Development of a highly potent and selective degrader of LRRK2.

The discovery of disease-modifying therapies for Parkinson's Disease (PD) represents a critical need in neurodegenerative medicine. Genetic mutations in leucine-rich repeat kinase 2 (LRRK2) are risk factors for the development of PD, and some of these mutations have been linked to increased LRRK2 kinase activity and neuronal toxicity in cellular and animal models. Furthermore, LRRK2 function as a scaffolding protein in several pathways has been implicated as a plausible mechanism underlying neurodegeneration caused by LRRK2 mutations. Given that both the kinase activity and scaffolding function of LRRK2 have been linked to neurodegeneration, we developed proteolysis-targeting chimeras (PROTACs) targeting LRRK2. The degrader molecule JH-XII-03-02 (6) displayed high potency and remarkable selectivity for LRKK2 when assessed in a of 468 panel kinases and serves the dual purpose of eliminating both the kinase activity as well as the scaffolding function of LRRK2.

Catalytic Degraders Effectively Address Kinase Site Mutations in EML4-ALK Oncogenic Fusions.

Heterobifunctional degraders, known as proteolysis targeting chimeras (PROTACs), theoretically possess a catalytic mode-of-action, yet few studies have either confirmed or exploited this potential advantage of event-driven pharmacology. Degraders of oncogenic EML4-ALK fusions were developed by conjugating ALK inhibitors to cereblon ligands. Simultaneous optimization of pharmacology and compound properties using ternary complex modeling and physicochemical considerations yielded multiple catalytic degraders that were more resilient to clinically relevant ATP-binding site mutations than kinase inhibitor drugs. Our strategy culminated in the design of the orally bioavailable derivative CPD-1224 that avoided hemolysis (a feature of detergent-like PROTACs), degraded the otherwise recalcitrant mutant L1196M/G1202R in vivo, and commensurately slowed tumor growth, while the third generation ALK inhibitor drug lorlatinib had no effect. These results validate our original therapeutic hypothesis by exemplifying opportunities for catalytic degraders to proactively address binding site resistant mutations in cancer.

Transcriptional Antagonism by CDK8 Inhibition Improves Therapeutic Efficacy of MEK Inhibitors.

Aberrant RAS/MAPK signaling is a common driver of oncogenesis that can be therapeutically targeted with clinically approved MEK inhibitors. Disease progression on single-agent MEK inhibitors is common, however, and combination therapies are typically required to achieve significant clinical benefit in advanced cancers. Here we focused on identifying MEK inhibitor-based combination therapies in neuroblastoma with mutations that activate the RAS/MAPK signaling pathway, which are rare at diagnosis but frequent in relapsed neuroblastoma. A genome-scale CRISPR-Cas9 functional genomic screen was deployed to identify genes that when knocked out sensitize RAS-mutant neuroblastoma to MEK inhibition. Loss of either CCNC or CDK8, two members of the mediator kinase module, sensitized neuroblastoma to MEK inhibition. Furthermore, small-molecule kinase inhibitors of CDK8 improved response to MEK inhibitors in vitro and in vivo in RAS-mutant neuroblastoma and other adult solid tumors. Transcriptional profiling revealed that loss of CDK8 or CCNC antagonized the transcriptional signature induced by MEK inhibition. When combined, loss of CDK8 or CCNC prevented the compensatory upregulation of progrowth gene expression induced by MEK inhibition. These findings propose a new therapeutic combination for RAS-mutant neuroblastoma and may have clinical relevance for other RAS-driven malignancies. SIGNIFICANCE: Transcriptional adaptation to MEK inhibition is mediated by CDK8 and can be blocked by the addition of CDK8 inhibitors to improve response to MEK inhibitors in RAS-mutant neuroblastoma, a clinically challenging disease.

Selective Macrocyclic Inhibitors of DYRK1A/B.

