Drug discovery strategies for acute radiation syndrome

Radioprotective effectiveness of a novel delta-tocotrienol prodrug on mouse hematopoietic system against 60Co gamma-ray irradiation through inducing granulocyte-colony stimulating factor production

Considering the increasing risk of nuclear attacks worldwide, the development of develop potent and safe radioprotective agents for nuclear emergencies is urgently needed. γ-tocotrienol (GT3) and δ-tocotrienol (DT3) have demonstrated a potent radioprotective effect by inducing the production of granulocyte-colony stimulating factor (G-CSF) in vivo. However, their application is limited because of their low bioavailability. The utilization of ester prodrugs can be an effective strategy for modifying the pharmacokinetic properties of drug molecules. In this study, we initially confirmed that DT3 exhibited the most significant potential for inducing G-CSF effects among eight natural vitamin E homologs. Consequently, we designed and synthesized a series of DT3 ester and ether derivatives, leading to improved radioprotective effects. The metabolic study conducted in vitro and in vivo has identified DT3 succinate 5b as a prodrug of DT3 with an approximately seven-fold higher bioavailability compared to DT3 alone. And DT3 ether derivative 8a were relatively stable and approximately 4 times more bioavailable than DT3 prototype. Furthermore, 5b exhibited superior ability to mitigate radiation-induced pancytopenia, enhance the recovery of bone marrow hematopoietic stem and progenitor cells, and promote splenic extramedullary hematopoiesis in sublethal irradiated mice. Similarly, 8a shown potential radiation protection, but its radiation protection is less than DT3. Based on these findings, we identified 5b as a DT3 prodrug, and providing an attractive candidate for further drug development.

DAMPs and radiation injury

The heightened risk of ionizing radiation exposure, stemming from radiation accidents and potential acts of terrorism, has spurred growing interests in devising effective countermeasures against radiation injury. High-dose ionizing radiation exposure triggers acute radiation syndrome (ARS), manifesting as hematopoietic, gastrointestinal, and neurovascular ARS. Hematopoietic ARS typically presents with neutropenia and thrombocytopenia, while gastrointestinal ARS results in intestinal mucosal injury, often culminating in lethal sepsis and gastrointestinal bleeding. This deleterious impact can be attributed to radiation-induced DNA damage and oxidative stress, leading to various forms of cell death, such as apoptosis, necrosis and ferroptosis. Damage-associated molecular patterns (DAMPs) are intrinsic molecules released by cells undergoing injury or in the process of dying, either through passive or active pathways. These molecules then interact with pattern recognition receptors, triggering inflammatory responses. Such a cascade of events ultimately results in further tissue and organ damage, contributing to the elevated mortality rate. Notably, infection and sepsis often develop in ARS cases, further increasing the release of DAMPs. Given that lethal sepsis stands as a major contributor to the mortality in ARS, DAMPs hold the potential to function as mediators, exacerbating radiation-induced organ injury and consequently worsening overall survival. This review describes the intricate mechanisms underlying radiation-induced release of DAMPs. Furthermore, it discusses the detrimental effects of DAMPs on the immune system and explores potential DAMP-targeting therapeutic strategies to alleviate radiation-induced injury.

CXCL10 upregulation in radiation-exposed human peripheral blood mononuclear cells as a candidate biomarker for rapid triage after radiation exposure

PURPOSE

In case of a nuclear accident, individuals with high-dose radiation exposure (>1-2 Gy) should be rapidly identified. While ferredoxin reductase (FDXR) was recently suggested as a radiation-responsive gene, the use of a single gene biomarker limits radiation dose assessment. To overcome this limitation, we sought to identify reliable radiation-responsive gene biomarkers.

MATERIALS AND METHODS

Peripheral blood mononuclear cells (PBMCs) were isolated from mice after total body irradiation, and gene expression was analyzed using a microarray approach to identify radiation-responsive genes.

