From endotoxins to newer immunomodulators: survival-promoting effects of microbial polysaccharide complexes in irradiated animals

Chemical and biological basis for development of novel radioprotective drugs for cancer therapy

Ionizing radiation (IR) causes chemical changes in biological systems through direct interaction with the macromolecules or by causing radiolysis of water. This property of IR is harnessed in the clinic for radiotherapy in almost 50% of cancers patients. Despite the advent of stereotactic radiotherapy instruments and other advancements in shielding techniques, the inadvertent deposition of radiation dose in the surrounding normal tissue can cause late effects of radiation injury in normal tissues. Radioprotectors, which are chemical or biological agents, can reduce or mitigate these toxic side-effects of radiotherapy in cancer patients and also during radiation accidents. The desired characteristics of an ideal radioprotector include low chemical toxicity, high risk to benefit ratio and specific protection of normal cells against the harmful effects of radiation without compromising the cytotoxic effects of IR on cancer cells. Since reactive oxygen species (ROS) are the major contributors of IR mediated toxicity, plethora of studies have highlighted the potential role of antioxidants to protect against IR induced damage. However, owing to the lack of any clinically approved radioprotector against whole body radiation, researchers have shifted the focus toward finding alternate targets that could be exploited for the development of novel agents. The present review provides a comprehensive insight in to the different strategies, encompassing prime molecular targets, which have been employed to develop radiation protectors/countermeasures. It is anticipated that understanding such factors will lead to the development of novel strategies for increasing the outcome of radiotherapy by minimizing normal tissue toxicity.

Bactericidal/permeability-increasing protein (rBPI21) and fluoroquinolone mitigate radiation-induced bone marrow aplasia and death

Identification of safe, effective treatments to mitigate toxicity after extensive radiation exposure has proven challenging. Only a limited number of candidate approaches have emerged, and the U.S. Food and Drug Administration has yet to approve any agent for a mass-casualty radiation disaster. Because patients undergoing hematopoietic stem cell transplantation undergo radiation treatment that produces toxicities similar to radiation-disaster exposure, we studied patients early after such treatment to identify new approaches to this problem. Patients rapidly developed endotoxemia and reduced plasma bactericidal/permeability-increasing protein (BPI), a potent endotoxin-neutralizing protein, in association with neutropenia. We hypothesized that a treatment supplying similar endotoxin-neutralizing activity might replace the BPI deficit and mitigate radiation toxicity and tested this idea in mice. A single 7-Gy radiation dose, which killed 95% of the mice by 30 days, was followed 24 hours later by twice-daily, subcutaneous injections of the recombinant BPI fragment rBPI21 or vehicle alone for 14 or 30 days, with or without an oral fluoroquinolone antibiotic with broad-spectrum antibacterial activity, including that against endotoxin-bearing Gram-negative bacteria. Compared to either fluoroquinolone alone or vehicle plus fluoroquinolone, the combined rBPI21 plus fluoroquinolone treatment improved survival, accelerated hematopoietic recovery, and promoted expansion of stem and progenitor cells. The observed efficacy of rBPI21 plus fluoroquinolone initiated 24 hours after lethal irradiation, combined with their established favorable bioactivity and safety profiles in critically ill humans, suggests the potential clinical use of this radiation mitigation strategy and supports its further evaluation.

Ipomoea obscura ameliorates cyclophosphamide-induced toxicity by modulating the immune system and levels of proinflammatory cytokine and GSH

Ipomoea obscura L. is a widely used medicinal plant. The objective of this study was to investigate its protective activity against cyclophosphamide (CTX)-induced toxicity in mouse models. Swiss albino mice were treated intraperitoneally with CTX (25 mg/kg body weight) along with I. obscura extract (10 mg/kg body weight) for 10 days. Extract significantly reduced myelosuppression caused by CTX and improved the relative organ weight, total white blood cell count, and bone marrow cellularity. The elevated levels of parameters related to pathophysiology of the liver, namely glutamate pyruvate transaminase, alkaline phosphatase, and lipid peroxidation, were significantly reduced by extract treatment. Reduction of liver and intestinal glutathione levels of CTX-treated animals was reversed by I. obscura. The lowered levels of cytokines, namely IFN-γ, IL-2, and granulocyte-monocyte colony-stimulating factor after CTX treatment were found to be increased in I. obscura treated animals. Treatment with I. obscura could also decrease the level of proinflammatory cytokine TNF-α. The data suggested that I. obscura can act as a potent chemoprotective agent and can be used as an adjuvant in chemotherapeutic applications.

