Radioprotective effects of ON 01210.Na upon oral administration

Serum microRNA profile of rhesus macaques following ionizing radiation exposure and treatment with a medical countermeasure, Ex-Rad

Exposure to ionizing radiation (IR) presents a formidable clinical challenge. Total-body or significant partial-body exposure at a high dose and dose rate leads to acute radiation syndrome (ARS), the complex pathologic effects that arise following IR exposure over a short period of time. Early and accurate diagnosis of ARS is critical for assessing the exposure dose and determining the proper treatment. Serum microRNAs (miRNAs) may effectively predict the impact of irradiation and assess cell viability/senescence changes and inflammation. We used a nonhuman primate (NHP) model-rhesus macaques (Macaca mulatta)-to identify the serum miRNA landscape 96 h prior to and following 7.2 Gy total-body irradiation (TBI) at four timepoints: 24, 36, 48, and 96 h. To assess whether the miRNA profile reflects the therapeutic effect of a small molecule ON01210, commonly known as Ex-Rad, that has demonstrated radioprotective efficacy in a rodent model, we administered Ex-Rad at two different schedules of NHPs; either 36 and 48 h post-irradiation or 48 and 60 h post-irradiation. Results of this study corroborated our previous findings obtained using a qPCR array for several miRNAs and their modulation in response to irradiation: some miRNAs demonstrated a temporary increased serum concentration within the first 24-36 h (miR-375, miR-185-5p), whereas others displayed either a prolonged decline (miR-423-5p) or a long-term increase (miR-30a-5p, miR-27b-3p). In agreement with these time-dependent changes, hierarchical clustering of differentially expressed miRNAs showed that the profiles of the top six miRNA that most strongly correlated with radiation exposure were inconsistent between the 24 and 96 h timepoints following exposure, suggesting that different biodosimetry miRNA markers might be required depending on the time that has elapsed. Finally, Ex-Rad treatment restored the level of several miRNAs whose expression was significantly changed after radiation exposure, including miR-16-2, an miRNA previously associated with radiation survival. Taken together, our findings support the use of miRNA expression as an indicator of radiation exposure and the use of Ex-Rad as a potential radioprotectant.

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.

Analysis of the Proteomic Profile in Serum of Irradiated Nonhuman Primates Treated with Ex-Rad, a Radiation Medical Countermeasure

There are currently four radiation medical countermeasures that have been approved by the United States Food and Drug Administration to mitigate hematopoietic acute radiation syndrome, all of which are repurposed radiomitigators. The evaluation of additional candidate drugs that may also be helpful for use during a radiological/nuclear emergency is ongoing. A chlorobenzyl sulfone derivative (organosulfur compound) known as Ex-Rad, or ON01210, is one such candidate medical countermeasure, being a novel, small-molecule kinase inhibitor that has demonstrated efficacy in the murine model. In this study, nonhuman primates exposed to ionizing radiation were subsequently administered Ex-Rad as two treatment schedules (Ex-Rad I administered 24 and 36 h post-irradiation, and Ex-Rad II administered 48 and 60 h post-irradiation) and the proteomic profiles of serum using a global molecular profiling approach were assessed. We observed that administration of Ex-Rad post-irradiation is capable of mitigating radiation-induced perturbations in protein abundance, particularly in restoring protein homeostasis, immune response, and mitigating hematopoietic damage, at least in part after acute exposure. Taken together, restoration of functionally significant pathway perturbations may serve to protect damage to vital organs and provide long-term survival benefits to the afflicted population.

