ROS-scavenger and radioprotective efficacy of the new PrC-210 aminothiol

Feasibility of Reducing Animal Numbers in Radiation Countermeasure Experiments from Historic Levels when using Sample Size Calculations

Historically, animal numbers have most often been in the hundreds for experiments designed to estimate the dose reduction factor (DRF) of a radiation countermeasure treatment compared to a control treatment. Before 2010, researchers had to rely on previous experience, both from others and their own, to determine the number of animals needed for a DRF experiment. In 2010, a formal sample size formula was developed by Kodell et al. This theoretical work showed that sample sizes for realistic, yet hypothetical, DRF experiments could be less than a hundred animals and still have sufficient power to detect clinically meaningful DRF values. However, researchers have been slow to use the formula for their DRF experiments, whether from ignorance to its existence or hesitancy to depart from "tried and true" sample sizes. Here, we adapt the sample size formula to better fit usual DRF experiments, and, importantly, we provide real experimental evidence from two independent DRF experiments that sample sizes smaller than what have typically been used can still statistically detect clinically meaningful DRF values. In addition, we update a literature review of DRF experiments which can be used to inform future DRF experiments, provide answers to questions that researchers have asked when considering sample size calculations rather than solely relying on previous experience, whether their own or others', and, in the supplementary material, provide R code implementing the formula, along with several exercises to familiarize the user with the adapted formula.

PrC-210 Protects against Radiation-Induced Hematopoietic and Intestinal Injury in Mice and Reduces Oxidative Stress

The development of safe, orally available, and effective prophylactic countermeasures to protect our warfighters is an unmet need because there is no such FDA-approved countermeasure available for use. Th 1-Propanethiol, 3-(methylamino)-2-((methylamino)methyl) (PrC-210), a synthetic small molecule, is a member of a new family of aminothiols designed to reduce toxicity while scavenging reactive oxygen species (ROS). Our study investigated the protective role of a single oral administration of PrC-210 against radiation-induced hematopoietic and intestinal injury in mice. Pre-treatment with PrC-210 significantly improved the survival of mice exposed to a lethal dose of radiation. Our findings indicated that the radioprotective properties of PrC-210 are achieved by accelerating the recovery of the hematopoietic system, stimulating bone marrow progenitor cells, and ameliorating additional biomarkers of hematopoietic injury. PrC-210 pre-treatment reduced intestinal injury in mice exposed to a lethal dose of radiation by restoring jejunal crypts and villi, reducing translocation of bacteria to the spleen, maintaining citrulline levels, and reducing the sepsis marker serum amyloid A (SAA) in serum. Finally, PrC-210 pre-treatment led to a significant reduction (~10 fold) of Nos2 expression (inducible nitric oxide) in the spleen and decreased oxidative stress by enhancing the antioxidant defense system. These data support the further development of PrC-210 to receive approval from the FDA to protect warfighters and first responders from exposure to the harmful effects of ionizing radiation.

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.

Synthesis and anti-Alzheimer potential of novel α-amino phosphonate derivatives and probing their molecular interaction mechanism with acetylcholinesterase

Pleiotropic interference may be a prerequisite for the efficient limitation of the progression of multi-factorial diseases such as Alzheimer's disease (AD). Concept of designing the single chemical entity acting on two or more targets of interest has potential advantage in AD therapy. In line with this, rational design and synthesis of frame work of hybrids bearing 2,3-disubstituted quinazolinone, vanillin and α-amino phosphonate scaffolds (5a─v) were carried out. A congeneric set of twenty-two synthetic derivatives (5a─v) were evaluated for their cholinesterase inhibitory, antioxidant, DNA nicking, DNA protection, neuroprotective and Aβ aggregation modulatory activities. Amongst tested activities, the most significant and worth mentioning is that the analogues 5m, 5p and 5u were found to be the most potent, selective, and mixed type inhibitors of EeAChE with IC₅₀ values of 0.296 ± 0.030, 0.289 ± 0.027, and 0.306 ± 0.028 μM, respectively. Further, the biophysical approaches indicated that the compounds 5m, 5p, and 5u have a strong binding affinity towards AChE. Kinetic and Molecular docking studies have revealed that the most active congeners were well oriented in the AChE active site by interacting with both catalytic active site (CAS) and peripheral anionic site (PAS). A few parameters derived from molecular dynamics (MD) simulation trajectories emphasized the stability of AChE-5p and 5m complexes throughout the 100 ns simulations, and the local conformational changes of the residues of AChE validate the stability of AChE-5p and 5m complexes. Further, these derivatives significantly impacted ABTS radical scavenging capacities and maximal DNA protection activity. Importantly, Thioflavin T (ThT) assay and FE-SEM study demonstrated compounds 5m, 5p and 5u as effective Aβ_1-42 fibril modulators at molecular level by the formation of micro size co-assembled mature structures, thus efficiently abolishing the cytotoxicity of Aβ_1-42. Finally, these active compounds are determined to be non-toxic and highly neuroprotective against H₂O₂-induced cell death in SK-N-SH cell lines. Furthermore, in silico ADMET prediction studies have revealed that the targeted analogues satisfied most of the characteristics of CNS acting drugs. These multi-functional efficacies indicated worthiness of these α-amino phosphonate derivatives being chosen for further pharmacokinetics, toxicity, and behavioral research to test their potential for AD treatment.

