesize that the intrinsic p53-binding determinants of FOXO4-DRI are confined to the FOXO4 CR3-mimetic helix (residues 1-23), and that the disordered Arg/Lys/Pro-rich CPP tail (residues 24-46) introduces conformational noise that has consistently degraded structure-prediction confidence in prior folds (pLDDT 0.56-0.61). A minimal 23-residue helix-only construct should fold into a cleaner amphipathic helix and produce a more interpretable interface with the p53 transactivation domain (TAD2, residues 35-59).","rationale":"Prior FOXO4-DRI folds (#12, #27, #40) all included the long cationic tail and all failed at low pLDDT, suggesting the tail is the dominant source of structural disorder rather than a contributor to specific p53 contacts. The CR3 region of native FOXO4 is the documented p53-binding element, and isolating it removes a known confound for AlphaFold-family models, which struggle with high-charge low-complexity poly-Arg segments. This fold also diverges from the last 3 lab folds (Humanin disulfide staple/CONFORMATION, TB-500 D-amino acid/STABILITY, SS-31 non-canonical AA/AFFINITY) by combining a fresh focus (CONFORMATION via simplification) with a fresh category (Fragment/truncation), satisfying the rotation rule.","predicted_outcome":"We expect the 23-residue fragment to fold as a single well-defined amphipathic α-helix with substantially higher pLDDT (>0.70) than prior full-length attempts, and to dock its hydrophobic face (Leu-3, Ile-11, Ile-15, Leu-17, Tyr-19) against the p53 TAD2 acidic interface in co-folding with p53, providing the first interpretable structural readout of the FOXO4-p53 interface for this peptide series.","mechanism_class":null,"biohacker_use":null},"confidence":{"plddt":0.6078009009361267,"ptm":0.39452722668647766,"iptm":0.20455197989940643,"chai_agreement":null,"chai1_gated_decision":"RAN_BORDERLINE","binding_probability":null,"binding_pic50":null,"predicted_binding_change":null},"profile":{"aggregation_propensity":0.116,"stability_score":0.607,"bbb_penetration_score":0.085,"half_life_estimate":"moderate-to-long (~1–6 hours)"},"narrative":{"tldr":null,"detailed_analysis":null,"executive_summary":null,"tweet_draft":null,"research_brief_markdown":null,"structural_caption":"The 23-residue FOXO4 CR3-mimetic fragment was co-folded with p53 TAD2 (residues 35-59) by Boltz-2, yielding moderate intra-chain confidence (pLDDT 0.61) but very low interface confidence (ipTM 0.20, pTM 0.39). The peptide is plausibly modeled as a short helical segment, but the docking pose against the p53 TAD2 acidic interface is not supported by the ensemble. No affinity-module output was produced, and no Chai-1 model was available for cross-validation. The structure therefore does not provide an interpretable readout of the FOXO4-p53 interface.","key_findings_summary":"FOXO4-DRI is a D-retro-inverso peptide originally designed to disrupt the FOXO4–p53 interaction in senescent cells, thereby selectively inducing apoptosis in senescent populations across multiple tissue types. The biological rationale rests on the observation that FOXO4 binds p53 in the nucleus to suppress pro-apoptotic signaling, and that blocking this interaction with FOXO4-DRI restores p53-dependent apoptosis selectively in senescent cells (Zhang et al., 2020; Li et al., 2024; Hu et al., 2025). This senolytic activity has been validated in diverse contexts including Leydig cells, endothelial cells, chondrocytes, fibroblasts, and cancer-associated fibroblasts, consistently implicating the p53/BCL-2/caspase-3 axis downstream of FOXO4-DRI treatment.\n\nThe most directly relevant structural paper for the hypothesis is the 2025 NMR study by Bourgeois et al. (PMID:40593617), which provides solution-state structural models of the p53 transactivation domain (TAD) in complex with both the FOXO4 forkhead domain and with FOXO4-DRI itself. Critically, this paper reports that FOXO4-DRI is intrinsically disordered and binds to the disordered p53 TAD2 (residues ~35–59), forming a transiently folded complex. Strikingly, the authors demonstrate that **both** the FOXO4-derived N-terminal region (CR3-mimetic helix) **and** the C-terminal cationic cell-permeability peptide (CPP) tail contribute to the p53 interaction. This is a direct challenge to the hypothesis that the CPP tail is merely a passive delivery vehicle introducing conformational noise.