Staff member

Blinding diseases due to the degeneration of photoreceptors (PhRs), such as geographic atrophy (GA) secondary to dry age-related macular degeneration and retinitis pigmentosa (RP), leave the rest of the retinal circuitry largely intact, albeit unable to respond to light. Gene therapy has been able to revert PhR degeneration, but it can be applied only to a rare mutation affecting a small subset of RP patients. Alternatively, implanted electronic retinal prostheses aim at a larger population by electrically stimulating surviving neurons. However, the treatment is invasive and costly and provides limited resolution. Photopharmacology can develop photoswitchable small molecules to restore vision impairment by conferring light sensitivity to ion channels that are widely expressed in the remaining inner retinal neurons, and a first-in-human clinical trial is ongoing. Here, we have developed novel photoswitchable small-molecule ligands of metabotropic glutamate 6 (mGlu6) receptors, which are located exclusively at the dendrites of ON bipolar cells (postsynaptic to PhRs) and can leverage a privileged position to mimic physiological signals in the remnant retinal circuit. These photoswitchable ligands (prosthe6) thus act as "molecular prostheses" that can restore the light input to the retina via upstream-targeted control of the circuit after PhR degeneration. Prosthe6 compounds are allosteric, drug-like, water-soluble, and display outstanding in vitro properties including full efficacy, nanomolar potency, fast deactivation in ambient white light, and fast reactivation in the dark. In vivo experiments show that they readily recover the saccadic eye movements of blinded zebrafish larvae and restore the innate light-avoidance behavior in the mouse models of blindness (GA and RP). These effects are mediated by mGlu6 receptors in vivo. In addition, at least two compounds (prosthe6-12 and -15) can restore sight by topical administration and display promising safety properties to become potential drug candidates for sight restoration in patients with degenerative blinding diseases.

JTD Keywords: Allosteric modulators, Bipolar cells, Blind mice, Ectopic expression, Gene-therapy, Human rod, Protein-coupled receptors, Restores visual responses, Retinal degeneration, Zebrafish models

The study of intact cells and their signaling circuits with light requires a stimulation strategy that is focused, deeply penetrating, and does not damage them. Implanted optic fibers, light-emitting diodes, and luminescent materials operated externally with tissue-penetrating infrared (IR) light are invasive or limited by light attenuation around the illumination point. To overcome these barriers, two-photon pharmacology takes advantage of femtosecond-pulsed IR laser light to produce deep and spatiotemporally precise cellular stimulation using specially designed photoswitchable drugs. Compounds that can be covalently tethered to the target neuroreceptor perform particularly well. However, the tethered photoswitches reported to date require mutagenesis of the target protein, which prevents the use of photopharmacology to stimulate the nervous system in wild-type animals. Here, we report the first two-photon optimized targeted covalent photoswitch (TCP2P) that combines the efficient two-photon isomerization of ortho-fluoro-substituted azobenzene with the ability to conjugate to nucleophilic residues of endogenous proteins (AMPA and kainate ionotropic glutamate receptors in neurons). TCP2P is readily obtained by click coupling of two precursor compounds prior to use, and after simple incubation, it enables controlling neuronal activity at one- and two-photon excitation up to 800 nm without genetic modifications.

JTD Keywords: Glutamate-receptor, Optical control

Acetylcholine and the cholinergic system are crucial to brain function, including functions such as consciousness and cognition. Dysregulation of this system is implicated in the pathophysiology of neurological conditions such as Alzheimer's disease. For this reason, cholinergic neuromodulation is relevant in both basic neuroscience and clinical neurology. In this study, we used photopharmacology to modulate neuronal activity using the novel selective type-1 muscarinic (M1) photoswitchable drugs: the agonist benzyl quinolone carboxylic acid-azo-iperoxo (BAI) and the antagonist cryptozepine-2. Our aim was to investigate the control over these cholinergic receptors using light and to investigate the effects of these drugs on physiological spontaneous slow waves and on epileptic activity in the cerebral cortex. First, we used transfected HEK cell cultures and demonstrated BAI's preferential activation of M1 muscarinic acetylcholine receptors (mAChRs) compared with M2 mAChRs. Next, we found that white-light illumination of BAI increased the frequency of spontaneous slow-wave activity in brain cortical networks of both active slices and anesthetized mice, through M1-mAChRs activation. Illumination of cryptozepine-2 with UV light effectively suppressed not only the muscarinic-induced increase in slow-wave frequency, but also muscarinic-induced epileptiform discharges. These findings not only shed light on the role of M1 acetylcholine receptors in the cortical network dynamics but also lay the groundwork for developing advanced light-based pharmacological therapies. Photopharmacology offers the potential for high-precision spatiotemporal control of brain networks with high pharmacological specificity in both healthy and pathological conditions.

JTD Keywords: Acetylcholine, Acetylcholine-receptors, Biological health and medical sciences, Brain, Epilepsy, Hz oscillation, Less-than-1 hz, Modulation, Network mechanisms, Neuromodulation, Neuroscienc, Pathology, Photopharmacology, Seizures, Slee, Slow oscillations

The field of G protein-coupled receptor (GPCR) research has greatly benefited from the spatiotemporal resolution provided by light controllable, i.e., photoswitchable ligands. Most of the developed tools have targeted the Rhodopsin-like family (Class A), the largest family of GPCRs. However, to date, all such Class A photoswitchable ligands were designed to act at the orthosteric binding site of these receptors. Herein, we report the development of the first photoswitchable allosteric modulators of Class A GPCRs, designed to target the M-1 muscarinic acetylcholine receptor. The presented benzyl quinolone carboxylic acid (BQCA) derivatives, Photo-BQCisA and Photo-BQCtrAns, exhibit complementary photopharmacological behavior and allow reversible control of the receptor using light as an external stimulus. This makes them valuable tools to further investigate M-1 receptor signaling and a proof of concept for photoswitchable allosteric modulators at Class A receptors.

