Keywords: Biology, Models, Methods, Modelling

Motivation: Isotope exchange at equilibrium complicates interpretation hyperpolarized [1-¹³C]pyruvate MR. Modelling this phenomenon could help to quantify the effect of exchange on HP MR signal.

Goal(s): Investigate how isotope exchange (compensatory backward conversion of unlabeled lactate concurrent with labeled lactate production) occurs and affects hyperpolarized [1-¹³C]pyruvate MR.

Approach: Develop a realistic computational model of pyruvate-lactate interconversion and apply it to characterize how different levels of endogenous lactate influence metabolic reaction kinetics and exchange.

Results: Elevation of unlabeled lactate increases isotope exchange at equilibrium. Net production of lactate occurs unless total lactate exceeds its equilibrium ratio with total pyruvate.

Impact: This in silico model of isotope exchange in hyperpolarized [1-13C]pyruvate MR realistically replicates spectroscopic measurements, with particle-level data for a range of conditions providing insight into metabolic dynamics relevant to complex cellular architectures with different local equilibria.

Keywords: Probes & Targets, Hyperpolarized MR (Non-Gas), Fumarate, meglumine, hyperpolarization, gluconeogenesis, solubility

Motivation: Clinical translation of many hyperpolarized substrates, including ¹³C-fumarate, has been obstructed by its low solubility in water, causing rapid precipitation of the substrates after dissolution when prepared in conventional glassing solvents. 

Goal(s): The goal of this study was to enhance water solubility and glassing properties of fumarate. 

Approach: We introduced a new formulation of fumarate for DNP by using meglumine as a counterion.

Results: Meglumine significantly improved the polarization performance of fumarate with excellent solubility and glassing properties and previously invisible products along gluconeogenesis were observed in rat kidneys in vivo. 

Impact: The solubilizing and vitrifying effect of meglumine counterion is not limited to fumarate. It is applicable to other 13C- and 15N-labeled compounds such as carboxylic acids and amino acids that have poor solubility and can form meglumine salts or adducts. 

Keywords: Small Animals, Oxygenation

Motivation: T2* MRI and photoacoustic imaging (PAI) offer non-invasive oxygenation measures, but their comparative effectiveness for placental study remains untested.

Goal(s): Our goal was to directly compare T2* MRI and PAI's ability and effectiveness to assess placental and fetal organ oxygenation responses under normoxic hypercapnia challenge.

Approach: Using pregnant rats, the study involved sequential scans of fetoplacental units with T2* MRI and PAI under normoxic hypercapnia challenge.

Results: We found discrepancies between MRI and PAI in detecting oxygenation changes. MRI displayed a marked response in placental oxygenation, not as prominently reflected in PAI measurements.

Impact: T2* MRI could accurately captures fetoplacental responses to hypercapnia, outperforming photoacoustic imaging. Investigating this performance gap is essential before combining these techniques in preeclampsia and fetal growth restriction studies.

Keywords: Small Animals, Quantitative Imaging

Motivation: Intravoxel incoherent motion (IVIM) imaging can evaluate tissue microperfusion and diffusion information respectively, which can more accurately evaluate renal fibrosis (RF) in chronic kidney disease. 

Goal(s): IVIM can reflect the occurrence and development of RF from two aspects of perfusion and diffusion respectively. It has a great application prospect for the evaluation of RF.

Approach: The dynamic changes of renal cortical and medullary signal with the progression of fibrosis were monitored by IVIM, and the compensatory effect of the contralateral kidney was analyzed. 

Results: Some IVIM parameters of the renal cortex and medulla were moderately or strongly negatively correlated with RF.

Impact: Early detection and dynamic evaluation of the process of RF are crucial for reversing renal function damage. IVIM can reflect the development of RF from two aspects of perfusion and diffusion, which has a great application prospect for evaluating RF.

