A Tumor-Targeting Near-Infrared Heptamethine Cyanine Photosensitizer with Twisted Molecular Structure for Enhanced Imaging-Guided Cancer Phototherapy.

In recent years, cancer phototherapy has been extensively studied as noninvasive cancer treatment. To present efficient recognition toward cancer cells, most photosensitizers (PSs) are required to couple with tumor-targeted ligands. Interestingly, the heptamethine cyanine IR780 displays an intrinsic tumor-targeted feature even without modification. However, the photothermal efficacy and photostability of IR780 are not sufficient enough for clinical use. Herein, we involve a twisted structure of tetraphenylethene (TPE) between two molecules of IR780 to improve the photothermal conversion efficiency (PCE). The obtained molecule T780T shows strong near-infrared (NIR) fluorescence and improved PCE (38.5%) in the dispersed state. Also, the photothermal stability and ROS generation capability of T780T at the NIR range (808 nm) are both promoted. In the aqueous phase, the T780T was formulated into uniform nanoaggregates (∼200 nm) with extremely low fluorescence and PTT response, which would reduce in vivo imaging background and side effect of PTT response in normal tissues. After intravenous injection into tumor-bearing mice, the T780T nanoaggregates display high tumor accumulation and thus remarkably inhibit the tumor growth. Moreover, the enhanced photostability of the T780T allows for twice irradiation after one injection and leads to more significant tumor inhibition. In summary, our study presents a tumor-targeted small-molecule PS for efficient cancer therapy and brings a new design of heptamethine cyanine PS for potential clinical applications.

Emissive oxidase-like nanozyme based on an organic molecular cage.

In this study, we introduced four "claw-like" units of dipicolylamine (DPA) to a tetraphenylethylene (TPE)-based organic molecular cage (DPA-TPE-Cage). Coordinated with Zn2+ ions, the obtained ZnDPA-TPE-Cage exhibited aggregation induced emission (AIE) effects and oxidase-like properties, which endowed it with the ability to selectively image and kill Gram-positive bacteria S. aureus efficiently.

Aggregation-Dependent Photoreactive Hemicyanine Assembly as a Photobactericide.

Organic materials that show substantial reactivity under visible light have received considerable attention due to their wide applications in chemical and biological systems. Hemicyanine pigments possess a strong intramolecular donor-acceptor structure and thereby display intense absorption in the visible spectral region. However, most excitons are consumed via the twisted intramolecular charge-transfer (TICT) process, making hemicyanines generally inert to light. Herein, we describe the development of an amphiphilic hemicyanine dye whose aggregation could be easily regulated using salt or counterions. More importantly, its intrinsic photoreactivity was successfully induced by steric restriction and cofacial arrangement within the H-aggregate, thus creating an effective photobactericide. This strategy could be extended to the development of photocatalysts for photosynthesis and a photosensitizer for photodynamic therapy.

Stiff-Stilbene Photoswitches: From Fundamental Studies to Emergent Applications.

Stiff-stilbene, a sterically restricted fused ring analogue of stilbene, has been regularly used as a model compound in theoretical studies of stilbene photoisomerization. Lately, owing to its excellent photoswitching properties, it is increasingly being applied to reversibly control the properties and function of chemical as well as biological systems. Stiff-stilbene photoswitches possess a number of advantageous properties including a high quantum yield for photoisomerization and a high thermal stability. Furthermore, they undergo a large geometrical change upon isomerization and their synthesis is straightforward. Herein, we provide an overview of the basic properties of stiff-stilbene and of recent applications in supramolecular chemistry, catalysis, and biological systems.

Water-Assisted/Water-Accelerated Photoreaction of trans-2,3,4',5-Tetrahydroxystilbene-2-O-ß-d-glucoside from the Roots of Polygonum multiflorum.

