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The cancer genomics revolution has served up a plethora of promising and challenging targets for the drug discovery community. The field of targeted protein degradation (TPD) uses small molecules to reprogram the protein homeostasis system to destroy desired target proteins. In the last decade, remarkable progress has enabled the rational development of degraders for a large number of target proteins, with over 20 molecules targeting more than 12 proteins entering clinical development. While TPD has been fully credentialed by the prior development of immunomodulatory drug (IMiD) class for the treatment of multiple myeloma, the field is poised for a "Gleevec moment" in which robust clinical efficacy of a rationally developed novel degrader against a preselected target is firmly established. Here, we endeavor to provide a high-level evaluation of exciting developments in the field and comment on steps that may realize the full potential of this new therapeutic modality. [Display omitted] Teng et al. present a summary of recent progress in the rapidly evolving field of targeted protein degradation, with a particular emphasis on the opportunities and approaches for translation. [ABSTRACT FROM AUTHOR]

In this issue of Cell Chemical Biology , Bonazzi et al. demonstrate that pharmacologically degrading the transcription factor Helios (IKZF2) results in destabilization of regulatory T cells, which normally restrain anti-tumor immunity. These results highlight how molecular glue degraders can selectively target previously undruggable proteins with potential applications in the clinic. [ABSTRACT FROM AUTHOR]

Building on years of basic scientific discovery, recent advances in the fields of cancer genetics and medicinal chemistry are now converging to revolutionize the treatment of cancer. Starting with serendipitous observations in rare subsets of cancer, a paradigm shift in clinical research is poised to ensure that new molecular insights are rapidly applied to shape emerging cancer therapies. Could this mark a turning point in the “War on Cancer”? [ABSTRACT FROM AUTHOR]

To identify novel proteins regulating the microtubule cytoskeleton, we screened a library of purine derivatives using mitotic spindle assembly in Xenopus egg extracts as an assay. Out of a collection of 1561 compounds, we identified 15 that destabilized microtubules without targeting tubulin directly, resulting in small spindles. Affinity chromatography with one compound, named diminutol, revealed a potential target as NQO1, an NADP-dependent oxidoreductase. A role for NQO1 in influencing microtubule polymerization was confirmed through inhibition studies using known inhibitors and immunodepletion. Therefore, this chemical approach has identified a novel factor required for microtubule morphogenesis and cell division. [Copyright &y& Elsevier]

Selective small-molecule inhibitors of protein kinases can serve as powerful tools to elucidate biological function. Efforts to develop potential drug candidates have yielded a wealth of kinase inhibitors. However, selecting the optimal kinase inhibitor for a particular application can be challenging. While the optimal inhibitor will be application specific, we have attempted to summarize some of the best reported inhibitors for various kinases. [ABSTRACT FROM AUTHOR]

Selective small-molecule inhibitors of protein kinases can serve as powerful tools to elucidate biological function. Efforts to develop potential drug candidates have yielded a wealth of kinase inhibitors. However, selecting the optimal kinase inhibitor for a particular application can be challenging. While the optimal inhibitor will be application specific, we have attempted to summarize some of the best reported inhibitors for various kinases. [ABSTRACT FROM AUTHOR]

Chemically induced protein degradation is a powerful strategy for perturbing cellular biochemistry. The predominant mechanism of action for protein degrader drugs involves an induced proximity between the cellular ubiquitin-conjugation machinery and a target. Unlike traditional small molecule enzyme inhibition, targeted protein degradation can clear an undesired protein from cells. We demonstrate here the use of peptide ligands for Kelch-like homology domain-containing protein 2 (KLHDC2), a substrate adapter protein and member of the cullin-2 (CUL2) ubiquitin ligase complex, for targeted protein degradation. Peptide-based bivalent compounds that can induce proximity between KLHDC2 and target proteins cause degradation of the targeted factors. The cellular activity of these compounds depends on KLHDC2 binding. This work demonstrates the utility of KLHDC2 for targeted protein degradation and exemplifies a strategy for the rational design of peptide-based ligands useful for this purpose. [Display omitted] • A PROTAC that induces protein degradation via the KLHDC2 E3 ubiquitin ligase • Pharmacological demonstration that KLHDC2 is suitable for targeted protein degradation • KLHDC2-mediated target degradation at low-cellular target occupancy Kim, Seo, Jeon et al. synthesized bivalent PROTAC molecules that link ATP-competitive kinase inhibitors with peptide ligands for the KLHDC2 E3 ubiquitin ligase. These compounds induce targeted protein degradation in human cancer cells. The authors use chemical controls and ubiquitin ligase inhibition to confirm that these compounds act on-mechanism. [ABSTRACT FROM AUTHOR]

Some of the most widely used drugs, such as aspirin and penicillin, are covalent drugs. Covalent binding can improve potency, selectivity, and duration of the effects, but the intrinsic reactivity represents a potential liability and may result in idiosyncratic toxicity. For decades, the cons were believed to outweigh the pros, and covalent targeting was deprioritized in drug discovery. Recently, several covalent inhibitors have been approved for cancer treatment, thus rebooting the field. In this review, we briefly reflect on the history of selective covalent targeting, and provide a comprehensive overview of emerging developments from a chemical biology stand-point. Our discussion will reflect on efforts to validate irreversible covalent ligands, expand the scope of targets, and discover new ligands and warheads. We conclude with a brief commentary of remaining limitations and emerging opportunities in selective covalent targeting. In this review, Zhang et al. provide a chemical biology perspective on the field of selective covalent targeting. The authors highlight approaches to robust validation and standards for irreversible covalent ligands, and comment on recent studies that expand the scope of targets, ligands and warheads. [ABSTRACT FROM AUTHOR]

