Synthesis, spectroscopic properties and photodynamic activity of two cationic BODIPY derivatives with application in the photoinactivation of microorganisms

Quaternized Curcumin Derivative-Synthesis, Physicochemical Characteristics, and Photocytotoxicity, Including Antibacterial Activity after Irradiation with Blue Light

Over the past few years, numerous bacterial strains have become resistant to selected drugs from various therapeutic groups. A potential tool in the fight against these strains is antimicrobial photodynamic therapy (APDT). APDT acts in a non-specific manner by generating reactive oxygen species and radicals, thereby inducing multidimensional intracellular effects. Importantly, the chance that bacteria will develop defense mechanisms against APDT is considered to be low. In our research, we performed the synthesis and physicochemical characterization of curcumin derivatives enriched with morpholine motifs. The obtained compounds were assessed regarding photostability, singlet oxygen generation, aggregation, and acute toxicity toward prokaryotic Aliivibrio fischeri cells in the Microtox® test. The impact of the compounds on the survival of eukaryotic cells in the MTT assay was also tested (WM266-4, WM115-melanoma, MRC-5-lung fibroblasts, and PHDF-primary human dermal fibroblasts). Initial studies determining the photocytotoxicity, and thus the potential APDT usability, were conducted with the following microbial strains: Candida albicans, Escherichia coli, Staphylococcus aureus, Streptococcus pneumoniae, and Pseudomonas aeruginosa. It was noted that the exposure of bacteria to LED light at 470 nm (fluence: 30 J/cm2) in the presence of quaternized curcumin derivatives at the conc. of 10 µM led to a reduction in Staphylococcus aureus survival of over 5.4 log.

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.

Porphyrin-BODIPY Dyad: Enhancing Photodynamic Inactivation via Antenna Effect

A porphyrin-BODIPY dyad (P-BDP) was obtained through covalent bonding, featuring a two-segment design comprising a light-harvesting antenna system connected to an energy acceptor unit. The absorption spectrum of P-BDP resulted from an overlap of the individual spectra of its constituent parts, with the fluorescence emission of the BODIPY unit experiencing significant quenching (96 %) due to the presence of the porphyrin unit. Spectroscopic, computational, and redox investigations revealed a competition between photoinduced energy and electron transfer processes. The dyad demonstrated the capability to sensitize both singlet molecular oxygen and superoxide radical anions. Additionally, P-BDP effectively induced the photooxidation of L-tryptophan. In suspensions of Staphylococcus aureus cells, the dyad led to a reduction of over 3.5 log (99.99 %) in cell survival following 30 min of irradiation with green light. Photodynamic inactivation caused by P-BDP was also extended to the individual bacterium level, focusing on bacterial cells adhered to a surface. This dyad successfully achieved the total elimination of the bacteria upon 20 min of irradiation. Therefore, P-BDP presents an interesting photosensitizing structure that takes advantage of the light-harvesting antenna properties of the BODIPY unit combined with porphyrin, offering potential to enhance photoinactivation of bacteria.

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.

Optimized strategies of ROS-based nanodynamic therapies for tumor theranostics

Reactive oxygen species (ROS) play a crucial role in regulating the metabolism of tumor growth, metastasis, death and other biological processes. ROS-based nanodynamic therapies (NDTs) are becoming attractive due to non-invasive, low side effects and tumor-specific advantages. NDTs have rapidly developed into numerous branches, such as photodynamic therapy, chemodynamic therapy, sonodynamic therapy and so on. However, the complexity of the tumor microenvironment and the limitations of existing sensitizers have greatly restricted the therapeutic effects of NDTs, which heavily rely on ROS levels. To address the limitations of NDTs, various strategies have been developed to increase ROS yield, which is an urgent aspect for the positive development of NDTs. In this review, the nanodynamic potentiation strategies in terms of unique properties and universalities of NDTs are comprehensively outlined. We mainly summarize the current dilemmas faced by each NDT and the respective solutions. Meanwhile, the NDTs universalities-based potentiation strategies and NDTs-based combined treatments are elaborated. Finally, we conclude with a discussion of the key issues and challenges faced in the development and clinical transformation of NDTs.