ROS-Responsive and pH-Sensitive Aminothiols Dual-Prodrug for Radiation Enteritis

Radiation exposure can immediately trigger a burst of reactive oxygen species (ROS), which can induce severe cell death and long-term tissue damage. Therefore, instantaneous release of sufficient radioprotective drugs is vital to neutralize those accumulated ROS in IR-exposed areas. To achieve this goal, we designed, synthesized, and evaluated a novel oral ROS-responsive radioprotective compound (M1) with high biocompatibility and efficient ROS-scavenging ability to act as a promising oral drug for radiation protection. The compound is stably present in acidic environments and is hydrolyzed in the intestine to form active molecules rich in thiols. M1 can significantly remove cellular ROS and reduce DNA damage induced by γ-ray radiation. An in vivo experiment showed that oral administration of M1 effectively alleviates acute radiation-induced intestinal injury. Immunohistochemical staining showed that M1 improved cell proliferation, reduced cell apoptosis, and enhanced the epithelial integrity of intestinal crypts. This study provides a promising oral ROS-sensitive agent for acute intestinal radiation syndrome.

Significant Reduction of Total-Body Irradiation-Induced Death in Mice Treated with PrC-210 24 Hours Postirradiation

The search for radiation countermeasures that can serve as: i. a pre-exposure agent to protect against subsequent irradiation, and/or ii. a post-exposure agent to mitigate the development of Acute Radiation Syndrome after radiation exposure, remains a prominent goal of the U.S. Government. This study was undertaken to determine whether PrC-210, when administered once, 24 h postirradiation, would provide a survival benefit and would mitigate Acute Radiation Syndrome in mice that had received an otherwise 95-100% lethal radiation dose. Our results show that a single intraperitoneal dose of PrC-210 (0.3-0.4 MTD, 151-201 ug/gm body weight) administered 24 h postirradiation, conferred: i. a 45% survival advantage (P = 0.002) in outbred ICR mice and a 25% survival advantage (P = 0.037) in inbred C57Bl/6 mice, ii. a significant increase in body weight in surviving mice (P = 0.012), iii. a discernible protection of intestinal structure by MRI imaging of live mice, iv. visibly denser jejunal villi and surface epithelium and v. visible bone marrow population in PrC-210-treated mice versus saline controls. The ability of PrC-210 to suppress 100% of radiation-induced death when administered minutes before irradiation, or roughly half of this effect (45%) when administered 24 h postirradiation is noteworthy. Determining the multiple paths by which PrC-210 protection is conferred is a process; the results in this report showing protection of two of the major systems central to Acute Radiation Syndrome damage, is a good first step. This was the first study of PrC-210 administered postirradiation; it conferred substantial survival benefit and suppression of Acute Radiation Syndrome. This outcome supports the continued development of PrC-210 to protect humans exposed to ionizing radiation.

The Effect of Antioxidant Added to Preservation Solution on the Protection of Kidneys before Transplantation

Ischemia–reperfusion injury is a key clinical problem of transplantology. Current achievements in optimizing organ rinse solutions and storage techniques have significantly influenced the degree of graft damage and its survival after transplantation. In recent years, intensive research has been carried out to maintain the viability of tissues and organs outside the integral environment of the body. Innovative solutions for improving the biochemical functions of the stored organ have been developed. The article discusses directions for modifying preservation solutions with antioxidants. Clinical and experimental studies aimed at optimizing these fluids, as well as perfusion and organ preservation techniques, are presented.

Common cancer treatments targeting DNA double strand breaks affect long-term memory and relate to immediate early gene expression in a sex-dependent manner

DNA double strand breaks (DSBs) have been highly studied in the context of cancers, as DSBs can lead to apoptosis or tumorigenesis. Several pharmaceuticals are widely used to target DSBs during cancer therapy. Amifostine (WR-2721) and etoposide are two commonly used drugs: amifostine reduces DSBs, whereas etoposide increases DSBs. Recently, a novel role for DSBs in immediate early gene expression, learning, and memory has been suggested. Neither amifostine nor etoposide have been assessed for their effects on learning and memory without confounding factors. Moreover, sex-dependent effects of these drugs have not been reported. We administered amifostine or etoposide to 3-4-month-old male and female C57Bl/6J mice before or after training in fear conditioning and assessed learning, memory, and immediate early genes. We observed sex-dependent baseline and drug-induced differences, with females expressing higher cFos and FosB levels than males. These were affected by both amifostine and etoposide. Post-training injections of amifostine affected long-term contextual fear memory; etoposide affected contextual and cued fear memory. These data support the hypothesis that DSBs contribute to learning and memory, and that these could play a part in cognitive side effects during common treatment regimens. The sex-dependent effects also highlight an important factor when considering treatment plans.

Amifostine (WR-2721) Mitigates Cognitive Injury Induced by Heavy Ion Radiation in Male Mice and Alters Behavior and Brain Connectivity

The deep space environment contains many risks to astronauts during space missions, such as galactic cosmic rays (GCRs) comprised of naturally occurring heavy ions. Heavy ion radiation is increasingly being used in cancer therapy, including novel regimens involving carbon therapy. Previous investigations involving simulated space radiation have indicated a host of detrimental cognitive and behavioral effects. Therefore, there is an increasing need to counteract these deleterious effects of heavy ion radiation. Here, we assessed the ability of amifostine to mitigate cognitive injury induced by simulated GCRs in C57Bl/6J male and female mice. Six-month-old mice received an intraperitoneal injection of saline, 107 mg/kg, or 214 mg/kg of amifostine 1 h prior to exposure to a simplified five-ion radiation (protons, 28Si, 4He, 16O, and 56Fe) at 500 mGy or sham radiation. Mice were behaviorally tested 2-3 months later. Male mice that received saline and radiation exposure failed to show novel object recognition, which was reversed by both doses of amifostine. Conversely, female mice that received saline and radiation exposure displayed intact object recognition, but those that received amifostine prior to radiation did not. Amifostine and radiation also had distinct effects on males and females in the open field, with amifostine affecting distance moved over time in both sexes, and radiation affecting time spent in the center in females only. Whole-brain analysis of cFos immunoreactivity in male mice indicated that amifostine and radiation altered regional connectivity in areas involved in novel object recognition. These data support that amifostine has potential as a countermeasure against cognitive injury following proton and heavy ion irradiation in males.

