Exploring BODIPY Derivatives as Singlet Oxygen Photosensitizers for PDT

Aggregation-Driven Photoinduced α-C(sp3)-H Bond Hydroxylation/C(sp3)-C(sp3) Coupling of Boron Dipyrromethene Dye in Water Reported by Near-Infrared Emission

Molecular aggregation is a powerful tool for tuning advanced materials' photophysical and electronic properties. Here we present a novel potential for the aqueous-solvated aggregated state of boron dipyrromethene (BODIPY) to facilitate phototransformations otherwise achievable only under harsh chemical conditions. We show that the photoinduced symmetry-breaking charge separation state can itself initiate catalyst-free redox chemistry, leading to selective α-C(sp3)-H bond activation/Csp3-Csp3 coupling on the BODIPY backbone. The photoproduction progress was tracked by monitoring the evolution of the strong Stokes-shifted near-infrared emission, resulting from selective self-assembly of the terminal heterodimeric photoproduct into well-ordered J-aggregates, as revealed by X-ray structural analysis. These findings provide a facile and green route to further explore the promising frontier of packing-triggered selective photoconversions via supramolecular engineering.

BODIPY-based photocages: rational design and their biomedical application

Photocages, also known as photoactivated protective groups (PPGs), have been utilized to achieve controlled release of target molecules in a non-invasive and spatiotemporal manner. In the past decade, BODIPY fluorophores, a well-established class of fluorescent dyes, have emerged as a novel type of photoactivated protective group capable of efficiently releasing cargo species upon irradiation. This is due to their exceptional properties, including high molar absorption coefficients, resistance to photochemical and thermal degradation, multiple modification sites, favorable uncaging quantum yields, and highly adjustable spectral properties. Compared to traditional photocages that mainly absorb UV light, BODIPY-based photocages that absorb visible/near-infrared (Vis/NIR) light offer advantages such as deeper tissue penetration and reduced bio-autofluorescence, making them highly suitable for various biomedical applications. Consequently, different types of photoactivated protective groups based on the BODIPY skeleton have been established. This highlight provides a comprehensive overview of the strategies employed to construct BODIPY photocages by substituting leaving groups at different positions within the BODIPY fluorophore, including the meso-methyl position, boron position, 2,6-position, and 3,5-position. Furthermore, the application of these BODIPY photocages in biomedical fields, such as fluorescence imaging and controlled release of active species, is discussed.

Designing Antitrypanosomal and Antileishmanial BODIPY Derivatives: A Computational and In Vitro Assessment

Leishmaniasis and Human African trypanosomiasis pose significant public health threats in resource-limited regions, accentuated by the drawbacks of the current antiprotozoal treatments and the lack of approved vaccines. Considering the demand for novel therapeutic drugs, a series of BODIPY derivatives with several functionalizations at the meso, 2 and/or 6 positions of the core were synthesized and characterized. The in vitro activity against Trypanosoma brucei and Leishmania major parasites was carried out alongside a human healthy cell line (MRC-5) to establish selectivity indices (SIs). Notably, the meso-substituted BODIPY, with 1-dimethylaminonaphthalene (1b) and anthracene moiety (1c), were the most active against L. major, displaying IC50 = 4.84 and 5.41 μM, with a 16 and 18-fold selectivity over MRC-5 cells, respectively. In contrast, the mono-formylated analogues 2b and 2c exhibited the highest toxicity (IC50 = 2.84 and 6.17 μM, respectively) and selectivity (SI = 24 and 11, respectively) against T. brucei. Further insights on the activity of these compounds were gathered from molecular docking studies. The results suggest that these BODIPYs act as competitive inhibitors targeting the NADPH/NADP+ linkage site of the pteridine reductase (PR) enzyme. Additionally, these findings unveil a range of quasi-degenerate binding complexes formed between the PRs and the investigated BODIPY derivatives. These results suggest a potential correlation between the anti-parasitic activity and the presence of multiple configurations that block the same site of the enzyme.

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 ∼ 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.

De Novo Access to BODIPY C-Glycosides as Linker-Free Nonsymmetrical BODIPY-Carbohydrate Conjugates

Recent years have witnessed an increasing interest in the synthesis and study of BODIPY-glycoconjugates. Most of the described synthetic methods toward these derivatives involve postfunctional modifications of the BODIPY core followed by the covalent attachment of the fluorophore and the carbohydrate through a "connector". Conversely, few de novo synthetic approaches to linker-free carbohydrate-BODIPY hybrids have been described. We have developed a reliable modular, de novo, synthetic strategy to linker-free BODIPY-sugar derivatives using the condensation of pyrrole C-glycosides with a pyrrole-carbaldehyde derivative mediated by POCl3. This methodology allows labeling of carbohydrate biomolecules with fluorescent-enough BODIPYs within the biological window, stable in aqueous media, and able to display singlet oxygen generation.

