CBLB613: a TLR 2/6 agonist, natural lipopeptide of Mycoplasma arginini , as a novel radiation countermeasure

A comprehensive review of sensors of radiation-induced damage, radiation-induced proximal events, and cell death

Radiation, a universal component of Earth's environment, is categorized into non-ionizing and ionizing forms. While non-ionizing radiation is relatively harmless, ionizing radiation possesses sufficient energy to ionize atoms and disrupt DNA, leading to cell damage, mutation, cancer, and cell death. The extensive use of radionuclides and ionizing radiation in nuclear technology and medical applications has sparked global concern for their capacity to cause acute and chronic illnesses. Ionizing radiation induces DNA damage either directly through strand breaks and base change or indirectly by generating reactive oxygen species (ROS) and reactive nitrogen species (RNS) via radiolysis of water. This damage triggers a complex cellular response involving recognition of DNA damage, cell cycle arrest, DNA repair mechanisms, release of pro-inflammatory cytokines, and cell death. This review focuses on the mechanisms of radiation-induced cellular damage, recognition of DNA damage and subsequent activation of repair processes, and the critical role of the innate immune response in resolution of the injury. Emphasis is placed on pattern recognition receptors (PRRs) and related receptors that detect damage-associated molecular patterns (DAMPs) and initiate downstream signaling pathways. Radiation-induced cell death pathways are discussed in detail. Understanding these processes is crucial for developing strategies to mitigate the harmful effects of radiation and improve therapeutic outcomes.

An Overview of Radiation Countermeasure Development in Radiation Research from 1954 to 2024

Preparation for medical responses to major radiation accidents, further driven by increases in the threat of nuclear warfare, has led to a pressing need to understand the underlying mechanisms of radiation injury (RI) alone or in combination with other trauma (combined injury, CI). The identification of these mechanisms suggests molecules and signaling pathways that can be targeted to develop radiation medical countermeasures. Thus far, the United States Food and Drug Administration (U.S. FDA) has approved seven countermeasures to mitigate hematopoietic acute radiation syndrome (H-ARS), but no drugs are available for prophylaxis and no agents have been approved to combat the other sub-syndromes of ARS, let alone delayed effects of acute radiation exposure or the effects of combined injury. From its inception, Radiation Research has significantly contributed to the understanding of the underlying mechanisms of radiation injury and combined injury, and to the development of radiation medical countermeasures for these indications through the publication of peer-reviewed research and review articles.

FSL-1: A Synthetic Peptide Increases Survival in a Murine Model of Hematopoietic Acute Radiation Syndrome

In the current geopolitical climate there is an unmet need to identify and develop prophylactic radiation countermeasures, particularly to ensure the well-being of warfighters and first responders that may be required to perform on radiation-contaminated fields for operational or rescue missions. Currently, no countermeasures have been approved by the U.S. FDA for prophylactic administration. Here we report on the efficacious nature of FSL-1 (toll-like receptor 2/6 agonist) and the protection from acute radiation syndrome (ARS) in a murine total-body irradiation (TBI) model. A single dose of FSL-1 was administered subcutaneously in mice. The safety of the compound was assessed in non-irradiated animals, the efficacy of the compound was assessed in animals exposed to TBI in the AFRRI Co-60 facility, the dose of FSL-1 was optimized, and common hematological parameters [complete blood cell (CBC), cytokines, and bone marrow progenitor cells] were assessed. Animals were monitored up to 60 days after exposure and radiation-induced damage was evaluated. FSL-1 was shown to be non-toxic when administered to non-irradiated mice at doses up to 3 mg/kg. The window of efficacy was determined to be 24 h prior to 24 h after TBI. FSL-1 administration resulted in significantly increased survival when administered either 24 h prior to or 24 h after exposure to supralethal doses of TBI. The optimal dose of FSL-1 administration was determined to be 1.5 mg/kg when administered prior to irradiation. Finally, FSL-1 protected the hematopoietic system (recovery of CBC and bone marrow CFU). Taken together, the effects of increased survival and accelerated recovery of hematological parameters suggests that FSL-1 should be developed as a novel radiation countermeasure for soldiers and civilians, which can be used either before or after irradiation in the aftermath of a radiological or nuclear event.

Sequential administration of delta-tocotrienol ameliorates radiation-induced myelosuppression in mice and non-human primates through inducing G-CSF production

To date only four recombinant growth factors, including Filgrastim (rhG-CSF), have been approved by FDA as radiomitigators to ameliorate hematopoietic acute radiation syndrome (H-ARS). These approved agents are not stable under room-temperature, needing to be stored at 2-8 °C, and would not be feasible in a mass casualty scenario where rapid and cost-effective intervention is crucial. Delta-tocotrienol (δ-T3H), the most potent G-CSF-inducing agent among vitamin E isoforms, exhibited efficiency and selectivity on G-CSF production in comparison with TLR and STING agonists in mice. Five-dose δ-T3H was utilized as the optimal therapeutic regimen due to long-term G-CSF production and the best peripheral blood (PB) recovery of irradiated mice. Comparable with rhG-CSF, sequential administration of δ-T3H post-irradiation improved hematologic recovery and accelerated the regeneration of hematopoietic stem cells (HSCs) and hematopoietic progenitor cells (HPCs) in the bone marrow (BM) and spleen of 6.5Gy irradiated mice; and consistently enhanced repopulation of BM-HSCs. In 4.0Gy irradiated nonhuman primates, δ-T3H exhibited comparable efficacy as rhG-CSF to promote PB recovery and colony-formation of BM-HPCs. Altogether, we demonstrated that sequential administration of delta-tocotrienol ameliorates radiation-induced myelosuppression in mice and non-human primates through inducing G-CSF production, indicated δ-T3H as a promising radiomitigator for the management of H-ARS, particularly in a mass casualty scenario.

Design, synthesis, biological evaluation and in silico studies of novel quinoline derivatives as potential radioprotective molecules targeting the TLR2 and p53 pathways

Ionizing radiation in space, radiation devices or nuclear disasters are major threats to human health and public security. In this paper, in order to find the potential novel compounds decreasing the radiation-induced damage by targeting p53 apoptosis pathway and TLR2 passway, a series of novel quinoline derivatives were designed, synthesized, and evaluated their biological activities. Most of the synthesized compounds showed significant radioprotective effects in vitro, and the compound 5 has the best performance. Therefore, we verified its radioprotective activity in vivo and investigated the mechanism of its excellent activity. The results in vivo indicated that compound 5 not only markedly enhanced the survival rate (80 %) of mice 30 days after lethal exposure to irradiation, but also significantly reduced the radiation-induced damage to haematopoietic system and intestinal tissue of mice. The mechanistic studies indicated that compound 5 acted on the p53 pathway to reduce radiation-induced cell apoptosis and at the same time stimulated TLR2 to up-regulate the expressions of radiation protection factors. Molecular dynamics study shows that compound 5 would effectively bind to the TLR2 protein and further revealed the binding mechanism. Taken together, all the findings of our study demonstrate the quinoline derivative 5 is a potent radioprotective compound, which holds a great therapeutic potential for further development.

The TLR2/TLR6 ligand FSL-1 mitigates radiation-induced hematopoietic injury in mice and nonhuman primates

Thrombocytopenia, hemorrhage, anemia, and infection are life-threatening issues following accidental or intentional radiation exposure. Since few therapeutics are available, safe and efficacious small molecules to mitigate radiation-induced injury need to be developed. Our previous study showed the synthetic TLR2/TLR6 ligand fibroblast stimulating lipopeptide (FSL-1) prolonged survival and provided MyD88-dependent mitigation of hematopoietic acute radiation syndrome (H-ARS) in mice. Although mice and humans differ in TLR number, expression, and function, nonhuman primate (NHP) TLRs are like those of humans; therefore, studying both animal models is critical for drug development. The objectives of this study were to determine the efficacy of FSL-1 on hematopoietic recovery in small and large animal models subjected to sublethal total body irradiation and investigate its mechanism of action. In mice, we demonstrate a lack of adverse effects, an easy route of delivery (subcutaneous) and efficacy in promoting hematopoietic progenitor cell proliferation by FSL-1. NHP given radiation, followed a day later with a single subcutaneous administration of FSL-1, displayed no adversity but showed elevated hematopoietic cells. Our analyses revealed that FSL-1 promoted red blood cell development and induced soluble effectors following radiation exposure. Cytologic analysis of bone marrow aspirates revealed a striking enhancement of mononuclear progenitor cells in FSL-1-treated NHP. Combining the efficacy of FSL-1 in promoting hematopoietic cell recovery with the lack of adverse effects induced by a single administration supports the application of FSL-1 as a viable countermeasure against H-ARS.

