Rapid and profound rewiring of brain lipid signaling networks by acute diacylglycerol lipase inhibition.

Diacylglycerol lipases (DAGLα and DAGLß) convert diacylglycerol to the endocannabinoid 2-arachidonoylglycerol. Our understanding of DAGL function has been hindered by a lack of chemical probes that can perturb these enzymes in vivo. Here, we report a set of centrally active DAGL inhibitors and a structurally related control probe and their use, in combination with chemical proteomics and lipidomics, to determine the impact of acute DAGL blockade on brain lipid networks in mice. Within 2 h, DAGL inhibition produced a striking reorganization of bioactive lipids, including elevations in DAGs and reductions in endocannabinoids and eicosanoids. We also found that DAGLα is a short half-life protein, and the inactivation of DAGLs disrupts cannabinoid receptor-dependent synaptic plasticity and impairs neuroinflammatory responses, including lipopolysaccharide-induced anapyrexia. These findings illuminate the highly interconnected and dynamic nature of lipid signaling pathways in the brain and the central role that DAGL enzymes play in regulating this network.

Two-step activity-based protein profiling of diacylglycerol lipase.

Diacylglycerol lipases (DAGL) produce the endocannabinoid 2-arachidonoylglycerol, a key modulator of neurotransmitter release. Chemical tools that visualize endogenous DAGL activity are desired. Here, we report the design, synthesis and application of a triazole urea probe for DAGL equipped with a norbornene as a biorthogonal handle. The activity and selectivity of the probe was assessed with activity-based protein profiling. This probe was potent against endogenous DAGLα (IC50 = 5 nM) and it was successfully applied as a two-step activity-based probe for labeling of DAGLα using an inverse electron-demand Diels-Alder ligation in living cells.

A natural substrate-based fluorescence assay for inhibitor screening on diacylglycerol lipase α.

The endocannabinoid 2-arachidonoylglycerol (2-AG) is predominantly biosynthesized by sn-1-diacylglycerol lipase α (DAGL-α) in the CNS. Selective inhibitors of DAGL-α will provide valuable insights in the role of 2-AG in endocannabinoid signaling processes and are potential therapeutics for the treatment of obesity and neurodegenerative diseases. Here, we describe the development of a natural substrate-based fluorescence assay for DAGL-α, using a coupled enzyme approach. The continuous setup of our assay allows monitoring of DAGL-α activity in real-time and in a 96-well plate format. This constitutes a major improvement to the currently available radiometric and LC/MS-based methods, which can be executed only in low-throughput formats. In addition, our assay circumvents the use of radioactive material. We demonstrate that our assay can be used to screen inhibitors of DAGL-α activity, using 1-stearoyl-2-arachidonoyl-sn-glycerol as the physiologically relevant natural substrate of DAGL-α. Furthermore, our method can be employed to measure DAGL activity and inhibition in the mouse brain membrane proteome. Consequently, our assay should serve as a valuable tool for rapid hit validation and lead optimization of DAGL-α inhibitors.

Highly Selective, Reversible Inhibitor Identified by Comparative Chemoproteomics Modulates Diacylglycerol Lipase Activity in Neurons.

Diacylglycerol lipase (DAGL)-α and -ß are enzymes responsible for the biosynthesis of the endocannabinoid 2-arachidonoylglycerol (2-AG). Selective and reversible inhibitors are required to study the function of DAGLs in neuronal cells in an acute and temporal fashion, but they are currently lacking. Here, we describe the identification of a highly selective DAGL inhibitor using structure-guided and a chemoproteomics strategy to characterize the selectivity of the inhibitor in complex proteomes. Key to the success of this approach is the use of comparative and competitive activity-based proteome profiling (ABPP), in which broad-spectrum and tailor-made activity-based probes are combined to report on the inhibition of a protein family in its native environment. Competitive ABPP with broad-spectrum fluorophosphonate-based probes and specific ß-lactone-based probes led to the discovery of α-ketoheterocycle LEI105 as a potent, highly selective, and reversible dual DAGL-α/DAGL-ß inhibitor. LEI105 did not affect other enzymes involved in endocannabinoid metabolism including abhydrolase domain-containing protein 6, abhydrolase domain-containing protein 12, monoacylglycerol lipase, and fatty acid amide hydrolase and did not display affinity for the cannabinoid CB1 receptor. Targeted lipidomics revealed that LEI105 concentration-dependently reduced 2-AG levels, but not anandamide levels, in Neuro2A cells. We show that cannabinoid CB1-receptor-mediated short-term synaptic plasticity in a mouse hippocampal slice model can be reduced by LEI105. Thus, we have developed a highly selective DAGL inhibitor and provide new pharmacological evidence to support the hypothesis that "on demand biosynthesis" of 2-AG is responsible for retrograde signaling.

