N-methyl-d-aspartate receptors are ionotropic glutamate receptors that mediate the slow component of excitatory neurotransmission. Modulators of NMDA receptor function have long been evaluated as pharmacotherapies to treat neurological disorders such as Parkinson’s Disease, Alzheimer’s disease, schizophrenia, stroke, and other neuropsychiatric and neurodegenerative disorders. We describe the mechanisms of action and explore the structural determinants underlying a phenomenon where GluN2B-specific negative allosteric modulators from the 93- and 96-series can be inverted to act as positive allosteric modulators by mutations at two GluN1 residues in their binding pocket located within the amino terminal domain. Mutations at GluN1-Y109 that invert the activity could each conceivably strengthen the interaction between the residue and 93-31, resulting in a switch from enhancement to relief of tonic inhibition of the receptor by protons. The demonstration that this binding site is capable of being tuned for either inhibition or potentiation provides an opportunity to design novel positive allosteric modulators for potential therapeutic development in humans.Significance StatementMutations of two residues in the NMDA receptor GluN1 subunit amino terminal domain independently interconvert GluN2B-selective negative allosteric modulators into positive allosteric modulators. This work provides a path for the discovery of the structural requirements for GluN2B-specific positive allosteric modulation.
The pregnane X receptor (PXR) is a key chemosensory protein that helps the organism adapt to its chemical environment. Indeed, humans are continuously exposed to a wide range of external chemicals, known as xenobiotics, which include environmental pollutants, food components, cosmetics, and pharmaceuticals. PXR has the unique property to sense a large variety of xenobiotics and regulate the expression of detoxifying enzymes and transporters, facilitating the clearance of these chemicals. However, prolonged activation of this pathway can lead to negative effects, such as drug-drug interactions, chemoresistance, endocrine disruption, a heightened risk of metabolic diseases, or enhanced cell growth and tumor aggressiveness. Understanding how PXR interacts with xenobiotics is crucial for predicting, assessing, and preventing the potential impacts of these chemicals on human health. Here, we present the structural and functional analysis of the interaction of PXR with 2 approved drugs (nimodipine and liranaftate), a natural flavor commonly used in cosmetics and the food industry (sclareol), and an environmentally relevant halogenated derivative of the emblematic endocrine disruptor bisphenol A (2,2'-dichlorobisphenol A). Cell-based assays show that these 4 compounds display different PXR binding potencies, stimulate the expression of key target genes related to drug metabolism and cell proliferation, and promote colon cancer cell proliferation to varying degrees. Crystallographic analysis reveals their distinct mechanisms of binding to PXR. The integrated functional and structural characterization pipeline we have established yields critical insights for both environmental risk assessment and the rational development of industrial and pharmaceutical compounds with minimal harmful PXR activity. Significance Statement The pregnane X receptor is an off-target of many pharmaceuticals and industrial chemicals whose activation is associated with clinically relevant drug-drug interactions. This study describes a pipeline for the identification and characterization of pregnane X receptor ligands, designed to support environmental risk assessment and the informed design of safer substitutes.
