Synthesis and Photophysical Properties of Tumor-Targeted Water-Soluble BODIPY Photosensitizers for Photodynamic Therapy

Pd and Pt Complexes of Benzo-Fused Dipyrrins: Synthesis, Structure, Electrochemical, and Optical Properties

Benzo-fused dipyrrins are π-extended analogs of conventional dipyrrins, which exhibit bathochromically shifted absorption and possess the synthetic capability to bind various metal ions. We aimed to investigate the synthetic potential of benzo-fused dipyrrins in the complexation with transition metals. Two new complexes with Pd2+ and Pt2+ were synthesized and characterized. X-ray crystallography reveals that both complexes exhibit a zigzag geometry with square planar coordination of the central metal. The Pd2+ complex possesses a very weak fluorescence at 665 nm, while the Pt2+ complex is completely nonemissive. Transient absorption spectroscopy confirmed triplet excited state formation for both complexes; however, they are short-lived and no phosphorescence was observed even at 77K. DFT calculations support the experimental observation, revealing the existence of the low-lying ligand-metal charge-transfer (LMCT) triplet state acting as an energy sink.

Triphenylphosphonium-functionalized dimeric BODIPY-based nanoparticles for mitochondria-targeting photodynamic therapy

The dimerization of boron dipyrromethene (BODIPY) moieties is an appealing molecular design approach for developing heavy-atom-free triplet photosensitizers (PSs). However, BODIPY dimer-based PSs generally lack target specificity, which limits their clinical use for photodynamic therapy. This study reports the synthesis of two mitochondria-targeting triphenylphosphonium (TPP)-functionalized meso-β directly linked BODIPY dimers (BTPP and BeTPP). Both BODIPY dimers exhibited solvent-polarity-dependent singlet oxygen (1O2) quantum yields, with maximum values of 0.84 and 0.55 for BTPP and BeTPP, respectively, in tetrahydrofuran. The compact orthogonal geometry of the BODIPY dimers facilitated the generation of triplet excited states via photoinduced charge separation (CS) and subsequent spin-orbit charge-transfer intersystem crossing (SOCT-ISC) processes and their rates were dependent on the energetic configuration between the frontier molecular orbitals of the two BODIPY subunits. The as-synthesized compounds were amphiphilic and hence formed stable nanoparticles (∼36 nm in diameter) in aqueous solutions, with a zeta potential of ∼33 mV beneficial for mitochondrial targeting. In vitro experiments with MCF-7 and HeLa cancer cells indicated the effective localization of BTPP and BeTPP within cancer-cell mitochondria. Under light irradiation, BTPP and BeTPP exhibited robust photo-induced therapeutic effects in both cell lines, with half-maximal inhibitory concentration (IC50) values of ∼30 and ∼55 nM, respectively.

Recent Developments in the Design of New Water-Soluble Boron Dipyrromethenes and Their Applications: An Updated Review

Boron-dipyrromethene (BODIPY) and its derivatives play an important role in the area of organic fluorophore chemistry. Recently, the water-soluble boron-dipyrromethene dyes have increasingly received interest. The structural modification of the BODIPY core by incorporating different neutral and ionic hydrophilic groups makes it water-soluble. The important hydrophilic groups, such as quaternary ammonium, sulfonate, oligoethylene glycol, dicarboxylic acid, and sugar moieties significantly increase the solubility of these dyes in water while preserving their photophysical properties. As a result, these fluorescent dyes are utilized in aqueous systems for applications such as chemosensors, cell imaging, anticancer, biolabeling, biomedicine, metal ion detection, and photodynamic treatment. This review covers the most current developments in the design and synthesis of water-soluble BODIPY derivatives and their wide applications since 2014.