Structure-Activity Relationship Studies of Pyrimidine-4-Carboxamides as Inhibitors of N-Acylphosphatidylethanolamine Phospholipase D.

N-Acylphosphatidylethanolamine phospholipase D (NAPE-PLD) is regarded as the main enzyme responsible for the biosynthesis of N-acylethanolamines (NAEs), a family of bioactive lipid mediators. Previously, we reported N-(cyclopropylmethyl)-6-((S)-3-hydroxypyrrolidin-1-yl)-2-((S)-3-phenylpiperidin-1-yl)pyrimidine-4-carboxamide (1, LEI-401) as the first potent and selective NAPE-PLD inhibitor that decreased NAEs in the brains of freely moving mice and modulated emotional behavior [Mock Nat Chem. Biol., 2020, 16, 667-675]. Here, we describe the structure-activity relationship (SAR) of a library of pyrimidine-4-carboxamides as inhibitors of NAPE-PLD that led to the identification of LEI-401. A high-throughput screening hit was modified at three different substituents to optimize its potency and lipophilicity. Conformational restriction of an N-methylphenethylamine group by replacement with an (S)-3-phenylpiperidine increased the inhibitory potency 3-fold. Exchange of a morpholine substituent for an (S)-3-hydroxypyrrolidine reduced the lipophilicity and further increased activity by 10-fold, affording LEI-401 as a nanomolar potent inhibitor with drug-like properties. LEI-401 is a suitable pharmacological tool compound to investigate NAPE-PLD function in vitro and in vivo.

Accurate non-invasive image-based cytotoxicity assays for cultured cells.

BACKGROUND: The CloneSelect Imager system is an image-based visualisation system for cell growth assessment. Traditionally cell proliferation is measured with the colorimetric MTT assay. RESULTS: Here we show that both the CloneSelect Imager and the MTT approach result in comparable EC50 values when assaying the cytotoxicity of cisplatin and oxaliplatin on various cell lines. However, the image-based technique was found non-invasive, considerably quicker and more accurate than the MTT assay. CONCLUSIONS: This new image-based technique has the potential to replace the cumbersome MTT assay when fast, unbiased and high-throughput cytotoxicity assays are requested.

Copper curcuminoids containing anthracene groups: fluorescent molecules with cytotoxic activity.

The coordination chemistry of the new curcuminoid ligand, 1,7-(di-9-anthracene-1,6-heptadiene-3,5-dione), abbreviated 9Accm has been studied, resulting in two new copper-9Accm compounds. Compound 1, [Cu(phen)Cl(9Accm)], was synthesized by reacting 9Accm with [Cu(phen)Cl(2)] in a 1:1 ratio (M:L) and compound 2, [Cu(9Accm)(2)], was prepared from Cu(OAc)(2) and 9Accm (1:2). UV-vis, electron paramagnetic resonance (EPR), and superconducting quantum interference device (SQUID) measurements were some of the techniques employed to portray these species; studies on single crystals of free 9Accm, [Cu(phen)Cl(9Accm)] and [Cu(9Accm)(2)(py)] provided detailed structural information about compounds 1 and 2·py, being the first two copper-curcuminoids crystallographically described. In addition the antitumor activity of the new compounds was studied and compared with free 9Accm for a number of human tumor cells. To provide more insight on the mode of action of these compounds under biological conditions, additional experiments were accomplished, including studies on the nature of their interactions with calf thymus DNA by UV-vis titration and Circular Dichroism. These experiments together with DNA-binding studies indicate electrostatic interactions between some of these species and the double helix, pointing out the weak nature of the interaction of the compounds with CT-DNA. The intrinsic fluorescence of the free ligand and both copper compounds provided valuable information over the cellular process and therefore, fluorescence microscopy studies were performed using a human osteosarcoma cell line. Studies in vitro using this technique suggest that the action of these molecules seems to occur outside the nuclei.

Chemical genetics strategy to profile kinase target engagement reveals role of FES in neutrophil phagocytosis.

