Genetic Analysis of T Cell Lymphomas in Carbon Ion-Irradiated Mice Reveals Frequent Interstitial Chromosome Deletions: Implications for Second Cancer Induction in Normal Tissues during Carbon Ion Radiotherapy

Abstract

Monitoring mice exposed to carbon ion radiotherapy provides an indirect method to evaluate the potential for second cancer induction in normal tissues outside the radiotherapy target volume, since such estimates are not yet possible from historical patient data. Here, male and female B6C3F1 mice were given single or fractionated whole-body exposure(s) to a monoenergetic carbon ion radiotherapy beam at the Heavy Ion Medical Accelerator in Chiba, Japan, matching the radiation quality delivered to the normal tissue ahead of the tumour volume (average linear energy transfer = 13 keV.μm-1) during patient radiotherapy protocols. The mice were monitored for the remainder of their lifespan, and a large number of T cell lymphomas that arose in these mice were analysed alongside those arising following an equivalent dose of 137Cs gamma ray-irradiation. Using genome-wide DNA copy number analysis to identify genomic loci involved in radiation-induced lymphomagenesis and subsequent detailed analysis of Notch1, Ikzf1, Pten, Trp53 and Bcl11b genes, we compared the genetic profile of the carbon ion- and gamma ray-induced tumours. The canonical set of genes previously associated with radiation-induced T cell lymphoma was identified in both radiation groups. While the pattern of disruption of the various pathways was somewhat different between the radiation types, most notably Pten mutation frequency and loss of heterozygosity flanking Bcl11b, the most striking finding was the observation of large interstitial deletions at various sites across the genome in carbon ion-induced tumours, which were only seen infrequently in the gamma ray-induced tumours analysed. If such large interstitial chromosomal deletions are a characteristic lesion of carbon ion irradiation, even when using the low linear energy transfer radiation to which normal tissues are exposed in radiotherapy patients, understanding the dose-response and tissue specificity of such DNA damage could prove key to assessing second cancer risk in carbon ion radiotherapy patients.

Space Radiation Biology for “Living in Space”

“…The greater carcinogenesis effects of HZE particle radiation have been analyzed from the viewpoint of a targeted effect (genetic change) and nontargeted effects. C-ioninduced lymphomas showed a marginal increase in the frequency of large interstitial deletions at various sites across the genome when compared with that of photon-induced lymphomas [133]. HZE particle irradiation promoted more aggressive cancers, such as increased growth rate, transcriptomic signatures, and metastasis when using a radiation/genetic mammary chimera mouse model of breast cancer [134].…”

Oxidative Stress in Hadrontherapy

“…Indeed, concerning carbon ions, literature on secondary tumors is still poor but a study pointed out that 30% of patients treated for cervical cancers developed distant metastases [63]; a case was reported of a brain tumor induced by heavy particle radiotherapy [64]. Preclinical studies, recently performed on mice exposed to carbon ions in comparison to photons, revealed that interstitial chromosome deletions were more increased in secondary cancers induced by carbon exposure [65]. They contradict previous results of Ando et al [66] showing the same induction in carbon locally irradiated mice of secondary tumors after γ-rays.…”

Clinical and Functional Assays of Radiosensitivity and Radiation-Induced Second Cancer

“…After controlling for the effect of radiation dose, the relationship between the type of first cancer and the risk of second cancers is much diminished (reviewed in [ 33 ]), although there remain some associations which might be explained by combined effects of concurrent chemotherapy or other treatment differences, selection effects, or inherent genetic susceptibility or shared etiology. Research into identifying radiation signatures in radiotherapy-induced cancers [ 35 , 36 , 37 ] would increase the sensitivity of epidemiology analyses by helping to differentiate between the background of spontaneous second cancers.…”