Cyclic GMP-AMP synthase (cGAS) initiates the innate immune system in response to cytosolic dsDNA. After binding and activation from dsDNA, cGAS uses ATP and GTP to synthesize 2′, 3′ -cGAMP (cGAMP), a cyclic dinucleotide second messenger with mixed 2′-5′ and 3′-5′ phosphodiester bonds. Inappropriate stimulation of cGAS has been implicated in autoimmune disease such as systemic lupus erythematosus, thus inhibition of cGAS may be of therapeutic benefit in some diseases; however, the size and polarity of the cGAS active site makes it a challenging target for the development of conventional substrate-competitive inhibitors. We report here the development of a high affinity (KD = 200 nM) inhibitor from a low affinity fragment hit with supporting biochemical and structural data showing these molecules bind to the cGAS active site. We also report a new high throughput cGAS fluorescence polarization (FP)-based assay to enable the rapid identification and optimization of cGAS inhibitors. This FP assay uses Cy5-labelled cGAMP in combination with a novel high affinity monoclonal antibody that specifically recognizes cGAMP with no cross reactivity to cAMP, cGMP, ATP, or GTP. Given its role in the innate immune response, cGAS is a promising therapeutic target for autoinflammatory disease. Our results demonstrate its druggability, provide a high affinity tool compound, and establish a high throughput assay for the identification of next generation cGAS inhibitors.

CBP and EP300 are highly homologous, bromodomain-containing transcription coactivators involved in numerous cellular pathways relevant to oncology. As part of our effort to explore the potential therapeutic implications of selectively targeting bromodomains, we set out to identify a CBP/EP300 bromodomain inhibitor that was potent both in vitro and in cellular target engagement assays and was selective over the other members of the bromodomain family. Reported here is a series of cell-potent and selective probes of the CBP/EP300 bromodomains, derived from the fragment screening hit 4-methyl-1,3,4,5-tetrahydro-2H-benzo [b][1,4]diazepin-2-one.

Interleukin-17A (IL-17A) is a principal driver of multiple inflammatory and immune disorders. Antibodies that neutralize IL-17A or its receptor (IL-17RAInterleukin-17 (IL-17) cytokines are homo or heterodimeric proteins formed by combinations of six distinct polypeptides designated IL17A-F 1 . They are essential to a fully functional immune system 2,3 , but dysregulated expression of IL-17A is implicated in autoimmune disorders such as psoriasis, psoriatic arthritis, rheumatoid arthritis and multiple sclerosis 4-6 . The IL-17A covalent homodimer's significance in psoriasis is evidenced by the recent success of anti-IL-17A biologics as therapeutics. Secukinumab (Costentyx TM ), a monoclonal antibody targeting IL-17A, was recently approved for the treatment of moderate to severe plaque psoriasis 7,8 and is being investigated in other IL-17A-driven immunological diseases 9 . Additionally, two other biologics, ixekizumab (anti-IL17A) 10,11 and brodalumab (an antibody to the IL-17 receptor, IL-17RA) 12,13 , have shown efficacy in psoriasis in late stage clinical trials.IL-17A signaling occurs through its membrane-bound receptors, IL-17RA and IL-17RC, and elicits multiple inflammatory and immune responses [14][15][16] . The cytokine binds to IL-17RA with low single-digit nanomolar affinity 14,15,17,18 . and the structure of their complex is known 17 . The emerging biologics block this interaction by binding to one or other of the partners, but our goal was to determine whether it could be blocked or modulated with a small molecule as this could afford orally active agents.Small-molecule inhibition of a protein-protein interaction (PPI) is invariably challenging 19 . Even the discovery of early lead matter tends to be difficult because corporate compound collections are largely designed to target the active centers of enzymes, and are deficient in compounds suitable to the longer and shallower binding sites on which PPIs tend to depend. As the industry expands the "druggable genome", continued efforts at small molecule inhibition of PPIs will be required 20 . ResultsLead small molecule IL-17A antagonists. Our effort to discover small-molecule antagonists of IL-17A was initiated from disclosed inhibitors 21,22 exemplified by compound 1 (Fig. 1), a polyamide with clear structure-activity relationships (SAR) representative of the series. For example, the amide bonds, correct chiral center and cyclopentyl group were all required for activity. Surface plasmon resonance (SPR) measurements showed

Cyclic GMP‐AMP synthase (cGAS) is activated by ds‐DNA binding to produce the secondary messenger 2′,3′‐cGAMP. cGAS is an important control point in the innate immune response; dysregulation of the cGAS pathway is linked to autoimmune diseases while targeted stimulation may be of benefit in immunoncology. We report here the structure of cGAS with dinucleotides and small molecule inhibitors, and kinetic studies of the cGAS mechanism. Our structural work supports the understanding of how ds‐DNA activates cGAS, suggesting a site for small molecule binders that may cause cGAS activation at physiological ATP concentrations, and an apparent hotspot for inhibitor binding. Mechanistic studies of cGAS provide the first kinetic constants for 2′,3′‐cGAMP formation, and interestingly, describe a catalytic mechanism where 2′,3′‐cGAMP may be a minor product of cGAS compared with linear nucleotides.

Protein lysine methyltransferases (KMTs) have emerged as important regulators of epigenetic signaling. These enzymes catalyze the transfer of donor methyl groups from the cofactor S-adenosylmethionine to specific acceptor lysine residues on histones, leading to changes in chromatin structure and transcriptional regulation. These enzymes also methylate an array of nonhistone proteins, suggesting additional mechanisms by which they influence cellular physiology. SMYD2 is reported to be an oncogenic methyltransferase that represses the functional activity of the tumor suppressor proteins p53 and RB. HTS screening led to identification of five distinct substrate-competitive chemical series. Determination of liganded crystal structures of SMYD2 contributed significantly to "hit-to-lead" design efforts, culminating in the creation of potent and selective inhibitors that were used to understand the functional consequences of SMYD2 inhibition. Taken together, these results have broad implications for inhibitor design against KMTs and clearly demonstrate the potential for developing novel therapies against these enzymes.