The Involvement of Macrophage Colony Stimulating Factor on Protein Hydrolysate Injection Mediated Hematopoietic Function Improvement

Protein hydrolysate injection (PH) is a sterile solution of hydrolyzed protein and sorbitol that contains 17 amino acids and has a molecular mass of 185.0-622.0 g/mol. This study investigated the effect of PH on hematopoietic function in K562 cells and mice with cyclophosphamide (CTX)-induced hematopoietic dysfunction. In these myelosuppressed mice, PH increased the number of hematopoietic cells in the bone marrow (BM) and regulated the concentration of several factors related to hematopoietic function. PH restored peripheral blood cell concentrations and increased the numbers of hematopoietic stem cells and progenitor cells (HSPCs), B lymphocytes, macrophages, and granulocytes in the BM of CTX-treated mice. Moreover, PH regulated the concentrations of macrophage colony stimulating factor (M-CSF), interleukin (IL)-2, and other hematopoiesis-related cytokines in the serum, spleen, femoral condyle, and sternum. In K562 cells, the PH-induced upregulation of hematopoiesis-related proteins was inhibited by transfection with M-CSF siRNA. Therefore, PH might benefit the BM hematopoietic system via the regulation of M-CSF expression, suggesting a potential role for PH in the treatment of hematopoietic dysfunction caused by cancer therapy.

Radiation countermeasures for hematopoietic acute radiation syndrome: growth factors, cytokines and beyond

PURPOSE

The intent of this article is to report the status of some of the pharmaceuticals currently in late stage development for possible use for individuals unwantedly and acutely injured as a result of radiological/nuclear exposures. The two major questions we attempt to address here are: (a) What medicinals are currently deemed by regulatory authorities (US FDA) to be safe and effective and are being stockpiled? (b) What additional agents might be needed to make the federal/state/local medicinal repositories more robust and useful in effectively managing contingencies involving radiation overexposures?

CONCLUSIONS

A limited number (precisely four) of medicinals have been deemed safe and effective, and are approved by the US FDA for the 'hematopoietic acute radiation syndrome (H-ARS).' These agents are largely recombinant growth factors (e.g. rhuG-CSF/filgrastim, rhuGM-CSF/sargramostim) that target and stimulate myeloid progenitors within bone marrow. Romiplostim, a small molecular agonist that enhances platelet production via stimulation of bone marrow megakaryocytes, has been recently approved and indicated for H-ARS. It is critical that additional agents for other major sub-syndromes of ARS (gastrointestinal-ARS) be approved. Future success in developing such medicinals will undoubtedly entail some form of a polypharmaceutical strategy, or perhaps novel, bioengineered chimeric agents with multiple, radioprotective/radiomitigative functionalities.

Analysis of the metabolomic profile in serum of irradiated nonhuman primates treated with Ex-Rad, a radiation countermeasure

To date, the United States Food and Drug Administration (FDA) has approved four drugs to mitigate hematopoietic acute radiation syndrome and all four are repurposed radiomitigators. There are several additional drug candidates currently under evaluation that may also be helpful for use during a widespread emergency. One possible candidate is Ex-Rad, also known as ON01210, a chlorobenzyl sulfone derivative (organosulfur compound), which is a novel, small-molecule kinase inhibitor with demonstrated efficacy in the murine model. In this study, we have evaluated the metabolomic and lipidomic profiles in serum samples of nonhuman primates (NHPs) treated with Ex-Rad after exposure to ionizing radiation. Two different dose administration schedules (Ex-Rad I administered 24 and 36 h post-irradiation, and Ex-Rad II administered 48 and 60 h post-irradiation), were used and evaluated using a global molecular profiling approach. We observed alterations in biochemical pathways relating to inflammation and oxidative stress after radiation exposure that were alleviated in animals that received Ex-Rad I or Ex-Rad II. The results from this study lend credence to the possible radiomitigative effects of this drug possibly via a dampening of metabolism-based tissue injury, thus aiding in recovery of vital, radiation-injured organ systems.

Synthesis and antitumor effects of novel benzyl naphthyl sulfoxide/sulfone derivatives derived from Rigosertib

In this work, a series of novel benzyl naphthyl sulfoxides/sulfones derived from Rigosertib were designed and synthesized as potential antitumor agents. The in vitro cytotoxicity against four human cancer cell lines (HeLa, MCF-7, HepG2 and SCC-15) and two normal human cell lines (HUVEC and 293T) indicated that some of the sulfones and sulfoxides possessed potent antineoplastic activity that reached nanomolar levels and relatively low toxicity to normal cells. Among them, (2-methoxy-5-((naphthalen-2-ylsulfonyl)methyl)phenyl)glycine (15b) was found to be a promising antitumor drug candidate that could significantly inhibit tumor cell migration and induce tumor cell apoptosis via the p53-Bcl-2-Bax signaling pathway at nanomolar concentrations.

