Lethality Assessments for Acutely Irradiated Cynomolgus Macaques Under Subject-based Care

Well-characterized animal models of acute radiation syndrome are needed for the development of radiation medical countermeasures to mitigate injury due to acute exposure to high doses of total- or partial-body radiation. Such animal models must reveal a radiation dose- and time-dependent relationship, pathogenesis of injury, and clinical presentation similar to humans. The focus of this study was to investigate clinical responses, principally lethality patterns, of cynomolgus macaques acutely exposed to relatively high doses of total-body radiation. Such investigations are currently relevant due to the limited availability of rhesus macaques, the dominant and preferred macaque subspecies, due to limited supply and their use in other high-priority areas. In this study employing cynomolgus macaques, a preliminary dose-response relationship was determined using three different radiation doses (4.7, 5.8 and 6.5 Gy, n = 24, n = 8/radiation dose) at a dose rate of 0.6 Gy/min. Animals were provided subject-based supportive care excluding blood products and were monitored for 60 days postirradiation for survival, which was the primary endpoint and the secondary endpoint was hematopoietic recovery. The lethality curve suggested LD30/60, LD50/60, and LD70/60 values as 4.8, 5.3, and 5.8 Gy, respectively. The initial results of this study are deemed critical for future efficacy assessments of newly developed medical countermeasures for acute radiation injuries by making use of an alternative subspecies of macaques, namely cynomolgus macaques (Macaca fascicularis).