Receptor Pharmacology & Drug Delivery

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    Identification of a novel allosteric modulator of acid-sensing ion channel 3
    (2016-03-23) Agharkar, Amruta; Gonzales, Eric PhD
    Acid-sensing ion channels (ASICs) are sodium selective channels that belong to the ENac/DEG family of ion channels. They are sensitive to changes in extracellular pH and are expressed in both the central and peripheral nervous system. There are multiple ASIC subtypes that are involved in different pathophysiological conditions, including neurodegeneration, and most recently, epilepsy. Crystal structure of chicken ASIC1 revealed that functional ASIC is a trimer with large extracellular domain that can interact with variety of ligands, and the focus of research has been to identify ASIC antagonists. The ASIC3 channel subtype is primarily expressed in DRG neurons and is involved in pain sensation, but may activate GABAergic interneurons. ASIC3 is modulated by nonproton ligands like 2-guanidine-4-methylquinazoline (GMQ) and agmatine. We have identified a guanidine compound with a different molecule structure than GMQ that allosterically modulates ASIC3. Here we characterize this guanidine ligand using whole-cell patch clamp electrophysiology and ASIC3 transfected CHO-K1 cells. We found that the ligand is able to activate ASIC3 channel at physiological pH of 7.4, similar to GMQ. Furthermore, the guanidine ligand alters low pH current and delays desensitization, indicating that the ligand may be an ASIC3 positive allosteric modulator. The activation by the guanidine ligand was found to be concentration dependent In the future, we will determine the effect of the guanidine ligand on the ASIC3 window current and identify potential binding sites within ASIC3.
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    A new technology platform for combating Zika and other mosquito-borne infectious diseases.
    (2016-03-23) Schetz, John PhD; Dalwadi, Dhwanil
    Purpose: Mosquitoes are a growing global concern and can transmit infectious diseases such as Zika, West Nile, Dengue, and Chikungunya viruses. Though programs to reduce mosquito populations are helpful, personal outdoor protective measures such as topically applied repellants are the best way to prevent disease transmission. The octopamine receptor (OctR) is a G protein-coupled receptor exclusive to invertebrates making it an attractive target for developing novel arthropod deterrents for use in vertebrates (e.g., humans, pets, livestock). The goal of this project is to develop and validate a high throughput assay that will facilitate the discovery of novel OctR ligands that act as arthropod deterrents. Materials and methods: A cell line stably expressing a cloned arthropod OctR was created as an in vitro model for high throughput evaluation of novel OctR ligands. A barnacle OctR was utilized as a proxy because the cloned mosquito OctR was not available at the time these studies were initiated. The functional activity of the OctR ligands was quantified using a fluorescent calcium sensitive probe to detect Gq-mediated changes in intracellular calcium. In order to complement the molecular assessment of our OctR ligands, a further evaluation was conducted in whole organisms by quantifying barnacle cyprid hyperactivity behavior. Results: Several potent and novel OctR agonists were discovered by measuring activation of a Gq-coupled arthropod OctR. These same compounds induced a hyperactivity response in cyprids. In both cases, their effects could be reversed by an OctR antagonist. These ligands were subsequently found to also protect against biting by two different species of disease-carrying mosquitos, including the Texas-inhabiting species that carries the Zika virus. The inference is that the cloned barnacle OctR serves as a reasonable tool for predicting the arthropod activity of OctR ligands. Conclusion: A high throughput assay was developed that enabled evaluation of the OctR as a target receptor for arthropod deterrents. Using this platform several OctR agonists were discovered whose in vivo properties are consistent with deterency behaviors in different arthropod species: loss of fine motor control as measured by hyperactivity responses in cyprids and prevention of biting in mosquitos. Potential future applications for this technology might include topically applied mosquito deterrents, as well as additives for marine antifouling coatings.