Photoswitchable Inhibitors of Microtubule Dynamics Optically Control Mitosis and Cell Death

Unraveling Solvent and Substituent Effects in the Photodynamics of Light-Dependent Microtubule Inhibitors for Cancer Phototherapy

In photopharmacology, molecular photoswitches enable light-controlled drug activities, offering precision in targeting biomolecular functions while minimizing side effects. Photostatins (PSTs) are photoswitchable analogs of combretastatin A-4 (CA4), designed to inhibit tubulin polymerization for cancer treatment. However, the influence of substituents and molecular environments on their photochemistry remains unclear. In this work, the cis-to-trans photodynamics of five PSTs (PST1 to PST5) in the vacuum and aqueous solution were simulated using the ab initio multiple spawning (AIMS) coupled with correlated multireference electronic structure calculations. Four distinct minima in the same conical intersection seam were discovered, serving as nonradiative decay channels. The aqueous environment slows photoisomerization and lowers its quantum yields and changes the structures near the conical intersection seam. Substituent position and electronegativity significantly impact the isomerization kinetics by altering energy gaps between MECIs and the S1 state at the Franck-Condon region. These findings provide useful insights into designing next-generation phototherapeutics for cancer.

Effects of binding partners on thermal reversion rates of photoswitchable molecules

The binding of photoswitchable molecules to partners forms the basis of many naturally occurring light-dependent signaling pathways and various photopharmacological and optogenetic tools. A critical parameter affecting the function of these molecules is the thermal half-life of the light state. Reports in the literature indicate that, in some cases, a binding partner can significantly influence the thermal half-life, while in other cases it has no effect. Here, we present a unifying framework for quantitatively analyzing the effects of binding partners on thermal reversion rates. We focus on photoswitchable protein/binder interactions involving LOV domains, photoactive yellow protein, and CBCR GAF domains with partners that bind either the light or the dark state of the photoswitchable domain. We show that the effect of a binding partner depends on the extent to which the transition state for reversion resembles the dark state or the light state. We quantify this resemblance with a ϕswitching value, where ϕswitching = 1 if the conformation of the part of the photoswitchable molecule that interacts with the binding partner closely resembles its dark state conformation and ϕswitching = 0 if it resembles its light state. In addition to providing information on the transition state for switching, this analysis can guide the design of photoswitchable systems that retain useful thermal half-lives in practice. The analysis also provides a basis for the use of simple kinetic measurements to determine effective changes in affinity even in complex milieu.

Conceptual expansion of photomedicine for spatiotemporal treatment methods

Photomedicine has evolved from basic phototherapy to a broad range of light-based technologies to achieve precise and minimally invasive therapeutic outcomes. Recent advances in light sources, photochemical reactions, and photoswitches have facilitated the development of light-activated methodologies for modulating biological processes. This review discusses the history of light therapy that leads to the emergence of a new field known as photopharmacology, mode of actions in photopharmacology such as photodynamic, photo-uncaging and photoswitchable methods, a few representative examples in photopharmacology, and a brief overview of its associated challenges. The current developments in photopharmacology hold great promise for the treatment of diseases such as cancer, with enhanced therapeutic precision, and minimal side effects. We foresee further expansion of photomedicine for novel approaches in precision medicine and healthcare, and unprecedented treatment methods.

Spatio-temporal control of mitosis using light via a Plk1 inhibitor caged for activity and cellular permeability

The ability to control the activity of kinases spatially and temporally is essential to elucidate the role of signalling pathways in development and physiology. Progress in this direction has been hampered by the lack of tools to manipulate kinase activity in a highly controlled manner in vivo. Here we report a strategy to modify BI2536, the well characterized inhibitor of the conserved and essential mitotic kinase Polo-like kinase 1 (Plk1). We introduce the same coumarin photolabile protecting group (PPG) at two positions of the inhibitor. At one position, the coumarin prevents the interaction with Plk1, at the second it masks an added carboxylic acid, important for cellular retention. Exposure to light results in removal of both PPGs, leading to the activation of the inhibitor and its trapping inside cells. We demonstrate the efficacy of the caged inhibitor in three-dimensional spheroid cultures: by uncaging it with a single light pulse, we can inhibit Plk1 and arrest cell division, a highly dynamic process, with spatio-temporal control. Our design can be applied to other small molecules, providing a solution to control their activity in living cells with unprecedented precision.

Precise photopharmacological eradication of metastatic tumor cells

Owing to their high efficacy, antimitotic chemotherapeutics are the mainstay for most cancer treatments. However, these drugs do not discriminate between tumor and healthy cells, thus show dose-limiting toxicity and severe adverse effects. To improve treatments, rendering chemotherapeutics tumor-cell specific is highly desirable. Although various strategies, such as targeted antibody-drug conjugates, aim to achieve this goal, the identification of a tumor-specific 'Achilles' heel' remains a challenge. Here, we followed an alternative approach, which does not rely on tumor-specific characteristics, but rather uses spatially confined illumination of the light-activatable microtubule inhibitor SBTubA4P to target its cytotoxic activity to tumor cells. We demonstrate that localized illumination of SBTubA4P allows for precise eradication of disseminated sarcoma cells in zebrafish xenografts without inducing systemic toxicity. In addition to the already-described light-dependent inhibition of microtubule dynamics by SBTubA4P, our data indicate that this molecule creates reactive oxygen species upon UV illumination, which significantly increases its cytotoxic effects. SBTubA4P is a valuable addition to the precision oncology toolbox, and zebrafish xenografts constitute a well-suited model to investigate photoactivatable compounds in vivo.

Cytoplasmic flow is a cell size sensor that scales anaphase

During early embryogenesis, fast mitotic cycles without interphase lead to a decrease in cell size, while scaling mechanisms must keep cellular structures proportional to cell size. For instance, as cells become smaller, if the position of nuclear envelope reformation (NER) did not adapt, NER would have to occur beyond the cell boundary. Here we found that NER position in anaphase scales with cell size via changes in chromosome motility, mediated by cytoplasmic flows that themselves scale with cell size. Flows are a consequence of friction between viscous cytoplasm and bulky cargo transported by dynein on astral microtubules. As an emerging property, confinement in cells of different sizes yields scaling of cytoplasmic flows. Thus, flows behave like a cell geometry sensor: astral microtubules approach the boundary causing flow velocity changes, which then affect the velocity of chromosome separation, thus scaling NER.

Engineering the novel azobenzene-based molecular photoswitches for suppressing bacterial infection through dynamic regulation of biofilm formation

BACKGROUND

Bacterial biofilm is a strong fortress for bacteria to resist harsh external environments, which can enhance their tolerance and exacerbate the drug/pesticide resistance risk. Currently, photopharmacology provides an advanced approach via precise spatiotemporal control for regulating biological activities by light-controlling the molecular configurations, thereby having enormous potential in the development of drug/pesticides.

