Sequentially-induced responses define tumour cell radiosensitivity.

Area of Science:

• Radiation biology
• Cellular biology
• Cancer research

Background:

• Understanding cellular radiosensitivity is crucial for optimizing radiation therapy.
• Existing models like the Hit-target (HT) and Linear-quadratic (LQ) models provide frameworks for radiosensitivity.
• Genotype and dose significantly influence cellular responses to radiation.

Purpose of the Study:

• To define dose-dependent and genotype-dependent components of radiosensitivity.
• To resolve patterns of radiation-induced clonal inactivation into specific cellular responses.
• To investigate the relationship between cellular responses and established radiobiological models.

Main Methods:

• Examined radiosensitivity and genotype in 10 tumor cell lines.
• Identified specific radiation doses triggering changes in clonogenic inactivation rates.
• Analyzed inactivation patterns using log-linear functions and compared them to HT and LQ models.
• Assessed cell-cycle redistribution and apoptosis as components of radiosensitivity.

Main Results:

• Identified four sequential, genotype-independent responses: hypersensitive (H), resistant (R), induced repair (alpha*), and sensitive (omega*).
• Specific dose ranges were associated with each response: H (0-0.10 Gy), R (0.1-0.2 Gy), alpha* (≥0.2 Gy), and omega* (≥3.0 Gy).
• Log-linear patterns fitted H, alpha*, and omega* responses, but not the R response.

Conclusions:

• Cellular radiosensitivity is composed of four distinct, sequentially induced responses.
• H and R responses are linked to low-dose hyper-radiosensitivity and early apoptosis.
• Alpha* and omega* responses align with HT and LQ models, associated with post-repair apoptosis.
• Radiation induces these responses at consistent doses across all cells, but inactivation rates are genotype-dependent.