This white paper discusses prospects for advancing hyperpolarization technology to better understand cancer metabolism, identify current obstacles to HP (hyperpolarized) 13C magnetic resonance imaging's (MRI's) widespread clinical use, and provide recommendations for overcoming them. Since the publication of the first NIH white paper on hyperpolarized 13C MRI in 2011, preclinical studies involving [1-13C]pyruvate as well a number of other 13C labeled metabolic substrates have demonstrated this technology's capacity to provide unique metabolic information. A dose-ranging study of HP [1-13C]pyruvate in patients with prostate cancer established safety and feasibility of this technique. Additional studies are ongoing in prostate, brain, breast, liver, cervical, and ovarian cancer. Technology for generating and delivering hyperpolarized agents has evolved, and new MR data acquisition sequences and improved MRI hardware have been developed. It will be important to continue investigation and development of existing and new probes in animal models. Improved polarization technology, efficient radiofrequency coils, and reliable pulse sequences are all important objectives to enable exploration of the technology in healthy control subjects and patient populations. It will be critical to determine how HP 13C MRI might fill existing needs in current clinical research and practice, and complement existing metabolic imaging modalities. Financial sponsorship and integration of academia, industry, and government efforts will be important factors in translating the technology for clinical research in oncology. This white paper is intended to provide recommendations with this goal in mind.

Vascular calcification is a complex biological process that is a hallmark of atherosclerosis. While macrocalcification confers plaque stability, microcalcification is a key feature of high-risk atheroma and is associated with increased morbidity and mortality. Positron emission tomography and X-ray computed tomography (PET/CT) imaging of atherosclerosis using ¹⁸F-sodium fluoride (¹⁸F-NaF) has the potential to identify pathologically high-risk nascent microcalcification. However, the precise molecular mechanism of ¹⁸F-NaF vascular uptake is still unknown. Here we use electron microscopy, autoradiography, histology and preclinical and clinical PET/CT to analyse ¹⁸F-NaF binding. We show that ¹⁸F-NaF adsorbs to calcified deposits within plaque with high affinity and is selective and specific. ¹⁸F-NaF PET/CT imaging can distinguish between areas of macro- and microcalcification. This is the only currently available clinical imaging platform that can non-invasively detect microcalcification in active unstable atherosclerosis. The use of ¹⁸F-NaF may foster new approaches to developing treatments for vascular calcification.

Dynamic nuclear polarization of ¹³ C-labeled cell substrates has been shown to massively increase their sensitivity to detection in NMR experiments. The sensitivity gain is sufficiently large that if these polarized molecules are injected intravenously, their spatial distribution and subsequent conversion into other cell metabolites can be imaged. We have used this method to image the conversion of fumarate to malate in a murine lymphoma tumor in vivo after i.v. injection of hyperpolarized [1,4- ¹³ C ₂ ]fumarate. In isolated lymphoma cells, the rate of labeled malate production was unaffected by coadministration of succinate, which competes with fumarate for transport into the cell. There was, however, a correlation with the percentage of cells that had lost plasma membrane integrity, suggesting that the production of labeled malate from fumarate is a sensitive marker of cellular necrosis. Twenty-four hours after treating implanted lymphoma tumors with etoposide, at which point there were significant levels of tumor cell necrosis, there was a 2.4-fold increase in hyperpolarized [1,4- ¹³ C ₂ ]malate production compared with the untreated tumors. Therefore, the formation of hyperpolarized ¹³ C-labeled malate from [1,4- ¹³ C ₂ ]fumarate appears to be a sensitive marker of tumor cell death in vivo and could be used to detect the early response of tumors to treatment. Given that fumarate is an endogenous molecule, this technique has the potential to be used clinically.

Significance: Patients with microsatellite stable (MSS) pancreatic (PDA) or colorectal cancer (CRC) do not respond to immunotherapy with inhibitors of T cell checkpoints. A possible explanation is suggested by finding that cancer cells in these tumors are coated with the chemokine, CXCL12, and that stimulation of CXCR4, the CXCL12 receptor on immune cells, suppresses directed migration mediated by other chemokine receptors on these cells. We assessed the relevance of these findings by treating patients for seven days with continuous infusion of AMD3100/Plerixafor, a CXCR4 inhibitor. Comparison of pre- and end-of-treatment paired biopsies of metastatic lesions by transcriptomic analysis revealed that AMD3100 induced an integrated immune response that is predictive of a clinical response to T cell checkpoint inhibition.