An appreciation of the science and philanthropy of Sir Oliver Scott, founder of the Gray Cancer Institute.

This Commentary focuses on the landmark paper about hypoxia in radiotherapy by Gray, Scott et al published in 1953. By then, it was known that hypoxic regions in tumours could make them resistant to radiation treatment and that this was a possible cause of failure. The paper proposed that oxygen breathing could substantially decrease this resistance without incurring significant additional damage to normal tissues, thus reducing the likelihood of recurrence.

Radiation-induced bystander and adaptive responses in cell and tissue models.

The use of microbeam approaches has been a major advance in probing the relevance of bystander and adaptive responses in cell and tissue models. Our own studies at the Gray Cancer Institute have used both a charged particle microbeam, producing protons and helium ions and a soft X-ray microprobe, delivering focused carbon-K, aluminium-K and titanium-K soft X-rays. Using these techniques we have been able to build up a comprehensive picture of the underlying differences between bystander responses and direct effects in cell and tissue-like models.

Histone H2AX phosphorylation in normal human cells irradiated with focused ultrasoft X rays: evidence for chromatin movement during repair.

DNA repair within the cell nucleus is a dynamic process involving a close interaction between repair proteins and chromatin structure. Recent studies have indicated a quantitative relationship between DNA double-strand break induction and histone H2AX phosphorylation. The dynamics of this process within individual cell nuclei is unknown.

Bystander-induced differentiation: a major response to targeted irradiation of a urothelial explant model.

A ureter primary explant technique, using porcine tissue sections was developed to study bystander effects under in vivo like conditions where dividing and differentiated cells are present. Targeted irradiations of ureter tissue fragments were performed with the Gray Cancer Institute charged particle microbeam at a single location (2 microm precision) with 10 3He2+ particles (5 MeV; LET 70 keV/microm). After irradiation the ureter tissue section was incubated for 7 days allowing explant outgrowth to be formed.

Bystander signaling between glioma cells and fibroblasts targeted with counted particles.

Radiation-induced bystander effects may play an important role in cancer risks associated with environmental, occupational and medical exposures and they may also present a therapeutic opportunity to modulate the efficacy of radiotherapy. However, the mechanisms underpinning these responses between tumor and normal cells are poorly understood. Using a microbeam, we investigated interactions between T98G malignant glioma cells and AG01522 normal fibroblasts by targeting cells through their nuclei in one population, then detecting cellular responses in the other co-cultured non-irradiated population.

Low-dose binary behavior of bystander cell killing after microbeam irradiation of a single cell with focused c(k) x rays.

Although conclusive evidence has been obtained for the presence of radiation-induced bystander effects, the mechanisms that trigger and regulate these processes are still largely unknown. The bystander effect may play a critical role in determining the biological effectiveness of low-dose exposures, but questions on how to incorporate it into current models and extrapolate the risks of radiation-induced carcinogenesis are still open. The Gray Cancer Institute soft X-ray microbeam has been used to investigate the dose-response relationship of the bystander effect below 0.

Evidence for induction of DNA double strand breaks in the bystander response to targeted soft X-rays in CHO cells.

This study investigated the role of DNA double strand breaks and DNA base damage in radiation-induced bystander responses in Chinese hamster ovary (CHO) cell lines. Two CHO repair-deficient clones, xrs5 (DNA double strand break repair-deficient) and EM9 (DNA base excision repair-deficient) were used in addition to the wild type (CHO). The Gray Cancer Institute ultrasoft X-ray microprobe is a powerful tool for investigating the bystander response, because it permits the irradiation of only a single nucleus of a cell, as reported previously.

Targeted cytoplasmic irradiation induces bystander responses.

The observation of radiation-induced bystander responses, in which cells respond to their neighbors being irradiated, has important implications for understanding mechanisms of radiation action particularly after low-dose exposure. Much of this questions the current dogma of direct DNA damage driving response in irradiated systems. In this study, we have used a charged-particle microbeam to target individual helium ions ((3)He(2+)) to individual cells within a population of radioresistant glioma cells cultured alone or in coculture with primary human fibroblasts.

Nitric oxide-mediated signaling in the bystander response of individually targeted glioma cells.

Bystander responses have been reported to be a major determinant of the response of cells to radiation exposure at low doses, including those of relevance to therapy. In this study, human glioblastoma T98G cell nuclei were individually irradiated with an exact number of helium ions using a single-cell microbeam. It was found that when only 1 cell in a population of approximately 1200 cells was targeted, with one or five ions, cellular damage measured as induced micronuclei was increased by 20%.

Bystander responses induced by low LET radiation.

Radiation-induced bystander responses are observed when cells respond to their neighbours being irradiated. Considerable evidence is now available regarding the importance of these responses in cell and tissue models. Most studies have utilized two approaches where either a media-transferable factor has been assessed or cells have been exposed to low fluences of charged particles, where only a few percent are exposed.

Local DNA damage by proton microbeam irradiation induces poly(ADP-ribose) synthesis in mammalian cells.

Cellular recovery from ionizing radiation (IR)-induced damage involves poly(ADP-ribose) polymerase (PARP-1 and PARP-2) activity, resulting in the induction of a signalling network responsible for the maintenance of genomic integrity. In the present work, a charged particle microbeam delivering 3.2 MeV protons from a Van de Graaff accelerator has been used to locally irradiate mammalian cells.

Radiation-induced bystander effects. Mechanisms, biological implications, and current investigations at the Leipzig LIPSION facility.

Background: The bystander effect is a relatively new area of radiobiological research, which is aimed at studying post-radiation changes in neighboring non-hit cells or tissues. The bystander effect of ionizing irradiation is important after low-dose irradiation in the range of up to 0.2 Gy, where a higher incidence of stochastic damage was observed than was expected from a linear-quadratic model.