\n\nThe preprint by Zhang et al. (2022, DOI:10.21203/rs.3.rs-2361374/v1) provides the most direct in silico and biophysical support for the hypothesis. Using computational hotspot mapping of the FOXO4-DRI sequence, the authors designed shorter peptides and demonstrated via biophysical assays that these truncated variants retained strong binding affinity to p53. They localized the binding hotspot to within the N-terminal FOXO4-derived region, suggesting the CR3-mimetic helix carries the primary p53-contact determinants. However, the preprint has not been formally peer-reviewed, and quantitative Kd values or explicit residue-level contact maps are not fully reported in the available abstract.\n\nRegarding the hypothesis about conformational noise: the Bourgeois et al. NMR study explicitly describes FOXO4-DRI as 'disordered' in solution, which is consistent with the low pLDDT scores (0.56–0.61) observed computationally. However, this disorder is characterized as a feature of the binding mechanism (coupled folding-upon-binding to the disordered p53 TAD2) rather than as a liability introduced by the CPP tail specifically. The hypothesis that removing the CPP tail will yield a 'cleaner amphipathic helix' and improve structure-prediction confidence is plausible given the polybasic/polyproline composition of residues 24–46, but the NMR evidence suggests the full-length peptide's disorder is intrinsic to its interaction mechanism with the disordered TAD2, not purely an artifact of the CPP tail. Whether a helix-only construct will genuinely fold into a stable amphipathic helix without the CPP tail remains to be demonstrated."},"structured":{"known_activity":null,"known_binders":null,"candidate_variants":null,"domain_annotations":null,"literature_context":{"pubmed":[{"pmid":"39994346","title":"FOXO4-DRI induces keloid senescent fibroblast apoptosis by promoting nuclear exclusion of upregulated p53-serine 15 phosphorylation.","abstract":"Keloids are pathological scars exhibiting tumour-like aggressiveness and high recurrence rate. Here we find increased proportion of pro-inflammatory and mesenchymal fibroblast subpopulations and senescent fibroblasts, and enhanced expression of senescence-associated secretory phenotype genes using single-cell RNA sequencing analysis, as well as elevated p16 protein and more β-galactosidase-positive cells in keloids. The up-regulated p53-serine15 phosphorylation (p53-pS15) in keloids is identified by phosphospecific protein microarray and western blotting. We further demonstrate that a senolytic FOXO4-D-retro-inverso-isoform peptide (FOXO4-DRI) promotes apoptosis and decreases G0/G1 phase cells in pro-senescence models of keloid organ cultures and fibroblasts, accompanied with p53-pS15 nuclear exclusion. Our study indicates that upregulation of p53-pS15 and p16 maintains a persistent senescent microenvironment to promote cell cycle arrest and apoptosis resistance in keloid fibroblasts. FOXO4-DRI shows potential as a treatment targeting the senescence and apoptosis resistance, and holds promise as an approach to prevent the aggressiveness and relapse of keloids.","authors":["Kong Yu-Xiang","Li Zhi-Shuai","Liu Yuan-Bo","Pan Bo","Fu Xin","Xiao Ran","Yan Li"],"year":2025,"journal":"Communications biology"},{"pmid":"39025385","title":"FOXO4-DRI improves spermatogenesis in aged mice through reducing senescence-associated secretory phenotype secretion from Leydig cells.","abstract":"Male ageing is always accompanied by decreased fertility. The forkhead O (FOXO) transcription factor FOXO4 is reported to be highly expressed in senescent cells. Upon activation, it binds p53 in the nucleus, preventing senescent cell apoptosis and maintaining senescent cells in situ. Leydig cells play key roles in assisting spermatogenesis. Leydig cell senescence leads to deterioration of the microenvironment of the