RESULTS

To further expand the photopharmacology application for discovering new antibiofilm agents, we prepared a series of light-controlled azo-active molecules and explored their photo isomerization, fatigue resistance, and anti-biofilm performance. Furthermore, their mechanisms of inhibiting biofilm formation were systematically investigated. Overall, designed azo-derivative A11 featured excellent anti-Xoo activity with an half-maximal effective concentration (EC50) value of 5.45 μg mL-1, and the EC50 value could be further elevated to 2.19 μg mL-1 after ultraviolet irradiation (converted as cis-configuration). The photo-switching behavior showed that A11 had outstanding anti-fatigue properties. An in-depth analysis of the action mechanism showed that A11 could effectively inhibit biofilm formation and the expression of relevant virulence factors. This performance could be dynamically regulated via loading with private light-switch property.

CONCLUSION

In this work, designed light-controlled azo molecules provide a new model for resisting bacterial infection via dynamic regulation of bacterial biofilm formation. © 2024 Society of Chemical Industry.

Chemo-optogenetic Dimerization Dissects Complex Biological Processes

Light offers superior control in terms of high temporal precision, high spatial precision, and non-invasiveness for the regulation of cellular functions. In recent years, chemical biologists have adopted chemo-optogenetic dimerization approaches, such as photo-triggered chemical inducers of dimerization (pCIDs), as a general tool for spatiotemporal regulation of cellular functions. Traditional chemo-optogenetic dimerization triggers either a single ON or a single OFF of cellular activity. However, more sophisticated approaches are introduced in recent years. These include the ability to turn ON and OFF using different wavelengths of light, tools enabling multi-layer control of cellular activities, and nanobody-tethered photodimerizers. These advancements not only shed light on the study of ubiquitously existing multi-functional proteins but also create new opportunities for investigating complex cellular activity networks.

Supramolecular Control of the Photoisomerization of a Coumarin-Based Photoswitch

The complex formation of the cationic stilbene-type photoswitch CP with the anionic macrocycles carboxylato-pillar[5]arene (WP5) and carboxylato-pillar[6]arene (WP6) has been investigated in aqueous solution by optical spectroscopic, NMR and isothermal calorimetric experiments and theoretical calculations. Subsequently, the photoisomerization reactions of the supramolecular complexes formed have been studied. CP consists of a 7-diethylamino-coumarin fluorophore and an N-methylpyridinium unit, which are connected via an ethene bridge. The trans isomer of CP is fluorescent, and its cis isomer is dark. The binding constants of the WP6 complexes of the two photoisomers of CP are larger by 2 orders of magnitude than those of the respective complexes with WP5, and trans-CP forms more stable complexes with the individual pillararenes than the cis isomer. As shown by NMR spectroscopic measurements and theoretical calculations, the two isomers of CP form external complexes with WP5 and inclusion complexes with WP6. On complexation with WP6, the quantum yields of both the trans-to-cis and cis-to-trans photoisomerization reactions of CP increase significantly, and the fluorescence quantum yield of trans-CP is also enhanced. These changes are due to the suppression of the TICT deactivation process, which is characteristic of 7-dialkylamino-coumarin derivatives.

Hemithioindigo-based histone deacetylase inhibitors induce a light-dependent anticancer effect

Photoswitchable molecules exhibit light-dependent biological activity which allow us to control the therapeutic effect of drugs with high precision. Such molecules could solve some of the limitations of anticancer drugs by providing a localised effect in the tumour. Histone deacetylase inhibitors (HDACis) constitute a promising drug class for oncology whose application is often limited by a lack of selectivity. Herein, we developed photoswitchable HDACis based on a hemithioindigo scaffold. We established synthetic routes to access them and determined the optimal conditions for isomerisation and their thermal stability. We then optimised their enzyme activity through three rounds of re-design to identify examples that are up to 6-fold more active under illumination than in the dark. We also confirmed that our best derivative reduces the viability of HeLa cells only under illumination. All in all, we disclose a series of derivatives containing a hemithioindigo moiety, which display a light-dependent effect on both HDAC inhibition and cancer cell viability.

A High-Quality Photoswitchable Probe that Selectively and Potently Regulates the Transcription Factor RORγ

Retinoic acid receptor-related orphan receptor γ (RORγ) is a nuclear hormone receptor with multiple biological functions in circadian clock regulation, inflammation, and immunity. Its cyclic temporal role in circadian rhythms, and cell-specific activity in the immune system, make it an intriguing target for spatially and temporally localised pharmacology. To create tools that can study RORγ biology with appropriate spatiotemporal resolution, we designed light-dependent inverse RORγ agonists by building azobenzene photoswitches into ligand consensus structures. Optimizations gave photoswitchable RORγ inhibitors combining a large degree of potency photocontrol, with remarkable on-target potency, and excellent selectivity over related off-target receptors. This still rare combination of performance features distinguishes them as high quality photopharmaceutical probes, which can now serve as high precision tools to study the spatial and dynamic intricacies of RORγ action in signaling and in inflammatory disorders.

A Photocaged Microtubule-Stabilising Epothilone Allows Spatiotemporal Control of Cytoskeletal Dynamics

The cytoskeleton is essential for spatial and temporal organisation of a wide range of cellular and tissue-level processes, such as proliferation, signalling, cargo transport, migration, morphogenesis, and neuronal development. Cytoskeleton research aims to study these processes by imaging, or by locally manipulating, the dynamics and organisation of cytoskeletal proteins with high spatiotemporal resolution: which matches the capabilities of optical methods. To date, no photoresponsive microtubule-stabilising tool has united all the features needed for a practical high-precision reagent: a low potency and biochemically stable non-illuminated state; then an efficient, rapid, and clean photoresponse that generates a high potency illuminated state; plus good solubility at suitable working concentrations; and efficient synthetic access. We now present CouEpo, a photocaged epothilone microtubule-stabilising reagent that combines these needs. Its potency increases approximately 100-fold upon irradiation by violet/blue light to reach low-nanomolar values, allowing efficient photocontrol of microtubule dynamics in live cells, and even the generation of cellular asymmetries in microtubule architecture and cell dynamics. CouEpo is thus a high-performance tool compound that can support high-precision research into many microtubule-associated processes, from biophysics to transport, cell motility, and neuronal physiology.

Effect of Leaving Centrosymmetric Character on Spectral Properties in Mono-, Bi-, and Triphotonic Absorption Spectroscopies

Numerical simulations of the absorption bands of photoswitch E-o-tetrafluoroazobenzene in DMSO solution under one-, two-, and three-photon absorption conditions combined with the analysis of the behavior of transition probability under distortion of planarity reveal many similarities between the mono- and triphoton spectroscopic behaviors with a two-photon spectrum being set apart. The position of the absorption peak for the studied nπ* and ππ* transitions appears shifted to lower energies (longer wavelengths) than the conventional estimate based on vertical excitation from the ground-state potential energy minimum.

