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

Abstract

BackgroundBoron 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.MethodsThe 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.ResultsProliferation 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.ConclusionsCompared 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.

Apoptosis through Bcl-2/Bax and Cleaved Caspase Up-Regulation in Melanoma Treated by Boron Neutron Capture Therapy

“…These data confirm apoptosis after BNCT, as also noted by Masunaga [20], [21], Wang [32] and Fujita [43], who observed apoptosis in vitro and in vivo in mouse lymphoma, glioma and oral squamous cell carcinoma, respectively. Some authors report that BNCT apoptosis may be specific to some tumor types, for example, Aromando [33] and Kamida [44], who studied hamster cheek pouch tumor and human oral squamous cell carcinoma xenografts, respectively.…”

“…Comparing these data with those obtained in melanoma cells, these findings were modestly significant, indicating that BNCT can induce damage to normal cells to a lesser degree (Figure 3A–D). BNCT has also been shown to decrease the expression of Bcl-2 and increase the expression of Bax in other tumor cells, such as glioma [32]. However, these markers were not affected in an oral cancer model treated by BNCT, as previously described [33].…”

Folate receptor-mediated boron-10 containing carbon nanoparticles as potential delivery vehicles for boron neutron capture therapy of nonfunctional pituitary adenomas

“…BNCT may induce glioma cell apoptosis via activation of Bax and downregulation of Bcl-2 [32]. Consistent with a previous study, we observed that neutron irradiation induced the apoptosis of NFPA cells incubated with carbon nanoparticles up to 28.6%, compared to controls (2.1%, without incubation of carbon nanoparticles or neutron irradiation).…”

LRIG1 Enhances Chemosensitivity by Modulating BCL-2 Expression and Receptor Tyrosine Kinase Signaling in Glioma Cells

“…BCL-2 is an inhibitor of apoptosis in tumors 35. Nordfors and colleagues found that downregulation of BCL-2 expression can increase the chemosensitivity of glioma cells 36,37,38,39. These results suggested that LRIG1 enhances chemosensitivity by regulating the expression of BCL-2 in gliomas.…”