吉林大学学报(医学版)  2018, Vol. 44 Issue (01): 52-57

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于雷, 王志成, 王铁君
YU Lei, WANG Zhicheng, WANG Tiejun
咖啡因联合电离辐射对沉默Chk-1肝癌干细胞的增殖抑制和凋亡诱导作用
Inhibitory effect of caffeine combined with ionizing radiation on proliferation of hepatocellular carcinoma stem cells silenced by Chk-1 and its apoptosis-induced effect
吉林大学学报(医学版), 2018, 44(01): 52-57
Journal of Jilin University (Medicine Edition), 2018, 44(01): 52-57
10.13481/j.1671-587x.20180110

文章历史

收稿日期: 2017-06-02
咖啡因联合电离辐射对沉默Chk-1肝癌干细胞的增殖抑制和凋亡诱导作用
于雷1 , 王志成2 , 王铁君1     
1. 吉林大学第二医院放疗科, 吉林 长春 130041;
2. 吉林大学公共卫生学院 卫生部放射生物学重点实验室, 吉林 长春 130021
[摘要]: 目的: 利用咖啡因联合X射线照射处理沉默检查点激酶1(Chk-1)的肝癌干细胞,通过检测细胞增殖、周期和凋亡,探讨二者对肝癌干细胞的协同杀伤效应。方法: 沉默Chk-1的慢病毒载体转染293T细胞,慢病毒感染肝癌HepG2细胞后,Western blotting检测Chk-1蛋白表达,确定沉默效果,同时设非靶对照,分别命名为HepG2-Chk-1和HepG2-control。利用悬浮培养法获得CD133高表达的肝癌干细胞,命名为S-HepG2-Chk-1和S-HepG2-control,分为对照组、咖啡因组、4 Gy组和咖啡因+4 Gy组,咖啡因作用后给予4 Gy X射线照射,分别利用MTT法检测细胞增殖活性,利用PI单染和Annexin Ⅴ-FITC双染流式细胞术检测细胞周期分布和凋亡率。结果: Western blotting法检测,慢病毒感染HepG2细胞后Chk-1蛋白表达明显降低,而非靶对照组则无明显变化,表明成功获得沉默Chk-1的HepG2细胞模型HepG2-Chk-1和非靶对照模型HepG2-control。将HepG2-Chk-1和HepG2-control细胞悬浮培养后,细胞内的CD133蛋白表达水平均升高,表明存在高比例的CD133+细胞,即肝癌干细胞。与对照组比较,咖啡因组和4 Gy组细胞增殖活性明显降低(P < 0.05或P < 0.01),G1/M期细胞百分率和凋亡率明显升高(P < 0.05或P < 0.01),且咖啡因组S期细胞百分率明显升高(P < 0.05),4 Gy组G0/G1期细胞百分率明显升高(P < 0.05或P < 0.01),咖啡因+4 Gy组协同作用更强。与S-HepG2-control细胞比较,咖啡因组和4 Gy组S-HepG2-Chk-1细胞增殖活性明显降低(P < 0.05或P < 0.01),细胞凋亡率明显升高(P < 0.05或P < 0.01),且G1/M期细胞百分率明显降低(P < 0.05或P < 0.01)。结论: 成功获得沉默Chk-1且CD133+的肝癌干细胞,咖啡因和X射线照射均能抑制细胞增殖和诱导凋亡,并增强G2/M期阻滞,且二者具有协同增强作用。
关键词: 咖啡因    X射线    肝肿瘤    肿瘤干细胞    细胞增殖    细胞凋亡    
Inhibitory effect of caffeine combined with ionizing radiation on proliferation of hepatocellular carcinoma stem cells silenced by Chk-1 and its apoptosis-induced effect
YU Lei1, WANG Zhicheng2, WANG Tiejun1     
1. Department of Radiotherapy, Second Hospital, Jilin University, Changchun 130041, China;
2. Key Laboratory of Radiobiology, Ministry of Health, School of Public Health, Jilin University, Changchun 130021, China
[Abstract]: Objective: To treat the hepatocellular carcinoma stem cells silenced by Chk-1 withcaffeine combined with 4 Gy X-ray irradiaition, and to explore their synergistic killing effects on the hepatocellular carcinoma stem cells by detecting the cell proliferation, cell cycle and apoptosis. Methods: The lentivirus silencing Chk-1 was transfected into the 293T cells; after the HepG2 cells were infected