Suppression of Inflammation-Associated Kidney Damage Post-Transplant Using the New PrC-210 Free Radical Scavenger in Rats

Allograft kidney transplantation, which triggers host cellular- and antibody-mediated rejection of the kidney, is a major contributor to kidney damage during transplant. Here, we asked whether PrC-210 would suppress damage seen in allograft kidney transplant. Brown Norway (BN) rat kidneys were perfused in situ (UW Solution) with or without added 30 mM PrC-210, and then immediately transplanted into Lewis (LEW) rats. 20 h later, the transplanted BN kidneys and LEW rat plasma were analyzed. Kidney histology, and kidney/serum levels of several inflammation-associated cytokines, were measured to assess mismatch-related kidney pathology, and PrC-210 protective efficacy. Twenty hours after the allograft transplants: (i) significant histologic kidney tubule damage and mononuclear inflammatory cell infiltration were seen in allograft kidneys; (ii) kidney function metrics (creatinine and BUN) were significantly elevated; (iii) significant changes in key cytokines, i.e., TIMP-1, TNF-alpha and MIP-3A/CCL20, and kidney activated caspase levels were seen. In PrC-210-treated kidneys and recipient rats, (i) kidney histologic damage (Banff Scores) and mononuclear infiltration were reduced to untreated background levels; (ii) creatinine and BUN were significantly reduced; and (iii) activated caspase and cytokine changes were significantly reduced, some to background. In conclusion, the results suggest that PrC-210 could provide broadly applicable organ protection for many allograft transplantation conditions; it could protect transplanted kidneys during and after all stages of the transplantation process-from organ donation, through transportation, re-implantation and the post-operative inflammation-to minimize acute and chronic rejection.

Metabolic Rewiring in Radiation Oncology Toward Improving the Therapeutic Ratio

To meet the anabolic demands of the proliferative potential of tumor cells, malignant cells tend to rewire their metabolic pathways. Although different types of malignant cells share this phenomenon, there is a large intracellular variability how these metabolic patterns are altered. Fortunately, differences in metabolic patterns between normal tissue and malignant cells can be exploited to increase the therapeutic ratio. Modulation of cellular metabolism to improve treatment outcome is an emerging field proposing a variety of promising strategies in primary tumor and metastatic lesion treatment. These strategies, capable of either sensitizing or protecting tissues, target either tumor or normal tissue and are often focused on modulating of tissue oxygenation, hypoxia-inducible factor (HIF) stabilization, glucose metabolism, mitochondrial function and the redox balance. Several compounds or therapies are still in under (pre-)clinical development, while others are already used in clinical practice. Here, we describe different strategies from bench to bedside to optimize the therapeutic ratio through modulation of the cellular metabolism. This review gives an overview of the current state on development and the mechanism of action of modulators affecting cellular metabolism with the aim to improve the radiotherapy response on tumors or to protect the normal tissue and therefore contribute to an improved therapeutic ratio.

Determination of plasma levels of the active thiol form of the direct-acting PrC-210 ROS-scavenger using a fluorescence-based assay

PrC-210 is a direct-acting ROS-scavenger. It's active when administered orally, IV, or topically; it has none of the nausea/emesis nor hypotension side effects that have precluded human amifostine use. PrC-210 confers 100% survival to mice and rats that received an otherwise 100% lethal radiation dose and 36% reduction of ischemia-reperfusion-induced mouse myocardial infarct damage, and thus is a viable candidate to prevent human ROS-induced ischemia-reperfusion and ionizing radiation toxicities. We report the first assay for the pharmacologically active PrC-210 thiol in blood. PrC-210 has no double-bonds nor light absorption, so derivatizing the thiol with a UV-absorbing fluorochrome enables quantification. This assay: i) is done on the benchtop; it's read with a fluorescence plate reader, ii) provides linear product formation through 60 min, iii) quantifies μM to low mM rodent blood levels of PrC-210 that confer complete radioprotection, iv) accurately reflects PrC-210 thiol formation of mixed disulfides with other thiols in blood, and v) shows excellent between-day assay outcome with very low standard deviation and coefficient of variation. A fluorescence assay quantifying formation of a PrC-210 thiol-bimane adduct enables measurement of blood PrC-210 thiol. A blood assay will help in the development of PrC-210 for use in the human clinical setting.

