Models for Evaluating Agents Intended for the Prophylaxis, Mitigation and Treatment of Radiation Injuries Report of an NCI Workshop, December 3–4, 2003

IEPA, a novel radiation countermeasure, alleviates acute radiation syndrome in rodents

Repurposing therapeutic agents with existing clinical data is a common strategy for developing radiation countermeasures. IEPA (imidazolyl ethanamide pentandioic acid) is an orally bioavailable small molecule pseudopeptide with myeloprotective properties, a good clinical safety profile, and stable chemical characteristics facilitating stockpiling. Here, we evaluated IEPA's radiomitigative efficacy in the hematopoietic subsyndrome of acute radiation syndrome (H-ARS) using total-body irradiation (TBI) models in C57BL/6J mice and WAG/RijCmcr rats, applying various posology schemes and introducing syringe feeding of the IEPA formulation in the pudding. Additionally, we assessed IEPA in the delayed effects of acute radiation exposure (DEARE) model after partial-body irradiation (PBI) in WAG/RijCmcr rats. Endpoints included survival, body weight, hematology, and pulmonary parameters, depending on the model. Results from mouse and rat TBI models demonstrated survival improvements with repeated IEPA dosing at 10 mg/kg, with the largest benefits observed in the bi-daily (BID) treatment over the 30-day ARS phase in female rats. Survival across PBI-DEARE subsyndromes was comparable between IEPA and vehicle groups, though IEPA improved pulmonary parameters in female rats during the lung-DEARE phase. Sex-related differences in response to irradiation and IEPA were noted, with females showing a survival advantage. IEPA treatment is compatible with Neulasta® (Pegfilgrastim; PEG-G-CSF); adequately powered studies are needed to confirm the trend toward improved survival over standard care alone. IEPA is a promising development candidate as a medical countermeasure against the effects of acute radiation syndrome. Further confirmatory studies in small and large animal models should validate the robustness and translatability of preliminary rodent data on IEPA's radiomitigative efficacy.

The potential longevity-promoting hypoxic-hypercapnic environment as a measure for radioprotection

Many biological mechanisms of aging well converge with radiation's biological effects. We used scientific insights from the field of aging to establish a novel hypoxic-hypercapnic environment (HHE) concept for radioprotection. According to this concept, HHE which possesses an anti-aging and longevity-promoting potential, should also act as a radiomitigator and radioprotector. As such, it might contribute greatly to the safety and wellbeing of individuals exposed to high levels of radiation, whether in planned events (e.g. astronauts) or in unplanned events (e.g. first responders in nuclear accidents).

Regulation of Circulating miR-342-3p Alleviates the Radiation-Induced Immune System Injury

Ionizing radiation in space, radiation devices or nuclear disasters are major threats to human health and public security. Expanding countermeasures for dealing with accidental or occupational radiation exposure is crucial for the protection of radiation injuries. Circulating microRNAs (miRNAs) have emerged as promising radiation biomarkers in recent years. However, the origin, distribution and functions of radiosensitive circulating miRNAs remain unclear, which obstructs their clinical applications in the future. In this study, we found that mmu-miR-342-3p (miR-342) in mouse serum presents a stable and significant decrease after X-ray total-body irradiation (TBI). Focusing on this miRNA, we investigated the influences of circulating miR-342 on the radiation-induced injury. Through tail vein injection of Cy5-labeled synthetic miR-342, we found the exogenous miR-342-Cy5 was mainly enriched in metabolic and immune organs. Besides, the bioinformatic analysis predicted that miR-342 might involve in immune-related processes or pathways. Further, mice were tail vein injected with synthetic miR-342 mimetics (Ago-miR-342) after irradiation to upregulate the level of miR-342 in circulating blood. The results showed that the upregulation of circulating miR-342 alleviated the radiation-induced depletion of CD3+CD4+ T lymphocytes and influenced the levels of IL-2 and IL-6 in irradiated mice. Moreover, the injection of Ago-miR-342 improved the survival rates of mice with acute radiation injury. Our findings demonstrate that upregulation of circulating miR-342 alleviates the radiation-induced immune system injury, which provides us new insights into the functions of circulating miRNAs and the prospect as the targets for mitigation of radiation injuries.

Mitigation of acute radiation syndrome (ARS) with human umbilical cord blood

PURPOSE

The growing concern over potential unintended nuclear accidents or malicious activities involving nuclear/radiological devices cannot be overstated. Exposure to whole-body doses of radiation can result in acute radiation syndrome (ARS), colloquially known as "radiation sickness," which can severely damage various organ systems. Long-term health consequences, such as cancer and cardiovascular disease, can develop many years post-exposure. Identifying effective medical countermeasures and devising a strategic medical plan represents an urgent, unmet need. Various clinical studies have investigated the therapeutic use of umbilical cord blood (UCB) for a range of illnesses, including ARS. The objective of this review is to thoroughly discuss ARS and its sub-syndromes, and to highlight recent findings regarding the use of UCB for radiation injury. UCB, a rich source of stem cells, boasts numerous advantages over other stem cell sources, like bone marrow, owing to its ease of collection and relatively low risk of severe graft-versus-host disease. Preclinical studies suggest that treatment with UCB, and often UCB-derived mesenchymal stromal cells (MSCs), results in improved survival, accelerated hematopoietic recovery, reduced gastrointestinal tract damage, and mitigation of radiation-induced pneumonitis and pulmonary fibrosis. Interestingly, recent evidence suggests that UCB-derived exosomes and their microRNAs (miRNAs) might assist in treating radiation-induced damage, largely by inhibiting fibrotic pathways.

CONCLUSION

UCB holds substantial potential as a radiation countermeasure, and future research should focus on establishing treatment parameters for ARS victims.

PEGylated thrombopoietin mimetic, JNJ‑26366821 a novel prophylactic radiation countermeasure for acute radiation injury

Thrombopoietin (TPO) is the primary regulator of platelet generation and a stimulator of multilineage hematopoietic recovery following exposure to total body irradiation (TBI). JNJ‑26366821, a novel PEGylated TPO mimetic peptide, stimulates platelet production without developing neutralizing antibodies or causing any adverse effects. Administration of a single dose of JNJ‑26366821 demonstrated its efficacy as a prophylactic countermeasure in various mouse strains (males CD2F1, C3H/HeN, and male and female C57BL/6J) exposed to Co-60 gamma TBI. A dose dependent survival efficacy of JNJ‑26366821 (- 24 h) was identified in male CD2F1 mice exposed to a supralethal dose of radiation. A single dose of JNJ‑26366821 administered 24, 12, or 2 h pre-radiation resulted in 100% survival from a lethal dose of TBI with a dose reduction factor of 1.36. There was significantly accelerated recovery from radiation-induced peripheral blood neutropenia and thrombocytopenia in animals pre-treated with JNJ‑26366821. The drug also increased bone marrow cellularity and megakaryocytes, accelerated multi-lineage hematopoietic recovery, and alleviated radiation-induced soluble markers of bone marrow aplasia and endothelial damage. These results indicate that JNJ‑26366821 is a promising prophylactic radiation countermeasure for hematopoietic acute radiation syndrome with a broad window for medical management in a radiological or nuclear event.

