Synthesis and optical properties of tyramine-functionalized boron dipyrromethene dyes for cell bioimaging.

Tyramine signaling amplification (TSA) technology is generally applied in immunofluorescence, enzyme-linked immunoassays, in situ hybridization techniques, etc. Successful amplification of fluoresence signals cannot be achieved without excellent fluorescent dyes. BODIPY fluorophore is an ideal probe for cell fluorescence imaging, but pristine BODIPY cannot be direct used in the TSA system. In the paper, the new red-shifted tyramide-conjugated BODIPY (BDP-B/C/D) was synthesized via the Knoevenagel condensation reaction, which based on the tyramide-conjugated BODIPY (BDP-A). The synthesized dyes were combined with tyramine to obtain which could be used as a fluorescent substrate for enzymatic reaction of TSA. By using the selected substrate (BDP-C) in TSA, we found it to be more sensitive than the commercial dye 594 styramide for the detection of low-abundance antigen proteins.

Biotin-Pt(IV)-Ru(II)-Boron-Dipyrromethene Prodrug as "Platin Bullet" for Targeted Chemo- and Photodynamic Therapy.

Using the principle of "Magic Bullet", a cisplatin-derived platinum(IV) prodrug heterobimetallic Pt(IV)-Ru(II) complex, cis,cis,trans-[Pt(NH3)2Cl2{Ru(tpy-BODIPY)(tpy-COO)}(biotin)]Cl2 (Pt-Ru-B, 2), having two axial ligands, namely, biotin as water-soluble B-vitamin for enhanced cellular uptake and a BODIPY-ruthenium(II) (Ru-B, 1) photosensitizer having N,N,N-donor tpy (4'-phenyl-2,2':6',2″-terpyridine) bonded to boron-dipyrromethene (BODIPY), is developed as a "Platin Bullet" for targeted photodynamic therapy (PDT). Pt-Ru-B exhibited intense absorption near 500 nm and emission near 513 nm (λex = 488 nm) in a 10% dimethyl sulfoxide-Dulbecco's phosphate-buffered saline medium (pH 7.2). The BODIPY complex on light activation generates singlet oxygen as the reactive oxygen species (ROS) giving a quantum yield (ΦΔ) of ∼0.64 from 1,3-diphenylisobenzofuran experiments. Pt-Ru-B exhibited preferential cellular uptake in cancer cells over noncancerous cells. The dichlorodihydrofluorescein diacetate assay confirmed the generation of cellular ROS. Confocal images revealed its mitochondrial internalization. Pt-Ru-B showed submicromolar photocytotoxicity in visible light (400-700 nm) in A549 and multidrug-resistant MDA-MB-231 cancer cells. It remained nontoxic in the dark and less toxic in nontumorigenic cells. Cellular apoptosis and alteration of the mitochondrial membrane potential were evidenced from the respective Annexin V-FITC/propidium iodide assay and JC-1 dye assay. A wound healing assay using A549 cells and Pt-Ru-B revealed inhibition of cancer cell migration, highlighting its potential as an antimetastatic agent.

Boron Dipyrromethene-Based Nanotheranostic System for Sonophotoassisted Therapy and Simultaneous Monitoring of Tumor Immune Microenvironment Reprogramming.

Therapy-induced modulation of the tumor microenvironment (TME) to overcome the immunosuppressive TME is considered to be an opportunity for cancer treatment. However, monitoring of TME modulation during the therapeutic process to accurately determine immune responses and adjust treatment plans in a timely manner remains to be challenging. Herein, we report a carrier-free nanotheranostic system (CANPs) assembled by two boron dipyrromethene (BODIPY) dyes, a sonophotosensitizer C-BDP, and a nitric oxide (NO) probe amino-BODIPY (A-BDP). CANPs can exert combined sonophototherapeutic effects of C-BDP under ultrasound and light irradiation and simultaneously induce inflammatory TME, as well as emit bright fluorescence via A-BDP by monitoring tumor-associated macrophages (TAMs) repolarization through the released NO in vitro and in vivo. Of note, transforming growth factor-ß (TGF-ß) could be the key cytokine involved in the sonophototherapy-induced TME reprogramming. By virtue of high physiological stability, good biocompatibility, and effective tumor targetability, CANPs could be a potential nanotheranostic system for the simultaneous induction and detection of TME reprogramming triggered by sonophototherapy.