In this work, a series of novel benzyl naphthyl sulfoxides/sulfones derived from Rigosertib were designed and synthesized as potential antitumor agents.

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.

Radiation protection by Ex-RAD: a systematic review

Protection of normal tissues against ionizing radiation-induced damages is a critical issue in clinical and environmental radiobiology. One of the ways of accomplishing radiation protection is through the use of radioprotectors. In the search for the most effective radioprotective agent, factors such as toxicity, effect on tumors, number of tissues protected, ease of administration, long-term stability, and compatibility with other drugs need to be assessed. Thus, in the present study, we systematically review existing studies on a chemical radioprotector, Ex-RAD, with the aim of examining its efficacy of radiation protection as well as underlying mechanisms. To this end, a systematic search of the electronic databases including Pubmed, Scopus, Embase, and Google Scholar was conducted to retrieve articles investigating the radioprotective effect of Ex-RAD. From an initial search of 268 articles, and after removal of duplicates as well as applying the predetermined inclusion and exclusion criteria, 10 articles were finally included for this systematic review. Findings from the reviewed studies indicated that Ex-RAD showed potentials for effective radioprotection of the studied organs with no side effect. Furthermore, the inhibition of apoptosis through p53 signaling pathway was the main mechanism of radioprotection by Ex-RAD. However, its radioprotective effect would need to be investigated for more organs in future studies.

Smart Oral Administration of Polydopamine-Coated Nanodrugs for Efficient Attenuation of Radiation-Induced Gastrointestinal Syndrome

High-dose ionizing radiation can lead to death from the unrecoverable damage of the gastrointestinal tract, especially the small intestine. Until now, the lack of predilection for the small intestine and rapid clearance by digestive fluids limit the effects of conventional radioprotective formulations. Herein, an innovative radioprotective strategy is developed for attenuating gastrointestinal syndrome by smart oral administration nanodrugs. The nanodrug is first engineered by encapsulating thalidomide into chitosan-based nanoparticles, and then coated with polydopamine. The behaviors of gastric acid-resistance, and pH-switchable controlled release in the small intestine enhance the oral bioavailability of the pyroptosis inhibitor thalidomide. In a mouse model, nanodrugs demonstrate prolonged small intestinal residence time and accessibility to the crypt region deep in the mucus. Furthermore, the nanodrugs ameliorate survival rates of C57BL/6J mice irradiated by 14 Gy of subtotal body irradiation and also maintain their epithelial integrity. This work may provide a promising new approach for efficiently attenuating lethal radiation-induced gastrointestinal syndrome and add insights into developing nanodrug-based therapies with improved efficacy and minimum side effects.

Dimethyl sulfoxide, a potent oral radioprotective agent, confers radioprotection of hematopoietic stem and progenitor cells independent of apoptosis

In mass casualty events involving radiation exposure, there is a substantial unmet need for identifying and developing an orally bioavailable agent that can be used to protect the hematopoietic stem cell pool and regenerate hematopoiesis after radiation injury. Dimethyl sulfoxide (DMSO), a free-radical scavenger, has shown therapeutic benefits in many preclinical and clinical studies. This study investigates the radioprotective effects of DMSO on oral administration. Single dose of oral DMSO administrated before irradiation conferred 100% survival of C57BL6/J mice receiving otherwise lethal as well as super-lethal radiation dose, with wide radioprotective time frame (from 15min to 4h). Oral DMSO not only protected radiation-induced acute hematopoietic stem and progenitor cell (HSPC) injury, but also ameliorated long-term BM suppression following irradiation in mice. Mechanistically, DMSO directly protected HSPC survival after irradiation in vitro and in vivo, whereas no radioprotective effect was seen in MLL-AF9-induced leukemia cells. Unexpectedly, DMSO treatment did not inhibit radiation-induced HSPC apoptosis, and the HSPC survival from Trp53-and PUMA-deficient mice after irradiation was also protected by DMSO. In conclusion, our findings demonstrate the radioprotective efficacy of oral DMSO. Given its oral efficacy and little toxicity, DMSO is an attractive candidate for human use in a wide variety of settings, including nuclear accidents and medical radiation.