Red fluorescent BODIPY-based nanoparticles for targeted cancer imaging-guided photodynamic therapy

Imaging-guided diagnosis and treatment of cancer hold potential to significantly improve therapeutic accuracies and efficacies. Central to this theragnostic approach has been the use of multicomponent-based multimodal nanoparticles (NPs). Apart from this conventional approach, here we propose a design strategy for the simple and straightforward formulation of NPs based on boron dipyrromethene (BODIPY) derivatives, LaB-X (X = H, Et, and Br). Specifically, the conjugation of lactose to the inherently hydrophobic BODIPY promoted the formation of LaB-X NPs in water. Furthermore, the BODIPY backbone was subjected to distyrylation, dibromination, and diethylation to tailor the optical window and the balance between fluorescence and singlet oxygen generation capabilities. We demonstrate that while the photoinduced anticancer activities of LaB-H and LaB-Et NPs were trivial, LaB-Br NPs effectively induced the apoptotic death of hepatocellular carcinoma cells under red light irradiation while allowing fluorescence cell imaging in the phototherapeutic window. This dual fluorescence photosensitizing activity of LaB-Br NPs could be switched off and on, so that both fluorescence and singlet oxygen generation were paused during NP formation in an aqueous solution, while both processes resumed after cellular uptake, likely due to NP disassembly.

Bromine indirubin FLIM/PLIM sensors to measure oxygen in normoxic and hypoxic PDT conditions

BACKGROUND

The induction of phototoxicity during photodynamic therapy (PDT) is dependent on oxygen availability. For this reason, the development of sensors to measure oxygen and oxygen consumption is extremely important.

APPROACH

In this project we have used Fluorescence Lifetime imaging (FLIM) and Phosphorescence Lifetime Imaging/ delayed Fluorescence Lifetime Imaging (PLIM/dFLIM) to investigate the ability of bromine indirubin derivatives as oxygen sensors.

RESULTS

The oxygen sensitivity of bromine indirubins was detected through PLIM/dFLIM. Moreover, we have observed, by measuring nicotinamide adenine dinucleotide (NADH) FLIM, that bromine indirubin has a significant impact on cellular metabolism by shifting the SCC-4 Cells metabolism from oxidative phosphorylation (OXPHOS) to glycolysis.

CONCLUSIONS

In conclusion, this study successfully achieves its goals and provides important insights into the use of indirubin as a potential oxygen consumption sensor with the capability to identify and differentiate between normoxic and hypoxic regions within the cells.

A Fluorinated BODIPY-Based Zirconium Metal-Organic Framework for In Vivo Enhanced Photodynamic Therapy

Photodynamic therapy (PDT), an emergent noninvasive cancer treatment, is largely dependent on the presence of efficient photosensitizers (PSs) and a sufficient oxygen supply. However, the therapeutic efficacy of PSs is greatly compromised by poor solubility, aggregation tendency, and oxygen depletion within solid tumors during PDT in hypoxic microenvironments. Despite the potential of PS-based metal-organic frameworks (MOFs), addressing hypoxia remains challenging. Boron dipyrromethene (BODIPY) chromophores, with excellent photostability, have exhibited great potential in PDT and bioimaging. However, their practical application suffers from limited chemical stability under harsh MOF synthesis conditions. Herein, we report the synthesis of the first example of a Zr-based MOF, namely, 69-L2, exclusively constructed from the BODIPY-derived ligands via a single-crystal to single-crystal post-synthetic exchange, where a direct solvothermal method is not applicable. To increase the PDT performance in hypoxia, we modify 69-L2 with fluorinated phosphate-functionalized methoxy poly(ethylene glycol). The resulting 69-L2@F is an oxygen carrier, enabling tumor oxygenation and simultaneously acting as a PS for reactive oxygen species (ROS) generation under LED irradiation. We demonstrate that 69-L2@F has an enhanced PDT effect in triple-negative breast cancer MDA-MB-231 cells under both normoxia and hypoxia. Following positive results, we evaluated the in vivo activity of 69-L2@F with a hydrogel, enabling local therapy in a triple-negative breast cancer mice model and achieving exceptional antitumor efficacy in only 2 days. We envision BODIPY-based Zr-MOFs to provide a solution for hypoxia relief and maximize efficacy during in vivo PDT, offering new insights into the design of promising MOF-based PSs for hypoxic tumors.

Highly crystalline and fluorescent BODIPY-labelled phenyl-triazole-coumarins as n-type semiconducting materials for OFET devices

In this work, the synthesis of BODIPY-phenyl-triazole labelled coumarins (BPhTCs) using a two-step approach is described. The influence of the BODIPY appending on the photophysical, electrochemical and thermal properties of the phenyl-triazole-coumarin precursors (PhTCs) was investigated. Band gap energies were measured by absorption spectroscopy (2.20 ± 0.02 eV in the solid and 2.35 ± 0.01 eV in solution) and cyclic voltammetry (2.10 ± 0.05 eV). The results are supported by DFT calculations confirming the presence of lowest LUMO levels that facilitate the electron injection and stabilize the electron transport. Their charge-transport parameters were measured in Organic Field-Effect Transistor (OFET) devices. BPhTCs showed an ambipolar transistor behavior with good n-type charge mobilities (10-2 cm2V-1s-1) allowing these derivatives to be employed as promising semiconducting crystalline and fluorescent materials with good thermal and air stability up to 250 °C.

