Low-dose radiation therapy of cancer: role of immune enhancement

The clinical regimens and cell membrane camouflaged nanodrug delivery systems in hematologic malignancies treatment

Hematologic malignancies (HMs), also referred to as hematological or blood cancers, pose significant threats to patients as they impact the blood, bone marrow, and lymphatic system. Despite significant clinical strategies using chemotherapy, radiotherapy, stem cell transplantation, targeted molecular therapy, or immunotherapy, the five-year overall survival of patients with HMs is still low. Fortunately, recent studies demonstrate that the nanodrug delivery system holds the potential to address these challenges and foster effective anti-HMs with precise treatment. In particular, cell membrane camouflaged nanodrug offers enhanced drug targeting, reduced toxicity and side effects, and/or improved immune response to HMs. This review firstly introduces the merits and demerits of clinical strategies in HMs treatment, and then summarizes the types, advantages, and disadvantages of current nanocarriers helping drug delivery in HMs treatment. Furthermore, the types, functions, and mechanisms of cell membrane fragments that help nanodrugs specifically targeted to and accumulate in HM lesions are introduced in detail. Finally, suggestions are given about their clinical translation and future designs on the surface of nanodrugs with multiple functions to improve therapeutic efficiency for cancers.

Low-dose radiation therapy mobilizes antitumor immunity: New findings and future perspectives

Radiotherapy has unique immunostimulatory and immunosuppressive effects. Although high-dose radiotherapy has been found to have systemic antitumor effects, clinically significant abscopal effects were uncommon on the basis of irradiating single lesion. Low-dose radiation therapy (LDRT) emerges as a novel approach to enhance the antitumor immune response due to its role as a leverage to reshape the tumor immune microenvironment (TIME). In this article, from bench to bedside, we reviewed the possible immunomodulatory role of LDRT on TIME and systemic tumor immune environment, and outlined preclinical evidence and clinical application. We also discussed the current challenges when LDRT is used as a combination therapy, including the optimal dose, fraction, frequency, and combination of drugs. The advantage of low toxicity makes LDRT potential to be applied in multiple lesions to amplify antitumor immune response in polymetastatic disease, and its intersection with other disciplines might also make it a direction for radiotherapy-combined modalities.

Case Report: A novel mixture of dose-fractioned radiation and immunotherapy for treatment of cholangiocarcinoma

Malignant tumors of the biliary tract exhibit a high degree of malignancy and heterogeneity with a poor overall prognosis. Immunotherapy has limited benefits for patients with cholangiocarcinoma. Radiation therapy can change the tumor microenvironment, but its effect heavily depends on radiation dose and fraction. We report a case of advanced intrahepatic cholangiocarcinoma in a 43-year-old male patient, with a huge liver mass of 16.5 cm in diameter, with bone and liver metastases at the first diagnosis. First-line treatment with chemotherapy and PD1 inhibitor was sustained only for 8 months. In second-line treatment, radiotherapy was administered, with 5 Gy in 5 fractions administered to the entire tumor area and 25 Gy in 5 fractions to the solid lesions of the tumor. After the completion of radiotherapy, programmed cell death 1 inhibitor combined with tyrosine kinase inhibitor was maintained. The patient achieved a progression-free-survival time of 12 months and an overall survival time of 25 months. The success of our case suggests that mixed low- and high-dose radiation can significantly improve tumor control and survival time. In clinical practice, based on the characteristics of the tumor and existing treatment options, the rational combination of existing treatment regimens can improve the prognosis of cholangiocarcinoma.

Chrysin Encapsulated Copper Nanoparticles with Low Dose of Gamma Radiation Elicit Tumor Cell Death Through p38 MAPK/NF-κB Pathways

Improving radiation effect on tumor cells using radiosensitizers is gaining traction for improving chemoradiotherapy. This study aimed to evaluate copper nanoparticles (CuNPs) synthesized using chrysin as radiosensitizer with γ-radiation on biochemical and histopathological approaches in mice bearing Ehrlich solid tumor. CuNPs were characterized with irregular round sharp shape with size range of 21.19-70.79 nm and plasmon absorption at 273 nm. In vitro study on MCF-7 cells detected cytotoxic effect of CuNPs with IC50 of 57.2 ± 3.1 μg. In vivo study was performed on mice transplanted with Ehrlich solid tumor (EC). Mice were injected with CuNPs (0.67 mg/kg body weight) and/or exposed to low dose of gamma radiation (0.5 Gy). EC mice exposed to combined treatment of CuNPs and radiation showed a marked reduction in tumor volume, ALT and CAT, creatinine, calcium, and GSH, along with elevation in MDA, caspase-3 in parallel with inhibition of NF-κB, p38 MAPK, and cyclin D1 gene expression. Comparing histopathological findings of treatment groups ends that combined treatment was of higher efficacy, showing tumor tissue regression and increase in apoptotic cells. In conclusion, CuNPs with a low dose of gamma radiation showed more powerful ability for tumor suppression via promoting oxidative state, stimulating apoptosis, and inhibiting proliferation pathway through p38MAPK/NF-κB and cyclinD1.

Low-dose radiotherapy effects the progression of anti-tumor response

The history of low-dose radiotherapy (LDRT or LDR) as a treatment modality for malignant tumors dates back to the 1920s. Even with the minimal total dose administered during treatment, LDRT can result in long-lasting remission. Autocrine and paracrine signaling are widely recognized for fostering the growth and development of tumor cells. LDRT exerts systemic anti-tumor effects through various mechanisms, such as enhancing the activity of immune cells and cytokines, shifting the immune response towards an anti-tumor phenotype, influencing gene expression, and blocking crucial immunosuppressive pathways. Additionally, LDRT has been demonstrated to enhance the infiltration of activated T cells and initiate a series of inflammatory processes while modulating the tumor microenvironment. In this context, the objective of receiving radiation is not to directly kill tumor cells but to reprogram the immune system. Enhancing anti-tumor immunity may be a critical mechanism by which LDRT plays a role in cancer suppression. Therefore, this review primarily focuses on the clinical and preclinical efficacy of LDRT in combination with other anti-cancer strategies, such as the interaction between LDRT and the tumor microenvironment, and the remodeling of the immune system.

Exploring low-dose radiotherapy to overcome radio-immunotherapy resistance

Immune checkpoint inhibitors (ICIs) have revolutionized the current treatment landscape for cancer, yet the response rates of ICIs remain unmet. Synergistic with immunotherapy, low-dose radiotherapy (LDRT) has been demonstrated to activate anti-tumor immunity - a transition from traditional radiation therapy geared toward local radical treatment to a type of immunological adjuvant. As such, studies utilizing LDRT to enhance the efficacy of immunotherapy have been increasing preclinically and clinically. This paper reviews the recent strategies of using LDRT to overcome the resistance of ICIs, as well as providing potential opportunities in cancer treatment. Despite the potential of LDRT in immunotherapy is recognized, the mechanisms behind this form of treatment remain largely elusive. Thus, we reviewed history, mechanisms and challenges associated with this form of treatment, as well as different modes of its application, to provide relatively accurate practice standards for LDRT as a sensitizing treatment when combined with immunotherapy or radio-immunotherapy.