Interleukin (IL)-2-inducible T cell kinase (ITK) is essential for T cell receptor (TCR) signaling and plays an integral role in T cell proliferation and differentiation. Unlike the ITK homolog BTK, no inhibitors of ITK are currently US Food and Drug Administration (FDA) approved. In addition, recent studies have identified mutations within BTK that confer resistance to both covalent and non-covalent inhibitors. Here, as an alternative strategy, we report the development of BSJ-05-037, a potent and selective heterobifunctional degrader of ITK. BSJ-05-037 displayed enhanced anti-proliferative effects relative to its parent inhibitor BMS-509744, blocked the activation of NF-kB/GATA-3 signaling, and increased the sensitivity of T cell lymphoma cells to cytotoxic chemotherapy both in vitro and in vivo. In summary, targeted degradation of ITK is a novel approach to modulate TCR signal strength that could have broad application for the investigation and treatment of T cell-mediated diseases. [Display omitted] • Development of an ITK-selective small-molecule degrader • ITK degradation suppresses canonical NF-κB pathway and GATA-3 expression • ITK degradation overcomes chemotherapy resistance in T cell lymphomas ITK transduces constitutive TCR signaling and contributes to chemoresistance in T cell lymphoproliferative diseases. Here, Jiang and colleagues develop BSJ-05-037, a degrader with proteome-wide selectivity for ITK. Targeted ITK degradation induced by BSJ-05-037 allows controlling of key gene expression in TCR/NF-κB signaling and thus overcomes chemoresistance in T cell lymphoma. [ABSTRACT FROM AUTHOR]

Recent interest in the role that extracellular signal-regulated kinase 5 (ERK5) plays in various diseases, particularly cancer and inflammation, has grown. Phenotypes observed from genetic knockdown or deletion of ERK5 suggested that targeting ERK5 could have therapeutic potential in various disease settings, motivating the development ATP-competitive ERK5 inhibitors. However, these inhibitors were unable to recapitulate the effects of genetic loss of ERK5, suggesting that ERK5 may have key kinase-independent roles. To investigate potential non-catalytic functions of ERK5, we report the development of INY-06-061, a potent and selective heterobifunctional degrader of ERK5. In contrast to results reported through genetic knockdown of ERK5, INY-06-061-induced ERK5 degradation did not induce anti-proliferative effects in multiple cancer cell lines or suppress inflammatory responses in primary endothelial cells. Thus, we developed and characterized a chemical tool useful for validating phenotypes reported to be associated with genetic ERK5 ablation and for guiding future ERK5-directed drug discovery efforts. [Display omitted] • PROTACs that incorporate XMD17-109 and JWG-071 are not selective for ERK5 • INY-06-061 is a potent and highly selective heterobifunctional degrader of ERK5 • INY-06-061 treatment does not compromise viability in multiple cancer cell lines • INY-06-061 does not affect pro-inflammatory cytokine secretion in endothelial cells You et al. report the development and characterization of INY-06-061, a potent and highly selective ERK5 degrader. While pharmacological ERK5 degradation did not result in potent anti-proliferative or anti-inflammatory effects in this study, INY-06-061 can serve as a useful chemical probe to further dissect/investigate the biological functions of ERK5. [ABSTRACT FROM AUTHOR]

Targeted protein degradation (TPD) uses small molecules to recruit E3 ubiquitin ligases into the proximity of proteins of interest, inducing ubiquitination-dependent degradation. A major bottleneck in the TPD field is the lack of accessible E3 ligase ligands for developing degraders. To expand the E3 ligase toolbox, we sought to convert the Kelch-like ECH-associated protein 1 (KEAP1) inhibitor KI696 into a recruitment handle for several targets. While we were able to generate KEAP1-recruiting degraders of BET family and murine focal adhesion kinase (FAK), we discovered that the target scope of KEAP1 was narrow, as targets easily degraded using a cereblon (CRBN)-recruiting degrader were refractory to KEAP1-mediated degradation. Linking the KEAP1-binding ligand to a CRBN-binding ligand resulted in a molecule that induced degradation of KEAP1 but not CRBN. In sum, we characterize tool compounds to explore KEAP1-mediated ubiquitination and delineate the challenges of exploiting new E3 ligases for generating bivalent degraders. [Display omitted] • DGY-06-177-pk2 induced KEAP1-dependent BRD4 degradation • NJH-04-098 results in FAK degradation in mice but not human cells • KEAP1-recruiting PROTACs are less versatile than VHL or CRBN • CRBN-based KEAP1 PROTAC effectively degrades KEAP1 Du et al. explores a variety of bivalent KEAP1-recruiting degraders to assess the generality of KEAP as an E3 ligase for targeted protein degradation They found the targets easily degraded using a cereblon (CRBN)- or VHL-recruiting degrader were refractory to KEAP1-mediated degradation. [ABSTRACT FROM AUTHOR]

Reactivation of fetal hemoglobin expression by the downregulation of BCL11A is a promising treatment for β-hemoglobinopathies. A detailed understanding of BCL11A-mediated repression of γ-globin gene (HBG1/2) transcription is lacking, as studies to date used perturbations by shRNA or CRISPR-Cas9 gene editing. We leveraged the dTAG PROTAC degradation platform to acutely deplete BCL11A protein in erythroid cells and examined consequences by nascent transcriptomics, proteomics, chromatin accessibility, and histone profiling. Among 31 genes repressed by BCL11A, HBG1/2 and HBZ show the most abundant and progressive changes in transcription and chromatin accessibility upon BCL11A loss. Transcriptional changes at HBG1/2 were detected in <2 h. Robust HBG1/2 reactivation upon acute BCL11A depletion occurred without the loss of promoter 5-methylcytosine (5mC). Using targeted protein degradation, we establish a hierarchy of gene reactivation at BCL11A targets, in which nascent transcription is followed by increased chromatin accessibility, and both are uncoupled from promoter DNA methylation at the HBG1/2 loci. [Display omitted] • PROTAC-mediated degradation of BCL11A reactivates high-level γ-globin expression • BCL11A represses <31 primary target genes; HBG , HBZ most induced upon BCL11A loss • Presence of BCL11A is the major barrier to γ-globin promoter activation • Upon BCL11A loss, increased chromatin accessibility closely follows transcription Reactivation of γ-globin by the downregulation of BCL11A expression is a promising strategy for the treatment of sickle cell disease. In this issue of Cell Chemical Biology , Mehta et al. use PROTAC-mediated depletion of BCL11A to identify a small set of target genes and chart the kinetics of γ-globin induction. [ABSTRACT FROM AUTHOR]

