Heavy-Ion Microbeam Irradiation Induces Bystander Killing of Human Cells

Abstract

Significant evidence indicates that ionizing radiation causes biological effects in nonirradiated bystander cells having received signals from directly irradiated cells. There is little information available hitherto as to the bystander effect of energetic heavy ions; however, our previous work has shown that in confluent cultures of normal human fibroblast AG01522 cells, targeted exposure of 0.0003% of cells to microbeams of 18.3 MeV/u 12 C (103 keV/µm) and 13.0 MeV/u 20 Ne (375 keV/µm) ions can similarly cause almost 10% decreases in the clonogenic survival, and twofold increments in the incidence of apoptosis whose temporal kinetics varies between irradiated and bystander cells. Using this experimental system, here we further report that bystander responses of AG01522 cells to 17.5 MeV/u 20 Ne ions (294 keV/µm) are consistent with those to 18.3 MeV/u 12 C and 13.0 MeV/u 20 Ne ions. We also demonstrate that such bystander-induced reductions in the survival are less pronounced and occur independently of Bcl-2 overexpression in human cervical cancer HeLa cells.

The Bystander Response to Heavy-Ion Radiation: Intercellular Signaling Between Irradiated and Non-Irradiated Cells

“…Concerning the direct intercellular interactionmediated bystander effect, the survival of human cervical cancer HeLa cells was decreased in bystanders irrespective of ion species (103-375 keV/µm) and Bcl-2 overexpression, but was less pronounced than in fibroblasts (Hamada et al, 2008g). In human lung cancer A549 cells, bystander-induced reductions in the survival were observed in a GJIC-dependent fashion (Harada et al, 2009).…”

Heavy-Ion Microbeams for Biological Science: Development of System and Utilization for Biological Experiments in QST-Takasaki

“…Bystander studies using normal human fibroblasts were performed with the focus of attention on various endpoints, such as cell survival rate, frequency of micronucleus formation, phosphorylation of histone H2AX, apoptosis, and induction of p53 protein [34][35][36][37][38][39]. Moreover, gene expression analysis of bystander cells using the DNA microarray assay revealed that the G protein/PI-3 kinase pathways were activated in the bystander cells but not in directly irradiated cells [40].…”

Model Assembly for Estimating Cell Surviving Fraction for Both Targeted and Nontargeted Effects Based on Microdosimetric Probability Densities

“…In the LSq fitting, we approximated that numerical values of the parameters were the same for Bcl-2 cells and Neo cells, because the nontargeted effect occurs independent of Bcl-2 overexpression [16]. We also assumed that the parameters related to the dose dependence of the triggering probability, a 1 and a 2 , were the same for all cell lines and radiation types, and their numerical values were determined from the X-ray microbeam irradiation experiment.…”

“…In this study, we determined the nontargeted model parameters except for z n,thre by the LSq fitting of the SF of Bcl-2 cells and Neo cells irradiated with heavy-ion microbeam [16] as well as that of the WI-38 normal human fibroblasts irradiated with synchrotron X-ray microbeam [30] . In these experiments, the number of Bcl-2 cells, Neo cells and WI-38 cells in each whole population, N W , was 2.67e6, 2.68e6 and 7.0e5, respectively, and such cell population sizes were determined by the conventional automatic counting of trypsinized cells.…”

“…In this study, the parameters used in the model assembly were determined by the least-square (LSq) fitting of the experimentally determined SF of Bcl-2 cells (Bcl-2 overexpressing HeLa cells) and Neo cells (neomycin resistant gene-expressing HeLa cells) irradiated with microbeam or broadbeam of heavy ions [13] , [16] , as well as the WI-38 normal human fibroblasts irradiated with X-ray microbeam [30] . The details of the calculation procedures together with the comparison results between the computationally and experimentally determined SF are given below.…”