Modeling the biological response of normal human cells, including repair processes, to fractionated carbon beam irradiation

Neon ion (20 Ne10 + ) charged particle beams manipulate rapid tumor reoxygenation in syngeneic mouse models

Charged particle beams induce various biological effects by creating high-density ionization through the deposition of energy along the beam's trajectory. Charged particle beams composed of neon ions (20 Ne10+ ) hold great potential for biomedical applications, but their physiological effects on living organs remain uncertain. In this study, we demonstrate that neon-ion beams expedite the process of reoxygenation in tumor models. We simulated mouse SCCVII syngeneic tumors and exposed them to either X-ray or neon-ion beams. Through an in vivo radiobiological assay, we observed a reduction in the hypoxic fraction in tumors irradiated with 8.2 Gy of neon-ion beams 30 h after irradiation compared to 6 h post-irradiation. Conversely, no significant changes in hypoxia were observed in tumors irradiated with 8.2 Gy of X-rays. To directly quantify hypoxia in the irradiated living tumors, we utilized dynamic contrast-enhanced magnetic resonance imaging (MRI) and diffusion-weighted imaging. These combined MRI techniques revealed that the non-hypoxic fraction in neon-irradiated tumors was significantly higher than that in X-irradiated tumors (69.53% vs. 47.67%). Simultaneously, the hypoxic fraction in neon-ion-irradiated tumors (2.77%) was lower than that in X-irradiated tumors (4.27%) and non-irradiated tumors (32.44%). These results support the notion that accelerated reoxygenation occurs more effectively with neon-ion beam irradiation compared to X-rays. These findings shed light on the physiological effects of neon-ion beams on tumors and their microenvironment, emphasizing the therapeutic advantage of using neon-ion charged particle beams to manipulate tumor reoxygenation.

Predominant contribution of the dose received from constituent heavy-ions in the induction of gastrointestinal tumorigenesis after simulated space radiation exposure

Gastrointestinal (GI) cancer risk among astronauts after encountering galactic cosmic radiation (GCR) is predicted to exceed safe permissible limits in long duration deep-space missions. Current predictions are based on relative biological effectiveness (RBE) values derived from in-vivo studies using single-ion beams, while GCR is essentially a mixed radiation field composed of protons (H), helium (He), and heavy ions. Therefore, a sequentially delivered proton (H) → Helium (He) → Oxygen (O) → Silicon (Si) beam was designed to simulate simplified-mixed-field GCR (Smf-GCR), and Apc^1638N/+ mice were total-body irradiated to sham or γ (¹⁵⁷Cs) or Smf-GCR followed by assessment of GI-tumorigenesis at 150 days post-exposure. Further, GI-tumor data from equivalent doses of heavy-ions (i.e., 0.05 Gy of O and Si) in 0.5 Gy of Smf-GCR were compared to understand the contributions of heavy-ions in GI-tumorigenesis. The Smf-GCR-induced tumor and carcinoma count were significantly greater than γ-rays, and male preponderance for GI-tumorigenesis was consistent with our earlier findings. Comparison of tumor data from Smf-GCR and equivalent doses of heavy ions revealed an association between higher GI-tumorigenesis where dose received from heavy-ions contributed to > 95% of the total GI-tumorigenic effect observed after Smf-GCR. This study provides the first experimental evidence that cancer risk after GCR exposure could largely depend on doses received from constituent heavy-ions.

Targeting the Hedgehog pathway in combination with X‑ray or carbon ion radiation decreases migration of MCF‑7 breast cancer cells

The use of carbon ion therapy for cancer treatment is becoming more widespread due to the advantages of carbon ions compared with X‑rays. Breast cancer patients may benefit from these advantages, as the surrounding healthy tissues receive a lower dose, and the increased biological effectiveness of carbon ions can better control radioresistant cancer cells. Accumulating evidence indicates that the Hedgehog (Hh) pathway is linked to the development and progression of breast cancer, as well as to resistance to X‑irradiation and the migratory capacity of cancer cells. Hence, there is an increasing interest in targeting the Hh pathway in combination with radiotherapy. Several studies have already investigated this treatment strategy with conventional radiotherapy. However, to the best of our knowledge, the combination of Hh inhibitors with particle therapy has not yet been explored. The aim of the present study was to investigate the potential of the Hh inhibitor GANT61 as an effective modulator of radiosensitivity and migration potential in MCF‑7 breast cancer cells, and compare potential differences between carbon ion irradiation and X‑ray exposure. Although Hh targeting was not able to radiosensitise cells to any radiation type used, the combination of GANT61 with X‑rays or carbon ions (energy: 95 MeV/n; linear energy transfer: 73 keV/µm) was more effective in decreasing MCF‑7 cell migration compared with either radiation type alone. Gene expression of the Hh pathway was affected to different degrees in response to X‑ray and carbon ion irradiation, as well as in response to the combination of GANT61 with irradiation. In conclusion, combining Hh inhibition with radiation (X‑rays or carbon ions) more effectively decreased breast cancer cell migration compared with radiation treatment alone.

