Lotten Ragnarsson

Expression and Pharmacology of Endogenous Cav Channels in SH-SY5Y Human Neuroblastoma Cells

SH-SY5Y human neuroblastoma cells provide a useful in vitro model to study the mechanisms underlying neurotransmission and nociception. These cells are derived from human sympathetic neuronal tissue and thus, express a number of the Cav channel subtypes essential for regulation of important physiological functions, such as heart contraction and nociception, including the clinically validated pain target Cav2.2. We have detected mRNA transcripts for a range of endogenous expressed subtypes Cav1.3, Cav2.2 (including two Cav1.3, and three Cav2.2 splice variant isoforms) and Cav3.1 in SH-SY5Y cells; as well as Cav auxiliary subunits α2δ1–3, β1, β3, β4, γ1, γ4–5, and γ7. Both high- and low-voltage activated Cav channels generated calcium signals in SH-SY5Y cells. Pharmacological characterisation using ω-conotoxins CVID and MVIIA revealed significantly (∼ 10-fold) higher affinity at human versus rat Cav2.2, while GVIA, which interacts with Cav2.2 through a distinct pharmacophore had similar affinity for both species. CVID, GVIA and MVIIA affinity was higher for SH-SY5Y membranes vs whole cells in the binding assays and functional assays, suggesting auxiliary subunits expressed endogenously in native systems can strongly influence Cav2.2 channels pharmacology. These results may have implications for strategies used to identify therapeutic leads at Cav2.2 channels.

Spermine modulation of the glutamatenmda receptor is differentially responsive to conantokins in normal and Alzheimer's disease human cerebral cortex

The pharmacology of the N‐methyl‐d‐aspartate (NMDA) receptor site was examined in pathologically affected and relatively spared regions of cerebral cortex tissue obtained at autopsy from Alzheimers disease cases and matched controls. The affinity and density of the [3H]MK‐801 binding site were delineated along with the enhancement of [3H]MK‐801 binding by glutamate and spermine. Maximal enhancement induced by either ligand was regionally variable; glutamate‐mediated maximal enhancement was higher in controls than in Alzheimers cases in pathologically spared regions, whereas spermine‐mediated maximal enhancement was higher in controls in areas susceptible to pathological damage. These and other data suggest that the subunit composition of NMDA receptors may be locally variable. Studies with modified conantokin‐G (con‐G) peptides showed that Ala(7)–con‐G had higher affinity than Lys(7)–con‐G, and also defined two distinct binding sites in controls. Nevertheless, the affinity for Lys(7)–con‐G was higher overall in Alzheimers brain than in control brain, whereas the reverse was true for Ala(7)–con‐G. Over‐excitation mediated by specific NMDA receptors might contribute to localized brain damage in Alzheimers disease. Modified conantokins are useful for identifying the NMDA receptors involved, and may have potential as protective agents.

Multiple myeloma cells are killed by syndecan-1-directed superantigen-activated T cells

Abstract. Multiple myeloma (MM) is an incurable plasma cell/plasmablast malignancy with a great need for innovative treatment strategies. Since experimental immunotherapy with targeted superantigens (SAg) proved to be effective in other haematopoietic tumours, we investigated whether this would also hold true for MM. We used the bacterial SAg Staphylococcus enterotoxin A (SEA), a potent activator of T cell cytotoxicity by means of its binding to particular T cell receptor Vß sequences on effector cells and MHC class II molecules on target cells. To eliminate potentially unspecific binding via MHC class II, SEA was point mutated (SEAm). In a second step SEAm was genetically fused to protein A (PA), resulting in a fusion protein (PA-SEAm). This fusion protein was used together with four different plasma-cell-specific/associated mAbs to direct T cells towards 10 MM target cell lines. Three of these mAbs were directed against syndecan-1/CD138, known to be highly expressed on MM and plasma cells, but absent on other haematopoietic cells. All MM cell lines proved to be sensitive to SAg-activated T cell killing (15–50% lysis), as measured in a 51Cr-release assay. This effect was clearly mediated via the plasma-cell-reactive antibodies, as control antibodies only conferred a low background lysis. MM therapy based on targeted SAgs could in theory be hampered by dysfunctional T cells in MM patients. However, we show that T cells from MM patients and healthy controls responded equally well to activation by SAg.