The photoreaction of 2,3,4',5-tetrahydroxystilbene-2-O-ß-d-glucoside (TSG) has been investigated. Water-assisted/water-accelerated photodimerization of trans-TSG favored the formation of syn-head-to-tail [2 + 2] photocyclobutane under 365 nm irradiation as a result of hydrophobic association and a fluorescent solute-solute aggregate from their excited singlet states. In contrast, irradiation with 254 nm led to [2 + 2] photocycloreversion. The two cyclobutane dimers were first obtained through straightforward photoreaction and identified as multiflorumiside A and multiflorumiside C through the detailed analysis of high-resolution electrospray ionization mass spectrometry and one- and two-dimensional nuclear magnetic resonance. Therefore, trans-TSG should be protected from light and water.

Photoswitching off the Antiproliferative Activity of Combretastatin A-4 Analogues.

The photostability and antiproliferative activity of combretastatin A-4 (CA-4) analogues against human epidermoid carcinoma cells A-431 were studied. For the first time, it was shown that UV or sunlight irradiation of furanone analogues of CA-4 results in a photorearrangement giving products with relatively low antiproliferative activity. The observed ability of this series CA-4 to the photodegradation can be used for the design of a new class of drug candidates with high selectivity to cancer cells.

Endo- and Exo-Functionalized Tetraphenylethylene M12L24 Nanospheres: Fluorescence Emission inside a Confined Space.

The intrinsic relationship between the properties of green fluorescent protein (GFP) and its encapsulated small molecular light machine has spurred many biomimicking studies, aiming at revealing the detailed mechanism and further promoting its wide applications in different disciplines. However, how to build a similar confined microenvironment to mimic the cavity of a ß-barrel and the fluorescence turn-on process is a fundamental challenge for both chemists and biologists. Herein, two distinct exo- and endo-functionalized tetraphenylethylene (TPE)-based M12L24 nanospheres with precise distribution of anchored TPE moieties and unique photophysical properties were constructed by means of a coordination-driven self-assembly strategy. Under dilute conditions, the nanospheres fluoresce more strongly than the corresponding TPE subcomponents. Meanwhile, the endo-functionalized sphere is able to induce a higher local concentration and more restrained motion of the enclosed 24 TPE units compared with exo-functionalized counterpart and thus induces much stronger emission due to the restriction of the rotation of the pendant TPE units. The biomimetic methodology developed here represents a promising way to understand and construct artificial GFP materials on the platforms of supramolecular coordination complexes.

A red mitochondria-targeted AIEgen for visualizing H2S in living cells and tumours.

Hydrogen sulfide (H2S) exists in the cytosol and mitochondria of mammalian cells as a signaling molecule. Scientists have explored many important physiological functions of H2S, such as regulating vasodilator relaxation, protecting living cells and avoiding damage. The measurement of H2S is therefore necessary for exploring the biological function of cells and tissues. Herein, we report the design and synthesis of a new aggregation-induced emission luminogen (AIEgen) with greater conjugation and more positive charges, based on previous research on mitochondrial-targeted luminogens. The Indo-TPE-Indo can enter cells rapidly, as compared with an AIEgen with only one indolium (TPE-indo), and can selectively recognize HS- in mitochondria with the nucleophilic reaction of indolium and HS-. The linear range (1-100 µM) of HS- sensing can satisfy the requirement for HS- concentration in living cells and tumors.

A Photoresponsive Stiff-Stilbene Ligand Fuels the Reversible Unfolding of G-Quadruplex DNA.

The polymorphic nature of G-quadruplex (G4) DNA structures points to a range of potential applications in nanodevices and an opportunity to control G4 in biological settings. Light is an attractive means for the regulation of oligonucleotide structure as it can be delivered with high spatiotemporal precision. However, surprisingly little attention has been devoted towards the development of ligands for G4 that allow photoregulation of G4 folding. We report a novel G4-binding chemotype derived from stiff-stilbene. Surprisingly however, whilst the ligand induces high stabilization in the potassium form of human telomeric DNA, it causes the unfolding of the same G4 sequence in sodium buffer. This effect can be reversed on demand by irradiation with 400 nm light through deactivation of the ligand by photo-oxidation. By fuelling the system with the photolabile ligand, the conformation of G4 DNA was switched five times.