A Novel Boron Dipyrromethene-Erlotinib Conjugate for Precise Photodynamic Therapy against Liver Cancer.

Photodynamic Therapy (PDT) is recognized for its exceptional effectiveness as a promising cancer treatment method. However, it is noted that overexposure to the dosage and sunlight in traditional PDT can result in damage to healthy tissues, due to the low tumor selectivity of currently available photosensitizers (PSs). To address this challenge, we introduce herein a new strategy where the small molecule-targeted agent, erlotinib, is integrated into a boron dipyrromethene (BODIPY)-based PS to form conjugate 6 to enhance the precision of PDT. This conjugate demonstrates optical absorption, fluorescence emission, and singlet oxygen generation efficiency comparable to the reference compound 7, which lacks erlotinib. In vitro studies reveal that, after internalization, conjugate 6 predominantly accumulates in the lysosomes of HepG2 cells, exhibiting significant photocytotoxicity with an IC50 value of 3.01 µM. A distinct preference for HepG2 cells over HELF cells is observed with conjugate 6 but not with compound 7. In vivo experiments further confirm that conjugate 6 has a specific affinity for tumor tissues, and the combination treatment of conjugate 6 with laser illumination can effectively eradicate H22 tumors in mice with outstanding biosafety. This study presents a novel and potential PS for achieving precise PDT against cancer.

ß-Galactosidase-Triggered Photodynamic Elimination of Senescent Cells with a Boron Dipyrromethene-Based Photosensitizer.

Senescence is a cellular response having physiological and reparative functions to preserve tissue homeostasis and suppress tumor growth. However, the accumulation of senescent cells would cause deleterious effects that lead to age-related dysfunctions and cancer progression. Hence, selective detection and elimination of senescent cells are crucial yet remain a challenge. A ß-galactosidase (ß-gal)-activated boron dipyrromethene (BODIPY)-based photosensitizer (compound 1) is reported here that can selectively detect and eradicate senescent cells. It contains a galactose moiety connected to a pyridinium BODIPY via a self-immolative nitrophenylene linker, of which the photoactivity is effectively quenched. Upon interactions with the senescence-associated ß-gal, it undergoes enzymatic hydrolysis followed by self-immolation, leading to the release of an activated BODIPY moiety by which the fluorescence emission and singlet oxygen generation are restored. The ability of 1 to detect and eliminate senescent cells is demonstrated in vitro and in vivo, using SK-Mel-103 tumor-bearing mice treated with senescence-inducing therapy. The results demonstrate that 1 can be selectively activated in senescent cells to trigger a robust senolytic effect upon irradiation. This study breaks new ground in the design and application of new senolytic agents based on photodynamic therapy.

Light-Harvesting Crystals Formed from BODIPY-Proline Biohybrid Conjugates: Antenna Effects and Excitonic Coupling.

A boron dipyrromethene (BODIPY) derivative bearing a cis-proline residue at the meso-position crystallizes in the form of platelets with strong (i.e., ΦF = 0.34) red fluorescence, but the absorption and emission spectra differ markedly from those for dilute solutions. A key building block for the crystal is a pseudo-dimer where hydrogen bonding aligns the proline groups and separates the terminal chromophores by ca. 25 Å. Comparison with a covalently linked bichromophore suggests that one-dimensional (1D) excitonic coupling between the terminals is too small to perturb the optical properties. However, accretion of the pseudo-dimer forms narrow channels possessing a high density of chromophores. The resultant absorption spectrum exhibits strong excitonic splitting, which can be explained quantitatively using the extended dipole approach and allowing for coupling between ca. 30 BODIPY units. Fluorescence, which decays with a lifetime of 2.2 ns, is assigned to a delocalized and (slightly) super-radiant BODIPY dimer situated at the interface and populated via electronic energy transfer from the interior.

Dual Color Imaging from a Single BF2-Azadipyrromethene Fluorophore Demonstrated in vivo for Lymph Node Identification.

