Inhibition of tyrosine kinase Fgr mitigates hematopoietic acute radiation syndrome (H-ARS) - Mass exposure to total body irradiation (TBI) could occur from a nuclear accident or nuclear attack. Ionizing radiation (IR) causes inflammation and acute damage to both hematopoietic (H) and gastrointestinal (GI) systems [1-2]. The bone marrow damage due to radiation exposure is known as the acute hematopoietic radiation syndrome (H-ARS) [3]. FDA approved drugs to H-ARS are mostly recombinant growth factors such as G-CSF that do not seek to address the root cause of inflammation [4-5]. Therefore, there is an urgent need for novel medical countermeasures (MCMs) that will target master regulators of inflammation, proliferation, and tissue regeneration in response to TBI injury [6]. We have discovered that Fgr, a non-receptor tyrosine kinase, is the master regulator of bone marrow (BM) inflammation following TBI, and Fgr inhibitor TL02-59 is a novel mitigator of H-ARS. In preliminary experiments we found 1) Significant increase in Fgr expression in irradiated mouse BM cells. We have verified this result in non-human primate (NHP) bone marrow cells following TBI, in collaboration with Dr. Mark Cline’s laboratory, at the Wake Forest University. 2) Significant improvement in BM cellularity, and dramatic improvement in survival of irradiated Fgr-knockout mice, and of mice that receive the Fgr-inhibitor TL02-59. 3) Increase in pro-hematopoietic proteins including G-CSF, GM-CSF, and reduction of inflammatory proteins in the BM of Fgr-/- mice, 4) The Fgr-/- BM is more radioresistant measured in an assay for multilineage hematopoietic cells and increased CFU-GEMM colonies. 5) Fgr inhibitor TL02-59 reduces secretion of inflammatory proteins from irradiated BM stromal cells. We hypothesize that Fgr is a master regulator of bone marrow inflammation, which leads to BM failure, and absence of Fgr mitigates radiation-induced inflammatory damage. We will establish that induction of Fgr as a key detrimental event in inducing BMF in the hematopoietic microenvironment. Using mouse and non-human primate models of BMF induced by total body irradiation and administering Fgr inhibitor TL02-59 in mice, we will establish that Fgr tyrosine kinase is a master regulator of bone marrow inflammation leading to H-ARS. In Aim 1, We will Establish that tyrosine kinase Fgr plays a key role in BM inflammation that precedes H-ARS demonstrating that ionizing radiation exposure leads to induction of Fgr in specific BM cell phenotypes in mouse and in non-human primates. Using inducible Fgr knockout mice, we will prove that removal of H-ARS leads to upregulation of pro-hematopoietic proteins, and suppression of inflammatory proteins. In Aim 2, we will determine that ablation or inhibition of Fgr by TL02-59 mitigates H-ARS in TBI treated mice, and mice with BM specific knockout of Fgr. We will establish that inhibition of Fgr using a small molecule inhibitor mitigates radiation induced bone marrow inflammation. Successful completion of the experiments proposed in the Aims will lead to the discovery of a most potent mitigator of H-ARS yet reported. Moreover, by addressing the root cause of inflammation, the Fgr inhibitor treatment will lead to a complete mitigation of H-ARS at 24 h after TBI.
