The effect of hyperthermia on vascular function, pH, and cell survival

Area of Science:

• Oncology
• Physiology
• Biomedical Engineering

Background:

• Hyperthermia is a cancer treatment modality that uses heat to damage and kill cancer cells.
• Understanding the physiological response of tumors and surrounding tissues to hyperthermia is crucial for optimizing treatment efficacy.
• Tumor blood flow plays a significant role in heat distribution and oxygenation, impacting treatment outcomes.

Purpose of the Study:

• To investigate the effects of hyperthermia on blood flow, temperature, and pH in rodent tumors and surrounding normal tissues.
• To explore the relationship between vascular changes, physiological parameters, and tumor cell viability following hyperthermia treatment.

Main Methods:

• Rats bearing Walker tumors and mice bearing SCK tumors were subjected to controlled hyperthermia at various temperatures (41.5-45.0°C) for one hour.
• Blood flow was measured in skin, muscle, and tumors using established techniques.
• Tumor and muscle temperatures were monitored, and tissue pH was assessed.
• Clonogenic cell assays were performed on tumor samples post-hyperthermia.

Main Results:

• Heating at 43°C significantly increased blood flow in rat skin and muscle (3-4 fold), but not in Walker tumors.
• Walker tumor blood flow decreased after heating at 45°C.
• Walker tumors exhibited higher temperatures than surrounding muscle during heating, attributed to reduced blood flow and inefficient heat dissipation.
• Severe vascular occlusion was observed in SCK tumors after heating.
• Tumor pH decreased significantly, while muscle pH increased during hyperthermia.
• In situ hyperthermia resulted in a continuous decrease in clonogenic tumor cell number.

Conclusions:

• Hyperthermia induces differential effects on blood flow in tumors versus normal tissues, potentially impairing heat dissipation in tumors.
• Tumor vascular occlusion and increased acidity following hyperthermia contribute to progressive tumor cell death.
• These findings highlight the complex physiological responses to hyperthermia and suggest mechanisms underlying its anti-tumor effects.