Models for Evaluating Agents Intended for the Prophylaxis, Mitigation and Treatment of Radiation Injuries Report of an NCI Workshop, December 3–4, 2003

Multiple parameter radiation injury assessment using a nonhuman primate radiation model-biodosimetry applications

There are urgent needs to establish capability to rapidly assess radiation injury in mass casualty and population monitoring scenarios. This study's objective was to evaluate several currently available biomarkers that can provide early diagnostic triage information after radiation exposure. Hematology and blood chemistry measurements were performed on samples derived from a nonhuman primate (Macaca mulatta; n = 8) total-body irradiation (TBI) model (6.5-Gy Co gamma rays at 0.6 Gy min). The results from this study demonstrate: a) time course for changes in C-reactive protein (CRP) (-2 d to 15 d after TBI); b) time-dependent (-2 d, 1-4 d after TBI) changes in blood cell counts [i.e., lymphocytes decrease to 5-8% of pre-study levels at 1 to 4 d after TBI; ratio of neutrophil to lymphocytes increases by 44 +/- 18 (p = 0.016), 12 +/- 4 (p = 0.001), 8 +/- 2 (p = 0.0020), and 5.0 +/- 2 (p = 0.002) fold at 1, 2, 3, and 4 days after TBI, respectively]; and c) 4.5 +/- 0.8 (p = 0.002)-fold increases in serum amylase activity 1 d after TBI. Plasma CRP levels at 1 d after exposure were 22 +/- 13 (p = 0.0005) (females) and 44 +/- 11 (p = 0.0004) (males)-fold elevated above baseline levels. One hundred percent successful separation of samples from exposed macaques (24 h after TBI) vs. samples from the same macaque taken before irradiation using a discriminant analysis based on four biomarkers (i.e., lymphocytes, neutrophils, ratio of neutrophils to lymphocytes, and serum amylase activity) was demonstrated. These results demonstrate the practical use of multiple parameter biomarkers to enhance the discrimination of exposed vs. non-exposed individuals and justify a follow-on rhesus macaque dose-response study.

Can the therapeutic gain of radiotherapy be increased by concurrent administration of Asian botanicals?

Therapeutic gain by radiotherapy can be achieved through improved targeting, selectively sensitizing malignant cells, or protecting normal tissue. The majority of synthetic chemical radiation sensitizers and normal tissue protectors have proved to be too toxic at effective clinical doses. However, Asian botanicals (from both Chinese and Ayurvedic medicine) are being evaluated for their ability to improve therapeutic gain through the modulation of reactive oxygen species. An increase in the efficacy of radiotherapy on tumor tissue allows a reduction in the dose applied to normal tissues. In addition, some botanicals may selectively protect normal tissue or increase its repair following radiation therapy. The results are promising enough to consider clinical trials.

COX-2 inhibitors are contraindicated for treatment of combined injury

Casualties of radiation dispersal devices, nuclear detonation or major ionizing radiation accidents, in addition to radiation exposure, may sustain physical and/or thermal trauma. Radiation exposure plus additional tissue trauma is known as combined injury. There are no definitive therapeutic agents. Cyclooxygenase-2 (COX-2), an inducible enzyme expressed in pathological disorders and radiation injury, plays an important role in inflammation and the production of cytokines and prostaglandin E(2) (PGE(2)) and could therefore affect the outcome for victims of combined injury. The COX-2 inhibitors celecoxib and meloxicam were evaluated for their therapeutic value against combined injury in mice. In survival studies, the COX-2 inhibitors had no beneficial effect on 30-day survival, wound healing or body weight gain after radiation injury alone or after combined injury. Meloxicam accelerated death in both wounded and combined injury mice. These drugs also induced severe hepatic toxicity, exaggerated inflammatory processes, and did not enhance hematopoietic cell regeneration. This study points to potential contraindications for use of COX-2 inhibitors in patients undergoing therapy for radiation injury and combined injury.

Renin-Angiotensin system suppression mitigates experimental radiation pneumonitis

PURPOSE

To find the mitigators of pneumonitis induced by moderate doses of thoracic radiation (10-15 Gy).

METHODS AND MATERIALS

Unanesthetized WAG/RijCmcr female rats received a single dose of X-irradiation (10, 12, or 15 Gy at 1.615 Gy/min) to the thorax. Captopril (an angiotensin-converting enzyme inhibitor) or losartan (an angiotensin receptor blocker) was administered in the drinking water after irradiation. Pulmonary structure and function were assessed after 8 weeks in randomly selected rats by evaluating the breathing rate, ex vivo vascular reactivity, and histopathologic findings. Survival analysis was undertaken on all animals, except those scheduled for death.

RESULTS

Survival after a dose of 10 Gy to the thorax was not different from that of unirradiated rats for <or=1 year. Survival decreased to <50% by 45 weeks after 12 Gy and by 8-9 weeks after 15 Gy. Captopril (17-56 mg/kg/d) improved survival and reduced radiation-induced increases in breathing rate, changes in vascular reactivity, and histopathologic evidence of injury. Radiation-induced increases in the breathing rate were prevented even if captopril was started 1 week after irradiation or if it was discontinued after 5 weeks. Losartan, although effective in reducing mortality, was not as efficacious as captopril in mitigating radiation-induced increases in the breathing rate or altered vasoreactivity.

CONCLUSION

In rats, a moderate thoracic radiation dose induced pneumonitis and morbidity. These injuries were mitigated by captopril even when it was begun 1 week after radiation or if discontinued 5 weeks after exposure. Losartan was less effective in protecting against radiation-induced changes in vascular reactivity or tachypnea.

