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Isotonitazene belongs to a potent class of μ‐opioid receptor (μOR) ligands, known as nitazenes. The lack of knowledge surrounding this agonist and others in its class has sparked thorough re‐investigations. To aid in these investigations, the purportedly covalent yet underexplored nitazene BIT was biochemically re‐evaluated in this work, along with a newly synthesized analogue, Iso‐BIT. Moreover, in the pursuit of understanding the mechanism, function and interactions of the μOR, this study involved developing photoswitchable nitazene derivatives as potential probe molecules. Converting known ligands into azo‐containing photoswitchable derivatives offers the opportunity to modulate ligand structure with light, allowing for photocontrol of compound activity. While photocontrol of μOR activity could not be entirely achieved, photophysical evaluation of these 2‐benzimidazole azo‐arenes revealed a novel photoswitch scaffold that responds to visible light. Furthermore, azo‐containing 2 e and 3 e emerged as promising nitazene derivatives that were able to form an exceptionally high fraction of covalent‐ligand receptor complexes with wild‐type μOR at physiological pH. [ABSTRACT FROM AUTHOR]

Photoremovable protecting groups (PPGs) releasable by two‐photon excitation (2PE) provide spatio‐temporal control over the photoactivation of biological effectors to study biological systems. We synthesized four derivatives of the (8‐cyano‐7‐hydroxyquinolin‐2‐yl)methyl (CyHQ) chromophore by functionalization of position C4 to generate four different derivatives (MeO‐CyHQ, Mor‐CyHQ, pTol‐CyHQ, and TMP‐CyHQ) for studying the release of tertiary amines via 2PE. Sulpiride, an anti‐dopaminergic drug, was selected as a model substrate. All probes had excellent properties for use in biological settings, including high quantum yield (Φu), hydrolytic stability, and good aqueous solubility in simulated physiological buffer. The TMP‐CyHQ probe enhanced the two‐photon uncaging action cross‐section (δu) 8‐fold (2.64 GM) compared to the parent CyHQ‐sulpiride. The optimized PPG was used to mediate the photoactivation of various biological effectors containing the tertiary amine functionality (tamoxifen, 4‐hydroxytamoxifen, yohimbine) using 2PE. All constructs showed excellent efficiency with δu ranging from 1.21 to 2.42 GM and moderate to excellent yields of tertiary amines released. [ABSTRACT FROM AUTHOR]

The TAM kinase family arises as a promising therapeutic target for cancer therapy, as well as auto‐immune and viral diseases. In this study, we report the first photoactivatable caged inhibitors of Tyro3 and Mer. This strategy enables spatial and temporal control of the biological activity of the inhibitor upon irradiation with UV light. We describe the design, synthesis, photocleavage properties, and inhibitory activities of four Tyro3 and Mer photoactivatable small molecules. The proof of concept on the TAM kinase family was achieved in vitro, since irradiation by UV light restored the full inhibitory activity of two prodrugs. [ABSTRACT FROM AUTHOR]

We developed a method to control gene activation and base editing in mammalian cells and zebrafish embryos via photochemically activated, caged guide RNAs. Four evenly distributed, caged nucleobases are installed in the 5'‐protospacer region of the gRNA to block interaction between the dCas9:gRNA complex and the dsDNA target. Upon light activation, gRNA:dsDNA hybridization is restored and catalytically dead Cas9‐based CRISPR activation or base editing is achieved. Caged gRNAs are customizable in design, offer spatiotemporal control of transcription activation and base editing in both mammalian cells and zebrafish embryos, and preserve the ability to form dCas9:gRNA complexes for enhanced gRNA stability. We hereby offer a versatile tool for conditional control of interactions between dCas9‐based regulators with their programmed genomic loci, thereby facilitating parsing of spatiotemporally complex genetic events, such as transcription regulation and single‐base mutagenesis. [ABSTRACT FROM AUTHOR]

Light activation is an effective way to impart spatiotemporal control over oligonucleotide probes that are widely applied for gene expression regulation and target function investigation. Among the major oligonucleotide caging strategies, cyclization with a photocleavable linker is an elegant design, which affords both atom efficiency and stability in many biological environments. Here, we introduce an improved protocol for circular oligonucleotide synthesis requiring only one round of HPLC purification. With a series of poly‐U oligonucleotide strands of different sizes and backbone modifications, the pre‐photolysis caging stability and post‐photolysis target binding affinity were studied through a denaturing gel assay and melting temperature measurements. A 14 U 2'‐OMe RNA probe was selected, with strong potential application in transcriptome in vivo analysis (TIVA) for mRNA isolation. [ABSTRACT FROM AUTHOR]