Widely Applicable AIE Chemosensor for On-Site Fast Detection of Drugs Based on the POSS-Core Dendrimer with the Controlled Self-Assembly Mechanism.

A novel fluorescence chemosensor that can quickly on-site detect synthetic drugs and undergo prescreening is first reported. An eight tetraphenylethene (TPE)-modified polyhedral oligomeric silsesquioxane (POSS) dendrimer is designed and synthesized as an aggregation-induced emission (AIE) chemosensor, which exhibits great enhancement of unique monomer emission in pure tetrahydrofuran (THF) and AIE emission in THF/water, thanks to forming different self-assembly morphologies. In addition, POSS-TPE can sensitively detect methamphetamine and ketamine even in artificial saliva by noncovalent interaction forces. It has great potential to be a new widely applicable AIE chemosensor for aromatic molecules.

Hollow-Core-Photonic-Crystal-Fiber-Based Miniaturized Sensor for the Detection of Aggregation-Induced-Emission Molecules.

A miniature sensor for detection of aggregation-induced-emission (AIE) molecules is proposed in this work. The sensing head is fabricated by use of hollow-core photonic crystal fiber with a core diameter of about 4.8 µm. The cladding holes are sealed with a fusion splicing technique, and the central hole remains open to allow the filtration of solution with AIE molecules. When the solution is excited by an ultraviolet lamp, the fluorescence is received by a fiber-optic spectrometer. The fluorescence intensity is associated with the concentration of AIE molecules and the infiltrated-core length. In the whole process of the experiments, the output-peak wavelength is stable, which indicates that the existing forms of AIE particles are stable, and the fluorescence reabsorption can be neglected. The experimental results obtained are in accordance with traditional microplate-spectrophotometer methods. The most exciting result is that the amount of sample measured can be as low as 0.36 nL, which allows the detection of AIE molecules at only 0.02 pmol. In addition, the miniature sensor was successfully applied to the detection of an AIE-based bioprobe for evaluating the activity of the dipeptidyl-peptidase 4 (DPP-4) inhibitor sitagliptin with an IC50 of 59.80 ± 3.06 nM. The advantages of small device size and nanoliter-scale sample volumes suggest that the proposed sensor is promising for many biosensing applications.

Intramolecular Proton and Charge Transfer of Pyrene-based trans-Stilbene Salicylic Acids Applied to Detection of Aggregated Proteins.

Two analogues to the fluorescent amyloid probe 2,5-bis(4'-hydroxy-3'-carboxy-styryl)benzene (X-34) were synthesized based on the trans-stilbene pyrene scaffold (Py1SA and Py2SA). The compounds show strikingly different emission spectra when bound to preformed Aß1-42 fibrils. This remarkable emission difference is retained when bound to amyloid fibrils of four distinct proteins, suggesting a common binding configuration for each molecule. Density functional theory calculations show that Py1SA is twisted, while Py2SA is more planar. Still, an analysis of the highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) of the two compounds indicates that the degree of electronic coupling between the pyrene and salicylic acid (SA) moieties is larger in Py1SA than in Py2SA. Excited state intramolecular proton transfer (ESIPT) coupled-charge transfer (ICT) was observed for the anionic form in polar solvents. We conclude that ICT properties of trans-stilbene derivatives can be utilized for amyloid probe design with large changes in emission spectra and decay times from analogous chemical structures depending on the detailed physical nature of the binding site.

Testing of resveratrol microemulsion photostability and protective effect against UV induced oxidative stress.

