Enhanced survival from radiation pneumonitis by combined irradiation to the skin

Cell Therapies for Acute Radiation Syndrome

The risks of severe ionizing radiation exposure are increasing due to the involvement of nuclear powers in combat operations, the increasing use of nuclear power, and the existence of terrorist threats. Exposure to a whole-body radiation dose above about 0.7 Gy results in H-ARS (hematopoietic acute radiation syndrome), which is characterized by damage to the hematopoietic system; higher doses result in further damage to the gastrointestinal and nervous systems. Only a few medical countermeasures for ARS are currently available and approved for use, although others are in development. Cell therapies (cells or products produced by cells) are complex therapeutics that show promise for the treatment of radiation injury and have been shown to reduce mortality and morbidity in animal models. Since clinical trials for ARS cannot be ethically conducted, animal testing is extremely important. Here, we describe cell therapies that have been tested in animal models. Both cells and cell products appear to promote survival and lessen tissue damage after whole-body irradiation, although the mechanisms are not clear. Because radiation exposure often occurs in conjunction with other traumatic injuries, animal models of combined injury involving radiation and future countermeasure testing for these complex medical problems are also discussed.

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.

Polypharmacy to Mitigate Acute and Delayed Radiation Syndromes

There is a need for countermeasures to mitigate lethal acute radiation syndrome (ARS) and delayed effects of acute radiation exposure (DEARE). In WAG/RijCmcr rats, ARS occurs by 30-days following total body irradiation (TBI), and manifests as potentially lethal gastrointestinal (GI) and hematopoietic (H-ARS) toxicities after >12.5 and >7 Gy, respectively. DEARE, which includes potentially lethal lung and kidney injuries, is observed after partial body irradiation >12.5 Gy, with one hind limb shielded (leg-out PBI). The goal of this study is to enhance survival from ARS and DEARE by polypharmacy, since no monotherapy has demonstrated efficacy to mitigate both sets of injuries. For mitigation of ARS following 7.5 Gy TBI, a combination of three hematopoietic growth factors (polyethylene glycol (PEG) human granulocyte colony-stimulating factor (hG-CSF), PEG murine granulocyte-macrophage-CSF (mGM-CSF), and PEG human Interleukin (hIL)-11), which have shown survival efficacy in murine models of H-ARS were tested. This triple combination (TC) enhanced survival by 30-days from ∼25% to >60%. The TC was then combined with proven medical countermeasures for GI-ARS and DEARE, namely enrofloxacin, saline and the angiotensin converting enzyme inhibitor, lisinopril. This combination of ARS and DEARE mitigators improved survival from GI-ARS, H-ARS, and DEARE after 7.5 Gy TBI or 13 Gy PBI. Circulating blood cell recovery as well as lung and kidney function were also improved by TC + lisinopril. Taken together these results demonstrate an efficacious polypharmacy to mitigate radiation-induced ARS and DEARE in rats.

Wound Trauma Exacerbates Acute, but not Delayed, Effects of Radiation in Rats: Mitigation by Lisinopril

The goal of this study is to understand and mitigate the effects of wounds on acute radiation syndrome (ARS) and delayed effects of acute radiation exposure (DEARE), for preparedness against a radiological attack or accident. Combined injuries from concomitant trauma and radiation are likely in these scenarios. Either exacerbation or mitigation of radiation damage by wound trauma has been previously reported in preclinical studies. Female WAG/RijCmcr rats received 13 Gy X-rays, with partial-body shielding of one leg. Within 2 h, irradiated rats and non-irradiated controls were given full-thickness skin wounds with or without lisinopril, started orally 7 days after irradiation. Morbidity, skin wound area, breathing interval and blood urea nitrogen were measured up to 160 days post-irradiation to independently evaluate wound trauma and DEARE. Wounding exacerbated morbidity in irradiated rats between 5 and 14 days post-irradiation (during the ARS phase), and irradiation delayed wound healing. Wounding did not alter delayed morbidities from radiation pneumonitis or nephropathy after 30 days post-irradiation. Lisinopril did not mitigate wound healing, but markedly decreased morbidity during DEARE from 31 through 160 days. The results derived from this unique model of combined injuries suggest different molecular mechanisms of injury and healing of ARS and DEARE after radiation exposure.

WAG/RijCmcr rat models for injuries to multiple organs by single high dose ionizing radiation: similarities to nonhuman primates (NHP)

Purpose: Defined animal models are needed to pursue the FDA Animal Rule for approval of medical countermeasure for radiation injuries. This study compares WAG/RijCmcr rat and nonhuman primate (NHP) models for acute radiation syndrome (ARS) and delayed effects of acute radiation exposure (DEARE).Materials and methods: Irradiation models include total body irradiation, partial body irradiation with bone marrow sparing and whole thorax lung irradiations. Organ-specific sequelae of radiation injuries were compared using dose-response relationships.Results and conclusions: Rats and NHP manifest similar organ dysfunctions after radiation, starting with acute gastrointestinal (GI-ARS) and hematopoietic (H-ARS) syndromes followed by lung, heart and kidney toxicities. Humans also manifest these sequelae. Latencies for injury were earlier in rats than in NHP. After whole thorax lung irradiations (WTLI) up to 13 Gy, there was recovery of lung function from pneumonitis in rats. This has not been evaluated in NHP. The latency, incidence, severity and progression of radiation pneumonitis was not influenced by early multi-organ injury from ARS in rats or NHP. Rats developed more severe radiation nephropathy than NHP, and also progressed more rapidly. Dosimetry, anesthesia, environment, supportive care, euthanasia criteria etc., may account for the alterations in radiation sensitivity observed between species.

