Photoswitchable paclitaxel-based microtubule stabilisers allow optical control over the microtubule cytoskeleton

"Clicked" Hydrazone Photoswitches

The length of the linker connecting a photoswitch to a material significantly influences the latter's properties, with "zero-length" linkers being ideal for optimal photomodulation. The 1,2,3-triazole formed through the "click" reaction between an azide and an alkyne has been used as such a linking motif in various areas of research spanning from materials to biological chemistry. However, its effect, as well as that of its regioisomers, on the photoswitching properties has not been fully elucidated. Here, we report on a series of triazole-containing hydrazone photoswitches, investigating how the connectivity (1,4 vs 1,5) between the triazole and the switch affects the photoswitching properties. The structure-property analysis and DFT/TD-DFT calculations show that the switching efficiency of N-connected 1,4-triazole hydrazones is lower than their C-connected counterparts, while the 1,5-triazole hydrazone exhibits an overall better photoswitching efficiency.

Photopharmacology and photoresponsive drug delivery

Light serves as an excellent external stimulus due to its high spatial and temporal resolution. The use of light to regulate biological processes has evolved into a vibrant field over the past decade. Employing light on chemical substances such as bioactive molecules and drug delivery systems offers a promising therapeutic approach to achieve precise control over biological processes. In this review, we provide an overview of the advancements in optochemical technologies for controlling bioactive molecules (photopharmacology) and drug delivery systems (photoresponsive drug delivery), with an emphasis on their relationship and biomedical applications. Gaining a deeper understanding of the underlying mechanisms and emerging research will facilitate the development of optochemically controlled bioactive molecules and photoresponsive drug delivery systems, further enhancing light technologies in biomedical applications.

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.

Applying Spatiotemporal Modeling of Cell Dynamics to Accelerate Drug Development

Cells act as physical computational programs that utilize input signals to orchestrate molecule-level protein-protein interactions (PPIs), generating and responding to forces, ultimately shaping all of the physiological and pathophysiological behaviors. Genome editing and molecule drugs targeting PPIs hold great promise for the treatments of diseases. Linking genes and molecular drugs with protein-performed cellular behaviors is a key yet challenging issue due to the wide range of spatial and temporal scales involved. Building predictive spatiotemporal modeling systems that can describe the dynamic behaviors of cells intervened by genome editing and molecular drugs at the intersection of biology, chemistry, physics, and computer science will greatly accelerate pharmaceutical advances. Here, we review the mechanical roles of cytoskeletal proteins in orchestrating cellular behaviors alongside significant advancements in biophysical modeling while also addressing the limitations in these models. Then, by integrating generative artificial intelligence (AI) with spatiotemporal multiscale biophysical modeling, we propose a computational pipeline for developing virtual cells, which can simulate and evaluate the therapeutic effects of drugs and genome editing technologies on various cell dynamic behaviors and could have broad biomedical applications. Such virtual cell modeling systems might revolutionize modern biomedical engineering by moving most of the painstaking wet-laboratory effort to computer simulations, substantially saving time and alleviating the financial burden for pharmaceutical industries.

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.

Atropisomeric 1-phenylbenzimidazoles affecting microtubule organization: influence of axial chirality

Benzimidazoles are frequently used in medicinal chemistry. Their anticancer effect is among the most prominent biological activities exhibited by this scaffold. Although numerous benzimidazole derivatives have been synthesized, possible atropisomerism of ortho-substituted 1-phenylbenzimidazoles has been largely overlooked. The aim of this research was to synthesize a small library of novel atropisomeric benzimidazole derivatives and explore their biological activity in various cancer and normal human cell lines. The new unique structural motif provides an interesting 3D architecture with axial chirality, which further contributes to molecular complexity and specificity. Racemates and their separated atropisomers arrested the cell cycle, caused apoptosis, and affected microtubule organization in cancer cells in vitro at different intensities. Moreover, this phenomenon was also verified by the inhibition of endothelial cell migration. These results showed that (+)-atropisomers, especially 5n, exhibit a stronger effect and show promise as agents for cancer therapy.

