Anthracycline anticancer drugs doxorubicin and aclarubicin have been used in the clinic for several decades to treat various cancers. Although closely related structures, their molecular mode of... Show moreAnthracycline anticancer drugs doxorubicin and aclarubicin have been used in the clinic for several decades to treat various cancers. Although closely related structures, their molecular mode of action diverges, which is reflected in their biological activity profile. For a better understanding of the structure-function relationship of these drugs, we synthesized ten doxorubicin/aclarubicin hybrids varying in three distinct features: aglycon, glycan, and amine substitution pattern. We continued to evaluate their capacity to induce DNA breaks, histone eviction, and relocated topoisomerase II alpha in living cells. Furthermore, we assessed their cytotoxicity in various human tumor cell lines. Our findings underscore that histone eviction alone, rather than DNA breaks, contributes strongly to the overall cytotoxicity of anthracyclines, and structures containing N,N-dimethylamine at the reducing sugar prove that are more cytotoxic than their nonmethylated counterparts. This structural information will support further development of novel anthracycline variants with improved anticancer activity. Show less
Self-adjuvanting vaccines, wherein an antigenic peptide is covalently bound to an immunostimulating agent, have been shown to be promising tools for immunotherapy. Synthetic Toll-like receptor (TLR... Show moreSelf-adjuvanting vaccines, wherein an antigenic peptide is covalently bound to an immunostimulating agent, have been shown to be promising tools for immunotherapy. Synthetic Toll-like receptor (TLR) ligands are ideal adjuvants for covalent linking to peptides or proteins. We here introduce a conjugation-ready TLR4 ligand, CRX-527, a potent powerful lipid A analogue, in the generation of novel conjugate-vaccine modalities. Effective chemistry has been developed for the synthesis of the conjugation-ready ligand as well as the connection of it to the peptide antigen. Different linker systems and connection modes to a model peptide were explored, and in vitro evaluation of the conjugates showed them to be powerful immune-activating agents, significantly more effective than the separate components. Mounting the CRX-527 ligand at the N-terminus of the model peptide antigen delivered a vaccine modality that proved to be potent in activation of dendritic cells, in facilitating antigen presentation, and in initiating specific CD8+ T-cell-mediated killing of antigen-loaded target cells in vivo. Synthetic TLR4 ligands thus show great promise in potentiating the conjugate vaccine platform for application in cancer vaccination. Show less
Zhou, J.; Mock, E.D.; Al Ayed, K.; Di, X.; Kantae, V.; Burggraaff, L.; ... ; Stelt, M. van der 2020
The phospholipase A and acyltransferase (PLAAT) family of cysteine hydrolases consists of five members, which are involved in the Ca2+-independent production of N-acylphosphatidylethanolamines ... Show moreThe phospholipase A and acyltransferase (PLAAT) family of cysteine hydrolases consists of five members, which are involved in the Ca2+-independent production of N-acylphosphatidylethanolamines (NAPEs). NAPEs are lipid precursors for bioactive N-acylethanolamines (NAEs) that are involved in various physiological processes such as food intake, pain, inflammation, stress, and anxiety. Recently, we identified α-ketoamides as the first pan-active PLAAT inhibitor scaffold that reduced arachidonic acid levels in PLAAT3-overexpressing U2OS cells and in HepG2 cells. Here, we report the structure–activity relationships of the α-ketoamide series using activity-based protein profiling. This led to the identification of LEI-301, a nanomolar potent inhibitor for the PLAAT family members. LEI-301 reduced the NAE levels, including anandamide, in cells overexpressing PLAAT2 or PLAAT5. Collectively, LEI-301 may help to dissect the physiological role of the PLAATs. Show less