Dual-specificity tyrosine-(Y)-phosphorylation regulated kinase 1A (DYRK1A) is a therapeutic target of interest due to the roles it plays in both neurological diseases and cancer. We present the development of the first macrocyclic inhibitors of DYRK1A. Initial lead inhibitor JH-XIV-68-3 (3) displayed selectivity for DYRK1A and close family member DYRK1B in biochemical and cellular assays, and demonstrated antitumor efficacy in head and neck squamous cell carcinoma (HNSCC) cell lines. However, we noted that it suffered from rapid aldehyde oxidase (AO)-mediated metabolism. To overcome this liability, we generated a derivative (JH-XVII-10 (10)), where fluorine was introduced to block the 2-position of the azaindole and render the molecule resistant to AO activity. We showed that 10 maintains remarkable potency and selectivity in biochemical and cellular assays as well as antitumor efficacy in HNSCC cell lines and improved metabolic stability. Therefore, 10 represents a promising new scaffold for developing DYRK1A-targeting chemical probes and therapeutics.

A Novel HER2-Selective Kinase Inhibitor Is Effective in HER2 Mutant and Amplified Non-Small Cell Lung Cancer.

In-frame insertions in exon 20 of HER2 are the most common HER2 mutations in patients with non-small cell lung cancer (NSCLC), a disease in which approved EGFR/HER2 tyrosine kinase inhibitors (TKI) display poor efficiency and undesirable side effects due to their strong inhibition of wild-type (WT) EGFR. Here, we report a HER2-selective covalent TKI, JBJ-08-178-01, that targets multiple HER2 activating mutations, including exon 20 insertions as well as amplification. JBJ-08-178-01 displayed strong selectivity toward HER2 mutants over WT EGFR compared with other EGFR/HER2 TKIs. Determination of the crystal structure of HER2 in complex with JBJ-08-178-01 suggests that an interaction between the inhibitor and Ser783 may be responsible for HER2 selectivity. The compound showed strong antitumoral activity in HER2-mutant or amplified cancers in vitro and in vivo. Treatment with JBJ-08-178-01 also led to a reduction in total HER2 by promoting proteasomal degradation of the receptor. Taken together, the dual activity of JBJ-08-178-01 as a selective inhibitor and destabilizer of HER2 represents a combination that may lead to better efficacy and tolerance in patients with NSCLC harboring HER2 genetic alterations or amplification. SIGNIFICANCE: This study describes unique mechanisms of action of a new mutant-selective HER2 kinase inhibitor that reduces both kinase activity and protein levels of HER2 in lung cancer.

Development of Highly Potent and Selective Pyrazolopyridine Inhibitor of CDK8/19.

CDK8 and its paralog CDK19 are cyclin-dependent kinases that are core components of the so-called Mediator complex that has essential roles as a positive and negative regulator of gene expression. Several efforts to develop inhibitors have yielded natural and synthetic ATP-competitive compounds including cortistatin A, Sel120, BCD-115, CCT251921 (1), and MSC2530818 (2). Here, we used a hybridization approach starting from CCT251921 and MSC2530818 to derive new inhibitors with the aim of developing highly potent and selective inhibitors of CDK8/19. Initial compounds suffered from rapid aldehyde oxidase-mediated metabolism. This liability was overcome by utilizing a pyrazolopyridine hinge binder with a chlorine at the C-3 position. These efforts resulted in JH-XVI-178 (compound 15), a highly potent and selective inhibitor of CDK8/19 that displays low clearance and moderate oral pharmacokinetic properties.

Discovery of a Selective, Covalent IRAK1 Inhibitor with Antiproliferative Activity in MYD88 Mutated B-Cell Lymphoma.

Interleukin 1 (IL-1) receptor-associated kinases (IRAKs) are serine/threonine kinases that play critical roles in initiating the innate immune response against foreign pathogens. Additionally, dysregulation of IRAK1 signaling plays a role in neoplastic disorders. For example, IRAK1 was shown to be important for survival and proliferation in many B-cell lymphomas, including Waldenström's macroglobulinemia (WM) and ABC subtype Diffused Large B-cell Lymphoma (DLBCL) cells. Here, we report the discovery of a highly potent and selective covalent inhibitor of IRAK1, JH-X-119-01. Intact protein MS labeling studies confirmed that JH-X-119-01 irreversibly labels IRAK1 at C302. This compound exhibited cytotoxic activity at single digit micromolar concentrations in a panel of WM, DLBCL, and lymphoma cell lines expressing MYD88. Cotreatment of JH-X-119-01 with the BTK inhibitor ibrutinib resulted in synergistic killing effects in these systems. Taken together, JH-X-119-01 represents a highly selective probe of IRAK1 for further development.