Photodynamic Therapy: From the Basics to the Current Progress of N-Heterocyclic-Bearing Dyes as Effective Photosensitizers

Photodynamic therapy, an alternative that has gained weight and popularity compared to current conventional therapies in the treatment of cancer, is a minimally invasive therapeutic strategy that generally results from the simultaneous action of three factors: a molecule with high sensitivity to light, the photosensitizer, molecular oxygen in the triplet state, and light energy. There is much to be said about each of these three elements; however, the efficacy of the photosensitizer is the most determining factor for the success of this therapeutic modality. Porphyrins, chlorins, phthalocyanines, boron-dipyrromethenes, and cyanines are some of the N-heterocycle-bearing dyes' classes with high biological promise. In this review, a concise approach is taken to these and other families of potential photosensitizers and the molecular modifications that have recently appeared in the literature within the scope of their photodynamic application, as well as how these compounds and their formulations may eventually overcome the deficiencies of the molecules currently clinically used and revolutionize the therapies to eradicate or delay the growth of tumor cells.

Cationic BODIPY Photosensitizers for Mitochondrion-Targeted Fluorescence Cell-Imaging and Photodynamic Therapy

The straightforward synthesis of three cationic boron-dipyrromethene (BODIPY) derivatives and their mitochondria-targeting and photodynamic therapeutic (PDT) capabilities are reported. Two cancer cell lines (HeLa and MCF-7) were used to investigate the PDT activity of the dyes. Compared to their non-halogenated counterparts, halogenated BODIPY dyes exhibit lower fluorescence quantum yields and enable the efficient production of singlet oxygen species. Following LED light irradiation at 520 nm, the synthesized dyes displayed good PDT capabilities against the treated cancer cell lines, with low cytotoxicity in the dark. In addition, functionalization of the BODIPY backbone with a cationic ammonium moiety enhanced the hydrophilicity of the synthesized dyes and, consequently, their uptake by the cells. The results presented here collectively demonstrate the potential of cationic BODIPY-based dyes as therapeutic drugs for anticancer photodynamic therapy.

Photophyical and photosensitizing properties of BODIPYs substantially changed by alkyl- and phenyl-amino groups on meso carbon

meso-RNH (R = C₃H₇, C₄H₉, PhCH₂, H, and Ph) substituted BODIPY compounds have been prepared to examine their photophysical properties and photosensitizing abilities. We have measured the UV-vis absorption, steady state and time resolved fluorescence, excited triplet state formation using laser flash photolysis, singlet oxygen generation ability using chemical trapping method. The results show that the presence of meso-RNH leads to large blue shift of absorption and emission wavelength, remarkable decrease in fluorescence quantum yield and lifetime values, and significant increase in singlet oxygen formation quantum yield. Quantum chemical calculation also reveals the photoinduced charge transfer (PCT) mechanism. We conclude that property changes are due to: 1) S₀ and S₁ geometry, 2) ground state structural isomerization, and 3) intramolecular PCT. These results and mechanisms are helpful for designing new functional materials.

Bromo- and glycosyl-substituted BODIPYs for application in photodynamic therapy and imaging

The introduction of heavy atoms into the BODIPY-core structure has proven to be a straightforward strategy for optimizing the design of such dyes towards enhanced generation of singlet oxygen rendering them suitable as photosensitizers for photodynamic therapy (PDT). In this work, BODIPYs are presented by combining the concept of bromination with nucleophilic aromatic substitution (S_NAr) of a pentafluorophenyl or a 4-fluoro-3-nitrophenyl moiety to introduce functional groups, thus improving the phototoxic effect of the BODIPYs as well as their solubility in the biological environment. The nucleophilic substitution enabled functionalization with various amines and alcohols as well as unprotected thiocarbohydrates. The phototoxic activity of these more than 50 BODIPYs has been assessed in cellular assays against four cancer cell lines in order to more broadly evaluate their PDT potential, thus accounting for the known variability between cell lines with respect to PDT activity. In these investigations, dibrominated polar-substituted BODIPYs, particularly dibrominated glyco-substituted compounds, showed promising potential as photomedicine candidates. Furthermore, the cellular uptake of the glycosylated BODIPYs has been confirmed via fluorescence microscopy.

