Photodynamic Therapy with Targeted Release of Boron-Dipyrromethene Dye from Cobalt(III) Prodrugs in Red Light.

Boron-dipyrromethene (BODIPY) dyes are promising photosensitizers for cellular imaging and photodynamic therapy (PDT) owing to their excellent photophysical properties and the synthetically tunable core. Metalation provides a convenient way to overcome the drawbacks arising from their low aqueous solubility. New photo-/redox-responsive Co(III) prodrug chaperones are developed as anticancer PDT agents for efficient cellular delivery of red-light-active BODIPY dyes. The photobiological activity of heteroleptic Co(III) complexes derived from tris(2-pyridylmethyl)amine (TPA) and acetylacetone-conjugated PEGylated distyryl BODIPY (HL1) or its dibromo analogue (HL2), [CoIII(TPA)(L1/L2)](ClO4)2 (1 and 2), are investigated. The Co(III)/Co(II) redox potential is tuned using the Co(III)-TPA scaffold. Complex 1 displays the in vitro release of BODIPY on red light irradiation. Complex 2, having good singlet oxygen quantum yield (ΦΔ âˆ¼ 0.28 in DMSO), demonstrates submicromolar photocytotoxicity to HeLa cancer cells (IC50 ≈ 0.23 µM) while being less toxic to HPL1D normal cells in red light. Cellular imaging using the emissive complex 1 shows mitochondrial localization and significant penetration into the HeLa tumor spheroids. Complex 2 shows supercoiled DNA photocleavage activity and apoptotic cell death through phototriggered generation of reactive oxygen species. The Co(III)-BODIPY prodrug conjugates exemplify new type of phototherapeutic agents with better efficacy than the organic dyes alone in the phototherapeutic window.

Discovery of Subcellular-Targeted Aza-BODIPY Photosensitizers for Efficient Photodynamic Antitumor Therapy.

In this study, we linked classical organelle-targeting groups, such as triphenylphosphonium, pentafluorobenzene, and morpholine, to our previously reported potent monoiodo Aza-BODIPY photosensitizer (BDP-15). They were conveniently prepared and retained the advantages of Aza-BODIPY PS with intense NIR absorption, moderate quantum yield, potent photosensitizing efficiency, and good stability. The in vitro antitumor assessment indicated that mitochondria-targeting and lysosome-targeting groups were more effective than ER-targeting groups. Considering undesirable dark toxicity of triphenylphosphonium-modified PSs, compound 6 containing amide-linked morpholine possessed a favorable dark/phototoxicity ratio (>6900 for tumor cells) and was localized in lysosomes with Pearson's coefficient of 0.91 to Lyso-Tracker Green DND-26. 6 exhibited significantly increased intracellular ROS production and resulted in early/late apoptosis and necrosis to disrupt tumor cells. Moreover, in vivo antitumor efficacy exploration suggested that even under a slightly low dose of light (30 J/cm2) and single-time photoirradiation, 6 retarded tumor growth dramatically and displayed much better PDT activity over BDP-15 and Ce6.

Lysosome directed red light photodynamic therapy using glycosylated iron-(III) conjugates of boron-dipyrromethene.

To overcome the drawbacks associated with chemotherapeutic and porphyrin-based photodynamic therapy (PDT) agents, the use of BODIPY (boron-dipyrromethene) scaffold has gained prominence in designing a new generation of photosensitizers-cum-cellular imaging agents. However, their poor cell permeability and limited solubility in aqueous medium inhibits the in-vitro application of their organic form. This necessitates the development of metal-BODIPY conjugates with improved physiological stability and enhanced therapeutic efficacy. We have designed two iron(III)-BODIPY conjugates, [Fe(L1/2)(L3)Cl] derived from benzyl-dipicolylamine and its glycosylated analogue along with a BODIPY-tagged catecholate. The complexes showed intense absorption bands (ε âˆ¼ 55,000 M-1 cm-1) and demonstrated apoptotic PDT activity upon red-light irradiation (30 J/cm2, 600-720 nm). The complex with singlet oxygen quantum yield value of ∼0.34 gave sub-micromolar IC50 (half-maximal inhibitory concentration) value (∼0.08 µM) in both HeLa and H1299 cancer cells with a photocytotoxicity index value of >1200. Both the complexes were found to have significantly lower cytotoxic effects in non-cancerous HPL1D (human peripheral lung epithelial) cells. Singlet oxygen was determined to be the prime reactive oxygen species (ROS) responsible for cell damage from pUC19 DNA photo-cleavage studies, 1,3-diphenylisobenzofuran and SOSG (Singlet Oxygen Sensor Green) assays. Cellular imaging studies showed excellent fluorescence from complex 2 within 4 h, with localization in lysosomes. Significant drug accumulation into the core of 3D multicellular tumor spheroids was observed within 8 h from intense in-vitro emission. The complexes exemplify iron-based targeted PDT agents and show promising results as potential transition metal-based drugs for ROS mediated red light photocytotoxicity with low dosage requirement.