Light-Activatable, Cell-Type Specific Labeling of the Nascent Proteome

Elucidating the mechanisms by which protein synthesis contributes to complex biological processes has remained a challenging endeavor. This is particularly true in the field of neuroscience, where multiple, tightly regulated periods of new protein synthesis in different cell-types are thought to facilitate intricate neurological functions, such as memory formation. Current methods for labeling the de novo proteome have lacked the spatial and temporal resolution to accurately discriminate these overlapping and often competing windows of mRNA translation. To address this technological limitation, here we describe a novel, light-inducible specific method for labeling newly synthesized proteins within a targeted cell-type.By developing Opto-ANL, a photocaged version of the nonendogenous amino acid azidonorleucine (ANL), we can selectively label newly synthesized proteins in specific cell-types through the targeted expression of a mutant methionyl-tRNA synthetase (L274G-MetRS). We demonstrate that Opto-ANL can be rapidly uncaged by UV light treatment in both cell culture and mouse brain slices, with Opto-ANL labeled proteins being able to be visualized via fluorescent noncanonical amino acid tagging. We also reveal that pretreatment with Opto-ANL not only allows for the period of de novo proteomic labeling to be tightly controlled, but also improves labeling efficiency compared to regular ANL. To demonstrate the potential applications of this novel technique, we use Opto-ANL to detect insulin-induced increases in protein synthesis and to label the excitatory neuronal de novo proteome in mouse brain slices. We believe that this application of photopharmacology will allow researchers to generate novel insights into how the translational landscape is altered across cell-types during complex neurological phenomena such as memory formation.

Azologs of the Fatty Acid Mimetic Drug Cinalukast Enable Light-Induced PPARα Activation

Photo-switchable nuclear receptor modulators ("photohormones") enable spatial and temporal control over transcription factor activity and are valuable precision tools for biological studies. We have developed a new photohormone chemotype by incorporating a light-switchable motif in the scaffold of a cinalukast-derived PPARα ligand and tuned light-controlled activity by systematic structural variation. An optimized photohormone exhibited PPARα agonism in its light-induced (Z)-configuration and strong selectivity over related lipid-activated transcription factors representing a valuable addition to the collection of light-controlled tools to study nuclear receptor activity.

Harnessing Light for G-Quadruplex Modulation: Dual Isomeric Effects of an Ortho-Fluoroazobenzene Derivative

G-quadruplexes (G4s) are important therapeutic and photopharmacological targets in cancer research. Small-molecule ligands targeting G4s offer a promising strategy to block DNA transactions and induce genetic instability in cancer cells. While numerous G4-ligands have been reported, relatively few examples exist of compounds whose G4-interactive binding properties can be modulated using light. Herein, we report the photophysical characterization of a novel ortho-fluoroazobenzene derivative, Py-Azo4F-3N, that undergoes reversible two-way isomerization upon visible light exposure. Using a combination of biophysical techniques, including affinity and selectivity assays, structural and computational analysis, and cytotoxicity experiments in cancer cell lines, we carefully characterized the G4-interactive binding properties of both isomers. We identify the trans isomer as the most promising form of interacting and stabilizing G4s, enhancing their ablation capability in cancer cells. Our research highlights the importance of light-responsive molecules in achieving precise control over G4 structures, demonstrating their potential in innovative anticancer strategies.

The cytotoxic natural compound erianin binds to colchicine site of β-tubulin and overcomes taxane resistance

Erianin, a natural compound derived from Dendrobium, has shown significant anticancer properties against a wide range of cancer cells. Despite the identification of multiple mechanisms of action for erianin, none of these mechanisms fully account for its broad-spectrum effect. In this study, we aimed to identify the cellular target and underlying mechanism responsible for the broad-spectrum antitumor effects of erianin. We found that erianin effectively inhibited tubulin polymerization in cancer cells and purified tubulin. Through competition binding assays and X-ray crystallography, it was revealed that erianin bound to the colchicine site of β-tubulin. Importantly, the X-ray crystal structure of the tubulin-erianin complex was solved, providing clear insight into the orientation and position of erianin in the colchicine-binding site. Erianin showed activity against paclitaxel-resistant cells, evidenced by G2/M cell cycle arrest, apoptosis-related PARP and Caspase-3 cleavage, and in vivo xenograft studies. The study concluded that erianin bound reversibly to the colchicine site of β-tubulin, inhibited tubulin polymerization, and displayed anticancer activity against paclitaxel-resistant cells, offering valuable insights for further exploration as potential anticancer agents.

A photo-SAR study of photoswitchable azobenzene tubulin-inhibiting antimitotics identifying a general method for near-quantitative photocontrol

Azobenzene analogues of the tubulin polymerisation inhibitor combretastatin A4 (PSTs) were previously developed to optically control microtubule dynamics in living systems, with subsecond response time and single-cell spatial precision, by reversible in situ photoswitching of their bioactivity with near-UV/visible light. First-generation PSTs were sufficiently potent and photoswitchable for use in live cells and embryos. However, the link between their seconds-scale and hours-scale bioactivity remained untested. Furthermore, the scope for modifications to tune their photo-structure-activity-relationship or expand their function was unknown. Here, we used large-field-of-view, long-term tandem photoswitching/microscopy to reveal the temporal onset of cytostatic effects. We then synthesised a panel of novel PSTs exploring structural variations that tune photoresponse wavelengths and lipophilicity, identifying promising blue-shifted analogues that are better-compatible with GFP/YFP imaging. Taken together, these results can guide new design and applications for photoswitchable microtubule inhibitors. We also identified tolerated sites for linkers to attach functional cargos; and we tested fluorophores, aiming at RET isomerisation or reporter probes. Instead we found that these antennas greatly enhance long-wavelength single-photon photoisomerisation, by an as-yet un-explored mechanism, that can now drive general progress towards near-quantitative long-wavelength photoswitching of photopharmaceuticals in living systems, with minimal molecular redesign and broad scope.

131I Induced In Vivo Proteolysis by Photoswitchable azoPROTAC Reinforces Internal Radiotherapy

Photopharmacology, incorporating photoswitches such as azobenezes into drugs, is an emerging therapeutic method to realize spatiotemporal control of pharmacological activity by light. However, most photoswitchable molecules are triggered by UV light with limited tissue penetration, which greatly restricts the in vivo application. Here, this study proves that 131I can trigger the trans-cis photoisomerization of a reported azobenezen incorporating PROTACs (azoPROTAC). With the presence of 50 µCi mL-1 131I, the azoPROTAC can effectively down-regulate BRD4 and c-Myc levels in 4T1 cells at a similar level as it does under light irradiation (405 nm, 60 mW cm-2). What's more, the degradation of BRD4 can further benefit the 131I-based radiotherapy. The in vivo experiment proves that intratumoral co-adminstration of 131I (300 µCi) and azoPROTC (25 mg kg-1) via hydrogel not only successfully induce protein degradation in 4T1 tumor bearing-mice but also efficiently inhibit tumor growth with enhanced radiotherapeutic effect and anti-tumor immunological effect. This is the first time that a radioisotope is successfully used as a trigger in photopharmacology in a mouse model. It believes that this study will benefit photopharmacology in deep tissue.