BODIPYs in PDT: A Journey through the Most Interesting Molecules Produced in the Last 10 Years

Over the past 30 years, photodynamic therapy (PDT) has shown great development. In the clinical setting the few approved molecules belong almost exclusively to the porphyrin family; but in the scientific field, in recent years many researchers have been interested in other families of photosensitizers, among which BODIPY has shown particular interest. BODIPY is the acronym for 4,4-difluoro-4-bora-3a, 4a-diaza-s-indacene, and is a family of molecules well-known for their properties in the field of imaging. In order for these molecules to be used in PDT, a structural modification is necessary which involves the introduction of heavy atoms, such as bromine and iodine, in the beta positions of the pyrrole ring; this change favors the intersystem crossing, and increases the ¹O₂ yield. This mini review focused on a series of structural changes made to BODIPYs to further increase ¹O₂ production and bioavailability by improving cell targeting or photoactivity efficiency.

BODIPY nanoparticles functionalized with lactose for cancer-targeted and fluorescence imaging-guided photodynamic therapy

A series of four lactose-modified BODIPY photosensitizers (PSs) with different substituents (-I, -H, -OCH₃, and -NO₂) in the para-phenyl moiety attached to the meso-position of the BODIPY core were synthesized; the photophysical properties and photodynamic anticancer activities of these sensitizers were investigated, focusing on the electronic properties of the different substituent groups. Compared to parent BODIPY H, iodine substitution (BODIPY I) enhanced the intersystem crossing (ISC) to produce singlet oxygen (¹O₂) due to the heavy atom effect, and maintained a high fluorescence quantum yield (Φ_F) of 0.45. Substitution with the electron-donating methoxy group (BODIPY OMe) results in a significant perturbation of occupied frontier molecular orbitals and consequently achieves higher ¹O₂ generation capability with a high Φ_F of 0.49, while substitution with the electron-withdrawing nitro group (BODIPY NO2) led a perturbation of unoccupied frontier molecular orbitals and induces a forbidden dark S₁ state, which is negative for both fluorescence and ¹O₂ generation efficiencies. The BODIPY PSs formed water-soluble nanoparticles (NPs) functionalized with lactose as liver cancer-targeting ligands. BODIPY I and OMe NPs showed good fluorescence imaging and PDT activity against various tumor cells (HeLa and Huh-7 cells). Collectively, the BODIPY NPs demonstrated high ¹O₂ generation capability and Φ_F may create a new opportunity to develop useful imaging-guided PDT agents for tumor cells.

Mitochondrion-Targeting PEGylated BODIPY Dyes for Near-Infrared Cell Imaging and Photodynamic Therapy

A series of 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene-based photosensitizers (AmBXI, X = H, M, Br) featuring a cationic mitochondrion-targeting group and near-infrared (NIR) absorption was synthesized. After extending the photosensitizers’ π–π conjugation via Knoevenagel...

BODIPY derivatives as fluorescent reporters of molecular activities in living cells

Fluorescent compounds have become indispensable tools for imaging molecular activities in the living cell. 4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) is currently one of the most popular fluorescent reporters due to its unique photophysical properties. This review provides a general survey and presents a summary of recent advances in the development of new BODIPY-based cellular biomarkers and biosensors. The review starts with the consideration of the properties of BODIPY derivatives required for their application as cellular reporters. Then review provides examples of the design of sensors for different biologically important molecules, ions, membrane potential, temperature and viscosity defining the live cell status. Special attention is payed to BODPY-based phototransformable reporters.

The bibliography includes 339 references.

Bringing Color to Sugars: The Chemical Assembly of Carbohydrates to BODIPY Dyes

The combination of carbohydrates with BODIPY fluorophores gives rise to a family of BODIPY-carbohydrate hybrids or glyco-BODIPYs, which mutually benefit from the encounter. Thus, from the carbohydrates standpoint, glyco-BODIPYs can be regarded as fluorescent glycoconjugate derivatives with application in imaging techniques, whereas from the fluorophore view the BODIPY-carbohydrate hybrids benefit from the biocompatibility, water-solubility, and reduced toxicity, among others, brought about by the sugar moiety. In this Account we have intended to present the collection of available methods for the synthesis of BODIPY-carbohydrate hybrids, with a focus on the chemical transformations on the BODIPY core.

