Discovery of a pocket network on the domain 5 of the TrkB receptor - A potential new target in the quest for the new ligands.

The important role that the neurotrophin tyrosine kinase receptor - TrkB has in the pathogenesis of several neurodegenerative conditions such are Alzheimer's disease, Parkinson's disease, Huntington's disease, has been well described. This shouldn't be a surprise, since in the physiological conditions, once activated by brain-derived neurotrophic factor (BDNF) and neurotrophin-4/5 (NT-4/5), the TrkB receptor promotes neuronal survival, differentiation and synaptic function. Considering that the natural ligands for TrkB receptor are large proteins, it is a challenge to discover small molecule capable to mimic their effects. Even though, the surface of receptor that is interacting with BDNF or NT-4/5 is known, there was always a question which pocket and interaction is responsible for activation of it. In order to answer this challenging question, we have used molecular dynamic (MD) simulations and Pocketron algorithm which enabled us to detect, for the first time, a pocket network existing in the interacting domain (d5) of the receptor; to describe them and to see how they are communicating with each other. This new discovery gave us potential new areas on receptor that can be targeted and used for structure-based drug design approach in the development of the new ligands.

Development of Pleiotropic TrkB and 5-HT4 Receptor Ligands as Neuroprotective Agents.

One common event that is the most detrimental in neurodegenerative disorders, even though they have a complex pathogenesis, is the increased rate of neuronal death. Endogenous neurotrophins consist of the major neuroprotective factors, while brain-derived neurotrophic factor (BDNF) and its high-affinity tyrosine kinase receptor TrkB are described in a number of studies for their important neuronal effects. Normal function of this receptor is crucial for neuronal survival, differentiation, and synaptic function. However, studies have shown that besides direct activation, the TrkB receptor can be transactivated via GPCRs. It has been proven that activation of the 5-HT4 receptor and transactivation of the TrkB receptor have a positive influence on neuronal differentiation (total dendritic length, number of primary dendrites, and branching index). Because of that and based on the main structural characteristics of LM22A-4, a known activator of the TrkB receptor, and RS67333, a partial 5-HT4 receptor agonist, we have designed and synthesized a small data set of novel compounds with potential dual activities in order to not only prevent neuronal death, but also to induce neuronal differentiation in neurodegenerative disorders.

Assessment of the potential of novel and classical opioids to induce respiratory depression in mice.

BACKGROUND AND PURPOSE: Opioid-induced respiratory depression limits the use of µ-opioid receptor agonists in clinical settings and is the main cause of opioid overdose fatalities. The relative potential of different opioid agonists to induce respiratory depression at doses exceeding those producing analgesia is understudied despite its relevance to assessments of opioid safety. Here we evaluated the respiratory depressant and anti-nociceptive effects of three novel opioids and relate these measurements to their in vitro efficacy. EXPERIMENTAL APPROACH: Respiration was measured in awake, freely moving male CD-1 mice using whole body plethysmography. Anti-nociception was measured using the hot plate test. Morphine, oliceridine and tianeptine were administered intraperitoneally, whereas methadone, oxycodone and SR-17018 were administered orally. Receptor activation and arrestin-3 recruitment were measured in HEK293 cells using BRET assays. KEY RESULTS: Across the dose ranges examined, all opioids studied depressed respiration in a dose-dependent manner, with similar effects at the highest doses, and with tianeptine and oliceridine showing reduced duration of effect, when compared with morphine, oxycodone, methadone and SR-17018. When administered at doses that induced similar respiratory depression, all opioids induced similar anti-nociception, with tianeptine and oliceridine again showing reduced duration of effect. These data were consistent with the in vitro agonist activity of the tested compounds. CONCLUSION AND IMPLICATIONS: In addition to providing effective anti-nociception, the novel opioids, oliceridine, tianeptine and SR-17018 depress respiration in male mice. However, the different potencies and kinetics of effect between these novel opioids may be relevant to their therapeutic application in different clinical settings.

Todd's paralysis due to hyperperfusion syndrome after carotid endarterectomy mimicking postoperative stroke.