Chemical tools to monitor drug-target engagement of endogenously expressed protein kinases are highly desirable for preclinical target validation in drug discovery. Here, we describe a chemical genetics strategy to selectively study target engagement of endogenous kinases. By substituting a serine residue into cysteine at the DFG-1 position in the ATP-binding pocket, we sensitize the non-receptor tyrosine kinase FES towards covalent labeling by a complementary fluorescent chemical probe. This mutation is introduced in the endogenous FES gene of HL-60 cells using CRISPR/Cas9 gene editing. Leveraging the temporal and acute control offered by our strategy, we show that FES activity is dispensable for differentiation of HL-60 cells towards macrophages. Instead, FES plays a key role in neutrophil phagocytosis via SYK kinase activation. This chemical genetics strategy holds promise as a target validation method for kinases.

Ruthenium polypyridyl complexes and their modes of interaction with DNA: is there a correlation between these interactions and the antitumor activity of the compounds?

Various interaction modes between a group of six ruthenium polypyridyl complexes and DNA have been studied using a number of spectroscopic techniques. Five mononuclear species were selected with formula [Ru(tpy)L(1)L(2)]((2-n)+), and one closely related dinuclear cation of formula [{Ru(apy)(tpy)}(2){mu-H(2)N(CH(2))(6)NH(2)}](4+). The ligand tpy is 2,2':6',2''-terpyridine and the ligand L(1) is a bidentate ligand, namely, apy (2,2'-azobispyridine), 2-phenylazopyridine, or 2-phenylpyridinylmethylene amine. The ligand L(2) is a labile monodentate ligand, being Cl(-), H(2)O, or CH(3)CN. All six species containing a labile L(2) were found to be able to coordinate to the DNA model base 9-ethylguanine by (1)H NMR and mass spectrometry. The dinuclear cationic species, which has no positions available for coordination to a DNA base, was studied for comparison purposes. The interactions between a selection of four representative complexes and calf-thymus DNA were studied by circular and linear dichroism. To explore a possible relation between DNA-binding ability and toxicity, all compounds were screened for anticancer activity in a variety of cancer cell lines, showing in some cases an activity which is comparable to that of cisplatin. Comparison of the details of the compound structures, their DNA binding, and their toxicity allows the exploration of structure-activity relationships that might be used to guide optimization of the activity of agents of this class of compounds.

ABHD2 Inhibitor Identified by Activity-Based Protein Profiling Reduces Acrosome Reaction.

ABHD2 is a serine hydrolase that belongs to the subgroup of the α,ß-hydrolase fold-containing proteins, which is involved in virus propagation, immune response, and fertilization. Chemical tools to selectively modulate the activity of ABHD2 in an acute setting are highly desired to investigate its biological role, but are currently lacking. Here, we report a library-versus-library screening using activity-based protein profiling (ABPP) to evaluate in parallel the selectivity and activity of a focused lipase inhibitor library against ABHD2 and a panel of closely related ABHD proteins. This screen resulted in the rapid identification of novel inhibitors for ABHD2. The selectivity of the inhibitor was further investigated in native mouse testis proteome by competitive ABPP, revealing a highly restricted off-target profile. The progesterone-induced acrosome reaction was reduced in a dose-dependent manner by the newly identified inhibitor, which provides further support for the key-role of ABHD2 in the P4-stimulated acrosome reaction. On this basis, the ABHD2 inhibitor is an excellent starting point for further optimization of ABHD2 inhibitors that can modulate sperm fertility and may lead to novel contraceptives.

Identification of α,ß-Hydrolase Domain Containing Protein 6 as a Diacylglycerol Lipase in Neuro-2a Cells.

The endocannabinoid 2-arachidonoylglycerol (2-AG) is involved in neuronal differentiation. This study aimed to identify the biosynthetic enzymes responsible for 2-AG production during retinoic acid (RA)-induced neurite outgrowth of Neuro-2a cells. First, we confirmed that RA stimulation of Neuro-2a cells increases 2-AG production and neurite outgrowth. The diacylglycerol lipase (DAGL) inhibitor DH376 blocked 2-AG production and reduced neuronal differentiation. Surprisingly, CRISPR/Cas9-mediated knockdown of DAGLα and DAGLß in Neuro-2a cells did not reduce 2-AG levels, suggesting another enzyme capable of producing 2-AG in this cell line. Chemical proteomics revealed DAGLß and α,ß-hydrolase domain containing protein (ABHD6) as the only targets of DH376 in Neuro-2a cells. Biochemical, genetic and lipidomic studies demonstrated that ABHD6 possesses DAGL activity in conjunction with its previously reported monoacylglycerol lipase activity. RA treatment of Neuro-2a cells increased by three-fold the amount of active ABHD6. Our study shows that ABHD6 exhibits significant DAG lipase activity in Neuro-2a cells in addition to its known MAG lipase activity and suggest it is involved in neuronal differentiation.

