Ⅲ-4. Radiation Chemistry & Biology

RIKEN Accel. Prog. Rep. 47 (2014)

Cell-killing eﬀect of low doses of high-LET heavy ions (VI)
M. Tomita,∗1,∗2 T. Tsukada,∗1 and M. Izumi∗1
Non-DNA-targeted eﬀects are not a direct consequence of radiation-induced initial lesions produced incellular DNA, but are an indirect consequence of intraand intercellular communications involving both irradiated and nonirradiated cells. These eﬀects include
low-dose hyper-radiosensitivity (HRS) and radiationinduced bystander response (RIBR).1,2) RIBR is a cellular response induced in nonirradiated cells that receive bystander signals from directly irradiated cells
within an irradiated cell population.1,2) RIBR induced
by low doses of high-LET radiations is an important
issue concerning the health of astronauts and in heavyion radiation cancer therapy. Here, we investigatedthe molecular mechanisms underlying and biologicalimplications of RIBR induced by such low doses ofhigh-LET radiations. We previously found that HRS
was induced in normal human ﬁbroblast WI-38 cells
that were irradiated with low doses of high-LET argon(Ar) and iron (Fe) ions, suggesting that RIBR was induced.3–5) Nitric oxide (NO) was found to be involvedin this process.3–5) Furthermore, we found that reactive oxygen species (ROS), gap-junction intercellularcommunication (GJIC), and cyclooxygenase-2 (COX2) protein as well as NO may be involved in Ar-ioninduced bystander signal transfer.4) Here, we examined the eﬀects of a scavenger of ROS (DMSO) andan inhibitor of GJIS (lindane) or COX-2 (NS-398) on
Fe-ion-induced RIBR.
Here, we have shown the revised clonogenic survival
curve of WI-38 cells irradiated with Fe ions; the curve
was obtained by adding new data to previous results3)[Fig.1]. HRS could be clearly observed in cells irradiated with Fe ions at doses lower than 0.2 Gy and waspartly suppressed by pretreatment with carboxy-PTIO(c-PTIO), an NO scavenger.
Next, we examined HRS suppression at 0.1 Gy byDMSO, lindane, c-PTIO or NS-398 pretreatment [Fig.
2]. Lindane and NS-398 were dissolved in DMSO.
DMSO did not signiﬁcantly suppress the HRS, although the standard errors of the mean (SEM) werelarge. In contrast, lindane, NS-393, and c-PTIO significantly suppressed HRS to similar levels. These results
suggested that the GJIC and COX-2 mediated pathway as well as NO was also involved in Fe-ion-induced
bystander signal transfer. Currently, we are examining the role of the NF-κB/Cox-2/prostaglandin E2 andNF-κB/iNOS/NO pathways,2) which may be activatedin bystander cells that have been subjected to ROS andNO, in HRS induced by high-LET radiations.
∗1∗2

RIKEN Nishina CenterRadiation Safety Research Center, Central Research Institute of Electric Power Industry- 284 -Fig. 1. Cell-survival curves of WI-38 cells. Conﬂuent
monolayers of WI-38 cells were irradiated with 90
MeV/u Fe ions (1000 keV/µm) and some of the cells
were pretreated with c-PTIO (20 µM). The surviving
fraction was determined by a colony forming assay. Theerror bars represent the standard error of the mean(SEM) (n=3-5).

Fig. 2. Eﬀect of inhibitors or scavengers. DMSO (0.1%),
lindane (Lin, 50 µM), c-PTIO (20 µM) or NS-398 (50µM) was added to the medium 2 h before irradiation.6)
WI-38 cells were irradiated with 0.1 Gy Fe ions. The error bars represent the standard error of the mean (SEM)(n=3-4).

References
1) K. M. Prise et al.: Radiat. Prot. Dosimetry 99, 223(2002).
2) T. K. Hei et al.: Curr. Mol. Pharmacol 4, 96 (2011).
3) M. Tomita et al.: RIKEN Accel. Prog. Rep. 43, 276(2010).
4) M. Tomita et al.: RIKEN Accel. Prog. Rep. 45, 207(2012).
5) M. Tomita et al.: RIKEN Accel. Prog. Rep. 46, 253(2013).
6) M. Tomita et al.: Radiat. Res. 173, 380 (2010).