Todd's paralysis is a neurological deficit that is observed in <10% of patients following epileptic seizures. Cerebral hyperperfusion syndrome (CHS) is a rare complication following carotid endarterectomy (CEA), seen in 0-3% of the patients, characterized by focal neurological deficit, headache, disorientation, and sometimes seizures. In this case report, we present a case of CHS after CEA followed by seizures and Todd's paralysis that mimicked postoperative stroke. A 75-year-old female patient was admitted for CEA of the right internal carotid artery, following a transient ischemic attack two months prior. Four hours after CEA with graft interposition, the patient suffered a temporary weakness of the left arm and leg followed by generalized spasms within a few seconds. CT angiography showed regular patency of the carotid arteries and the graft, and brain CT showed no sign of oedema, ischemia or hemorrhage. However, left-sided hemiplegia occurred following the seizure, and the patient suffered four more seizures over the next 48 hours, with persisting hemiplegia. On the second postoperative day, the motor skills of the left side fully recovered, and the patient was communicative, and of orderly mental status. Brain CT performed on the third postoperative day showed entire right hemisphere oedema. A moderate hemiparesis with seizures as a consequence of CHS after CEA has been described, however in all cases with seizures and hemiplegia, the underlying cause was always a verified stroke or intracerebral hemorrhage. This case highlights the importance of considering Todd's paralysis in patients with seizures after CEA due to CHS and prolonged periods of hemiplegia after the seizures.

Design, synthesis and biological characterization of novel activators of the TrkB neurotrophin receptor.

Numerous studies have been published about the implication of the neurotrophin brain-derived neurotrophic factor (BDNF) and its receptor TrkB in the pathogenesis of several neurodegenerative conditions such as Alzheimer's disease, Parkinson's disease, Multiple Sclerosis and motor neuron disease. BDNF activates the TrkB receptor with high potency and specificity, promoting neuronal survival, differentiation and synaptic plasticity. Based on the main structural characteristics of LM22A-4, a previously published small molecule that acts as activator of the TrkB receptor, we have designed and synthesized a small data set of compounds. The lead idea for the design of the new compounds was to modify the third position of the LM22A-4, by introducing different substitutions in order to obtain compounds which will have not only better physicochemical properties but selective activity as well. ADME and toxicity profiles of molecules have been evaluated as well as their biological properties through the TrkB receptor and affinity to promote neurite differentiation.

C3-Symmetric Ligands in Drug Design: When the Target Controls the Aesthetics of the Drug.

A number of proteins are able to adopt a homotrimeric spatial conformation. Among these structures, this feature appears as crucial for biologic targets, since it facilitates the design of C3-symmetric ligands that are especially suitable for displaying optimized ligand-target interactions and therapeutic benefits. Additionally, DNA as a therapeutic target, even if its conformation into a superhelix does not correspond to a C3-symmetry, can also take advantage of these C3-symmetric ligands for better interactions and therapeutic effects. For the moment, this opportunity appears to be under-exploited, but should become more frequent with the discovery of new homotrimeric targets such as the SARS-CoV2 spike protein. Besides their potential therapeutic interest, the synthetic access to these C3-symmetric ligands often leads to chemical challenges, although drug candidates with an aesthetic structure are generally obtained.

In silico identification of novel 5-HT2A antagonists supported with ligand- and target-based drug design methodologies.

A wide range of neuropsychological disorders is caused by serotonin 5-HT2A receptor (5-HT2AR) malfunction. Therefore, this receptor had been frequently used as target in CNS drug research. To design novel potent 5-HT2AR antagonists, we have combined ligand-based and target-based approaches. This study was performed on wide range of structurally diverse antagonists that were divided into three different clusters: clozapine, ziprasidone, and ChEMBL240876 derivatives. By performing the 50 ns long molecular dynamic simulations with each cluster representative in complex with 5-HT2A receptor, we have obtained virtually bioactive conformations of the ligands and three different antagonist-bound, inactive, conformations of the 5-HT2AR. These three 5-HT2AR conformations were further used for docking studies and generation of the bioactive conformations of the data set ligands in each cluster. Subsequently, selected conformers were used for 3D-Quantitative Structure Activity Relationship (3D-QSAR) modelling and pharmacophore analysis. The reliability and predictive power of the created model was assessed using an external test set compounds and showed reasonable external predictability. Statistically significant variables were used to define the most important structural features required for 5-HT2A antagonistic activity. Conclusions obtained from performed ligand-based (3D-QSAR) and target-based (molecular docking and molecular dynamics) methods were compiled and used as guidelines for rational drug design of novel 5-HT2AR antagonists.Communicated by Ramaswamy H. Sarma.