BODIPY Derivatives for Photodynamic Therapy: Influence of Configuration versus Heavy Atom Effect

Recent advances in developing bioorthogonally activatable photosensitizers for photodynamic therapy

Photodynamic therapy (PDT) is a promising and powerful cancer therapeutic modality, which can generate cytotoxic reactive oxygen species (ROS) from light-irradiated photosensitizers (PSs) to eradicate tumors. To overcome the drawbacks of currently used PSs, researchers have leveraged the advantages of bioorthogonal reactions to design diverse bioorthogonally activatable photosensitizers with excellent tumor selectivity, high ROS generation controllability, and low adverse effect for effective antitumor photodynamic therapy. In this review, we comprehensively summarize and highlight the recent advances in the development of bioorthogonally activatable photosensitizers, including the structure types, designing strategies, activation patterns, photophysical properties, ROS generation efficiency, in vitro and in vivo activities, biological applications, and limitations. We also provide directions and perspectives to address the therapeutic challenges of bioorthogonally activatable photosensitizers for promoting clinical applications. We believe that the principles summarized here will offer useful references for further development of next-generation advanced intelligent photosensitizers and related strategies to realize precise and efficient tumor treatment in the future.

Donor-acceptor mixed-ligand MOF with energy transfer-mediated high-efficiency singlet oxygen generation for boosted organic photosynthesis

Integrating energy donor and acceptor chromophores as ligands within one MOF for advanced artificial photosynthesis is of great interest but appears to be a major challenge. Herein, via a simple one-pot synthetic strategy, an energy acceptor porphyrin ligand 5,15-di(p-benzoato)porphyrin (H2DPBP) was successfully integrated into an energy donor 1,4-naphthalenedicarboxylic acid (H2NDC)-based MOF (UiO-66-NDC) to construct a mixed-ligand MOF, donated as UiO-66-NDC-H2DPBP. Benefiting from the ample overlap between the emission spectrum of H2NDC and the absorption spectrum of H2DPBP, an efficient energy transfer (EnT) process from the donor H2NDC to the acceptor H2DPBP within UiO-66-NDC-H2DPBP can occur and be captured by time-resolved spectroscopy. Furthermore, the singlet oxygen (1O2) generation efficiency of UiO-66-NDC-H2DPBP mediated by this EnT process as well as the EnT process from the triplet state (T1) of the photosensitizer H2DPBP ligand to the ground state of molecular oxygen (3O2) upon light irradiation can be maximized via simply regulating the loading amount of H2DPBP, leading to boosted photocatalytic activities toward important aerobic oxidation reactions of amines and sulfides, even under sunlight and ambient air. This work explores an avenue to construct high-efficiency energy donor and acceptor-based light-harvesting systems by utilizing mixed-ligand MOFs as platforms to advanced artificial photosynthesis.

Fast Imaging of Mitochondria and Efficient Generation of Singlet Oxygen by Red Fluorescent BODIPY Photosensitizers

The biomedical applications of BODIPY fluorophores are limited by challenges such as short-wavelength emission, high hydrophobicity, and poor selectivity. To address these issues, two water-soluble red-emitting BODIPY derivatives, namely, PSPyBDP and I-PSPyBDP, were synthesized by conjugating pyridine units to the BODIPY core, followed by the ring-opening reactions with 1,3-propanesulfonate. Notably, PSPyBDP showed fast mitochondrial imaging capability (∼5 min), indicating its potential as an alternative to mitochondria tracker. I-PSPyBDP, with the heavy-atom effect, could effectively produce singlet oxygen (1O2) under irradiation at 660 nm in a short time (∼1 min) with a 1O2 quantum yield of 0.89. Cytotoxicity assays revealed that the BODIPY derivatives exhibited phototoxicity to HeLa cells while maintaining low dark toxicity. Interestingly, they had low toxicity against normal COS-7 cells. Confocal imaging and flow cytometry confirmed that the BODIPY derivatives could increase intracellular reactive oxygen species (ROS), reduce mitochondrial membrane potential, and induce apoptosis upon irradiation. These findings suggest their promising application in photodynamic therapy (PDT) for tumors.

Green Light Activated Dual-Action Pt(IV) Prodrug with Enhanced PDT Activity

Light induced release of cisplatin from Pt(IV) prodrugs is a promising tool for precise spatiotemporal control over the antiproliferative activity of Pt-based chemotherapeutic drugs. A combination of light-controlled chemotherapy (PACT) and photodynamic therapy (PDT) in one molecule has the potential to overcome crucial drawbacks of both Pt-based chemotherapy and PDT via a synergetic effect. Herein we report green-light-activated Pt(IV) prodrug GreenPt with BODIPY-based photosentitizer in the axial position with an incredible high light response and singlet oxygen generation ability. GreenPt demonstrated the ability to release cisplatin under low-dose green light irradiation up to 1 J/cm2. The investigation of the photoreduction mechanism of GreenPt prodrug using DFT modeling and ΔG0 PET estimation revealed that the anion-radical formation and substituent photoinduced electron transfer from the triplet excited state of the BODIPY axial ligand to the Pt(IV) center is the key step in the light-induced release of cisplatin. Green-light-activated BODIPY-based photosentitizers 5 and 8 demonstrated outstanding photosensitizing properties with an extraordinary phototoxicity index (PI)>1300. GreenPt prodrug demonstrated gradual intracellular accumulation and light-induced phototoxicity with PI>100, thus demonstrating dual action through light-controlled release of both cisplatin and a potent BODIPY-based photosensitizer.

Quantum Chemical and Trajectory Surface Hopping Molecular Dynamics Study of Iodine-Based BODIPY Photosensitizer

A computational study of I-BODIPY (2-ethyl-4,4-difluoro-6,7-diiodo-1,3-dimethyl-4-bora-3a,4a-diaza-s-indacene) has been carried out to investigate its key photophysical properties as a potential triplet photosensitizer capable of generating singlet oxygen. Multireference CASPT2 and CASSCF methods have been used to calculate vertical excitation energies and spin-orbit couplings (SOCs), respectively, in a model (mono-iodinated BODIPY) molecule to assess the applicability of the single-reference second-order algebraic diagrammatic construction, ADC(2), method to this and similar molecules. Subsequently, time-dependent density functional theory (TD-DFT), possibly within the Tamm-Dancoff approximation (TDA), using several exchange-correlation functionals has been tested on I-BODIPY against ADC(2), both employing a basis set with a two-component pseudopotential on the iodine atoms. Finally, the magnitudes of SOC between excited electronic states of all types found have thoroughly been discussed using the Slater-Condon rules applied to an arbitrary one-electron one-center effective spin-orbit Hamiltonian. The geometry dependence of SOCs between the lowest-lying states has also been addressed. Based on these investigations, the TD-DFT/B3LYP and TD-DFT(TDA)/BHLYP approaches have been selected as the methods of choice for the subsequent nuclear ensemble approach absorption spectra simulations and mixed quantum-classical trajectory surface hopping (TSH) molecular dynamics (MD) simulations, respectively. Two bright states in the visible spectrum of I-BODIPY have been found, exhibiting a redshift of the main peak with respect to unsubstituted BODIPY caused by the iodine substituents. Excited-state MD simulations including both non-adiabatic effects and SOCs have been performed to investigate the relaxation processes in I-BODIPY after its photoexcitation to theS 1 $$ {\mathrm{S}}_1 $$ state. The TSH MD simulations revealed that intersystem crossings occur on a time scale comparable to internal conversions and that after an initial phase of triplet population growth a "saturation" is reached where the ratio of the net triplet to singlet populations is about 4:1. The calculated triplet quantum yield of 0.85 is in qualitative agreement with the previously reported experimental singlet oxygen generation yield of 0.99± $$ \pm $$ 0.06.