Summary Persistent accumulation of misfolded proteins causes endoplasmic reticulum (ER) stress, a prominent feature in many neurodegenerative diseases including amyotrophic lateral sclerosis (ALS). Here we report the identification of homeodomain interacting protein kinase 2 (HIPK2) as the essential link that promotes ER-stress-induced cell death via the IRE1α-ASK1-JNK pathway. ER stress, induced by tunicamycin or SOD1 G93A , activates HIPK2 by phosphorylating highly conserved serine and threonine residues (S359/T360) within the activation loop of the HIPK2 kinase domain. In SOD1 G93A mice, loss of HIPK2 delays disease onset, reduces cell death in spinal motor neurons, mitigates glial pathology, and improves survival. Remarkably, HIPK2 activation positively correlates with TDP-43 proteinopathy in NEFH -tTA/ tetO -hTDP-43ΔNLS mice, sporadic ALS and C9ORF72 ALS, and blocking HIPK2 kinase activity protects motor neurons from TDP-43 cytotoxicity. These results reveal a previously unrecognized role of HIPK2 activation in ER-stress-mediated neurodegeneration and its potential role as a biomarker and therapeutic target for ALS. Video Abstract [ABSTRACT FROM AUTHOR]

Summary Dengue virus infects more than 300 million people annually, yet there is no widely protective vaccine or drugs against the virus. Efforts to develop antivirals against classical targets such as the viral protease and polymerase have not yielded drugs that have advanced to the clinic. Here, we show that the allosteric Abl kinase inhibitor GNF-2 interferes with dengue virus replication via activity mediated by cellular Abl kinases but additionally blocks viral entry via an Abl-independent mechanism. To characterize this newly discovered antiviral activity, we developed disubstituted pyrimidines that block dengue virus entry with structure-activity relationships distinct from those driving kinase inhibition. We demonstrate that biotin- and fluorophore-conjugated derivatives of GNF-2 interact with the dengue glycoprotein, E, in the pre-fusion conformation that exists on the virion surface, and that this interaction inhibits viral entry. This study establishes GNF-2 as an antiviral compound with polypharmacological activity and provides “lead” compounds for further optimization efforts. [ABSTRACT FROM AUTHOR]

Summary The Hippo/YAP signaling pathway is a crucial regulator of tissue growth, stem cell activity, and tumorigenesis. However, the mechanism by which YAP controls transcription remains to be fully elucidated. Here, we utilize global chromatin occupancy analyses to demonstrate that robust YAP binding is restricted to a relatively small number of distal regulatory elements in the genome. YAP occupancy defines a subset of enhancers and superenhancers with the highest transcriptional outputs. YAP modulates transcription from these elements predominantly by regulating promoter-proximal polymerase II (Pol II) pause release. Mechanistically, YAP interacts and recruits the Mediator complex to enhancers, allowing the recruitment of the CDK9 elongating kinase. Genetic and chemical perturbation experiments demonstrate the requirement for Mediator and CDK9 in YAP-driven phenotypes of overgrowth and tumorigenesis. Our results here uncover the molecular mechanisms employed by YAP to exert its growth and oncogenic functions, and suggest strategies for intervention. [ABSTRACT FROM AUTHOR]

Summary Triple-negative breast cancer (TNBC) is a highly aggressive form of breast cancer that exhibits extremely high levels of genetic complexity and yet a relatively uniform transcriptional program. We postulate that TNBC might be highly dependent on uninterrupted transcription of a key set of genes within this gene expression program and might therefore be exceptionally sensitive to inhibitors of transcription. Utilizing kinase inhibitors and CRISPR/Cas9-mediated gene editing, we show here that triple-negative but not hormone receptor-positive breast cancer cells are exceptionally dependent on CDK7, a transcriptional cyclin-dependent kinase. TNBC cells are unique in their dependence on this transcriptional CDK and suffer apoptotic cell death upon CDK7 inhibition. An “Achilles cluster” of TNBC-specific genes is especially sensitive to CDK7 inhibition and frequently associated with super-enhancers. We conclude that CDK7 mediates transcriptional addiction to a vital cluster of genes in TNBC and CDK7 inhibition may be a useful therapy for this challenging cancer. [ABSTRACT FROM AUTHOR]

Protein kinases are a large family of approximately 530 highly conserved enzymes that transfer a γ-phosphate group from ATP to a variety of amino acid residues, such as tyrosine, serine, and threonine, that serves as a ubiquitous mechanism for cellular signal transduction. The clinical success of a number of kinase-directed drugs and the frequent observation of disease causing mutations in protein kinases suggest that a large number of kinases may represent therapeutically relevant targets. To date, the majority of clinical and preclinical kinase inhibitors are ATP competitive, noncovalent inhibitors that achieve selectivity through recognition of unique features of particular protein kinases. Recently, there has been renewed interest in the development of irreversible inhibitors that form covalent bonds with cysteine or other nucleophilic residues in the ATP-binding pocket. Irreversible kinase inhibitors have a number of potential advantages including prolonged pharmacodynamics, suitability for rational design, high potency, and ability to validate pharmacological specificity through mutation of the reactive cysteine residue. Here, we review recent efforts to develop cysteine-targeted irreversible protein kinase inhibitors and discuss their modes of recognizing the ATP-binding pocket and their biological activity profiles. In addition, we provided an informatics assessment of the potential “kinase cysteinome” and discuss strategies for the efficient development of new covalent inhibitors. [ABSTRACT FROM AUTHOR]

Summary: The c-Fes protein-tyrosine kinase modulates cellular signaling pathways governing differentiation, the innate immune response, and vasculogenesis. Here, we report the identification of types I and II kinase inhibitors with potent activity against c-Fes both in vitro and in cell-based assays. One of the most potent inhibitors is the previously described anaplastic lymphoma kinase inhibitor TAE684. The crystal structure of TAE684 in complex with the c-Fes SH2-kinase domain showed excellent shape complementarity with the ATP-binding pocket and a key role for the gatekeeper methionine in the inhibitory mechanism. TAE684 and two pyrazolopyrimidines with nanomolar potency against c-Fes in vitro were used to establish a role for this kinase in osteoclastogenesis, illustrating the value of these inhibitors as tool compounds to probe the diverse biological functions associated with this unique kinase. [Copyright &y& Elsevier]

Summary: The mitogen-activated kinases JNK1/2/3 are key enzymes in signaling modules that transduce and integrate extracellular stimuli into coordinated cellular response. Here, we report the discovery of irreversible inhibitors of JNK1/2/3. We describe two JNK3 cocrystal structures at 2.60 and 2.97 Å resolution that show the compounds form covalent bonds with a conserved cysteine residue. JNK-IN-8 is a selective JNK inhibitor that inhibits phosphorylation of c-Jun, a direct substrate of JNK, in cells exposed to submicromolar drug in a manner that depends on covalent modification of the conserved cysteine residue. Extensive biochemical, cellular, and pathway-based profiling establish the selectivity of JNK-IN-8 for JNK and suggests that the compound will be broadly useful as a pharmacological probe of JNK-dependent signal transduction. Potential lead compounds have also been identified for kinases, including IRAK1, PIK3C3, PIP4K2C, and PIP5K3. [ABSTRACT FROM AUTHOR]

