Current therapies for chronic pain can have insufficient efficacy and lead to side effects, necessitating research of novel targets against pain. Although originally identified as an oncogene, Tropomyosinrelated kinase A (TrkA) is linked to pain and elevated levels of NGF (the ligand for TrkA) are associated with chronic pain. Antibodies that block TrkA interaction with its ligand, NGF, are in clinical trials for pain relief. Here, we describe the identification of TrkA-specific inhibitors and the structural basis for their selectivity over other Trk family kinases. The X-ray structures reveal a binding site outside the kinase active site that uses residues from the kinase domain and the juxtamembrane region. Three modes of binding with the juxtamembrane region are characterized through a series of ligand-bound complexes. The structures indicate a critical pharmacophore on the compounds that leads to the distinct binding modes. The mode of interaction can allow TrkA selectivity over TrkB and TrkC or promiscuous, pan-Trk inhibition. This finding highlights the difficulty in characterizing the structure-activity relationship of a chemical series in the absence of structural information because of substantial differences in the interacting residues. These structures illustrate the flexibility of binding to sequences outside of-but adjacent to-the kinase domain of TrkA. This knowledge allows development of compounds with specificity for TrkA or the family of Trk proteins.TrkA | kinase | pain | inhibition | selectivity

Checkpoint inhibitors have demonstrated unprecedented efficacy and are evolving to become standard of care for certain types of cancers. However, low overall response rates often hamper the broad utility and potential of these breakthrough therapies. Combination therapy strategies are currently under intensive investigation in the clinic, including the combination of PD-1/PD-L1 agents with IDO1 inhibitors. Here, we report the discovery of a class of IDO1 heme-binding inhibitors featuring a unique amino-cyclobutarene motif, which was discovered through SBDD from a known and weakly active inhibitor. Subsequent optimization efforts focused on improving metabolic stability and were greatly accelerated by utilizing a robust SNAr reaction of a facile nitro-furazan intermediate to quickly explore different polar side chains. As a culmination of these efforts, compound 16 was identified and demonstrated a favorable overall profile with superior potency and selectivity. Extensive studies confirmed the chemical stability and drug-like properties of compound 16, rendering it a potential drug candidate.

The action of arginase, a metalloenzyme responsible for the hydrolysis of arginine to urea and ornithine, is hypothesized to suppress immune-cell activity within the tumor microenvironment, and thus its inhibition may constitute a means by which to potentiate the efficacy of immunotherapeutics such as anti-PD-1 checkpoint inhibitors. Taking inspiration from reported enzyme–inhibitor cocrystal structures, we designed and synthesized novel inhibitors of human arginase possessing a fused 5,5-bicyclic ring system. The prototypical member of this class, 3, when dosed orally, successfully demonstrated serum arginase inhibition and concomitant arginine elevation in a syngeneic mouse carcinoma model, despite modest oral bioavailability. Structure-based design strategies to improve the bioavailability of this class, including scaffold modification, fluorination, and installation of active-transport recognition motifs were explored.

Indoleamine-2,3-dioxygenase-1 (IDO1) has emerged as an attractive target for cancer immunotherapy. An automated ligand identification system screen afforded the tetrahydroquinoline class of novel IDO1 inhibitors. Potency and pharmacokinetic (PK) were key issues with this class of compounds. Structure-based drug design and strategic incorporation of polarity enabled the rapid improvement on potency, solubility, and oxidative metabolic stability. Metabolite identification studies revealed that amide hydrolysis in the D-pocket was the key clearance mechanism for this class. Strategic survey of amide isosteres revealed that carbamates and N-pyrimidines, which maintained exquisite potencies, mitigated the amide hydrolysis issue and led to an improved rat PK profile. The lead compound 28 is a potent IDO1 inhibitor, with clean off-target profiles and the potential for quaque die dosing in humans.

ABSTRACT:A novel series of non-ATP-competitive MK2 inhibitors based on a furan-2-carboxyamide scaffold was discovered through highthroughput screening using the affinity selectionÀmass spectrometry-based Automated Ligand Identification System platform. Medicinal chemistry efforts optimized the initial screening hit to leadlike compounds with significant improvements in biochemical and cellular potencies, while maintaining excellent kinase selectivity and in vitro pharmacokinetic properties. Biophysical and biochemical studies confirmed the unique non-ATP-competitive binding mode of this series and suggested that highly selective inhibitors of MK2 should be feasible by targeting the outside ATP pocket. KEYWORDS:Mitogen-activated protein kinase-activated protein kinase 2, non-ATP-competitive inhibitors, Automated Ligand Identification System (ALIS), saturation-transfer-difference (STD) NMR, 1 H/ 15 N-HSQC (heteronuclear single quantum coherence) U nregulated protein kinase activity is often associated with inflammatory diseases, such as rheumatoid arthritis, which is characterized by autoimmune-mediated cartilage and bone destruction that leads to intolerable joint pain and crippling and afflicts about 1% of the world's population. 1 Activation of the p38/mitogen-activated protein kinase-activated protein kinase 2 (MAPKAPK2 or MK2) pathway has been implicated in promoting pro-inflammatory cytokine production and related inflammatory diseases. 2À4 However, despite numerous assessments of potent inhibitors in early stage clinical trials, no p38 MAPK inhibitors have progressed beyond phase II trials largely because of dose-dependent toxicities and unimpressive efficacies. 4,5 The broad involvement of p38R MAPK and its downstream substrates in diverse cellular processes may be a major cause of related clinical trial failures. 4,6,7 To minimize the apparent side effects caused by directly targeting p38R MAPK, several discovery teams have attempted inhibiting targets downstream of p38R MAPK that are responsible for its pro-inflammatory cytokine-regulating properties in macrophages. 4,7 Of these MK2, a serine/threonine protein kinase that directly associates with p38R MAPK to form a heterodimer and is phosphorylated and activated by p38R MAPK has emerged as the most attractive downstream target. 7À10 For example, in studies employing genetically engineered mouse models wherein MK2, MK3, and MK5 genes were knocked out, it was shown that MK2 is the primary MAPKAPK family member required for lipopolysaccharide (LPS)-induced tumor necrosis factor R (TNFR) and interleukin 6 (IL6) production. 11À13 Furthermore, MK2-null mice were shown to have reduced joint damage in a collagen-induced arthritis model and no induction of asthma in a lung ovalbumin sensitization model. 14,15 In contrast to the embryonic lethality associated with knocking out the geneencoding p38R MAPK, MK2-null mice were fertile and healthy, suggesting that inhibition of MK2 in inflammatory disease states may provide efficacy comparable to direct p38R MAPK in...