testes and impairs spermatogenesis. In this study, we observed that FOXO4-DRI, a specific FOXO4- p53 binding blocker, induced apoptosis in senescent Leydig cells, reduced the secretion of certain Senescence-Associated Secretory Phenotype and improved the proliferation of cocultured GC-1 SPG cells. In naturally aged mice, FOXO4-DRI-treated aged mice exhibited increased sperm quality and improved spermatogenesis.","authors":["Li Yanqing","Zhang Chi","Cheng Haicheng","Lv LinYan","Zhu Xinning","Ma Menghui","Xu Zhenhan","He Junxian","Xie Yun","Yang Xing","Liang Xiaoyan","Deng Chunhua","Liu Guihua"],"year":2024,"journal":"Experimental gerontology"},{"pmid":"31959736","title":"FOXO4-DRI alleviates age-related testosterone secretion insufficiency by targeting senescent Leydig cells in aged mice.","abstract":"Male late-onset hypogonadism is an age-related disease, the core mechanism of which is dysfunction of senescent Leydig cells. Recent studies have shown that elimination of senescent cells can restore proper homeostasis to aging tissue. In the present study, we found that the fork head box O (FOXO) transcription factor FOXO4 was specially expressed in human Leydig cells and that its translocation to the nucleus in the elderly was related to decreased testosterone synthesis. Using hydrogen peroxide-induced senescent TM3 Leydig cells as an in vitro model, we observed that FOXO4 maintains the viability of senescent Leydig cells and suppresses their apoptosis. By disrupting the FOXO4-p53 interaction, FOXO4-DRI, a specific FOXO4 blocker, selectively induced p53 nuclear exclusion and apoptosis in senescent Leydig cells. In naturally aged mice, FOXO4-DRI improved the testicular microenvironment and alleviated age-related testosterone secretion insufficiency. These findings reveal the therapeutic potential of FOXO4-DRI for the treatment of male late-onset hypogonadism.","authors":["Zhang Chi","Xie Yun","Chen Haicheng","Lv Linyan","Yao Jiahui","Zhang Min","Xia Kai","Feng Xin","Li Yanqing","Liang Xiaoyan","Sun Xiangzhou","Deng Chunhua","Liu Guihua"],"year":2020,"journal":"Aging"},{"pmid":"40593617","title":"The disordered p53 transactivation domain is the target of FOXO4 and the senolytic compound FOXO4-DRI.","abstract":"A central process contributing to the phenotype of aging is cellular senescence. We recently identified the FOXO4 - p53 axis as pivotal in maintaining the viability of senescent cells, and that senescent cells can be targeted selectively with the senolytic peptide FOXO4-DRI. Here, we solve the solution NMR structural models of the p53 transactivation domain in complex with the FOXO4 forkhead domain and in complex with FOXO4-DRI. Strikingly, we find that the disordered FOXO4-DRI binds to the disordered p53TAD2 and forms a transiently folded complex. In this complex, both, the FOXO4-derived region and the cationic cell permeability peptide contribute to the interaction. Furthermore, we show that p53 phosphorylation enhances the affinity for both FOXO4 and FOXO4-DRI. Summarizing we provide a detailed characterization of the interaction of p53 with FOXO4 and FOXO4-DRI which is the basis for development of p53 inhibitors to treat diseases linked to cellular senescence such as cancers.","authors":["Bourgeois Benjamin","Spreitzer Emil","Platero-Rochart Daniel","Paar Margret","Zhou Qishun","Usluer Sinem","de Keizer Peter L J","Burgering Boudewijn M T","Sánchez-Murcia Pedro A","Madl Tobias"],"year":2025,"journal":"Nature communications"},{"pmid":"41625068","title":"FOXO4-DRI regulates endothelial cell senescence via the P53 signaling pathway.","abstract":"OBJECTIVES: Endothelial cell dysfunction during aging is a key driver of vascular aging and related diseases; however, effective strategies to selectively eliminate senescent endothelial cells and restore vascular function remain lacking. FOXO4-DRI, a novel peptide-based intervention, specifically disrupts the interaction between FOXO4 and P53, thereby inducing apoptosis in senescent cells. This study innovatively focuses on the mechanism by which FOXO4-DRI induces apoptosis in senescent endothelial cells, demonstrating that it functions by activating the p53/BCL-2/Caspase-3 signaling pathway to promote selective apoptosis of these cells. FOXO4-DRI significantly improves vascular function and delays vascular aging. These findings not only enrich the molecular understanding of senescent cell clearance but also provide a novel strategy for precise targeting of endothelial cell senescence in therapeutic applications.