Radiotherapy modulates tumor cell fate decisions: a review

Cancer has always been a worldwide problem, and the application of radiotherapy has greatly improved the survival rate of cancer patients. Radiotherapy can modulate multiple cell fate decisions to kill tumor cells and achieve its therapeutic effect. With the development of radiotherapy technology, how to increase the killing effect of tumor cells and reduce the side effects on normal cells has become a new problem. In this review, we summarize the mechanisms by which radiotherapy induces tumor cell apoptosis, necrosis, necroptosis, pyroptosis, ferroptosis, autophagy, senescence, mitotic catastrophe, and cuproptosis. An in-depth understanding of these radiotherapy-related cell fate decisions can greatly improve the efficiency of radiotherapy for cancer.

Effect of low-dose radiation on thyroid function and the gut microbiota

BACKGROUND

The thyroid-gut axis has a great influence on the maintenance of human health; however, we know very little about the effects of low-dose ionizing radiation (LDR) on thyroid hormone levels and gut microbiota composition.

AIM

To investigate the potential effects of low-dose X-ray radiation to male C57BL/6J mice.

METHODS

Peripheral blood was collected for enzyme-linked immunosorbent assay (ELISA), and stool samples were taken for 16S ribosomal RNA (rRNA) gene sequencing after irradiation.

RESULTS

We found that LDR caused changes in thyroid stimulating hormone (TSH) levels in the irradiated mice, suggesting a dose-dependent response in thyroid function to ionizing radiation. No changes in the diversity and richness of the gut microbiota were observed in the LDR-exposed group in comparison to the controls. The abundance of Moraxellaceae and Enterobacteriaceae decreased in the LDR-exposed groups compared with the controls, and the Lachnospiraceae abundance increased in a dose-dependent manner in the radiated groups. And the abundances of uncultured_bacterium_g_Acinetobacter, uncultured_bacterium_ o_Mollicutes_RF39, uncultured_bacterium_g_Citrobacter, and uncultured_ bacterium_g_Lactococcus decreased in the radiated groups at the genus level, which showed a correlation with radiation exposure and diagnostic efficacy. Analysis of functional metabolic pathways revealed that biological metabolism was predicted to have an effect on functional activities, such as nucleotide metabolism, carbohydrate metabolism, and glycan biosynthesis and metabolism. Furthermore, Kyoto Encyclopedia of Genes and Genomes pathway annotation also suggested that changes in the gut microbiota were related to processing functions, including translation, replication and repair.

CONCLUSION

LDR can change thyroid function and the gut microbiota, and changes in the abundances of bacteria are correlated with the radiation dose.

Assessment of bone dose response using ATR-FTIR spectroscopy: A potential method for biodosimetry

The health care application of ionizing radiation has expanded worldwide during the last several decades. While the health impacts of ionizing radiation improved patient care, inaccurate handling of radiation technology is more prone to potential health risks. Therefore, the present study characterizes the bone dose response using bovine femurs from a slaughterhouse. The gamma irradiation was designed into low-doses (0.002, 0.004 and 0.007 kGy) and high-doses (1, 10, 15, 25, 35, 50 and 60 kGy), all samples received independent doses. The combination of FTIR spectroscopy and PLS-DA allows the detection of differences in the control group and the ionizing dose, as well as distinguishing between high and low radiation doses. In this way, our findings contribute to future studies of the dose response to track ionizing radiation effects on biological systems.

Targeted Anti-Cancer Provascular Therapy Using Ultrasound, Microbubbles, and Nitrite to Increase Radiotherapy Efficacy

Hypoxia is an important mechanism of resistance to radiation therapy in many human malignancies including prostate cancer. It has been recently shown that ultrasound targeted microbubble cavitation (UTMC) can increase blood perfusion in skeletal muscle by triggering nitric oxide signaling. Interestingly, this effect was amplified with a sodium nitrite coinjection. Since sodium nitrite has been shown to synergize with radiotherapy (RT), we hypothesized that UTMC with a sodium nitrite coinjection could further radiosensitize solid tumors by increasing blood perfusion and thus reduce tumor hypoxia. We evaluated (1) the ability of UTMC with and without nitrite to increase perfusion in muscle (mouse hindlimbs) and human prostate tumors using different pulse lengths and pressure; (2) the efficacy of this approach as a provascular therapy given directly before RT in the human prostate subcutaneous xenografts PC3 tumor model. Using long pulses with various pressures, in muscle, the provascular response following UTMC was strong (6.61 ± 4.41-fold increase in perfusion post-treatment). In tumors, long pulses caused an increase in perfusion (2.42 ± 1.38-fold) at lower mechanical index (MI = 0.25) but not at higher MI (0.375, 0.5, and 0.750) when compared to control (no UTMC). However, when combined with RT, UTMC with long pulses (MI = 0.25) did not improve tumor growth inhibition. With short pulses, in muscle, the provascular response following UTMC (SONOS) + nitrite was strong (13.74 ± 8.60-fold increase in perfusion post-treatment). In tumors, UTMC (SONOS) + nitrite also caused a provascular response (1.94 ± 1.20-fold increase in perfusion post-treatment) that lasted for at least 10 min, but not with nitrite alone. Interestingly, the blunted provascular response observed for long pulses at higher MI without nitrite was reversed with the addition of nitrite. UTMC (SONOS) with and without nitrite caused an increase in perfusion in tumors. The provascular response observed for UTMC (SONOS) + nitrite was confirmed by histology. Finally, there was an improved growth inhibition for the 8 Gy RT dose + nitrite + UTMC group vs 8 Gy RT + nitrite alone. This effect was not significant with mice treated by UTMC + nitrite and receiving doses of 0 or 2 Gy RT. In conclusion, UTMC + nitrite increased blood flow leading to an increased efficacy of higher doses of RT in our tumor model, warranting further study of this strategy.

Hematological Changes Following Low Dose Radiation Therapy and Comparison to Current Standard of Care Cancer Treatments

Cancer is the second leading cause of mortality worldwide accounting for almost 10 million deaths in 2020. Current standard of care treatment varies depending on the type and stage of disease, but commonly includes surgery, chemotherapy, and/or radiation therapy. There is evidence that whole- and half-body exposure to low dose ionizing radiation can also be an effective therapeutic due to its stimulation of anti-cancer immunity. One of the limiting factors for past clinical trials using low dose radiation therapy has been adverse hematological events. However, similar hematological changes are also frequently reported following standard of care treatments in oncology. This review summarizes the effects of various cancer therapies on hematologic toxicity through the evaluation of complete blood count reports. The reviewed literature elucidates hematological trends in patients undergoing chemotherapy, and both high and low dose radiation therapy. In general, high dose radiation and chemotherapy can result in widespread changes in blood counts, with the most severe effects related to leukopenia. Overall, compared to standard of care treatments, low dose radiation results in similar, yet more mild hematological changes. Taken together, hematological toxicities should not be a limiting factor in the applicability of low dose radiation as a cancer therapeutic.

