Utilizing Intramolecular Photoinduced Electron Transfer to Enhance Photothermal Tumor Treatment of Aza-BODIPY-Based Near-Infrared Nanoparticles

A BODIPY-tagged trivalent glycocluster for receptor-targeting fluorescence imaging of live cells

Multivalent glycoclusters have been extensively used as a targeting agent for drug delivery. However, tools capable of investigating their dynamic interactions with a target receptor remain elusive. Here, we synthesized fluorescently-tagged galactoclusters for the fluorescence imaging of cells that overly express the asialoglycoprotein receptor (ASGPr). A trivalent galactoside was synthesized, to which a boron dipyrromethene (BODIPY) dye was conjugated. The resulting fluorescent glycocluster was used for the targeted fluorescence imaging of liver cancer cells with a high ASGPr expression level. The trivalent probe was also demonstrated to be applicable for super-resolution imaging of ASGPr-mediated ligand endocytosis and the dynamic intracellular translocation to the lysosomes. As such, this study provides a suitable chemical tool for the study of receptor dynamics using fluorescently tagged glycoclusters.

Thiophene engineering of near-infrared D-π-A nano-photosensitizers for enhanced multiple phototheranostics and inhibition of tumor metastasis

Phototherapy including photothermal therapy (PTT) and photodynamic therapy (PDT) is widely used for cancer treatment because of its non-invasiveness, spatiotemporal controllability, and low side effects. However, the PTT and PDT capabilities of photosensitizers (PSs) compete so it's still a crucial challenge to simultaneously enhance the PDT and PTT capabilities of PSs. In this work, donor-π-acceptor (D-π-A)-based boron dipyrromethene (BODIPY) dyes were developed via molecular engineering and applied for enhanced phototherapy of triple-negative breast cancer. With thiophene engineering and iodine addition, D-π-A BDP dyes possessed a low energy gap between the singlet and triplet states (ΔES1-T1). After the BDP dyes were prepared into nanoparticles (NPs), the BDP4 NPs showed increased generation of type I and II reactive oxygen species (ROS) as well as a high photothermal conversion efficiency (44 %). Furthermore, folate (FA)-modified BDP4 NPs achieved high tumor targeting via near-infrared bioimaging. With these advantages, BDP4 NPs with FA achieved total tumor eradication and tumor metastasis suppression via a single injection and 808 nm laser irradiation. This work provided a rational design of D-π-A PSs for simultaneously enhancing their photodynamic and photothermal performance, achieving efficient cancer therapy.

Exceptional Near-Infrared II Organic Small Molecule Nanoagent for Photoacoustic/Photothermal Imaging-Guided Highly Efficient Therapy in Cancer

Near-infrared II (NIR-II) photoacoustic (PA)/photothermal imaging-guided tumor therapy holds great promise in precision medicine for cancer treatment. This work reports on the synthesis and application of an organic small molecule nanoagent that has exceptional PA and photothermal properties in the near-infrared region. BCy-TPE was constructed by linking an NIR-II absorbing cyanine dye BCy-Cl with a twisted tetraphenylethene unit. The synthesized BCy-TPE exhibited an intense absorption peak at 1032 nm. After encapsulation into water-dispersible nanoparticles (NPs), BCy-TPE NPs exhibited two absorption peaks at 880 and 1046 nm. Notably, under 1064 nm laser excitation, BCy-TPE NPs deliver a remarkable photothermal conversion efficiency of 92%, together with superior biocompatibility, photostability, and PA/photothermal imaging capability. Moreover, after intravenous administration of BCy-TPE NPs into 4T1 tumor-bearing mice and treatment with safe-intensity (1.0 W cm-2 and 1064 nm) laser irradiation, tumor temperature increased rapidly to 52 °C within 1 min and tumors are completely ablated after a single photothermal therapy treatment. Overall, this work offers a novel strategy to develop superb NIR-II photothermal agents for PA/photothermal imaging-guided highly efficient therapy in cancer.

Unravelling the influence of structure on the optical properties of a pair of aza-BODIPY isomers and their application in photodynamic therapy

A pair of aza-BODIPY isomers, 1,7-di-tert-butyl-3,5-dinaphthyl (Nap-BDP) and 1,7-dinaphthyl-3,5-di-tert-butyl (revNap-BDP), were prepared in this study. According to the single crystal X-ray analysis, Nap-BDP exhibited an orthogonal structure. Owing to the difference in orthogonality and -tBu rotation between Nap-BDP and revNap-BDP, their spectral performances, including maximum absorption and emission, full width at half maximum, fluorescence quantum yield, photostability, singlet oxygen generation and photothermal conversion efficiency, were obviously different. The corresponding calculation results were in good agreement with the experimental results. Furthermore, the self-assembly of Nap-BDP nanoparticles could effectively promote cancer cell death by inducing singlet oxygen. Hence, this approach holds potential as a therapeutic strategy for enhancing cancer cell eradication via photodynamic therapy.

