UTS-1401 as a Medical Countermeasure to H-ARS Consequent to a Radiation Mass Casualty - Abstract: Our long term objective is to develop a new class of radiation mitigating agents with attractive chemical, physical and biological characteristics required to be an effective drug that can be distributed widely. We have identified a small molecule, UTS-1401 [5-(methylthiomethyl) isoxazole-3-carboxylic acid] which demonstrates mitigation of hematopoietic stem cell death when administered at either 24h or 48h following whole body irradiation (WBI). Using the endogenous spleen colony assay, we demonstrated a mitigating effect in that the colony number with and without UTS-1401 was 3.5 ± 0.4 for a 24h interval and 2.3 ± 0.5 for a 48h interval. We have recently demonstrated a significant radioprotection for both mouse survival and hematopoietic stem cells for this compound when administered up to 72h before irradiation (Valeriote et al, Radiation Research, 202:16- 25, 2024). In this application, we propose to further examine solely the mitigating effect on the hematopoietic acute radiation syndrome (H-ARS) using survival as the endpoint in specific aim 1. Groups of Swiss mice will receive a series of graded doses of WBI (in 0.5 Gy increments) around the LD50 for this syndrome (approximately 7.5 Gy in females and 8.5 Gy in males) with and without the administration of 150 mg/kg UTS-1401. The single dose of UTS-1401 being used in all studies is the highest dose administrable due to its aqueous solubility (in tartrate buffered saline). The radiation mitigation factors will be calculated as the ratio of the LD50 for radiation plus UTS-1401 versus that for radiation alone. The degree of mitigation will be examined at 24, 48 and 72 h following WBI to determine the radiation mitigation fraction as a function of time after radiation exposure. Three routes of drug delivery, intravenous (iv), oral, and subcutaneous (sc), will be examined and compared. Radiation will be delivered by 16 MeV electrons from a Linac. In specific aim 2, we will examine the pharmacokinetics (PK) for 150 mg/kg UTS-1401 comparing the iv, oral, and sc routes to obtain a determination of both the drug kinetics and bioavailability. The AUC values will be correlated with the extent of mitigation. For both specific aims, both male and female mice will be separately studied. The results from these studies are expected to demonstrate an effective first-in-class compound, UTS-1401, which has a small molecular weight, is chemically stable, nontoxic, aqueous soluble and inexpensive with H-ARS radiation mitigating properties which extend for a number of days following WBI. The mechanism studies (not proposed here) are expected to demonstrate UTS- 1401 as a new class of agents for mitigating the cytokine storm consequent to the irradiation.