Cytomodulatory characteristics of Granulocyte-Macrophage Colony-Stimulating Factor (GM-CSF) against cypermethrin on skin fibroblast cells (HFF-1)

The hematopoietic factor granulocyte macrophage-colony stimulating factor (GM-CSF) has been identified via its capacity to promote bone marrow progenitors' development and differentiation into granulocytes and macrophages. Extensive pre-clinical research has established its promise as a critical therapeutic target in an assortment of inflammatory and autoimmune disorders. Despite the broad literature on GM-CSF as hematopoietic of stem cells, the cyto/geno protective aspects remain unknown. This study aimed to assess the cyto/geno protective possessions of GM-CSF on cypermethrin-induced cellular toxicity on HFF-1 cells as an in vitro model. In pre-treatment culture, cells were exposed to various GM-CSF concentrations (5, 10, 20, and 40 ng/mL) with cypermethrin at IC50 (5.13 ng/mL). Cytotoxicity, apoptotic rates, and genotoxicity were measured using the MTT, Annexin V-FITC/PI staining via flow-cytometry, and the comet assay. Cypermethrin at 5.13 ng/mL revealed cytotoxicity, apoptosis, oxidative stress, and genotoxicity while highlighting GM-CSF's protective properties on HFF-1. GM-CSF markedly attenuated cypermethrin-induced apoptotic cell death (early and late apoptotic rates). GM-CSF considerably regulated oxidative stress and genotoxicity by reducing the ROS and LPO levels, maintaining the status of GSH and activity of SOD, and suppressing genotoxicity in the comet assay parameters. Therefore, GM-CSF could be promising as an antioxidant, anti-apoptotic, genoprotective and cytomodulating agent.

The role of bacteria and its derived biomaterials in cancer radiotherapy

Bacteria-mediated anti-tumor therapy has received widespread attention due to its natural tumor-targeting ability and specific immune-activation characteristics. It has made significant progress in breaking the limitations of monotherapy and effectively eradicating tumors, especially when combined with traditional therapy, such as radiotherapy. According to their different biological characteristics, bacteria and their derivatives can not only improve the sensitivity of tumor radiotherapy but also protect normal tissues. Moreover, genetically engineered bacteria and bacteria-based biomaterials have further expanded the scope of their applications in radiotherapy. In this review, we have summarized relevant researches on the application of bacteria and its derivatives in radiotherapy in recent years, expounding that the bacteria, bacterial derivatives and bacteria-based biomaterials can not only directly enhance radiotherapy but also improve the anti-tumor effect by improving the tumor microenvironment (TME) and immune effects. Furthermore, some probiotics can also protect normal tissues and organs such as intestines from radiation via anti-inflammatory, anti-oxidation and apoptosis inhibition. In conclusion, the prospect of bacteria in radiotherapy will be very extensive, but its biological safety and mechanism need to be further evaluated and studied.

Feasibility of Reducing Animal Numbers in Radiation Countermeasure Experiments from Historic Levels when using Sample Size Calculations

Historically, animal numbers have most often been in the hundreds for experiments designed to estimate the dose reduction factor (DRF) of a radiation countermeasure treatment compared to a control treatment. Before 2010, researchers had to rely on previous experience, both from others and their own, to determine the number of animals needed for a DRF experiment. In 2010, a formal sample size formula was developed by Kodell et al. This theoretical work showed that sample sizes for realistic, yet hypothetical, DRF experiments could be less than a hundred animals and still have sufficient power to detect clinically meaningful DRF values. However, researchers have been slow to use the formula for their DRF experiments, whether from ignorance to its existence or hesitancy to depart from "tried and true" sample sizes. Here, we adapt the sample size formula to better fit usual DRF experiments, and, importantly, we provide real experimental evidence from two independent DRF experiments that sample sizes smaller than what have typically been used can still statistically detect clinically meaningful DRF values. In addition, we update a literature review of DRF experiments which can be used to inform future DRF experiments, provide answers to questions that researchers have asked when considering sample size calculations rather than solely relying on previous experience, whether their own or others', and, in the supplementary material, provide R code implementing the formula, along with several exercises to familiarize the user with the adapted formula.

Protein biomarkers for radiation injury and testing of medical countermeasure efficacy: promises, pitfalls, and future directions

INTRODUCTION

Radiological/nuclear accidents, hostile military activity, or terrorist strikes have the potential to expose a large number of civilians and military personnel to high doses of radiation resulting in the development of acute radiation syndrome and delayed effects of exposure. Thus, there is an urgent need for sensitive and specific assays to assess the levels of radiation exposure to individuals. Such radiation exposures are expected to alter primary cellular proteomic processes, resulting in multifaceted biological responses.

AREAS COVERED

This article covers the application of proteomics, a promising and fast developing technology based on quantitative and qualitative measurements of protein molecules for possible rapid measurement of radiation exposure levels. Recent advancements in high-resolution chromatography, mass spectrometry, high-throughput, and bioinformatics have resulted in comprehensive (relative quantitation) and precise (absolute quantitation) approaches for the discovery and accuracy of key protein biomarkers of radiation exposure. Such proteome biomarkers might prove useful for assessing radiation exposure levels as well as for extrapolating the pharmaceutical dose of countermeasures for humans based on efficacy data generated using animal models.

EXPERT OPINION

The field of proteomics promises to be a valuable asset in evaluating levels of radiation exposure and characterizing radiation injury biomarkers.

TLR4-A Pertinent Player in Radiation-Induced Heart Disease?

The heart is one of the organs that is sensitive to developing delayed adverse effects of ionizing radiation (IR) exposure. Radiation-induced heart disease (RIHD) occurs in cancer patients and cancer survivors, as a side effect of radiation therapy of the chest, with manifestation several years post-radiotherapy. Moreover, the continued threat of nuclear bombs or terrorist attacks puts deployed military service members at risk of exposure to total or partial body irradiation. Individuals who survive acute injury from IR will experience delayed adverse effects that include fibrosis and chronic dysfunction of organ systems such as the heart within months to years after radiation exposure. Toll-like receptor 4 (TLR4) is an innate immune receptor that is implicated in several cardiovascular diseases. Studies in preclinical models have established the role of TLR4 as a driver of inflammation and associated cardiac fibrosis and dysfunction using transgenic models. This review explores the relevance of the TLR4 signaling pathway in radiation-induced inflammation and oxidative stress in acute as well as late effects on the heart tissue and the potential for the development of TLR4 inhibitors as a therapeutic target to treat or alleviate RIHD.

Exposure to ionizing radiations and changes in blood cells and interleukin-6 in radiation workers

Long-term exposure to ionizing radiation (IR) can cause dire health consequences even less than the dose limits. Previous biomonitoring studies have focused more on complete blood counts (CBCs), with non-coherent results. In this study, we aimed to investigate the association between exposure to IR and cytokine interleukin-6 (IL-6) along with hematological parameters in Tabriz megacity's radiation workers. In this hospital-based study, blood samples were taken from 33 radiation workers (exposed group) and 34 non-radiation workers (control group) in 4 hospitals. Absorbed radiation dose was measured by a personal film badge dosimeter in radiation workers. The studied biomarkers and all of the selected covariates were measured and analyzed using adjusted multiple linear regression models. The exposed doses for all radiation workers were under the dose limits (overall mean = 1.18 mSv/year). However, there was a significant association between exposure to ionizing radiation and IL-6 (49.78 vs 36.17; t = 2.4; p = 0.02) and eosinophils (0.17 vs 0.14; t = 2.02; p = 0.049). The difference between the mean of the other biomarkers in radiation workers was not statistically significant compared to the control group. This study demonstrated that long-term exposure to ionizing radiation, even under the dose limits, is related to a significantly increased level of some blood biomarkers (Il-6 and eosinophil) that, in turn, can cause subsequent health effects such as cancer.