Regulation of microtubule dynamics and function in living cells via cucurbit[7]uril host-guest assembly

Living systems utilize sophisticated biochemical regulators and various signal transduction mechanisms to program bio-molecular assemblies and their associated functions. Creating synthetic assemblies that can replicate the functional and signal-responsive properties of these regulators, while also interfacing with biomolecules, holds significant interest within the realms of supramolecular chemistry and chemical biology. This pursuit not only aids in understanding the fundamental design principles of life but also introduces novel capabilities that contribute to the advancements in medical and therapeutic research. In this study, we present a cucurbit[7]uril (CB[7]) host-guest system designed to regulate the dynamics and functions of microtubules (MTs) in living cells. To establish communication between MTs and CB[7] and to reversibly control MT function through host-guest recognition, we synthesized a two-faced docetaxel-p-xylenediamine (Xyl-DTX) derivative. While Xyl-DTX effectively stabilized polymerized MTs, inducing MT bundling and reducing dynamics in GFP-α-tubulin expressing cells, we observed a significant reduction in its MT-targeted activity upon threading with CB[7]. Leveraging the reversible nature of the host-guest complexation, we strategically reactivated the MT stabilizing effect by programming the guest displacement reaction from the CB[7]·Xyl-DTX complex using a suitable chemical signal, namely a high-affinity guest. This host-guest switch was further integrated into various guest activation networks, enabling 'user-defined' regulatory control over MT function. For instance, we demonstrated programmable control over MT function through an optical signal by interfacing it with a photochemical guest activation network. Finally, we showcased the versatility of this supramolecular system in nanotechnology-based therapeutic approaches, where a self-assembled nanoparticle system was employed to trigger the MT-targeted therapeutic effect from the CB[7]·Xyl-DTX complex.

Photo-activated microtubule targeting drugs: Advancing therapies for colorectal cancer

Over the years immunotherapy has demonstrably improved the field of cancer treatment. However, achieving long-term survival for colorectal cancer (CRC) patients remains a significant unmet need. Combination immunotherapies incorporating targeted drugs like MEK or multi-kinase inhibitors have offered some palliative benefit. Nevertheless, substantial gaps remain in the current therapeutic armamentarium for CRC. In recent years, there has been a surge of interest in exploring novel treatment strategies, including the application of light-activated drugs in conjunction with optical devices. This approach holds promise for achieving localized and targeted delivery of cytotoxic agents, such as microtubule-targeting drugs, directly to cancerous cells within the colon.

Copper(II) Complexes with Isomeric Morpholine-Substituted 2-Formylpyridine Thiosemicarbazone Hybrids as Potential Anticancer Drugs Inhibiting Both Ribonucleotide Reductase and Tubulin Polymerization: The Morpholine Position Matters

The development of copper(II) thiosemicarbazone complexes as potential anticancer agents, possessing dual functionality as inhibitors of R2 ribonucleotide reductase (RNR) and tubulin polymerization by binding at the colchicine site, presents a promising avenue for enhancing therapeutic effectiveness. Herein, we describe the syntheses and physicochemical characterization of four isomeric proligands H2L3-H2L6, with the methylmorpholine substituent at pertinent positions of the pyridine ring, along with their corresponding Cu(II) complexes 3-6. Evidently, the position of the morpholine moiety and the copper(II) complex formation have marked effects on the in vitro antiproliferative activity in human uterine sarcoma MES-SA cells and the multidrug-resistant derivative MES-SA/Dx5 cells. Activity correlated strongly with quenching of the tyrosyl radical (Y•) of mouse R2 RNR protein, inhibition of RNR activity in the cancer cells, and inhibition of tubulin polymerization. Insights into the mechanism of antiproliferative activity, supported by experimental results and molecular modeling calculations, are presented.

Development of Parallel On-the-Fly Algorithm for Global Exploration of Conical Intersection Seam Space

Conical intersection (CI) seams are configuration spaces of a molecular system where two or more (spin) adiabatic electronic states are degenerate in energy. They play essential roles in photochemistry because nonradiative decays often occur near the minima of the seam, i.e., the minimum energy CIs (MECIs). Thus, it is important to explore the CI seams and discover the MECIs. Although various approaches exist for CI seam exploration, most of them are local in nature, requiring reasonable initial guesses of geometries and nuclear gradients during the search. Global search algorithms, on the other hand, are powerful because they can fully sample the configurational space and locate important MECIs missed by local algorithms. However, global algorithms are often computationally expensive for large systems due to their poor scalability with respect to the number of degrees of freedom. To overcome this challenge, we develop the parallel on-the-fly Crystal algorithm to globally explore the CI seam space, taking advantage of its superior scaling behavior. Specifically, Crystal is coupled with on-the-fly evaluations of the excited and ground state energies using multireference electronic structure methods. Meanwhile, the algorithm is parallelized to further boost its computational efficiency. The effectiveness of this new algorithm is tested for three types of molecular photoswitches of significant importance in material and biomedical sciences: photostatin (PST), stilbene, and butadiene. A rudimentary implementation of the algorithm is applied to PST and stilbene, resulting in the discovery of all previously identified MECIs and several new ones. A refined version of the algorithm, combined with a systematic clustering technique, is applied to butadiene, resulting in the identification of an unprecedented number of energetically accessible MECIs. The results demonstrate that the parallel on-the-fly Crystal algorithm is a powerful tool for automated global CI seam exploration.

"On-the-fly" Crystal : How to reliably and automatically characterize and construct potential energy surfaces

In this work, the Crystal  code, developed previously by the authors to find "holes" as well as legitimate transition states in existing potential energy surface (PES) functions [JPC Lett. 11, 6468 (2020)], is retooled to perform on-the-fly "direct dynamics"-type PES explorations, as well as automatic construction of new PES functions. In all of these contexts, the chief advantage of Crystal  over other methods is its ability to globally map the PES, thereby determining the most relevant regions of configuration space quickly and reliably-even when the dimensionality is rather large. Here, Crystal  is used to generate a uniformly spaced grid of density functional theory (DFT) or ab initio points, truncated over the relevant regions, which can then be used to either: (a) hone in precisely on PES features such as minima and transition states, or; (b) create a new PES function automatically, via interpolation. Proof of concept is demonstrated via application to three molecular systems: water (H2 O), (reduced-dimensional) methane (CH4 ), and methylene imine (CH2 NH).

A methodology for specific disruption of microtubule polymerization into dendritic spines

Dendritic spines, the mushroom-shaped extensions along dendritic shafts of excitatory neurons, are critical for synaptic function and are one of the first neuronal structures disrupted in neurodevelopmental and neurodegenerative diseases. Microtubule (MT) polymerization into dendritic spines is an activity-dependent process capable of affecting spine shape and function. Studies have shown that MT polymerization into spines occurs specifically in spines undergoing plastic changes. However, discerning the function of MT invasion of dendritic spines requires the specific inhibition of MT polymerization into spines, while leaving MT dynamics in the dendritic shaft, synaptically connected axons and associated glial cells intact. This is not possible with the unrestricted, bath application of pharmacological compounds. To specifically disrupt MT entry into spines we coupled a MT elimination domain (MTED) from the Efa6 protein to the actin filament-binding peptide LifeAct. LifeAct was chosen because actin filaments are highly concentrated in spines and are necessary for MT invasions. Temporally controlled expression of this LifeAct-MTED construct inhibits MT entry into dendritic spines, while preserving typical MT dynamics in the dendrite shaft. Expression of this construct will allow for the determination of the function of MT invasion of spines and more broadly, to discern how MT-actin interactions affect cellular processes.