Photodynamic therapy for ESKAPE pathogens: An emerging approach to combat antimicrobial resistance (AMR)

The increase in antimicrobial resistance, particularly in ESKAPE pathogens, has resulted in the dire need for new therapeutic approaches. ESKAPE is an acronym for a group of bacteria that are responsible for a majority of nosocomial and community acquired infections. The acronym stands for Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species. These pathogens are known for their ability to develop resistance to multiple antibiotics, making them difficult to treat thus posing a significant threat to public health. In light of the alarming consequences of antimicrobial resistance, it has been estimated that, in the absence of a substantial increase in the rate of development of new effective drugs, the number of casualties related to these infections will increase from about 700,000 in 2016 up to nearly 10,000,000 in 2050 [1]. One potential strategy to treat these pathogens is photodynamic therapy (PDT). In the early 20th century, Oscar Raab observed the phototoxicity of acridine red against Paramecium caudatum, while Tappenier and Jesionek demonstrated the photodynamic effects of eosin for treating cutaneous diseases. These discoveries laid the foundation for Photodynamic Therapy (PDT), which utilizes a non-toxic photosensitizer (PS) followed by targeted light irradiation for treatment [2]. PDT involves the use of a photosensitizer, a light source, and oxygen to eliminate highly active infectious pathogens such as bacteria, viruses, and fungi. PDT is known to possess several advantages including localized treatment and fewer side effects. Various photosensitizers and light sources have been assessed in different strains, showing promising results suggesting PDT to be a promising potential treatment option. PDT utilizes PS compounds with suitable light absorption that showcase effective results against the pathogens in vitro and in vivo, including BODIPY derivatives, Methylene Blue, and other dyes like porphyrin derivatives, phthalocyanines, indole derivatives, Photophrin, etc., inhibiting the growth of infections, for both in planktonic cells and in biofilms. Combination of PDT with other therapies like efflux pump inhibitors or quorum sensing inhibitors has also proven to be efficacious. However, this domain further needs to be assessed before it reaches the society.

Cationic BODIPY Photosensitizers for Mitochondrion-Targeted Fluorescence Cell-Imaging and Photodynamic Therapy

The straightforward synthesis of three cationic boron-dipyrromethene (BODIPY) derivatives and their mitochondria-targeting and photodynamic therapeutic (PDT) capabilities are reported. Two cancer cell lines (HeLa and MCF-7) were used to investigate the PDT activity of the dyes. Compared to their non-halogenated counterparts, halogenated BODIPY dyes exhibit lower fluorescence quantum yields and enable the efficient production of singlet oxygen species. Following LED light irradiation at 520 nm, the synthesized dyes displayed good PDT capabilities against the treated cancer cell lines, with low cytotoxicity in the dark. In addition, functionalization of the BODIPY backbone with a cationic ammonium moiety enhanced the hydrophilicity of the synthesized dyes and, consequently, their uptake by the cells. The results presented here collectively demonstrate the potential of cationic BODIPY-based dyes as therapeutic drugs for anticancer photodynamic therapy.

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

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

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Mitochondrion-Targeting PEGylated BODIPY Dyes for Near-Infrared Cell Imaging and Photodynamic Therapy

A series of 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene-based photosensitizers (AmBXI, X = H, M, Br) featuring a cationic mitochondrion-targeting group and near-infrared (NIR) absorption was synthesized. After extending the photosensitizers’ π–π conjugation via Knoevenagel...

Discovery of Meso-(meta-Pyridinium) BODIPY Photosensitizers: In Vitro and In Vivo Evaluations for Antimicrobial Photodynamic Therapy

Antimicrobial photodynamic therapy (aPDT) has emerged as a novel and promising approach for the treatment of pathogenic microorganism infections. The efficacy of aPDT depends greatly on the behavior of the photosensitizer. Herein, we report the design, preparation, antimicrobial photodynamic activities, as well as structure-activity relationships of a series of photosensitizers modified at the meso position of a 1,3,5,7-tetramethyl BODIPY scaffold with various pyridinyl and pyridinium moieties. The photodynamic antimicrobial activities of all photosensitizers have been tested against Staphylococcus aureus, Escherichia coli, Candida albicans, and Methicillin-resistant S. aureus (MRSA). The methyl meso-(meta-pyridinium) BODIPY photosensitizer (3c) possessed the highest phototoxicity against these pathogens at minimal inhibitory concentrations (MIC) ranging from 0.63 to 1.25 μM with a light dose of 81 J/cm². Furthermore, 3c exhibited an impressive antimicrobial efficacy in S. aureus-infected mice wounds. Taken together, these findings suggest that 3c is a promising candidate as the antimicrobial photosensitizer for combating pathogenic microorganism infections.

