Department of Neurosurgery of Xijing Hospital, Fourth Military Medical University, Xi'an, Shaanxi 710032, PR China.
BMC Cancer. 2010 Dec 2;10:661. doi: 10.1186/1471-2407-10-661.
Boron neutron capture therapy (BNCT) is an alternative treatment modality for patients with glioma. The aim of this study was to determine whether induction of apoptosis contributes to the main therapeutic efficacy of BNCT and to compare the relative biological effect (RBE) of BNCT, γ-ray and reactor neutron irradiation.
The neutron beam was obtained from the Xi'an Pulsed Reactor (XAPR) and γ-rays were obtained from [60Co] γ source of the Fourth Military Medical University (FMMU) in China. Human glioma cells (the U87, U251, and SHG44 cell lines) were irradiated by neutron beams at the XAPR or [60Co] γ-rays at the FMMU with different protocols: Group A included control nonirradiated cells; Group B included cells treated with 4 Gy of [60Co] γ-rays; Group C included cells treated with 8 Gy of [60Co] γ-rays; Group D included cells treated with 4 Gy BPA (p-borono-phenylalanine)-BNCT; Group E included cells treated with 8 Gy BPA-BNCT; Group F included cells irradiated in the reactor for the same treatment period as used for Group D; Group G included cells irradiated in the reactor for the same treatment period as used for Group E; Group H included cells irradiated with 4 Gy in the reactor; and Group I included cells irradiated with 8 Gy in the reactor. Cell survival was determined using the 3-(4,5-dimethylthiazol-2-yl-2,5-diphenyltetrazolium (MTT) cytotoxicity assay. The morphology of cells was detected by Hoechst33342 staining and transmission electron microscope (TEM). The apoptosis rate was detected by flow cytometer (FCM). The level of Bcl-2 and Bax protein was measured by western blot analysis.
Proliferation of U87, U251, and SHG44 cells was much more strongly inhibited by BPA-BNCT than by irradiation with [60Co] γ-rays (P < 0.01). Nuclear condensation was determined using both a fluorescence technique and electron microscopy in all cell lines treated with BPA-BNCT. Furthermore, the cellular apoptotic rates in Group D and Group E treated with BPA-BNCT were significantly higher than those in Group B and Group C irradiated by [60Co] γ-rays (P < 0.01). The clonogenicity of glioma cells was reduced by BPA-BNCT compared with cells treated in the reactor (Group F, G, H, I), and with the control cells (P < 0.01). Upon BPA-BNCT treatment, the Bax level increased in glioma cells, whereas Bcl-2 expression decreased.
Compared with γ-ray and reactor neutron irradiation, a higher RBE can be achieved upon treatment of glioma cells with BNCT. Glioma cell apoptosis induced by BNCT may be related to activation of Bax and downregulation of Bcl-2.
硼中子俘获治疗(BNCT)是治疗脑胶质瘤患者的一种替代治疗方法。本研究旨在确定细胞凋亡的诱导是否有助于 BNCT 的主要治疗效果,并比较 BNCT、γ射线和反应堆中子照射的相对生物效应(RBE)。
中子束由西安脉冲堆(XAPR)获得,γ射线由中国第四军医大学(FMMU)的[60Co]γ源获得。用人脑胶质瘤细胞(U87、U251 和 SHG44 细胞系)进行不同方案的中子束照射:A 组包括未照射的对照细胞;B 组包括用 4 Gy[60Co]γ射线处理的细胞;C 组包括用 8 Gy[60Co]γ射线处理的细胞;D 组包括用 4 Gy BPA(对-硼苯丙氨酸)-BNCT 处理的细胞;E 组包括用 8 Gy BPA-BNCT 处理的细胞;F 组包括在反应堆中照射相同治疗期的细胞,与 D 组相同;G 组包括在反应堆中照射相同治疗期的细胞,与 E 组相同;H 组包括在反应堆中用 4 Gy 照射的细胞;I 组包括在反应堆中用 8 Gy 照射的细胞。用 3-(4,5-二甲基噻唑-2-基)-2,5-二苯基四唑(MTT)细胞毒性测定法测定细胞存活情况。用 Hoechst33342 染色和透射电子显微镜(TEM)检测细胞形态。用流式细胞仪(FCM)检测细胞凋亡率。用 Western blot 分析检测 Bcl-2 和 Bax 蛋白水平。
与用[60Co]γ射线照射相比,BPA-BNCT 对 U87、U251 和 SHG44 细胞的增殖抑制作用更强(P<0.01)。所有用 BPA-BNCT 处理的细胞系均通过荧光技术和电子显微镜检测到核浓缩。此外,用 BPA-BNCT 处理的 D 组和 E 组的细胞凋亡率明显高于用[60Co]γ射线照射的 B 组和 C 组(P<0.01)。与反应堆中的处理组(F、G、H、I)和对照组相比,BPA-BNCT 降低了胶质瘤细胞的克隆形成能力(P<0.01)。用 BPA-BNCT 处理后,胶质瘤细胞中的 Bax 水平增加,而 Bcl-2 表达减少。
与γ射线和反应堆中子照射相比,BNCT 治疗脑胶质瘤细胞可获得更高的 RBE。BNCT 诱导的胶质瘤细胞凋亡可能与 Bax 的激活和 Bcl-2 的下调有关。