An endoplasmic reticulum and lipid droplets dual-localized strategy to develop small molecular photosensitizers that induce ferroptosis during photodynamic therapy

Organelle-localized photosensitizers have been well-developed to enhance the photodynamic therapy (PDT) efficacy through triggering given cell death. The endoplasmic reticulum (ER) and lipid droplets (LDs) are two key organelles mutually regulating ferroptosis. Thus, in this study, small molecular photosensitizer CAR PSs were developed through fragment integration strategy and the heavy-atom modification. It was showed that the integration strategy did not affect the organelle localization and CAR PSs successfully achieved ER/LDs dual location. Besides, the heavy-atom modification help CAR PSs display good ROS generation efficiency. Importantly, ER/LDs dual-localized CAR PSs exhibited superior photo-toxicity and lower dark-toxicity against multiple breast cancer cell lines than the only ER-targeting Ce6, which further explained the superposition effect of dual organelle targeting. Preliminary studies revealed that CAR PSs induced enhanced ferroptosis via simultaneously triggering the ER stress and lipid peroxidation during PDT. Moreover, CAR-2 demonstrated significant in vivo PDT activity to suppress the tumor growth in 4T1 tumor bearing mice. These findings not only provide a promising photosensitizer CAR-2 exerting excellent in vitro and in vivo PDT effect through stimulating ferroptosis, but also propose a design strategy for the development of ER/LDs dual localized PSs.

Enhancing the efficacy of antimicrobial photodynamic therapy through curcumin modifications

Curcumin serves as a photosensitizer (PS) in the context of microbial inactivation when subjected to light exposure, to produce reactive oxygen species, which exhibit efficacy in eradicating microorganisms. This remarkable property underscores the growing potential of antimicrobial photodynamic therapy (aPDT) in the ongoing fight against bacterial infections. Considering this, we investigate the efficacy of various in vitro curcumin formulations within a PDT protocol designed to target Staphylococcus aureus. Specifically, we conduct a comparative analysis involving synthetic curcumin (Cur-Syn) and curcumin derivatives modified with chlorine (Cl), selenium (Se), and iodine (I) (Cur-Cl, Cur-Se, Cur-I). To assess the impact of aPDT, we subject S. aureus to incubation with curcumin, followed by irradiation at 450 nm with energy doses of 3.75, 7.5, and 15 J/cm2. Our investigation encompasses an evaluation of PS uptake and photobleaching across the various curcumin variants. Notably, all three modifications (Cur-Cl, Cur-Se, Cur-I) induce a significant reduction in bacterial viability, approximately achieving a 3-log reduction. Interestingly, the uptake kinetics of Cur-Syn and Cur-Se exhibit similarities, reaching saturation after 20 min. Our findings suggest that modifications to curcumin have a discernible impact on the photodynamic properties of the PS molecule.

Naphthalimide Nanoprobe with Enhanced Electron-Withdrawing Ability and Large Stokes Shift for NIR-II Fluorescence Imaging-Guided Phototheranostics

Nanoprobes with NIR-II fluorescence and a large Stokes shift are highly desirable for high-quality bioimaging applications. However, designing NIR-II fluorescent nanoprobes with the desired photophysical properties based on small organic molecules remains a significant challenge. Herein, we report a naphthalimide (NMI)-based NIR-II fluorescent molecule, NMI-BF2, by further enhancing the electron affinity of NMI through the incorporation of boron difluoride formazanate. NMI-BF2 exhibits a sufficient NIR-II quantum yield (QY) of 0.53%, a large Stokes shift of 263 nm, and excellent photostability. For biological applications, NMI-BF2 is coassembled with fetal bovine serum (FBS) to prepare a biocompatible nanoprobe, NMI-BF2/FBS, which maintains a good NIR-II QY of 0.21% and a photothermal conversion efficiency of 32.5%. In vitro and in vivo studies verified that the NMI-BF2/FBS nanoprobe shows an excellent photothermal antitumor therapeutic effect, guided by NIR-II fluorescence and photoacoustic imaging.

Investigation of simple BODIPY dyes as G-quadruplex recognizing ligands

An important class of fluorescent dyes used in studying interactions and visualization of vital biomolecules are compounds with a skeleton origin 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene, known as BODIPY. The objects of the presented study are the simple, polar and hydrophobic 3,7-dimethyl-substituted-core BODIPY dyes with the unmodified or modified phenyl aromatic ring at the meso position. Their optical properties as well as binding interactions with different DNA forms (i-motif, parallel G4, antiparallel G4, hybrid G4, dsDNA and ssDNA) were investigated by biophysical methods. The BODIPY derivatives interact more preferably with tetraplexes than other DNA forms. Especially, ligand 1 and 3 exibit tendency to destabilize parallel c-MYC G-quadruplex. The experiments with peroxidase-mimicking DNAzymes manifest that the main interaction between these BODIPY ligands and parallel G-quadruplex occurs via end-stacking mode. Moreover, their biological activity was evaluated by MTT assay.

Recent advances and design strategies for organic afterglow agents to enhance autofluorescence-free imaging performance

Long-lasting afterglow luminescence imaging that detects photons slowly being released from chemical defects has emerged, eliminating the need for real-time photoexcitation and enabling autofluorescence-free in vivo imaging with high signal-to-background ratios (SBRs). Organic afterglow nano-systems are notable for their tunability and design versatility. However, challenges such as unsatisfactory afterglow intensity, short emission wavelengths, limited activatable strategies, and shallow tissue penetration depth hinder their widespread biomedical applications and clinical translation. Such contradiction between promising prospects and insufficient properties has spurred researchers' efforts to improve afterglow performance. In this review, we briefly outline the general composition and mechanisms of organic afterglow luminescence, with a focus on design strategies and an in-depth understanding of the structure-property relationship to advance afterglow luminescence imaging. Furthermore, pending issues and future perspectives are discussed.

pH-Sensitive and Lysosome Targetable Photosensitizers Based on BODIPYs

Photodynamic therapy (PDT) is an effective and U.S. Food and Drug Administration (FDA) approved treatment for cancer and other diseases. Photosensitizer is one of the three key components that harvest the energy of light at a certain wavelength. Compared to the conventional fluorophores used as photosensitizers, boron dipyrromethene (BODIPY) derivatives have grown fast in recent years due to their low dark toxicity, versatile tunable sites, and easiness of being paired with other treatments. In this paper, two pH-sensitive BODIPY-based photosensitizers (BDC and BDBrC) were synthesized by adding carbazole moieties onto the BODIPY cores (BD and BDBr) through condensation reactions. BDBrC has two Br atoms at the BODIPY core that promote singlet oxygen generation and further red-shift the absorption maximum peak. Both compounds showed sensitivity toward pH change and generated more singlet oxygen under acidic conditions. The cellular uptake and cell imaging experiments showed that BDBrC can selectively target the lysosome organelle. The further dark cell viability and light cytotoxicity indicate the light triggered PDT treatment can be accomplished with BDBrC.

