Development of an Extended-release Formulation of Radioprotectin-1 for Mitigation of Gastrointestinal Acute Radiation Syndrome

Left unmitigated, high-dose ionizing radiation causes DNA damage resulting in cell death and manifestation of the acute radiation syndrome (ARS). Activation of the lysophosphatidic acid receptor subtype 2 (LPAR2) is one mechanism by which radiation damage can be mitigated. Our laboratory has previously developed 5-chloro-2-(N-(4-(1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)butyl)sulfamoyl)benzoic acid, designated as Radioprotectin-1 (RP-1), which is a potent LPAR2-specific agonist and radiation mitigator. We previously reported that an aqueous (AQ) formulation of RP-1 provides significant survival advantage in a murine gastrointestinal ARS (GI-ARS) model when given in a three-day regimen of twice-daily subcutaneous injections administered starting 24 h after irradiation. To improve the dosing formulation suitable for the field treatment of mass casualties, an extended-release dosing regimen was developed utilizing a water-in-oil-in-water (W/O/W) multilayered microemulsion (ME) formulation. The ME significantly extended plasma half-life, mean residence time, and exposure time while slowing plasma clearance compared to the AQ formulation in C57BL/6J mice as well as in non-human primates (NHP). This formulation provides a significant survival advantage in a GI-ARS model with only two subcutaneous injections at 24 and 72 h postirradiation. Additionally, RP-1 ME treatment protects intestinal crypts in irradiated mice, resulting in an increase in both total and actively regenerating crypts at day 5 postirradiation. Finally, LPAR2 activation by RP-1 leads to prolonged and sustained activation of the pro-survival kinases ERK1/2 and Akt up to 16 h postirradiation and reduces caspase-mediated apoptosis in irradiated mouse embryonic fibroblasts, providing a mechanism for RP-1 radiation mitigation.