by the lentivirus, the Chk-1 protein expression was detected by Western blotting to confirm the silencing efficency, and non-target control was established, and HepG2-Chk-1 and HepG2-control were named.The cells highly expressed CD133 were cultured by suspension culture method, S-HepG2-Chk-1 and S-HepG2-control were named respectively.After the cells were treated by caffeine, they were irradiated by 4 Gy X-ray; the proliferation activity was measured by MTT, and the cell cycle distribution and the apoptotic rate were measured by PI single staining and AnnexinⅤ-FITC double staining using FCM, respectively.For proliferation, cell cycle and apoptosis assays, there were control, caffeine, 4 Gy and caffeine+4 Gy groups. Results: The Western blotting results showed that after the HepG2 cells were infected by lentivirus, the Chk-1 protein expression was significantly decreased, but it was not obvious in non-target control group, it demonstrated that the cell models HepG2-Chk-1 and HepG2-control were obtained successfully.After the HepG2-Chk-1 and HepG2-control cells were cultivated by suspension, the CD133 protein expression were increased, it demonstrated that there were high proportion of CD133+ cells, they were hepatocellular carcinoma stem cells.Compared with control group, the proliferation activities in caffeine group and 4 Gy group were significantly decreased (P < 0.05 or P < 0.01), the percentages of cells at G2/M phage and the apoptotic rates were significantly increased (P < 0.05 or P < 0.01), and the percentage of cells at S phage in caffeine group was significantly increased (P < 0.05);the percentage of cells at G0/G1 phage in 4 Gy group was increased (P < 0.05 or P < 0.01), the effect was more stronger in caffeine+4 Gy group.Compared with S-HepG2-control, the proliferation activities of S-HepG2-Chk-1 cells in caffeine group and 4 Gy group were decreased, the apoptotic rates were increased (P < 0.05 or P < 0.01), and the percentage of cells at G1/M phage was significantly decreased (P < 0.05 or P < 0.01). Conclusion: The hepatoccellular carcinoma stem cells silenced by Chk-1 with positive CD133 are obtained successfully; Caffeine combined with X-ray irradiation can inhibit the cell proliferation and induce the apoptosis, and enhance the G2/M arrest, and both of them have synergistic effects.
Key words: caffeine     X-ray     liver neoplasms     cancer stem cell     cell proliferation     apoptosis    