Many of the major challenges associated with drug delivery can potentially be addressed by linking drug action to light irradiation. These challenges include the spacing, timing and amount of a drug's activity. Once a drug's activity is linked to light, this activity can be more easily manipulated, because light itself is easy to manipulate. One of the main issues that light control can address is off‐target toxicity. This has the potential to be limited if drugs are activated only in target tissues using light. For drugs that are needed at varying concentrations through the day, varying light has the potential to temporally modulate drug release. Because of these and other advantages, a range of mechanisms for using light to manipulate drug activity has been developed, including photocleavage control, photoconformational control, photothermal control and photodegradation control. These major themes of light control will be described in this minireview, and illustrated with examples. In addition, the issue of tissue light permittivity, arguably the major challenge for the discipline, will be described and analyzed. [ABSTRACT FROM AUTHOR]

Ifenprodil is an important negative allosteric modulator of the N‐methyl‐D‐aspartate (NMDA) receptor. We have synthesized caged and photoswitchable derivatives of this small molecule drug. Caged ifenprodil was biologically inert before photolysis, and UV irradiation efficiently released the drug allowing selective inhibition of GluN2B‐containing NMDA receptors. Azobenzene‐modified ifenprodil, on the other hand, is inert in both its trans and cis configurations, although in silico modeling predicted the trans form to be able to bind to the receptor. The disparity in effectiveness between the two compounds reflects, in part, the inherent ability of each method in manipulating the binding properties of drugs. With appropriate structure‐activity relationship uncaging enables binary control of effector binding, whereas photoswitching using freely diffusible chromophores shifts the dose‐response curve of drug‐receptor interaction. Our data suggest that the efficacy of pharmacophores having a confined binding site such as ifenprodil can be controlled more easily by uncaging in comparison to photoswitching. [ABSTRACT FROM AUTHOR]

Photopharmacological tools enable the precise spatiotemporal control of small molecule drugs. Amongst them, caged compounds incorporate a photolabile moiety which is released under illumination, thus liberating the active molecule. Caging groups have long been known and many chemical scaffolds have already been used in different applications. However, most of the initial examples are cleaved with UV light, which suffers from low tissue permeability and cell damage. Recently, caging groups that are released under visible light have been reported, which expand their utility. In this review, we outline the chemical strategies that have been used to increase the absorption wavelengths; we compare their photophysical properties, discuss their synthetic accessibility, and exemplify some of their biological applications. [ABSTRACT FROM AUTHOR]

Photopharmacology, which uses chemical photoswitches for the optical manipulation of biological process, holds immense potential for neuroscience and clinical medicine due to its high specificity, fast response, and versatility. However, enabling photopharmacology in living subjects has been an arduous undertaking mainly because of limitations of the available tools. Conventional approaches to drug delivery and photostimulation involve the use of bulky, rigid, and tethered implants in the form of metal cannulas and optical fibers. These prevent highly precise, spatially matching stimulation with drugs and light, aggravates adverse tissue responses, and causes undue stress in the freely‐moving subject. Recent advances in materials science and device engineering have led to the development of miniaturized, standalone multimodal implants referred to as "optofluidic" devices, which allow wireless delivery of both light and drugs. Herein, we review state‐of‐the‐art wireless optofluidic systems, which can open up new horizons for in vivo photopharmacology, and discuss future directions for further technology developments. [ABSTRACT FROM AUTHOR]

Considerable effort has previously been invested in a light‐controlled inhibition of the enzyme acetylcholinesterase (AChE). We found that a novel azobenzene‐based bistacrine AChE inhibitor switched faster than the known dithienylethene based bistacrine and inverted the photo‐controlled interactions of the photoisomers compared to its dithienylethene congener. Furthermore, we have optimized a previously described light‐controlled tacrine‐based AChE inhibitor. Isomerization upon irradiation with UV light of the novel inhibitor was observed in aqueous medium and showed no fatigue over several cycles. The cis‐enriched form showed an 8.4‐fold higher inhibition of hAChE compared with its trans‐enriched form and was about 30‐fold more active than the reference compound tacrine with a single‐digit nanomolar inhibition. We went beyond proof‐of‐concept to discover photoswitchable AChE inhibitors with pharmacologically desirable nanomolar inhibition, "cis‐on" effect, and pronounces differences between the photoisomers. [ABSTRACT FROM AUTHOR]