Radiation nephropathy is not mitigated by antagonists of oxidative stress

Abstract Persistent, chronic oxidative injury may play a mechanistic role in late radiation injury. Thus antioxidants may be useful as mitigators of radiation injury. The antioxidants deferiprone, genistein and apocynin were tested in a rat radiation nephropathy model that uses single-fraction total-body irradiation (TBI) followed by syngeneic bone marrow transplant. Deferiprone was added to the drinking water at 1.0 or 2.5 g/liter, starting 3 days after the TBI. Urinary bleomycin-detectable iron, which could enhance production of oxygen radicals, was reduced in the rats on deferiprone compared to untreated rats, but deferiprone did not mitigate radiation nephropathy. Genistein added to the chow at 750 mg/kg starting immediately after TBI did not mitigate radiation nephropathy. Apocynin added to the drinking water at 250 mg/liter immediately after TBI did not mitigate radiation nephropathy. Thus three different types of antioxidants, when used at doses consistent with an antioxidant effect, had no mitigation efficacy against radiation nephropathy.

Nuclear factor kappaB inhibitors alleviate and the proteasome inhibitor PS-341 exacerbates radiation toxicity in zebrafish embryos

Inflammatory changes are a major component of the normal tissue response to ionizing radiation, and increased nuclear factor kappaB (NF-kappaB) activity is an important mediator of inflammatory responses. Here, we used zebrafish embryos to assess the capacity of two different classes of pharmacologic agents known to target NF-kappaB to modify radiation toxicity in the vertebrate organism. These were proteasome inhibitors, including lactacystin, MG132, and PS-341 (Bortezomib/VELCADE), and direct inhibitors of NF-kappaB activity, including ethyl pyruvate (EP) and the synthetic triterpenoid CDDO-TFEA (RTA401), among others. The proteasome inhibitors either did not significantly affect radiation sensitivity of zebrafish embryos (MG132, lactacystin) or rendered zebrafish embryos more sensitive to the lethal effects of ionizing radiation (PS-341). Radiosensitization by PS-341 was reduced in fish with impaired p53 expression or function but not associated with enhanced expression of select p53 target genes. In contrast, the direct NF-kappaB inhibitors EP and CDDO-TFEA significantly improved overall survival of lethally irradiated zebrafish embryos. In addition, direct NF-kappaB inhibition reduced radiation-induced apoptosis in the central nervous system, abrogated aberrations in body axis development, restored metabolization and secretion of a reporter lipid through the gastrointestinal system, and improved renal clearance compromised by radiation. In contrast to amifostine, EP and CDDO-TFEA not only protected against but also mitigated radiation toxicity when given 1 to 2 hours postexposure. Finally, four additional IkappaB kinase inhibitors with distinct mechanisms of action similarly improved overall survival of lethally irradiated zebrafish embryos. In conclusion, inhibitors of canonical pathways to NF-kappaB activation may be useful in alleviating radiation toxicity in patients.

Protection of mice against X-ray injuries by the post-irradiation administration of guanosine and inosine

PURPOSE

To examine the radioprotective action of guanosine (Guo) and inosine (Ino) administered to mice after irradiation with X-rays.

MATERIALS AND METHODS

Survival of mice exposed to lethal and sublethal doses of X-rays was studied. Peripheral blood cells were counted using a light microscope. The damage to bone marrow cells was assessed by micronucleus (MN) test. Damage and repair of DNA in blood leukocytes were estimated using the comet assay.

RESULTS

Mice injected intraperitoneally (i.p.) with Guo or Ino ( approximately 30 microg g(-1), i.e., approximately 0.6 mg per 20-g mouse) 15 min after acute whole-body irradiation with 7 Gy recovered from X-ray injury. On the 30th day after irradiation, 50 and 40% of mice injected with Guo and Ino, respectively, remained alive. The dose reduction factor (DRF) was 1.23 for Guo and 1.15 for Ino. The protective effect gradually decreased as the time interval between the irradiation and injection was increased to 3, 5, 8 h. Guo and Ino facilitated the restoration of peripheral blood cell counts. These compounds protected bone marrow cells from damage and normalized erythropoiesis. Guo and Ino contributed to a more rapid and complete repair of DNA in mouse leukocytes irradiated both in vitro and in vivo.

CONCLUSION

Guo and Ino introduced shortly after irradiation reduce leukopenia and thrombocytopenia and offer promise as therapeutic agents for treatment of radiation injuries.

High-dose selenium for the mitigation of radiation injury: a pilot study in a rat model

The purpose of this study was to evaluate in an animal model the safety and efficacy of dietary supplementation with high doses of selenium for the mitigation of the type of radiation injury that might be sustained during a nuclear accident or an act of radiological terrorism. Age-matched male rats were exposed to 10 Gy (single dose) of total-body irradiation (TBI) followed by a syngeneic bone marrow transplant, then randomized to standard drinking water or drinking water supplemented with sodium selenite or seleno-l-methionine. At 21 weeks after TBI, most rats on standard drinking water had severe renal failure with a mean blood urea nitrogen (BUN) level of 124 +/- 29 mg/dl (geometric mean +/- SE) whereas rats on selenium-supplemented drinking water (100 microg/day) had a mean BUN level of 67 +/- 12 mg/dl. The mitigating effect of selenium was confirmed by histopathological analyses. None of the animals on high-dose selenium showed signs of selenium toxicity. Our results suggest that dietary supplementation with high-dose selenium may provide a safe, effective and practical way to mitigate radiation injury to kidneys.

