Patricia L.P. Romaine

Radiation countermeasure agents: an update (2011 – 2014)

Introduction: Despite significant scientific advances over the past 60 years towards the development of a safe, nontoxic and effective radiation countermeasure for the acute radiation syndrome (ARS), no drug has been approved by the US FDA. A radiation countermeasure to protect the population at large from the effects of lethal radiation exposure remains a significant unmet medical need of the US citizenry and, thus, has been recognized as a high priority area by the government. Area covered: This article reviews relevant publications and patents for recent developments and progress for potential ARS treatments in the area of radiation countermeasures. Emphasis is placed on the advanced development of existing agents since 2011 and new agents identified as radiation countermeasure for ARS during this period. Expert opinion: A number of promising radiation countermeasures are currently under development, seven of which have received US FDA investigational new drug status for clinical investigation. Four of these agents, CBLB502, Ex-RAD, HemaMax and OrbeShield, are progressing with large animal studies and clinical trials. G-CSF has high potential and well-documented therapeutic effects in countering myelosuppression and may receive full licensing approval by the US FDA in the future.

Medical Countermeasures for Radiation Exposure and Related Injuries: Characterization of Medicines, FDA-Approval Status and Inclusion into the Strategic National Stockpile

AbstractWorld events over the past decade have highlighted the threat of nuclear terrorism as well as an urgent need to develop radiation countermeasures for acute radiation exposures and subsequent bodily injuries. An increased probability of radiological or nuclear incidents due to detonation of nuclear weapons by terrorists, sabotage of nuclear facilities, dispersal and exposure to radioactive materials, and accidents provides the basis for such enhanced radiation exposure risks for civilian populations. Although the search for suitable radiation countermeasures for radiation-associated injuries was initiated more than half a century ago, no safe and effective radiation countermeasure for the most severe of these injuries, namely acute radiation syndrome (ARS), has been approved by the United States Food and Drug Administration (FDA). The dearth of FDA-approved radiation countermeasures has prompted intensified research for a new generation of radiation countermeasures. In this communication, the authors have listed and reviewed the status of radiation countermeasures that are currently available for use, or those that might be used for exceptional nuclear/radiological contingencies, plus a limited few medicines that show early promise but still remain experimental in nature and unauthorized for human use by the FDA.

Biologics as countermeasures for acute radiation syndrome: where are we now?

Despite significant scientific advances toward the development of a safe, nontoxic and effective radiation countermeasure for acute radiation syndrome (ARS) over the past six decades, no drug has been approved by the US FDA. Several biologics are currently under development as radiation countermeasures for ARS, of which three have received FDA Investigational New Drug (IND) status for clinical investigation. Presently, two of these agents, entolimod (CBLB502) and HemaMax (recombinant human IL-12) are progressing with large animal studies and clinical trials. Neupogen (G-CSF, filgrastim) has recently been recommended for approval by an FDA Advisory Committee. Filgrastim, GM-CSF (Leukine, sargramostim), and PEGylated G-CSF (Neulasta) have high potential and well-documented therapeutic effects in countering myelosuppression and may receive full licensing approval by the FDA in the future. The former two biologics are available in the US Strategic National Stockpile (SNS) for use in the event of nuclear or radiological emergency. The Emergency Use Authorization (EAU) application for entolimod may be filed soon with the FDA. Biologics are attractive agents that are progressing along the path for FDA approval, to fill the unmet need for ARS countermeasures.

Radioprotective efficacy of delta-tocotrienol, a vitamin E isoform, is mediated through granulocyte colony-stimulating factor

AIMS The objectives of this study were to determine the cytokine induction by delta tocotrienol (DT3, a promising radiation countermeasure) and to investigate the role of granulocyte colony-stimulating factor (G-CSF) in its radioprotective efficacy against ionizing radiation in mice. MAIN METHODS Multiplex Luminex was used to analyze cytokines induced by DT3 and other tocols (gamma-tocotrienol and tocopherol succinate) in CD2F1 mice. Mice were injected with an optimal dose of DT3 and a G-CSF antibody, and their 30-day survival against cobalt-60 gamma-irradiation was monitored. The neutralization of G-CSF by the administration of a G-CSF-specific antibody in DT3-injected mice was investigated by multiplex Luminex. KEY FINDINGS Our data demonstrate that DT3 induced high levels of various cytokines comparable to other tocols being developed as radiation countermeasures. DT3 significantly protected mice against ionizing radiation, and the administration of a G-CSF neutralizing antibody to DT3-treated animals resulted in the complete abrogation of DT3s radioprotective efficacy and neutralization of G-CSF in peripheral blood. SIGNIFICANCE Our study findings suggest that G-CSF induced by DT3 mediates its radioprotective efficacy against ionizing radiation in mice.

