Although radiation therapy is an important cancer treatment modality, patients may experience adverse effects. The use of a radiation-effect modulator may help improve the outcome and health-related quality of life (HRQOL) of patients undergoing radiation therapy either by enhancing tumor cell killing or by protecting normal tissues. Historically, the successful translation of radiation-effect modulators to the clinic has been hindered due to the lack of focused collaboration between academia, pharmaceutical companies and the clinic, along with limited availability of support for such ventures. The U.S. Government has been developing medical countermeasures against accidental and intentional radiation exposures to mitigate the risk and/or severity of acute radiation syndrome (ARS) and the delayed effects of acute radiation exposures (DEARE), and there is now a drug development pipeline established. Some of these medical countermeasures could potentially be repurposed for improving the outcome of radiation therapy and HRQOL of cancer patients. With the objective of developing radiation-effect modulators to improve radiotherapy, the Small Business Innovation Research (SBIR) Development Center at the National Cancer Institute (NCI), supported by the Radiation Research Program (RRP), provided funding to companies from 2011 to 2014 through the SBIR contracts mechanism. Although radiation-effect modulators collectively refer to radioprotectors, radiomitigators and radiosensitizers, the focus of this article is on radioprotection and mitigation of radiation injury. This specific SBIR contract opportunity strengthened existing partnerships and facilitated new collaborations between academia and industry. In this commentary, we assess the impact of this funding opportunity, outline the review process, highlight the organ/site-specific disease needs in the clinic for the development of radiation-effect modulators, provide a general understanding of a framework for gathering preclinical and clinical evidence to obtain regulatory approval and provide a basis for broader venture capital needs and support from pharmaceutical companies to fully capitalize on the advances made thus far in this field.

Cell populations that have been exposed to high-charge and energy (HZE) particle radiation, and then challenged by expression of a rare-cutting nuclease, show an increased frequency of deletions and translocations originating at the enzyme cut sites. Here, we examine whether this effect also occurs in nonirradiated cells that have been co-cultured with irradiated cells. Human cells were irradiated with 0.3–1.0 Gy of either 600 MeV/u ⁵⁶Fe or 1,000 MeV/u ⁴⁸Ti ions or with 0.3–3.0 Gy of 320 kV X rays. These were co-cultured with I-SceI-expressing reporter cells at intervals up to 21 days postirradiation. Co-culture with HZE-irradiated cells led to an increase in the frequency of I-SceI-stimulated translocations and deletions in the nonirradiated cells. The effect size was similar to that seen previously in directly irradiated populations (maximum effect in bystander cells of 1.7- to 4-fold depending on ion and end point). The effect was not observed when X-ray-irradiated cells were co-cultured with nonirradiated cells, but was correlated with an increase in γ-H2AX foci-positive cells in the nonirradiated population, suggesting the presence of genomic stress. Transcriptional profiling of a directly irradiated cell population showed that many genes for cytokines and other secretory proteins were persistently upregulated, but their induction was not well correlated with functional effects on repair in co-cultured cells, suggesting that this transcriptional response alone is not sufficient to evoke the effect. The finding that HZE-irradiated cells influence the DNA double-strand break repair fidelity in their nonirradiated neighbors has implications for risk in the space radiation environment.

With the increased incidence of esophageal cancer, chemoradiotherapy continues to play an important role in the management of this disease. Developing potent radiosensitizers is therefore critical for improving outcomes. The use of drugs that have already undergone clinical testing is an appealing approach once the side effects and tolerated doses are established. Here, we demonstrate that the aminopeptidase inhibitor, CHR-2797/tosedostat, increases the radiosensitivity of esophageal cancer cell lines (FLO-1 and OE21) in vitro in both normoxic and physiologically relevant low oxygen conditions. To our knowledge, the effective combination of CHR-2797 with radiation exposure has not been reported previously in any cancer cell type. The mechanism of increased radiosensitivity was not dependent on the induction of DNA damage or DNA repair kinetics. Our data support the need for further preclinical testing of CHR-2797 in combination with radiotherapy for the treatment of esophageal cancer.

In this study, the effects of radiation exposure on cognitive performance were evaluated. Rats were exposed to either helium (⁴He) particles (1,000 MeV/n; 0.1–10 cGy; head only) or cesium ¹³⁷Cs gamma rays (50–400 cGy; whole body), after which their cognitive performance was evaluated. The results indicated that exposure to doses of ⁴He particles as low as 0.1 cGy disrupted performance in a variety of cognitive tasks, including plus-maze performance (baseline anxiety), novel location recognition (spatial performance) and operant responding on an ascending fixed-ratio reinforcement schedule (motivation and responsiveness to changes in environmental contingencies) but not on novel object recognition performance (learning and memory). In contrast, after exposure to ¹³⁷Cs gamma rays only plus-maze performance was affected. There were no significant effects on any other task. Because exposure to both types of radiation produce oxidative stress, these results indicate that radiation-produced oxidative stress may be a necessary condition for the radiation-induced disruption of cognitive performance, but it is not a sufficient condition.