Oxygen Self-Supplying Nanotherapeutic for Mitigation of Tissue Hypoxia and Enhanced Photodynamic Therapy of Bacterial Keratitis.

Hypoxia, a common characteristic of bacterial infections, is known to be closely associated with the emergence of multidrug-resistant bacteria, which hastens the need to develop advanced microbicides and antibacterial techniques. Photodynamic therapy is a promising strategy to reduce bacterial antibiotic resistance and employs photosensitizers, excitation light sources, and sufficient oxygen to generate toxic reactive oxygen species (ROS). The inherent limitation of PDT is that the generation of ROS is restricted by the hypoxic microenvironment in infection sites. Here, an oxygen self-supplying nanotherapeutic is developed to enhance antibacterial activity against multidrug-resistant bacteria on the basis of fluorinated boron dipyrromethene (BODIPY)-based glycomimetics. The nanotherapeutic not only could capture the bacteria efficiently but also was able to act as an oxygen carrier to relieve the hypoxic microenvironment of bacterial infections, thus achieving enhanced PDT efficacy. In a Pseudomonas aeruginosa infection of a rat cornea, typical administration of the nanotherapeutic decreased the infiltrate and showed a faster healing capacity in comparison with BODIPY-based glycomimetics. Self-supplying oxygen nanotherapeutics that relieve the hypoxic microenvironment and interfere with bacterial colonization have been shown to be a promising candidate for the management of drug-resistant microbial keratitis.

Chitosan/boron nitride nanobiocomposite films with improved properties for active food packaging applications.

Chitosan (CS)/boron nitride nanoplatelet (BNNP) nanobiocomposite films were successfully prepared. Morphological results showed good dispersion of BNNPs in the CS matrix. After loading with BNNPs, water solubility (WS) and moisture absorption of the CS film decreased. The WS decreased from 41.2 to 27.8% at 7 wt% BNNP loading. Additionally, water vapor permeation decreased from 4.2 × 10-11 for pure CS film to 2.9 × 10-11 g m-1s-1Pa-1 at 7 wt% BNNP inclusion. The oxygen permeability of CS film decreased by up to 84% at 7 wt% BNNP loading. The composites showed better sodium hydroxide resistance compared with pure CS. Thermal stability of the composites was higher than the pure CS, up to 35 °C increase at 7 wt% BNNP loading. The addition of 5 wt% BNNPs improved Young's modulus by up to 45% compared with pure CS film. Cytotoxicity of the films decreased after loading with BNNPs.

Oxoplatin-B, a cisplatin-based platinum(IV) complex with photoactive BODIPY for mitochondria specific "chemo-PDT" activity.

Oxoplatin-B, a platinum(IV) complex [Pt(NH3)2Cl2(L1)(OH)] (1) of 4-methylbenzoic acid (HL1) functionalized with 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) was prepared, characterized and its antitumor activity studied. [Pt(NH3)2Cl2(L2)(OH)] (2) of 4-methylbenzoic acid (HL2) was studied as a control. Complex 1 showed an absorption band at 500 nm (ɛ = 4.34 × 104 M-1 cm-1) and an emission band at 515 nm (λex = 488 nm, ΦF = 0.64) in 1% dimethyl sulfoxide/Dulbecco's Modified Eagle's Medium (pH = 7.2). Visible light-induced (400-700 nm) generation of singlet oxygen was evidenced from 1,3-diphenylisobenzofuran titration study. Complex 1 showed photo-induced cytotoxicity in visible light (400-700 nm, 10 J cm-2) against human breast cancer (MCF-7), cervical cancer (HeLa) and lung cancer (A549) cells (IC50: 1.1-3.8 µM) while being less toxic in normal cells. Confocal imaging showed mitochondrial localization with additional evidence from platinum content from isolated mitochondria and 5,5,6,6'-tetrachloro-1,1',3,3' tetraethylbenzimi-dazoylcarbocyanine iodide (JC-1) assay. Cellular apoptosis was observed from Annexin-V-FITC (fluorescein isothiocyanate)/propidium iodide assay.

Biodegradable Polymersomes with Structure Inherent Fluorescence and Targeting Capacity for Enhanced Photo-Dynamic Therapy.

