Filter-exchange spectroscopy is sensitive to gradual cell membrane degradation.

Transmembrane water permeability changes occur after initialization of necrosis and are a mechanism for early detection of cell death. Filter-exchange spectroscopy (FEXSY) is sensitive to transmembrane water permeability and enables its quantification by magnetic resonance via the apparent exchange rate (AXR). In this study, we investigate AXR changes during necrotic cell death. FEXSY measurements of yeast cells in different necrotic stages were performed and compared with established fluorescence cell death markers and pulsed gradient spin echo measurements. Furthermore, the influence of T2 relaxation on AXR was examined in a two-compartment system. The AXR of yeast cells increased slightly after incubation with 20% isopropanol, whereas it peaked sharply after incubation with 25% isopropanol. At this point, almost all the yeast cells were vital but showed compromised membranes. After incubation with 30% isopropanol, AXR measurements showed high variability, at a point corresponding to a majority of the yeast cells being in late-stage necrosis with disrupted cell membranes. Simulations revealed that, for FEXSY measurements in a two-compartment system, a long filter echo time (TEf), compared with the T2 of the slow-diffusing compartment, filters out a fraction of the slow-diffusing compartment signal and leads to overestimation of apparent diffusion coefficient (ADC) and underestimation of AXR. Our results demonstrate that AXR is sensitive to gradual permeabilization of the cell membrane of living cells in different permeabilization stages without exogenous contrast agents. AXR measurements were sensitive to permeability changes induced by relatively low concentrations of isopropanol, at levels for which no measurable effect was detectable by ADC measurements. TEf may act as a signal filter that affects the estimated AXR value of a system consisting of a variety of local diffusivities and a range of T2 that includes T2 values shorter or comparable with the TEf.

Current methods for hyperpolarized [1-13C]pyruvate MRI human studies.

MRI with hyperpolarized (HP) 13C agents, also known as HP 13C MRI, can measure processes such as localized metabolism that is altered in numerous cancers, liver, heart, kidney diseases, and more. It has been translated into human studies during the past 10 years, with recent rapid growth in studies largely based on increasing availability of HP agent preparation methods suitable for use in humans. This paper aims to capture the current successful practices for HP MRI human studies with [1-13C]pyruvate-by far the most commonly used agent, which sits at a key metabolic junction in glycolysis. The paper is divided into four major topic areas: (1) HP 13C-pyruvate preparation; (2) MRI system setup and calibrations; (3) data acquisition and image reconstruction; and (4) data analysis and quantification. In each area, we identified the key components for a successful study, summarized both published studies and current practices, and discuss evidence gaps, strengths, and limitations. This paper is the output of the "HP 13C MRI Consensus Group" as well as the ISMRM Hyperpolarized Media MR and Hyperpolarized Methods and Equipment study groups. It further aims to provide a comprehensive reference for future consensus, building as the field continues to advance human studies with this metabolic imaging modality.

New Horizons in Hyperpolarized 13C MRI.

Hyperpolarization techniques significantly enhance the sensitivity of magnetic resonance (MR) and thus present fascinating new directions for research and applications with in vivo MR imaging and spectroscopy (MRI/S). Hyperpolarized 13C MRI/S, in particular, enables real-time non-invasive assessment of metabolic processes and holds great promise for a diverse range of clinical applications spanning fields like oncology, neurology, and cardiology, with a potential for improving early diagnosis of disease, patient stratification, and therapy response assessment. Despite its potential, technical challenges remain for achieving clinical translation. This paper provides an overview of the discussions that took place at the international workshop "New Horizons in Hyperpolarized 13C MRI," in March 2023 at the Bavarian Academy of Sciences and Humanities, Munich, Germany. The workshop covered new developments, as well as future directions, in topics including polarization techniques (particularly focusing on parahydrogen-based methods), novel probes, considerations related to data acquisition and analysis, and emerging clinical applications in oncology and other fields.

Quo Vadis Hyperpolarized 13C MRI?