RESULTS

In light of the essential role of the immune response following radiation exposure, we selected several immune-related candidate genes upregulated by radiation exposure in both mouse and human PBMCs. In particular, the expression of ACOD1 and CXCL10 increased in a radiation dose-dependent manner, while remaining unchanged following lipopolysaccharide (LPS) stimulation in human PBMCs. The expression of both genes was further evaluated in the blood of cancer patients before and after radiotherapy. CXCL10 expression exhibited a distinct increase after radiotherapy and was positively correlated with FDXR expression.

CONCLUSIONS

CXCL10 expression in irradiated PBMCs represents a potential biomarker for radiation exposure.

Temporary Knockdown of p53 During Focal Limb Irradiation Increases the Development of Sarcomas

Approximately half of patients with cancer receive radiotherapy and, as cancer survivorship increases, the low rate of radiation-associated sarcomas is rising. Pharmacologic inhibition of p53 has been proposed as an approach to ameliorate acute injury of normal tissues from genotoxic therapies, but how this might impact the risk of therapy-induced cancer and normal tissue injuries remains unclear. We utilized mice that express a doxycycline (dox)-inducible p53 short hairpin RNA to reduce Trp53 expression temporarily during irradiation. Mice were placed on a dox diet 10 days prior to receiving 30 or 40 Gy hind limb irradiation in a single fraction and then returned to normal chow. Mice were examined weekly for sarcoma development and scored for radiation-induced normal tissue injuries. Radiation-induced sarcomas were subjected to RNA sequencing. Following single high-dose irradiation, 21% of animals with temporary p53 knockdown during irradiation developed a sarcoma in the radiation field compared with 2% of control animals. Following high-dose irradiation, p53 knockdown preserves muscle stem cells, and increases sarcoma development. Mice with severe acute radiation-induced injuries exhibit an increased risk of developing late persistent wounds, which were associated with sarcomagenesis. RNA sequencing revealed radiation-induced sarcomas upregulate genes related to translation, epithelial-mesenchymal transition (EMT), inflammation, and the cell cycle. Comparison of the transcriptomes of human and mouse sarcomas that arose in irradiated tissues revealed regulation of common gene programs, including elevated EMT pathway gene expression. These results suggest that blocking p53 during radiotherapy could minimize acute toxicity while exacerbating late effects including second cancers.

SIGNIFICANCE

Strategies to prevent or mitigate acute radiation toxicities include pharmacologic inhibition of p53 and other cell death pathways. Our data show that temporarily reducing p53 during irradiation increases late effects including sarcomagenesis.

Irradiation-Induced Intestinal Injury is Associated With Disorders of Bile Acids Metabolism

PURPOSE

Intestinal injury commonly occurs in radiation therapy, but its pathogenesis is not well understood. The relationship between irradiation-induced intestinal injury and bile acids (BAs) metabolism remains elusive. This study intends to clarify the role of BAs metabolism in irradiation-induced intestinal injury and the potential for supplementation with BAs to alleviate this injury.

MATERIALS AND METHODS

BAs metabolomic analysis of fecal pellets from normal and 12 Gy γ-ray total abdominal irradiation (TAI) treated mice was performed. The effects of a crude bile extract (BAmix) or lithocholic acid (LCA) on mice exposed to 12 Gy γ-ray TAI were determined by analyzing weight loss, colon length, villus length, crypt number, and the expression of leucine-rich repeat-containing G protein-coupled receptor 5 (Lgr5) and yes-associated protein 1 (YAP1). The effects of BAmix or LCA on intestinal organoids after 4 Gy irradiation were analyzed. ELISA assay was applied to test IL-1β, IL-6 and TNF-α levels in mouse intestine. The expression changes of G protein-coupled receptor 1 (TGR5) and YAP1 in the colonic mucosa of patients with radiation-induced intestinal injury were determined by IHC.