L-Arginine reverses radiation-induced immune dysfunction: the need for optimum treatment window

The aim of the present study was to investigate the protective efficacy of l-arginine in mitigating the injury induced by 2 Gy of total-body gamma radiation (TBI). Mice exposed to radiation (TBI group) had significantly decreased spleen weight, splenocyte numbers and bone marrow cellularity. Administration of l-arginine 2 h after TBI (TBI + l-arginine group) was effective in reducing the radiation-induced depletion of spleen and bone marrow cellularity but was not effective when administered before TBI (l-arginine + TBI group). The radiation-induced decrease in Con A-induced spleen cell proliferation, specific antibody response of spleen B cells to sheep red blood cells, and spleen RNA content was reversed in mice in the TBI + l-arginine group. The radiation-induced increase in serum TNF-alpha levels, serum nitrate/nitrite (NOx) levels, spleen DNA fragmentation, spleen nitric oxide synthase (NOS) activity, spleen inducible NOS (iNOS) activity, and hepatic iNOS activity was reversed in mice in the TBI + l-arginine group. l-Arginine administered before TBI could not reverse these changes. Mice in the TBI + l-arginine group had significantly increased spleen arginase activity compared to mice from either the TBI or l-arginine + TBI group. The results suggest the importance of the time of administration of l-arginine and the l-arginine pathway in mitigating the radiation-induced host immune dysfunction.

American Ginseng Modifies Cs-Induced DNA Damage and Oxidative Stress in Human Lymphocytes

The multifold bioactive medicinal properties of ginseng have been closely linked to its antioxidative ability, which is related to its ginsenoside content. Since the key mechanism of radiation-induced cell death and tissue damage is the generation of reactive oxygen species (ROS) that attack cellular DNA, this study focuses on the impact of a standardized North American ginseng extract (NAGE) on (137)Cs-induced oxidative stress in human peripheral lymphocytes (PBL) obtained from 10 healthy individuals (6M/4F), 42.7 +/- 4.6 years of age. At two different time points (0 h and 24 h before irradiation), we applied NAGE (250 - 1000 microg ml(-1)) to mononuclear cell cultures for cytokinesis-block micronuclei (MN) assay and determination of the state of oxidative stress in PBL. We found that at both time points, NAGE significantly reduced the MN yields in PBL after irradiation (1 and 2 Gy) in a concentration-dependent manner (P<0.001). Compared with radiation alone, the maximum reduction rate of MN yield were 51.1% and 49.1% after 1 Gy and 2 Gy exposures, respectively. We also found that before irradiation the presence of NAGE in the culture medium resulted in a significant increased intracellular total antioxidant capacity (TAC) in PBL. At both time points, the increment of (137)Cs-induced MN yields in PBL was positively correlated with the increment of intracellular ROS production (R = 0.6 - 0.7, P = 0.002), but negatively correlated with the reduction of TAC levels (R = -0.4 -0.5, P = 0.02 - 0.004). However, the presence of NAGE in the culture medium significantly increased the TAC levels, while concomitantly decreasing both ROS production and MN yields in PBL (P<0.001). Our findings that NAGE is effective in protecting human PBL against radiation-induced oxidative stress should encourage further in vivo study of dietary supplementation with NAGE as an effective natural radiation countermeasure.

Effect of North American ginseng on 137Cs-induced micronuclei in human lymphocytes: a comparison with WR-1065

To explore the radioprotective effect of a standardized North American ginseng extract (NAGE) on human peripheral blood lymphocytes (PBL), a micronuclei (MN) assay was conducted in PBL obtained from 12 volunteers. NAGE (50-1000 microg/mL) and WR-1065 (1 mM and 3 mM) were applied to PBL cultures at 0 h and 90 min post-irradiation. It was found that (1) the baseline MN yield of PBL ranged from 14.4 +/- 1.5 to 15.9 +/- 1.5 per 1000 binucleated cells (p > 0.05); after irradiation (1 Gy and 2 Gy), the MN yield increased sharply; (2) MN yields declined with increasing concentrations of NAGE and WR-1065. Even at 90 min post-irradiation of 1 Gy, the maximum level of MN reduction rate caused by NAGE and WR-1065 was 53.8% and 59.2%, respectively; after 2 Gy irradiation, it was 37.3% and 42%, respectively; (3) the MN distribution in PBL followed a non-Poisson distribution in all cases; and (4) both NAGE and WR-1065 showed no significant effect on the proliferation index of lymphocytes. The results indicate that NAGE is a relatively non-toxic natural product, which can be administered as a dietary supplement and has the potential to be a radiation countermeasure.

Modulation of radiation-induced life shortening by systemic intravenous MnSOD-plasmid liposome gene therapy

To determine whether systemic administration of MnSOD-PL protected mice from the acute hematopoietic syndrome and delayed death after total-body irradiation (TBI), C57BL/ 6J mice were injected intravenously with 100 microl liposomes containing 100 microg of human MnSOD-transgene plasmid 24 h prior to irradiation with 9.5 Gy or 1.0 Gy. The dose of 9.5 Gy was lethal to 42% of irradiated control female mice and 74% of irradiated control male mice at 30 days, with bone marrow hypocellularity consistent with the hematopoietic syndrome. A statistically significant increase in survival was observed in MnSOD-PL-treated female mice out to 400 days and in male mice out to 340 days. The incidence of tumors was similar between surviving groups. Between 350 and 600 days, the outcome was similar for both MnSOD-PL-treated and control irradiated groups, consistent with aging, with no difference in gross or microscopic pathological evidence of tumors. Male and female mice receiving 1.0 Gy TBI showed radiation-induced life shortening after 120 days that was decreased by MnSOD-PL administration and that was not associated with an increase in rate of tumor-associated death. Therefore, systemic MnSOD-PL radioprotective gene therapy is not associated with a detectably higher incidence of late carcinogenesis.