Membrane-Active Singlet Oxygen Photogenerators as a Paradigm for Broad-Spectrum Antivirals: The Case of Halogenated (BOron)-DIPYrromethenes

Enveloped viruses, such as flaviviruses and coronaviruses, are pathogens of significant medical concern that cause severe infections in humans. Some photosensitizers are known to possess virucidal activity against enveloped viruses, targeting their lipid bilayer. Here we report a series of halogenated difluoroboron-dipyrromethene (BODIPYs) photosensitizers with strong virus-inactivating activity. Our structure-activity relationship analysis revealed that BODIPY scaffolds with a heavy halogen atom demonstrate significant efficacy against both tick-borne encephalitis virus (TBEV; Flaviviridae family) and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2; Coronaviridae family) along with high singlet oxygen quantum yields. Moreover, select compounds also inactivated other enveloped viruses, such as herpes simplex virus type 1 and monkeypox virus. The nature and length of the alkyl side chain notably influenced the virus-inactivating activity of BODIPY molecules. Furthermore, molecular dynamics studies highlighted the critical importance of the positioning of the chromophore moiety within the lipid bilayer. As membrane-targeting photosensitizers, BODIPYs interact directly with virus particles, causing damage to the viral envelope membranes. Thus, TBEV pretreated with BODIPY was completely noninfective for lab mice. Consequently, BODIPY-based photosensitizers hold potential either as broad-spectrum virus-inactivating antivirals against a variety of phylogenetically unrelated enveloped viruses or as potent inactivators of viruses for the development of vaccines for preventing life-threatening emerging viral diseases.

Generation of Triplet States by Host-Stabilized Through-Space Conjugation for the Construction of Efficient Supramolecular Photocatalysts

Promoting the generation of triplet states is essential for developing efficient photocatalytic systems. This research presents a novel approach of host-stabilized through-space conjugation via the combination of covalent and non-covalent methods. The designed building block, 4,4'-(1,4(1,4)-dibenzene cyclohexaphane-1,4-diyl)bis(1-phenylpyridinium) chloride, features inherently stable through-space conjugation. When this block forms a 1 : 1 host-guest complex with cucurbit[8]uril, the through-space conjugation is further stabilized within the confined cavity. Both the generation and lifetime of triplet state are significantly increased, resulting from the host-stabilized through-space conjugation. Additionally, the ultrahigh binding constant of 6.58×1014 M-1 ensures the persistence of host-stabilization effect. As a result, the host-guest complex acts as a highly efficient catalyst in the photocatalytic oxidation of thioether and aromatic alcohol. In the photodegradation of lignin, a complex natural product, the host-guest complex also exhibits high efficiency, demonstrating its robustness. This line of research is anticipated to enrich the toolbox of supramolecular photochemistry and provide a strategy for fabricating efficient supramolecular photocatalysts.

Moderately Heavy Atom-Substituted BODIPY Photosensitizer with Mitochondrial Targeting Ability for Imaging-Guided Photodynamic Therapy

Advanced photodynamic therapy requires photosensitizers with targeting, diagnostic, and therapeutic properties. To fulfill this multifunctionality, we report the synthesis of two triphenylphosphonium (TPP)-functionalized boron-dipyrromethene (BODIPY) dyes, TPPB-H and TPPB-Br, which incorporate a hydrogen atom and dibrominated vinyl moiety at the 6-position of the BODIPY core, respectively. The heavy-atom effect of the moderately heavy bromine atoms allowed TPPB-Br to achieve a proper balance between the toxic singlet oxygen (1O2) production and fluorescence efficiencies. In this dye, the bromine atom-induced stimulation of the singlet-to-triplet intersystem crossing dynamics resulted in an approximately 45-fold increase in the 1O2 quantum yield with respect to that of the nonbrominated counterpart (0.0059 and 0.28 for TPPB-H and TPPB-Br, respectively). This increase was accompanied only a 2-fold reduction in the fluorescence quantum yield (0.54 and 0.22 for TPPB-H and TPPB-Br, respectively). During multicolor confocal laser scanning microscopy observations conducted using two carcinomas, MCF-7 and HeLa, both BODIPY dyes exhibited high targeting specificity toward cancer cell mitochondria owing to the TPP cation functionalization. The two dyes also showed the feasibility of fluorescence cell imaging; however, only the dibrominated BODIPY TPPB-Br manifested pronounced photocytotoxicity with half-maximal inhibitory concentrations of 0.12 and 0.77 μM obtained for MCF-7 and HeLa cells, respectively. These findings demonstrate the potential applicability of TPPB-Br as an imaging-guided photodynamic therapy agent with mitochondrial specificity.

Efficient light-induced reactive oxygen species production from a far-red ER-targeting BODIPY dye

Generation of reactive oxygen species (ROS) within the ER evokes stress leading to immunogenic cell death. A red light activated BODIPY dye capable of subcellular localization within the ER producing high quantum yields of ROS is reported. The ability of this dye to act as a photodynamic therapy (PDT) agent in breast cancer cells suggests promising organelle-targeted therapeutics.

Devising Biocompatible, NIR-Activated Helical Pyroptosis Agents via 𝛑-Twisting Strategy for Promoting Antitumor Immunity

Specifically controlling cell pyroptosis is advantageous for oncotherapy as it allows simultaneous ablation of primary tumors and activation of immunogenicity of tumor environment. Herein, a facile and robust strategy is presented to construct efficient NIR-activated helical pyroptosis agents (PyroAs) with negligible dark cytotoxicity. It is demonstrated that the construction of four intramolecular B-X bonds (X = O or N) within the BODIPY chromophore enforces a significant twisting of its π-conjugation, yielding a variety of helical HBD molecules with desired high photosensitivity and negligible dark toxicity. A robust approach is established to extend HBD into the near-infrared (NIR) region through site-selective incorporation of an electron-withdrawing ester moiety. It is also proved that targeted delivery of the NIR-activated HBD-ER to the endoplasmic reticulum (ER) specifically activates pyroptosis pathway by equipping it with an ER-targeting moiety. Finally, the favorable biocompatibility, excellent antitumor efficacy, and remarkable systematic immune response of this unique NIR-activated helical PyroAs are shown in vivo, demonstrating its potential application in solid tumor immunotherapy.

Orthogonal Geometry Enhancing the Intersystem Crossing and Photosensitive Efficiency of Spiro Organoboron Compounds

Based on the reported spiro organoboron compounds (PS1 and PS2 as potent 1O2 sensitizers), several new organoboron molecules (PS4-PS9) were constructed through structural modification, and their low-lying excited states and photophysical properties have been explored by density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. The predicted effective intersystem crossing (ISC) processes arise from the S1→T2 transition for PS4-PS6 and the S1→T4 transition for PS1, and corresponding KISC rate constants reach the order of magnitude of 109 (s-1). The organoboron compounds with a (N, N) chelate acceptor are predicted to exhibit relatively higher ISC efficiency than those bearing a (N, O) acceptor, and the planar C3NBN ring and the orthogonal configuration between the donor and acceptor moieties are responsible for the ISC rate enhancement. Importantly, the geometric features of the lowest singlet excited state (S1) for these compounds play a decisive role in their photosensitive efficiency. The present results provide a basis for better understanding of the photosensitivity of these spiro organoboron compounds and the structural modification effect.

