LIFE01200604005 Shri Somnath Ghosh - Homi Bhabha National ...

CHAPTER 3
RESULTS
3.2 Proton beam induced signaling in mammalian cells and its comparison with Gamma
irradiation.
Having established that among the three cell lines, A549 was the most radioresistant, the
variance in signaling pattern and effectiveness of cell killing with the change in LET was looked
at. In this study, A549 cells were irradiated with either 2Gy proton beam or 2Gy γ-radiation and
ensuing activation of few important components involved in DNA repair, cell cycle arrest, and
apoptosis pathways were followed to elucidate the mechanisms behind observed cellular
response. Despite the variability in effectiveness of these two radiations, equal doses of each
were chosen to ensure that each cell is hit by proton beam and no bystander effects are
manifested. Essentially all biological differences between proton and gamma radiations arise
from differences in their ionization tracks. Equitoxic doses were not preferred because the
probability of unhit cells would increase. How this qualitative difference of radiation is translated
into activation of crucial intracellular pathways was the focus of the study.
3.2.1 Cell Survival Assay
There was only 23±2 % of A549 cells were survived that had been exposed to 2Gy of proton
beam where as 56±2.2 % cells were survived that had been exposed to 2Gy of γ-radiation as
observed with clonogenic assay (Fig.3.2.1). This result clearly showed that proton beam is more
cytotoxic than gamma radiation.
3.2.2 Differential modulation of Gene expression following proton beam and gamma irradiation
Expression of ATM, DNA-PK and Chk2 genes were significantly upregulated after 4h of
irradiation only in A549 cells that had been exposed to proton beam (2Gy) (Fig.3.2.2 A, C),
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