Parahydrogen-Polarized Fumarate for Preclinical in Vivo Metabolic Magnetic Resonance Imaging

Abstract

We present a versatile method for the preparation of hyperpolarized [1-13 C]fumarate as a contrast agent for preclinical in vivo MRI, using parahydrogen-induced polarization (PHIP). To benchmark this process, we compared a prototype PHIP polarizer to a state-of-the-art dissolution dynamic nuclear polarization (d-DNP) system. We found comparable polarization, volume, and concentration levels of the prepared solutions, while the preparation effort is significantly lower for the PHIP process, which can provide a preclinical dose every 10 min, opposed to around 90 min for d-DNP systems. With our approach, a 100 mM [1-13 C]-fumarate solution of volumes up to 3 mL with 13−20% 13 C-hyperpolarization after purification can be produced. The purified solution has a physiological pH, while the catalyst, the reaction side products, and the precursor material concentrations are reduced to nontoxic levels, as confirmed in a panel of cytotoxicity studies. The in vivo usage of the hyperpolarized fumarate as a perfusion agent in healthy mice and the metabolic conversion of fumarate to malate in tumor-bearing mice developing regions with necrotic cell death is demonstrated. Furthermore, we present a one-step synthesis to produce the 13 C-labeled precursor for the hydrogenation reaction with high yield, starting from 13 CO 2 as a cost-effective source for 13 C-labeled compounds.

Combined Homogeneous and Heterogeneous Hydrogenation with Parahydrogen to Yield Catalyst-Free Solutions of Hyperpolarized [1-13C]Succinate

“…This is not necessary if higher hydrogen gas pressure and starting material concentration are used, to form fumarate in ≳200 mM concentration to allow direct precipitation from the reaction solution . 40 In high resolution 1 H NMR spectra we observed that the succinate formed was partially deuterated during the heterogeneous hydrogenation reaction (i.e., while the sample was in the presence of the heterogeneous catalyst). We carried out six additional 30 s hydrogenation experiments at 90 • C using 10, 15, and 20 wt.% Pd/Al2O3, and observed 16.5±1.5% deuteration of the succinate: 43% succinate-h4, 50% succinate-d1 and 8% succinate-2,3-d2.…”

StereoPHIP: Stereoselective Parahydrogen‐Induced Polarization

“…Hydrogenative PHIP generally uses homogeneous rhodium‐based catalysts for the addition of para‐H 2 to unsaturated precursors. This process requires specific chemistry (unsaturated precursor and optimal J coupling network in the product) and therefore, only a limited number of in vivo studies have been performed with HP‐ 13 C‐labeled metabolic probes generated by this technique [6–8] . Elegant work by Reineri and co‐workers overcame this limitation by parahydrogenating an unsaturated functional group attached to the substrate through a cleavable bond, typically an ester (side‐arm hydrogenation, SAH) [9–14] .…”

“…This process requires specific chemistry (unsaturated precursor and optimal J coupling network in the product) and therefore, only a limited number of in vivo studies have been performed with HP-13 C-labeled metabolic probes generated by this technique. [6][7][8] Elegant work by Reineri and co-workers overcame this limitation by parahydrogenating an unsaturated functional group attached to the substrate through a cleavable bond, typically an ester (side-arm hydrogenation, SAH). [9][10][11][12][13][14] SAH-PHIP often suffers from low 13 C polarization levels because of the weak long range J coupling between the heteroatom and the 1 H spins originating from para-H 2 .…”

In Vivo Metabolic Imaging of [1-13C]Pyruvate-d3 Hyperpolarized By Reversible Exchange With Parahydrogen

“…Parahydrogen-induced polarization (PHIP) techniques have emerged as promising candidates to address this need for efficient polarization methods. [12][13][14][15][16][17][18][19][20][21][22][23][24][25] PHIP utilizes the nuclear spin singlet isomer of molecular hydrogen, parahydrogen (pH2), which acts as a cost-efficient source of hyperpolarization.…”