Role of Bee Venom and Melittin on Restraining Angiogenesis and Metastasis in γ-Irradiated Solid Ehrlich Carcinoma-Bearing Mice

Pathological angiogenesis and apoptosis evasion are common hallmarks of cancer. The present work was an endeavor to evaluate the influence of bee venom (BV) or its major constituent melittin (MEL) as antiapoptotic and angiogenic regulator modifier on the tumor growth and the cell sensitivity to ionizing radiation targeting the improvement of cancer therapeutic protocols. BV (0.56 mg/kg/day) and MEL (500 µg/kg body weight/day) were injected intraperitoneally to mice bearing 1 cm³ solid tumor of Ehrlich ascites carcinoma (EAC) for 21 consecutive days. Mice were whole-body exposed to 1 Gray (Gy) of γ-radiation (2 fractionated doses). Treatment with BV or MEL markedly suppresses the proliferation of tumor in EAC mice. The concentrations of m-RNA for angiogenic factors (TNF-α, VEGF) as well as MMPs 2 and 9 activities and NO concentration were significantly decreased, combined with improvements in apoptotic regulators (caspase-3 activity) and normal cells redox tone (catalase and free radicals content) compared with EAC mice. Moreover, the histopathological investigation confirms the improvement exerted by BV or MEL in the EAC mice group or EAC + R group. Exposure to γ-radiation sustained the modulatory effect of BV on tumor when compared with EAC + BV mice. Convincingly, the role of BV or MEL as a natural antiangiogenic in the biological sequelae after radiation exposure is verified. Hence, BV and its major constituent MEL might represent a potential therapeutic strategy for increasing the radiation response of solid tumors.

Radiation dose and fraction in immunotherapy: one-size regimen does not fit all settings, so how does one choose?

Recent evidence indicates that ionizing radiation can enhance immune responses to tumors. Advances in radiation delivery techniques allow hypofractionated delivery of conformal radiotherapy. Hypofractionation or other modifications of standard fractionation may improve radiation’s ability to promote immune responses to tumors. Other novel delivery options may also affect immune responses, including T-cell activation and tumor-antigen presentation changes. However, there is limited understanding of the immunological impact of hypofractionated and unique multifractionated radiotherapy regimens, as these observations are relatively recent. Hence, these differences in radiotherapy fractionation result in distinct immune-modulatory effects. Radiation oncologists and immunologists convened a virtual consensus discussion to identify current deficiencies, challenges, pitfalls and critical gaps when combining radiotherapy with immunotherapy and making recommendations to the field and advise National Cancer Institute on new directions and initiatives that will help further development of these two fields.

This commentary aims to raise the awareness of this complexity so that the need to study radiation dose, fractionation, type and volume is understood and valued by the immuno-oncology research community. Divergence of approaches and findings between preclinical studies and clinical trials highlights the need for evaluating the design of future clinical studies with particular emphasis on radiation dose and fractionation, immune biomarkers and selecting appropriate end points for combination radiation/immune modulator trials, recognizing that direct effect on the tumor and potential abscopal effect may well be different. Similarly, preclinical studies should be designed as much as possible to model the intended clinical setting. This article describes a conceptual framework for testing different radiation therapy regimens as separate models of how radiation itself functions as an immunomodulatory ‘drug’ to provide alternatives to the widely adopted ‘one-size-fits-all’ strategy of frequently used 8 Gy×3 regimens immunomodulation.

Effects of Low-Dose X-Ray on Cell Growth, Membrane Permeability, DNA Damage and Gene Transfer Efficiency

Background

We aimed to reveal if low dose X-rays would induce harmful or beneficial effect or dual response on biological cells and whether there are conditions the radiation can enhance gene transfer efficiency and promote cell growth but without damage to the cells.

Method

A systematic study was performed on the effects of Kilo-V and Mega-V X-rays on the cell morphology, viability, membrane permeability, DNA damage, and gene transfection of 293 T and CHO cells.

Results

The Kilo-V X-rays of very low doses from 0.01 to 0.04 Gray in principle didn't induce any significant change in cell morphology, growth, membrane permeability, and cause DNA damage. The Mega-V X-ray had a damage threshold between 1.0 and 1.5 Gray. The 0.25 Gray Mega-V-X-ray could promote cell growth and gene transfer, while the 1.5 Gray Mega-V X-ray damaged cells.

Conclusion

The very low dose of KV X-rays is safe to cells, while the effects of Mega-V-X-rays are dose-dependent. Mega-V-X-rays with a dose higher than the damage threshold would be harmful, that between 1.0 -1.5 Gray can evoke dual effects, whereas 0.25 Gray MV X-ray is beneficial for both cell growth and gene transfer, thus would be suitable for radiation-enhanced gene transfection.

A combinatorial approach of a polypharmacological adjuvant 2-deoxy-D-glucose with low dose radiation therapy to quell the cytokine storm in COVID-19 management

COVID-19, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a pandemic disease and is the major cause of deaths worldwide. The clinical complexities (inflammation, cytokine storm, and multi-organ dysfunction) associated with COVID-19 poses constraints to effective management of critically ill COVID-19 patients. Low dose radiation therapy (LDRT) has been evaluated as a potential therapeutic modality for COVID-19 pneumonia. However, due to heterogeneity in disease manifestation and inter-individual variations, effective planning for LDRT is limited for this large-scale event. 2-deoxy-D-glucose (2-DG) has emerged as a polypharmacological agent for COVID-19 treatment due to its effects on the glycolytic pathway, anti-inflammatory action, and interaction with viral proteins. We suggest that 2-DG will be a potential adjuvant to enhance the efficacy of LDRT in the treatment of COVID-19 pneumonia. Withal, azido analog of 2-DG, 2-azido-2-DG can produce rapid catastrophic oxidative stress and quell the cytokine storm in critically ill COVID-19 patients.

Modulation of Immuno-biome during Radio-sensitization of Tumors by Glycolytic Inhibitors

The Tumor Microenvironment (TME) comprising stromal cells, fibroblasts and various components of the immune system forms a pro-tumorigenic cocoon around the tumor cells with the reprogramming of the metabolism in the form of Warburg phenotype (enhanced aerobic glycolysis) in tumor as well as non-tumor cells. This reprogramming plays a significant role in suppressing the immune response leading to the survival and proliferation of tumor cells and resistance to therapies. Therefore, there is a considerable interest in developing strategies involving metabolic modifiers to improve the therapeutic efficacy that restores immune competence, besides enhancing the direct effects on tumor cells. Inhibitors of glycolysis like 2-deoxy-D-glucose (2-DG; a hexokinase inhibitor), dichloroacetate and small molecule inhibitors of lactate transport (MCT-1) are some of the metabolic modifiers investigated for their therapeutic as well as adjuvant potential. Among these, 2-DG has been widely investigated and established as an ideal adjuvant in the radio- and chemotherapy of tumors. Modulation of the immuno-biome in the form of cytokine shifts, differential transcriptional regulation, abrogation of immunosuppressive network and reduced accumulation of lactate are some of the contributing factors for immune stimulation linked to the radio- and chemosensitization by glycolytic inhibitors.