The mechanosensitive Piezo1 channel is crucial for the regulation of calcium (Ca2+) signaling within myeloid tissue macrophages. However, the current lack of comprehensive pharmacological characterization for existing Piezo1 agonists complicates the assessment of Piezo1 agonism as a viable therapeutic strategy. We report inhibition of the voltage-gated Kv1.3 potassium (K+) channel as a critical off-target effect of the most widely used Piezo1 agonists, Yoda1 and Yoda2. Kv1.3 is essential for the activation and innate immune functions of tissue macrophages. Patch-clamp electrophysiological experiments demonstrate that Yoda1 (IC50 = 9.0 μM) and Yoda2 (IC50 = 5.9 μM) state-independently inhibit Kv1.3 by accelerating channel inactivation. Functionally, blockade of Kv1.3 by Yoda2 in Piezo1-deficient bone marrow-derived macrophages depolarizes membrane potential and reduces store-operated calcium entry and interleukin-1β release. Using RosettaLigand docking and molecular dynamics simulations, we identified a network of key residues near the Kv1.3 outer pore as the potential binding site. Our results suggest that Kv1.3 blockade likely contributes substantially to the reported anti-inflammatory effects of Yoda1 and Yoda2. This provides a plausible mechanism that aligns with the established principle that reducing Ca2+ signaling is anti-inflammatory, while helping to reconcile existing literature discrepancies regarding Piezo1 activation. SIGNIFICANCE STATEMENT: Targeting Ca2+ channels such as Piezo1 is vital for controlling chronic inflammation, but selectivity is challenging. This study reveals that the best-known Piezo1 agonists exhibit a critical off-target effect by blocking the Kv1.3 channel, which is essential for macrophage and microglial immune function. This concurrent inhibition reduces inflammatory Ca2+ signaling and interleukin-1β secretion. This work underscores the necessity for rigorous selectivity screening of Piezo1 drugs and establishes Kv1.3 inactivation modification as a viable strategy for designing novel anti-inflammatory therapeutics.
Impaired excitatory synaptic function and synapse loss are early hallmarks of Alzheimer’s disease (AD). There is strong biochemical, genetic, physiological, and anatomical evidence that the accumulation of soluble amyloid beta (Aβ) oligomers in the brain leads to AD-related synapse dysfunction and cognitive impairment. Long-term potentiation (LTP), a key form of synaptic plasticity for learning and memory, is disrupted in several mouse models harboring familial early-onset AD–linked mutations that lead to Aβ accumulation, and even acute applications of Aβ oligomers block LTP within minutes and promote synapse loss within days. How does Aβ cause such profound synaptic dysfunction? It is increasingly appreciated that Aβ hijacks normal synaptic signaling pathways involved in plasticity, biasing them toward long-term depression (LTD) and eventual synapse elimination. LTP and LTD in the hippocampus are ultimately driven by insertion and removal of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid–type glutamate receptors (AMPARs) from synapses, respectively, in response to Ca2+ signals generated by N-methyl-d-aspartate–type glutamate receptors or L-type voltage-gated Ca2+ channels. Central to the signaling pathways regulating AMPAR trafficking during LTP and LTD is a postsynaptic Ser/Thr kinase/phosphatase signaling network that is coordinated by the scaffold protein A-kinase anchoring protein (AKAP) 79/150 (human79/rodent150; AKAP5/Akap5 gene). This AKAP-organized signalosome includes N-methyl-d-aspartate–type glutamate receptors, AMPARs, L-type voltage-gated Ca2+ channels, G-protein–coupled receptors, adenylyl cyclase, the cyclic adenosine mono-phosphate (cAMP)-dependent protein kinase, and the Ca2+-calmodulin–dependent protein phosphatase 2B/calcineurin. This minireview will highlight recent findings that Gαs-coupled β2-adrenergic and Gαq-coupled group 1 metabotropic glutamate (mGlu1/5) receptors signal through AKAP79/150-anchored cAMP-dependent protein kinase and protein phosphatase 2B/calcineurin to mediate multiple aspects of Aβ synaptotoxicity. Significance Statement Recent studies reveal that amyloid beta engages A-kinase anchoring protein–scaffolded G-protein–coupled receptor signaling pathways to disrupt synaptic plasticity and promote synapse loss. These pathways contain several potential therapeutic targets involved in both local cAMP-dependent protein kinase and calcineurin/protein phosphatase 2B (CaN) signaling that regulates L-type voltage-gated calcium channels, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors, and N-methyl-d-aspartate receptors to impair synaptic plasticity as well as distal CaN signaling to the nucleus that regulates gene expression to drive synapse loss.