Keywords: Small Animals, CEST & MT

Motivation: There is lack of a comprehensive MRI technique to comprehensively detect the acute kidney injury (AKI) induced by ischemia reperfusion injury (IRI).

Goal(s): We aimed to develop the mpMRI for diagnosis of AKI induced by ischemia reperfusion IRI.

Approach: The IRI-AKI model of 40-minutes ischemia in rats were established, and mpMRI is conducted at 0, 1, 3, 7, 14, and 28 days. Several MRI indexes signal and their diagnosis performance were compare, respectively.

Results: Multi-parametric MRI may shows comprehensive variations in IRI-AKI, and amine-CEST may exhibits the highest accuracy for diagnosis of IRI-AKI.

Impact: This may provide guideline for clinical application of renal mpMRI.

Keywords: Electron Paramagnetic Resonance, Oxygenation, EPR oximetry, Ox071

Motivation: EPR oximetry using Ox071 holds promise in detecting chemotherapy-induced acute kidney injury by monitoring pO₂ distribution. 

Goal(s): Using EPR, our study assessed the ability to discern pO₂ variations between healthy kidneys and kidney injury models induced by intraperitoneal cyclophosphamide treatment. 

Approach: To validate these changes, we performed ex vivo histological assessments with pimonidazole staining, comparing these results with EPR based pO₂ maps. 

Results: Analysis of the hypoxic fraction in tumor tissues via pimonidazole staining revealed a transient reduction at 2 days post-treatment, followed by recovery at 30 days. EPR oximetry results consistently mirrored these trends, affirming its reliability as a non-invasive method.

Impact: Historically, EPR oximetry focused on tumor hypoxia due to Ox063's limitations in well-oxygenated tissues. Using Ox071, a deuterated analog, current research extends oximetry to normoxic tissues, notably the kidneys.

Keywords: Biomarkers, Cancer, ITPP, EPRI, Immunotherapy, Radiosensitizer, Breast Cancer

Motivation: We showed previously that multispectral optoacoustic tomography (MSOT) measures oxygen saturation (%sO₂) of intravascular hemoglobin which can indirectly evaluate the effect of a radiosensitizer, inositol tripyrophosphate (ITPP), on tumor oxygenation. Electron paramagnetic resonance imaging (EPRI) could serve as a more direct biomarker by measuring the extravascular, extracellular oxygen pressure (pO₂) in pre-clinical tumor models.

Goal(s): Validate prior MSOT results showing decrease in hemoglobin saturation with ITPP.

Approach: Use EPRI to observe extracellular oxygenation before and after treatment with ITPP compared with vehicle control.

Results: Tumors treated with ITPP demonstrated lower extracellular oxygenation compared to pretreatment levels (p = 0.003).

Impact: An imaging biomarker to determine how much a radiosensitizer improves tumor pO2 would dramatically impact clinical care by potentially improving response to radiotherapy and immunotherapy.  EPRI could evaluate the effect of a radiosensitizer allowing for more personalized treatment approaches. 

Keywords: Small Animals, Cancer

Motivation: Many cancer studies concentrate in isolated markers like oxygenation, pH or relaxivity measurements. We believe studying all biomarkers and its interactions as microenvironments is the key.

Goal(s): Our goal is to build a library of multiparametric data with pH-derived habitats to aid treatment response in the future.

Approach: Mice with flank implanted pancreatic tumors were imaged to estimate tumor volume, pH, R₂* and susceptibility maps. All maps were compared using one-way ANOVA between two pH-derived habitats.

Results: Significant differences in susceptibility and R₂* were found between pH-derived habitats for large tumors. The same trend, without significant differences, was found in smaller tumors. 

Impact: The study of different tumor microenvironments defined by CEST-derived pH habitats was demonstrated. A larger subset of animals with different tumor volumes and other multiparametric data will help understand tumor microenvironment better and aid treatment response in the future.