Use of biomarkers for assessing radiation injury and efficacy of countermeasures

Several candidate drugs for acute radiation syndrome (ARS) have been identified that have low toxicity and significant radioprotective and radiomitigative efficacy. Inasmuch as exposing healthy human volunteers to injurious levels of radiation is unethical, development and approval of new radiation countermeasures for ARS are therefore presently based on animal studies and Phase I safety study in healthy volunteers. The Animal Efficacy Rule, which underlies the Food and Drug Administration approval pathway, requires a sound understanding of the mechanisms of injury, drug efficacy, and efficacy biomarkers. In this context, it is important to identify biomarkers for radiation injury and drug efficacy that can extrapolate animal efficacy results, and can be used to convert drug doses deduced from animal studies to those that can be efficacious when used in humans. Here, we summarize the progress of studies to identify candidate biomarkers for the extent of radiation injury and for evaluation of countermeasure efficacy.

Radioprotective Efficacy of Gamma-Tocotrienol in Nonhuman Primates

The search for treatments to counter potentially lethal radiation-induced injury over the past several decades has led to the development of multiple classes of radiation countermeasures. However, to date only granulocyte colony-stimulating factor (G-CSF; filgrastim, Neupogen)and pegylated G-CSF (pegfilgrastim, Neulasta) have been approved by the United States Food and Drug Administration (FDA) for the treatment of hematopoietic acute radiation syndrome (ARS). Gamma-tocotrienol (GT3) has demonstrated strong radioprotective efficacy in the mouse model, indicating the need for further evaluation in a large animal model. In this study, we evaluated GT3 pharmacokinetics (PK) and efficacy at different doses of cobalt-60 gamma radiation (0.6 Gy/min) using the nonhuman primate (NHP) model. The PK results demonstrated increased area under the curve with increasing drug dose and half-life of GT3. GT3 treatment resulted in reduced group mean neutropenia by 3–5 days and thrombocytopenia by 1–5 days. At 5.8 and 6.5 Gy total-body irradiation, GT3 treatment completely prevented thrombocytopenia. The capability of GT3 to reduce severity and duration of neutropenia and thrombocytopenia was dose dependent; 75 mg/kg treatment was more effective than 37.5 mg/kg treatment after a 5.8 Gy dose. However, the higher GT3 dose (75 mg/kg) was associated with higher frequency of adverse skin effects (small abscess) at the injection site. GT3 treatment of irradiated NHPs caused no significant difference in animal survival at 60 days postirradiation, however, low mortality was observed in irradiated, vehicle-treated groups as well. The data from this pilot study further elucidate the role and pharmacokinetics of GT3 in hematopoietic recovery after irradiation in a NHP model, and demonstrate the potential of GT3 as a promising radioprotector.

Progenitors mobilized by gamma-tocotrienol as an effective radiation countermeasure.

The purpose of this study was to elucidate the role of gamma-tocotrienol (GT3)-mobilized progenitors in mitigating damage to mice exposed to a supralethal dose of cobalt-60 gamma-radiation. CD2F1 mice were transfused 24 h post-irradiation with whole blood or isolated peripheral blood mononuclear cells (PBMC) from donors that had received GT3 72 h prior to blood collection and recipient mice were monitored for 30 days. To understand the role of GT3-induced granulocyte colony-stimulating factor (G-CSF) in mobilizing progenitors, donor mice were administered a neutralizing antibody specific to G-CSF or its isotype before blood collection. Bacterial translocation from gut to heart, spleen and liver of irradiated recipient mice was evaluated by bacterial culture on enriched and selective agar media. Endotoxin in serum samples also was measured. We also analyzed the colony-forming units in the spleens of irradiated mice. Our results demonstrate that whole blood or PBMC from GT3-administered mice mitigated radiation injury when administered 24 h post-irradiation. Furthermore, administration of a G-CSF antibody to GT3-injected mice abrogated the efficacy of blood or PBMC obtained from such donors. Additionally, GT3-mobilized PBMC inhibited the translocation of intestinal bacteria to the heart, spleen, and liver, and increased colony forming unit-spleen (CFU-S) numbers in irradiated mice. Our data suggests that GT3 induces G-CSF, which mobilizes progenitors and these progenitors mitigate radiation injury in recipient mice. This approach using mobilized progenitor cells from GT3-injected donors could be a potential treatment for humans exposed to high doses of radiation.