The main protease of coronaviruses and the 3C protease of enteroviruses share a similar active-site architecture and a unique requirement for glutamine in the P1 position of the substrate. Because... Show moreThe main protease of coronaviruses and the 3C protease of enteroviruses share a similar active-site architecture and a unique requirement for glutamine in the P1 position of the substrate. Because of their unique specificity and essential role in viral polyprotein processing, these proteases are suitable targets for the development of antiviral drugs. In order to obtain near-equipotent, broad-spectrum antivirals against alphacoronaviruses, betacoronaviruses, and enteroviruses, we pursued a structure-based design of peptidomimetic alpha-ketoamides as inhibitors of main and 3C proteases. Six crystal structures of protease-inhibitor complexes were determined as part of this study. Compounds synthesized were tested against the recombinant proteases as well as in viral replicons and virus-infected cell cultures; most of them were not cell-toxic. Optimization of the P2 substituent of the alpha-ketoamides proved crucial for achieving near-equipotency against the three virus genera. The best near-equipotent inhibitors, 11u (P2 = cyclopentylmethyl) and 11r (P2 = cyclo-hexylmethyl), display low-micromolar EC50 values against enteroviruses, alphacoronaviruses, and betacoronaviruses in cell cultures. In Huh7 cells, 11r exhibits three-digit picomolar activity against the Middle East Respiratory Syndrome coronavirus. Show less
CC chemokine receptors 2 (CCR2) and 5 (CCR5) are involved in many inflammatory diseases; however, most CCR2 and CCR5 clinical candidates have been unsuccessful. (Pre)clinical evidence suggests that... Show moreCC chemokine receptors 2 (CCR2) and 5 (CCR5) are involved in many inflammatory diseases; however, most CCR2 and CCR5 clinical candidates have been unsuccessful. (Pre)clinical evidence suggests that dual CCR2/CCR5 inhibition might be more effective in the treatment of such multifactorial diseases. In this regard, the highly conserved intracellular binding site in chemokine receptors provides a new avenue for the design of multitarget ligands. In this study, we synthesized and evaluated the biological activity of a series of triazolopyrimidinone derivatives in CCR2 and CCR5. Radioligand binding assays first showed that they bind to the intracellular site of CCR2, and in combination with functional assays on CCR5, we explored structure−affinity/activity relationships in both receptors. Although most compounds were CCR2-selective, 39 and 43 inhibited β-arrestin recruitment in CCR5 with high potency. Moreover, these compounds displayed an insurmountable mechanism of inhibition in both receptors, which holds promise for improved efficacy in inflammatory diseases. Show less
Janssen, A.P.A.; Hengst, J.M.A. van; Béquignon, O.J.M.; Deng, H.; Westen, G.J.P. van; Stelt, M. van der 2019
Drug discovery programs of covalent irreversible, mechanism-based enzyme inhibitors often focus on optimization of potency as determined by IC50-values in biochemical assays. These assays do not... Show moreDrug discovery programs of covalent irreversible, mechanism-based enzyme inhibitors often focus on optimization of potency as determined by IC50-values in biochemical assays. These assays do not allow the characterization of the binding activity (Ki) and reactivity (kinact) as individual kinetic parameters of the covalent inhibitors. Here, we report the development of a kinetic substrate assay to study the influence of the acidity (pKa) of heterocyclic leaving group of triazole urea derivatives as diacylglycerol lipase (DAGL)-α inhibitors. Surprisingly, we found that the reactivity of the inhibitors did not correlate with the pKa of the leaving group, whereas the position of the nitrogen atoms in the heterocyclic core determined to a large extent the binding activity of the inhibitor. This finding was confirmed and clarified by molecular dynamics simulations on the covalently bound Michaelis−Menten complex. A deeper understanding of the binding properties of covalent serine hydrolase inhibitors is expected to aid in the discovery and development of more selective covalent inhibitors. Show less
Yoon, J.S.; Kim, G.; Jarhad, D.B.; Kim, H.R.; Shin, Y.S.; Qu, S.H.; ... ; Jeong, L.S. 2019
