The effect of lidocaine on PpIX photobleaching and outcome of ALA-PDT in vitro

Summary 

Background

Photodynamic therapy (PDT) is based on the light exposure of neoplastic tissue after selective accumulation of photosensitizers in neoplastic cells. One of the major side effects of ALA-PDT is pain during light exposure. Lidocaine is one of several anaesthetics used to relieve this pain. Although its anaesthetic role is well known, it has been proposed that it may act as a hydroxyl radical and singlet oxygen scavenger. The effectiveness of PDT is directly linked to the yield of singlet oxygen. The aim of this study was to investigate possible scavenging properties of lidocaine in photosensitization.

Methods

Photodegradation of PpIX in dimethyl sulfoxide (DMSO) solution and in WiDr cells alone or in the presence of lidocaine was investigated by fluorescence spectroscopy. The influence of lidocaine on PDT outcome was evaluated by measuring the colony forming ability of the cells.

Results

Lidocaine in DMSO had no significant effect (p<0.05) on PpIX photodegradation, although it seems to induce a slight increase in the photobleaching rate. The rate of PpIX photodegradation and the photosensitivity in cells were similar in the absence and in the presence of lidocaine.

Conclusion

Lidocaine had no significant influence on PpIX photobleaching and ALA-PDT outcome in vitro.

Keywords: Photodynamic therapy, Lidocaine, Singlet oxygen, Photobleaching