Ras proteins are functionally dependent on one or more lipid modifications.1,2 The dynamic palmitoylation of N-Ras by DHHC palmitoyl acyltransferases and depalmitoylation by ABHD17 serine hydrolases is essential for the growth of NRAS-mutant acute myeloid leukemia (AML) cells.3-6 Here we show that ABD778, an in vivo-active ABHD17 inhibitor, selectively reduces the growth of NRAS-mutant AML and melanoma cell lines and is synergistic with the MEK inhibitor PD0325901 (PD901; mirdametinib). Mechanistically, ABD778 and PD901 induce deep and durable suppression of mitogen activated protein kinase (MAPK) pathway activation. Co-treatment extended the survival of mice transplanted with NrasG12D AMLs, which acquired by-pass mutations at relapse that conferred drug resistance and restored MAPK activation. ABD778 augmented the anti-leukemia activity of PI3 kinase, pan-Ras tri-complex, and FLT3 inhibitors, and restored gilteritinib sensitivity in a patient-derived xenograft model of FLT3 inhibitor resistance. These studies validate the palmitoylation cycle as a therapeutic target in NRAS-mutant cancers.

Chemical proteomics has identified covalent ligands targeting cysteine residues across many hundreds of human proteins. The functional effects of these liganding events, however, remain challenging to assign at scale. Here we describe ESCAPE (Endogenous Site-specific Competition Assays using Prime Editors), a platform for the site-resolved functional analysis of covalent ligands in cells. In this method, cysteine-to-serine substitutions are generated by prime editing to abrogate covalent ligand-protein interactions, and the impact of these edits on ligand-induced cellular phenotypes is quantified through allele frequency-based resistance scores. Applied to ligandable cysteines mapped by activity-based protein profiling in 50+ proteins, ESCAPE identified multiple covalent ligand-protein interactions that impair cancer cell growth, including azetidine butynamides that target a non-orthosteric cysteine in the RNA helicase DDX49 to disrupt 18S rRNA processing, 40S ribosome assembly, and protein synthesis. ESCAPE thus provides a scalable framework for the functional characterization of covalent ligands targeting structurally and mechanistically diverse proteins.

Type I/II cytokine receptors mediate cytokine-specific biological responses by employing a defined combination of four Janus kinases (JAKs) and seven signal transducers and activators of transcription (STATs) for cellular signal transduction. Deregulation of the JAK-STAT pathway leads to various diseases, with JAK and STAT proteins representing attractive therapeutic targets. Fifteen JAK inhibitors are approved for several immunological and haematological diseases, offering significant benefits for patients. However, safety restrictions have limited their clinical use. Mechanistic and structural insights are driving current drug development approaches focused on improving their potency, selectivity and safety. Development of STAT inhibitors has been more challenging, and none has yet received clinical approval, although promising new compounds are now entering clinical trials. This Review discusses the recent advances in JAK and STAT inhibitor development and presents emerging therapeutic indications for JAK-STAT inhibition.

Covalent chemistry coupled with activity-based protein profiling (ABPP) offers a versatile approach for small-molecule ligand discovery in native biological contexts. The covalent ligandability maps generated by ABPP that target cysteine have frequently leveraged the acrylamide as a reactive group due to its tempered electrophilicity and presence in many advanced tool compounds and therapeutics. More recently, alternative cysteine-directed reactive groups such as the butynamide have emerged as an additional source of covalent probes and drugs, but their global reactivity with the proteome remains largely unexplored. Here, we compare the ligandability maps of stereochemically defined acrylamide and butynamide compounds (stereoprobes) built from a common tryptoline core and find that the butynamides, despite exhibiting attenuated intrinsic and proteome-wide reactivity, preferentially engage a diverse set of proteins in human cancer cells. Among the butynamide-preferring proteins was the actin maturation protease (ACTMAP or C19orf54), a cysteine protease required for the post-translational processing of actin. We show that (1S,3R)-tryptoline butynamides stereoselectively react with the catalytic nucleophile of ACTMAP, leading to accumulation of N-terminally unprocessed actin in cancer cells. Our findings support reactive group diversification as a strategy for expanding the ligandability of the human proteome and the butynamide, more specifically, as a differentiated cysteine-directed electrophile for chemical probe discovery.