肝癌是全球5大常见肿瘤之一,放射治疗已经成为原发性肝癌的治疗手段,并在我国的原发性肝癌诊治指南得到推荐[1]。但是,由于肿瘤干细胞(cancer stem cell,CSC)的存在,导致肿瘤的复发和转移,而且是肿瘤放疗抵抗的重要原因之一[2],因此如何提高肝癌放疗效果成为目前研究的热点之一。肿瘤细胞受到辐射后,DNA的损伤如未修复则发生细胞凋亡[3],检查点激酶1(checkpoint kinase1,Chk-1)是一种进化上高度保守的丝氨酸/苏氨酸蛋白激酶,可有效调节细胞周期进程,具有重要的生理功能,当Chk-1被抑制后,则调控周期阻滞的功能消失,使其成为肿瘤治疗的重要靶点。另外,咖啡因(caffeine)是一种茶叶、可可豆和咖啡果中的提取物,近期研究显示其具有抗肿瘤作用,并且取得了较好的效果[4-6]。本研究探讨咖啡因增强辐射对沉默了Chk-1的CD133+肝癌HepG2细胞增殖、周期和凋亡的作用,为改善肝癌细胞放疗抵抗提供新的思路。

1 材料与方法 1.1 细胞株及主要试剂

人肝癌HepG2细胞和人肾上皮293T细胞由吉林大学公共卫生学院王志成博士惠赠。培养血清及高糖DMEM培养基(江苏恩莫阿塞生物技术有限公司),DMEM/F12培养基、靶向沉默Chk-1的慢病毒载体pGIPZ-Chk-1 shRNA(第6外显子)、非靶对照载体pGIPZ-control shRNA、质粒pMD2G和pSPAX2由吉林大学卫生部放射生物学重点实验室保存;转染试剂Lipofectamine 2000和B27(美国Invitrogen公司),puromycin、MTT试剂、咖啡因和碘化丙啶(PI)(美国Sigma公司),重组人碱性成纤维细胞生长因子(bFGF)和重组人表皮生长因子(EGF)(美国Peprtech公司),牛血清白蛋白(BSA)(美国Gbico公司),AnnexinⅤ-FITC凋亡检测试剂盒(南京凯基生物公司),CD133一抗(美国Abcam公司),GAPDH、Chk-1兔多克隆抗体和ECL发光试剂盒(美国Santa Cruz公司),辣根过氧化物酶标记的抗兔二抗(北京中山金桥公司),其他试剂为国产分析纯。

1.2 沉默Chk-1的HepG2细胞模型的建立

293T细胞接种6孔板,待80%~90%融合时,利用Lipofectamine 2000转染试剂将pGIPZ-Chk-1 shRNA、pMD2G和pSPAX2质粒共转染到293T细胞中,48和72 h收取上清液并利用0.45 μm滤膜过滤后加到培养于6孔板80%~90%融合的HepG2细胞中,共感染2次。通过观察绿色荧光的状态判定感染的效率,并加入50 g·L-1的puromycin 10 μL进行阳性筛选,将获得的细胞命名为HepG2-Chk-1,以pGIPZ-control作为非靶对照,命名为HepG2-control,冻存备用。

1.3 Western blotting法检测Chk-1蛋白的表达

收集HepG2、HepG2-Chk-1和HepG2-control组细胞,利用RIPA裂解细胞,总蛋白提取后进行定量,按照25 μg蛋白上样进行SDS-PAGE电泳,将蛋白转到硝酸纤维膜后,利用TBST配置的5%脱脂奶粉封闭1 h,4℃过夜GAPDH和Chk-1一抗孵育。含有0.05%Tween 20的TBST洗3次,每次5 min,辣根过氧化物酶标记的二抗37℃下孵育1 h,TBST洗3次,利用化学发光试剂ECL进行显像,并进行拍照分析。

1.4 沉默Chk-1的肝癌干细胞的获得

参照文献[7-8]进行肝癌干细胞的悬浮培养,DMEM/F12培养基中加入20 μg·L-1 EGF、10 μg·L-1 bFGF、2% B27、0.4% BSA、100 U· mL-1青霉素和100 mg·L-1链霉素,于37℃、5% CO2条件下培养,约6 d可形成悬浮球,采用Western blotting法检测CD133蛋白表达确定是否为肝癌干细胞,命名为S-HepG2-Chk-1细胞(沉默Chk-1的肝癌干细胞)和S-HepG2-control细胞(肝癌干细胞)。

1.5 细胞分组和照射

S-HepG2-Chk-1和S-HepG2-control细胞分别分为对照组、咖啡因(0.2 mmol·L-1)组、4 Gy组和4 Gy+咖啡因组。X射线照射采用X-RAD320生物辐照仪(美国PXI公司),照射条件:电压180 kV,电流12.0 mA,靶皮距70 cm,剂量率1.0 Gy·min-1,总剂量为4 Gy。

1.6 MTT法检测细胞增殖活性

收集各组肝癌干细胞悬浮球,0.25%胰蛋白酶消化后按照1× 104个/孔接种96孔板,参照1.4中的方法继续培养,12 h后加入终浓度为0.2 mmol·L-1的咖啡因,24 h后进行X射线照射,计为0 h,分别于4、12、24和48 h加入MTT试剂,再培养4 h后吸去上清,加DMSO到孔底结晶处,于酶标仪上490 nm处测定吸光度[A(490)]值,代表其增殖活性。

