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.
Proton Medical Research Center, Graduate School of Comprehensive Human Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan.
Ariungerel
A
Gerelchuluun
Zhengshan
Z
Hong
Lue
L
Sun
Kenshi
K
Suzuki
Toshiyuki
T
Terunuma
Kiyoshi
K
Yasuoka
Takeji
T
Sakae
Takashi
T
Moritake
Koji
K
Tsuboi
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