Epstein-Barr virus infection and plasma transforming growth factor-beta1 levels in head and neck cancers

CONCLUSIONS

In addition to the correlation of transforming growth factor (TGF)-beta1 levels to the radiation toxicity, both Epstein-Barr virus (EBV) infection and postoperative status play roles in the change in plasma TGF-beta1 levels in patients with head and neck cancers.

OBJECTIVES

To assess the parameters involved in the change in plasma TGF-beta1 level during concurrent chemoradiotherapy (CCRT).

PATIENTS AND METHODS

Blood samples (n=307) before, during, and after treatment were obtained from 39 patients with head and neck cancers treated with definitive or adjuvant CCRT. In situ hybridization (ISH) was used to identify EBV-encoded RNA (EBER) in tissues from the primary tumor or metastatic lymph nodes. Plasma TGF-beta1 level, white blood cell (WBC), and platelet count were assayed immediately before the first fraction of radiotherapy (RT), once a week during RT, and at the end of the RT course. The grades of mucositis and dermatitis were recorded weekly during CCRT.

RESULTS

Pretreatment TGF-beta1 level and radiation toxicity were found to be significantly correlated with the increase of the plasma TGF-beta1 level during CCRT (p<0.05), but correlation of platelet count was only found in patients whose tumors were EBV-positive (p=0.0042), and WBC count in those treated with postoperative adjuvant CCRT (p=0.004).

Molecular markers of radiation-related normal tissue toxicity

Over the past five decades, those interested in markers of radiation effect have focused primarily on tumor response. More recently, however, the view has broadened to include irradiated normal tissues-markers that predict unusual risk of side-effects, prognosticate during the prodromal and therapeutic phases, diagnose a particular toxicity as radiation-related, and, in the case of bioterror, allow for tissue-specific biodosimetry. Currently, there are few clinically useful radiation-related biomarkers. Notably, levels of some hormones such as thyroid-stimulating hormone (TSH) have been used successfully as markers of dysfunction, indicative of the need for replacement therapy, and for prevention of cancers. The most promising macromolecular markers are cytokines: TGFbeta, IL-1, IL-6, and TNFalpha being lead molecules in this class as both markers and targets for therapy. Genomics and proteomics are still in nascent stages and are actively being studied and developed.

Radioprotection in vitro and in vivo by minicircle plasmid carrying the human manganese superoxide dismutase transgene

Manganese superoxide dismutase plasmid liposomes (MnSOD-PL) confer organ-specific in vivo ionizing irradiation protection. To prepare for potential intravenous clinical trials of systemic MnSOD-PL for radioprotection in humans, plasmid and bacterial sequences were removed and a new minicircle construct was tested. Minicircle MnSOD was purified and then cotransfected into 32D cl 3 murine interleukin-3-dependent hematopoietic progenitor cells along with another plasmid carrying the neo gene. Cells were selected in G418 (50 microg/ml) and cloned by limiting dilution. Biochemical analysis of minicircle MnSOD-transfected cells showed an MnSOD biochemical activity level of 5.8 +/- 0.5 U/mg compared with 2.7 +/- 0.1 U/mg for control 32D cl 3 cells (p = 0.0039). 32D-mc-MnSOD cells were as radioresistant as full-length MnSOD-PL transgene-expressing 2C6 cells, relative to 32D cl 3 parent cells, with an increased shoulder on the radiation survival curve (n = 4.8 +/- 0.2 and n = 4.6 +/- 0.2, respectively, compared with 1.5 +/- 0.5 for 32D cl 3 cells; p = 0.007). C57BL/6NHsd mice received intraoral mc-MnSOD-PL, mc-DsRed-PL control, full-length MnSOD-PL, or blank-PL and then were irradiated 24 hr later with 31 Gy to the esophagus. Mice receiving mc-MnSOD-PL showed increased survival compared with control mice or mice treated with mc-DsRed-PL (p = 0.0003 and 0.039, respectively), and comparable to full-length MnSOD-PL. Intravenous, systemic administration of mc-MnSOD-PL protected mice from total body irradiation (9.75 Gy). Therefore, minicircle DNA containing the human MnSOD transgene confers undiminished radioprotection in vitro and in vivo.

