Recent advances in medical countermeasure development against acute radiation exposure based on the US FDA animal rule

Discovery of a novel quinoxaline derivative modulator via a dual P53/TLR2 targeting strategy for the alleviation of radiation damage

With the development of nuclear technology, the risk of people being exposed to nuclear radiation is increasing. So the development of efficient and safe radiation protection agents for nuclear emergencies is urgent. In this study, a series of novel quinoxaline molecules were designed and synthesized with Ex-RAD and TLR2 agonist as the lead, showing anti-radiation effects and compound Z9 was the best one of them. Our work indicated that Z9 emerged as a potent dual modulator targeting both TLR2 and P53 pathway, remarkably preventing the radiation-induced death in mice with the survival rate of 100 %. In the same time, Z9 had significant radioprotection of the haematopoietic system and intestinal villi in mice. In addition, Z9 significantly reduced radiation-induced apoptosis, DNA damage, P53 and Bax expression of AHH-1, while Z9 up-regulated the expressions of TLR2 downstream proteins MyD88 and P65 of HUVECs. Notably, Z9 showed excellent stability and affinity for the TLR2 protein conjugate in molecular docking and molecular dynamics simulations. These findings suggested that Z9 was worth further research being a potential candidate for anti-radiation drugs, as the dual modulator of P53/TLR2.

TRAIL agonists rescue mice from radiation-induced lung, skin, or esophageal injury

Radiotherapy can be limited by pneumonitis, which is impacted by innate immunity, including pathways regulated by TRAIL death receptor DR5. We investigated whether DR5 agonists could rescue mice from toxic effects of radiation and found that 2 different agonists, parenteral PEGylated trimeric TRAIL (TLY012) and oral TRAIL-inducing compound (TIC10/ONC201), could reduce pneumonitis, alveolar wall thickness, and oxygen desaturation. Lung protection extended to late effects of radiation including less fibrosis at 22 weeks in TLY012-rescued survivors versus unrescued surviving irradiated mice. Wild-type orthotopic breast tumor-bearing mice receiving 20 Gy thoracic radiation were protected from pneumonitis with disappearance of tumors. At the molecular level, radioprotection appeared to be due to inhibition of CCL22, a macrophage-derived chemokine previously associated with radiation pneumonitis and pulmonary fibrosis. Treatment with anti-CCL22 reduced lung injury in vivo but less so than TLY012. Pneumonitis severity was worse in female versus male mice, and this was associated with increased expression of X-linked TLR7. Irradiated mice had reduced esophagitis characterized by reduced epithelial disruption and muscularis externa thickness following treatment with the ONC201 analog ONC212. The discovery that short-term treatment with TRAIL pathway agonists effectively rescues animals from pneumonitis, dermatitis, and esophagitis following high doses of thoracic radiation exposure has important translational implications.

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.

Development of a Multi-Organ Radiation Injury Model with Precise Dosimetry with Focus on GI-ARS

