Chunyan Bao

Highly discriminating photorelease of anticancer drugs based on hypoxia activatable phototrigger conjugated chitosan nanoparticles.

An ultimately selective photorelease system of chitosan-nanoparticles is constructed. Only under unique aspects of tumor-hypoxia physiological conditions, the preliminary locked phototrigger is unlocked by biological reduction to enable the release of the caged drug either by visible light or two-photon near-IR (NIR) excitation. This approach provides a highly discriminating photorelease of anticancer drug to hypoxic tumor cells, but not to healthy normal cells.

Target-activated coumarin phototriggers specifically switch on fluorescence and photocleavage upon bonding to thiol-bearing protein.

A new concept in which only the molecular target, such as a thiol-bearing protein, can activate the phototrigger has been demonstrated. Such target-activatable phototriggers comprise three parts: a 7-aminocoumarin phototrigger, an electron acceptor (maleimide) that efficiently quenches the coumarin excited state, and a caged leaving group attached to the coumarin. In the absence of mercaptans, photoinduced electron transfer between coumarin and maleimide effectively blocks both the fluorescence and photocleavage pathways. Thiol-bearing molecules, however, readily annihilate the electron acceptor and thus restore the phototrigger for photorelease of the caged cargo (e.g., biotin). Unlike traditional phototriggers, functional-group-activated phototriggers allow easy handling under ambient light, report specific bonding to the target, and enable photocleavage capability selectively at the binding site in situ, thus effectively positioning the photoreleased cargo at the target. Meanwhile, the unique feature of thiol-specific activation of the fluorescence and photocleavage make our new phototrigger a universal tool that can be used to identify accurately protein cysteine S-nitrosylation, a physiologically important posttranslational modification.

Spatiotemporally Controllable and Cytocompatible Approach Builds 3D Cell Culture Matrix by Photo‐Uncaged‐Thiol Michael Addition Reaction

DOI: 10.1002/adma.201306061 proved harmless to live cells. [ 5a , 9 ] However, the spontaneous reaction caused by intrinsic Michael reactivity forfeits all spatial and temporal control. In addition, free thiol groups are susceptible to air oxidation and thus severely limit the storage and extent of crosslinking reactions, [ 1c ] which is indispensable in 3D gel forming, both in thiol-ene and thiol-Michael reactions. Herein, a new concept of photocrosslinking mechanism is demonstrated, in which light controls where and when thiolMichael addition occurs in 3D and light dose controls gel stiffness, thus providing a unique approach particularly suitable for fabricating 3D cell-culture matrix. Specifi cally, Scheme 1 depicts a distinct methacrylate monomer attached with macrocyclic coumarin-caged thiol (MCT) was copolymerized with polyethyleneglycol methacrylate (PEG-MA) to generate the desired photo-responsive gelling macromolecule (PGM). Upon photo-excitation, the intramolecular photocleavage of PGM liberated free thiols by a photoheterolysis mechanism through ion pairs but not free radical intermediates, [ 10 ] which subsequently reacted with another macromolecule bearing multimaleimide groups via thiol-Michael addition to generate hydrogels. The results of the photo-uncaged-thiol Michael addition reaction produce a spatiotemporally controllable gelation without reliance on the free radical formation. Such a phototriggered thiol-Michael addition offers additional salient features: (i) no oxygen inhibition and less thiols oxidation because thiols are generated in situ; (ii) no cytotoxic smallmolecules generated during the photo-gelling because of the unique macrocyclic photo-uncaging mechanism; (iii) no UV-damage to live cells because visible light (λ > 400 nm) or two photon excitation is used to phototrigger gelation. A series of PGMs have been prepared by varying the molar ratio of MCT to PEG-MA (Figure S1 and Table S1), and PGM4 (the molar ratio of MCT to PEG-MA is 1:4, as verifi ed by nitrogen elemental analysis (N% = 4.4%) and GPC (M n = 32 662 g mol −1 , PDI = 2.23)) was chosen as the gelling material because of its appropriate content of caged thiols and hydrophilic properties. Photo-irradiating PGM4 produced free thiols in situ, which crossed linked four-arm PEG tetra-maleimide (PEG-4Mal, 10 kDa) or a Dextran maleimide (Dextran-Mal, 10 kDa) via a Michael addition reaction. Eliminating non-specifi c interactions to biomolecules, PEGyl molecule was chosen as a model building material and enabled us to tailor the biophysical properties of the polymeric gels as a “blank slate” material. [ 11 ] Dextran-Mal was utilized as another alternative building materials due to its biodegradable feature With the rapid progress of tissue engineering and regenerative medicine, the cell-friendly construction of 3D extracellular matrix (ECM) in a precisely controlled manner is urgently needed. [ 1 ] This important concept in 3D cell culture resides in the biomimicry of native extracellular matrix, which recapitulates major aspects of the native cellular microenvironment, infl uencing cell differentiation, proliferation, survival and migration through both biochemical interactions and mechanical cues. [ 2 ] Among all ECM candidates, hydrogels—a highly hydrated and cross-linked polymeric network emerges as an attractive one because their biocompatibility and controllable intrinsic structures allow facilely incorporating essential biophysical and biochemical signals to cells. [ 3 ]

Building Biomedical Materials using Photochemical Bond Cleavage

Light can be used as an external trigger to precisely determine where and when a process is initiated as well as how much of the process is being consumed. Phototriggers are a type of photoresponsive functional group that undergo an irreversible photolysis reaction by selectively breaking a chemical bond, enabling three fundamental functions: the photoactivation of fluorescent and bioactive molecules; the photocleavable degradation of macromolecular materials; and the photorelease of drugs, active groups, or surface charges from carriers and interfaces. With the expanded applications of light-controlled technology, particularly in living systems, new challenges and improvements of phototriggers are required to fulfill the demands for better sensitivity, faster kinetics, and more-demanding biomedical applications. Here, improvements to several conventional phototriggers are highlighted, and their notable, representative biomedical applications and their challenges are discussed.

