Boron neutron capture therapy induces apoptosis of glioma cells through Bcl-2/Bax.
BACKGROUND
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.


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
Department of Neurosurgery of Xijing Hospital, Fourth Military Medical University, Xi'an, Shaanxi 710032, PR China.
Peng
P
Wang
Haining
H
Zhen
Xinbiao
X
Jiang
Wei
W
Zhang
Xin
X
Cheng
Geng
G
Guo
Xinggang
X
Mao
Xiang
X
Zhang
D017209:Apoptosis / Q000528:radiation effects*; D015153:Blotting, Western; D001896:Boron Compounds / Q000494:pharmacology; D016754:Boron Neutron Capture Therapy; D001932:Brain Neoplasms / Q000378:metabolism* / Q000473:pathology; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D048430:Cell Shape; D002470:Cell Survival; D003037:Cobalt Radioisotopes; D004307:Dose-Response Relationship, Radiation; D005434:Flow Cytometry; D005720:Gamma Rays; D005909:Glioblastoma / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D046529:Microscopy, Electron, Transmission; D009502:Neutrons; D010649:Phenylalanine / Q000031:analogs & derivatives / Q000494:pharmacology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology; D013997:Time Factors; D051028:bcl-2-Associated X Protein / Q000378:metabolism*
C494826:BAX protein, human; D001896:Boron Compounds; D003037:Cobalt Radioisotopes; D019253:Proto-Oncogene Proteins c-bcl-2; D011838:Radiation-Sensitizing Agents; D051028:bcl-2-Associated X Protein; D010649:Phenylalanine; C033685:4-boronophenylalanine