Transcriptomes of Wet Skin Biopsies Predict Outcomes after Ionizing Radiation Exposure with Potential Dosimetric Applications in a Mouse Model

Countermeasures for radiation diagnosis, prognosis, and treatment are trailing behind the proliferation of nuclear energy and weaponry. Radiation injury mechanisms at the systems biology level are not fully understood. Here, mice skin biopsies at h2, d4, d7, d21, and d28 after exposure to 1, 3, 6, or 20 Gy whole-body ionizing radiation were evaluated for the potential application of transcriptional alterations in radiation diagnosis and prognosis. Exposure to 20 Gy was lethal by d7, while mice who received 1, 3, or 6 Gy survived the 28-day time course. A Sammon plot separated samples based on survival and time points (TPs) within lethal (20 Gy) and sublethal doses. The differences in the numbers, regulation mode, and fold change of significantly differentially transcribed genes (SDTGs, p < 0.05 and FC > 2) were identified between lethal and sublethal doses, and down and upregulation dominated transcriptomes during the first post-exposure week, respectively. The numbers of SDTGs and the percentages of upregulated ones revealed stationary downregulation post-lethal dose in contrast to responses to sublethal doses which were dynamic and largely upregulated. Longitudinal up/downregulated SDTGs ratios suggested delayed and extended responses with increasing IR doses in the sublethal range and lethal-like responses in late TPs. This was supported by the distributions of common and unique genes across TPs within each dose. Several genes with potential dosimetric marker applications were identified. Immune, fibrosis, detoxification, hematological, neurological, gastric, cell survival, migration, and proliferation radiation response pathways were identified, with the majority predicted to be activated after sublethal and inactivated after lethal exposures, particularly during the first post-exposure week.

Chemical and biological basis for development of novel radioprotective drugs for cancer therapy

Ionizing radiation (IR) causes chemical changes in biological systems through direct interaction with the macromolecules or by causing radiolysis of water. This property of IR is harnessed in the clinic for radiotherapy in almost 50% of cancers patients. Despite the advent of stereotactic radiotherapy instruments and other advancements in shielding techniques, the inadvertent deposition of radiation dose in the surrounding normal tissue can cause late effects of radiation injury in normal tissues. Radioprotectors, which are chemical or biological agents, can reduce or mitigate these toxic side-effects of radiotherapy in cancer patients and also during radiation accidents. The desired characteristics of an ideal radioprotector include low chemical toxicity, high risk to benefit ratio and specific protection of normal cells against the harmful effects of radiation without compromising the cytotoxic effects of IR on cancer cells. Since reactive oxygen species (ROS) are the major contributors of IR mediated toxicity, plethora of studies have highlighted the potential role of antioxidants to protect against IR induced damage. However, owing to the lack of any clinically approved radioprotector against whole body radiation, researchers have shifted the focus toward finding alternate targets that could be exploited for the development of novel agents. The present review provides a comprehensive insight in to the different strategies, encompassing prime molecular targets, which have been employed to develop radiation protectors/countermeasures. It is anticipated that understanding such factors will lead to the development of novel strategies for increasing the outcome of radiotherapy by minimizing normal tissue toxicity.

Prebiotic Mannan Oligosaccharide Pretreatment Improves Mice Survival Against Lethal Effects of Gamma Radiation by Protecting GI Tract and Hematopoietic Systems

Total body irradiation (TBI) results in critical injuries in a dose dependent manner that primarily damages highly proliferating tissues including hematopoietic stem cells (HSCs) and intestinal crypt stem cells etc. This may result in hematopoietic syndrome leading to bone marrow failure and gastrointestinal syndrome leading to chronic intestinal functional alterations. Death results from the gastrointestinal syndrome due to sepsis, bleeding, dehydration, and multi-system organ failure. We demonstrate that the prebiotic mannan oligosaccharide (MOS) pretreatment substantially prolongs survival in both male and female mice when administered 2 h prior to radiation either through oral or intraperitoneal route. The radioprotective efficacy of MOS was found to be age dependent and improves survival even in aged mice (12–13 months old). MOS pretreatment effectively abrogates radiation-induced hematopoietic injury and accelerates recovery of lymphocytes and WBCs and alleviates depletion of circulatory blood cells. Results also illustrate that MOS pretreatment abolishes crypt cell death and denudation of villi in comparison to the respective irradiated animals and ameliorates the overall radiation-induced damage to the GI system. MOS pretreatment facilitates intestinal recovery leading to enhanced animal survival demonstrating its protection efficacy against TBI induced mortality. Moreover, MOS pretreated animals show signs of accelerated recovery in terms of severity of radiation sickness symptoms including weight loss and completely abolish TBI associated mortality.

Heat Killed Salmonella typhimurium Protects Intestine Against Radiation Injury Through Wnt Signaling Pathway

Gastrointestinal (GI) toxicity caused by ionizing radiation (IR) is a dose limiting factor in radiotherapy and a great threat for individual nuclear-related military missions. However, there are currently no available strategies to effectively prevent the damage on the intestine induced by IR. In the present study, the protective activity of Heat Killed Salmonella typhimurium (HKST) on intestine against IR was investigated. Through mouse intestinal organoids and whole body irradiation of mice, we found that the pretreatment with HKST significantly preserved the structure of small intestine upon IR exposure and promoted the proliferation of intestinal cells post-IR. Further study revealed that the radioprotective effects of HKST were involved in DNA damage response (DDR) signaling. Moreover, the stimulation of DDR signaling by HKST upon radiation damage was mediated by Wnt signaling, in which the inhibition of Wnt signaling diminished the radioprotective effects of HKST. To sum up, our study suggested HKST as a potential radioprotectant used for prevention of IR-induced GI toxicity.

Celebrating 60 Years of Accomplishments of the Armed Forces Radiobiology Research Institute1

Chartered by the U.S. Congress in 1961, the Armed Forces Radiobiology Research Institute (AFRRI) is a Joint Department of Defense (DoD) entity with the mission of carrying out the Medical Radiological Defense Research Program in support of our military forces around the globe. In the last 60 years, the investigators at AFRRI have conducted exploratory and developmental research with broad application to the field of radiation sciences. As the only DoD facility dedicated to radiation research, AFRRI's Medical Radiobiology Advisory Team provides deployable medical and radiobiological subject matter expertise, advising commanders in the response to a U.S. nuclear weapon incident and other nuclear or radiological material incidents. AFRRI received the DoD Joint Meritorious Unit Award on February 17, 2004, for its exceptionally meritorious achievements from September 11, 2001 to June 20, 2003, in response to acts of terrorism and nuclear/radiological threats at home and abroad. In August 2009, the American Nuclear Society designated the institute a nuclear historic landmark as the U.S.'s primary source of medical nuclear and radiological research, preparedness and training. Since then, research has continued, and core areas of study include prevention, assessment and treatment of radiological injuries that may occur from exposure to a wide range of doses (low to high). AFRRI collaborates with other government entities, academic institutions, civilian laboratories and other countries to research the biological effects of ionizing radiation. Notable early research contributions were the establishment of dose limits for major acute radiation syndromes in primates, applicable to human exposures, followed by the subsequent evolution of radiobiology concepts, particularly the importance of immune collapse and combined injury. In this century, the program has been essential in the development and validation of prophylactic and therapeutic drugs, such as Amifostine, Neupogen®, Neulasta®, Nplate® and Leukine®, all of which are used to prevent and treat radiation injuries. Moreover, AFRRI has helped develop rapid, high-precision, biodosimetry tools ranging from novel assays to software decision support. New drug candidates and biological dose assessment technologies are currently being developed. Such efforts are supported by unique and unmatched radiation sources and generators that allow for comprehensive analyses across the various types and qualities of radiation. These include but are not limited to both 60Co facilities, a TRIGA® reactor providing variable mixed neutron and γ-ray fields, a clinical linear accelerator, and a small animal radiation research platform with low-energy photons. There are five major research areas at AFRRI that encompass the prevention, assessment and treatment of injuries resulting from the effects of ionizing radiation: 1. biodosimetry; 2. low-level and low-dose-rate radiation; 3. internal contamination and metal toxicity; 4. radiation combined injury; and 5. radiation medical countermeasures. These research areas are bolstered by an educational component to broadcast and increase awareness of the medical effects of ionizing radiation, in the mass-casualty scenario after a nuclear detonation or radiological accidents. This work provides a description of the military medical operations as well as the radiation facilities and capabilities present at AFRRI, followed by a review and discussion of each of the research areas.