Radioprotection and Radiomitigation: From the Bench to Clinical Practice

The development of protective agents against harmful radiations has been a subject of investigation for decades. However, effective (ideal) radioprotectors and radiomitigators remain an unsolved problem. Because ionizing radiation-induced cellular damage is primarily attributed to free radicals, radical scavengers are promising as potential radioprotectors. Early development of such agents focused on thiol synthetic compounds, e.g., amifostine (2-(3-aminopropylamino) ethylsulfanylphosphonic acid), approved as a radioprotector by the Food and Drug Administration (FDA, USA) but for limited clinical indications and not for nonclinical uses. To date, no new chemical entity has been approved by the FDA as a radiation countermeasure for acute radiation syndrome (ARS). All FDA-approved radiation countermeasures (filgrastim, a recombinant DNA form of the naturally occurring granulocyte colony-stimulating factor, G-CSF; pegfilgrastim, a PEGylated form of the recombinant human G-CSF; sargramostim, a recombinant granulocyte macrophage colony-stimulating factor, GM-CSF) are classified as radiomitigators. No radioprotector that can be administered prior to exposure has been approved for ARS. This differentiates radioprotectors (reduce direct damage caused by radiation) and radiomitigators (minimize toxicity even after radiation has been delivered). Molecules under development with the aim of reaching clinical practice and other nonclinical applications are discussed. Assays to evaluate the biological effects of ionizing radiations are also analyzed.

Significant Improvement in Rat Kidney Cold Storage Using UW Organ Preservation Solution Supplemented With the Immediate-Acting PrC-210 Free Radical Scavenger

Ischemia-reperfusion injury, including injury from warm- and cold-ischemia (CI) organ storage, remains a significant problem for all solid organ transplants. Suppressing CI damage would reduce delayed graft function and increase the donor organ pool size. PrC-210 has demonstrated superior prevention of damage in several preclinical studies as an immediate-acting free-radical scavenger. Here, we describe its profound efficacy in suppressing CI injury in a rat kidney model.

Pharmacological management of ionizing radiation injuries: current and prospective agents and targeted organ systems

Introduction: There is a limited array of currently available medicinals that are useful for either the prevention, mitigation or treatment of bodily injuries arising from ionizing radiation exposure.Area covered: In this brief article, the authors review those pharmacologic agents that either are currently being used to counter the injurious effects of radiation exposure, or those that show promise and are currently under development.Expert opinion: Although significant, but limited progress has been made in the development and fielding of safe and effective pharmacotherapeutics for select types of acute radiation-associated injuries, additional effort is needed to broaden the scope of drug development so that overall health risks associated with both short- and long-term injuries in various organ systems can be reduced and effectively managed. There are several promising radiation countermeasures that may gain regulatory approval from the government in the near future for use in clinical settings and in the aftermath of nuclear/radiological exposure contingencies.

Impact of the PrC-210 Radioprotector Molecule on Cancer Deaths in p53-Deficient Mice

Radiation-induced cancer is an ongoing and significant problem, with sources that include clinics worldwide in which 3.1 billion radiology exams are performed each year, as well as a variety of other scenarios such as space travel and nuclear cleanup. These radiation exposures are typically anticipated, and the exposure is typically well below 1 Gy. When radiation-induced (actually ROS-induced) DNA mutation is prevented, then so too are downstream radiation-induced cancers. Currently, there is no protection available against the effects of such <1 Gy radiation exposures. In this study, we address whether the new PrC-210 ROS-scavenger is effective in protecting p53-deficient (p53^-/-) mice against X-ray-induced accelerated tumor mortality; this is the most sensitive radiation tumorigenesis model currently known. Six-day-old p53^-/- pups received a single intraperitoneal PrC-210 dose [0.5 maximum tolerated dose (MTD)] or vehicle, and 25 min later, pups received 4.0 Gy X-ray irradiation. At 5 min postirradiation, blood was collected to quantify white blood cell c-H2AX foci. Over the next 250 days, tumor-associated deaths were recorded. Findings revealed that when administered 25 min before 4 Gy X-ray irradiation, PrC-210 reduced DNA damage (c-H2AX foci) by 40%, and in a notable coincidence, caused a 40% shift in tumor latency/incidence, and the 0.5 MTD PrC210 dose had no discernible toxicities in these p53^-/- mice. Essentially, the moles of PrC-210 thiol within a single 0.5 MTD PrC-210 dose suppressed the moles of ROS generated by 40% of the 4 Gy X-ray dose administered to p53^-/- pups, and in doing so, eliminated the lifetime leukemia/lymphoma risk normally residing "downstream" of that 40% of the 4 Gy dose. In conclusion: 1. PrC-210 is readily tolerated by the 6-day-old p53^-/- mice, with no discernible lifetime toxicities; 2. PrC-210 does not cause the nausea, emesis or hypotension that preclude clinical use of earlier aminothiols; and 3. PrC-210 significantly increased survival after 4 Gy irradiation in the p53^-/- mouse model.

Radiation Modifiers

Radiation therapy is one of the most commonly used treatments for cancer. Radiation modifiers are agents that alter tumor or normal tissue response to radiation, such as radiation sensitizers and radiation protectors. Radiation sensitizers target aspects of tumor molecular biology or physiology to enhance tumor cell killing after irradiation. Radioprotectors prevent damage of normal tissues selectively. Radiation modifiers remain largely investigational at present, with the promise that molecular characterization of tumors may enhance the capacity for successful clinical development moving forward. A variety of radiation modifiers are described.

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.

