Optical Control of Lysophosphatidic Acid Signaling

A Bright Future for Photopharmaceuticals Addressing Central Nervous System Disorders: State of the Art and Challenges Toward Clinical Translation

Photopharmacology is an innovative approach that uses light to activate drugs. This method offers the potential for highly localized and precise drug activation, making it particularly promising for the treatment of neurological disorders. Despite the enticing prospects of photopharmacology, its application to treat human central nervous system (CNS) diseases remains to be demonstrated. In this review, we provide an overview of prominent strategies for the design and activation of photopharmaceutical agents in the field of neuroscience. Photocaged and photoswitchable drugs and bioactive molecules are discussed, and an instructive list of examples is provided to highlight compound design strategies. Special emphasis is placed on photoactivatable compounds for the modulation of glutamatergic, GABAergic, dopaminergic, and serotonergic neurotransmission for the treatment of neurological conditions, as well as various photoresponsive molecules with potential for improved pain management. Compounds holding promise for clinical translation are discussed in-depth and their potential for future applications is assessed. Neurophotopharmaceuticals have yet to achieve breakthrough in the clinic, as both light delivery and drug design have not reached full maturity. However, by describing the current state of the art and providing illustrative case studies, we offer a perspective on future opportunities in the field of neurophotopharmacology focused on addressing CNS disorders.

Synthetic Lipid Biology

Cells contain thousands of different lipids. Their rapid and redundant metabolism, dynamic movement, and many interactions with other biomolecules have justly earned lipids a reputation as a vexing class of molecules to understand. Further, as the cell's hydrophobic metabolites, lipids assemble into supramolecular structures─most commonly bilayers, or membranes─from which they carry out myriad biological functions. Motivated by this daunting complexity, researchers across disciplines are bringing order to the seeming chaos of biological lipids and membranes. Here, we formalize these efforts as "synthetic lipid biology". Inspired by the idea, central to synthetic biology, that our abilities to understand and build biological systems are intimately connected, we organize studies and approaches across numerous fields to create, manipulate, and analyze lipids and biomembranes. These include construction of lipids and membranes from scratch using chemical and chemoenzymatic synthesis, editing of pre-existing membranes using optogenetics and protein engineering, detection of lipid metabolism and transport using bioorthogonal chemistry, and probing of lipid-protein interactions and membrane biophysical properties. What emerges is a portrait of an incipient field where chemists, biologists, physicists, and engineers work together in proximity─like lipids themselves─to build a clearer description of the properties, behaviors, and functions of lipids and membranes.

Lipin1 depletion coordinates neuronal signaling pathways to promote motor and sensory axon regeneration after spinal cord injury

Adult central nervous system (CNS) neurons down-regulate growth programs after injury, leading to persistent regeneration failure. Coordinated lipids metabolism is required to synthesize membrane components during axon regeneration. However, lipids also function as cell signaling molecules. Whether lipid signaling contributes to axon regeneration remains unclear. In this study, we showed that lipin1 orchestrates mechanistic target of rapamycin (mTOR) and STAT3 signaling pathways to determine axon regeneration. We established an mTOR-lipin1-phosphatidic acid/lysophosphatidic acid-mTOR loop that acts as a positive feedback inhibitory signaling, contributing to the persistent suppression of CNS axon regeneration following injury. In addition, lipin1 knockdown (KD) enhances corticospinal tract (CST) sprouting after unilateral pyramidotomy and promotes CST regeneration following complete spinal cord injury (SCI). Furthermore, lipin1 KD enhances sensory axon regeneration after SCI. Overall, our research reveals that lipin1 functions as a central regulator to coordinate mTOR and STAT3 signaling pathways in the CNS neurons and highlights the potential of lipin1 as a promising therapeutic target for promoting the regeneration of motor and sensory axons after SCI.