Protective effects of new aryl sulfone derivatives against radiation-induced hematopoietic injury

The hematopoietic system is sensitive to radiation. In this research, new aryl sulfone derivatives (XH-201 and XH-202) containing a nitrogen heterocycle were designed and synthesized and their radio-protective efficacies with regard to the hematopoietic system were evaluated. XH-201 administration significantly increased the survival rate of mice after 8.0 Gy total body irradiation (TBI). The results showed that XH-201 treatment not only increased the white blood cells, platelets counts and the percentage of hematopoietic progenitor cells and hematopoietic stem cells in mice exposed to 4.0 Gy TBI but also decreased DNA damage, as determined by flow cytometric analysis of histone H2AX phosphorylation. In addition, our data demonstrated that XH-201 decreased the mitochondrial reactive oxygen species (ROS) levels in hematopoietic cells. Overall, these data suggest that XH-201 is beneficial for the protection of the hemoatopoietic system against radiation-induced injuries.

17α-Ethinyl-androst-5-ene-3β, 17β-diol, a Novel Potent Oral Radioprotective Agent, Confers Radioprotection of Hematopoietic Stem and Progenitor Cells in a Granulocyte Colony-Stimulating Factor-Independent Manner

PURPOSE

The risk of radiation exposure is considered to have increased in recent years. For convenience and simple administration, development of an effective orally administered radioprotective agent is highly desirable. The steroid 5-androstene-3β, 17β-diol (5-AED) has been evaluated as both a radioprotector and a radiomitigator in mice and nonhuman primates; however, poor oral bioavailability has limited its development. A variant compound-17α-ethinyl-androst-5-ene-3β, 17β-diol (EAD)-exhibits significant oral bioavailability. We investigated the radioprotective effects of EAD via oral administration in mice.

METHODS AND MATERIALS

Survival assays were performed in lethally (9.0-10.0 Gy) irradiated mice. Peripheral blood cell counts were monitored in lethally (9.5 Gy) or sublethally (6.5 Gy) irradiated mice. We performed histologic analysis of bone marrow (BM) and frequency and functional analysis of hematopoietic stem and progenitor cells in mice irradiated with 6.5 Gy. To investigate multilineage engraftment of irradiated hematopoietic stem cells after BM transplantation, competitive repopulation assays were conducted. Plasma granulocyte colony-stimulating factor was measured by enzyme-linked immunosorbent assay.

RESULTS

Oral administration of EAD on 3 consecutive days before irradiation conferred 100% survival in mice, against otherwise 100% death, at a 9.5-Gy lethal dose of total body irradiation. EAD ameliorated radiation-induced pancytopenia at the same dose. EAD augmented BM cellular recovery and colony-forming ability, promoted hematopoietic stem and progenitor cell recovery, and expanded the pool of functionally superior hematopoietic stem cells in the BM of sublethally irradiated mice. Unlike 5-AED, EAD did not increase granulocyte colony-stimulating factor levels in mice and exhibited no therapeutic effects on hematologic recovery after irradiation; nevertheless, its radioprotective efficacy was superior to that of 5-AED.

CONCLUSIONS

Our findings demonstrate the radioprotective efficacy of EAD and reveal that the 17α-ethinyl group is essential for its oral activity. Given its oral efficacy and low toxicity, EAD has potential as an optimal radioprotector for use by first responders, as well as at-risk civilian populations.

