18F-FLT体外监测结肠癌细胞早期放射反应

18F-FLT uptake in human colorectal cancer cells in relation to early response to radiation therapy：an in vitro study

目的 评价18F-脱氧胸腺嘧啶核苷（FLT）监测结肠癌细胞早期放射反应的作用.方法 应用四甲基偶氮唑蓝（MTT）检测并绘制SW480细胞受X线照射后生长曲线,光学显微镜下观察细胞形态变化.流式细胞仪检测照射后肿瘤细胞增殖周期的重新分布.分别于体外细胞以及肿瘤内检测照射前、后细胞摄取18F-FLT的变化.将18F-FLT（0.05±0.01）MBq加入培养液孵育细胞,分别于30,60,90,120 min测定细胞摄取18F-FLT的放射性.经荷瘤裸鼠尾静脉注射18F-FLT（1.90±0.85）MBq（0.25 ml）,60 min后处死动物,切除肿瘤与肌肉、肺、肝等,测定肿瘤与其他脏器摄取放射性比值变化.应用单因素方差分析进行统计学处理.结果 X线照射后,SW480细胞增殖受到明显的抑制,呈剂量依赖性.细胞形态随照射剂量的不同发生不同的变化.照射后细胞周期发生重新分布.10 Gy组,S期细胞百分比24 h从33.23%降至15.19%,72 h后降至12.44%.20 Gy组,S期细胞百分比24 h后从33.23%降至9.24%,72 h后降至5.43%.体外摄取实验发现,注射后60 min,SW480细胞摄取18F-FLT百分比为（5.21±1.60）%,10 Gy照射24 h后下降至（4.27±0.48）%,72 h降至（3.39±0.59）%.20 Gy组：照射后24 h,SW480摄取的放射性百分比下降至（3.41±0.58）%,72 h后降至（1.63±0.49）%.两照射组在72 h内分别下降了34.94%,69.72%（24 h∶F=8.253,P=0.009;72 h∶F=36.715,P＜0.001）.单位质量肿瘤组织摄取的18F-FLT随照射剂量的增加而逐渐降低（10Gy组：F=12.388,P=0.007;20 Gy组：F=16.744,P=0.004）.结论 18F-FLT在结肠癌细胞内的摄取可以快速反映照射治疗后的细胞变化,18F-FLT可能用于检测结肠癌放射治疗早期反应.

Objective To evaluate whether 18F-fluorothymidine（FLT） can be used to monitor early response to irradiation in colorectal cancer （CRC）.Methods SW480 cells were cultured and irradiated with 0, 10, and 20 Gy.Twenty-four hours later, morphological changes, apoptosis, necrosis, proliferation,and cell cycle phases were observed.Uptake of 18F-FLT was measured in these tumors in vitro from 24 h to 72 h after irradiation.The one-way analysis of variance was used to analyze the data.Results Apoptotic and necrotic cells were detected 24 h after radiotherapy.SW480 cells proliferation was significantly delayed after irradiation in 3-（4,5-dimethylthiazol-2-yl）-2,5-diphenylte-trazolium bromide （MTI） assay.Cell cycle analysis showed that SW480 cells had a decreased fraction of cells in S phase（ from 33.23% to 9.24%,then to 5.43% ） and an arrested fraction in G0-G1.After SW480 cells were cultured for60 min, the uptake of 18F-FLT was （5.21 ± 1.60） % and 24 h after irradiation of 10 Gy, the uptake decreased significantly to （4.27±0.48）% （F=8.253, P=0.009）.And 72 h after irradiation, the uptake further decreased significantly to （3.39 ± 0.59） % （ F = 36.715, P〈0.001 ）.In tumor tissue, the uptake of 18F-FLT reduced significantly 72 h after radiotherapy （10 Gy：F = 12.388, P = 0.007 20 Gy：F = 16.744, P = 0.004） and the attenuation degree increased with the radiation dose.Conclusion The uptake of 18F-FLT in SW480 cells or in CRC could reflect the changes of SW480 cells in proliferation, cell cycle re-distribution, cell apoptosis and necrosis.The results suggest that 18F-FLT may be used for monitoring early response to irradiation of CRC.