Discovery of Trametinib as an orchestrator for cytoskeletal vimentin remodeling

The dynamic remodeling of the cytoskeletal network of vimentin intermediate filaments supports various cellular functions, including cell morphology, elasticity, migration, organelle localization, and resistance against mechanical or pathological stress. Currently available chemicals targeting vimentin predominantly induce network reorganization and shrinkage around the nucleus. Effective tools for long-term manipulation of vimentin network dispersion in living cells are still lacking, limiting in-depth studies on vimentin function and potential therapeutic applications. Here, we verified that a commercially available small molecule, trametinib, is capable of inducing spatial spreading of the cellular vimentin network without affecting its transcriptional or Translational regulation. Further evidence confirmed its low cytotoxicity and similar effects on different cell types. Importantly, Trametinib has no impact on the other two cytoskeletal systems, actin filaments and the microtubule network. Moreover, Trametinib regulates vimentin network dispersion rapidly and efficiently, with effects persisting for up to 48 h after drug withdrawal. We also ruled out the possibility that Trametinib directly affects the phosphorylation level of vimentin. In summary, we identified an unprecedented regulator Trametinib, which is capable of spreading the vimentin network toward the cell periphery, and thus complemented the existing repertoire of vimentin remodeling drugs in the field of cytoskeletal research.

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.

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.

Recent Progress in Implantable Drug Delivery Systems

In recent years, tremendous effort is devoted to developing platforms, such as implantable drug delivery systems (IDDSs), with temporally and spatially controlled drug release capabilities and improved adherence. IDDSs have multiple advantages: i) the timing and location of drug delivery can be controlled by patients using specific stimuli (light, sound, electricity, magnetism, etc.). Some intelligent "closed-loop" IDDS can even realize self-management without human participation. ii) IDDSs enable continuous and stable delivery of drugs over a long period (months to years) and iii) to administer drugs directly to the lesion, thereby helping reduce dosage and side effects. iv) IDDSs enable personalized drug delivery according to patient needs. The high demand for such systems has prompted scientists to make efforts to develop intelligent IDDS. In this review, several common stimulus-responsive mechanisms including endogenous (e.g., pH, reactive oxygen species, proteins, etc.) and exogenous stimuli (e.g., light, sound, electricity, magnetism, etc.), are given in detail. Besides, several types of IDDS reported in recent years are reviewed, including various stimulus-responsive systems based on the above mechanisms, radio frequency-controlled IDDS, "closed-loop" IDDS, self-powered IDDS, etc. Finally, the advantages and disadvantages of various IDDS, bottleneck problems, and possible solutions are analyzed to provide directions for subsequent research.

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.

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.

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.

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.

The microtubule cytoskeleton: A validated target for the development of 2-Aryl-1H-benzo[d]imidazole derivatives as potential anticancer agents

In this study, a series of 2-Aryl-1H-benzo[d]imidazole derivatives were developed to target intra- and extracellular microtubule networks. Compounds O-7 and O-10 showed impressive anti-proliferative activity across various tested cell lines, demonstrating selectivity indexes of 151.7 and 61.9, respectively. O-7 achieved an IC50 value of 0.236 ± 0.096 μM, while O-10 showed an IC50 value of 0.622 ± 0.13 μM against A549 cell lines. The induction of early-stage apoptosis in a dose-dependent manner further underscored the potential of O-7 and O-10 as effective anti-proliferative agents. O-7 and O-10 exhibited substantial inhibition of wound closure, with wound closure percentages decreasing from 23% at 0 μM to 0.43% and 2.62% at 20 μM, respectively. Colony formation reduction rates were impressive, with O-7 at 74.2% and O-10 at 81.2%. These results indicate that the O-7 and O-10 can impede cancer cell migration and have a high potential to curtail colony formation. The mode of action investigations for O-7 and O-10 revealed that O-7 could inhibit in vitro tubulin polymerization and disrupt the intracellular microtubule cytoskeleton. This disruption led to cell cycle arrest in the G2/M phase, indicating that O-7 exerts its anticancer activity through microtubule destabilization. However, O-10 shows a different mode of action than O-7 and requires further investigation. Overall, our study showcases the potential of the synthesized benzimidazole derivatives as novel and selective anticancer agents, motivating further exploration of their pharmacological properties and therapeutic applications.

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.

DNA Nanobarrel-Based Drug Delivery for Paclitaxel and Doxorubicin

Co-delivery of anticancer drugs and target agents by endogenous materials is an inevitable approach towards targeted and synergistic therapy. Employing DNA base pair complementarities, DNA nanotechnology exploits a unique nanostructuring method and has demonstrated its capacity for nanoscale positioning and templated assembly. Moreover, the water solubility, biocompatibility, and modifiability render DNA structure suitable candidate for drug delivery applications. We here report single-stranded DNA tail conjugated antitumor drug paclitaxel (PTX), and the co-delivery of PTX, doxorubicin and targeting agent mucin 1 (MUC-1) aptamer on a DNA nanobarrel carrier. We investigated the effect of tail lengths on drug release efficiencies and dual drug codelivery-enabled cytotoxicity. Owing to the rapidly developing field of structural DNA nanotechnology, functional DNA-based drug delivery is promising to achieve clinical therapeutic applications.

