5-HT2C Receptor Structures Reveal the Structural Basis of GPCR Polypharmacology.

Drugs frequently require interactions with multiple targets-via a process known as polypharmacology-to achieve their therapeutic actions. Currently, drugs targeting several serotonin receptors, including the 5-HT2C receptor, are useful for treating obesity, drug abuse, and schizophrenia. The competing challenges of developing selective 5-HT2C receptor ligands or creating drugs with a defined polypharmacological profile, especially aimed at G protein-coupled receptors (GPCRs), remain extremely difficult. Here, we solved two structures of the 5-HT2C receptor in complex with the highly promiscuous agonist ergotamine and the 5-HT2A-C receptor-selective inverse agonist ritanserin at resolutions of 3.0 Å and 2.7 Å, respectively. We analyzed their respective binding poses to provide mechanistic insights into their receptor recognition and opposing pharmacological actions. This study investigates the structural basis of polypharmacology at canonical GPCRs and illustrates how understanding characteristic patterns of ligand-receptor interaction and activation may ultimately facilitate drug design at multiple GPCRs.

Deconstructing Lipid Kinase Inhibitors by Chemical Proteomics.

Diacylglycerol kinases (DGKs) regulate lipid metabolism and cell signaling through ATP-dependent phosphorylation of diacylglycerol to biosynthesize phosphatidic acid. Selective chemical probes for studying DGKs are currently lacking and are needed to annotate isoform-specific functions of these elusive lipid kinases. Previously, we explored fragment-based approaches to discover a core fragment of DGK-α (DGKα) inhibitors responsible for selective binding to the DGKα active site. Here, we utilize quantitative chemical proteomics to deconstruct widely used DGKα inhibitors to identify structural regions mediating off-target activity. We tested the activity of a fragment (RLM001) derived from a nucleotide-like region found in the DGKα inhibitors R59022 and ritanserin and discovered that RLM001 mimics ATP in its ability to broadly compete at ATP-binding sites of DGKα as well as >60 native ATP-binding proteins (kinases and ATPases) detected in cell proteomes. Equipotent inhibition of activity-based probe labeling by RLM001 supports a contiguous ligand-binding site composed of C1, DAGKc, and DAGKa domains in the DGKα active site. Given the lack of available crystal structures of DGKs, our studies highlight the utility of chemical proteomics in revealing active-site features of lipid kinases to enable development of inhibitors with enhanced selectivity against the human proteome.

The Ligand Binding Landscape of Diacylglycerol Kinases.

Diacylglycerol kinases (DGKs) are integral components of signal transduction cascades that regulate cell biology through ATP-dependent phosphorylation of the lipid messenger diacylglycerol. Methods for direct evaluation of DGK activity in native biological systems are lacking and needed to study isoform-specific functions of these multidomain lipid kinases. Here, we utilize ATP acyl phosphate activity-based probes and quantitative mass spectrometry to define, for the first time, ATP and small-molecule binding motifs of representative members from all five DGK subtypes. We use chemical proteomics to discover an unusual binding mode for the DGKα inhibitor, ritanserin, including interactions at the atypical C1 domain distinct from the ATP binding region. Unexpectedly, deconstruction of ritanserin yielded a fragment compound that blocks DGKα activity through a conserved binding mode and enhanced selectivity against the kinome. Collectively, our studies illustrate the power of chemical proteomics to profile protein-small molecule interactions of lipid kinases for fragment-based lead discovery.

Molecular dynamics of serotonin and ritanserin interacting with the 5-HT2 receptor.

A three-dimensional model of the serotonin (5-hydroxytrytamine; 5-HT) 5-HT2 receptor was constructed from the amino acid sequence by molecular graphics techniques, molecular mechanics energy calculations and molecular dynamics simulations. The receptor model has 7 alpha helical segments which form a membrane-spanning duct with a putative ligand binding site. Most of the synaptic domains and the ligand binding site were surrounded by negative electrostatic potentials, suggesting that positively charged ligands are attracted to the receptor by electrostatic forces. The cytoplasmic domains, except the C-terminal tail, had mainly positive electrostatic potentials. The molecular dynamics of the receptor-ligand complex was examined in 100 ps simulations with 5-HT or ritanserin at a postulated binding site. During the simulations the helices moved from an initial circular arrangement into a more oval arrangement, and became slightly tilted relative to each other. The protonated ligands neutralized the negative electrostatic potentials around Asp 120 and Asp 155 in the central core of the receptor. 5-HT had only weak interactions with Asp 155 but strong interactions with Asp 120 during the simulations, with the amino group of 5-HT tightly bound to the carboxylic side chain of Asp 120. Ritanserin showed similarly strong interactions with Asp 120 and Asp 155 during the simulations.

