C3H mice with transplanted mammalian carcinoma tumor on legs were injected with 12.5 mg/kg Photofrin irradiated 24 hours prior light treatment. To manipulate tumor oxygenation, the animals were subjected to 100% O2 in an enclosed chamber at either normobaric or 3 atmospheric pressure. The tumors were irradiated with 630 nm laser during the hyper-oxygenation inside the chamber. Various light delivery rate was tested as listed below. To further distinguish the mechanisms how hyper-oxygenation manipulates tumor oxygenation, clamps/rubber band were used to stop blood flow into the tumor during a PDT treatment. Tumor responses to various hyper-oxygenation schemes have been investigated in following experimental groups:

• Control: no treatment as contro
• PDT200: PDT (200J/cm2, 150 mW/cm2) as treatment control
• PDT200-HBO: PDT (200J/cm2, 150 mW/cm2) in hyperbaric chamber (3 atp, 100% O2) (HPDT200)
• PDT200-O2: PDT (200J/cm2, 150 mW/cm2) in normobaric chamber (1 atp, 100% O2)
• 30HNPDT200: PDT (200J/cm2, 150 mW/cm2) in normobaric chamber as above, but with the 150 mW/cm2 light irradiation chopped into 30 seconds on/off cycle.
• 30PDT200: PDT (200J/cm2, 150 mW/cm2) in room air with the 150 mW/cm2 light irradiation chopped into 30 seconds on/off cycle.
• HNPDT200(75): PDT (200J/cm2, 75 mW/cm2) in hyperbaric chamber
• RPDT200: PDT (200J/cm2, 150 mW/cm2) with tumor leg clamped
• RHPDT: PDT (200J/cm2, 150 mW/cm2) in hyperbaric chamber and tumor leg clamped
• RHNPDT: PDT (200J/cm2, 150 mW/cm2) in normobaric chamber and tumor leg clamped
• PDT (50J/cm2, 150 mW/cm2) in hyperbaric chamber
• PDT (50J/cm2, 150 mW/cm2) in normobaric chamber
• Clamp Only: No PDT treatment, leg tumor clamped
• HBOonly: No PDT treatment, HBO only.

We also measured tumor oxygenation. An oxygen microelectrode was inserted into tumor hypoxic region and tissue pO2 was continuously recorded in all phases of a PDT/Hyper-oxygenation treatment.

Results and Discussion:

Figure 1 shows a typical dynamic changes of tumor pO2 during a PDT/Hyper-oxygenation treatment. Note that the oxygen electrode is linearly calibrated between 0-50 mmHg. We have confirmed that tumor oxygenation can be directly manipulated by subjecting tumor bearing animals to various hyper-oxygenation conditions. When animals are treated in either normo- or hyperbaric oxygen chamber, their tumor oxygen level in previous hypoxic region can be improved significantly. PDT treatment can reduce tumor pO2 level, but not to diminish it.

The results from leg tumors treated with 200J/cm2 (bolded groups above) are summarized in Figure 2. It clearly shows that hyper-oxygenation enhances tumor response to a PDT treatment. In specific:

1. Hyperoxygenation PDT (by combining PDT with either hyper- or normobaric oxygen) significantly increases tumor control.
2. In the investigated tumor system, combining PDT and hyperoxygenation is more effective than delivering the PDT treatment only with either fractionating light dose or reducing dose rate.
3. PDT treatment in a normobaric oxygen chamber is at least as effective, maybe even more, than PDT delivered in hyperbaric oxygen chamber.
4. Clamping the blood supply to the tumor during hyperoxygenation/PDT significantly reduces the effectiveness of the treatment, suggesting systematic improvement of oxygen delivery is a key mechanism in the modality.