DIFFERENCE IN DEGREE OF SUB-LETHAL DAMAGE RECOVERY BETWEEN CLINICAL PROTON BEAMS AND X-RAYS

Fractionated proton beam radiotherapy is spreading worldwide these days. However, biological data of sub-lethal damage recovery (SLDR) after proton irradiation is not known yet. We here conducted split-dose experiments (20-360 min intervals) to clarify SLDR kinetics, and also compared the kinetics between cells with different repairability of DNA double-strand breaks. CHO and 51D1 cell lines but not V3 cell line showed significant SLDR, which reached plateau in 4-6 h. The recovery rates and recovery halftime of SLDR after X-rays were significantly higher and shorter than proton beams for CHO and 51D1 cells, respectively. Additionally, the frequency of remaining gamma-H2AX foci after two fractions was remarkably higher for X-rays than proton beams. These data suggest that there is a difference between proton beam and X-rays in SLDR and the retained DNA double-strand breaks after split-dose irradiation.

Recovery from sublethal damage and potentially lethal damage : Proton beam irradiation vs. X‑ray irradiation

PURPOSE

In order to clarify the biological response of tumor cells to proton beam irradiation, sublethal damage recovery (SLDR) and potentially lethal damage recovery (PLDR) induced after proton beam irradiation at the center of a 10 cm spread-out Bragg peak (SOBP) were compared with those seen after X‑ray irradiation.

METHODS

Cell survival was determined by a colony assay using EMT6 and human salivary gland tumor (HSG) cells. First, two doses of 4 Gy/GyE (Gray equivalents, GyE) were given at an interfraction interval of 0-6 h. Second, five fractions of 1.6 Gy/GyE were administered at interfraction intervals of 0-5 min. Third, a delayed-plating assay involving cells in plateau-phase cultures was conducted. The cells were plated in plastic dishes immediately or 2-24 h after being irradiated with 8 Gy/GyE of X‑rays or proton beams. Furthermore, we investigated the degree of protection from the effects of X‑rays or proton beams afforded by the radical scavenger dimethyl sulfoxide to estimate the contribution of the indirect effect of radiation.

RESULTS

In both the first and second experiments, SLDR was more suppressed after proton beam irradiation than after X‑ray irradiation. In the third experiment, there was no difference in PLDR between the proton beam and X‑ray irradiation conditions. The degree of protection tended to be higher after X‑ray irradiation than after proton beam irradiation.

CONCLUSION

Compared with that seen after X‑ray irradiation, SLDR might take place to a lesser extent after proton beam irradiation at the center of a 10 cm SOBP, while the extent of PLDR does not differ significantly between these two conditions.

Radiosensitizing Effect of TRPV1 Channel Inhibitors in Cancer Cells

Radiosensitizers are used in cancer therapy to increase the γ-irradiation susceptibility of cancer cells, including radioresistant hypoxic cancer cells within solid tumors, so that radiotherapy can be applied at doses sufficiently low to minimize damage to adjacent normal tissues. Radiation-induced DNA damage is repaired by multiple repair systems, and therefore these systems are potential targets for radiosensitizers. We recently reported that the transient receptor potential vanilloid type 1 (TRPV1) channel is involved in early responses to DNA damage after γ-irradiation of human lung adenocarcinoma A549 cells. Therefore, we hypothesized that TRPV1 channel inhibitors would have a radiosensitizing effect by blocking repair of radiation-induced cell damage. Here, we show that pretreatment of A549 cells with the TRPV1 channel inhibitors capsazepine, AMG9810, SB366791 and BCTC suppressed the γ-ray-induced activation of early DNA damage responses, i.e., activation of the protein kinase ataxia-telangiectasia mutated (ATM) and accumulation of p53-binding protein 1 (53BP1). Further, the decrease of survival fraction at one week after γ-irradiation (2.0 Gy) was enhanced by pretreatment of cells with these inhibitors. On the other hand, inhibitor pretreatment did not affect cell viability, the number of apoptotic or necrotic cells, or DNA synthesis at 24 h after irradiation. These results suggest that inhibition of DNA repair by TRPV1 channel inhibitors in irradiated A549 cells caused gradual loss of proliferative ability, rather than acute facilitation of apoptosis or necrosis. TRPV1 channel inhibitors could be novel candidates for radiosensitizers to improve the efficacy of radiation therapy, either alone or in combination with other types of radiosensitizers.

