Tumor Po2 changes during photodynamic therapy depend upon photosensitizer type and time after injection

• Published in: Comparative biochemistry and physiology. Part A, Molecular & integrative physiology Molecular & integrative physiology, 2002-05, Vol.132 (1), p.177-184
• Main Authors: Pogue, Brian W, O'Hara, Julia A, Goodwin, Isak A, Wilmot, Carmen J, Fournier, Gregory P, Akay, Altug R, Swartz, Harold
• Format: Article
• Language: English
• Subjects: Benzoporphyrin derivative; EPR; Oxygen; Photochemotherapy; Photodynamic; Po2; RIF-1 tumor; Singlet oxygen
• ISSN: 1095-6433; 1531-4332
• DOI: 10.1016/S1095-6433(01)00545-1

In this study, the vascular and tissue oxygen changes induced by photodynamic therapy in the RIF-1 tumor were examined, using electron paramagnetic resonance (EPR) oximetry. Two photosensitizers, including verteporfin (BPD-MA in a lipid-based formulation) and aminolevulinic acid-induced protoporphyrin IX (ALA-PPIX), were investigated with optical irradiation, sufficient to induce sub-curative damage in the tumor tissue, and the transient changes in P o 2 and vascular perfusion were examined. A large increase in tissue oxygenation (from 3 up to 9.5 mmHg) was observed when treated with ALA-PPIX based photodynamic therapy, which lasted during the treatment and a small residual increase that returned back to baseline levels by 48 h after treatment. With verteporfin-based photodynamic therapy, one group of animals was irradiated 15 min after injection and exhibited a small decrease in oxygenation relative to pre-irradiation levels. The second group was irradiated at 3 h after injection and exhibited a large increase in the average P o 2, (from 3 to 15 mmHg) by the end of the treatment. These observations indicate that photodynamic therapy significantly increases tissue P o 2 under certain treatment conditions, with the potential cause being either increased local blood flow or decreased local oxygen metabolic consumption due to cellular damage.