RESULTS

The relative abundance of secondary BAs was decreased while the relative abundance of primary BAs was increased in irradiated mice, and LCA was the most obvious change. BAmix and LCA alleviated irradiation-induced intestinal injury in a mouse model, as reflected by reduced body weight loss, longer colon, higher villus, more crypts, and increased Lgr5 expression. In intestinal organoids, BAmix and LCA enhanced newborn crypts formation after irradiation. LCA treatment improved the expression of TGR5 and YAP1 in mouse intestinal crypts. LCA has potential to reduce the inflammation levels in irradiated mice. Additionally, the expression levels of TGR5 and YAP1 in the colonic mucosa of patients with radiation enteritis were also significantly decreased.

CONCLUSIONS

Radiation-induced intestinal injury is associated with disorders of BAs metabolism, and treatment with LCA had a protective effect against radiation-induced intestinal injury in mice by modulating TGR5 and YAP1.

A wearable gamma radiation-responsive granulocyte colony-stimulating factor microneedle system protecting against ionizing radiation-induced injury

Exposure to a nuclear accident or a radiological attack may cause serious death events due to ionizing radiation-induced injury and acute radiation syndrome (ARS). Recombinant human granulocyte colony-stimulating factor (G-CSF) is now used for the treatment of ARS. However, the current injection formulation might not ensure treatment as early as possible after a nuclear accident, resulting in a decrease in therapeutic efficiency. In the present study, we have developed a G-CSF wearable system (GWS) consisting of a commercial microchip, a temperature sensor, a gamma-ray detection sensor, a flexible heater, and a G-CSF temperature-sensitive microneedle (GTSMN) patch. G-CSF-containing hyaluronic acid solutions were cast into the mold to obtain G-CSF microneedles (GMNs), which were coated with a temperature-sensitive layer of dodecanoic acid-cetylamine salt to obtain GTSMNs. The flexible heater was prepared by jet printing Ag nanoparticle inks. The GWS and its components are explored and optimized in the aspects of electronics, mechanics, heat transfer and drug diffusion. The γ radiation signal is sensitively monitored by the GWS. The wearable G-CSF system immediately releases G-CSF into the body in response to signal feedback and provides maximal protection against ionizing radiation-induced injury. Therefore, the GWS is a promising wearable system against emergent ionizing radiation injury. STATEMENT OF SIGNIFICANCE: Ionizing radiation-induced injury is always the very important public health problem all the global people care. Some medicines have been applied to protect the body from the injury. Unfortunately, sometimes the injuries accidently happen and the medicines cannot be administered in time, leading to serious acute radiation syndrome. Here, we design a wearable system loading G-CSF that has been approved by FDA to protect the body from ionizing radiation-induced injury. This system consists of a commercial microchip, a temperature sensor, a Gamma-ray detection sensor, a flexible heater, and a G-CSF temperature-sensitive microneedle patch. It can monitor γ radiation and immediately release G-CSF into the body to protect the body to the maximal extent. Therefore, the system is a promising wearable medical device against emergent ionizing radiation injury.

JAC4 Protects from X-Ray Radiation-Induced Intestinal Injury by JWA-Mediated Anti-Oxidation/Inflammation Signaling

Radiation-induced intestinal injury is one of the major side effects in patients receiving radiation therapy. There is no specific treatment for radiation-induced enteritis in the clinic. We synthesized a compound, named JAC4, which is an agonist and can increase JWA protein expression. JWA has been shown to reduce oxidative stress, DNA damage, anti-apoptosis, and anti-inflammatory; in addition, the small intestine epithelium showed dysplasia in JWA knockout mice. We hypothesized that JAC4 might exert a protective effect against radiation-induced intestinal damage. Herein, X-ray radiation models were built both in mice and in intestinal crypt epithelial cells (IEC-6). C57BL/6J mice were treated with JAC4 by gavage before abdominal irradiation (ABI); the data showed that JAC4 significantly reduced radiation-induced intestinal mucosal damage and increased the survival rate. In addition, radiation-induced oxidative stress damage and systemic inflammatory response were also mitigated by JAC4 treatment. Moreover, JAC4 treatment alleviated DNA damage, decreased cell apoptosis, and maintained intestinal epithelial cell proliferation in mice. In vitro data showed that JAC4 treatment significantly inhibited ROS formation and cell apoptosis. Importantly, all the above protective effects of JAC4 on X-ray radiation-triggered intestinal injury were no longer determined in the intestinal epithelium of JWA knockout mice. Therefore, our results provide the first evidence that JAC4 protects the intestine from radiation-induced enteritis through JWA-mediated anti-oxidation/inflammation signaling.