Enhanced Singlet Oxygen Generation in Aggregates of Naphthalene-Fused BODIPY and Its Application in Photodynamic Therapy

Several reports are available on aggregation-induced emission and its applications in biomedical imaging and other material sciences. However, enhancement of singlet oxygen generation in nanoaggregates is rarely reported. Here, we report the synthesis of Naph-BODIPY Br2, which absorbs at 661 nm (monomer) with a high molar absorption coefficient. The presence of bromine promotes intersystem crossing, thereby enhancing the singlet oxygen quantum yield (ΦΔ ∼ 0.50 in methanol). In order to increase hydrophilicity, we developed Naph-BODIPY Br2 nanoaggregates (∼100 nm), which demonstrated aggregation-induced properties and exhibited a bathochromic shift with an absorption maximum at 757 nm. The bathochromic shift in the UV-vis spectra due to aggregation is corroborated by TD-DFT analysis. The computational data also confirm the presence of a low-lying triplet state, which enhances the generation of singlet oxygen, making it effective for photodynamic therapy. These aggregates showed excellent singlet oxygen generation in aqueous media, compared to their monomeric form and standard methylene blue. Their hydrophilic nature and high singlet oxygen generation enabled significant phototoxicity against human carcinoma cells with IC50 values of 4.06 ± 0.01 and 4.09 ± 0.1 μM, respectively, for MCF-7 and A549 cells upon 5 min exposure to light. Moreover, their phototoxicity further increases with an increasing exposure time of light for both cell lines. Notably, Naph-BODIPY Br2 nanoaggregates exhibited nearly zero dark cell toxicity and effectively induced apoptosis in cancer cells upon light activation, highlighting their potential as powerful photosensitizers for photodynamic cancer therapy.

Liposomal Formulations of Novel BODIPY Dimers as Promising Photosensitizers for Antibacterial and Anticancer Treatment

Synthesis, photochemical properties, liposomal encapsulation, and in vitro photodynamic activity studies of novel BODIPY dimer connected at meso-meso positions and its brominated and iodinated analogs were described. UV-Vis measurements indicated that the dimeric structure of obtained BODIPYs did not significantly influence the positions of the absorption maxima. Emission properties and singlet oxygen generation studies revealed a strong heavy atom effect of brominated and iodinated BODIPY dimers, manifested by fluorescence intensity reduction and increased singlet oxygen generation ability compared to analog without halogen atoms. For the in vitro photodynamic activity studies, dimers were incorporated into two different types of liposomes: positively charged DOTAP:POPC and negatively charged POPG:POPC. The photoinactivation studies revealed high activity of brominated and iodinated dimers incorporated into DOTAP:POPC liposomes on both Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli. Anticancer studies on human breast adenocarcinoma MDA-MB-231 and human ovarian carcinoma A2780 cells revealed that DOTAP:POPC liposomes containing brominated and iodinated dimers were active even at low nanomolar concentrations. In addition, they were more active against MDA-MB-231 cells than A2780 cells, which is particularly important since the MDA-MB-231 cell line represents triple-negative breast cancer, which has limited therapeutic options.

A BODIPY-Ferrocene Conjugate for the Combined Photodynamic Therapy and Chemodynamic Therapy with Improved Antitumor Efficiency

Photodynamic therapy (PDT) can destroy tumor cells by generating singlet oxygen (1O2) under light irradiation, which is limited by the hypoxia of the neoplastic tissue. Chemodynamic therapy (CDT) can produce toxic hydroxyl radical (⋅OH) to eradicate tumor cells by catalytic decomposition of endogenous hydrogen peroxide (H2O2), the therapeutic effect of which is highly dependent on the concentration of H2O2. Herein, we propose a BODIPY-ferrocene conjugate with a balanced 1O2 and ⋅OH generation capacity, which can serve as a high-efficiency antitumor agent by combining PDT and CDT. The ferrocene moieties endow the as-prepared conjugates with the ability of chemodynamic killing of tumor cells. Moreover, combined PDT/CDT therapy with improved antitumor efficiency can be realized after exposure to light irradiation. Compared with the monotherapy by PDT or CDT, the BODIPY-ferrocene conjugates can significantly increase the intracellular ROS levels of the tumor cells after light irradiation, thereby inducing the tumor cell apoptosis at low drug doses. In this way, a synergistic antitumor treatment is achieved by the combination of PDT and CDT.

Mechanistic Investigation into Chemiluminescence from 1,4-Benzoquinone

Tetrahalogen-1,4-benzoquinone (THBQ) represents a category of H2O2-dependent substrates for chemiluminescence (CL), including tetrafluoro-, tetrachloro-, tetrabromo-, and tetraiodo-1,4-benzoquinone (TFBQ, TCBQ, TBBQ, and TIBQ). A deep understanding of the CL mechanism of THBQ is essential for all H2O2-dependent CL and even some bioluminescence. This article systematically investigates the CL process of THBQ by density functional theory and multireference state theory. The theoretical results confirm the generality of the CL mechanism previously proposed in studies on TCBQ and TBBQ. The dissociation steps producing the emitter of light from dihalogenquinone dioxetane (DHD) and its anion (DHD-), formed by the oxidation of THBQ, were carefully considered. Findings show that the dissociation of DHD/DHD- follows the entropy trap/gradually reversible charge-transfer-induced luminescence (GRCTIL) mechanisms. The dissociation of DHD- is kinetically more advantageous compared with that of DHD. At the practical experimental pH value, the decrease in the electron-withdrawing inductive effect from F to I substituents results in the decrease in the proportions of easily dissociated DHD-, and the increase in the heavy-atom effect from F to I substituents leads to the increase in the phosphorescence emission. These combined factors successively decrease the CL intensity from TFBQ to TCBQ, TBBQ, and TIBQ. The conclusions are verified by the previous experiments on TCBQ and TBBQ, and they are expected to be confirmed by future experiments on TFBQ and TIBQ.

Immunological nanomaterials to combat cancer metastasis

Metastasis causes greater than 90% of cancer-associated deaths, presenting huge challenges for detection and efficient treatment of cancer due to its high heterogeneity and widespread dissemination to various organs. Therefore, it is imperative to combat cancer metastasis, which is the key to achieving complete cancer eradication. Immunotherapy as a systemic approach has shown promising potential to combat metastasis. However, current clinical immunotherapies are not effective for all patients or all types of cancer metastases owing to insufficient immune responses. In recent years, immunological nanomaterials with intrinsic immunogenicity or immunomodulatory agents with efficient loading have been shown to enhance immune responses to eliminate metastasis. In this review, we would like to summarize various types of immunological nanomaterials against metastasis. Moreover, this review will summarize a series of immunological nanomaterial-mediated immunotherapy strategies to combat metastasis, including immunogenic cell death, regulation of chemokines and cytokines, improving the immunosuppressive tumour microenvironment, activation of the STING pathway, enhancing cytotoxic natural killer cell activity, enhancing antigen presentation of dendritic cells, and enhancing chimeric antigen receptor T cell therapy. Furthermore, the synergistic anti-metastasis strategies based on the combinational use of immunotherapy and other therapeutic modalities will also be introduced. In addition, the nanomaterial-mediated imaging techniques (e.g., optical imaging, magnetic resonance imaging, computed tomography, photoacoustic imaging, surface-enhanced Raman scattering, radionuclide imaging, etc.) for detecting metastasis and monitoring anti-metastasis efficacy are also summarized. Finally, the current challenges and future prospects of immunological nanomaterial-based anti-metastasis are also elucidated with the intention to accelerate its clinical translation.

