Factors governing hyperthermia-induced pH changes in Yoshida sarcomas

Area of Science:

• Oncology
• Biophysics
• Medical Physics

Background:

• Tumor acidity is a critical factor influencing treatment response.
• Understanding the tumor microenvironment during hyperthermia is essential for optimizing cancer therapy.

Purpose of the Study:

• To investigate the impact of localized ultrasound hyperthermia on tumor tissue acidification.
• To explore the influence of factors such as heating rate, tumor size, and tumor region on pH changes during hyperthermia.

Main Methods:

• Yoshida sarcomas were implanted in Sprague-Dawley rats.
• Tumor tissue pH was measured using miniaturized needle glass pH electrodes.
• Localized ultrasound hyperthermia (1.7 MHz, 44°C for 60 min) was applied under varying heating rates and tumor sizes.

Main Results:

• Normothermic tumor pH averaged 6.87 ± 0.21, with a peripheral-to-central pH gradient of 0.17.
• Hyperthermia reduced mean tumor pH to 6.71 ± 0.20.
• pH reduction was size-dependent, most pronounced in medium-sized tumors (2.4 g, ΔpH = 0.26).
• Slower heating rates (<0.7°C/min) resulted in more severe acidification (ΔpH = 0.40).
• Hyperthermia induced interstitial edema, particularly in smaller tumors (1.4 g).
• Systemic changes like increased perfusion pressure and elevated blood glucose may contribute to pH drop.

Conclusions:

• Localized ultrasound hyperthermia induces significant tumor tissue acidification.
• Heating rate and tumor size are key modulators of pH changes during hyperthermia.
• These findings highlight the dynamic changes in the tumor microenvironment under hyperthermia, potentially affecting treatment efficacy.