Potentiation Effect of Iodine Species on the Antimicrobial Capability of Surfaces Coated with Electroactive Phthalocyanines

The spreading of different infections can occur through direct contact with glass surfaces in commonly used areas. Incorporating the use of alternative therapies in these materials seems essential to reduce and also avoid bacterial resistance. In this work, the capability to kill microbes of glass surfaces coated with two electroactive metalated phthalocyanines (ZnPc-EDOT and CuPc-EDOT) is assessed. The results show that both of these materials are capable of producing reactive oxygen species; however, the polymer with Zn(II) (ZnPc-PEDOT) has a singlet oxygen quantum yield 8-fold higher than that of the Cu(II) containing analogue. This was reflected in the in vitro experiments where the effectiveness of the surfaces was tested in bacterial suspensions, monitoring single microbe inactivation upon attachment to the polymers, and eliminating mature biofilms. Furthermore, we evaluated the use of an inorganic salt (KI) to potentiate the photodynamic inactivation mediated by an electropolymerized surface. The addition of the salt improved the efficiency of phototherapy at least two times for both polymers; nevertheless, the material coated with ZnPc-PEDOT was the only one capable of eliminating >99.98% of the initial microbes loading under different circumstances.

Porphyrin-Schiff Base Conjugates Bearing Basic Amino Groups as Antimicrobial Phototherapeutic Agents

New porphyrin–Schiff base conjugates bearing one (6) and two (7) basic amino groups were synthesized by condensation between tetrapyrrolic macrocycle-containing amine functions and 4-(3-(N,N-dimethylamino)propoxy)benzaldehyde. This approach allowed us to easily obtain porphyrins substituted by positive charge precursor groups in aqueous media. These compounds showed the typical Soret and four Q absorption bands with red fluorescence emission (Φ_F ~ 0.12) in N,N-dimethylformamide. Porphyrins 6 and 7 photosensitized the generation of O₂(¹Δ_g) (Φ_Δ ~ 0.44) and the photo-oxidation of L-tryptophan. The decomposition of this amino acid was mainly mediated by a type II photoprocess. Moreover, the addition of KI strongly quenched the photodynamic action through a reaction with O₂(¹Δ_g) to produce iodine. The photodynamic inactivation capacity induced by porphyrins 6 and 7 was evaluated in Staphylococcus aureus, Escherichia coli, and Candida albicans. Furthermore, the photoinactivation of these microorganisms was improved using potentiation with iodide anions. These porphyrins containing basic aliphatic amino groups can be protonated in biological systems, which provides an amphiphilic character to the tetrapyrrolic macrocycle. This effect allows one to increase the interaction with the cell wall, thus improving photocytotoxic activity against microorganisms.

A Targeted Photosensitizer Mediated by Visible Light for Efficient Therapy of Bacterial Keratitis

Bacterial keratitis is a serious bacterial infection of the cornea that can cause sight loss in severe cases because of the sharp decline of efficacious antibiotics. Herein, a targeted photosensitizer based on BODIPY severing as a photobactericidal agent was developed for treating bacterial keratitis. The water solubility of the material was as high as 10 mg/mL, which was attributable to the introduction of pathogen-targeting galactose and fucose. The photosensitizer was able to preferentially bind Pseudomonas aeruginosa instead of mammalian cells and trigger the aggregation of bacteria, which ultimately facilitated effective pathogen ablation upon the generation of reactive oxygen species (ROS) via laser irradiation. Photoexcited targeted photosensitizers can promote wound healing by eradicating P. aeruginosa in rat eyes and reducing the inflammatory response, thus exhibiting the significant therapeutic effect on bacterial keratitis. We also performed molecular level mechanistic studies using the unique field-induced droplet ionization mass spectrometry methodology and confirmed that the generated ROS were mainly singlet oxygen that caused lipid peroxidation (Type II mechanism). We anticipate that the targeted photosensitizer will have great potential in the application of clinical photodynamic therapy to ocular infection.