Dual emissions at ~700 and 800 nm have been achieved from a single NIR-AZA fluorophore 1 by establishing parameters in which it can exist in either its isolated molecular or aggregated states. Dual near infrared (NIR) fluorescence color lymph node (LN) mapping with 1 was achieved in a large-animal porcine model, with injection site, channels and nodes all detectable at both 700 and 800 nm using a preclinical open camera system. The fluorophore was also compatible with imaging using two clinical instruments for fluorescence guided surgery. Methods: An NIR-AZA fluorophore with hydrophilic and phobic features was synthesised in a straightforward manner and its aggregation properties characterised spectroscopically and by TEM imaging. Toxicity was assessed in a rodent model and dual color fluorescence imaging evaluated by lymph node mapping in a large animal porcine models and in ex-vivo human tissue specimen. Results: Dual color fluorescence imaging has been achieved in the highly complex biomedical scenario of lymph node mapping. Emissions at 700 and 800 nm can be achieved from a single fluorophore by establishing molecular and aggregate forms. Fluorophore was compatible with clinical systems for fluorescence guided surgery and no toxicity was observed in high dosage testing. Conclusion: A new, biomedical compatible form of NIR-dual emission wavelength imaging has been established using a readily accessible fluorophore with significant scope for clinical translation.

Click Conjugation of Boron Dipyrromethene (BODIPY) Fluorophores to EGFR-Targeting Linear and Cyclic Peptides.

Through a simple 1,3-cycloaddition reaction, three BODIPY-peptide conjugates that target the extracellular domain of the epidermal growth factor receptor (EGFR) were prepared and their ability for binding to EGFR was investigated. The peptide ligands K(N3)LARLLT and its cyclic analog cyclo(K(N3)larllt, previously shown to have high affinity for binding to the extracellular domain of EGFR, were conjugated to alkynyl-functionalized BODIPY dyes 1 and 2 via a copper-catalyzed click reaction. This reaction produced conjugates 3, 4, and 5 in high yields (70-82%). In vitro studies using human carcinoma HEp2 cells that overexpress EGFR demonstrated high cellular uptake, particularly for the cyclic peptide conjugate 5, and low cytotoxicity in light (~1 J·cm-2) and darkness. Surface plasmon resonance (SPR) results show binding affinity of the three BODIPY-peptide conjugates for EGFR, particularly for 5 bearing the cyclic peptide. Competitive binding studies using three cell lines with different expressions of EGFR show that 5 binds specifically to EGFR-overexpressing colon cancer cells. Among the three conjugates, 5 bearing the cyclic peptide exhibited the highest affinity for binding to the EGFR protein.

Highly efficient BODIPY-doped upconversion nanoparticles for deep-red luminescence bioimaging in vivo.

We demonstrate a 3,5-di(p-oxethyl)styryl conjugated BODIPY showing deep-red upconversion luminescence with a high efficiency of 16.6%. Furthermore, water-soluble BODIPY-doped upconversion nanoparticles with efficiency up to 6.9% under low excitation power density (∼1 mW cm-2) are developed and enable high-performance bioimaging in vivo.

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.

A Boron Dipyrromethene-Based Fluorescence 'OFF-ON' Probe for Sensitive and Selective Detection of Palladium(II) Ions and Its Application in Live Cell Imaging.

A novel boron dipyrromethene (BODIPY)-based fluorescent probe BDP-Pd was designed and synthesized. Upon coordination with Pd2+ , the emission of the probe at 508 nm significantly increased, showing an 'OFF-ON' fluorescence response. The complexation of BDP-Pd with Pd2+ in both acetonitrile and aqueous solution were then studied by absorption and fluorescence spectra. The binding stoichiometry between the probe and Pd2+ was found to be 1 : 2, and the binding constant was determined to be 8.5×1010  M-2 and 8.2×1010  M-2 in acetonitrile and aqueous solution, respectively. The probe exhibited a detection limit as low as 0.72 ppb toward Pd2+ with no obvious interference from up to 21 species of common metal ions, suggesting BDP-Pd as a sensitive and selective fluorescent probe for Pd2+ detection. The fast fluorescence 'OFF-ON' phenomenon of the probe upon coordination with Pd2+ ions could be easily observed by a hand-hold UV lamp under naked eye in solution as well as on homemade test trips. Density functional theory (DFT) calculations were carried out to give the optimized structure of complex BDP-Pd : 2Pd2+ and rationalize the detection mechanism through a prohibited intramolecular photoinduced electron transfer (PET) process. The bio-imaging application of the probe was investigated and it showed excellent cell permeability for fluorescent imaging of Pd2+ ions in A549 human non-small cell lung cancer cells.