Development of CDK2 and CDK5 Dual Degrader TMX-2172.

Cyclin-dependent kinase 2 (CDK2) is a potential therapeutic target for the treatment of cancer. Development of CDK2 inhibitors has been extremely challenging as its ATP-binding site shares high similarity with CDK1, a related kinase whose inhibition causes toxic effects. Here, we report the development of TMX-2172, a heterobifunctional CDK2 degrader with degradation selectivity for CDK2 and CDK5 over not only CDK1, but transcriptional CDKs (CDK7 and CDK9) and cell cycle CDKs (CDK4 and CDK6) as well. In addition, we demonstrate that antiproliferative activity in ovarian cancer cells (OVCAR8) depends on CDK2 degradation and correlates with high expression of cyclin E1 (CCNE1), which functions as a regulatory subunit of CDK2. Collectively, our work provides evidence that TMX-2172 represents a lead for further development and that CDK2 degradation is a potentially valuable therapeutic strategy in ovarian and other cancers that overexpress CCNE1.

A kinase-independent role for CDK8 in BCR-ABL1+ leukemia.

Cyclin-dependent kinases (CDKs) are frequently deregulated in cancer and represent promising drug targets. We provide evidence that CDK8 has a key role in B-ALL. Loss of CDK8 in leukemia mouse models significantly enhances disease latency and prevents disease maintenance. Loss of CDK8 is associated with pronounced transcriptional changes, whereas inhibiting CDK8 kinase activity has minimal effects. Gene set enrichment analysis suggests that the mTOR signaling pathway is deregulated in CDK8-deficient cells and, accordingly, these cells are highly sensitive to mTOR inhibitors. Analysis of large cohorts of human ALL and AML patients reveals a significant correlation between the level of CDK8 and of mTOR pathway members. We have synthesized a small molecule YKL-06-101 that combines mTOR inhibition and degradation of CDK8, and induces cell death in human leukemic cells. We propose that simultaneous CDK8 degradation and mTOR inhibition might represent a potential therapeutic strategy for the treatment of ALL patients.

Recent Advances in Selective and Irreversible Covalent Ligand Development and Validation.

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.

Quinoline and thiazolopyridine allosteric inhibitors of MALT1.

Quinolines and thiazolopyridines were developed as allosteric inhibitors of MALT1, with good cellular potency and exquisite selectivity. Mouse pharmacokinetic (PK) profiling showed these to have low in vivo clearance, and moderate oral exposure. The thiazolopyridines were less lipophilic than the quinolines, and one thiazolopyridine example was active in our hIL10 mouse pharmacodynamic (PD) model upon oral dosing.

Peptide-based covalent inhibitors of MALT1 paracaspase.

Potent and selective substrate-based covalent inhibitors of MALT1 protease were developed from the tetrapeptide tool compound Z-VRPR-fmk. To improve cell permeability, we replaced one arginine residue. We further optimized a series of tripeptides and identified compounds that were potent in both a GloSensor reporter assay measuring cellular MALT1 protease activity, and an OCI-Ly3 cell proliferation assay. Example compounds showed good overall selectivity towards cysteine proteases, and one compound was selected for further profiling in ABL-DLBCL cells and xenograft efficacy models.

Conformational flexibility and inhibitor binding to unphosphorylated interleukin-1 receptor-associated kinase 4 (IRAK4).