Tissue-Integratable and Biocompatible Photogelation by the Imine Crosslinking Reaction.

A novel photogelling mechanism by the phototriggered-imine-crosslinking (PIC) reaction is demonstrated. Hyaluronic acid grafted with o-nitrobenzene, a photogenerated aldehyde group, can quickly photo-crosslink with amino-bearing polymers or proteins. Once the in situ photogelling on a wound occurs, the PIC gelling process can well integrate a hydrogel with surrounding tissue by covalent bonding, thus making it a powerful tool for tissue engineering and regenerative medicine.

7-Amino coumarin based fluorescent phototriggers coupled with nano/bio-conjugated bonds: Synthesis, labeling and photorelease

By several synthetic pathways, we designed and synthesized a new series of unsymmetrical substituted 7-amino coumarin-based phototriggers with various nano/bio-conjugated bonds. The photophysical properties of most of the substituted coumarin-based phototriggers, except for compound P9 with maleimide group, showed no significant change compared with that of 7-(diethylamino)-4-(hydroxylmethyl) coumarin (DEACM-OH, the reported symmetric substituted 7-amine coumarin based phototrigger). Four compounds (P2, P4, P9, 14) were successfully conjugated with typical carriers such as mesoporous silica nanoparticles, biocompatible polymer PEG and common protein BSA, respectively. The efficient photorelease of ibuprofen (IBU) in the model cargo delivery system of MD4 confirmed that our designed phototriggers could serve well as a photo-cage for bioactive molecules and the release can be regulated precisely by manipulating the external irradiation conditions. All the results hinted at the superiority of using these coumarin functional compounds for photo-regulated release in biotechnology and biomedical areas.

Sequential Control over Thiol Click Chemistry by a Reversibly Photoactivated Thiol Mechanism of Spirothiopyran

A novel photocontrolled thiol click chemistry based on spirothiopyran and maleimide is reported. Upon irradiation with λ=365 nm light, the spirothiopyran can isomerize to the open merocyanine form, a thiophenolate group, which can rapidly react with maleimide. The unreacted MC will readily isomerize back to the starting spirothiopyran, which can be repeatedly photoactivated as needed. Thus, this reversible photoactivated thiol confers spatiotemporal sequential control on the thiol-maleimide reaction using only one type of photochemical reaction. Polymer post-functionalization and hydrogel building with subsequent multipatterning using different maleimide molecules in a temporal sequential manner indicate that this photocontrolled Michael addition reaction can modulate the specific chemical events in a sequence.

Photocleavable coumarin crosslinkers based polystyrene microgels: phototriggered swelling and release

Two types of photocleavable crosslinkers (CLA and CLB) based on 7-amino coumarin moieties have been synthesized. The ingenious design for the crosslinkers with different vinyl functionalities was aimed to investigate the influence of the crosslinker’s structure on the photodegradation and photoswelling behavior of the constructed microgels. Analysis of DLS, UV spectra and fluorescence spectra verified the original intention and the generated microgels revealed structure-dependent photo-regulated swelling and degradation behavior. The successive loading and release of the hydrophobic Nile Red (NR) dye of the microgel upon visible light irradiation further showed its ability to be used as an excellent nanocarrier for hydrophobic compounds.

Disulfide-phenylazide: a reductively cleavable photoreactive linker for facile modification of nanoparticle surfaces

In this study, a reductively cleavable photoreactive linker, disulfide-phenylazide (SPA), was synthesized and used to functionalize inorganic mesoporous silica nanoparticles (MSNs) by simple amidation reaction. Changed zeta potential, FT-IR and UV-vis or fluorescence spectra confirmed the successful photo-responsive functionalization of dextran (DSPA-MSNs) and immobilization of model avidin protein (ASPA-MSNs). With treatment by reducing agents, both DSPA-MSNs (with 10 mM DTT) and ASPA-MSNs (with 10 mM GSH) exhibited the reductive-responsive controllable release of coumarin 460 and bioactive protein. These results implied that the designed photo-affinity functional agent SPA with reductive-responsive cleavage provided a promising method to functionalize inorganic nanoparticles to improve their biocompatibility and biomedical applications.

Efficient synthetic supramolecular channels and their light-deactivated ion transport in bilayer lipid membranes

Inspired by the critical role of ion channel proteins in the regulation of cellular activities, here we developed a new type of synthetic ion channel by simple benzocrown ether-based derivatives M1 and M2, where M1 had a dodecyl tail and M2 had a diethylene glycol-conjugated dodecyl tail. Being amphiphilic in nature, the two small molecules were assumed to form crown ether channels through supramolecular interactions in bilayer lipid membranes (BLMs). The efficient ion transport was investigated by both a fluorescence-based vesicle assay and a planar bilayer conductance measurement, and M2 with diethylene glycol substitution exhibited more efficient activity comparable to amphotericin B. Moreover, the presence of a photosensitive o-nitrobenzyl group provided the light-regulation to deactivate ion transport by destroying the channel assembly of the molecules in BLMs, which provides new opportunities for developing intelligent light-regulated systems for biomedical applications based on synthetic small molecules.