Microwave-assisted synthesis, photochemical and electrochemical studies of long-wavelength BODIPY dyes

Novel BODIPY derivatives possessing different styryl substituents were synthesized using different methods of Knoevenagel-type condensation with conventional heating and microwave radiation in two conditions. Microwave-assisted synthesis significantly reduces reaction time while enhancing its efficiency. The introduction of styryl substituents at the 3 and 5 positions of the BODIPY core resulted in a substantial bathochromic shift, which was affected by the substituents within styryl groups. Depending on the solvents, the BODIPY with unsubstituted styryl groups possesses absorption maxima (λAbs) between 616 and 626 nm. While the analogs containing electron-donating methoxy and methylthio groups exhibited bathochromically shifted bands with λAbs values in the 633-654 nm range. Fluorescence studies revealed intensive emission of tested BODIPYs with fluorescence quantum yields at the 0.41-0.83 range. On the other hand, singlet oxygen quantum yields were very low. In the electrochemical studies, the CV and DPV scans showed the presence of three redox processes. The calculated electrochemical gaps were in the range of 1.71-1.87 V.

BODIPY(aryl)iodonium salts in the efficient synthesis of diversely functionalized BODIPYs and selective detection of serum albumin

BODIPY(aryl)iodonium salts were readily accessible from the high-yielding reaction of BODIPY with iodoarenes or hydroxyl(tosyloxy)iodoarenes in the presence of m-CPBA. The prepared BODIPY(aryl)iodonium salts bearing substituents of varied electronic nature were utilized for the direct syntheses of thiocyanate, azide, amine and acrylate functionalized BODIPYs and β,β'-bis-BODIPYs. The regioselective syntheses of α-piperidinyl and β-piperidinyl substituted BODIPYs were achieved through the reaction of BODIPY(aryl)iodonium salts with piperidine in the absence and presence of copper(I). Expeditious and high yielding (79-82%) synthesis of β,β'-bis-BODIPYs was also developed through the palladium-catalyzed reductive coupling of the easily accessible BODIPY(aryl)iodonium salts. Some of the indole-appended BODIPYs and bis-BODIPYs displayed strong absorption in the visible region (∼610 nm). The BODIPY(aryl)iodonium salts also showed significant binding with serum albumin and were observed to be selective serum protein sensors with estimated limits of detection as low as 7 μg mL-1 in some cases.

Molecular engineering to design a bright near-infrared red photosensitizer: cellular bioimaging and phototherapy

Near-infrared red (NIR) fluorescence imaging guide phototherapeutic therapy (PDT) has the advantages of deep tissue penetration, real-time monitoring of drug treatment and disease, little damage to normal tissue, low cytotoxicity and almost no side effects, and thus, it is attracting increasing research attention and is expected to show promising potential for clinical tumor treatment. The photosensitizer (PS), light source and oxygen are the three basic and important factors to construct PDT technology, and highly efficient PSs are still being passionately pursued because they determine the PDT efficiency. Ideal PSs should have properties such as good biocompatibility, deep tissue penetration, and highly efficient reactive oxygen species (ROS) generation despite the hypoxic environment. Therefore, pure organic type I PSs with NIR fluorescence have been receiving increasing attention due to their deep penetration and hypoxia resistance. However, reported NIR-active type I PSs usually require complex synthetic procedures, which presents a challenge for mass production. In this research work, based on the molecular design ideas of introducing the heavy atom effect and intramolecular charge transfer, we prepared three NIR-active type I PSs (TNZ, TNZBr, and TNZCHO) using a very simple method with one or two synthetic steps. Clear characterizations of photophysical properties, ROS performance tests, and fluorescent imaging of human umbilical vein endothelial (HUVE) cells and PDT treatment of HepG2 cells were carried out. The results revealed that the heavy atom and intramolecular charge transfer (ICT) effects could obviously enhance the ROS efficiency, and both PSs produce only type I ROS without any type II ROS (1O2) generation. The good NIR fluorescence brightness and type I ROS efficiency ensure satisfactory bioimaging and PDT outcomes. This research provides the possibility of preparing NIR-active type I PSs via mass production.

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.

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.

Near infra-red absorbing Quinolizidine fused curcuminoid-BF2 chelate and its applications in photodynamic therapy using MCF-7 and A549 cells

Metal-free near-infrared absorbing photosensitizers (PS) have been considered promising candidates for photodynamic therapy. Curcumin, curcuminoid, and its derivatives have therapeutic values due to their anti-inflammatory, antifungal, and antiproliferative properties. Curcuminoid-BF2 chelates have also been studied as cell imaging probes, however, their applications in photodynamic therapy are rare. In this article, we describe the synthesis and therapeutic evaluation of quinolizidine fused curcuminoid-BF2 chelate (Quinolizidine CUR-BF2) containing an acid-sensitive group. This donor-acceptor-donor curcuminoid-BF2 derivative exhibits absorption and emission in the deep red region with an absorption band maximum of ∼647 nm and a weak emission band at approximately 713 nm. It is interesting to note that this derivative has a high molar extinction coefficient (164,655 M-1cm-1). Quinolizidine CUR-BF2 possesses intramolecular charge transfer properties, facilitating the production of singlet oxygen (1O2), which plays a crucial role in cell death. Additionally, Quinolizidine CUR-BF2 can enable the selective release of active ingredients in an acidic medium (pH 5). Furthermore, the nanoaggregates of PS were prepared by encapsulating Quinolizidine CUR-BF2 within Pluronic F127 block co-polymer for better water-dispersibility and enhanced cellular uptake. Dark cytotoxicity of nanoaggregates was found to be negligible, whereas they exhibited significant photoinduced cytotoxicity towards cancer cells (MCF-7 and A549) under irradiation of 635 nm light. Further, the cell death pathway using Quinolizidine CUR-BF2 nanoaggregates as PS is found to occur through apoptosis. Specifically, the present study deals with the successful preparation of Quinolizidine CUR-BF2 nanoaggregates for enhanced water-dispersibility and cellular uptake as well as the efficacy evaluation of developed nanoaggregates for photodynamic therapy.

