Adapting BODIPYs to singlet oxygen production on silica nanoparticles

Polymer Dots with Delayed Fluorescence and Tunable Cellular Uptake for Photodynamic Therapy and Time-Gated Imaging

By combining bioimaging and photodynamic therapy (PDT), it is possible to treat cancer through a theranostic approach with targeted action for minimum invasiveness and side effects. Thermally activated delayed fluorescence (TADF) probes have gained recent interest in theranostics due to their ability to generate singlet oxygen (1O2) while providing delayed emission that can be used in time-gated imaging. However, it is still challenging to design systems that simultaneously show (1) high contrast for imaging, (2) low dark toxicity but high phototoxicity and (3) tunable biological uptake. Here, we circumvent shortcomings of TADF systems by designing block copolymers and their corresponding semiconducting polymer dots (Pdots) that encapsulate a TADF dye in the core and expose an additional boron-dipyrromethene (BODIPY) oxygen sensitizer in the corona. This architecture provides orange-red luminescent particles (ΦPL up to 18 %) that can efficiently promote PDT (1O2 QY=42 %) of HeLa cells with very low photosensitizer loading (IC50 ~0.05-0.13 μg/mL after 30 min). Additionally, we design Pdots with tunable cellular uptake but similar PDT efficiencies using either polyethylene glycol or guanidinium-based coronas. Finally, we demonstrate that these Pdots can be used for time-gated imaging to effectively filter out background fluorescence from biological samples and improve image contrast.

Anthraquinone-Modified Silica Nanoparticles as Heterogeneous Photocatalyst for the Oxidative Hydroxylation of Arylboronic Acids

In this work, the synthesis and characterization of a heterogeneous photocatalyst based on spherical silica nanoparticles superficially modified with anthraquinone 2-carboxylic acid (AQ-COOH) are presented. The nanomaterial was characterized by TEM, SEM, FT-IR, diffuse reflectance, fluorescence, NMR, DLS, XRD and XPS. These analyses confirm the covalent linking of AQ-COOH with the NH2 functionality in the nanomaterial and, more importantly, the photocatalyst retains its photophysical properties once bound. The heterogeneous photocatalyst was successfully employed in the aerobic hydroxylation of arylboronic acids to phenols under sustainable reaction conditions. Phenols were obtained in high yields (up to 100 %) with low catalyst loading (3.5 mol %), reaching TOF values of 3.7 h-1 . Using 2-propanol as solvent at room temperature, the visible light photocatalysis produced H2 O2 as a key intermediate to promote the aerobic hydroxylation of arylboronic acids. The heterogeneous photocatalyst was reused at least 5 times, without modification of the nanomaterial structure and morphology. This simple heterogeneous system showed great catalytic activity under sustainable reaction conditions.

Efficient Magneto-Luminescent Nanosystems based on Rhodamine-Loaded Magnetite Nanoparticles with Optimized Heating Power and Ideal Thermosensitive Fluorescence

Nanosystems that simultaneously contain fluorescent and magnetic modules can offer decisive advantages in the development of new biomedical approaches. A biomaterial that enables multimodal imaging and contains highly efficient nanoheaters together with an intrinsic temperature sensor would become an archetypical theranostic agent. In this work, we have designed a magneto-luminescent system based on Fe3O4 NPs with large heating power and thermosensitive rhodamine (Rh) fluorophores that exhibits the ability to self-monitor the hyperthermia degree. Three samples composed of highly homogeneous Fe3O4 NPs of ∼25 nm and different morphologies (cuboctahedrons, octahedrons, and irregular truncated-octahedrons) have been finely synthesized. These NPs have been thoroughly studied in order to choose the most efficient inorganic core for magnetic hyperthermia under clinically safe radiofrequency. Surface functionalization of selected Fe3O4 NPs has been carried out using fluorescent copolymers composed of PMAO, PEG and Rh. Copolymers with distinct PEG tail lengths (5-20 kDa) and different Rh percentages (5, 10, and 25%) have been synthesized, finding out that the copolymer with 20 kDa PEG and 10% Rh provides the best coating for an efficient fluorescence with minimal aggregation effects. The optimized Fe3O4@Rh system offers very suitable fluorescence thermosensitivity in the therapeutic hyperthermia range. Additionally, this sample presents good biocompatibility and displays an excellent heating capacity within the clinical safety limits of the AC field (≈ 1000 W/g at 142 kHz and 44 mT), which has been confirmed by both calorimetry and AC magnetometry. Thus, the current work opens up promising avenues toward next-generation medical technologies.

