Radiation Therapy And Its Effect On the Cell Cycle
Radiation exposure can greatly alter cells. These effects may involve gross biological and physiological aberrations. Typically such changes are pathologic in nature. Nonetheless, radiation may be employed for therapeutic purposes. Changes in the cell cycle which contribute to cell death can potentially be used in the treatment of cancer.
The various forms of radiation include ionizing radiation, non-ionizing radiation, and electromagnetic fields. All of these different types have been shown both in vivo and in vitro to significantly alter cells (14:1135). Among the various treatment modalities for cancer, ionizing radiation (e.g., gamma-radiation or U.V. light), in particular, alters cells' ability to reproduce. This ultimately leads to cell death.
A typical eukaryotic response to ionizing radiation includes growth arrest, DNA repair, and lethality (1:637-642). In general, cell cycle perturbations corresponding to cellular changes appear early. Such damage may be inflicted before chromosome damage, mitosis, and mitotic death occur (15:59-74). Mammalian cells' sensitivity to ionizing radiation has been found to depend largely on their position in the cell cycle. While variation does exist among different cell lines, cells exposed in the G1 phase of the cell cycle can be the most vulnerable under certain conditions (4:23-38). In addition, early studies demonstrated that cells often experience a period of radiosensitivity as they progress from G1 into early S-phase (12:857). These same studies observed, however, that cells in late S phase exhibit increased resistance to radiation. Such results imply that cell cultures which are artificially enriched in either the S or the early G2 cell cycle phases might be less sensitive to the cytotoxic and mutagenic effects of radiation exposure. Unfortunately though, the various effects of radiation on the c...