The goal of this study was to establish a model of partial-body irradiation (PBI) sparing 2.5% of the bone marrow (BM2.5-PBI) that accurately recapitulates radiological/nuclear exposure scenarios. Here we have reported a model which produces gastrointestinal (GI) damage utilizing a clinical linear accelerator (LINAC) with precise dosimetry, which can be used to develop medical countermeasures (MCM) for GI acute radiation syndrome (ARS) under the FDA animal rule. The PBI model (1 hind leg spared) was developed in male and female C57BL/6 mice that received radiation doses ranging from 12-17 Gy with no supportive care. GI pathophysiology was assessed by crypt cell loss and correlated with peak lethality between days 4 and 10 after PBI. The radiation dose resulting in 50% mortality in 30 days (LD50/30) was determined by probit analysis. Differential blood cell counts in peripheral blood, colony forming units (CFU) in bone marrow, and sternal megakaryocytes were analyzed between days 1-30, to assess the extent of hematopoietic ARS (H-ARS) injury. Radiation-induced GI damage was also assessed by measuring: 1. bacterial load (16S rRNA) by RT-PCR on days 4 and 7 after PBI in liver, spleen and jejunum, 2. liposaccharide binding protein (LBP) levels in liver, and 3. fluorescein isothiocyanate (FITC)-dextran, E-selectin, sP-selectin, VEGF, FGF-2, MMP-9, citrulline, and serum amyloid A (SAA) levels in serum. The LD50/30 of male mice was 14.3 Gy (95% confidence interval 14.1-14.7 Gy) and of female mice was 14.5 Gy (95% confidence interval 14.3-14.7 Gy). Secondary endpoints included loss of viable crypts, higher bacterial loads in spleen and liver, higher LBP in liver, increased FITC-dextran and SAA levels, and decreased levels of citrulline and endothelial biomarkers in serum. The BM2.5-PBI model, developed for the first time with precise dosimetry, showed acute radiation-induced GI damage that is correlated with lethality, as well as a response to various markers of inflammation and vascular damage. Sex-specific differences were observed with respect to radiation dose response. Currently, no MCM is available as a mitigator for GI-ARS. This BM2.5-PBI mouse model can be regarded as the first high-throughput PBI model with precise dosimetry for developing MCMs for GI-ARS under the FDA animal rule.

The delayed effects of acute radiation exposure (DEARE): characteristics, mechanisms, animal models, and promising medical countermeasures

PURPOSE

Terrorist use of nuclear weapons and radiation accidents put the human population at risk for exposure to life-threatening levels of radiation. Victims of lethal radiation exposure face potentially lethal acute injury, while survivors of the acute phase are plagued with chronic debilitating multi-organ injuries for years after exposure. Developing effective medical countermeasures (MCM) for the treatment of radiation exposure is an urgent need that relies heavily on studies conducted in reliable and well-characterized animal models according to the FDA Animal Rule. Although relevant animal models have been developed in several species and four MCM for treatment of the acute radiation syndrome are now FDA-approved, animal models for the delayed effects of acute radiation exposure (DEARE) have only recently been developed, and there are no licensed MCM for DEARE. Herein, we provide a review of the DEARE including key characteristics of the DEARE gleaned from human data as well as animal, mechanisms common to multi-organ DEARE, small and large animal models used to study the DEARE, and promising new or repurposed MCM under development for alleviation of the DEARE.

CONCLUSIONS

Intensification of research efforts and support focused on better understanding of mechanisms and natural history of DEARE are urgently needed. Such knowledge provides the necessary first steps toward the design and development of MCM that effectively alleviate the life-debilitating consequences of the DEARE for the benefit of humankind worldwide.

Where are the medical countermeasures against the ARS and DEARE? A current topic relative to an animal model research platform, radiation exposure context, the acute and delayed effects of acute exposure, and the FDA animal rule

PURPOSE

A question echoed by the National Biodefense Science Board (NBSB) in 2010, remains a reasonable question in 2023; 'Where are the Countermeasures?'. A critical path for development of medical countermeasures (MCM) against acute, radiation-induced organ-specific injury within the acute radiation syndrome (ARS) and the delayed effects of acute radiation exposure (DEARE) requires the recognition of problems and solutions inherent in the path to FDA approval under the Animal Rule. Keep Rule number one in mind, It's not easy.

CONSIDERATIONS

The current topic herein is focused on defining the nonhuman primate model(s) for efficient MCM development relative to consideration of prompt and delayed exposure in the context of the nuclear scenario. The rhesus macaque is a predictive model for human exposure of partial-body irradiation with marginal bone marrow sparing that allows definition of the multiple organ injury in the acute radiation syndrome (ARS) and the delayed effects of acute radiation exposure (DEARE). The continued definition of natural history is required to delineate an associative or causal interaction within the concurrent multi-organ injury characteristic of the ARS and DEARE. A more efficient development of organ specific MCM for both pre-exposure and post-exposure prophylaxis to include acute radiation-induced combined injury requires closing critical gaps in knowledge and urgent support to rectify the national shortage of nonhuman primates. The rhesus macaque is a validated, predictive model of the human response to prompt and delayed radiation exposure, medical management and MCM treatment. A rational approach to further development of the cynomolgus macaque as a comparable model is urgently required for continued development of MCM for FDA approval.