The downfall of the linear non-threshold model

The linear non-threshold model (LNTM) is a theoretical dose-response function as a result of extrapolating the late effects of high-dose exposure to ionizing radiation to the low-dose range, but there is great uncertainty about its validity. The acceptance of LNTM as the dominant probabilistic model have survived to the present day and it is actually the cornerstone of current radiation protection policies. In the last decades, advances in molecular and evolutive biology, cancer immunology, and many epidemiological and animal studies have cast serious doubts about the reliability of the NLTM, as well as suggesting alternative models, like the hormetic theory. Considering the given evidences, a discussion between the involved scientific societies and the regulatory commissions is promtly required in order to to reach a redefiniton of theradiation protection basis, as it would be specially crucial in the medical field.

Repeated 0.2-Gy γ-Ray Irradiation Attenuates the Inflammatory Process and Endotoxin Damage Induced by Lipopolysaccharides

Endotoxin damage is an acute, multi-organ disease, the most typical symptoms of which are liver injury and inflammatory cytokine storm. Endotoxin tolerance is described as the pretreatment of lipopolysaccharides (LPS) before the toxin invasion, which is consistent with the adaptive response induced by low-dose radiation (LDR). In this study, we verified that LDR could resist the endotoxin damage by suppressing the increase of inflammatory cytokines, including interleukin 6, tumor necrosis factor, and NO, to improve the survival and relieve the inflammatory cell infiltration, in which low dose of LPS performed consistently with LDR.

Impact of Low-dose Ionising Radiation on the Composition of the Gut Microbiota of Mice

BACKGROUND

Although the importance of the gut microbiota in the maintenance of human health has been well established, little is known about the impact of low-dose ionising radiation (exposure to a dose of less than 0.5 Gy of low linear energy transfer radiation such as γ- or X-rays [LDR]) on the composition and functional role of the gut microbiota. The aim of the present study was to investigate and compare the composition of the gut microbiota in mice exposed to LDR.

METHODS AND MATERIALS

Male BALB/c mice were exposed to low-dose Co60 radiation. Faecal samples taken prior to and after irradiation were used for high-throughput sequencing of 16S rRNA gene sequence amplicons.

RESULTS

We observed substantial changes in the composition of the gut microbiota, including alpha diversity and beta diversity, in mice exposed to LDR compared to the non-radiated control group. Moreover, at the genus level, the abundance of Clostridium, Helicobacter and Oscilibacter increased, and those of Bacteroides and Barnesiella decreased, in a time-dependent manner in the radiated groups compared to the non-radiated control group. The functional metabolic pathway analysis indicated that Bacteroides spp. and members of the other genera that were found are predicted to play roles in bacterial toxin production, DNA repair, and Type II diabetes. Furthermore, these alterations in the gut microbiota were accompanied by changes in the abundance of multiple metabolites, which were predicted to be involved in multiple signalling pathways, including glucagon, central carbon metabolism, and type II diabetes.

CONCLUSIONS

The possibility of microbiota-mediated pathophysiology resulting from LDR may be an as yet unrecognised hazard that merits further experimental examination. This study provides a conceptual and analytical foundation for further research into the chronic effects of LDR on human health, and points to potential novel targets for intervention to prevent the adverse effects of radiation.

Resensitization of cisplatin resistance ovarian cancer cells to cisplatin through pretreatment with low-dose fraction radiation

Objective

Cisplatin is the first‐line chemotherapy for ovarian cancer. However, cisplatin resistance is severely affecting the treatment efficacy. FOXO3a has been reported to be involved in reversing chemotherapy resistance. However, whether low‐dose fraction radiation therapy (LDFRT) can reverse cisplatin resistance remains unclear. This study aimed to explore the effect of LDFRT on cisplatin resistance and its relation with FOXO3a expression in vitro.

Methods

The toxicity of cisplatin on SKOV3/DDP cells was evaluated by CCK8 assay and cell apoptosis was measured by Annexin V‐FITC staining as well as Hoechst33342 staining. The expression of FOXO3a and other relative proteins was measured by western blot.

Results

Our study found that LDFRT enhanced cisplatin‐induced apoptosis of SKOV3/DDP cells and promoted the expression of FOXO3a and pro‐apoptotic protein PUMA. In addition, overexpression of FOXO3a promoted PUMA activity and toxicity of cisplatin on SKOV3/DDP cells.

Conclusion

LDFRT reverses cisplatin resistance of SKOV3/DDP cells possibly by upregulating the expression of FOXO3a and its downstream target PUMA, suggesting that LDFRT might be a potent chemosensitizer for the treatment of ovarian cancer.

Radon Therapy Is Very Promising as a Primary or an Adjuvant Treatment for Different Types of Cancers: 4 Case Reports

We report on the application of radon inhalation therapy to patients with 4 types of cancer: colon, uterine, lung, and liver cell. The radon treatments were given to improve the efficacy of chemotherapy and were potent in all 4 cases. Marker values decreased and disease symptoms were alleviated. We include a lengthy discussion on the mechanism that may be responsible for the observed results. While employing the radon generator to treat the patient with hepatocellular carcinoma, we discovered that a concentration of 6 MBq/m3 was very effective, while 1 MBq/m3 was marginal. This implies different, and rather high, radon concentration thresholds for the treatment of different types of cancer. The evidence from these 4 cases suggests that radon inhalation may be beneficial against various cancer types as an important adjuvant therapy to conventional chemotherapy and for local high-dose radiotherapy, which would address the problem of distant metastasis. A previous case report on 2 patients with advanced breast cancer, who refused chemotherapy or radiotherapy, indicates that radon may be effective as a primary therapy for cancer. Clinical trials should be carried out to determine the best radon concentrations for treatment of other types of cancer, at different stages of progression.

Adaptive responses to low doses of radiation or chemicals: their cellular and molecular mechanisms

This article reviews the current knowledge on the mechanisms of adaptive response to low doses of ionizing radiation or chemical exposure. A better knowledge of these mechanisms is needed to improve our understanding of health risks at low levels of environmental or occupational exposure and their involvement in cancer or non-cancer diseases. This response is orchestrated through a multifaceted cellular program involving the concerted action of diverse stress response pathways. These evolutionary highly conserved defense mechanisms determine the cellular response to chemical and physical aggression. They include DNA damage repair (p53, ATM, PARP pathways), antioxidant response (Nrf2 pathway), immune/inflammatory response (NF-κB pathway), cell survival/death pathway (apoptosis), endoplasmic response to stress (UPR response), and other cytoprotective processes including autophagy, cell cycle regulation, and the unfolded protein response. The coordinated action of these processes induced by low-dose radiation or chemicals produces biological effects that are currently estimated with the linear non-threshold model. These effects are controversial. They are difficult to detect because of their low magnitude, the scarcity of events in humans, and the difficulty of corroborating associations over the long term. Improving our understanding of these biological consequences should help humans and their environment by enabling better risk estimates, the revision of radiation protection standards, and possible therapeutic advances.

