Additive antitumor effect of arsenic trioxide with exposure to ionizing radiation to human acute promyelocytic leukemia HL­60 cells.

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 radiation­resistant HL60 (Res­HL60) cell line was generated by subjecting the native cells to 4­Gy irradiation every week for 4 weeks. The half­maximal 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 Res­HL60 was 2.24 µM (R2=0.91). IR exposure increased the sub­G1 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 sub­G1 phase was examined in greater detail, the sub­G1 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. Res­HL60 supplemented with ATO showed a higher rate of sub­G1 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 Res­HL60 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 Res­HL60 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.

Dose-dependent expression of extracellular microRNAs in HCT116 colorectal cancer cells exposed to high-dose-rate ionising radiation.

Biomarkers of tumour response to radiotherapy may help optimise cancer treatment. The aim of the present study was to identify changes in extracellular microRNAs (miRNAs) as a biomarker of radiation-induced damage to human colorectal cancer cells. HCT116 cells were exposed to increasing doses of X-rays, and extracellular miRNAs were analysed by microarray. The results were correlated with the frequency of micronuclei. A total of 59 miRNAs with a positive correlation and 4 with a negative correlation between dose (up to 6 Gy) and extracellular miRNA expression were identified. In addition, for doses between 0 and 10 Gy, 12 miRNAs among those 59 miRNAs with a positive correlation were identified; for these extracellular miRNAs, a significantly positive correlation was observed between their expression and the frequency of micronuclei for doses up to 10 Gy. These results suggest that specific miRNAs may be considered as cell damage markers and may serve as secreted radiotherapy response biomarkers for colorectal cancer; however, the results must be further validated in serum samples collected from patients undergoing radiotherapy.

[Screening for Biological Marker of Dose-optimization in Cancer Radiotherapy].

PURPOSE AND METHODS: External radiotherapy of target regions using high-energy beams leads to excessive exposure along with individual variation in therapeutic and adverse effects. However, high-precision radiotherapy utilizes 3D-multi detector computed tomography to confirm both target position and administer radiation dose. To install the individual bioinformation in the radiotherapy plan (particularly, radiosensitivity into the target region and/or the around normal tissue), the investigation of biomarkers, which are able to estimate their radiosensitivity was performed. The aim of this investigation is to screen for suitable radiosensitivity biomarkers using the human colorectal cancer-derived HCT 116 cell line. RESULTS: We found that cell damage and micronucleus frequency significantly increased dose dependently after exposure to 6 Gy X-irradiation (1 Gy/min). In contrast, total RNA concentration (69.8-85.2 ng/ml) remained stable in the cell culture supernatant despite radiation dose variation. Additionally, 52 specific micro RNAs were detected after exposure to 6 Gy X-irradiation. CONCLUSION: These results suggest that radiosensitivity, including extent of cellular damage in target or normal tissue, can be indirectly estimated by monitoring the expression of micro RNAs.

A radioresistant fraction of acute promyelocytic leukemia cells exhibit CD38 cell-surface antigen and mRNA expression.

In the present study, the cell viability and cluster of differentiation (CD)38 mRNA expression were evaluated in radioresistant (Res)-HL60 acute promyelocytic leukemia (APL) cells. Cell viability in Res-HL60 cells was higher compared with wild-type HL60 cells, but did not differ between high and mid/low CD38 antigen expression groups in Res-HL60 cells. A higher expression of CD38 mRNA in Res-HL60 cells was observed, particularly in the CD38high cell subpopulation. Furthermore, the expression of CD38 mRNA was upregulated following exposure to X-irradiation. In contrast, the characteristic expression of CD45 and CCAAT/enhancer-binding protein α mRNA were not altered. These results suggest that the accumulation of CD38 protein in radioresistant APL cells, resulting from the constant expression of CD38 mRNA induced by X-irradiation, is a characteristic response of the radioresistant-surviving fraction; however, the accumulation of CD38 did not influence the extent of radioresistant behavior.