PROJECT SUMMARY/ABSTRACT The general population continues to be at risk of exposure to ionizing radiation because of nuclear warfare, terrorism, or radiological accidents. Such exposures are known to cause both short- and long-term injuries in multiple organ systems. Hence, there is an urgent need for FDA-approved biomarkers, with the ability to accurately determine radiation exposure and predict injuries that may follow, based on easily accessible biofluids (e.g., blood) from exposed individuals. The reconstruction of absorbed dose alone does not necessarily identify the type and degree of radiation injury, information that is required for triage and treatment decisions. Thus, effective medical management of a suspected high-dose (i.e., life threatening) exposure necessitates a multiple- parameter-based approach to combine biodosimetry and injury biomarker endpoints. This proposed supplement brings together three inter-disciplinary research teams with expertise in radiation biology, animal models of tissue injury, biomarker development, biostatistics, and bioinformatics to develop the first concept of an analytically validated rapid and minimally invasive assay that constructs both absorbed radiation dose and predicts radiation injury. For this purpose, we will for the first time perform studies to integrate our previously developed FAST- DOSE tool that makes use of leukocyte protein biomarkers, designed for rapid retrospective dose classification/reconstruction within a week after exposure with our CardioWatch panel, a plasma multi-omics panel that predicts the development of late injury in the heart before clinical manifestations are apparent. We will make use of use a highly translational rat model of leg-out X-ray partial body irradiation, which will allow us to collect data on a wide range of early and late organ injuries. Peripheral blood samples collected up to 3 months after irradiation will be used to validate both the FAST-DOSE tool and CardioWatch panel. Echocardiography will provide data on cardiac function at time points up to 9 months after irradiation. Performing these studies in one set of animals will allow us to integrate both assays, using state of the art machine learning approaches. Innovation lies in the different strengths and capabilities of these two biomarker systems which can be used in tandem to correlate in vivo dose reconstruction with radiation injury. The goal of our collaborative supplement is to build on an existing infrastructure and share samples for maximum output. Moreover, the work proposed herein, falls well within the original scope of both approved projects, and speaks to the common goal of building biomarker panels for radiation-specific molecular alterations.