From cells to form: A roadmap to study shape emergence in vivo

Organogenesis arises from the collective arrangement of cells into progressively 3D-shaped tissue. The acquisition of a correctly shaped organ is then the result of a complex interplay between molecular cues, responsible for differentiation and patterning, and the mechanical properties of the system, which generate the necessary forces that drive correct shape emergence. Nowadays, technological advances in the fields of microscopy, molecular biology, and computer science are making it possible to see and record such complex interactions in incredible, unforeseen detail within the global context of the developing embryo. A quantitative and interdisciplinary perspective of developmental biology becomes then necessary for a comprehensive understanding of morphogenesis. Here, we provide a roadmap to quantify the events that lead to morphogenesis from imaging to image analysis, quantification, and modeling, focusing on the discrete cellular and tissue shape changes, as well as their mechanical properties.

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.

Fabrication of a composite 3D-printed titanium alloy combined with controlled in situ drug release to prevent osteosarcoma recurrence

Osteosarcoma is a malignant bone tumor occurring in adolescents. Surgery combined with adjuvant or neoadjuvant chemotherapy is the standard treatment. However, systemic chemotherapy is associated with serious side effects and a high risk of postoperative tumor recurrence, leading to a high amputation rate and mortality in cancer patients. Implant materials that can simultaneously repair large bone defects and prevent osteosarcoma recurrence are in urgent need. Herein, an intelligent system comprising 3D-printed titanium scaffold (TS) and pH-responsive PEGylated paclitaxel prodrugs was fabricated for bone defect reconstruction and recurrence prevention following osteosarcoma surgery. The drug-loaded implants exhibited excellent stability and biocompatibility for supporting the activity of bone stem cells under normal body fluid conditions and the rapid release of drugs in response to faintly acidic environments. An in vitro study demonstrated that five human osteosarcoma cell lines could be efficiently eradicated by paclitaxel released in an acidic microenvironment. Using mice models, we demonstrated that the drug-loaded TS can enable a pH-responsive treatment of postoperative tumors and effectively prevent osteosarcoma recurrence. Therefore, local implantation of this composite scaffold may be a promising topical therapeutic method to prevent osteosarcoma recurrence.

Improvement strategy for immune checkpoint blockade: A focus on the combination with immunogenic cell death inducers

Cancer immunotherapies have yielded promising outcomes in various malignant tumors by blocking specific immune checkpoint molecules, such as programmed cell death 1 and cytotoxic T lymphocyte antigen 4. However, only a few patients respond to immune checkpoint blockade therapy because of the poor immunogenicity of tumor cells and immune-suppressive tumor microenvironment. Accumulating evidence suggests that chemotherapeutic agents, including oxaliplatin and doxorubicin, not only mediate direct cytotoxicity in tumor cells but also induce immunogenic cancer cell death to stimulate a powerful anti-cancer immune response in the tumor microenvironment. In this review, we summarize the recent advances in cancer combination therapy based on immune checkpoint inhibitors plus immunogenic cell death inducers. Despite some clinical failures and challenges, immunogenic cell death inducers have displayed great potential when combined with immune checkpoint inhibitors for anti-cancer treatment in both preclinical studies and clinical trials.

Exhaustive Catalytic ortho-Alkoxylation of Azobenzenes: Flexible Access to Functionally Diverse Yellow-Light-Responsive Photoswitches

We develop the first method for catalytic, exhaustive ortho-alkoxylation of azobenzene photoswitches. Alkoxylation is known to improve the photoswitch properties that control azobenzenes' success in chemical biology or materials sciences, e.g., better completeness of both E → Z and Z → E photoisomerizations and >100 nm red shift of photoresponse. Our method enables straightforward late-stage diversification of photoswitches with interesting functional handles. We showcase four applications: using it to rationally tune lipophilicity, prepare isotopic tracers for metabolism studies, install full water solubility without ionic charges, and efficiently access previously difficult mixed-substituent photoswitches. We also identified a previously unexplored mixed-substituent tetra-ortho family, difluoro-dialkoxy-azobenzenes, whose photoresponse can outperform previous 'gold standard' tetrafluoro-, dichloro-difluoro-, and tetrachloro-azobenzenes in significant ways. We thus expect that both the scaffolds we showcase and the method we develop will impact broadly on photochemistry and photopharmacology.