Resveratrol is well known for its antioxidant activity and susceptibility to ultraviolet radiation. Development of formulations providing improved stability and relevant drug delivery of resveratrol is still a challenging task. The aim of this study was to determine protective characteristics of formulated microemulsions by evaluating photoisomerization of resveratrol and to investigate the effects of resveratrol on human keratinocyte cells under oxidative stress caused by ultraviolet radiation. Incorporation of resveratrol into microemulsions resulted in increased photostability of active compounds and the results demonstrated that photodegradation of resveratrol was significantly delayed. Results of biopharmaceutical evaluation in vitro demonstrated that up to 60 % of resveratrol was released from microemulsions within 6 hours under a constant release rate profile. In vivo biological testing confirmed the ability of resveratrol to protect cells from oxidative stress and to increase cell viability. It was concluded that microemulsions might be considered in the development of UV light sensitive compounds.

High temperature and UV-C treatments affect stilbenoid accumulation and related gene expression levels in Gnetum parvifolium

Background: Gnetum parvifolium stems and roots have been used for a long time in traditional Chinese medicines. Stilbenes are bioactive compounds present in G. parvifolium plants, and they possess antioxidative and anticancer properties. However, little is known about the responses of G. parvifolium stilbene biosynthetic pathways to stress conditions. Therefore, we investigated stilbene biosynthesis, including the expression of relevant genes, in G. parvifolium exposed to high-temperature and ultraviolet-C treatments. Results: High temperatures did not influence the accumulation of total stilbenes in stems but decreased stilbene concentrations in roots at 3 h, with a subsequent restoration to control levels. In contrast, ultraviolet irradiation induced the accumulation of total stilbenes in stems but not in roots. We also observed that high temperatures inhibited the production of resveratrol and piceatannol in G. parvifolium stems and roots, whereas ultraviolet treatments initially inhibited their accumulation (up to 6 h) but induced their production at later time points. Analyses of specific genes (i.e., PAL, C4H, 4CL, STS, and CYP) revealed that their expression levels generally increased in stress-treated stems and roots, although there was some variability in the expression profiles during treatments. Conclusions: Our results indicated that high temperatures and ultraviolet irradiation differentially affect the biosynthesis of specific stilbenes in G. parvifolium stems and roots. Therefore, cultivating G. parvifolium seedlings under optimal stress conditions may increase the biosynthesis of specific stilbene compounds.

Excited-State Proton Transfer in Resveratrol and Proposed Mechanism for Plant Resistance to Fungal Infection.

Steady-state and time-resolved fluorescence techniques were employed to study the photophysics and photochemistry of trans-resveratrol. trans-Resveratrol is found in large quantities in fungi-infected grapevine-leaf tissue and plays a direct role in the resistance to plant disease. We found that trans-resveratrol in liquid solution undergoes a trans-cis isomerization process in the excited state at a rate that depends partially on the solvent viscosity, as was found in previous studies on trans-stilbene. The hydroxyl groups of the phenol moieties in resveratrol are weak photoacids. In water and methanol solutions containing weak bases such as acetate, a proton is transferred to the base within the lifetime of the excited state. When resveratrol is adsorbed on cellulose (also a component of the plant's cell wall), the cis-trans process is slow and the lifetime of the excited state increases from several tens of picoseconds in ethanol to about 1.5 ns. Excited-state proton transfer occurs when resveratrol is adsorbed on cellulose and acetate ions are in close proximity to the phenol moieties. We propose that proton transfer from excited resveratrol to the fungus acid-sensing chemoreceptor is one of the plant's resistance mechanisms to fungal infection.

Comprehensive evaluation of the photo-transformation routes of trans-resveratrol.