Introducing of an Unexplored Aza-BODIPY Diradicaloids with 4-(2,6-Ditert-butyl)phenoxyl Radicals Located in 1,7-Positions of the Aza-BODIPY Core

We have prepared and characterized two diradicaloid systems 5a and 5b that originated from the oxidation of a 1,7-(4-(2,6-di-tert-butyl)phenol)-substituted aza-BODIPY core. The aza-BODIPY diradicaloids were characterized by a large array of experimental and computational methods. The diamagnetic closed-shell state was postulated as the ground state in solution and a solid-state with the substantial thermal population originating from both open-shell diradical and open-shell triplet states observed at room temperature. Transient absorption spectroscopy indicates fast (<10 ps) excited state deactivation pathways associated with the target compounds' diradical character in solution at room temperature. Variable-temperature 1H NMR spectra indicate the solvent dependency of the diradical character in 5a and 5b. The diradicaloids could be stepwise reduced to the mixed-valence radical-anion and dianion states upon consequent single-electron reductions. Similarly, deprotonated 1,7-(4-(2,6-di-tert-butyl)phenol)-substituted aza-BODIPYs can be oxidized to the diradicaloid form. Both mixed-valence and dianionic forms exhibit an intense absorption in the NIR region. Density functional theory (DFT) and time-dependent DFT calculations were used to explain the transformations in the UV-Vis-NIR spectra of all target compounds.

Aggregation-Induced Emission-Active Organic Nanoagent with High Photothermal Conversion Efficiency for Near-Infrared Imaging-Guided Tumor Photothermal Therapy

Photothermal therapy (PTT) provides a great prospect for noninvasive cancer therapy. However, it is still highly challenging to construct photothermal agents (PTAs) with the desired performances for imaging-guided PTT applications. Herein, a D-A-D-type naphthalene diamine (NDI)-based photothermal nano-PTAs NDS-BPN NP with near-infrared region (NIR) emission at 822 nm, aggregation-induced emission (AIE), high photothermal conversion efficiency (55.05%), and excellent photothermal stability is successfully designed and prepared through a simple two-step engineering method by using a new AIE molecule NDS-BPN and DSPE-PEG2000 as precursors. The prepared PTT nanoagents NDS-BPN NPs have been further applied for efficient photothermal ablation of cancer cells in vitro and also achieved the NIR fluorescent image-guided PTT tumor therapy in vivo with satisfactory results. We believe that this work provides an attractive NIR AIE NDI-based nano-PTA for the phototherapy of tumors as well as develops the construction strategy of NDI molecular-based photothermal nanoagents with desired performances for imaging-guided PTT.

Potentiating light-harvesting tactics through an A-D-A structure: repolarization of tumor-associated macrophages through phototherapy

Aiming to decrease the recurrence of tumors and achieve patient satisfaction, the elicitation of immunotherapy and its integrated synergistic employment is a bright new direction in oncotherapy, yet an emergently challenging task. In particular, tumor-associated macrophage (TAM) regulation though light-induced photodynamic and photothermal therapy (PDT and PTT) is regarded as a powerful approach, which focuses on the systemic immune system instead of the tumor itself. Herein, this study reports an acceptor-donor-acceptor (A-D-A) aggregation-induced emission luminogen (AIEgen), named TPA-2CN, which was applied as a photosensitizer (PS) and photothermal agent (PTA). Attributed to its A-D-A structure and AIE properties, TPA-2CN exhibits a high molar absorption coefficient and acts as a perfect template in regulating radiative and nonradiative transitions, which mainly utilize excited energy. The generation of type I reactive oxygen promoted its application in hypoxic tumor sites and the combination of hyperpyrexia forcefully induces macrophages to polarize towards the immune response M1 phenotype. In in vitro and in vivo, the successful reversion and reprogramming of the immune microenvironment was impressively proved. This method optimally concentrated immune therapy, PDT and PTT as one and exhibited excellent synergistic therapeutic effects with good biosafety.

Easy but Efficient: Facile Approach to Molecule with Theoretically Justified Donor-Acceptor Structure for Effective Photothermal Conversion and Intravenous Photothermal Therapy

To accelerate the pace in the field of photothermal therapy (PTT), it is urged to develop easily accessible photothermal agents (PTAs) showing high photothermal conversion efficiency (PCE). As a proof-of-concept, hereby a conventional strategy is presented to prepare donor-acceptor (D-A) structured PTAs through cycloaddition-retroelectrocyclization (CA-RE) reaction, and the resultant PTAs give high PCE upon near-infrared (NIR) irradiation. By joint experimental-theoretical study, these PTAs exhibit prominent D-A structure with strong intramolecular charge transfer (ICT) characteristics and significantly twisting between D and A units which account for the high PCEs. Among them, the DMA-TCNQ exhibits the strongest absorption in NIR range as well as the highest PCE of 91.3% upon irradiation by 760-nm LED lamp (1.2 W cm-2). In vitro and in vivo experimental results revealed that DMA-TCNQ exhibits low dark toxicity and high phototoxicity after IR irradiation along with nude mice tumor inhibition up to 81.0% through intravenous therapy. The findings demonstrate CA-RE reaction as a convenient approach to obtain twisted D-A structured PTAs for effective PTT and probably promote the progress of cancer therapies.