Hemipiperazines as peptide-derived molecular photoswitches with low-nanomolar cytotoxicity

Molecular photoswitches transform light energy into reversible structural changes. Their combination with known pharmacophores often allows for photomodulation of the biological activity. The effort to apply such compounds in photopharmacology as light-activated pro-drugs is, however, hampered by serious activity reduction upon pharmacophore modifications, or limited biostability. Here we report that a potent antimitotic agent plinabulin and its derivatives demonstrate up to 56-fold reversible activity photomodulation. Alternatively, irreversible photoactivation with cyan light can enhance the cytotoxicity up to three orders of magnitude-all without compromising the original activity level, as the original pharmacophore structure is unchanged. This occurs due to the presence of a peptide-derived photoswitchable motif hemipiperazine inside the plinabulin scaffold. Furthermore, we systematically describe photochromism of these thermally stable and biocompatible hemipiperazines, as well as a photoswitchable fluorophore derived from plinabulin. The latter may further expand the applicability of hemipiperazine photochromism towards super-resolution microscopy.

Tools for studying the cytoskeleton during plant cell division

The plant cytoskeleton regulates fundamental biological processes, including cell division. How to experimentally perturb the cytoskeleton is a key question if one wants to understand the role of both actin filaments (AFs) and microtubules (MTs) in a given biological process. While a myriad of mutants are available, knock-out in cytoskeleton regulators, when nonlethal, often produce little or no phenotypic perturbation because such regulators are often part of a large family, leading to functional redundancy. In this review, alternative techniques to modify the plant cytoskeleton during plant cell division are outlined. The different pharmacological and genetic approaches already developed in cell culture, transient assays, or in whole organisms are presented. Perspectives on the use of optogenetics to perturb the plant cytoskeleton are also discussed.

Opto-katanin, an optogenetic tool for localized, microtubule disassembly

Microtubules are cytoskeletal polymers that separate chromosomes during mitosis and serve as rails for intracellular transport and organelle positioning. Manipulation of microtubules is widely used in cell and developmental biology, but tools for precise subcellular spatiotemporal control of microtubules are currently lacking. Here, we describe a light-activated system for localized recruitment of the microtubule-severing enzyme katanin. This system, named opto-katanin, uses targeted illumination with blue light to induce rapid, localized, and reversible microtubule depolymerization. This tool allows precise clearing of a subcellular region of microtubules while preserving the rest of the microtubule network, demonstrating that regulation of katanin recruitment to microtubules is sufficient to control its severing activity. The tool is not toxic in the absence of blue light and can be used to disassemble both dynamic and stable microtubules in primary neurons as well as in dividing cells. We show that opto-katanin can be used to locally block vesicle transport and to clarify the dependence of organelle morphology and dynamics on microtubules. Specifically, our data indicate that microtubules are not required for the maintenance of the Golgi stacks or the tubules of the endoplasmic reticulum but are needed for the formation of new membrane tubules. Finally, we demonstrate that this tool can be applied to study the contribution of microtubules to cell mechanics by showing that microtubule bundles can exert forces constricting the nucleus.

Synthesis and Study of Dibenzo[b, f]oxepine Combined with Fluoroazobenzenes—New Photoswitches for Application in Biological Systems

Dibenzo[b, f]oxepine derivatives are an important scaffold in natural, medicinal chemistry, and these derivatives occur in several medicinally relevant plants. Two dibenzo[b, f]oxepines were selected and connected with appropriate fluorine azobenzenes. In the next step, the geometry of E/Z isomers was analyzed using density functional theory (DFT) calculations. Then the energies of the HOMO and LUMO orbitals were calculated for the E/Z isomers to determine the HOMO-LUMO gap. Next, modeling of the interaction between the obtained isomers of the compounds and the colchicine α and β-tubulin binding site was performed. The investigated isomers interact with the colchicine binding site in tubulin with a part of the dibenzo[b, f]oxepine or in a part of the azo switch, or both at the same time. Based on the UV-VIS spectra, it was found that in the case of compounds with an azo bond in the meta position, the absorption bands n→π* for both geometric isomers and their separation from π→π* are visible. These derivatives therefore have the potential to be used in photopharmacology.

Light-induced stabilization of microtubules by photo-crosslinking of a Tau-derived peptide

For light-induced stabilization of microtubules (MTs) to manipulate cells, a photo-reactive diazirine group was conjugated to a Tau-derived peptide, a motif binding on the inside of MTs. Ultraviolet (UV) light irradiation induced significant stabilization of MTs via the formation of a covalent bond of the peptide and showed toxicity.