Over the last two decades, hyperpolarized 13C MRI has gained significance in both preclinical and clinical studies, hereby relying on technologies like PHIP-SAH (ParaHydrogen-Induced Polarization-Side Arm Hydrogenation), SABRE (Signal Amplification by Reversible Exchange), and dDNP (dissolution Dynamic Nuclear Polarization), with dDNP being applied in humans. A clinical dDNP polarizer has enabled studies across 24 sites, despite challenges like high cost and slow polarization. Parahydrogen-based techniques like SABRE and PHIP offer faster, more cost-efficient alternatives but require molecule-specific optimization. The focus has been on imaging metabolism of hyperpolarized probes, which requires long T1, high polarization and rapid contrast generation. Efforts to establish novel probes, improve acquisition techniques and enhance data analysis methods including artificial intelligence are ongoing. Potential clinical value of hyperpolarized 13C MRI was demonstrated primarily for treatment response assessment in oncology, but also in cardiology, nephrology, hepatology and CNS characterization. In this review on biomedical hyperpolarized 13C MRI, we summarize important and recent advances in polarization techniques, probe development, acquisition and analysis methods as well as clinical trials. Starting from those we try to sketch a trajectory where the field of biomedical hyperpolarized 13C MRI might go.

Lithium isotopes differentially modify mitochondrial amorphous calcium phosphate cluster size distribution and calcium capacity.

Lithium is commonly prescribed as a mood stabilizer in a variety of mental health conditions, yet its molecular mode of action is incompletely understood. Many cellular events associated with lithium appear tied to mitochondrial function. Further, recent evidence suggests that lithium bioactivities are isotope specific. Here we focus on lithium effects related to mitochondrial calcium handling. Lithium protected against calcium-induced permeability transition and decreased the calcium capacity of liver mitochondria at a clinically relevant concentration. In contrast, brain mitochondrial calcium capacity was increased by lithium. Surprisingly, 7Li acted more potently than 6Li on calcium capacity, yet 6Li was more effective at delaying permeability transition. The size distribution of amorphous calcium phosphate colloids formed in vitro was differentially affected by lithium isotopes, providing a mechanistic basis for the observed isotope specific effects on mitochondrial calcium handling. This work highlights a need to better understand how mitochondrial calcium stores are structurally regulated and provides key considerations for future formulations of lithium-based therapeutics.

Current Methods for Hyperpolarized [1-13C]pyruvate MRI Human Studies.

MRI with hyperpolarized (HP) 13C agents, also known as HP 13C MRI, can measure processes such as localized metabolism that is altered in numerous cancers, liver, heart, kidney diseases, and more. It has been translated into human studies during the past 10 years, with recent rapid growth in studies largely based on increasing availability of hyperpolarized agent preparation methods suitable for use in humans. This paper aims to capture the current successful practices for HP MRI human studies with [1-13C]pyruvate - by far the most commonly used agent, which sits at a key metabolic junction in glycolysis. The paper is divided into four major topic areas: (1) HP 13C-pyruvate preparation, (2) MRI system setup and calibrations, (3) data acquisition and image reconstruction, and (4) data analysis and quantification. In each area, we identified the key components for a successful study, summarized both published studies and current practices, and discuss evidence gaps, strengths, and limitations. This paper is the output of the "HP 13C MRI Consensus Group" as well as the ISMRM Hyperpolarized Media MR and Hyperpolarized Methods & Equipment study groups. It further aims to provide a comprehensive reference for future consensus building as the field continues to advance human studies with this metabolic imaging modality.

Interleukin-6-controlled, mesenchymal stem cell-based sodium/iodide symporter gene therapy improves survival of glioblastoma-bearing mice.