Biodegradable nanostructures displaying aggregation-induced emission (AIE) are desirable from a biomedical point of view, due to the advantageous features of loading capacity, emission brightness, and fluorescence stability. Herein, biodegradable polymers comprising poly (ethylene glycol)-block-poly(caprolactone-gradient-trimethylene carbonate) (PEG-P(CLgTMC)), with tetraphenylethylene pyridinium-TMC (PAIE) side chains have been developed, which self-assembled into well-defined polymersomes. The resultant AIEgenic polymersomes are intrinsically fluorescent delivery vehicles. The presence of the pyridinium moiety endows the polymersomes with mitochondrial targeting ability, which improves the efficiency of co-encapsulated photosensitizers and improves therapeutic index against cancer cells both in vitro and in vivo. This contribution showcases the ability to engineer AIEgenic polymersomes with structure inherent fluorescence and targeting capacity for enhanced photodynamic therapy.

Low-cost commercial borosilicate glass slides for passive radiation dosimetry.

For x- and gamma- irradiations delivering entrance doses from 2- up to 1000 Gy to commercial 1.0 mm thick borosilicate glass microscope slides, study has been made of their thermoluminescence yield. With an effective atomic number of 10.6 (approximating bone equivalence), photon energy dependency is apparent in the low x-ray energy range, with interplay between the photoelectric effect and attenuation. As an example, over the examined dose range, at 120 kVp the photon sensitivity has been found to be some 5× that of 60Co gamma irradiations, also with repeatability to within ~1%. The glow-curves, taking the form of a single prominent broad peak, have been deconvolved yielding at best fit a total of five peaks, the associated activation energies and frequency factors also being obtained. The results indicate borosilicate glass slides to offer promising performance as a low-cost passive radiation dosimeter, with utility for both radiotherapy and industrial applications.

Discovery of a Monoiodo Aza-BODIPY Near-Infrared Photosensitizer: in vitro and in vivo Evaluation for Photodynamic Therapy.

Photodynamic therapy (PDT) as a rising platform of the cancer treatment method is receiving increased attention. Through systematic evaluation of halogen substitution on aza-4,4-difluoro-4-bora-3a,4a-diaza-s-indacenes (BODIPY), we have found that monoiodo-derived aza-BODIPYs provided greater efficacy than other halogenated aza-BODIPY PSs. 4 and 15 as monoiodinated aza-BODIPY dyes containing p-methoxyphenyl moiety were identified to be potent NIR aza-BODIPY-type PSs with IC50 values against HeLa cells at a light dose of 54 J/cm2 as low as 76 and 81 nM, respectively. 4 possessed superior phototoxicity, low dark toxicity, and good thermal/photostability and distributed majorly in mitochondria in cells. Apoptosis was verified to be the main cell death pathway, and in vitro reactive oxygen species generation was demonstrated. In vivo whole-body fluorescence imaging and ex vivo organ distribution studies suggested that 4 afforded an excellent PDT effect with a low drug dose under single-time light irradiation and revealed advantages over known PSs of ADPM06 and Ce6.

Exploring the relationship between structure and activity in BODIPYs designed for antimicrobial phototherapy.

A synthetic strategy to BODIPY dyes is presented giving access to a range of new compounds relevant in the context of antimicrobial photodynamic therapy (aPDT). BODIPYs with the 8-(4-fluoro-3-nitrophenyl) and the 8-pentafluorophenyl substituents were used for the synthesis of new mono- and dibrominated BODIPYs. The para-fluorine atoms in these electron-withdrawing groups facilitate functional modification via nucleophilic aromatic substitution (SNAr) with a number of amines and thio-carbohydrates. Subsequently, the antibacterial phototoxic activity of these BODIPYs has been assessed in bacterial assays against the Gram-positive germ S. aureus and also against the Gram-negative germ P. aeruginosa. The bacterial assays allowed to identify substitution patterns which ensured antibacterial activity not only in phosphate-buffered saline (PBS) but also in the presence of serum, hereby more realistically modelling the complex biological environment that is present in clinical applications.

Water-Soluble BODIPY Photocages with Tunable Cellular Localization.