Summary: Selective protein kinase inhibitors have only been developed against a small number of kinase targets. Here we demonstrate that “high-throughput kinase profiling” is an efficient method for the discovery of lead compounds for established as well as unexplored kinase targets. We screened a library of 118 compounds constituting two distinct scaffolds (furan-thiazolidinediones and pyrimido-diazepines) against a panel of 353 kinases. A distinct kinase selectivity profile was observed for each scaffold. Selective inhibitors were identified with submicromolar cellular activity against PIM1, ERK5, ACK1, MPS1, PLK1-3, and Aurora A,B kinases. In addition, we identified potent inhibitors for so far unexplored kinases such as DRAK1, HIPK2, and DCAMKL1 that await further evaluation. This inhibitor-centric approach permits comprehensive assessment of a scaffold of interest and represents an efficient and general strategy for identifying new selective kinase inhibitors. [ABSTRACT FROM AUTHOR]

Summary: Protein kinases are intensely studied mediators of cellular signaling, yet important questions remain regarding their regulation and in vivo properties. Here, we use a probe-based chemoprotemics platform to profile several well studied kinase inhibitors against >200 kinases in native cell proteomes and reveal biological targets for some of these inhibitors. Several striking differences were identified between native and recombinant kinase inhibitory profiles, in particular, for the Raf kinases. The native kinase binding profiles presented here closely mirror the cellular activity of these inhibitors, even when the inhibition profiles differ dramatically from recombinant assay results. Additionally, Raf activation events could be detected on live cell treatment with inhibitors. These studies highlight the complexities of protein kinase behavior in the cellular context and demonstrate that profiling with only recombinant/purified enzymes can be misleading. [ABSTRACT FROM AUTHOR]

Summary: Eukaryotic cells counteract oxidative and other environmental stress through the activation of Nrf2, the transcription factor that controls the expression of a host of protective enzymes by binding to the antioxidant response element (ARE). The electrophilic molecules that are able to activate Nrf2 and its downstream target genes have demonstrated therapeutic potential in carcinogen-induced tumor models. Using a high-throughput cellular screen, we discovered a class of ARE activator, which we named AI-1, that activates Nrf2 by covalently modifying Keap1, the negative regulator of Nrf2. Biochemical studies indicated that modification of Cys151 of Keap1 by AI-1 disrupted the ability of Keap1 to serve as an adaptor for Cul3-Keap1 ubiquitin ligase complex, thereby causing stabilization and transcriptional activation of Nrf2. AI-1 and its biotinylated derivative are useful pharmacological probes for investigating the molecular details of the cellular antioxidant response. [Copyright &y& Elsevier]

Summary: The fibroblast growth factor receptor tyrosine kinases (FGFR1, 2, 3, and 4) represent promising therapeutic targets in a number of cancers. We have developed the first potent and selective irreversible inhibitor of FGFR1, 2, 3, and 4, which we named FIIN-1 that forms a covalent bond with cysteine 486 located in the P loop of the FGFR1 ATP binding site. We demonstrated that the inhibitor potently inhibits Tel-FGFR1-transformed Ba/F3 cells (EC50 = 14 nM) as well as numerous FGFR-dependent cancer cell lines. A biotin-derivatized version of the inhibitor, FIIN-1-biotin, was shown to covalently label FGFR1 at Cys486. FIIN-1 is a useful probe of FGFR-dependent cellular phenomena and may provide a starting point of the development of therapeutically relevant irreversible inhibitors of wild-type and drug-resistant forms of FGFR kinases. [Copyright &y& Elsevier]

Summary: The mTORC1 and mTORC2 pathways regulate cell growth, proliferation, and survival. We identify DEPTOR as an mTOR-interacting protein whose expression is negatively regulated by mTORC1 and mTORC2. Loss of DEPTOR activates S6K1, Akt, and SGK1, promotes cell growth and survival, and activates mTORC1 and mTORC2 kinase activities. DEPTOR overexpression suppresses S6K1 but, by relieving feedback inhibition from mTORC1 to PI3K signaling, activates Akt. Consistent with many human cancers having activated mTORC1 and mTORC2 pathways, DEPTOR expression is low in most cancers. Surprisingly, DEPTOR is highly overexpressed in a subset of multiple myelomas harboring cyclin D1/D3 or c-MAF/MAFB translocations. In these cells, high DEPTOR expression is necessary to maintain PI3K and Akt activation and a reduction in DEPTOR levels leads to apoptosis. Thus, we identify a novel mTOR-interacting protein whose deregulated overexpression in multiple myeloma cells represents a mechanism for activating PI3K/Akt signaling and promoting cell survival. [Copyright &y& Elsevier]

Summary: Kinase inhibitors that bind to the ATP cleft can be broadly classified into two groups: those that bind exclusively to the ATP site with the kinase assuming a conformation otherwise conducive to phosphotransfer (type I), and those that exploit a hydrophobic site immediately adjacent to the ATP pocket made accessible by a conformational rearrangement of the activation loop (type II). To date, all type II inhibitors were discovered by using structure-activity-guided optimization strategies. Here, we describe a general pharmacophore model of type II inhibition that enables a rational “hybrid-design” approach whereby a 3-trifluoromethylbenzamide functionality is appended to four distinct type I scaffolds in order to convert them into their corresponding type II counterparts. We demonstrate that the designed compounds function as type II inhibitors by using biochemical and cellular kinase assays and by cocrystallography with Abl. [Copyright &y& Elsevier]

Summary: We describe a multicopy gene suppression screen of drug sensitivity in Saccharomyces cerevisiae that facilitates the identification of cellular targets of small molecules. An array of yeast transformants harboring a multicopy yeast genomic library was screened for resistance to growth inhibitors. Comparison of array growth patterns for several such inhibitors allowed the differentiation of general and molecule-specific genetic suppressors. Specific resistance to phenylaminopyrimidine (1), an inhibitor identified from a kinase-directed library, was associated with the overexpression of Pkc1 and a subset of downstream kinases. Components of two other pathways (pheromone response/filamentous growth and Pho85 kinase) that genetically interact with the PKC1 MAPK signaling cascade were also identified. Consistent with the suppression screen, inhibitor 1 bound to Pkc1 in yeast cell lysate and inhibited its activity in vitro. These results demonstrate the utility of this approach for the rapid deconvolution of small-molecule targets. [Copyright &y& Elsevier]