Conopeptide ρ-TIA Defines a New Allosteric Site on the Extracellular Surface of the α1B-Adrenoceptor

Background: Mechanistic insight into allosteric modulation of GPCRs can facilitate antagonist design. Results: Extracellular surface residues (ECS) of the α1B-adrenoceptor at the base of extracellular loop 3 interact with the allosteric antagonist TIA. Conclusion: The identified ECS pharmacophore provides the first structural constraints for allosteric antagonist design at α1-adrenoceptors. Significance: Binding to the ECS of a GPCR can allosterically inhibit agonist signaling. The G protein-coupled receptor (GPCR) superfamily is an important drug target that includes over 1000 membrane receptors that functionally couple extracellular stimuli to intracellular effectors. Despite the potential of extracellular surface (ECS) residues in GPCRs to interact with subtype-specific allosteric modulators, few ECS pharmacophores for class A receptors have been identified. Using the turkey β1-adrenergic receptor crystal structure, we modeled the α1B-adrenoceptor (α1B-AR) to help identify the allosteric site for ρ-conopeptide TIA, an inverse agonist at this receptor. Combining mutational radioligand binding and inositol 1-phosphate signaling studies, together with molecular docking simulations using a refined NMR structure of ρ-TIA, we identified 14 residues on the ECS of the α1B-AR that influenced ρ-TIA binding. Double mutant cycle analysis and docking confirmed that ρ-TIA binding was dominated by a salt bridge and cation-π between Arg-4-ρ-TIA and Asp-327 and Phe-330, respectively, and a T-stacking-π interaction between Trp-3-ρ-TIA and Phe-330. Water-bridging hydrogen bonds between Asn-2-ρ-TIA and Val-197, Trp-3-ρ-TIA and Ser-318, and the positively charged N terminus and Glu-186, were also identified. These interactions reveal that peptide binding to the ECS on transmembrane helix 6 (TMH6) and TMH7 at the base of extracellular loop 3 (ECL3) is sufficient to allosterically inhibit agonist signaling at a GPCR. The ligand-accessible ECS residues identified provide the first view of an allosteric inhibitor pharmacophore for α1-adrenoceptors and mechanistic insight and a new set of structural constraints for the design of allosteric antagonists at related GPCRs.

NMDA receptor subunit-dependent modulation by conantokin-G and Ala(7)-conantokin-G

The modulation of recombinant NMDA receptors by conantokin‐G (con‐G) and Ala(7)‐conantokin‐G (Ala(7)‐Con‐G) was investigated in Xenopus oocytes injected with capped RNA coding for NR1 splice variants and NR2 subunits using the two‐electrode voltage clamp technique. Glutamate exhibited a marginally higher apparent affinity for NR2A‐containing receptors than NR2B‐containing receptors, regardless of the NR1 subunit present. Conantokins were bath applied to give cumulative concentration responses in the presence of 3 and 30 μm glutamate. Both contantokins exhibited biphasic concentration‐response relationships at NR2A‐containing NMDA receptors, producing potentiation at low conantokin concentrations and inhibition at high concentrations. These effects were stronger with glutamate concentrations near its EC50, and less marked at saturating concentrations. In contrast, the conantokin concentration‐response relation was monophasic and inhibitory at NR2B‐containing receptors. We conclude that the combinations of subunits that comprise the NMDA receptor complex influence conantokin and glutamate affinities and the nature of the responses to conantokins.

Glycerotoxin stimulates neurotransmitter release from N-type Ca2+ channel expressing neurons

Glycerotoxin (GLTx) is capable of stimulating neurotransmitter release at the frog neuromuscular junction by directly interacting with N‐type Ca2+ (Cav2.2) channels. Here we have utilized GLTx as a tool to investigate the functionality of Cav2.2 channels in various mammalian neuronal preparations. We first adapted a fluorescent‐based high‐throughput assay to monitor glutamate release from rat cortical synaptosomes. GLTx potently stimulates glutamate secretion and Ca2+ influx in synaptosomes with an EC50 of 50 pm. Both these effects were prevented using selective Cav2.2 channel blockers suggesting the functional involvement of Cav2.2 channels in mediating glutamate release in this system. We further show that both Cav2.1 (P/Q‐type) and Cav2.2 channels contribute equally to depolarization‐induced glutamate release. We then investigated the functionality of Cav2.2 channels at the neonatal rat neuromuscular junction. GLTx enhances both spontaneous and evoked neurotransmitter release causing a significant increase in the frequency of postsynaptic action potentials. These effects were blocked by specific Cav2.2 channel blockers demonstrating that either GLTx or its derivatives could be used to selectively enhance the neurotransmitter release from Cav2.2‐expressing mammalian neurons.

Conopeptide-Derived κ-Opioid Agonists (Conorphins): Potent, Selective, and Metabolic Stable Dynorphin A Mimetics with Antinociceptive Properties.

Opioid receptor screening of a conopeptide library led to a novel selective κ-opioid agonist peptide (conorphin T). Intensive medicinal chemistry, guided by potency, selectivity, and stability assays generated a pharmacophore model supporting rational design of highly potent and selective κ-opioid receptor (KOR) agonists (conorphins) with exceptional plasma stability. Conorphins are defined by a hydrophobic benzoprolyl moiety, a double arginine sequence, a spacer amino acid followed by a hydrophobic residue and a C-terminal vicinal disulfide moiety. The pharmacophore model was supported by computational docking studies, revealing receptor-ligand interactions similar to KOR agonist dynorphin A (1-8). A conorphin agonist inhibited colonic nociceptors in a mouse tissue model of chronic visceral hypersensitivity, suggesting the potential of KOR agonists for the treatment of chronic abdominal pain. This new conorphine KOR agonist class and pharmacophore model provide opportunities for future rational drug development and probes for exploring the role of the κ-opioid receptor.

