ACS Medicinal Chemistry Letters

Ligand optimization is central to drug discovery as hundreds of analogs might be designed and synthesized between an initial hit and a therapeutic candidate. The efficiency of this process is unclear, at least partly because there is no random background for optimization against which to compare. Such a random background might emerge from synthetically accessible but otherwise systematic random small substitutions across starting ligands, measuring likelihood of achieving a substantial improvement in affinity/potency or other property by any single perturbation. Recent literature and ligand-affinity/potency databases suggest that perhaps 10% of analogs with minor modifications improve upon a parents potency substantially (by [≥]10-fold), but this number is clouded by reporting bias, intentional improvement, and inter-group reproducibility. To begin to establish a background expectation for ligand optimization, we comprehensively and systematically modified 18 lead molecules across six targets with single atom changes; 257 compounds were synthesized. Unexpectedly, 11.2% of these random small perturbation analogs improved potency by [≥]10-fold over their parents. Conversely, these more potent analogs typically had worse in vitro pharmacokinetics (e.g. reduced metabolic stability, lower plasma free fraction). While it was possible to find analogs where the potency increase compensated for inferior exposure and half-life, resulting in more potent compounds in vivo, overall a frustrated landscape for ligand optimization is revealed. This study begins to establish a background expectation for ligand potency optimization and offers a simple strategy to do so. It also begins to quantify the challenges confronting the field in moving beyond in vitro potency.

Histone deacetylase 6 (HDAC6) is a class IIb histone deacetylase that regulates diverse cytosolic acetylation through its two catalytic deacetylase domains and a C-terminal zinc finger ubiquitin-binding domain (ZnF-UBD). This ZnF-UBD mediates key protein-protein interactions (PPIs) that couple deacetylation and ubiquitin-dependent degradation. While most HDAC6 inhibitors target the catalytic domains, the ZnF-UBD represents an underexplored target. Here, we validate previously reported small-molecule inhibitors of the HDAC6 ZnF-UBD/ubiquitin interaction and describe novel N-alkyl moieties based on quinazolinone and phthalazinone scaffolds. Starting from known quinazolinone and phthalazinone scaffolds, a literature and modeling-guided scaffold hop revealed potential for an extended phthalazinone series. Results obtained both in fluorescence polarization (FP) and differential scanning fluorimetry (DSF) confirm this hypothesis. Additionally, late-stage diversification yields compounds with improved predicted physicochemical properties. Finally, machine-learning-based co-folding affinity predictions correlate with experimental IC{square}{square} rank order, highlighting their utility in PPI inhibitor design. These studies continue expanding the chemical space of HDAC6 ZnF-UBD inhibitors and build upon existing foundations for future therapeutic and mechanistic exploration of HDAC6- ubiquitin signaling.

The use of covalent warheads targeting the catalytic cysteine has been a cornerstone in coronavirus main protease (Mpro) inhibitor development, where various electrophilic motifs have been used including aldehydes, nitriles, ketoamides, and hydroxymethyl ketones (HMKs). Recent efforts have been mostly centered around nitrile warheads, given the success of compounds like Nirmatrelvir and Ensitrelvir in the clinic. However, finding and advancing alternative chemotypes with differentiating chemical and pharmacological profiles is essential for future pandemic preparedness. Among such alternatives, HMKs hold special interest because they balance reduced intrinsic electrophilicity with an excellent selectivity profile. Nevertheless, early HMK-based compounds, such as the clinical-stage Mpro inhibitor PF-00835231, suffered from poor oral bioavailability and therefore required intravenous administration, with or without prodrug derivatization of the hydroxyl group. Here, we describe our efforts in advancing the HMK field via the discovery of mCMX110, a lead that has superior potency, increased unbound exposure in vivo, and favorable oral bioavailability in preclinical studies. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=105 SRC="FIGDIR/small/725542v1_ufig1.gif" ALT="Figure 1"> View larger version (22K): org.highwire.dtl.DTLVardef@abe1c9org.highwire.dtl.DTLVardef@746a08org.highwire.dtl.DTLVardef@dd5861org.highwire.dtl.DTLVardef@1d572c7_HPS_FORMAT_FIGEXP M_FIG C_FIG

The deubiquitinating enzyme, ubiquitin C-terminal hydrolase L3 (UCHL3), has been implicated as a potential therapeutic target for cancer with a role in regulating the DNA damage response pathways. While the target has been studied using genetic methods there is a lack of reliable chemical probes to selectivity target UCHL3. In this study we report hit identification and optimization of a new chemical scaffold that irreversibly inhibits UCHL3. The observed structure-activity relationships are corroborated by ligand-bound crystal structures that confirm covalent adduct formation with the catalytic cysteine of the enzyme. Finally, through gel-shift assays using a ubiquitin activity-based probe we demonstrate on-target engagement with UCHL3 in two cell lines. The work as a whole presents a comprehensive evaluation of the new scaffold that can be utilized to probe UCHL3 in different biological contexts.