Analysis of the urinary metabolic profiles in irradiated rats treated with Activated Protein C (APC), a potential mitigator of radiation toxicity

PURPOSE

The goal of the current study was to identify longitudinal changes in urinary metabolites following IR exposure and to determine potential alleviation of radiation toxicities by administration of recombinant APC formulations.

MATERIALS AND METHODS

Female adult WAG/RijCmcr rats were irradiated with 13.0 Gy leg-out partial body X-rays; longitudinally collected urine samples were subject to LC-MS based metabolomic profiling. Sub-cohorts of rats were treated with three variants of recombinant APC namely, rat wildtype (WT) APC, rat 3K3A mutant form of APC, and human WT APC as two bolus injections at 24 and 48 hours post IR.

RESULTS

Radiation induced robust changes in the urinary profiles leading to oxidative stress, severe dyslipidemia, and altered biosynthesis of PUFAs, glycerophospholipids, sphingolipids, and steroids. Alterations were observed in multiple metabolic pathways related to energy metabolism, nucleotide biosynthesis and metabolism that were indicative of disrupted mitochondrial function and DNA damage. On the other hand, sub-cohorts of rats that were treated with rat wildtype-APC showed alleviation of radiation toxicities, in part, at the 90-day time point, while rat 3K3A-APC showed partial alleviation of radiation induced metabolic alterations 14 days after irradiation.

CONCLUSIONS

Taken together, these results show that augmenting the Protein C pathway and activity via administration of recombinant APC may be an effective approach for mitigation of radiation induced normal tissue toxicity.

Imidazolyl Ethanamide Pentandioic Acid (IEPA) as Potential Radical Scavenger during Tumor Therapy in Human Hematopoietic Stem Cells

Radiochemotherapy-associated leuco- or thrombocytopenia is a common complication, e.g., in head and neck cancer (HNSCC) and glioblastoma (GBM) patients, often compromising treatments and outcomes. Currently, no sufficient prophylaxis for hematological toxicities is available. The antiviral compound imidazolyl ethanamide pentandioic acid (IEPA) has been shown to induce maturation and differentiation of hematopoietic stem and progenitor cells (HSPCs), resulting in reduced chemotherapy-associated cytopenia. In order for it to be a potential prophylaxis for radiochemotherapy-related hematologic toxicity in cancer patients, the tumor-protective effects of IEPA should be precluded. In this study, we investigated the combinatorial effects of IEPA with radio- and/or chemotherapy in human HNSCC and GBM tumor cell lines and HSPCs. Treatment with IEPA was followed by irradiation (IR) or chemotherapy (ChT; cisplatin, CIS; lomustine, CCNU; temozolomide, TMZ). Metabolic activity, apoptosis, proliferation, reactive oxygen species (ROS) induction, long-term survival, differentiation capacity, cytokine release, and DNA double-strand breaks (DSBs) were measured. In tumor cells, IEPA dose-dependently diminished IR-induced ROS induction but did not affect the IR-induced changes in metabolic activity, proliferation, apoptosis, or cytokine release. In addition, IEPA showed no protective effect on the long-term survival of tumor cells after radio- or chemotherapy. In HSPCs, IEPA alone slightly enhanced CFU-GEMM and CFU-GM colony counts (2/2 donors). The IR- or ChT-induced decline of early progenitors could not be reversed by IEPA. Our data indicate that IEPA is a potential candidate for the prevention of hematologic toxicity in cancer treatment without affecting therapeutic benefits.

Looking for the phoenix: the current research on radiation countermeasures

PURPOSE

Ionizing radiation (IR) is widely applied in radiotherapy for the treatment of over 50% of cancer patients. IR is also intensively used in medical diagnostics on a daily basis in imaging. Moreover, recent geopolitical events have re-ignited the real threat of the use of nuclear weapons. Medical radiation countermeasures represent one of the effective protection strategies against the effects of IR. The aim of this review was to summarize the most commonly used strategies and procedures in the development of radiation countermeasures and to evaluate the current state of their research, with a focus on those in the clinical trial phase.

METHODS

Clinical trials for this review were selected in accordance with the preferred reporting items for systematic reviews and meta-analyses (PRISMA) statement. The search was performed in the clinicaltrials.gov database as of May 2022.

RESULTS

Our search returned 263 studies, which were screened and of which 25 were included in the review. 10 of these studies had been completed, 3 with promising results: KMRC011 increased G-CSF, IL-6, and neutrophil counts suggesting potential for the treatment of hematopoietic acute radiation syndrome (H-ARS); GC4419 reduced the number of patients with severe oral mucositis and its duration; the combination of enoxaparin, pentoxifylline, and ursodeoxycholic acid reduced the incidence of focal radiation-induced liver injury.

CONCLUSION

The agents discovered so far show significant side effects or low efficacy, and hence most of the tested agents terminate in the early stages of development. In addition, the low profitability of this type of drug demotivates the private sector to invest in such research. To overcome this problem, there is a need to involve more public resources in funding. Among the technological opportunities, a deeper use of in silico approaches seems to be prospective.

Development of gamma-tocotrienol as a radiation medical countermeasure for the acute radiation syndrome: current status and future perspectives

INTRODUCTION

The possibility of exposure to high doses of total- or partial-body ionizing radiation at a high dose rate due to radiological/nuclear accidents or terrorist attacks is increasing. Despite research and development during the last six decades, there is a shortage of nontoxic, safe, and effective radiation medical countermeasures (MCMs) for radiological and nuclear emergencies. To date, the US Food and Drug Administration (US FDA) has approved only four agents for the mitigation of hematopoietic acute radiation syndrome (H-ARS).

AREA COVERED

We present the current status of a promising radiation countermeasure, gamma-tocotrienol (GT3; a component of vitamin E) as a radiation MCM that has been investigated in murine and nonhuman primate models of H-ARS. There is significant work with this agent using various omic platforms during the last few years to identify its efficacy biomarkers.