Keywords: Biomarkers, Cancer, Hyperpolarized MRI, Immunotherapy, Melanoma, CEST, Esomeprazole

Motivation: Biomarkers to predict immunotherapy response are needed. AcidoCEST MRI and hyperpolarized magnetic resonance spectroscopy (HP-MRS) may predict response.

Goal(s):

1. Establish baseline pHe and lactate to pyruvate ratio in tumors with varying immunotherapy response.
2. Observe changes after combination treatment with esomeprazole and immune checkpoint blockade (ICB).

Approach: AcidoCEST MRI and HP-MRS were used to measure extracellular pH (pHe) and lactate to pyruvate ratio. Imaging was performed on treated and untreated groups.

Results: Baseline lactate to pyruvate ratio and pHe were higher in the most resistant model compared to other models, but were unchanged in treatment vs control groups for the most resistant model.

Impact: Robust clinical tools are sorely needed to predict immunotherapy response. Development of a non-invasive clinical imaging tool would allow for less wasted time trying ineffective medications and more personalized treatment plans tailored so treatment is as effective as possible.

Keywords: Small Animals, Preclinical, Quantitative Imaging

Motivation: The project assessed the glucose uptake in brown adipose tissue (BAT) without using ionizing radiation since current methods, such as PET, have safety risks.

Goal(s): In a preclinical study we investigated whether chemical exchange saturation transfer MRI (CEST-MRI) could quantify the uptake of exogenous glucose in BAT.

Approach: We utilized CEST-MRI to monitor and analyze the glucose uptake in 6 mice following intravenous (i.v.) and intraperitoneal (i.p.) administration of glucose.

Results: GlucoCEST MRI successfully detected glucose uptake in BAT and revealed distinct glucose kinetics after i.v. and i.p. administration.

Impact: GlucoCEST is a promising radiation-free technique to measure relative glucose uptake in BAT, which can be used to investigate BAT activity e.g. in metabolic diseases. Additionally, it can provide further insight into BAT function and pharmacological activation.

Keywords: Biomarkers, Hyperpolarized MR (Gas), Dynamic Gas Exchange Spectroscopy, Look-locker, Chemical Shift Saturation Recovery, Rapid Acquisition

Motivation: Hyperpolarized ¹²⁹Xe Chemical Shift Saturation Recovery (CSSR), commonly employed for assessing pulmonary physiological function, is time-consuming and prone to weak signals and potential errors at short exchange times.

Goal(s): To accelerate the acquisition of CSSR while ensuring the precise physiological parameter extraction.

Approach: Techniques of inversion recovery (IR) and look-locker (LL) were combined with conventional CSSR (refer to as IR-LL-CSSR), and the results were compared with that obtained by conventional CSSR and IR-CSSR.

Results: By using the proposed method (IR-LL-CSSR), the acquisition could be accelerated for eight times, and meanwhile preserve the accuracy of the extracted physiological parameters.

Impact: IR-LL-CSSR substantially accelerates CSSR acquisition with ¹²⁹Xe MRS and also ensures a precise physiological parameter assessment, showing promise for improving the pulmonary assessment in clinic.

Keywords: Biology, Models, Methods, Head & Neck/ENT, Oxygen-enhanced MRI, Hypoxia, Radiation, Biomarker

Motivation: Tumour hypoxia is associated with radioresistance and is a negative factor in the prognosis of oral cavity squamous cell carcinoma. Non-invasive methods to rapidly quantify the extent and heterogeneity of tumour hypoxia would offer clinical benefit in treatment planning.

Goal(s): To assess the utility of oxygen-enhanced (OE-) MRI to image hypoxia and provide predictive imaging biomarkers of radiation response.

Approach: OE-MRI was performed in murine oral carcinoma allografts prior to 8Gy irradiation, and relationships with subsequent overall tumour response sought.

Results: Tumours exhibiting voxels with a marked hyperoxia-induced reduction in R₂* yet negligible ΔR₁ were more radiosensitive.