Targeting Lysosome for Enhanced Cancer Photodynamic/Photothermal Therapy in a "One Stone Two Birds" Pattern

Highly immunogenic programmed death of tumor cells, such as immunogenic cell death (ICD) and pyroptosis, strengthens antitumor responses and thus represents a promising target for cancer immunotherapy. However, the development of ICD and pyroptosis inducers remains challenging, and their efficiency is typically compromised by self-protective autophagy. Here, we report a potent ICD and pyroptosis-inducing strategy by coupling combined photodynamic/photothermal therapy (PTT/PDT) to biological processes in cancer cells. For this purpose, we rationally synthesize a lysosomal-targeting boron-dipyrromethene dimer (BDPd) with intense NIR absorption/emission, high reactive oxygen species (ROS) yield, and photothermal abilities, which can be self-assembled with Pluronic F127, producing lysosomal-acting nanomicelles (BDPd NPs) to facilitate cancer cell internalization of BDPd and generation of intracellular ROS. Owing to the favorable lysosomal-targeting ability of the morpholine group on BDPd, the intracellular BDPd NPs can accumulate in the lysosome and induce robust lysosomal damage in cancer cells upon 660 nm laser irradiation, which results in the synergetic induction of pyroptosis and ICD via activating NLRP3/GSDMD and caspase-3/GSDME pathways simultaneously. More importantly, PTT/PDT-induced self-protective autophagic degradation was blocked due to the dysfunction of lysosomes. Either intratumorally or intravenously, the injected BDPd NPs could markedly inhibit the growth of established tumor tissues upon laser activation, provoke local and systemic antitumor immune responses, and prolong the survival time in the mouse triple-negative breast cancer model. Collectively, this work represents a promising strategy to boost the therapeutic potential of PTT/PDT by coupling phototherapeutic reagents with the subcellular organelles, creating a "one stone two birds" pattern.

Synthesis and biological evaluation of bi-modal BODIPY-conjugated Hoechst applicable for Auger-electron and photodynamic cancer therapy

Current therapeutic approaches to cancer are not fully effective, and so development of more effective treatment is needed. Auger-electron therapy and photodynamic therapy have attracted marked attentions as a promising strategy in cancer treatment. In this study, we synthesized [125I]BH-2/BH-2, which comprised Hoechst and 2,6-diiodo-substituted BODIPY, and evaluated its usefulness as a bi-modal agent for Auger-electron/photodynamic therapy by comparison with the previously reported compound [125I]BH/BH. [125I]BH-2 was obtained at a 13% radiochemical yield. [125I]BH-2 showed similar uptake into the nucleus to [125I]BH, suggesting that Hoechst can function as a nuclear localization tag. HeLa cell viabilities were reduced in both cells exposed to [125I]BH-2 and [125I]BH. γ-H2AX foci in HeLa cells exposed to [125I]BH-2 or [125I]BH were increased in a dose-dependent manner, indicating that DNA double-strand breaks may have occurred. No significant difference was observed between [125I]BH-2 and [125I]BH at these investigations. For PDT application, BH-2 showed a higher singlet oxygen quantum yield (ΦΔ) and caused superior photo-induced cytotoxicity in HeLa cells compared with BH. These results suggest that bi-modal [125I]BH-2/BH-2 can cause anti-tumor effects with Auger-electron and photodynamic therapy.

Antiproliferative activity of meso-substituted BODIPY photocages: Effect of electrophiles vs singlet oxygen

A series of BODIPY compounds with a methylphenol substituent at the meso-position and halogen atoms on the BODIPY core, or OCH3 or OAc substituents at the phenolic moiety was synthesized. Their spectral and photophysical properties and the photochemical reactivity upon irradiation in CH3OH were investigated. The molecules with the phenolic substituent at the meso-position undergo more efficient photo-methanolysis at the boron atom, while the introduction of the OCH3 group at the phenolic moiety changes the reaction selectivity towards the cleavage at the meso-position. The introduction of the halogen atoms into the BODIPY increases the photo-cleavage reaction efficiency, as well as the ability of the molecules to sensitize oxygen and form reactive oxygen species (ROS). The efficiency of the ROS formation was measured in comparison with that of tetraphenylporphyrin. The antiproliferative effect of BODIPY molecules was investigated against three human cancer cell lines MCF-7 (breast carcinoma), H460 (lung carcinoma), HCT116 (colon carcinoma), and two non-cancer cell lines, HEK293T (embryonic kindey) and HaCaT (keratinocytes), with the cells kept in the dark or irradiated with visible light. For most of the compounds a modest or no antiproliferative activity was observed for cells in the dark. However, when cells were irradiated, a dramatic increase in cytotoxicity was observed (more than 100-fold), with IC50 values in the submicromolar concentration range. The enhancement of the cytotoxic effect was explained by the formation of ROS, which was studied for cells in vitro. However, for some BODIPY compounds, the effects due to the formation of electrophilic species (carbocations and quinone methides, which react with biomolecules) cannot be disregarded. Confocal fluorescence microscopy images of H460 cells and HEK293T show that the compounds enter the cells and are retained in the cytoplasm and membranes of the various organelles. When the cells treated with the compounds are irradiated, photo-processes lead to cell death by apoptosis. The study performed is important because it provides bases for the development of novel photo-therapeutics capable of exerting photo-cytotoxic effects in both oxygenated and hypoxic cells.

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(L^1/2)(L³)Cl] derived from benzyl-dipicolylamine and its glycosylated analogue along with a BODIPY-tagged catecholate. The complexes showed intense absorption bands (ε ∼ 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.