Genistein protects against biomarkers of delayed lung sequelae in mice surviving high-dose total body irradiation

The effects of genistein on 30-day survival and delayed lung injury were examined in C57BL/6J female mice. A single subcutaneous injection of vehicle (PEG-400) or genistein (200 mg/kg) was administered 24 h before total body irradiation (7.75 Gy (60)Co, 0.6 Gy/min). Experimental groups were: No treatment + Sham (NC), Vehicle + Sham (VC), Genistein + Sham (GC), Radiation only (NR), Vehicle + Radiation (VR), Genistein + Radiation (GR). Thirty-day survivals after 7.75 Gy were: NR 23%, VR 53%, and GR 92%, indicating significant protection from acute radiation injury by genistein. Genistein also mitigated radiation-induced weight loss on days 13-28 postirradiation. First generation lung fibroblasts were analyzed for micronuclei 24 h postirradiation. Fibroblasts from the lungs of GR-treated mice had significantly reduced micronuclei compared with NR mice. Collagen deposition was examined by histochemical staining. At 90 days postirradiation one half of the untreated and vehicle irradiated mice had focal distributions of small collagen-rich plaques in the lungs, whereas all of the genistein-treated animals had morphologically normal lungs. Radiation reduced the expression of COX-2, transforming growth factor-beta receptor (TGFbetaR) I and II at 90 days after irradiation. Genistein prevented the reduction in TGFbetaRI. However, by 180 days postirradiation, these proteins normalized in all groups. These results demonstrate that genistein protects against acute radiation-induced mortality in female mice and that GR-treated mice have reduced lung damage compared to NR or VR. These data suggest that genistein is protective against a range of radiation injuries.

Hippocampal neuron number is unchanged 1 year after fractionated whole-brain irradiation at middle age

PURPOSE

To determine whether hippocampal neurons are lost 12 months after middle-aged rats received a fractionated course of whole-brain irradiation (WBI) that is expected to be biologically equivalent to the regimens used clinically in the treatment of brain tumors.

METHODS AND MATERIALS

Twelve-month-old Fischer 344 X Brown Norway male rats were divided into WBI and control (CON) groups (n = 6 per group). Anesthetized WBI rats received 45 Gy of (137)Cs gamma rays delivered as 9 5-Gy fractions twice per week for 4.5 weeks. Control rats were anesthetized but not irradiated. Twelve months after WBI completion, all rats were anesthetized and perfused with paraformaldehyde, and hippocampal sections were immunostained with the neuron-specific antibody NeuN. Using unbiased stereology, total neuron number and the volume of the neuronal and neuropil layers were determined in the dentate gyrus, CA3, and CA1 subregions of hippocampus.

RESULTS

No differences in tissue integrity or neuron distribution were observed between the WBI and CON groups. Moreover, quantitative analysis demonstrated that neither total neuron number nor the volume of neuronal or neuropil layers differed between the two groups for any subregion.

CONCLUSIONS

Impairment on a hippocampal-dependent learning and memory test occurs 1 year after fractionated WBI at middle age. The same WBI regimen, however, does not lead to a loss of neurons or a reduction in the volume of hippocampus.

Dietary antioxidants protect hematopoietic cells and improve animal survival after total-body irradiation

The purpose of this study was to determine whether a dietary supplement consisting of L-selenomethionine, vitamin C, vitamin E succinate, alpha-lipoic acid and N-acetyl cysteine could improve the survival of mice after total-body irradiation. Antioxidants significantly increased the 30-day survival of mice after exposure to a potentially lethal dose of X rays when given prior to or after animal irradiation. Pretreatment of animals with antioxidants resulted in significantly higher total white blood cell and neutrophil counts in peripheral blood at 4 and 24 h after 1 Gy and 8 Gy. Antioxidants were effective in preventing peripheral lymphopenia only after low-dose irradiation. Antioxidant supplementation was also associated with increased bone marrow cell counts after irradiation. Supplementation with antioxidants was associated with increased Bcl2 and decreased Bax, caspase 9 and TGF-beta1 mRNA expression in the bone marrow after irradiation. Maintenance of the antioxidant diet was associated with improved recovery of the bone marrow after sublethal or potentially lethal irradiation. Taken together, oral supplementation with antioxidants appears to be an effective approach for radioprotection of hematopoietic cells and improvement of animal survival, and modulation of apoptosis is implicated as a mechanism for the radioprotection of the hematopoietic system by antioxidants.

Medical response to a radiologic/nuclear event: integrated plan from the Office of the Assistant Secretary for Preparedness and Response, Department of Health and Human Services

The end of the Cold War led to a reduced concern for a major nuclear event. However, the current threats from terrorism make a radiologic (dispersal or use of radioactive material) or nuclear (improvised nuclear device) event a possibility. The specter and enormousness of the catastrophe resulting from a state-sponsored nuclear attack and a sense of nihilism about the effectiveness of a response were such that there had been limited civilian medical response planning. Although the consequences of a radiologic dispersal device are substantial, and the detonation of a modest-sized (10 kiloton) improvised nuclear device is catastrophic, it is both possible and imperative that a medical response be planned. To meet this need, the Office of the Assistant Secretary for Preparedness and Response in the Department of Health and Human Services, in collaboration within government and with nongovernment partners, has developed a scientifically based comprehensive planning framework and Web-based "just-in-time" medical response information called Radiation Event Medical Management (available at http://www.remm.nlm.gov). The response plan includes (1) underpinnings from basic radiation biology, (2) tailored medical responses, (3) delivery of medical countermeasures for postevent mitigation and treatment, (4) referral to expert centers for acute treatment, and (5) long-term follow-up. Although continuing to evolve and increase in scope and capacity, current response planning is sufficiently mature that planners and responders should be aware of the basic premises, tools, and resources available. An effective response will require coordination, communication, and cooperation at an unprecedented level. The logic behind and components of this response are presented to allow for active collaboration among emergency planners and responders and federal, state, local, and tribal governments.