Evaluation of the safety and efficacy of carbon ion radiotherapy for locally advanced adenoid cystic carcinoma of the tongue base

BACKGROUND

Most cases of adenoid cystic carcinoma (ACC) of the tongue base are radioresistant, and are diagnosed in the advanced stage. Therefore, we evaluated the safety and efficacy of carbon ion radiotherapy (C-ion RT) for locally advanced ACC of the tongue base.

METHODS

Eighteen patients with ACC of the tongue base were treated with C-ion RT between May 2002 and April 2014. Seventeen patients had T4a disease and 1 patient had T2 disease before C-ion RT.

RESULTS

The median follow-up period was 57 months (range, 10-132 months). The 5-year local control rate was 92%. The 5-year overall survival (OS) and disease-free survival (DFS) rates were 72% and 44%, respectively. Regarding late reactions, 2 patients developed grade 3 mandible osteoradionecrosis, and 1 had grade 3 hemorrhage of the tongue base.

CONCLUSION

C-ion RT was effective with acceptable toxicities for locally advanced ACC of the tongue base. © 2016 Wiley Periodicals, Inc. Head Neck 38: E2122-E2126, 2016.

A generalized target theory and its applications

Different radiobiological models have been proposed to estimate the cell-killing effects, which are very important in radiotherapy and radiation risk assessment. However, most applied models have their own scopes of application. In this work, by generalizing the relationship between "hit" and "survival" in traditional target theory with Yager negation operator in Fuzzy mathematics, we propose a generalized target model of radiation-induced cell inactivation that takes into account both cellular repair effects and indirect effects of radiation. The simulation results of the model and the rethinking of "the number of targets in a cell" and "the number of hits per target" suggest that it is only necessary to investigate the generalized single-hit single-target (GSHST) in the present theoretical frame. Analysis shows that the GSHST model can be reduced to the linear quadratic model and multitarget model in the low-dose and high-dose regions, respectively. The fitting results show that the GSHST model agrees well with the usual experimental observations. In addition, the present model can be used to effectively predict cellular repair capacity, radiosensitivity, target size, especially the biologically effective dose for the treatment planning in clinical applications.

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

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.

Outcome and toxicity of stereotactic body radiotherapy with helical tomotherapy for inoperable lung tumor: analysis of Grade 5 radiation pneumonitis

To analyze outcomes and toxicities of stereotactic body radiotherapy with helical tomotherapy (HT-SBRT) for inoperable lung tumors, the medical records of 30 patients with 31 lung tumors treated with HT-SBRT were reviewed. The 3-year local control, cause-specific survival and overall survival rates (LC, CCS and OS, respectively) were analyzed using the Kaplan-Meier method. Toxicities were graded using Common Terminology Criteria for Adverse Events ver. 4. To investigate the factors associated with Grade 5 radiation pneumonitis (G5 RP), several parameters were analyzed: (i) patient-specific factors (age, gross tumor volume and PTV, and the interstitial pulmonary shadow on pretreatment CT); and (ii) dosimetry-specific factors (conformity index, homogeneity index, mean lung dose, and V5, V10, V15, V20 and V25 of the total lungs). The median duration of observation for all patients was 36.5 months (range, 4-67 months). The 3-year LC, CCS and OS were 82, 84 and 77%, respectively. Regarding Grade 3 or higher toxicities, two patients (6.7%) developed G5 RP. GTV was significantly associated with G5 RP (P = 0.025), and there were non-significant but slight associations with developing G5 RP for V5 (P = 0.067) and PTV (P = 0.096). HT-SBRT led to standard values of LC, CCS and OS, but also caused a markedly higher incidence of G5 RP. It is essential to optimize patient selection so as to avoid severe radiation pneumonitis in HT-SBRT.

Applicability of the linear-quadratic model to single and fractionated radiotherapy schedules: an experimental study

The aim of this study was to examine the applicability of the linear-quadratic (LQ) model to single and fractionated irradiation in EMT6 cells. First, the α/β ratio of the cells was determined from single-dose experiments, and a biologically effective dose (BED) for 20 Gy in 10 fractions (fr) was calculated. Fractional doses yielding the same BED were calculated for 1-, 2-, 3-, 4-, 5-, 7-, 15- and 20-fraction irradiation using LQ formalism, and then irradiation with these schedules was actually given. Cell survival was determined by a standard colony assay. Differences in cell survival between pairs of groups were compared by t-test. The α/β ratio of the cells was 3.18 Gy, and 20 Gy in 10 fr corresponded to a BED3.18 of 32.6 Gy. The effects of 7-, 15- and 20-fraction irradiation with a BED3.18 of 32.6 Gy were similar to those of the 10-fraction irradiation, while the effects of 1- to 5-fraction irradiation were lower. In this cell line, the LQ model was considered applicable to 7- to 20-fraction irradiation or doses per fraction of 2.57 Gy or smaller. The LQ model might be applicable in the dose range below the α/β ratio.