EXPERT OPINION

GT3 is a newer type of radioprotector having significant injury-countering potential and is currently under advanced development for H-ARS. As a pre-exposure drug, it requires only single doses, lacks significant toxicity, and has minimal, ambient temperature storage requirements; thus, GT3 appears to be an ideal MCM for military and first responders as well as for storage in the Strategic National Stockpile.

Review of compounds that exhibit radioprotective and/or mitigatory effects after application of diagnostic or therapeutic ionizing radiation

PURPOSE

Exposure to ionizing radiation can be accidental or for medical purposes. Analyzes of the frequency of radiation damage in the general population, it has been determined that by far the most common are those that occur as a result of diagnostic or therapeutic procedures. Damage caused by radiation, either accidentally or for therapeutic purposes, can be reduced by the use of radioprotectors, mitigators or other therapeutic agents. A detailed research of the available literature shows that there is little systematized data of potentially radioprotective and/or mitigating effects of drugs from the personal therapy of patients during the application of therapeutic ionizing radiation. The aim of this paper is to present review of compounds, especially personal therapy drugs, that exhibit radioprotective and/or mitigating effects after the application of diagnostic or therapeutic ionizing radiation.

CONCLUSIONS

Given the widespread use of ionizing radiation for diagnostic and therapeutic purposes, there is a clear need to create a strategy and recommendations of relevant institutions for the use of radioprotectors and mitigators in everyday clinical practice, with individual evaluation of the patient's condition and selection of the compounds that will show the greatest benefit in terms of radioprotection.

Angiotensin converting enzyme (ACE) inhibitors as radiation countermeasures for long-duration space flights

Angiotensin converting enzyme (ACE) inhibitors are effective countermeasures to chronic radiation injuries in rodent models, and there is evidence for similar effects in humans. In rodent models ACE inhibitors are effective mitigators of radiation injury to kidney, lung, central nervous system (CNS) and skin, even when started weeks after irradiation. In humans, the best data for their efficacy as radiation countermeasures comes from retrospective studies of injuries in radiotherapy patients. We propose that ACE inhibitors, at doses approved for human use for other indications, could be used to reduce the risk of chronic radiation injuries from deep-space exploration. Because of the potential interaction of ACE inhibitors and microgravity (due to effects of ACE inhibitors on fluid balance) use might be restricted to post-exposure when/if radiation exposures reached a danger level. A major unresolved issue for this approach is the sparse evidence for the efficacy of ACE inhibitors after low-dose-rate exposure and/or for high-LET radiations (as would occur on long-duration space flights). A second issue is that the lack of a clear mechanism of action of the ACE inhibitors as mitigators makes obtaining an appropriate label under the Food and Drug Administration Animal Rule difficult.

The emerging role of exosomes in radiotherapy

Presently, more than half of cancer patients receive radiotherapy to cure localized cancer, palliate symptoms, or control the progression of cancer. However, radioresistance and radiation-induced bystander effects (RIBEs) are still challenging problems in cancer treatment. Exosomes, as a kind of extracellular vesicle, have a significant function in mediating and regulating intercellular signaling pathways. An increasing number of studies have shown that radiotherapy can increase exosome secretion and alter exosome cargo. Furthermore, radiation-induced exosomes are involved in the mechanism of radioresistance and RIBEs. Therefore, exosomes hold great promise for clinical application in radiotherapy. In this review, we not only focus on the influence of radiation on exosome biogenesis, secretion and cargoes but also on the mechanism of radiation-induced exosomes in radioresistance and RIBEs, which may expand our insight into the cooperative function of exosomes in radiotherapy.

Investigating the attenuating effect of telmisartan against radiation-induced intestinal injury using 18F-FDG micro-PET imaging

BACKGROUND AND OBJECTIVE

This study was aimed to investigate the ability of ¹⁸F-Fluro-deoxy-glucose (¹⁸F-FDG)-based micro-positron emission tomography (microPET) imaging to evaluate the efficacy of telmisartan, a highly selective angiotensin II receptor antagonist (ARA), in intestinal tissue recovery process after in vivo irradiation.

METHODS

Male Balb/c mice were randomly divided into four groups of control, telmisartan, irradiation, and telmisartan + irradiation. A solution of telmisartan in phosphate-buffered saline (PBS) was administered orally at 12 mg/kg body weight for seven consecutive days prior to whole body exposing to a single sub-lethal dose of 5 Gy X-rays. The mice were imaged using ¹⁸F-FDG microPET at 9 and 30 days post-irradiation. The ¹⁸F-FDG uptake in jejunum was determined according to the mean standardized uptake value (SUVmean) index. Tissues were also processed in similar time points for histological analysis.

RESULTS

The ¹⁸F-FDG microPET imaging confirmed the efficacy of telmisartan as a potent attenuating agent for ionizing radiation-induced injury of intestine in mice model. The results were also in line with the histological analysis indicating that pretreatment with telmisartan reduced damage to the villi, crypts, and intestinal mucosa compared with irradiated and non-treated group from day 9 to 30 after irradiation.

CONCLUSION

The results revealed that ¹⁸F-FDG microPET imaging could be a good candidate to replace time-consuming and invasive biological techniques for screening of radioprotective agents. These findings were also confirmed by histological examinations which indicated that telmisartan can effectively attenuates radiation injury caused by ionizing-irradiation.

Radiomitigation by Melatonin in C57BL/6 Mice: Possible Implications as Adjuvant in Radiotherapy and Chemotherapy

BACKGROUND/AIM

Melatonin (N-acetyl-5-methoxytryptamine), a chief secretory molecule of the pineal gland, has multiple properties, and numerous clinical investigations regarding its actions are in progress. This study investigated the radiomitigative role of melatonin in C57BL/6 mice.

MATERIALS AND METHODS

Melatonin (100 mg/kg) was orally administered once daily starting at 1 h on day 1 and subsequently every 24 h until day 7 after whole-body irradiation (WBI) and survival was monitored for 30 days. The bone marrow, spleen, and intestine were studied to evaluate the mitigative potential of melatonin after radiation-induced damage.

RESULTS

Melatonin significantly improved the survival upto 60% and 90% after 9 Gy (lethal) and 7.5 Gy (sub-lethal) WBI, respectively. Melatonin alleviated WBI-induced myelosuppression and pancytopenia, and increased white blood cell, red blood cell, platelet, and lymphocyte (CD4⁺ and CD8⁺) counts in peripheral blood. Bone marrow and spleen cellularity were restored through enhanced haematopoiesis. Melatonin ameliorated the damage in the small intestine, and promoted recovery of villi length, crypts number, and goblet cell count.