Homeodomain-interacting protein kinase 4 (HIPK4) remains an understudied member of the dark kinome. While genetic knockout studies suggest roles for HIPK4 in spermiogenesis and cutaneous squamous cell carcinoma, whether these cellular functions can be recapitulated by pharmacological inhibition remains to be determined. However, such investigations have been hampered by a lack of high-quality chemical tools. To address this, we employed a rational design strategy utilizing macrocyclization of a bosutinib-based scaffold. Systematic optimization led to the discovery of AZ137 (28e), a potent and selective HIPK4 inhibitor (IC50 = 11 nM; cellular EC50 = 76 nM). AZ137 exhibits exceptional selectivity across three comprehensive orthogonal panels, high solubility, and no detectable cytotoxicity. Its cellular activity was confirmed in cell-based assays of HIPK4-dependent F-actin remodeling. Together with a negative control compound, this probe set provides a foundational framework for the validating HIPK4 as a therapeutic target and a high-quality resource to elucidate its roles in normal physiology and disease. For Table of Contents Only O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=106 SRC="FIGDIR/small/720179v1_ufig1.gif" ALT="Figure 1"> View larger version (28K): org.highwire.dtl.DTLVardef@12438borg.highwire.dtl.DTLVardef@11083beorg.highwire.dtl.DTLVardef@1395fb4org.highwire.dtl.DTLVardef@1ba3db8_HPS_FORMAT_FIGEXP M_FIG C_FIG

Metastatic melanoma is an aggressive cutaneous malignancy frequently driven by the oncogenic V600E mutation within the BRAF kinase. While first-generation Type IS BRAF inhibitors, such as dabrafenib, are currently prescribed to target this specific molecular vulnerability, paradoxical MAPK pathway activation, and acquired drug resistance necessitate the continuous development of structurally optimized lead molecules. In this study, chemical intuition, bioisosteric replacement, and computational molecular docking were employed to propose two novel BRAFV600E drug candidates. The proposed therapeutics, engineered to incorporate constrained sp3-hybridized aliphatic rings and a sulfoximine bioisostere, demonstrated thermodynamically superior docking scores within the mutant catalytic cleft compared to dabrafenib. Lastly, a homology analysis determined that Mus musculus is a suitable model organism for future preclinical studies and confirmed crucial structural selectivity against microbial off-target kinases.

Premarineosin A undergoes rapid, chemoselective C12 halogenation under mild conditions, providing brominated, chlorinated, fluorinated, and iodinated analogs. These derivatives retained potent antiplasmodial activity against both chloroquine-sensitive and -resistant Plasmodium falciparum strains and displayed smaller reductions in potency against the resistant strain than the parent compound.

Structure-based drug discovery is known to apply computational methods in a tiered hierarchy, with each layer narrowing the candidate set and refining the binding picture before committing to the next, more expensive step. We present a four-tiered computational benchmarking study evaluating five engines against a panel of 36 compounds targeting B-secretase 1 (BACE1), a validated Alzheimer's disease target with extensive co-crystal ground truth. This study evaluates Flexible Docking and Boltz2 Cofolding as the primary tier, followed by Ensemble Docking, and then Protein-Ligand MD with MM/PBSA and MM/GBSA post-processing. This is then concluded with Relative Binding Free Energy Perturbation (RevFEP) as the terminal refinement layer. Each method was benchmarked against the experimental binding free energies derived from the co-crystal structures spanning -7.85 to -11.35 kcal/mol. Our findings revealed that Flexible Docking reproduced the co-crystal binding mode for 35 of 36 ligands (97.2% within 2.0 A RMSD) but did not rank potency at this resolution. Boltz2 CoFolding provided an orthogonal structural cross-check with a receptor backbone RMSD of 0.293 A against the experimental co-crystal structure. Ensemble Docking identified the optimal receptor conformation for downstream FEP setup. MD with MM/GBSA decomposition identified van der Waals complementarity as the primary potency driver (Pearson r = +0.855, R2 = 0.732 on a 10-compound subset). RevFEP delivered the highest affinity correlation of any method (Pearson r = +0.662, R2 = 0.438, Spearman p = +0.624, mean absolute error 1.02 kcal/mol across all 36 ligands), resolving potency differences within a narrow 3.5 kcal/mol congeneric window that no other engine could discriminate. We characterize what each engine contributes independently and where RevFEP delivers signals no other engine achieves.

