Purpose: Radiation therapy (RT), by using ionizing radiation (IR), destroys cancer cells inducing DNA damage. Despite several studies are continuously performed to identify the best curative dose of IR, the role of dose-rate, IR delivered per unit of time, on tumor control is still largely unknown.

Materials and methods: Rhabdomyosarcoma (RMS) and prostate cancer (PCa) cell lines were irradiated with 2 or 10 Gy delivered at dose-rates of 1.5, 2.5, 5.5 and 10.1 Gy/min. Cell-survival rate and cell cycle distribution were evaluated by clonogenic assays and flow cytometry, respectively. The production of reactive oxygen species (ROS) was detected by cytometry. Quantitative polymerase chain reaction assessed the expression of anti-oxidant-related factors including NRF2, SODs, CAT and GPx4 and miRNAs (miR-22, -126, -210, -375, -146a, -34a). Annexin V and caspase-8, -9 and -3 activity were assessed to characterize cell death. Senescence was determined by assessing β-galactosidase (SA-β-gal) activity. Immunoblotting was performed to assess the expression/activation of: i) phosphorylated H2AX (γ-H2AX), markers of DNA double strand breaks (DSBs); ii) p19^Kip1/Cip1, p21^Waf1/Cip1 and p27^Kip1/Cip1, senescence-related-markers; iii) p62, LC3-I and LC3-II, regulators of autophagy; iv) ATM, RAD51, DNA-PKcs, Ku70 and Ku80, mediators of DSBs repair.

Results: Low dose-rate (LDR) more efficiently induced apoptosis and senescence in RMS while high dose-rate (HDR) necrosis in PCa. This paralleled with a lower ability of LDR-RMS and HDR-PCa irradiated cells to activate DSBs repair. Modulating the dose rate did not differently affect the anti-oxidant ability of cancer cells.

Conclusion: The present results indicate that a stronger cytotoxic effect was induced by modulating the dose-rate in a cancer cell-dependent manner, this suggesting that choose the dose-rate based on the individual patient’s tumor characteristics could be strategic for effective RT exposures.

目的：放射治疗（RT）通过使用电离辐射（IR）破坏癌细胞，诱导DNA损伤。尽管连续进行了多项研究以鉴定最佳的IR治疗剂量，但单位剂量IR剂量率对肿瘤控制的作用仍是未知之数。

材料和方法：用2或10 Gy照射横纹肌肉瘤（RMS）和前列腺癌（PCa）细胞系，以1.5、2.5、5.5和10.1 Gy / min的剂量率递送。细胞存活率和细胞周期分布分别通过克隆形成测定和流式细胞术评估。通过细胞计数检测活性氧（ROS）的产生。定量聚合酶链反应评估了抗氧化剂相关因子（包括NRF2，SOD，CAT和GPx4和miRNA）的表达（miR-22，-126，-210，-375，-146a，-34a）。评估膜联蛋白V和caspase-8，-9和-3活性来表征细胞死亡。通过评估β-半乳糖苷酶（SA-β-gal）活性来确定衰老。进行了免疫印迹以评估以下的表达/激活：i）磷酸化的H2AX（γ-H2AX），DNA双链断裂（DSB）的标记；ii）第19页^{Kip1 / Cip1}，p21 ^{Waf1 / Cip1}和p27 ^{Kip1 / Cip1}，衰老相关标记；iii）p62，LC3-I和LC3-II，自噬调节剂；iv）ATM，RAD51，DNA-PKcs，Ku70和Ku80，DSB修复的介体。

结果：低剂量率（LDR）可以更有效地诱导RMS凋亡和衰老，而PCa中高剂量率（HDR）坏死。这与LDR-RMS和HDR-PCa照射的细胞激活DSB修复的能力较低有关。调节剂量率并没有不同地影响癌细胞的抗氧化能力。

结论：目前的结果表明通过以癌细胞依赖性方式调节剂量率可以诱导更强的细胞毒性作用，这表明根据个体患者的肿瘤特征选择剂量率可能是有效RT暴露的策略。