A derivative of vitamin B3 applied several days after exposure reduces lethality of severely irradiated mice

Most, if not all, of the hitherto tested substances exert more or less pronounced pro-survival effects when applied before or immediately after the exposure to high doses of ionizing radiation. In the present study we demonstrate for the first time that 1-methyl nicotinamide (MNA), a derivative of vitamin B3, significantly (1.6 to 1.9 times) prolonged survival of BALB/c mice irradiated at LD30/30 (6.5 Gy), LD50/30 (7.0 Gy) or LD80/30 (7.5 Gy) of γ-rays when the MNA administration started as late as 7 days post irradiation. A slightly less efficient and only after the highest dose (7.5 Gy) of γ-rays was another vitamin B3 derivative, 1-methyl-3-acetylpyridine (1,3-MAP) (1.4-fold prolonged survival). These pro-survival effects did not seem to be mediated by stimulation of haematopoiesis, but might be related to anti-inflammatory and/or anti-thrombotic properties of the vitamin B3 derivatives. Our results show that MNA may represent a prototype of a radioremedial agent capable of mitigating the severity and/or progression of radiation-induced injuries when applied several hours or days after exposure to high doses of ionizing radiation.

Ionizing radiation and toll like receptors: A systematic review article

Ionizing radiation, including X and gamma rays, are used for various purposes such as; medicine, nuclear power, research, manufacturing, food preservation and construction. Furthermore, people are also exposed to ionizing radiation from their workplace or the environment. Apart from DNA fragmentation resulting in apoptosis, several additional mechanisms have been proposed to describe how radiation can alter human cell functions. Ionizing radiation may alter immune responses, which are the main cause of human disorders. Toll like receptors (TLRs) are important human innate immunity receptors which participate in several immune and non-immune cell functions including, induction of appropriate immune responses and immune related disorders. Based on the role played by ionizing radiation on human cell systems, it has been hypothesized that radiation may affect immune responses. Therefore, the main aim of this review article is to discuss recent information regarding the effects of ionizing radiation on TLRs and their related disorders.

Potential utility of peptides against damage induced by ionizing radiation

Radioprotection is the process whereby biological systems are aided against undesirable radiation hazards. Primitive radioprotectors suffered from either having crucial side effects or low efficacy in clinical applications. Therefore, the search for less toxic but more capable radioprotectants has continued for decades. Peptides have been investigated as radioprotectants in a variety of preclinical models both in vitro and in vivo. Peptides exert their influence through scavenging free radicals, modifying cell signaling and inhibiting cell apoptosis. Demonstrating potential in vivo properties, peptide radiation countermeasures might find enough credit for use in humans in the future. This article reviews the potential therapeutic value of currently known radioprotective peptides and attempts to provide a comprehensive source for further scientific research in this area.

Radioprotection and Radiomitigation: From the Bench to Clinical Practice

The development of protective agents against harmful radiations has been a subject of investigation for decades. However, effective (ideal) radioprotectors and radiomitigators remain an unsolved problem. Because ionizing radiation-induced cellular damage is primarily attributed to free radicals, radical scavengers are promising as potential radioprotectors. Early development of such agents focused on thiol synthetic compounds, e.g., amifostine (2-(3-aminopropylamino) ethylsulfanylphosphonic acid), approved as a radioprotector by the Food and Drug Administration (FDA, USA) but for limited clinical indications and not for nonclinical uses. To date, no new chemical entity has been approved by the FDA as a radiation countermeasure for acute radiation syndrome (ARS). All FDA-approved radiation countermeasures (filgrastim, a recombinant DNA form of the naturally occurring granulocyte colony-stimulating factor, G-CSF; pegfilgrastim, a PEGylated form of the recombinant human G-CSF; sargramostim, a recombinant granulocyte macrophage colony-stimulating factor, GM-CSF) are classified as radiomitigators. No radioprotector that can be administered prior to exposure has been approved for ARS. This differentiates radioprotectors (reduce direct damage caused by radiation) and radiomitigators (minimize toxicity even after radiation has been delivered). Molecules under development with the aim of reaching clinical practice and other nonclinical applications are discussed. Assays to evaluate the biological effects of ionizing radiations are also analyzed.

Entolimod as a radiation countermeasure for acute radiation syndrome

High doses of total-body or partial-body radiation exposure can result in a life-threatening acute radiation syndrome as manifested by severe morbidity. Entolimod (CBLB502) is effective in protecting against, and mitigating the development of, the hematopoietic and gastrointestinal subsyndromes of the acute radiation syndrome in rodents and nonhuman primates. Entolimod treatment reduces radiation-induced apoptosis and accelerates the regeneration of progenitors in radiation-damaged tissues. The drug has been evaluated clinically for its pharmacokinetics (PK), toxicity, and biomarkers. The US Food and Drug Administration (FDA) has granted investigational new drug, fast-track, and orphan drug statuses to entolimod. Its safety, efficacy, and animal-to-human dose conversion data allowed its progression with a pre-emergency use authorization application submission.

Heat-killed Salmonella Typhimurium protects mice against carbon ion radiation

OBJECTIVE

Patients receiving carbon-ion radiation therapy and astronauts exploring outer space are inevitably exposed to heavy ion radiation. The aim of this study was to develop radioprotectors to minimize the injuries induced by carbon ion radiation.

METHODS

Heat-killed Salmonella Typhimurium (HKST) was administered to mice by gavage prior to irradiation with a ¹²C⁶⁺ heavy ion accelerator. Hematoxylin and eosin staining and immunofluorescence TdT-mediated dUTP Nick-End Labeling staining were used to assess the radioprotective effect of HKST on organ damage and levels of apoptosis, respectively, in mice. To investigate the mechanism underlying the radioprotective effect of HKST, levels of the pro-apoptotic proteins BAX and caspase 3 as well as interferon-regulatory factor (IRF) 3/7 in the femur, testis and intestine were assessed using immunofluorescence.

RESULTS

Injuries induced by carbon ion radiation were significantly eased by pretreatment with HKST. Both apoptosis and high expression levels of pro-apoptotic proteins induced by heavy ion radiation were inhibited by HKST pretreatment. The radioprotective effect of HKST was associated with stimulation of Toll-like receptor signaling mediated by enhanced IRF3 and IRF7 signaling.

CONCLUSION

HKST was an effective radioprotector alleviating damage to multiple organs caused by heavy ion radiation.

