Date of Award
Doctor of Philosophy (PhD)
Ivan J. Dmochowski
Genetically encoded (GE) contrast agents are proteins that enable visualization of gene expression, cell proliferation, and metabolite flux. Optical GE contrast agents such as green fluorescent protein (GFP) have revolutionized the field of biomolecular imaging, but their utility in large opaque organisms is limited by the strong scattering of light by tissue. There is thus a need for GE contrast agents detectable by alternative imaging modalities such as magnetic resonance imaging (MRI). MRI is a non-invasive, non-ionizing imaging technique that offers excellent spatiotemporal resolution at virtually unlimited penetration depths. Nuclear hyperpolarization of 129Xe provides a novel strategy to overcome the sensitivity limitations of conventional 1H MRI. Using hyperpolarized (hp) 129Xe in combination with chemical exchange saturation transfer, an MR contrast approach known as hyper-CEST, enables ultrasensitive protein detection for biomolecular imaging applications.
Our group identified TEM-1 β-lactamase (TEM1) as the first monomeric protein capable of serving as a GE contrast agent for hp 129Xe NMR. TEM1 reports a unique CEST contrast response 60 ppm downfield of the 129Xe-H2O frequency, allowing nanomolar TEM1 to be detected in mammalian cells. Follow-up experiments involving protein crystallography and molecular dynamics (MD) simulations have provided additional insights regarding the Xe-TEM1 CEST interaction. Additionally, our group has characterized the periplasmic binding proteins (PBPs) as a platform for developing analyte-sensitive GE MRI contrast agents. 129Xe hyper-CEST was used to quantify maltose (32 nM to 1 mM) through its modulation of conformational change and xenon exchange in maltose binding protein (MBP). More recently, we have engineered ribose binding protein (RBP) as a GE contrast agent suitable for ribose detection at physiological concentrations, and efforts are underway to similarly develop glucose/galactose binding protein (GGBP) for glucose detection.
Roose, Benjamin William, "Genetically Encoded Contrast Agents For Hyperpolarized Xenon Nmr" (2018). Publicly Accessible Penn Dissertations. 3177.