CONCLUSION

Melatonin mitigates the radiation-induced injury in the gastrointestinal and haematopoietic systems. The observed radiomitigative properties of melatonin can also be useful in the context of adjuvant therapy for cancer and radiotherapy.

Effects of Concurrent Exposure to Chronic Restraint-Induced Stress and Total-Body Iron Ion Radiation on Induction of Kidney Injury in Mice

Concurrent exposure to ionizing radiation (IR) and psychological stress (PS) may affect the development of adverse health consequences in scenarios such as space missions, radiotherapy and nuclear accidents. IR can induce DNA damage and cell apoptosis in the kidneys, thus potentially leading to renal fibrosis, which is the ultimate outcome of various chronic progressive nephropathies and the morphological manifestation of a continuous coordinated response after renal injury. However, little is known regarding the effects of concurrent IR exposure and PS on renal damage, particularly renal fibrosis. In this study, using a chronic restraint-induced PS (CRIPS) model, we exposed Trp53-heterozygous mice to total body irradiation with 0.1 or 2 Gy ⁵⁶Fe ions on the eighth day of 28 consecutive days of a restraint regimen. At the end of the restraint period, the kidneys were collected. The histopathological changes and the degree of kidney fibrosis were assessed with H&E and Masson staining, respectively. Fibronectin (FN) and alpha smooth muscle actin (α-SMA), biomarkers of fibrosis, were detected by immunohistochemistry. Analysis of 8-hydroxy-2 deoxyguanosine (8-OHdG), a biomarker of oxidative DNA damage, was performed with immunofluorescence, and terminal deoxynucleotidyl transferase-mediated nick end labeling assays were used to detect apoptotic cells. Histopathological observations did not indicate significant structural damage induced by IR or CRIPS + IR. Western blotting revealed that the expression of α-SMA was much higher in the CRIPS + IR groups than the CRIPS groups. However, no differences in the average optical density per area were observed for FN, α-SMA and 8-OHdG between the IR and CRIPS + IR groups. No difference in the induction of apoptosis was observed between the IR and CRIPS + IR groups. These results suggested that exposure to IR (0.1 and 2 Gy ⁵⁶Fe ions), 28 consecutive days of CRIPS or both did not cause renal fibrosis. Thus, CRIPS did not alter the IR-induced effects on renal damage in Trp53-heterozygous mice in our experimental setup.

Therapeutic implications of exosomes in the treatment of radiation injury

Radiotherapy is one of the main cancer treatments, but it may damage normal tissue and cause various side effects. At present, radioprotective agents used in clinics have side effects such as nausea, vomiting, diarrhea and hypotension, which limit their clinical application. It has been found that exosomes play an indispensable role in radiation injury. Exosomes are lipid bilayer vesicles that carry various bioactive substances, such as proteins, lipids and microRNA (miRNA), that play a key role in cell-to-cell communication and affect tissue injury and repair. In addition, studies have shown that radiation can increase the uptake of exosomes in cells and affect the composition and secretion of exosomes. Here, we review the existing studies and discuss the effects of radiation on exosomes and the role of exosomes in radiation injury, aiming to provide new insights for the treatment of radiation injury.

A novel oral formulation of BIO 300 confers prophylactic radioprotection from acute radiation syndrome in mice

PURPOSE

Exposure to high doses of ionizing radiation can result in hematopoietic acute radiation syndrome (H-ARS) and delayed effects of acute radiation exposure (DEARE). There is no radiation medical countermeasure (MCM) approved by the U.S. Food and Drug Administration which can be used prior to radiation exposure to protect exposed individuals. Different formulations containing synthetic genistein (BIO 300) are being developed to counter the harmful effects of radiation exposure.

MATERIALS AND METHODS

We investigated the efficacy of a BIO 300 oral powder (OP) formulation as a prophylactic radiation MCM against a lethal dose of cobalt-60 gamma-radiation in CD2F1 male mice while comparing to other formulations of BIO 300 and Neulasta (PEGylated filgrastim), a standard of care drug for H-ARS.

RESULTS

BIO 300 OP provided significant radioprotection against ionizing radiation in mice when administered twice per day for six days prior to total-body radiation exposure. Its radioprotective efficacy in the murine model was comparable to the efficacy of a single subcutaneous (sc) injection of Neulasta administered after total-body radiation exposure.

CONCLUSIONS

Our results demonstrate that BIO 300 OP, which can be administered orally, is a promising prophylactic radiation countermeasure for H-ARS.

Gene Therapy for Systemic or Organ Specific Delivery of Manganese Superoxide Dismutase

Manganese superoxide dismutase (MnSOD) is a dominant component of the antioxidant defense system in mammalian cells. Since ionizing irradiation induces profound oxidative stress, it was logical to test the effect of overexpression of MnSOD on radioresistance. This task was accomplished by introduction of a transgene for MnSOD into cells in vitro and into organs in vivo, and both paradigms showed clear radioresistance following overexpression. During the course of development and clinical application of using MnSOD as a radioprotector, several prominent observations were made by Larry Oberley, Joel Greenberger, and Michael Epperly which include (1) mitochondrial localization of either manganese superoxide dismutase or copper/zinc SOD was required to provide optimal radiation protection; (2) the time required for optimal expression was 12-18 h, and while acceptable for radiation protection, the time delay was impractical for radiation mitigation; (3) significant increases in intracellular elevation of MnSOD activity were required for effective radioprotection. Lessons learned during the development of MnSOD gene therapy have provided a strategy for delivery of small molecule SOD mimics, which are faster acting and have shown the potential for both radiation protection and mitigation. The purpose of this review is to summarize the current status of using MnSOD-PL and SOD mimetics as radioprotectors and radiomitigators.

Metabolomics-based predictive biomarkers of radiation injury and countermeasure efficacy: current status and future perspectives

INTRODUCTION

There is an urgent need for specific and sensitive bioassays to augment biodosimetric assessments of unwanted and excessive radiation exposures that originate from unexpected nuclear/radiological events, including nuclear accidents, acts of terrorism, or the use of a radiological dispersal device. If sufficiently intense, such ionizing radiation exposures are likely to impact normal metabolic processes within the cells and organs of the body, thus inducing multifaceted biological responses.