Revolutionary Pyrazole-based Aza-BODIPY: Harnessing Photothermal Power Against Cancer Cells and Bacteria

In the realm of cancer therapy and treatment of bacterial infection, photothermal therapy (PTT) stands out as a potential strategy. The challenge, however, is to create photothermal agents that can perform both imaging and PTT, a so-called theranostic agent. Photothermal agents that absorb and emit in the near-infrared region (750-900 nm) have recently received a lot of attention due to the extensive penetration of NIR light in biological tissues. In this study, we combined pyrazole with aza-BODIPY (PY-AZB) to develop a novel photothermal agent. PY-AZB demonstrated great photostability with a photothermal conversion efficiency (PCE) of up to 33 %. Additionally, PY-AZB can permeate cancer cells at a fast accumulation rate in less than 6 hours, according to the confocal images. Furthermore, in vitro photothermal therapy results showed that PY-AZB effectively eliminated cancer cells by up to 70 %. Interestingly, PY-AZB exhibited antibacterial activities against both gram-negative bacteria, Escherichia coli 780, and gram-positive bacteria, Staphylococcus aureus 1466. The results exhibit a satisfactory bactericidal effect against bacteria, with a killing efficiency of up to 100 % upon laser irradiation. As a result, PY-AZB may provide a viable option for photothermal treatment.

Aza-BODIPY-based polymeric nanoparticles for photothermal cancer therapy in a chicken egg tumor model

A new push-pull aza-BODIPY (AZB-CF3) derivative comprised of dimethylamino groups and trifluoromethyl moieties was successfully synthesized. This derivative exhibited broad absorption in the near-infrared region in the range from 798 to 832 nm. It also exhibited significant near-infrared (NIR) signals in low-polar solvents with emission peaks around 835-940 nm, while non-fluorescence in high-polar environments due to the twisted intramolecular charge transfer (TICT) phenomenon. The nanoprecipitation of this compound with phospholipid-based polyethylene glycol (DSPE-PEG) yielded AZB-CF3@DSPE-PEG nanoparticles (NPs) with a hydrodynamic size of 70 nm. The NPs exhibited good photostability, colloidal stability, biocompatibility, and excellent photothermal (PTT) competence with a conversion efficiency (η) of 44.9%. These NPs were evaluated in vitro and in ovo in a 4T1 breast cancer cell line for NIR light-trigger photothermal therapy. Proven in the chicken egg tumor model, AZB-CF3@DSPE-PEG NPs induced severe vascular damage (∼40% vascular destruction), showed great anticancer efficacy (∼75% tumor growth inhibition), and effectively inhibited distant metastasis via photothermal treatment. As such, this PTT-based nanocarrier system could be a potential candidate for a clinical cancer therapy approach.

Self-Reporting Molecular Prodrug for In Situ Quantitative Sensing of Drug Release by Ratiometric Photoacoustic Imaging

Understanding the pharmacokinetics of prodrugs in vivo necessitates quantitative, noninvasive, and real-time monitoring of drug release, despite its difficulty. Ratiometric photoacoustic (PA) imaging, a promising deep tissue imaging technology with a unique capacity for self-calibration, can aid in solving this problem. Here, for the first time, a methylamino-substituted Aza-BODIPY (BDP-N) and the chemotherapeutic drug camptothecin (CPT) are joined via a disulfide chain to produce the molecular theranostic prodrug (BSC) for real-time tumor mapping and quantitative visualization of intratumoral drug release using ratiometric PA imaging. Intact BSC has an extremely low toxicity, with a maximum absorption at ∼720 nm; however, endogenous glutathione (GSH), which is overexpressed in tumors, will cleave the disulfide bond and liberate CPT (with full toxicity) and BDP-N. This is accompanied by a significant redshift in absorption at ∼800 nm, resulting in the PA800/PA720 ratio. In vitro, a linear relationship is successfully established between PA800/PA720 values and CPT release rates, and subsequent experiments demonstrate that this relationship can also be applied to the quantitative detection of intratumoral CPT release in vivo. Notably, the novel ratiometric strategy eliminates nonresponsive interference and amplifies the multiples of the signal response to significantly improve the imaging contrast and detection precision. Therefore, this research offers a viable alternative for the design of molecular theranostic agents for the clinical diagnosis and treatment of tumors.

Recent Advances in Monocomponent Visible Light Photoinitiating Systems Based on Sulfonium Salts

During the last decades, multicomponent photoinitiating systems have been the focus of intense research efforts, especially for the design of visible light photoinitiating systems. Although highly reactive three-component and even four-component photoinitiating systems have been designed, the complexity to elaborate such mixtures has incited researchers to design monocomponent Type II photoinitiators. Using this approach, the photosensitizer and the radical/cation generator can be combined within a unique molecule, greatly simplifying the elaboration of the photocurable resins. In this field, sulfonium salts are remarkable photoinitiators but these structures lack absorption in the visible range. Over the years, various structural modifications have been carried out in order to redshift their absorptions in the visible region. In this work, an overview of the different sulfonium salts activable under visible light and reported to date is proposed.

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.

Aza-BODIPY-based Fluorescent and Colorimetric Sensors and Probes

Aza-boron-dipyrromethenes (Aza-BODIPYs) represent an important class of chromophores absorbing and emitting in the near-infrared (NIR) region. They have unique optical and electronic features and higher physiological and photo stability than other NIR dyes. Especially after the development of facile synthetic routes, Aza-BODIPYs have become indispensable fluors that can find various applications ranging from chemosensors, bioimaging, phototherapy, solar energy materials, photocatalysis, photon upconversion, lasers, and optoelectronics. Herein, we review Aza-BODIPY based fluorescent and colorimetric chemosensors. We show the potential and untapped toolbox of Aza-BODIPY based fluorescent and colorimetric chemosensors. Hence, we divide the fluorescent and colorimetric chemosensors and probes into five sections according to the target analytes. The first section begins with the chemosensors developed for pH. Next, we discuss Aza-BODIPY based ion sensors, including metal ions and anions. Finally, we present the chemosensors and probes concerning reactive oxygen (ROS) and nitrogen species (RNS) along with biologically relevant species in the last two sections. We believe that Aza-BODIPYs are still in their infancy, and they have a promising future for translation from the bench to real biomedical and materials science applications. After two decades of intensive research, it seems that there are many more to come in this already fertile field. Overall, we hope that future work will further expand the applications of Aza-BODIPY in many areas.