A novel tricationic fullerene C60 as broad-spectrum antimicrobial photosensitizer: mechanisms of action and potentiation with potassium iodide

A novel amphiphilic photosensitizing agent based on a tricationic fullerene C₆₀ (DMC₆₀³⁺) was efficiently synthesized from its non-charged analogue MMC₆₀. These fullerenes presented strong UV absorptions, with a broad range of less intense absorption up to 710 nm. Both compounds showed low fluorescence emission and were able to photosensitize the production of reactive oxygen species. Furthermore, photodecomposition of L-tryptophan sensitized by both fullerenes indicated an involvement of type II pathway. DMC₆₀³⁺ was an effective agent to produce the photodynamic inactivation (PDI) of Staphylococcus aureus, Escherichia coli and Candida albicans. Mechanistic insight indicated that the photodynamic action sensitized by DMC₆₀³⁺ was mainly mediated by both photoprocesses in bacteria, while a greater preponderance of the type II pathway was found in C. albicans. In presence of potassium iodide, a potentiation of PDI was observed due to the formation of reactive iodine species. Therefore, the amphiphilic DMC₆₀³⁺ can be used as an effective potential broad-spectrum antimicrobial photosensitizer.

Exploiting a Neutral BODIPY Copolymer as an Effective Agent for Photodynamic Antimicrobial Inactivation

We report the synthesis and photophysical properties of a neutral BODIPY photosensitizing copolymer (poly-8-(4-hydroxymethylphenyl)-4,4-difluoro-2,6-diethynyl-4-bora-3a,4a-diaza-s-indacene) containing ethynylbenzene links between the BODIPY units. The copolymer absorbs further towards the red in the UV-vis spectrum compared to the BODIPY precursor. Photolysis of the polymer produces a singlet excited state which crosses to the triplet surface in less than 300 ps. This triplet state was used to form singlet oxygen with a quantum yield of 0.34. The steps leading to population of the triplet state were studied using time-resolved spectroscopic techniques spanning the pico- to nanosecond timescales. The ability of the BODIPY polymer to generate a biocidal species for bactericidal activity in both solution- and coating-based studies was assessed. When the BODIPY copolymer was dropcast onto a surface, 4 log and 6 log reductions in colony forming units/ml representative of Gram-positive and Gram-negative bacteria, respectively, under illumination at 525 nm were observed. The potent broad-spectrum antimicrobial activity of a neutral metal-free copolymer when exposed to visible light conditions may have potential clinical applications in infection management.

Enhancement of tumor lethality of ROS in photodynamic therapy

In the process of photodynamic therapy (PDT) treatment of tumors, reactive oxygen species (ROS) plays a key role in destroying tumor tissues. However, traditional PDT often has limited ROS killing capacity due to hypoxia in the tumor microenvironment (TME) or obstruction by the ROS defense system, resulting in poor efficacy. Therefore, enhancing the killing effect of ROS on tumors is the core of enhancing the anti-tumor effect of PDT. In recent years, many studies have developed a series of strategies to enhance the ability of ROS to kill tumors in view of the limitations of the TME on PDT. This article summarizes the commonly used or innovative strategies in recent years, including not only frequently used methods for hypoxia in the TME but also innovative strategies to inhibit the ROS defense system.