New treatment strategies are urgently needed for glioblastoma (GBM)-a tumor resistant to standard-of-care treatment with a high risk of recurrence and extremely poor prognosis. Based on their intrinsic tumor tropism, adoptively applied mesenchymal stem cells (MSCs) can be harnessed to deliver the theranostic sodium/iodide symporter (NIS) deep into the tumor microenvironment. Interleukin-6 (IL-6) is a multifunctional, highly expressed cytokine in the GBM microenvironment including recruited MSCs. MSCs engineered to drive NIS expression in response to IL-6 promoter activation offer the possibility of a new tumor-targeted gene therapy approach of GBM. Therefore, MSCs were stably transfected with an NIS-expressing plasmid controlled by the human IL-6 promoter (IL-6-NIS-MSCs) and systemically applied in mice carrying orthotopic GBM. Enhanced radiotracer uptake by 18F-Tetrafluoroborate-PET/magnetic resonance imaging (MRI) was detected in tumors after IL-6-NIS-MSC application as compared with mice that received wild-type MSCs. Ex vivo analysis of tumors and non-target organs showed tumor-specific NIS protein expression. Subsequent 131I therapy after IL-6-NIS-MSC application resulted in significantly delayed tumor growth assessed by MRI and improved median survival up to 60% of GBM-bearing mice as compared with controls. In conclusion, the application of MSC-mediated NIS gene therapy focusing on IL-6 biology-induced NIS transgene expression represents a promising approach for GBM treatment.

PD-1 instructs a tumor-suppressive metabolic program that restricts glycolysis and restrains AP-1 activity in T cell lymphoma.

The PDCD1-encoded immune checkpoint receptor PD-1 is a key tumor suppressor in T cells that is recurrently inactivated in T cell non-Hodgkin lymphomas (T-NHLs). The highest frequencies of PDCD1 deletions are detected in advanced disease, predicting inferior prognosis. However, the tumor-suppressive mechanisms of PD-1 signaling remain unknown. Here, using tractable mouse models for T-NHL and primary patient samples, we demonstrate that PD-1 signaling suppresses T cell malignancy by restricting glycolytic energy and acetyl coenzyme A (CoA) production. In addition, PD-1 inactivation enforces ATP citrate lyase (ACLY) activity, which generates extramitochondrial acetyl-CoA for histone acetylation to enable hyperactivity of activating protein 1 (AP-1) transcription factors. Conversely, pharmacological ACLY inhibition impedes aberrant AP-1 signaling in PD-1-deficient T-NHLs and is toxic to these cancers. Our data uncover genotype-specific vulnerabilities in PDCD1-mutated T-NHL and identify PD-1 as regulator of AP-1 activity.

Parahydrogen-Polarized [1-13 C]Pyruvate for Reliable and Fast Preclinical Metabolic Magnetic Resonance Imaging.

Hyperpolarization techniques increase nuclear spin polarization by more than four orders of magnitude, enabling metabolic MRI. Even though hyperpolarization has shown clear value in clinical studies, the complexity, cost and slowness of current equipment limits its widespread use. Here, a polarization procedure of [1-13 C]pyruvate based on parahydrogen-induced polarization by side-arm hydrogenation (PHIP-SAH) in an automated polarizer is demonstrated. It is benchmarked in a study with 48 animals against a commercial dissolution dynamic nuclear polarization (d-DNP) device. Purified, concentrated (≈70-160 mM) and highly hyperpolarized (≈18%) solutions of pyruvate are obtained at physiological pH for volumes up to 2 mL within 85 s in an automated process. The safety profile, image quality, as well as the quantitative perfusion and lactate-to-pyruvate ratios, are equivalent for PHIP and d-DNP, rendering PHIP a viable alternative to established hyperpolarization techniques.

Simultaneous magnetic resonance imaging of pH, perfusion and renal filtration using hyperpolarized 13C-labelled Z-OMPD.

pH alterations are a hallmark of many pathologies including cancer and kidney disease. Here, we introduce [1,5-13C2]Z-OMPD as a hyperpolarized extracellular pH and perfusion sensor for MRI which allows to generate a multiparametric fingerprint of renal disease status and to detect local tumor acidification. Exceptional long T1 of two minutes at 1 T, high pH sensitivity of up to 1.9 ppm per pH unit and suitability of using the C1-label as internal frequency reference enables pH imaging in vivo of three pH compartments in healthy rat kidneys. Spectrally selective targeting of both 13C-resonances enables simultaneous imaging of perfusion and filtration in 3D and pH in 2D within one minute to quantify renal blood flow, glomerular filtration rates and renal pH in healthy and hydronephrotic kidneys with superior sensitivity compared to clinical routine methods. Imaging multiple biomarkers within a single session renders [1,5-13C2]Z-OMPD a promising new hyperpolarized agent for oncology and nephrology.

