Macrocyclic Carbon-Linked Pyrazoles As Novel Inhibitors of MCL-1.

Myeloid cell leukemia-1 (MCL-1) is a member of the antiapoptotic BCL-2 proteins family and a key regulator of mitochondrial homeostasis. Overexpression of MCL-1 is found in many cancer cells and contributes to tumor progression, which makes it an attractive therapeutic target. Pursuing our previous study of macrocyclic indoles for the inhibition of MCL-1, we report herein the impact of both pyrazole and indole isomerism on the potency and overall properties of this family of compounds. We demonstrated that the incorporation of a fluorine atom on the naphthalene moiety was a necessary step to improve cellular potency and that, combined with the introduction of various side chains on the pyrazole, it enhanced solubility significantly. This exploration culminated in the discovery of compounds (Ra)-10 and (Ra)-15, possessing remarkable cellular potency and properties.

Discovery of Potent and Orally Bioavailable Pyridine N-Oxide-Based Factor XIa Inhibitors through Exploiting Nonclassical Interactions.

Activated factor XI (FXIa) inhibitors are promising novel anticoagulants with low bleeding risk compared with current anticoagulants. The discovery of potent FXIa inhibitors with good oral bioavailability has been challenging. Herein, we describe our discovery effort, utilizing nonclassical interactions to improve potency, cellular permeability, and oral bioavailability by enhancing the binding while reducing polar atoms. Beginning with literature-inspired pyridine N-oxide-based FXIa inhibitor 1, the imidazole linker was first replaced with a pyrazole moiety to establish a polar C-H···water hydrogen-bonding interaction. Then, structure-based drug design was employed to modify lead molecule 2d in the P1' and P2' regions, with substituents interacting with key residues through various nonclassical interactions. As a result, a potent FXIa inhibitor 3f (Ki = 0.17 nM) was discovered. This compound demonstrated oral bioavailability in preclinical species (rat 36.4%, dog 80.5%, and monkey 43.0%) and displayed a dose-dependent antithrombotic effect in a rabbit arteriovenous shunt model of thrombosis.

Gut-Restricted Selective Cyclooxygenase-2 (COX-2) Inhibitors for Chemoprevention of Colorectal Cancer.

Selective cyclooxygenase (COX)-2 inhibitors have been extensively studied for colorectal cancer (CRC) chemoprevention. Celecoxib has been reported to reduce the incidence of colorectal adenomas and CRC but is also associated with an increased risk of cardiovascular events. Here, we report a series of gut-restricted, selective COX-2 inhibitors characterized by high colonic exposure and minimized systemic exposure. By establishing acute ex vivo 18F-FDG uptake attenuation as an efficacy proxy, we identified a subset of analogues that demonstrated statistically significant in vivo dose-dependent inhibition of adenoma progression and survival extension in an APCmin/+ mouse model. However, in vitro-in vivo correlation analysis showed their chemoprotective effects were driven by residual systemic COX-2 inhibition, rationalizing their less than expected efficacies and highlighting the challenges associated with COX-2-mediated CRC disease chemoprevention.

Pharmacologic Characterization of JNJ-42226314, [1-(4-Fluorophenyl)indol-5-yl]-[3-[4-(thiazole-2-carbonyl)piperazin-1-yl]azetidin-1-yl]methanone, a Reversible, Selective, and Potent Monoacylglycerol Lipase Inhibitor.