Long-Lived Local Triplet Excited State and Charge Transfer State of 4,4'-Dimethoxy Triphenylamine-BODIPY Compact Electron Donor/Acceptor Dyads

The spin-orbit charge transfer intersystem crossing (SOCT-ISC) and the formation of a long-lived charge transfer (CT) state were studied with a series of 4,4'-dimethoxy triphenylamine-BODIPY compact electron donor/acceptor dyads. Different torsion freedoms were applied in the dyads to tune the electronic coupling between the donor and acceptor, and a red-shifted CT absorption band was observed for one dyad. The dyads show solvent polarity-dependent singlet oxygen photosensitizing ability (quantum yields 3%-79%). Nanosecond transient absorption spectra of the dyad in nonpolar solvent confirm the formation of triplet states. The intrinsic triplet state lifetime is up to 383 μs (in fluid solution), which is much longer than that accessed with the heavy atom effect (276 μs). Intermolecular triplet photosensitizing of the dyads in a polar solvent produces a long-lived ³CT state (lifetime, τ_CT = 8.0 μs supported by the electron spin density surface analysis). The triplet state lifetime of the dyads doped in a Clear Flex 50 polymer film is exceptionally long (7.6-11.4 ms), and formation of a long-lived CT state (37 μs) was observed. Triplet-triplet annihilation upconversion was performed with the electron donor/acceptor dyads used as the triplet photosensitizer and perylene used as the triplet acceptor; the upconversion quantum yield is up to 15.8%.

BODIPY-Based Photosensitizers as Potential Anticancer and Antibacterial Agents: Role of the Positive Charge and the Heavy Atom Effect

Boron-dipyrromethene derivatives, including cationic and iodinated analogs, were obtained and subjected to physicochemical and in vitro photodynamic activity studies. Iodinated derivatives revealed a substantial heavy atom effect manifested by a bathochromic shift of the absorption band by about 30 nm and fluorescence intensity reduced by about 30-35 times, compared to that obtained for non-iodinated ones. In consequence, singlet oxygen generation significantly increased with Φ_Δ values in the range 0.69-0.97. The in vitro photodynamic activity was evaluated on Gram-positive Staphylococcus aureus, Gram-negative Escherichia coli, and on human androgen-sensitive prostate adenocarcinoma cells (LNCaP). The novel cationic, iodinated BODIPY, demonstrated the highest activity toward all studied cells. An excellent cytotoxic effect was found against LNCaP cells with an IC₅₀ value of 19.3 nM, whereas the viability of S. aureus was reduced by >5.6 log₁₀ at 0.25 μM concentration and by >5.3 log₁₀ in the case of E. coli at 5 μM. Thus, this analog seems to be a very promising candidate for the application in both anticancer and antimicrobial photodynamic therapy.

BODIPYs bearing a dimethylaminopropoxy substituent for imaging and photodynamic inactivation of bacteria

A new BODIPY (BDP 1) bearing a dimethylaminopropoxy group attached to a phenylene unit was synthesized. This compound was brominated to obtain the halogenated analog BDP 2, which was designed to enhance the photodynamic effect of BODIPY to kill bacteria without an intrinsic cationic charge. The basic amino group located at the end of the propoxy bridge can acquire a positive charge by protonation in an aqueous medium, increasing the binding to bacterial cells. Interaction and photokilling activity mediated by these compounds was evaluated in Staphylococcus aureus and Escherichia coli. BDP 1 and BDP 2 were rapidly bound to bacterial cells, showing bioimages with green emission. Complete elimination of S. aureus was detected when cells were incubated with 1 μM BDP 2 and irradiated for 5 min. Comparable photoinactivation was obtained with E. coli, after an irradiation of 30 min. Furthermore, BDP 2 was effective to kill bacteria at very low concentration (0.5 μM). Thus, BDP 1 showed mainly interesting properties as a fluorophore, whereas BDP 2 was highly effective photosensitizer as a broad-spectrum antibacterial agent.

Anchoring BODIPY photosensitizers enable pan-microbial photoinactivation

Photodynamic antimicrobial chemotherapy (PACT) is an effective strategy to inactivate pathogenic and resistant microbes. However, pan-microbial photoinactivation has hardly achieved. In this manuscript, we built anti-microbial PSs based on 2,6-diiodo-1,3,5,7-tetramethyl BODIPY (2I-BDP) using anchoring strategy through modifications on boron atom with bis-cationic moieties. With appropriate bis-cationic anchoring, we could achieve effective PACT for pan-microbial photoinactivation via straight forward modifications. Our studies suggested that integration of an efficient photosensitizer, good amphiphilicity, as well as tight interaction with microbial membrane could be essential for effective PACT.