Yeast DEL assay detects protection against radiation-induced cytotoxicity and genotoxicity: adaptation of a microtiter plate version

The DEL assay in yeast detects DNA deletions that are inducible by many carcinogens. Here we use the colorimetric agent MTS to adapt the yeast DEL assay for microwell plate measurement of ionizing radiation-induced cell killing and DNA deletions. Using the microwell-based DEL assay, cell killing and genotoxic DNA deletions both increased with radiation dose between 0 and 2000 Gy. We used the microwell-based DEL assay to assess the effectiveness of varying concentrations of five different radioprotectors, N-acetyl-l-cysteine, l-ascorbic acid, DMSO, Tempol and Amifostine, and one radiosensitizer, 5-bromo-2-deoxyuridine. The microwell format of the DEL assay was able to successfully detect protection against and sensitization to both radiation-induced cytotoxicity and genotoxicity. Such radioprotection and sensitization detected by the microwell-based DEL assay was validated and compared with similar measurements made using the traditional agar-based assay format. The yeast DEL assay in microwell format is an effective tool for rapidly detecting chemical protectors and sensitizers to ionizing radiation and is automatable for chemical high-throughput screening purposes.

Role of cyclooxygenases in the stimulatory effect of carcinogen 1,2-dimethylhydrazine on stem cell survival in the intestinal epithelium and bone marrow

In vivo experimental studies showed that 1,2-dimethylhydrazine and product of its metabolism in the body azoximethane improve postradiation survival of two types of stem cells in the adult organism: hemopoietic stem cells and intestinal epithelial stem cells. This effect similar to the well-known radioprotective effect of E. coli lipopolysaccharide was observed, when the carcinogen was administered 1 day before gamma-irradiation. Treatment with 1,2-dimethylhydrazine prolonged the mean life-span of mice irradiated in supralethal doses inducing death of the majority of intestinal epithelial stem cells. Nonspecific cyclooxygenase inhibitor indometacin weakened this radioprotective effect of 1,2-dimethylhydrazine. We also found that carcinogen 1,2-dimethylhydrazine improved survival of hemopoietic stem cells. However, in contrast to intestinal epithelial stem cells, indometacin did not inhibit the radioprotective effect of the carcinogen. The radioprotective effect of 1,2-dimethylhydrazine and lipopolysaccharide on stem cells in the presence of indometacin was a sum of individual effects of these preparations and indometacin.

Gene expression profiles in the liver of mice irradiated with (60)Co gamma rays and treated with soybean isoflavone

PURPOSE

To better understand the molecular mechanisms underlying the radio-protective effect of soybean isoflavone that we observed in our recent animal experiments.

MATERIALS AND METHODS

We utilized a cDNA microarray to investigate the expression profiles of 4,096 known genes in the livers of irradiated-mice with or without soybean isoflavone treatment. Dye swap approach was employed to control for gene-specific dye bias and quantitative real-time RT-PCR was performed on several genes to validate the cDNA microarray data.

RESULTS

Compared with the control group, 68 genes were up-regulated and 28 genes were down-regulated in mice treated with irradiation alone, whereas only 6 genes were down-regulated and 35 genes were up-regulated in mice treated with soybean isoflavone. Interestingly, some of the down-regulated genes in the irradiated group, such as DNA repair and stress response genes and cytoskeleton-associated genes, which are markers of cellular damage after irradiation, were maintained at close to normal expression levels after soybean isoflavone treatment.

CONCLUSIONS

Comparison of gene expression profiles in the livers of irradiated-mice treated with or without soybean isoflavone suggested that soybean isoflavone may be an efficient tool to reverse irradiation damage of the liver through multiple-pathways and also provides important clues to further pursue the molecular mechanisms underlying the radio-protective activity of soybean isoflavone.

N‐Palmitoylation of the Radioprotective Domain of Interleukin‐1 Affords Inhibition of LPS‐Induced Nitric Oxide Generation

Interleukin-1beta (IL-1beta), a cytokine involved in homeostatic processes such as the immune system and inflammatory reactions, is a potent inducer of nitric oxide. The nonapeptide of human IL-1beta (VQGEESNDK, position 163-171, specific radioprotective domain--SRD) has been shown to retain radioprotective, immunostimulatory, and adjuvant activities of the native molecule without any inflammatory and pyrogenic properties. Unlike the parent IL-1, SRD did not induce nitric oxide (NO) in control or irradiated RAW 264.7 cells nor did it affect inducible nitric oxide synthase (iNOS) as shown by ELISA based mRNA assay (Quantikine). A lipophillic derivative of the SRD (a palmitoyl residue at the amino terminus of the SRD) was synthesized (palmitoyl specific radioprotective domain, P-SRD) to find out if this structural derivatization would restore the NO-inducing ability of IL-1. Surprisingly, P-SRD not only did not induce NO, but significantly inhibited lipopolysaccharide (LPS) stimulated nitric oxide (NO) production. Quantikine studies indicated that P-SRD also inhibited iNOS in LPS stimulated macrophage cells, suggesting that decrease in NO production in the presence of P-SRD was the result of iNOS mRNA inhibition. These results indicate that N-palmitoylation of SRD may effectively ameliorate potentially fatal symptoms of LPS-induced endotoxemic hypotensive shock associated with IL-1 without inflammatory and pyrogenic toxic side effects.