Nicotinamide N-methyltransferase (NNMT) catalyzes the methylation of nicotinamide to form N-methylnicotinamide. Overexpression of NNMT is associated with a variety of diseases, including a number... Show moreNicotinamide N-methyltransferase (NNMT) catalyzes the methylation of nicotinamide to form N-methylnicotinamide. Overexpression of NNMT is associated with a variety of diseases, including a number of cancers and metabolic disorders, suggesting a role for NNMT as a potential therapeutic target. By structural modification of a lead NNMT inhibitor previously developed in our group, we prepared a diverse library of inhibitors to probe the different regions of the enzyme’s active site. This investigation revealed that incorporation of a naphthalene moiety, intended to bind the hydrophobic nicotinamide binding pocket via π–π stacking interactions, significantly increases the activity of bisubstrate-like NNMT inhibitors (half-maximal inhibitory concentration 1.41 μM). These findings are further supported by isothermal titration calorimetry binding assays as well as modeling studies. The most active NNMT inhibitor identified in the present study demonstrated a dose-dependent inhibitory effect on the cell proliferation of the HSC-2 human oral cancer cell line. Show less
The development of covalent ligands for G protein-coupled receptors (GPCRs) is not a trivial process. Here, we report a streamlined workflow thereto from synthesis to validation, exemplified by the... Show moreThe development of covalent ligands for G protein-coupled receptors (GPCRs) is not a trivial process. Here, we report a streamlined workflow thereto from synthesis to validation, exemplified by the discovery of a covalent antagonist for the human adenosine A3 receptor (hA3AR). Based on the 1H,3H-pyrido[2,1-f]purine-2,4-dione scaffold, a series of ligands bearing a fluorosulfonyl warhead and a varying linker was synthesized. This series was subjected to an affinity screen, revealing compound 17b as the most potent antagonist. In addition, a nonreactive methylsulfonyl derivative 19 was developed as a reversible control compound. A series of assays, comprising time-dependent affinity determination, washout experiments, and [35S]GTPγS binding assays, then validated 17b as the covalent antagonist. A combined in silico hA3AR-homology model and site-directed mutagenesis study was performed to demonstrate that amino acid residue Y2657.36 was the unique anchor point of the covalent interaction. This workflow might be applied to other GPCRs to guide the discovery of covalent ligands. Show less
Subunit-selective proteasome inhibitors are valuable tools to assess the biological and medicinal relevance of individual proteasome active sites. Whereas the inhibitors for the β1c, β1i, β5c, and... Show more Subunit-selective proteasome inhibitors are valuable tools to assess the biological and medicinal relevance of individual proteasome active sites. Whereas the inhibitors for the β1c, β1i, β5c, and β5i subunits exploit the differences in the substrate-binding channels identified by X-ray crystallography, compounds selectively targeting β2c or β2i could not yet be rationally designed because of the high structural similarity of these two subunits. Here, we report the development, chemical synthesis, and biological screening of a compound library that led to the identification of the β2c- and β2i-selective compounds LU-002c (4; IC50 β2c: 8 nM, IC50 β2i/β2c: 40-fold) and LU-002i (5; IC50 β2i: 220 nM, IC50 β2c/β2i: 45-fold), respectively. Co-crystal structures with β2 humanized yeast proteasomes visualize protein–ligand interactions crucial for subunit specificity. Altogether, organic syntheses, activity-based protein profiling, yeast mutagenesis, and structural biology allowed us to decipher significant differences of β2 substrate-binding channels and to complete the set of subunit-selective proteasome inhibitors. Show less
Zacarias, N.V.O.; Veldhoven, J.P.D. van; Portner, L.; Spronsen, E. van; Ullo, S; Veenhuizen, M.; ... ; IJzerman, A.P. 2018
The recent crystal structures of CC chemokine receptors 2 and 9 (CCR2 and CCR9) have provided structural evidence for an allosteric, intracellular binding site. The high conservation of residues... Show moreThe recent crystal structures of CC chemokine receptors 2 and 9 (CCR2 and CCR9) have provided structural evidence for an allosteric, intracellular binding site. The high conservation of residues involved in this site suggests its presence in most chemokine receptors, including the close homologue CCR1. By using [H-3]CCR2-RA-[R], a high-affinity, CCR2 intracellular ligand, we report an intracellular binding site in CCR1, where this radioligand also binds with high affinity. In addition, we report the synthesis and biological characterization of a series of pyrrolone derivatives for CCR1 and CCR2, which allowed us to identify several high-affinity intracellular ligands, including selective and potential multitarget antagonists. Evaluation of selected compounds in a functional [S-35]GTP gamma S assay revealed that they act as inverse agonists in CCR1, providing a new manner of pharmacological modulation. Thus, this intracellular binding site enables the design of selective and multitarget inhibitors as a novel therapeutic approach. Show less
