Intracellular Photobleaching of 5,10,15,20-Tetrakis(m-hydroxyphenyl) chlorin (Foscan®) Exhibits a Complex Dependence on Oxygen Level and Fluence Rate¶

Abstract

The understanding of photosensitizer photobleaching is important not only for mechanistic studies, but also for the development of monitoring techniques for clinical dosimetry in photodynamic therapy. In this study, we investigated the intracellular photobleaching of 5,10,15,20-tetrakis(m-hydroxyphenyl)chlorin (mTHPC, Foscan) in the murine macrophage cell line J774A.1, using quantitative fluorescence imaging microscopy, microspectrofluorometry and microspectrophotometry. Using 652 nm laser irradiation, it was found that mTHPC exhibits oxygen- and fluence rate-dependent intracellular photobleaching. The kinetics showed an inverse dose-rate behavior, i.e. a reduction of fluence rate resulted in more photobleaching at comparable fluences. The effect of deoxygenation was found to be more complex, with decreased bleaching at low fluence rates and increased bleaching at higher fluence rates. The intracellular formation of reactive oxygen species was measured using 2',7'-dichlorodihydrofluorescein diacetate. The results are analyzed in terms of competitive Type-I and Type-II mechanisms.

Calculation of Singlet Oxygen Dose from Photosensitizer Fluorescence and Photobleaching During mTHPC Photodynamic Therapy of MLL Cells¶

“…The first model, which was based on the proportionality between singlet oxygen production and the number of photons absorbed by the PS, is similar to the approach of Robinson et al (9) in assessing the PDT dose using ALA-induced PpIX in vivo. This dose metric was The lack of significant oxygen depletion for high fluence rates or high sensitizer concentrations explains the absence of a fluence rate effect observed in other in vitro investigations of mTHPC PDT (40,41). For the experiment where the oxygen has been depleted by nitrogen bubbling, the singlet oxygen dose has been overestimated by approximately 400%.…”

Photosensitisation studies of silicone polymer doped with methylene blue and nanogold for antimicrobial applications

“…Photobleaching of dyes in different polymer matrices has been reported, 29 and MB photobleaching generally results in the formation of a colourless 'leuco' form most likely via Type 1 photoreduction mechanisms, either involving electron transfer from MB or other substrates to the MB triplet state. 31 In the MB AuNP-encapsulated silicone polymer for a laser light dose of 45 J cm À2 (the same light dose as used bactericidal studies, Fig. 31 In the MB AuNP-encapsulated silicone polymer for a laser light dose of 45 J cm À2 (the same light dose as used bactericidal studies, Fig.…”

Unusual Photoinduced Response of mTHPC Liposomal Formulation (Foslip)

“…Kasselouri et al (15) detected mono-, di-and tri-hydroxy-mTHPC as major photoproducts of mTHPC in ethanol-water medium. mTHPC photobleaching kinetics in spheroids and monolayer cultured cells were consistent with singlet oxygen-mediated mechanism (16) and depended on the dye intracellular concentration, fluence rate and oxygen partial pressure (17)(18)(19). Except for a single study where photobleaching of a liposomal mTHPC gel formulation was registered after its topical application in patients with skin carcinomas (20), this process has not been yet investigated for liposomal forms of mTHPC.…”

“…Numerous studies have addressed the mechanism of mTHPC photobleaching in cells and cell-free systems (13)(14)(15)(16)(17)(18)(19). This process is oxygen dependent and is inhibited by singlet oxygen quenchers in serum-enriched solutions (13).…”