High-affinity Receptor Binding Research Articles

Cipaglucosidase alfa plus miglustat: linking mechanism of action to clinical outcomes in late-onset Pompe disease.

Enzyme replacement therapy (ERT) is the only approved disease-modifying treatment modality for Pompe disease, a rare, inherited metabolic disorder caused by a deficiency in the acid α-glucosidase (GAA) enzyme that catabolizes lysosomal glycogen. First-generation recombinant human GAA (rhGAA) ERT (alglucosidase alfa) can slow the progressive muscle degeneration characteristic of the disease. Still, most patients experience diminished efficacy over time, possibly because of poor uptake into target tissues. Next-generation ERTs aim to address this problem by increasing bis-phosphorylated high mannose (bis-M6P) N-glycans on rhGAA as these moieties have sufficiently high receptor binding affinity at the resultant low interstitial enzyme concentrations after dosing to drive uptake by the cation-independent mannose 6-phosphate receptor on target cells. However, some approaches introduce bis-M6P onto rhGAA via non-natural linkages that cannot be hydrolyzed by natural human enzymes and thus inhibit the endolysosomal glycan trimming necessary for complete enzyme activation after cell uptake. Furthermore, all rhGAA ERTs face potential inactivation during intravenous delivery (and subsequent non-productive clearance) as GAA is an acid hydrolase that is rapidly denatured in the near-neutral pH of the blood. One new therapy, cipaglucosidase alfa plus miglustat, is hypothesized to address these challenges by combining an enzyme enriched with naturally occurring bis-M6P N-glycans with a small-molecule stabilizer. Here, we investigate this hypothesis by analyzing published and new data related to the mechanism of action of the enzyme and stabilizer molecule. Based on an extensive collection of in vitro, preclinical, and clinical data, we conclude that cipaglucosidase alfa plus miglustat successfully addresses each of these challenges to offer meaningful advantages in terms of pharmacokinetic exposure, target-cell uptake, endolysosomal processing, and clinical benefit.

High-Affinity-Mediated Viral Entry Triggers Innate Affinity Escape Resulting in Type I IFN Resistance and Impaired T Cell Immunity.

Increased receptor binding affinity may allow viruses to escape from Ab-mediated inhibition. However, how high-affinity receptor binding affects innate immune escape and T cell function is poorly understood. In this study, we used the lymphocytic choriomeningitis virus (LCMV) murine infection model system to create a mutated LCMV exhibiting higher affinity for the entry receptor α-dystroglycan (LCMV-GPH155Y). We show that high-affinity receptor binding results in increased viral entry, which is associated with type I IFN (IFN-I) resistance, whereas initial innate immune activation was not impaired during high-affinity virus infection in mice. Consequently, IFN-I resistance led to defective antiviral T cell immunity, reduced type II IFN, and prolonged viral replication in this murine model system. Taken together, we show that high-affinity receptor binding of viruses can trigger innate affinity escape including resistance to IFN-I resulting in prolonged viral replication.

FcγRI FG-loop functions as a pH sensitive switch for IgG binding and release.

Understanding the molecular mechanism underlying the hierarchic binding between FcγRs and IgG antibodies is critical for therapeutic antibody engineering and FcγR functions. The recent determination of crystal structures of FcγRI-Fc complexes, however, resulted in two controversial mechanisms for the high affinity receptor binding to IgG. Here, we describe high resolution structures of a bovine FG-loop variant of FcγRI in complex with the Fc fragment of IgG1 crystallized in three different conditions at neutral pH, confirming the characteristic FG loop-Fc interaction is critical to the high affinity immunoglobulin binding. We showed that the FcγRI D2-domain FG-loop functioned as a pH-sensing switch for IgG binding. Further live cell imaging of FcγRI-mediated internalization of immune complexes showed a pH sensitive temporal-spatial antibody-antigen uptake and release. Taken together, we demonstrate that the structures of FcγRI-Fc crystallized at neutral and acidic pH, respectively, represent the high and low affinity binding states of the receptor for IgG uptake and release. These results support a role for FcγRI in antigen delivery, highlight the importance of Fc glycan in antibody binding to the high affinity receptor and provide new insights to future antibody engineering.