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

Metabolic magnetic resonance imaging (MRI) using hyperpolarized (HP) pyruvate is becoming a non-invasive technique for diagnosing, staging, and monitoring response to treatment in cancer and other diseases. The clinically established method for producing HP pyruvate, dissolution dynamic nuclear polarization, however, is rather complex and slow. Signal Amplification By Reversible Exchange (SABRE) is an ultra-fast and low-cost method based on fast chemical exchange. Here, for the first time, we demonstrate not only in vivo utility, but also metabolic MRI with SABRE. We present a novel routine to produce aqueous HP [1-13 C]pyruvate-d3 for injection in 6 minutes. The injected solution was sterile, non-toxic, pH neutral and contained ≈30 mM [1-13 C]pyruvate-d3 polarized to ≈11 % (residual 250 mM methanol and 20 µM catalyst). It was obtained by rapid solvent evaporation and metal filtering, which we detail in this manuscript. This achievement makes HP pyruvate MRI available to a wide biomedical community for fast metabolic imaging of living organisms.

Repeatability and reproducibility of apparent exchange rate measurements in yeast cell phantoms using filter-exchange imaging.

OBJECTIVES: Development of a protocol for validation and quality assurance of filter-exchange imaging (FEXI) pulse sequences with well-defined and reproducible phantoms. MATERIALS AND METHODS: A FEXI pulse sequence was implemented on a 7 T preclinical MRI scanner. Six experiments in three different test categories were established for sequence validation, demonstration of the reproducibility of phantoms and the measurement of induced changes in the apparent exchange rate (AXR). First, an ice-water phantom was used to investigate the consistency of apparent diffusion coefficient (ADC) measurements with different diffusion filters. Second, yeast cell phantoms were utilized to validate the determination of the AXR in terms of repeatability (same phantom and session), reproducibility (separate but comparable phantoms in different sessions) and directionality of diffusion encodings. Third, the yeast cell phantoms were, furthermore, used to assess potential AXR bias because of altered cell density and temperature. In addition, a treatment experiment with aquaporin inhibitors was performed to evaluate the influence of these compounds on the cell membrane permeability in yeast cells. RESULTS: FEXI-based ADC measurements of an ice-water phantom were performed for three different filter strengths, showed good agreement with the literature value of 1.099 × 10-3 mm2/s and had a maximum coefficient of variation (CV) of 0.55% within the individual filter strengths. AXR estimation in a single yeast cell phantom and imaging session with five repetitions resulted in an overall mean value of (1.49 ± 0.05) s-1 and a CV of 3.4% between the chosen regions of interest. For three separately prepared phantoms, AXR measurements resulted in a mean value of (1.50 ± 0.04) s-1 and a CV of 2.7% across the three phantoms, demonstrating high reproducibility. Across three orthogonal diffusion directions, a mean value of (1.57 ± 0.03) s-1 with a CV of 1.9% was detected, consistent with isotropy of AXR in yeast cells. Temperature and AXR were linearly correlated (R2 = 0.99) and an activation energy EA of 37.7 kJ/mol was determined by Arrhenius plot. Furthermore, a negative correlation was found between cell density (as determined by the reference ADC/fe) and AXR (R2 = 0.95). The treatment experiment resulted in significantly decreased AXR values at different temperatures in the treated sample compared to the untreated control indicating an inhibiting effect. CONCLUSIONS: Using ice-water and yeast cell-based phantoms, a protocol for the validation of FEXI pulse sequences was established for the assessment of stability, repeatability, reproducibility and directionality. In addition, a strong dependence of AXR on cell density and temperature was shown. As AXR is an emerging novel imaging biomarker, the suggested protocol will be useful for quality assurance of AXR measurements within a study and potentially across multiple sites.

Spectrally selective bSSFP using off-resonant RF excitations permits high spatiotemporal resolution 3D metabolic imaging of hyperpolarized [1-13 C]Pyruvate-to-[1-13 C]lactate conversion.

