Hanahan and Weinberg recently updated their conceptual framework of the “Hallmarks of Cancer”. The original article, published in 2000, is among the most highly cited reviews in the field of oncology. The goal of this review is to highlight important discoveries in radiation biology that pertain to the Hallmarks. We identified early studies that exemplified how ionizing radiation affects the hallmarks or how radiation was used experimentally to advance the understanding of key hallmarks. A literature search was performed to obtain relevant primary research, and topics were assigned to a particular hallmark to allow an organized, chronological account of the radiobiological advancements. The hallmarks are reviewed in an order that flows from cellular to microenvironmental effects.

The detonation of an improvised nuclear device during a radiological terrorist attack could result in the exposure of thousands of civilians and first responders to lethal or potentially lethal doses of ionizing radiation (IR). There is a major effort in the United States to develop phamacological mitigators of radiation lethality that would be effective particularly if administered after irradiation. We show here that giving female C57BL/6 mice a subcutaneous surgical incision after whole body exposure to an LD_50/30 X-ray dose protects against radiation lethality and increases survival from 50% to over 90% (P = 0.0001). The increase in survival, at least in part, appears to be due to enhanced recovery of hematopoiesis, notably red blood cells, neutrophils and platelets. While a definitive mechanism has yet to be elucidated, we propose that this approach may be used to identify potentially novel mechanisms and pathways that could aid in the development of novel pharmacological radiation countermeasures.

Recent epidemiological studies have suggested that radiation exposure from pediatric CT scanning is associated with small excess cancer risks. However, the majority of CT scans are performed on adults, and most radiation-induced cancers appear during middle or old age, in the same age range as background cancers. Consequently, a logical next step is to investigate the effects of CT scanning in adulthood on lifetime cancer risks by conducting adult-based, appropriately designed epidemiological studies. Here we estimate the sample size required for such studies to detect CT-associated risks. This was achieved by incorporating different age-, sex-, time- and cancer type-dependent models of radiation carcinogenesis into an in silico simulation of a population-based cohort study. This approach simulated individual histories of chest and abdominal CT exposures, deaths and cancer diagnoses. The resultant sample sizes suggest that epidemiological studies of realistically sized cohorts can detect excess lifetime cancer risks from adult CT exposures. For example, retrospective analysis of CT exposure and cancer incidence data from a population-based cohort of 0.4 to 1.3 million (depending on the carcinogenic model) CT-exposed UK adults, aged 25–65 in 1980 and followed until 2015, provides 80% power for detecting cancer risks from chest and abdominal CT scans.

Detonation of an improvised nuclear device near a population center would cause significant casualties from the acute radiation syndrome (ARS) due to exposure to mixed neutron/gamma fields (MF). The pathophysiology of ARS involves inflammation, microvascular damage and alterations in immune function. Interactions between endothelial cells (EC) and hematopoietic cells are important not only for regulating immune cell traffic and function, but also for providing the microenvironment that controls survival, differentiation and migration of hematopoietic stem and progenitor cells in blood-forming tissues. Endothelial cells/leukocyte interactions also influence tumor progression and the results of anticancer therapies. In this study, we hypothesized that irradiation of endothelial cells would modulate their effects on hematopoietic cells and vice versa. Human umbilical vein endothelial cells (HUVEC) and immortalized T lymphocytes (Jurkat cells) were cultured individually and in co-culture after exposure to mixed fields. Effects of nonirradiated cells were compared to effects of irradiated cells and alterations in signaling pathways were determined. Mitogen-activated protein kinases (MAPKs) p38 and p44/42 (ERK1/2) in HUVEC exhibited higher levels of phosphorylated protein after exposure to mixed field radiation. IL-6, IL-8, G-CSF, platelet derived growth factor (PDGF) and angiopoietin 2 (ANG2) protein expression were upregulated in HUVEC by exposure to mixed field radiation. PCR arrays using HUVEC mRNA revealed alterations in gene expression after exposure to mixed fields and/or co-culture with Jurkat cells. The presence of HUVEC also influenced the function of Jurkat cells. Nonirradiated Jurkat cells showed an increase in proliferation when co-cultured with nonirradiated HUVEC, and a decrease in proliferation when co-cultured with irradiated HUVEC. Additionally, nonirradiated Jurkat cells incubated in media from irradiated HUVEC exhibited upregulation of activated caspase 3. Irradiation of Jurkat cells caused a G₂/M arrest and increased adherence to HUVEC. When co-cultured with HUVEC, irradiated Jurkat cells exhibited G₀/G₁ arrest and increased apoptosis. The data indicate that gene expression and cell function of endothelial cells and hematopoietic cells are influenced by radiation and by interactions between the two cell types. These phenomena may affect the success of therapies for ARS and cancer.