Photoswitchable Diazocine-Based Estrogen Receptor Agonists: Stabilization of the Active Form inside the Receptor

Photopharmacology is an emerging approach in drug design and pharmacological therapy. Light is used to switch a pharmacophore between a biologically inactive and an active isomer with high spatiotemporal resolution at the site of illness, thus potentially avoiding side effects in neighboring healthy tissue. The most frequently used strategy to design a photoswitchable drug is to replace a suitable functional group in a known bioactive molecule with azobenzene. Our strategy is different in that the photoswitch moiety is closer to the drug's scaffold. Docking studies reveal a very high structural similarity of natural 17β-estradiol and the E isomers of dihydroxy diazocines, but not their Z isomers, respectively. Seven dihydroxy diazocines were synthesized and subjected to a biological estrogen reporter gene assay. Four derivatives exhibit distinct estrogenic activity after irradiation with violet light, which can be shut off with green light. Most remarkably, the photogenerated, active E form of one of the active compounds isomerizes back to the inactive Z form with a half-life of merely several milliseconds in water, but nevertheless is active for more than 3 h in the presence of the estrogen receptor. The results suggest a significant local impact of the ligand-receptor complex toward back-isomerization. Thus, drugs that are active when bound but lose their activity immediately after leaving the receptor could be of great pharmacological value because they strongly increase target specificity. Moreover, the drugs are released into the environment in their inactive form. The latter argument is particularly important for drugs that act as endocrine disruptors.

Precise control of microtubule disassembly in living cells

Microtubules tightly regulate various cellular activities. Our understanding of microtubules is largely based on experiments using microtubule-targeting agents, which, however, are insufficient to dissect the dynamic mechanisms of specific microtubule populations, due to their slow effects on the entire pool of microtubules. To overcome this technological limitation, we have used chemo and optogenetics to disassemble specific microtubule subtypes, including tyrosinated microtubules, primary cilia, mitotic spindles, and intercellular bridges, by rapidly recruiting engineered microtubule-cleaving enzymes onto target microtubules in a reversible manner. Using this approach, we show that acute microtubule disassembly swiftly halts vesicular trafficking and lysosomal dynamics. It also immediately triggers Golgi and ER reorganization and slows the fusion/fission of mitochondria without affecting mitochondrial membrane potential. In addition, cell rigidity is increased after microtubule disruption owing to increased contractile stress fibers. Microtubule disruption furthermore prevents cell division, but does not cause cell death during interphase. Overall, the reported tools facilitate detailed analysis of how microtubules precisely regulate cellular architecture and functions.

Beyond the centrosome: The mystery of microtubule organising centres across mammalian preimplantation embryos

Mammalian preimplantation embryogenesis depends on the spatio-temporal dynamics of the microtubule cytoskeleton to enable exceptionally fast changes in cell number, function, architecture, and fate. Microtubule organising centres (MTOCs), which coordinate the remodelling of microtubules, are therefore of fundamental significance during the first days of a new life. Despite its indispensable role during early mammalian embryogenesis, the origin of microtubule growth remains poorly understood. In this review, we summarise the most recent discoveries on microtubule organisation and function during early human embryogenesis and compare these to innovative studies conducted in alternative mammalian models. We emphasise the differences and analogies of centriole inheritance and their role during the first cleavage. Furthermore, we highlight the significance of non-centrosomal MTOCs for embryo viability and discuss the potential of novel in vitro models and light-inducible approaches towards unravelling microtubule formation in research and assisted reproductive technologies.

Optochemical Control of Therapeutic Agents through Photocatalyzed Isomerization

A Ru(bpy)₃Cl₂ photocatalyst is applied to the rapid trans to cis isomerization of a range of alkene‐containing pharmacological agents, including combretastatin A‐4 (CA‐4), a clinical candidate in oncology, and resveratrol derivatives, switching their configuration from inactive substances to potent cytotoxic agents. Selective in cellulo activation of the CA‐4 analog Res‐3M is demonstrated, along with its potent cytotoxicity and inhibition of microtubule dynamics.

Photopharmacology of Antimitotic Agents

Antimitotic agents such as the clinically approved vinca alkaloids, taxanes and epothilone can arrest cell growth during interphase and are therefore among the most important drugs available for treating cancer. These agents suppress microtubule dynamics and thus interfere with intracellular transport, inhibit cell proliferation and promote cell death. Because these drugs target biological processes that are essential to all cells, they face an additional challenge when compared to most other drug classes. General toxicity can limit the applicable dose and therefore reduce therapeutic benefits. Photopharmacology aims to avoid these side-effects by introducing compounds that can be applied globally to cells in their inactive form, then be selectively induced to bioactivity in targeted cells or tissue during a defined time window. This review discusses photoswitchable analogues of antimitotic agents that have been developed by combining different photoswitchable motifs with microtubule-stabilizing or microtubule-destabilizing agents.