PURPOSE: To develop a high spatiotemporal resolution 3D dynamic pulse sequence for preclinical imaging of hyperpolarized [1-13 C]pyruvate-to-[1-13 C]lactate metabolism at 7T. METHODS: A standard 3D balanced SSFP (bSSFP) sequence was modified to enable alternating-frequency excitations. RF pulses with 2.33 ms duration and 900 Hz FWHM were placed off-resonance of the target metabolites, [1-13 C]pyruvate (by approximately -245 Hz) and [1-13 C]lactate (by approximately 735 Hz), to selectively excite those resonances. Relatively broad bandwidth (compared to those metabolites' chemical shift offset) permits a short TR of 6.29 ms, enabling higher spatiotemporal resolution. Bloch equation simulations of the bSSFP response profile guided the sequence parameter selection to minimize spectral contamination between metabolites and preserve magnetization over time. RESULTS: Bloch equation simulations, phantom studies, and in vivo studies demonstrated that the two target resonances could be cleanly imaged without substantial bSSFP banding artifacts and with little spectral contamination between lactate and pyruvate and from pyruvate hydrate. High spatiotemporal resolution 3D images were acquired of in vivo pyruvate-lactate metabolism in healthy wild-type and endogenous pancreatic tumor-bearing mice, with 1.212 s acquisition time per single-metabolite image and (1.75 mm)3 isotropic voxels with full mouse abdomen 56 × 28 × 21 mm3 FOV and fully-sampled k-space. Kidney and tumor lactate/pyruvate ratios of two consecutive measurements in one animal, 1 h apart, were consistent. CONCLUSION: Spectrally selective bSSFP using off-resonant RF excitations can provide high spatio-temporal resolution 3D dynamic images of pyruvate-lactate metabolic conversion.

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

We present a versatile method for the preparation of hyperpolarized [1-13C]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 [1-13C]-fumarate solution of volumes up to 3 mL with 13-20% 13C-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 13C-labeled precursor for the hydrogenation reaction with high yield, starting from 13CO2 as a cost-effective source for 13C-labeled compounds.

Mesenchymal Stem Cell-mediated Image-guided Sodium Iodide Symporter (NIS) Gene Therapy Improves Survival of Glioblastoma-bearing Mice.

PURPOSE: Mesenchymal stem cells (MSC) have emerged as cellular-based vehicles for the delivery of therapeutic genes in cancer therapy based on their inherent tumor-homing capability. As theranostic gene, the sodium iodide symporter (NIS) represents a successful target for noninvasive radionuclide-based imaging and therapy. In this study, we applied genetically engineered MSCs for tumor-targeted NIS gene transfer in experimental glioblastoma (GBM)-a tumor with an extremely poor prognosis. EXPERIMENTAL DESIGN: A syngeneic, immunocompetent GL261 GBM mouse model was established by subcutaneous and orthotopic implantation. Furthermore, a subcutaneous xenograft U87 model was used. Bone marrow-derived MSCs were stably transfected with a NIS-expressing plasmid driven by the constitutively active cytomegalovirus promoter (NIS-MSC). After multiple or single intravenous injection of NIS-MSCs, tumoral iodide uptake was monitored in vivo using 123I-scintigraphy or 124I-PET. Following validation of functional NIS expression, a therapy trial with 131I was performed on the basis of the most optimal application regime as seen by 124I-PET imaging in the orthotopic approach. RESULTS: A robust tumoral NIS-specific radionuclide accumulation was observed after NIS-MSC and radioiodide application by NIS-mediated in vivo imaging. NIS immunofluorescence staining of GBM and non-target tissues showed tumor-selective MSC homing along with NIS expression. Application of therapeutically effective 131I led to significantly delayed tumor growth and prolonged median survival after NIS-MSC treatment as compared with controls. CONCLUSIONS: A strong tumor-selective recruitment of systemically applied MSCs into GBM was found using NIS as reporter gene followed by successful therapeutic application of radioiodide demonstrating the potential use of NIS-based MSCs as therapy vehicles as a new GBM therapy approach.

Functional noninvasive detection of glycolytic pancreatic ductal adenocarcinoma.

