Heavy-atom-free BODIPY dendrimer: utilizing the spin-vibronic coupling mechanism for two-photon photodynamic therapy in zebrafish

In this study, the heavy-atom-free BODIPY dendrimer TM4-BDP was synthesized for near-infrared photodynamic therapy, and was composed of a triphenylamine-BODIPY dimer and four 1-(2-morpholinoethyl)-1H-indole-3-ethenyl groups. The TM4-BDP could achieve near-infrared photodynamic therapy through two different photosensitive pathways, which include one-photon excitation at 660 nm and two-photon excitation at 1000 nm. In the one-photon excitation pathway, the TM4-BDP could generate singlet oxygen and superoxide radicals under 660 nm illumination. In addition, the one-photon PDT experiment in human nasopharyngeal carcinoma (CNE-2) cells also indicated that the TM4-BDP could specifically accumulate in lysosomes and show great cell phototoxicity with an IC50 of 22.1 μM. In the two-photon excitation pathway, the two-photon absorption cross-section at 1030 nm of TM4-BDP was determined to be 383 GM, which means that it could generate reactive oxygen species (ROS) under 1000 nm femtosecond laser excitation. Moreover, the two-photon PDT experiment in zebrafish also indicated the TM4-BDP could be used for two-photon fluorescence imaging and two-photon induced ROS generation in biological environments. Furthermore, in terms of the ROS generation mechanism, the TM4-BDP employed a novel spin-vibronic coupling intersystem crossing (SV-ISC) process for the mechanism of ROS generation and the femtosecond transient absorption spectra indicated that this novel SV-ISC mechanism was closely related to its charge transfer state lifetime. These above experiments of TM4-BDP demonstrate that the dendrimer design is an effective strategy for constructing heavy-atom-free BODIPY photosensitizers in the near-infrared region and lay the foundation for two-photon photodynamic therapy in future clinical trials.

Near-infrared BODIPY photosensitizers for two-photon excited singlet oxygen generation and tumor cell photodynamic therapy

In this paper, two near-infrared BODIPY photosensitizers, Id-BDPI and Cz-BDPI, were obtained by modifying the indole and carbazole aromatic heterocycles in the core of BODIPY. The maximum absorption wavelengths of Id-BDPI and Cz-BDPI were 694 nm and 722 nm, and their singlet oxygen yields were 48% and 48.4%, respectively. In the simulated tumor cell photodynamic therapy, Id-BDPI and Cz-BDPI could effectively inhibit the growth of A549 tumor cells under near-infrared light. Meanwhile, the lysosomal co-localization coefficients of Id-BDPI and Cz-BDPI with A549 tumor cells were 0.94 and 0.89, respectively, showing high lysosomal targeting ability and biocompatibility. The two-photon absorption cross sections measured at 1050 nm by the Z-scanning method were 661.8 GM and 715.6 GM, respectively, and Cz-BDPI was further successfully applied to two-photon fluorescence imaging and two-photon excited singlet oxygen generation in zebrafish. The above results indicate that the introduction of aromatic heterocycles can effectively enhance the photodynamic efficacy of BODIPY photosensitizers, and the larger two-photon absorption cross section also brings potential for two-photon photodynamic therapy applications.

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.

BODIPY precursors and their cyclotriphosphazene Derivatives: Synthesis, photochemical properties and their application in PDT

Photodynamic therapy (PDT) is a treatment method consisting of common combination of oxygen, light energy and a light absorbing molecule called a photosensitizer. In this work, four new compounds consisting of BODIPY precursors and BODIPY-cyclotriphosphazene derivatives were synthesized to investigate the PDT effects. The chemical structures of the compounds were characterized and then their photophysical properties were determined by spectroscopic techniques. The precursor BODIPYs and their cyclotriphosphazene derivatives exhibited similar properties such as strong absorption intensity, high photostability and low fluorescence profile in the NIR region. Additionally, the singlet oxygen production capacities of these compounds were determined using the photobleaching technique of 1,3-diphenylisobenzofuran (DPBF) under light illumination. By introducing iodine atoms into the molecule, which are responsible for the intersystem transition (ISC) enhancement, a more efficient singlet oxygen production was achieved in both the iodinated-BODIPY and its cyclotriphosphazene derivative. Anticancer activities of the precursor BODIPYs and their cyclotriphosphazene derivatives in the absence and presence of light illumination were evaluated on cancerous cell lines (PC3 and DU145) and non-tumorigenic prostate epithelial PNT1a cell. The compounds triggered the death of cancer cell PC3 the more significantly in the presence of red light compared to the healthy cells (PNT1a).

