Synchrotron X-Ray Radiation-Induced Bystander Effect: An Impact of the Scattered Radiation, Distance From the Irradiated Site and p53 Cell Status.

Pavel Lobachevsky,Valentin G Djonov,Carl N Sprung,Olga A Martin,Helen B Forrester,Alesia Ivashkevich,Joel Mason,Andrew W Stevenson,Chris J Hall

doi:10.3389/fonc.2021.685598

Abstract

Synchrotron radiation, especially microbeam radiotherapy (MRT), has a great potential to improve cancer radiotherapy, but non-targeted effects of synchrotron radiation have not yet been sufficiently explored. We have previously demonstrated that scattered synchrotron radiation induces measurable γ-H2AX foci, a biomarker of DNA double-strand breaks, at biologically relevant distances from the irradiated field that could contribute to the apparent accumulation of bystander DNA damage detected in cells and tissues outside of the irradiated area. Here, we quantified an impact of scattered radiation to DNA damage response in “naïve” cells sharing the medium with the cells that were exposed to synchrotron radiation. To understand the effect of genetic alterations in naïve cells, we utilised p53-null and p53-wild-type human colon cancer cells HCT116. The cells were grown in two-well chamber slides, with only one of nine zones (of equal area) of one well irradiated with broad beam or MRT. γ-H2AX foci per cell values induced by scattered radiation in selected zones of the unirradiated well were compared to the commensurate values from selected zones in the irradiated well, with matching distances from the irradiated zone. Scattered radiation highly impacted the DNA damage response in both wells and a pronounced distance-independent bystander DNA damage was generated by broad-beam irradiations, while MRT-generated bystander response was negligible. For p53-null cells, a trend for a reduced response to scattered irradiation was observed, but not to bystander signalling. These results will be taken into account for the assessment of genotoxic effects in surrounding non-targeted tissues in preclinical experiments designed to optimise conditions for clinical MRT and for cancer treatment in patients.

Highlights

Abscopal, or distant, effects of ionising radiation (IR) were first described by Mole in 1953 [1], and have been regularly documented subsequently [2]
From our earlier study [23], the g-H2AX response of HCT-116 cells to 2.5-Gy conventional X-ray radiation was common for targeted cells, where most of DNA damage was efficiently repaired by 24 hours post-irradiation
We suggest an interpretation that assumes the reduction by p53-null status of the response to scattered radiation, which is a major contributor in microbeam radiotherapy (MRT) case, but not to bystander signalling, which significantly contributes in broad beam (BB) case

Summary

Introduction

Distant, effects of ionising radiation (IR) were first described by Mole in 1953 [1], and have been regularly documented subsequently [2]. X-ray beams produced by the third-generation synchrotron source such as Australian Synchrotron (AS) in Melbourne, Australia and the first fourthgeneration European Synchrotron Radiation Facility (ESRF) in Grenoble, France, have the advantage of delivering high radiation doses to a very small volume with low beam divergence [9, 10]. These features facilitate the study of in vitro and in vivo non-targeted effects

Methods

Results

Conclusion