AREAS COVERED

This review covers the application of metabolomics, an emerging and promising technology based on quantitative and qualitative determinations of small molecules in biological samples for the rapid assessment of an individual's exposure to ionizing radiation. Recent advancements in the analytics of high-resolution chromatography, mass spectrometry, and bioinformatics have led to untargeted (global) and targeted (quantitative phase) approaches to identify biomarkers of radiation injury and countermeasure efficacy. Biomarkers are deemed essential for both assessing the radiation exposure levels and for extrapolative processes involved in determining scaling factors of a given radiation countering medicinal between experimental animals and humans.

EXPERT OPINION

The discipline of metabolomics appears to be highly informative in assessing radiation exposure levels and for identifying biomarkers of radiation injury and countermeasure efficacy.

Radioprotective Role of Natural Polyphenols: From Sources to Mechanisms

The identification and development of radioprotective agents has emerged as a subject matter of research during recent years due to the growing usage of ionizing radiation in different areas of human life. Previous work on synthetic radioprotectors has achieved limited progress because of the numerous issues associated with toxicity. Compounds extracted from plants have potential to serve as lead candidates for developing ideal radioprotectors due to their low cost, safety and selectivity. Polyphenols are the most abundant and commonly dispersed group of biologically active molecules possessing broad range of pharmacological activities. Polyphenols have displayed efficacy for radioprotection during various investigations and can be administered at high doses with lesser toxicity. Detoxification of free radicals, modulating inflammatory responses, DNA repair, stimulation of hematopoietic recovery, and immune functions are the main mechanisms for radiation protection with polyphenols. Epicatechin, epigallocatechin-3-gallate, apigenin, caffeic acid phenylethylester, and silibinin provide cytoprotection together with the suppression of many pro-inflammatory cytokines owing to their free radical scavenging, anti-oxidant, and anti-inflammatory properties. Curcumin, resveratrol, quercetin, gallic acid, and rutin's radioprotective properties are regulated primarily by direct or indirect decline in cellular stress. Thus, polyphenols may serve as potential candidates for radioprotection in the near future, however, extensive investigations are still required to better understand their protection mechanisms.

Preclinical Evaluation of Safety, Pharmacokinetics, Efficacy, and Mechanism of Radioprotective Agent HL-003

Amifostine is a radioprotector with high efficacy but poor safety, short half-life, no oral formulation, and poor compliance, which limits its application. With the increasing risk of exposure to radiation, the development of new radioprotective agents is critical. We previously synthesized a new amifostine derivative, the small molecule compound HL-003. In this study, we focused on evaluating the radioprotective properties of HL-003. Using the in vitro 2,2-diphenyl-1-picrylhydrazyl assay, we initially confirmed HL-003 as a strong antioxidant and demonstrated that its free radical scavenging activity was stronger than that of amifostine. Then, we performed an acute toxicity test, a 28-day toxicity test, a 30-day survival rate test, and a pharmacokinetic study, all of which provided aggregate evidence that HL-003 functioned as a small molecule radioprotector with high efficacy, a favorable safety profile, a long half-life, and oral administration. The intestinal radioprotective mechanism of HL-003 was explored in male C57 mice after abdominal irradiation by analyzing intestinal tissue samples with hematoxylin-eosin staining, immunohistochemistry, TUNEL staining, and immunofluorescence detection. The results showed that HL-003 protected intestinal DNA from radiation damage and suppressed the expression of phosphorylated histone H2AX, phosphorylated p53, and the apoptosis-related proteins caspase-8 and caspase-9, which contributed to maintaining the normal morphology of the small intestine and provided insights into the mechanism of radioprotection. Thus, HL-003 is a small molecule radioprotector with a potential application in radiation medicine.

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.

BIO 300: a promising radiation countermeasure under advanced development for acute radiation syndrome and the delayed effects of acute radiation exposure

INTRODUCTION

There are no radioprotectors currently approved by the United States Food and Drug Administration (US FDA) for either the hematopoietic acute radiation syndrome (H-ARS) or for the acute radiation gastrointestinal syndrome (GI-ARS). There are currently, however, three US FDA-approved medicinals that serve to mitigate acute irradiation-associated hematopoietic injury.

AREA COVERED

We present the current status of a promising radiation countermeasure, BIO 300 (a genistein-based agent), that has been extensively investigated in murine models of H-ARS and models of the delayed effects of acute radiation exposure (DEARE) and is currently being evaluated in large animal models. It is also being developed for the prevention of radiation-induced toxicities associated with solid tumor radiotherapy and is the subject of two active Investigational New Drug (IND) applications. We have included a listing and brief review of significant investigations of this promising medical countermeasure.

EXPERT OPINION

BIO 300 is a leading radioprotector under advanced development for H-ARS and DEARE, as well as for select oncologic indication(s). Efficacy following oral administration (po), lack of clinical side effects, storage at ambient temperature, and intended dual use makes BIO 300 an ideal candidate for military and civilian use as well as for storage in the Strategic National Stockpile.

Pre-clinical Research on Bladder Toxicity After Radiotherapy for Pelvic Cancers: State-of-the Art and Challenges

Despite the dramatic advancements in pelvic radiotherapy, urinary toxicity remains a significant side-effect. The assessment of clinico-dosimetric predictors of radiation cystitis (RC) based on clinical data has improved substantially over the last decade; however, a thorough understanding of the physiopathogenetic mechanisms underlying the onset of RC, with its variegated acute and late urinary symptoms, is still largely lacking, and data from pre-clinical research is still limited. The aim of this review is to provide an overview of the main open issues and, ideally, to help investigators in orienting future research. First, anatomy and physiology of bladder, as well as the current knowledge of dose and dose-volume effects in humans, are briefly summarized. Subsequently, pre-clinical radiobiology aspects of RC are discussed. The findings suggest that pre-clinical research on RC in animal models is a lively field of research with growing interest in the development of new radioprotective agents. The availability of new high precision micro-irradiators and the rapid advances in small animal imaging might lead to big improvement into this field. In particular, studies focusing on the definition of dose and fractionation are warranted, especially considering the growing interest in hypo-fractionation and ablative therapies for prostate cancer treatment. Moreover, improvement in radiotherapy plans optimization by selectively reducing radiation dose to more radiosensitive substructures close to the bladder would be of paramount importance. Finally, thanks to new pre-clinical imaging platforms, reliable and reproducible methods to assess the severity of RC in animal models are expected to be developed.

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.

Second-generation Probiotics Producing IL-22 Increase Survival of Mice After Total Body Irradiation

BACKGROUND/AIM

Intestinal damage induced by total body irradiation (TBI) reduces leucine-rich repeat-containing G-protein-coupled receptor 5 (Lgr5)-expressing stem cells, goblet, and Paneth cells, breaching the epithelial lining, and facilitating bacterial translocation, sepsis, and death.