The age-dependent effect of high-dose X-ray radiation on NFκB signaling, structure, and mechanical behavior of the intervertebral disc

Purpose: Ionizing radiation damages tissue and provokes inflammatory responses in multiple organ systems. We investigated the effects of high-dose X-ray radiation on the molecular inflammation and mechanical function of the intervertebral disc (IVD).Methods: Functional spine units (FSUs) containing the vertebrae-IVDs-vertebrae structure extracted from 1-month, 6-month, and 16-month-old NFκB-luciferase reporter mice and from 6-month-old myeloid differentiation factor 88 (MyD88)-null mice. After a preconditioning period in culture, the FSUs were subjected a single dose of ionizing X-ray radiation at 20 Gys, and then NFκB expression was monitored. The IVDs were then subjected to mechanical testing using dynamic compression, glycosaminoglycan (GAG) quantification, and histological analyses.Results: In the 1-month-old FSUs, the NFκB-driven luciferase activity was significantly elevated for 1 day following the exposure to radiation. The 6-month-old FSUs showed increased NFκB activity for 3 days, while the 16-month-old FSUs sustained elevated levels of NFκB activity throughout the 10-day culture period. All irradiated groups showed significant loss of disc height, GAG content, mechanical function and changes in structure. Ablation of MyD88 blunted the radiation-mediated NFκB signaling, and preserved GAG content, and the IVDs' structure and mechanical performance.Conclusions: These results suggest that high-dose radiation affects the IVDs' NFκB-dependent inflammatory processes that subsequently lead to functional deterioration. Blocking the transactivation potential of NFκB via MyD88 ablation preserved the structure and mechanical function of the FSUs. The long-term effects of radiation on IVD homeostasis should be considered in individuals susceptible to occupational and medical exposure.

Targeting innate sensing in the tumor microenvironment to improve immunotherapy

The innate immune sensing pathways play critical roles in the defense against pathogen infection, but their roles in cancer immunosurveillance and cancer therapies are less defined. We propose that defective innate immune sensing inside the tumor microenvironment might limit T-cell responses to immunotherapy. A recent mechanistic understanding of conventional therapies revealed that both innate immune sensing and T-cell responses are essential for optimal antitumor efficacy. T-cell-based immunotherapy, particularly immune checkpoint blockade, has achieved great success in reactivating antitumor immune responses to lead to tumor regression, but only in a small fraction of patients. Therefore, incorporating conventional therapy that can increase innate sensing and immunotherapy should lead to promising strategies for cancer patients. Here, we review the innate sensing pathways related to cancer initiation/progression and therapies, summarize the recent key findings in innate immune sensing related to conventional therapies, evaluate current combination strategies, and highlight the potential issues of combinational therapies in terms of antitumor efficacy and toxicities.

Diverse functions of the thrombopoietin receptor agonist romiplostim rescue individuals exposed to lethal radiation

In cases of radiological accidents, especially victims exposed to high-dose ionizing radiation, the administration of appropriate approved pharmaceutical drugs is the most rapid medical treatment. However, currently, there are no suitable candidates. The thrombopoietin receptor (TPOR) agonist romiplostim (RP) is a therapeutic agent for immune thrombocytopenia and has potential to respond to such victims. Here, we show that RP administration in mice exposed to lethal-dose radiation leads not only to the promotion of haematopoiesis in multiple organs, including the lungs but also a reduction in damage to organs and cells. RP also causes a rapid increase in the number of mesenchymal stem cells in the spleen. In addition, RP suppresses the expression of several miRNAs involved in radiation-induced leukemogenesis, suggesting the presence of targets other than TPOR. Among the currently approved pharmaceutical drugs, RP is the most suitable candidate for victims exposed to high-dose ionizing radiation.

Radiation therapy and immunotherapy: what is the optimal timing or sequencing?

Radiotherapy is a component of the standard of care for many patients with locally advanced nonmetastatic tumors and increasingly those with oligometastatic tumors. Despite encouraging advances in local control and progression-free and overall survival outcomes, continued manifestation of tumor progression or recurrence leaves room for improvement in therapeutic efficacy. Novel combinations of radiation with immunotherapy have shown promise in improving outcomes and reducing recurrences by overcoming tumor immune tolerance and evasion mechanisms via boosting the immune system's ability to recognize and eradicate tumor cells. In this review, we discuss preclinical and early clinical evidence that radiotherapy and immunotherapy can improve treatment outcomes for locally advanced and metastatic tumors, elucidate underlying molecular mechanisms and address strategies to optimize timing and sequencing of combination therapy for maximal synergy.

NOD2 agonist murabutide alleviates radiation-induced injury through DNA damage response pathway mediated by ATR

Injury-induced by ionizing radiation (IR) severely reduces the quality of life of victims. The development of radiation protectors is regarded as one of the most resultful strategies to alleviate damages caused by IR exposure. In the present study, we investigated the radioprotective effects of the agonist of nucleotide-binding-oligomerization-domain-containing proteins 2 called murabutide (MBD) and clarified the potential mechanisms. Our results showed that the pretreatment with MBD effectively protected cultured cells and mice against IR-induced toxicity and the pretreatment with MBD in vitro and in vitro also inhibited apoptosis caused by IR exposure. The downregulation of γ-H2AX and the upregulation of ATR signaling pathways by MBD treatment indicated that the radioprotective effects of MBD were due to the stimulation of DNA damage response (DDR) pathway to repair DNA double-strand breaks caused by IR exposure. As the radioprotective effects of MBD were diminished by the ATR selective inhibitor rather than the ATM inhibitor, ATR pathway was confirmed to be a more crucial checkpoint pathway in mediating the stimulation of DDR pathway by MBD. Taken together, our data provide a novel and effective protector to relieve the injury induced by IR exposure.

Drug discovery strategies for acute radiation syndrome

Introduction: There are at the minimum two major, quite different approaches to advance drug discovery. The first being the target-based drug discovery (TBDD) approach that is commonly referred to as the molecular approach. The second approach is the phenotype-based drug discovery (PBDD), also known as physiology-based drug discovery or empirical approach. Area covered: The authors discuss, herein, the need for developing radiation countermeasure agents for various sub-syndromes of acute radiation syndromes (ARS) following TBDD and PBDD approaches. With time and continuous advances in radiation countermeasure drug development research, the expectation is to have multiple radiation countermeasure agents for each sub-syndrome made available to radiation exposed victims. Expert opinion: The majority of the countermeasures currently being developed for ARS employ the PBDD approach, while the TBDD approach is clearly under-utilized. In the future, an improved drug development strategy might be a 'hybrid' strategy that is more reliant on TBDD for the initial drug discovery via large-scale screening of potential candidate agents, while utilizing PBDD for secondary screening of those candidates, followed by tertiary analytics phase in order to pinpoint efficacious candidates that target the specific sub-syndromes of ARS.

Proteomic Changes in Mouse Spleen after Radiation-Induced Injury and its Modulation by Gamma-Tocotrienol

Gamma-tocotrienol (GT3), a naturally occurring vitamin E isomer, a promising radioprotector, has been shown to protect mice against radiation-induced hematopoietic and gastrointestinal injuries. We analyzed changes in protein expression profiles of spleen tissue after GT3 treatment in mice exposed to gamma radiation to gain insights into the molecular mechanism of radioprotective efficacy. Male CD2F1 mice, 12-to-14 weeks old, were treated with either vehicle or GT3 at 24 h prior to 7 Gy total-body irradiation. Nonirradiated vehicle, nonirradiated GT3 and age-matched naïve animals were used as controls. Blood and tissues were harvested on days 0, 1, 2, 4, 7, 10 and 14 postirradiation. High-resolution mass-spectrometry-based radioproteomics was used to identify differentially expressed proteins in spleen tissue with or without drug treatment. Subsequent bioinformatic analyses helped delineate molecular markers of biological pathways and networks regulating the cellular radiation responses in spleen. Our results show a robust alteration in spleen proteomic profiles including upregulation of the Wnt signaling pathway and actin-cytoskeleton linked proteins in mediating the radiation injury response in spleen. Furthermore, we show that 24 h pretreatment with GT3 attenuates radiation-induced hematopoietic injury in the spleen by modulating various cell signaling proteins. Taken together, our results show that the radioprotective effects of GT3 are mediated, via alleviation of radiation-induced alterations in biochemical pathways, with wide implications on overall hematopoietic injury.