Hymenialdisine (HMD) is a sponge-derived natural product kinase inhibitor with nanomolar activity against CDKs, Mek1, GSK3β, and CK1 and micromolar activity against Chk1. In order to explore the broader application of the pyrrolo[2,3-c]azepine skeleton of HMD as a general kinase inhibitory scaffold, we searched for additional protein targets using affinity chromatography in conjunction with the synthesis of diverse HMD analogs and profiled HMD against a panel of 60 recombinant enzymes. This effort has led to nanomolar to micromolar inhibitors of 11 new targets including p90RSK, KDR, c-Kit, Fes, MAPK1, PAK2, PDK1, PKCθ, PKD2, Rsk1, and SGK. The synthesis of HMD analogs has resulted in the identification of compounds with enhanced and/or dramatically altered selectivities relative to HMD (28n) and in molecules with antiproliferative activities 30-fold higher than HMD (28p). [Copyright &y& Elsevier]

MKK4/7 are kinases that phosphorylate JNKs and regulate the MAPK signaling pathway. Their overexpression has been associated with tumorigenesis and aggressiveness in cancers such as breast, prostate, non-small cell lung, and pediatric leukemia, making them a potential target for inhibitor development. Here, we report the discovery, development, and validation of a dual MKK4/7 inhibitor, BSJ-04-122, that covalently targets a conserved cysteine located before the DFG motif and displays excellent kinome selectivity. BSJ-04-122 exhibits potent cellular target engagement and induces robust target-specific downstream effects. The combination of the dual MKK4/7 inhibitor with a selective, covalent JNK inhibitor demonstrated an enhanced antiproliferative activity against triple-negative breast cancer cells. Taken together, the results show that BSJ-04-122 represents a pharmacological probe for MKK4/7 and credential covalent targeting as a way to explore the therapeutic potential of these kinases. • BSJ-04-122 displays excellent selectivity both in vitro and in cellular conditions • BSJ-04-122 induces robust reduction of JNK phosphorylation • Combination of BSJ-04-122 with JNK-IN-8 showed enhanced antiproliferative effects Jiang et al. develop and characterize the first dual MKK4/7 covalent inhibitor BSJ-04-122 by labeling the cysteine before DFG. They demonstrate that BSJ-04-122 exhibits excellent selectivity, induces robust reduction of JNK phosphorylation, and demonstrates enhanced antiproliferative effects when combined with JNK-IN-8. [ABSTRACT FROM AUTHOR]

MKK7 (MEK7) is a key regulator of the JNK stress signaling pathway and targeting MKK7 has been proposed as a chemotherapeutic strategy. Detailed understanding of the MKK7 structure and factors that affect its activity is therefore of critical importance. Here, we present a comprehensive set of MKK7 crystal structures revealing insights into catalytic domain plasticity and the role of the N-terminal regulatory helix, conserved in all MAP2Ks, mediating kinase activation. Crystal structures harboring this regulatory helix revealed typical structural features of active kinase, providing exclusively a first model of the MAP2K active state. A small-molecule screening campaign yielded multiple scaffolds, including type II irreversible inhibitors a binding mode that has not been reported previously. We also observed an unprecedented allosteric pocket located in the N-terminal lobe for the approved drug ibrutinib. Collectively, our structural and functional data expand and provide alternative targeting strategies for this important MAP2K kinase. • The N-terminal regulatory helix allosterically stabilizes an active state in MKK7 • Diverse covalent type I and type II inhibitors target flexible region in MKK7 • Unprecedented discovery of an allosteric binding site for ibrutinib Schröder et al. presents a first structure of active MKK7 revealing an allosteric role of the N-terminal helix, providing a model for the MAP2K activation mechanism. Screening identified potent chemically diverse MKK7 inhibitors with diverse binding modes abrogating JNK signaling. Crystal structure revealed ibrutinib binding at an unprecedented allosteric site. [ABSTRACT FROM AUTHOR]

Doublecortin-like kinase 1 (DCLK1) is critical for neurogenesis, but overexpression is also observed in multiple cancers and is associated with poor prognosis. Nevertheless, the function of DCLK1 in cancer, especially the context-dependent functions, are poorly understood. We present a "toolkit" that includes the DCLK1 inhibitor DCLK1-IN-1, a complementary DCLK1-IN-1-resistant mutation G532A, and kinase dead mutants D511N and D533N, which can be used to investigate signaling pathways regulated by DCLK1. Using a cancer cell line engineered to be DCLK1 dependent for growth and cell migration, we show that this toolkit can be used to discover associations between DCLK1 kinase activity and biological processes. In particular, we show an association between DCLK1 and RNA processing, including the identification of CDK11 as a potential substrate of DCLK1 using phosphoproteomics. • Overexpression or DCLK1 in DLD-1 cells results in DCLK1-dependent growth • Genetic or chemical ablation of DCLK1 activity inhibits DCLK1-transformed cell growth • The DCLK1 mutation G532A results in DCLK1-IN-1-resistance • DCLK1 inhibition decreases RNA processing and other cellular processes DCLK1 overexpression occurs in cancer, suggesting that DCLK1 is a therapeutic target. We report a tool kit for the study of DCLK1, including engineered DCLK1-dependent cancer cells, a DCLK1 inhibitor, and DCLK1 mutations that ablate kinase activity or confer drug resistance. We found a new association between DCLK1 and RNA processing. [ABSTRACT FROM AUTHOR]