Toll-like receptors change morphine-induced antinociception, tolerance and dependence: Studies using male and female TLR and signalling gene KO mice

Toll-like receptors (TLR) have been proposed as a site of action that alters opioid pharmacodynamics. However, a comprehensive assessment of acute opioid antinociception, tolerance and withdrawal behaviours in genetic null mutant strains with altered innate immune signalling has not been performed. Nor has the impact of genetic deletion of TLR2/4 on high-affinity opioid receptor binding. Here we show that diminished TLR signalling potentiates acute morphine antinociception equally in male and female mice. However, only male TIR8 null mutant mice showed reduced morphine analgesia. Analgesic tolerance was prevented in TLR2 and TLR4 null mutants, but not MyD88 animals. Withdrawal behaviours were only protected in TLR2−/− mice. In silico docking simulations revealed opioid ligands bound preferentially to the LPS binding pocket of MD-2 rather than TLR4. There was no binding of [3H](-)-naloxone or [3H]diprenorphine to TLR4 in the concentrations explored. These data confirm that opioids have high efficacy activity at innate immune pattern recognition binding sites but do not bind to TLR4 and identify critical pathway and sex-specific effects of the complex innate immune signalling contributions to opioid pharmacodynamics. These data further support the behavioural importance of the TLR-opioid interaction but fail to demonstrate direct evidence for high-affinity binding of the TLR4 signalling complex to ligands.

Adamantane-derived scaffolds targeting the sigma-2 receptor; an in vitro and in silico study

Novel adamantane-based compounds were synthesized and assessed as potential sigma-2 receptor ligands. Molecular docking and 50 ns molecular dynamic simulation were carried out to determine the binding modes, mechanism of interaction, and stability of these compounds within the active site of the sigma-2 receptor. In addition, the ADME-T properties have been explored. The cytotoxicity in cancer cell lines that express sigma-2 receptors was also examined. In addition, the in silico and cytotoxicity data for the new compounds were compared to a reference sigma-2 receptor ligand with high receptor-binding affinity and selectivity. The data suggests that the new compounds interact with the sigma-2 receptor in a comparable manner to the reference compound, and that adamantane can be used as a scaffold to synthesize sigma-2 receptor ligands with useful functional groups that can be used to conjugate moieties for tumor-imaging or cytotoxic cargo delivery.

Natural Chemical Entities as Bioactive Moiety from Weaver Ant, Oecophylla smaragdina: An In Vitro and In-silico Study

Background: Since time immemorial, the ethnic community of Mayrubhanj District, Odisha, India has preferred Olecophylla smaragdina as traditional medicine for their multiple ailments. Hence, the objective of this investigation is to scientifically examine the myth behind ethno-zoological claims using chemometric analysis as well as in vitro and in silico study. Materials and Methods: The maceration method was used for the extraction of O. smaragdina using hexane and methanol. In this study, various bioactive compounds of O. smaragdina were identified through GC-MS analysis followed by an antimicrobial activity. The species were further studied for their binding modes for in silico inhibition of a choice of bacterial proteins using Biovia Discovery studio software. Results: Tetradecanoic acid, hexadecanoic acid, methyl ester, hexadecenoic acid, n-hexadecanoic acid, 9-octadecenoic acid, methyl ester, oleic acid and 9-octadecenamide are some important bioactive constituents identified through GCMS analysis. The hexane extract was found to have maximum inhibitory activity against Staphyllococus aureus. The inhibitory activity of hexane and methanolic extract against S. aureus at a concentration of 400 μg/mL was found to be 90% and 83%, respectively. The high inhibitory capacity of the n-hexane extract was comparable to the standard drug Gentamycin which further supported the high receptor binding affinity of the identified compound Octadecanoic acid towards Tyrosol-t RNA synthetase of staphylococcus aureus (PDB ID: 1JIK). Conclusion: Interestingly, this is probably the first report that obtained bioactive molecules from O. smaragdina showing the binding site identification to carry out molecular docking studies, and better affinity to bind with suitable targeted moiety.