Spectroscopic and In Vitro Investigations of Boron(III) Complex with Meso-4-Methoxycarbonylpropylsubstituted Dipyrromethene for Fluorescence Bioimaging Applications.

This study focuses on the behavior of a new fluorescent marker for labeling individual biomolecules and staining cell organelles developed on a meso-substituted BODIPY platform. Boron(III) complex with meso-4-methoxycarbonylpropylsubstituted 3,3',5,5'-tetramethyl-2,2'-dipyrromethene has been synthesized and identified via visible, UV-, NMR- and MS-spectra X-ray. The behavior of fluorophore in solutions has been studied with various experimental techniques. It has been found that luminophore exhibits a high quantum yield (almost ~100-75%) in the blue-green region (513-520 nm) and has high photostability. In addition, biological analysis indicates that the fluorophore exhibits a tendency to effectively penetrate into cell membranes. On the other hand, the proposed BODIPY can be used to study the significant differences among a large number of pathogens of mycotic infections, as well as to visualize structural changes in the plasma membrane, which is necessary for the clearance of mammalian cells undergoing apoptotic cell death.

Strong Affinity of Triazolium-Appended Dipyrromethenes (TADs) for BF4.

Because BF4- is a labile, non- or weakly coordinating anion, it is generally chosen by chemists who do not want the anion to interfere with the associated cation. Herein, we demonstrate that BF4- actually strongly binds to triazole-appended dipyrromethenes (TADs). In particular, HETCOR NMR experiments and DFT calculations were used to rationalize the results observed with anion titrations. Hence, special care should be taken when considering that BF4- is innocent.

Carbon-Dipyrromethenes: Bright Cationic Fluorescent Dyes and Potential Application in Revealing Cellular Trafficking of Mitochondrial Glutathione Conjugates.

Boron-dipyrromethenes (Bodipys), since first reported in 1968, have emerged as a fascinating class of dyes in the past few decades due to their excellent photophysical properties including bright fluorescence, narrow emission bandwidth, resistance to photobleaching, and environment insensitivity. However, typical Bodipys are highly lipophilic, which often results in nonfluorescent aggregates in aqueous solution and also severely limits their bioavailability to cells and tissues. In this work, based on a simple one-atom B → C replacement in the Bodipy scaffold, we present a new class of carbon-dipyrromethenes (Cardipys for short) fluorescent dyes with tunable emission wavelengths covering the visible and near-infrared regions. These Cardipys not only retain the excellent photophysical properties of conventional Bodipys but also show improved water solubility and photostability due to their cationic character. Moreover, the cationic character also makes them extremely easy to penetrate the cell membrane and specifically accumulate into mitochondria without resorting to any mitochondria-targeted groups. Interestingly, several Cardipys bearing active styryl groups could serve as fluorescent indicators to map cellular trafficking of the glutathione conjugates produced within mitochondria under the catalysis of glutathione S-transferase (GST), thus showing potential in either exploring the detoxification mechanism of the mitochondrial GST/GSH system or evaluating the drug resistance of cancer cells that is closely related with GST activity.

In Vivo Imaging of Senescent Vascular Cells in Atherosclerotic Mice Using a ß-Galactosidase-Activatable Nanoprobe.

Senescence-associated diseases have severely diminished the quality of life and health of patients. However, a sensitive assay of these diseases remains limited due to a lack of straightforward methods. Considering that senescence-associated ß-galactosidase (SA-ß-Gal) is overexpressed in senescent cells, the detection of SA-ß-Gal in senescent cells and tissues might be a feasible strategy for the early diagnosis of SA diseases. In this study, a ß-galactosidase-activatable nanoprobe BOD-L-ßGal-NPs was developed for the imaging of senescent cells and vasculature in atherosclerotic mice via real-time monitoring of ß-Gal. BOD-L-ßGal-NPs was fabricated by encapsulating a newly designed NIR ratiometric probe BOD-L-ßGal within a poly(lactic-co-glycolic) acid (PLGA) core. Nanoprobe BOD-L-ßGal-NPs showed good accumulation in arteries, thus successfully visualizing senescent cells and vasculature in atherosclerotic mice by tail vein injection. Our findings indicated that nanoprobe BOD-L-ßGal-NPs holds great potential for the early diagnosis and therapy of atherosclerosis and other aging-associated diseases.

Photodynamic treatment of melanoma cells using aza-dipyrromethenes as photosensitizers.