Tocols induce G-CSF and mobilise progenitors that mitigate radiation injury

Tocols induce high levels of granulocyte-colony-stimulating factor (G-CSF). G-CSF mobilises progenitors that allow mice that have been severely immunocompromised by exposure to acute, high-dose ionising irradiation to recover and to survive. The neutralisation of G-CSF abrogates the radioprotective efficacy of tocols. This article reviews studies in which CD2F1 mice were irradiated with sufficiently high doses to cause acute radiation syndrome symptoms and then administered (iv) progenitor-enriched whole blood or peripheral blood mononuclear cells from tocol- and AMD3100-injected donor mice (AMD3100 is a chemokine receptor antagonist used to improve the yield of mobilised progenitors). In some experiments, G-CSF was neutralised completely. Irradiated recipient mice were observed for 30 d post-irradiation for survival, a primary endpoint used for determining therapeutic effectiveness. Additionally, potential tocol-induced biomarkers (cytokines, chemokines and growth factors) were quantified. The authors suggest that tocols are highly effective agents for mobilising progenitors with significant therapeutic potential.

Medical countermeasures for unwanted CBRN exposures: part II radiological and nuclear threats with review of recent countermeasure patents

ABSTRACT Introduction: The global threat of a chemical, biological, radiological, or nuclear (CBRN) disaster is an important priority for all government agencies involved in domestic security and public health preparedness. Radiological/nuclear (RN) attacks or accidents have become a larger focus of the United States Food and Drug administration (US FDA) over time because of their increased likeliness. Clinical signs and symptoms of a developing acute radiation syndrome (ARS) are grouped into three sub-syndromes named for the dominant organ system affected, namely the hematopoietic (H-ARS), gastrointestinal (GI-ARS), and neurovascular systems. The availability of safe and effective countermeasures against radiological/nuclear threats currently represents a significant unmet medical need. Areas covered: This article reviews the development of RN threat medical countermeasures and highlights those specific countermeasures that have been recently patented and approved following the FDA Animal Rule. Patents for such agents from 2015 have been presented. Expert opinion: Two granulocyte colony-stimulating factor (G-CSF)-based radiation countermeasures (Neupogen® (Amgen, Thousand Oaks, CA) and Neulasta® (Amgen, Thousand Oaks, CA)) have recently been approved by the FDA for treatment of H-ARS and both these agents are radiomitigators, used after radiation exposure. To date, there are no FDA-approved radioprotectors for ARS.

Combined immunomodulator and antimicrobial therapy eliminates polymicrobial sepsis and modulates cytokine production in combined injured mice.

Purpose: A combination therapy for combined injury (CI) using a non-specific immunomodulator, synthetic trehalose dicorynomycolate and monophosphoryl lipid A (STDCM-MPL), was evaluated to augment oral antimicrobial agents, levofloxacin (LVX) and amoxicillin (AMX), to eliminate endogenous sepsis and modulate cytokine production. Materials and methods: Female B6D2F1/J mice received 9.75 Gy cobalt-60 gamma-radiation and wound. Bacteria were isolated and identified in three tissues. Incidence of bacteria and cytokines were compared between treatment groups. Results: Results demonstrated that the lethal dose for 50% at 30 days (LD50/30) of B6D2F1/J mice was 9.42 Gy. Antimicrobial therapy increased survival in radiation-injured (RI) mice. Combination therapy increased survival after RI and extended survival time but did not increase survival after CI. Sepsis began five days earlier in CI mice than RI mice with Gram-negative species predominating early and Gram-positive species increasing later. LVX plus AMX eliminated sepsis in CI and RI mice. STDCM-MPL eliminated Gram-positive bacteria in CI and most RI mice but not Gram-negative. Treatments significantly modulated 12 cytokines tested, which pertain to wound healing or elimination of infection. Conclusions: Combination therapy eliminates infection and prolongs survival time but does not assure CI mouse survival, suggesting that additional treatment for proliferative-cell recovery is required.