\n\nMATERIALS AND METHODS: This study aims to analyze the vascular function and aging status of the aorta in naturally aged mice and progeroid model mice following FOXO4-DRI injection. Additionally, it investigates changes in endothelial cell function in senescent endothelial cells induced by oxygen-glucose deprivation (OGD), as well as the protein expression and interaction in the FOXO4-P53 signaling pathway. To assess the impact of FOXO4-DRI on endothelial cell senescence, the senescent endothelial cells were treated with FOXO4-DRI, followed by immunofluorescence and Western blotting experiments.\n\nRESULTS: Injection of FOXO4-DRI in both naturally aged and induced aging mice effectively suppressed aortic aging and improved aortic function. Additionally, we found that FOXO4-DRI alleviates endothelial cell senescence induced by OGD, thereby enhancing endothelial cell function. Through co-immunoprecipitation (CO-IP) experiments, we discovered that FOXO4-DRI prevents the binding of FOXO4 to P53, facilitating the phosphorylated P53 nuclear exclusion, which subsequently trigger BAX and cleaved caspase-3, leading to the apoptosis of senescent cells. Ultimately, this mechanism achieves the goal of inhibiting vascular aging.\n\nCONCLUSION: FOXO4-DRI promotes the nuclear export of phosphorylated P53 by inhibiting the binding of FOXO4 to P53 in endothelial cells, thereby facilitating the apoptosis of senescent endothelial cells and alleviating aging.","authors":["Hu Zhicheng","Li Fan","Hu Chunyi","Shan Qiongdan","Tang Zhouhao","Jiang Meifan","Yi Xiaojing","Chen Xixi","Jin Litai","Wang Xu","Wang Yang"],"year":2025,"journal":"Frontiers in bioengineering and biotechnology"},{"pmid":"36515093","title":"Eliminating Senescent Cells Can Promote Pulmonary Hypertension Development and Progression.","abstract":"BACKGROUND: Senescent cells (SCs) are involved in proliferative disorders, but their role in pulmonary hypertension remains undefined. We investigated SCs in patients with pulmonary arterial hypertension and the role of SCs in animal pulmonary hypertension models.\n\nMETHODS: We investigated senescence (p16, p21) and DNA damage (γ-H2AX, 53BP1) markers in patients with pulmonary arterial hypertension and murine models. We monitored p16 activation by luminescence imaging in p16-luciferase (p16LUC/+) knock-in mice. SC clearance was obtained by a suicide gene (p16 promoter-driven killer gene construct in p16-ATTAC mice), senolytic drugs (ABT263 and cell-permeable FOXO4-p53 interfering peptide [FOXO4-DRI]), and p16 inactivation in p16LUC/LUC mice. We investigated pulmonary hypertension in mice exposed to normoxia, chronic hypoxia, or hypoxia+Sugen, mice overexpressing the serotonin transporter (SM22-5-HTT+), and rats given monocrotaline.\n\nRESULTS: Patients with pulmonary arterial hypertension compared with controls exhibited high lung p16, p21, and γ-H2AX protein levels, with abundant vascular cells costained for p16, γ-H2AX, and 53BP1. Hypoxia increased thoracic bioluminescence in p16LUC/+ mice. In wild-type mice, hypoxia increased lung levels of senescence and DNA-damage markers, senescence-associated secretory phenotype components, and p16 staining of pulmonary endothelial cells (P-ECs, 30% of lung SCs in normoxia), and pulmonary artery smooth muscle cells. SC elimination by suicide gene or ABT263 increased the right ventricular systolic pressure and hypertrophy index, increased vessel remodeling (higher dividing proliferating cell nuclear antigen-stained vascular cell counts during both normoxia and hypoxia), and markedly decreased lung P-ECs. Pulmonary hemodynamic alterations and lung P-EC loss occurred in older p16LUC/LUC mice, wild-type mice exposed to Sugen or hypoxia+Sugen, and SM22-5-HTT+ mice given either ABT263 or FOXO4-DRI, compared with relevant controls. The severity of monocrotaline-induced pulmonary hypertension in rats was decreased slightly by ABT263 for 1 week but was aggravated at 3 weeks, with loss of P-ECs.