Significant reduction of ischemia-reperfusion cell death in mouse myocardial infarcts using the immediate-acting PrC-210 ROS-scavenger

Managing myocardial infarction (MI) to reduce cardiac cell death relies primarily on timely reperfusion of the affected coronary site, but reperfusion itself induces cell death through a toxic, ROS-mediated process. In this study, we determined whether the PrC-210 aminothiol ROS-scavenger could prevent ROS-induced damage in post-MI hearts. In a series of both in vitro and in vivo experiments, we show that: (a) in vitro, PrC-210 was the most potent and effective ROS-scavenger when functionally compared to eight of the most commonly studied antioxidants in the MI literature, (b) in vitro PrC-210 ROS-scavenging efficacy was both immediate (seconds) and long-lasting (hours), which would make it effective in both (1) real-time (seconds), as post-MI or cardiac surgery hearts are reperfused with PrC-210-containing blood, and (2) long-term (hours), as hearts are bathed with systemic PrC-210 after MI or surgery, (c) systemic PrC-210 caused a significant 36% reduction of mouse cardiac muscle death following a 45-minute cardiac IR insult; in a striking coincidence, the PrC-210 36% reduction in cardiac muscle death equals the 36% of the MI-induced cardiac cell death estimated 6 years ago by Ovize and colleagues to result from "reperfusion injury," (d) hearts in PrC-210-treated mice performed better than controls after heart attacks when functionally analyzed using echocardiography, and (e) the PrC-210 ROS-scavenging mechanism of action was corroborated by its ability to prevent >85% of the direct, H2O2-induced killing of neonate cardiomyocytes in cell culture. PrC-210 does not cause the nausea, emesis, nor hypotension that preclude clinical use of the WR-1065/amifostine aminothiol. PrC-210 is a highly effective ROS-scavenger that significantly reduces IR injury-associated cardiac cell death.

Significant Reduction of Murine Renal Ischemia-Reperfusion Cell Death Using the Immediate-Acting PrC-210 Reactive Oxygen Species Scavenger

Background.

Ischemia-reperfusion (IR) injury remains a significant problem for all solid organ transplants; thus, an important unmet need in transplantation is the prevention of IR injury. PrC-210 has demonstrated superior prevention of reactive oxygen species damage in several preclinical studies as a free radical scavenger. Here, we describe its profound efficacy in suppressing IR injury in a murine model of kidney IR injury.

Methods.

C57/B6 mice underwent laparotomy with the left renal pedicle occluded for 30 minutes to induce IR injury. Right nephrectomy was performed at the time of surgery. Mice received a single systemic dose of the PrC-210, PrC-211, or PrC-252 aminothiols 20 minutes before IR injury. Twenty-four hours following IR injury, blood and kidney tissue were collected for analysis. Kidney caspase-3 level (a marker of cell death), direct histological analysis of kidneys, and serum blood urea nitrogen (BUN) were measured in animals to assess reactive oxygen species scavenger protective efficacies.

Results.

A single systemic PrC-210 dose 20 minutes before IR injury resulted in significant reductions in (1) IR-induced kidney caspase level (P < 0.0001); caspase was reduced to levels not significantly different than control caspase levels seen in unperturbed kidneys, (2) IR-induced renal tubular injury scores (P < 0.0001); brush border loss and tubular dilation were markedly reduced, and (3) serum BUN compared with control IR injury kidneys (P < 0.0001). The ranked protective efficacies of PrC-210 > PrC-211 >> PrC-252 paralleled previous radioprotection studies of the molecules.

Conclusions.

A single PrC-210 dose, minutes before the IR insult, profoundly reduced caspase, renal tubular injury, and serum BUN in mice exposed to standard kidney IR injury. These findings support further development of the PrC-210 molecule to suppress or prevent IR injury in organ transplant and other IR injury settings.

Reduction of X-ray-induced DNA damage in normal human cells treated with the PrC-210 radioprotector

The aim of our study was to determine the protective efficacy of the PrC-210 aminothiol radioprotector against X-ray-induced DNA damage in normal human cells and to establish dose- and time-effect models for future PrC-210 use in humans. The PrC-210 structure has a branched structure which enables scavenging of reactive oxygen species (ROS) away from DNA. Normal human blood lymphocytes, fibroblasts and naked genomic DNA were exposed to PrC-210 seconds to hours prior to irradiation. Biological (γ-H2AX foci), chemical (8-oxo-deoxyguanosine) and physical (genomic DNA electrophoretic migration) DNA damage endpoints were scored to determine the ability of PrC-210 to suppress radiation-induced DNA damage. X-ray-induced γ-H2AX foci in blood lymphocytes were reduced by 80% after irradiation with 10, 50 and 100 mGy, and DNA double-strand breaks in fibroblasts were reduced by 60% after irradiation with 20 Gy. Additionally, we observed a reduction of 8-oxo-deoxyguanosine (an ROS-mediated, DNA damage marker) in human genomic DNA to background in a PrC-210 dose-dependent manner. PrC-210 also eliminated radiation-induced cell death in colony formation assays after irradiation with 1 Gy. The protective efficacy of PrC-210 in each of these assay systems supports its development as a radioprotector for humans in multiple radiation exposure settings.

Summary: A new strategy is decribed, using a new radioprotector (PrC-210) to significantly reduce radiation-induced DNA damage.

The Protective Effect of New Compound XH-103 on Radiation-Induced GI Syndrome

Background

Radiation-induced intestinal injury is one of the side effects in patients receiving radiotherapy. The aim of the present study was to investigate the protective effect of XH-103 on radiation-induced small intestinal injury and to explore its mechanism.

Methods

C57BL/6N mice were irradiated and treated with XH-103. Firstly, the survival rate of mice exposed to 9.0 Gy and 11.0 Gy total body irradiation (TBI) was examined. Subsequently, at 3.5 d after IR, the small intestinal morphological changes were examined by HE. The numbers of crypt cells, the villus height, the expression of Ki67 and Lgr5, and the apoptotic cells in the intestinal crypts were examined by immunohistochemistry. Furthermore, the expression of p53 and Bax was analyzed by WB.

