In cancer, macrophages play a multifaceted role in disease progression and response to therapies. Tumor- associated macrophages (TAMs) serve several pro-tumoral functions including the expression of factors promoting growth, immune suppression and angiogenesis. A high TAM burden in the tumor microenvironment is often associated with poor prognosis and therapeutic resistance to certain immunotherapies. Moreover, TAMs are emerging as a target for anti-cancer therapeutics. Overall, an imaging probe that can non-invasively detect TAM burden could help stratify patients and personalize treatments to improve response rates. Recently, our laboratory has developed novel molecular probes enabling sensitive and precise imaging of inflammatory foci in vivo. We synthesized functionalized fluorocarbon nanoemulsions incorporating a fluorous-encapsulated radiometal chelate (FERM). Pre-formed FERM nanoemulsion rapidly captures zirconium-89 into the fluorous phase. The highly hydrophobic nature of fluorocarbons helps exclude competition from water, cations, lipids and proteins that contribute to the dissociation of 89Zr from the carrier. By encapsulating the radiometal inside the volume of nanoemulsion droplet one can achieve a high payload and cell detection sensitivity, with low background. Following an intravenous injection of FERM, nanoemulsion droplets are scavenged by phagocytic macrophages. The labeled cells accumulate at inflammatory sites resulting in sensitive and quantifiable positron emission tomography (PET) signals reflecting predominantly macrophage burden. Preliminary PET results from our lab demonstrate excellent sensitivity and versatility of the FERM probe in a diversity of inflammation rodent models, including solid tumor, acute infection and autoimmune disease. Building on these results, our project has three Aims: Aim 1. 89Zr FERM formulation. We will perform FERM nanoemulsion formulation optimization and scale-up. We will also develop optimal radiopharmacy methods to maximize labeling efficiency of FERM and product yield. Aim 2. Biological characterizations. Cell-based assays will be performed to evaluate potential toxicity of 89Zr FERM. Moreover, we will characterize the in vivo blood half-life, probe stability, and preliminary dosimetry. Aim 3. In vivo immuno-oncology studies. We will characterize the effectiveness of FERM for TAM detection and quantification, responsiveness to treatments that deplete TAM burden, and the probe’s potential for predicting response to immunotherapeutic interventions in multiple murine solid tumor models. Parallel phenotypic profiling of FERM-labeled cells in the tumor will be performed. The proposed studies will generate essential data needed to drive potential clinical translation of the FERM imaging biomarker for use in future immuno-oncology clinical trials.