Radiation exposure causes DNA breaks leading to structural chromosome aberrations that can be carcinogenic. Lifetime cancer risks are elevated in irradiated children compared to similarly exposed adults. To determine the extent to which age influences the frequency and types of chromosome damage in response to ionizing radiation, peripheral blood samples were collected from 20 adults (aged 22–78 years) and from the umbilical cords of 10 newborns and acutely exposed to 0 (control), 1, 2, 3 or 4 Gy of cobalt-60 gamma rays. Cells were cultured in the presence of the mitogen phytohemagglutinin, harvested at 48 h and then evaluated for structural chromosome aberrations by fluorescence in situ hybridization whole chromosome painting. Regression analyses were used to evaluate radiation-induced translocated chromosomes, dicentrics, acentric fragments, color junctions and aberrant cells to determine whether the frequencies of these events was dependent upon age. Peripheral blood lymphocytes from newborns showed statistically significant increases in the induced frequencies of translocated chromosomes, dicentrics, acentric fragments, color junctions and abnormal cells at several radiation doses when compared to blood from adults. No significant changes in sensitivity with age were observed when adults were evaluated separately. We conclude that peripheral lymphocytes from newborns are significantly more prone to radiation-induced chromosome aberrations than peripheral lymphocytes from adults. The increased sensitivity of newborns in this study relative to adults was found to be 37(±9)%, 18(±4)%, 12(±2)% and 4(±5)% at doses of 1, 2, 3 and 4 Gy, respectively. These data may be relevant when making radiation exposure risk assessments.

Sixteen male Djungarian hamsters, serving as their own controls, were individually exposed to RF-EMF (900 MHz, GSM modulation) at 0 (sham), 0.08, 0.4 or 4 W/kg specific absorption rate (SAR) in specially constructed rectangular waveguides. Exposure duration was one week per condition, followed by one week without exposure. Once per day, the temperatures of the hamsters' back fur (a surrogate for skin temperature) and the cornea of the eye (a surrogate for body temperature), were measured by infrared thermography. Oxygen, carbon dioxide and humidity were measured continuously in the ambient and exhaled air. Food and water consumption, as well as body weight were recorded once per week. Only at the highest SAR level were the following effects observed: fur temperatures were elevated by approximately 0.5°C (P < 0.001), while the temperatures of the eyes' surface were not affected; food consumption was lowered (P < 0.05), while water consumption and body weight were not affected; the production of carbon dioxide was lowered during the day (P < 0.01) and unaffected during the night, while oxygen consumption levels remained unaffected and finally the respiratory quotient (carbon dioxide production divided by oxygen consumption) was lower during the day (P < 0.05) and also somewhat lower during the night (not significant). The results demonstrate the usefulness of our methods for experiments dealing with metabolic effects of RF-EMF exposure in rodents. They also confirm the assumption that even though the metabolism is reduced at high SAR levels, the body core temperature is being kept constant by the energy uptake from the RF-EMF exposure which is able to physiologically compensate for the reduced metabolism.

In a recent published study, we investigated the response of an experimental prostate carcinoma (R3327-AT1) after irradiation with 1, 2 or 6 fractions of carbon ions or photons, respectively. The original intention of this study was to measure the dose-dependent local control probability as well as the related relative biological effectiveness of carbon ions. However, we now report an increased metastatic rate when the number of fractions was increased from 2 to 6. In a total of 246 animals, the actuarial metastatic rates for 1, 2 and 6 fractions were 5.1 ± 3.5%, 5.7 ± 4.0% and 15.3 ± 7.1% for photons and 9.8 ± 7.5%, 4.0 ± 3.9% and 20.3 ± 6.5% for carbon ions, respectively. The increase was significant only for carbon ions (6 vs. 2 fractions,P = 0.03). Although the original experiment was not designed to investigate metastatic rates, this observation may be of general interest to researchers studying radiation-modulated metastatic activity.

A novel technique has been employed to investigate the simultaneous damage to DNA components induced by soft X rays (1.5 keV) and low-energy electrons (0–30 eV) in thin films of thymidine deposited on glass and tantalum substrates and irradiated under atmospheric pressure and temperature. The films were surrounded by either an N₂ or O₂ environment. The formation of four radiation-induced products is reported in this article: base release, 5-hydroxymethyl-2′-deoxyuridine (5-HMdUrd), 5-formyl-2′-deoxyuridine (5-FordUrd) and 5,6-dihydrothymidine (5,6-DHThd). Analysis with LC-MS/MS shows larger damage yields in the samples deposited on tantalum than in those deposited on glass, which is attributed to the interaction of the additional low-energy electrons that are photoemitted from the metal surface. From a comparison of the results obtained from N₂ and O₂ environment, we report a dramatic effect from 6 O₂: an approximately threefold increase in the yield of products, attributed to the reaction of O₂ with initial carbon-centered thymidine radicals generated in the film during irradiation.