Inhibition of c-Fos expression attenuates IgE-mediated mast cell activation and allergic inflammation by counteracting an inhibitory AP1/Egr1/IL-4 axis

BackgroundActivator protein-1 (AP1), a c-Fos–JUN transcription factor complex, mediates many cytobiological processes. c-Fos has been implicated in immunoglobulin (Ig)E activation of mast cells (MCs) via high-affinity IgE Fc receptor (FcεRI) binding. This study examined c-Fos involvement in MC activation and tested the effects of the c-Fos/AP1 inhibitor T-5224 on MCs activation and allergic responses.MethodsIn vitro studies were conducted with two MC model systems: rat basophilic leukemia cells (RBLs) and mouse bone marrow derived mast cells (BMMCs). MC degranulation and effector functions were examined with β-hexosaminidase release and cytokine secretion assays. c-Fos/AP1 was inhibited with T-5224. c-Fos activity was suppressed with short hairpin RNA targeting c-Fos (shFos). In vivo immune responses were evaluated in passive cutaneous anaphylaxis (PCA) and ovalbumin-induced active systemic anaphylaxis (ASA) models, as well as in an oxazolone (OXA)-induced model of atopic dermatitis, a common allergic disease.Resultsc-Fos expression was elevated transcriptionally and translationally in IgE-stimulated MCs. c-Fos binding of the Egr1 (early growth response 1) promoter upregulated Egr1 transcription, leading to production of interleukin (IL)4. T-5224 reduced FcεRI-mediated MC degranulation (evidenced by β-hexosaminidase activity and histamine levels) and diminished EGR1 and IL4 expression. T-5224 attenuated IgE-mediated allergic responses in PCA and ASA models, and it suppressed MC-mediated atopic dermatitis in mice.ConclusionIgE binding can activate MCs via a c-Fos/Egr1/IL-4 axis. T-5224 suppresses MC activation in vitro and in vivo and thus represents a promising potential strategy for targeting MC activation to treat allergic diseases.

Synthesis of Novel Fluorinated Xanthine Derivatives with High Adenosine A2B Receptor Binding Affinity.

The G protein-coupled adenosine A2B receptor is suggested to be involved in various pathological processes accompanied by increased levels of adenosine as found in inflammation, hypoxia, and cancer. Therefore, the adenosine A2B receptor is currently in focus as a novel target for cancer therapy as well as for noninvasive molecular imaging via positron emission tomography (PET). Aiming at the development of a radiotracer labeled with the PET radionuclide fluorine-18 for imaging the adenosine A2B receptor in brain tumors, one of the most potent and selective antagonists, the xanthine derivative PSB-603, was selected as a lead compound. As initial biodistribution studies in mice revealed a negligible brain uptake of [3H]PSB-603 (SUV3min: 0.2), structural modifications were performed to optimize the physicochemical properties regarding blood–brain barrier penetration. Two novel fluorinated derivatives bearing a 2-fluoropyridine (5) moiety and a 4-fluoro-piperidine (6) moiety were synthesized, and their affinity towards the four adenosine receptor subtypes was determined in competition binding assays. Both compounds showed high affinity towards the adenosine A2B receptor (Ki (5) = 9.97 ± 0.86 nM; Ki (6) = 12.3 ± 3.6 nM) with moderate selectivity versus the other adenosine receptor subtypes.

Perioperative Management Considerations for Patients on Methadone and Buprenorphine