Optical Control of Proteasomal Protein Degradation with a Photoswitchable Lipopeptide

Photolipids have emerged as attractive tools for the optical control of lipid functions. They often contain an azobenzene photoswitch that imparts a cis double-bond upon irradiation. Herein, we present the application of photoswitching to a lipidated natural product, the potent proteasome inhibitor cepafungin I. Several azobenzene-containing lipids were attached to the cyclopeptide core, yielding photoswitchable derivatives. Most notably, PhotoCep4 exhibited a 10-fold higher cellular potency in its light-induced cis-form, matching the potency of natural cepafungin I. The length of the photolipid tail and distal positioning of the azobenzene photoswitch with respect to the macrocycle is critical for this activity. In a proteome-wide experiment, light-triggered PhotoCep4 modulation showed high overlap with constitutively active cepafungin I. The mode of action was studied using crystallography and revealed an identical binding of the cyclopeptide in comparison to cepafungin I, suggesting that differences in their cellular activity originate from switching the tail structure. The photopharmacological approach described herein could be applicable to many other natural products as lipid conjugation is common and often necessary for potent activity. Such lipids are often introduced late in synthetic routes, enabling facile chemical modifications.

Rapid Formation of Non-canonical Phospholipid Membranes by Chemoselective Amide-Forming Ligations with Hydroxylamines

There has been increasing interest in methods to generate synthetic lipid membranes as key constituents of artificial cells or to develop new tools for remodeling membranes in living cells. However, the biosynthesis of phospholipids involves elaborate enzymatic pathways that are challenging to reconstitute in vitro. An alternative approach is to use chemical reactions to non-enzymatically generate natural or non-canonical phospholipids de novo. Previous reports have shown that synthetic lipid membranes can be formed in situ using various ligation chemistries, but these methods lack biocompatibility and/or suffer from slow kinetics at physiological pH. Thus, it would be valuable to develop chemoselective strategies for synthesizing phospholipids from water-soluble precursors that are compatible with synthetic or living cells Here, we demonstrate that amide-forming ligations between lipid precursors bearing hydroxylamines and α-ketoacids (KAs) or potassium acyltrifluoroborates (KATs) can be used to prepare non-canonical phospholipids at physiological pH conditions. The generated amide-linked phospholipids spontaneously self-assemble into cell-like micron-sized vesicles similar to natural phospholipid membranes. We show that lipid synthesis using KAT ligation proceeds extremely rapidly, and the high selectivity and biocompatibility of the approach facilitates the in situ synthesis of phospholipids and associated membranes in living cells.

Functional modulation of lysophosphatidic acid type 2 G-protein coupled receptor facilitates alveolar bone formation

Lipid biosynthesis is recently studied its functions in a range of cellular physiology including differentiation and regeneration. However, it still remains to be elucidated in its precise function. To reveal this, we evaluated the roles of lysophosphatidic acid (LPA) signaling in alveolar bone formation using the LPA type 2 receptor (LPAR2) antagonist AMG-35 (Amgen Compound 35) using tooth loss without periodontal disease model which would be caused by trauma and usually requires a dental implant to restore masticatory function. In this study, in vitro cell culture experiments in osteoblasts and periodontal ligament fibroblasts revealed cell type-specific responses, with AMG-35 modulating osteogenic differentiation in osteoblasts in vitro. To confirm the in vivo results, we employed a mouse model of tooth loss without periodontal disease. Five to 10 days after tooth extraction, AMG-35 facilitated bone formation in the tooth root socket as measured by immunohistochemistry for differentiation markers KI67, Osteocalcin, Periostin, RUNX2, transforming growth factor beta 1 (TGF-β1) and SMAD2/3. The increased expression and the localization of these proteins suggest that AMG-35 elicits osteoblast differentiation through TGF-β1 and SMAD2/3 signaling. These results indicate that LPAR2/TGF-β1/SMAD2/3 represents a new signaling pathway in alveolar bone formation and that local application of AMG-35 in traumatic tooth loss can be used to facilitate bone regeneration and healing for further clinical treatment.