Molecular modeling of serotonin, ketanserin, ritanserin and their 5-HT2C receptor interactions.

Molecular modeling techniques were used to build a three-dimensional model of the rat 5-HT2C receptor, which was used to examine receptor interactions for protonated forms of serotonin, ketanserin and ritanserin. Molecular dynamics simulations which were started with the fluoro benzene moiety of ketanserin and ritanserin oriented towards the cytoplasmic side of the receptor model, produced the strongest antagonist-receptor interactions. The fluoro bezene ring(s) of the antagonists interacted strongly with aromatic residues in the receptor model, which predicts slightly different orientations and ligand-receptor interactions of ketanserin and ritanserin at a putative binding site. The model suggests that Asn333 (transmembrane helix 6) is involved in a hydrogen-bonding interaction with ketanserin, but not with ritanserin. The model also also suggests that the position corresponding to Cys362 (transmembrane helix 7) may be an important determinant for specifying 5-HT2A receptor selectivity in ketanserin binding.

The structure of human serotonin 2c G-protein-coupled receptor bound to agonists and antagonists.

We used the MembStruk computational procedure to predict the three-dimensional (3D) structure for the serotonin 5-HT(2C) G-protein-coupled receptor (GPCR). Using this structure, we used the MSCDock computational procedure to predict the 3D structures for bound ligand-protein complexes for agonists such as serotonin and antagonists such as ritanserin, metergoline, and methiothepin. In addition, we predicted the SAR data for a series of psilocybin analogs, both agonists and antagonists. We performed molecular dynamics (MD) on serotonin bound to 5-HT(2C) and we find the protein and binding site to be stable after 5ns. We find good agreement with the currently known experimental data and we predict a number of new mutations which could be used to validate further our predicted structures. This agreement between theory and experiment suggests that our 3D structure is sufficiently accurate for use in drug design. We also compare a preliminary prediction for 5-HT(2B) with our prediction for 5-HT(2C) and find a difference in TM5 that contributes to different serotonin binding modes in 5-HT(2B) and 5-HT(2C).

El desarrollo de nuevas drogas antipsicoticas / Development of new antipsychotic drugs

Se da por sentado que en la esquizofrenia, los efectos terapéuticos de los neurolépticos se basan en el bloqueo de los receptores de dopamina situados en el cerebro. Sin embargo, también se admite que los neurolépticos "clásicos" presentan algunos incovenientes importantes: su relativa falta de efectos sobre los síntomas negativos y su capacidad de inducción de síntomas extrapoiramidales (SEP). Experiencias clínicas llevadas a cabo con pipamperona mostraron que un antagonista combinado de serotinina 5-HT2 y dopamina D2 presentaba ventajas en el tratamiento de la esquizofrenia. Esto se hizo patente a través de los efectos antiautísticos observados, de la regulación de los ritmos de sueño y de vigilia perturbados y de la baja tendencia a la inducción de SEP. Los estudios realizados con setoperona, compuesto de perfil farmacológico comparable, confirmaron estas observaciones. No se pudo explorar la exacta implicación del antagnista 5-HT2 en los tratamientos psicofarmacológicos de la esquizofrenia hasta no haberse realizado la síntesis del receptor antagonista selectivo y específico: la ritanserina. En efecto las pruebas de doble ciego efectuadas demostraron una majoría sensible de los síntomas negativos y extrapiramidales. Puesto que las ventajas de la monoterapia en el tratamiento de la esquizofrenia son innegables, lo lógico era pasar a la selección de un compuesto con un antagonismo central comparable al de...