1.7 流式细胞术检测细胞周期

收集肝癌干细胞悬浮球,0.25%胰蛋白酶消化后按照4 × 105个/孔接种24孔板,参照1.4中的方法继续培养12 h后加入终浓度为0.2mmol·L-1的咖啡因,24 h后进行X射线照射,24 h后收集细胞,1 mol·L-1PBS洗2次,每个管中加入200 μLPI和100 μL RNaseA,轻微震荡混匀,室温条件避光20 min,上机收细胞,CellQuest软件收集,ModFit软件分析数据,结果以各期细胞百分率表示。

1.8 流式细胞术检测细胞凋亡率

收集各组肝癌干细胞悬浮球,0.25%胰蛋白酶消化后按照4 × 105个/孔接种24孔板,参照1.4中的方法继续培养,12 h后加入终浓度为0.2 mmol·L-1的咖啡因[9],24 h后进行X射线照射,24 h后收细胞,1 mol·L-1的PBS洗2次,每个管中加入5 μL PI和5 μL Annexin V-FITC试剂,混匀后避光10 min,上机收细胞,CellQuest软件收集数据,ModFit软件分析,细胞凋亡率以百分率表示。

1.9 统计学分析

采用SPSS 13.0统计软件进行统计学分析。细胞增殖活性、细胞周期百分率和凋亡率均符合正态分布,以x±s表示,两两比较采用两独立样本t检验。以P < 0.05表示差异有统计学意义。

2 结果 2.1 沉默Chk-1的HepG2细胞模型的鉴定

利用转染293T细胞获得的慢病毒感染HepG2细胞后获得稳定沉默Chk-1的细胞模型,通过Western blotting法检测Chk-1蛋白的表达。HepG2和非靶对照shRNA的HepG2细胞中均可见Chk-1蛋白的表达,而靶向沉默Chk-1的HepG2细胞中Chk-1蛋白低表达,表明本研究获得的沉默Chk-1的HepG2细胞模型成功。见图 1

Lane 1:HepG2cells; Lane 2:HepG2-control shRNA cells; Lane 3:HepG2-Chk-1 shRNA cells. 图 1 Western blotting法检测Chk-1蛋白表达电泳图 Figure 1 Electrophoregram of Chk-1 protein expression measured by Western blotting method
2.2 肝癌干洗胞悬浮球中CD133蛋白的表达

根据Yoshikawa等[10]报道,肝癌干细胞表面标志为CD133。在悬浮培养6 d后,收集细胞采用Western blotting法检测,HepG2-control和HepG2-Chk-1细胞中可见CD133蛋白表达,而将2种细胞悬浮培养后,CD133蛋白均高表达,提示细胞中高比例的CD133+细胞为肝癌干细胞。见图 2

Lane 1:HepG2-controlcells; Lane 2:HepG2-Chk-1 cells; Lane 3:S-HepG2-control cells; Lane 4:S-HepG2-Chk-1 cells. 图 2 Western blotting法检测CD133蛋白表达电泳图 Figure 2 Electrophoregram of CD133 protein expressions measured by Western blotting method
2.3 各组细胞增殖活性

采用MTT比色法检测细胞增殖活性。在相同时间点,与对照组比较,同一种细胞的增殖活性均明显降低(除了4 h时S-HepG2-control细胞)(P < 0.05或P < 0.01),且以咖啡因+ 4 Gy组的细胞活性最低;与S-HepG2-control细胞比较,48 h时对照组,4、12、24和48 h时咖啡因组,12、24和48 h时4 Gy组,以及4、12、24和48 h时咖啡因+4 Gy组S-HepG2-Chk-1细胞活性均明显降低(P < 0.01)。见表 1