Results

Compared to the irradiation group, XH-103 improved the mice survival rate, protected the intestinal morphology of mice, decreased the apoptotic rate of intestinal crypt cells, maintained cell regeneration, and promoted crypt proliferation and differentiation. XH-103 also reduced the expression of p53 and Bax in the small intestine compared to the IR group.

Conclusion

These data demonstrate that XH-103 can prevent radiation-induced intestinal injury, which is beneficial for the protection of radiation injuries.

Significant Suppression of CT Radiation-Induced DNA Damage in Normal Human Cells by the PrC-210 Radioprotector

While computed tomography (CT) is now commonly used and considered to be clinically valuable, significant DNA double-strand breaks (γ-H2AX foci) in white blood cells from adult and pediatric CT patients have been frequently reported. In this study to determine whether γ-H2AX foci and X-ray-induced naked DNA damage are suppressed by administration of the PrC-210 radioprotector, human blood samples were irradiated in a CT scanner at 50-150 mGy with or without PrC-210, and γ-H2AX foci were scored. X-ray-induced naked DNA damage was also studied, and the DNA protective efficacy of PrC-210 was compared against 12 other common "antioxidants." PrC-210 reduced CT radiation-induced γ-H2AX foci in white blood cells to near background ( P < 0.0001) at radiation doses of 50-150 mGy. PrC-210 was most effective among the 13 "antioxidants" in reducing naked DNA X-ray damage, and its addition at 30 s before an ^•OH pulse reduced to background the ^•OH insult that otherwise induced >95% DNA damage. A systemic PrC-210 dose known to confer 100% survival in irradiated mice had no discernible effect on micro-CT image signal-to-noise ratio and CT image integrity. PrC-210 suppressed DNA damage to background or near background in each of these assay systems, thus supporting its development as a radioprotector for humans in multiple radiation exposure settings.

A review of radiation countermeasures focusing on injury-specific medicinals and regulatory approval status: part III. Countermeasures under early stages of development along with 'standard of care' medicinal and procedures not requiring regulatory approval for use

PURPOSE

Terrorist attacks, with their intent to maximize psychological and economic damage as well as inflicting sickness and death on given targeted populations, are an ever-growing worldwide concern in government and public sectors as they become more frequent, violent, and sensational. If given the chance, it is likely that terrorists will use radiological or nuclear weapons. To thwart these sinister efforts, both physical and medical countermeasures against these weapons are currently being researched and developed so that they can be utilized by the first responders, military, and medical providers alike. This is the third article of a three-part series in which we have reviewed additional radiation countermeasures that are currently under early preclinical phases of development using largely animal models and have listed and discussed clinical support measures, including agents used for radiation-induced emesis, as well as countermeasures not requiring Food and Drug Administration approval.

CONCLUSIONS

Despite the significant progress that has been made in this area during the last several years, additional effort is needed in order to push promising new agents, currently under development, through the regulatory pipeline. This pipeline for new promising drugs appears to be unreasonably slow and cumbersome; possible reasons for this inefficiency are briefly discussed. Significant and continued effort needs to be afforded to this research and development area, as to date, there is no approved radioprotector that can be administered prior to high dose radiation exposure. This represents a very significant, unmet medical need and a significant security issue. A large number of agents with potential to interact with different biological targets are under development. In the next few years, several additional radiation countermeasures will likely receive Food and Drug Administration approval, increasing treatment options for victims exposed to unwanted ionizing irradiation.

A review of radiation countermeasures focusing on injury-specific medicinals and regulatory approval status: part I. Radiation sub-syndromes, animal models and FDA-approved countermeasures

PURPOSE

The increasing global risk of nuclear and radiological accidents or attacks has driven renewed research interest in developing medical countermeasures to potentially injurious exposures to acute irradiation. Clinical symptoms and signs of a developing acute radiation injury, i.e. the acute radiation syndrome, are grouped into three sub-syndromes named after the dominant organ system affected, namely the hematopoietic, gastrointestinal, and neurovascular systems. The availability of safe and effective countermeasures against the above threats currently represents a significant unmet medical need. This is the first article within a three-part series covering the nature of the radiation sub-syndromes, various animal models for radiation countermeasure development, and the agents currently approved by the United States Food and Drug Administration for countering the medical consequences of several of these prominent radiation exposure-associated syndromes.

CONCLUSIONS

From the U.S. and global perspectives, biomedical research concerning medical countermeasure development is quite robust, largely due to increased government funding following the 9/11 incidence and subsequent rise of terrorist-associated threats. A wide spectrum of radiation countermeasures for specific types of radiation injuries is currently under investigation. However, only a few radiation countermeasures have been fully approved by regulatory agencies for human use during radiological/nuclear contingencies. Additional research effort, with additional funding, clearly will be needed in order to fill this significant, unmet medical health problem.