Lysosome-targeted Aza-BODIPY photosensitizers for anti-cancer photodynamic therapy

Developing effective near-infrared (NIR) photosensitizers (PSs) has been an attractive goal of photodynamic therapy (PDT) for cancer treatment. In this study, we synthesized N, N-diethylaminomethylphenyl-containing Aza-BODIPY photosensitizers and comprehensively investigated their photophysical/photochemical properties, as well as cell-based and animal-based anti-tumor studies. Among them, BDP 1 has strong NIR absorption at 680 nm and higher singlet oxygen yield in PBS which showed favorable pH-activatable and lysosome-targeting ability. BDP 1 could be easily taken up by tumor cells and showed negligible dark activity (IC50 > 50 μM), however strong phototoxicity upon exposure to light irradiation. The acceptable fluorescence emission from BDP 1 allowed convenient in vivo fluorescence imaging for organ distribution studies in mice. After PDT treatment with upon single time PDT treatment at the beginning using relatively low light dose (54 J/ cm2), BDP 1 (2 mg/kg, 0.1 mL) was found to have strong efficacy to inhibit tumor growth and even to ablate off tumor without causing body weight loss. Therefore, pH-activatable and lysosome-targeted PS may become an effective way to develop potent PDT agent.

A fluorescent probe for bioimaging of GSH in cancer cells

A fluorescent probe CTP2-IMC was designed for bioimaging of glutathione (GSH) in cancer cells with indomethacin (IMC), coumarin and bromide as the targeting group, fluorophore and receptor, respectively. Due to the π-π interaction between coumarin and IMC, CTP2-IMC mainly exists in the form of folded state in aqueous solution. The non-radiative transitions caused by the photo-induced electron transfer (PET) process from IMC to the fluorophore as well as the heavy-atom effect led to non-fluorescent of CTP2-IMC. The substitution of Br by GSH and unfolded conformation induced by IMC acceptor on cancer cells resulted in significant fluorescence enhancement, which enabled CTP2-IMC to bioimage GSH in cancer cells rather than in normal one.

Synthesis and evaluation of novel meso-substitutedphenyl dithieno[3,2-b]thiophene-fused BODIPY derivatives as efficient photosensitizers for photodynamic therapy

The discovery of new photosensitizer drugs with long wavelength Uv-vis absorption, high efficiency and low side-effects is still a challenge in photodynamic therapy. Here a series of novel meso-substitutedphenyl thieno[3,2-b]thiophene-fused BODIPY derivatives were designed, synthesized and characterized. All these compounds have strong absorption at 640-680 nm and obvious fluorescence emission at 650-760 nm. They exhibited high singlet oxygen generation ability and significant photodynamic efficiency against Eca-109 cancer cells. Compounds II4, II6, II9, II10 and II13 could generate intracellular ROS and induce cell apoptosis after laser irradiation, which displayed superior photodynamic efficiency against Eca-109 cells than Temoporfin in vitro and in vivo. Among them, compound II4 specifically exhibited excellent anti-tumor efficacy, and could be selected as a new drug candidate for PDT.

Heavy Atom Effect on the Intersystem Crossing of a Boron Difluoride Formazanate Complex-Based Photosensitizer: Experimental and Theoretical Studies

Photodynamic therapy (PDT) is a photochemical-based treatment approach that involves using light to activate photosensitizers (PSs). Attractively, PDT is one of the alternative cancer treatments due to its noninvasive technique. By utilizing the heavy atom effect, this work modified a class of formazan dyes to improve intersystem crossing (ISC) to improve reactive oxygen species (ROS) generation for PDT treatment. Two methods were used to observe the ROS generation enhanced by ISC of the synthesized complexes including, (1) recording DPBF decomposition caused by the ROS, and (2) calculating the potential energy curves for photophysical mechanisms of BF2 -formazanate dyes using the DFT and nudged elastic band (NEB) methods. The photophysical properties of the dyes were studied using spectroscopic techniques and X-ray crystallography, as well as DFT calculations. The experimental and theoretical results and in vitro cellular assays confirmed the potential use of the newly synthesized iodinated BF2 -formazanate dyes in PDT.

Synthesis and characterization of novel BODIPYs and their antioxidant, antimicrobial, photodynamic antimicrobial, antibiofilm and DNA interaction activities

In the current study, we synthesized and characterized new BODIPY derivatives (1-4) having pyridine or thienyl-pyridine substituents at meso- position and 4-dibenzothienyl or benzo[b]thien-2-yl moieties at 2-,6- positions. We investigated fluorescence properties and the ability to form singlet oxygen. In addition, various biological activities of BODIPYs such as DPPH scavenging, DNA binding/cleavage ability, cell viability inhibition, antimicrobial activity, antimicrobial photodynamic therapy (aPDT) and biofilm inhibition properties were performed. BODIPY derivatives BDPY-3 (3) and BDPY-4 (4) have high fluorescence quantum yields as 0.50 and 0.61 and 1 O2 quantum yields were calculated as 0.83 for BDPY-1 (1), 0.12 for BDPY-2 (2), 0.11 for BDPY-3 and 0.23 for BDPY-4. BODIPY derivatives BDPY-2, BDPY-3 and BDPY-4 displayed 92.54 ± 5.41%, 94.20 ± 5.50%, and 95.03 ± 5.54% antioxidant ability, respectively. BODIPY compounds showed excellent DNA chemical nuclease activity. BDPY-2, BDPY-3 and BDPY-4 also exhibited 100% APDT activity against E. coli at all tested concentrations. In addition to these, they demonstrated a highly effective biofilm inhibition activity against Staphyloccous aureus and Pseudomans aeruginosa. BDPY-4 showed the most effective antioxidant and DNA cleavage activity, while BDPY-3 exhibited the most effective antimicrobial and antibiofilm activity.

Far-red BODIPY-based oxime esters: photo-uncaging and drug delivery

Far-red BODIPY-based oxime esters for photo-uncaging were designed to release molecules of interest with carboxylic acids. The low power red LED light breaks the N-O oxime ester bond and frees the caged molecules. We studied the mechanism and kinetics of the uncaging procedure using a 1H NMR spectrometer. Moreover, the drug delivery strategy to release valproic acid (VPA) on demand was tested in vitro using this far-red BODIPY photo-uncaging strategy to induce apoptosis in tumor cells.

Near-Infrared BODIPY Photosensitizer for Modulating Mitochondrial Fusion Proteins and Inhibiting Choroidal Neovascularization

Photosensitizers have emerged as cytotoxic reactive oxygen species (ROS) activators in photodynamic therapy (PDT), which induced cell apoptosis. As the major contributors to ROS and oxidative stress, mitochondria play an important role in cell apoptosis. Although there are many reports about near-infrared 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) as photosensitizers (PSs) for PDT, this kind of PS has rarely been used for treating mitochondrial function and choroidal neovascularization application at the same time. Herein, a novel near-infrared PS (BDP2) characterized by good water solubility, long wavelength excitation, and high ROS quantum yield has been made. Under near-infrared light irradiation, BDP2 would generate ROS with high yield, induce a mitochondrial morphology change, and trigger cell apoptosis by changing the fusion protein level. Deep investigation revealed that BDP2 can cause oxidative stress, break the balance between fusion and fission of mitochondrial dynamics protein through decreasing fusion protein MFN2 and OPA1 expression, and finally cause cell apoptosis. Due to these characteristics, the BDP2 PS was used to treat choroidal neovascularization in animal models and can inhibit neovascularization.