Introduction: Patients with chronic pain or opioid use disorders (OUD) are often managed with prescriptions or medication-assisted treatments (MAT) involving methadone and buprenorphine. The pharmacology and mu opioid receptor (μOR) binding affinity of methadone and buprenorphine presents a multitude of challenges perioperatively, increasing the risk of ineffective pain management, marginalization, opioid withdrawal, and relapse. Literature review: Thorough preoperative assessment and preparation of patients on methadone and buprenorphine is advised to establish a tailored perioperative plan and postoperative analgesic expectations. Several perioperative pain management guidelines and protocols have been suggested, but there remains a lack of high quality evidence-based research and consensus to guide anesthesia and pain management providers. Appropriate strategies for patients on methadone and buprenorphine requires a multidisciplinary approach that considers the patient’s history with pain management, substance abuse, opioid use or abuse, and history of effective analgesic therapies. Existing case studies, expert opinions, and clinical practice advisories recommend continuation of methadone and buprenorphine perioperatively to avoid regimen disruptions and drug level fluctuations. Most recommendations are also in agreement for providers to implement multimodal analgesia and incorporate regional/neuraxial anesthesia when appropriate. Description of the case: The patient was a 52-year-old female undergoing spinal cord stimulator removal. Patient’s chart indicated a history of chronic pain and methadone therapy. Preoperative assessment was performed methodically to evaluate patient’s compliance with methadone. Although patient reported to have discontinued methadone therapy approximately six months prior, optimal perioperative pain management was addressed with a short-acting opioid, multimodal analgesia, and local anesthesia infiltration. Patient did not experience postoperative complications or inadequate pain control and was discharged within the same day. Discussion and conclusions: Methadone is a full μOR agonist with significant analgesic properties and should be continued on the day of surgery. Abrupt discontinuation of methadone can result in opioid withdrawal or place the patient at risk for relapse. Optimal perioperative pain management for patients on methadone includes utilization of short-acting opioid agonists, multimodal analgesia, regional/neuraxial anesthesia, and other non-opioid interventions. Consider incorporating agents such as volatile anesthetics, ketamine, benzodiazepines, acetaminophen, non-steroidal anti-inflammatory drugs (NSAIDs), gabapentinoids, alpha-2 adrenergic receptor agonists, local anesthetics, and regional/neuraxial anesthesia. Buprenorphine is a partial μOR agonist with high receptor binding affinity and slow dissociation properties. Perioperative buprenorphine management varies widely, but many guidelines and protocols recommend continuing buprenorphine preoperatively. Appropriate pain management may be achieved with administration of multimodal analgesia, regional/neuraxial anesthesia, and opioid agonists with similar μOR binding affinity to buprenorphine. Hydromorphone and sufentanil are examples of full μOR agonists with high Ki values that may be used to overcome the receptor.

Molecular architecture and domain arrangement of the placental malaria protein VAR2CSA suggests a model for carbohydrate binding

VAR2CSA is the placental-malaria–specific member of the antigenically variant Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) family. It is expressed on the surface of Plasmodium falciparum-infected host red blood cells and binds to specific chondroitin-4-sulfate chains of the placental proteoglycan receptor. The functional ∼310 kDa ectodomain of VAR2CSA is a multidomain protein that requires a minimum 12-mer chondroitin-4-sulfate molecule for specific, high affinity receptor binding. However, it is not known how the individual domains are organized and interact to create the receptor-binding surface, limiting efforts to exploit its potential as an effective vaccine or drug target. Using small angle X-ray scattering and single particle reconstruction from negative-stained electron micrographs of the ectodomain and multidomain constructs, we have determined the structural architecture of VAR2CSA. The relative locations of the domains creates two distinct pores that can each accommodate the 12-mer of chondroitin-4-sulfate, suggesting a model for receptor binding. This model has important implications for understanding cytoadherence of infected red blood cells and potentially provides a starting point for developing novel strategies to prevent and/or treat placental malaria.

Lysine in the lariat loop of arrestins does not serve as phosphate sensor.

Arrestins demonstrate strong preference for phosphorylated over unphosphorylated receptors, but how arrestins "sense" receptor phosphorylation is unclear. A conserved lysine in the lariat loop of arrestins directly binds the phosphate in crystal structures of activated arrestin-1, -2, and -3. The lariat loop supplies two negative charges to the central polar core, which must be disrupted for arrestin activation and high-affinity receptor binding. Therefore, we hypothesized that receptor-attached phosphates pull the lariat loop via this lysine, thus removing the negative charges and destabilizing the polar core. We tested the role of this lysine by introducing charge elimination (Lys->Ala) and reversal (Lys->Glu) mutations in arrestin-1, -2, and -3. These mutations in arrestin-1 only moderately reduced phospho-rhodopsin binding and had no detectable effect on arrestin-2 and -3 binding to cognate non-visual receptors in cells. The mutations of Lys300 in bovine and homologous Lys301 in mouse arrestin-1 on the background of pre-activated mutants had variable effects on the binding to light-activated phosphorylated rhodopsin, while affecting the binding to unphosphorylated rhodopsin to a greater extent. Thus, conserved lysine in the lariat loop participates in receptor binding, but does not play a critical role in phosphate-induced arrestin activation.