The Role of Toll-Like Receptor in Inflammation and Tumor Immunity

Toll-like receptors (TLRs) activation enables host to recognize a large number of pathogen-associated molecule patterns (PAMPs), ignite immune cells to discriminate between self and non-self, and then promote the following innate and adaptive immune responses. Accumulated clinical/preclinical evidences have proven TLRs to be critical role in the autoimmune diseases, including inflammatory and tumor-associated diseases. Activation of TLRs is becoming or has been a target for cancer treatment. It is shown that TLRs can induce preferable anti-tumor effect by eliciting inflammatory cytokines expression and cytotoxic T lymphocytes (CTLs) response. As adjuvant, TLRs agonists can launch a strong immune response to assist cancer radiotherapy and bio-chemotherapy. On the other hand, tumor-associated antigens acting as PAMPs, can also activate TLRs and induce tumor gene-related programmed cell death, including apoptosis, autophagy and programmed necrosis. While there are also arguments that the excessive TLRs expression will promote tumor deterioration in various organisms, as the TLR-induced inflammation will accelerate the cancer cells boost in the tumor microenvironment (TME). However, the effect of TLRs acting on cancers is still not quite clear today. In this review, we will summarize the recent researches of TLRs in cancer treatment and their role in TME, giving a brief overview on future expectation.

Mannan oligosaccharide requires functional ETC and TLR for biological radiation protection to normal cells

BACKGROUND

Low LET Ionizing radiation is known to alter intracellular redox balance by inducing free radical generation, which may cause oxidative modification of various cellular biomolecules. The extent of biomolecule-modifications/ damages and changes in vital processes (viz. cellular homeostasis, inter-/intra-cellular signaling, mitochondrial physiology/dynamics antioxidant defence systems) are crucial which in turn determine fate of cells.

RESULTS

In the present study, we expended TLR expressing (normal/ transformed) and TLR null cells; and we have shown that mannan pretreatment in TLR expressing normal cells offers survival advantage against lethal doses of ionizing radiation. On the contrary, mannan pretreatment does not offer any protection against radiation to TLR null cells, NKE ρ° cells and transformed cells. In normal cells, abrupt decrease in mitochondrial membrane potential and endogenous ROS levels occurs following treatment with mannan. We intend to irradiate mannan-pretreated cells at a specific stage of perturbed mitochondrial functioning and ROS levels to comprehend if mannan pretreatment offers any survival advantage against radiation exposure to cells. Interestingly, pre-irradiation treatment of cells with mannan activates NFκB, p38 and JNK, alters mitochondrial physiology, increases expression of Cu/ZnSOD and MnSOD, minimizes oxidation of mitochondrial phospholipids and offers survival advantage in comparison to irradiated group, in TLR expressing normal cells.

CONCLUSION

The study demonstrates that TLR and mitochondrial ETC functions are inevitable in radio-protective efficacy exhibited by mannan.

The Toll-Like Receptor 2/6 Agonist, FSL-1 Lipopeptide, Therapeutically Mitigates Acute Radiation Syndrome

Risks of radiation exposure from nuclear incidents and cancer radiotherapy are undeniable realities. These dangers urgently compel the development of agents for ameliorating radiation–induced injuries. Biologic pathways mediated by myeloid differentiation primary response gene 88 (MyD88), the common adaptor for toll–like receptor (TLR) and Interleukin–1 receptor signaling, are critical for radioprotection. Treating with agonists prior to radiation enhances survival by activating TLR signaling, whereas radiomitigating TLR–activating therapeutics given after exposure are less defined. We examine the radiomitigation capability of TLR agonists and identify one that is superior for its efficacy and reduced toxic consequences compared to other tested agonists. We demonstrate that the synthetic TLR2/6 ligand Fibroblast–stimulating lipopeptide (FSL–1) substantially prolongs survival in both male and female mice when administered 24 hours after radiation and shows MyD88–dependent function. FSL–1 treatment results in accelerated hematopoiesis in bone marrow, spleen and periphery, and augments systemic levels of hematopoiesis–stimulating factors. The ability of FSL–1 to stimulate hematopoiesis is critical, as hematopoietic dysfunction results from a range of ionizing radiation doses. The efficacy of a single FSL–1 dose for alleviating radiation injury while protecting against adverse effects reveals a viable radiation countermeasures agent.

Appraisal of biochemical classes of radioprotectors: evidence, current status and guidelines for future development

The search for efficient radioprotective agents to protect from radiation-induced toxicity, due to planned or accidental radiation exposure, is still ongoing worldwide. Despite decades of research and development of widely different biochemical classes of natural and derivative compounds, a safe and effective radioprotector is largely unmet. In this comprehensive review, we evaluated the evidence for the radioprotective performance of classical thiols, vitamins, minerals, dietary antioxidants, phytochemicals, botanical and bacterial preparations, DNA-binding agents, cytokines, and chelators including adaptogens. Where radioprotection was demonstrated, the compounds have shown moderate dose modifying factors ranging from 1.1 to 2.7. To date, only few compounds found way to clinic with limited margin of dose prescription due to side effects. Most of these compounds (amifostine, filgratism, pegfilgrastim, sargramostim, palifermin, recombinant salmonella flagellin, Prussian blue, potassium iodide) act primarily via scavenging of free radicals, modulation of oxidative stress, signal transduction, cell proliferation or enhance radionuclide elimination. However, the gain in radioprotection remains hampered with low margin of tolerance. Future development of more effective radioprotectors requires an appropriate nontoxic compound, a model system and biomarkers of radiation exposure. These are important to test the effectiveness of radioprotection on physiological tissues during radiotherapy and field application in cases of nuclear eventualities.

A review of radiation countermeasures focusing on injury-specific medicinals and regulatory approval status: part III. Countermeasures under early stages of development along with 'standard of care' medicinal and procedures not requiring regulatory approval for use

PURPOSE

Terrorist attacks, with their intent to maximize psychological and economic damage as well as inflicting sickness and death on given targeted populations, are an ever-growing worldwide concern in government and public sectors as they become more frequent, violent, and sensational. If given the chance, it is likely that terrorists will use radiological or nuclear weapons. To thwart these sinister efforts, both physical and medical countermeasures against these weapons are currently being researched and developed so that they can be utilized by the first responders, military, and medical providers alike. This is the third article of a three-part series in which we have reviewed additional radiation countermeasures that are currently under early preclinical phases of development using largely animal models and have listed and discussed clinical support measures, including agents used for radiation-induced emesis, as well as countermeasures not requiring Food and Drug Administration approval.

CONCLUSIONS

Despite the significant progress that has been made in this area during the last several years, additional effort is needed in order to push promising new agents, currently under development, through the regulatory pipeline. This pipeline for new promising drugs appears to be unreasonably slow and cumbersome; possible reasons for this inefficiency are briefly discussed. Significant and continued effort needs to be afforded to this research and development area, as to date, there is no approved radioprotector that can be administered prior to high dose radiation exposure. This represents a very significant, unmet medical need and a significant security issue. A large number of agents with potential to interact with different biological targets are under development. In the next few years, several additional radiation countermeasures will likely receive Food and Drug Administration approval, increasing treatment options for victims exposed to unwanted ionizing irradiation.