MATERIALS AND METHODS

Survival was measured after TBI in animals that received wild-type or recombinant bacteria producing interleukin-22 (IL-22). Changes in survival due to microbially delivered IL-22 were measured. Lactobacillus reuteri producing IL-22, or Escherichia coli-IL-22 were compared to determine which delivery system is better.

RESULTS

C57BL/6 mice receiving IL-22 probiotics at 24 h after 9.25 Gy TBI, demonstrated green fluorescent protein-positive bacteria in the intestine, doubled the number of Lgr5+ intestinal stem cells, and increased 30-day survival. Bacteria were localized to the jejunum, ileum, and colon.

CONCLUSION

Second-generation probiotics appear to be valuable for mitigation of TBI, and radiation protection during therapeutic total abdominal irradiation.

Radiomodifying action, Pharmacokinetic and Biodistribution of Ethyl 3, 4, 5-trihydroxybenzoate-Implication in development of radiomitigator

Ethyl 3, 4, 5-trihydroxybenzoate (GAE) is a major bioactive constituent of Hippophae Rhamnoides L. leaves and extract prepared from H. rhamnoides leaves exhibited radioprotective and pharmacological activity. Radiomodifying properties of polyphenol compounds through free radical neutralizing have been reported earlier. However, to date pharmacokinetic (PK) and biodistribution of polyphenol compounds post 60Co-γ-irradiation (5 Gy) exposure have not been studied yet. The study aims to investigate the radio modifying and inflammatory action, PK and biodistribution of GAE at a radioprotective dose and changes, if any, induced after irradiation. Male C 57 BL/6 mice (28-30 g) were administered GAE (200 mg/kg b.wt) orally 15 minutes post to irradiation. Mice were sacrificed at 15, 30 min, 1,2,4,8 and 24 h. PK and biodistribution of GAE in plasma and tissues were studied. The radiomodifying potential was assessed in terms of mitigating NF-kB activity and SGOT, SGPT, urea and creatinine levels in liver and kidney post irradiation. Our study suggested the potential use of GAE as radiomodifying agent inhibits NF-kB expression and maintains the SGOT 24.10 ± 2.4, SGPT 36.01 ± 6.1 U/l, urea18.16 ± 0.003, and creatinine 1.05 ± 0.04 mg/dL upto 8 h in comparison to irradiated mice. Moreover, in biodistribution studies, showed that GAE crosses the blood-brain barrier and is found in brain tissue. Plasma level of GAE peaked at about 15 min, with Cmax 4390.85 ± 285.20 in GAE and in 3391.78 ± 78.13 ng/mL in radiation + GAE-treated animals, Biodistribution resulted in the highest concentration to be found in liver and kidney. These radiomodifying and pharmacokinetic result may be useful for study of the bioactive mechanism associated with radiation injury and to develop a potent formulation of GAE for clinical application.

The efficacy and safety of amifostine for the acute radiation syndrome

Introduction: A radiation countermeasure that can be used prior to radiation exposure to protect the population from the harmful effects of radiation exposure remains a major unmet medical need and is recognized as an important area for research. Despite substantial advances in the research and development for finding nontoxic, safe, and effective prophylactic countermeasures for the acute radiation syndrome (ARS), no such agent has been approved by the United States Food and Drug Administration (FDA). Area covered: Despite the progress made to improve the effectiveness of amifostine as a radioprotector for ARS, none of the strategies have resolved the issue of its toxicity/side effects. Thus, the FDA has approved amifostine for limited clinical indications, but not for non-clinical uses. This article reviews recent strategies and progress that have been made to move forward this potentially useful countermeasure for ARS. Expert opinion: Although the recent investigations have been promising for fielding safe and effective radiation countermeasures, additional work is needed to improve and advance drug design and delivery strategies to get FDA approval for broadened, non-clinical use of amifostine during a radiological/nuclear scenario.

Saving normal tissues - a goal for the ages

Almost since the earliest utilization of ionizing radiation, many within the radiation community have worked toward either preventing (i.e. protecting) normal tissues from unwanted radiation injury or rescuing them from the downstream consequences of exposure. However, despite over a century of such investigations, only incremental gains have been made toward this goal and, with certainty, no outright panacea having been found. In celebration of the 60th anniversary of the International Journal of Radiation Biology and to chronicle the efforts that have been made to date, we undertook a non-rigorous survey of the articles published by normal tissue researchers in this area, using those that have appeared in the aforementioned journal as a road map. Three 'snapshots' of publications on normal tissue countermeasures were taken: the earliest (1959-1963) and most recent (2013-2018) 5-year of issues, as well as a 5-year intermediate span (1987-1991). Limiting the survey solely to articles appearing within International Journal of Radiation Biology likely reduced the number of translational studies interrogated given the basic science tenor of this particular publication. In addition, by taking 'snapshots' rather than considering the entire breadth of the journal's history in this field, important papers that were published during the interim periods were omitted, for which we apologize. Nonetheless, since the journal's inception, we observed that, during the chosen periods, the majority of studies undertaken in the field of normal tissue countermeasures, whether investigating radiation protectants, mitigators or treatments, have focused on agents that interfere with the physical, chemical and/or biological effects known to occur during the acute period following whole body/high single dose exposures. This relatively narrow approach to the reduction of normal tissue effects, especially those that can take months, if not years, to develop, seems to contradict our growing understanding of the progressive complexities of the microenvironmental disruption that follows the initial radiation injury. Given the analytical tools now at our disposal and the enormous benefits that may be reaped in terms of improving patient outcomes, as well as the potential for offering countermeasures to those affected by accidental or mass casualty exposures, it appears time to broaden our approaches to developing normal tissue countermeasures. We have no doubt that the contributors and readership of the International Journal of Radiation Biology will continue to contribute to this effort for the foreseeable future.

Utility of the ACE Inhibitor Captopril in Mitigating Radiation-associated Pulmonary Toxicity in Lung Cancer: Results From NRG Oncology RTOG 0123

OBJECTIVES

The primary objective of NRG Oncology Radiation Therapy Oncology Group 0123 was to test the ability of the angiotensin-converting enzyme inhibitor captopril to alter the incidence of pulmonary damage after radiation therapy for lung cancer; secondary objectives included analyzing pulmonary cytokine expression, quality of life, and the long-term effects of captopril.

