PROJECT SUMMARY: This proposal addresses a major challenge that radiologists and other physicians encounter frequently, namely distinguishing active infection from other processes in the human body. Existing clinical techniques target the host immune response, for example 111In SPECT white blood cell scanning or 18F-FDG PET. Although these modalities can sometimes be useful, they lack the specificity required to distinguish living bacteria from sterile inflammation, cancer, and other highly metabolic tissues. Therefore we are proposing a PET imaging technique that exploits metabolic pathways specific to bacteria, targeting both gram-positive and gram- negative organisms. We believe a technique that detects ALL or at least a majority of pathogenic bacteria will be most useful in clinical practice. Once an imaging abnormality has been identified as infection, tissue sampling, staining and culture may still be required. An imaging method that could distinguish active infection from frequent mimics, would instantly become the standard of care in a variety of inpatient and outpatient settings. In this proposal, we develop 18F and 11C tracers for positron emission tomography (PET) using D-Met derived tracers, and study them for the first time in human patients with spinal infections. We have identified 11C D-met as a radiotracer with (1) a simple, high-yield radiosynthesis (2) good in vivo stability (3) appropriate mimicry of the endogenous substrate (4) high rate of incorporation into bacterial peptidoglycan and (5) low uptake in background tissues. We will start by refining the synthesis of enantiopure 11C D-met, and investigating close structural relatives of 11C D-met for enhanced bacterial uptake (Specific Aim 1). We will then study our lead D-met tracer in compelling preclinical infection models, including models of vertebral osteomyelitis-discitis (Specific Aim 2). In Specific Aim 3, we will take all steps needed for an investigational new drug (IND) approval for our lead tracer, and study its performance in patients suffering from spinal infection.