Challenges and Benefits of Repurposing Products for Use during a Radiation Public Health Emergency: Lessons Learned from Biological Threats and other Disease Treatments

The risk of a radiological or nuclear public health emergency is a major growing concern of the U.S. government. To address a potential incident and ensure that the government is prepared to respond to any subsequent civilian or military casualties, the U.S. Department of Health and Human Services and the Department of Defense have been charged with the development of medical countermeasures (MCMs) to treat the acute and delayed injuries that can result from radiation exposure. Because of the limited budgets in research and development and the high costs associated with bring promising approaches from the bench through advanced product development activities, and ultimately, to regulatory approval, the U.S. government places a priority on repurposing products for which there already exists relevant safety and other important information concerning their use in humans. Generating human data can be a costly and time-consuming process; therefore, the U.S. government has interest in drugs for which such relevant information has been established (e.g., products for another indication), and in determining if they could be repurposed for use as MCMs to treat radiation injuries as well as chemical and biological insults. To explore these possibilities, the National Institute of Allergy and Infectious Diseases (NIAID) convened a workshop including U.S. government, industry and academic subject matter experts, to discuss the challenges and benefits of repurposing products for a radiation indication. Topics covered included a discussion of U.S. government efforts (e.g. funding, stockpiling and making products available for study), as well unique regulatory and other challenges faced when repurposing patent protected or generic drugs. Other discussions involved lessons learned from industry on repurposing pre-license, pipeline products within drug development portfolios. This report reviews the information presented, as well as an overview of discussions from the meeting.

Changes in miRNA in the lung and whole blood after whole thorax irradiation in rats

We used a rat model of whole thorax x-ray irradiation to profile the microRNA (miRNA) in lung and blood up to 4 weeks after radiation. MiRNA from normal and irradiated Wistar rat lungs and whole blood were analyzed by next-generation sequencing and the changes by radiation were identified by differential deRNA-seq 1, 2, 3 and 4 weeks after irradiation. The average total reads/library was 2,703,137 with a mean of 88% mapping to the rat genome. Detailed profiles of 100 of the most abundant miRNA in rat blood and lung are described. We identified upregulation of 4 miRNA, miR-144-5p, miR-144-3p, miR-142-5p and miR-19a-3p in rat blood 2 weeks after radiation that have not previously been shown to be altered after radiation to the lung. Ingenuity Pathway Analysis identified signaling of inflammatory response pathways. These findings will support development of early detection methods, as well as mechanism(s) of injury and mitigation in patients after radiotherapy or radiological accidents.

Captopril Increases Survival after Whole-Body Ionizing Irradiation but Decreases Survival when Combined with Skin-Burn Trauma in Mice

Past and recent radiation events have involved a high incidence of radiation combined injury where victims often succumb to serious infections as a consequence of bacterial translocation and subsequent sepsis. The risk of infection is exacerbated in radiation combined skin-burn injury (RCI), which increase vulnerability. Furthermore, no suitable countermeasures for radiation combined skin-burn injury have been established. In this study, we evaluated captopril as a potential countermeasure to radiation combined skin-burn injury. Captopril is an FDA-approved angiotensin-converting enzyme inhibitor that was previously reported to stimulate hematopoietic recovery after exposure to ionizing radiation. Female B6D2F1/J mice were whole-body bilateral (60)Co gamma-photon irradiated (dose rate of 0.4 Gy/min) with 9.5 Gy (LD70/30 for RCI), followed by nonlethal dorsal skin-burn injury under anesthesia (approximately 15% total-body surface-area burn). Mice were provided with acidified drinking water with or without dissolved captopril (0.55 g/l) for 30 days immediately after injury and were administered topical gentamicin (0.1% cream; day 1-10) and oral levofloxacin (90-100 mg/kg; day 3-16). Surviving mice were euthanized on day 30 after analyses of water consumption, body weight and survival. Our data demonstrate that, while treatment with captopril did mitigate mortality induced by radiation injury (RI) alone (55% captopril vs. 80% vehicle; n = 20, P < 0.05), it also resulted in decreased survival after radiation combined skin-burn injury (22% captopril vs. 41% vehicle; n = 22, P < 0.05). Moreover, captopril administration via drinking water produced an uneven dosage pattern among the different injury groups ranging from 74 ± 5.4 to 115 ± 2.2 mg/kg/day. Captopril treatment also did not counteract the negative alterations in hematology, splenocytes or bone marrow cellularity after either radiation injury or radiation combined skin-burn injury. These data suggest that captopril may exert its actions differently between the two injury models (RI vs. RCI) and that captopril dosing, when combined with topical and systemic antibiotic treatments, may not be a suitable countermeasure for RCI.