Concanavalin A-Rose Bengal bioconjugate for targeted Gram-negative antimicrobial photodynamic therapy

• Published in: Journal of photochemistry and photobiology. B, Biology Biology, 2020-05, Vol.206, p.111852-111852, Article 111852
• Main Authors: Cantelli, Andrea, Piro, Francesca, Pecchini, Pietro, Di Giosia, Matteo, Danielli, Alberto, Calvaresi, Matteo
• Format: Article
• Language: English
• Subjects: Antiinfectives and antibacterials; Antimicrobial photodynamic therapy; Bacteria; Binding; Bioconjugation; Carbohydrate-lectin recognition process; Cell culture; Cell membranes; Cell walls; Concanavalin A; Conjugates; Conjugation; E coli; Gram-negative bacteria; Gram-negative bacteria targeting; Gram-positive bacteria; Irradiation; Light emitting diodes; Lipopolysaccharides; Peroxide; Photodynamic therapy; Radiation; Rose Bengal; Singlet oxygen; Superoxide; White light
• ISSN: 1011-1344; 1873-2682
• DOI: 10.1016/j.jphotobiol.2020.111852

Photodynamic therapy (PDT) is considered a very promising therapeutic modality for antimicrobial therapy. Although several studies have demonstrated that Gram-positive bacteria are very sensitive to PDT, Gram-negative bacteria are more resistant to photodynamic action. This difference is due to a different cell wall structure. Gram-negative bacteria have an outer cell membrane containing lipopolysaccharides (LPS) that hinder the binding of photosensitizer molecules, protecting the bacterial cells from chemical attacks. Combination of the lipopolysaccharides-binding activity of Concanavalin A (ConA) with the photodynamic properties of Rose Bengal (RB) holds the potential of an innovative protein platform for targeted photodynamic therapy against Gram-negative bacteria. A ConA-RB bioconjugate was synthesized and characterized. Approximately 2.4 RB molecules were conjugated per ConA monomer. The conjugation of RB to ConA determines a decrease of the singlet oxygen generation and an increase of superoxide and peroxide production. The photokilling efficacy of the ConA-RB bioconjugate was demonstrated in a planktonic culture of E. coli. Irradiation with white light from a LED lamp produced a dose-dependent photokilling of bacteria. ConA-RB conjugates exhibited a consistent improvement over RB (up to 117-fold). The improved uptake of the photosensitizer explains the enhanced PDT effect accompanying increased membrane damages induced by the ConA-RB conjugate. The approach can be readily generalized (i) using different photo/sonosensitizers, (ii) to target other pathogens characterized by cell membranes containing lipopolysaccharides (LPS). •The conjugation of RB with ConA determines a decrease of the 1O2 and an increase of peroxide and superoxide production.•The conjugation of RB to ConA leads to a more effective targeting of RB to Gram (−)bacteria.•ConA-RB conjugates exhibited a consistent improvement over RB (up to 117-fold).•The recognition of LPS by ConA, contributes to the enhanced uptake and improved photodynamic effect of ConA-RB.