Monoacylglycerol lipase (MGLL or MAGL) is a critical point of regulation of both endocannabinoid and eicosanoid signaling pathways in the brain, thereby providing novel therapeutic opportunities... Show moreMonoacylglycerol lipase (MGLL or MAGL) is a critical point of regulation of both endocannabinoid and eicosanoid signaling pathways in the brain, thereby providing novel therapeutic opportunities for neurological and neurodegenerative diseases. In this issue Cisar et al. disclose the discovery, optimization, and initial preclinical profiling of ABX-1431, a covalent, irreversible MGLL inhibitor. Activity-based protein profiling was key to the discovery of ABX-1431. ABX-1431 is a first-in-class experimental drug that was well-tolerated and safe in phase 1 clinical studies. Data from an exploratory phase 1b study indicate that it has the potential to treat symptoms of adult patients with syndrome of Gilles de la Tourette. ABX-1431 is currently entering clinical phase 2 studies for this neurological disorder as well as for other indications, such as neuromyeltis optica and multiple sclerosis. Show less
Yang, X.; Michiels, T.J.M.; Jong, C. de; Soethoudt, M.; Dekker, N.; Gordon, E.; ... ; IJzerman, A.P. 2018
Using activity-based protein profiling (ABPP), functional proteins can be interrogated in their native environment. Despite their pharmaceutical relevance, G protein-coupled receptors (GPCRs) have... Show moreUsing activity-based protein profiling (ABPP), functional proteins can be interrogated in their native environment. Despite their pharmaceutical relevance, G protein-coupled receptors (GPCRs) have been difficult to address through ABPP. In the current study, we took the prototypical human adenosine A 2A receptor (hA(2A)R) as the starting point for the construction of a chemical toolbox allowing two-step affinity-based labeling of GPCRs. First, we equipped an irreversibly binding hA(2A)R ligand with a terminal alkyne to serve as probe. We showed that our probe irreversibly and concentration-dependently labeled purified hA(2A)R Click-ligation with a sulfonated cyanine-3 fluorophore allowed us to visualize the receptor on SDS-PAGE. We further demonstrated that labeling of the purified hA(2A)R by our probe could be inhibited by selective antagonists. Lastly, we showed successful labeling of the receptor in cell membranes overexpressing hA(2A)R, making our probe a promising affinity-based tool compound that sets the stage for the further development of probes for GPCRs. Show less
Covalent labeling of G protein-coupled receptors (GPCRs) by small molecules is a powerful approach to understand binding modes, mechanism of action, pharmacology, and even facilitate structure... Show more Covalent labeling of G protein-coupled receptors (GPCRs) by small molecules is a powerful approach to understand binding modes, mechanism of action, pharmacology, and even facilitate structure elucidation. We report the first covalent positive allosteric modulator (PAM) for a class C GPCR, the mGlu2 receptor. Three putatively covalent mGlu2 PAMs were designed and synthesized. Pharmacological characterization identified 2 to bind the receptor covalently. Computational modeling combined with receptor mutagenesis revealed T7917.29×30 as the likely position of covalent interaction. We show how this covalent ligand can be used to characterize the PAM binding mode and that it is a valuable tool compound in studying receptor function and binding kinetics. Our findings advance the understanding of the mGlu2 PAM interaction and suggest that 2 is a valuable probe for further structural and chemical biology approaches. Show less