MATERIALS AND METHODS

Eligible patients included stage II-IIIB non-small cell lung cancer, stage I central non-small cell lung cancer, or limited-stage small cell. Patients who met eligibility for randomization at the end of radiotherapy received either captopril or standard care for 1 year. The captopril was to be escalated to 50 mg three times a day. Primary endpoint was incidence of grade 2+ radiation-induced pulmonary toxicity in the first year.

RESULTS

Eighty-one patients were accrued between June 2003 and August 2007. Given the low accrual rate, the study was closed early. No significant safety issues were encountered. Eight patients were ineligible for registration or withdrew consent before randomization and 40 patients were not randomized postradiation. Major reasons for nonrandomization included patients' refusal and physician preference. Of the 33 randomized patients, 20 were analyzable (13 observation, 7 captopril). The incidence of grade 2+ pulmonary toxicity attributable to radiation therapy was 23% (3/13) in the observation arm and 14% (1/7) in the captopril arm.

CONCLUSIONS

Despite significant resources and multiple amendments, NRG Oncology Radiation Therapy Oncology Group 0123 was unable to test the hypothesis that captopril mitigates radiation-induced pulmonary toxicity. It did show the safety of such an approach and the use of newer angiotensin-converting enzyme inhibitors started during radiotherapy may solve the accrual problems.

Mechanism and therapeutic window of a genistein nanosuspension to protect against hematopoietic-acute radiation syndrome

There are no FDA-approved drugs that can be administered prior to ionizing radiation exposure to prevent hematopoietic-acute radiation syndrome (H-ARS). A suspension of synthetic genistein nanoparticles was previously shown to be an effective radioprotectant against H-ARS when administered prior to exposure to a lethal dose of total body radiation. Here we aimed to determine the time to protection and the duration of protection when the genistein nanosuspension was administered by intramuscular injection, and we also investigated the drug's mechanism of action. A single intramuscular injection of the genistein nanosuspension was an effective radioprotectant when given prophylactically 48 h to 12 h before irradiation, with maximum effectiveness occurring when administered 24 h before. No survival advantage was observed in animals administered only a single dose of drug after irradiation. The dose reduction factor of the genistein nanosuspension was determined by comparing the survival of treated and untreated animals following different doses of total body irradiation. As genistein is a selective estrogen receptor beta agonist, we also explored whether this was a central component of its radioprotective mechanism of action. Mice that received an intramuscular injection of an estrogen receptor antagonist (ICI 182,780) prior to administration of the genistein nanosuspension had significantly lower survival following total body irradiation compared with animals only receiving the nanosuspension (P < 0.01). These data define the time to and duration of radioprotection following a single intramuscular injection of the genistein nanosuspension and identify its likely mechanism of action.

Protective and adaptogenic role of peroxiredoxin 2 (Prx2) in neutralization of oxidative stress induced by ionizing radiation

A radioprotective effect of exogenous recombinant peroxiredoxin 2 (Prx2) was revealed and characterized using an animal model of whole body X-ray irradiation at sublethal and lethal doses. Prx2 belongs to an evolutionarily ancient family of peroxidases that are involved in enzymatic degradation of a wide variety of organic and inorganic hydroperoxides. Apart from that, the oxidized form of Prx2 also exhibits chaperone activity, thereby preventing protein misfolding and aggregation under oxidative stress. Intravenous administration of Prx2 in animals at a concentration of 20 µg/g 15 min before exposure to ionizing radiation contributes to a significantly higher survival rate, suppresses the development of leucopenia and thrombocytopenia, as well as protects the bone marrow cells from genome DNA damage. Moreover, injection of Prx2 leads to suppression of apoptosis, stimulates cell proliferation and results in a more rapid recovery of the cell redox state. Exogenous Prx2 neutralizes the effect of the priming dose on the second irradiation of the cells. The radioprotective properties of exogenous Prx2 are stipulated by its broad substrate peroxidase activity, chaperone activity in the oxidized state, and are also due to the signal-regulatory function of Prx2 mediated by the regulation of the level of hydroperoxides as well as via interaction with redox-sensitive regulatory proteins.

Radioprotective Role of Peroxiredoxin 6

Peroxiredoxin 6 (Prdx6) is a member of an evolutionary ancient family of peroxidase enzymes with diverse functions in the cell. Prdx6 is an important enzymatic antioxidant. It reduces a wide range of peroxide substrates in the cell, thus playing a leading role in the maintenance of the redox homeostasis in mammalian cells. Beside peroxidase activity, Prdx6 has been shown to possess an activity of phospholipase A2, an enzyme playing an important role in membrane phospholipid metabolism. Moreover, Prdx6 takes part in intercellular and intracellular signal transduction due to its peroxidase and phospholipase activity, thus facilitating the initiation of regenerative processes in the cell, suppression of apoptosis, and activation of cell proliferation. Being an effective and important antioxidant enzyme, Prdx6 plays an essential role in neutralizing oxidative stress caused by various factors, including action of ionizing radiation. Endogenous Prdx6 has been shown to possess a significant radioprotective potential in cellular and animal models. Moreover, intravenous infusion of recombinant Prdx6 to animals before irradiation at lethal or sublethal doses has shown its high radioprotective effect. Exogenous Prdx6 effectively alleviates the severeness of radiation lesions, providing normalization of the functional state of radiosensitive organs and tissues, and leads to a significant elevation of the survival rate of animals. Prdx6 can be considered as a potent and promising radioprotective agent for reducing the pathological effect of ionizing radiation on mammalian organisms. The radioprotective properties and mechanisms of radioprotective action of Prdx6 are discussed in the current review.

Evaluation of Different Formulations and Routes for the Delivery of the Ionizing Radiation Mitigator GS-Nitroxide (JP4-039)

BACKGROUND/AIM

The mitochondrial targeted GS-nitroxide, JP4-039, is an effective total body irradiation (TBI) mitigator when delivered intravenously (IV) up to 72 h after exposure. Effective systemic and localized administration to oral cavity/oropharynx and esophagus has been demonstrated. The objective of the study was to establish alternatives to IV administration suitable for JP4-039 delivery to mass casualties.

MATERIALS AND METHODS

JP4-039 was administered to C57BL/6 mice by topically applied carboxy-methyl-cellulose microneedle arrays (MNAs) or by intramuscular (IM) injection. Three different formulations that have passed Food and Drug Administration review, namely Captisol, 2-hydroxypropyl-β-cyclodextrin (cyclodextrin), and Miglyol-812-N, were used for drug delivery. Intraoral (IO) administration with each formulation was also evaluated.

