DEVELOPMENT OF METHODOLOGIES AND PROBES FOR METABOLIC DETECTION OF PATHOGENIC MICROORGANISMS

PROJECT SUMMARY:This proposal addresses a major clinical challenge that radiologists and other physicians encounter frequently,namely distinguishing active infection from other processes in the human body. Existing clinical tools fordetecting infection, including 111In SPECT white blood cell scanning or 18F-FDG PET, target the immuneresponse to bacteria and not the bacteria themselves. Although these modalities can sometimes be useful,they lack the specificity required to distinguish living bacteria from sterile inflammation, cancer, and other highlymetabolic tissues. In this proposal, we describe a hyperpolarized (HP) 13C magnetic resonance (MR) imagingtechnique that identifies metabolic pathways specific to bacteria. HP 13C MR is a powerful technology that hasexploded in the recent few years. Put simply, we will employ this modality to develop biomarkers (smallmolecule byproducts) using HP probes that only bacteria (but not mammalian cells) can make from theseprecursors. We will show its feasibility without ionizing radiation, and using HP 13C probes that are safe forhuman use. A fast, high-specificity method of diagnosing infection and its location would revolutionize clinicalpractice.Here we develop and test 3 novel probes for imaging infection in representative gram positive (S. aureus) andgram-negative (E. coli) bacteria as well as mammalian cells (including cancer cells and activated immune cells)to show specificity to microbial metabolism. We have already shown in preliminary data that HP [2-13C]pyruvate forms significant quantities of [1-13C] acetate when administered to both S. aureus (gram-positive)and E. coli (gram-negative) in vitro. In contrast, we have never observed [1-13C] acetate in mammalian celllines. In Specific Aim 1, we will optimize a novel MR-compatible 3D culture platform (bioreactor) for studyingthe bacterial metabolism of hyperpolarized agents in a rigorous fashion. In Specific Aim 2, we will optimize thepreparation of the candidate HP probes for dynamic nuclear polarization and use the bioreactor tosystematically study its metabolism using the above mentioned cells. Finally, in Specific Aim 3, we willimplement optimized MR imaging methods to test our novel HP 13C probe in an in vitro phantom modelcontaining the bacteria and some negative controls, to demonstrate spatial localization of bacteria.Furthermore, HP pyruvic acid has already been used in human phase 1 clinical trials and can be polarizedusing commercially-available clinical-grade equipment. Clinical polarizers for human use are currently installedin multiple sites throughout the world. Therefore, if successful, the approaches explored in this work willbe translatable to clinical imaging at our institution and at other sites.