Photocontrolling Microtubule Dynamics with Photoswitchable Chemical Reagents

Microtubule dynamics can be inhibited with sub-second temporal resolution and cellular-scale spatial resolution, by using precise illuminations to optically pattern where and when photoswitchable microtubule-inhibiting chemical reagents exert their latent bioactivity. The recently available reagents (SBTub, PST, STEpo, AzTax, PHTub) now enable researchers to use light to reversibly modulate microtubule-dependent processes in eukaryotes, in 2D and 3D cell culture as well as in vivo, across a variety of model organisms: with applications in fields from cargo transport to cell migration, cell division, and embryonic development.Here we give an introduction to using these photoswitchable microtubule inhibitors in cells. We describe the theory of small molecule photoswitching, and the unique performance features, usage requirements, and limitations that photoswitchable chemical reagents have; then we summarize the major classes of photoswitchable microtubule inhibitors that are currently available, with the properties that suit them to different applications, and troubleshooting measures for avoiding common mistakes. We outline workflows to establish cellular assays where they are used to optically control microtubule dynamics in a temporally reversible fashion with spatial specificity down to a single selected cell within a field of view. The methods in this chapter also equip the reader to tackle advanced uses of photoswitchable chemical reagents, in 3D culture and in vivo.

Recent Approaches to the Identification of Novel Microtubule-Targeting Agents

Microtubules are key components of the eukaryotic cytoskeleton with essential roles in cell division, intercellular transport, cell morphology, motility, and signal transduction. They are composed of protofilaments of heterodimers of α-tubulin and β-tubulin organized as rigid hollow cylinders that can assemble into large and dynamic intracellular structures. Consistent with their involvement in core cellular processes, affecting microtubule assembly results in cytotoxicity and cell death. For these reasons, microtubules are among the most important targets for the therapeutic treatment of several diseases, including cancer. The vast literature related to microtubule stabilizers and destabilizers has been reviewed extensively in recent years. Here we summarize recent experimental and computational approaches for the identification of novel tubulin modulators and delivery strategies. These include orphan small molecules, PROTACs as well as light-sensitive compounds that can be activated with high spatio-temporal accuracy and that represent promising tools for precision-targeted chemotherapy.

In Vivo Photocontrol of Microtubule Dynamics and Integrity, Migration and Mitosis, by the Potent GFP-Imaging-Compatible Photoswitchable Reagents SBTubA4P and SBTub2M

Photoswitchable reagents are powerful tools for high-precision studies in cell biology. When these reagents are globally administered yet locally photoactivated in two-dimensional (2D) cell cultures, they can exert micron- and millisecond-scale biological control. This gives them great potential for use in biologically more relevant three-dimensional (3D) models and in vivo, particularly for studying systems with inherent spatiotemporal complexity, such as the cytoskeleton. However, due to a combination of photoswitch isomerization under typical imaging conditions, metabolic liabilities, and insufficient water solubility at effective concentrations, the in vivo potential of photoswitchable reagents addressing cytosolic protein targets remains largely unrealized. Here, we optimized the potency and solubility of metabolically stable, druglike colchicinoid microtubule inhibitors based on the styrylbenzothiazole (SBT) scaffold that are nonresponsive to typical fluorescent protein imaging wavelengths and so enable multichannel imaging studies. We applied these reagents both to 3D organoids and tissue explants and to classic model organisms (zebrafish, clawed frog) in one- and two-protein imaging experiments, in which spatiotemporally localized illuminations allowed them to photocontrol microtubule dynamics, network architecture, and microtubule-dependent processes in vivo with cellular precision and second-level resolution. These nanomolar, in vivo capable photoswitchable reagents should open up new dimensions for high-precision cytoskeleton research in cargo transport, cell motility, cell division, and development. More broadly, their design can also inspire similarly capable optical reagents for a range of cytosolic protein targets, thus bringing in vivo photopharmacology one step closer to general realization.