Protein phosphatase 2A (PP2A) enzymes can suppress tumors, but they are often inactivated in human cancers overexpressing inhibitory proteins. Here, we identify a class of small-molecule iHAPs (improved heterocyclic activators of PP2A) that kill leukemia cells by allosterically assembling a specific heterotrimeric PP2A holoenzyme consisting of PPP2R1A (scaffold), PPP2R5E (B56ε, regulatory), and PPP2CA (catalytic) subunits. One compound, iHAP1, activates this complex but does not inhibit dopamine receptor D2, a mediator of neurologic toxicity induced by perphenazine and related neuroleptics. The PP2A complex activated by iHAP1 dephosphorylates the MYBL2 transcription factor on Ser241, causing irreversible arrest of leukemia and other cancer cells in prometaphase. In contrast, SMAPs, a separate class of compounds, activate PP2A holoenzymes containing a different regulatory subunit, do not dephosphorylate MYBL2, and arrest tumor cells in G1 phase. Our findings demonstrate that small molecules can serve as allosteric switches to activate distinct PP2A complexes with unique substrates. • Phenothiazine analog iHAP1 activates PP2A-B56ε and potently kills malignant cells • iHAP1 does not inhibit dopamine signaling or cause prohibitive neurologic toxicity • PP2A-B56ε dephosphorylates MYBL2-Ser241, causing prometaphase arrest with apoptosis • Other PP2A activators, SMAPs, activate PP2A-B55α and target different substrates Protein phosphatase 2A (PP2A) enzymes often function as tumor suppressors but are typically unmutated in cancers. Therefore, they are potentially attractive targets for small-molecule activators. Morita et al. show that different PP2A holoenzymes, composed of distinct subunits and acting on unique substrates, can be specifically targeted by different small-molecule allosteric activators. [ABSTRACT FROM AUTHOR]

Mammalian tissues engage in specialized physiology that is regulated through reversible modification of protein cysteine residues by reactive oxygen species (ROS). ROS regulate a myriad of biological processes, but the protein targets of ROS modification that drive tissue-specific physiology in vivo are largely unknown. Here, we develop Oximouse, a comprehensive and quantitative mapping of the mouse cysteine redox proteome in vivo. We use Oximouse to establish several paradigms of physiological redox signaling. We define and validate cysteine redox networks within each tissue that are tissue selective and underlie tissue-specific biology. We describe a common mechanism for encoding cysteine redox sensitivity by electrostatic gating. Moreover, we comprehensively identify redox-modified disease networks that remodel in aged mice, establishing a systemic molecular basis for the long-standing proposed links between redox dysregulation and tissue aging. We provide the Oximouse compendium as a framework for understanding mechanisms of redox regulation in physiology and aging. • A comprehensive and quantitative map of the mouse cysteine redox proteome in vivo • Redox networks are highly tissue selective and underlie tissue-specific biology • Cysteine thiol redox sensitivity is encoded by local electrostatic gating • Identification of redox-modified protein disease networks that remodel in aged mice A technology to study the tissue-specific effects of redox signaling enables a deeper understanding of the role of ROS in physiology and aging. [ABSTRACT FROM AUTHOR]

KRAS is the most frequently mutated oncogene found in pancreatic, colorectal, and lung cancers. Although it has been challenging to identify targeted therapies for cancers harboring KRAS mutations, KRASG12C can be targeted by small-molecule inhibitors that form covalent bonds with cysteine 12 (C12). Here, we designed a library of C12-directed covalent degrader molecules (PROTACs) and subjected them to a rigorous evaluation process to rapidly identify a lead compound. Our lead degrader successfully engaged CRBN in cells, bound KRASG12C in vitro , induced CRBN/KRASG12C dimerization, and degraded GFP-KRASG12C in reporter cells in a CRBN-dependent manner. However, it failed to degrade endogenous KRASG12C in pancreatic and lung cancer cells. Our data suggest that inability of the lead degrader to effectively poly-ubiquitinate endogenous KRASG12C underlies the lack of activity. We discuss challenges for achieving targeted KRASG12C degradation and proposed several possible solutions which may lead to efficient degradation of endogenous KRASG12C. • A comprehensive degrader molecule (PROTAC) library for KRASG12C is described • Lead compound degrades GFP-KRASG12C in a CRBN-dependent manner • Challenges and solutions for achieving endogenous KRASG12C degradation are discussed KRASG12C is an oncoprotein of high interest for drug development. Zeng et al. investigate targeting KRASG12C for degradation using small-molecule degraders (PROTACs) and document challenges and opportunities in this area. [ABSTRACT FROM AUTHOR]

The PI3K/AKT signaling cascade is one of the most commonly dysregulated pathways in cancer, with over half of tumors exhibiting aberrant AKT activation. Although potent small-molecule AKT inhibitors have entered clinical trials, robust and durable therapeutic responses have not been observed. As an alternative strategy to target AKT, we report the development of INY-03-041, a pan-AKT degrader consisting of the ATP-competitive AKT inhibitor GDC-0068 conjugated to lenalidomide, a recruiter of the E3 ubiquitin ligase substrate adaptor Cereblon (CRBN). INY-03-041 induced potent degradation of all three AKT isoforms and displayed enhanced anti-proliferative effects relative to GDC-0068. Notably, INY-03-041 promoted sustained AKT degradation and inhibition of downstream signaling effects for up to 96 h, even after compound washout. Our findings suggest that AKT degradation may confer prolonged pharmacological effects compared with inhibition, and highlight the potential advantages of AKT-targeted degradation. • An AKT-selective heterobifunctional degrader was developed • AKT degradation induced stronger anti-proliferative effects than AKT inhibition • AKT loss and inhibition of downstream signaling was sustained, even after washout You and Erickson et al. report the development and characterization of INY-03-041, a highly selective AKT degrader. The authors demonstrate that INY-03-041 not only exhibits more potent anti-proliferative effects than the catalytic inhibitor GDC-0068, but also induces sustained AKT destabilization and inhibition of downstream signaling, even after compound washout. [ABSTRACT FROM AUTHOR]

The G1/S cell cycle checkpoint is frequently dysregulated in cancer, leaving cancer cells reliant on a functional G2/M checkpoint to prevent excessive DNA damage. Wee1 regulates the G2/M checkpoint by phosphorylating CDK1 at Tyr15 to prevent mitotic entry. Previous drug development efforts targeting Wee1 resulted in the clinical-grade inhibitor, AZD1775. However, AZD1775 is burdened by dose-limiting adverse events, and has off-target PLK1 activity. In an attempt to overcome these limitations, we developed Wee1 degraders by conjugating AZD1775 to the cereblon (CRBN)-binding ligand, pomalidomide. The resulting lead compound, ZNL-02-096, degrades Wee1 while sparing PLK1, induces G2/M accumulation at 10-fold lower doses than AZD1775, and synergizes with Olaparib in ovarian cancer cells. We demonstrate that ZNL-02-096 has CRBN-dependent pharmacology that is distinct from AZD1775, which justifies further evaluation of selective Wee1 degraders. • A selective Wee1 degrader was generated by conjugating pomalidomide to AZD1775 • Wee1 degradation induced G2/M accumulation at lower doses than Wee1 inhibition • Wee1 degradation synergized with Olaparib in ovarian cancer cells Li, Pinch et al. develop and characterize the first selective Wee1 degrader, ZNL-02-096, by linking the clinical candidate inhibitor, AZD1775, to the cereblon-binding ligand, pomalidomide. They demonstrate that ZNL-02-096 exhibits cereblon-dependent pharmacology, induces G2/M phase accumulation and apoptosis at lower doses than AZD1775, and synergizes with Olaparib. [ABSTRACT FROM AUTHOR]

