Background: Tumor cells frequently show high rates of aerobic glycolysis, which provides the glycolytic intermediates needed for the increased biosynthetic demands of rapid cell growth and proliferation. Existing clinical methods (fluorodeoxyglucose PET and carbon 13 MRI and spectroscopy) do not allow quantitative images of glycolytic flux. Purpose: To evaluate the use of deuterium (hydrogen 2 [ 2 H]) MR spectroscopic imaging for quantitative mapping of tumor glycolytic flux and to assess response to chemotherapy. Materials and Methods: A fast three-dimensional 2 H MR spectroscopic imaging pulse sequence, with a time resolution of 10 minutes, was used to image glycolytic flux in a murine tumor model after bolus injection of D-[6,6'-2 H 2 ]glucose before and 48 hours after treatment with a chemotherapeutic agent. Tumor lactate labeling, expressed as the lactate-to-water and lactate-to-glucose signal ratios, was also assessed in localized 2 H MR spectra. Statistical significance was tested with a one-sided paired t test. Results: 2 H MR spectroscopic imaging showed heterogeneity in glycolytic flux across the tumor and an early decrease in flux following treatment with a chemotherapeutic drug. Spectroscopy measurements on five animals showed a decrease in the lactate-to-water signal ratio, from 0.33 6 0.10 to 0.089 6 0.039 (P = .005), and in the lactate-to-glucose ratio, from 0.27 6 0.12 to 0.12 6 0.06 (P = .04), following drug treatment. Conclusion: Rapidly acquired deuterium (hydrogen 2) MR spectroscopic images can provide quantitative and spatially resolved measurements of glycolytic flux in tumors that can be used to assess treatment response. Published under a CC BY 4.0 license.

Invasion of erythrocytes by Plasmodium falciparum merozoites is necessary for malaria pathogenesis and is therefore a primary target for vaccine development. RH5 is a leading subunit vaccine candidate because anti-RH5 antibodies inhibit parasite growth and the interaction with its erythrocyte receptor basigin is essential for invasion. RH5 is secreted, complexes with other parasite proteins including CyRPA and RIPR, and contains a conserved N-terminal region (RH5Nt) of unknown function that is cleaved from the native protein. Here, we identify P113 as a merozoite surface protein that directly interacts with RH5Nt. Using recombinant proteins and a sensitive protein interaction assay, we establish the binding interdependencies of all the other known RH5 complex components and conclude that the RH5Nt-P113 interaction provides a releasable mechanism for anchoring RH5 to the merozoite surface. We exploit these findings to design a chemically synthesized peptide corresponding to RH5Nt, which could contribute to a cost-effective malaria vaccine.

Metabolic imaging has been widely used to measure the early responses of tumors to treatment. Here, we assess the abilities of PET measurement of [ 18 F]FDG uptake and MRI measurement of hyperpolarized [1-13 C]pyruvate metabolism to detect early changes in glycolysis following treatmentinduced cell death in human colorectal (Colo205) and breast adenocarcinoma (MDA-MB-231) xenografts in mice. A TRAIL agonist that binds to human but not mouse cells induced tumor-selective cell death. Tumor glycolysis was assessed by injecting [1,6-13 C 2 ]glucose and measuring 13 C-labeled metabolites in tumor extracts. Injection of hyperpolarized [1-13 C]pyruvate induced rapid reduction in lactate labeling. This decrease, which correlated with an increase in histologic markers of cell death and preceded decrease in tumor volume, reflected reduced flux from glucose to lactate and decreased lactate concentration. However, [ 18 F]FDG uptake and phosphorylation were maintained following treatment, which has been attributed previously to increased [ 18 F]FDG uptake by infiltrating immune cells. Quantification of [ 18 F]FDG uptake in flow-sorted tumor and immune cells from disaggregated tumors identified CD11b þ /CD45 þ macrophages as the most [ 18 F]FDG-avid cell type present, yet they represented <5% of the cells present in the tumors and could not explain the failure of [ 18 F]FDG-PET to detect treatment response. MRI measurement of hyperpolarized [1-13 C]pyruvate metabolism is therefore a more sensitive marker of the early decreases in glycolytic flux that occur following cell death than PET measurements of [ 18 F]FDG uptake. Significance: These findings demonstrate superior sensitivity of MRI measurement of hyperpolarized [1-13 C]pyruvate metabolism versus PET measurement of 18 F-FDG uptake for detecting early changes in glycolysis following treatmentinduced tumor cell death.