Room temperature serial crystallography offers advantages over conventional cryo-crystallography, such as simplified crystal handling and the possibility to avoid potential artefacts associated with cryo-trapping. However, to be considered as an alternative for drug discovery, where compound availability may be limited and speed of structure delivery is a key factor, it suffers from several limitations. To address these challenges, we have optimized a serial crystallography workflow for ligand soaking, data collection and data processing, significantly reducing time and reagent consumption to make it a viable option for drug discovery applications, herein exemplified by crystallographic fragment screening. Our approach incorporates the use of dried-in fragment cocktails on fixed target supports, compatible with 96-well plates for crystal soaking, and an efficient data processing pipeline tailored for serial crystallography. To validate our workflow, we conducted an in-crystal fragment screen at room temperature on the protein soluble epoxide hydrolase. The screen comprised 384 compounds and resulted in identification of 40 fragment binders corresponding to a hit rate of 10.4 %. The resulting room-temperature structures are of high quality and reveal opportunities for specific interaction within the highly hydrophobic active site of soluble epoxide hydrolase. Finally, we discuss potential avenues for further workflow optimization, highlighting the future potential of this approach for drug discovery. SynopsisWe have developed a workflow that allowed us to efficiently conduct a fragment screen at room temperature using serial crystallography, of interest for future drug discovery campaigns.

Targeting viral macrodomains (Mac) has emerged as a promising strategy for antiviral drug development, especially after the outbreak of COVID-19 that claimed millions of lives worldwide. Several severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Mac1 inhibitors have been reported in the past few years. In the present work, we converted GS-441524 (IC50 of [~]10 M for SARS-CoV-2 Mac1) to KP-S54 (18c), a potent inhibitor of both SARS-CoV-2 Mac1 (IC50: 44 nM) and Middle East respiratory syndrome coronavirus (MERS-CoV) Mac1 (IC50: 91 nM) through an iterative direct-to-biology approach. This approach leverages efficient amide-coupling reaction and the mix-and-read fluorescence polarization (FP) assays where reaction mixtures could be screened directly without purification. Cocrystal structure of a selected derivative (12p) binding to SARS-CoV-2 Mac1 revealed the binding mode, which will guide future drug development against viral macrodomains.

Alzheimers disease (AD) is a multifactorial disease with mixed pathologies. Consequentially, drugs targeting multiple pathological processes may offer synergistic benefits. While histone deacetylase (HDAC) inhibitors have demonstrated efficacy in alleviating AD-related pathologies in animal models, the neuroprotective Wnt/{beta}-catenin signaling pathway remains compromised in AD brain. CI-994 is a class I HDAC inhibitor containing N-(2-aminophenyl)-benzamide. Our recent studies indicate that CI-994 is also an activator of Wnt/{beta}-catenin signaling by stabilizing Wnt co-receptor LRP6. We herein use CI-994 as a scaffold to develop novel potent dual modulators of class I HDACs and Wnt/{beta}-catenin signaling for AD therapy. Our lead compound, W2A-28, selectively inhibits class I HDAC1, 2 and 3 with IC50 values of 0.51 M, 0.68 M, and 0.22 M, respectively, and shows no inhibitory activities on other HDACs. Furthermore, W2A-28 potently activates Wnt reporter activity with an EC50 value of 1.61 M in Wnt-3A-expressing HEK293 cells. As expected, activation of Wnt/{beta}-catenin signaling by W2A-28 is associated with elevated LRP6 protein level. Importantly, W2A-28 displays excellent microsomal stability in both mouse and human liver microsomal stability assays, alongside high permeability and a lack of active efflux in MDR1-MDCKII models. Critically, W2A-28 treatment significantly enhances histone acetylation, activates Wnt/{beta}-catenin signaling, and suppresses tau phosphorylation in AD patient-specific cerebral organoids carrying APOE {varepsilon}4/{varepsilon}4 or APOE {varepsilon}3/{varepsilon}4 with PSEN1 M146V mutation. Our findings position W2A-28 as a promising multi-target drug candidate for AD therapy.