CONCLUSION

It is imperative to examine the key variables relative to animal model development and validation, The pharmacokinetics, pharmacodynamics and exposure profiles, of candidate MCM relative to route, administration schedule and optimal efficacy define the fully effective dose. The conduct of adequate and well-controlled pivotal efficacy studies as well as safety and toxicity studies support approval under the FDA Animal Rule and label definition for human use.

Profiling mRNA, miRNA and lncRNA expression changes in endothelial cells in response to increasing doses of ionizing radiation

Recent and past research have highlighted the importance of the endothelium in the manifestation of radiation injury. Our primary focus is on medical triage and management following whole body or partial-body irradiation. Here we investigated the usability of endothelial cells' radiation response for biodosimetry applications. We profiled the transcriptome in cultured human endothelial cells treated with increasing doses of X-rays. mRNA expression changes were useful 24 h and 72 h post-radiation, microRNA and lncRNA expression changes were useful 72 h after radiation. More mRNA expressions were repressed than induced while more miRNA and lncRNA expressions were induced than repressed. These novel observations imply distinct radiation responsive regulatory mechanisms for coding and non-coding transcripts. It also follows how different RNA species should be explored as biomarkers for different time-points. Radiation-responsive markers which could classify no radiation (i.e., '0 Gy') and dose-differentiating markers were also predicted. IPA analysis showed growth arrest-related processes at 24 h but immune response coordination at the 72 h post-radiation. Collectively, these observations suggest that endothelial cells have a precise dose and time-dependent response to radiation. Further studies in the laboratory are examining if these differences could be captured in the extracellular vesicles released by irradiated endothelial cells.

Responding to radiation accidents: what more do we need to know?

A short review of the various types of radiation incidents and accidents that have occurred is used to provide a context for discussing the findings on medical management of the victims of such incidents and accidents reported in a recent Special Issue of the Journal of Radiological Protection. The review demonstrates that accidents and incidents giving rise to high radiation doses may involve over-exposure of a single individual, a few individuals, or very large numbers. In general, these exposures will be relatively short-term, ranging from a few seconds to a few days, but chronic situations resulting in high exposures can occur. Some of these exposures may be highly localised, whereas others may result in almost uniform whole-body irradiation. This diversity of situations means that it is not feasible to have a single protocol for the diagnosis and treatment of over-exposed individuals. If the over-exposures are limited to one or a few individuals, these can be addressed on a case-by-case basis. However, where large numbers have been exposed or may have been exposed, there is a need to implement a rapid and effective system of triage. Furthermore, this system is likely to have to be implemented by individuals who have little or no direct experience of radiation-induced injuries. For those individuals who may have been significantly exposed, the key consideration is not to determine the radiation dose that they have received, but to establish their present clinical status and how it is likely to develop with time. There is at most a very limited role for bone-marrow transplantation in the treatment of acute radiation syndrome, whereas there are good arguments for administering various treatments to boost bone marrow function together with other supportive interventions, e.g. in control of infections and handling both fluid loss and bleeding. However, there is concern that the focus to date has been only on the licencing of drugs related to the management of haematopoietic effects. Although a great deal is known about the diagnosis and treatment of injuries arising from high dose exposures, this knowledge is biased towards situations in which there is relatively uniform, external whole-body exposure. More attention needs to be given to assessing the implications of various inhomogeneous exposure regimes and to developing medical countermeasures optimised for addressing the complex, multi-organ effects likely to arise from such inhomogeneous exposures.