Interleukin-1 receptor-associated kinase 4 (IRAK4) is a key player in innate immune and inflammatory responses, performing a critical role in signal transduction downstream of Toll-like receptors and interleukin-1 (IL-1) receptors. Upon ligand binding and via its N-terminal death domain, IRAK4 is recruited to an oligomeric receptor that is proximal to the Myddosome signaling complex, inducing IRAK4 kinase domain dimerization, autophosphorylation, and activation. To date, all known IRAK4 structures are in the active conformation, precluding a good understanding of IRAK4's conformational dynamics. To address this issue, here we first solved three crystal structures of the IRAK4 kinase domain (at ≤2.6 Å resolution), in its unphosphorylated, inactive state bound to either the ATP analog AMP-PNP or to one of the two small-molecule inhibitors JH-I-25 and JH-I-17. The structures disclosed that although the structure in complex with AMP-PNP is in an "αC-out" inactive conformation, those in complex with type I inhibitors assume an active "Asp-Phe-Gly (DFG)-in" and "αC-in" conformation. The ability of unphosphorylated IRAK4 to take on variable conformations prompted us to screen for small-molecule inhibitors that bind preferentially to unphosphorylated IRAK4, leading to the identification of ponatinib and HG-12-6. Solving the structures of unphosphorylated IRAK4 in complex with these two inhibitors, we found that they both bind as type II inhibitors with IRAK4 in a "DFG-out" conformation. Collectively, these structures reveal conformational flexibility of unphosphorylated IRAK4 and provide unexpected insights into the potential use of small molecules to modulate IRAK4 activity in cancer, autoimmunity, and inflammation.

Specific covalent inhibition of MALT1 paracaspase suppresses B cell lymphoma growth.

The paracaspase MALT1 plays an essential role in activated B cell-like diffuse large B cell lymphoma (ABC DLBCL) downstream of B cell and TLR pathway genes mutated in these tumors. Although MALT1 is considered a compelling therapeutic target, the development of tractable and specific MALT1 protease inhibitors has thus far been elusive. Here, we developed a target engagement assay that provides a quantitative readout for specific MALT1-inhibitory effects in living cells. This enabled a structure-guided medicinal chemistry effort culminating in the discovery of pharmacologically tractable, irreversible substrate-mimetic compounds that bind the MALT1 active site. We confirmed that MALT1 targeting with compound 3 is effective at suppressing ABC DLBCL cells in vitro and in vivo. We show that a reduction in serum IL-10 levels exquisitely correlates with the drug pharmacokinetics and degree of MALT1 inhibition in vitro and in vivo and could constitute a useful pharmacodynamic biomarker to evaluate these compounds in clinical trials. Compound 3 revealed insights into the biology of MALT1 in ABC DLBCL, such as the role of MALT1 in driving JAK/STAT signaling and suppressing the type I IFN response and MHC class II expression, suggesting that MALT1 inhibition could prime lymphomas for immune recognition by cytotoxic immune cells.

Development of Highly Potent and Selective Steroidal Inhibitors and Degraders of CDK8.

Cortistatin A is a natural product isolated from the marine sponge Corticium simplex and was found to be a potent and selective inhibitor of CDK8. Many synthetic groups have reported total syntheses of Cortistatin A; however, these syntheses require between 16 and 30 steps and report between 0.012-2% overall yields, which is not amenable to large-scale production. Owing to similarities between the complex core of Cortistatin A and the simple steroid core, we initiated a campaign to design simple, more easily prepared CDK8 inhibitors based on a steroid scaffold that would be more convenient for large-scale synthesis. Herein, we report the discovery and optimization of JH-VIII-49, a potent and selective inhibitor of CDK8 with a simple steroid core that has an eight-step synthesis with a 33% overall yield, making it suitable for large-scale preparation. Using this scaffold, we then developed a bivalent small molecule degrader, JH-XI-10-02, that can recruit the E3 ligase CRL4Cereblon to promote the ubiquitination and proteosomal degradation of CDK8.

SRPKIN-1: A Covalent SRPK1/2 Inhibitor that Potently Converts VEGF from Pro-angiogenic to Anti-angiogenic Isoform.

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.

Crystal structure of human IRAK1.