We have developed and characterized a potent and cell active tau tubulin kinase 1 and 2 (TTBK1 and TTBK2) inhibitor, 13. Compound 13 demonstrates in-cell, kinome-wide selectivity, and potently inhibits both TTBK1 and TTBK2. As part of our medicinal chemistry campaign, we also identified a structurally similar negative control, compound 5, which lacks in-cell affinity for TTBK1 and TTBK2. Based on their substrates, which include TDP-43, tau, and tubulin, TTBK1 and TTBK2 inhibition has been pursued as a therapeutic approach for Alzheimers disease, frontotemporal lobe dementia, and amyotrophic lateral sclerosis. TTBK2 is also an effector of ciliogenesis, acting in concert with CEP164, CP110, and CEP83 to initiate the biogenesis of primary cilia. The development of selective chemical tools for these kinases facilitates investigation into TTBK1/2-mediated pathways and potential disease-altering ramifications linked to their pharmacological perturbation.

RAB27A and RAB27B are homologous small GTPases that regulate intracellular vesicle trafficking, orchestrating endocytic and exocytic processes that affect cellular communication, immune responses, and dynamics of the cellular microenvironment. Through their interactions with effector proteins, RAB27A/B play roles in tumor metastasis and chronic inflammation. However, pharmacological modulation of their activity faces challenges typical of small GTPases, including a lack of well-defined pockets outside the conserved GTP binding site, and large RAB27-effector protein-protein interaction (PPI) surfaces. Here, we present the discovery and development of the first cell-active, rationally designed covalent inhibitors of the RAB27-effector interaction, targeting a non-conserved cysteine residue flanking the PPI interface. An electrophile-first biochemical screen led to a novel class of acrylamide covalent inhibitors, and X-ray crystallography structure-guided design led to optimized inhibitors and probes that enantioselectively target RAB27A/B-Cys123 in cells. Potency and selectivity were confirmed through biochemical and cellular assays, including chemical proteomics and phenotype recapitulation in melanocytes alongside a matched inactive enantioprobe control. In contrast, a previously reported compound, Nexinhib-20, was found to be toxic and to exert its activity through non-selective reactivity. This work provides the first toolbox of cell-active chemical probes for RAB27 which can be used in future studies to shed light on the function of this protein and its potential as a therapeutic target.

For more than 55 million people living with dementia worldwide, no oral disease-modifying treatment is currently available. Alzheimers disease (AD) remains one of the most urgent unmet needs in neurology, with recent genetic evidence estimating that 72-93% of AD burden is attributable to common APOE allelic variation. Mechanistically, the APOE {varepsilon}4 isoform impairs cholesterol transport in the brain, promoting cholesteryl ester accumulation in microglia; these lipid-laden cells lose phagocytic capacity for amyloid-{beta} clearance and autophagy-mediated degradation of phosphorylated tau, linking a single upstream metabolic disruption to both hallmark pathologies of AD. ACAT1/SOAT1, the brains predominant cholesterol-esterifying enzyme, is an attractive therapeutic target: its inhibition reduces cholesteryl ester formation, restoring microglial A{beta} clearance, reducing A{beta} production, and promoting tau degradation via autophagy, supporting a multimodal mechanism not addressed by currently approved therapies. However, prior ACAT inhibitor programs were limited by isoform non-selectivity, excessive lipophilicity, and lack of CNS optimization. Addressing these constraints, we present the CuraGenAI Drug Discovery Platform for the design of oral, brain-penetrant ACAT1-targeted small-molecule candidates. The pipeline integrates scaffold-constrained generative chemistry with multi-objective ADMET optimization across more than 30 criteria. From approximately 6 million generated molecules, multi-stage filtering yielded approximately 7,300 CNS-optimized candidates with predicted oral brain-penetrant profiles distinct from prior ACAT clinical compounds. Three nominated lead candidates showed predicted BBB probabilities >0.93, favorable CNS drug-like physicochemical profiles, and stable ACAT1 binding poses, and are prioritized for synthesis and in vitro validation.