Melatonin as a radioprotective agent: a review

Melatonin (N-acetyl-5-methoxytryptamine), the chief secretory product of the pineal gland in the brain, is well known for its functional versatility. In hundreds of investigations, melatonin has been documented as a direct free radical scavenger and an indirect antioxidant, as well as an important immunomodulatory agent. The radical scavenging ability of melatonin is believed to work via electron donation to detoxify a variety of reactive oxygen and nitrogen species, including the highly toxic hydroxyl radical. It has long been recognized that the damaging effects of ionizing radiation are brought about by both direct and indirect mechanisms. The direct action produces disruption of sensitive molecules in the cells, whereas the indirect effects ( approximately 70%) result from its interaction with water molecules, which results in the production of highly reactive free radicals such as *OH, *H, and e(aq)- and their subsequent action on subcellular structures. The hydroxyl radical scavenging ability of melatonin was used as a rationale to determine its radioprotective efficiency. Indeed, the results from many in vitro and in vivo investigations have confirmed that melatonin protects mammalian cells from the toxic effects of ionizing radiation. Furthermore, several clinical reports indicate that melatonin administration, either alone or in combination with traditional radiotherapy, results in a favorable efficacy:toxicity ratio during the treatment of human cancers. This article reviews the literature from laboratory investigations that document the ability of melatonin to scavenge a variety of free radicals (including the hydroxyl radical induced by ionizing radiation) and summarizes the evidence that should be used to design larger translational research-based clinical trials using melatonin as a radioprotector and also in cancer radiotherapy. The potential use of melatonin for protecting individuals from radiation terrorism is also considered.

Radiation protective effect of an extract from Chelidonium majus

We earlier reported that CM-AIa isolated from Chelidonium majus had mitogenic activity, generated lymphokine-activated killer cells, and increased the number of granulocyte-macrophage colony-forming cells (GM-CFC). In an extended effort to search for other immunostimulatory effects, we evaluated the protective effects of in vivo injected CM-AIa against irradiation. CM-AIa was found to increase the number of bone marrow cells, spleen cells, GM-CFC, and platelets in irradiated mice. In addition, this agent induced endogenous production of cytokines such as interleukin 1 and tumor necrosis factor alpha, which are required for hematopoietic recovery. We also demonstrated that CM-AIa treatment 24 hours before irradiation protected mice with 80% survival at lethal dose 100/15. These findings indicate that CM-AIa may be a useful agent for reducing the time needed for reconstitution of hematopoietic cells after irradiation treatment.

Radioprotective effects of ginsan, an immunomodulator

We previously reported that ginsan, a purified polysaccharide isolated from Panax ginseng, had a mitogenic activity, induced LAK cells, and increased levels of several cytokines. In an effort to identify other immunostimulatory effects, we evaluated the protective effects of ginsan injected in vivo against radiation by measuring its effects on the CFU-S bone marrow cells and spleen cells. Ginsan was found to significantly increase the number of bone marrow cells, spleen cells, granulocyte-macrophage colony-forming cells (GM-CFC), and circulating neutrophils, lymphocytes and platelets in irradiated mice. In addition, ginsan induced the endogenous production of cytokines such as Il1, Il6, Ifng and Il12, which are required for hematopoietic recovery, and was able to enhance Th1 function while interfering with the Th2 response in irradiated mice. We demonstrated that pretreatment with ginsan protected mice from the lethal effects of ionizing radiation more effectively than when it was given immediately after or at various times after irradiation. A significant increase in the LD(50/30) from 7.54 Gy for PBS injection to 10.93 Gy for mice pretreated with 100 mg/kg ginsan was observed. These findings indicate that ginsan may be a useful agent to reduce the time necessary for reconstituting hematopoietic cells after irradiation.