Synthesis and radioprotective effects of novel benzyl naphthyl sulfoxide (sulfone) derivatives transformed from Ex-RAD

In this work, a series of novel benzyl naphthyl sulfoxides (sulfones) derived from Ex-RAD were designed and synthesized as potential radioprotective agents. Some of the compounds considerably protected HUVECs against 60Co γ-irradiation, accompanied by the absence of cytotoxicity. Compared to Ex-RAD, compound 8n not only exhibited a significant protective effect on cell survival and radiation-induced DNA damage, but also remarkably enhanced the survival (100%) of mice in 30 days after being exposed to irradiation. The results suggested that some target compounds are valuable for further research as promising radioprotectors.

Salidroside, a scavenger of ROS, enhances the radioprotective effect of Ex-RAD® via a p53-dependent apoptotic pathway

Salidroside (Sal), the predominant component of a Chinese medicinal herb, Rhodiola rosea L., has become an attractive bioagent due to its significant anti-radiation, antioxidant and immune adjustment effects. We explored the radioprotective effect of Sal to ascertain whether it could enhance the anti-radiation effect of ON 01210.Na (Ex-RAD®) in vivo and in vitro, and elucidate its underlying mechanism. Our data demonstrated that Sal inhibited radiation-induced apoptosis, scavenged reactive oxygen species (ROS), and decreased the DNA damage of human umbilical vein endothelial cells (HUVECs). Sal downregulated the expression of Bax and p53 and increased the ratio of Bcl-2/Bax, which indicated that Sal inhibited the radiation-induced apoptosis through p53-dependent pathways. The radioprotection of the Sal pretreatment was also evidenced by an increasing survival rate of the mice, maintaining antioxidant enzyme levels in the liver, and accelerating hematopoietic recovery. The results suggest that Sal exhibits an excellent radioprotective effect with powerful antioxidant activity in vitro and in vivo. Sal enhanced the radioprotective effect of Ex-RAD by improving the antioxidant effect, the scavenging of ROS, by accelerating hematopoietic recovery and DNA repair as well as by regulating apoptotic and repair signaling pathways. Combined modality treatments were more effective than single-agent treatments, demonstrating the value of multiple-agent radioprotectants.

Pharmacological Modulation of Radiation Damage. Does It Exist a Chance for Other Substances than Hematopoietic Growth Factors and Cytokines?

In recent times, cytokines and hematopoietic growth factors have been at the center of attention for many researchers trying to establish pharmacological therapeutic procedures for the treatment of radiation accident victims. Two granulocyte colony-stimulating factor-based radiation countermeasures have been approved for the treatment of the hematopoietic acute radiation syndrome. However, at the same time, many different substances with varying effects have been tested in animal studies as potential radioprotectors and mitigators of radiation damage. A wide spectrum of these substances has been studied, comprising various immunomodulators, prostaglandins, inhibitors of prostaglandin synthesis, agonists of adenosine cell receptors, herbal extracts, flavonoids, vitamins, and others. These agents are often effective, relatively non-toxic, and cheap. This review summarizes the results of animal experiments, which show the potential for some of these untraditional or new radiation countermeasures to become a part of therapeutic procedures applicable in patients with the acute radiation syndrome. The authors consider β-glucan, 5-AED (5-androstenediol), meloxicam, γ-tocotrienol, genistein, IB-MECA (N⁶-(3-iodobezyl)adenosine-5'-N-methyluronamide), Ex-RAD (4-carboxystyryl-4-chlorobenzylsulfone), and entolimod the most promising agents, with regards to their contingent use in clinical practice.

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.

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.

Acute toxicity of subcutaneously administered vitamin E isomers delta- and gamma-tocotrienol in mice

The toxicity of parenterally administered vitamin E isomers, delta-tocotrienol (DT3) and gamma-tocotrienol (GT3), was evaluated in male and female CD2F1 mice. In an acute toxicity study, a single dose of DT3 or GT3 was administered subcutaneously in a dose range of 200 to 800 mg/kg. A mild to moderately severe dermatitis was observed clinically and microscopically in animals at the injection site at doses above 200 mg/kg. The severity of the reaction was reduced when the drug concentration was lowered. Neither drug produced detectable toxic effects in any other tissue at the doses tested. Based on histopathological analysis for both DT3 and GT3, and macroscopic observations of inflammation at the injection site, a dose of 300 mg/kg was selected as the lowest toxic dose in a 30-day toxicity study performed in male mice. At this dose, a mild skin irritation occurred at the injection site that recovered completely by the end of the experimental period. At a dose of 300 mg/kg of DT3 or GT3, no adverse effects were observed in any tissues or organs.