Photoactivation of bioactive molecules allows manipulation of cellular processes with high spatiotemporal precision. The recent emergence of visible-light excitable photoprotecting groups has the potential to further expand the established utility of the photoactivation strategy in biological applications by offering higher tissue penetration, diminished phototoxicity, and compatibility with other light-dependent techniques. Nevertheless, a critical barrier to such applications remains the significant hydrophobicity of most visible-light excitable photocaging groups. Here, we find that applying the conventional 2,6-sulfonation to meso-methyl BODIPY photocages is incompatible with their photoreaction due to an increase in the excited state barrier for photorelease. We present a simple, remote sulfonation solution to BODIPY photocages that imparts water solubility and provides control over cellular permeability while retaining their favorable spectroscopic and photoreaction properties. Peripherally disulfonated BODIPY photocages are cell impermeable, making them useful for modulation of cell-surface receptors, while monosulfonated BODIPY retains the ability to cross the cellular membrane and can modulate intracellular targets. This new approach is generalizable for controlling BODIPY localization and was validated by sensitization of mammalian cells and neurons by visible-light photoactivation of signaling molecules.

pH-Activatable Singlet Oxygen-Generating Boron-dipyrromethenes (BODIPYs) for Photodynamic Therapy and Bioimaging.

Singlet oxygen can severely damage biological tissue, which is exploited in photodynamic therapy (PDT). In PDT, the effective range is limited by the distribution of the photosensitizer (PS) and the illuminated area. However, no distinction is made between healthy and pathological tissue, which can cause undesired damage. This encouraged us to exploit the more acidic pH of cancerous tissue and design pH-controllable singlet oxygen-generating boron-dipyrromethene (BODIPY) dyes. A pH sensitivity of the dyes is achieved by the introduction of an electronically decoupled, photoinduced electron transfer (PET)-capable subunit in meso-position of the BODIPY core. To favor triplet-state formation as required for singlet oxygen generation, iodine substituents were introduced at the chromophore core. The resulting pH-controlled singlet oxygen-generating dyes with pKa values in the physiological range were subsequently assessed regarding their potential as pH-controlled PS for PDT. Using HeLa cells, we could successfully demonstrate markedly different pH-dependent cytotoxicities upon illumination.

A bioorthogonally activatable photosensitiser for site-specific photodynamic therapy.

A boron dipyrromethene based photosensitiser substituted with a 1,2,4,5-tetrazine moiety has been prepared of which the photoactivity can be activated upon an inverse-electron-demand Diels-Alder reaction with trans-cyclooctene derivatives. By using a biotin-conjugated trans-cyclooctene to tag the biotin-receptor-positive HeLa cells, this photosensitiser exhibits site-specific activation through cycloaddition, leading to high photocytotoxicity.

Self-quenching synthesis of coordination polymer pre-drug nanoparticles for selective photodynamic therapy.

The design and preparation of a photoactive coordination polymer nanoplatform with tumor-related stimuli-activatability and biodegradability is highly desirable for achieving highly precise photodynamic therapy (PDT). Herein, novel "pre-photodynamic" nanoparticles (Fe-IBDP NPs) with a tumor microenvironment (TME)-activatable PDT and good biodegradability were synthesized by carrying out facile coordination assembly of an IBDP photosensitizer with an Fe3+ quenching agent. After being taken up by cancer cells, our "inactive" Fe-IBDP NPs were activated by the TME and as a result decomposed and released the photoactive carboxyl-functionalized diiodo-substituted BODIPY (IBDP) photosensitizer, which generated cytotoxic singlet oxygen (1O2) under light irradiation. By contrast, these NPs showed relatively low cytotoxicity in normal cells. This work also provided a feasible method for preparing the next generation of photoactive nanomedicines for use in precise phototherapy.

A Conformationally Restricted Aza-BODIPY Platform for Stimulus-Responsive Probes with Enhanced Photoacoustic Properties.

Photoacoustic (PA) dyes, which absorb near-infrared (NIR) light to generate an ultrasonic signal, can be detected at centimeter depths in tissues with significantly higher resolution than dyes imaged with fluorescence-based methods. As such, PA agents show great promise as research tools for the study of live-animal disease models. However, the development of activatable PA probes has been hampered by the relative scarcity of appropriate PA-active molecular platforms with properties that can be manipulated in a rational manner. Herein we synthesized and evaluated six modifications to the aza-BODIPY dye platform with respect to their absorbance, fluorescence, and PA properties. We identified a promising conformationally restricted aza-BODIPY (CRaB) scaffold that prioritizes three criteria necessary for the design of stimulus-responsive dyes with optimal ratiometric PA response: absorbance at NIR wavelengths, strong PA intensity, and large Δλ upon interaction with the desired stimulus. Using this scaffold, we synthesized three chemically diverse stimulus-responsive PA probes and demonstrated between 2- and 8-fold improvements in theoretical ratiometric response in vitro. This suggests that improvements in PA parameters are generalizable. Finally, we validated the in vitro turnover of each CRaB PA probe and demonstrated the in vivo potential of the CRaB scaffold by direct comparison to an established hypoxia-responsive probe for the detection of tumor hypoxia.