Impact: OE-MRI revealed extensive hypoxia in murine oral carcinoma allografts, and have the potential to predict tumour radiosensitivity based on the combined degree of hypoxia and haemodynamic vasculature.

Keywords: Probes & Targets, Hyperpolarized MR (Non-Gas)

Motivation: Investigating metabolic changes in glycolysis within Tramp C1 cells due to photon irradiation, focusing on the role of HP ${}^{}$13C pyruvate.

Goal(s): To determine how photon irradiation affects pyruvate-to-lactate flux in vitro, indicating metabolic reprogramming.

Approach: Utilizing benchtop NMR to monitor HP ${}^{}$13C dynamics in irradiated versus control cells, targeting lactate production.

Results: Photon irradiation elevated ${}^{}$¹³C lactate production by two-fold on Day 0, with persistently higher levels observed on Day 3, signifying altered metabolic flux post-irradiation.

Impact: This study's findings reveal photon irradiation's potent effect on cellular metabolism, potentially influencing radiation therapy strategies. It opens avenues for targeted metabolic interventions and underscores the metabolic resilience in Tramp C1 cells, crucial for cancer treatment optimization.

Keywords: Other Preclinical, CEST & MT, hydrogel

Motivation: Biocompatible materials with detectable APT effects are lacking for biomedical applications.  

Goal(s): To validate the APT properties of a new synthesised biocompatible copolymer p(MPC-AE)₅₅ hydrogel which has potential exchange between its MPC and AE cross-linkage.  

Approach: An experimental phantom with variable copolymer concentration and existing egg protein model was imaged with a research application APT-CEST sequence at 3T and analysed both inline and using CEST-EVAL software.

Results: APT of the new hydrogel increased accordingly with its concentration and this was validated by results for egg protein which agreed with previous work. Both analysis methods were in agreement.  

Impact: Understanding the properties of newly synthesized copolymer hydrogel extends its value in biomedical applications including potential for phantoms that could support translation of APT-CEST.

Keywords: Atherosclerosis, Atherosclerosis

Motivation: The molecular imaging and relationship between the brain and atherosclerosis are poorly understood.

Goal(s): To study the brain during atherosclerosis development and the association of atherosclerosis and brain using CEST MRI.

Approach: 3 months old ApoE –/– and C57BL/6 mouse brains were imaged using 3T preclinical MRI and CEST was applied, then three offsets, 3.5, –1.6 and –3.5 ppm, were extracted for post-processing.

Results: ApoE –/–  mouse showed higher APT and rNOE signals than WT in thalamus, hippocampus and cortex, which are associated with neuroinflammation and cholesterol deposition during atherosclerosis development. 

Impact: The underlying molecular changes of the brain during atherosclerosis development could enhance the identification of diseases at early stage using CEST MRI.

Keywords: Biology, Models, Methods, Metabolism

Motivation: NMR-based analyses of lipids can reveal the sources and pathways contributing to lipid biosynthesis in cells grown in the presence of ¹³C-labeled tracers. 

Goal(s): Our goal was to determine whether treatment of FLCN-deficient renal cell carcinoma (RCC) cells with the Complex I inhibitor metformin modulated cellular biosynthesis of lipids.

Approach: We utilized ¹H-¹³C HSQC NMR analysis of cellular lipids in FLCN-deficient tumor cells to assess incorporation of acetyl groups derived ¹³C₆-glucose or ¹³C₅¹⁵N₂-L-glutamine into cellular lipids during treatment with metformin.

Results: We observed a sharp decrease in incorporation of ¹³C-glucose-derived carbon into lipid acyl chains and cholesterol methyl groups following metformin treatment.

Impact: We found that metformin decreased synthesis of lipids from glucose while enhancing lipid synthesis from glutamine in renal tumor cells. These findings demonstrate that targeting Complex I may be a promising therapeutic avenue for treatment and prevention of FLCN-deficient RCC.