Application of magnetic resonance spectroscopy (MRS) to the real-time monitoring of metabolic processes in living systems has been advanced tremendously by the introduction of dissolution dynamic nuclear polarization (DNP) as a means of improving sensitivity. With this improvement has come the promise of using metabolic signatures in the diagnosis of disease and in the subsequent monitoring of treatment. Because of the need to prolong storage of polarization and maintain good sensitivity, most applications have been based on polarization and direct observation of 13C enriched at carbonyl or carboxyl sites in metabolic precursors such as pyruvic acid. These non-protonated sites have low relaxation rates, and polarization can be stored for several tens of seconds. However, a much broader range of metabolic pathways could be monitored with suitable attention to the use of other magnetic nuclei, to the use of new means of prolonging polarization storage, and to the development of methodology for observation of polarized sites in a broader range of metabolic products. We have recently developed methodology for exchange facilitated indirect detection of deuterated 15N and 13C sites as a means of improving sensitivity and expanding the range of metabolic applications. We propose to now explore potential applications through the synthesis and testing of an expanded set of metabolic precursors. We also propose the synthesis and testing of new reagents capable of prolonged polarization storage in a singlet state. These reagents have potential in both metabolic monitoring and MR imaging .
The specific aims i nclude 1) extending polarization storage times of normally protonated 15N and 13C sites in substrates through deuteration and improving detection of products through exchange facilitated indirect detection, 2) synthesizing novel bioorthogonal reagents capable of singlet state storage and monitoring of cell-surface glycan modification, and 3) developing improved apparatus and protocols for in-cell testing of substrates and reagents.
The rate of metabolic conversion of DNP enhanced pyruvate to lactate is already documented as a viable indicator in the detection and grading of various cancers. However, the diagnostic potential of DNP enhanced substrates can be greatly expanded through the development of methods that allow a broad investigation of metabolic pathways with diagnostic importance for cancer and other diseases.