Fotossensibilizadores de protoporfirina IX funcionalizados com inibidores de bomba de efluxo derivados de capsaicina para potencializar a terapia fotodinâmica contra as bactérias resistentes Staphylococcus aureus e Escherichia coli

Abstract

Antimicrobial resistance is listed among the top 10 global health threats by the World Health Organization (WHO) in 2023. Bacterial infections are becoming increasingly resistant to conventional treatments, with an estimated 10 million deaths per year projected by 2050. In this context, Antimicrobial Photodynamic Therapy (aPDT) emerges as a promising approach to combat the rise of bacterial resistance. Therefore, this study aimed to synthesize and evaluate the biological activity of two derivatives of Protoporphyrin IX (PpIX) structurally modified with one or two capsaicin fragments, a well-known inhibitor of the NorA efflux pump. The physicochemical, photophysical properties, and photoinactivation potential of these new compounds were investigated in both susceptible and resistant bacteria, including Gram- positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) strains. The derivatives were obtained with yields of 17% for PpIX-capsaicin 1 (one capsaicin fragment) and 40% for PpIX-capsaicin 2 (two capsaicin fragments), aiming to enhance bacterial photoinactivation through a synergistic effect associated with increased cellular uptake. Photophysical and photochemical studies included fluorescence and singlet oxygen quantum yield determinations, as well as the assessment of photodegradation under different LED devices. Structural modifications resulted in minor variations in photochemical properties compared to PpIX, with lower photostability linked to higher singlet oxygen production. Self-aggregation studies in water/DMSO mixtures indicated a lower tendency to aggregate for PpIX-capsaicin 1, whereas PpIX-capsaicin 2 exhibited the formation of different types of aggregates (H- and J-type) in predominantly aqueous media, similar to the precursor PpIX. Regarding lipophilicity, a significant increase was observed only in the derivative with two capsaicin fragments. Finally, photoinactivation assays showed greater efficacy against Gram-positive bacteria, particularly in susceptible S. aureus, where a 2.9-log reduction was obtained with derivative 1, while PpIX resulted in a 1.7-log reduction at 1.2 μM and 30 J/cm². Conversely, Gram-negative bacteria, such as E. coli, showed lower susceptibility, with only a 1.2-log reduction. These findings highlight the potential of PpIX-capsaicin derivatives, particularly PpIX-capsaicin 1, as promising candidates for aPDT applications.