Inhibition of LPS-induced nitric oxide production in RAW cells by radioprotective thiols

Nitric oxide (NO) is involved in producing damage after exposure to radiation and also in the toxicity associated with bacterial endotoxin (lipopolysaccharide, LPS). We have evaluated different radioprotective thiols for their effects on LPS-stimulated NO production in mouse macrophage cells, RAW 264.7. Our results indicate that although thiols inhibited NO production in general, the degree of inhibition depended upon the thiol compound. Long-chain aminothiols like WR-1065 [N-(2-mercaptoethyl)-1,3-diaminopropane] exerted a strong inhibition; but its parent drug, amifostine, which protects mice against radiation lethality, was not as effective as WR-1065. Diethyl dithiocarbamate, which is less effective than amifostine as a radioprotector, strongly inhibited NO production from macrophages. These results indicate that the radioprotective potential of sulfhydryl compounds is not related to its ability to inhibit NO production by macrophages and suggest that some of the thiol radioprotectors may effectively ameliorate the fatal symptoms of hypotensive shock, associated with endotoxin (LPS)-induced NO production.

Protective effects of Rasayanas on cyclophosphamide- and radiation-induced damage

Rasayanas are a group of herbal drug preparations widely used in Ayurveda to improve the general health of the body. In mice, Rasayanas are potent myeloprotective agents against chemotherapeutic agents and radiation. Rasayanas are also effective myeloprotectors in patients with cancer undergoing chemotherapy and/or radiotherapy. In this study, we provide further evidence to support the chemoprotective and radioprotective efficacy of four Rasayanas in mice. Rasayanas were found to reduce the loss of body weight and organ weight induced by cyclophosphamide and radiation significantly. Rasayanas were also found to protect tissue from cytotoxic injury associated with reduced serum and liver lipid peroxides, alkaline phosphatase, and glutamate pyruvate transaminase in cyclophosphamide- and radiation-treated animals. These results suggest the potential chemoprotective and radioprotective effects of Rasayanas, which require further study to explore their complete usefulness in cancer therapy.

In vivo radioprotection by 5-androstenediol: stimulation of the innate immune system

We showed previously that 5-androstenediol stimulates myelopoiesis, increases the numbers of circulating neutrophils and platelets, and enhances resistance to infection in gamma-irradiated mice. We have extended those studies to include monocytes, natural killer (NK) cells, eosinophils and basophils, and we have measured the activation marker CD11b using flow cytometry. Androstenediol (160 mg/kg) was administered subcutaneously to female B6D2F1 mice 24 h before whole-body gamma irradiation. Androstenediol treatments increased the blood levels of neutrophils, monocytes and NK cells in unirradiated animals; decreased the numbers of circulating eosinophils; and ameliorated radiation-induced decreases in neutrophils, monocytes, NK cells, erythrocytes and platelets. The androstenediol treatments had no significant effect on the numbers of circulating B cells or T cells. CD11b labeling intensity on monocytes was decreased slightly after androstenediol treatment. In contrast, radiation or androstenediol alone caused increases in CD11b labeling intensity on NK cells. Androstenediol and radiation combined caused a marked increase in NK cell CD11b. The results indicate that androstenediol increases the numbers of the three major cell types of the innate immune system (neutrophils, monocytes and NK cells), that androstenediol-induced changes in blood elements in irradiated animals persist for at least several weeks, and that there is a significant positive interaction between radiation and administration of androstenediol in the activation of NK cells.

Radioprotection of haemopoietic stem cells by a single injection of bacterial lysate - IRS-19 administered to mice before or after irradiation

Data in this report describes the effect of a single injection of bacterial lysate IRS-19 prior to irradiation of C57Bl/6 mice on recovery of colony-forming cells (CFC) after sublethal and lethal doses of radiation. The injection of IRS-19 promoted an earlier recovery of colony-forming cells in the bone marrow and spleen. For example, 5 and 9 days after 7.5 Gy irradiation, the number of CFU-S per femur was approximately 1.7-2.3-fold higher in IRS-19-injected mice than in saline-injected mice. Also, pretreatment of mice with IRS-19 induced an increase in the number of endogenous haemopoietic stem cells (endoCFU-S). In the postradiation period (5-21 days) significantly increased bone marrow and spleen cellularity and accelerated myelopoietic regeneration (committed progenitor granulocyte-macrophage-colony-forming cells, GM-CFC) in the bone marrow and spleen compared with saline-treated controls. At the time of presumed irradiation, (i.e. 24 h after administration of the drug to the non-irradiated mice), there was no significant difference between the control mice and mice treated with IRS-19 in numbers of femoral and spleen GM-CFC. In contrast, the number of nucleated femoral cells decreased significantly in the group treated with IRS-19. Moreover, treatment with IRS-19 caused a sustained increase in serum colony-stimulating activity which was followed by an enhanced repopulation of GM-CFC in the femoral marrow and spleen. Administration of the agent 24 h prior to irradiation rather than postirradiation appeared most effective with respect to radioprotection. Intravenous rather than i.p. and p.o. was the most effective route of administration in the mouse. Furthermore, single, high-dose injection appeared to be more effective than repeated, lower dose injections. Results suggest that the radioprotective properties associated with the administration of IRS-19 are largely a consequence of the induction of haemopoietic colony-stimulating activities and potentially the activation and/or enhancement of cytokine cascades in the recipient animals. These changes may ultimately impact the cell cycle profile of the haemopoietic cells and therefore their ability to withstand and/or recover from radiation insult.

