Table 1.

Drug discovery pathways for small molecule radiation protector/mitigator agents.

Basic science observations	Unbiased siRNA screen
↘	↙
Target validation
↓
Chemical synthesis (rational drug design principles)
↓
Radiation survival curves 32D cl3 mouse IL-3 dependent hematopoietic progenitor cell line
↓
Assays for biological screening of method of action: Apotag, H2AX, ATM phosphorylation
↓
Comparison of several categories of drugs within each chemical synthesis group (GS-nitroxides – JP4-039, XJB-5-131, XJB-5-175)
↓
Radiation survival curves with human cell lines (KM101 human bone marrow stromal cell line, IB-3 human bronchoepithelial cell line, fresh human umbilical cord blood in CFU-GEMM assay)
In vivo assays, total body irradiation of C57BL/6HNsd mice to LD 50/30 irradiation dose of 9.5 Gy
↓
Three experiments on three successive dates demonstrating statistical significance at 30 days with respect to survival. Holding mice for 60 days to look for late deaths and evidence of true bone marrow stem cell recovery (60 vs. 30 days)
↓
Experiments to optimize protection and mitigation paradigm
Protection: drug given before total body irradiation compared to 1, 24 h prior to TBI
Mitigation: drug given immediately after irradiation, 1, 4, 24, 48, and 72 h after irradiation
↓
Pathway toward drug development
↓
Elaboration of the potential mechanism of protection or mitigation (amelioration of irradiation effects on DNA repair, mitochondrial mediated apoptosis, inflammatory cytokines, and/or other mechanism)
↓
Path to licensing
↓
Preparation for translation to the clinic: FDA “animal rule” two species assays