Liquid chromatography (LC) combined with accurate mass spectrometry (MS), based on the use of a hybrid quadrupole time-of-flight (TOF) MS system, is employed to systematically investigate the photo-transformation routes of trans-resveratrol. Experiments were performed in quartz tubes, containing ethanolic solutions (12% v/v) of the precursor compound, exposed to different ultraviolet (UV) sources and to solar light. Time-courses of trans-resveratrol and transformation products (TPs) were investigated by direct injection of different reaction times aliquots in the LC-QTOF-MS system. Structural elucidation of detected TPs was derived from interpretation of their accurate product ion scan spectra. Trans-resveratrol labelled with (13)C6 in the mono-hydroxylated ring was also employed to further confirm the exact positions of some substituents in the generated TPs. In addition to the well-known trans-/cis-isomerization process, three different main reactions pathways were noticed under all the investigated conditions: (1) water addition to the exocycle double bond followed by oxidation to a ketone and cleavage of the molecule, (2) intramolecular cyclization to render a trihydroxylated phenanthrene, and (3) oxidation of the phenanthrene-like derivative to generate an orto-diquinone. Both, the trihydroxylated phenanthrene and the orto-diquinone underwent further aromatic hydroxylation reactions. The above transformation routes were also noticed for cis-resveratrol and the two analogue phytoalexins piceid and piceatannol. In addition to above transformation pathways, under solar light exposure, resveratrol underwent a molecular re-arrangement rendering the so-called resveratrone, whose structure consists of two fused aromatic rings bonded to a linear chain containing a carbonyl group conjugated with a double bond.

Photostability evaluation of five UV-filters, trans-resveratrol and beta-carotene in sunscreens.

Trans-resveratrol (RES) is used in cosmetic formulations and beta-carotene (BTC) is a classical sunscreen antioxidant, but their photostability in sunscreens, a property directly correlated to performance and safety has not been addressed in the literature. This paper reports the assessment of RES and/or BTC influence on the photostability of five UV-filters (octyl methoxycinnamate - OMC, avobenzone -AVO, octocrylene - OCT, bemotrizinole - BMZ, octyltriazone - OTZ) in three different combinations after UVA exposure followed by the identification of degradation products and the assessment of photoreactivity. The evaluation of sunscreen photostability was performed by HPLC and spectrophotometric analysis, and degradation products were identified by GC-MS analysis. Components RES, BTC, OMC and AVO were significantly degraded after UV exposure (reduction of around 16% in recovery). According to HPLC analysis, all formulations presented similar photostability profiles. Eleven degradation products were identified in GC-MS analysis, among them products of RES, BTC, OMC and AVO photodegradation. All evaluated formulations were considered photoreactive, as well as the isolated compounds RES and AVO. Considering HPLC, spectrophotometric and GC-MS results, it is suggested that formulations containing BMZ were considered the most photostable. The combination RES+BTC in a sunscreen improved the photostability of AVO. The benefits of using a combination of antioxidants in sunscreens was demonstrated by showing that using RES+BTC+studied UV-filters led to more photostable formulations, which in turn implies in better safety and efficacy.

Gamma-irradiated resveratrol negatively regulates LPS-induced MAPK and NF-κB signaling through TLR4 in macrophages.

Resveratrol was irradiated at various doses of 15, 30, 50, and 70kGy for the development of physiological functionalities through modification of the structural properties. Gamma irradiation induced a decrease in the resveratrol peak, and the appearance of several new peaks by gamma irradiation was gradually increased up to 70kGy. Gamma-irradiated resveratrol did not exert cytotoxicity to macrophages in dose ranges from 15 to 70kGy; therefore, 70kGy gamma-irradiated resveratrol was used as the maximum dose throughout subsequent experiments. Treatment of LPS-stimulated macrophages with 70kGy gamma-irradiated resveratrol resulted in a dose-dependent decrease in iNOS-mediated NO, PGE2, and pro-inflammatory cytokine level, such as TNF-α, IL-6 and IL-1ß. 70kGy gamma-irradiated resveratrol significantly inhibited cyclooxygenase-2 levels, as well as the expression of cell surface molecules, such as CD80 and CD86, in LPS-induced macrophages. Furthermore, the inhibitory action of these pro-inflammatory mediators occurred through an inhibition of MAPKs (ERK1/2, p38 and JNK) and NF-κB signaling pathways based on a toll-like receptor 4 in macrophages, which may be closely mediated with the radiolysis products of resveratrol transformed by gamma-irradiation. From these findings, it seems likely that gamma irradiation can be an effective tool for a reduction of the toxicity and play a potent role in the treatment of inflammatory disease.