Triggered azobenzene-based prodrugs and drug delivery systems

Azobenzene-based molecules show unique trans-cis isomerization upon ultraviolet light irradiation, which induce the change of polarity, crystallinity, stability, and binding affinity with pharmacological target. Moreover, azobenzene is the substrate of azoreductase that is often overexpressed in many pathological sites, e.g. hypoxic solid tumor. Therefore, azobenzene can be a multifunctional molecule in material science, pharmaceutical science and biomedicine because of its sensitivity to light, hypoxia and certain enzymes, hence showing potential application in site-specific smart therapy. Herein we focus on the employment of azobenzene and its derivatives for engineering triggered prodrug and drug delivery systems, and provide an overview of photoswitchable azo-based prodrugs, the associated problems regarding ultraviolet light and reversible isomerization, as well as the potential solutions. We also present the advance of azo-bearing delivery vehicles wherein azobenzene act as the linker, capping agent, and building block, and discuss the corresponding mechanisms for controlled cargo release, endocytosis enhancement and sensitization of free radical cancer therapy.

Photoswitchable Epothilone-Based Microtubule Stabilisers Allow GFP-Imaging-Compatible, Optical Control over the Microtubule Cytoskeleton

Optical methods to modulate microtubule dynamics show promise for reaching the micron- and millisecond-scale resolution needed to decrypt the roles of the cytoskeleton in biology. However, optical microtubule stabilisers are under-developed. We introduce "STEpos" as GFP-orthogonal, light-responsive epothilone-based microtubule stabilisers. They use a novel styrylthiazole photoswitch in a design to modulate hydrogen-bonding and steric effects that control epothilone potency. STEpos photocontrol microtubule dynamics and cell division with micron- and second-scale spatiotemporal precision. They substantially improve potency, solubility, and ease-of-use compared to previous optical microtubule stabilisers, and the structure-photoswitching-activity relationship insights in this work will guide future optimisations. The STEpo reagents can contribute greatly to high-precision research in cytoskeleton biophysics, cargo transport, cell motility, cell division, development, and neuroscience.

Optical Control of Mitosis with a Photoswitchable Eg5 Inhibitor

Eg5 is a kinesin motor protein that is responsible for bipolar spindle formation and plays a crucial role during mitosis. Loss of Eg5 function leads to the formation of monopolar spindles, followed by mitotic arrest, and subsequent cell death. Several cell-permeable small molecules have been reported to inhibit Eg5 and some have been evaluated as anticancer agents. We now describe the design, synthesis, and biological evaluation of photoswitchable variants with five different pharmacophores. Our lead compound Azo-EMD is a cell permeable azobenzene that inhibits Eg5 more potently in its light-induced cis form. This activity decreased the velocity of Eg5 in single-molecule assays, promoted formation of monopolar spindles, and led to mitotic arrest in a light dependent way.

Encapsulation of Nanomaterials Inside Microtubules by Using a Tau-Derived Peptide

Microtubules (MTs) are tubular cytoskeletons, which are used for the various applications such as active matters and therapeutic targets. Although modification of the exterior surface of MTs is frequently used for functionalization of MTs, there was no approach to introduce molecules inside MTs. We previously developed a unique peptide binding to the inner surface of MT, which is derived from a MT-associated protein, Tau. The Tau-derived peptide (TP) can be used to introduce various nanomaterials inside MTs. Here we describe the TP-based encapsulation of fluorescent dye, gold nanoparticle, green fluorescent protein, and magnetic CoPt nanoparticles inside MTs.

Pyrrole Hemithioindigo Antimitotics with Near-Quantitative Bidirectional Photoswitching that Photocontrol Cellular Microtubule Dynamics with Single-Cell Precision*

We report the first cellular application of the emerging near-quantitative photoswitch pyrrole hemithioindigo, by rationally designing photopharmaceutical PHTub inhibitors of the cytoskeletal protein tubulin. PHTubs allow simultaneous visible-light imaging and photoswitching in live cells, delivering cell-precise photomodulation of microtubule dynamics, and photocontrol over cell cycle progression and cell death. This is the first acute use of a hemithioindigo photopharmaceutical for high-spatiotemporal-resolution biological control in live cells. It additionally demonstrates the utility of near-quantitative photoswitches, by enabling a dark-active design to overcome residual background activity during cellular photopatterning. This work opens up new horizons for high-precision microtubule research using PHTubs and shows the cellular applicability of pyrrole hemithioindigo as a valuable scaffold for photocontrol of a range of other biological targets.