Nano adamantane-conjugated BODIPY for lipase affinity and light driven antibacterial

The increasing number of resistant bacterial strains has raised efforts in developing alternative treatment strategies. Lipase is highly expressed in most bacteria and lipase targeting dyes will be non-sacrificed materials for a sustainable method against microorganism. The combination of chemotherapy and antimicrobial photodynamic inactivation (aPDI) method will be an effective method due to enhanced antibacterial activity. Here we reported the spectroscopic features of five boron dipyrrolylmethene (BODIPY) derivatives with different functional groups for lipase affinity and antibacterial activity. Lipase affinity tests and antibacterial assays were conducted by spectroscopic methods. Adamantane-conjugated BODIPY (BDP-2) was found to be the active compound against E. coli. Next, BDP-2 was brominated, and then assembled with PEG resulting biocompatible BDP2-Br₂@mPEG nanoparticles. The MTT assay indicated that BDP2-Br₂@mPEG was less toxicity on BGC-823 cancer cells without irradiation. The BDP2-Br₂@mPEG can inhibit the proliferation of E. coli and damage the membrane of bacterial cell under green LED light irradiation. The results proved BDP2-Br₂@mPEG can be a very promising green LED light driven antibacterial material.

A Highly-Efficient Type I Photosensitizer with Robust Vascular-Disruption Activity for Hypoxic-and-Metastatic Tumor Specific Photodynamic Therapy

Hypoxia severely impedes photodynamic therapy (PDT) efficiency. Worse still, considerable tumor metastasis will occur after PDT. Herein, an organic superoxide radical (O2∙- ) nano-photogenerator as a highly effcient type I photosensitizer with robust vascular-disrupting efficiency to combat these thorny issues is designed. Boron difluoride dipyrromethene (BODIPY)-vadimezan conjugate (BDPVDA) is synthesized and enwrapped in electron-rich polymer-brushes methoxy-poly(ethylene glycol)-b-poly(2-(diisopropylamino) ethyl methacrylate) (mPEG- PPDA) to afford nanosized hydrophilic type I photosensitizer (PBV NPs). Owing to outstanding core-shell intermolecular electron transfer between BDPVDA and mPEG-PPDA, remarkable O2∙- can be produced by PBV NPs under near-infrared irradiation even in severe hypoxic environment (2% O2 ), thus to accomplish effective hypoxic-tumor elimination. Simultaneously, the efficient ester-bond hydrolysis of BDPVDA in the acidic tumor microenvironment allows vadimezan release from PBV NPs to disrupt vasculature, facilitating the shut-down of metastatic pathways. As a result, PBV NPs will not only be powerful in resolving the paradox between traditional type II PDT and hypoxia, but also successfully prevent tumor metastasis after type I PDT treatment (no secondary-tumors found in 70 days and 100% survival rate), enabling enhancement of existing hypoxic-and-metastatic tumor treatment.

Phenotypic Resistance in Photodynamic Inactivation Unravelled at the Single Bacterium Level

Herein we report a simple fluorescence microscopy methodology that, jointly with four photosensitizers (PSs) and a cell viability marker, allows monitoring of phenotypic bacterial resistance to photodynamic inactivation (PDI) treatments. The PSs, composed of BODIPY dyes, were selected according to their ability to interact with the cell wall and the photoinactivating mechanism involved (type I or type II). In a first approach, the phenotypic heterogeneity allowing bacteria to persist during PDI treatment was evaluated in methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli as Gram-positive and Gram-negative models, respectively. By means of propidium iodide (PI), we monitored with spatiotemporal resolution cell viability at the single bacterium level. All the PSs were effective at inactivating pathogens; however, the cationic nonhalogenated PS (compound 1) surpassed the others and was capable of photoinactivating E. coli even under optimal growth conditions. Compound 1 was further tested on two other Gram-negative strains, Pseudomonas aeruginosa and Klebsiella pneumoniae, with outstanding results. All bacterial strains used here are well-known ESKAPE pathogens, which are the leading cause of nosocomial infections worldwide. Thorough data analysis of individual cell survival times revealed clear phenotypic variation expressed in the cell wall that affected PI permeation and thus its intercalation with DNA. For the same bacterial sample, death times may vary from seconds to hours. In addition, the PI incorporation time is also a parameter governed by the phenotypic characteristics of the microbes. Finally, we demonstrate that the results gathered for the bacteria provide direct and unique experimental evidence that supports the time-kill curve profiles.