Interleukin 1 (IL-1) receptor-associated kinases (IRAKs) are serine/threonine kinases that play critical roles in initiating innate immune responses against foreign pathogens and other types of dangers through their role in Toll-like receptor (TLR) and interleukin 1 receptor (IL-1R) mediated signaling pathways. Upon ligand binding, TLRs and IL-1Rs recruit adaptor proteins, such as myeloid differentiation primary response gene 88 (MyD88), to the membrane, which in turn recruit IRAKs via the death domains in these proteins to form the Myddosome complex, leading to IRAK kinase activation. Despite their biological and clinical significance, only the IRAK4 kinase domain structure has been determined among the four IRAK family members. Here, we report the crystal structure of the human IRAK1 kinase domain in complex with a small molecule inhibitor. The structure reveals both similarities and differences between IRAK1 and IRAK4 and is suggestive of approaches to develop IRAK1- or IRAK4-specific inhibitors for potential therapeutic applications. While the IRAK4 kinase domain is capable of homodimerization in the unphosphorylated state, we found that the IRAK1 kinase domain is constitutively monomeric regardless of its phosphorylation state. Additionally, the IRAK1 kinase domain forms heterodimers with the phosphorylated, but not unphosphorylated, IRAK4 kinase domain. Collectively, these data indicate a two-step kinase activation process in which the IRAK4 kinase domain first homodimerizes in the Myddosome, leading to its trans-autophosphorylation and activation. The phosphorylated IRAK4 kinase domain then forms heterodimers with the IRAK1 kinase domain within the Myddosome, leading to its subsequent phosphorylation and activation.

Small-Molecule Inhibitors of LRRK2.

Mutations in the leucine-rich repeat kinase 2 (LRRK2) protein have been genetically and functionally linked to Parkinson's disease (PD). The kinase activity of LRRK2 is increased by pathogenic mutations; therefore, modulation of LRRK2 kinase activity by a selective small-molecule inhibitor has been proposed as a potentially viable treatment for Parkinson's disease. This chapter presents a historical overview of the development and bioactivity of several small-molecule LRRK2 inhibitors that have been used to inhibit LRRK2 kinase activity in vitro or in vivo. These compounds are important tools for understanding the cellular biology of LRRK2 and for evaluating the potential of LRRK2 inhibitors as disease-modifying PD therapies.

Discovery of a Highly Potent and Selective Indenoindolone Type 1 Pan-FLT3 Inhibitor.

For a subpopulation of acute myeloid leukemia (AML) patients, the mutationally activated tyrosine kinase FLT3, has emerged as a promising target for therapy. The development of drug resistance due to mutation is a growing concern for mutant FLT3 inhibitors, such as PKC412, Quizartinib, PLX3397, and Crenolanib. Thus, there is a need to develop novel FLT3 inhibitors that overcome these mutations. Here we report the development of a novel type I ATP competitive inhibitor, JH-IX-179, that is extremely potent and selective for FLT3. JH-IX-179 also has the highest affinity for three constitutively active isoforms of FLT3 (FLT3-ITD, FLT3-N841I, and FLT3-D835V) compared to a panel 456 other kinases. The unique and specific kinase inhibition profile suggests that this chemotype may represent an attractive starting point for the development of further improved FLT3 inhibitors with therapeutic potential in tumors harboring deregulated FLT3 activity.

Discovery of Inhibitors That Overcome the G1202R Anaplastic Lymphoma Kinase Resistance Mutation.

The treatment of patients with advanced non-small-cell lung cancer harboring chromosomal rearrangements of anaplastic lymphoma kinase (ALK) has been revolutionized by the development of crizotinib, a small-molecule inhibitor of ALK, ROS1, and MET. However, resistance to crizotinib inevitably develops through a variety of mechanisms, leading to relapse both systemically and in the central nervous system (CNS). This has motivated the development of "second-generation" ALK inhibitors, including alectinib and ceritinib, that overcome some of the mutations leading to resistance. However, most of the reported ALK inhibitors do not show inhibition of the G1202R mutant, which is one of the most common mutations. Herein, we report the development of a structural analogue of alectinib (JH-VIII-157-02) that is potent against the G1202R mutant as well as a variety of other frequently observed mutants. In addition, JH-VIII-157-02 is capable of penetrating the CNS of mice following oral dosing.