Accurate prediction of 11B NMR chemical shift of BODIPYs via machine learning

In this article, we present the results of developing a model based on an RFR machine learning method using the ISIDA fragment descriptors for predicting the ¹¹B NMR chemical shift of BODIPYs. The model is freely available at https://ochem.eu/article/146458. The model demonstrates the high quality of predicting the ¹¹B NMR chemical shift (RMSE, 5CV (FINALE training set) = 0.40 ppm, RMSE (TEST set) = 0.14 ppm). In addition, we compared the "cost" and the user-friendliness for calculations using the quantum-chemical model with the DFT/GIAO approach. The ¹¹B NMR chemical shift prediction accuracy (RMSE) of the model considered is more than three times higher and tremendously faster than the DFT/GIAO calculations. As a result, we provide a convenient tool and database that we collected for all researchers, that allows them to predict the ¹¹B NMR chemical shift of boron-containing dyes. We believe that the new model will make it easier for researchers to correctly interpret the ¹¹B NMR chemical shifts experimentally determined and to select more optimal conditions to perform an NMR experiment.

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.

Photophysical Insights of Halogenated Dipyrrolonaphthyridine-Diones as Potential Photodynamic Therapy Agents†

We report the synthesis and photophysical characterization of novel halogenated dipyrrolonaphthyridine-diones (X2 -DPNDs, X = Cl, Br, and I), as candidates for photodynamic therapy (PDT) application. Apart from the heavy atom-induced spin-orbit coupling (SOC) dynamics in the investigated X2 -DPNDs, it was found that the position of the halogen atom (relative to the nitrogen of the pyrrole ring) also influenced the triplet excited state behavior. Interestingly, the faster/efficiency sensitization of 3 O2 to 1 O2 using X2 -DPND correlates with the rate of triplet population, kISC  >1.6 × 108 s-1 for I2 -DPND vs kISC  >2.9 × 109 s-1 for Cl2 -DPND and Br2 -DPND (where τISC  = 343 ± 3 ps for I2 -DPND and τISC  = 5-6 ns for Cl2 -DPND and Br2 -DPND are the lowest time constants/values for ISC). Furthermore, the heavy atom-induced SOC in Cl2 -DPND and Br2 -DPND did not lead to a reduction of the corresponding fluorescence (ca 75% vs 67% for the parent DPND). The attractive photophysical characteristics of Cl2 /Br2 -DPND put them on the landscape as not only promising PDT agents but also as fluorescence probes. The present study is a stepping stone in the development of novel organic photosystems for synergistic photomedicinal applications.

Cell Uptake of Steroid-BODIPY Conjugates and Their Internalization Mechanisms: Cancer Theranostic Dyes

Estradiol-BODIPY linked via an 8-carbon spacer chain and 19-nortestosterone- and testosterone-BODIPY linked via an ethynyl spacer group were evaluated for cell uptake in the breast cancer cell lines MCF-7 and MDA-MB-231 and prostate cancer cell lines PC-3 and LNCaP, as well as in normal dermal fibroblasts, using fluorescence microscopy. The highest level of internalization was observed with 11β-OMe-estradiol-BODIPY 2 and 7α-Me-19-nortestosterone-BODIPY 4 towards cells expressing their specific receptors. Blocking experiments showed changes in non-specific cell uptake in the cancer and normal cells, which likely reflect differences in the lipophilicity of the conjugates. The internalization of the conjugates was shown to be an energy-dependent process that is likely mediated by clathrin- and caveolae-endocytosis. Studies using 2D co-cultures of cancer cells and normal fibroblasts showed that the conjugates are more selective towards cancer cells. Cell viability assays showed that the conjugates are non-toxic for cancer and/or normal cells. Visible light irradiation of cells incubated with estradiol-BODIPYs 1 and 2 and 7α-Me-19-nortestosterone-BODIPY 4 induced cell death, suggesting their potential for use as PDT agents.

Erlotinib-Modified BODIPY Photosensitizers for Targeted Photodynamic Therapy

Photodynamic therapy (PDT) is an innovative, non-invasive and highly selective therapeutic modality for tumours and non-malignant diseases. BODIPY based molecules can function as new generation photosensitizers (PSs) in various PDT applications. Despite numerous conjugated PS systems are available, BODIPYs containing erlotinib lagged behind other photosensitizer units. In this study, smart photosensitizers containing BODIPY, erlotinib and hydrophilic units were prepared for the first time, their physicochemical properties and PDT effects were investigated. Compared with non-halogenated compound, halogenated derivatives possessed much lower fluorescence profile as well as the good ROS generation ability under red light. In vitro PDT studies were performed on both healthy (PNT1a) and prostate cancerous cells (PC3) to determine the selectivity of the compounds on cancerous cells and their effects under light. The halogenated conjugates, exposed to low dose of light illumination exhibited potent activity on cancer cell viability and the calculated IC₅₀ values proved the high phototoxicity of the photosensitizers. It was also determined that the PSs have very low dark toxicity and that the light illumination and ROS formation are required for the initiation of the cell death mechanism. As a result, erlotinib modified BODIPYs could serve as promising agents in anticancer photodynamic therapy.