Comparative investigation on metabolites changes in soybean leaves by ethylene and activation of collagen synthesis

Genistein and daidzein are predominant phytoestrogens for an estrogen alternative due to their higher receptor binding affinity. The present study illustrated the effective method to produce isoflavone riched soybean leaves (IRSL). Notably, ethylene application to soybean leaves under dark condition led a distinctive increase in genistin, daidzin, malonylgenistin and malonyldaidzin, which raised to total 25,911 μg/g of isoflavones in comparison to control leaves (>200 μg/g). Genistin and daidzin derivatives were enhanced with 120-fold (123→14,996 μg/g) and 185-fold (59→10,916 μg/g), respectively. The changes in metabolites by ethylene were systematically identified by UPLC–ESI-TOF/MS to give successfully PLS-DA score and heatmap analysis. The identified nine isoflavones were markedly increased, whereas rest main metabolites, kaempferols and soyasaponins were not affected. Furthermore, in contrast to the control leaves, the IRSL extract showed stimulation of collagen synthesis and induced gene expressions, in particular COL1A1 and COL3A1, in human dermal fibroblast.

SARS-CoV-2: A Piece of Bad News.

A shocking third species emerged from a family of coronaviruses (CoV) in late 2019 following viruses causing SARS (Severe Acute Respiratory Syndrome-CoV) in 2003 and MERS (Middle East Respiratory Syndrome-CoV) in 2012; it’s a novel coronavirus now called severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2; formerly called 2019-nCoV). First emerging in China, it has spread rapidly across the globe, giving rise to significant social and economic costs and imposing severe strain on healthcare systems. Since many attempts to control viral spread has been futile, the only old practice of containment including city lockdown and social distancing are working to some extent. Unfortunately, specific antiviral drugs and vaccines remain unavailable yet. Many factors are encountered to play essential roles in viral pathogenesis. These include a broad viral-host range with high receptor binding affinity to various human tissues, viral adaptation to humans, a high percentage of asymptomatic but infected carriers, prolonged incubation, and viral shedding periods. There are also a wide variety of pulmonary and extrapul-monary tissue damage mechanisms including direct cell injury or immune-mediated damages involving the immune cells, upregulation of proinflammatory cytokines, and antibody dependent enhancement that can result in multi-organ failure. In this article, we summarise some evidence on the various steps in SARS-CoV-2 pathogenesis and immune evasion strategies to assess their contribution to our understanding of unresolved problems related to SARS-CoV-2 prevention, control, and treatment protocols.

Target-Mediated Population Pharmacokinetic Modeling of Endothelin Receptor Antagonists.

Bosentan, clazosentan, and tezosentan are three small-molecule endothelin receptor antagonists (ERAs), displacing endothelin-1 (ET-1) from its binding site. A target-mediated drug disposition (TMDD) pharmacokinetic (PK) model described the non-linearity in the PK of bosentan caused by its high receptor binding affinity with time-dependent varying receptor expression or reappearance. The aim of this analysis was to investigate the presence of TMDD for clazosentan and tezosentan and to corroborate the hypothesis of a diurnal receptor synthesis. PK data from healthy subjects after intravenous (i.v.) administration of single ascending doses of bosentan, clazosentan, and tezosentan were analyzed. Frequent blood samples for PK measurements were collected. Population analyses, simulations, and evaluations were performed using a non-linear mixed-effects modeling approach. Two-compartment TMDD models were successfully developed describing the PK of all three ERAs with different receptor-complex internalization properties. The observed multiple peaks in the concentration-time profiles were captured with cosine functions on the receptor synthesis rate mimicking a diurnal receptor expression or reappearance. The results strongly suggest that TMDD is a class effect of ERAs. The developed TMDD PK models are a next step towards understanding the complex PK of ERAs and further support the hypothesis that TMDD is a class effect of ERAs.

Development of [18F]AlF-NOTA-NT as PET Agents of Neurotensin Receptor-1 Positive Pancreatic Cancer

Several studies have suggested that neurotensin receptors (NTRs) and neurotensin (NT) greatly affect the growth and survival of pancreatic ductal adenocarcinoma (PDAC). Developing NTR-targeted PET probes could therefore be important for the management of a pancreatic cancer patient by providing key information on the NTR expression profile noninvasively. Despite the initial success on the synthesis of 18F-labeled NT PET probes, the labeling procedure generally requires lengthy steps including azeotropic drying of 18F. Using a straightforward chelation method, here we report the simple preparation of aluminum-18F-NOTA-NT starting from aqueous 18F. The cell binding test demonstrated that [19F]AlF-NOTA-NT maintained high receptor-binding affinity to NTR1. This probe was then further evaluated in NTR1 positive pancreatic tumor models (AsPC-1 and PANC-1). After the administration of [18F]AlF-NOTA-NT, small animal PET studies showed a high contrast between tumor and background in both models at 1 and 4 h time points. A blocking experiment was performed to demonstrate the receptor specificity: the tumor uptake in AsPC1 without and with blocking agent was 1.0 ± 0.2 and 0.1 ± 0.0%ID/g, respectively, at 4 h post injection. In summary, a NTR specific PET agent, [18F]AlF-NOTA-NT, was prepared through the simple chelation method. This NTR-targeted PET probe may not only be used to detect NTR1 positive pancreatic tumors (diagnosis), but also it may be fully integrated to NTR target therapy leading to personalized medicine (theranostic).