Multifunctional protein-based self-assembled nanoplatform: overcoming hypoxic tumor microenvironment for enhanced imaging-guided photodynamic therapy

Photodynamic therapy (PDT) has emerged as a promising modality for cancer treatment, but its efficacy is often limited by tumour hypoxia. Here, we report the development of a novel protein-based, self-assembled nanoplatform, CAT-I-BODIPY NPs (CIB NPs), to address this limitation. We first design and synthesize an I-BODIPY photosensitizer based on the heavy atom effect and modification of the electron-donating group, which exhibits excellent capabilities in generating reactive oxygen species and enabling near-infrared (NIR) fluorescence imaging. The incorporation of an oxygen-producing enzyme, catalase (CAT), within these nanoassemblies enables in situ oxygen generation to counteract hypoxic constraints. Controllable self-assembly by multiple supramolecular interactions into highly ordered architecture not only guarantees CAT's catalytic activity but also leads to excellent NIR fluorescence imaging ability and enhanced PDT efficacy. Notably, the visualization of optimal accumulation of CIB NPs within tumour sites 18 h post-injection offers precise PDT application guidance. Both in vitro and in vivo studies corroborate the remarkable anti-tumour efficacy of CIB NPs under NIR illumination, providing a significant advancement in PDT. The favourable biosafety profile of CIB NPs further emphasizes their potential for clinical application in hypoxic tumour therapy.

Towards Ruthenium(II)-Rhenium(I) Binuclear Complexes as Photosensitizers for Photodynamic Therapy

The search for new metal-based photosensitizers (PSs) for anticancer photodynamic therapy (PDT) is a fast-developing field of research. Knowing that polymetallic complexes bear a high potential as PDT PSs, in this study, we aimed at combining the known photophysical properties of a rhenium(I) tricarbonyl complex and a ruthenium(II) polypyridyl complex to prepare a ruthenium-rhenium binuclear complex that could act as a PS for anticancer PDT. Herein, we present the synthesis and characterization of such a system and discuss its stability in aqueous solution. In addition, one of our complexes prepared, which localized in mitochondria, was found to have some degree of selectivity towards two types of cancerous cells: human lung carcinoma A549 and human colon colorectal adenocarcinoma HT29, with interesting photo-index (PI) values of 135.1 and 256.4, respectively, compared to noncancerous retinal pigment epithelium RPE1 cells (22.4).

A type I and II compatible vinyl-pyridine modified BODIPY dimer photosensitizer for photodynamic therapy in A-549 cells

In this paper, the vinyl-pyridine group was used to modify the BODIPY dimer photosensitizer (T-BDP2) to obtain a VP-BDP2 photosensitizer. Compared with the T-BDP2 photosensitizer, the VP-BDP2 photosensitizer could work under pure water conditions, the singlet oxygen yield was increased from 9.38% to 22.2%, the charge transfer rate was increased from about 30 ps to about 10 ps, and the red emission was enhanced in fluorescence imaging. In addition, the VP-BDP2 photosensitizer could also generate the superoxide radical (O2˙-) under pure water conditions. The ROS generation mechanism of the VP-BDP2 photosensitizer was considered to be the spin-orbit charge-transfer intersystem crossing (SOCT-ISC) mechanism, which was verified by fs-transient absorption spectra and theoretical calculation. In the photodynamic therapy of A-549 cells, the VP-BDP2 photosensitizers could generate singlet oxygen and superoxide radicals (O2˙-) under biological conditions, and showed high phototoxicity with the IC50 value at 12.1 μM under light at 525 nm. Additionally, the multiple dipolar configuration meant that the VP-BDP2 photosensitizer could be used in two-photon fluorescence zebrafish imaging under 800 nm excitation, which sets the stage for future two-photon photodynamic therapy.

Theranostic imaging and multimodal photodynamic therapy and immunotherapy using the mTOR signaling pathway

Tumor metastases are considered the leading cause of cancer-associated deaths. While clinically applied drugs have demonstrated to efficiently remove the primary tumor, metastases remain poorly accessible. To overcome this limitation, herein, the development of a theranostic nanomaterial by incorporating a chromophore for imaging and a photosensitizer for treatment of metastatic tumor sites is presented. The mechanism of action reveals that the nanoparticles are able to intervene by local generation of cellular damage through photodynamic therapy as well as by systemic induction of an immune response by immunotherapy upon inhibition of the mTOR signaling pathway which is of crucial importance for tumor onset, progression and metastatic spreading. The nanomaterial is able to strongly reduce the volume of the primary tumor as well as eradicates tumor metastases in a metastatic breast cancer and a multi-drug resistant patient-derived hepatocellular carcinoma models in female mice.

Formylation as a Chemical Tool to Modulate the Performance of Photosensitizers Based on Boron Dipyrromethene Dimers

Heavy-atom-free photosensitizers are envisioned as the next generation of photoactive molecules for photo-theragnosis. In this approach, and after suitable irradiation, a single molecular scaffold is able to visualize and kill tumour cells by fluorescence signalling and photodynamic therapy (PDT), respectively, with minimal side effects. In this regard, BODIPY-based orthogonal dimers have irrupted as suitable candidates for this aim. Herein, we analyse the photophysical properties of a set of formyl-functionalized BODIPY dimers to ascertain their suitability as fluorescent photosensitizers. The conducted computationally aided spectroscopic study determined that the fluorescence/singlet oxygen generation dual performance of these valuable BODIPY dimers not only depends on the BODIPY-BODIPY linkage and the steric hindrance around it, but also can be modulated by proper formyl functionalization at specific chromophoric positions. Thus, we propose regioselective formylation as an effective tool to modulate such a delicate photonic balance in BODIPY-based dimeric photosensitizers. The taming of the excited-state dynamics, in particular intramolecular charge transfer as the key underlying process mediating fluorescence deactivation vs. intersystem crossing increasing, could serve to increase fluorescence for brighter bioimaging, enhance the generation of singlet oxygen for killing activity, or balance both for photo-theragnosis.

Exploring anticancer properties of novel Nano-Formulation of BODIPY Compound, Photophysicochemical, in vitro and in silico evaluations

A new BODIPY complex (C4) composed of meso- thienyl-pyridine substituted core unit diiodinated from 2- and 6- positions and distyryl moieties at 3- and 5- positions is synthesized. Nano-sized formulation of C4 is prepared by single emulsion method using poly(ε-caprolactone)(PCL) polymer. Encapsulation efficiency and loading capacity values of C4 loaded PCL nanoparticles (C4@PCL-NPs) are calculated and in vitro release profile of C4 is determined. The cytotoxicity and anti-cancer activity are conducted on the L929 and MCF-7 cell lines. Cellular uptake study is performed and interaction between C4@PCL-NPs and MCF-7 cell line is investigated. Anti-cancer activity of C4 is predicted with molecular docking studies and the inhibition property on EGFR, ERα, PR and mTOR are investigated for its anticancer properties. Molecular interactions, binding positions and docking score energies between C4 and EGFR, ERα, PR and mTOR targets are revealed using in silico methods. The druglikeness and pharmacokinetic properties of C4 are evaluated using the SwissADME and its bioavailability and toxicity profiles are assessed using the SwissADME, preADMET and pkCSM servers. In conclusion, the potential use of C4 as an anti-cancer agent is evaluated in vitro and in silico methods. Also, photophysicochemical properties are studied to investigate the potential of using Photodynamic Therapy (PDT). In photochemical studies, the calculated singlet oxygen quantum yield (Φ_Δ) value was 0.73 for C4 and in photopysical studies, the calculated fluorescence quantum yield Φ_F value was 0.19 for C4.