Idiopathic pulmonary fibrosis (IPF) is a progressive and fatal interstitial lung disease with limited therapeutic options, highlighting the need for new molecular targets and effective antifibrotic agents. In this study, we investigated the role of B-cell lymphoma 9 (BCL9) in IPF and evaluated the antifibrotic potential of ZD-4009, a novel small-molecule inhibitor targeting BCL9. BCL9 was upregulated in fibrotic lung tissues, suggesting a possible association between BCL9 and pulmonary fibrosis progression. ZD-4009 showed high-affinity binding to β-catenin (pKD = 7.36 ± 0.01, KD = 44.72 nM). In vitro, ZD-4009 inhibited fibroblast activation, suppressed extracellular matrix deposition, and reduced the expression of fibrosis-associated markers, including COL1A1 and α-SMA. Mechanistically, ZD-4009 suppressed HIF-1α-associated glycolytic reprogramming and inhibited TGF-β/SMAD signaling, suggesting that its antifibrotic effects are associated with coordinated regulation of metabolic and profibrotic pathways. In vivo, ZD-4009 treatment was associated with alleviated bleomycin-induced pulmonary fibrosis, as reflected by improved survival from 55% in the bleomycin group to 82% in the bleomycin + ZD-4009 group, reduced relative collagen content from 61% to 48%, and ameliorated micro-CT-assessed fibrotic changes. In the tested model, ZD-4009 showed favorable antifibrotic effects compared with nintedanib, while liposome-encapsulated ZD-4009 reduced treatment-related toxicity. Together, these findings nominate ZD-4009 as a promising antifibrotic candidate and highlight BCL9 as a potential therapeutic target for IPF.
Sacituzumab govitecan (SG), an antibody-drug conjugate (ADC) approved for the treatment of triple negative breast cancer and HR-positive breast cancer, is currently undergoing clinical trials in multiple forms of cancer. However, there is currently no preclinical information relating to whether senescence is one component of the response to this ADC in tumor cells. Our studies provide evidence for senescence in response to SG (β-galactosidase staining with quantification by flow cytometry, up-regulation of p21 and down regulation of Lamin B1, and expression of IL-6, IL-8 and IL-1β) in 9 tumor cell lines derived from breast, prostate, lung, ovarian and colorectal cancer. Senescence induction was associated with a transient growth arrest followed by proliferative recovery. Similar results were generated using SN-38, the toxic payload that is released from Sacituzumab-govitecan. We conclude that one central component of the tumor cell response to Sacituzumab-govitecan is a transient senescence-associated growth arrest that can generate a pool of surviving tumor cells with the potential to contribute to disease recurrence. Significance Antibody-drug conjugates are among the newest anticancer therapies. The current studies demonstrate, for the first time, that one component of the response to an antibody-drug conjugate, Sacituzumab-govitecan, is the promotion of senescence. This raises the possibility that the inclusion of senolytics or senomorphics in combination with antibody-drug conjugates, could improve their clinical effectiveness and interfere with disease recurrence.
G protein-coupled receptor 3 (GPR3) is a constitutively active G protein-coupled receptor known to regulate β-amyloid deposition in the brain and metabolism in brown adipose tissue. Although multiple compounds have been proposed to activate GPR3 signaling, it is still considered an orphan receptor. Recently, structural evidence revealed a hydrophobic tunnel in GPR3, suggesting that a lipid may be an endogenous agonist for GPR3. We sought to characterize the reported agonists for GPR3 to determine which might be authentic agonists and found that only the synthetic ligand, diphenyleneiodonium chloride, and the endogenous lipids, oleoylethanolamide (OEA) and oleamide, stimulated cAMP generation in a GPR3-dependent manner. Although treatment of cells with diphenyleneiodonium chloride stimulated rapid cAMP generation, we observed gradual increases in GPR3 activation over multiple hours after OEA treatment. Additionally, we found that chronic stimulation with OEA caused an increase in GPR3 cell surface expression. Coupled with the slow activation kinetics of OEA-stimulated GPR3 signaling, these findings suggest that OEA does not behave strictly as a classical agonist for GPR3. Indeed, we found that the OEA-mediated increase in GPR3 on the cell surface can be blocked by inhibiting receptor forward trafficking through the endoplasmic reticulum and Golgi, which positions OEA as a pharmacological chaperone that increases GPR3 signaling by promoting receptor trafficking to the cell surface. These findings suggest a novel mechanism for the regulation of the constitutively active receptor GPR3, whereby the amount of receptor at the plasma membrane, and therefore, the receptor's signaling activity, can be regulated by lipid binding in the endoplasmic reticulum/Golgi. SIGNIFICANCE STATEMENT: This study proposes a novel mechanism for the regulation of the activity of the G protein-coupled receptor, G protein-coupled receptor 3. This study found that the endogenous lipid oleoylethanolamide functions as a pharmacological chaperone by promoting the accumulation of G protein-coupled receptor 3 at the plasma membrane through increased forward trafficking, thereby inducing increased receptor signaling activity.