Adaptors serve as hubs to regulate diverse protein complexes in cells. This multitude of functions can complicate the study of adaptors, as their genetic disruption may simultaneously impair the activities of several compositionally distinct complexes (or adaptor 'complexoforms'). Here we describe the chemical proteomic discovery of bicyclopyrrolidine acrylamide stereoprobes that react with C100 of the methyltransferase (MT) adaptor TRMT112 in human cells. Curiously, the stereoprobes showed negligible reactivity with uncomplexed recombinant TRMT112 and we found that this interaction was restored exclusively in the presence of METTL5 but not other MTs. A cocrystal structure revealed stereoprobe binding to a composite pocket proximal to C100 of TRMT112 that is templated by METTL5 and absent in other TRMT112:MT complexes. Structural rearrangements promoted by stereoprobe binding in turn lead to allosteric agonism of METTL5, thus revealing how covalent ligands targeting a pleiotropic adaptor can confer partner-specific functional effects through reactivity with a single complexoform.

Breast cancer progression is facilitated by the epithelial to mesenchymal transition (EMT), generating cancer cells with enhanced metastatic capacity and resistance to chemotherapeutics. The fungus-derived sesterterpenoid natural produce compound, ophiobolin A (OpA), possesses nanomolar cytotoxic activity and a high therapeutic index, although its molecular targets and mechanism of action are not well characterized. Herein, we utilized a model of mammary epithelial cells and breast cancer cell lines with and without EMT features to characterize the mechanism of selectivity towards EMT(+) cells by OpA. Proteins interacting with OpA in EMT(+) cells, including mitochondrial glutathione transporter SLC25A40, were identified through via mass spectrometry. We utilized trans-mitochondrial cybrids to determine that mitochondria mediate sensitivity to OpA. Furthermore, we report effects on glycolysis, oxidative metabolism, and disruption of metabolite abundance in the TCA cycle. Antioxidant mechanisms are activated by OpA in EMT(+) cells via the NRF2-ARE pathway, verified by decreased cytotoxicity in EMT(+) cells pretreated with the NRF2 activator CDDO. Collectively, we conclude that OpA selectivity toward EMT is mediated by the mitochondria, and at sub-cytotoxic levels, generates a metabolic shift leading to cell death countered by antioxidant mechanisms.

Deciphering how genes interact within human cells is essential for understanding their functional wiring and for developing targeted therapeutic strategies. In this study, we present a genome-scale map of genetic interactions in the human haploid cell line HAP1, based on CRISPR-based perturbation of ∼4 million gene pairs. The resulting network comprises ∼89,000 high-confidence gene-gene interactions, organizing genes into hierarchical modules corresponding to protein complexes and pathways, biological processes, and cellular compartments, mirroring principles observed in yeast and highlighting the functional architecture of a human cell. This large-scale genetic network complements the DepMap gene co-essentiality network by capturing unique functional information, uncovering roles of previously uncharacterized genes, and identifying molecular determinants of cancer-cell-line-specific genetic dependencies. This study presents a general data-driven strategy for systematically exploring the roles of genes and their functional connections in human cell lines.

Chemical inducers of proximity (CIPs) stabilize biomolecular interactions, often causing an emergent rewiring of cellular biochemistry. While the discovery of heterobifunctional CIPs is expedited by rational design strategies, molecular glues have relied predominantly on serendipity. We hypothesized that preexisting ligands could be systematically decorated with chemical modifications to discover compounds that recruit proteins to a composite protein-ligand interface. Using sulfur(VI) fluoride exchange-based high-throughput chemistry (HTC) to install 3,163 structurally diverse building blocks onto ENL (eleven-nineteen leukemia) and BRD4 (bromodomain-containing protein 4) ligands, we screened each analog for degrader activity. This revealed dHTC1, an ENL degrader that recruits CRL4CRBN complex through an extended interface of protein-protein contacts and only engages CRBN after pre-forming the ENL:dHTC1 complex. We also identified dHTC3, a molecular glue that selectively dimerizes BRD4 bromodomain 1 to SCFFBXO3, an E3 ligase not previously accessible for chemical rewiring. Altogether, this study introduces HTC as a facile tool to discover new CIPs and new effectors for proximity pharmacology.

Some aggressive cancers exhibit a level of rapid genome change and therapy resistance that is difficult to explain. Research over the past decade has shown that extrachromosomal DNA (ecDNA) can be the cause. When oncogenic genetic elements untether from chromosomes and no longer follow Mendelian inheritance, genomic chaos and accelerated evolution ensue, generating unique ecDNA biology and non-traditional therapeutic vulnerabilities distinct from traditional mutation-targeting approaches. Here, we put forward a holistic view where ecDNA is integrated into the broader Hallmarks of Cancer framework to better understand the problem and chart a path forward.