CAPON (NOS1AP) is an adaptor protein involved in neuronal nitric oxide synthase (nNOS) signaling and has been implicated in Alzheimers disease (AD), excitotoxicity, and tau-associated neurodegeneration. Here, we report the identification of cyclic peptide ligands targeting CAPON using phage display screening of a disulfide-constrained peptide library. Phage enrichment, ELISA validation, microscale thermophoresis (MST), and biolayer interferometry (BLI) identified CAP1 as the lead peptide, exhibiting low micromolar binding affinity toward CAPON. Computational studies further supported stable CAPON-CAP1 interactions through complementary hydrophobic and electrostatic contacts. Functionally, CAP1 attenuated A{beta}42-induced neuronal toxicity, suppressed NMDA-driven nitric oxide production, and reduced pathological tau phosphorylation in neuronal models under AD-relevant stress conditions. In addition, CAP1 demonstrated favorable preliminary pharmacokinetic properties, including good aqueous solubility, plasma stability, and measurable membrane permeability. Collectively, these findings establish the first cyclic peptide ligands targeting CAPON and identify CAP1 as a promising scaffold for modulation of CAPON-dependent neurodegenerative signaling.

Class B1 G-protein-coupled receptors (GPCRs), such as the calcitonin gene-related peptide (CGRP) receptor and parathyroid hormone 1 (PTH1) receptor, require native lipid interactions to maintain signalling-competent conformations. However, conventional detergents disrupt these environments. Amphipathic copolymers offer a detergent-free alternative, yet the field still lacks a clear understanding of which polymer architectures best preserve active-state GPCR pharmacology, limiting their broader translational utility. Here, we examine how distinct copolymer chemistries influence the functional integrity of class B1 GPCRs by comparing SMA 2000, DIBMA-12, and the electroneutral sulfo-DIBMA. Using NanoLuciferase bioluminescence resonance energy transfer (NanoBRET) ligand-binding, competition, and mini-G-protein recruitment assays on nanodisc-encapsulated receptors, we show that all three copolymers maintain high-affinity extracellular ligand binding but differ markedly in their ability to preserve intracellular signalling. Despite lower receptor extraction efficiency, only sulfo-DIBMA support mini-Gs engagement at the CGRP receptor and enable G-protein-dependent allosteric modulation at the PTH1 receptor, including conserved ligand affinity and prolonged residence time. These data reveal that polymer charge and backbone chemistry, rather than extraction yield, determine whether native-like nanodiscs retain the conformational landscape required for active-state signalling. Controlling non-specific ligand binding to the copolymer is a key requirement for a successful assay. Our findings identify sulfo-DIBMALP as a particularly superior environment for preserving native signalling behaviour in class B1 GPCRs, highlighting copolymer chemistry as an important determinant in detergent-free membrane protein studies. HIGHLIGHTSO_LISulfo-DIBMA encapsulated nanodiscs preserve active-state conformation of human calcitonin gene-related peptide receptor and parathyroid hormone 1 receptor. C_LIO_LIAll three copolymers (SMA 2000, DIBMA-12 and sulfo-DIBMA) preserve extracellular ligand binding but only sulfo-DIBMA preserves intracellular functional competence, including mini-Gs recruitment and G-protein-dependent allosteric modulation. C_LIO_LICopolymer chemistry, particularly the electroneutral, aliphatic nature of sulfo-DIBMA, may influence the preservation of signalling-competent states in two class B1 GPCRs by minimising charge-driven perturbations during solubilisation. C_LIO_LISulfo-DIBMALP provides a novel platform for studying dynamic membrane proteins with potential to provide mechanistic insights and facilitate drug discovery programmes in the future. C_LI GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=103 SRC="FIGDIR/small/724797v1_ufig1.gif" ALT="Figure 1"> View larger version (20K): org.highwire.dtl.DTLVardef@12db163org.highwire.dtl.DTLVardef@d8efb3org.highwire.dtl.DTLVardef@610dbaorg.highwire.dtl.DTLVardef@1cc3ce4_HPS_FORMAT_FIGEXP M_FIG C_FIG

Triggering receptor expressed on myeloid cells 2 (TREM2) is a key regulator of microglial function and a promising therapeutic target in Alzheimers disease. While current strategies have largely focused on antibody-based agonists, alternative modalities capable of modulating TREM2 signaling remain underexplored. Here, we report the discovery of TREM2-binding cyclic peptides using a disulfide-constrained phage display library. Screening and biophysical validation identified multiple binders, with TREM2-6 and TREM2-12 exhibiting micromolar affinity. Both peptides modulated microglial responses in human iPSC-derived model of amyloid stress and in neuron-microglia co-cultures. Molecular dynamics simulations supported stable peptide-TREM2 interactions, with TREM2-12 displaying a more constrained binding mode. In vitro pharmacokinetic profiling revealed favorable plasma and intestinal stability but limited permeability, consistent with cyclic peptide scaffolds. Together, these findings establish cyclic peptides as a viable modality for targeting TREM2 and provide a foundation for the development of tunable neuroimmune therapeutics. Insert Table of Contents artwork here O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=135 SRC="FIGDIR/small/720287v1_ufig1.gif" ALT="Figure 1"> View larger version (43K): org.highwire.dtl.DTLVardef@1977a2aorg.highwire.dtl.DTLVardef@1d571c1org.highwire.dtl.DTLVardef@1f6a22org.highwire.dtl.DTLVardef@70eea7_HPS_FORMAT_FIGEXP M_FIG C_FIG