Free and Poly-Methyl-Methacrylate-Bounded BODIPYs: Photodynamic and Antimigratory Effects in 2D and 3D Cancer Models

Several limitations, including dark toxicity, reduced tumor tissue selectivity, low photostability and poor biocompatibility hamper the clinical use of Photodynamic therapy (PDT) in cancer treatment. To overcome these limitations, new PSs have been synthetized, and often combined with drug delivery systems, to improve selectivity and reduce toxicity. In this context, BODIPYs (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) have recently emerged as promising and easy-to-handle scaffolds for the preparation of effective PDT antitumor agents. In this study, the anticancer photodynamic effect of newly prepared negatively charged polymethyl methacrylate (nPMMA)-bounded BODIPYs (3@nPMMA and 6@nPMMA) was evaluated on a panel of 2D- and 3D-cultured cancer cell lines and compared with free BODIPYs. In particular, the effect on cell viability was evaluated, along with their ability to accumulate into the cells, induce apoptotic and/or necrotic cell death, and inhibit cellular migration. Our results indicated that 3@nPMMA and 6@nPMMA reduce cancer cell viability in 3D models of HC116 and MCF7 cells more effectively than the corresponding free compounds. Importantly, we demonstrated that MDA-MB231 and SKOV3 cell migration ability was significantly impaired by the PDT treatment mediated by 3@nPMMA and 6@nPMMA nanoparticles, likely indicating the capability of this approach to reduce metastatic tumor potential.

Halogen-free photosensitizers based on meso-enamine-BODIPYs for bioimaging and photodynamic therapy

The search for efficient heavy atom free photosensitizers (PSs) for photodynamic therapy (PDT) is a very active field. We describe herein a simple and easily accessible molecular design based on the attachment of an enamine group as an electron-donor moiety at the meso position of the BODIPY core with different alkylation patterns. The effect of the alkylation degree and solvent polarity on the photophysical properties in terms of splitting absorption bands, fluorescence efficiencies and singlet oxygen production is analyzed in depth experimentally using spectroscopic techniques, including femtosecond and nanosecond transient absorption (fs- and ns-TA) and using computational simulations based on time-dependent density functional theory. The correlation between the theoretical/experimental results permits the rationalization of the observed photophysical behavior exhibited by meso-enamine-BODIPY compounds and the determination of mechanistic details, which rule the population of the triplet state manifold. The potential applicability as a theragnostic agent for the most promising compound is demonstrated through in vitro assays in HeLa cells by analyzing the internalization, localization and phototoxic action.

Ratiometric Singlet Oxygen Sensor Based on BODIPY-DPA Dyad

Compounds sensitive to reactive oxygen species are widely used in the study of processes in living cells and in the development of therapeutic agents for photodynamic therapy. In the present work, we have synthesized a dyad in which the BODIPY dye is chemically bound to 9,10-diphenylanthracene (DPA). Here, DPA acts as a specific sensor of singlet oxygen and BODIPY as a reference dye. We studied the photophysical properties of the BODIPY-DPA dyad and showed that energy transfer occurs between the chromophores. As a result, the compound has excitation maxima in the absorption region of both DPA and BODIPY, but the fluorescence emission occurs mainly from BODIPY. In the presence of singlet oxygen, the excitation maximum of DPA decreases, while the intensity of the excitation maximum of BODIPY remains almost unchanged. This allows the BODIPY-DPA dyad to be used as a ratiometric sensor of singlet oxygen.

BODIPY-Ethynylestradiol molecular rotors as fluorescent viscosity probes in endoplasmic reticulum

Due to their capability for sensing changes in viscosity, fluorescent molecular rotors (FMRs) have emerged as potential tools to develop several promising viscosity probes; most of them, however, localize non-selectively within cells, precluding changes in the viscosity of specific cellular microdomains to be studied by these means. Following previous reports on enhanced fluorophore uptake efficiency and selectivity by incorporation of biological submolecular fragments, here we report two potential BODIPY FMRs based on an ethynylestradiol spindle, a non-cytotoxic semisynthetic estrogen well recognized by human cells. A critical evaluation of the potential of these fluorophores for being employed as FMRs is presented, including the photophysical characterization of the probes, SXRD studies and TD-DFT computations, as well as confocal microscopy imaging in MCF-7 (breast cancer) cells.

Stability of Dibromo-Dipyrromethene Complexes Coordinated with B, Zn, and Cd in Solutions of Various Acidities

The spectral luminescent properties of dipyrromethenates halogenated with bromine on both ends of the long axis and coordinated using boron fluoride, zinc, or cadmium in neutral ethanol and acidified with hydrochloric acid solutions were studied. The constants of the acid-base equilibrium of the complexes in the proton-donor solvents in the ground and excited states was determined. The mechanisms of complex protonation were discussed, depending on the structure of the compounds. The electronic structures of the neutral and protonated compounds were modeled and analyzed based on the quantum-chemical method. The structures and spectral-luminescence properties were calculated using the SMD model of ethanol solvent using the TD-DFT theory with the B3LYP functional and the composite def2-SVP/def2-TZVP/def2-TZVPP_ECP basis sets, depending on the atomic number of the elements.