Structural and Mechanical Response of Two-Component Photoswitchable Lipid Bilayer Vesicles

Optical control of phospholipids is an attractive option for the rapid, reversible, and tunable manipulation of membrane structure and dynamics. Azo-PC, a lipid with an azobenzene group within one acyl chain, undergoes a light-induced trans-to-cis isomerization and thus arises as a powerful tool for manipulating lipid order and dynamics. Here, we report on vesicle-scale micropipette measurements and atomistic simulations to probe the elastic stretching modulus, water permeability, toughness, thickness, and membrane area upon isomerization. We investigated both dynamics and steady-state properties. In pure azo-PC membranes, we found that the molecular area in trans was 16% smaller than that in cis, the membrane's stretching modulus kA was 2.5 ± 0.3 times greater, and the water permeability PW was 3.5 ± 0.5 times smaller. We also studied mixtures of azo-PC with the miscible, unsaturated lipid DOPC. Atomistic molecular dynamics simulations show how the membrane thickness, chain order, and correlations across membrane leaflets explain the experimental data. Together, these data show how one rotating bond changes the molecular- and membrane-scale properties. These results will be useful for photopharmacology and for developing new materials whose permeability, elasticity, and toughness may be switched on demand.

Current Status and Future Strategies for Advancing Functional Circuit Mapping In Vivo

The human brain represents one of the most complex biological systems, containing billions of neurons interconnected through trillions of synapses. Inherent to the brain is a biochemical complexity involving ions, signaling molecules, and peptides that regulate neuronal activity and allow for short- and long-term adaptations. Large-scale and noninvasive imaging techniques, such as fMRI and EEG, have highlighted brain regions involved in specific functions and visualized connections between different brain areas. A major shortcoming, however, is the need for more information on specific cell types and neurotransmitters involved, as well as poor spatial and temporal resolution. Recent technologies have been advanced for neuronal circuit mapping and implemented in behaving model organisms to address this. Here, we highlight strategies for targeting specific neuronal subtypes, identifying, and releasing signaling molecules, controlling gene expression, and monitoring neuronal circuits in real-time in vivo Combined, these approaches allow us to establish direct causal links from genes and molecules to the systems level and ultimately to cognitive processes.

Photo-Lipids: Light-Sensitive Nano-Switches to Control Membrane Properties

Biological membranes are described as a complex mixture of lipids and proteins organized according to thermodynamic principles. This chemical and spatial complexity can lead to specialized functional membrane domains enriched with specific lipids and proteins. The interaction between lipids and proteins restricts their lateral diffusion and range of motion, thus altering their function. One approach to investigating these membrane properties is to use chemically accessible probes. In particular, photo-lipids, which contain a light-sensitive azobenzene moiety that changes its configuration from trans- to cis- upon light irradiation, have recently gained popularity for modifying membrane properties. These azobenzene-derived lipids serve as nanotools for manipulating lipid membranes in vitro and in vivo. Here, we will discuss the use of these compounds in artificial and biological membranes as well as their application in drug delivery. We will focus mainly on changes in the membrane's physical properties as well as lipid membrane domains in phase-separated liquid-ordered/liquid-disordered bilayers driven by light, and how these changes in membrane physical properties alter transmembrane protein function.

Concise Synthesis of Glycerophospholipids

Glycerophospholipids are major components of cellular membranes and provide important signaling molecules. Besides shaping membrane properties, some bind to specific receptors to activate biological pathways. Untangling the roles of individual glycerophospholipids requires clearly defined molecular species, a challenge that can be best addressed through chemical synthesis. However, glycerophospholipid syntheses are often lengthy due to the contrasting polarities found within these lipids. We now report a general strategy to quickly access glycerophospholipids via opening of a phosphate triester epoxide with carboxylic acids catalyzed by Jacobsen's Co(salen) complex. We show that this method can be applied to a variety of commercially available fatty acids, photoswitchable fatty acids, and other carboxylic acids to provide the corresponding glycerophosphate derivatives.

Optical control of neuronal activities with photoswitchable nanovesicles

Precise modulation of neuronal activity by neuroactive molecules is essential for understanding brain circuits and behavior. However, tools for highly controllable molecular release are lacking. Here, we developed a photoswitchable nanovesicle with azobenzene-containing phosphatidylcholine (azo-PC), coined 'azosome', for neuromodulation. Irradiation with 365 nm light triggers the trans-to-cis isomerization of azo-PC, resulting in a disordered lipid bilayer with decreased thickness and cargo release. Irradiation with 455 nm light induces reverse isomerization and switches the release off. Real-time fluorescence imaging shows controllable and repeatable cargo release within seconds (< 3 s). Importantly, we demonstrate that SKF-81297, a dopamine D1-receptor agonist, can be repeatedly released from the azosome to activate cultures of primary striatal neurons. Azosome shows promise for precise optical control over the molecular release and can be a valuable tool for molecular neuroscience studies.