Covalent kinase inhibitors, which typically target cysteine residues, represent an important class of clinically relevant compounds. Approximately 215 kinases are known to have potentially targetable cysteines distributed across 18 spatially distinct locations proximal to the ATP-binding pocket. However, only 40 kinases have been covalently targeted, with certain cysteine sites being the primary focus. To address this disparity, we have developed a strategy that combines the use of a multi-targeted acrylamide-modified inhibitor, SM1-71, with a suite of complementary chemoproteomic and cellular approaches to identify additional targetable cysteines. Using this single multi-targeted compound, we successfully identified 23 kinases that are amenable to covalent inhibition including MKNK2, MAP2K1/2/3/4/6/7, GAK, AAK1, BMP2K, MAP3K7, MAPKAPK5, GSK3A/B, MAPK1/3, SRC, YES1, FGFR1, ZAK (MLTK), MAP3K1, LIMK1, and RSK2. The identification of nine of these kinases previously not targeted by a covalent inhibitor increases the number of targetable kinases and highlights opportunities for covalent kinase inhibitor development. • Our study highlights a multi-targeted strategy to identify druggable cysteines • We identified 23 covalent kinase targets across multiple spatial locations • Nine of these have previously not been covalently targeted by an inhibitor • Our findings highlight potential means to advance covalent drug discovery efforts The current work by Rao et al. describes using a promiscuous ligand as a tool to identify new targets for drug discovery. The findings from this study highlight previously unknown targets against which irreversible inhibitors can be developed. These targets are typically deregulated in diseases including cancer. [ABSTRACT FROM AUTHOR]

Cyclin-dependent kinase 14 (CDK14) and other TAIRE family kinases (CDKs 15–18) are proteins that lack functional annotation but are frequent off-targets of clinical kinase inhibitors. In this study we develop and characterize FMF-04-159-2, a tool compound that specifically targets CDK14 covalently and possesses a TAIRE kinase-biased selectivity profile. This tool compound and its reversible analog were used to characterize the cellular consequences of covalent CDK14 inhibition, including an unbiased investigation using phospho-proteomics. To reduce confounding off-target activity, washout conditions were used to deconvolute CDK14-specific effects. This investigation suggested that CDK14 plays a supporting role in cell-cycle regulation, particularly mitotic progression, and identified putative CDK14 substrates. Together, these results represent an important step forward in understanding the cellular consequences of inhibiting CDK14 kinase activity. • A covalent, cell-permeable inhibitor of CDK14 was developed • Methods for assessing cellular engagement of TAIRE family kinases are described • Kinase motif analysis and phospho-proteomics identified putative CDK14 substrates Cyclin-dependent kinase 14 (CDK14) is an understudied kinase that lacks functional annotation. The authors develop and characterize a covalent CDK14 inhibitor, FMF-04-159-2, and use it to interrogate the role of CDK14 in the cell cycle and phospho-signaling. [ABSTRACT FROM AUTHOR]

Cyclin-dependent kinase 7 (CDK7) regulates both cell cycle and transcription, but its precise role remains elusive. We previously described THZ1, a CDK7 inhibitor, which dramatically inhibits superenhancer-associated gene expression. However, potent CDK12/13 off-target activity obscured CDK7s contribution to this phenotype. Here, we describe the discovery of a highly selective covalent CDK7 inhibitor. YKL-5-124 causes arrest at the G 1 /S transition and inhibition of E2F-driven gene expression; these effects are rescued by a CDK7 mutant unable to covalently engage YKL-5-124, demonstrating on-target specificity. Unlike THZ1, treatment with YKL-5-124 resulted in no change to RNA polymerase II C-terminal domain phosphorylation; however, inhibition could be reconstituted by combining YKL-5-124 and THZ531, a selective CDK12/13 inhibitor, revealing potential redundancies in CDK control of gene transcription. These findings highlight the importance of CDK7/12/13 polypharmacology for anti-cancer activity of THZ1 and posit that selective inhibition of CDK7 may be useful for treatment of cancers marked by E2F misregulation. • Development of YKL-5-124 a potent, selective and covalent CDK7 inhibitor • Selective CDK7 inhibition results in cell-cycle inhibition rather than apoptosis • YKL-5-124 exhibited little effect on RNA polymerase II phosphorylation status Olson et al. describe the development and characterization of YKL-5-124, a potent, selective, and covalent CDK7 inhibitor. YKL-5-124 displays biochemical and cellular selectivity for CDK7 over CDK12/13, structurally related kinases. CDK7 inhibition by YKL-5-124 induces a strong cell-cycle arrest and a surprisingly weak effect on RNA Pol II phosphorylation. [ABSTRACT FROM AUTHOR]

Summary The design of selective small molecules is often stymied by similar ligand binding pockets. Here, we report BSJ-03-123, a phthalimide-based degrader that exploits protein-interface determinants to achieve proteome-wide selectivity for the degradation of cyclin-dependent kinase 6 (CDK6). Pharmacologic CDK6 degradation targets a selective dependency of acute myeloid leukemia cells, and transcriptomics and phosphoproteomics profiling of acute degradation of CDK6 enabled dynamic mapping of its immediate role in coordinating signaling and transcription. Graphical Abstract Highlights • Development of a CDK6-selective small-molecule degrader • Mechanistically understood selectivity via differential ternary complex formation • Profiling of consequences of CDK6 degradation on signaling and gene regulation • Precise exploitation of genetic dependencies through homolog-selective degradation Brand et al. describe BSJ-03-123, a degrader with proteome-wide selectivity for CDK6. Specificity emerges from differential ternary complex formation with the E3 ligase CRL4CRBN. BSJ-03-123 exploits a dependency of AML cells on CDK6, and rapid degradation allowed assaying the role of CDK6 in coordinating signaling and gene control in AML. [ABSTRACT FROM AUTHOR]