BACKGROUND: Pancreatic ductal adenocarcinoma (PDAC) lacks effective treatment options beyond chemotherapy. Although molecular subtypes such as classical and QM (quasi-mesenchymal)/basal-like with transcriptome-based distinct signatures have been identified, deduced therapeutic strategies and targets remain elusive. Gene expression data show enrichment of glycolytic genes in the more aggressive and therapy-resistant QM subtype. However, whether the glycolytic transcripts are translated into functional glycolysis that could further be explored for metabolic targeting in QM subtype is still not known. METHODS: We used different patient-derived PDAC model systems (conventional and primary patient-derived cells, patient-derived xenografts (PDX), and patient samples) and performed transcriptional and functional metabolic analysis. These included RNAseq and Illumina HT12 bead array, in vitro Seahorse metabolic flux assays and metabolic drug targeting, and in vivo hyperpolarized [1-13C]pyruvate and [1-13C]lactate magnetic resonance spectroscopy (HP-MRS) in PDAC xenografts. RESULTS: We found that glycolytic metabolic dependencies are not unambiguously functionally exposed in all QM PDACs. Metabolic analysis demonstrated functional metabolic heterogeneity in patient-derived primary cells and less so in conventional cell lines independent of molecular subtype. Importantly, we observed that the glycolytic product lactate is actively imported into the PDAC cells and used in mitochondrial oxidation in both classical and QM PDAC cells, although more actively in the QM cell lines. By using HP-MRS, we were able to noninvasively identify highly glycolytic PDAC xenografts by detecting the last glycolytic enzymatic step and prominent intra-tumoral [1-13C]pyruvate and [1-13C]lactate interconversion in vivo. CONCLUSION: Our study adds functional metabolic phenotyping to transcriptome-based analysis and proposes a functional approach to identify highly glycolytic PDACs as candidates for antimetabolic therapeutic avenues.

Dual EGFR- and TfR-targeted gene transfer for sodium iodide symporter gene therapy of glioblastoma.

Sodium iodide symporter (NIS) gene transfer for active accumulation of iodide in tumor cells is a powerful theranostic strategy facilitating both diagnostic and therapeutic application of radioiodide. In glioblastoma (GBM), the blood-brain barrier (BBB) presents an additional delivery barrier for nucleic acid nanoparticles. In the present study, we designed dual-targeted NIS plasmid DNA complexes containing targeting ligands for the transferrin receptor (TfR) and the epidermal growth factor receptor (EGFR), thus providing the potential for active transport across the BBB followed by targeting of tumor cells. In vitro 125I transfection studies confirmed TfR- and EGFR-dependent transfection efficiency and NIS-specific iodide uptake of dual-targeted polyplexes. In vivo gene transfer in mice bearing orthotopic U87 GBM xenografts was assessed at 48 h after intravenous polyplex injection by positron emission tomography (PET) imaging using 18F-labeled tetrafluoroborate (TFB) as tracer. The tumoral 18F-TFB uptake of mice treated with dual-targeted polyplexes (0.56% ± 0.08% ID/mL) was significantly higher compared with mice treated with EGFR-mono-targeted (0.33% ± 0.03% ID/mL) or TfR-mono-targeted (0.27% ± 0.04% ID/mL) polyplexes. In therapy studies, application of 131I induced a superior therapeutic effect of the dual-targeted therapy, demonstrated by a significant delay in tumor growth and prolonged survival.

The sodium iodide symporter (NIS) as theranostic gene: its emerging role in new imaging modalities and non-viral gene therapy.

Cloning of the sodium iodide symporter (NIS) in 1996 has provided an opportunity to use NIS as a powerful theranostic transgene. Novel gene therapy strategies rely on image-guided selective NIS gene transfer in non-thyroidal tumors followed by application of therapeutic radionuclides. This review highlights the remarkable progress during the last two decades in the development of the NIS gene therapy concept using selective non-viral gene delivery vehicles including synthetic polyplexes and genetically engineered mesenchymal stem cells. In addition, NIS is a sensitive reporter gene and can be monitored by high resolution PET imaging using the radiotracers sodium [124I]iodide ([124I]NaI) or [18F]tetrafluoroborate ([18F]TFB). We performed a small preclinical PET imaging study comparing sodium [124I]iodide and in-house synthesized [18F]TFB in an orthotopic NIS-expressing glioblastoma model. The results demonstrated an improved image quality using [18F]TFB. Building upon these results, we will be able to expand the NIS gene therapy approach using non-viral gene delivery vehicles to target orthotopic tumor models with low volume disease, such as glioblastoma.Trial registration not applicable.