Past and recent radiation events have involved a high incidence of radiation combined injury where victims often succumb to serious infections as a consequence of bacterial translocation and subsequent sepsis. The risk of infection is exacerbated in radiation combined skin-burn injury (RCI), which increase vulnerability. Furthermore, no suitable countermeasures for radiation combined skin-burn injury have been established. In this study, we evaluated captopril as a potential countermeasure to radiation combined skin-burn injury. Captopril is an FDA-approved angiotensin-converting enzyme inhibitor that was previously reported to stimulate hematopoietic recovery after exposure to ionizing radiation. Female B6D2F1/J mice were whole-body bilateral ⁶⁰Co gamma-photon irradiated (dose rate of 0.4 Gy/min) with 9.5 Gy (LD_70/30 for RCI), followed by nonlethal dorsal skin-burn injury under anesthesia (approximately 15% total-body surface-area burn). Mice were provided with acidified drinking water with or without dissolved captopril (0.55 g/l) for 30 days immediately after injury and were administered topical gentamicin (0.1% cream; day 1–10) and oral levofloxacin (90–100 mg/kg; day 3–16). Surviving mice were euthanized on day 30 after analyses of water consumption, body weight and survival. Our data demonstrate that, while treatment with captopril did mitigate mortality induced by radiation injury (RI) alone (55% captopril vs. 80% vehicle; n = 20, P < 0.05), it also resulted in decreased survival after radiation combined skin-burn injury (22% captopril vs. 41% vehicle; n = 22, P < 0.05). Moreover, captopril administration via drinking water produced an uneven dosage pattern among the different injury groups ranging from 74 ± 5.4 to 115 ± 2.2 mg/kg/day. Captopril treatment also did not counteract the negative alterations in hematology, splenocytes or bone marrow cellularity after either radiation injury or radiation combined skin-burn injury. These data suggest that captopril may exert its actions differently between the two injury models (RI vs. RCI) and that captopril dosing, when combined with topical and systemic antibiotic treatments, may not be a suitable countermeasure for RCI.

Accurate and mechanistically plausible mathematical models of DNA double-strand break (DSB) rejoining kinetics are needed to correctly estimate the dependence of cell death and transformation on linear energy transfer, radiation dose and time. When integrated into more comprehensive risk estimation approaches, such models are potentially valuable tools in applications such as treatment planning for radiotherapy. In this study, we compared 10 DSB rejoining models based on data collected from 61 mammalian cell lines after high-dose-rate photon or heavy ion irradiation. The set of models included formalisms with: 1. one, two or three discrete first-order rejoining rates; 2. continuously distributed first-order rejoining rates; and 3. second-order rejoining rates. The Akaike information criterion was used to quantify the relative support for each model from the data, accounting for goodness of fit and model complexity. The best performance was exhibited by a bi-exponential model with two discrete rejoining rates and a model with gamma-distribution rejoining rates. Models with more than three free parameters overfitted the data and models with single DSB rejoining rates or with an inflexible distribution of rejoining rates lacked accuracy. Of special note is that the analyzed data provide little support for models that rely on pairwise interactions to describe DSB rejoining kinetics. Consequently, kinetic cell survival models reflecting bi-exponential DSB rejoining might be preferable to models based on the kinetics of intra- and inter-lesion rejoining.

Workers from the Sellafield nuclear facility (Cumbria, UK) with occupational exposures to external sources of ionizing radiation were examined for translocation frequencies in peripheral blood lymphocytes using fluorescence in situ hybridization (FISH). This is an extension of an earlier study of retired workers, and includes analyses of additional samples from the earlier collection, bringing the total to 321. Another 164 samples from both current and retired employees, including 26 repeat samples, were obtained from a new collection, thus giving a combined dataset of 459 workers. This all-male population of workers was divided into 6 dose groups comprising 97 with recorded external occupational doses <50 mGy, 118 with 50–249 mGy, 129 with 250–499 mGy, 89 with 500–749 mGy, 17 with 750–999 mGy and 9 with >1,000 mGy. Univariate analysis showed a significant association between external dose and translocation frequency (P < 0.001) with the estimate of slope ± standard error being 1.174 ± 0.164 × 10⁻² translocations per Gy. Multivariate analysis revealed that age increased the rate of translocations by 0.0229 ± 0.0052 × 10⁻² per year (P < 0.001). However, the impact of age adjustment on the radiation dose response for translocation frequencies was minor with the new estimate of slope ± standard error being 1.163 ± 0.162 × 10⁻² translocations per Gy. With the dose response for the induction of translocations by chronic in vivo low-LET radiation now well characterized, cytogenetic analysis can play an integral role in retrospective dose reconstruction of chronic exposure in epidemiological studies of exposed populations.