Heart failure is a major cause of morbidity and mortality worldwide, representing the end-stage of cardiovascular diseases that induce pathological cardiac remodeling. At the cellular level, pathological remodeling includes myocyte hypertrophy and decreased survival, changes in myocyte metabolism and contractility, and interstitial myocardial fibrosis, all of which are controlled by a complex network of intracellular signaling pathways. At the outer nuclear envelope (ONM) of the cardiomyocyte, A-kinase anchoring protein 6β (AKAP6β, also known as mAKAPβ) organizes multimolecular signaling complexes called “signalosomes” that include over 25 different signaling enzymes and effector proteins that in response to cAMP, calcium, and phosphoinositide second messengers regulate gene expression. The AKAP6β scaffold also binds other scaffold proteins such as AKAP9, permitting higher order interactions between signaling molecules at the nuclear envelope and adjacent Golgi apparatus. Together these protein complexes present novel opportunities for compartmentalized inhibition of pathophysiological cardiac remodeling. Both basic molecular mechanisms and potential therapeutic approaches are considered, as this review highlights recent advances in the role of AKAP6 in coordinating compartmentalized signaling and the regulation of cardiomyocyte gene expression promoting heart failure.
Phosphorylation participates in the signaling, localization, and trafficking of G protein-coupled receptors. In this study, the amino acids known to be phosphorylated in α1A-adrenergic receptors were substituted with nonphosphorylatable residues in intracellular loop 3 (IL3) mutant, the carboxyl terminus (CTerm) mutant, and both structural regions (IL3-CTerm mutant). Their functions were compared with those of the wild-type (WT) receptor. Agonist- and protein kinase C-induced receptor phosphorylation was markedly decreased in the IL3-CTerm mutant, confirming the major roles of both domains in this process. Surprisingly, the substitutions did not affect the agonist-induced increase in intracellular calcium. Similarly, neither the WT nor the mutant receptors were desensitized by protein kinase C activation; however, agonist stimulation markedly desensitized the receptors, and this effect was diminished in the IL3 mutant, suggesting a role for this domain in this process. Extracellular signal-regulated kinase 1/2 phosphorylation was strong but transient in cells expressing the WT receptor, strong and sustained in those expressing the CTerm mutant, and markedly reduced in those expressing the IL3 and IL3-CTerm mutants. These findings suggest that IL3 phosphorylation sites modulate extracellular signal-regulated kinase activity. A weak and slow agonist-induced receptor-β-arrestin interaction was detected in cells expressing the WT receptor but was barely detectable in any of the mutants. Consistent with these findings, agonist- and phorbol ester-induced receptor internalization was observed in cells expressing the WT receptor but was markedly decreased in cells expressing the distinct mutants. SIGNIFICANCE STATEMENT: Phosphorylation sites in both intracellular loop 3 (IL3) and carboxyl terminus domains affect receptor function in distinct but complementary ways. The IL3 mutant showed decreased agonist-induced desensitization of the calcium response and agonist-activated extracellular signal-regulated kinase phosphorylation. α1A-Adrenergic receptor internalization and interaction with β-arrestin were decreased in all mutants containing phosphorylation site substitutions. Phosphorylation sites in the IL3 and carboxyl terminus domains appear to be functionally relevant for this receptor. The approach employed could be used to expand knowledge on other G protein-coupled receptors.