The LNT model for cancer induction is not supported by radiobiological data

The hallmarks of cancer have been the focus of much research and have influenced the development of risk models for radiation-induced cancer. However, natural defenses against cancer, which constitute the hallmarks of cancer prevention, have largely been neglected in developing cancer risk models. These natural defenses are enhanced by low doses and dose rates of ionizing radiation, which has aided in the continuation of human life over many generations. Our natural defenses operate at the molecular, cellular, tissue, and whole-body levels and include epigenetically regulated (epiregulated) DNA damage repair and antioxidant production, selective p53-independent apoptosis of aberrant cells (e.g. neoplastically transformed and tumor cells), suppression of cancer-promoting inflammation, and anticancer immunity (both innate and adaptive components). This publication reviews the scientific bases for the indicated cancer-preventing natural defenses and evaluates their implication for assessing cancer risk after exposure to low radiation doses and dose rates. Based on the extensive radiobiological evidence reviewed, it is concluded that the linear-no-threshold (LNT) model (which ignores natural defenses against cancer), as it relates to cancer risk from ionizing radiation, is highly implausible. Plausible models include dose-threshold and hormetic models. More research is needed to establish when a given model (threshold, hormetic, or other) applies to a given low-dose-radiation exposure scenario.

The failure of radical treatments to cure cancer: can less deliver more?

All too often attempts to deliver improved cancer cure rates by increasing the dose of a particular treatment are not successful enough to justify the accompanying increase in toxicity and reduction in quality of life suffered by a significant number of patients. In part, this drive for using higher levels of treatment derives from the nature of the process for testing and incorporation of new protocols. Indeed, new treatment regimens must now consider the key role of immunity in cancer control, a component that has been largely ignored until very recently. The recognition that some drugs developed for cytotoxicity at higher doses can display alternative anticancer activities at lower doses including through modulation of immune responses is prompting a significant re-evaluation of treatment protocol development. Given that tumours are remarkably heterogeneous and with inherent genetic instability it is probably only the adaptive immune response with its flexibility and extensive repertoire that can rise to the challenge of effecting significant control and ultimately elimination of a patient's cancer. This article discusses some of the elements that have limited higher levels of treatment outcomes and where too much proved less effective. We explore observations that less can often be as effective, if not more effective especially with some chemotherapy regimens, and discuss how this can be exploited in combination with immunotherapies to deliver nontoxic improved tumour responses.

Are We Approaching the End of the Linear No-Threshold Era?

The linear no-threshold (LNT) model for radiation-induced cancer was adopted by national and international advisory bodies in the 1950s and has guided radiation protection policies worldwide since then. The resulting strict regulations have increased the compliance costs for the various uses of radiation, including nuclear medicine. The concerns about low levels of radiation due to the absence of a threshold have also resulted in adverse consequences. Justification of the LNT model was based on the concept that low levels of radiation increase mutations and that increased mutations imply increased cancers. This concept may not be valid. Low-dose radiation boosts defenses such as antioxidants and DNA repair enzymes. The boosted defenses would reduce the endogenous DNA damage that would have occurred in the subsequent period, and so the result would be reduced DNA damage and mutations. Whereas mutations are necessary for causing cancer, they are not sufficient since the immune system eliminates cancer cells or keeps them under control. The immune system plays an extremely important role in preventing cancer, as indicated by the substantially increased cancer risk in immune-suppressed patients. Hence, since low-dose radiation enhances the immune system, it would reduce cancers, resulting in a phenomenon known as radiation hormesis. There is considerable evidence for radiation hormesis and against the LNT model, including studies of atomic bomb survivors, background radiation, environmental radiation, cancer patients, medical radiation, and occupational exposures. Though Commentary 27 published by the National Council on Radiation Protection and Measurements concluded that recent epidemiologic studies broadly support the LNT model, a critical examination of the studies has shown that they do not. Another deficiency of Commentary 27 is that it did not consider the vast available evidence for radiation hormesis. Other advisory body reports that have supported the LNT model have similar deficiencies. Advisory bodies are urged to critically evaluate the evidence supporting both sides and arrive at an objective conclusion on the validity of the LNT model. Considering the strength of the evidence against the LNT model and the weakness of the evidence for it, the present analysis indicates that advisory bodies would be compelled to reject the LNT model. Hence, we may be approaching the end of the LNT model era.

Health Impacts of Low-Dose Ionizing Radiation: Current Scientific Debates and Regulatory Issues

Health impacts of low-dose ionizing radiation are significant in important fields such as X-ray imaging, radiation therapy, nuclear power, and others. However, all existing and potential applications are currently challenged by public concerns and regulatory restrictions. We aimed to assess the validity of the linear no-threshold (LNT) model of radiation damage, which is the basis of current regulation, and to assess the justification for this regulation. We have conducted an extensive search in PubMed. Special attention has been given to papers cited in comprehensive reviews of the United States (2006) and French (2005) Academies of Sciences and in the United Nations Scientific Committee on Atomic Radiation 2016 report. Epidemiological data provide essentially no evidence for detrimental health effects below 100 mSv, and several studies suggest beneficial (hormetic) effects. Equally significant, many studies with in vitro and in animal models demonstrate that several mechanisms initiated by low-dose radiation have beneficial effects. Overall, although probably not yet proven to be untrue, LNT has certainly not been proven to be true. At this point, taking into account the high price tag (in both economic and human terms) borne by the LNT-inspired regulation, there is little doubt that the present regulatory burden should be reduced.

Validating the pivotal role of the immune system in low-dose radiation-induced tumor inhibition in Lewis lung cancer-bearing mice

Although low-dose radiation (LDR) possesses the two distinct functions of inducing hormesis and adaptive responses, which result in immune enhancement and tumor inhibition, its clinical applications have not yet been elucidated. The major obstacle that hinders the application of LDR in the clinical setting is that the mechanisms underlying induction of tumor inhibition are unclear, and the risks associated with LDR are still unknown. Thus, to overcome this obstacle and elucidate the mechanisms mediating the antitumor effects of LDR, in this study, we established an in vivo lung cancer model to investigate the participation of the immune system in LDR-induced tumor inhibition and validated the pivotal role of the immune system by impairing immunity with high-dose radiation (HDR) of 1 Gy. Additionally, the LDR-induced adaptive response of the immune system was also observed by sequential HDR treatment in this mouse model. We found that LDR-activated T cells and natural killer cells and increased the cytotoxicity of splenocytes and the infiltration of T cells in the tumor tissues. In contrast, when immune function was impaired by HDR pretreatment, LDR could not induce tumor inhibition. However, when LDR was administered before HDR, the immunity could be protected from impairment, and tumor growth could be inhibited to some extent, indicating the induction of the immune adaptive response by LDR. Therefore, we demonstrated that immune enhancement played a key role in LDR-induced tumor inhibition. These findings emphasized the importance of the immune response in tumor radiotherapy and may help promote the application of LDR as a novel approach in clinical practice.