Exposure to ionizing radiation causes cellular damage, which can lead to premature cell death or accumulation of somatic mutations, resulting in malignancy. The damage is mediated in part by free radicals, particularly reactive oxygen species. Fermented papaya preparation (FPP), a product of yeast fermentation of Carica papaya Linn, has been shown to act as an antioxidant. In this study, we investigated the potential of FPP to prevent radiation-induced damage. FPP (0–100 μg/ml) was added to cultured human foreskin fibroblasts and myeloid leukemia (HL-60) cells either before or after irradiation (0–18 Gy). After 1–3 days, the cells were assayed for: intracellular labile iron, measured by staining with calcein; reactive oxygen species generation, measured with dichlorofluorescein diacetate; apoptosis, determined by phosphatidylserine exposure; membrane damage, determined by propidium iodide uptake; and cell survival, determined by a cell proliferation assay. DNA damage was estimated by measuring 8-oxoguanine, a parameter of DNA oxidation, using a fluorescent-specific probe and by the comet assay. These parameters were also assayed in bone marrow cells of mice treated with FPP (by adding it to the drinking water) either before or after irradiation. Somatic mutation accumulation was determined in their peripheral red blood cells, and their survival was monitored. FPP significantly reduced the measured radiation-induced cytotoxic parameters. These findings suggest that FPP might serve as a radioprotector, and its effect on DNA damage and mutagenicity might reduce the long-term effects of radiation, such as primary and secondary malignancy.

The major limitation to reaching a curative radiation dose in radioresistant tumors such as malignant gliomas is the high sensitivity to radiation and subsequent damage of the surrounding normal tissues. Novel dose delivery methods such as minibeam radiation therapy (MBRT) may help to overcome this limitation. MBRT utilizes a combination of spatial fractionation of the dose and submillimetric (600 μm) field sizes with an array (“comb”) of parallel thin beams (“teeth”). The dose profiles in MBRT consist of peaks and valleys. In contrast, the seamless irradiations of the several squared centimeter field sizes employed in standard radiotherapy result in homogeneous dose distributions (and consequently, flat dose profiles). The innovative dose delivery methods employed in MBRT, unlike standard radiation therapy, have demonstrated remarkable normal tissue sparing. In this pilot work, we investigated the tolerance of the rat brain after whole-brain MBRT irradiation. A dose escalation was used to study the tissue response as a function of dose, so that a threshold could be established: doses as high as 100 Gy in one fraction were still well tolerated by the rat brain. This finding suggests that MBRT may be used to deliver higher and potentially curative radiation doses in clinical practice.

Microbeam radiation treatment (MRT) using synchrotron radiation has shown great promise in the treatment of brain tumors, with a demonstrated ability to eradicate the tumor while sparing normal tissue in small animal models. With the goal of expediting the advancement of MRT research beyond the limited number of synchrotron facilities in the world, we recently developed a compact laboratory-scale microbeam irradiator using carbon nanotube (CNT) field emission-based X-ray source array technology. The focus of this study is to evaluate the effects of the microbeam radiation generated by this compact irradiator in terms of tumor control and normal tissue damage in a mouse brain tumor model. Mice with U87MG human glioblastoma were treated with sham irradiation, low-dose MRT, high-dose MRT or 10 Gy broad-beam radiation treatment (BRT). The microbeams were 280 μm wide and spaced at 900 μm center-to-center with peak dose at either 48 Gy (low-dose MRT) or 72 Gy (high-dose MRT). Survival studies showed that the mice treated with both MRT protocols had a significantly extended life span compared to the untreated control group (31.4 and 48.5% of life extension for low- and high-dose MRT, respectively) and had similar survival to the BRT group. Immunostaining on MRT mice demonstrated much higher DNA damage and apoptosis level in tumor tissue compared to the normal brain tissue. Apoptosis in normal tissue was significantly lower in the low-dose MRT group compared to that in the BRT group at 48 h postirradiation. Interestingly, there was a significantly higher level of cell proliferation in the MRT-treated normal tissue compared to that in the BRT-treated mice, indicating rapid normal tissue repairing process after MRT. Microbeam radiation exposure on normal brain tissue causes little apoptosis and no macrophage infiltration at 30 days after exposure. This study is the first biological assessment on MRT effects using the compact CNT-based irradiator. It provides an alternative technology that can enable widespread MRT research on mechanistic studies using a preclinical model, as well as further translational research towards clinical applications.

Cancer stem-like cells (CSCs) have been suggested to be the principal cause of tumor radioresistance, dormancy and recurrence after radiotherapy. However, little is known about CSC behavior in response to clinical radiotherapy, particularly with regard to CSC communication with bulk cancer cells. In this study, CSCs and nonstem-like cancer cells (NSCCs) were co-cultured, and defined cell types were chosen and irradiated, respectively, with proton microbeam. The bidirectional rescue effect in the combinations of the two cell types was then investigated. The results showed that out of all four combinations, only the targeted, proton irradiated NSCCs were protected by bystander CSCs and showed less accumulation of 53BP1, which is a widely used indicator for DNA double-strand breaks. In addition, supplementation with c-PTIO, a specific nitric oxide scavenger, can show a similar effect on targeted NSCCs. These results, showed that the rescue effect of CSCs on targeted NSCCs involves nitric oxide in the process, suggesting that the cellular communication between CSCs and NSCCs may be important in determining the survival of tumor cells after radiation therapy. To our knowledge, this is the first report demonstrating a rescue effect of CSCs to irradiated NSCCs that may help us better understand CSC behavior in response to cancer radiotherapy.