Colony-stimulating factors for the treatment of the hematopoietic component of the acute radiation syndrome (H-ARS): a review

One of the greatest national security threats to the United States is the detonation of an improvised nuclear device or a radiological dispersal device in a heavily populated area. As such, this type of security threat is considered to be of relatively low risk, but one that would have an extraordinary high impact on health and well-being of the US citizenry. Psychological counseling and medical assessments would be necessary for all those significantly impacted by the nuclear/radiological event. Direct medical interventions would be necessary for all those individuals who had received substantial radiation exposures (e.g., >1 Gy). Although no drugs or products have yet been specifically approved by the United States Food and Drug Administration (US FDA) to treat the effects of acute radiation syndrome (ARS), granulocyte colony-stimulating factor (G-CSF), granulocyte macrophage colony-stimulating factor (GM-CSF), and pegylated G-CSF have been used off label for treating radiation accident victims. Recent threats of terrorist attacks using nuclear or radiologic devices makes it imperative that the medical community have up-to-date information and a clear understanding of treatment protocols using therapeutically effective recombinant growth factors and cytokines such as G-CSF and GM-CSF for patients exposed to injurious doses of ionizing radiation. Based on limited human studies with underlying biology, we see that the recombinants, G-CSF and GM-CSF appear to have modest, but significant medicinal value in treating radiation accident victims. In the near future, the US FDA may approve G-CSF and GM-CSF as ‘Emergency Use Authorization’ (EUA) for managing radiation-induced aplasia, an ARS-related pathology. In this article, we review the status of growth factors for the treatment of radiological/nuclear accident victims.

Radioprotective Agents: Strategies and Translational Advances

Radioprotectors are agents required to protect biological system exposed to radiation, either naturally or through radiation leakage, and they protect normal cells from radiation injury in cancer patients undergoing radiotherapy. It is imperative to study radioprotectors and their mechanism of action comprehensively, looking at their potential therapeutic applications. This review intimately chronicles the rich intellectual, pharmacological story of natural and synthetic radioprotectors. A continuous effort is going on by researchers to develop clinically promising radioprotective agents. In this article, for the first time we have discussed the impact of radioprotectors on different signaling pathways in cells, which will create a basis for scientific community working in this area to develop novel molecules with better therapeutic efficacy. The bright future of exceptionally noncytotoxic derivatives of bisbenzimidazoles is also described as radiomodulators. Amifostine, an effective radioprotectant, has been approved by the FDA for limited clinical use. However, due to its adverse side effects, it is not routinely used clinically. Recently, CBLB502 and several analog of a peptide are under clinical trial and showed high success against radiotherapy in cancer. This article reviews the different types of radioprotective agents with emphasis on the strategies for the development of novel radioprotectors for drug development. In addition, direction for future strategies relevant to the development of radioprotectors is also addressed.

Use of biomarkers for assessing radiation injury and efficacy of countermeasures

Several candidate drugs for acute radiation syndrome (ARS) have been identified that have low toxicity and significant radioprotective and radiomitigative efficacy. Inasmuch as exposing healthy human volunteers to injurious levels of radiation is unethical, development and approval of new radiation countermeasures for ARS are therefore presently based on animal studies and Phase I safety study in healthy volunteers. The Animal Efficacy Rule, which underlies the Food and Drug Administration approval pathway, requires a sound understanding of the mechanisms of injury, drug efficacy, and efficacy biomarkers. In this context, it is important to identify biomarkers for radiation injury and drug efficacy that can extrapolate animal efficacy results, and can be used to convert drug doses deduced from animal studies to those that can be efficacious when used in humans. Here, we summarize the progress of studies to identify candidate biomarkers for the extent of radiation injury and for evaluation of countermeasure efficacy.

The Toll-Like Receptor 5 Agonist Entolimod Mitigates Lethal Acute Radiation Syndrome in Non-Human Primates

There are currently no approved medical radiation countermeasures (MRC) to reduce the lethality of high-dose total body ionizing irradiation expected in nuclear emergencies. An ideal MRC would be effective even when administered well after radiation exposure and would counteract the effects of irradiation on the hematopoietic system and gastrointestinal tract that contribute to its lethality. Entolimod is a Toll-like receptor 5 agonist with demonstrated radioprotective/mitigative activity in rodents and radioprotective activity in non-human primates. Here, we report data from several exploratory studies conducted in lethally irradiated non-human primates (rhesus macaques) treated with a single intramuscular injection of entolimod (in the absence of intensive individualized supportive care) administered in a mitigative regimen, 1-48 hours after irradiation. Following exposure to LD50-70/40 of radiation, injection of efficacious doses of entolimod administered as late as 25 hours thereafter reduced the risk of mortality 2-3-fold, providing a statistically significant (P<0.01) absolute survival advantage of 40-60% compared to vehicle treatment. Similar magnitude of survival improvement was also achieved with drug delivered 48 hours after irradiation. Improved survival was accompanied by predominantly significant (P<0.05) effects of entolimod administration on accelerated morphological recovery of hematopoietic and immune system organs, decreased severity and duration of thrombocytopenia, anemia and neutropenia, and increased clonogenic potential of the bone marrow compared to control irradiated animals. Entolimod treatment also led to reduced apoptosis and accelerated crypt regeneration in the gastrointestinal tract. Together, these data indicate that entolimod is a highly promising potential life-saving treatment for victims of radiation disasters.

A critical role of toll-like receptor 2 (TLR2) and its' in vivo ligands in radio-resistance

The role of Toll-like receptor-2 (TLR2) in radio-resistance remained largely unknown. TLR2 knockout (TLR2^−/−) mice received radiation of 6.5 Gy, and then were studied. We found that radiation resulted in more severe mortality and morbidity rates in TLR2^−/− mice. The cause of death in TLR2^−/− mice may be severe and persistent bone marrow cell loss. Injection of the TLR2 agonist Pam₃CSK₄ into wild type (WT) mice induced radio-resistance. Myd88^−/− mice were more susceptible to radiation. In conclusion, our data indicate that, similar to TLR4, TLR2 plays a critical role in radio-resistance.

Amelioration of radiation-induced hematopoietic syndrome by an antioxidant chlorophyllin through increased stem cell activity and modulation of hematopoiesis

Hematopoietic stem cells and progenitor cells (HSPC) are low in abundance and exhibit high radiosensitivity and their ability to divide dramatically decreases following exposure to ionizing radiation. Our earlier studies have shown antiapoptotic, immune-stimulatory, and antioxidant effects of chlorophyllin, a constituent of the over the counter drug derifil. Here we describe the beneficial effects of chlorophyllin against radiation-induced hematopoietic syndrome. Chlorophyllin administration significantly enhanced the abundance of HSPC in vivo. It induced a transient cell cycle arrest in lineage-negative cells in the bone marrow. However, the chlorophyllin-treated mice exposed to whole body irradiation (WBI) had a significantly higher proportion of actively dividing HSPC in the bone marrow as compared to only WBI-exposed mice. It significantly increased the number of colony forming units (CFUs) by bone marrow cells in vitro and spleen CFUs in irradiated mice in vivo. Pharmacokinetic study showed that chlorophyllin had a serum half-life of 141.8 min in mice. Chlorophyllin upregulated antiapoptotic genes and antioxidant machinery via activation of prosurvival transcription factors Nrf-2 and NF-κB and increased the survival and recovery of bone marrow cells in mice exposed to WBI. Chlorophyllin stimulated granulocyte production in bone marrow and increased the abundance of peripheral blood neutrophils by enhancing serum levels of granulocyte-colony stimulation factor (GCSF). Most importantly, prophylactic treatment of mice with chlorophyllin significantly abrogated radiation-induced mortality. Chlorophyllin mitigates radiation-induced hematopoietic syndrome by increasing the abundance of hematopoietic stem cells, enhancing granulopoiesis, and stimulating prosurvival pathways in bone marrow cells and lymphocytes.

Patents for Toll-like receptor ligands as radiation countermeasures for acute radiation syndrome

Acute radiation exposure induces apoptosis of tissues in the hematopoietic, digestive, cutaneous, cardiovascular and nervous systems; extensive apoptosis of these tissues ultimately leads to acute radiation syndrome. A novel strategy for developing radiation countermeasures has been to imitate the genetic mechanisms acquired by radiation-resistant tumors. Two mechanisms that underlie this ability of tumor cells are the p53 and NF-κB pathways. The loss of p53 function results in the inactivation of pro-apoptotic control mechanisms, while constitutive activation of NF-κB results in the up-regulation of anti-apoptotic genes. Various Toll-like receptor ligands are capable of up regulating the NF-κB pathway, which increases radio-resistance and reduces radiation-induced apoptosis in various tissues. Several Toll-like receptor ligands have been patented and are currently under development as radiation countermeasures for acute radiation syndrome. Ongoing studies suggest that a few of these attractive agents are progressing well along the US FDA approval pathway to become radiation countermeasures.