Near-Infrared-Absorbing B-N Lewis Pair-Functionalized Anthracenes: Electronic Structure Tuning, Conformational Isomerism, and Applications in Photothermal Cancer Therapy

B-N-fused dianthracenylpyrazine derivatives are synthesized to generate new low gap chromophores. Photophysical and electrochemical, crystal packing, and theoretical studies have been performed. Two energetically similar conformers are identified by density functional theory calculations, showing that the core unit adopts a curved saddle-like shape (x-isomer) or a zig-zag conformation (z-isomer). In the solid state, the z-isomer is prevalent according to an X-ray crystal structure of a C₆F₅-substituted derivative (4-Pf), but variable-temperature nuclear magnetic resonance studies suggest a dynamic behavior in solution. B-N fusion results in a large decrease of the HOMO-LUMO gap and dramatically lowers the LUMO energy compared to the all-carbon analogues. 4-Pf in particular shows significant absorbance at greater than 700 nm while being almost transparent throughout the visible region. After encapsulation in the biodegradable polymer DSPE-mPEG₂₀₀₀, 4-Pf nanoparticles (4-Pf-NPs) exhibit good water solubility, high photostability, and an excellent photothermal conversion efficiency of ∼41.8%. 4-Pf-NPs are evaluated both in vitro and in vivo as photothermal therapeutic agents. These results uncover B-N Lewis pair functionalization of PAHs as a promising strategy toward new NIR-absorbing materials for photothermal applications.

PEGylated Aza-BODIPY Nanoparticles for Photothermal Therapy

Photothermal therapy is a promising treatment modality in the realm of cancer therapy. Photothermal nanomaterials that absorb and emit in the near-infrared range (750-900 nm) have drawn a lot of attention recently because of the deep penetration of NIR light in biological tissue. Most nanomaterials, however, are produced by encapsulating or altering the surface of a nanoplatform, which has limited loading capacity and long-term storage. Herein, we developed a stable polymer conjugated with aza-BODIPY that self-assembled to form nanoparticles (aza-BODIPY-mPEG) with better hydrophilicity and biocompatibility while retaining the dye's photothermal conversion characteristics. Aza-BODIPY-mPEG with a hydrodynamic size of around 170 nm exhibited great photostability and excellent photothermal therapy in vitro and in ovo. Aza-BODIPY-mPEG exhibits approximately 30% better anti-angiogenesis and antitumor activity against implanted xenograft human HCT116 tumor in the chick embryo compared to parent aza-BODIPY-A, altogether suggesting that aza-BODIPY-mPEG is a promising material for cancer photothermal therapy.

Boron Dipyrromethene-Based Phototheranostics for Near Infrared Fluorescent and Photoacoustic Imaging-Guided Synchronous Photodynamic and Photothermal Therapy of Cancer

The regulation of photochemical properties of phototheranostics, especially the absorption, fluorescence, singlet oxygen (¹O₂) generation, and photothermal conversion efficiency, is a hot research topic. Here, we designed and synthesized four boron dipyrromethene (BODIPY) derivatives with high absorption coefficients and intense fluorescence in the near-infrared (NIR) region. The substituted electron-donating group significantly improved ¹O₂ generation and fluorescence of BODIPYs, whereas the electron-withdrawing group boosts photothermal conversion. These hydrophobic BODIPYs were further coated with DSPE-PEG-2000 to form water dispersible nanoparticles (NPs). Among these BODIPY NPs, the B-OMe-NPs with methoxyl substituted at the meso-position showed the highest ¹O₂ generation, a photothermal conversion efficiency of 66.5%, and an NIR fluorescence peak at 809 nm. In vitro and in vivo experiments demonstrated that B-OMe-NPs might be used for NIR fluorescent and photoacoustic imaging-guided photodynamic and photothermal therapy of cancer.

Research Progress of Photothermal Nanomaterials in Multimodal Tumor Therapy

The aggressive growth of cancer cells brings extreme challenges to cancer therapy while triggering the exploration of the application of multimodal therapy methods. Multimodal tumor therapy based on photothermal nanomaterials is a new technology to realize tumor cell thermal ablation through near-infrared light irradiation with a specific wavelength, which has the advantages of high efficiency, less adverse reactions, and effective inhibition of tumor metastasis compared with traditional treatment methods such as surgical resection, chemotherapy, and radiotherapy. Photothermal nanomaterials have gained increasing interest due to their potential applications, remarkable properties, and advantages for tumor therapy. In this review, recent advances and the common applications of photothermal nanomaterials in multimodal tumor therapy are summarized, with a focus on the different types of photothermal nanomaterials and their application in multimodal tumor therapy. Moreover, the challenges and future applications have also been speculated.