AbstractWe expanded on a series of pyrido[2,1-f]purine-2,4-dione derivatives as human adenosine A3 receptor (hA3R) antagonists to determine their kinetic profiles and affinities. Many compounds... Show moreAbstractWe expanded on a series of pyrido[2,1-f]purine-2,4-dione derivatives as human adenosine A3 receptor (hA3R) antagonists to determine their kinetic profiles and affinities. Many compounds showed high affinities and a diverse range of kinetic profiles. We found hA3R antagonists with very short residence time (RT) at the receptor (2.2 min for 5) and much longer RTs (e.g., 376 min for 27 or 391 min for 31). Two representative antagonists (5 and 27) were tested in [35S]GTPγS binding assays, and their RTs appeared correlated to their (in)surmountable antagonism. From a kon-koff-KD kinetic map, we divided the antagonists into three subgroups, providing a possible direction for the further development of hA3R antagonists. Additionally, we performed a computational modeling study that sheds light on the crucial receptor interactions, dictating the compounds' binding kinetics. Knowledge of target binding kinetics appears useful for developing and triaging new hA3R antagonists in the early phase of drug discovery. Show less
We expanded on a series of pyrido[2,1-f]purine-2,4-clione derivatives as human adenosine A(3) receptor (hA(3)R) antagonists to determine their kinetic profiles and affinities. Many compounds showed... Show moreWe expanded on a series of pyrido[2,1-f]purine-2,4-clione derivatives as human adenosine A(3) receptor (hA(3)R) antagonists to determine their kinetic profiles and affinities. Many compounds showed high affinities and a diverse range of kinetic profiles. We found hA(3)R antagonists with very short residence time (RT) at the receptor (2.2 min for 5) and much longer RTs (e.g., 376 min for 27 or 391 min for 31). Two representative antagonists (5 and 27) were tested in [S-35]GTP gamma S binding assays, and their RTs appeared correlated to their (in)surmountable antagonism. From a k(on)-k(off)-K-D kinetic map, we divided the antagonists into three subgroups, providing a possible direction for the further development of hA(3)R antagonists. Additionally, we performed a computational modeling study that sheds light on the crucial receptor interactions, dictating the compounds' binding kinetics. Knowledge of target binding kinetics appears useful for developing and triaging new hA(3)R antagonists in the early phase of drug discovery. Show less
We expanded on a series of pyrido[2,1-f]purine-2,4-clione derivatives as human adenosine A(3) receptor (hA(3)R) antagonists to determine their kinetic profiles and affinities. Many compounds showed... Show moreWe expanded on a series of pyrido[2,1-f]purine-2,4-clione derivatives as human adenosine A(3) receptor (hA(3)R) antagonists to determine their kinetic profiles and affinities. Many compounds showed high affinities and a diverse range of kinetic profiles. We found hA(3)R antagonists with very short residence time (RT) at the receptor (2.2 min for 5) and much longer RTs (e.g., 376 min for 27 or 391 min for 31). Two representative antagonists (5 and 27) were tested in [S-35]GTP gamma S binding assays, and their RTs appeared correlated to their (in)surmountable antagonism. From a k(on)-k(off)-K-D kinetic map, we divided the antagonists into three subgroups, providing a possible direction for the further development of hA(3)R antagonists. Additionally, we performed a computational modeling study that sheds light on the crucial receptor interactions, dictating the compounds' binding kinetics. Knowledge of target binding kinetics appears useful for developing and triaging new hA(3)R antagonists in the early phase of drug discovery. Show less
Doornbos, M.L.J.; Cid, J.M.; Haubrich, J.; Nunes, A.G.; Sande, J.W. van de; Vermond, S.C.; ... ; Tresadern, G. 2017
We report the synthesis and biological evaluation of a series of 7-aryl-1,2,4-triazolo[4,3-a]pyridines with mGlu2 positive allosteric modulator (PAM) activity and affinity. Besides traditional in... Show moreWe report the synthesis and biological evaluation of a series of 7-aryl-1,2,4-triazolo[4,3-a]pyridines with mGlu2 positive allosteric modulator (PAM) activity and affinity. Besides traditional in vitro parameters of potency and affinity, kinetic parameters kon, koff and residence time (RT) were determined. The PAMs showed various kinetic profiles; kon values ranged over 2 orders of magnitude, whereas RT values were within a 10-fold range. Association rate constant kon was linearly correlated to affinity. Evaluation of a short, medium, and long RT compound in a label-free assay indicated a correlation between RT and functional effect. The effects of long RT compound 9 on sleep–wake states indicated long RT was translated into sustained inhibition of rapid eye movement (REM) in vivo. These results show that affinity-only driven selection would have resulted in mGlu2 PAMs with high values for kon but not necessarily optimized RT, which is key to predicting optimal efficacy in vivo. Show less
