TITLE: Targeting P2RX7 Signaling as a Biomarker for ADRD ABSTRACT Inflammation in the brain has been proposed to be an early predictor for a range of neurodegenerative diseases such as Alzheimer’s disease (AD) and related dementias, Parkinson’s disease, ischemia-reperfusion injury, epilepsy, amyotrophic lateral sclerosis, and traumatic brain injury. Identification and development of biomarkers of neuroinflammation would permit researchers and clinicians to identify “at risk” subjects for these disorders, evaluate severity of disease stage, and effectiveness of possible treatments. Previous work on imaging agents to monitor neuroinflammation has resulted in sub-optimal radiopharmaceuticals that are only correlative in nature. To overcome these limitations, we propose to target the P2X7 receptor (P2X7R) found within the central nervous system and expressed primarily on immune cells. These receptors become activated in neurodegenerative diseases, and are an ideal target to monitor disease progression and therapy response. Previous efforts to develop ligands against this target have been stymied by the presence of P451L mutations that cause dysfunctional P2X7R signaling commonly used animal models. Recent development and characterization of a wild-derived mouse panel showed a high degree of overlap with human neuroinflammation, which is likely due to the retention of functional P2X7R, making them an ideal tool to advance ligands against this receptor. We hypothesize that neuroinflammation is a major initiator of neurodegenerative disease, where P2X7 receptors play a central role; and that developing a novel PET tracer against this receptor will enable phenotypic and therapeutic assessment during aging. Our goal is to characterize the third generation agent (i.e. [18F]GSK1482160) in human cell based assays, and in acute and chronic neuroinflammation models. In Aim 1, we will characterize [18F]-GSK14821604 in vitro in human iPSC derived microglia expressing human P2X7R (hP2X7R) in the APOEE3/E3 or APOEE4/E4 to understand: a) the radioligand depletion conditions for Ki (Aim 1.1); b) binding kinetics for kon, koff, Kd, Bmax (Aim 1.2), and Bp via saturation and association/dissociation kinetics (Aim 1.3). To understand the role of P2X7R in acute and chronic neuroinflammation, in Aim 2, we will use dynamic PET/CT in cross-sectional cohorts of female CAST/EiJ, PWK/PhJ, PWK.APP/PS1 and CAST.APP/PS1 mice. Using dynamic PET/CT we will determine the role of acute (Aim 2.2) and chronic (Aim 2.4) inflammation, where biodistribution (Aim 2.3), thus permitting allometric organ dosimetry for first in human studies. In addition, to validate the sensitivity and specificity of this ligand, (Aim 2.5) dynamic [18F]-GSK1482160 PET/CT at peak P2X7R expression will be conducted, allowing determination of maximum (CAST.APP/PS1) and non-specific (CAST.APP/PS1P2X7R-/-) binding relative to homeostatic levels of microglia (CAST/EiJ). Lastly, to establish test-retest reliability ...