Synthesis, structure, photophysical, electrochemical properties and antibacterial activity of brominated BODIPYs as an inhibitor of DNA gyrase B of S. aureus

BODIPYs with 3-thienyl and 4-acetamido phenyl groups substituted at the meso-position are subjected to regioselective bromination using three equivalents of [Formula: see text]-bromosuccinimide (NBS) to yield their 2-mono and 2,6-di bromoderivatives. Their photophysical, electrochemical and antimicrobial properties are investigated. This paper presents a mechanistic investigation of the antibacterial effect of brominated BODIPYs, particularly against Staphylococcus aureus. Fluorescence microscopic images reveal that the compounds are internalized effectively within the bacterial cells, making it an ideal antibacterial drug. Morphological analysis of the bacterial cells after the treatment with the test compounds showed that the compounds did not affect the cell membrane or cell wall and the antibacterial effect of these compounds is achieved via a different mechanism. The most effective compound was selected to explore the target of action. Molecular docking studies were performed on 22 selected proteins in S. aureus and the in silico results were validated by in vitro experiments. It was observed that the supercoiling activity of DNA gyrase was completely inhibited by the 2,6-dibromo-1,3,5,7-tetramethyl-8-(4-acetamido)-4-bora-3a,4a-diaza-[Formula: see text]-indacene, 3c by forming H-bonds with the ASP 81 residue of the enzyme.

Light-Harvesting Antenna and Proton-Activated Photodynamic Effect of a Novel BODIPY-Fullerene C60 Dyad as Potential Antimicrobial Agent

A covalently linked BODIPY-fullerene C₆₀ dyad (BDP-C₆₀ ) was synthesized as a two-segment structure, which consists of a visible light-harvesting antenna attached to an energy or electron acceptor moiety. This structure was designed to improve the photodynamic action of fullerene C₆₀ to inactivate bacteria. The absorption spectrum of BDP-C₆₀ was found to be a superposition of the spectra of its constitutional moieties, whereas the fluorescence emission of the BODIPY unit was strongly quenched by the fullerene C₆₀ . Spectroscopic, calculations, and redox studies indicate a competence between photoinduced energy and electron transfer. Protonating the dimethylaminophenyl substituent through addition of an acidic medium led to a substantial increase in the fluorescence emission, triplet excited state formation, and singlet molecular oxygen production. At physiological pH, photosensitized inactivation of Staphylococcus aureus mediated by 1 μM BDP-C₆₀ exhibited a 4.5 log decrease of cell survival (>99.997 %) after 15 min irradiation. A similar result was obtained with Escherichia coli using 30 min irradiation. Moreover, proton-activated photodynamic action of BDP-C₆₀ turned this dyad into a highly effective photosensitizer to eradicate E. coli. Therefore, BDP-C₆₀ is an interesting photosensitizing structure in which the light-harvesting antenna effect of the BODIPY unit combined with the protonation of dimethylaminophenyl group can be used to improve the photoinactivation of bacteria.

Photoinactivation of ESKAPE pathogens: overview of novel therapeutic strategy

The emergence of antimicrobial drug resistance requires development of alternative therapeutic options. Multidrug-resistant strains of Enterococcus spp., Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumanii, Pseudomonas aeruginosa and Enterobacter spp. are still the most commonly identified antimicrobial-resistant pathogens. These microorganisms are part of the so-called 'ESKAPE' pathogens to emphasize that they currently cause the majority of hospital acquired infections and effectively 'escape' the effects of antibacterial drugs. Thus, alternative, safer and more efficient antimicrobial strategies are urgently needed, especially against 'ESKAPE' superbugs. Antimicrobial photodynamic inactivation is a therapeutic option used in the treatment of infectious diseases. It is based on a combination of a photosensitizer, light and oxygen to remove highly metabolically active cells.