Photodynamic Therapy by Glucose Transporter 1-Selective Light Inactivation

Chromophore-assisted light inactivation (CALI) was applied to molecule-targeted photodynamic therapy (PDT). In order to identify organic photosensitizers suitable for CALI, the carbonic anhydrase II (CAII) ligand, 4-sulfamoylbenzoic acid 1, was conjugated with several photosensitizers to produce compounds 2-7, whose CALI ability was evaluated by measuring their effect on CAII enzymatic activity. Di-iodinated BODIPY (I₂BODIPY) exhibited excellent CAII inactivation ability, similar to that of Ru(bpy)₃. The glucose-I₂BODIPY conjugate (8) was synthesized as an inactivation of glucose transporter 1 (GLUT1), a protein overexpressed in many cancer cells. Under light irradiation, 8 exhibited concentration-dependent cytotoxicity with half maximal inhibitory concentration (IC₅₀) values of 5.49, 11.14, and 8.73 μM, against human cervical carcinoma (HeLa), human lung carcinoma (A549), and human hepatocellular carcinoma (HepG2) cell lines, respectively. The GLUT1 inhibitor phloretin suppressed the cytotoxicity induced by 8 under light irradiation in a concentration-dependent manner. Western blot analysis indicated that GLUT1 was not detected in cell lines treated with 10 μM 8 under light irradiation. Furthermore, 8 reduced the levels of epidermal growth factor receptor tyrosine kinase (EGFR), phospho-ERK (Y204), and GLUT1 without affecting ERK, α-tubulin, and PCNA protein levels, whereas talaporfin sodium, a clinically approved photosensitizer for PDT, nonspecifically reduced intracellular protein levels in HeLa cells, indicating that 8 has a GLUT1-specific inactivation ability and causes light-induced cytotoxicity by modulating the EGFR/MAPK signaling pathway.

Property Regulation of Conjugated Oligoelectrolytes with Polyisocyanide to Achieve Efficient Photodynamic Antibacterial Biomimetic Hydrogels

Fabricating antibacterial hydrogels with antimicrobial drugs and synthetic biocompatible biomimetic hydrogels is a promising strategy for practical medical applications. Here, we report a bicomponent hydrogel composed of a biomimetic polyisocyanopetide (PIC) hydrogel and a photodynamic antibacterial membrane-intercalating conjugated oligoelectrolyte (COE). The aggregation behavior and aggregate size of the COEs in water can be regulated using the PIC hydrogel, which could induce COEs with higher reactive oxygen species (ROS) production efficiency and increased association of COEs toward bacteria, therefore enhancing the antibacterial efficiency. This strategy provides a facile method for developing biomimetic hydrogels with high antibacterial capability.

Functionalization of Photosensitized Silica Nanoparticles for Advanced Photodynamic Therapy of Cancer

BODIPY dyes have recently attracted attention as potential photosensitizers. In this work, commercial and novel photosensitizers (PSs) based on BODIPY chromophores (haloBODIPYs and orthogonal dimers strategically designed with intense bands in the blue, green or red region of the visible spectra and high singlet oxygen production) were covalently linked to mesoporous silica nanoparticles (MSNs) further functionalized with PEG and folic acid (FA). MSNs approximately 50 nm in size with different functional groups were synthesized to allow multiple alternatives of PS-PEG-FA decoration of their external surface. Different combinations varying the type of PS (commercial Rose Bengal, Thionine and Chlorine e6 or custom-made BODIPY-based), the linkage design, and the length of PEG are detailed. All the nanosystems were physicochemically characterized (morphology, diameter, size distribution and PS loaded amount) and photophysically studied (absorption capacity, fluorescence efficiency, and singlet oxygen production) in suspension. For the most promising PS-PEG-FA silica nanoplatforms, the biocompatibility in dark conditions and the phototoxicity under suitable irradiation wavelengths (blue, green, or red) at regulated light doses (10-15 J/cm2) were compared with PSs free in solution in HeLa cells in vitro.