Optical control of neuronal activities with photoswitchable nanovesicles

Precise modulation of neuronal activity by neuroactive molecules is essential for understanding brain circuits and behavior. However, tools for highly controllable molecular release are lacking. Here, we developed a photoswitchable nanovesicle with azobenzene-containing phosphatidylcholine (azo-PC), coined 'azosome', for neuromodulation. Irradiation with 365 nm light triggers the trans-to-cis isomerization of azo-PC, resulting in a disordered lipid bilayer with decreased thickness and cargo release. Irradiation with 455 nm light induces reverse isomerization and switches the release off. Real-time fluorescence imaging shows controllable and repeatable cargo release within seconds (< 3 s). Importantly, we demonstrate that SKF-81297, a dopamine D1-receptor agonist, can be repeatedly released from the azosome to activate cultures of primary striatal neurons. Azosome shows promise for precise optical control over the molecular release and can be a valuable tool for molecular neuroscience studies.

Lipid mimetics: A versatile toolbox for lipid biology and beyond

Being the principal component of biological membranes lipids are essential building blocks of life. Given their huge biological importance, the investigation of lipids, their properties, interactions and metabolic pathways is of prime importance for the fundamental understanding of living cells and organisms as well as the emergence of diseases. Different strategies have been applied to investigate lipid-mediated biological processes, one of them being the use of lipid mimetics. They structurally resemble their natural counterparts but are equipped with functionality that can be used to probe or manipulate lipid-mediated biological processes and biomembranes. Lipid mimetics therefore constitute an indispensable toolbox for lipid biology and membrane research but also beyond for potential applications in medicine or synthetic biology. Herein, we highlight recent advances in the development and application of lipid-mimicking compounds.

Imaging and Editing the Phospholipidome

Membranes are multifunctional supramolecular assemblies that encapsulate our cells and the organelles within them. Glycerophospholipids are the most abundant component of membranes. They make up the majority of the lipid bilayer and play both structural and functional roles. Each organelle has a different phospholipid composition critical for its function that results from dynamic interplay and regulation of numerous lipid-metabolizing enzymes and lipid transporters. Because lipid structures and localizations are not directly genetically encoded, chemistry has much to offer to the world of lipid biology in the form of precision tools for visualizing lipid localization and abundance, manipulating lipid composition, and in general decoding the functions of lipids in cells.In this Account, we provide an overview of our recent efforts in this space focused on two overarching and complementary goals: imaging and editing the phospholipidome. On the imaging front, we have harnessed the power of bioorthogonal chemistry to develop fluorescent reporters of specific lipid pathways. Substantial efforts have centered on phospholipase D (PLD) signaling, which generates the humble lipid phosphatidic acid (PA) that acts variably as a biosynthetic intermediate and signaling agent. Though PLD is a hydrolase that generates PA from abundant phosphatidylcholine (PC) lipids, we have exploited its transphosphatidylation activity with exogenous clickable alcohols followed by bioorthogonal tagging to generate fluorescent lipid reporters of PLD signaling in a set of methods termed IMPACT.IMPACT and its variants have facilitated many biological discoveries. Using the rapid and fluorogenic tetrazine ligation, it has revealed the spatiotemporal dynamics of disease-relevant G protein-coupled receptor signaling and interorganelle lipid transport. IMPACT using diazirine photo-cross-linkers has enabled identification of lipid-protein interactions relevant to alcohol-related diseases. Varying the alcohol reporter can allow for organelle-selective labeling, and varying the bioorthogonal detection reagent can afford super-resolution lipid imaging via expansion microscopy. Combination of IMPACT with genome-wide CRISPR screening has revealed genes that regulate physiological PLD signaling.PLD enzymes themselves can also act as tools for precision editing of the phospholipid content of membranes. An optogenetic PLD for conditional blue-light-stimulated synthesis of PA on defined organelle compartments led to the discovery of the role of organelle-specific pools of PA in regulating oncogenic Hippo signaling. Directed enzyme evolution of PLD, enabled by IMPACT, has yielded highly active superPLDs with broad substrate tolerance and an ability to edit membrane phospholipid content and synthesize designer phospholipids in vitro. Finally, azobenzene-containing PA analogues represent an alternative, all-chemical strategy for light-mediated control of PA signaling.Collectively, the strategies described here summarize our progress to date in tackling the challenge of assigning precise functions to defined pools of phospholipids in cells. They also point to new challenges and directions for future study, including extension of imaging and membrane editing tools to other classes of lipids. We envision that continued application of bioorthogonal chemistry, optogenetics, and directed evolution will yield new tools and discoveries to interrogate the phospholipidome and reveal new mechanisms regulating phospholipid homeostasis and roles for phospholipids in cell signaling.