The emerging tools for precisely manipulating microtubules

Cells generate a highly diverse microtubule network to carry out different activities. This network is comprised of distinct tubulin isotypes, tubulins with different post-translational modifications, and many microtubule-based structures. Defects in this complex system cause numerous human disorders. However, how different microtubule subtypes in this network regulate cellular architectures and activities remains largely unexplored. Emerging tools such as photosensitive pharmaceuticals, chemogenetics, and optogenetics enable the spatiotemporal manipulation of structures, dynamics, post-translational modifications, and cross-linking with actin filaments in target microtubule subtypes. This review summarizes the design rationale and applications of these new approaches and aims to provide a roadmap for researchers navigating the intricacies of microtubule dynamics and their post-translational modifications in cellular contexts, thereby opening new avenues for therapeutic interventions.

ANTICANCER IMMUNOGENIC POTENTIAL OF ONCOLYTIC PEPTIDES: RECENT ADVANCES AND NEW PROSPECTS

Oncolytic peptides are derived from natural host defense peptides/antimicrobial peptides produced in a wide variety of life forms. Over the past two decades, they have attracted much attention in both basic research and clinical applications. Oncolytic peptides were expected to act primarily on tumor cells and also trigger the immunogenic cell death. Their ability in the tumor microenvironment remodeling and potentiating the anticancer immunity has long been ignored. Despite the promising results, clinical application of oncolytic peptides is still hindered by their unsatisfactory bioactivity and toxicity to normal cells. To ensure safer therapy, various approaches are being developed. The idea of the Ukrainian research group was to equip peptide molecules with a "molecular photoswitch" - a diarylethene fragment capable of photoisomerization, allowing for the localized photoactivation of peptides within tumors reducing side effects. Such oncolytic peptides that may induce the membrane lysis-mediated cancer cell death and subsequent anticancer immune responses in combination with the low toxicity to normal cells have provided a new paradigm for cancer therapy. This review gives an overview of the broad effects and perspectives of oncolytic peptides in anticancer immunity highlighting the potential issues related to the use of oncolytic peptides in cancer immunotherapy. We summarize the current status of research on peptide-based tumor immunotherapy in combination with other therapies including immune checkpoint inhibitors, chemotherapy, and targeted therapy.

Principles of organelle positioning in motile and non-motile cells

Cells are equipped with asymmetrically localised and functionally specialised components, including cytoskeletal structures and organelles. Positioning these components to specific intracellular locations in an asymmetric manner is critical for their functionality and affects processes like immune responses, tissue maintenance, muscle functionality, and neurobiology. Here, we provide an overview of strategies to actively move, position, and anchor organelles to specific locations. By conceptualizing the cytoskeletal forces and the organelle-to-cytoskeleton connectivity, we present a framework of active positioning of both membrane-enclosed and membrane-less organelles. Using this framework, we discuss how different principles of force generation and organelle anchorage are utilised by different cells, such as mesenchymal and amoeboid cells, and how the microenvironment influences the plasticity of organelle positioning. Given that motile cells face the challenge of coordinating the positioning of their content with cellular motion, we particularly focus on principles of organelle positioning during migration. In this context, we discuss novel findings on organelle positioning by anchorage-independent mechanisms and their advantages and disadvantages in motile as well as stationary cells.

Reversible Influence of Hemipiperazine Photochromism on the Early Development of Zebrafish Embryo

This study explores the potential of controlling organismal development with light by using reversible photomodulation of activity in bioactive compounds. Specifically, our research focuses on plinabulin 1, an inhibitor of tubulin dynamics that contains a photochromic motif called hemipiperazine. The two isomeric forms, Z-1 and E-1, can partially interconvert with light, yet show remarkable thermal stability in darkness. The Z-isomer exhibits higher cytotoxicity due to stronger binding to α-tubulin's colchicine site. The less toxic E-1 form, considered a "pro-drug", can be isolated in vitro and stored. Upon activation by blue or cyan light, it predominantly generates the more toxic Z-1 form. Here we demonstrate that 1 can effectively photomodulate epiboly, a critical microtubule-dependent cell movement during gastrulation in zebrafish embryos. This research highlights the potential of photomodulation for precise and reversible control of cellular activities and organismal development.

Aryl Azocyclopropeniums: Minimalist, Visible-Light Photoswitches

We report convenient syntheses of aryl azocyclopropeniums and a study of their photochemical properties. Incorporation of the smallest arene leads to pronounced redshift of the π-π* absorbance band, compared to azobenzenes. Photoisomerization under purple or green light irradiation affords Z- or E-isomers in ratios up to 94% Z or 90% E, and the switches proved stable over multiple irradiation cycles. Thermal half-lives of metastable Z-isomers range from minutes to hours in acetonitrile and water. These properties together with the concise, versatile syntheses render aryl azocyclopropeniums exciting additions to the tool kit of readily available molecular photoswitches for wide ranging applications.

Recent clinical trials and optical control as a potential strategy to develop microtubule-targeting drugs in colorectal cancer management

Colorectal cancer (CRC) has remained the second and the third leading cause of cancer-related death worldwide and in the United States, respectively. Although significant improvement in overall survival has been achieved, death in adult populations under the age of 55 appears to have increased in the past decades. Although new classes of therapeutic strategies such as immunotherapy have emerged, their application is very limited in CRC so far. Microtubule (MT) inhibitors such as taxanes, are not generally successful in CRC. There may be some way to make MT inhibitors work effectively in CRC. One potential advantage that we can take to treat CRC may be the combination of optical techniques coupled to an endoscope or other fiber optics-based devices. A combination of optical devices and photo-activatable drugs may allow us to locally target advanced CRC cells with highly potent MT-targeting drugs. In this Editorial review, we would like to discuss the potential of optogenetic approaches in CRC management.

Supramolecular Modulation of Fluid Flow in a Self-Powered Enzyme Micropump

Regulating macroscopic fluid flow by catalytic harnessing of chemical energy could potentially provide a solution for powerless microfluidic devices. Earlier reports have shown that surface-anchored enzymes can actuate the surrounding fluid in the presence of the respective substrate in a concentration-dependent manner. It is also crucial to have control over the flow speed of a self-powered enzyme micropump in various applications where controlled dosing and mixing are required. However, modulating the flow speed independent of the fuel concentration remains a significant challenge. In a quest to regulate the fluid flow in such a system, a supramolecular approach has been adopted, where reversible regulation of enzyme activity was achieved by a two-faced synthetic receptor bearing sulfonamide and adamantane groups. The bovine carbonic anhydrase (BCA) enzyme containing a single binding site favorable to the sulfonamide group was used as a model enzyme, and the enzyme activity was inhibited in the presence of the two-faced inhibitor. The same effect was reflected when the immobilized enzyme was used as an engine to actuate the fluid flow. The flow velocity was reduced up to 53% in the presence of 100 μM inhibitor. Later, upon addition of a supramolecular "host" CB[7], the inhibitor was sequestered from the enzyme due to the higher binding affinity of CB[7] with the adamantane functionality of the inhibitor. As a result, the flow velocity was restored to ∼72%, thus providing successful supramolecular control over a self-powered enzyme micropump.