Activity-Based Protein Profiling Identifies α-Ketoamides as Inhibitors for Phospholipase A2 Group XVI.

Phospholipase A2, group XVI (PLA2G16) is a thiol hydrolase from the HRASLS family that regulates lipolysis in adipose tissue and has been identified as a host factor enabling the cellular entry of picornaviruses. Chemical tools are essential to visualize and control PLA2G16 activity, but they have not been reported to date. Here, we show that MB064, which is a fluorescent lipase probe, also labels recombinant and endogenously expressed PLA2G16. Competitive activity-based protein profiling (ABPP) using MB064 enabled the discovery of α-ketoamides as the first selective PLA2G16 inhibitors. LEI110 was identified as a potent PLA2G16 inhibitor ( Ki = 20 nM) that reduces cellular arachidonic acid levels and oleic acid-induced lipolysis in human HepG2 cells. Gel-based ABPP and chemical proteomics showed that LEI110 is a selective pan-inhibitor of the HRASLS family of thiol hydrolases (i.e., PLA2G16, HRASLS2, RARRES3 and iNAT). Molecular dynamic simulations of LEI110 in the reported crystal structure of PLA2G16 provided insight in the potential ligand-protein interactions to explain its binding mode. In conclusion, we have developed the first selective inhibitor that can be used to study the cellular role of PLA2G16.

Development of a Retinal-Based Probe for the Profiling of Retinaldehyde Dehydrogenases in Cancer Cells.

Retinaldehyde dehydrogenases belong to a superfamily of enzymes that regulate cell differentiation and are responsible for detoxification of anticancer drugs. Chemical tools and methods are of great utility to visualize and quantify aldehyde dehydrogenase (ALDH) activity in health and disease. Here, we present the discovery of a first-in-class chemical probe based on retinal, the endogenous substrate of retinal ALDHs. We unveil the utility of this probe in quantitating ALDH isozyme activity in a panel of cancer cells via both fluorescence and chemical proteomic approaches. We demonstrate that our probe is superior to the widely used ALDEFLUOR assay to explain the ability of breast cancer (stem) cells to produce all-trans retinoic acid. Furthermore, our probe revealed the cellular selectivity profile of an advanced ALDH1A1 inhibitor, thereby prompting us to investigate the nature of its cytotoxicity. Our results showcase the application of substrate-based probes in interrogating pathologically relevant enzyme activities. They also highlight the general power of chemical proteomics in driving the discovery of new biological insights and its utility to guide drug discovery efforts.

Synthesis, crystal structure, studies in solution and cytotoxicity of two new fluorescent platinum(II) compounds containing anthracene derivatives as a carrier ligand.

Two new cytotoxic fluorescent platinum(II) compounds, cis-[Pt(A9opy)Cl2] (1) and cis-[Pt(A9pyp)(DMSO)Cl2] (2),have been designed, synthesized, and characterized by IR, 1H NMR, and 195Pt NMR spectroscopy; electrospray ionization mass spectrometry (ESI-MS); and single-crystal X-ray diffraction. The carrier ligands selected for thesynthesis of these fluorescent platinum(II) compounds are E-2-[1-(9-anthryl)-3-oxo-3-prop-2-enylpyridine] (abbreviatedas A9opy) and E-1-(9-anthryl)-3-(2-pyridyl)-2-propenone (abbreviated as A9pyp). The compound cis-[Pt(A9opy)Cl2](1) comprises a peculiar cis-platinum(II) organometallic compound, in which the platinum(II) ion is bound to the photoisomerizable carbon-carbon double bond of the carrier ligand. The effects of the metal-ion coordination on the photoisomerization of the carbon-carbon double bond of the ligand have been studied. In contrast, the carrier ligand A9pyp used for the synthesis of the cis-[Pt(A9pyp)(DMSO)Cl2] compound (2) does not undergo such anisomerization process and remains in the E conformation, while coordinated to the platinum(II) ion through the nitrogen of the pyridine ring. In addition to the synthesis and characterization, solution studies of both compounds have also been performed in detail, including NMR and ESI-MS spectroscopy. Moreover, a high degree of cytotoxicactivity of compound 1 was found, as compared to cisplatin and its corresponding platinum-free molecule, in a series of human tumor cell lines. Compound 2 was also found to be highly active against these cell lines but appeared less active compared to the platinum-free molecule.