Differential Radiation Effect in Tumor and Normal Tissue after Treatment with Ramipril, an Angiotensin-Converting Enzyme Inhibitor

The angiotensin-converting enzyme inhibitor, ramipril, has been shown to mitigate radiation injury in normal tissues. Using A549 cell xenografts grown in athymic mice, we measured the effect of ramipril on radiation damage to tumors. Ramipril did not alter tumor response to radiation despite different times of drug administration with respect to radiation delivery (drug started 2 weeks before or immediately after irradiation). In contrast, using the same dose, ramipril reduced normal tissue radiation injury (30 Gy x 2 or 6 Gy x 10) as assessed by a semi-quantitative scale of skin damage and relative leg contraction. The results indicate that ramipril could offer therapeutic gain due to its different effect on normal tissues and tumors.

Radiation effects on neural precursor cells in the dentate gyrus

Ionizing irradiation is an effective treatment for intracranial tumors but is limited by the potential adverse effects induced in surrounding normal brain. These effects can include cognitive impairments, and whereas the pathogenesis of such injury has not yet been definitively established, it may involve injury to the neurogenic cell population that exists in the dentate subgranular zone (SGZ) of the hippocampus. Understanding the issues surrounding this topic could have a major impact in the management of specific sequelae associated with cranial irradiation. Although radiation is now becoming a useful tool in investigations into the biology of neurogenesis, the perspective of this review is directed more toward the potential relevance of studying radiation and the stem/precursor cell response.

Modulation of gamma-ray-induced apoptosis in human peripheral blood leukocytes by famotidine and vitamin C

To study the radioprotective effects of vitamin C and famotidine against radiation-induced apoptosis in human peripheral blood leukocytes, peripheral blood was obtained from six healthy volunteers including three males and three females. Twelve microlitres of blood sample diluted in 1 ml complete RPMI-1640 medium was irradiated with various doses of gamma-rays (4, 8 and 12 Gy) in the presence or absence of various doses of vitamin C and famotidine. After 48 and 72 h incubation in a 37 degrees C CO(2) incubator, neutral comet assay was performed for all samples. At least 1000 cells were analyzed for each sample for presence of apoptosis. Data were statistically evaluated using Mann-Whitney non-parametric and ANOVA tests. Results show a significant increase in apoptosis induction following gamma-irradiation with a dose dependent manner compared to controls (p<0.001). Presence of famotidine at 200 microg/ml produced a significant protective effect against radiation-induced apoptosis for various doses of radiation. Similar effects were observed for vitamin C at much lower doses (10 microg/ml). Dose reduction factor (DRF) calculated for famotidine treatment was about 1.5, and above 2 for vitamin C treatment. These results suggest that both vitamin C and famotidine suppresses radiation-induced apoptosis when used with various doses of gamma-irradiation (4-12 Gy) probably via *OH radical scavenging and an intracellular antioxidation mechanism.

Role of the angiotensin II type-2 receptor in radiation nephropathy

Experimental studies have shown that blockade of the angiotensin II type-1 (AT(1)) receptor is effective in the mitigation and treatment of radiation-induced chronic renal failure. Also, blockade of the angiotensin II type-2 (AT(2)) receptor with PD-123319 also had a modest, but reproducible, beneficial effect in experimental radiation nephropathy, and it might augment the efficacy of an AT(1) blocker (L-158,809). Those studies could not exclude the possibility that the effects of AT(2) blockade were nonspecific. The current studies confirm the efficacy of AT(2) blockade for mitigation of experimental radiation nephropathy but paradoxically find no detectable level of AT(2) receptor binding in renal membranes. However, the results of a bioassay showed that the circulating levels of the AT(2) blocker were orders-of-magnitude too low to block AT(1) receptors. The effect of AT(2) blockade in radiation nephropathy cannot be explained by binding to the AT(1) receptor, and the efficacy of the AT(1) blockade in the same model cannot be explained by unopposed overstimulation of the AT(2) receptor.

Subcutaneous administration of genistein prior to lethal irradiation supports multilineage, hematopoietic progenitor cell recovery and survival

PURPOSE

Genistein, a non-toxic isoflavone from soybeans, has immunomodulating and radioprotective properties. In this study we investigated the mechanism for genistein-induced radioprotection by evaluating the recovery of bone marrow cells and peripheral blood hematology in lethally irradiated mice.

MATERIALS AND METHODS

CD2F1 male mice received a single subcutaneous injection of genistein (200 mg/kg) 24 h prior to a lethal, total body irradiation dose (8.75 Gy) of cobalt-60 gamma radiation. Survival and hematopoietic reconstitution were evaluated over nine weeks post-irradiation. Hematopoietic progenitor colony-forming cell assays were used to assess the reconstitution of bone marrow after radiation-induced myelosuppression.

RESULTS

A total of 97% of genistein-treated mice survived after 30 days while 31% of vehicle-treated and 0% of untreated mice survived. The improvement in survival was related to accelerated neutrophil and platelet recovery, resulting from earlier and more pronounced multilineage, hematopoietic progenitor cell reconstitution in the femoral marrow compartment. Myeloid and erythroid progenitor cell numbers at day 15 post-irradiation were 6-fold to 20-fold higher in genistein-treated animals than in control animals.

CONCLUSIONS

These results demonstrate that a single subcutaneous administration of genistein 24 h before irradiation provides significant radioprotection to the hematopoietic progenitor cell compartment.