In this study, we report for the first time the use of four aza-dipyrromethenes (ADPMs) as photosensitizers for cancer PDT. The synthesis and characterization of the ADPMs and their photodynamic action against B16F10 melanoma cells were assessed. ADPM 2 is the best singlet oxygen generator and the most phototoxic (at 2.5 µM) towards B16F10 cells.

Electrochemiluminescent detection of glucose in human serum by BODIPY-based chemodosimeters for hydrogen peroxide using accelerated self-immolation of boronates.

BODIPY-based ECL chemodosimeters were developed for the detection of hydrogen peroxide. The reactivity of boronate towards hydrogen peroxide was enhanced by adjacent fluorine atoms. In combination with glucose oxidase, a fluorine-substituted probe successfully quantified the glucose level in human serum, providing its potential as a versatile tool in point-of-care testing applications.

Design, Synthesis and Characterization of a New Series of Fluorescent Metabotropic Glutamate Receptor Type 5 Negative Allosteric Modulators.

In recent years, new drug discovery approaches based on novel pharmacological concepts have emerged. Allosteric modulators, for example, target receptors at sites other than the orthosteric binding sites and can modulate agonist-mediated activation. Interestingly, allosteric regulation may allow a fine-tuned regulation of unbalanced neurotransmitter' systems, thus providing safe and effective treatments for a number of central nervous system diseases. The metabotropic glutamate type 5 receptor (mGlu5R) has been shown to possess a druggable allosteric binding domain. Accordingly, novel allosteric ligands are being explored in order to finely regulate glutamate neurotransmission, especially in the brain. However, before testing the activity of these new ligands in the clinic or even in animal disease models, it is common to characterize their ability to bind mGlu5Rs in vitro. Here, we have developed a new series of fluorescent ligands that, when used in a new NanoBRET-based binding assay, will facilitate screening for novel mGlu5R allosteric modulators.

A glutathione-responsive photosensitizer with fluorescence resonance energy transfer characteristics for imaging-guided targeting photodynamic therapy.

Here, we have synthesized and characterized a novel activatable photosensitizer (PS) 8a in which two well-designed boron dipyrromethene (BODIPY) derivatives are utilized as the photosensitizing fluorophore and quencher respectively, which are connected by a disulfide linker via two successive Cu (І) catalyzed click reactions. The fluorescence emission and singlet oxygen production of 8a are suppressed via intramolecular fluorescence resonance energy transfer (FRET) from the excited BODIPY-based PS part to quencher unit, but both of them can be simultaneously switched on by cancer-related biothiol glutathione (GSH) in phosphate buffered saline (PBS) solution with 0.05% Tween 80 as a result of cleavage of disulfide. Also, 8a exhibits a bright fluorescence image and a substantial ROS production in A549 human lung adenocarcinoma, HeLa human cervical carcinoma and H22 mouse hepatoma cells having a relatively high concentration of GSH, thereby leading to a significant photocytotoxicity, with IC50 values as low as 0.44 µM, 0.67 µM and 0.48 µM, respectively. In addition, the photosensitizer can be effectively activated and imaged in H22 transplanted hepatoma tumors of mice and shows a strong inhibition on tumor growth. All these results suggest that such a GSH-responsive photosensitizer based on FRET mechanism may provide a new strategy for tumor-targeted and fluorescence imaging-guided cancer therapy.

Tailoring nanoparticles based on boron dipyrromethene for cancer imaging and therapy.

Boron dipyrromethene (BODIPY), as a traditional fluorescent dye, has drawn increasing attention because of its excellent photophysical properties like adjustable spectra and outstanding photostability. BODIPY dyes could be assembled into nanoparticles for cancer imaging and therapy via rational design. In this review, the bio-applications of BODIPY-containing nanoparticles are introduced in detail, such as cellular imaging, near-infrared fluorescence imaging, computed tomography imaging, photoacoustic imaging, phototherapy, and theranostics. The construction strategies of BODIPY-containing nanoparticles are emphasized so the review has three sections-self-assembly of small molecules, chemical conjugation with hydrophilic compounds, and physical encapsulation. This review not only summarizes various and colorific bio-applications of BODIPY-containing nanoparticles, but also provides reasonable design methods of BODIPY-containing nanoparticles for cancer theranostics. This article is categorized under: Diagnostic Tools > in vivo Nanodiagnostics and Imaging.