Spider venoms and chronic pain – developing novel pharmacological tools from the spider venoms to target P2X4 in microglia

Today, one in five adults experience chronic pain and this figure increases for those over 65 years old. However, frustration is mounting over the inadequate treatment for chronic neuropathic pain since its symptoms are challenging to treat and often resistant to opioids. Processing of pain signals relies on the activities of ion channels with the microglial P2X4 receptor being an important player. Animal venoms play an essential role in drug discovery as they contain a rich source of bioactive molecules evolutionarily fine-tuned to target ion channels such as P2X receptors. First, we have established and validated several fluorescent-based high throughput screening assays for assessing the activity of venom toxins at P2X receptors. Second, a diverse selection of 180 crude venoms has been screened against human P2X4 in HEK293 and 1321N21 cells, resulting in several venoms containing inhibitors against hP2X4. Two of them, LK-601 and LK-729, were confirmed to be structurally uncharacterized acylpolyamines, which potently inhibited hP2X4 with the apparent IC50 values between 1.1 – 4.5 μM, however only LK-601 showed a relatively high level of selectivity over hP2X3, hP2X7 and NMDA 1a/2a. Species differences were evident with no effect at rat P2X4, however, blocking the mouse P2X4. Using LK-601 as a structural guide, the fragment-based screening was carried out and five smaller toxin analogues chemically synthesized. One of them, LA-3, was found to block the hP2X4 (IC50 of 9.7 – 18.6 μM) and showed selectivity to hP2X4 over hP2X3, hP2X7 and rP2X4 with a modest inhibition at mP2X4. Due to the differential sensitivity of LA-3 to block P2X4 orthologues, the potential binding site were identified, and the validation showed that two crucial amino acid residues, D220 and N238, might be involved in LA-3 binding to hP2X4; however, more experiments are needed to confirm that effect fully. In summary, we discovered a novel toxin from a spider venom with inhibitory activity at human P2X4 ion channels that shows selectivity at hP2X4 over other P2X receptors. Further characterization and validation are required to understand whether these novel compounds could be useful as analgesics

Development of high-throughput fluorescent-based screens to accelerate discovery of P2X inhibitors from animal venoms

Animal venoms can play an important role in drug discovery, as they are a rich source of evolutionarily tuned compounds that target a variety of ion channels and receptors. To date, there are six FDA-approved drugs derived from animal venoms, with recent work using high-throughput platforms providing a variety of new therapeutic candidates. However, high-throughput methods for screening animal venoms against purinoceptors, one of the oldest signaling receptor families, have not been reported. Here, we describe a variety of quantitative fluorescent-based high-throughput screening (HTS) cell-based assays for screening animal venoms against ligand-gated P2X receptors. A diverse selection of 180 venoms from arachnids, centipedes, hymenopterans, and cone snails were screened, analyzed, and validated, both analytically and pharmacologically. Using this approach, we performed screens against human P2X3, P2X4, and P2X7 using three different fluorescent-based dyes on stable cell lines and isolated the active venom components. Our HTS assays are performed in 96-well format and allow simultaneous screening of multiple venoms on multiple targets, improving testing characteristics while minimizing costs, specimen material, and testing time. Moreover, utilizing our assays and applying them to the other natural product libraries, rather than venoms, might yield other novel natural products that modulate P2X activity

Design and development of stapled transmembrane peptides that disrupt the activity of G-protein coupled receptor oligomers

Membrane proteins can associate into larger complexes. Examples include receptor tyrosine complexes, ion channels, transporters and G-protein coupled receptors (GPCRs). For the latter, there is abundant evidence indicating that GPCRs, assemble into complexes, through both homo or heterodimerization. However, the tools for studying and disrupting these complexes, GPCR or otherwise, are limited. Here we have developed stabilized interference peptides for this purpose. We have previously reported that tetrahydrocannabinol-mediated cognitive impairment arises from homo- or hetero-oligomerization between the GPCRs cannabinoid receptor type 1 (CB1R) and 5-hydroxytryptamine 2A (5-HT2AR) receptors. Here, to disrupt this interaction through targeting CB1–5-HT2A receptor heteromers in HEK293 cells and using an array of biochemical techniques, including calcium and cAMP measurements, bimolecular fluorescence complementation assays, and CD-based helicity assessments, we developed a NanoLuc binary technology (NanoBiT)-based reporter assay to screen a small library of aryl-carbon–stapled transmembrane mimicking peptides produced by solid-phase peptide synthesis. We found that these stapling peptides have increased α-helicity and improved proteolytic resistance without any loss of disrupting activity in vitro, suggesting that this approach may also have utility in vivo. In summary, our results provide proof of concept for using NanoBiT to study membrane protein complexes and for stabilizing disrupting peptides to target such membrane complexes through hydrocarbon-mediated stapling. We propose that these peptides could be developed to target previously un-druggable GPCR heteromers

Bug Off Pain: An Educational Virtual Reality Game on Spider Venoms and Chronic Pain for Public Engagement