Protein tyrosine kinases are important regulators of cell signaling, and aberrant kinase activity contributes to many human diseases, including cancers. All protein tyrosine kinases share a highly-conserved ATP binding pocket but diverge in their substrate binding sites in order to mediate distinct signaling events. Many potent and efficacious ATP-competitive tyrosine kinase inhibitors have been developed, however it remains challenging to achieve on-target selectivity across different kinases and target specific disease mutants, given the high degree of conservation in the ATP-binding pocket. By contrast, the variable substrate-binding site offers an opportunity for selective inhibition, provided molecules can be targeted to this site. Here, we present a modular strategy to design selective, peptide-based covalent inhibitors of tyrosine kinases with a distinct binding mode from existing ATP-competitive inhibitors. Using Src kinase as a model system, we demonstrate that Src-selective reactivity can be achieved by first designing an optimized substrate peptide and then strategically positioning an electrophile on the peptide to target a non-conserved cysteine on the kinase. We show that substrate-derived covalent peptides can inhibit kinase activity, bind simultaneously with an ATP-competitive inhibitor, and even inhibit the activity of kinases bearing a common drug resistance mutation. We further explore the application of this approach to develop an inhibitor of the cancer-relevant fibroblast growth factor receptor 1 kinase that shows selectivity for an oncogenic mutant over the wild-type enzyme. Our modular strategy to generate selective covalent peptides targeting protein tyrosine kinases provides a promising framework for future chemical probe and drug development efforts.

Immune inhibitory signaling in microglia contributes to impaired amyloid clearance and neuroinflammation in Alzheimers disease (AD), yet small molecule modulators targeting these pathways remain largely unexplored. Here, we report the development of a high-throughput cellular thermal shift assay (HT-CETSA) platform for identification of small molecule binders targeting the inhibitory immune receptor ILT3 (LILRB4). Screening of [~]40,000 compounds yielded multiple validated hits, including IB15C, a submicromolar ILT3 binder identified through preliminary structure-activity relationship optimization. Orthogonal validation by microscale thermophoresis, surface plasmon resonance, docking, and site-directed mutagenesis confirmed direct and target-specific ILT3 engagement. Functionally, IB15C disrupted the ILT3-ApoE interaction and restored microglial activity in human iPSC-derived microglia, reducing SHP1/2, suppressing cytokine secretion, and enhancing amyloid uptake. IB15C also demonstrated favorable in vitro pharmacokinetic and safety properties, supporting further development of ILT3-targeted neuroimmune therapeutics.

Talin-induced integrin activation is a central regulator of cell adhesion and signaling. Intracellular Targeting of this pathway remains to be challenging. Here, we report the structure-guided development of next-generation stapled peptidomimetics derived from the RIAM talin-binding site (TBS). Using biochemical, structural, and cellular analyses, we show that the second-generation S2-TBS enhances talin binding and inhibitory potency but exhibits reduced cell uptake due to an extended linker. Guided by these insights, we designed a minimized third-generation peptide, S3-TBS, which restores structural order, improves thermal stability and cell uptake, and retains strong talin binding. NMR and crystallographic analyses confirm conserved binding to specific interfaces in talin head and talin rod domains. Functionally, optimized peptides potently inhibit talin-mediated integrin interactions and suppress invadopodia-driven matrix degradation in cancer cells. These findings establish key principles for balancing affinity, conformational stability, and molecular size in the design of intracellular stapled peptide inhibitors. HIGHLIGHTSO_LIStructure-guided optimization converts a flexible stapled peptide into a highly ordered, high-affinity talin inhibitor. C_LIO_LIS2-TBS increases binding affinity but introduces conformational heterogeneity due to a longer linker. C_LIO_LIS3-TBS achieves improved stability, reduced size, and a well-defined stapled conformation. C_LIO_LIOptimized peptides inhibit talin-mediated integrin function and suppress cancer cell matrix degradation. C_LI