Spatiotemporally Precise Optical Manipulation of Intracellular Molecular Activities

Controlling chemical processes in live cells is a challenging task. The spatial heterogeneity of biochemical reactions in cells is often overlooked by conventional means of incubating cells with desired chemicals. A comprehensive understanding of spatially diverse biochemical processes requires precise control over molecular activities at the subcellular level. Herein, a closed-loop optoelectronic control system is developed that allows the manipulation of biomolecular activities in live cells at high spatiotemporal precision. Chemical-selective fluorescence signals are utilized to command lasers that trigger specific chemical processes or control the activation of photoswitchable inhibitors at desired targets. This technology is fully compatible with laser scanning confocal fluorescence microscopes. The authors demonstrate selective interactions of a 405 nm laser with targeted organelles and simultaneous monitoring of cell responses by fluorescent protein signals. Notably, blue laser interaction with the endoplasmic reticulum leads to a more pronounced reduction in cytosolic green fluorescent protein signals in comparison to that with nuclei and lipid droplets. Moreover, when combined with a photoswitchable inhibitor, microtubule polymerization is selectively inhibited within the subcellular compartments. This technology enables subcellular spatiotemporal optical manipulation over chemical processes and drug activities, exclusively at desired targets, while minimizing undesired effects on non-targeted locations.

Triplet-triplet annihilation photon upconversion-mediated photochemical reactions

Photon upconversion is a method for harnessing high-energy excited states from low-energy photons. Such photons, particularly in the red and near-infrared wavelength ranges, can penetrate tissue deeply and undergo less competitive absorption in coloured reaction media, enhancing the efficiency of large-scale reactions and in vivo phototherapy. Among various upconversion methodologies, the organic-based triplet-triplet annihilation upconversion (TTA-UC) stands out - demonstrating high upconversion efficiencies, requiring low excitation power densities and featuring tunable absorption and emission wavelengths. These factors contribute to improved photochemical reactions for fields such as photoredox catalysis, photoactivation, 3D printing and immunotherapy. In this Review, we explore concepts and design principles of organic TTA-UC-mediated photochemical reactions, highlighting notable advancements in the field, as well as identify challenges and propose potential solutions. This Review sheds light on the potential of organic TTA-UC to advance beyond the traditional photochemical reactions and paves the way for research in various fields and clinical applications.

Design, Synthesis, and Bioevaluation of Novel Reversibly Photoswitchable PI3K Inhibitors Based on Phenylazopyridine Derivatives toward Light-Controlled Cancer Treatment

Photopharmacology is an emerging approach for achieving light-controlled drug activity. Herein, we design and synthesize a novel series of photoswitchable PI3K inhibitors by replacing a sulfonamide moiety with an azo group in a 4-methylquinazoline-based scaffold. Through structure-activity relationship studies, compound 6g is identified to be effectively switched between its trans- and cis-configuration under irradiation with proper wavelengths. Molecular docking studies show the cis-isomer of 6g is favorable to bind to the PI3K target, supporting compound 6g in the PSS365 (cis-isomer enriched) was more potent than that in the PSSdark (trans-isomer dominated) in PI3K enzymatic assay, cell antiproliferative assay, Western blotting analysis on PI3K downstream effectors, cell cycle analysis, colony formation assay, and wound-healing assay. Relative to the cis-isomer, the trans-isomer is more metabolically stable and shows good pharmacokinetic properties in mice. Moreover, compound 6g inhibits tumor growth in nude mice and a zebrafish HGC-27 xenograft model.

Identification of the growth cone as a probe and driver of neuronal migration in the injured brain

Axonal growth cones mediate axonal guidance and growth regulation. We show that migrating neurons in mice possess a growth cone at the tip of their leading process, similar to that of axons, in terms of the cytoskeletal dynamics and functional responsivity through protein tyrosine phosphatase receptor type sigma (PTPσ). Migrating-neuron growth cones respond to chondroitin sulfate (CS) through PTPσ and collapse, which leads to inhibition of neuronal migration. In the presence of CS, the growth cones can revert to their extended morphology when their leading filopodia interact with heparan sulfate (HS), thus re-enabling neuronal migration. Implantation of an HS-containing biomaterial in the CS-rich injured cortex promotes the extension of the growth cone and improve the migration and regeneration of neurons, thereby enabling functional recovery. Thus, the growth cone of migrating neurons is responsive to extracellular environments and acts as a primary regulator of neuronal migration.

A Methodology for Specific Disruption of Microtubules in Dendritic Spines

Dendritic spines, the mushroom-shaped extensions along dendritic shafts of excitatory neurons, are critical for synaptic function and are one of the first neuronal structures disrupted in neurodevelopmental and neurodegenerative diseases. Microtubule (MT) polymerization into dendritic spines is an activity-dependent process capable of affecting spine shape and function. Studies have shown that MT polymerization into spines occurs specifically in spines undergoing plastic changes. However, discerning the function of MT invasion of dendritic spines requires the specific inhibition of MT polymerization into spines, while leaving MT dynamics in the dendritic shaft, synaptically connected axons and associated glial cells intact. This is not possible with the unrestricted, bath application of pharmacological compounds. To specifically disrupt MT entry into spines we coupled a MT elimination domain (MTED) from the Efa6 protein to the actin filament-binding peptide LifeAct. LifeAct was chosen because actin filaments are highly concentrated in spines and are necessary for MT invasions. Temporally controlled expression of this LifeAct-MTED construct inhibits MT entry into dendritic spines, while preserving typical MT dynamics in the dendrite shaft. Expression of this construct will allow for the determination of the function of MT invasion of spines and more broadly, to discern how MT-actin interactions affect cellular processes.

Bidirectional Regulation of Intracellular Enzyme Activity Using Light-Driven Nano-Inhibitors

Photochemical regulation provides precise control over enzyme activities with high spatiotemporal resolution. A promising approach involves anchoring "photoswitches" at enzyme active sites to modulate substrate recognition. However, current methods often require genetic mutations and irreversible enzyme modifications for the site-specific anchoring of "photoswitches", potentially compromising the enzyme activities. Herein, we present a pioneering reversible nano-inhibitor based on molecular imprinting technique for bidirectional regulation of intracellular enzyme activity. The nano-inhibitor employs a molecularly imprinted polymer nanoparticle as its body and azobenzene-modified inhibitors ("photoswitches") as the arms. By using a target enzyme as the molecular template, the nano-inhibitor acquires oriented binding sites on its surface, resulting in a high affinity for the target enzyme and non-covalently firm anchoring of the azobenzene-modified inhibitor to the enzyme active site. Harnessing the reversible isomerization of azobenzene units upon exposure to ultraviolet and visible light, the nano-inhibitor achieves bidirectional enzyme activity regulation by precisely docking and undocking inhibitor at the active site. Notably, this innovative approach enables the facile in situ regulation of intracellular endogenous enzymes, such as carbonic anhydrase. Our results represent a practical and versatile tool for precise enzyme activity regulation in complex intracellular environments.