Chemical proteomics can provide global portraits of small molecule-protein interactions in native biological systems. Such ligandability maps have, however, been mostly restricted to readily accessible cell lines and primary immune cells. Here, we describe an activity-based protein profiling (ABPP) strategy for mapping the covalent ligandability of primary brain cells isolated from mice. By investigating sets of stereochemically defined electrophilic small molecules (stereoprobes), we identify liganding events for diverse brain cell proteins, including many with nervous system-enriched expression. In this category were multiple hyperpolarization-activated cyclic nucleotide-gated (HCN) ion channels, which we show are covalently liganded by tryptoline acrylamide stereoprobes at a conserved cysteine in their cyclic nucleotide-binding domain. The stereoprobes were found to block cAMP-dependent shifts in voltage dependence while sparing basal activity of HCN channels. We thus describe an advanced ABPP platform for identifying ligands targeting nervous system-enriched proteins, including chemical probes that modulate HCN channel function in cells.

No therapies directly block apoptosis in tissue injury or the many diseases driven by cell loss. The BCL-2 family protein BAX is a central mediator of this pathway and C126 resides within a key regulatory region where physiologic or pharmacologic ligands can activate or inhibit its function. Here, we report enantioselective covalent BAX inhibitors that site-specifically react with C126 and confer cytoprotection across multiple cell types. These ligands constrain BAX conformation and suppress apoptosis in a strictly BAX-dependent manner. Medicinal chemistry optimization yielded covalent BAX inhibitor 3 (CBI-3), an analog with pharmacokinetics suitable for in vivo studies. In a murine model of Fas-induced fulminant hepatic failure, CBI-3 reduced hepatocyte apoptosis and preserved liver histology and survival. CBI-3 also conferred cytoprotection of motor neurons derived from human induced pluripotent stem cells of healthy and amyotrophic lateral sclerosis donors. These findings establish covalent BAX inhibition as a therapeutic strategy to directly block pathologic cell death.

Emerging and reemerging viruses pose a significant threat to global health. Although direct-acting antivirals have shown success, their efficacy is limited by the rapid emergence of drug-resistant viral variants. Hence, there is an urgent need for additional broad spectrum antiviral therapeutic strategies. Here, we identify by phenotypic screening a set of stereochemically defined photoreactive small molecules (photo-stereoprobes) that stereoselectively suppress SARS-CoV-2 replication in human lung epithelial cells. Structure-activity relationship-guided chemical proteomics identified the eukaryotic translation termination factor 1 (ETF1) as a target of the photo-stereoprobes, and this interaction was recapitulated with recombinant purified ETF1. We found that the photo-stereoprobes modulate programmed ribosomal frameshifting mechanisms essential for SARS-CoV-2 infection without causing ETF1 degradation, thus distinguishing the photo-stereoprobes from other known ETF1-directed small molecules. We finally show that the photo-stereoprobes also inhibit the replication of additional viruses with noncanonical ribosomal frameshifting mechanisms. Our findings identify a mechanistically distinct class of ETF1 ligands that implicate host translation termination processes as a potential drug target for antiviral development.

RNA-binding proteins (RBPs) play important roles in mRNA transcription, processing, and translation. Chemical tools are lacking for RBPs, which has hindered efforts to perturb and understand RBP function in cells. We previously described a chloroacetamide compound (R)-SKBG-1 that covalently binds the RBP NONO and stabilizes its interactions with mRNAs, leading to transcriptional remodeling and suppression of cancer cell growth. Here, we report the crystal structure of an (R)-SKBG-1:NONO complex, which confirms covalent modification of cysteine-145 at a pocket proximal to the RNA-binding interface of the protein. We show that this pocket can also be targeted by a lower reactivity chlorofluoroacetamide analog (R, R)-GL-373, which retains the pharmacological properties of (R)-SKBG-1, including blockade of estrogen receptor expression in breast cancer cells, while displaying much greater proteome-wide selectivity. Our findings thus show that NONO can be targeted by covalent ligands with high specificity to pharmacologically suppress pro-tumorigenic gene products in cancer cells.

Extrachromosomal DNAs (ecDNAs) are acentric circular DNA elements that frequently mediate oncogene amplification and genomic rearrangements in human cancers. Found across diverse adult and paediatric malignancies, ecDNA drives rapid tumour evolution, metabolic adaptation and treatment resistance. Its presence in precancerous lesions and association with poor outcome underscore the need for improved detection and therapeutic targeting. Recent advances have substantially expanded our understanding of ecDNA biology, revealing mechanisms underlying oncogene plasticity and treatment failure. This Review synthesizes key findings on ecDNA biology, the challenges faced by current therapeutic and detection approaches and the recent discoveries that point to emerging therapeutic vulnerabilities. We propose future directions to ecDNA-focused therapeutic development, including the utility of chemical proteomics approaches, and discuss efforts required to integrate ecDNA diagnostics into the clinic, presenting a roadmap from bench to bedside.

