Stendard Form 298 NOv 2 89) powbi w ANSI 44 231 16 2lW-102 SICUlryt CLASStFCATION Of rMIS PAGI .-CLASSIFIED BY: DECLASSIFY ON4: Wim",' C AWKC ¶of OF rmiS PAGE ARMED FORCES RAD1OIOBKOGY RESEARCH INSTITUE

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.

Primary responsibility for the induction of various acute phase reactions has been ascribed to interleukin 1 (IL-1), tumor necrosis factor (TNF), or IL-6, suggesting that these cytokines may have many overlapping activities. Thus, it is difficult to identify the cytokine primarily responsible for a particular biologic effect, since IL-1 and TNF stimulate one another, and both IL-1 and TNF stimulate IL-6. In this work, the contribution of IL-6 in radioprotection, induction of adrenocorticotropic hormone (ACTH), and induction of hypoglycemia was assessed by blocking IL-6 activity. Administration of anti-IL-6 antibody to otherwise untreated mice greatly enhanced the incidence of radiation-induced mortality, indicating that like IL-1 and TNF, IL-6 also contributes to innate resistance to radiation. Anti-IL-6 antibody given to IL-1-treated or TNF-treated mice reduced survival from lethal irradiation, demonstrating that IL-6 is also an important mediator of both IL-1- and TNF-induced hemopoietic recovery. A similar IL-1/IL-6 interaction was observed in the case of ACTH induction. Anti-IL-6 antibody blocked the IL-1-induced increase in plasma ACTH, whereas recombinant IL-6 by itself did not induce such an increase. Anti-IL-6 antibody also mitigated TNF-induced hypoglycemia, but did not reverse IL-1-induced hypoglycemia. It is, therefore, likely that TNF and IL-1 differ in their mode of induction of hypoglycemia. Our results suggest that an interaction of IL-6 with IL-1 and TNF is a prerequisite for protection from radiation lethality, and its interaction with IL-1 for induction of ACTH.

No abstract

SummaryStudies of radioresistance and radioprotection provide an excellent in vivo model for dissection of the pathophysiological role of cytokines . The availability of neutralizing antibodies to cytokines has made it possible to assess the contribution of cytokines to host defense and repair processes involved in radioresistance and radioprotection. Administration of anti-interleukin 1 receptor (IIAR) antibody (35F5) or anti-tumor necrosis factor (TNF) antibody (TN3 19 .12) reduced survival of irradiated CD2F1 mice. These results demonstrate conclusively that natural levels of Ilrl and TNF contribute to radioresistance of normal mice . Furthermore, the radioprotective effect of administered IL1 was blocked not only with anti-IIr1R antibody but also with anti-TNF antibody. Similarly, the radioprotective effect of TNF was reduced with anti-IIAR antibody. These data suggest that cooperative interaction of both cytokines is necessary to achieve successful radioprotection . Finally, when LPS was used as a radioprotector, the combined administration of anti-IIAR and antiTNF not only blocked the radioprotection with LPS, but actually revealed LPS to have a radiosensitizing effect. This effect may be due to induction of TGF-a, since administration of this cytokine results in reduced survival of irradiated mice.