Efficient Photodynamic Therapy against Gram-Positive and Gram-Negative Bacteria Using Rose Bengal Encapsulated in Metallocatanionic Vesicles in the Presence of Visible Light

Significant consumption of antibiotics has generated multidrug resistance in bacteria, which is a major menace to human beings. Antibacterial photodynamic therapy (aPDT) is a progressing technique for inhibition of bacterial infection with minimal side effects. Metals and delivering agents play a major role in aPDT efficiency. Herein, we report a formulation to enrich the antibacterial photodynamic therapy utilizing metallocatanionic vesicles (MCVs) against both Gram-positive and Gram-negative bacteria. These MCVs were synthesized by utilizing iron-based double-chain metallosurfactant [FeCPC(II)] as a cationic surfactant and AOT, a double-chain anionic surfactant. These synthesized MCV fractions were characterized by distinct techniques like DLS, zeta potential, FE-SEM, confocal microscopy, SAXS, and UV-Visible spectroscopy. Polyhedral-shaped MCVs with a size of 200 nm were formed, wherein the charge and size of the catanionic vesicle can be controlled by varying the mixing ratios. Both Gram-positive bacteria, i.e., methicillin-resistant Staphylococcus aureus (MRSA), and Gram-negative bacteria, i.e., Escherichia coli (E. coli), were used for aPDT using Rose Bengal (RB) as a photosensitizer (PS) encapsulated in MCVs in the presence of a 532 nm wavelength laser. The aPDT against bacterial cells was evaluated for both dark and light toxicities. Pure MCVs also exhibited good antibacterial properties; however, much enhancement was observed in the presence of RB encapsulated in MCVs under light, where eradication of bacteria (E. coli and MRSA) was achieved in 30 min. The observations demonstrated that it is the presence of metal that enhances the singlet oxygen quantum yield of RB and MCVs help in retarding self-quenching and enhanced solubilization of RB. The cationic surfactant-rich fraction shows strong adhesion toward bacteria via electrostatic interactions. The outcome of this research shows that these newly fabricated metal-based metallocatanionic vesicles were effective against both Gram-positive and Gram-negative bacteria using aPDT and must be exploited for clinical applications as well as an alternative for antibiotics in the future.

Functionalized Fluorescent Silica Nanoparticles for Bioimaging of Cancer Cells

Functionalized fluorescent silica nanoparticles were designed and synthesized to selectively target cancer cells for bioimaging analysis. The synthesis method and characterization of functionalized fluorescent silica nanoparticles (50-60 nm), as well as internalization and subcellular localization in HeLa cells is reported here. The dye, rhodamine 101 (R101) was physically embedded during the sol-gel synthesis. The dye loading was optimized by varying the synthesis conditions (temperature and dye concentration added to the gel) and by the use of different organotriethoxysilanes as a second silica precursor. Additionally, R101, was also covalently bound to the functionalized external surface of the silica nanoparticles. The quantum yields of the dye-doped silica nanoparticles range from 0.25 to 0.50 and demonstrated an enhanced brightness of 230-260 fold respect to the free dye in solution. The shell of the nanoparticles was further decorated with PEG of 2000 Da and folic acid (FA) to ensure good stability in water and to enhance selectivity to cancer cells, respectively. In vitro assays with HeLa cells showed that fluorescent nanoparticles were internalized by cells accumulating exclusively into lysosomes. Quantitative analysis showed a significantly higher accumulation of FA functionalized fluorescent silica nanoparticles compared to nanoparticles without FA, proving that the former may represent good candidates for targeting cancer cells.

Exploring BODIPY Derivatives as Singlet Oxygen Photosensitizers for PDT

This minireview is devoted to honoring the memory of Dr. Thomas Dougherty, a pioneer of modern photodynamic therapy (PDT). It compiles the most important inputs made by our research group since 2012 in the development of new photosensitizers based on BODIPY chromophore which, thanks to the rich BODIPY chemistry, allows a finely tuned design of the photophysical properties of this family of dyes to serve as efficient photosensitizers for the generation of singlet oxygen. These two factors, photophysical tuning and workable chemistry, have turned BODIPY chromophore as one of the most promising dyes for the development of improved photosensitizers for PDT. In this line, this minireview is mainly related to the establishment of chemical methods and structural designs for enabling efficient singlet oxygen generation in BODIPYs. The approaches include the incorporation of heavy atoms, such as halogens (iodine or bromine) in different number and positions on the BODIPY scaffold, and also transition metal atoms, by their complexation with Ir(III) center, for instance. On the other hand, low-toxicity approaches, without involving heavy metals, have been developed by preparing several orthogonal BODIPY dimers with different substitution patterns. The advantages and drawbacks of all these diverse molecular designs based on BODIPY structural framework are described.