A self-assembled nanophotosensitizer targets lysosomes and induces lysosomal membrane permeabilization to enhance photodynamic therapy

We report the self-assembly of amphiphilic BDQ photosensitizers into lysosome-targeting nanophotosensitizer BDQ-NP for highly effective photodynamic therapy (PDT). Molecular dynamics simulation, live cell imaging, and subcellular colocalization studies showed that BDQ strongly incorporated into lysosome lipid bilayers to cause continuous lysosomal membrane permeabilization. Upon light irradiation, the BDQ-NP generated a high level of reactive oxygen species to disrupt lysosomal and mitochondrial functions, leading to exceptionally high cytotoxicity. The intravenously injected BDQ-NP accumulated in tumours to achieve excellent PDT efficacy on subcutaneous colorectal and orthotopic breast tumor models without causing systemic toxicity. BDQ-NP-mediated PDT also prevented metastasis of breast tumors to the lungs. This work shows that self-assembled nanoparticles from amphiphilic and organelle-specific photosensitizers provide an excellent strategy to enhance PDT.

Rational Design of Mesoporous Coordination Polymer Nanophotosensitizers for Photodynamic Tumor Ablation

Effective clinical practice of precise photodynamic therapy (PDT) is severely impeded by the inherent drawbacks and aggregation propensity of conventional photosensitizers. An all-in-one approach is highly desired to optimize structural features, photophysical properties, and pharmacokinetic behaviors of photosensitizers. Herein, we have fabricated mesoporous boron dipyrromethene-bridged coordination polymer nanophotosensitizers (BCP-NPs) for high-performance PDT via a unique solvent-assisted assembly strategy. Distinctive photophysical and structural characteristics of BCP-NPs confer enhanced photodynamic activities, together with high cellular uptake and ultrahigh stability. Moreover, BCP-NPs showed excellent tumor accumulation and prolonged tumor retention, achieving eradication of the triple-negative breast cancer (TNBC) model under low-power-density LED irradiation. This work has provided a valuable paradigm for the construction of mesoporous photoactive nanomaterials for biophotonic applications.

BODIPY as a Multifunctional Theranostic Reagent in Biomedicine: Self-Assembly, Properties, and Applications

The use of boron dipyrromethene (BODIPY) in biomedicine is reviewed. To open, its synthesis and regulatory strategies are summarized, and inspiring cutting-edge work in post-functionalization strategies is highlighted. A brief overview of assembly model of BODIPY is then provided: BODIPY is introduced as a promising building block for the formation of single- and multicomponent self-assembled systems, including nanostructures suitable for aqueous environments, thereby showing the great development potential of supramolecular assembly in biomedicine applications. The frontier progress of BODIPY in biomedical application is thereafter described, supported by examples of the frontiers of biomedical applications of BODIPY-containing smart materials: it mainly involves the application of materials based on BODIPY building blocks and their assemblies in fluorescence bioimaging, photoacoustic imaging, disease treatment including photodynamic therapy, photothermal therapy, and immunotherapy. Lastly, not only the current status of the BODIPY family in the biomedical field but also the challenges worth considering are summarized. At the same time, insights into the future development prospects of biomedically applicable BODIPY are provided.

Synthesis and Spectroscopic Properties of Selenophene[3, 2-b]-Fused BODIPYs

Fusion selenophene endows the chromophore with more intrinsic and special functions. Herein, nonsymmetric selenophene-fused BODIPYs were designed and synthesized starting from the selenophene unit. The fused ring of selenophene not only maintains the rigid structure of BODIPY but also further modulates its spectral properties. The newly prepared dyes possessed many promising properties including large molar extinction coefficients, low fluorescence quantum yields, and moderate singlet oxygen generation. Quantum calculations affirmed that the smaller singlet-triplet energy gap and larger spin-orbit coupling cause efficient intersystem crossing, thus enhancing the singlet oxygen generation yield. Furthermore, selenophene-fused BODIPY exhibited significant phototoxicity with negligible dark cytotoxicity, based on the fluorescence imaging of the reactive oxygen species detection experiment.

Effects of Heavy Iodine Atoms and π-Expanded Conjugation on Charge Transfer Dynamics in Carboxylic Acid BODIPY Derivatives as Triplet Photosensitizers

Borondipyrromethene (BODIPY) chromophores are composed of a functional-COOH group at meso position with or without a biphenyl ring, and their compounds with heavy iodine atoms at -2, -6 positions of the BODIPY indacene core were synthesized. The photophysical properties of the compounds were studied with steady-state absorption and fluorescence measurements. It was observed that the absorption band is significantly red-shifted, and fluorescence signals are quenched in the presence of iodine atoms. In addition to that, it was indicated that the biphenyl ring does not affect the spectral shifting in the absorption as well as fluorescence spectra. In an attempt to investigate the effect of π-expanded biphenyl moieties and heavy iodine atoms on charge transfer dynamics, femtosecond transient absorption spectroscopy measurements were carried out in the environment of the tetrahydrofuran (THF) solution. Based on the performed ultrafast pump-probe spectroscopy, BODIPY compounds with iodine atoms lead to intersystem crossing (ISC) and ISC rates were determined as 150 ps and 180 ps for iodine BODIPY compounds with and without π-expanded biphenyl moieties, respectively. According to the theoretical results, the charge transfer in the investigated compounds mostly appears to be intrinsic local excitations, corresponding to high photoluminescence efficiency. These experimental findings are useful for the design and study of the fundamental photochemistry of organic triplet photosensitizers.

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.

Modification of a SOCT-ISC type triphenylamine-BODIPY photosensitizer by a multipolar dendrimer design for photodynamic therapy and two-photon fluorescence imaging

In this study, a series of multipolar triphenylamine-BODIPY photosensitizers T-BDP_n (n = 1, 2, 3) was synthesized. Compared with T-BDP₁ of D-A configuration, the multipolar T-BDP₃ dendrimer have higher singlet oxygen efficiency (44%), better fluorescence quantum yield (7.45%), and could be used in the simulated photodynamic therapy in A-549 cells and two-photon fluorescence imaging in zebrafish. The theoretical calculation and fs-transient absorption spectra indicated that the reason of its higher singlet oxygen efficiency was that the multipolar T-BDP₃ dendrimer could generate more nearly degenerate charge transfer (CT) states and triplet states, which could further increase the possibility of spin-orbit charge-transfer intersystem crossing (SOCT-ISC) process. In the simulated photodynamic therapy of A-549 cells, T-BDP₃ shows good cytocompatibility, great phototoxicity with its IC₅₀ value of 3.17 μM, and could kill cancer cells effectively with the dosage of 5 μM under 10 min irradiation in the AO/EB double-staining experiment. In the fluorescence imaging of zebrafish, the experiment results indicate that T-BDP₃ could generate superoxide radical (O₂˙^-) in the body of zebrafish and could be applied to the two-photon fluorescence imaging under 800 nm excitation. The above experiment results shown that the multipolar dendrimer design was an effective approach to improve the key parameters of SOCT-ISC-type BODIPY photosensitizer and was ready for further two-photon photodynamic therapy in organisms.