Cancer immunotherapy: how low-level ionizing radiation can play a key role

The cancer immunoediting hypothesis assumes that the immune system guards the host against the incipient cancer, but also "edits" the immunogenicity of surviving neoplastic cells and supports remodeling of tumor microenvironment towards an immunosuppressive and pro-neoplastic state. Local irradiation of tumors during standard radiotherapy, by killing neoplastic cells and generating inflammation, stimulates anti-cancer immunity and/or partially reverses cancer-promoting immunosuppression. These effects are induced by moderate (0.1-2.0 Gy) or high (>2 Gy) doses of ionizing radiation which can also harm normal tissues, impede immune functions, and increase the risk of secondary neoplasms. In contrast, such complications do not occur with exposures to low doses (≤0.1 Gy for acute irradiation or ≤0.1 mGy/min dose rate for chronic exposures) of low-LET ionizing radiation. Furthermore, considerable evidence indicates that such low-level radiation (LLR) exposures retard the development of neoplasms in humans and experimental animals. Here, we review immunosuppressive mechanisms induced by growing tumors as well as immunomodulatory effects of LLR evidently or likely associated with cancer-inhibiting outcomes of such exposures. We also offer suggestions how LLR may restore and/or stimulate effective anti-tumor immunity during the more advanced stages of carcinogenesis. We postulate that, based on epidemiological and experimental data amassed over the last few decades, whole- or half-body irradiations with LLR should be systematically examined for its potential to be a viable immunotherapeutic treatment option for patients with systemic cancer.

Hormetic Response to Low-Dose Radiation: Focus on the Immune System and Its Clinical Implications

The interrelationship between ionizing radiation and the immune system is complex, multifactorial, and dependent on radiation dose/quality and immune cell type. High-dose radiation usually results in immune suppression. On the contrary, low-dose radiation (LDR) modulates a variety of immune responses that have exhibited the properties of immune hormesis. Although the underlying molecular mechanism is not fully understood yet, LDR has been used clinically for the treatment of autoimmune diseases and malignant tumors. These advancements in preclinical and clinical studies suggest that LDR-mediated immune modulation is a well-orchestrated phenomenon with clinical potential. We summarize recent developments in the understanding of LDR-mediated immune modulation, with an emphasis on its potential clinical applications.

Immunomodulatory effects of radiation: what is next for cancer therapy?

Despite its former reputation as being immunosuppressive, it has become evident that radiation therapy can enhance antitumor immune responses. This quality can be harnessed by utilizing radiation as an adjuvant to cancer immunotherapies. Most studies combine the standard radiation dose and regimens indicated for the given disease state, with novel cancer immunotherapies. It has become apparent that low-dose radiation, as well as doses within the hypofractionated range, can modulate tumor cells making them better targets for immune cell reactivity. Herein, we describe the range of phenotypic changes induced in tumor cells by radiation, and explore the diverse mechanisms of immunogenic modulation reported at these doses. We also review the impact of these doses on the immune cell function of cytotoxic cells in vivo and in vitro.

Polarization of macrophages towards M1 phenotype by a combination of 2-deoxy-d-glucose and radiation: Implications for tumor therapy

2-Deoxy-d-glucose (2-DG) has been found to enhance the cytotoxicity of ionizing radiation and chemotherapeutic drugs in several tumor cell lines in vitro. Systemic administration of 2-DG together with localized irradiation of the tumor leads to tumor regression and cure (disease free survival), which correlate with the differential levels of anti-tumor immunity observed in Ehrlich ascites tumor (EAT) bearing mice. Macrophages being a major player of the innate immune system, we investigated the activation status of splenic macrophages during radio-sensitization of EAT in mice as well as in peritoneal macrophages ex vivo and macrophagic cell line (Raw 264.7) in vitro. Results suggest that under in vivo conditions, the combined treatment (2-DG+radiation) restores the M1 phenotype in spleen that correlated with the tumor response. However, 2-DG neither induced significant cytotoxicity nor enhanced radiation-induced cell death in peritoneal macrophages and the macrophage cell line (Raw 264.7). Further, increased arborization and enhanced functional status (expression of MHC class II, CD80, CD86 and phagocytosis) were observed after the combined treatment. Besides this activation, the combined treatment also skewed the macrophages towards M1 phenotype as evidenced by the enhanced secretion of IL-12, IL-2, TNF-α and IFN-γ. These observations suggest that 2-DG not only preserves the survival of normal macrophages during irradiation, but also activates macrophages by polarizing towards M1 phenotype, which is known to be tumoricidal in nature. This study for the first time sheds light on a potential antitumor immune activation by 2-DG involving macrophagic stimulation during in vivo radio-sensitization of tumors, besides the other known antitumor effects of this glucose analogue.

Beneficial effects of low dose radiation in response to the oncogenic KRAS induced cellular transformation

Recently low dose irradiation has gained attention in the field of radiotherapy. For lack of understanding of the molecular consequences of low dose irradiation, there is much doubt concerning its risks on human beings. In this article, we report that low dose irradiation is capable of blocking the oncogenic KRAS-induced malignant transformation. To address this hypothesis, we showed that low dose irradiation, at doses of 0.1 Gray (Gy); predominantly provide defensive response against oncogenic KRAS -induced malignant transformation in human cells through the induction of antioxidants without causing cell death and acts as a critical regulator for the attenuation of reactive oxygen species (ROS). Importantly, we elucidated that knockdown of antioxidants significantly enhanced ROS generation, invasive and migratory properties and abnormal acini formation in KRAS transformed normal as well as cancer cells. Taken together, this study demonstrates that low dose irradiation reduces the KRAS induced malignant cellular transformation through diminution of ROS. This interesting phenomenon illuminates the beneficial effects of low dose irradiation, suggesting one of contributory mechanisms for reducing the oncogene induced carcinogenesis that intensify the potential use of low dose irradiation as a standard regimen.