Summary Viral envelope proteins are required for productive viral entry and initiation of infection. Although the humoral immune system provides ample evidence for targeting envelope proteins as an antiviral strategy, there are few pharmacological interventions that have this mode of action. In contrast to classical antiviral targets such as viral proteases and polymerases, viral envelope proteins as a class do not have a well-conserved active site that can be rationally targeted with small molecules. We previously identified compounds that inhibit dengue virus by binding to its envelope protein, E. Here, we show that these small molecules inhibit dengue virus fusion and map the binding site of these compounds to a specific pocket on E. We further demonstrate inhibition of Zika, West Nile, and Japanese encephalitis viruses by these compounds, providing pharmacological evidence for the pocket as a target for developing broad-spectrum antivirals against multiple, mosquito-borne flavivirus pathogens. [ABSTRACT FROM AUTHOR]

Summary The SRPK family of kinases regulates pre-mRNA splicing by phosphorylating serine/arginine (SR)-rich splicing factors, signals splicing control in response to extracellular stimuli, and contributes to tumorigenesis, suggesting that these splicing kinases are potential therapeutic targets. Here, we report the development of the first irreversible SRPK inhibitor, SRPKIN-1, which is also the first kinase inhibitor that forms a covalent bond with a tyrosine phenol group in the ATP-binding pocket. Kinome-wide profiling demonstrates its selectivity for SRPK1/2, and SRPKIN-1 attenuates SR protein phosphorylation at submicromolar concentrations. Vascular endothelial growth factor (VEGF) is a known target for SRPK-regulated splicing and, relative to the first-generation SRPK inhibitor SRPIN340 or small interfering RNA-mediated SRPK knockdown, SRPKIN-1 is more potent in converting the pro-angiogenic VEGF-A165a to the anti-angiogenic VEGF-A165b isoform and in blocking laser-induced neovascularization in a murine retinal model. These findings encourage further development of SRPK inhibitors for treatment of age-related macular degeneration. [ABSTRACT FROM AUTHOR]

Summary Irreversible inhibition of transcriptional cyclin-dependent kinases (CDKs) provides a therapeutic strategy for cancers that rely on aberrant transcription; however, lack of understanding of resistance mechanisms to these agents will likely impede their clinical evolution. Here, we demonstrate upregulation of multidrug transporters ABCB1 and ABCG2 as a major mode of resistance to THZ1, a covalent inhibitor of CDKs 7, 12, and 13 in neuroblastoma and lung cancer. To counter this obstacle, we developed a CDK inhibitor, E9 , that is not a substrate for ABC transporters, and by selecting for resistance, determined that it exerts its cytotoxic effects through covalent modification of cysteine 1039 of CDK12. These results highlight the importance of considering this common mode of resistance in the development of clinical analogs of THZ1, identify a covalent CDK12 inhibitor that is not susceptible to ABC transporter-mediated drug efflux, and demonstrate that target deconvolution can be accomplished through selection for resistance. [ABSTRACT FROM AUTHOR]

Summary Heterobifunctional molecules that recruit E3 ubiquitin ligases, such as cereblon, for targeted protein degradation represent an emerging pharmacological strategy. A major unanswered question is how generally applicable this strategy is to all protein targets. In this study, we designed a multi-kinase degrader by conjugating a highly promiscuous kinase inhibitor with a cereblon-binding ligand, and used quantitative proteomics to discover 28 kinases, including BTK, PTK2, PTK2B, FLT3, AURKA, AURKB, TEC, ULK1, ITK, and nine members of the CDK family, as degradable. This set of kinases is only a fraction of the intracellular targets bound by the degrader, demonstrating that successful degradation requires more than target engagement. The results guided us to develop selective degraders for FLT3 and BTK, with potentials to improve disease treatment. Together, this study demonstrates an efficient approach to triage a gene family of interest to identify readily degradable targets for further studies and pre-clinical developments. [ABSTRACT FROM AUTHOR]

Summary There is considerable evidence that chromosome structure plays important roles in gene control, but we have limited understanding of the proteins that contribute to structural interactions between gene promoters and their enhancer elements. Large DNA loops that encompass genes and their regulatory elements depend on CTCF-CTCF interactions, but most enhancer-promoter interactions do not employ this structural protein. Here, we show that the ubiquitously expressed transcription factor Yin Yang 1 (YY1) contributes to enhancer-promoter structural interactions in a manner analogous to DNA interactions mediated by CTCF . YY1 binds to active enhancers and promoter-proximal elements and forms dimers that facilitate the interaction of these DNA elements. Deletion of YY1 binding sites or depletion of YY1 protein disrupts enhancer-promoter looping and gene expression. We propose that YY1-mediated enhancer-promoter interactions are a general feature of mammalian gene control. [ABSTRACT FROM AUTHOR]

Summary Targeted covalent small molecules have shown promise for cancers driven by KRAS G12C. Allosteric compounds that access an inducible pocket formed by movement of a dynamic structural element in KRAS, switch II, have been reported, but these compounds require further optimization to enable their advancement into clinical development. We demonstrate that covalent quinazoline-based switch II pocket (SIIP) compounds effectively suppress GTP loading of KRAS G12C, MAPK phosphorylation, and the growth of cancer cells harboring G12C. Notably we find that adding an amide substituent to the quinazoline scaffold allows additional interactions with KRAS G12C, and remarkably increases the labeling efficiency, potency, and selectivity of KRAS G12C inhibitors. Structural studies using X-ray crystallography reveal a new conformation of SIIP and key interactions made by substituents located at the quinazoline 2-, 4-, and 7-positions. Optimized lead compounds in the quinazoline series selectively inhibit KRAS G12C-dependent signaling and cancer cell growth at sub-micromolar concentrations. [ABSTRACT FROM AUTHOR]

Summary Processive elongation of RNA Polymerase II from a proximal promoter paused state is a rate-limiting event in human gene control. A small number of regulatory factors influence transcription elongation on a global scale. Prior research using small-molecule BET bromodomain inhibitors, such as JQ1, linked BRD4 to context-specific elongation at a limited number of genes associated with massive enhancer regions. Here, the mechanistic characterization of an optimized chemical degrader of BET bromodomain proteins, dBET6, led to the unexpected identification of BET proteins as master regulators of global transcription elongation. In contrast to the selective effect of bromodomain inhibition on transcription, BET degradation prompts a collapse of global elongation that phenocopies CDK9 inhibition. Notably, BRD4 loss does not directly affect CDK9 localization. These studies, performed in translational models of T cell leukemia, establish a mechanism-based rationale for the development of BET bromodomain degradation as cancer therapy. [ABSTRACT FROM AUTHOR]