Although neo-adjuvant radiotherapy is generally successful in treatment of advanced prostate cancer, radioresistance is still a major therapeutic problem in many patients. In the current study, we investigated the effects of metformin (1,1-dimethylbiguanide hydrochloride), a widely used antidiabetic drug, on tumor cell radiosensitivity in prostate cancer. Through clonogenic survival assays, we found that metformin treatment enhanced radiosensitivity of prostate cancer cells with a dose enhancement factor. Moreover, irradiation of subcutaneous C4-2 tumors in mice treated with metformin resulted in an increase in radiation-induced tumor growth delay (17.3 days to 29.5 days, P < 0.01), which indicates that the tumor radiosensitivity increased by metformin in vivo. We also measured the sublethal damage repair and analyzed double-strand breaks (DSBs) in X-irradiated cells. γ-H2AX, as an indicator of DSBs, had significantly more foci per cell in the group treated with metformin and radiation compared to groups treated with metformin or irradiation, respectively. Moreover, mice with subcutaneous tumor implants lived longer after a combined treatment of metformin and radiation. In addition, the reduced phosphorylation of DNA-PKcs caused by EGFR/PI3K/Akt down-regulation is essential for metformin to induce radiosensitivity in prostate cancer cells. Our results indicate that metformin enhances prostate cancer cell radiosensitivity in vitro and in vivo. Exposure to metformin before radiation therapy could be a beneficial option for the treatment of prostate cancer.

Ionizing radiation (IR) is commonly used for cancer therapy, however, its potential influence on cancer metastatic potential remains controversial. In this study, we elucidated the role of integrins in regulation of IR-altered adhesion between breast cancer cells and extracellular matrix (ECM) proteins, which is a key step in the initial phase of metastasis. Our data suggest that the extent of effect that ionizing radiation had on cell adhesion depended on the genetic background of the breast cancer cells. Ionizing radiation was a better adhesion inducer for p53-mutated cells, such as MDA-MB-231 cells, than for p53 wild-type cells, such as MCF-7 cells. While IR-induced adhesions between MDA-MB-231 cells to fibronectin, laminin, collagen I and collagen IV, only blocking of the adhesion between α5β1 integrin and fibronectin using anti-α5β1 integrin antibody could completely inhibit the radiation-induced adhesion of the cells. A soluble Arg-Gly-Asp peptide, the binding motif for fibronectin binding integrins, could also reduce the adhesion of the cells to fibronectin with or without ionizing radiation exposure. The inhibition of the cell-fibronectin interaction also affected, but did not always correlate with, transwell migration of the cancer cells. In addition, our data showed that the total expression of α5 integrin and surface expression of α5β1 integrin were increased in the cells treated with ionizing radiation. The increased surface expression of α5β1 integrin, along with the adhesion between the cells and fibronectin, could be inhibited by both ataxia telangiectasia mutated (ATM) and Rad3-related (ATR) kinase inhibitors. These results suggested that ATM/ATR-mediated surface expression of α5β1 integrin might play a central role in regulation of ionizing radiation-altered adhesion.

Monte Carlo simulations were used to calculate the yields for the primary species (e^–_aq, H^•, H₂, ^•OH and H₂O₂) formed from the radiolysis of neutral liquid water by mono-energetic 2 MeV neutrons at temperatures between 25–350°C. The 2 MeV neutron was taken as representative of a fast neutron flux in a reactor. For light water, the moderation of these neutrons generated elastically scattered recoil protons of ∼1.264, 0.465, 0.171 and 0.063 MeV, which at 25°C, had linear energy transfers (LETs) of ∼22, 43, 69 and 76 keV/μm, respectively. Neglecting the radiation effects due to oxygen ion recoils and assuming that the most significant contribution to the radiolysis came from these first four recoil protons, the fast neutron yields could be estimated as the sum of the yields for these protons after allowance was made for the appropriate weightings according to their energy. Yields were calculated at 10⁻⁷, 10⁻⁶ and 10⁻⁵ s after the ionization event at all temperatures, in accordance with the time range associated with the scavenging capacities generally used for fast neutron radiolysis experiments. The results of the simulations agreed reasonably well with the experimental data, taking into account the relatively large uncertainties in the experimental measurements, the relatively small number of reported radiolysis yields, and the simplifications included in the model. Compared with data obtained for low-LET radiation (⁶⁰Co γ rays or fast electrons), our computed yields for fast neutron radiation showed essentially similar temperature dependences over the range of temperatures studied, but with lower values for yields of free radicals and higher values for molecular yields. This general trend is a reflection of the high-LET character of fast neutrons. Although the results of the simulations were consistent with the experiment, more experimental data are required to better describe the dependence of radiolytic yields on temperature and to test more thoroughly our modeling calculations.

Radiation-induced gastrointestinal syndrome occurs when the body is exposed to a high dose of radiation. Currently, safe and effective radioprotectants are not available. Apoptosis was reported to play a primary role in radiation-induced injury. Recent evidence suggests that stimulation of α7 nicotinic acetylcholine receptor (α7nAChR) prevents cell death by inhibition of apoptosis. In this study, we demonstrated that a single dose of PNU282987 (100 μg/kg, i.p.), a selective α7nAChR agonist, protected mice from intestinal injury and significantly improved survival when administered prior to lethal 8 Gy total body irradiation. In vitro, PNU282987 protected against 8 Gy radiation-induced cell death in human umbilical venous endothelial cells by inhibiting apoptosis. We conclude that activation of α7nAChR may provide a new therapeutic pathway for the treatment of radiation-induced damage and mortality.