Unleashing Precision and Freedom in Optical Manipulation: Software-Assisted Real-Time Precision Opto-Control of Intracellular Molecular Activities and Cell Functions

The traditional method in biological science to regulate cell functions often employs chemical interventions, which commonly lack precision in space and time. While optical manipulation offers superior spatial precision, existing technologies are constrained by limitations in flexibility, accuracy, and response time. Here, we present an adaptable and interactive optical manipulation platform that integrates laser scanning, chemical sensing, synchronized multi-laser control, adaptable target selection, flexible decision-making, and real-time monitoring of sample responses. This software-assisted real-time precision opto-control (S-RPOC) platform facilitates automatic target selection driven by optical signals while permitting user-defined manual delineation. It allows the treatment of mobile or stationary targets with varying laser dosages and wavelengths simultaneously at diffraction-limited spatial precision and optimal accuracy. Significantly, S-RPOC showcases versatile capabilities including adaptive photobleaching, comprehensive quantification of protein dynamics, selective organelle perturbation, control of cell division, and manipulation of individual cell behaviors within a population. With its unprecedented spatiotemporal precision and adaptable decision-making, S-RPOC holds the potential for extensive applications in biological science.

Design, synthesis and biological evaluation of novel dihydroquinolin-4(1H)-one derivatives as novel tubulin polymerization inhibitors

A series of novel dihydroquinolin-4(1H)-one derivatives targeting colchicine binding site on tubulin were designed, synthesized and evaluated as anticancer agents. The most potent compound 6t showed remarkable antiproliferative activities against four cancer cell lines with IC50 values among 0.003-0.024 μM and tubulin polymerization inhibitory activity (IC50 = 3.06 μM). Further mechanism studies revealed that compound 6t could induce K562 cells apoptosis and arrest at the G2/M phase. Meanwhile, 6t significantly inhibited migration and invasion of MDA-MB-231 cells, and disrupted the angiogenesis in human umbilical vein endothelial cells (HUVECs) in vitro. In addition, compound 6t inhibited tumor growth in H22 allograft tumor model with a tumor growth inhibition (TGI) rate of 63.3 % (i.v., 20 mg/kg per day) without obvious toxicity. Collectively, these results indicated that compound 6t was a novel tubulin polymerization inhibitor with potent anticancer properties in vitro and in vivo.

Photoresponsive peptide materials: Spatiotemporal control of self-assembly and biological functions

Peptides work as both functional molecules to modulate various biological phenomena and self-assembling artificial materials. The introduction of photoresponsive units to peptides allows the spatiotemporal remote control of their structure and function upon light irradiation. This article overviews the photoresponsive peptide design, interaction with biomolecules, and applications in self-assembling materials over the last 30 years. Peptides modified with photochromic (photoisomerizable) molecules, such as azobenzene and spiropyran, reversibly photo-controlled the binding to biomolecules and nanostructure formation through self-assembly. Photocleavable molecular units irreversibly control the functions of peptides through cleavage of the main chain and deprotection by light. Photocrosslinking between peptides or between peptides and other biomolecules enhances the structural stability of peptide assemblies and complexes. These photoresponsive peptides spatiotemporally controlled the formation and dissociation of peptide assemblies, gene expressions, protein-drug interactions, protein-protein interactions, liposome deformation and motility, cytoskeleton structure and stability, and cell functions by appropriate light irradiation. These molecular systems can be applied to photo-control biological functions, molecular robots, artificial cells, and next-generation smart drug delivery materials.

Exploring Photoswitchable Binding Interactions with Small-Molecule- and Peptide-Based Inhibitors of Trypsin

The ability to photochemically activate a drug, both when and where needed, requires optimisation of the difference in biological activity between each isomeric state. As a step to this goal, we report small-molecule- and peptide-based inhibitors of the same protease-trypsin-to better understand how photoswitchable drugs interact with their biological target. The best peptidic inhibitor displayed a more than fivefold difference in inhibitory activity between isomeric states, whereas the best small-molecule inhibitor only showed a 3.4-fold difference. Docking and molecular modelling suggest this result is due to a large change in 3D structure in the key binding residues of the peptidic inhibitor upon isomerisation; this is not observed for the small-molecule inhibitor. Hence, we demonstrate that significant structural changes in critical binding motifs upon irradiation are essential for maximising the difference in biological activity between isomeric states. This is an important consideration in the design of future photoswitchable drugs for clinical applications.

Photoactivated Protein Degrader for Optical Control of Synaptic Function

Hundreds of proteins determine the function of synapses, and synapses define the neuronal circuits that subserve myriad brain, cognitive, and behavioral functions. It is thus necessary to precisely manipulate specific proteins at specific sub-cellular locations and times to elucidate the roles of particular proteins and synapses in brain function. We developed PHOtochemically TArgeting Chimeras (PHOTACs) as a strategy to optically degrade specific proteins with high spatial and temporal precision. PHOTACs are small molecules that, upon wavelength-selective illumination, catalyze ubiquitylation and degradation of target proteins through endogenous proteasomes. Here, we describe the design and chemical properties of a PHOTAC that targets Ca2+/calmodulin-dependent protein kinase II alpha (CaMKIIα), which is abundant and crucial for the baseline synaptic function of excitatory neurons. We validate the PHOTAC strategy, showing that the CaMKIIα-PHOTAC is effective in mouse brain tissue. Light activation of CaMKIIα-PHOTAC removed CaMKIIα from regions of the mouse hippocampus only within 25 μm of the illuminated brain surface. The optically controlled degradation decreases synaptic function within minutes of light activation, measured by the light-initiated attenuation of evoked field excitatory postsynaptic potential (fEPSP) responses to physiological stimulation. The PHOTACs methodology should be broadly applicable to other key proteins implicated in synaptic function, especially for evaluating their precise roles in the maintenance of long-term potentiation and memory within subcellular dendritic domains.

On the Simulation of Thermal Isomerization of Molecular Photoswitches in Biological Systems

Molecular photoswitches offer precise, reversible photocontrol over biomolecular functions and are promising light-regulated drug candidates with minimal side effects. Quantifying thermal isomerization rates of photoswitches in their target biomolecules is essential for fine-tuning their light-controlled drug activity. However, the effects of protein binding on isomerization kinetics remain poorly understood, and simulations are crucial for filling this gap. Challenges in the simulation include describing multireference electronic structures near transition states, disentangling competing reaction pathways, and sampling protein-ligand interactions. To overcome these challenges, we used multiscale simulations to characterize the thermal isomerization of photostatins (PSTs), which are light-regulated microtubule inhibitors for potential cancer phototherapy. We employed a new ab initio multireference electronic structure method in a quantum mechanics/molecular mechanics setting and combined it with enhanced sampling techniques to characterize the cis to trans free-energy profiles of three PSTs in a vacuum, aqueous solution, and tubulin dimer. The significant advantage of our novel approach is the efficient treatment of the multireference character in PSTs' electronic wavefunction throughout the conformational sampling of protein-ligand interactions along their isomerization pathways. We also benchmarked our calculations using high-level ab initio multireference electronic structure methods and explored the competing isomerization pathways. Notably, calculations in a vacuum and implicit solvent models cannot predict the order of the PSTs' thermal half-lives in the aqueous solution observed in the experiment. Only by explicitly treating the solvent molecules can the correct order of isomerization kinetics be reproduced. Protein binding perturbs free-energy barriers due to hydrogen bonding between PSTs and nearby polar residues. Our work generates comprehensive, high-quality benchmark data and offers guidance for selecting computational methods to study the thermal isomerization of photoswitches. Ab initio multireference free-energy calculations in explicit molecular environments are crucial for predicting the effects of substituents on the thermal half-lives of photoswitches in biological systems.