Fluorescent protein chromophores modified with aromatic heterocycles for photodynamic therapy and two-photon fluorescence imaging

In this paper, three fluorescent protein chromophore analogs PFPAr (PFPP, PFPC, and PFPT) were synthesized and proved to be useful for photodynamic therapy and two-photon fluorescence imaging. By adding five- or six-membered aromatic heterocycles to the photosensitizer PFP, we obtained three fluorescent protein photosensitizers PFPAr with better performances. As a demonstration, compared with the reported photosensitizer PFP, photosensitizer PFPP exhibits larger emission wavelengths (701 nm) and achieves a slight enhancement in the efficiency of singlet oxygen (ΦΔ = 23%). Notably, PFPP can perform good two-photon fluorescence imaging with an 800 nm femtosecond laser in zebrafish. In in vitro cytotoxicity assays, PFPP shows good phototoxicity (IC50 = 4.12 μM) and acceptable dark toxicity (cell viability assay >90%). The reactive oxygen imaging experiments and AO/EB double staining assay indicate that PFPP can generate singlet oxygen to eliminate A-549 tumor cells effectively with photoexcitation of 460 nm blue light (20 mW cm-2). Furthermore, PFPP can label the lysosomes of tumor cells with high specificity for lysosomes (Pearson's correlation coefficient of 0.91). Thus, our study demonstrated that the rational introduction of aromatic heterocycles into fluorescent protein photosensitizers can effectively enhance the key parameters of photosensitivity and pave the way for further two-photon photodynamic therapy.

NIR ditriphenylamine Indole-BODIPY photosensitizer: synthesis, photodynamic therapy in A549 cells and two-photon fluorescence imaging in zebrafish

In this study, the ditriphenylamine Indole-BODIPY photosensitizer T2BDP-lyso was synthesized for near-infrared photodynamic therapy and two-photon fluorescence imaging. The photosensitizer T2BDP-lyso exhibits absorption above 700 nm and emission above 800 nm, respectively. Theoretical calculations show the energy gap from the excited state S1 to the excited state T2 is 0.14 eV, which indicated that the photosensitizer T2BDP-lyso could reach the triplet state by intersystem crossing from the singlet state. Under NIR light, the singlet oxygen yield of photosensitizer T2BDP-lyso was calculated to be 0.64 in CH2Cl2. The photosensitizer T2BDP-lyso can effectively produce reactive oxygen species in A549 cells and zebrafish under 660 nm light for 5 min. The photosensitizer T2BDP-lyso exhibited lower dark toxicity and higher phototoxicity (IC50 = 1.49 μM), as well as lysosomal targeting ability (Pearson coefficient = 0.89). In the AO/EB double staining assay simulating photodynamic therapy at the cellular level, 3 μM of T2BDP-lyso light for 10 min was effective in killing cancer cells. Moreover, the photosensitizer T2BDP-lyso has a large two-photon absorption cross section at 1050 nm, which was calculated to be 138.7 GM in THF by Z-scan method, and two-photon fluorescence imaging was performed in zebrafish. The above results indicate the potential application of the photosensitizer T2BDP-lyso in near-infrared photodynamic therapy and two-photon fluorescence imaging.

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.

BODIPY-Based Fluorescent Probes for Selective Visualization of Endogenous Hypochlorous Acid in Living Cells via Triazolopyridine Formation

In this work, the two pyridylhydrazone-tethered BODIPY compounds (2 and 3) were synthesized. These compounds aimed to detect hypochlorous acid (HOCl) species via cyclic triazolopyridine formation. The open forms and the resulting cyclic forms of BODIPYs (2, 3, 4, and 5) were fully characterized by nuclear magnetic resonance, mass spectrometry, infrared spectroscopy, and single-crystal X-ray diffraction. These two probes can selectively detect HOCl through a fluorescence turn-on mechanism with the limit of detections of 0.21 µM and 0.77 µM for compounds 2 and 3, respectively. This fluorescence enhancement phenomenon could be the effect from C = N isomerization inhibition due to HOCl-triggered triazolopyridine formation. In cell imaging experiments, these compounds showed excellent biocompatibility toward RAW 264.7 murine live macrophage cells and greatly visualized endogenous HOCl in living cells stimulated with lipopolysaccharide.