Time-resolved singlet oxygen luminescence detection under photodynamic therapy relevant conditions: comparison ofex vivoapplication of two photosensitizer formulations

Abstract

Singlet oxygen plays a crucial role in photo-dermatology and photodynamic therapy (PDT) of cancer. Its direct observation by measuring the phosphorescence at 1270 nm, however, is still challenging due to the very low emission probability. It is especially challenging for the time-resolved detection of singlet oxygen kinetics in vivo which is of special interest for biomedical applications. Photosensitized generation of singlet oxygen, in pig ear skin as model for human skin, is investigated here. Two photosensitizers (PS) were topically applied to the pig ear skin and examined in a comparative study, which include the amphiphilic pheophorbide-a and the highly hydrophobic perfluoroalkylated zinc phthalocyanine (F64PcZn). Fluorescence microscopy indicates the exclusive accumulation of pheophorbide-a in the stratum corneum, while F64PcZn can also accumulate in deeper layers of the epidermis of the pig ear skin. The kinetics obtained with phosphorescence measurements show the singlet oxygen interaction with the PS microenvironment. Different generation sites of singlet oxygen correlate with the luminescence kinetics. The results show that singlet oxygen luminescence detection can be used as a diagnostic tool, not only for research, but also during treatment. The detection methodology is suitable for the monitoring of chemical quenchers’ oxidation as well as saturation at singlet oxygen concentration levels relevant to PDT treatment protocols.

Singlet oxygen-based electrosensing by molecular photosensitizers

“…3). The photocurrents were completely suppressed on N 2 purges, whether HQ was present or not, but recovered completely on admission of air, consistent with a Type II mechanism and the high 1 O 2 quantum yield ( Φ Δ ∼0.6 in acetone, methanol) previously reported for F 64 PcZn23242532. Intriguingly, for SPE|F 64 PcZn the anaerobic photocurrent (under N 2 ) exhibits a sign reversal in the presence of HQ, suggesting a direct electron transfer from HQ to F 64 PcZn and, eventually to the electrode, in agreement with a recent report on the direct photoreduction of F 64 PcZn by an electron donor in strictly oxygen-free conditions30.…”

“…The essential role of O 2 for substrate detection using the photodynamic effect observed for F 64 PcZn in solution2425 and ex vivo 2332, was confirmed by comparing photocurrents obtained in an air-saturated buffer with those obtained under an inert N 2 atmosphere (Fig. 3).…”

Correlation of in vivo tumor response and singlet oxygen luminescence detection in mTHPC-mediated photodynamic therapy

“…This extends work in photosensitizer solution, tumor cells in vitro and normal tissue (skin) in vivo, reported previously by ourselves 8,9 and by other groups [10][11][12]14 using variations on the SOLD instrumentation, measurement technique and biological models. The most direct comparison can be made with the in vivo study by Yamamoto et al, 13 in which 1 O 2 luminescence dosimetry was used in a gliosarcoma tumor xenograft model, assessing the PDT response by quantitative histopathology.…”

“…8 Importantly, this response curve is independent of the individual treatment parameters such as photosensitizer concentration, light dose and oxygenation. Its validity has also been demonstrated in normal skin models 9,10 and in normal human skin using a timeintegrated technique, 11,12 15 have shown that it may not work for all photosensitizers, depending on parameters such as the level of oxygenation.…”

Effects of pulse width and repetition rate of pulsed laser on kinetics and production of singlet oxygen luminescence

“…[4][5][6] PDT involves three major components: light, PS and molecular oxygen. 7 Continuous-wave (CW) and pulsed lasers were widely used as excitation light sources for activating PS in PDT, and the e®ects of PS types, 8,9 oxygen concentration 10,11 on 1 O 2 production have been intensively evaluated, respectively. However, as one of the three essential components of PDT, the e®ects of laser parameters (i.e., pulse width, repetition rate) for pulsed lasers on the kinetics and production of 1 O 2 luminescence have not been fully explored.…”