Subtle modifications to oxytocin produce ligands that retain potency and improved selectivity across species

An oxytocin derivative that may not trigger adverse side effects has been generated. A more selective oxytocin receptor agonist Oxytocin is clinically used to induce labor, and there is interest in using this peptide to treat social disorders. However, oxytocin triggers adverse cardiovascular side effects because it activates the vasopressin receptor and the oxytocin receptor. Muttenthaler et al. generated ligands based on oxytocin with subtle modifications, yielding a lead compound that was more selective for the oxytocin receptor than for the vasopressin receptors. It reduced social fear in mice and induced contractile activity in human myometrial strips without affecting cultured cardiomyocytes. Given the cross-talk between oxytocin, vasopressin, and their receptors, this compound will also be helpful in identifying effects that are solely mediated by the oxytocin receptor. Oxytocin and vasopressin mediate various physiological functions that are important for osmoregulation, reproduction, cardiovascular function, social behavior, memory, and learning through four G protein–coupled receptors that are also implicated in high-profile disorders. Targeting these receptors is challenging because of the difficulty in obtaining ligands that retain selectivity across rodents and humans for translational studies. We identified a selective and more stable oxytocin receptor (OTR) agonist by subtly modifying the pharmacophore framework of human oxytocin and vasopressin. [Se-Se]-oxytocin-OH displayed similar potency to oxytocin but improved selectivity for OTR, an effect that was retained in mice. Centrally infused [Se-Se]-oxytocin-OH potently reversed social fear in mice, confirming that this action was mediated by OTR and not by V1a or V1b vasopressin receptors. In addition, [Se-Se]-oxytocin-OH produced a more regular contraction pattern than did oxytocin in a preclinical labor induction and augmentation model using myometrial strips from cesarean sections. [Se-Se]-oxytocin-OH had no activity in human cardiomyocytes, indicating a potentially improved safety profile and therapeutic window compared to those of clinically used oxytocin. In conclusion, [Se-Se]-oxytocin-OH is a novel probe for validating OTR as a therapeutic target in various biological systems and is a promising new lead for therapeutic development. Our medicinal chemistry approach may also be applicable to other peptidergic signaling systems with similar selectivity issues.

Structural mechanisms for α-conotoxin activity at the human α3β4 nicotinic acetylcholine receptor

Nicotinic acetylcholine receptors (nAChR) are therapeutic targets for a range of human diseases. α-Conotoxins are naturally occurring peptide antagonists of nAChRs that have been used as pharmacological probes and investigated as drug leads for nAChR related disorders. However, α-conotoxin interactions have been mostly characterised at the α7 and α3β2 nAChRs, with interactions at other subtypes poorly understood. This study provides novel structural insights into the molecular basis for α-conotoxin activity at α3β4 nAChR, a therapeutic target where subtype specific antagonists have potential to treat nicotine addiction and lung cancer. A co-crystal structure of α-conotoxin LsIA with Lymnaea stagnalis acetylcholine binding protein guided the design and functional characterisations of LsIA analogues that identified the minimum pharmacophore regulating α3β4 antagonism. Interactions of the LsIA R10F with β4 K57 and the conserved –NN– α-conotoxin motif with β4 I77 and I109 conferred α3β4 activity to the otherwise inactive LsIA. Using these structural insights, we designed LsIA analogues with α3β4 activity. This new understanding of the structural basis of protein-protein interactions between α-conotoxins and α3β4 may help rationally guide the development of α3β4 selective antagonists with therapeutic potential.

Targeted superantigens for immunotherapy of haematopoietic tumours

With the exception of childhood common acute lymphoblastic leukaemia (cALL), treatment of other hematopoietic B cell lineage tumours such as non‐ Hodgkins lymphoma (B‐NHL), adult ALL and multiple myeloma (MM) is unsatisfactory. Similarly, the therapeutic outcome of acute and chronic myeloid leukaemia (AML, CML) is frequently dismal. At the same time, leukae‐ mia/lymphoma cells represent ideal targets for immunotherapy. The present review summarizes our preclinical experience with a novel type of cytotoxic T cell based immunotherapy for B‐lineage and myeloid tumours. Staphylococcal enterotoxin‐derived superantigens (SAgs) are among the most potent T cell activators known, linking the T cell receptor to HLA‐DR on natural target cells. SAgs were genetically engineered to reduce DR binding and were then fused to Fab parts of tumour‐directed monoclonal antibodies (mAbs). Using these “targeted” SAgs, highly efficient lysis of B‐lineage (B‐NHL, B‐CLL, ALL, MM) and myeloid (AML, CML) tumour cells by T‐cells was achieved in vitro and in an animal model. We are entering an interesting era of innovative cancer therapy based on novel man‐made biotherapeutic agents.