Neurovasculoglial cross-talk underlying breakdown of the neurovascular unit is a central, yet poorly understood, component of many neurodegenerative disorders of the CNS, including retinal disease. Primary fatty acid amides have been identified to regulate this cross-talk between vasculature and neuronal tissues, but specific molecules and mechanisms remain unresolved. Here we show, using an unbiased high-resolution metabolomics screen, that erucamide, a 22:1 monounsaturated omega-9 fatty acid amide, is highly dysregulated during photoreceptor degeneration in mice. In vivo delivery of erucamide using organosilane-modified porous silicon nanoparticles activated retinal myeloid cells, leading to the upregulation of angiogenic and neurotrophic cytokines that limited vascular and neuronal degeneration. We identified TMEM19 as a binding protein for erucamide that is crucial for myeloid cell activation and subsequent neuroprotection. These findings reveal a previously unknown primary fatty acid amide pathway that modulates neuroimmune interactions during retinal degenerative diseases. We propose erucamide and analogs as candidate therapeutics.

Innate immune cells, such as monocytes and macrophages, provide the earliest defense against intracellular pathogen infection by initiating signaling pathways and restricting pathogen replication. However, the full complement of proteins that mediate cell-autonomous immunity remains incompletely defined. Here, we applied cysteine-directed activity-based protein profiling (ABPP) to map proteome-wide cysteine reactivity changes in THP-1 monocytes and primary human monocyte-derived macrophages during Mycobacterium tuberculosis (Mtb) infection. Across both cell types, we quantified 148 cysteine residues with altered reactivity. Knockdown of a subset of proteins harboring infection-induced reactivity significantly altered Mtb replication in THP-1 monocytes, linking proteins with reactive cysteines to antimicrobial defense. These data define previously unrecognized host protein changes during Mtb infection and provide a resource for investigating post-translational events that regulate innate immune responses to intracellular bacteria.

Genetic and dietary cues are known drivers of obesity, yet how they converge at the molecular level is incompletely understood. Here we show that PPARγ supports hypertrophic expansion of adipose tissue via transcriptional control of LPCAT3, an endoplasmic reticulum (ER)-resident O-acyltransferase that selectively enriches diet-derived omega-6 polyunsaturated fatty acids (n-6 PUFAs) in the membrane lipidome. In mice fed a high-fat diet, lowering membrane n-6 PUFA levels through genetic or dietary interventions results in aberrant adipose triglyceride (TG) turnover, ectopic fat deposition and insulin resistance. Additionally, we detail a non-canonical adaptive response in ‘lipodystrophic’ Lpcat3–/– adipose tissues that engages a futile lipid cycle to increase metabolic rate and offset lipid overflow to ectopic sites. Live-cell imaging, lipidomics and molecular dynamics simulations reveal that adipocyte LPCAT3 activity enriches n-6 arachidonate in the phosphatidylethanolamine (PE)-dense ER–lipid droplet interface. Functionally, this localized PE remodelling optimizes TG storage by driving the formation of large droplets that exhibit greater resistance to adipose TG lipase activity. These findings highlight the PPARγ–LPCAT3 axis as a mechanistic link between dietary n-6 PUFA intake, adipose expandability and systemic energy balance. Dietary n-6 PUFAs enhance adipose tissue expandability through the PPARγ–LPCAT3 membrane remodelling axis.

Targeted protein degradation (TPD) offers a promising approach for chemical probe and drug discovery that uses small molecules or biologics to direct proteins to the cellular machinery for destruction. Among the >600 human E3 ligases, CRBN and VHL have served as workhorses for ubiquitin–proteasome system-dependent TPD. Identification of additional E3 ligases capable of supporting TPD would unlock the full potential of this mechanism for both research and pharmaceutical applications. This perspective discusses recent strategies to expand the scope of TPD and the surprising convergence of these diverse screening efforts on a handful of E3 ligases, specifically DCAF16, DCAF11 and FBXO22. We speculate that a combination of properties, including superficial ligandability, potential for promiscuous substrate interactions and high occupancy in Cullin–RING complexes, may position these E3 ligases as ‘low-hanging fruit’ in TPD screens. We also discuss complementary approaches that might further expand the E3 ligase landscape supporting TPD. This Perspective discusses recent strategies to expand the scope of targeted protein degradation (TPD) and the implications of unexpected convergence of diverse screening efforts on a small subset of TPD-competent E3 ligases in the human proteome.