Adenovirus-mediated transfer of HST-1/FGF-4 gene protects mice from lethal irradiation

Intraperitoneal injection of a replication-deficient adenovirus containing the HST-1 (FGF-4) gene (Adex1HST-1) increased peripheral platelet counts in mice, and also effectively prevented experimentally induced thrombocytopenia. Here, we report the therapeutic potential of Adex1HST-1 on severely injured mice after exposure to otherwise lethal irradiation. Eighteen out of 20 mice that received Adex1HST-1 prior to gamma-irradiation (9 Gy) survived, while all the 20 mice with prior administration of control adenoviruses died after irradiation (P<0.0001). Hematological and histopathological analyses revealed that Adex1HST-1 acts as a potent protector against lethal irradiation, which causes injury of intestinal tract as well as myelosuppression in the bone marrow and spleen. These data demonstrate that the protective effects of administration of Adex1HST-1 against irradiation are superior to any other protective effects of cytokines against a lethal dose of irradiation, and that the pre-administration of Adex1HST-1 may be useful for lessening the side effects of currently used chemo- and radio-therapy against cancer.

Combined modality radioprotection: enhancement of survival and hematopoietic recovery in gamma-irradiated mice by the joint use of liposomal muramyl tripeptide phosphatidylethanolamine (MTP-PE) and indomethacin

We have reported previously [Fedorocko, P., Int. J. Radiat., Biol. 65:465, 1994] that liposomal muramyl tripeptidephosphatidyl ethanolamine (MTP-PE/MLV) given prior to irradiation results in augmented hemopoietic recovery and enhanced animal survival as evidenced by increased pluripotent stem cells (CFU-S) and progenitor cells committed to granulocyte and/or macrophage development (GM-CFC) or white blood cells, neutrophil counts, as well as by survival rates of lethally irradiated mice. In this report the effects of liposomal MTP-PE (radioprotective immunomodulator; 10 mg/kg i.p., 24 h before irradiation) and indomethacin (inhibitor of prostaglandin production; 2 mg/kg i.m., 24 h and 3 h before irradiation) were studied. Both of the agents were administered either alone or in combination. The results included the assessment of preirradiation hemopoietic effects of drugs and postirradiation hemopoietic recovery in terms of bone marrow cellularity, number of bone marrow GM-CFC, endogenous spleen colony formation (endoCFU-S), and the determination of the survival of lethally irradiated mice. Experimental evidence elevated by the increased preirradiation numbers of GM-CFC and hydroxyurea kill of GM-CFC as well as a simultaneous significant diminution in bone marrow cellularity indicated that the beneficial action of the combined treatment could be a consequence of increased cell proliferation in the hemopoietic tissue and mobilization with redistribution of stem cells from bone marrow into the circulation. In the postirradiation period (3-14 days), combined pretreatment of mice accelerated myelopoietic regeneration in the bone marrow compared to treatment with MTP-PE/MLV alone or indomethacin alone. Combined administration of MTP-PE/MLV (10 mg/kg, -24 h, i.p.) and indomethacin (2 mg/kg, -24 h and -3 h, i.m.) to mice, prior to lethal irradiation, exerted an additional radioprotective effect and protected 100% of the C57B1/6 mice.

Radioprotective effects of combination broncho-vaxom, a macrophage activator, and indomethacin, an inhibitor of prostaglandin production: relationship to myelopoiesis

The effects of the bacterial extract broncho-vaxom (BV; radioprotective immunomodulator; 500 micrograms/mouse i.p., -24 h) and indomethacin (INDO; inhibitor of prostaglandin production; 2 x 40 micrograms/mouse i.m., -24 h and -3 h) on the post-irradiation recovery of hemopoietic functions in mice were investigated. Both agents were administered either alone or in combination. Endogenous spleen colony formation was increased in all treatment groups, with combination-treated mice exhibiting the greatest effects. Similarly, 24 h after combined administration of BV and INDO (i.e. at the time of presumed irradiation) to the non-irradiated mice granulocyte-macrophage colony-forming cell (GM-CFC) numbers were greater in the bone marrow and spleen. Also, as determined by hydroxyurea injection, there was an increase in the number of GM-CFC in the S-phase of the cell cycle in the bone marrow. However, GM-CFC in the spleen of combination pretreated mice was not stimulated to significant proliferation as compared to GM-CFC in the spleen of mice injected with BV alone. Combined modality treatment was also more effective than single agent treatments in accelerating bone marrow cellularity and GM-CFC regeneration, but not in accelerating GM-CFC regeneration in the spleen. Combined administration of BV and INDO to mice prior to lethal irradiation exerted an additional radioprotective effect and protected 95% of the C57Bl/6 mice.