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

Recent advances in medical countermeasures (MCMs) has been dependent on the Food and Drug Administration (FDA) animal rule (AR) and the final guidance document provided for industry on product development. The criteria outlined therein establish the path for approval under the AR. The guidance document, along with the funding and requirements from the federal agencies provided the basic considerations for animal model development in assessing radiation effects and efficacy against the potential lethal effects of acute radiation injury and the delayed effects of acute exposure. Animal models, essential for determining MCM efficacy, were developed and validated to assess organ-specific, potentially lethal, radiation effects against the gastrointestinal (GI) and hematopoietic acute radiation syndrome (H-ARS), and radiation-induced delayed effects to lung and associated comorbidities of prolonged immune suppression, GI, kidney and heart injury. Partial-body irradiation models where marginal bone marrow was spared resulted in the ability to evaluate the concomitant evolution of multiple organ injury in the acute and delayed effects in survivors of acute radiation exposure. There are no MCMs for prophylaxis against the major sequelae of the ARS or the delayed effects of acute exposure. Also lacking are MCMs that will mitigate the GI ARS consequent to potentially lethal exposure from a terrorist event or major radiation accident. Additionally, the gap in countermeasures for prophylaxis may extend to mixed neutron/gamma radiation if current modelling predicts prompt exposure from an improvised nuclear device. However, progress in the field of MCM development has been made due to federal and corporate funding, clarification of the critical criteria for efficacy within the FDA AR and the concomitant development and validation of additional animal models. These models provided for a strategic and tactical approach to determine radiation effects and MCM efficacy.

Editing flagellin derivatives for exploration of potent radioprotective agents

Exploration of medical radiation countermeasures (MRCs) has great implications in protection of mammals from radiation damages. While flagellin has been recently reported to show radioprotective effects, the relationships between flagellin structure and radioprotective activity are rarely explored. Herein, we deliberately edited the amino acid sequence of flagellin in its binding domain with toll-like receptor 5 (TLR5) for exploration of potent flagellin derivatives (Fds). An in vitro screening paradigm was developed to examine the radioprotective effects of six engineered Fds. Notably, mutation of 103 threonine on flagellin into asparagine resulted in a potent MRC candidate (Fd-T103N) displaying 1.28-fold increment of interactions with TLR5. Fd-T103N was able to further activate NF-κB pathway, induce immune protective cytokine (e.g. G-CSF) release, and significantly ameliorate γ-irradiation induced cell death. The protection effects of Fd-T103N were further validated in mice exposed to 10 Gy γ-irradiations. Compared to parent flagellin, Fd-T103N treatment showed higher G-CSF release in mouse blood, lower intestine damages, and 13% increments of mouse survival rates. In short, the established predictive paradigm could greatly reduce the labor-, time- and animal-costs in exploration of MRC candidates. Fd-T103N is a promising candidate of investigational new drug for radioprotection.

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.