Future strategies for mitigation and treatment of chronic radiation-induced normal tissue injury

Until the mid-1990s, radiation-induced normal-tissue injury was generally assumed to be solely caused by the delayed mitotic death of parenchymal or vascular cells, and these injuries were held to be progressive and untreatable. From this assumption, it followed that postirradiation interventions would be unlikely to reduce either the incidence or the severity of radiation-induced normal tissue injury. It is now clear that parenchymal and vascular cells are active participants in the response to radiation injury, an observation that allows for the possibility of pharmacologic mitigation and/or treatment of these injuries. Mitigation or treatment of chronic radiation injuries has now been experimentally shown in multiple organ systems (eg, lung, kidney, and brain), with different pharmacologic agents (eg, angiotensin-converting enzyme inhibitors, pentoxifylline, and superoxide dismutase mimetics) and with seemingly different mechanisms (eg, suppression of the renin-angiotensin system and suppression of chronic oxidative stress). Unfortunately, the mechanistic basis for most of the experimental successes has not been established, and assessment of the utility of these agents for clinical use has been slow. Clinical development of pharmacologic approaches to mitigation or treatment of chronic radiation injuries could lead to significant improvement in survival and quality of life for radiotherapy patients and for victims of radiation accidents or nuclear terrorism.

Spatial Learning and Memory Deficits after Whole-Brain Irradiation are Associated with Changes in NMDA Receptor Subunits in the Hippocampus

Whole-brain irradiation is used for the treatment of brain tumors, but can it also induce neural changes, with progressive dementia occurring in 20-50% of long-term survivors. The present study investigated whether 45 Gy of whole-brain irradiation delivered to 12-month-old Fischer 344 x Brown Norway rats as nine fractions over 4.5 weeks leads to impaired Morris water maze (MWM) performance 12 months later. Compared to sham-irradiated rats, the irradiated rats demonstrated impaired MWM performance. The relative levels of the NR1 and NR2A but not the NR2B subunits of the NMDA receptor were significantly higher in hippocampal CA1 of irradiated rats compared to control rats. No significant differences were detected for these NMDA subunits in CA3 or dentate gyrus. Further analysis of CA1 revealed that the relative levels of the GluR1 and GluR2 subunits of the AMPA receptor and synaptophysin were not altered by whole-brain irradiation. In summary, a clinically relevant regimen of fractionated whole-brain irradiation led to significant impairments in spatial learning and reference memory and alterations in the relative levels of subunits of the NMDA, but not the AMPA, receptors in hippocampal CA1. These findings suggest for the first time that radiation-induced cognitive impairments may be associated with alterations in glutamate receptor composition.

Antitransforming growth factor-beta antibody 1D11 ameliorates normal tissue damage caused by high-dose radiation

PURPOSE

The aim of this study was to determine whether a neutralizing transforming growth factor-beta (TGFbeta) antibody can prevent radiation (RT) induced lung injury.

METHODS AND MATERIALS

Fractionated and sham right lung irradiation in Fischer 344 rats was delivered to assess the radioprotective effect of the antibodies. Animals were divided into the following groups: (1) control (sham RT, control antibody 13C4); (2) RT (800cGy x 5)+13C4); (3) RT + 0.1 mg/kg 1D11 anti-TGFbeta antibody; and (4) RT + 1 mg/kg 1D11 antibody. Antibodies were intraperitoneally administered immediately after the last fraction of RT. Animals were sacrificed at 6 and 26 weeks after irradiation. Lungs were assessed for histologic changes, activation of macrophages, expression/activation of TGFbeta and its signal transduction pathway.

RESULTS

At 6 weeks post-RT, there was a significant reduction in macrophage accumulation (p = 0.041), alveolar wall thickness (p = 0.0003), and TGF-beta activation (p = 0.032) in animals receiving 1.0 mg/kg 1D11 vs. in the control group. However, at 6 weeks, the low dose of 1D11 antibody (0.1 mg/kg) failed to produce any significant changes. At 6 months post-RT, radioprotection is apparent for the group receiving 1.0 mg/kg 1D11, with activated macrophages (p = 0.037), alveolar wall thickness (p = 0.0002), TGFbeta activation (p = 0.002) and its signal transduction proteins (p < 0.05) compared with the control group.

CONCLUSIONS

Administration of a single dose of 1.0 mg/kg of the anti-TGFbeta antibody 1D11 resulted in decreased morphologic changes, inflammatory response, and reduced expression and activation of TGFbeta 6 weeks and 6 months after 40 Gy to the right hemithorax. Targeting the TGFbeta pathway may be a useful strategy to prevent radiation-induced lung injury.

Adverse event reporting and developments in radiation biology after normal tissue injury: International Atomic Energy Agency consultation

PURPOSE

Recent research has enhanced our understanding of radiation injury at the molecular-cellular and tissue levels; significant strides have occurred in standardization of adverse event reporting in clinical trials. In response, the International Atomic Energy Agency, through its Division of Human Health and its section for Applied Radiation Biology and Radiotherapy, organized a consultation meeting in Atlanta (October 2, 2004) to discuss developments in radiobiology, normal tissue reactions, and adverse event reporting.

METHODS AND MATERIALS

Representatives from cooperative groups of African Radiation Oncology Group, Curriculo Radioterapeutica Ibero Latino Americana, European Organization for Research and Treatment of Cancer, National Cancer Institute of Canada Clinical Trials Group, Radiation Therapy Oncology Group, and Trans-Tasman Radiation Oncology Group held the meeting discussion.

RESULTS

Representatives of major radiotherapy groups/organizations and prominent leaders in radiotherapy discussed current understanding of normal tissue radiobiologic effects, the design and implementation of future clinical and translational projects for normal tissue injury, and the standardization of adverse-event reporting worldwide.