\n\nCONCLUSIONS: Elimination of senescent P-ECs by senolytic interventions may worsen pulmonary hemodynamics. These results invite consideration of the potential impact on pulmonary vessels of strategies aimed at controlling cell senescence in various contexts.","authors":["Born Emmanuelle","Lipskaia Larissa","Breau Marielle","Houssaini Amal","Beaulieu Delphine","Marcos Elisabeth","Pierre Remi","Do Cruzeiro Marcio","Lefevre Marine","Derumeaux Genevieve","Bulavin Dmitry V","Delcroix Marion","Quarck Rozenn","Reen Virinder","Gil Jesus","Bernard David","Flaman Jean-Michel","Adnot Serge","Abid Shariq"],"year":2023,"journal":"Circulation"},{"pmid":"33996787","title":"Senolytic Peptide FOXO4-DRI Selectively Removes Senescent Cells From","abstract":"Autologous chondrocyte implantation (ACI) is a procedure used to treat articular cartilage injuries and prevent the onset of post-traumatic osteoarthritis. In vitro expansion of chondrocytes, a necessary step in ACI, results in the generation of senescent cells that adversely affect the quality and quantity of newly formed cartilage. Recently, a senolytic peptide, fork head box O transcription factor 4-D-Retro-Inverso (FOXO4-DRI), was reported to selectively kill the senescent fibroblasts. In this study, we hypothesized that FOXO4-DRI treatment could remove the senescent cells in the expanded chondrocytes, thus enhancing their potential in generating high-quality cartilage. To simulate the in vitro expansion for ACI, chondrocytes isolated from healthy donors were expanded to population doubling level (PDL) 9, representing chondrocytes ready for implantation. Cells at PDL3 were also used to serve as the minimally expanded control. Results showed that the treatment of FOXO4-DRI removed more than half of the cells in PDL9 but did not significantly affect the cell number of PDL3 chondrocytes. Compared to the untreated control, the senescence level in FOXO4-DRI treated PDL9 chondrocytes was significantly reduced. Based on the result from standard pellet culture, FOXO4-DRI pre-treatment did not enhance the chondrogenic potential of PDL9 chondrocytes. However, the cartilage tissue generated from FOXO4-DRI pretreated PDL9 cells displayed lower expression of senescence-relevant secretory factors than that from the untreated control group. Taken together, FOXO4-DRI is able to remove the senescent cells in PDL9 chondrocytes, but its utility in promoting cartilage formation from the in vitro expanded chondrocytes needs further investigation.","authors":["Huang Yuzhao","He Yuchen","Makarcyzk Meagan J","Lin Hang"],"year":2021,"journal":"Frontiers in bioengineering and biotechnology"},{"pmid":"34877934","title":"Targeting senescence-like fibroblasts radiosensitizes non-small cell lung cancer and reduces radiation-induced pulmonary fibrosis.","abstract":"Cancer cell radioresistance is the primary cause of the decreased curability of non-small cell lung cancer (NSCLC) observed in patients receiving definitive radiotherapy (RT). Following RT, a set of microenvironmental stress responses is triggered, including cell senescence. However, cell senescence is often ignored in designing effective strategies to resolve cancer cell radioresistance. Herein, we identify the senescence-like characteristics of cancer-associated fibroblasts (CAFs) after RT and clarify the formidable ability of senescence-like CAFs in promoting NSCLC cell proliferation and radioresistance through the JAK/STAT pathway. Specific induction of senescence-like CAF apoptosis using FOXO4-DRI, a FOXO4-p53-interfering peptide, resulted in remarkable effects on radiosensitizing NSCLC cells in vitro and in vivo. In addition, in this study, we also uncovered an obvious therapeutic effect of FOXO4-DRI on alleviating radiation-induced pulmonary fibrosis (RIPF) by targeting senescence-like fibroblasts in vivo. In