Development of novel cationic chitosan-and anionic alginate-coated poly(D,L-lactide-co-glycolide) nanoparticles for controlled release and light protection of resveratrol.

BACKGROUND: Resveratrol, like other natural polyphenols, is an extremely photosensitive compound with low chemical stability, which limits the therapeutic application of its beneficial effects. The development of innovative formulation strategies, able to overcome physicochemical and pharmacokinetic limitations of this compound, may be achieved via suitable carriers able to associate controlled release and protection. In this context, nanotechnology is proving to be a powerful strategy. In this study, we developed novel cationic chitosan (CS)- and anionic alginate (Alg)-coated poly(d,l-lactide-co-glycolide) nanoparticles (NPs) loaded with the bioactive polyphenolic trans-(E)-resveratrol (RSV) for biomedical applications. METHODS: NPs were prepared by the nanoprecipitation method and characterized in terms of morphology, size and zeta potential, encapsulation efficiency, Raman spectroscopy, swelling properties, differential scanning calorimetry, and in vitro release studies. The protective effect of the nanosystems under the light-stressed RSV and long-term stability were investigated. RESULTS: NPs turned out to be spherical in shape, with size ranging from 135 to about 580 nm, depending on the composition and the amount of polyelectrolytes, while the encapsulation efficiencies increased from 8% of uncoated poly(d,l-lactide-co-glycolide) (PLGA) to 23% and 32% of Alg- and CS-coated PLGA NPs, respectively. All nanocarriers are characterized by a biphasic release pattern, and more effective controlled release rates are obtained for NPs formulated with higher polyelectrolyte concentrations. Stability studies revealed that encapsulation provides significant protection against light-exposure degradation, by reducing the trans-cis photoisomerization reaction. Moreover, the nanosystems are able to prevent the degradation of trans isoform and the leakage of RSV from the carrier for a period of 6 months. CONCLUSION: Our findings indicated that the newly developed CS- and Alg-coated PLGA NPs are suitable to be used for the delivery of bioactive RSV. The encapsulation of RSV into optimized polymeric NPs provides improved drug loading, effective controlled release, and protection against light-exposure degradation, thus opening new perspectives for the delivery of bioactive related phytochemicals to be used for (nano)chemoprevention/chemotherapy.

Ultraviolet irradiation of trans-resveratrol and HPLC determination of trans-resveratrol and cis-resveratrol in Romanian red wines.

A reversed-phase high-performance liquid chromatography method with diode array detection was developed for the determination of trans- and cis-resveratrol in red wines. Separation was achieved after direct injection by the use of a BDS Hypersil C18 column (250 × 4.6 mm) with gradient elution (solvent A: acetic acid 2%, solvent B: acetonitrile). Detection of trans- and cis-resveratrol was performed at 306 and 286 nm, respectively. The retention times of trans- and cis-resveratrol were 22.2 and 26.1 min, respectively. Good linearity and precision were obtained for the two isomers. Detection limits of 0.004 mg/L for trans-resveratrol and 0.02 mg/L for cis-reveratrol were obtained. The developed method was applied to determine cis- and trans-resveratrol in 30 red wines produced in Oltenia (southwestern Romania). The wines came from different vineyards harvested in various vintages. The concentration of trans-resveratrol ranged from 0.287 to 7.188 mg/L, while the content of cis-resveratrol ranged from 0.718 to 6.587 mg/L. The highest amount of trans-resveratrol was found in Merlot from Vanju Mare, Mehedinti (7.188 mg/L), followed by Sirah from Corcova, Mehedinti (4.738 mg/L), both from the 2010 harvest. The paper also approaches the study of the transformation of trans-resveratrol into the cis form after ultraviolet irradiation through glass and quartz. At the irradiation of a trans-resveratrol solution through quartz, the formation of another two compounds apart from cis-resveratrol was observed.