Contribution of Dual Oxidase 2 (DUOX2) to Hyper-Radiosensitivity in Human Gastric Cancer Cells

Whole-abdominal radiotherapy (WART) is a primary method for managing gastrointestinal cancers that have disseminated into intra-abdominal tissues. While effective, this approach is limited because of the increased toxicity to normal tissue associated with combined WART and full-dose chemotherapy regimens. Recent studies have demonstrated a survival advantage in a novel treatment paradigm that allows for the safe use of full-dose systemic chemotherapy in combination with low-dose fractionated radiotherapy (LDFRT). Traditionally, radiation doses greater than 120 cGy have been used in radiotherapy because lower doses were thought to be ineffective for tumor therapy. However, we now know that LDFRT can produce hyper-radiosensitivity (HRS), a phenomenon where cells undergo apoptosis at radiation doses as low as 15 cGy, in a number of proliferating cells. The objectives of our current study were to determine whether LDFRT can induce HRS in gastrointestinal cancer cells and to identify biomarkers of chemopotentiation by LDFRT. Our data indicate that three consecutive daily fractions of 15 cGy produced HRS in gastric cancer cells and potentiated a modified regimen of docetaxel, cisplatin and 5'-fluorouracil (mDCF). Colony survival assays indicated that 15 cGy was sufficient to kill 90% of the cells when LDFRT was combined with mDCF whereas a dose almost 10 times higher (135 cGy) was needed to achieve the same rate when using conventional radiotherapy alone. RT(2) PCR Profiler™ array analysis indicated that this combined regimen upregulated dual oxidase 2 (DUOX2), an enzyme functioning in the production of hydrogen peroxide, without upregulating genes involved in DNA repair. Moreover, downregulation of DUOX2 increased radioresistance at every radiation dose tested. In addition, our data indicate that reactive oxygen species (ROS) increase up to 3.5-fold in cells exposed to LDFRT and mDCF. Furthermore, inhibition of NADPH oxidase abrogated the killing efficiency of this combined regimen. Taken together these data suggest that chemopotentiation by LDFRT in gastric cancer cells may be due, at least in part, to increased ROS production (DUOX2) without upregulation of the DNA repair machinery. These data thus provide a rationale for further explorations of potential clinical applications of LDFRT, such as in WART, as a chemopotentiator for advanced and metastatic gastric cancers.

Additive protection by LDR and FGF21 treatment against diabetic nephropathy in type 2 diabetes model

The onset of diabetic nephropathy (DN) is associated with both systemic and renal changes. Fibroblast growth factor (FGF)-21 prevents diabetic complications mainly by improving systemic metabolism. In addition, low-dose radiation (LDR) protects mice from DN directly by preventing renal oxidative stress and inflammation. In the present study, we tried to define whether the combination of FGF21 and LDR could further prevent DN by blocking its systemic and renal pathogeneses. To this end, type 2 diabetes was induced by feeding a high-fat diet for 12 wk followed by a single dose injection of streptozotocin. Diabetic mice were exposed to 50 mGy LDR every other day for 4 wk with and without 1.5 mg/kg FGF21 daily for 8 wk. The changes in systemic parameters, including blood glucose levels, lipid profiles, and insulin resistance, as well as renal pathology, were examined. Diabetic mice exhibited renal dysfunction and pathological abnormalities, all of which were prevented significantly by LDR and/or FGF21; the best effects were observed in the group that received the combination treatment. Our studies revealed that the additive renal protection conferred by the combined treatment against diabetes-induced renal fibrosis, inflammation, and oxidative damage was associated with the systemic improvement of hyperglycemia, hyperlipidemia, and insulin resistance. These results suggest that the combination treatment with LDR and FGF21 prevented DN more efficiently than did either treatment alone. The mechanism behind these protective effects could be attributed to the suppression of both systemic and renal pathways.

Low-dose splenic radiation inhibits liver tumor development of rats through functional changes in CD4+CD25+Treg cells

The increased number of CD4(+)CD25(+)Treg cells in tumor local and peripheral splenic tissues is related to the low immune function as well as to tumor recurrence and metastasis. Our pre-clinical studies showed that low-dose radiation (LDR) of the spleen in liver cancer patients significantly improves immune functions. However, the molecular mechanisms of such radiation remained ill defined. This study explores the role of CD4(+)CD25(+)Treg cells in radiation-induced immunomodulatory effects. Using the diethylnitrosamine (DEN)-induced rat liver tumor model and in vitro cell experiments, the percentage of CD4(+)CD25(+)Treg/CD4(+) cells in the blood and the expressions of Foxp3(+), IL-10, TGF-β, and cytotoxic T lymphocyte-associated antigen-4(CTLA-4) in spleen and liver tumors significantly decreased after LDR of the spleen in rats with liver cancer. The tumors became smaller than those in the non-radiated group, with both showing a parallel relation. Flow cytometry and MTT results revealed that LDR failed to inhibit CD4(+)CD25(+)Treg cell proliferation. Conversely, apoptosis was reduced and proliferation was stimulated. This process also changed CTLA-4 molecule expression on the surfaces of CD4(+)CD25(+)Treg cells and reduced their inhibitory function against CD4(+)CD25(-)T cell proliferation, and the suppression function of CD4(+)CD25(+)Treg cells was further weakened with the introduction of the CTLA-4 inhibitor. Findings demonstrate that the reduction of CTLA-4 expression on the CD4(+)CD25(+)Treg cell surface and the further inhibition of cell function may be considered as important regulators of LDR-induced immunomodulatory effects. This study provides experimental evidence to elucidate the immune enhancement induced by this process and presents a novel method for liver cancer immunotherapy.

Correcting systemic deficiencies in our scientific infrastructure

Scientific method is inherently self-correcting. When different hypotheses are proposed, their study would result in the rejection of the invalid ones. If the study of a competing hypothesis is prevented because of the faith in an unverified one, scientific progress is stalled. This has happened in the study of low dose radiation. Though radiation hormesis was hypothesized to reduce cancers in 1980, it could not be studied in humans because of the faith in the unverified linear no-threshold model hypothesis, likely resulting in over 15 million preventable cancer deaths worldwide during the past two decades, since evidence has accumulated supporting the validity of the phenomenon of radiation hormesis. Since our society has been guided by scientific advisory committees that ostensibly follow the scientific method, the long duration of such large casualties is indicative of systemic deficiencies in the infrastructure that has evolved in our society for the application of science. Some of these deficiencies have been identified in a few elements of the scientific infrastructure, and remedial steps suggested. Identifying and correcting such deficiencies may prevent similar tolls in the future.

Differential expression of thymic DNA repair genes in low-dose-rate irradiated AKR/J mice

We previously determined that AKR/J mice housed in a low-dose-rate (LDR) ((137)Cs, 0.7 mGy/h, 2.1 Gy) γ-irradiation facility developed less spontaneous thymic lymphoma and survived longer than those receiving sham or high-dose-rate (HDR) ((137)Cs, 0.8 Gy/min, 4.5 Gy) radiation. Interestingly, histopathological analysis showed a mild lymphomagenesis in the thymus of LDR-irradiated mice. Therefore, in this study, we investigated whether LDR irradiation could trigger the expression of thymic genes involved in the DNA repair process of AKR/J mice. The enrichment analysis of Gene Ontology terms and Kyoto Encyclopedia of Genes and Genomes pathways showed immune response, nucleosome organization, and the peroxisome proliferator-activated receptors signaling pathway in LDR-irradiated mice. Our microarray analysis and quantitative polymerase chain reaction data demonstrated that mRNA levels of Lig4 and RRM2 were specifically elevated in AKR/J mice at 130 days after the start of LDR irradiation. Furthermore, transcriptional levels of H2AX and ATM, proteins known to recruit DNA repair factors, were also shown to be upregulated. These data suggest that LDR irradiation could trigger specific induction of DNA repair-associated genes in an attempt to repair damaged DNA during tumor progression, which in turn contributed to the decreased incidence of lymphoma and increased survival. Overall, we identified specific DNA repair genes in LDR-irradiated AKR/J mice.