The serine hydrolase monoacylglycerol lipase (MAGL) is the rate-limiting enzyme responsible for the degradation of the endocannabinoid 2-arachidonoylglycerol (2-AG) into arachidonic acid and glycerol. Inhibition of 2-AG degradation leads to elevation of 2-AG, the most abundant endogenous agonist of the cannabinoid receptors (CBs) CB1 and CB2. Activation of these receptors has demonstrated beneficial effects on mood, appetite, pain, and inflammation. Therefore, MAGL inhibitors have the potential to produce therapeutic effects in a vast array of complex human diseases. The present report describes the pharmacologic characterization of [1-(4-fluorophenyl)indol-5-yl]-[3-[4-(thiazole-2-carbonyl)piperazin-1-yl]azetidin-1-yl]methanone (JNJ-42226314), a reversible and highly selective MAGL inhibitor. JNJ-42226314 inhibits MAGL in a competitive mode with respect to the 2-AG substrate. In rodent brain, the compound time- and dose-dependently bound to MAGL, indirectly led to CB1 occupancy by raising 2-AG levels, and raised norepinephrine levels in cortex. In vivo, the compound exhibited antinociceptive efficacy in both the rat complete Freund's adjuvant-induced radiant heat hypersensitivity and chronic constriction injury-induced cold hypersensitivity models of inflammatory and neuropathic pain, respectively. Though 30 mg/kg induced hippocampal synaptic depression, altered sleep onset, and decreased electroencephalogram gamma power, 3 mg/kg still provided approximately 80% enzyme occupancy, significantly increased 2-AG and norepinephrine levels, and produced neuropathic antinociception without synaptic depression or decreased gamma power. Thus, it is anticipated that the profile exhibited by this compound will allow for precise modulation of 2-AG levels in vivo, supporting potential therapeutic application in several central nervous system disorders. SIGNIFICANCE STATEMENT: Potentiation of endocannabinoid signaling activity via inhibition of the serine hydrolase monoacylglycerol lipase (MAGL) is an appealing strategy in the development of treatments for several disorders, including ones related to mood, pain, and inflammation. [1-(4-Fluorophenyl)indol-5-yl]-[3-[4-(thiazole-2-carbonyl)piperazin-1-yl]azetidin-1-yl]methanone is presented in this report to be a novel, potent, selective, and reversible noncovalent MAGL inhibitor that demonstrates dose-dependent enhancement of the major endocannabinoid 2-arachidonoylglycerol as well as efficacy in models of neuropathic and inflammatory pain.

Modular Protein Ligation: A New Paradigm as a Reagent Platform for Pre-Clinical Drug Discovery.

Significant resource is spent by drug discovery project teams to generate numerous, yet unique target constructs for the multiple platforms used to drive drug discovery programs including: functional assays, biophysical studies, structural biology, and biochemical high throughput screening campaigns. To improve this process, we developed Modular Protein Ligation (MPL), a combinatorial reagent platform utilizing Expressed Protein Ligation to site-specifically label proteins at the C-terminus with a variety of cysteine-lysine dipeptide conjugates. Historically, such proteins have been chemically labeled non-specifically through surface amino acids. To demonstrate the feasibility of this approach, we first applied MPL to proteins of varying size in different target classes using different recombinant protein expression systems, which were then evaluated in several different downstream assays. A key advantage to the implementation of this paradigm is that one construct can generate multiple final products, significantly streamlining the reagent generation for multiple early drug discovery project teams.

Development of a high-content imaging assay for screening compound aggregation.

Aggregated compounds can promiscuously and nonspecifically associate with proteins resulting in either false inhibition or activation of many different protein target classes. We developed a high-content imaging assay in a 384-well format using fluorescently labeled target proteins and an Operetta cell imager to screen for compound aggregates that interact with target proteins. The high-throughput assay can not only directly detect the interaction between compound aggregators and the target of interest, but also determine the critical aggregation concentration (CAC) of a given promiscuous small molecule.

Author Correction: Prioritizing multiple therapeutic targets in parallel using automated DNA-encoded library screening.

This corrects the article DOI: 10.1038/ncomms16081.

High-Throughput Assessment of Structural Continuity in Biologics.

We demonstrate a high-throughput chemoprinting platform that confirms the consistency in the higher-order structure of protein biologics and is sensitive enough to detect single-point mutations. This method addresses the quality and consistency of the tertiary and quaternary structure of biologic drug products, which is arguably the most important, yet rarely examined, parameter. The method described uses specific small-molecule ligands as molecular probes to assess protein structure. Each library of probe molecules provides a "fingerprint" when taken holistically. After proof-of-concept experiments involving enzymes and antibodies, we were able to detect minor conformational perturbations between four 48 kDa protein mutants that only differ by one amino acid residue.

Prioritizing multiple therapeutic targets in parallel using automated DNA-encoded library screening.

The identification and prioritization of chemically tractable therapeutic targets is a significant challenge in the discovery of new medicines. We have developed a novel method that rapidly screens multiple proteins in parallel using DNA-encoded library technology (ELT). Initial efforts were focused on the efficient discovery of antibacterial leads against 119 targets from Acinetobacter baumannii and Staphylococcus aureus. The success of this effort led to the hypothesis that the relative number of ELT binders alone could be used to assess the ligandability of large sets of proteins. This concept was further explored by screening 42 targets from Mycobacterium tuberculosis. Active chemical series for six targets from our initial effort as well as three chemotypes for DHFR from M. tuberculosis are reported. The findings demonstrate that parallel ELT selections can be used to assess ligandability and highlight opportunities for successful lead and tool discovery.

Discovery of a Novel 2,6-Disubstituted Glucosamine Series of Potent and Selective Hexokinase 2 Inhibitors.