Photoswitchable Isoprenoid Lipids Enable Optical Control of Peptide Lipidation

Photoswitchable lipids have emerged as attractive tools for the optical control of lipid bioactivity, metabolism, and biophysical properties. Their design is typically based on the incorporation of an azobenzene photoswitch into the hydrophobic lipid tail, which can be switched between its trans- and cis-form using two different wavelengths of light. While glycero- and sphingolipids have been successfully designed to be photoswitchable, isoprenoid lipids have not yet been investigated. Herein, we describe the development of photoswitchable analogs of an isoprenoid lipid and systematically assess their potential for the optical control of various steps in the isoprenylation processing pathway of CaaX proteins in Saccharomyces cerevisiae. One photoswitchable analog of farnesyl diphosphate (AzoFPP-1) allowed effective optical control of substrate prenylation by farnesyltransferase. The subsequent steps of isoprenylation processing (proteolysis by either Ste24 or Rce1 and carboxyl methylation by Ste14) were less affected by photoisomerization of the group introduced into the lipid moiety of the substrate a-factor, a mating pheromone from yeast. We assessed both proteolysis and methylation of the a-factor analogs in vitro and the bioactivity of a fully processed a-factor analog containing the photoswitch, exogenously added to cognate yeast cells. Combined, these data describe the first successful conversion of an isoprenoid lipid into a photolipid and suggest the utility of this approach for the optical control of protein prenylation.

Caged-carvedilol as a new tool for visible-light photopharmacology of β-adrenoceptors in native tissues

Adrenoceptors are G protein-coupled receptors involved in a large variety of physiological processes, also under pathological conditions. This is due in large part to their ubiquitous expression in the body exerting numerous essential functions. Therefore, the possibility to control their activity with high spatial and temporal precision would constitute a valuable research tool. In this study, we present a caged version of the approved non-selective β-adrenoceptor antagonist carvedilol, synthesized by alkylation of its secondary amine with a coumarin derivative. Introducing this photo-removable group abolished carvedilol physiological effects in cell cultures, mouse isolated perfused hearts and living zebrafish larvae. Only after visible light application, carvedilol was released and the different physiological systems were pharmacologically modulated in a similar manner as the control drug. This research provides a new photopharmacological tool for a wide range of research applications that may help in the development of future precise therapies.

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We report a diffusible caged antagonist based on the beta blocker carvedilol (C-C)

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Carvedilol release from C-C is produced by light on the visible range (405 nm)

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Light-dependent effects are assessed in cells, mice hearts, and zebrafish larvae

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Physiological processes can be regulated by C-C and light (heart rate and behavior)

Photoswitchable Serotonins for Optical Control of the 5-HT2A Receptor

Serotonin receptors play central roles in neuromodulation and are critical drug targets for psychiatric disorders. Optical control of serotonin receptor subtypes has the potential to greatly enhance our understanding of the spatiotemporal dynamics of receptor function. While other neuromodulatory receptors have been successfully rendered photoswitchable, reversible photocontrol of serotonin receptors has not been achieved, representing a major gap in GPCR photopharmacology. Herein, we develop the first tools that allow for such control. Azo5HT-2 shows light-dependent 5-HT_2A R agonism, with greater activity in the cis-form. Based on docking and test compound analysis, we also develop photoswitchable orthogonal, remotely-tethered ligands (PORTLs). These BG-Azo5HTs provide rapid, reversible, and repeatable optical control following conjugation to SNAP-tagged 5-HT_2A R. Overall, this study provides a foundation for the broad extension of photopharmacology to the serotonin receptor family.