Potassium (K+) channels are targeted by a wide range of chemical and biological substances, with peptide ligands standing out due to their exceptional affinity and selectivity. Although most of these molecules belong to venom-derived compounds, novel ligands from various less investigated or less popular sources are being discovered. Application of polypeptides is not restricted to fundamental studies and can be expanded to drug discovery, clinical pharmacology, and pharmaceutics. In this report, we offer a concise overview of the diversity of K+ channel ligands and their sources, briefly summarizing recent developments in the field and providing an outlook. SIGNIFICANCE STATEMENT: This paper provides a concise overview of the diversity of K+ channel ligands and their natural sources, highlights recent advances, and outlines future directions. Although venom-derived polypeptides remain the main source, growing interest is focused on nonvenomous organisms such as plants and mammals. We also discuss artificial polypeptides developed using mutagenesis, and the potential of machine learning and neural networks as promising tools for further molecular design.
Hepatic transport protein organic anion transporting polypeptide 1B1 (OATP1B1) is a key determinant of drug-drug interactions. We reported OATP1B1 lysine acetylation recently, however, the lysine deacetylase (KDAC), also known as histone deacetylase (HDAC), involved in its deacetylation remains uninvestigated. This study determined the role of KDAC6/HDAC6, a major cytosolic KDAC, on OATP1B1 acetylation and transport function. Loss-of-function of KDAC6 by CRISPR/Cas9-mediated knockout in HEK293T cells or by treatment with the selective KDAC6 inhibitor tubacin (TBC) (5 μM, 24 hours) in transporter-expressing HEK293 cells markedly reduces OATP1B1-mediated transport of [3H]estradiol-17-ß-D-glucuronide to 0.62 ± 0.095- and 0.28 ± 0.007-fold of control, respectively. TBC treatment did not affect OATP1B1 mRNA, protein levels and colocalization with plasma membrane marker Na/K-ATPase, suggesting a regulation at a post-translational level. TBC treatment also reduces [3H]rosuvastatin accumulation in primary human hepatocytes. Quantitative comparison of post-translational modifications (PTMs) between TBC treatment and control showed concurrent increase in lysine acetylation at K675 (to 5.16 ± 2.7-fold of control) and decrease in dual phosphorylation at Ser659-Ser663 (to 0.34 ± 0.13-fold of control). A variant S659A-S663A-K675Q-OATP1B1 that mimics these concurrent PTM changes reduces OATP1B1-mediated transport compared with the wild-type control, supporting a role for altered PTMs in downregulation of OATP1B1 transport function upon KDAC6 loss-of-function. In addition, K49, a residue important in maintaining OATP1B1 transport function, was identified as acetylated for the first time. This study identifies KDAC6 as a key enzyme regulating lysine acetylation of OATP1B1 and maintaining OATP1B1 transport function, thereby implying a novel KDAC6-linked mechanism in OATP1B1-mediated drug-drug interactions. SIGNIFICANCE STATEMENT: This study identifies lysine deacetylase 6 (KDAC6) as a key enzyme involved in post-translational regulation of OATP1B1. Current findings demonstrate that KDAC6-dependent acetylation-phosphorylation axis modulates OATP1B1 transport function and provides a mechanistic basis by which altered KDAC6 activity may influence OATP1B1-mediated drug-drug interactions.
Cell-free DNA (cfDNA) level is a core liquid biopsy biomarker. However, it exhibits low detection sensitivity in early-stage diseases and carries a risk of information loss. Traditionally regarded as anucleate and DNA-deficient, platelets have recently been confirmed to actively take up and carry extracellular DNA—termed platelet DNA (pDNA). We summarized pDNA uptake mechanisms, including clathrin-mediated endocytosis of DNA-loaded extracellular vesicles and direct internalization of free DNA, as well as its pharmacological regulation. Compared with plasma cfDNA levels, pDNA shows superior stability, higher mutant allele frequencies, and resistance to nucleases. We elaborated its clinical potential for early cancer detection by capturing low-abundance tumor mutations and for noninvasive prenatal testing by overcoming the scarcity of fetal cfDNA in early pregnancy. Finally, we discussed integrating pDNA analysis using multiomics and artificial intelligence to advance precision liquid biopsy. Significance Statement Platelet DNA level reshapes platelets’ role from hemostatic cells to genetic carriers, resolving plasma cell-free DNA level’s limitations. It enables early cancer detection and prenatal testing, advancing liquid biopsy toward precision medicine for better diagnostic outcomes.