Microtubule-dependent subcellular organisation of pluripotent cells

With the advancement of cutting-edge live imaging technologies, microtubule remodelling has evolved as an integral regulator for the establishment of distinct differentiated cells. However, despite their fundamental role in cell structure and function, microtubules have received less attention when unravelling the regulatory circuitry of pluripotency. Here, we summarise the role of microtubule organisation and microtubule-dependent events required for the formation of pluripotent cells in vivo by deciphering the process of early embryogenesis: from fertilisation to blastocyst. Furthermore, we highlight current advances in elucidating the significance of specific microtubule arrays in in vitro culture systems of pluripotent stem cells and how the microtubule cytoskeleton serves as a highway for the precise intracellular movement of organelles. This Review provides an informed understanding of the intrinsic role of subcellular architecture of pluripotent cells and accentuates their regenerative potential in combination with innovative light-inducible microtubule techniques.

Light-controlled micron-scale molecular motion

The micron-scale movement of biomolecules along supramolecular pathways, mastered by nature, is a remarkable system requiring strong yet reversible interactions between components under the action of a suitable stimulus. Responsive microscopic systems using a variety of stimuli have demonstrated impressive relative molecular motion. However, locating the position of a movable object that travels along self-assembled fibres under an irresistible force has yet to be achieved. Here, we describe a purely supramolecular system where a molecular 'traveller' moves along a 'path' over several microns when irradiated with visible light. Real-time imaging of the motion in the solvated state using total internal reflection fluorescence microscopy shows that anionic porphyrin molecules move along the fibres of a bis-imidazolium gel upon irradiation. Slight solvent changes mean movement and restructuring of the fibres giving microtoroids, indicating control of motion by fibre mechanics with solvent composition. The insight provided here may lead to the development of artificial travellers that can perform catalytic and other functions.

Azoacetylenes for the Synthesis of Arylazotriazole Photoswitches

We report a modular approach toward novel arylazotriazole photoswitches and their photophysical characterization. Addition of lithiated TIPS-acetylene to aryldiazonium tetrafluoroborate salts gives a wide range of azoacetylenes, constituting an underexplored class of stable intermediates. In situ desilylation transiently leads to terminal arylazoacetylenes that undergo copper-catalyzed cycloadditions (CuAAC) with a diverse collection of organoazides. These include complex molecules derived from natural products or drugs, such as colchicine, taxol, tamiflu, and arachidonic acid. The arylazotriazoles display near-quantitative photoisomerization and long thermal Z-half-lives. Using the method, we introduce for the first time the design and synthesis of a diacetylene platform. It permits implementation of consecutive and diversity-oriented approaches linking two different conjugants to independently addressable acetylenes within a common photoswitchable azotriazole. This is showcased in the synthesis of several photoswitchable conjugates, with potential applications as photoPROTACs and biotin conjugates.

Intranasal Paclitaxel Alters Alzheimer's Disease Phenotypic Features in 3xTg-AD Mice

BACKGROUND

Microtubule stabilizing drugs, commonly used as anti-cancer therapeutics, have been proposed for treatment of Alzheimer's disease (AD); however, many do not cross the blood-brain barrier.

OBJECTIVE

This research investigated if paclitaxel (PTX) delivered via the intranasal (IN) route could alter the phenotypic progression of AD in 3xTg-AD mice.

METHODS

We administered intranasal PTX in 3XTg-AD mice (3xTg-AD n = 15, 10 weeks and n = 10, 44 weeks, PTX: 0.6 mg/kg or 0.9%saline (SAL)) at 2-week intervals. After treatment, 3XTg-AD mice underwent manganese-enhanced magnetic resonance imaging to measure in vivo axonal transport. In a separate 3XTg-AD cohort, PTX-treated mice were tested in a radial water tread maze at 52 weeks of age after four treatments, and at 72 weeks of age, anxiety was assessed by an elevated-plus maze after 14 total treatments.

RESULTS

PTX increased axonal transport rates in treated 3XTg-AD compared to controls (p≤0.003). Further investigation using an in vitro neuron model of Aβ-induced axonal transport disruption confirmed PTX prevented axonal transport deficits. Confocal microscopy after treatment found fewer phospho-tau containing neurons (5.25±3.8 versus 8.33±2.5, p < 0.04) in the CA1, altered microglia, and reduced reactive astrocytes. PTX improved performance of 3xTg-AD on the water tread maze compared to controls and not significantly different from WT (Day 5, 143.8±43 versus 91.5±77s and Day 12, 138.3±52 versus 107.7±75s for SAL versus PTX). Elevated plus maze revealed that PTX-treated 3xTg-AD mice spent more time exploring open arms (Open arm 129.1±80 versus 20.9±31s for PTX versus SAL, p≤0.05).

CONCLUSION

Taken collectively, these findings indicate that intranasal-administered microtubule-stabilizing drugs may offer a potential therapeutic option for treating AD.