Self-Assembly of Amphiphilic BODIPY Derivatives on Micropatterned Ionic Liquid Surfaces for Fluorescent Films with Excellent Stability and Sensing Performance

Fluorescent films have been widely recognized as one of the most powerful tools for trace analyte detection. However, their use has been limited due to the poor photochemical stability of fluorophores at a gas-solid interface and inefficient film mass transfer. Herein, novel fluorescent films were developed through self-assembly of amphiphilic BODIPY derivatives on micropatterned ionic liquid surfaces. Unlike solid-state films, the obtained monolayer films exhibit excellent photochemical stability, similar to that of a solution. Moreover, the interfacial assembly of amphiphilic fluorophores can avoid gas diffusion inside the microdroplets, significantly improving the sensing performance. The 1/1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF₄) monolayer exhibits high sensitivity, high selectivity, and a fast response to detect diethylchlorophosphate (DCP) vapor. The detection limit was 226 ppt, with a response time to DCP of 2.0 s. Importantly, the 1/[BMIM]BF₄ monolayer can be reused for at least 50 cycles with no obvious signal fading. This study is expected to benefit the development of new strategies for designing fluorescence sensing films and lay a solid foundation for the fabrication of multifunctional sensing devices with excellent photochemical stability and sensing performance.

Chemical Design of Activatable Photoacoustic Probes for Precise Biomedical Applications

Photoacoustic (PA) imaging technology, a three-dimensional hybrid imaging modality that integrates the advantage of optical and acoustic imaging, has great application prospects in molecular imaging due to its high imaging depth and resolution. To endow PA imaging with the ability for real-time molecular visualization and precise biomedical diagnosis, numerous activatable molecular PA probes which can specifically alter their PA intensities upon reacting with the targets or biological events of interest have been developed. This review highlights the recent developments of activatable PA probes for precise biomedical applications including molecular detection of the biotargets and imaging of the biological events. First, the generation mechanism of PA signals will be given, followed by a brief introduction to contrast agents used for PA probe design. Then we will particularly summarize the general design principles for the alteration of PA signals and activatable strategies for developing precise PA probes. Furthermore, we will give a detailed discussion of activatable PA probes in molecular detection and biomedical imaging applications in living systems. At last, the current challenges and outlooks of future PA probes will be discussed. We hope that this review will stimulate new ideas to explore the potentials of activatable PA probes for precise biomedical applications in the future.

Precise Diagnosis and Therapy of Bone Cancer Using Near-Infrared Lights

Bone is a preferred site for both primary and metastasis tumors. Current diagnosis of osteopathia typically relies on noninvasive skeleton radiography technology. However, due to the limited resolution of ionizing radiation, accurate diagnosis and effective identification impairment areas are still lacking. Near-infrared (NIR) bioimaging, especially in the NIR-II (1000-1700 nm) regions, can provide high sensitivity and spatiotemporal resolution bioimaging compared to the conventional radiography. Thus, NIR bioimaging affords intraoperative visualization and imaging-guided surgery, aiming to overcome challenges associated with theranostics of osteopathia and bone tumors. The present review aimed to summarize the latest evidence on the use of NIR probes for the targeting bone imaging. We further highlight the recent advances in bone photoX (X presents thermal, dynamic, and immuno) therapy through NIR probes, in particular combination with other customized therapeutic agents could provide high-efficiency treatment for bone tumors.

Boosting Photothermal Theranostics via TICT and Molecular Motions for Photohyperthermia Therapy of Muscle-Invasive Bladder Cancer

The development of photothermal agents with high photothermal conversion efficiency (PCE) can help to reduce drug and laser dosage, but still remains a big challenge. Herein, a novel approach is reported to design photothermal agents with high PCE values by promoting nonradiative heat generation processes through the cooperation of twisted intramolecular charge transfer (TICT) and molecular motions. Within the designed molecule 2DMTT-BBTD, the tetraphenylethenes act as molecular rotors, the long alkyl chain grafted thiophene helps to twist the molecular geometry to facilitate TICT state formation and preserve molecular motions in aggregate, while the strong electron-withdrawing BBTD unit enhances TICT effect. 2DMTT-BBTD exhibits NIR-absorption and a high PCE value of 74.8% under 808 nm laser irradiation. Gambogic acid (GA) which surmounts tumor cell thermotolerance by inhibiting heat shock protein 90 (HSP90) expression is coloaded into the nanoparticles, RGD peptide is further introduced to the nanoparticle surface to improve tumor accumulation. The resultant nanoparticles facilitate the effective low-temperature hyperthermia therapy of muscle-invasive bladder cancer (MIBC) with minimal damage to surrounding heathy tissues. This work delivers a new design concept for development of highly efficient photothermal agents, which also provides a safer approach for noninvasive treatment of MIBC and other malignant tumors.

1,7-Di-tert-butyl-Substituted aza-BODIPYs by Low-Barrier Rotation to Enhance a Photothermal-Photodynamic Effect

1,7-Di-tert-butyl-substituted aza-BODIPYs (tBu-azaBDP) were successfully obtained for the first time. The structures of tBu-azaBDP and Ph-azaBDP were confirmed by X-ray crystal analysis, and tBu-azaBDP 2 is more twisted than Ph-azaBDP 5. tBu-azaBDPs have significant photo-stability and enhanced water solubility. tBu-azaBDPs possess excellent optical properties, such as high molar extinction coefficients, broad full width half maxima, and large Stokes shifts, which is comparable to those of the parent dye Ph-azaBDP. Although the low-barrier rotation of the distal -tBu groups in tBu-azaBDPs results in low quantum yield, photothermal conversion efficiency and singlet oxygen generation ability of tBu-azaBDPs are more effective than those of Ph-azaBDP, which is highly desirable for a photothermal-photodynamic therapy agent.