Tetrahydroquinoline Ring as a Versatile Bioisostere of Tetralin for Melatonin Receptor Ligands.

A new family of melatonin receptor ligands, characterized by a tetrahydroquinoline (THQ) scaffold carrying an amide chain in position 3, was devised as conformationally constrained analogs of flexible N-anilinoethylamides previously developed. Molecular superposition models allowed to identify the patterns of substitution conferring high receptor binding affinity and to support the THQ ring as a suitable scaffold for the preparation of melatonin ligands. The biological activity of 3-acylamino-THQs was compared with that of the corresponding tetralin derivatives. The THQ ring proved to be a versatile scaffold for easy feasible MT1 and MT2 ligands, which resulted as more polar bioisosteres of their tetralin analogs. Potent partial agonists, with subnanomolar binding affinity for the MT2 receptor, were obtained, and a new series of THQ derivatives is presented. The putative binding mode of potent THQs and tetralines was discussed on the basis of their conformational equilibria as inferred from molecular dynamics simulations and experimental NMR data.

IL-15 promotes human myogenesis and mitigates the detrimental effects of TNF\u03b1 on myotube development

Studies in murine cell lines and in mouse models suggest that IL-15 promotes myogenesis and may protect against the inflammation-mediated skeletal muscle atrophy which occurs in sarcopenia and cachexia. The effects of IL-15 on human skeletal muscle growth and development remain largely uncharacterised. Myogenic cultures were isolated from the skeletal muscle of young and elderly subjects. Myoblasts were differentiated for 8 d, with or without the addition of recombinant cytokines (rIL-15, rTNFα) and an IL-15 receptor neutralising antibody. Although myotubes were 19% thinner in cultures derived from elderly subjects, rIL-15 increased the thickness of myotubes (MTT) from both age groups to a similar extent. Neutralisation of the high-affinity IL-15 receptor binding subunit, IL-15rα in elderly myotubes confirmed that autocrine concentrations of IL-15 also support myogenesis. Co-incubation of differentiating myoblasts with rIL-15 and rTNFα, limited the reduction in MTT and nuclear fusion index (NFI) associated with rTNFα stimulation alone. IL-15rα neutralisation and rTNFα decreased MTT and NFI further. This, coupled with our observation that myotubes secrete IL-15 in response to TNFα stimulation supports the notion that IL-15 serves to mitigate inflammatory skeletal muscle loss. IL-15 may be an effective therapeutic target for the attenuation of inflammation-mediated skeletal muscle atrophy.

Functional role of the three conserved cysteines in the N domain of visual arrestin-1

Arrestins specifically bind active and phosphorylated forms of their cognate G protein-coupled receptors, blocking G protein coupling and often redirecting the signaling to alternative pathways. High-affinity receptor binding is accompanied by two major structural changes in arrestin: release of the C-tail and rotation of the two domains relative to each other. The first requires detachment of the arrestin C-tail from the body of the molecule, whereas the second requires disruption of the network of charge-charge interactions at the interdomain interface, termed the polar core. These events can be facilitated by mutations destabilizing the polar core or the anchoring of the C-tail that yield "preactivated" arrestins that bind phosphorylated and unphosphorylated receptors with high affinity. Here we explored the functional role in arrestin activation of the three native cysteines in the N domain, which are conserved in all arrestin subtypes. Using visual arrestin-1 and rhodopsin as a model, we found that substitution of these cysteines with serine, alanine, or valine virtually eliminates the effects of the activating polar core mutations on the binding to unphosphorylated rhodopsin while only slightly reducing the effects of the C-tail mutations. Thus, these three conserved cysteines play a role in the domain rotation but not in the C-tail release.

Reformulating a Pharmacophore for 5-HT2A Serotonin Receptor Antagonists.

