Hyperpolarization of 15N in an amino acid derivative

Hyperpolarization of 15N-Pyridinium by Using Parahydrogen Enables Access to Reactive Oxygen Sensors and Pilot In Vivo Studies

Magnetic resonance with hyperpolarized contrast agents is one of the most powerful and noninvasive imaging platforms capable for investigating in vivo metabolism. While most of the utilized hyperpolarized agents are based on 13C nuclei, a milestone advance in this area is the emergence of 15N hyperpolarized contrast agents. Currently, the reported 15N hyperpolarized agents mainly utilize the dissolution dynamic nuclear polarization (d-DNP) protocol. The parahydrogen enhanced 15N probes have proven to be elusive and have been tested almost exclusively in organic solvents. Herein, we designed a reaction based reactive oxygen sensor 15N-boronobenzyl-2-styrylpyridinium (15N-BBSP) which can be hyperpolarized with para-hydrogen. Reactive oxygen species plays a vital role as one of the essential intracellular signalling molecules. Disturbance of the H2O2 level usually represents a hallmark of pathophysiological conditions. This H2O2 probe exhibited rapid responsiveness toward H2O2 and offered spectrally resolvable chemical shifts. We also provide strategies to bring the newly developed probe from the organic reaction solution into a biocompatible injection buffer and demonstrate the feasibility of in vivo 15N signal detection. The present work manifests its great potential not only for reaction based reactive sensing probes but also promises to serve as a platform to develop other contrast agents.

Characterizing Metabolic Heterogeneity of Hepatocellular Carcinoma with Hyperpolarized 13C Pyruvate MRI and Mass Spectrometry

Purpose To characterize the metabolomic profiles of two hepatocellular carcinoma (HCC) rat models, track evolution of these profiles to a stimulated tumor state, and assess their effect on lactate flux with hyperpolarized (HP) carbon 13 (13C) MRI. Materials and Methods Forty-three female adult Fischer rats were implanted with N1S1 or McA-RH7777 HCC tumors. In vivo lactate-to-pyruvate ratio (LPR) was measured with HP 13C MRI at 9.4 T. Ex vivo mass spectrometry was used to measure intratumoral metabolites, and Ki67 labeling was used to quantify proliferation. Tumors were first compared with three normal liver controls. The tumors were then compared with stimulated variants via off-target hepatic thermal ablation treatment. All comparisons were made using the Mann-Whitney test. Results HP 13C pyruvate MRI showed greater LPR in N1S1 tumors compared with normal liver (mean [SD], 0.564 ± 0.194 vs 0.311 ± 0.057; P < .001 [n = 9]), but not for McA-RH7777 (P = .44 [n = 8]). Mass spectrometry confirmed that the glycolysis pathway was increased in N1S1 tumors and decreased in McA-RH7777 tumors. The pentose phosphate pathway was also decreased only in McA-RH7777 tumors. Increased proliferation in stimulated N1S1 tumors corresponded to a net increase in LPR (six stimulated vs six nonstimulated, 0.269 ± 0.148 vs 0.027 ± 0.08; P = .009), but not in McA-RH7777 (eight stimulated vs six nonstimulated, P = .13), despite increased proliferation and metastases. Mass spectrometry demonstrated relatively increased lactate production with stimulation in N1S1 tumors only. Conclusion Two HCC subtypes showed divergent glycolytic dependency at baseline and during transformation to a high proliferation state. This metabolic heterogeneity in HCC should be considered with use of HP 13C MRI for diagnosis and tracking. Keywords: Molecular Imaging-Probe Development, Liver, Abdomen/GI, Oncology, Hepatocellular Carcinoma © RSNA, 2024 See also commentary by Ohliger in this issue.