Complete prevention of radiation-induced dermatitis using topical adrenergic vasoconstrictors

Radiation dermatitis is a commonly occurring, painful, side effect of cancer radiotherapy that causes some patients to withdraw from the radiotherapy course. Our goal was to test and optimize topical application of an adrenergic vasoconstrictor to rat skin in a preclinical test to prevent radiation-induced dermatitis. A radiation dermatitis assay was developed in which 17.2 Gy to a 1.5 × 3.0 cm rectangle on the clipped dorsal back of rats yielded Grade 3 radiation dermatitis over the irradiated area 13 days later. Single, topical applications of each of three adrenergic vasoconstrictors, epinephrine, norepinephrine, or phenylephrine, in various vehicle formulations, doses, and application schedules, were tested to determine their efficacy in preventing radiation dermatitis. Each of the three adrenergic agonists conferred 100 % prevention of radiation dermatitis in linear, dose-dependent manners and their EC₅₀ potencies in preventing radiation dermatitis correlated well with their individual K _d association constants for binding to mammalian α-adrenergic receptors. Topical vasoconstrictor application as little as 3-12 min before irradiation gave 80-100 % prevention, respectively, of radiation dermatitis. There was a strong correlation between the extent (0-100 %) of skin blanch present in skin immediately before irradiation and prevention of radiation dermatitis scored 13 days after irradiation. The data presented here demonstrate that topical application of adrenergic vasoconstrictors to rat skin before a large, 17.2 Gy, radiation insult confers 100 % protection against radiation dermatitis and support ongoing clinical trials and commercial development of a vasoconstrictor-based product to prevent radiotherapy-induced dermatitis.

Molecular hydrogen attenuates radiation-induced nucleobase damage to DNA in aerated aqueous solutions

PURPOSE

The main aim of the present study is to gain mechanistic insights into the modulating effect of molecular hydrogen on the γ-radiation-induced alteration pathways of DNA nucleobases.

MATERIALS AND METHODS

Aerated aqueous solutions of calf thymus DNA were exposed to a (60)Co source at doses ranging from 0 to 55 Gy under normoxic conditions, in the presence or not of 0.7 MPa hydrogen or helium. The measurement of several modified bases was performed using HPLC associated with electrospray ionization tandem pass spectrometry (HPLC-ESI-MS/MS). Bleaching of aqueous solutions of p-nitrosodimethylaniline (p-NDA) solutions was also used to allow the quantification of hydroxyl radical (•OH) formation.

RESULTS

pNDA bleaching was significantly reduced in the presence of hyperbaric hydrogen. This is undoubtedly due to (•)OH scavenging by H2 since, under the same conditions, He had no effect. Similarly, base alterations were significantly reduced in the presence of hydrogen, as compared to controls under normal atmosphere or in the presence of helium. The relative proportions of modified nucleobases were not changed, showing that the only effect of H2 is to scavenge (•)OH without exhibiting reducing properties.

CONCLUSIONS

Our findings demonstrate that H2 exerts a significant protection against radiation-induced DNA base damage in aqueous solutions, (•)OH scavenging being the only mechanism involved.

Radioprotective Agents: Strategies and Translational Advances

Radioprotectors are agents required to protect biological system exposed to radiation, either naturally or through radiation leakage, and they protect normal cells from radiation injury in cancer patients undergoing radiotherapy. It is imperative to study radioprotectors and their mechanism of action comprehensively, looking at their potential therapeutic applications. This review intimately chronicles the rich intellectual, pharmacological story of natural and synthetic radioprotectors. A continuous effort is going on by researchers to develop clinically promising radioprotective agents. In this article, for the first time we have discussed the impact of radioprotectors on different signaling pathways in cells, which will create a basis for scientific community working in this area to develop novel molecules with better therapeutic efficacy. The bright future of exceptionally noncytotoxic derivatives of bisbenzimidazoles is also described as radiomodulators. Amifostine, an effective radioprotectant, has been approved by the FDA for limited clinical use. However, due to its adverse side effects, it is not routinely used clinically. Recently, CBLB502 and several analog of a peptide are under clinical trial and showed high success against radiotherapy in cancer. This article reviews the different types of radioprotective agents with emphasis on the strategies for the development of novel radioprotectors for drug development. In addition, direction for future strategies relevant to the development of radioprotectors is also addressed.

Radioprotective Effect of Aminothiol PrC-210 on Irradiated Inner Ear of Guinea Pig

Radiotherapy of individuals suffering with head & neck or brain tumors subserve the risk of sensorineural hearing loss. Here, we evaluated the protective effect of Aminothiol PrC-210 (3-(methyl-amino)-2-((methylamino)methyl)propane-1-thiol) on the irradiated inner ear of guinea pigs. An intra-peritoneal or intra-tympanic dose of PrC-210 was administered prior to receiving a dose of gamma radiation (3000 cGy) to each ear. Auditory Brainstem Responses (ABRs) were recorded one week and two weeks after the radiation and compared with the sham animal group. ABR thresholds of guinea pigs that received an intra-peritoneal dose of PrC-210 were significantly better compared to the non-treated, control animals at one week post-radiation. Morphologic analysis of the inner ear revealed significant inflammation and degeneration of the spiral ganglion in the irradiated animals not treated with PrC-210. In contrast, when treated with PrC-210 the radiation effect and injury to the spiral ganglion was significantly alleviated. PrC-210 had no apparent cytotoxic effect in vivo and did not affect the morphology or count of cochlear hair cells. These findings suggest that aminothiol PrC-210 attenuated radiation-induced cochlea damage for at least one week and protected hearing.

Radiation resistance: Cancer stem cells (CSCs) and their enigmatic pro-survival signaling

Despite the fact that radiation therapy is a highly effective therapeutic approach, a small intratumoral cell subpopulation known as "cancer stem cells" (CSCs) is radiation-resistant and possesses specific molecular properties protecting it against radiation-induced damage. The exact mechanisms of this radioresistance are still not fully elucidated, but they relate to these cells' enhanced DNA repair capacities and their low intracellular ROS concentrations, resulting from their up-regulation of ROS scavengers. The low ROS content is accompanied by disturbances in cell cycle regulation, so it can be assumed that either CSCs are quiescent or dormant themselves, or that this cell population consists of at least two cell subpopulations: the normally and the slowly proliferating cells (quiescent or dormant cells). Slowly dividing CSCs show concomitant dysregulation of the signaling molecules mediating both cell cycle progression and maintenance of cell stemness. Despite a massive accumulation of data concerning the mechanisms underlying DNA damage response in CSCs, it represents a challenge to researchers in the era of personalized medicine to elucidate the role of intracellular ROS and of signaling pathways associated with the radiation resistance of these cells; there is a clear need to understand the molecular mechanisms helping CSCs to survive radiation exposure.

