Induction of in situ DNA double-strand breaks and apoptosis by 200 MeV protons and 10 MV X-rays in human tumour cell lines.
OBJECTIVE
To clarify the properties of clinical high-energy protons by comparing with clinical high-energy X-rays.


METHODS
Human tumor cell lines, ONS76 and MOLT4, were irradiated with 200 MeV protons or 10 MV X-rays. In situ DNA double-strand breaks (DDSB) induction was evaluated by immunocytochemical staining of phosphorylated histone H2AX (γ-H2AX). Apoptosis was measured by flow-cytometry after staining with Annexin V. The relative biological effectiveness (RBE) was obtained by clonogenic survival assay.


RESULTS
DDSB induction was significantly higher for protons than X-rays with average ratios of 1.28 (ONS76) and 1.59 (MOLT4) at 30 min after irradiation. However the differences became insignificant at 6 h. Also, apoptosis induction in MOLT4 cells was significantly higher for protons than X-rays with an average ratio of 2.13 at 12 h. However, the difference became insignificant at 20 h. RBE values of protons to X-rays at 10% survival were 1.06 ± 0.04 and 1.02 ± 0.15 for ONS76 and MOLT4, respectively.


CONCLUSIONS
Cell inactivation may differ according to different timings and/or endpoints. Proton beams demonstrated higher cell inactivation than X-rays in the early phases. These data may facilitate the understanding of the biological properties of clinical proton beams.
Gerelchuluun
Ariungerel
A
Proton Medical Research Center, Graduate School of Comprehensive Human Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan.
Hong
Zhengshan
Z
Sun
Lue
L
Suzuki
Kenshi
K
Terunuma
Toshiyuki
T
Yasuoka
Kiyoshi
K
Sakae
Takeji
T
Moritake
Takashi
T
Tsuboi
Koji
K
D017209:Apoptosis / Q000528:radiation effects*; D045744:Cell Line, Tumor; D053903:DNA Breaks, Double-Stranded; D004307:Dose-Response Relationship, Radiation; D006657:Histones / Q000378:metabolism; D006801:Humans; D008527:Medulloblastoma / Q000378:metabolism / Q000473:pathology / Q000532:radiotherapy; D010315:Particle Accelerators; D054218:Precursor T-Cell Lymphoblastic Leukemia-Lymphoma / Q000378:metabolism / Q000473:pathology / Q000532:radiotherapy; D011522:Protons; D011882:Radiotherapy, High-Energy / Q000295:instrumentation; D012062:Relative Biological Effectiveness; D017356:Synchrotrons; D014410:Tumor Stem Cell Assay
C468783:H2AX protein, human; D006657:Histones; D011522:Protons