表 1 各组沉默Chk-1的肝癌干细胞的增殖活性 Table 1 Proliferation activities of hepatocellular carcinoma stem cells silenced by Chk-1 in various groups
(n=6, x±s)
Group Cells A (490) value
(t/h)    4 12 24 48
Control S-HepG2-control 0.62±0.02 0.68±0.01 0.74±0.02 0.85±0.01
S-HepG2-Chk-1 0.62±0.01 0.67±0.02 0.71±0.01 0.80±0.01△△
Caffeine S-HepG2-control 0.60±0.01 0.64±0.01* 0.68±0.01* 0.69±0.02**
S-HepG2-Chk-1 0.56±0.02*△ 0.61±0.01*△ 0.63±0.02**△ 0.55±0.02**△△
4 Gy S-HepG2-control 0.54±0.02** 0.58±0.01** 0.63±0.01** 0.70±0.01**
S-HepG2-Chk-1 0.50±0.01** 0.53±0.01**△ 0.57±0.01**△ 0.59±0.01**△△
Caffeine + 4 Gy S-HepG2-control 0.41±0.02** 0.42±0.01** 0.54±0.01** 0.56±0.01**
S-HepG2-Chk-1 0.11±0.01**△△ 0.12±0.01**△△ 0.21±0.02**△△ 0.31±0.01**△△
* P < 0.05, * * P < 0.01 vs control group; P < 0.05, △△ P < 0.01 vs S-HepG2-control cells.
2.4 各组细胞不同细胞周期百分率

与对照组比较,咖啡因组S期和G2/M期细胞百分率明显增加(P < 0.05或P < 0.01),4 Gy组G0/G1期和G2/M期细胞百分率明显增加(P < 0.01);咖啡因+ 4 Gy组S期细胞百分率明显降低,而G2/M期细胞百分率明显增加(P < 0.05或P < 0.01)。与S-HepG2-control细胞比较,S-HepG2-Chk-1细胞G2/M期细胞百分率均明显降低(P < 0.05或P < 0.01)。见表 2

表 2 各组沉默Chk-1的肝癌干细胞不同周期细胞百分率 Table 2 Percentages of hepatocellular carcinoma stem cells silenced by Chk-1 at different phages in various groups
(n=3, x±s, η/%)
Group Cells Percentage of cells
G0/G1 S G2/M
Control S-HepG2-control 47.07±0.93 49.57±0.92 3.36±0.21
S-HepG2-Chk-1 53.95±0.35 45.00±0.34 1.05±0.06?
Caffeine S-HepG2-control 32.80±1.49** 60.43±1.62* 6.77±0.31**
S-HepG2-Chk-1 45.31±0.63**△ 49.24±0.71*△ 5.45±0.40*△
4 Gy S-HepG2-control 50.20±0.66* 31.84±1.33** 17.96±0.69**
S-HepG2-Chk-1 57.03±0.28**△ 33.00±0.47** 9.97±0.71**△△
Caffeine+4 Gy S-HepG2-control 34.67±0.92** 39.03±0.55** 26.30±1.11**
S-HepG2-Chk-1 50.14±0.87*△△ 30.85±0.49**△△ 19.01±0.47**△
* P < 0.05, * * P < 0.01 vs control group; P < 0.05, △△ P < 0.01 vs S-HepG2-control cells.
2.5 各组细胞凋亡率

与对照组比较,咖啡因组、4 Gy组和咖啡因+ 4 Gy组细胞凋亡率均明显增加(P < 0.05或P < 0.01),且咖啡因+ 4 Gy组增加最明显;与S-HepG2-control细胞比较,各组S-HepG2-Chk-1细胞凋亡率均明显增加(P < 0.05或P < 0.01)。见表 3图 3

表 3 各组沉默Chk-1的肝癌干细胞的凋亡率 Table 3 Apoptotic rates of hepatocellular carcinoma stem cells silenced by Chk-1 in various groups
(n=3, x±s, η/%)
Group Apoptotic rate
S-HepG2-control S-HepG2-Chk-1
Control 13.47±0.56 21.70±0.63△△
Caffeine 17.45±0.50* 25.33±1.42*△
4 Gy 24.95±0.82** 29.47±1.68*△
Caffeine+4 Gy 30.33±0.71** 49.40±0.71**△△
* P < 0.05, * * P < 0.01 vs control group; P < 0.05,
△△ P < 0.01 vs S-HepG2-control cells.
A-D:S-HepG2-control cells; E-H:S-HepG2-Chk-1 cells; A, E:Control group; B, F:Caffeine group; C, G:4 Gy group; D, H:Caffeine+4 Gy group. 图 3 流式细胞术检测各组肝癌干细胞凋亡率 Figure 3 Apoptotic rates of hepatocellular carcinoma stem cell in various groups detected by flow cytometry
3 讨论