A first-in-human study of KMRC011, a potential treatment for acute radiation syndrome, to explore tolerability, pharmacokinetics, and pharmacodynamics

KMRC011 is a novel Toll-like receptor 5 agonist under development as a treatment for acute radiation syndrome (ARS). The aim of this first-in-human study was to investigate the tolerability, pharmacokinetics, and pharmacodynamics of a single intramuscular dose of KMRC011 in healthy subjects. A randomized, single-blind, placebo-controlled, single dose-escalation study was conducted with the starting dose of 5 μg. Eight (4 only for 5 μg cohort) subjects per cohort were randomly assigned to KMRC011 or placebo in a 3:1 ratio. Dose-limiting toxicity (DLT) was assessed throughout the study. Serum concentrations of KMRC011, granulocyte colony-stimulating factor (G-CSF), and interleukin-6 (IL-6) were measured up to 48 h postdose. Based on safety review, the dose of KMRC011 escalated up to 20 μg, and consequently, a total of 4 dose levels (5, 10, 15, and 20 μg) were explored. The most common adverse event was injection site reaction, showing no dose-related trend. Three DLTs (2 cases of hepatic enzyme increased and 1 of pyrexia) were observed; 1 in the 15 μg cohort and 2 in the 20 μg cohort. A developed method could not detect any KMRC011 in serum. KMRC011 15 μg and 20 μg showed significant increases of G-CSF, IL-6, and absolute neutrophil counts, compared with the placebo. A single intramuscular administration of KMRC011 ranging from 5 to 15 μg was tolerated in healthy subjects. Doses of KMRC011 equal to or greater than 15 μg exerted TLR5 agonist-like activities by increasing serum G-CSF and IL-6. It suggests that KMRC011 has the potential for a treatment for ARS.

Oral Codelivery of WR-1065 Using Curcumin-Linked ROS-Sensitive Nanoparticles for Synergistic Radioprotection

Protecting the body from radiation damage is a huge medical challenge. Amifostine and curcumin are both effective radioprotectants, but their use has been greatly restricted due to various reasons including low bioavailability. Nanoscale drug delivery systems of poly(ethylene glycol)-poly(ε-caprolactone) copolymers can improve the bioavailability of drugs due to excellent biocompatibility, biodegradability, and long circulation characteristics. In this study, a new reactive oxygen species-sensitive nanocarrier fabricated by linking curcumin and thioketal to poly(ethylene glycol)-poly(ε-caprolactone) polymer was used for delivery of WR-1065 (the active ingredient of amifostine). The content of curcumin in this polymer was about 7.6%, and the drug loading of WR-1065 was 44%. The WR-1065-loaded nanoparticles (NPs) had an average size of 128.6 nm and uniform spherical morphology. These WR-1065-loaded NPs reduced the metabolism of curcumin and WR-1065 in the gastrointestinal tract and could be well absorbed by cells and distributed to multiple organs. Compared with a single drug, oral administration of WR-1065-loaded NPs demonstrated obvious radioprotective effects on the hematopoietic system and prevented intestinal injury. The 30-day survival rate after half-lethal dose (7.2 Gy) of total body irradiation was 100%. In general, WR-1065-loaded NPs improved the oral bioavailability of WR-1065 and curcumin. This multifunctional nanocarrier provides a possibility for combination therapy in treating ionizing radiation damage.

Integrative network analyses of transcriptomics data reveal potential drug targets for acute radiation syndrome

Recent political unrest has highlighted the importance of understanding the short- and long-term effects of gamma-radiation exposure on human health and survivability. In this regard, effective treatment for acute radiation syndrome (ARS) is a necessity in cases of nuclear disasters. Here, we propose 20 therapeutic targets for ARS identified using a systematic approach that integrates gene coexpression networks obtained under radiation treatment in humans and mice, drug databases, disease-gene association, radiation-induced differential gene expression, and literature mining. By selecting gene targets with existing drugs, we identified potential candidates for drug repurposing. Eight of these genes (BRD4, NFKBIA, CDKN1A, TFPI, MMP9, CBR1, ZAP70, IDH3B) were confirmed through literature to have shown radioprotective effect upon perturbation. This study provided a new perspective for the treatment of ARS using systems-level gene associations integrated with multiple biological information. The identified genes might provide high confidence drug target candidates for potential drug repurposing for ARS.

