Determination of the relative biological effectiveness and oxygen enhancement ratio for micronuclei formation using high-LET radiation in solid tumor cells: An in vitro and in vivo study

Ryoichi Hirayama; Akiko Uzawa; Maki Obara; Nobuhiro Takase; Kana Koda; Masakuni Ozaki; Miho Noguchi; Yoshitaka Matsumoto; Huizi Li; Kei Yamashita; Sachiko Koike; Koichi Ando; Toshiyuki Shirai; Naruhiro Matsufuji; Yoshiya Furusawa

doi:10.1016/j.mrgentox.2015.08.003

Determination of the relative biological effectiveness and oxygen enhancement ratio for micronuclei formation using high-LET radiation in solid tumor cells: An in vitro and in vivo study

Mutat Res Genet Toxicol Environ Mutagen. 2015 Nov:793:41-7. doi: 10.1016/j.mrgentox.2015.08.003. Epub 2015 Aug 14.

Authors

Affiliations

¹ Medical Physics Research Program, Research Center for Charged Particle Therapy, National Institute of Radiological Sciences (NIRS), 4-9-1 Anagawa, Inage-ku, Chiba-shi, Chiba 263-8555, Japan. Electronic address: hirayama@nirs.go.jp.
² Medical Physics Research Program, Research Center for Charged Particle Therapy, National Institute of Radiological Sciences (NIRS), 4-9-1 Anagawa, Inage-ku, Chiba-shi, Chiba 263-8555, Japan.
³ School of Engineering, Tokai University, 1117 Kitakaname, Hiratsuka-shi, Kanagawa 259-1292, Japan.
⁴ Advanced Science Research Center, Japan Atomic Energy Agency (JAEA), 2-4 Shirakata-Shirane, Tokai-mura, Naka-gun, Ibaraki 319-1195, Japan.
⁵ Heavy Ion Medical Center, Gunma University, 3-39-22 Showa-machi, Maebashi-shi, Gunma 371-8511, Japan.

PMID: 26520371
DOI: 10.1016/j.mrgentox.2015.08.003

Abstract

We determined the relative biological effectiveness (RBE) and oxygen enhancement ratio (OER) of micronuclei (MN) formation in clamped (hypoxic) and non-clamped (normoxic) solid tumors in mice legs following exposure to X-rays and heavy ions. Single-cell suspensions (aerobic) of non-irradiated tumors were prepared in parallel and used directly to determine the radiation response for aerobic cells. Squamous cell carcinoma (SCCVII) cells were transplanted into the right hind legs of syngeneic C3H/He male mice. Irradiation doses with either X-rays or heavy ions at a dose-averaged LET (linear energy transfer) of 14-192keV/μm were delivered to 5-mm diameter tumors and aerobic single-cells in sample-tubes. After irradiation, the tumors were excised and trypsinized to observe MN in single-cells. The single-cell suspensions were used for MN formation assays. The RBE values increased with increasing LET. The maximum RBE values for the three different oxygen conditions; hypoxic tumor, normoxic tumor, and aerobic cells, were 8.18, 5.30, and 3.76 at an LET of 192keV/μm, respectively. After X-irradiation, the OERh/n values (hypoxic tumor/normoxic tumor) were lower than the OERh/a (hypoxic tumor/aerobic cells), and were 1.73 and 2.58, respectively. We found that the OER for the in vivo studies were smaller in comparison to that for the in vitro studies. Both of the OER values at 192keV/μm were small in comparison to those of the X-ray irradiated samples. The OERh/n and OERh/a values at 192keV/μm were 1.12 and 1.19, respectively. Our results suggest that high LET radiation has a large biological effect even if a solid tumor includes substantial numbers of hypoxic cells. To conclude, we found that the RBE values under each oxygen state for non-MN fraction increased with increasing LET and that the OER values for both tumors in vivo and cells in vitro decreased with increasing LET.

Keywords: High LET radiation; In vivo solid tumor; Micronucleus formation; OER: oxygen enhancement ratio; RBE: relative biological effectiveness.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Animals
Carcinoma, Squamous Cell / genetics*
Carcinoma, Squamous Cell / metabolism*
Cell Line, Tumor
Dose-Response Relationship, Radiation
Heavy Ions
In Vitro Techniques
Linear Energy Transfer
Male
Mice
Mice, Inbred C3H
Micronuclei, Chromosome-Defective / radiation effects*
Micronucleus Tests
Neoplasm Transplantation
Oxygen Consumption / radiation effects*
Relative Biological Effectiveness
X-Rays