A novel series of potent and selective hexokinase 2 (HK2) inhibitors, 2,6-disubstituted glucosamines, has been identified based on HTS hits, exemplified by compound 1. Inhibitor-bound crystal structures revealed that the HK2 enzyme could adopt an "induced-fit" conformation. The SAR study led to the identification of potent HK2 inhibitors, such as compound 34 with greater than 100-fold selectivity over HK1. Compound 25 inhibits in situ glycolysis in a UM-UC-3 bladder tumor cell line via (13)CNMR measurement of [3-(13)C]lactate produced from [1,6-(13)C2]glucose added to the cell culture.

Development of a high-throughput screen to detect inhibitors of TRPS1 sumoylation.

Small ubiquitin-like modifier (SUMO) belongs to the family of ubiquitin-like proteins (Ubls) that can be reversibly conjugated to target-specific lysines on substrate proteins. Although covalently sumoylated products are readily detectible in gel-based assays, there has been little progress toward the development of robust quantitative sumoylation assay formats for the evaluation of large compound libraries. In an effort to identify inhibitors of ubiquitin carrier protein 9 (Ubc9)-dependent sumoylation, a high-throughput fluorescence polarization assay was developed, which allows detection of Lys-1201 sumoylation, corresponding to the major site of functional sumoylation within the transcriptional repressor trichorhino-phalangeal syndrome type I protein (TRPS1). A minimal hexapeptide substrate peptide, TMR-VVK1201TEK, was used in this assay format to afford high-throughput screening of the GlaxoSmithKline diversity compound collection. A total of 728 hits were confirmed but no specific noncovalent inhibitors of Ubc9 dependent trans-sumoylation were found. However, several diaminopyrimidine compounds were identified as inhibitors in the assay with IC50 values of 12.5 µM. These were further characterized to be competent substrates which were subject to sumoylation by SUMO-Ubc9 and which were competitive with the sumoylation of the TRPS1 peptide substrates.

Protein phosphorylation by semisynthesis: from paper to practice.

Deconvolution of specific phosphorylation events can be complicated by the reversibility of modification. Protein semisynthesis with phosphonate analogues offers an attractive approach to functional analysis of signaling pathways. In this technique, N- and C-terminal synthetic peptides containing nonhydrolyzable phosphonates at target residues can be ligated to recombinant proteins of interest. The resultant semisynthetic proteins contain site specific, stoichiometric phosphonate modifications and are completely resistant to phosphatases. Control of stoichiometry, specificity, and reversibility allows for complex signaling systems to be broken down into individual events and discretely examined. This chapter outlines the general methods and considerations for designing and carrying out phosphoprotein semisynthetic projects.

Co-oxidation by cyclooxygenases.

Cyclooxygenases (COXs; prostaglandin H(2) synthases) catalyze the bis-dioxygenation of arachidonic acid (AA) to generate prostaglandin (PG) G(2) followed by the peroxidative cleavage of PGG(2) to yield PGH(2), the precursor to all of the vasoactive PGs. These enzymes utilize a Fe-protoporhyrin IX (heme) co-factor to catalyze peroxide bond cleavage, which puts the Fe at a higher oxidation state (Fe(3+) → Fe(5+)). The heme Fe requires two electrons (e(-)) to return to its resting state (Fe(3+)) for the next round of catalysis. Peroxide bond cleavage thus occurs via compound I and compound II, observed for horseradish peroxidase. To return to Fe(3+), electrons come from "co-reductants" and their subsequent oxidation by the enzyme is known as "co-oxidation". The protocols in this unit are aimed at characterizing this side reaction of COXs.

Analysis of serotonin N-acetyltransferase regulation in vitro and in live cells using protein semisynthesis.

Serotonin N-acetyltransferase [arylalkylamine N-acetyltransferase (AANAT)] is a key circadian rhythm enzyme that drives the nocturnal production of melatonin in the pineal. Prior studies have suggested that its light and diurnal regulation involves phosphorylation on key AANAT Ser and Thr residues which results in 14-3-3zeta recruitment and changes in catalytic activity and protein stability. Here we use protein semisynthesis by expressed protein ligation to systematically explore the effects of single and dual phosphorylation of AANAT on acetyltransferase activity and relative affinity for 14-3-3zeta. AANAT Thr31 phosphorylation on its own can enhance catalytic efficiency up to 7-fold through an interaction with 14-3-3zeta that lowers the substrate K m. This augmented catalytic profile is largely abolished by double phosphorylation at Thr31 and Ser205. A possible basis for this difference is the dual anchoring of doubly phosphorylated AANAT via one 14-3-3zeta heterodimer. We have developed a novel solution phase assay for accurate K D measurements of 14-3-3zeta-AANAT interaction using 14-3-3zeta fluorescently labeled with rhodamine by expressed protein ligation. We have also generated a doubly fluorescently labeled AANAT which can be used to assess the stability of this protein in a live cell, real-time assay by fluorescence resonance energy transfer measured by microscopic imaging. These studies offer new insights into the molecular basis of melatonin regulation and 14-3-3zeta interaction.