Chemotherapy-induced peripheral neuropathy is a common side effect of chemotherapy drugs. Currently, no effective preventive strategies or treatments are available. In recent years, histone deacetylase inhibitors (HDACis), initially approved for hematologic malignancies, have been proposed for neuroprotective purposes. HDACis inhibit histone deacetylases, a group of enzymes involved in the regulation of both histone and nonhistone proteins. In this study, we tested the antitumorigenic abilities of 3 different HDACis (SAHA, romidepsin, and SW-100) in combination with oxaliplatin (OHP) in 3 colorectal cancer cell lines (HT-29, HCT-15, and Caco-2). OHP is the gold standard antineoplastic therapy for the treatment of colorectal cancer, and it is also known to induce peripheral neuropathy, which affects patients' quality of life. OHP treatment often forces a reduction of the clinical effective drug dose, or even an interruption in anticancer treatment. Therefore, we also assessed the efficacy of 3 HDACis in mitigating the neurotoxicity induced by OHP in E15 rat embryo dorsal root ganglia. Apoptotic and cell proliferation pathways were tested through immunoblot analysis, immunofluorescence, and cell survival analysis. The results of this study show that SW-100, a selective histone deacetylase 6 inhibitor, induces apoptosis and reduces cell viability in both HT-29 and HCT-15 when used in combination with OHP. Besides its antineoplastic activity, SW-100 can protect against OHP neurotoxicity, limiting the activation of caspase 3 and selectively inducing α-tubulin acetylation to possibly stabilize axonal transport. In conclusion, we propose SW-100 and OHP as a viable combination for future studies on the treatment of chemotherapy-induced peripheral neuropathy. Significance Statement Chemotherapy-induced peripheral neuropathy is a common side effect of oxaliplatin, a drug used for the treatment of colorectal cancer. This study demonstrated that in vitro cotreatment with the histone deacetylase 6 selective inhibitor, SW-100, attenuates the neurotoxic effect of oxaliplatin while maintaining the efficacy of the treatment.
Histamine receptors (H1R-H4R) are G protein-coupled receptors with large physiological and therapeutic relevance. Despite extensive research, a systematic and cross-database overview of ligands is missing. This review integrates the Psychoactive Drug Screening Program (PDSP) Ki database and the International Union of Basic and Clinical Pharmacology/British Pharmacological Society (IUPHAR/BPS) Guide to Pharmacology, both having different scopes and curation principles, and evaluates concordance of HxR ligands across databases and experimental systems. Binding affinities (Ki) for 302 ligands targeting recombinant human HxR were extracted from the PDSP Ki database (accessed January 2026) and converted to pKi. A total of 302 ligands with relevant binding affinities were identified, including approved drugs and experimental compounds. Functional annotations and further binding affinities were retrieved from the IUPHAR/BPS Guide to Pharmacology and complementary literature, revealing missing or incomplete functional characterization for 69 ligands. Although most ligands were selective for a single HxR, others displayed multireceptor affinity. Cross-database comparisons found limited overlap in ligands, differences in primary literature, and pKi deviations. Comparisons with native human tissues and nonhuman species demonstrated substantial variability, with deviations of up to pKi 4.2 in human brain tissues and up to pKi 3.2 across species. This database-driven analysis highlights strengths and limitations of the PDSP Ki database (broad data aggregation) and the IUPHAR/BPS Guide to Pharmacology (curated representative selection). Although together they provide extensive coverage of HxR ligands, incomplete overlap and selective data inclusion limit direct comparability and may give the impression of missing data despite substantial experimental data. Systematic integration is essential to improve data reliability, summarize knowledge, and support future drug development. SIGNIFICANCE STATEMENT: This review provides a systematic overview of ligand binding affinities and functional profiles across all 4 HxR. It integrates data from the PDSP Ki database and the IUPHAR/ BPS Guide to Pharmacology and compares recombinant human HxR with native tissues and several species. Substantial data gaps, inconsistencies, and context-dependent variability are revealed. The PDSP Ki database has large potential for use in scientific research and in the support of drug development.
