Pulse mode of laser photodynamic treatment induced cell apoptosis

• The continuous wave and pulse irradiation modes at PDT were compared theoretically.
• The pulse irradiation mode PDT is more effective in singlet oxygen production due to re-oxygenation.
• PDT with pulse irradiation mode induces k562 cell death mainly by apoptosis.
• The temporal distribution of singlet oxygen generation can determine the cell death type.

One of the factors limiting photodynamic therapy (PDT) is hypoxia in tumor cells during photodynamic action. PDT with pulse mode irradiation and appropriate irradiation parameters could be more effective in the singlet oxygen generation and tissue re-oxygenation than continuous wave (CW) mode. We theoretically demonstrate differences between the cumulative singlet oxygen concentration in PDT using pulse mode and CW mode of laser irradiation. In vitro experimental results show that photodynamic treatment with pulse mode irradiation has similar cytotoxicity to CW mode and induces mainly cell apoptosis, whereas CW mode induces necrotic cell death. We assume that the cumulative singlet oxygen concentration and the temporal distribution of singlet oxygen are important in photodynamic cytotoxicity and apoptosis initiation. We expect our research may improve irradiation protocols and photodynamic therapy efficiency.

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