De novo discovery of serotonin N-acetyltransferase inhibitors.

Serotonin N-acetyltransferase (arylalkylamine N-acetyltransferase, AANAT) is a member of the GCN5 N-acetyltransferase (GNAT) superfamily and catalyzes the penultimate step in the biosynthesis of melatonin; a large daily rhythm in AANAT activity drives the daily rhythm in circulating melatonin. We have used a structure-based computational approach to identify the first druglike and selective inhibitors of AANAT. Approximately 1.2 million compounds were virtually screened by 3D high-throughput docking into the active site of X-ray structures for AANAT, and in total 241 compounds were tested as inhibitors. One compound class, containing a rhodanine scaffold, exhibited low micromolar competitive inhibition against acetyl-CoA (AcCoA) and proved to be effective in blocking melatonin production in pineal cells. Compounds from this class are predicted to bind as bisubstrate inhibitors through interactions with the AcCoA and serotonin binding sites. Overall, this study demonstrates the feasibility of using virtual screening to identify small molecules that are selective inhibitors of AANAT.

Structural basis for the inhibition of the LSD1 histone demethylase by the antidepressant trans-2-phenylcyclopropylamine.

Histone modifications, such as acetylation and methylation, are important epigenetic marks that regulate diverse biological processes that use chromatin as the template, including transcription. Dysregulation of histone acetylation and methylation leads to the silencing of tumor suppressor genes and contributes to cancer progression. Inhibitors of enzymes that catalyze the addition and removal of these epigenetic marks thus have therapeutic potential for treating cancer. Lysine-specific demethylase 1 (LSD1) is the first discovered histone lysine demethylase and, with the help of its cofactor CoREST, specifically demethylates mono- and dimethylated histone H3 lysine 4 (H3-K4), thus repressing transcription. Because LSD1 belongs to the family of flavin adenine dinucleotide (FAD)-dependent amine oxidases, certain inhibitors of monoamine oxidases (MAOs), including the clinically used antidepressant trans-2-phenylcyclopropylamine (PCPA; tranylcypromine; Parnate), are also capable of inhibiting LSD1. In this study, we have further measured the kinetic parameters of the inhibition of LSD1 by PCPA and determined the crystal structure of LSD1-CoREST in the presence of PCPA. Our structural and mass spectrometry analyses are consistent with PCPA forming a covalent adduct with FAD in LSD1 that is distinct from the FAD-PCPA adduct of MAO B. The structure also reveals that the phenyl ring of the FAD-PCPA adduct in LSD1 does not form extensive interactions with active-site residues. This study thus provides the basis for designing more potent inhibitors of LSD1 that contain substitutions on the phenyl ring of PCPA to fully engage neighboring residues.

Structural basis of histone demethylation by LSD1 revealed by suicide inactivation.

Histone methylation regulates diverse chromatin-templated processes, including transcription. The recent discovery of the first histone lysine-specific demethylase (LSD1) has changed the long-held view that histone methylation is a permanent epigenetic mark. LSD1 is a flavin adenine dinucleotide (FAD)-dependent amine oxidase that demethylates histone H3 Lys4 (H3-K4). However, the mechanism by which LSD1 achieves its substrate specificity is unclear. We report the crystal structure of human LSD1 with a propargylamine-derivatized H3 peptide covalently tethered to FAD. H3 adopts three consecutive gamma-turns, enabling an ideal side chain spacing that places its N terminus into an anionic pocket and positions methyl-Lys4 near FAD for catalysis. The LSD1 active site cannot productively accommodate more than three residues on the N-terminal side of the methyllysine, explaining its H3-K4 specificity. The unusual backbone conformation of LSD1-bound H3 suggests a strategy for designing potent LSD1 inhibitors with therapeutic potential.

Mechanistic analysis of a suicide inactivator of histone demethylase LSD1.

