Compositions and methods for enhanced fluorine-19 magnetic resonance imaging cell tracking

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A common need for clinical developers of cell therapies, such as immunotherapeutic and stem cells, is a non- invasive means to visualize the fate of cells following injection. Imaging of cell trafficking can provide critical feedback regarding the persistence, motility, optimal routes of delivery and therapeutic doses. This project aims to synthesize and biologically evaluate innovative new imaging probes for sensitive in vivo cell tracking using fluorine-19 (19F) magnetic resonance imaging (MRI). We will advance the formulation science of a compelling new class of ‘metallo-perfluorocarbon’ (MPFC) nanoemulsion imaging probes. These agents will be a key element to a multi-pronged strategy to advance cell detection sensitivity by an order of magnitude over current 19F MRI cell detection technologies. Overall, in 19F cell tracking, cell populations of interest are initially labeled in culture using perfluorocarbon nanoemulsions. Following transfer to the subject, cells are tracked in vivo using 19F MRI. The fluorine inside the cells yields cell-specific images, with no background signal. One of the bottlenecks preventing the broader adoption of 19F based cell tracking is sensitivity limits to sparse cell numbers. The sensitivity of this technology can be improved by a three-pronged approach: (1) molecular design and synthesis to improve the intrinsic sensitivity of the molecular signal generator and (2) nanoemulsion probe formulation with cell targeting to enhance intracellular delivery and uptake, and (3) employing MRI data acquisition schemes that have a more efficient signal-to-noise ratio per acquisition time (SNR/t). Recent results have demonstrated dramatically-enhanced sensitivity of fluorine MRI by molecular design. We have created a new class of molecules that combine highly fluorinated nanoemulsions with the magnetic properties of metals that are solubilized into the fluorous phase. Solubilized paramagnetic metal ions provide a dramatic reduction in the 19F spin-lattice relaxation time thereby enhancing SNR/t and cell detection sensitivity. It was discovered that iron is most effective metal at enhancing the fluorine MRI signal. Building on these preliminary results, the proposal has four Specific Aims: Aim 1. Chelation strategies for MPFCs. We will evaluate a range of suitable chelate molecules and synthesis strategies to stably incorporate metal ions into PFC. Aim 2. Enhanced cell delivery of MPFC nanoemulsion using cell penetrating peptides (CPPs). Successful MRI detection of cells critically requires optimal intracellular delivery of emulsified MPFC ex vivo. We will develop novel MPFC nanoemulsion formulations incorporating CPPs attached to the nanoemulsion surfactant to rapidly and optimally label cells for cell tracking. Aim 3. “Smart” in vivo targeted nanoemulsions. As an exploratory extension of this work, we devise MPFC nanoemulsions that target tumors in vivo. Aim 4. In vivo imaging methods to track immunotherapeutic T cells in cancer. To evaluate new MPFC nanoemulsion probes, we will label T cells and deliver these to immunotherapeutic cancer models. To image these models, sparse sampling MRI acquisition methods (e.g., compressed sensing) will be implemented and optimized for MPFC agents to maximize SNR/t.