The metabotropic glutamate (mGlu) receptors are family C G protein-coupled receptors that are widely expressed throughout the central nervous system and function as either homodimers or heterodimers. Recent literature suggests that specific mGlu heterodimer subtypes play critical functional roles in the brain and show unique pharmacological signatures relative to homodimers. We have previously shown that mGlu7/8 heterodimers may modulate the induction of hippocampal synaptic plasticity using negative allosteric modulators that differentiate between mGlu7/7 homodimers and mGlu7/8 heterodimers in vitro. However, we have yet to characterize positive allosteric modulators (PAMs) targeting mGlu7 and mGlu8 in a heterodimer-specific assay. Here, we investigated the molecular pharmacology of mGlu7/8 heterodimers relative to mGlu7/7 and mGlu8/8 homodimers using PAMs and various orthosteric agonists using functional assays of controlled receptor activity in HEK293 cells. We demonstrate that an mGlu8-selective agonist is only active at mGlu8/8 homodimers and acts as an antagonist at mGlu7/8 heterodimers. In addition, we show that specific PAMs, such as VU0155094, show greater efficacy at mGlu7/8 heterodimers in specific assays. Overall, these findings have important implications for the physiological and behavioral roles of mGlu heterodimers and homodimers as it relates to the pharmacology of these compounds. In addition, this study provides a rationale for using a pharmacological toolkit to selectively probe mGlu7/7, mGlu8/8, and mGlu7/8 dimers in native tissues. SIGNIFICANCE STATEMENT: Pharmacological profiling of ligands at mGlu7/8 heterodimers reveals that this receptor exhibits a unique pharmacological signature relative to mGlu7/7 and mGlu8/8 homodimers. This study provides an incentive to investigate the pharmacology of other mGlu heterodimers, screen for heterodimer selective compounds, and use pharmacological tools to investigate the physiological effects of mGlu7/8 dimers in native tissues.
Ivermectin (IVM) is a widely used antiparasitic drug that acts through allosteric activation and potentiation of the glutamate-gated chloride channel present in neurons and muscle cells of helminths and insects. In mammals, IVM activates several members of the Cys-loop ion channel family, including the GABAA receptor. Although the centrally located GABAA receptors are protected against the actions of IVM by the transporter protein P-glycoprotein 1 present in the blood-brain barrier, many peripheral GABAA receptors are exposed to blood-borne IVM. Here, we have investigated the activating and modulatory effects of IVM on α5β3γ2L and α1β3γ2L GABAA receptors expressed in Xenopus oocytes. We show that IVM is a potent and efficacious agonist of the α5β3γ2L receptor with an EC50 of 0.06 μM and a maximal probability of being in the active state >0.3. IVM, unlike typical agonists of the GABAA receptor, does not desensitize the receptor even in 20-minute-long applications. Receptors desensitized by high concentrations of GABA are reactivated upon exposure to IVM. Coapplication of IVM with GABA or the allosteric agonist, etomidate, manifests as simple additivity of individual responses rather than potentiation. The application of the allosteric agonist, pentobarbital, is without effect or reduces the response to IVM. Overall, GABAA receptor activation by IVM exhibits a number of unique properties not encountered with commonly used or studied GABAergic drugs. Significance Statement Peripheral GABAA receptors are accessible to the widely used antiparasitic agent ivermectin (IVM). This study shows that IVM activates the α5β3γ2L and α1β3γ2L subtypes at therapeutic concentrations. Responses to IVM are not potentiated by the transmitter GABA or the allosteric agonists etomidate or pentobarbital. Receptors activated by IVM do not exhibit desensitization, while receptors desensitized by GABA are reactivated upon exposure to IVM.