JTD Keywords: Agonist, Allosterism, Gpcr, Muscarinic ligands, Photopharmacology, Photoswitc, Selective activation, Serie

Gorostiza, Pau

JTD

To interrogate neural circuits and crack their codes, in vivo brain activity imaging must be combined with spatiotemporally precise stimulation in three dimensions using genetic or pharmacological specificity. This challenge requires deep penetration and focusing as provided by infrared light and multiphoton excitation, and has promoted two-photon photopharmacology and optogenetics. However, three-photon brain stimulation in vivo remains to be demonstrated. We report the regulation of neuronal activity in zebrafish larvae by three-photon excitation of a photoswitchable muscarinic agonist at 50 pM, a billion-fold lower concentration than used for uncaging, and with mid-infrared light of 1560 nm, the longest reported photoswitch wavelength. Robust, physiologically relevant photoresponses allow modulating brain activity in wild-type animals with spatiotemporal and pharmacological precision. Computational calculations predict that azobenzene-based ligands have high three-photon absorption cross-section and can be used directly with pulsed infrared light. The expansion of three-photon pharmacology will deeply impact basic neurobiology and neuromodulation phototherapies.© 2023 Wiley-VCH GmbH.

JTD Keywords: absorption, azobenzene photoswitches, deep, glutamate-receptor, intravital microscopy, multiphoton excitation, muscarinic neuromodulation, photopharmacology, two-photon lithography and polymerization, 2-photon excitation, Animals, Azobenzene, Infrared rays, Ligands, Multiphoton excitation, Muscarinic neuromodulation, Photons, Photopharmacology, Photopharmacology, azobenzene, muscarinic neuromodulation, multiphoton excitation, two-photon lithography and polymerization, Two-photon lithography and polymerization, Zebrafish

Understanding the dopaminergic system is a priority in neurobiology and neuropharmacology. Dopamine receptors are involved in the modulation of fundamental physiological functions, and dysregulation of dopaminergic transmission is associated with major neurological disorders. However, the available tools to dissect the endogenous dopaminergic circuits have limited specificity, reversibility, resolution, or require genetic manipulation. Here, we introduce azodopa, a novel photoswitchable ligand that enables reversible spatiotemporal control of dopaminergic transmission. We demonstrate that azodopa activates D1-like receptors in vitro in a light-dependent manner. Moreover, it enables reversibly photocontrolling zebrafish motility on a timescale of seconds and allows separating the retinal component of dopaminergic neurotransmission. Azodopa increases the overall neural activity in the cortex of anesthetized mice and displays illumination-dependent activity in individual cells. Azodopa is the first photoswitchable dopamine agonist with demonstrated efficacy in wild-type animals and opens the way to remotely controlling dopaminergic neurotransmission for fundamental and therapeutic purposes.

JTD Keywords: azobenzene, behavior, brainwave, d-1, dopamine, gpcr, in vivo electrophysiology, inhibitors, optogenetics, optopharmacology, photochromism, photopharmacology, photoswitch, stimulation, zebrafish, Animals, Animals, wild, Azobenzene, Behavior, Brainwave, Dopamine, Gpcr, In vivo electrophysiology, Ligands, Mice, Optogenetics, Optopharmacology, Photochromism, Photopharmacology, Photoswitch, Receptors, Synaptic transmission, Zebrafish

Tricyclic chemical structures are the core of many important drugs targeting all neurotransmitter pathways. These medicines enable effective therapies to treat from peptic ulcer disease to psychiatric disorders. However, when administered systemically, they cause serious adverse effects that limit their use. To obtain localized and on-demand pharmacological action using light, we have designed photoisomerizable ligands based on azobenzene that mimic the tricyclic chemical structure and display reversibly controlled activity. Pseudo-analogues of the tricyclic antagonist pirenzepine demonstrate that this is an effective strategy in muscarinic acetylcholine receptors, showing stronger inhibition upon illumination both in vitro and in cardiac atria ex vivo. Despite the applied chemical modifications to make pirenzepine derivatives sensitive to light stimuli, the most potent candidate of the set, cryptozepine-2, maintained a moderate but promising M-1 vs M-2 subtype selectivity. These photoswitchable crypto-azologs of tricyclic drugs might open a general way to spatiotemporally target their therapeutic action while reducing their systemic toxicity and adverse effects.

JTD Keywords: Binding, Dose-response relationship, drug, Drug design, Humans, M1, Molecular structure, Muscarinic antagonists, Pirenzepine, Rat-brain, Receptor, Receptors, muscarinic, Structure-activity relationship

Light-triggered reversible modulation of physiological functions offers the promise of enabling on-demand spatiotemporally controlled therapeutic interventions. Optogenetics has been successfully implemented in the heart, but significant barriers to its use in the clinic remain, such as the need for genetic transfection. Herein, we present a method to modulate cardiac function with light through a photoswitchable compound and without genetic manipulation. The molecule, named PAI, was designed by introduction of a photoswitch into the molecular structure of an M2 mAChR agonist. In vitro assays revealed that PAI enables light-dependent activation of M2 mAChRs. To validate the method, we show that PAI photoisomers display different cardiac effects in a mammalian animal model, and demonstrate reversible, real-time photocontrol of cardiac function in translucent wildtype tadpoles. PAI can also effectively activate M2 receptors using two-photon excitation with near-infrared light, which overcomes the scattering and low penetration of short-wave-length illumination, and offers new opportunities for intravital imaging and control of cardiac function.

JTD