Antimicrobial photodynamic therapy against Acinetobacter baumannii

Acinetobacter baumannii (A. baumannii) has emerged as a pathogen of global importance able to cause opportunistic infections on the skin, urinary tract, lungs, and bloodstream, being frequently involved in hospital outbreaks. Such bacterium can resist a variety of environmental conditions and develop resistance to different classes of antibiotics. Antimicrobial photodynamic therapy (aPDT) has been considered a promising approach to overcome bacterial resistance once it does not cause selective environmental pressure on bacteria. In this review, studies on aPDT were accessed on PubMed, and their findings were summarized regarding its efficacy against A. baumannii. The data obtained from the literature show that exogenous photosensitizers belonging to different chemical classes are effective against multidrug-resistant A. baumannii strains. However, most of such data is from in vitro studies, and additional studies are necessary to evaluate if the exogenous photosensitizers may induce selective pressure on A. baumannii and the effectiveness of such photosensitizers in clinical practice.

Photochemical Properties and Stability of BODIPY Dyes

The present study is devoted to the combined experimental and theoretical description of the photophysical properties and photodegradation of the new boron-dipyrromethene (BODIPY) derivatives obtained recently for biomedical applications, such as bacteria photoinactivation (Piskorz et al., Dyes and Pigments 2020, 178, 108322). Absorption and emission spectra for a wide group of solvents of different properties for the analyzed BODIPY derivatives were investigated in order to verify their suitability for photopharmacological applications. Additionally, the photostability of the analyzed systems were thoroughly determined. The exposition to the UV light was found first to cause the decrease in the most intensive absorption band and the appearance of the hypsochromically shifted band of similar intensity. On the basis of the chromatographic and computational study, this effect was assigned to the detachment of the iodine atoms from the BODIPY core. After longer exposition to UV light, photodegradation occurred, leading to the disappearance of the intensive absorption bands and the emergence of small intensity signals in the strongly blue-shifted range of the spectrum. Since the most intensive bands in original dyes are ascribed to the molecular core bearing the BF₂ moiety, this result can be attributed to the significant cleavage of the BF₂ ring. In order to fully characterize the obtained molecules, the comprehensive computational chemistry study was performed. The influence of the intermolecular interactions for their absorption in solution was analyzed. The theoretical data entirely support the experimental outcomes.

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.

Broadband Visible Light-Absorbing [70]Fullerene-BODIPY-Triphenylamine Triad: Synthesis and Application as Heavy Atom-Free Organic Triplet Photosensitizer for Photooxidation

A broadband visible light-absorbing [70]fullerene-BODIPY-triphenylamine triad (C70-B-T) has been synthesized and applied as a heavy atom-free organic triplet photosensitizer for photooxidation. By attaching two triphenylmethyl amine units (TPAs) to the π-core of BODIPY via ethynyl linkers, the absorption range of the antenna is extended to 700 nm with a peak at 600 nm. Thus, the absorption spectrum of C70-B-T almost covers the entire UV-visible region (270-700 nm). The photophysical processes are investigated by means of steady-state and transient spectroscopies. Upon photoexcitation at 339 nm, an efficient energy transfer (ET) from TPA to BODIPY occurs both in C70-B-T and B-T, resulting in the appearance of the BODIPY emission at 664 nm. Direct or indirect (via ET) excitation of the BODIPY-part of C70-B-T is followed by photoinduced ET from the antenna to C70, thus the singlet excited state of C70 (1C70*) is populated. Subsequently, the triplet excited state of C70 (3C70*) is produced via the intrinsic intersystem crossing of C70. The photooxidation ability of C70-B-T was studied using 1,5-dihydroxy naphthalene (DHN) as a chemical sensor. The photooxidation efficiency of C70-B-T is higher than that of the individual components of C70-1 and B-T, and even higher than that of methylene blue (MB). The photooxidation rate constant of C70-B-T is 1.47 and 1.51 times as that of C70-1 and MB, respectively. The results indicate that the C70-antenna systems can be used as another structure motif for a heavy atom-free organic triplet photosensitizer.