Hypoxic cell sensitizers and heavy charged-particle radiations

Area of Science:

• Radiation biology
• Radiooncology
• Biophysics

Background:

• The oxygen enhancement ratio (OER) quantifies the increased biological effectiveness of radiation under aerobic conditions compared to hypoxic conditions.
• Hypoxic cells are common in solid tumors and are resistant to radiation therapy.
• Hypoxic-cell sensitizers are drugs designed to mimic the effect of oxygen, increasing the radiosensitivity of hypoxic cells.

Purpose of the Study:

• To investigate the effect of hypoxic-cell sensitizers on the OER of various types of radiation, including X-rays and energetic ion beams.
• To determine the potential benefit of these sensitizers in radiotherapy, particularly when using high linear energy transfer (LET) radiation.

Main Methods:

• Stationary-phase Chinese hamster V-79 cells were irradiated with 250 kV X-rays and Bragg peaks of He-, C-, Ne-, and A-ion beams.
• Cells were suspended in air-saturated and nitrogen-saturated medium, with and without hypoxic-cell sensitizers (metronidazole and misonidazole).
• Survival curves were generated to calculate OERs for each radiation type and condition.

Main Results:

• The OERs for X-rays without sensitizers were 2.0 (with metronidazole) and 1.6 (with misonidazole).
• The OERs for He-, C-, Ne-, and A-ion Bragg peaks without sensitizers were 2.4, 1.7, 1.6, and 1.4, respectively.
• The presence of hypoxic-cell sensitizers consistently reduced the measured OERs for all radiation types tested.

Conclusions:

• Hypoxic-cell sensitizers effectively reduce the OER across different radiation types, including high LET ion beams.
• These findings support the use of hypoxic-cell sensitizers in radiotherapy, especially when employing high LET radiation, to enhance tumor cell killing.