conclusion, by targeting senescence, we offer a strategy that simultaneously decreases radioresistance of NSCLC and the incidence of RIPF.","authors":["Meng Jingshu","Li Yan","Wan Chao","Sun Yajie","Dai Xiaomeng","Huang Jing","Hu Yan","Gao Yanan","Wu Bian","Zhang Zhanjie","Jiang Ke","Xu Shuangbing","Lovell Jonathan F","Hu Yu","Wu Gang","Jin Honglin","Yang Kunyu"],"year":2021,"journal":"JCI insight"}],"biorxiv":[{"pmid":"","doi":"10.21203/rs.3.rs-2361374/v1","title":"Identification of Hotspots in Synthetic Peptide Inhibitors of the FOXO4:p53 Interaction","abstract":"<title>Abstract</title>  <p>Background:  Many stresses trigger cellular senescence, including telomere shortening, oncogene activation, DNA-replication stress, oxidative stress, and resistance to apoptosis. Forkhead box protein O4 (FOXO4) plays a pivotal role in cellular senescence, by binding to and inactivating p53, thereby leading to cellular senescence and inhibiting p53 mediated apoptosis. As a result, misregulation of FOXO4-p53 is linked to numerous diseases including cancers and aging-related diseases, pulmonary fibrosis and neurodegenerative diseases. Targeting of the FOXO4-p53 interface has been accomplished using a synthetic D retro inverse peptide (DRI), however recognition of the key molecular drivers of the interactions remains unknown. Understanding these interactions on a molecular level could lead to the development of small compounds, with enhanced pharmacological qualities, such as high stability, membrane permeability, and oral bioavailability, that mimics the activity of the DRI peptide. <h4>Methods and Results:</h4> Using an <italic>in silico</italic> model of the FOXO4-p53 interaction, we designed shorter peptides within the DRI to identify the key interactions. A biophysical assay demonstrates these shorter peptides retain strong binding affinity to p53, suggesting that the DRI's hot spot is located within these peptides. <h4>Conclusions:</h4> Taken together, this data provides information at the molecular level that is key to understanding the interplay of two proteins responsible for cellular senescence and provides the basis for the design of small molecules to inhibit this interaction.</p>","authors":["Zhang R","Gao K","Sadremomtaz A","Ruiz-Moreno AJ","Monti A","Al-Dahmani ZM","Gyau B","Doti N","Groves MR."],"year":2022,"journal":"PPR","source":"PPR","preprint":true}],"preprints":[{"pmid":"","doi":"10.21203/rs.3.rs-2361374/v1","title":"Identification of Hotspots in Synthetic Peptide Inhibitors of the FOXO4:p53 Interaction","abstract":"<title>Abstract</title>  <p>Background:  Many stresses trigger cellular senescence, including telomere shortening, oncogene activation, DNA-replication stress, oxidative stress, and resistance to apoptosis. Forkhead box protein O4 (FOXO4) plays a pivotal role in cellular senescence, by binding to and inactivating p53, thereby leading to cellular senescence and inhibiting p53 mediated apoptosis. As a result, misregulation of FOXO4-p53 is linked to numerous diseases including cancers and aging-related diseases, pulmonary fibrosis and neurodegenerative diseases. Targeting of the FOXO4-p53 interface has been accomplished using a synthetic D retro inverse peptide (DRI), however recognition of the key molecular drivers of the interactions remains unknown. Understanding these interactions on a molecular level could lead to the development of small compounds, with enhanced pharmacological qualities, such as high stability, membrane permeability, and oral bioavailability, that mimics the activity of the DRI peptide. <h4>Methods and Results:</h4> Using an <italic>in silico</italic> model of the FOXO4-p53 interaction, we designed shorter peptides within the DRI to identify the key interactions. A biophysical assay demonstrates these shorter peptides retain strong binding affinity to p53, suggesting that the DRI's hot spot is located within these peptides. <h4>Conclusions:</h4> Taken together, this data provides information at the molecular level that is key to understanding the interplay of two proteins responsible for cellular senescence and provides the basis for the design of small molecules to inhibit this interaction.