739. ¹H/¹⁵N NMR and Low-Field ¹H MRI of SABRE-Hyperpolarized Pyrazinamide – An Approved Antibiotic and Potential MRI Contrast Agent
Zahid Siraj, Anthony F. Petrilla, Ishani M. Senanayake, Nadiya Iqbal, Joseph N. Gyesi, Jasilyn Westerfield, Praveen J. Daluwathumullagamage, Roman V. Shchepin, Sudarshan Ragunathan, Eduard Y. Chekmenev, Boyd M. Goodson, JChemPhysB, (2025), 10.1021/acs.jpcb.5c05707
Pyrazinamide (PZA), an FDA-approved antibiotic, was investigated for potential use as a hyperpolarized MRI contrast agent. PZA was readily hyperpolarized via parahydrogen-based NMR Signal Amplification By Reversible Exchange (SABRE) at ∼5.5 mT, allowing 1H polarization and relaxation dynamics to be characterized. More importantly, performing SABRE hyperpolarization in the microtesla regime (i.e., SABRE in SHield Enables Alignment Transfer to Heteronuclei, SABRE-SHEATH) allowed direct detection of enhanced 15N NMR and corresponding polarization/relaxation dynamics to be characterized in this system for the first time, despite the low natural abundance of 15N. Initial experiments detected at 9.4 T following SABRE-SHEATH at 0.2 μT permitted observation of a single 15N resonance at 332.7 ppm (tentatively assigned to the ring N site meta to the amide group, based on the 1H enhancement pattern, suggesting the less sterically hindered N site dominates this substrate’s interaction with the Ir-based SABRE catalyst). Direct SABRE-SHEATH 15N hyperpolarization using a more optimized setup (with respect to mixing field, temperature, p-H2 flow rate, etc.) that is directly coupled to a 1.4 T benchtop NMR system resulted in improved detection sensitivity, including 15N enhancements of >140,000-fold for the primary 15N resonance (corresponding to a polarization of ∼7% with substrate concentration of over 100 mM). This effort also yielded a 15N T1 measurement for PZA of over 2 min at 1.4 T. Finally, the potential utility of hyperpolarized PZA as a contrast agent was also demonstrated via quantitative 1H MRI studies performed using a low-field (64 mT) portable “point-of-care” clinical scanner.