Changes in tumor interstitial pressure induced by photodynamic therapy

Area of Science:

• Oncology
• Biomedical Engineering
• Pharmacology

Background:

• Photodynamic therapy (PDT) is a cancer treatment modality.
• Tumor interstitial pressure dynamics are crucial for drug delivery and treatment efficacy.
• Understanding pressure changes during PDT can optimize therapeutic strategies.

Purpose of the Study:

• To investigate the changes in tumor interstitial pressure during and after photodynamic therapy (PDT).
• To elucidate the mechanisms underlying these pressure changes using pharmacological inhibitors.
• To determine the role of thromboxane and serotonin in PDT-induced interstitial pressure variations.

Main Methods:

• Subcutaneous chondrosarcoma tumors were implanted in rats.
• Animals received Photofrin II and were exposed to 630 nm light.
• Tumor interstitial pressure was monitored using implanted chambers and transducers.
• Indomethacin (thromboxane inhibitor) and Ketanserin (serotonin antagonist) were administered prior to light treatment.

Main Results:

• PDT induced an initial decrease followed by a rapid rise in tumor interstitial pressure.
• Effective pressure modification was observed with specific porphyrin and light doses.
• Indomethacin abolished the pressure increase post-treatment, while Ketanserin blocked the initial decrease.
• Higher doses of porphyrin or light did not lead to further pressure increases.

Conclusions:

• Two independent mechanisms contribute to the observed pressure changes during PDT.
• Serotonin release appears to play a significant role in the pressure elevation component of PDT.
• Thromboxane synthesis inhibition prevents the post-treatment pressure rise.