三氧化二砷（ATO）有望成为一种针对急性早幼粒细胞白血病（APL）（急性髓系白血病的一种）具有抗肿瘤活性的化学药物。在日本，其抗肿瘤作用已在APL临床试验中得到证实，并已在世界各国获得批准。然而，目前还没有关于ATO对放射抗性白血病细胞的抗肿瘤作用的报道，这种抗肿瘤作用可以在放射治疗过程中以及与治疗性放射束联合使用时产生。本研究旨在阐明 ATO 对具有抗辐射能力的 APL 细胞的抗肿瘤作用，并确定其与电离辐射 (IR) 联合使用时的疗效。抗辐射 HL60 (Res-HL60) 细胞系是通过将天然细胞每周接受 4 Gy 照射，持续 4 周而产生的。 ATO 对天然细胞的细胞增殖半数抑制浓度 (IC50) 为 0.87 µM (R2=0.67)，而 ATO 对 Res-HL60 的细胞增殖半数抑制浓度 (IC50) 为 2.24 µM (R2=0.91)。红外线照射增加了两种细胞系的亚 G1 和 G2/M 期比率。添加 ATO 导致 24 小时而不是 48 小时后 G2/M 群体增多。当更详细地检查亚 G1 期的变化率时，两个不含 ATO 的对照细胞的亚 G1 期在 24 小时暴露于 IR 后显着增加，但仅在 2 Gy 照射的条件下，它才显着增加。 48 h 继续增加。补充 ATO 的 Res-HL60 在 24 小时显示出更高的亚 G1 变化率；然而，2 Gy 照射导致与对照相比有所下降。 ATO孵育24 h后，细胞G2/M期比例显着增加，2 Gy照射引起更大的增加。为了确定细胞增殖的抑制和细胞周期破坏是否与活性氧 (ROS) 活性有关，使用流式细胞术测定细胞内 ROS 水平。尽管在没有照射的情况下，Res-HL60的ROS水平高于天然细胞，但在0.5或2 Gy照射后，它们没有变化。此外，在 Res-HL60 中添加 ATO 会降低细胞内 ROS 水平。这些发现提供了重要信息，即抗辐射白血病细胞对 ATO 的抗肿瘤作用和 IR 的联合作用的反应不同。

Arsenic trioxide (ATO) is expected to be a chemical drug with antitumor activity against acute promyelocytic leukemia (APL), a type of acute myeloid leukemia. In Japan, its antitumor effects were confirmed in clinical trials for APL, and it has been approved in various countries around the world. However, there have been no reports on ATO's antitumor effects on radioresistant leukemia cells, which can be developed during radiotherapy and in combination with therapeutic radiation beams. The present study sought to clarify the antitumor effect of ATO on APL cells with radiation resistance and determine its efficacy when combined with ionizing radiation (IR). The radiation‑resistant HL60 (Res‑HL60) cell line was generated by subjecting the native cells to 4‑Gy irradiation every week for 4 weeks. The half‑maximal inhibitory concentration (IC50) for cell proliferation by ATO on native cell was 0.87 µM (R2=0.67), while the IC50 for cell proliferation by ATO on Res‑HL60 was 2.24 µM (R2=0.91). IR exposure increased the sub‑G1 and G2/M phase ratios in both cell lines. The addition of ATO resulted in a higher population of G2/M after 24 h rather than 48 h. When the rate of change in the sub‑G1 phase was examined in greater detail, the sub‑G1 phase in both control cells without ATO significantly increased by exposure to IR at 24 h, but only under the condition of 2 Gy irradiation, it had continued to increase at 48 h. Res‑HL60 supplemented with ATO showed a higher rate of sub‑G1 change at 24 h; however, 2 Gy irradiation resulted in a decrease compared with the control. There was a significant increase in the ratio of the G2/M phase in cells after incubation with ATO for 24 h, and exposure to 2 Gy irradiation caused an even greater increase. To determine whether the inhibition of cell proliferation and cell cycle disruptions is related to reactive oxygen species (ROS) activity, intracellular ROS levels were measured with a flow cytometric assay. Although the ROS levels of Res‑HL60 were higher than those of native cells in the absence of irradiation, they did not change after 0.5 or 2 Gy irradiation. Furthermore, adding ATO to Res‑HL60 reduced intracellular ROS levels. These findings provide important information that radioresistant leukemia cells respond differently to the antitumor effect of ATO and the combined effect of IR.