A visible-light activated ROS generator multilayer film for antibacterial coatings

The current scenario of antibiotic-resistant bacteria and pandemics caused by viruses makes research in the area of antibacterial and antiviral materials and surfaces more urgent than ever. In this regard, salicylideneimine based tetracoordinate boron-containing organic compounds are emerging as a new class of photosensitizers for singlet oxygen generation. However, the inherent inability of small organic molecules to be processed limits their potential use in functional coatings. Here we show the synthesis of a novel polymer functionalized with diiodosalicylideneimine-boron difluoride (PEI-BF2) and its utility for surface coating inside glass vials via layer-by-layer (LbL) assembly. The multilayer thin films are characterized using AFM and UV-Vis spectroscopy and the resultant coatings display excellent stability. The multilayer coating could be activated using visible light, and owing to the photocatalytic activity of the incorporated PEI-BF2, the surface coating is able to generate singlet oxygen efficiently upon light irradiation. Further, the multilayer coated surfaces exhibit remarkable antimicrobial activity towards both Gram-positive and Gram-negative bacteria under a variety of conditions. Thus, owing to the simple synthesis and the convenient methodology adopted for the preparation of multilayer coatings, the material reported here could pave the way for the development of sunlight activated large area self-sterile surfaces.

Switching of Photocatalytic Tyrosine/Histidine Labeling and Application to Photocatalytic Proximity Labeling

Weak and transient protein interactions are involved in dynamic biological responses and are an important research subject; however, methods to elucidate such interactions are lacking. Proximity labeling is a promising technique for labeling transient ligand–binding proteins and protein–protein interaction partners of analytes via an irreversible covalent bond. Expanding chemical tools for proximity labeling is required to analyze the interactome. We developed several photocatalytic proximity-labeling reactions mediated by two different mechanisms. We found that numerous dye molecules can function as catalysts for protein labeling. We also identified catalysts that selectively modify tyrosine and histidine residues and evaluated their mechanisms. Model experiments using HaloTag were performed to demonstrate photocatalytic proximity labeling. We found that both ATTO465, which catalyzes labeling by a single electron transfer, and BODIPY, which catalyzes labeling by singlet oxygen, catalyze proximity labeling in cells.

Photodynamic inactivation of Staphylococcus aureus in the presence of aggregation-prone photosensitizers based on BODIPY used at submicromolar concentrations

Two new brominated BODIPYs (1 and 2) bearing amino acid-based chains (l-valine for 1, and dimethyl-l-lysine for 2) were synthesized and characterized. In organic solvents, 1 and 2 were fully soluble and showed the photophysical properties expected for brominated BODIPY dyes, including efficient generation of singlet oxygen (¹O₂), upon irradiation. In contrast, in aqueous media, both compounds were prone to aggregation and the photo-induced generation of ¹O₂ was halted. Despite the lack of generation of this reactive species in aqueous media (in cuvette), both 1 and 2 have positive antimicrobial Photodynamic Inactivation (aPDI) effect. The activity against gram-positive Staphylococcus aureus and gram-negative Escherichia coli was determined through the inactivation curves, with a total energy dose of 5.3 J/cm² (white light LED used as an energy source). Compound 2 was highly active against both gram-positive and gram-negative bacteria (3 log CFU/mL reduction was obtained at 0.16 μM for S. aureus and 2.5-5.0 μM for E. coli), whereas 1 was less effective to kill S. aureus (3 log CFU/mL at 0.32 μM) and ineffective for E. coli. The higher efficiency of 2, as compared to 1, to reduce the population of bacteria, can reside in the presence of a protonatable residue in 2, allowing a more effective interaction of this molecule with the cell walls of the microorganisms. In order to explain the lack of reactivity in pure aqueous media (in cuvette) and the contrasting good activity in the presence of bacterial cells it can be hypothesized that upon interaction with the walls of the microorganisms, the aggregated photosensitizers suffer a disaggregation process restoring the ability to generate ¹O₂, and hence leading to efficient photodynamic activity against these pathogenic microorganisms, in agreement with the similar effect observed recently for porphyrinoid photosensitizers.

Selenophene-Modified Boron Dipyrromethene-Based Photosensitizers Exhibit Photodynamic Inhibition on a Broad Range of Bacteria

Microorganisms are crucial for human survival in view of both mutualistic and pathogen interactions. The control of the balance could be achieved by use of the antibiotics. There is a continuous arms race that exists between the pathogen and the antibiotics. The emergence of multidrug-resistant (MDR) bacteria threatens health even for insignificant injuries. However, the discovery of new antibiotics is not a fast process, and the healthcare system will suffer if the evolution of MDR lingers in its current frequency. The cationic photosensitizers (PSs) provide a unique approach to develop novel, light-inducible antimicrobial drugs. Here, we examine the antimicrobial activity of innovative selenophene-modified boron dipyrromethene (BODIPY)-based PSs on a variety of Gram (+) and Gram (-) bacteria. The candidates demonstrate a level of confidence in both light-dependent and independent inhibition of bacterial growth. Among them, selenophene conjugated PS candidates (BOD-Se and BOD-Se-I) are promising agents to induce photodynamic inhibition (PDI) on all experimented bacteria: E. coli, S. aureus, B. cereus, and P. aeruginosa. Further characterizations revealed that photocleavage ability on DNA molecules could be potentially advantageous over extracellular DNA possessing biofilm-forming bacteria such as B. cereus and P. aeruginosa. Microscopy analysis with fluorescent BOD-H confirmed the colocalization on GFP expressing E. coli.

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.

One-Pot Synthesis Bodipy Nano-Precipitations for Prostate Cancer Treatment

Here in this study, we proposed a polystyrene maleic anhydride (PSMA) stabilized Bodipy nanoparticles (PB NPs) in a one-pot approach for the photodynamic therapy (PDT) of prostate cancer. The nanoparticle formed by precipitation method was then employed to treat PC-3 cells and PC-3 tumor bearing nude mice model. It was shown that this platform showed promising anticancer performance than free bodipy with reduced side effects.