Click chemistry and optogenetic approaches to visualize and manipulate phosphatidic acid signaling

The simple structure of phosphatidic acid (PA) belies its complex biological functions as both a key phospholipid biosynthetic intermediate and a potent signaling molecule. In the latter role, PA controls processes including vesicle trafficking, actin dynamics, cell growth, and migration. However, experimental methods to decode the pleiotropy of PA are sorely lacking. Because PA metabolism and trafficking are rapid, approaches to accurately visualize and manipulate its levels require high spatiotemporal precision. Here, we describe recent efforts to create a suite of chemical tools that enable imaging and perturbation of PA signaling. First, we describe techniques to visualize PA production by phospholipase D (PLD) enzymes, which are major producers of PA, called Imaging Phospholipase D Activity with Clickable Alcohols via Transphosphatidylation (IMPACT). IMPACT harnesses the ability of endogenous PLD enzymes to accept bioorthogonally tagged alcohols in transphosphatidylation reactions to generate functionalized reporter lipids that are subsequently fluorescently tagged via click chemistry. Second, we describe two light-controlled approaches for precisely manipulating PA signaling. Optogenetic PLDs use light-mediated heterodimerization to recruit a bacterial PLD to desired organelle membranes, and photoswitchable PA analogs contain azobenzene photoswitches in their acyl tails, enabling molecular shape and bioactivity to be controlled by light. We highlight select applications of these tools for studying GPCR-Gq signaling, discovering regulators of PLD signaling, tracking intracellular lipid transport pathways, and elucidating new oncogenic signaling roles for PA. We envision that these chemical tools hold promise for revealing many new insights into lipid signaling pathways.

A system for artificial light signal transduction via molecular translocation in a lipid membrane

Light signal transduction pathways are central components of the mechanisms that regulate plant development, in which photoreceptors receive light and participate in light signal transduction. Chemical systems can be designed...

Optical Control of Glycerolipids and Sphingolipids

Glycerolipids, sphingolipids, and sterols are the three major classes of membrane lipids. Both glycerolipids and sphingolipids are comprised of combinations of polar headgroups and fatty acid tails. The fatty acid tail can be chemically modified with an azobenzene photoswitch giving rise to photoswitchable lipids. This approach has yielded a number of photopharmacological tools that allow for the control various of aspects of lipid assembly, metabolism, and physiology with light.

Rational Remodeling of Atypical Scaffolds for the Design of Photoswitchable Cannabinoid Receptor Tools

Azobenzene-embedded photoswitchable ligands are the widely used chemical tools in photopharmacological studies. Current approaches to azobenzene introduction rely mainly on the isosteric replacement of typical azologable groups. However, atypical scaffolds may offer more opportunities for photoswitch remodeling, which are chemically in an overwhelming majority. Herein, we investigate the rational remodeling of atypical scaffolds for azobenzene introduction, as exemplified in the development of photoswitchable ligands for the cannabinoid receptor 2 (CB2). Based on the analysis of residue-type clusters surrounding the binding pocket, we conclude that among the three representative atypical arms of the CB2 antagonist, AM10257, the adamantyl arm is the most appropriate for azobenzene remodeling. The optimizing spacer length and attachment position revealed AzoLig 9 with excellent thermal bistability, decent photopharmacological switchability between its two configurations, and high subtype selectivity. This structure-guided approach gave new impetus in the extension of new chemical spaces for tool customization for increasingly diversified photo-pharmacological studies and beyond.