The antioxidant paradox: what are antioxidants and how should they be used in a therapeutic context for cancer

So-called antioxidants have yet to make a clinical impact on the treatment of human cancer. The reasons for this failure are several. First, many agents that are called antioxidants are truly antioxidants at a given dose, but this dose may not have been given in clinical trials. Second, many agents are not antioxidants at all. Third, not all tumors use reactive oxygen as a signaling mechanism. Finally, reactive oxygen inhibition is often insufficient to kill or regress a tumor cell by itself, but requires sequential introduction of a therapeutic agent for maximal effect. We hope to provide a framework for the logical use of these agents in cancer.

A new strategy to prevent chemotherapy and radiotherapy-induced alopecia using topically applied vasoconstrictor

In a new strategy, we sought to determine whether topically applied vasoconstrictor, with its accompanying transient skin hypoxia and exclusion of systemic drug, would prevent or suppress radiotherapy or chemotherapy-induced alopecia. Topical vasoconstrictor was applied to 1-cm(2) skin patches on the backs of 10-day-old rats and minutes later they received either 7.1 gray (Gy) whole-body radiation or systemic N-nitroso-N-methylurea (MNU) or Cytoxan. The degree of alopecia was scored 10 days later by visual assessment (% coat retention) and hair follicle histologic analysis. Topical application of epinephrine or norepinephrine in an alcohol:water delivery vehicle induced clear skin blanch, and in a dose-dependent manner, topical epinephrine or norepinephrine (20-1,000 mM) applied before 7.1 Gy irradiation conferred 95% of coat retention in the treated skin patches versus 0% coat retention in vehicle controls, or in skin outside the treated patches. By histology, small numbers of dystrophic hair follicles were observed in hairless skin versus the normal density of anagen follicles in the immediately adjacent, drug-protected skin patches at day 20; protected coats were retained into adulthood. Topical epinephrine or norepinephrine before systemic MNU (30 ug/gm body weight) conferred up to 95% of coat retention in treated skin patches versus 0% coat retention elsewhere. Epinephrine-conferred % coat retention dropped to 16% in rats that received systemic Cytoxan, a drug whose plasma half-life is at least 8- to 10-fold longer than MNU. A general strategy is discussed for the use of topical epinephrine or norepinephrine in the clinic to provide an inexpensive and convenient strategy to prevent cancer therapy-induced alopecia.

Practical advice on calculating confidence intervals for radioprotection effects and reducing animal numbers in radiation countermeasure experiments

The dose of a substance that causes death in P% of a population is called an LDP, where LD stands for lethal dose. In radiation research, a common LDP of interest is the radiation dose that kills 50% of the population by a specified time, i.e., lethal dose 50 or LD50. When comparing LD50 between two populations, relative potency is the parameter of interest. In radiation research, this is commonly known as the dose reduction factor (DRF). Unfortunately, statistical inference on dose reduction factor is seldom reported. We illustrate how to calculate confidence intervals for dose reduction factor, which may then be used for statistical inference. Further, most dose reduction factor experiments use hundreds, rather than tens of animals. Through better dosing strategies and the use of a recently available sample size formula, we also show how animal numbers may be reduced while maintaining high statistical power. The illustrations center on realistic examples comparing LD50 values between a radiation countermeasure group and a radiation-only control. We also provide easy-to-use spreadsheets for sample size calculations and confidence interval calculations, as well as SAS® and R code for the latter.

Radioprotective efficacy and toxicity of a new family of aminothiol analogs

PURPOSE

A family of 17 new nucleophilic-polyamine and aminothiol structures was designed and synthesized to identify new topical or systemic radioprotectors with acceptable mammalian toxicity profiles. design elements included: (i) Length and charge of the DNA-interacting, alkylamine backbone, (ii) nucleophilicity of the reactive oxygen species (ROS)-scavenging group, and (iii) non-toxic drug concentration achievable in animal tissues.

MATERIALS AND METHODS

Mouse maximum tolerated doses (MTD) were determined by increasing intraperitoneal (IP) doses. To assess radioprotective efficacy, mice received IP 0.5 MTD doses prior to an LD95 radiation dose (8.63 Gy), and survival was monitored. Topically applied aminothiol was also scored for prevention of radiation-induced dermatitis (17.3 Gy to skin).

RESULTS

The most radioprotective aminothiols had 4-6 carbons and 1-2 amines, and unlike amifostine and its analogs, displayed a terminal thiol from an alkyl side chain that projected the thiol away from the DNA major groove into the environment surrounding the DNA. The five carbon, single thiol, alkylamine, PrC-210, conferred 100% survival to an otherwise 100% lethal dose of whole-body radiation and achieved 100% prevention of Grade 2-3 radiation dermatitis. By mass spectrometry analysis, the one aminothiol that was tested formed mixed disulfides with cysteine and glutathione.

CONCLUSIONS

Multiple, highly radioprotective, aminothiol structures, with acceptable systemic toxicities, were identified.