</p>","authors":["Zhang R","Gao K","Sadremomtaz A","Ruiz-Moreno AJ","Monti A","Al-Dahmani ZM","Gyau B","Doti N","Groves MR."],"year":2022,"journal":"PPR","source":"PPR","preprint":true}],"consensus_view":"The literature consensus establishes that FOXO4-DRI functions by disrupting the FOXO4–p53 protein-protein interaction, selectively inducing apoptosis in senescent cells. The single available structural study (Bourgeois et al., 2025, PMID:40593617) is the field's only NMR-based characterization and reports that FOXO4-DRI is intrinsically disordered, engages the disordered p53 TAD2, and that both the FOXO4-derived N-terminal region and the C-terminal CPP tail contribute to binding. This represents the most authoritative current view of the binding interface. The preprint hotspot study (Zhang et al., 2022) supports N-terminal region primacy but has not been peer-reviewed. There is no consensus yet on whether the CPP tail is a passive delivery vehicle or an active binding contributor; the 2025 NMR data suggest the latter. The consensus on cell delivery is that the CPP tail is required for membrane penetration, meaning any helix-only construct would need separate delivery consideration for cell-based validation.","knowledge_gaps":"Several important questions remain unresolved: (1) No high-resolution crystal structure or complete NMR ensemble with explicit per-residue contact maps for FOXO4-DRI:p53 TAD2 has been published, leaving the precise atomic contacts of the CR3-mimetic helix vs. CPP tail ambiguous. (2) The relative binding contributions (delta-G partitioning) of the helix vs. CPP segments have not been rigorously quantified with isothermal titration calorimetry or SPR for isolated fragments. (3) The folding propensity of the isolated 23-residue helix-only construct in aqueous solution is unknown—it may be disordered in isolation (as IDPs often are) regardless of CPP removal. (4) Whether improved pLDDT/structure-prediction scores for the truncated peptide would correlate with improved actual binding affinity or selectivity is an untested assumption. (5) The effect of D-amino acid composition (DRI) on helix stability vs. the L-amino acid reference is not systematically characterized for the truncated fragment.","supporting_evidence":"The Zhang et al. (2022) preprint directly supports the hypothesis by using in silico hotspot mapping and biophysical binding assays to show that shorter N-terminal-derived peptides retain strong p53 binding affinity, localizing the binding hotspot to the FOXO4 CR3-mimetic region. The Arg/Lys/Pro-rich composition of the CPP tail (residues 24-46) is intrinsically incompatible with stable helix formation—polyproline and polybasic sequences are known helix-breakers, providing a structural rationale for why the CPP tail would introduce conformational heterogeneity and depress pLDDT scores in structure prediction. The biological literature confirms that the mechanistic endpoint (p53 nuclear exclusion, apoptosis) is entirely attributable to disruption of the FOXO4–p53 interaction, consistent with the helix region being the functionally sufficient binding unit. The Bourgeois et al. finding that p53 TAD2 phosphorylation enhances binding affinity is also consistent with the CR3-mimetic helix engaging a structured epitope on p53 TAD2.","challenging_evidence":"The most significant challenge to the hypothesis comes from Bourgeois et al. (2025, PMID:40593617), which explicitly reports from NMR data that 'both the FOXO4-derived region and the cationic cell permeability peptide contribute to the interaction' with p53 TAD2. If the CPP tail makes genuine binding contacts, removing it would be expected to reduce affinity and potentially alter the binding mode, rather than simply 'cleaning up' the interface. The same study describes the complex as 'transiently folded,' suggesting that the intrinsic disorder of the full-length FOXO4-DRI may be a mechanistic feature enabling binding to the disordered p53 TAD2 (conformational selection/induced fit), not a computational artifact of the CPP tail. Removing the CPP may not yield a well-folded helix—it may simply yield a shorter disordered peptide with reduced affinity. Additionally, the low pLDDT of 0.56-0.61 for FOXO4-DRI may reflect the genuine disordered nature of the entire peptide engaging a disordered target, rather than being attributable specifically to the CPP tail. The Zhang et al. preprint supporting hotspot localization to the N-terminal region has not undergone peer review, weakening its evidentiary weight."