Administration of the bacterial extract Broncho-Vaxom enhances radiation recovery and myelopoietic regeneration

In the present study, we show that the bacterial extract Broncho-Vaxom (BV, 500 micrograms/mouse; free of endotoxin) has radiation recovery activity when administered i.p. 24 h before sublethal irradiation. In the postirradiation period (5-12 days), pretreatment of mice with BV induced significantly increased bone marrow cellularity and accelerated myelopoietic regeneration (committed progenitor granulocyte-macrophage colony-forming cells; GM-CFC) in the bone marrow compared with saline-treated controls. The earlier hemopoietic recovery in BV-injected mice was not associated with an increase in the number of bone marrow GM-CFC and CFU-S (colony-forming units-spleen) within 24 h after injection. Simultaneously, a significant diminution in bone marrow cellularity occurred. In addition, the percentage of both GM-CFC and CFU-S in the S-phase of the cell cycle was significantly increased 24 h after a single treatment. In our experiments colony stimulating activity (CSA) in the serum of treated mice was not observed within 24 h after injection. Administration of BV 24 h prior to lethal irradiation, resulted in an increase in the number of surviving mice. Combined administration of BV (24 h) and indomethacin (24 h and 3 h) to mice, prior to irradiation, caused an additional radioprotective effect. These results demonstrate that BV stimulates myelopoietic regeneration and suggest a mechanism by which this treatment protects mice from otherwise lethal irradiation.

Effects of combination of immunomodulators and an adrenochrome derivative on survival of irradiated mice

PURPOSE

The combined effects of immunomodulators (lithium or OK432) and an adrenochrome derivative (AMM), an agent found to activate granulocyte-macrophage colony stimulating activity, on the survival of irradiated ddY mice is described.

METHODS AND MATERIALS

ddY mice at 4-5 weeks old were whole body irradiated with X rays at 8.5 Gy. Sole injection and combined injection of AMM and/or one of the immunomodulators were performed before or after irradiation. Then, survival was monitored daily for 30 days after irradiation.

RESULTS

Lithium at 60 mg/kg had no radioprotective effect; rather it accelerated radiation induced death. Sole treatment with AMM (100 mg/kg) had no effect on survival of irradiated mice. However, combination of both drugs caused a slight radioprotection. OK432 (25 KE/kg), which activates a variety of cellular effector cells had radioprotective effect. When combined with AMM, however, it totally lost radioprotective effect.

CONCLUSION

Lithium chloride cannot be used as a radioprotector because of its adverse effect. Combination with AMM showed slight radioprotection, but the extent thereof may not be clinically useful. OK432 was proved to be a potent radioprotector. However, combination with AMM should be avoided, since the radioprotection was totally eliminated.

Liposomal muramyl tripeptide phosphatidylethanolamine (MTP-PE) promotes haemopoietic recovery in irradiated mouse

Pretreatment of C57B1/6 mouse with the macrophage activator muramyl tripeptide phosphatidylethanolamine encapsulated in liposomes (MTP-PE/MLV) induced haemopoietic recovery in subsequently irradiated mouse. An optimal endoCFU-S survival was observed when 200 micrograms MTP-PE/MLV was administered i.p. 24 h before irradiation. MTP-PE/MLV did not affect the day 8 exogenous CFU-S survival in the bone marrow immediately after irradiation. However, 3, 6, 9 and 14 days after irradiation the number of day 8 CFU-S was almost 2 to 4-fold higher in the bone marrow of the MTP-PE/MLV injected mouse. Also, recovery of the GM-CFC pools in femoral bone marrow after irradiation proceeded at a faster rate in the MTP-PE/MLV-treated animal than in control groups. After a single i.p. injection of MTP-PE/MLV to the non-irradiated mouse, the number of CFU-S in bone marrow was not significantly different from controls, whereas the number of GM-CSC was significantly increased. In addition, the percentage of day 8 CFU-S and GM-CFC in S-phase of the cell cycle was significantly increased, as was colony-stimulating activity present in the serum of treated animals. Pretreatment with MTP-PE/MLV protected the C57Bl/6 mouse in a dose-dependent manner from the lethal effects of ionizing radiation. A single dose (100 or 200 micrograms) injected i.p. 24 h, or 100 micrograms MTP-PE/MLV injected i.v. 24 h before 9.5 Gy gamma-rays protected 47, 85 and 59% of C57B1/6 mouse, respectively. The dose reduction factor in the case when the MTP-PE/MLV (200 micrograms per mouse) was administered i.p. at that time was 1.17 (95% CL 1.13, 1.21). Combined administration of MTP-PE/MLV (24 h) and indomethacin (24 and 3 h) to mouse prior to irradiation exerted an additional radioprotective effect.