The tumor phototherapeutic application of nanoparticles constructed by the relationship between PTT/PDT efficiency and 2,6- and 3,5-substituted BODIPY derivatives

BODIPY dyes have recently been used for photothermal and photodynamic therapy of tumors. However, complex multi-material systems, multiple excitation wavelengths and the unclear relationship between BODIPY structures and their PTT/PDT efficiency are still major issues. In our study, nine novel BODIPY near-infrared dyes were designed and successfully synthesized and then, the relationships between BODIPY structures and their PTT/PDT efficiency were investigated in detail. The results showed that modifications at position 3,5 of the BODIPY core with conjugated structures have better effects on photothermal and photodynamic efficiency than the modifications at position 2,6 with halogen atoms. Density functional theory (DFT) calculations showed that this is mainly due to the extension of the conjugated chain and the photoinduced electron transfer (PET) effect. By encapsulating BDPX-M with amphiphilic DSPE-PEG₂₀₀₀-RGD and lecithin, the obtained NPs not only show good water solubility and biological stability, but also could act as superior agents for photothermal and photodynamic synergistic therapy of tumors. Finally, we obtained BODIPY NPs that exhibited excellent photothermal and photodynamic effects at the same time under single irradiation with an 808 nm laser (photothermal conversion efficiency: 42.76%, A/A₀: ∼0.05). In conclusion, this work provides a direction to design and construct phototherapeutic nanoparticles based on BODIPY dyes for tumor treatment.

Water-Soluble Visible Light Sensitive Photoinitiating System Based on Charge Transfer Complexes for the 3D Printing of Hydrogels

The development of visible-light 3D printing technology by using water-soluble initiating systems has attracted widespread attention due to their potential applications in the manufacture of hydrogels. Besides, at present, the preparation of water-soluble photoinitiators suitable for visible light irradiation (such as LEDs) still remains a challenge. Therefore, this work is devoted to developing water-soluble photoinitiators (PI)/photoinitiating systems (PIS) upon irradiation with a LED @ 405 nm. In detail, a new water-slightly-soluble chalcone derivative dye [(E)-3-(4-(dimethylamino) phenyl)-1-(4-(2-(2-(2-methoxyethoxy) ethoxy) ethoxy) phenyl) prop-2-en-1-one] was synthesized here and used as a PI with a water-soluble coinitiator, i.e., triethanolamine (TEA) which was also used as an electron donor. When combined together, a charge transfer complex (CTC) formed immediately which exhibited excellent initiating ability for the free radical photopolymerization of poly(ethyleneglycol)diacrylate (PEG-DA). In light of the powerful CTC effect, the [dye-TEA] CTC could not only exhibit enhanced water solubility and mechanical properties but could also be effectively applied for 3D printing. This CTC system is environmentally friendly and cost-saving which demonstrates a great potential to prepare hydrogels via photopolymerization.

Leveraging BODIPY nanomaterials for enhanced tumor photothermal therapy

In the past ten years, photothermal therapy (PTT) has attracted widespread attention in tumor treatment due to its non-invasiveness and little side effects. PTT utilizes heat produced by photothermal agents under the irradiation of near-infrared light to kill tumor cells. Boron-dipyrromethene (BODIPY), an organic phototherapy agent, has been widely used in tumor phototherapy due to its higher molar extinction coefficient, robust photostability and good phototherapy effect. However, there are some issues in the application of BODIPY for tumor PTT, such as low photothermal conversion efficiency and short absorption wavelength. In this review, we focus on the latest development of BODIPY nanomaterials for overcoming the above problems and enhancing the PTT effect.

Nitric oxide release activated near-Infrared photothermal agent for synergistic tumor treatment

Activatable phototherapeutic agents (PTA) in one system with synergistic gas therapy (GT) and photothermal therapy (PTT) hold great promise for highly efficient tumor treatments. In this study, an activatable multifunctional platform with photothermal conversion "turn on" features via nitric oxide (NO) release for synergistic GT and PTT was rationally designed using an aryl N-nitrosamine (NO-donating unit) functionalized aza-BODIPY framework (S-NO). As expected, after NO release from S-NO, the product (Red-S) showed obviously enhanced heat production performance under a longer excited wavelength via improved near-infrared light absorption and decreased fluorescence emission. Furthermore, water-soluble and biocompatible S-NO nanoparticles (S-NO NPs) with negligible dark cytotoxicity successfully suppressed tumor growth and enhanced the survival rate of mice via synergistic GT and PTT under the guidance of multimode imaging. The study offered rational guidance to design better platforms for synergistic tumor treatments and validated that S-NO NPs can act as potential PTAs in biological applications.

