Radiotherapy (RT) treats cancer effectively with high doses of ionizing radiation (IR) to killing cancer cells and shrinking tumors while bearing the risk of developing different side effects, including secondary cancer, which is most concerning for long-term health consequences. Genomic instability (GI) is a characteristic of most cancer cells, and IR-induced GI can manifest as delayed homologous recombination (HR). Radioadaptive response (RAR) is capable of reducing genotoxicity, cell transformation, mutation, and carcinogenesis, but the rational evidence describing its contributions to the reduction of radiation risk, in particular, carcinogenesis, remains fragmented. In this work, to investigate the impact of RAR on high-dose, IR-induced GI measured as delayed HR, the frequency of recombinant cells was comparatively studied under RAR-inducible and -uninducible conditions in the nucleated cells in hematopoietic tissues (bone marrow and spleen) using the
Rosa26
Direct Repeat-green fluorescent protein (RaDR-GFP) homozygote mice. Results demonstrated that the frequency of recombinant cells was significantly lower in hematopoietic tissues under RAR-inducible condition. These findings suggest that reduction in delayed HR may be at least a part of the mechanisms underlying decreased carcinogenesis by RAR, and application of RAR would contribute to a more rigorous and scientifically grounded system of radiation protection in RT.
The research and development (R&D) of radioprotective agents (RAs) have been conducting since seven decades ago, and the safety and protection against undesirable effects of ionizing radiation (IR) has become an important issue especially for the benefit of patients receiving the radiotherapy, in addition to the applications in nuclear industry, military, outer space exploration and accidental exposures. Although the technology advancement makes the radiotherapy a promising better treatment by maximizing the effect of IR to the cancer cells, there are still needs for improvement in minimizing the toxicity to the normal cells. Aiming at providing the new researchers in the radiation protection field with an overall view for R&D of the RAs, this mini-review elucidates in brief a general understanding of the IR and its effects on the cell, the concepts of radiotherapy and therapeutic ratio, the categories of RAs and their mechanisms, and discusses on the strategies and challenge for R&D of the RAs.
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