Radioprotective effects of WR-2721, Broncho-Vaxom and their combinations: survival, myelopoietic restoration and induction of colony-stimulating activity in mice

The possibilities of combined radioprotection, using preirradiation WR-2721 administration and post- or preirradiation Broncho-Vaxom administration in lethally whole-body gamma-irradiated mice were investigated. LD50/30 dose reduction factors (DRFs) for mice treated with WR-2721 (200 mg/kg i.p. 30 min before irradiation), Broncho-Vaxom (25 mg/kg i.p. 24 h before irradiation), or both agents were 1.92, 1.17 and 2.07, respectively. These results demonstrated at least additive radioprotective effects of both agents, manifested in increased survival of irradiated mice. Radioprotection from 17 Gy was optimal when WR-2721 in combination with Broncho-Vaxom was given 30 min before irradiation and Broncho-Vaxom 24 h before or 4-8 h after irradiation. Combined modality treatments were also more effective than individual treatments alone in accelerating the bone marrow GM-CFC restoration. During the first days after irradiation enhanced colony-stimulating activity (CSA) of the lungs was observed in mice with postirradiation injection of Broncho-Vaxom alone or in mice injected with WR-2721 and Broncho-Vaxom (8 h after irradiation), as well as in mice only irradiated.

Effect of porphyrins on the hematopoietic recovery of mice treated with gamma-radiation

Porphyrins are a group of organic compounds involved in a wide spectrum of fundamental biological processes. Non-metallic, naturally occurring and synthetic porphyrin derivatives may produce cytotoxic effects in malignant or normal tissues exposed to visible light. Supra-clinical doses of the photosensitizing porphyrin, Photofrin are hematostimulatory when administered to normal and immunosuppressed inbred mice. To determine if a non-photosensitizing metalloporphyrin has similar hematostimulatory activity, we have synthesized iron (III) hematoporphyrin chloride (FeHp) and administered it to sub-lethally irradiated mice. FeHp (10 mg/kg) given 1 and 4 days or 1, 4 and 7 days following sub-lethal (7 Gy) whole body irradiation significantly increased spleen colony forming units of progenitor cells of the granulocyte-macrophage lineage (CFU-GM) 14 days post-irradiation, relative to irradiated controls. In addition, total splenocyte numbers were significantly increased 17 days post-irradiation in mice that had received FeHp 1 and 4 days post-irradiation. When FeHp was given 24 hours prior to irradiation and again 48 hours or 48 and 96 hours post-irradiation, significant increases in splenic CFU-GM and spleen cell numbers, relative to control mice, were observed 15 days post-irradiation. A non-metallic photosensitizing monomeric fraction of Photofrin, deuteroporphyrin IX, 2,4 (4,2) hydroxyethyl vinyl (HVD) was compared to Photofrin for its ability to influence the hematopoietic recovery of irradiated mice. Only Photofrin but not HVD given in 3 doses (10 mg/kg) 1, 4 and 7 days following irradiation (4.8 Gy) significantly enhanced the recovery of spleen cellularity and splenic CFU-GM. In addition, Photofrin significantly increased bone marrow CFU-GM 7 and 10 days following the sub-lethal dose of gamma-radiation. The mechanism by which certain porphyrins augment hematopoiesis in the mouse is unknown. However, the identification of FeHp as a non-photosensitizing monomeric porphyrin with hematostimulatory activity in vivo, indicates that further study of metalloporphyrins is warranted and may reveal their clinical potential within the context of therapeutically-induced immunosuppression.

Radioprotective effects of the immunostimulating lauroylpeptide LtriP (RP 56142)

The lipopeptide lauroyl-L-Ala-gamma-D-Glu-L,L-A2pm (LtriP) increased the resistance of mice to the lethal effect of gamma-ray irradiation. The radioprotective effect was dependent on the doses of LtriP and of radiation. Maximum survival was observed when the lipopeptide was injected on two successive days before irradiation. This activity seems to be related to immunostimulating functions, since the non-immunostimulating analog lauroyl-L-Ala-gamma-D-Glu-D,D-A2pm-Gly, containing D,D-diaminopimelic acid, was not radioprotective. The protective activity might result from an induction of cytokines, such as IL-1, TNF and M-CSF, since LtriP induced the mRNA expression and the secretion of these immunomodulators.