Radiation countermeasure agents: an update (2011-2014)

INTRODUCTION

Despite significant scientific advances over the past 60 years towards the development of a safe, nontoxic and effective radiation countermeasure for the acute radiation syndrome (ARS), no drug has been approved by the US FDA. A radiation countermeasure to protect the population at large from the effects of lethal radiation exposure remains a significant unmet medical need of the US citizenry and, thus, has been recognized as a high priority area by the government.

AREA COVERED

This article reviews relevant publications and patents for recent developments and progress for potential ARS treatments in the area of radiation countermeasures. Emphasis is placed on the advanced development of existing agents since 2011 and new agents identified as radiation countermeasure for ARS during this period.

EXPERT OPINION

A number of promising radiation countermeasures are currently under development, seven of which have received US FDA investigational new drug status for clinical investigation. Four of these agents, CBLB502, Ex-RAD, HemaMax and OrbeShield, are progressing with large animal studies and clinical trials. G-CSF has high potential and well-documented therapeutic effects in countering myelosuppression and may receive full licensing approval by the US FDA in the future.

Gamma tocotrienol, a potent radioprotector, preferentially upregulates expression of anti-apoptotic genes to promote intestinal cell survival

Gamma tocotrienol (GT3) has been reported as a potent ameliorator of radiation-induced gastrointestinal (GI) toxicity when administered prophylactically. This study aimed to evaluate the role of GT3 mediated pro- and anti-apoptotic gene regulation in protecting mice from radiation-induced GI damage. Male 10- to 12-weeks-old CD2F1 mice were administered with a single dose of 200 mg/kg of GT3 or equal volume of vehicle (5% Tween-80) 24 h before exposure to 11 Gy of whole-body γ-radiation. Mouse jejunum was surgically removed 4 and 24h after radiation exposure, and was used for PCR array, histology, immunohistochemistry, and immunoblot analysis. Results were compared among vehicle pre-treated no radiation, vehicle pre-treated irradiated, and GT3 pre-treated irradiated groups. GT3 pretreated irradiated groups, both 4h and 24h after radiation, showed greater upregulation of anti-apoptotic gene expression than vehicle pretreated irradiated groups. TUNEL staining and intestinal crypt analysis showed protection of jejunum after GT3 pre-treatment and immunoblot results were supportive of PCR data. Our study demonstrated that GT3-mediated protection of intestinal cells from a GI-toxic dose of radiation occurred via upregulation of antiapoptotic and downregulation of pro-apoptotic factors, both at the transcript as well as at the protein levels.

ON01210.Na (Ex-RAD®) mitigates radiation damage through activation of the AKT pathway

Development of radio-protective agents that are non-toxic is critical in light of ever increasing threats associated with proliferation of nuclear materials, terrorism and occupational risks associated with medical and space exploration. In this communication, we describe the discovery, characterization and mechanism of action of ON01210.Na, which effectively protects mouse and human bone marrow cells from radiation-induced damage both in vitro and in vivo. Our results show that treatment of normal fibroblasts with ON01210.Na before and after exposure to ionizing radiation provides dose dependent protection against radiation-induced damage. Treatment of mice with ON01210.Na prior to radiation exposure was found to result in a more rapid recovery of their hematopoietic system. The mechanistic studies described here show that ON01210.Na manifests its protective effects through the up-regulation of PI3-Kinase/AKT pathways in cells exposed to radiation. These results suggest that ON 01210.Na is a safe and effective radioprotectant and could be a novel agent for use in radiobiological disasters.