Lysine-specific demethylase 1 (LSD1) is a transcriptional repressor and a flavin-dependent amine oxidase that is responsible for the removal of methyl from lysine 4 of histone H3. In this study, we characterize the mechanism and scope of LSD1 inhibition by a propargylamine-derivatized histone H3 substrate (1). Unlike aziridinyl and cyclopropylamine-derivatized histone H3 peptide substrate analogues, compound 1 appears to covalently modify and irreversibly inactivate LSD1 with high potency. Accompanying this inactivation is a spectroscopic change, which shifts the absorbance maximum to 392 nm. Spectral changes associated with the 1-LSD1 complex and reactivity to decreased pH and sodium borohydride treatment were suggestive of a structure involving a flavin-linked inhibitor conjugate between N5 of the flavin and the terminal carbon of the inhibitor. Using a 13C-labeled inhibitor, NMR analysis of the 1-flavin conjugate was consistent with this structural assignment. Kinetic analysis of the spectroscopic shift induced by 1 showed that the flavin adduct formed in a reaction with kinetic constants similar to those of the LSD1 inactivation process. Taken together, these data support a mechanism of LSD1 inactivation by 1 involving amine oxidation followed by Michael addition to the propargylic imine. We further examined the potential for a biotinylated analogue of 1 (1-Btn) to be used as a tool in affinity pulldown experiments. Using 1-Btn, it was feasible to selectively pull down spiked and endogenous LSD1 from HeLa cell nuclear extracts, setting the stage for activity-based demethylase proteomics.

A mechanism-based inactivator for histone demethylase LSD1.

Histone demethylase LSD1 is a flavin-dependent amine oxidase that catalyzes the oxidative removal of one or two methyl groups from the methyl-lysine-4 side chain of histone H3. We have designed and synthesized two peptide-based inhibitor analogues that block LSD1. One of these inhibitors, compound 1, contains a propargylamine functionality and shows time-dependent inactivation of LSD1. Peptide substrate, diMeK4H3-21, protected LSD1 against inactivation by 1 in a concentration-dependent fashion. Mass spectrometric analysis showed that 1 forms a covalent interaction with FAD. Compound 1 did not detectably inhibit monoamine oxidase B in the concentration range studied. Compound 1 is thus a selective, mechanism-based inactivator of LSD1 and is likely to serve as a useful tool in the study of histone modifications and chromatin remodeling.

Formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dGuo) by PAH o-quinones: involvement of reactive oxygen species and copper(II)/copper(I) redox cycling.

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants and procarcinogens that require activation by host metabolism. Metabolic activation of PAHs by aldo-keto reductases (AKRs) leads to formation of reactive and redox active o-quinones, which may cause oxidatively generated DNA damage. Spectrophotometric assays showed that NADPH caused PAH o-quinones to enter futile redox cycles, which result in the depletion of excess cofactor. Copper(II) amplified NADPH-dependent redox cycling of the o-quinones. Concurrent with NADPH oxidation, molecular oxygen was consumed, indicating the production of ROS. To determine whether PAH o-quinones can cause 8-oxo-dGuo formation in salmon testis DNA, three prerequisite experimental conditions were satisfied. Quantitative complete enzymatic hydrolysis of DNA was achieved, adventitious oxidation of dGuo was eliminated by the use of chelex and desferal, and basal levels of less than 2.0 8-oxo-dGuo/10(5) dGuo were obtained. The HPLC-ECD analytical method was validated by spiking the DNA with standard 8-oxo-dGuo and demonstrating quantitative recovery. HPLC-ECD analysis revealed that in the presence of NADPH and Cu(II), submicromolar concentrations of PAH o-quinones generated >60.0 8-oxo-dGuo adducts/10(5) dGuo. The rank order of 8-oxo-dGuo generated in isolated DNA was NP-1,2-dione > BA-3,4-dione > 7,12-DMBA-3,4-dione > BP-7,8-dione. The formation of 8-oxo-dGuo by PAH o-quinones was concentration-dependent. It was completely or partially inhibited when catalase, tiron, or a Cu(I) specific chelator, bathocuproine, was added, indicating the requirement for H(2)O(2), O(2)(-), and Cu(I), respectively. Methional, which is a copper-hydroperoxo complex [Cu(I)OOH] scavenger, also suppressed 8-oxo-dGuo formation. By contrast, mannitol, sodium benzoate, and sodium formate, which act as hydroxyl radical scavengers, did not block its formation. Sodium azide, which can act as both a hydroxyl radical and a (1)O(2) scavenger, abolished the formation of 8-oxo-dGuo. These data showed that the production of 8-oxo-dGuo was dependent on Cu(II)/Cu(I) catalyzed redox cycling of PAH o-quinones to produce ROS and that the immediate oxidant was not hydroxyl radical or Cu(I)OOH and that it is more likely (1)O(2), which can produce a 4,8-endoperoxide-dGuo intermediate.