CSC为肿瘤组织中存在的非常小比例的细胞,具有无限自我更新和增殖能力,维持细胞群的生命力。CSC长时间处于休眠状态,对肿瘤的存活、增殖、转移和复发具有重要作用,同时也是肿瘤放疗抵抗和化疗多药耐药的影响因素之一,以CSC为靶点的肿瘤治疗策略越来越引起重视[11-12]。原发性肝癌包括肝细胞癌和肝内胆管癌,有学者认为可能部分起源于肝癌干细胞。目前,识别CSC的表面标志物被认为是鉴定CSC的重要途径。肝癌干细胞具有多个表面标志物,如CD133、CD90、CD44、OV6和EpCAM等[13]。在本研究中悬浮培养6 d后,检测肝癌干细胞表面标志物CD133蛋白表达结果显示:与未悬浮的相同细胞比较,CD133蛋白呈高表达,提示有高比例的肝癌干细胞存在,为后续实验提供了保障。

肿瘤放疗时损伤细胞的一个重要的机制就是诱导DNA损伤,继而导致细胞最终走向死亡。DNA损伤时细胞周期Chk-1/2在限制细胞周期进展的DNA损伤反应通路中发挥重要作用[14]。肿瘤临床放疗时,往往因肿瘤细胞逃避了凋亡,使得以诱导细胞凋亡为目的的治疗方案效果降低,这与细胞周期检查点的活化关系密切。当细胞遭受DNA损伤剂作用时,Chk1被激活,致使细胞停留在S和G2/M期检查点,保证DNA有充足的时间完成修复,从而维持基因组的稳定性[15]。本研究中靶向Chk-1第6外显子的靶向RNAi慢病毒pGIPZ-Chk-1感染肝癌细胞HepG2后,Western blotting法检测结果显示:Chk-1蛋白表达大大降低,具有较好的沉默效果,而对照序列的慢病毒则不影响Chk-1蛋白的表达。另外,流式细胞术检测Chk-1被沉默的HepG2细胞和对照序列的HepG2细胞周期结果显示:G2/M期细胞百分率明显降低,表明经过悬浮培养后沉默Chk-1的细胞更少的处于G2/M期。

2013年,美国国家综合癌症网络(NCCN)肝癌诊治指南推荐:原发性肝癌患者无论肿瘤位于何处,都适合外照射放疗。我国也在肝癌诊治指南中推荐肝癌放疗,而肿瘤放疗与其他疗法的联合应用则具有更高的治疗效果。咖啡因广泛存在于茶叶、咖啡和其他饮料中,有研究[16]表明:咖啡因能够通过诱发细胞凋亡和抑制增殖实现抗肿瘤效应。放疗也可以诱导肿瘤细胞凋亡,因此本研究将二者结合以增加彼此的诱导凋亡作用,并且以沉默了Chk-1的肝癌干细胞为靶细胞。沉默了Chk-1后G2/M期细胞比例减少,而该细胞周期是对X射线最敏感的期,这将对放射效果产生影响,但从本研究结果来看,二者协同作用于沉默Chk-1的肝癌干细胞能明显提高其增殖抑制和凋亡促进效果。另外,咖啡因对于细胞周期的影响主要集中在S相延迟和G2/M期阻滞,而4 Gy照射则诱导G0/G1和G2/M期阻滞,对于逆转因缺少Chk-1调控周期检查点监控失调具有一定的作用。

综上所述,由沉默了Chk-1的HepG2细胞悬浮培养获得的肝癌干细胞G2/M期比例降低,本身不利于细胞维持正常化,但对于肿瘤来说,则有利于以此为突破口进行靶向治疗。咖啡因和电离辐射均可诱导细胞凋亡,二者联合应用大大增强了单一治疗的效果。本研究结果为肝癌的放射治疗提供了新的实验数据和思路。