A photothermally-induced HClO-releasing nanoplatform for imaging-guided tumor ablation and bacterial prevention

Photothermal therapy (PTT) is a cure that can inhibit tumor growth effectively and even remove tumor via photo-induced local hyperthermia. However, its shortcoming lies in the fact that excessive heat is most likely to lead to thermal injury at the epidermis of the tumor region and even the area of the surrounding tissue. As a consequence, the exposure of the thermally-induced wound would result in the increased risk of bacterial infection. To date, few PTT platforms have attached importance to the prevention of bacterial infection at the photothermally-induced wound. Herein, we reported a thermally-sensitive liposome nanosystem (Lipo-B-TCCA) containing aza-BODIPY and trichloroisocyanuric acid, which is conductive for the PTT of tumor and the prevention of bacteria. It is observed that the designed nanoplatform could exhibit remarkable stability, high photothermal conversion efficiency (31.4%), and efficient HClO-releasing ability in vitro and in vivo. Moreover, Lipo-B-TCCA is able to eliminate tumor efficiently via near infrared fluorescence and photothermal imaging guidance with low side effects. Most importantly, Lipo-B-TCCA could prevent the growth of S. aureus in the thermal wound during the process of PTT. The imaging-guided photothermally-induced HClO-releasing PTT nanoplatform for tumor ablation and bacterial prevention shows excellent performance and great potential for biomedical applications.

Strategies for maximizing photothermal conversion efficiency based on organic dyes

Photothermal therapy (PTT) has emerged as a promising therapeutic approach for tumor control and ablation. Attention has focused on exploring advanced organic photothermal agents (OPTAs), with advantages of easy modification, adjustable photophysical and photochemical properties, good compatibility, and inherent biodegradability. However, few detailed studies on how to maximally channelize nonradiative heat generation from the viewpoint of the photothermal conversion mechanism have been reported. Thus, here we assimilate and elaborate on several available action mechanisms to maximize the photothermal conversion efficiency (PCE) of organic dyes. Moreover, we also propose several potential challenges that require substantial future work to address.

Mitochondria-Targeted BODIPY Nanoparticles for Enhanced Photothermal and Photoacoustic Imaging In Vivo

Short-wavelength absorption and emission (<600 nm), hydrophobicity, and low selectivity have greatly restricted the biomedical applications of BODIPY. Herein, a series of mitochondria-targeted BODIPY nanoparticles with a cationic triphenylphosphine (TPP) group (Mito-BDP1-5 NPs) bearing different lengths of ethylene glycol (0-4 units), along with HO-BDP5 without a cationic TPP group for comparison, have been rationally designed and prepared to investigate the interplay between their structures and the related properties. Our studies found that Mito-BDP1-4 NPs showed a tendency of aggregation and precipitation while Mito-BDP5 NPs could be stable in aqueous solutions. Compared with HO-BDP5, tailor-made Mito-BDP5 possessed a high photothermal conversion efficiency (PCE) of 76.6 vs 9.0% and exhibited the highest photoinduced cytotoxicity. Upon NIR irradiation, the temperature induced by Mito-BDP5 NPs increased rapidly from room temperature to 76.0 °C in vitro and 50.0 °C at the tumor site in vivo within 5 min. Furthermore, effective mitochondrial imaging in vitro, photothermal imaging (PTI), and photoacoustic imaging (PAI) in vivo were achieved. In this paper, we developed tailor-made photothermal agents for targeting mitochondria and enhancing the PTI and PAI performances, which could be potentially applied in clinical precision theranostics.

Highly stable organic photothermal agent based on near-infrared-II fluorophores for tumor treatment

BACKGROUND

The aim to develop a highly stable near-infrared (NIR) photoinduced tumor therapy agent stems from its considerable potential for biological application. Due to its long wavelength, biological imaging exhibits a high signal-to-background ratio, deep tissue penetration and maximum permissible light power, which can minimize damage to an organism during photoinduced tumor therapy.

RESULTS

A class of stable NIR-II fluorophores (NIR998, NIR1028, NIR980, NIR1030, and NIR1028-S) based on aza-boron-dipyrromethene (aza-BODIPY) dyes with donor-acceptor-donor structures have been rationally designed and synthesized by harnessing the steric relaxation effect and intramolecular photoinduced electron transfer (IPET). These fluorophores exhibit an intense range of NIR-II emission, large Stokes shift (≥ 100 nm), excellent photothermal conversion performance, and superior stability against photobleaching. Among the NIR-II fluorophores, NIR998 possesses better NIR-II emission and photothermal conversion performance. NIR998 nanoparticles (NIR998 NPs) can be encapsulated by liposomes. NIR998 NPs show superior stability in the presence of light, heat, and reactive oxygen nitrogen species than that of indocyanine green NPs, as well as a higher photothermal conversion ability (η = 50.5%) compared to other photothermal agents. Finally, under the guidance of photothermal imaging, NIR998 NPs have been proven to effectively eliminate tumors via their excellent photothermal conversion performance while presenting negligible cytotoxicity.

CONCLUSIONS

Utilizing IPET and the steric relaxation effect can effectively induce NIR-II emission of aza-BODIPY dyes. Stable NIR998 NPs have excellent photothermal conversion performance and negligible dark cytotoxicity, so they have the potential to act as photothermal agents in biological applications.