High Singlet Oxygen Yield Photosensitizer Based Polypeptide Nanoparticles for Low-Power Near-Infrared Light Imaging-Guided Photodynamic Therapy

NIR photosensitizer is attractive for photodynamic therapy (PDT). Low-power light irradiation and imaging-guided PDT makes it possible to increase tissue penetration depth. The pyrrole-substituted iodinated BODIPY (BDPI) molecule was designed and synthesized, and it possesses an intense NIR absorption and emission band, and exhibits a high singlet oxygen quantum yield (Φ_Δ = 0.80) which leads remarkable cytotoxicity upon low power illumination (IC50 = 0.60 μg/mL, 6.1 mW/cm²). After being encapsulated with biocompatibility polypeptide PEG-PLys, polymeric micelles nanoparticles (PBDPI NPs) was obtained that are water-dispersed and passively tumor-targetable. Such enhanced accumulation in tumor area makes it easily traced in vivo due to its NIR fluorescence. In addition, such nanoparticles offer an unprecedented photodynamic therapeutic effect by using a low-power irradiation light, which makes it possible to kill cancer cells in deep tissue efficiently.

Photodynamic inactivation of microorganisms sensitized by cationic BODIPY derivatives potentiated by potassium iodide

The photodynamic inactivation mediated by 1,3,5,7-tetramethyl-8-[4-(N,N,N-trimethylamino)phenyl]-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene 3 and 8-[4-(3-(N,N,N-trimethylamino)propoxy)phenyl]-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene 4 was investigated on Staphylococcus aureus, Escherichia coli and Candida albicans. In vitro experiments indicated that BODIPYs 3 and 4 were rapidly bound to microbial cells at short incubation periods. Also, fluorescence microscopy images showed green emission of BODIPYs bound to microbial cells. Photosensitized inactivation improved with an increase of the irradiation time. Similar photoinactivation activities were found for both BODIPYs in bacteria. The photoinactivation induced by these BODIPYs was effective for both bacteria. However, the Gram-positive bacterium was inactivated sooner and with a lower concentration of a photosensitizer than the Gram-negative bacterium. After 15 min irradiation, the complete eradication of S. aureus was obtained with 1 μM photosensitizer. A reduction of 4.5 log in the E. coli viability was found when using 5 μM photosensitizer and 30 min irradiation. Also, the last conditions produced a decrease of 4.5 log in C. albicans cells treated with BODIPY 3, while 4 was poorly effective. On the other hand, the effect of the addition of KI on photoinactivation at different irradiation periods and salt concentrations was investigated. A smaller effect was observed in S. aureus because the photosensitizers alone were already very effective. In E. coli, photokilling potentiation was mainly found at longer irradiation periods. Moreover, the photoinactivation of C. albicans mediated by these BODIPYs was increased in the presence of KI. In solution, an increase in the formation of the BODIPY triplet states was observed with the addition of the salt, due to the effect of external heavy atoms. The greater intersystem crossing together with the formation of reactive iodine species induced by BODIPYs may be contributing to enhance the inactivation of microorganisms. Therefore, these BODIPYs represent interesting photosensitizers to inactivate microorganisms. In particular, BODIPY 3 in combination with KI was highly effective as a broad spectrum antimicrobial photosensitizer.

BODIPYs to the rescue: Potential applications in photodynamic inactivation

4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) derivatives have been proposed in several potential biomedical applications. BODIPYs absorb strongly in blue-green region with high fluorescence emission, properties that convert them in effective fluorophores in the field of biological labeling. However, BODIPY structures can be conveniently modified by heavy atoms substitution to obtain photosensitizers with applications in photodynamic therapy. Also, external heavy atoms effect can be used to increase the photodynamic activity of these compounds. In recent years, BODIPYs have been proposed as phototherapeutic agents for the photodynamic inactivation of microorganisms. Therefore, BODIPY structures need to be optimized to produce an efficient photocytotoxic activity. In this way, amphiphilic cationic BODIPYs can selectively bind to microbial cells, inducing an effective photokilling of pathogenic microbial cells. This review summarizes the attributes of BODIPY derivatives for applications as antimicrobial photosensitizing agents.