Singlet oxygen phosphorescence detection in vivo identifies PDT-induced anoxia in solid tumors

Area of Science:

• Biomedical Optics
• Photodynamic Therapy
• Cancer Research

Background:

• Real-time surveillance of photodynamic therapy (PDT) is crucial for optimizing treatment efficacy.
• Singlet oxygen phosphorescence kinetics are key indicators of PDT impact.
• Non-invasive in vivo monitoring of these signals has been a long-standing challenge.

Purpose of the Study:

• To develop and validate a method for in vivo real-time surveillance of singlet oxygen phosphorescence during PDT.
• To investigate the in vivo behavior of pyropheophorbide-a photosensitizers in tumors and normal tissues.
• To explore the role of oxygen depletion in PDT efficacy.

Main Methods:

• Utilized high transmission optics (1200, 1270, 1340 nm) for selective singlet oxygen phosphorescence detection.
• Administered N-(2-Hydroxypropyl)methacrylamide copolymers conjugated with pyropheophorbide-a systemically in mice.
• Measured phosphorescence signals through skin in both tumor and normal tissues.

Main Results:

• Successfully measured weak singlet oxygen phosphorescence kinetics in vivo through mouse skin.
• Identified circulating drug in the bloodstream as the primary signal source in both tumor and normal tissues.
• Observed minimal detectable signal from extravasated photosensitizers in tumors, contrary to in vitro findings.
• Hypothesized oxygen depletion in tumors as the cause for the in vivo signal discrepancy.

Conclusions:

• Real-time in vivo singlet oxygen phosphorescence surveillance is feasible.
• Oxygen depletion in tumors significantly impacts photosensitizer signaling during PDT.
• This technique highlights the importance of monitoring singlet oxygen during PDT for treatment success.