Rational Design of Near-Infrared-Absorbing Pt(II)-Chelated Azadipyrromethene Dyes as a New Generation of Photosensitizers for Synergistic Phototherapy

Pt(II) photosensitizers are emerging as novel Pt anticancer agents for cancer photodynamic therapy (PDT) to avoid uncontrollable toxicity of cisplatin. However, the application of Pt(II) photosensitizers is limited by tumor hypoxia and the poor penetration depth of excitation light. To overcome these drawbacks, exploiting the next generation of Pt anticancer agents is of urgent need. According to theoretical calculations, novel near-infrared (NIR)-absorbing Pt(II)-chelated azadipyrromethene dyes (PtDP-X, where X = N, C, and S) were designed. Importantly, spin-orbit coupling of the Pt atom could promote the intersystem crossing of a singlet-to-triplet transition for converting oxygen to singlet oxygen (¹O₂), and the azadipyrromethene skeleton could provide a strong photothermal effect. As expected, PtDP-X exhibited intense NIR absorption and synergistic PDT and photothermal effects with low dark cytotoxicity. Furthermore, water-soluble and biocompatible PtDP-N nanoparticles (PtDP-N NPs) were prepared that achieved effective tumor cell elimination with low side effects under 730 nm light irradiation in vitro and in vivo. This pioneering work could push the exploitation of NIR-absorbing metal-chelated azadipyrromethene dyes, so as to promote the positive evolution of phototherapy agents.

3, 3,5 and 2,6 Expanded Aza-BODIPYs Via Palladium-Catalyzed Suzuki-Miyaura Cross-Coupling Reactions: Synthesis and Photophysical Properties

Novel symmetrical aza-borondipyrromethene (aza-BODIPY) compounds bearing 4-methoxyphenyl, 4-methoxybiphenyl, 2,4-dimethoxybipheny, 4-bromophenyl and N,N-diphenyl-4-biphenylamine groups on the 3, 3,5 and 2,6 positions of aza-BODIPY core were synthesized via Suzuki-Miyaura coupling reactions while unsymmetrical analogues were obtained from the starting mono Br-substituted aza-BODIPY material which was obtained from nitrosolated pyrrole derivative. The characterizations were performed by means of ¹H-NMR, ¹³C-NMR, FTIR and HRMS-TOF-ESI techniques. The spectral properties of the aza-BODIPY derivatives were investigated using absorption and fluorescence spectroscopy. The novel compounds with extended conjugation have broadband absorption in near infrared region and show significant shifts on their absorption and fluorescence spectra compared to unsubstituted analogues. The highest bathochromic shifts were observed π-extended and strong electron donating groups at 3,5 positions of the aza-BODIPY scaffold. Depend on substitution positions of attached groups to the indacene core, the fluorescence quantum yields of chromophores were determined to be drastic changes. The singlet oxygen generation capability of the compounds were evaluated and 2,6-bromine substituted compounds AA1 and CC1 showed high singlet oxygen quantum yields (71% and 74%, respectively). Enhanced photophysical properties such as intense absorption, extended conjugation and singlet oxygen production make the investigated aza-BODIPYs promising candidates for photodynamic therapy applications and organic photovoltaic cells in NIR region.

Conjugated BODIPY Oligomers with Controllable Near-Infrared Absorptions as Promising Phototheranostic Agents through Excited-State Intramolecular Rotations

Conjugated molecules with coplanar strong donor and acceptor (D-A) units have been widely used in the design of near-infrared (NIR) photothermal agents to increase an absorption band through intramolecular charge transfer and to control intramolecular motions in aggregated states. However, such conjugated D-A systems have strong dipolar moments and intermolecular interactions, which may inhibit other channels of photothermal conversion and are often susceptible to nucleophiles, especially in the presence of light irradiation. Now, we report a molecular guideline to develop novel NIR organic photothermal nanoagents based on conjugated boron dipyrromethene (BODIPY) oligomers. This oligomerization is helpful not only for their tunable NIR absorptions in the ground state with distinctly redshifted absorption maxima up to 1002 nm and high extinction coefficients but also for their highly efficient photothermal conversion because of the possible motion of the BODIPY motifs around the ethene linked group in the excited state. These oligomers were fabricated as ultra-photostable nanoagents for multiple imaging-guided phototherapies, which efficiently accumulated in tumors, and gave complete tumor ablation with NIR laser irradiation. This strategy of "ground-state conjugation, excited-state rotation" provides a novel guideline to develop advanced theranostic molecules with NIR absorption.

Aza-BODIPY Probe-Decorated Mesoporous Black TiO2 Nanoplatform for the Highly Efficient Synergistic Phototherapy

As an important noninvasive tumor treatment method, phototherapy has drawn extensive research interest. However, the requirements of separate excitation wavelengths, high degree of electron-hole recombination, and low reactive oxygen species (ROS) production capability are still the major barriers. This work reports the construction of a novel nanoplatform: design and synthesis of an aza-BODIPY (AB) probe-decorated mesoporous black titanium dioxide (TiO₂) (MT) nanoparticles (NPs) for enhanced photodynamic therapy and photothermal therapy under single-wavelength near-infrared (NIR) laser irradiation for the first time. AB probe-decorated MT NPs (abbreviated as MTAB) were synthesized through the Al reduction of mesoporous anatase TiO₂ NPs and subsequent adsorption of the AB probe. The mesoporous structure of MT ensured AB loading capacity and avoided the complicated modification and synthesis processes. Heterogeneous MTAB, which possessed staggered energy levels, were assessed for their capability for effective separation of photogenerated electrons and holes for the first time. Upon NIR laser light irradiation, MTAB exhibited sufficient ROS generation, resulting in distinct tumor cell killing and tumor tissue elimination. This unique heterogeneous nanoplatform with staggered energy levels provides a new strategy to enhance ROS generation and improve the therapeutic efficacy.