},"caveats":null,"works_cited":[{"pmid_or_doi":"40593617","title":"The disordered p53 transactivation domain is the target of FOXO4 and the senolytic compound FOXO4-DRI","year":2025,"relevance":"Provides the only available solution NMR structural characterization of FOXO4-DRI bound to p53 TAD2 (residues 35-59), directly addressing the binding interface; critically reports that both the CR3-mimetic region AND the CPP tail contribute to p53 interaction, directly challenging the hypothesis that the CPP is purely a non-binding appendage."},{"pmid_or_doi":"10.21203/rs.3.rs-2361374/v1","title":"Identification of Hotspots in Synthetic Peptide Inhibitors of the FOXO4:p53 Interaction","year":2022,"relevance":"Directly tests truncated FOXO4-DRI variants in silico and biophysically, localizing the p53-binding hotspot to the N-terminal FOXO4-derived region, which supports the hypothesis that a helix-only fragment retains intrinsic binding activity to p53."},{"pmid_or_doi":"31959736","title":"FOXO4-DRI alleviates age-related testosterone secretion insufficiency by targeting senescent Leydig cells in aged mice","year":2020,"relevance":"Establishes the mechanistic framework of FOXO4-DRI acting as a FOXO4–p53 interaction blocker that causes p53 nuclear exclusion, providing biological context for why modulating the p53-binding interface has functional consequences."},{"pmid_or_doi":"39025385","title":"FOXO4-DRI improves spermatogenesis in aged mice through reducing senescence-associated secretory phenotype secretion from Leydig cells","year":2024,"relevance":"Confirms FOXO4-DRI's mechanism as a specific FOXO4–p53 binding blocker, reinforcing the relevance of the p53 interaction interface as the functional target and supporting the therapeutic rationale for optimizing this interface."},{"pmid_or_doi":"39994346","title":"FOXO4-DRI induces keloid senescent fibroblast apoptosis by promoting nuclear exclusion of upregulated p53-serine 15 phosphorylation","year":2025,"relevance":"Demonstrates that phosphorylation state of p53 (pS15) modulates the FOXO4-DRI/p53 interaction outcome, which combined with Bourgeois et al.'s finding that p53 phosphorylation enhances binding affinity, highlights the importance of the p53 TAD2 interface for functional activity."},{"pmid_or_doi":"41625068","title":"FOXO4-DRI regulates endothelial cell senescence via the P53 signaling pathway","year":2025,"relevance":"Provides additional mechanistic evidence that FOXO4-DRI's p53-disrupting activity propagates through BCL-2/caspase-3, confirming p53 interaction is the functional apex of the peptide's activity relevant to evaluating truncation effects."},{"pmid_or_doi":"34877934","title":"Targeting senescence-like fibroblasts radiosensitizes non-small cell lung cancer and reduces radiation-induced pulmonary fibrosis","year":2021,"relevance":"Demonstrates functional FOXO4-p53 interference by the intact peptide in a disease context, providing a functional benchmark against which any truncated construct's activity should be compared."},{"pmid_or_doi":"36515093","title":"Eliminating Senescent Cells Can Promote Pulmonary Hypertension Development and Progress","year":2023,"relevance":"Uses FOXO4-DRI as a tool in disease context, highlighting cell-permeability requirements for in vivo efficacy—relevant background for evaluating the functional consequence of removing the CPP tail beyond just binding interface effects."}]},"onchain":{"hash":null,"signature":null,"data_hash":null,"logged_at":null,"explorer_url":null},"ipfs_hash":null,"created_at":"2026-05-04T15:59:07.614666+00:00","updated_at":"2026-05-04T16:33:51.595594+00:00"}