CONCLUSIONS

The consensus was to adopt NCI comprehensive adverse event reporting terminology and grading system (CTCAE v3.0) as the new standard for all cooperative group trials. Future plans included the implementation of coordinated research projects focusing on normal tissue biomarkers and data collection methods.

Radiation protectants: current status and future prospects

In today's heightened nuclear/biological/chemical threat environment, there is an increased need to have safe and effective means to protect not only special high-risk service groups, but also the general population at large, from the health hazards of unintended ionizing radiation exposures. An unfulfilled dream has been to have a globally effective pharmacologic that could be easily taken orally without any undue side effects prior to a suspected or impending nuclear/radiological event; such an ideal radioprotective agent has yet to be identified, let alone fully developed and approved for human use. No one would argue against the fact that this is problematic and needs to be corrected, but where might the ultimate solution to this difficult problem be found? Without question, representative species of the aminothiol family [e.g., Amifostine (MedImmune, Gaithersburg, Maryland)] have proven to be potent cytoprotectants for normal tissues subjected to irradiation or to radiomimetic chemicals. Although Amifostine is currently used clinically, drug toxicity, limited times of protection, and unfavorable routes of administration, all serve to limit the drug's utility in nonclinical settings. A full range of research and development strategies is being employed currently in the hunt for new safe and effective radioprotectants. These include: (1) large scale screening of new chemical classes or natural products; (2) restructuring/reformulating older protectants with proven efficacies but unwanted toxicities; (3) using nutraceuticals that are only moderately protective but are essentially nontoxic; (4) using low dose combinations of potentially toxic but efficacious agents that protect through different routes to foster radioprotective synergy; and (5) accepting a lower level of drug efficacy in lieu of reduced toxicity, banking on the premise that the protection afforded can be leveraged by post-exposure therapies. Although it is difficult to predict which of these strategies will ultimately prove to be successful, it is certain that the probability of a useful protectant being fielded is increased significantly. This is due to the resurgence of interest in radiation protection, increased resources being expended by federal agencies, and by the Food and Drug Administration's willingness to innovate relative to new approval guidance.

Non-small cell lung cancer therapy-related pulmonary toxicity: an update on radiation pneumonitis and fibrosis

Successful treatment of non-small cell lung cancer requires adequate local and systemic disease control. Although it has been shown to have superior results, high-dose radiation therapy is not a current practice largely because of concerns of normal tissue toxicity. This article reviews and updates the possible mechanism of radiation-induced pneumonitis and fibrosis, their associations with dose intensity, and the role they may play in making treatment decisions. The commonly used clinical terminology and grading systems are summarized. Pneumonitis and fibrosis after 3-dimensional conformal high-dose radiation are reviewed, including recent updates from radiation dose escalation trials. Chemotherapy- and chemoradiation-related lung toxicities are also discussed. Individual susceptibility and potential predictive models are examined; dose and 3-dimensional dosimetric parameters are reviewed along with estimation of normal tissue complication probability and biologic predictive assays. Based on the risk levels of toxicity for each patient, future clinical trials may be designed to maximize individual therapeutic gain.

Radioprotective potential of ginseng

A majority of potential radioprotective synthetic compounds have demonstrated limited clinical application owing to their inherent toxicity, and thus, the seeking of naturally occurring herbal products, such as ginseng, for their radioprotective capability has become an attractive alternative. In general, ginseng refers to the roots of the species of the genus Panax. As a medicinal herb, ginseng has been widely used in traditional Chinese medicine for its wide spectrum of medicinal effects, such as tonic, immunomodulatory, antimutagenic, adaptogenic and antiaging activities. Many of its medicinal effects are attributed to the triterpene glycosides known as ginsenosides (saponins). This review addresses the issue of the radioprotective effects of ginseng on mammalian cells both in vitro and in vivo. Results indicate that the water-soluble extract of whole ginseng appears to give a better protection against radiation-induced DNA damage than does the isolated ginsenoside fractions. Since free radicals play an important role in radiation-induced damage, the underlying radioprotective mechanism of ginseng could be linked, either directly or indirectly, to its antioxidative capability by the scavenging free radicals responsible for DNA damage. In addition, ginseng's radioprotective potential may also be related to its immunomodulating capabilities. Ginseng is a natural product with worldwide distribution, and in addition to its antitumor properties, ginseng appears to be a promising radioprotector for therapeutic or preventive protocols capable of attenuating the deleterious effects of radiation on human normal tissue, especially for cancer patients undergoing radiotherapy.

Priority list of research areas for radiological nuclear threat countermeasures

To help the nation prepare for the possibility of a terrorist attack using radiological and nuclear devices, the Office of Science and Technology Policy and the Homeland Security Council established an interagency working group. The working group deliberated on the research needs for radiological/ nuclear threat countermeasures and identified and prioritized 18 areas for further attention. The highest priorities were given to research on (1) radioprotectors for use prior to exposure; (2) therapeutic agents for postexposure treatment; (3) antimicrobial therapy for infections associated with radiation exposure; (4) cytokines and growth factors; (5) mechanisms of radiation injury at the molecular, cellular, tissue and organism levels; and (6) automation of biodosimetric assays. High priority was given to (1) developing biomarkers for biodosimetry; (2) enhancing training in the radiation sciences; (3) exploring the consequences of combined injury; (4) establishing a repository of information regarding investigational countermeasures; and (5) following the health of an exposed population to better prepare for subsequent events. The research areas that the committee felt required the attention of the radiation research community are described in this report in an effort to inform this community about the needs of the nation and to encourage researchers to address these critical issues.