Radioprotection by polysaccharides alone and in combination with aminothiols

We demonstrated that glucan, a beta-1,3 polysaccharide immunomodulator, enhances survival of mice when administered before radiation exposure. Glucan's prophylactic survival-enhancing effects are mediated by several mechanisms including (1) increasing macrophage-mediated resistance to potentially lethal postirradiation opportunistic infections, (2) increasing the D(o) of hematopoietic progenitor cells, and (3) accelerating hematopoietic reconstitution. In addition, even when administered shortly after some otherwise lethal doses of radiation, glucan increases survival. Glucan's therapeutic survival-enhancing effects are also mediated through its ability to enhance macrophage function and to accelerate hematopoietic reconstitution; glucan's therapeutic potential, however, is ultimately dependent on the survival of a critical number of hematopoietic stem cells capable of responding to glucan's stimulatory effects. Preirradiation administration of the traditional aminothiol radioprotectants WR-2721 and WR-3689 has been previously demonstrated to be an extremely effective means to increase hematopoietic stem cell survival. Therapeutic glucan treatment administered in combination with preirradiation WR-2721 or WR-3689 treatment synergistically increases both hematopoietic reconstitution and survival. Such combined modality treatments offer new promise in treating acute radiation injury.

Post-irradiation treatment with OK432 can prevent radiation-induced bone marrow death

The radioprotective effect of OK432, a Streptococcus haemolyticus preparation, on bone marrow death was examined in mice. The LD50 value was increased from 7.55 Gy in controls to 8.45 Gy in mice treated once with OK432 immediately after irradiation. Multiple administrations of the agent further elevated the LD50 value to 9.56 Gy. The radioprotective effect was also apparent when multiple treatments were commenced as late as 72 h after irradiation.

Catecholamine- and endotoxin-influenced cutaneous basophil hypersensitivity in chickens

1. Catecholamines suppress cutaneous basophil hypersensitivity (CBH) to intradermal phytohemagglutinin (PHA-P) challenge in chickens. 2. E. coli 0127:B8 endotoxin, reserpine, and propranolol prevented a norepinephrine-induced suppression of CBH. 3. PHA-P induced CBH appeared to be mediated through a beta-adrenergic receptor mechanism associated with plasma corticosterone in chickens.

New protective agents for bone marrow in cancer therapy

WR-2721 is a unique bone marrow protective agent which also protects other normal tissues against the toxic effects of radiation therapy and chemotherapy, especially with cisplatin and alkylating agents. In addition to protection against acute toxicities, WR-2721 has also been shown to protect against mutagenesis, cell transformation, and carcinogenesis which might be termed subacute and late toxicities. The protective mechanisms are not fully elucidated but oxygen free radical scavenging certainly plays a role and effects of enzymatic DNA repair mechanisms have also been reported. In the field of reduction of toxicity from anticancer treatment modalities, the properties of CSFs and other substances have been contrasted with WR-2721 the former being stimulators of bone marrow (and the immune system) rather than true protectors. Nonetheless, they also have a clinical role and combinations of a protector and stimulator may prove useful in the future. WR-2721 offers the prospect of increasing the therapeutic index of current cancer treatment and may allow the administration of higher than currently would be considered maximal tolerated doses (MTD). This may, in turn, lead to improved efficacy and the full potential of this agent is now being explored in a variety of randomized, controlled clinical trials.

Advances in radioprotection through the use of combined agent regimens

The most effective radioprotective agents exhibit toxicities that can limit their usefulness. It may be possible to use combinations of agents with different radioprotective mechanisms of action at less toxic doses, or to reduce the toxicity of the major protective compound by adding another agent. With regard to the latter possibility, improved radioprotection and reduced lethal toxicity of the phosphorothioate WR-2721 was observed when it was administered in combination with metals (selenium, zinc or copper). The known mechanisms of action of potential radioprotective agents and varying effects of different doses and times of administration in relation to radiation exposure must be considered when using combined-agent regimens. A number of receptor-mediated protectors and other biological compounds, including endotoxin, eicosanoids and cytokines, have at least an additive effect when administered with thiol protectors. Eicosanoids and other bioactive lipids must be administered before radiation exposure, whereas some immunomodulators have activity when administered either before or after radiation exposure. For example, the cytokine interleukin-1 administered simultaneously with WR-2721 before irradiation or after irradiation enhances the radioprotective efficacy of WR-2721. The most effective single agents or combinations of protectors result in a decrement in locomotor activity, an index of behavioral toxicity. Recent evidence indicates that administration of the CNS stimulant caffeine mitigates the behavioral toxicity of an effective radioprotective dose of the phosphorothioate WR-3689 without altering its radioprotective efficacy. These examples indicate that the use of combinations of agents is a promising approach for maximizing radioprotection with minimal adverse effects.