Spanning BODIPY fluorescence with self-assembled micellar clusters

BODIPY dyes possess favorable optical properties for a variety of applications including in vivo and in vitro diagnostics. However, their utilization might be limited by their water insolubility and incompatibility with chemical modifications, resulting in low aggregation stability. Here, we outline the route for addressing this issue. We have demonstrated two approaches, based on dye entrapment in micellar coordination clusters (MCCs); this provides a general solution for water solubility as well as aggregation stability of the seven BODIPY derivatives. These derivatives have various bulky aromatic substituents in the 2,3,5,6- and meso-positions and can rotate relative to a dipyrrin core, which also provides molecular rotor properties. The molecular structural features and the presence of aromatic groups allows BODIPY dyes to be used as "supporting molecules", thus promoting micelle-micelle interaction and micellar network stabilization. In the second approach, self-micellization, following BODIPY use, leads to MCC formation without the use of any mediators, including chelators and/or metal ions. In both approaches, BODIPY exhibits an excellent optical response, at a concentration beyond its solubilization limit in aqueous media and without undesired crystallization. The suggested approaches represent systems used to encapsulate BODIPY in a capsule-based surfactant environment, enabling one to track the aggregation of BODIPY; these approaches represent an alternative system to study and apply BODIPY's molecular rotor properties. The stabilized compounds, i.e., the BODIPY-loaded MCCs, provide a unique feature of permeability to hydrophilic ligand-switching proteins such as BSA; they exhibit a bright "turn-on" fluorescence signal within the clusters via macromolecular complexation, thus expanding the possibilities of water-soluble BODIPY-loaded MCCs utilization for functional indicators.

Antifungal effect of a new photosensitizer derived from BODIPY on Candida albicans biofilms

BACKGROUND

Photodynamic therapy (PDT) has been recognized as an alternative treatment of Candida albicans (C. albicans) infections. The aim of this study was to investigate the antifungal effect of PDT mediated by a new photosensitizer (PS) derived from BODIPY (BDP-4L) on C. albicans biofilms.

METHODS

C. albicans biofilms were incubated with BDP-4L of different concentrations and then irradiated at the light doses of 1.8, 3.6, 5.4, 7.2 and 9.0 J/cm². XTT reduction assay was conducted to determine the PS concentration and PDT parameters. Confocal light scanning microscopy (CLSM) and scanning electron microscope (SEM) were used to visualize and quantify the effect of BDP-4L on C. albicans biofilms after PDT.

RESULTS

C. albicans biofilms were inactivated in light dose-dependent and PS concentration-dependent manners using BDP-4L as PS. Without irradiation, no inactivation effect was observed when PS concentrations varied from 5 μM to 80 μM. 40 μM PS with 3.6 J/cm² irradiation resulted in a significant reduction of 83.8% in biofilm metabolic activities. CLSM assay demonstrated that cell viability was obviously inhibited by 82.6%. SEM images revealed ruptured and rough cell surface, indicating increased cell membrane permeability after PDT.

CONCLUSIONS

Our results suggested that BDP-4L mediated PDT exhibited a favorable antifungal effect on C. albicans biofilms.

BINOL blocks as accessible triplet state modulators in BODIPY dyes

BINOL moieties of different electronic demand are useful blocks for enabling the photo-production and modulation of triplet excited states in readily-accesible BINOL-based O-BODIPY dyes from standard F-BODIPY precursors. The rapid and rational development of smarter triplet-enabling BODIPY dyes on the basis of this strategy (e.g., TADF biomarker 4a or room temperature phosphor 4g) paves the way for advancing photonic applications based on organic triplet photosensitizers.

Photosensitizer Encryption with Aggregation Enhanced Singlet Oxygen Production

Chromophores that generate singlet oxygen (¹O₂) in water are essential to developing noninvasive disease treatments using photodynamic therapy (PDT). A facile approach for formation of stable colloidal nanoparticles of ¹O₂ photosensitizers, which exhibit aggregation enhanced ¹O₂ generation in water toward applications as PDT agents, is reported. Chromophore encryption within a fuchsonarene macrocyclic scaffold insulates the photosensitizer from aggregation induced deactivation pathways, enabling a higher chromophore density than typical ¹O₂ generating nanoparticles. Aggregation enhanced ¹O₂ generation in water is observed, and variation in molecular structure allows for regulation of the physical properties of the nanoparticles which ultimately affects the ¹O₂ generation. In vitro activity and the ability of the particles to pass through the cell membrane into the cytoplasm is demonstrated using confocal fluorescence microscopy with HeLa cells. Photosensitizer encryption in rigid macrocycles, such as fuchsonarenes, offers new prospects for the production of biocompatible nanoarchitectures for applications involving ¹O₂ generation.