参考文献
[1] 曾昭冲. 原发性肝癌放射治疗现状及前景[J]. 中国实用外科杂志, 2014, 34(8): 699–702.
[2] Burgess DJ. Stem cells:competitive behaviour of cancer mutations[J]. Nat Rev Cancer, 2014, 14(1): 5. DOI:10.1038/nrc3652
[3] Zhou ZR, Yang ZZ, Wang SJ, et al. The Chk1 inhibitor MK-8776 increases the radiosensitivity of human triple-negative breast cancer by inhibiting autophagy[J]. Acta Pharmacol Sin, 2017, 38(4): 513–523. DOI:10.1038/aps.2016.136
[4] Fujimaki S, Matsuda Y, Wakai T, et al. Blockade of ataxia telangiectasia mutated sensitizes hepatoma cell lines to sorafenib by interfering with Akt signaling[J]. Cancer Lett, 2012, 319(1): 98–108. DOI:10.1016/j.canlet.2011.12.043
[5] Kawano Y, Nagata M, Kohno T, et al. Caffeine increases the antitumor effect of Cisplatin in human hepatocellular carcinoma cells[J]. Biol Pharm Bull, 2012, 35(3): 400–407. DOI:10.1248/bpb.35.400
[6] Al-Ansari MM, Aboussekhra A. Caffeinemediates sustained inactivation of breast cancer-associated myofibroblasts via up-regulation of tumor suppressor genes[J]. PLoS One, 2014, 9(3): e90907. DOI:10.1371/journal.pone.0090907
[7] Wang L, Huang X, Zheng X, et al. Enrichment of prostate cancer stem-like cells from human prostate cancer cell lines by culture inserum-free medium and chemoradiotherapy[J]. Int J Biol Sci, 2013, 9(5): 472–479. DOI:10.7150/ijbs.5855
[8] Peng YC, Lu SD, Zhong JH, et al. Combination of 5-fluorouracil and 2-morphilino-8-phenyl-4H-chromen-4-one may inhibit livercancer stem cell activity[J]. Tumour Biol, 2016, 37(8): 10943–10958. DOI:10.1007/s13277-016-4915-3
[9] 刘寒旸, 宋军, 周艳, 等. 咖啡因与低剂量阿司匹林协同抑制结肠癌细胞生长的机制[J]. 中国癌症防治杂志, 2016, 8(6): 337–343.
[10] Yoshikawa S, Zen Y, Fujii T, et al. Characterization of CD133+ parenchymal cells in the liver:histology and culture[J]. World J Gastroenterol, 2009, 15(39): 4896–4906. DOI:10.3748/wjg.15.4896
[11] Kumazawa S, Kajiyama H, Umezu T, et al. Possible association between stem-like hallmark and radioresistance in human cervical carcinoma cells[J]. J Obstet Gynaecol Res, 2014, 40(5): 1389–1398. DOI:10.1111/jog.12357
[12] Han X, Du F, Jiang L, et al. A2780 human ovarian cancer cells with acquired paclitaxel resistance display cancer stem cell properties[J]. Oncol Lett, 2013, 6(5): 1295–1298. DOI:10.3892/ol.2013.1568
[13] 章健, 来维洁, 周秀梅, 等. 靶向肝癌干细胞的肿瘤治疗进展[J]. 中国细胞生物学学报, 2017, 39(1): 87–96. DOI:10.11844/cjcb.2017.01.0260
[14] Garrett MD, Collins I. Anticancer therapy with checkpoint inhibitors:what, where and when?[J]. Trends Pharmacol Sci, 2011, 32(5): 308–316. DOI:10.1016/j.tips.2011.02.014
[15] Carrassa L, Chilà R, Lupi M, et al. Combined inhibition of Chk1 and Wee1:in vitro synergistic effect translates to tumor growth inhibition in vivo[J]. Cell Cycle, 2012, 11(13): 2507–2517. DOI:10.4161/cc.20899
[16] Ku BM, Lee YK, Jeong JY, et al. Caffeine inhibits cell proliferation and regulates PKA/GSK3β pathways in U87MG human glioma cells[J]. Mol Cells, 2011, 31(3): 275–279. DOI:10.1007/s10059-011-0027-5