Design of Photosensitizing Agents for Targeted Antimicrobial Photodynamic Therapy

Photodynamic inactivation of microorganisms has gained substantial attention due to its unique mode of action, in which pathogens are unable to generate resistance, and due to the fact that it can be applied in a minimally invasive manner. In photodynamic therapy (PDT), a non-toxic photosensitizer (PS) is activated by a specific wavelength of light and generates highly cytotoxic reactive oxygen species (ROS) such as superoxide (O2-, type-I mechanism) or singlet oxygen (1O2*, type-II mechanism). Although it offers many advantages over conventional treatment methods, ROS-mediated microbial killing is often faced with the issues of accessibility, poor selectivity and off-target damage. Thus, several strategies have been employed to develop target-specific antimicrobial PDT (aPDT). This includes conjugation of known PS building-blocks to either non-specific cationic moieties or target-specific antibiotics and antimicrobial peptides, or combining them with targeting nanomaterials. In this review, we summarise these general strategies and related challenges, and highlight recent developments in targeted aPDT

Riboflavin-Vancomycin Conjugate Enables Simultaneous Antibiotic Photo-Release and Photodynamic Killing against Resistant Gram-Positive Pathogens

Decades of antibiotic misuse have led to alarming levels of antimicrobial resistance, and the development of alternative diagnostic and therapeutic strategies to delineate and treat infections is a global priority. In particular, the nosocomial, multidrug-resistant "ESKAPE" pathogens such as Gram-positive methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus spp (VRE) urgently require alternative treatments. Here, we developed light-activated molecules based on the conjugation of the FDA-approved photosensitizer riboflavin to the Gram-positive specific ligand vancomycin to enable targeted antimicrobial photodynamic therapy. The riboflavin-vancomycin conjugate proved to be a potent and versatile antibacterial agent, enabling the rapid, light-mediated, killing of MRSA and VRE with no significant off-target effects. The attachment of riboflavin on vancomycin also led to an increase in antibiotic activity against S. aureus and VRE. Simultaneously, we evidenced for the first time that the flavin subunit undergoes an efficient photoinduced bond cleavage reaction to release vancomycin, thereby acting as a photoremovable protecting group with potential applications in drug delivery

Red-Shifted Environmental Fluorophores and Their Use for the Detection of Gram-Negative Bacteria

Two novel, water-soluble, merocyanine fluorophores were readily prepared by microwave-assisted synthesis. Full optical characterization was performed in a series of protic and aprotic solvents, and the dyes displayed fluorescence in the red region with up to a 20-fold decrease in brightness in water, demonstrating a strong environmental sensitivity hereby termed as solvato-fluorogenicity (to distinguish from solvatochromism). Shorter fluorescent lifetimes were also measured in water, which confirmed this character. These dyes were conjugated to a modified polymyxin scaffold that allowed fluorescence “switch-on” upon binding to Gram-negative bacterial membranes, and selective fluorescence detection of bacteria in a wash-free protocol

Rapid detection of major Gram-positive pathogens in ocular specimens using a novel fluorescent vancomycin-based probe

Bacterial infections of the eye are significant causes of morbidity that can lead to permanent visual loss without rapid and adequate treatment, with Gram-positive bacteria causing the majority of ocular infections. Here we report a novel probe, based on the reductive amination of vancomycin with a 4-nitrobenzoxadiazole (NBD)-based aldehyde, that rapidly and specifically detects Gram positive infections from ocular samples

Nouvelles sondes moléculaires photo-activées pour la délivrance de principes actifs : de la conception aux applications biologiques

Photolabile protecting groups (PPGs) have attracted growing interests in many fields of chemistry and biology. Light-induced release of biological agents, commonly known as “uncaging”, has thus emerged as an interesting process for drug delivery or investigation of biological phenomena. Combining this tool with the intrinsic advantages of two-photon (2P) excitation (2PE) in the NIR is however a challenge. In this work, we use different engineering routes towards new efficient 2P uncagers.First we demonstrate that combining quadrupolar 2P light harvesting antennas with suitable uncaging subunits leads to efficient release of active molecules upon 2PE. In these FRET-based systems, gradual adjustments of the constitutive building blocks allowed us to tune key parameters such as photophysical properties, FRET efficiency, and kinetics of photorelease. In particular, coumarin-based tandem systems, in which absorption and emission of the donor-acceptor pair best match, eventually led to record δu values for uncaging of carboxylic acids.We then assessed the critical water-solubility issue by introducing hydrophilic units onto our cooperative PPGs. New hydrophilic and amphiphilic systems, suited for controlled release of neurotransmitters or anti-cancer agents, were designed from our multi-chromophoric systems.Finally, in our effort towards better understanding of the structure-properties relationships in coumarin PPGs, we synthesized a small library of π-extended DEAC cages bearing strong electron-withdrawing moieties, and assessed their efficacy for 2P uncaging of glycine. With this study, a step was made towards rationalization of the uncaging quantum yield in coumarin cages.La photolibération d'agents biologiques cagés par des groupements protecteurs photolabiles (PPGs) a récemment attiré un intérêt croissant en thérapie et physiologie. La combinaison de cet outil avec les avantages de l'absorption à deux photons (2PA) dans le proche IR est cependant un défi. Dans ces travaux, nous présentons deux voies différentes vers de nouveaux décageurs efficaces en 2PA.Nous élaborons d’abord une série de systèmes tandem basés sur le FRET, combinant des antennes quadrupolaires 2PA avec des modules PPGs appropriés. La modification des blocs constitutifs de ces composés nous a permis de moduler les paramètres clés tels que les propriétés photophysiques, l'efficacité de FRET et la cinétique de photolibération. Les systèmes synergiques à base de coumarines, dans lesquels la paire donneur-accepteur est la plus adaptée, ont finalement conduit à des valeurs de δu record pour la libération d’acides carboxyliques.La problématique critique de solubilité en milieu biologique a ensuite été étudiée en incorporant des motifs hydrosolubilisants dans nos systèmes coopératifs. De nouveaux outils hydrophiles et amphiphiles, adaptés respectivement à la délivrance de neurotransmetteurs et la thérapie anticancéreuse, ont ainsi été développés à partir de nos systèmes tandem.Enfin, pour mieux comprendre les relations structure-propriétés dans les PPGs de la famille des coumarines, nous avons synthétisé une série de cages DEAC π-étendues portant différents groupements électroattracteurs, et évalué leur efficacité pour la libération de glycine. Cette étude nous a permis de faire un pas vers la rationalisation du rendement quantique de photolibération chez les PPGs de ce type