Virtual reality (VR) technology has been capturing the public imagination for decades. VR software applications that allow for interactive immersion are emerging as a renowned medium in many areas, including educating the public in biochemistry-related subjects via public engagement events. This report provides information about an immersive, interactive and educational virtual reality (VR) game named Bug Off Pain that increases scientific literacy about chronic pain and spider venoms among the public and high school students. Here, VR was shown to be an innovative and fun approach to learning and public engagement in biochemistry. Bug Off Pain places the viewer inside the brain and shows the molecular system that allows people to sense pain. After securing three (learning) points via the multimedia-based clips, this experience translates to the interactive game. Here, a player has to choose a venom that shuts down the pain until that results in “pain over”. Bug Off Pain can be played (free of charge) on two different VR platforms: Oculus Rift and Android devices

Ginsenosides act as positive modulators of P2X4 receptors

We investigated the selectivity of protopanaxadiol ginsenosides from Panax ginseng acting as positive allosteric modulators on P2X receptors. ATP-induced responses were measured in stable cell lines overexpressing human P2X4 using a YOPRO-1 dye uptake assay, intracellular calcium measurements, and whole-cell patch-clamp recordings. Ginsenosides CK and Rd were demonstrated to enhance ATP responses at P2X4 by ∼twofold, similar to potentiation by the known positive modulator ivermectin. Investigations into the role of P2X4 in mediating a cytotoxic effect showed that only P2X7 expression in HEK-293 cells induces cell death in response to high concentrations of ATP, and that ginsenosides can enhance this process. Generation of a P2X7-deficient clone of BV-2 microglial cells using CRISPR/ Cas9 gene editing enabled an investigation of endogenous P2X4 in a microglial cell line. Compared with parental BV-2 cells, P2X7-deficient BV-2 cells showed minor potentiation of ATP responses by ginsenosides, and insensitivity to ATP 2 or ATP 1 ginsenoside-induced cell death, indicating a primary role for P2X7 receptors in both of these effects. Computational docking to a homology model of human P2X4, based on the open state of zfP2X4, yielded evidence of a putative ginsenoside binding site in P2X4 in the central vestibule region of the large ectodomain

Design and characterization of superpotent bivalent ligands targeting oxytocin receptor dimers via a channel-like structure

Dimeric/oligomeric states of G-protein coupled receptors have been difficult to target. We report here bivalent ligands consisting of two identical oxytocin-mimetics that induce a three order magnitude boost in G-protein signaling of oxytocin receptors (OTRs) in vitro and a 100- and 40-fold gain in potency in vivo in the social behavior of mice and zebrafish. Through receptor mutagenesis and interference experiments with synthetic peptides mimicking transmembrane helices (TMH), we show that such superpotent behavior follows from the binding of the bivalent ligands to dimeric receptors based on a TMH1-TMH2 interface. Moreover, in this arrangement, only the analogues with a well-defined spacer length (∼25 Å) precisely fit inside a channel-like passage between the two protomers of the dimer. The newly discovered oxytocin bivalent ligands represent a powerful tool for targeting dimeric OTR in neurodevelopmental and psychiatric disorders and, in general, provide a framework to untangle specific arrangements of G-protein coupled receptor dimers

Therapeutic targeting of HER2–CB2R heteromers in HER2-positive breast cancer

There is a subtype of breast cancer characterized by the overexpression of the oncogene HER2. Although most patients with this diagnosis benefit from HER2-targeted treatments, some do not respond to these therapies and others develop resistance with time. New tools are therefore warranted for the treatment of this patient population, and for early identification of those individuals at a higher risk of developing innate or acquired resistance to current treatments. Here, we show that HER2 forms heteromer complexes with the cannabinoid receptor CB2R, the expression of these structures correlates with poor patient prognosis, and their disruption promotes antitumor responses. Collectively, our results support HER2–CB2R heteromers as new therapeutic targets and prognostic tools in HER2+ breast cancer

Singular Location and Signaling Profile of Adenosine A2A-Cannabinoid CB1 Receptor Heteromers in the Dorsal Striatum

The dorsal striatum is a key node for many neurobiological processes such as motor activity, cognitive functions, and affective processes. The proper functioning of striatal neurons relies critically on metabotropic receptors. Specifically, the main adenosine and endocannabinoid receptors present in the striatum, ie, adenosine A2A receptor (A2AR) and cannabinoid CB1 receptor (CB1R), are of pivotal importance in the control of neuronal excitability. Facilitatory and inhibitory functional interactions between striatal A2AR and CB1R have been reported, and evidence supports that this cross-talk may rely, at least in part, on the formation of A2AR-CB1R heteromeric complexes. However, the specific location and properties of these heteromers have remained largely unknown. Here, by using techniques that allowed a precise visualization of the heteromers in situ in combination with sophisticated genetically-modified animal models, together with biochemical and pharmacological approaches, we provide a high resolution expression map and a detailed functional characterization of A2AR-CB1R heteromers in the dorsal striatum. Specifically, our data unveil that the A2AR-CB1R heteromer (i) is essentially absent from corticostriatal projections and striatonigral neurons, and, instead, is largely present in striatopallidal neurons, (ii) displays a striking G protein-coupled signaling profile, where co-stimulation of both receptors leads to strongly reduced downstream signaling, and (iii) undergoes an unprecedented dysfunction in Huntington’s disease, an archetypal disease that affects striatal neurons. Altogether, our findings may open a new conceptual framework to understand the role of coordinated adenosine-endocannabinoid signaling in the indirect striatal pathway, which may be relevant in motor function and neurodegenerative diseases