Innovative NIR light responsive nanoparticles for enhanced antibacterial PDT and singlet oxygen mediated antibiotic release – BaXygen

Antibiotics overuses, misuses and environmental factors led to a global increase in antimicrobial resistance - that is responsible of the death of 700,000 people/year, and if no action is taken the World Health Organization estimates that it could cause 10 million deaths/year by 2050. The development of new and effective treatment modalities is therefore extremely urgent to reduce not only infection-related mortality but also the related economic burden to patients and hospitals. With the effectiveness of antimicrobials declining as antimicrobial resistance continues, we must look to alternative strategies for the treatment of infections.
Photodynamic therapy (PDT) is a technique that involves light activation of a molecule called photosensitizer (PS), and this in turn can lead to the formation of singlet oxygen (1O2) which can induce bacteria death. Of note, PDT has a broader spectrum of action compared to classical antibiotics, and as the PS returns to the ground state it becomes available for another cycle. To further increase the efficiency of this approach we propose to combine it with antimicrobials. In order to have both, PDT and antibiotic localized at the same site, we will include PS and the lipid modified antibiotics into nanoparticles (NPs). The main objective of BaXygen is to develop a completely unexplored approach for combating bacteria that combines PDT which will kill bacteria but also trigger breakage of singlet oxygen-cleavable linker to locally release a “caged” antibiotic. Our NPs will be then used to confer antibacterial properties to medical devices in particular catheters because long-term catheter-related bloodstream infection (CRBSI) is a leading cause of nosocomial infections in intensive care units and it is an important cause of morbidity and mortality with a significant economic burden. To achieve our goal, the 4 following Tasks will be performed:
- Task 1: design and synthesis of aza-BODIPY (boron dipyrromethene) PS enabling highly efficient singlet oxygen generation using excitation wavelength in the phototherapeutic window (650 - 900nm). In parallel, efficient synthetic pathways for the preparation of self-immolative singlet oxygen-sensitive linkers bearing orthogonal functional groups to enable selective conjugation to lipid analogues will be developed. During this project, 3 types of 1O2 sensitive linkers will be evaluated: thioketal, 9,10-dialkoxyanthracene and aminoacrylate. We will use carbamate based self-immolative spacers in order to couple antibiotics such as the cephalosporin T-91825 and ciprofloxacin. To enable selective conjugation of the NPs to modified PolyUrethane (PU) catheters by Michael addition we will synthesize lipid analogs bearing a maleimide function.
- Task 2 will consist in the preparation of liposomes and lipid nanocapsules of different size and composition and containing various ratios of BODIPY based PS/lipid-ROS sensitive linker-antibiotic conjugates. To realize the coating, the PU catheters will undergo plasma treatment in presence of maleic anhydride in order to modify the PU surface with carboxylic acid functions. Those latter functions will be used to couple a spacer arm which will allow NP grafting (Michael reaction).
- Task 3 will focus on the physical and the photophysical evaluation of the NPs. The quantum yield of the singlet oxygen generation and the yield of released antibiotics (from NPs and from NPs-coated catheters) will be quantified. Different classes of antibiotics will be coupled to evaluate the scope of the technique.
- Task 4 will be focused on: i- the evaluation of the toxicity of the NPs +/- light irradiation on healthy human cells and check whether the NPs generate a pro-inflammatory response; ii- the antibacterial activity of the NPs +/- light on Gram(-) and (+) bacteria and biofilms as compared to the free antibiotic; iii- the vitro and in vivo (using a mouse model) antibacterial activity of the coated polyurethane catheters.