Radiosensitivity is predicted by DNA end-binding complex density, but not by nuclear levels of band components

Follistatin is induced by ionizing radiation and potentially predictive of radiosensitivity in radiation-induced fibrosis patient derived fibroblasts

Follistatin is a potent regulator of the inflammatory response and binds to and inhibits activin A action. Activin A is a member of the TGFβ protein superfamily which has regulatory roles in the inflammatory response and in the fibrotic process. Fibrosis can occur following cell injury and cell death induced by agents such as ionizing radiation (IR). IR is used to treat cancer and marked fibrotic response is a normal tissue (non-tumour) consequence in a fraction of patients under the current dose regimes. The discovery and development of a therapeutic to abate fibrosis in these radiosensitive patients would be a major advance for cancer radiotherapy. Likewise, prediction of which patients are susceptible to fibrosis would enable individualization of treatment and provide an opportunity for pre-emptive fibrosis control and better tumour treatment outcomes. The levels of activin A and follistatin were measured in fibroblasts derived from patients who developed severe radiation-induced fibrosis following radiotherapy and compared to fibroblasts from patients who did not. Both follistatin and activin A gene expression levels were increased following IR and the follistatin gene expression level was lower in the fibroblasts from fibrosis patients compared to controls at both basal levels and after IR. The major follistatin transcript variants were found to have a similar response to IR and both were reduced in fibrosis patients. Levels of follistatin and activin A secreted in the fibroblast culture medium also increased in response to IR and the relative follistatin protein levels were significantly lower in the samples derived from fibrosis patients. The decrease in the follistatin levels can lead to an increased bioactivity of activin A and hence may provide a useful measurement to identify patients at risk of a severe fibrotic response to IR. Additionally, follistatin, by its ability to neutralise the actions of activin A may be of value as an anti-fibrotic for radiation induced fibrosis.

BRCA1 and BRCA2 heterozygosity in embryonic stem cells reduces radiation-induced Rad51 focus formation but is not associated with radiosensitivity

PURPOSE

The breast cancer susceptibility genes BRCA1 (breast cancer 1) and BRCA2 (breast cancer 2) encode proteins involved in double-strand break (DSB) repair, whose functions include facilitating homologous recombination through interactions with Rad51, the human homologue of bacterial RecA. Homozygous deficiency inhibits Rad51 focus formation and enhances radiosensitivity, but the effects of heterozygosity have not been investigated in detail. The purpose of this work was to examine the effect of heterozygosity on Rad51 activation and clonogenicity following X-irradiation (XR).

MATERIALS AND METHODS

We used quantitative assessment of immunofluorescent foci to assess Rad51 activation in wild type mouse embryonic fibroblasts (MEF) and in paired mutant and wild type BRCA1 and BRCA2 embryonic stem cells (ES cells). We measured radiosensitivity in the same cell lines using clonogenic survival assays.

RESULTS

ES cells exhibit higher numbers of cells with Rad51 foci post radiation than MEF, likely due to differences in cell cycle distribution. Compared to wild type cells, BRCA1 and BRCA2 heterozygous ES cells demonstrate lower numbers of Rad51 foci per nucleus 4 and 24 hours post radiation. This was not associated with significantly enhanced radiosensitivity.

CONCLUSIONS

BRCA1/2 heterozygosity in ES cells is associated with a subtle reduction in Rad51 foci formation that is not associated with increased XR induced cytotoxicity.

Genetic predictors of adverse radiotherapy effects: the Gene-PARE project

PURPOSE

The development of adverse effects resulting from the radiotherapy of cancer limits the use of this treatment modality. The validation of a test capable of predicting which patients would be most likely to develop adverse responses to radiation treatment, based on the possession of specific genetic variants, would therefore be of value. The purpose of the Genetic Predictors of Adverse Radiotherapy Effects (Gene-PARE) project is to help achieve this goal.

METHODS AND MATERIALS

A continuously expanding biorepository has been created consisting of frozen lymphocytes and DNA isolated from patients treated with radiotherapy. In conjunction with this biorepository, a database is maintained with detailed clinical information pertaining to diagnosis, treatment, and outcome. The DNA samples are screened using denaturing high performance liquid chromatography (DHPLC) and the Surveyor nuclease assay for variants in ATM, TGFB1, XRCC1, XRCC3, SOD2, and hHR21. It is anticipated that additional genes that control the biologic response to radiation will be screened in future work.

RESULTS

Evidence has been obtained that possession of variants in genes, the products of which play a role in radiation response, is predictive for the development of adverse effects after radiotherapy.

CONCLUSIONS

It is anticipated that the Gene-PARE project will yield information that will allow radiation oncologists to use genetic data to optimize treatment on an individual basis.

Inhibition of radiation-induced EGFR nuclear import by C225 (Cetuximab) suppresses DNA-PK activity

BACKGROUND AND PURPOSE

Inhibition of EGFR-function can induce radiosensitization in tumor cells. Purpose of our investigation was to identify the possible molecular mechanism of radiosensitization following treatment with anti-EGFR-antibody C225 (Cetuximab).

MATERIALS AND METHODS

The effect of C225 on radiation response was determined in human cell lines of bronchial carcinoma (A549) and breast adenoma cells (MDA MB 231). The molecular effects of C225 on EGFR-function after irradiation were analyzed applying western blotting, immune-precipitation and kinase assays. Effects on DNA-repair were detected by quantification of gamma-H2AX positive foci 24h after irradiation.

RESULTS

The EGFR specific antibody C225 induced radiosensitization in A549 and also in MDA MB 231 cells. Radiosensitization in A549 was associated with blockage of radiation-induced EGFR transport into the nucleus, and immobilized the complex of EGFR with DNA-dependent protein kinase (DNA-PK) in the cytoplasm. As a consequence radiation-induced DNA-PK activation was abolished, a process that is essential for DNA-repair after radiation exposure. Likewise C225 treatment increased the residual amount of gamma-H2AX-positive foci 24h after irradiation in A549 and in MDA MB 231 cells.

CONCLUSIONS

Our results suggest that irradiation induced DNA-PK activation-essential for DNA repair-may be hampered specifically by use of the anti-EGFR-antibody C225. This process is associated with radiosensitization.