Recently, photochromic derivatives of nucleobases have drawn attention for regulating oligonucleotide hybridization with light for photopharmacological applications. The nucleobase moiety provides attractive interaction for hybridization, whereas the photochromic moiety can alter the interaction upon irradiation due to conformational changes. Herein we report the synthesis of 2‐phenyldiazenyl‐substituted 2'‐deoxyadenosine (dAAzo) and 2'‐deoxyguanosine (dGAzo) and investigate their influence in a DNA context by UV/Vis absorption, fluorescence and CD spectroscopies. For comparison, the literature‐known azobenzene C‐nucleoside DNAzo was used as a reference system. It could be shown that photochromic purines improve overall hybridization affinity compared to azobenzene C‐nucleosides. In particular, 2'‐deoxyadenosine analogue dAAzo increases melting temperatures by 7.5 °C in the favored trans state with 86 % of the switching efficiency of the reference system. [ABSTRACT FROM AUTHOR]

Herein, we present a comprehensive study of the photophysical properties of an ammonium‐tagged azobenzene in comparison to the unsubstituted compound in different solvents. It was shown that the thermal Z→E isomerization rate is decreased for the ammonium‐tagged azobenzene. Additionally, the rate is higher with increased permittivity of the solvent. The results have been supported by DFT computations. [ABSTRACT FROM AUTHOR]

We report on diarylethene (DAE)‐containing photoswitchable cell‐penetrating peptides (CPPs) capable of photocontrolled cell entry. We demonstrate in vitro that reversible photoisomerization of a DAE fragment in the backbones of non‐cytotoxic cyclic peptides influences their binding to cell membranes and subsequent CPP‐mediated cargo internalization. Benign red light can be used to activate cell entry of our compounds. We suggest that the observed differences in cell uptake of the two photoisomers are due to changes in the molecular flexibility achieved upon DAE photoisomerization. [ABSTRACT FROM AUTHOR]

Photo‐controlled affinity reagents seek to provide modular spatiotemporal control of bioactivity by conferring photo‐switchability of function on an affinity reagent scaffold. Herein we used Rosetta‐based computational methods to screen for sites on the Fynomer affinity reagent structure for attachment of photoswitchable cross‐linkers. Both established UV‐based cross‐linkers (azobenzene‐iodoacetamide (IAC)) and an azonium‐based efficient red‐light‐switchable cross‐linker, piperazino‐tetra‐ortho‐methoxy azobenzene (PIP), were then tested experimentally. Several sites compatible with Fynomer function were identified, including sites showing rapid (<10 s) red light (633 nm) modulation of function. Although a range of overall target binding affinities were observed, the degree of photo‐switchability of Fynomer function was generally small (

The underlying role that many kinases play in complex cellular pathways as well as disease remains unclear. To better understand the role that kinases play in both health and disease states, the use of light as an external stimulus to modulate kinase activity with high spatiotemporal resolution has gained increasing interest over the years. Herein we highlight the progress made towards the development of light‐responsive kinase enzymes and small molecule inhibitors. In these examples, photolabile caging groups and photoswitchable entities have been utilised to modulate either kinase activation or inhibition in a light‐controlled manner. [ABSTRACT FROM AUTHOR]

Keywords: drug activity; photoactivation; photocleavage; photopharmacology; toxicity EN drug activity photoactivation photocleavage photopharmacology toxicity 592 592 1 07/19/21 20210701 NES 210701 B The Front Cover b is a depiction of a major challenge for the light control of drug activity: Light (yellow) on the outside of the body must traverse skin and the interior of the body to reach the target (red), while being diminished and releasing heat with each centimetre it travels. Drug activity, photoactivation, photocleavage, photopharmacology, toxicity. [Extracted from the article]

Exposure to low-intensity radiation in the near-infrared (NIR) spectral region matching the optically transparent "phototherapeutic window" of biological tissues can be applied to directly populate spin-restricted excited states of light-responsive compounds. This unconventional and unprecedented approach is introduced herein as a new strategy to overcome some of the major unresolved problems observed in the rapidly emerging fields of photopharmacology and molecular photomedicine, where practical applications in living cells and organisms are still limited by undesired side reactions and insufficient light penetration. Water-soluble and biocompatible metal complexes with a significant degree of spin-orbit coupling were identified as target candidates for testing our new hypothesis. As a first example, a dark-stable manganese carbonyl complex acting as a visible-light-triggered CO-releasing molecule (Photo-CORM) is shown to be photoactivated by NIR radiation, although apparently no spectroscopically evident absorption bands are detectable in this low-energy region. This quite remarkable effect is ascribed to a strongly restricted, but obviously not completely forbidden optical population of the lowest triplet excited state manifold of the diamagnetic complex from the singlet ground state., Competing Interests: The authors declare no conflict of interest.