Medical Countermeasures for Radiation Exposure and Related Injuries: Characterization of Medicines, FDA-Approval Status and Inclusion into the Strategic National Stockpile

World events over the past decade have highlighted the threat of nuclear terrorism as well as an urgent need to develop radiation countermeasures for acute radiation exposures and subsequent bodily injuries. An increased probability of radiological or nuclear incidents due to detonation of nuclear weapons by terrorists, sabotage of nuclear facilities, dispersal and exposure to radioactive materials, and accidents provides the basis for such enhanced radiation exposure risks for civilian populations. Although the search for suitable radiation countermeasures for radiation-associated injuries was initiated more than half a century ago, no safe and effective radiation countermeasure for the most severe of these injuries, namely acute radiation syndrome (ARS), has been approved by the United States Food and Drug Administration (FDA). The dearth of FDA-approved radiation countermeasures has prompted intensified research for a new generation of radiation countermeasures. In this communication, the authors have listed and reviewed the status of radiation countermeasures that are currently available for use, or those that might be used for exceptional nuclear/radiological contingencies, plus a limited few medicines that show early promise but still remain experimental in nature and unauthorized for human use by the FDA.

NF-kB as a key player in regulation of cellular radiation responses and identification of radiation countermeasures

Nuclear factor (NF)-κB is a transcription factor that plays significant role in immunity, cellular survival and inhibition of apoptosis, through the induction of genetic networks. Depending on the stimulus and the cell type, the members of NF-κB related family (RelA, c-Rel, RelB, p50, and p52), forms different combinations of homo and hetero-dimers. The activated complexes (Es) translocate into the nucleus and bind to the 10bp κB site of promoter region of target genes in stimulus specific manner. In response to radiation, NF-κB is known to reduce cell death by promoting the expression of anti-apoptotic proteins and activation of cellular antioxidant defense system. Constitutive activation of NF-κB associated genes in tumour cells are known to enhance radiation resistance, whereas deletion in mice results in hypersensitivity to IR-induced GI damage. NF-κB is also known to regulate the production of a wide variety of cytokines and chemokines, which contribute in enhancing cell proliferation and tissue regeneration in various organs, such as the GI crypts stem cells, bone marrow etc., following exposure to IR. Several other cytokines are also known to exert potent pro-inflammatory effects that may contribute to the increase of tissue damage following exposure to ionizing radiation. Till date there are a series of molecules or group of compounds that have been evaluated for their radio-protective potential, and very few have reached clinical trials. The failure or less success of identified agents in humans could be due to their reduced radiation protection efficacy. In this review we have considered activation of NF-κB as a potential marker in screening of radiation countermeasure agents (RCAs) and cellular radiation responses. Moreover, we have also focused on associated mechanisms of activation of NF-κB signaling and their specified family member activation with respect to stimuli. Furthermore, we have categorized their regulated gene expressions and their function in radiation response or modulation. In addition, we have discussed some recently developed radiation countermeasures in relation to NF-κB activation

New approaches to radiation protection

Radioprotectors are compounds that protect against radiation injury when given prior to radiation exposure. Mitigators can protect against radiation injury when given after exposure but before symptoms appear. Radioprotectors and mitigators can potentially improve the outcomes of radiotherapy for cancer treatment by allowing higher doses of radiation and/or reduced damage to normal tissues. Such compounds can also potentially counteract the effects of accidental exposure to radiation or deliberate exposure (e.g., nuclear reactor meltdown, dirty bomb, or nuclear bomb explosion); hence they are called radiation countermeasures. Here, we will review the general principles of radiation injury and protection and describe selected examples of radioprotectors/mitigators ranging from small-molecules to proteins to cell-based treatments. We will emphasize agents that are in more advanced stages of development.

Tocols induce G-CSF and mobilise progenitors that mitigate radiation injury

Tocols induce high levels of granulocyte-colony-stimulating factor (G-CSF). G-CSF mobilises progenitors that allow mice that have been severely immunocompromised by exposure to acute, high-dose ionising irradiation to recover and to survive. The neutralisation of G-CSF abrogates the radioprotective efficacy of tocols. This article reviews studies in which CD2F1 mice were irradiated with sufficiently high doses to cause acute radiation syndrome symptoms and then administered (iv) progenitor-enriched whole blood or peripheral blood mononuclear cells from tocol- and AMD3100-injected donor mice (AMD3100 is a chemokine receptor antagonist used to improve the yield of mobilised progenitors). In some experiments, G-CSF was neutralised completely. Irradiated recipient mice were observed for 30 d post-irradiation for survival, a primary endpoint used for determining therapeutic effectiveness. Additionally, potential tocol-induced biomarkers (cytokines, chemokines and growth factors) were quantified. The authors suggest that tocols are highly effective agents for mobilising progenitors with significant therapeutic potential.

Radiation enteropathy--pathogenesis, treatment and prevention

Changes in cancer incidence and mortality have been modest during the past several decades, but the number of cancer survivors has almost tripled during the same period. With an increasing cohort of cancer survivors, efforts to prevent, diagnose and manage adverse effects of cancer therapy, in general, and those of radiation therapy specifically, have intensified. Many cancer survivors have undergone radiation therapy of tumours in the pelvis or abdomen, thus rendering the bowel at risk of injury. In fact, the current prevalence of patients who have long-term radiation-induced intestinal adverse effects exceeds that of IBD. Considerable progress towards reducing toxicity of radiation therapy has been made by the introduction of so-called dose-sculpting treatment techniques, which enable precise delivery of the radiation beam. Moreover, new insights into the underlying pathophysiology have resulted in an improved understanding of mechanisms of radiation-induced bowel toxicity and in development of new diagnostic strategies and management opportunities. This Review discusses the pathogenesis of early and delayed radiation-induced bowel toxicity, presents current management options and outlines priorities for future research. By adding insight into molecular and cellular mechanisms of related bowel disorders, gastroenterologists can substantially strengthen these efforts.

Preclinical development of a bridging therapy for radiation casualties: appropriate for high risk personnel

The authors demonstrate the efficacy of a bridging therapy in a preclinical animal model that allows the lymphohematopoietic system of severely immunocompromised individuals exposed to acute, high-dose ionizing irradiation to recover and to survive. CD2F1 mice were irradiated acutely with high doses causing severe, potentially fatal hematopoietic or gastrointestinal injuries and then transfused intravenously with progenitor-enriched, whole blood, or peripheral blood mononuclear cells from mice injected with tocopherol succinate- and AMD3100- (a chemokine receptor anatogonist used to improve the yield of mobilized progenitors). Survival of these mice over a 30-d period was used as the primary measured endpoint of therapeutic effectiveness. The authors demonstrate that tocopherol succinate and AMD3100 mobilize progenitors into peripheral circulation and that the infusion of mobilized progenitor enriched blood or mononuclear cells acts as a bridging therapy for lymphohematopoietic system recovery in mice exposed to whole-body ionizing irradiation. The results demonstrate that infusion of whole blood or blood mononuclear cells from tocopherol succinate (TS)- and AMD3100-injected mice improved the survival of mice receiving high radiation doses significantly. The efficacy of TS-injected donor mice blood or mononuclear cells was comparable to that of blood or cells obtained from mice injected with granulocyte colony-stimulating factor. Donor origin-mobilized progenitors were found to localize in various tissues. The authors suggest that tocopherol succinate is an optimal agent for mobilizing progenitors with significant therapeutic potential. The extent of progenitor mobilization that tocopherol succinate elicits in experimental mice is comparable quantitatively to clinically used drugs such as granulocyte-colony stimulating factor and AMD3100. Therefore, it is proposed that tocopherol succinate be considered for further translational development and ultimately for use in humans.