A genome-wide screen for tolerance to rose bengal photodynamic therapy and its use in onychomycosis treatment

摘要

The clinical use of photodynamic therapy (PDT) with rose bengal (RB) is emerging as an effective t reatment for a rangeof applications given its non-invasive and localised mode of delivery. In particular, rose bengal PDT has shownpromising antifungal action in vitro. While focus has largely been on the physical and chemical impacts of PDT on thecell, an understanding of the role of genetics underpinning the cellular response is still limited. We have, therefore,reported a screen of the entire non-essential gene library of the model organism, Saccharomyces cerevisiae, using rosebengal PDT to ascertain the key genetic pathways affecting fungal tolerance to PDT. We also investigated the dosage ofPDT required to eradicate Trichophyton rubrum spores, the main causative organism of onychomycosis infection.Following this, we conducted a pilot patient study of six patients (seven toenails) for the treatment of onychomycosisusing rose bengal PDT (140 μM RB and ~763 J/cm~2 green light), where the clinical treatment protocol was developed onthe basis of the in vitro outcomes. The key biochemical pathways identified by the genetic screen as having alteredtolerance to PDT included ergosterol biosynthesis, vacuolar acidification, and purine/S-adenosyl-L-methioninebiosynthesis. The subsequent pilot patient study saw the complete cure of onychomycosis for all pat ients within three tofive treatment sessions in the absence of pain or other local side effects. The outcome of the genetic screen for tolerancemay thus inform the development of efficient clinical treatments using rose bengal PDT.