Prediction of multiple pH compartments by deep learning in magnetic resonance spectroscopy with hyperpolarized 13C-labelled zymonic acid.

BACKGROUND: Hyperpolarization enhances the sensitivity of nuclear magnetic resonance experiments by between four and five orders of magnitude. Several hyperpolarized sensor molecules have been introduced that enable high sensitivity detection of metabolism and physiological parameters. However, hyperpolarized magnetic resonance spectroscopy imaging (MRSI) often suffers from poor signal-to-noise ratio and spectral analysis is complicated by peak overlap. Here, we study measurements of extracellular pH (pHe) by hyperpolarized zymonic acid, where multiple pHe compartments, such as those observed in healthy kidney or other heterogeneous tissue, result in a cluster of spectrally overlapping peaks, which is hard to resolve with conventional spectroscopy analysis routines. METHODS: We investigate whether deep learning methods can yield improved pHe prediction in hyperpolarized zymonic acid spectra of multiple pHe compartments compared to conventional line fitting. As hyperpolarized 13C-MRSI data sets are often small, a convolutional neural network (CNN) and a multilayer perceptron (MLP) were trained with either a synthetic or a mixed (synthetic and augmented) data set of acquisitions from the kidneys of healthy mice. RESULTS: Comparing the networks' performances compartment-wise on a synthetic test data set and eight real kidney data shows superior performance of CNN compared to MLP and equal or superior performance compared to conventional line fitting. For correct prediction of real kidney pHe values, training with a mixed data set containing only 0.5% real data shows a large improvement compared to training with synthetic data only. Using a manual segmentation approach, pH maps of kidney compartments can be improved by neural network predictions for voxels including three pH compartments. CONCLUSION: The results of this study indicate that CNNs offer a reliable, accurate, fast and non-interactive method for analysis of hyperpolarized 13C MRS and MRSI data, where low amounts of acquired data can be complemented to achieve suitable network training.

Conversion of Hyperpolarized [1-13C]Pyruvate in Breast Cancer Cells Depends on Their Malignancy, Metabolic Program and Nutrient Microenvironment.

Hyperpolarized magnetic resonance spectroscopy (MRS) is a technology for characterizing tumors in vivo based on their metabolic activities. The conversion rates (kpl) of hyperpolarized [1-13C]pyruvate to [1-13C]lactate depend on monocarboxylate transporters (MCT) and lactate dehydrogenase (LDH); these are also indicators of tumor malignancy. An unresolved issue is how glucose and glutamine availability in the tumor microenvironment affects metabolic characteristics of the cancer and how this relates to kpl-values. Two breast cancer cells of different malignancy (MCF-7, MDA-MB-231) were cultured in media containing defined combinations of low glucose (1 mM; 2.5 mM) and glutamine (0.1 mM; 1 mM) and analyzed for pyruvate uptake, intracellular metabolite levels, LDH and pyruvate kinase activities, and 13C6-glucose-derived metabolomics. The results show variability of kpl with the different glucose/glutamine conditions, congruent with glycolytic activity, but not with LDH activity or the Warburg effect; this suggests metabolic compartmentation. Remarkably, kpl-values were almost two-fold higher in MCF-7 than in the more malignant MDA-MB-231 cells, the latter showing a higher flux of 13C-glucose-derived pyruvate to the TCA-cycle metabolites 13C2-citrate and 13C3-malate, i.e., pyruvate decarboxylation and carboxylation, respectively. Thus, MRS with hyperpolarized [1-13C-pyruvate] is sensitive to both the metabolic program and the nutritional state of cancer cells.