Enzyme-enabled hyperpolarized 13C MRI for antibody-targeted imaging

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In keeping with the mission of NIBIB to support research and development of “new biomedical imaging and bioengineering techniques and devices to fundamentally improve the detection, treatment, and prevention of disease,” the overarching goal of this proposal is to develop a novel magnetic resonance imaging (MRI)-based method for antibody-targeted imaging without ionizing radiation. As part of the precision medicine approach to patient care, antibody-based targeted therapies have become an important tool for the treatment of cancer and their application holds promise in other diseases. In addition to their therapeutic use, the high specificity with which antibodies recognize and bind antigens is being exploited for diagnostic purposes. In particular, antibody- targeted imaging techniques can play important roles in diagnosis, patient risk stratification, selection of targeted therapies, evaluation of response to therapy and prediction of adverse effects. While antibody-targeted agents have been created for nearly every imaging modality the majority utilize radioactive and/or optical probes due to the high sensitivity of the respective modality. The development of antibody-targeted MRI strategies has been less successful due to the inherently low sensitivity of MRI coupled with the toxicity of strong MR contrast agents. The development of so-called hyperpolarized (HP) 13C MRI using externally pre-magnetized molecules produces signal enhancement on the order of four orders of magnitude. Using metabolically active compounds permits real-time observation of metabolic processes in vivo through measurement of both the injected agent and downstream metabolic products. Directly labeling and hyperpolarizing an antibody may be feasible, but the signal would be very weak at typical concentrations, and the polarization would likely be lost due to the fast relaxation before the antibodies reach their target. Here we propose to develop a new antibody-targeted MRI technique that leverages the multiple signal amplification factors inherent in both HP 13C MRI and enzyme catalysis. By linking the exogenous enzyme urease to an antibody targeting a specific antigen and using HP 13C- urea as the substrate the location of the antibody can be imaged without background signal through the detection of the metabolic products 13CO2 and 13C-bicarbonate. We will evaluate the method by linking urease to an antibody that targets the human epidermal growth factor receptor 2 (HER2) antigen as overexpression of HER2 has been identified in 20% of breast cancer (BCa) patients and is also a predictive factor of response to chemotherapy and hormonal treatment. Specifically, we will first evaluate the targeting specificity and the signal strength of the urease-antibody conjugate in BCa cell cultures (Aim 1) followed by evaluating the safety and efficacy of the technique for in vivo imaging in a murine BCa model (Aim 2). Although this proposal is focused on imaging HER2 expression in a BCa model the imaging approach can be applied to any cancers or other diseases that present unique antigens as a target.