Halogenated BODIPY photosensitizers: Photophysical processes for generation of excited triplet state, excited singlet state and singlet oxygen

We have systematically examined the formation of singlet oxygen O₂(¹Δ_g), the excited triplet state (T₁), and excited singlet state (S₁) for halogenated BODIPY photosensitizers (halogen = Cl, Br, and I) in eight solvents to understand how halogen atoms and solvent affect these properties. The phosphorescence spectra and lifetimes of singlet oxygen generated by these halogenated BODIPYs have been measured by steady state/time resolved NIR emission, while the formation quantum yield of singlet oxygen (Φ_Δ) has been determined by chemical method using diphenylisobenzofuran (DPBF) as the trapping agent. The formation quantum yield Φ_Δ of singlet oxygen can be as high as 0.96 for iodinated BODIPY and 0.71 for brominated BODIPY. The triplet state T₁ absorption spectra of brominated and iodinated BODIPYs have been recorded by laser flash photolysis method, in which T₁ shows high formation efficiency and long lifetime. The formation and decay of excited singlet state S₁ of four BODIPYs have been measured by ground state (S₀) absorption and steady state/time resolved fluorescence. The results show that larger halogen atoms on BODIPY core lead to smaller fluorescence quantum yield, shorter fluorescence lifetime and higher singlet oxygen formation quantum yield due to heavy atom effect that promotes the formation of triplet state. On the other hand, higher solvent polarity causes lower singlet oxygen formation quantum yield, smaller fluorescence quantum yield, and shorter fluorescence lifetime. This solvent effect is explained by the presence of photoinduced charge transfer (ICT) process from halogen atoms to BODIPY. The ICT efficiency has been estimated and the results are agreed with ICT theory. ICT process in halogenated BODIPYs has never been revealed in literature. HOMO/LUMO obtained from DFT calculation also supports the presence of ICT. The involvement of ICT in the photosensitizing process of halogenated BODIPYs provides new insights for designing BODIPY photosensitizers for photodynamic therapy of tumor.

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...

Bis-borylated arylisoquinoline-derived dyes with a central aromatic core: towards efficient fluorescent singlet-oxygen photosensitizers

Polycyclic aromatic hydrocarbon chromophores that show an ideal bipartition between fluorescence and singlet oxygen production have been developed.

Orthogonally aligned cyclic BODIPY arrays with long-lived triplet excited states as efficient heavy-atom-free photosensitizers

In photosensitizers, long triplet excited state lifetimes are key to their efficient electron transfer or energy transfer processes. Herein, we report a novel class of cyclic trimeric BODIPY arrays which were efficiently generated from easily accessible meso-mesityldipyrrinone and arylboronic acids in one pot. Arylboronic acid, for the first time, was used to provide a boron source for BODIPY derivatives. Due to the well-defined and orthogonally aligned BODIPY cores as verified by X-ray crystallography, these BODIPY arrays show strong exciton coupling effects and efficient intersystem crossings, and are novel heavy-atom-free photosensitizers with a long-lived triplet excited state (lifetime up to 257.5 μs) and good reactive oxygen species generation efficiency (up to 0.72) contributed by both 1O2 and O2 -˙ under light irradiation.

Photoremovable Protecting Groups: Across the Light Spectrum to Near- Infrared Absorbing Photocages

We discuss the past decade of progress in the field of photoremovable protecting groups that allowed the development of photocages activatable by near-IR light and highlight the individual conceptual advancements that lead to general guidelines to design new such photoremovable protecting groups. We emphasize the importance of understanding the individual photochemical reaction mechanisms that was necessary to achieve this progress and provide an outlook of the subsequent steps to facilitate a swift translation of this research into clinical praxis. Since this issue of CHIMIA is dedicated to the late Prof. Thomas Bally, we decided to provide a personal perspective on the field to which he contributed himself. We tried to write this review with the general readership of CHIMIA in mind in a hope to pay a tribute to the extraordinary dedication and clarity with which Thomas Bally used to explain abstract chemical concepts to his students or colleagues. We are uncertain whether we matched such challenge but we believe that he would have liked such approach very much.

A Green-Absorbing, Red-Fluorescent Phenalenone-Based Photosensitizer as a Theranostic Agent for Photodynamic Therapy

Phenalenone is a synthetically accessible, highly efficient photosensitizer with a near-unity singlet oxygen quantum yield. Unfortunately, its UV absorption and lack of fluorescence has made it unsuitable for fluorescence-guided photodynamic therapy against cancer. In this work, we synthesized a series of phenalenone derivatives containing electron-donating groups to red-shift the absorption spectrum and bromine(s) to permit good singlet oxygen production via the heavy-atom effect. Of the derivatives synthesized, the phenalenone containing an amine at the 6-position with bromines at the 2- and 5-positions (OE19) exhibited the longest absorption wavelength (i.e., green) and produced both singlet oxygen and red fluorescence efficiently. OE19 induced photocytotoxicity with nanomolar potency in 2D cultured PANC-1 cancer cells as well as light-induced destruction of PANC-1 spheroids with minimal dark toxicity. Overall, OE19 opens up the possibility of employing phenalenone-based photosensitizers as theranostic agents for photodynamic cancer therapy.

Eu(III)-DO3A and BODIPY dyad as a chemosensor for anthrax biomarker

The sensitive and selective determination of Bacillus anthracis spores before the infection is vital for human health and safety. Dipicolinic acid (DPA) is an excellent biomarker due to its presence in the nucleus of bacterial spores at high concentrations (up to 1 M, about 15% dry weight). In the present work, a new molecular chemosensor 1, based on europium(III)-DO3A and BODIPY dyad, is developed to detect DPA in phosphate-buffered saline (PBS) buffered solution and tap water samples. Also, 1 can be used as a ratiometric optical chemosensor to track DPA.