Design of new molecular tools for light-induced delivery of bioactive compounds

La photolibération d'agents biologiques cagés par des groupements protecteurs photolabiles (PPGs) a récemment attiré un intérêt croissant en thérapie et physiologie. La combinaison de cet outil avec les avantages de l'absorption à deux photons (2PA) dans le proche IR est cependant un défi. Dans ces travaux, nous présentons deux voies différentes vers de nouveaux décageurs efficaces en 2PA.Nous élaborons d’abord une série de systèmes tandem basés sur le FRET, combinant des antennes quadrupolaires 2PA avec des modules PPGs appropriés. La modification des blocs constitutifs de ces composés nous a permis de moduler les paramètres clés tels que les propriétés photophysiques, l'efficacité de FRET et la cinétique de photolibération. Les systèmes synergiques à base de coumarines, dans lesquels la paire donneur-accepteur est la plus adaptée, ont finalement conduit à des valeurs de δu record pour la libération d’acides carboxyliques.La problématique critique de solubilité en milieu biologique a ensuite été étudiée en incorporant des motifs hydrosolubilisants dans nos systèmes coopératifs. De nouveaux outils hydrophiles et amphiphiles, adaptés respectivement à la délivrance de neurotransmetteurs et la thérapie anticancéreuse, ont ainsi été développés à partir de nos systèmes tandem.Enfin, pour mieux comprendre les relations structure-propriétés dans les PPGs de la famille des coumarines, nous avons synthétisé une série de cages DEAC π-étendues portant différents groupements électroattracteurs, et évalué leur efficacité pour la libération de glycine. Cette étude nous a permis de faire un pas vers la rationalisation du rendement quantique de photolibération chez les PPGs de ce type.Photolabile protecting groups (PPGs) have attracted growing interests in many fields of chemistry and biology. Light-induced release of biological agents, commonly known as “uncaging”, has thus emerged as an interesting process for drug delivery or investigation of biological phenomena. Combining this tool with the intrinsic advantages of two-photon (2P) excitation (2PE) in the NIR is however a challenge. In this work, we use different engineering routes towards new efficient 2P uncagers.First we demonstrate that combining quadrupolar 2P light harvesting antennas with suitable uncaging subunits leads to efficient release of active molecules upon 2PE. In these FRET-based systems, gradual adjustments of the constitutive building blocks allowed us to tune key parameters such as photophysical properties, FRET efficiency, and kinetics of photorelease. In particular, coumarin-based tandem systems, in which absorption and emission of the donor-acceptor pair best match, eventually led to record δu values for uncaging of carboxylic acids.We then assessed the critical water-solubility issue by introducing hydrophilic units onto our cooperative PPGs. New hydrophilic and amphiphilic systems, suited for controlled release of neurotransmitters or anti-cancer agents, were designed from our multi-chromophoric systems.Finally, in our effort towards better understanding of the structure-properties relationships in coumarin PPGs, we synthesized a small library of π-extended DEAC cages bearing strong electron-withdrawing moieties, and assessed their efficacy for 2P uncaging of glycine. With this study, a step was made towards rationalization of the uncaging quantum yield in coumarin cages

Tandem Systems for Two‐Photon Uncaging of Bioactive Molecules

International audienc

Two-Photon Absorption: An Open Door to the NIR-II Biological Window?

The way in which photons travel through biological tissues and subsequently become scattered or absorbed is a key limitation for traditional optical medical imaging techniques using visible light. In contrast, near-infrared wavelengths, in particular those above 1000 nm, penetrate deeper in tissues and undergo less scattering and cause less photo-damage, which describes the so-called “second biological transparency window”. Unfortunately, current dyes and imaging probes have severely limited absorption profiles at such long wavelengths, and molecular engineering of novel NIR-II dyes can be a tedious and unpredictable process, which limits access to this optical window and impedes further developments. Two-photon (2P) absorption not only provides convenient access to this window by doubling the absorption wavelength of dyes, but also increases the possible resolution. This review aims to provide an update on the available 2P instrumentation and 2P luminescent materials available for optical imaging in the NIR-II window