The synthesis, chemical and biological properties of dichlorido(azpy)gold(III) chloride (azpy=2-(phenylazo)pyridine) and the gold-induced conversion of the azpy ligand to the chloride of the novel tricyclic pyrido[2,1-c][1,2,4]benzotriazin-11-ium cation.

A new Au(III) coordination compound with the ligand 2-(phenylazo)pyridine has been synthesized and fully characterized by means of elemental analysis, IR, UV-visible, conductivity measurements, NMR, electrospray ionization (ESI-MS) and inductively coupled plasma optical emission spectrometry (ICP-OES). The chemical stability of the cation in this compound, [Au(azpy)Cl(2)](+) (abbreviated: Au-azpy), was analyzed by means of several physicochemical methods. While stable in the solid state, stability studies performed with the gold compound in solution showed an unexpected and unprecedented reactivity. A cationic organic derivative of 2-(phenylazo)pyridine, (abbreviated: pyrium), was produced from the solution and has been isolated as its chloride salt and characterized by crystal structure determination, elemental analysis, NMR, ESI-MS and conductivity studies in solution. This cyclization reaction is reported for the first time in the case of gold coordination compounds. The Au adduct and the pyrium cation were investigated as potential cytotoxic and anticancer agents, and both show moderate to high cytotoxic properties in cisplatin-sensitive and cisplatin-resistant ovarian carcinoma cell lines, A2780; and cisplatin-sensitive and cisplatin-resistant murine lymphocytic leukemia cell lines, L1210. Significant anticancer activity against the cisplatin resistant cell lines was found for the pyrium salt, ruling out the occurrence of cross resistance phenomena.

Triazole Ureas Act as Diacylglycerol Lipase Inhibitors and Prevent Fasting-Induced Refeeding.

Triazole ureas constitute a versatile class of irreversible inhibitors that target serine hydrolases in both cells and animal models. We have previously reported that triazole ureas can act as selective and CNS-active inhibitors for diacylglycerol lipases (DAGLs), enzymes responsible for the biosynthesis of 2-arachidonoylglycerol (2-AG) that activates cannabinoid CB1 receptor. Here, we report the enantio- and diastereoselective synthesis and structure-activity relationship studies. We found that 2,4-substituted triazole ureas with a biphenylmethanol group provided the most optimal scaffold. Introduction of a chiral ether substituent on the 5-position of the piperidine ring provided ultrapotent inhibitor 38 (DH376) with picomolar activity. Compound 38 temporarily reduces fasting-induced refeeding of mice, thereby emulating the effect of cannabinoid CB1-receptor inverse agonists. This was mirrored by 39 (DO34) but also by the negative control compound 40 (DO53) (which does not inhibit DAGL), which indicates the triazole ureas may affect the energy balance in mice through multiple molecular targets.

Activity-based protein profiling reveals off-target proteins of the FAAH inhibitor BIA 10-2474.

A recent phase 1 trial of the fatty acid amide hydrolase (FAAH) inhibitor BIA 10-2474 led to the death of one volunteer and produced mild-to-severe neurological symptoms in four others. Although the cause of the clinical neurotoxicity is unknown, it has been postulated, given the clinical safety profile of other tested FAAH inhibitors, that off-target activities of BIA 10-2474 may have played a role. Here we use activity-based proteomic methods to determine the protein interaction landscape of BIA 10-2474 in human cells and tissues. This analysis revealed that the drug inhibits several lipases that are not targeted by PF04457845, a highly selective and clinically tested FAAH inhibitor. BIA 10-2474, but not PF04457845, produced substantial alterations in lipid networks in human cortical neurons, suggesting that promiscuous lipase inhibitors have the potential to cause metabolic dysregulation in the nervous system.

Combinatorial discovery of new asymmetric cis platinum anticancer complexes is made possible with solid-phase synthetic methods.

To efficiently access asymmetric cis platinum (II) complexes for biological evaluation, a new solid-phase synthesis was designed. This synthesis was used for the preparation of a small library of platinum compounds. Several compounds from this library revealed promising activity during a cytotoxicity screen. Two active compounds were, therefore, synthesised on a larger scale and tested more extensively against a larger panel of cell-lines, confirming their high potential as antitumour compounds. The work presented illustrates how a combination of a new methodology and established techniques can speed up the search for platinum complexes with improved cytotoxic profiles compared to cisplatin.

Extending solid-phase methods in inorganic synthesis: the first dinuclear platinum complex synthesised via the solid phase.

A method for obtaining potentially anti-tumour active dinuclear platinum coordination compounds via solid-phase inorganic synthesis is described for the first time.