Linear No-Threshold Model VS. Radiation Hormesis

The atomic bomb survivor cancer mortality data have been used in the past to justify the use of the linear no-threshold (LNT) model for estimating the carcinogenic effects of low dose radiation. An analysis of the recently updated atomic bomb survivor cancer mortality dose-response data shows that the data no longer support the LNT model but are consistent with a radiation hormesis model when a correction is applied for a likely bias in the baseline cancer mortality rate. If the validity of the phenomenon of radiation hormesis is confirmed in prospective human pilot studies, and is applied to the wider population, it could result in a considerable reduction in cancers. The idea of using radiation hormesis to prevent cancers was proposed more than three decades ago, but was never investigated in humans to determine its validity because of the dominance of the LNT model and the consequent carcinogenic concerns regarding low dose radiation. Since cancer continues to be a major health problem and the age-adjusted cancer mortality rates have declined by only ∼10% in the past 45 years, it may be prudent to investigate radiation hormesis as an alternative approach to reduce cancers. Prompt action is urged.

The effects of residence duration in high background radiation areas on immune surveillance

Purpose:

The effective dose received by humans from natural sources is about 2.4 mSv y^-1, but this is 10.2 mSv y^-1 for inhabitants of Ramsar, a city in northern Iran. Carcinogenesis is one of the most studied effects of radiation, especially in high doses. Nonetheless carcinogenesis of low doses is uncertain. A recent epidemiological study in high background radiation areas of Ramsar showed that the cancer incidence in this era is lower than neighbors. The reason of this different behavior is under study yet. NK cells, helper, and Cytotoxic T cells are most important components of the tumor immune surveillance. The counts and activities of these cells and also leukocytes, lymphocyte, neutrophil cells, and other important parameters were studied in the residents of Ramsar with different duration of exposure to chronic low dose radiation.

Materials and Methods:

Fifty residents of high background radiation areas, who were between 25 and 35 years and fully healthy, were selected randomly and their consent was obtained. Then, 2 cc fresh peripheral bloods were taken in sterile conditions. Complete blood cell counts were performed by an automatic hematology analyzer and CD4+, CD8+, NK, and CD107a+ cell counts were determined by monoclonal antibodies and flowcytometry. CD4+ and CD8+ percentages and the CD4/CD8 ratio were determined and the data were analyzed using SPSS 16.

Results:

The percentages of CD4+ cells increase, but the counts of CD107a+ cells decline in higher exposure durations. The other parameters did not have significant regression with exposure duration.

Conclusions:

These confirm that living in high background radiation areas may induce changes in the immune system gradually and address more investigations.

Reciprocal complementation of the tumoricidal effects of radiation and natural killer cells

The tumor microenvironment is a key determinant for radio-responsiveness. Immune cells play an important role in shaping tumor microenvironments; however, there is limited understanding of how natural killer (NK) cells can enhance radiation effects. This study aimed to assess the mechanism of reciprocal complementation of radiation and NK cells on tumor killing. Various tumor cell lines were co-cultured with human primary NK cells or NK cell line (NK-92) for short periods and then exposed to irradiation. Cell proliferation, apoptosis and transwell assays were performed to assess apoptotic efficacy and cell viability. Western blot analysis and immunoprecipitation methods were used to determine XIAP (X-linked inhibitor of apoptosis protein) and Smac (second mitochondria-derived activator of caspase) expression and interaction in tumor cells. Co-culture did not induce apoptosis in tumor cells, but a time- and dose-dependent enhancing effect was found when co-cultured cells were irradiated. A key role for caspase activation via perforin/granzyme B (Grz B) after cell-cell contact was determined, as the primary radiation enhancing effect. The efficacy of NK cell killing was attenuated by upregulation of XIAP to bind caspase-3 in tumor cells to escape apoptosis. Knockdown of XIAP effectively potentiated NK cell-mediated apoptosis. Radiation induced Smac released from mitochondria and neutralized XIAP and therefore increased the NK killing. Our findings suggest NK cells in tumor microenvironment have direct radiosensitization effect through Grz B injection while radiation enhances NK cytotoxicity through triggering Smac release.

Identification of radiation-sensitive expressed genes in the ICR and AKR/J mouse thymus

We have investigated radiation-sensitive expressed genes (EGs), their signal pathways, and the effects of ionizing radiation in the thymus of ICR and AKR/J mice. Whole-body and relative thymus weights were taken and microarray analyses were done on the thymuses of high-dose-rate (HDR, (137) Cs, 0.8 Gy/min, a single dose of 4.5 Gy) and low-dose-rate (LDR, (137) Cs, 0.7 mGy/h, a cumulative dose of 1.7 Gy) irradiated ICR and AKR/J mice. Gene expression patterns were validated by quantitative polymerase chain reaction (qPCR). The effect of ionizing radiation on thymus cell apoptosis was measured terminal deoxynucleotidyl-transferase-mediated dUTP-end labeling (TUNEL). LDR-irradiation increased the mean whole-body weight, but decreased the relative thymus weight of AKR/J mice. Radiation-sensitive EGs were found by comparing HDR- and LDR-irradiated ICR and AKR/J mice. qPCR analysis showed that 12 EGs had dose and dose-rate dependent expression patterns. Gene-network analysis indicated that Ighg, Igh-VJ558, Defb6, Reg3g, and Saa2 may be involved in the immune response, leukocyte migration, and apoptosis. Our data suggest that expression of the HDR (Glut1, Glut4, and PKLR) and LDR radiation-response genes (Ighg and Igh-VJ558) can be dose or dose-rate dependent. There was an increased number of apoptotic cells in HDR-irradiated ICR mice and LDR-irradiated AKR/J mice. Thus, changes of the mean whole-body weight and relative thymus weight, EGs, signal pathways, and the effects of ionizing radiation on the thymus of ICR and AKR/J mice are described.

Shifting the paradigm in radiation safety

The current radiation safety paradigm using the linear no-threshold (LNT) model is based on the premise that even the smallest amount of radiation may cause mutations increasing the risk of cancer. Autopsy studies have shown that the presence of cancer cells is not a decisive factor in the occurrence of clinical cancer. On the other hand, suppression of immune system more than doubles the cancer risk in organ transplant patients, indicating its key role in keeping occult cancers in check. Low dose radiation (LDR) elevates immune response, and so it may reduce rather than increase the risk of cancer. LNT model pays exclusive attention to DNA damage, which is not a decisive factor, and completely ignores immune system response, which is an important factor, and so is not scientifically justifiable. By not recognizing the importance of the immune system in cancer, and not exploring exercise intervention, the current paradigm may have missed an opportunity to reduce cancer deaths among atomic bomb survivors. Increased antioxidants from LDR may reduce aging-related non-cancer diseases since oxidative damage is implicated in these. A paradigm shift is warranted to reduce further casualties, reduce fear of LDR, and enable investigation of potential beneficial applications of LDR.