RESULTS

All tested formulations and MNAs successfully delivered JP4-039. However, IM delivery of the Miglyol-812-N displayed very efficient and highly reproducible radiation mitigation.

CONCLUSION

Effective IM delivery of JP4-039 in animal models after TBI or partial-body irradiation suggested the use of the Miglyol-812-N formulation in both medical indications and radiation countermeasures.

Application of a Novel Murine Ear Vein Model to Evaluate the Effects of a Vascular Radioprotectant on Radiation-Induced Vascular Permeability and Leukocyte Adhesion

Vascular injury after radiation exposure contributes to multiple types of tissue injury through a cascade of events. Some of the earliest consequences of radiation damage include increased vascular permeability and promotion of inflammation, which is partially manifested by increased leukocyte-endothelial (L/E) interactions. We describe herein a novel intravital imaging method to evaluate L/E interactions, as a function of shear stress, and vascular permeability at multiple time points after local irradiation to the ear. This model permitted analysis of quiescent vasculature that was not perturbed by any surgical manipulation prior to imaging. To evaluate the effects of radiation on vascular integrity, fluorescent dextran was injected intravenously and its extravasation in the extravascular space surrounding the ear vasculature was measured at days 3 and 7 after 6 Gy irradiation. The vascular permeability rate increased approximately twofold at both days 3 and 7 postirradiation ( P < 0.05). Leukocyte rolling, which is indicative of L/E interactions, was significantly increased in mice at 24 h postirradiation compared to that of nonirradiated mice. To assess our model, as a means for assessing vascular radioprotectants, we treated additional cohorts of mice with a thrombopoietin mimetic, TPOm (RWJ-800088). In addition to stimulating platelet formation, thrombopoietin can protect vasculature after several forms of injury. Thus, we hypothesized that TPOm would reduce vascular permeability and L/E adhesion after localized irradiation to the ear vasculature of mice. If TPOm reduced these consequences of radiation, it would validate the utility of our intravital imaging method. TPOm reduced radiation-induced vascular leakage to control levels at day 7. Furthermore, L/E cell interactions were also reduced in irradiated mice treated with TPOm, compared with mice receiving irradiation alone, particularly at high shear stress ( P = 0.03, Kruskal-Wallis). We conclude that the ear model is useful for monitoring quiescent normal tissue vascular injury after radiation exposure. Furthermore, the application of TPOm, for preventing early inflammatory response created by damage to vascular endothelium, suggests that this drug may prove useful in reducing toxicities from radiotherapy, which damage microvasculature that critically important to tissue function.

Normal tissue damage: its importance, history and challenges for the future

Sir Oliver Scott, a philanthropist and radiation biologist and, therefore, the epitome of a gentleman and a scholar, was an early Director of the BECC Radiobiology Research Unit at Mount Vernon. His tenure preceded that of Jack Fowler, with both contributing to basic, translational and clinical thought and application in radiation across the globe. With respect to this review, Fowler's name in particular has remained synonymous with the use of models, both animal and mathematical, that assess and quantify the biological mechanisms that underlie radiation-associated normal tissue toxicities. An understanding of these effects is critical to the optimal use of radiation therapy in the clinic; however, the role that basic sciences play in clinical practice has been undergoing considerable change in recent years, particularly in the USA, where there has been a growing emphasis on engineering and imaging to improve radiation delivery, with empirical observations of clinical outcome taking the place of models underpinned by evidence from basic science experiments. In honour of Scott and Fowler's work, we have taken this opportunity to review how our respective fields of radiation biology and radiation physics have intertwined over the years, affecting the clinical use of radiation with respect to normal tissue outcomes. We discuss the past and current achievements, with the hope of encouraging a revived interest in physics and biology as they relate to radiation oncology practice, since, like Scott and Fowler, we share the goal of improving the future outlook for cancer patients.

Efficient protective activity of a planar catechin analogue against radiation-induced apoptosis in rat thymocytes

About two thirds of biological damage due to low linear energy transfer (LET) radiation, such as X-rays and the plateau region of heavy-ion beams, is known to be caused by the hydroxyl radical (˙OH), the most powerful reactive oxygen species (ROS), generated via ionisation and excitation of water molecules. Thus, compounds having an efficient scavenging activity against ROS are expected to exhibit a radioprotective activity. A planar catechin analogue, where an isopropyl fragment was introduced into the catechol ring of (+)-catechin, showed an efficient protective effect against X-ray induced apoptosis in rat thymocytes compared to (+)-catechin. The planar catechin scavenged 2,2-diphenyl-1-picrylhydrazyl radicals (DPPH˙) solubilised in water by β-cyclodextrin about 10-fold faster than (+)-catechin in phosphate buffer (0.1 M, pH 7.4) at 298 K. Furthermore, the experimental log P value of the planar catechin (1.22) is reported to be significantly larger than that of (+)-catechin (0.44). The higher radical-scavenging activity and lipophilicity of the planar catechin than those of (+)-catechin may contribute in part to the higher protective activity against X-ray-induced apoptosis in rat thymocytes.

A planar catechin analogue showed a significant higher protective activity against X-ray induced apoptosis in rat thymocytes than (+)-catechin.

Modifiers of radiation effects in the eye

World events, including the threat of radiological terrorism and the fear of nuclear accidents, have highlighted an urgent need to develop medical countermeasures to prevent or reduce radiation injury. Similarly, plans for manned spaceflight to a near-Earth asteroid or journey to Mars raise serious concerns about long-term effects of space radiation on human health and the availability of suitable therapeutic interventions. At the same time, the need to protect normal tissue from the deleterious effects of radiotherapy has driven considerable research into the design of effective radioprotectors. For more than 70 years, animal models of radiation cataract have been utilized to test the short and long-term efficacy of various radiation countermeasures. While some compounds, most notably the Walter Reed (WR) class of radioprotectors, have reported limited effectiveness when given before exposure to low-LET radiation, the human toxicity of these molecules at effective doses limits their usefulness. Furthermore, while there has been considerable testing of eye responses to X- and gamma irradiation, there is limited information about using such models to limit the injurious effects of heavy ions and neutrons on eye tissue. A new class of radioprotector molecules, including the sulfhydryl compound PrC-210, are reported to be effective at much lower doses and with far less side effects. Their ability to modify ocular radiation damage has not yet been examined. The ability to non-invasively measure sensitive, radiation-induced ocular changes over long periods of time makes eye models an attractive option to test the radioprotective and radiation mitigating abilities of new novel compounds.

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.