Center for Radiological Research, College of Physician and Surgeons, Columbia University Medical Center, New York, New York.
State Key Laboratory of Radiation Medicine and Protection, School of Radiation Medicine and Protection, Institute of Space Life Sciences, Medical College of Soochow University, Collaborative Innovation Center of Radiological Medicine of Jiangsu Higher Education Institutions, Suzhou 215123, China.
Radiat Res. 2022 Jun 1;197(6):569-582. doi: 10.1667/RADE-21-00181.1.
Radiation therapy (RT) plays an important role in cancer treatment. The clinical efficacy of radiation therapy is, however, limited by normal tissue toxicity in areas surrounding the irradiated tumor. Compared to conventional radiation therapy (CONV-RT) in which doses are typically delivered at dose rates between 0.03-0.05 Gy/s, there is evidence that radiation delivered at dose rates of orders of magnitude higher (known as FLASH-RT), dramatically reduces the adverse side effects in normal tissues while achieving similar tumor control. The present study focused on normal cell response and tested the hypothesis that proton-FLASH irradiation preserves mitochondria function of normal cells through the induction of phosphorylated Drp1. Normal human lung fibroblasts (IMR90) were irradiated under ambient oxygen concentration (21%) with protons (LET = 10 keV/µm) delivered at dose rates of either 0.33 Gy/s or 100 Gy/s. Mitochondrial dynamics, functions, cell growth and changes in protein expression levels were investigated. Compared to lower dose-rate proton irradiation, FLASH-RT prevented mitochondria damage characterized by morphological changes, functional changes (membrane potential, mtDNA copy number and oxidative enzyme levels) and oxyradical production. After CONV-RT, the phosphorylated form of Dynamin-1-like protein (p-Drp1) underwent dephosphorylation and aggregated into the mitochondria resulting in mitochondria fission and subsequent cell death. In contrast, p-Drp1 protein level did not significantly change after delivery of similar FLASH doses. Compared with CONV irradiation, FLASH irradiation using protons induces minimal mitochondria damage; our results highlight a possible contribution of Drp1-mediated mitochondrial homeostasis in this potential novel cancer treatment modality.
放射治疗（RT）在癌症治疗中起着重要作用。然而，由于辐射肿瘤周围正常组织的毒性，放射治疗的临床疗效受到限制。与常规放射治疗（CONV-RT）相比，CONV-RT 的剂量通常以 0.03-0.05Gy/s 的剂量率提供，有证据表明，以更高数量级（称为 FLASH-RT）的剂量率提供的辐射，在实现类似肿瘤控制的同时，大大降低了正常组织的不良反应。本研究侧重于正常细胞反应，并测试了以下假设：质子 FLASH 照射通过诱导磷酸化 Drp1 来维持正常细胞的线粒体功能。正常人类肺成纤维细胞（IMR90）在环境氧浓度（21%）下用质子（LET=10keV/μm）照射，剂量率分别为 0.33Gy/s 或 100Gy/s。研究了线粒体动力学、功能、细胞生长和蛋白质表达水平的变化。与低剂量率质子照射相比，FLASH-RT 可防止线粒体损伤，其特征为形态变化、功能变化（膜电位、mtDNA 拷贝数和氧化酶水平）和氧自由基产生。在 CONV-RT 后，Dynamin-1 样蛋白（p-Drp1）的磷酸化形式经历去磷酸化并聚集到线粒体中，导致线粒体裂变和随后的细胞死亡。相比之下，在提供类似的 FLASH 剂量后，p-Drp1 蛋白水平没有显著变化。与 CONV 照射相比，质子的 FLASH 照射诱导最小的线粒体损伤；我们的结果强调了 Drp1 介导的线粒体动态平衡在这种潜在的新型癌症治疗模式中的可能贡献。