Atorvastatin Inhibits Endothelial PAI-1-Mediated Monocyte Migration and Alleviates Radiation-Induced Enteropathy

Intestinal injury is observed in cancer patients after radiotherapy and in individuals exposed to radiation after a nuclear accident. Radiation disrupts normal vascular homeostasis in the gastrointestinal system by inducing endothelial damage and senescence. Despite advances in medical technology, the toxicity of radiation to healthy tissue remains an issue. To address this issue, we investigated the effect of atorvastatin, a commonly prescribed hydroxy-3-methylglutaryl-coenzyme A reductase inhibitor of cholesterol synthesis, on radiation-induced enteropathy and inflammatory responses. We selected atorvastatin based on its pleiotropic anti-fibrotic and anti-inflammatory effects. We found that atorvastatin mitigated radiation-induced endothelial damage by regulating plasminogen activator inhibitor-1 (PAI-1) using human umbilical vein endothelial cells (HUVECs) and mouse model. PAI-1 secreted by HUVECs contributed to endothelial dysfunction and trans-endothelial monocyte migration after radiation exposure. We observed that PAI-1 production and secretion was inhibited by atorvastatin in irradiated HUVECs and radiation-induced enteropathy mouse model. More specifically, atorvastatin inhibited PAI-1 production following radiation through the JNK/c-Jun signaling pathway. Together, our findings suggest that atorvastatin alleviates radiation-induced enteropathy and supports the investigation of atorvastatin as a radio-mitigator in patients receiving radiotherapy.

Design and evaluation of pH-responsive hydrogel for oral delivery of amifostine and study on its radioprotective effects

The purpose of this study was to develop a novel pH-sensitive hydrogel which was used to regulate the acute radiation syndrome (ARS). The hydrogel was fabricated by grafting polycaprolactone onto methacrylic acid copolymer (MAC-g-PCL). Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (¹H NMR) confirmed the obtaining of MAC-g-PCL hydrogel. The hydrogel was pH-sensitive, at pH 1.2, it was compact hydrogel, but at pH7.4, it was dissolved solution. Its inner 3D morphology was observed by scanning electron microscope (SEM). Cell experiments indicated that the MAC-g-PCL hyrogel was out of cytotoxicity. The release profile of amifostine showed that small amount drug release in simulated gastric fluid (pH 1.2) and burst release in simulated intestinal fluid (pH 7.4). Thus, the pH-sensitive hydrogels could protect amifostine from enzymatic degradation in acidic stomach and deliver effectively in the intestine. The radioprotective efficacy was determined by peripheral complete blood parameters and 30-day survival study in mice acutely exposed to 4 Gy γ-ray total body irradiation. Results suggested that oral administration MAC-g-PCL/Ami before total body irradiation protected the mice from hematopoietic ARS and enhanced their survival. Furthermore, in vivo bio-distribution studies indicated that the drug could be sustained delivered at intestinal tract and entered the bloodstream. These results demonstrated that oral administration of amifostine hydrogel provided effective radioprotection to reduce the ARS injury.

Medical countermeasures for radiation induced health effects: report of an Interagency Panel Session held at the NASA Human Research Program Investigator's Workshop, 26 January 2017

An Interagency Panel Session organized by the NASA Human Research Program (HRP) Space Radiation Program Element (SRPE) was held during the NASA HRP Investigator’s Workshop (IWS) in Galveston, Texas on 26 January 2017 to identify complementary research areas that will advance the testing and development of medical countermeasures (MCMs) in support of radioprotection and radiation mitigation on the ground and in space. There were several areas of common interest identified among the various participating agencies. This report provides a summary of the topics discussed by each agency along with potential areas of intersection for mutual collaboration opportunities. Common goals induded repurposing of pharmaceuticals, nutraceuticals for use as radioprotectors and/or mitigators, low-dose/chronic exposure paradigms, late effects post-radiation exposure, mixed-field exposures of gamma-neutron, performance decrements, and methods to determine individual exposure levels.