Several pharmacophore models have been proposed for 5-HT2A serotonin receptor antagonists. These typically consist of two aromatic/hydrophobic moieties separated by a given distance from each other, and from a basic amine. Although specified distances might vary, the models are relatively similar in their general construction. Because our preliminary data indicated that two aromatic (hydrophobic) moieties might not be required for such action, we deconstructed the serotonin-dopamine antipsychotic agent risperidone (1) into four smaller structural fragments that were thoroughly examined in 5-HT2A receptor binding and functional (i.e., two-electrode voltage clamp (TEVC) and intracellular calcium release) assays. It was apparent that truncated risperidone analogues behaved as antagonists. In particular, 6-fluoro-3-(1-methylpiperidin-4-yl)benzisoxazole (4) displayed high affinity for 5-HT2A receptors (Ki of ca. 12 nM) relative to risperidone (Ki of ca. 5 nM) and behaved as a potent 5-HT2A serotonin receptor antagonist. These results suggest that multiple aromatic (hydrophobic) moieties are not essential for high-affinity 5-HT2A receptor binding and antagonist activity and that current pharmacophore models for such agents are very much in need of revision.

Abstract 1332: Dual antibody gold nanoconjugate significantly enhances cytotoxicity in metastatic breast cancer

Abstract Background: Metastatic breast cancer is the second leading cause of cancer-related deaths of women in the United States. First line treatment for Her2-positive metastatic breast cancer patient is combination therapy involving pertuzumab, trastuzumab, and docetaxel. Both pertuzumab and trastuzumab targets Her2, but works in complementary ways in increasing the cytotoxicity. Indeed, combination of these two antibody drugs for treatment has shown excellent survival benefits. We hypothesized that by covalently attaching these two antibodies to a single nanoparticle would accelerate the cancer cell death in lower concentrations of antibodies. In this study, we covalently conjugated trastuzumab and pertuzumab to gold nanoparticle (AuNP) and investigated the cytotoxicity in metastatic breast cancer cells. Methods: Gold nanoparticles of core size 16 nm were prepared and modified using heterofunctional end terminal carboxylic polyethylene glycol (PEG) linker. The carboxyl terminals were activated by conventional EDC/NHS procedure followed by simultaneous addition of antibodies. The dual antibody gold nanoconjugates (AuNP-Dual Ab) was purified by HPLC using size exclusion column and characterized in detail by routine analytical techniques. Detailed proteomic analysis was performed on the dual antibody gold nanoconjugate. The binding affinity of AuNP-Dual Ab was investigated on HER2+ve SkBR3 cells using dark field microscopy. In vitro cytotoxicity evaluations of AuNP-Dual Ab were performed on HER2 expressing SKBR3 and BT474 cell lines. The effect of AuNP-Dual Ab on signal transduction and phosphorylation status mediated by HER family proteins were evaluated by monitoring the HER2, HER3, AKT, ERK, MEK protein expression through western blot analysis. In vivo studies have been performed in metastatic breast tumor mice models to evaluate the therapeutic efficacy of the nanoconjugate. Results: AuNP-Dual Ab was isolated from the free antibodies by HPLC. We confirmed both the presence and the structural identity of antibodies covalently attached to AuNP using proteomics. TEM immunohistochemistry and dark field microscopy showed AuNP-Dual-Ab possess high receptor binding affinity with Her2+ve breast cancer cells. We investigated the cytotoxicity of AuNP-Dual-Ab in SKBR-3 and BT474 human breast cancer cells. Our studies reveal that AuNP-Dual-Ab is 60 fold higher cytotoxic than non-antibody coated AuNPs, antibodies, and combination antibodies. Western blot analysis showed down regulation of AkT and phospho-AkT proteins while expression of MEK and phospho-MEK proteins was un-altered. We believe the increase in cytotoxicity is possibly due to effective transport of antibodies to cancer cells. Conclusions: The in vitro studies demonstrate that AuNP-Dual Ab is promising and can potentially overcome the problem of resistance. In vivo studies are ongoing on metastatic breast tumor mice models for therapy evaluation. Citation Format: Ajit Zambre, Anandhi Upendran, Matthew Leevy, Sarah Chapman, Raghuraman Kannan. Dual antibody gold nanoconjugate significantly enhances cytotoxicity in metastatic breast cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1332.