Novel aza-BODIPY based small molecular NIR-II fluorophores for in vivo imaging.

The development of new NIR-II fluorophores, particularly those with facile syntheses, high fluorescence quantum yields, and stable and tunable photophysical properties, is challenging. Herein, we report a new class of small molecular NIR-II fluorophores based on aza-dipyrromethene boron difluoride (aza-BODIPY) dyes. We demonstrate promising photophysical properties of these dyes, such as large Stokes shift, superior photostability, and good fluorescence brightness as nanoparticles in aqueous solution. Because of these properties and high resolution and deep penetration NIR-II imaging ability, the aza-BODIPY based dyes show great potential as NIR-II imaging agents.

A novel BODIPY-based photosensitizer with pH-active singlet oxygen generation for photodynamic therapy in lysosomes.

A novel photosensitizer BDPI-lyso has been developed for photodynamic therapy (PDT). The photosensitizer BDPI-lyso showed a high singlet oxygen quantum yield (ΦΔ = 0.95) and low fluorescence quantum yield (ΦF = 0.05) in EtOH. Different singlet oxygen quantum yields were found in acidic solution (pH = 5, ΦΔ = 0.51) and in neutral solution (pH = 7, ΦΔ = 0.38). DFT and TD-DFT calculations of BDPI-lyso and its protonated product BDPI-lysoH+ indicated that the S1/T3 transition was responsible for the intersystem crossing (ISC) enhancement which would promote the production of singlet oxygen. The negligible dark cytotoxicity toward the hepatoma cell line Bel-7402 was confirmed by MTT assay, AO/EB dual staining, and cell images. Upon exposure to a low dose of light illumination, the disruption of the cell plasma membrane and the calculated half-maximal inhibitory concentration (IC50) of 0.4 µM showed a high phototoxicity of the photosensitizer BDPI-lyso. The light-induced intracellular ROS generation was verified as the PDT mechanism of BDPI-lyso. Colocalization experiments of LysoTracker Green and BDPI-lyso in the dark indicated the good lysosome-targeting ability of BDPI-lyso. The images of cells costained with LysoTracker Green and BDPI-lyso, and the appearance of intracellular and extracellular blebs with green fluorescence after light illumination revealed the light-induced dysfunction of lysosomes and cell apoptosis.

Enantioselective [2+2] Cycloadditions of Cinnamate Esters: Generalizing Lewis Acid Catalysis of Triplet Energy Transfer.

We report the enantioselective [2+2] cycloaddition of simple cinnamate esters, the products of which are useful synthons for the controlled assembly of cyclobutane natural products. This method utilizes a cocatalytic system in which a chiral Lewis acid accelerates the transfer of triplet energy from an excited-state Ir(III) photocatalyst to the cinnamate ester. Computational evidence indicates that the principal role of the Lewis acid cocatalyst is to lower the absolute energies of the substrate frontier molecular orbitals, leading to greater electronic coupling between the sensitizer and substrate and increasing the rate of the energy transfer event. These results suggest Lewis acids can have multiple beneficial effects on triplet sensitization reactions, impacting both the thermodynamic driving force and kinetics of Dexter energy transfer.

Mitochondrial Localization of Highly Fluorescent and Photostable BODIPY-Based Ruthenium(II), Rhodium(III), and Iridium(III) Metal Complexes.

A new N,O-based BODIPY ligand was synthesized and further utilized to develop highly fluorescent and photostable Ru(II), Rh(III), and Ir(III) metal complexes. The complexes were fully characterized by different analytical techniques including single-crystal XRD studies. The photostabilities and live cell imaging capabilities of the complexes were investigated via confocal microscopy. The complexes localized specifically in the mitochondria of live cells and showed negligible cytotoxicities at a concentration used for imaging purposes. They also exhibited high photostabilities, with fluorescence intensities remaining above 50% after 1800 scans.

A highly selective and ultrasensitive ratiometric fluorescent probe for peroxynitrite and its two-photon bioimaging applications.

In this work, taking full advantage of the intramolecular charge transfer (ICT) mechanism, a hydroxynaphthalimide-based ratiometric two-photon fluorescent probe RTP-PN was synthesized to detect ONOO-. Probe RTP-PN could accurately detect ONOO- in the range of 1.4 nM-1.4 µM with the detection limit of 1.4 nM by a ratiometric fluorescence spectroscopy method. Additionally, probe RTP-PN exhibited an ultrafast response for ONOO- than other various species including H2O2 and ClO-. Finally, probe RTP-PN was successfully adopted to detect intracellular ONOO- by the two-photon excitation microscopy.