Isomerization of bioactive acylhydrazones triggered by light or thiols

The acylhydrazone unit is well represented in screening databases used to find ligands for biological targets, and numerous bioactive acylhydrazones have been reported. However, potential E/Z isomerization of the C=N bond in these compounds is rarely examined when bioactivity is assayed. Here we analysed two ortho-hydroxylated acylhydrazones discovered in a virtual drug screen for modulators of N-methyl-D-aspartate receptors and other bioactive hydroxylated acylhydrazones with structurally defined targets reported in the Protein Data Bank. We found that ionized forms of these compounds, which are populated under laboratory conditions, photoisomerize readily and the isomeric forms have markedly different bioactivity. Furthermore, we show that glutathione, a tripeptide involved with cellular redox balance, catalyses dynamic E⇄Z isomerization of acylhydrazones. The ratio of E to Z isomers in cells is determined by the relative stabilities of the isomers regardless of which isomer was applied. We conclude that E/Z isomerization may be a common feature of the bioactivity observed with acylhydrazones and should be routinely analysed.

First-in-Class Colchicine-Based Visible Light Photoswitchable Microtubule Dynamics Disrupting Agent

Compounds that disrupt microtubule dynamics, such as colchicine, paclitaxel, or Vinca alkaloids, have been broadly used in biological studies and have found application in clinical anticancer medications. However, their main disadvantage is the lack of specificity towards cancerous cells, leading to severe side effects. In this paper, we report the first synthesis of 12 new visible light photoswitchable colchicine-based microtubule inhibitors AzoCols. Among the obtained compounds, two photoswitches showed light-dependent cytotoxicity in cancerous cell lines (HCT116 and MCF-7). The most promising compound displayed a nearly twofold increase in potency. Moreover, dissimilar inhibition of purified tubulin polymerisation in cell-free assay and light-dependent disruption of microtubule organisation visualised by immunofluorescence imaging sheds light on the mechanism of action as microtubule photoswitchable destabilisers. The presented results provide a foundation towards the synthesis and development of a novel class of photoswitchable colchicine-based microtubule polymerisation inhibitors.

Reversible Control of RNA Splicing by Photoswitchable Small Molecules

Dynamics are intrinsic to both RNA function and structure. Yet, the available means to precisely provide RNA-based processes with spatiotemporal resolution are scarce. Here, our work pioneers a reversible approach to regulate RNA splicing within primary patient-derived cells by synthetic photoswitches. Our small molecule enables conditional real-time control at mRNA and protein levels. NMR experiments, together with theoretical calculations, photochemical characterization, fluorescence polarization measurements, and living cell-based assays, confirmed light-dependent exon inclusion as well as an increase in the target functional protein. Therefore, we first demonstrated the potential of photopharmacology modulation in splicing, tweaking the current optochemical toolkit. The timeliness on the consolidation of RNA research as the driving force toward therapeutical innovation holds the promise that our approach will contribute to redrawing the vision of RNA.

Microtubule depolymerization contributes to spontaneous neurotransmitter release in vitro

Microtubules are key to multiple neuronal functions involving the transport of organelles, however, their relationship to neurotransmitter release is still unresolved. Here, we show that microtubules present in the presynaptic compartment of cholinergic autaptic synapses are dynamic. To investigate how the balance between microtubule growth and shrinkage affects neurotransmission we induced synchronous microtubule depolymerization by photoactivation of the chemical inhibitor SBTub3. The consequence was an increase in spontaneous neurotransmitter release. An analogous effect was obtained by dialyzing the cytosol with Kif18A, a plus-end-directed kinesin with microtubule depolymerizing activity. Kif18A also inhibited the refilling of the readily releasable pool of synaptic vesicles during high frequency stimulation. The action of Kif18A was associated to one order of magnitude increases in the numbers of exo-endocytic pits and endosomes present in the presynaptic terminal. An enhancement of spontaneous neurotransmitter release was also observed when neurons were dialyzed with stathmin-1, a protein with a widespread presence in the nervous system that induces microtubule depolymerization. Taken together, these results support that microtubules restrict spontaneous neurotransmitter release as well as promote the replenishment of the readily releasable pool of synaptic vesicles.

A Photoisomerizable Zinc (II) Complex Inhibits Microtubule Polymerization for Photoactive Therapy

The photoisomerization-induced cytotoxicity in photopharmacology provides a unique pathway for phototherapy because it is independent of endogenous oxygen. In this study, we developed a biosafe photoisomerizable zinc(II) complex (Zn1), which releases its trans ligand (trans-L1) after being irradiated with blue light. This causes the complex to undergo photoisomerization and produce the toxic cis product (cis-L1) and generate singlet oxygen (¹ O₂ ). The resulting series of events caused impressive phototoxicity in hypoxic A431 skin cancer cells, as well as in a tumor model in vivo. Interestingly, Zn1 was able to inhibit tumor microtubule polymerization, while still showing good biocompatibility and biosafety in vivo. This photoisomerizable zinc(II) complex provides a novel strategy for addressing the oxygen-dependent limitation of traditional photodynamic therapy.

Ligand-Directed Photocatalysts and Far-Red Light Enable Catalytic Bioorthogonal Uncaging inside Live Cells

Described are ligand-directed catalysts for live-cell, photocatalytic activation of bioorthogonal chemistry. Catalytic groups are localized via a tethered ligand either to DNA or to tubulin, and red light (660 nm) photocatalysis is used to initiate a cascade of DHTz oxidation, intramolecular Diels-Alder reaction, and elimination to release phenolic compounds. Silarhodamine (SiR) dyes, more conventionally used as biological fluorophores, serve as photocatalysts that have high cytocompatibility and produce minimal singlet oxygen. Commercially available conjugates of Hoechst dye (SiR-H) and docetaxel (SiR-T) are used to localize SiR to the nucleus and microtubules, respectively. Computation was used to assist the design of a new class of redox-activated photocage to release either phenol or n-CA4, a microtubule-destabilizing agent. In model studies, uncaging is complete within 5 min using only 2 μM SiR and 40 μM photocage. In situ spectroscopic studies support a mechanism involving rapid intramolecular Diels-Alder reaction and a rate-determining elimination step. In cellular studies, this uncaging process is successful at low concentrations of both the photocage (25 nM) and the SiR-H dye (500 nM). Uncaging n-CA4 causes microtubule depolymerization and an accompanying reduction in cell area. Control studies demonstrate that SiR-H catalyzes uncaging inside the cell, and not in the extracellular environment. With SiR-T, the same dye serves as a photocatalyst and the fluorescent reporter for microtubule depolymerization, and with confocal microscopy, it was possible to visualize microtubule depolymerization in real time as the result of photocatalytic uncaging in live cells.