Optical Control of Phosphatidic Acid Signaling

Phosphatidic acids (PAs) are glycerophospholipids that regulate key cell signaling pathways governing cell growth and proliferation, including the mTOR and Hippo pathways. Their acyl chains vary in tail length and degree of saturation, leading to marked differences in the signaling functions of different PA species. For example, in mTOR signaling, saturated forms of PA are inhibitory, whereas unsaturated forms are activating. To enable rapid control over PA signaling, we describe here the development of photoswitchable analogues of PA, termed AzoPA and dAzoPA, that contain azobenzene groups in one or both lipid tails, respectively. These photolipids enable optical control of their tail structure and can be reversibly switched between a straight trans form and a relatively bent cis form. We found that cis-dAzoPA selectively activates mTOR signaling, mimicking the bioactivity of unsaturated forms of PA. Further, in the context of Hippo signaling, whose growth-suppressing activity is blocked by PA, we found that the cis forms of both AzoPA and dAzoPA selectively inhibit this pathway. Collectively, these photoswitchable PA analogues enable optical control of mTOR and Hippo signaling, and we envision future applications of these probes to dissect the pleiotropic effects of physiological and pathological PA signaling.

A Photohormone for Light-Dependent Control of PPARα in Live Cells

Photopharmacology enables the optical control of several biochemical processes using small-molecule photoswitches that exhibit different bioactivities in their cis- and trans-conformations. Such tool compounds allow for high spatiotemporal control of biological signaling, and the approach also holds promise for the development of drug molecules that can be locally activated to reduce target-mediated adverse effects. Herein, we present the expansion of the photopharmacological arsenal to two new members of the peroxisome proliferator-activated receptor (PPAR) family, PPARα and PPARδ. We have developed a set of highly potent PPARα and PPARδ targeting photohormones derived from the weak pan-PPAR agonist GL479 that can be deactivated by light. The photohormone 6 selectively activated PPARα in its trans-conformation with high selectivity over the related PPAR subtypes and was used in live cells to switch PPARα activity on and off in a light- and time-dependent fashion.

A Photosensitive Polymeric Carrier with a Renewable Singlet Oxygen Reservoir Regulated by Two NIR Beams for Enhanced Antitumor Phototherapy

Photodynamic therapy (PDT), which utilizes photosensitizer to convert molecular oxygen into singlet oxygen (¹ O₂ ) upon laser irradiation to ablate tumors, will exacerbate the already oxygen shortage of most solid tumors and is thus self-limiting. Herein, a sophisticated photosensitive polymeric material (An-NP) that allows sustained ¹ O₂ generation and sufficient oxygen supply during the entire phototherapy is engineered by alternatively applying PDT and photothermal therapy (PTT) controlled by two NIR laser beams. In addition to a photosensitizer that generates ¹ O₂ , An-NP consists of two other key components: a molecularly designed anthracene derivative capable of trapping/releasing ¹ O₂ with superior reversibility and a dye J-aggregate with superb photothermal performance. Thus, in 655 nm laser-triggered PDT process, An-NP generates abundant ¹ O₂ with extra ¹ O₂ being trapped via the conversion into EPO-NP; while in the subsequent 785 nm laser-driven PTT process, the converted EPO-NP undergoes thermolysis to liberate the captured ¹ O₂ and regenerates An-NP. The intratumoral oxygen level can be replenished during the PTT cycle for the next round of PDT to generate ¹ O₂ . The working principle and phototherapy efficacy are preliminarily demonstrated in living cells and tumor-bearing mice, respectively.

Short Photoswitchable Ceramides Enable Optical Control of Apoptosis

We report short ceramide analogs that can be activated with light and further functionalized using azide-alkyne click chemistry. These molecules, termed scaCers, exhibit increased cell permeability compared to their long-chain analogs as demonstrated using mass spectrometry and imaging. Notably, scaCers enable optical control of apoptosis, which is not observed with long-chain variants. Additionally, they function as photoswitchable substrates for sphingomyelin synthase 2 (SMS2), exhibiting inverted light-dependence compared to their extended analogs.

Reversible spatial and temporal control of lipid signaling

Herein, we introduce versatile molecular tools that enable specific delivery and visualization of photoswitchable lipids at cellular membranes, namely at the plasma membrane and internal membranes. These molecules were prepared by tethering ortho-nitrobenzyl-based fluorescent cages with a signaling lipid bearing an azobenzene photoswitch. They permit two sequential photocontrolled reactions, which are uncaging of a lipid analogue and then its repeated activation and deactivation. We used these molecules to activate GPR40 receptor transiently expressed in HeLa cells and demonstrated downstream modulation of intracellular Ca2+ levels.