Monitoring chemotherapeutic response by hyperpolarized 13C-fumarate MRS and diffusion MRI

Carboxylesterase Activatable Molecular Probe for Personalized Treatment Guidance by Analyte-Induced Molecular Transformation

Accurate visualization of tumor microenvironment is of great significance for personalized medicine. Here, we develop a near-infrared (NIR) fluorescence/photoacoustic (FL/PA) dual-mode molecular probe (denoted as NIR-CE) for distinguishing tumors based on carboxylesterase (CE) level by an analyte-induced molecular transformation (AIMT) strategy. The recognition moiety for CE activity is the acetyl unit of NIR-CE, generating the pre-product, NIR-CE-OH, which undergoes spontaneous hydrogen atom exchange between the nitrogen atoms in the indole group and the phenol hydroxyl group, eventually transforming into NIR-CE-H. In cellular experiments and in vivo blind studies, the human hepatoma cells and tumors with high level of CE were successfully distinguished by both NIR FL and PA imaging. Our findings provide a new molecular imaging strategy for personalized treatment guidance.

Parahydrogen-induced polarization allows 2000-fold signal enhancement in biologically active derivatives of the peptide-based drug octreotide

Octreotide, a somatostatin analogue, has shown its efficacy for the diagnostics and treatment of various types of cancer, i.e., in octreotide scan, as radio-marker after labelling with a radiopharmaceutical. To avoid toxicity of radio-labeling, octreotide-based assays can be implemented into magnetic resonance techniques, such as MRI and NMR. Here we used a Parahydrogen-Induced Polarization (PHIP) approach as a cheap, fast and straightforward method. Introduction of L-propargyl tyrosine as a PHIP marker at different positions of octreotide by manual Solid-Phase Peptide Synthesis (SPPS) led to up to 2000-fold proton signal enhancement (SE). Cell binding studies confirmed that all octreotide variants retained strong binding affinity to the surface of human-derived cancer cells expressing somatostatin receptor 2. The hydrogenation reactions were successfully performed in methanol and under physiologically compatible mixtures of water with methanol or ethanol. The presented results open up new application areas of biochemical and pharmacological studies with octreotide.

Deuterium MRSI of tumor cell death in vivo following oral delivery of 2 H-labeled fumarate

PURPOSE

There is an unmet clinical need for direct and sensitive methods to detect cell death in vivo, especially with regard to monitoring tumor treatment response. We have shown previously that tumor cell death can be detected in vivo from 2 H MRS and MRSI measurements of increased [2,3-2 H2 ]malate production following intravenous injection of [2,3-2 H2 ]fumarate. We show here that cell death can be detected with similar sensitivity following oral administration of the 2 H-labeled fumarate.

METHODS

Mice with subcutaneously implanted EL4 tumors were fasted for 1 h before administration (200 μl) of [2,3-2 H2 ]fumarate (2 g/kg bodyweight) via oral gavage without anesthesia. The animals were then anesthetized, and after 30 min, tumor conversion of [2,3-2 H2 ]fumarate to [2,3-2 H2 ]malate was assessed from a series of 13 2 H spectra acquired over a period of 65 min. The 2 H spectra and 2 H spectroscopic images were acquired using a surface coil before and at 48 h after treatment with a chemotherapeutic drug (etoposide, 67 mg/kg).

RESULTS

The malate/fumarate signal ratio increased from 0.022 ± 0.03 before drug treatment to 0.12 ± 0.04 following treatment (p = 0.023, n = 4). Labeled malate was undetectable in spectroscopic images acquired before treatment and increased in the tumor area following treatment. The increase in the malate/fumarate signal ratio was similar to that observed previously following intravenous administration of labeled fumarate.

CONCLUSION

Orally administered [2,3-2 H2 ]fumarate can be used to detect tumor cell death noninvasively following treatment with a sensitivity that is similar to that obtained with intravenous administration.

Recent advances in the application of parahydrogen in catalysis and biochemistry

Nuclear Magnetic Resonance (NMR) spectroscopy and Magnetic Resonance Imaging (MRI) are analytical and diagnostic tools that are essential for a very broad field of applications, ranging from chemical analytics, to non-destructive testing of materials and the investigation of molecular dynamics, to in vivo medical diagnostics and drug research. One of the major challenges in their application to many problems is the inherent low sensitivity of magnetic resonance, which results from the small energy-differences of the nuclear spin-states. At thermal equilibrium at room temperature the normalized population difference of the spin-states, called the Boltzmann polarization, is only on the order of 10-5. Parahydrogen induced polarization (PHIP) is an efficient and cost-effective hyperpolarization method, which has widespread applications in Chemistry, Physics, Biochemistry, Biophysics, and Medical Imaging. PHIP creates its signal-enhancements by means of a reversible (SABRE) or irreversible (classic PHIP) chemical reaction between the parahydrogen, a catalyst, and a substrate. Here, we first give a short overview about parahydrogen-based hyperpolarization techniques and then review the current literature on method developments and applications of various flavors of the PHIP experiment.

A "Self-Checking" pH/Viscosity-Activatable NIR-II Molecule for Real-Time Evaluation of Photothermal Therapy Efficacy

We present a second near-infrared (NIR-II) self-checking molecule, LET-1052, for acidic tumor microenvironment (TME) turn-on photothermal therapy (PTT), followed by viscosity based therapeutic efficacy evaluation by itself in two independent channels, denoted as "self-checking" strategy. In acidic TME, LET-1052 was protonated and turned on NIR-II absorption for PTT under 1064 nm laser irradiation. Subsequently, PTT-induced cellular death increases intracellular viscosity, which inhibited the intramolecular rotation of LET-1052, resulting in the enhancement of NIR-I fluorescence for real-time evaluation of PTT efficacy. After PTT of tumor-bearing mice for different periods of NIR-II laser irradiation, NIR-I fluorescence in the tumor region showed positive correlation with tumor growth inhibition rate, demonstrating reliable and prompt prediction of PTT efficacy. The strategy may be expanded for instant evaluation of other therapeutic modalities for personalized medicine.

In vivo Human MR Spectroscopy Using a Clinical Scanner: Development, Applications, and Future Prospects

MR spectroscopy (MRS) is a unique and useful method for noninvasively evaluating biochemical metabolism in human organs and tissues, but its clinical dissemination has been slow and often limited to specialized institutions or hospitals with experts in MRS technology. The number of 3-T clinical MR scanners is now increasing, representing a major opportunity to promote the use of clinical MRS. In this review, we summarize the theoretical background and basic knowledge required to understand the results obtained with MRS and introduce the general consensus on the clinical utility of proton MRS in routine clinical practice. In addition, we present updates to the consensus guidelines on proton MRS published by the members of a working committee of the Japan Society of Magnetic Resonance in Medicine in 2013. Recent research into multinuclear MRS equipped in clinical MR scanners is explained with an eye toward future development. This article seeks to provide an overview of the current status of clinical MRS and to promote the understanding of when it can be useful. In the coming years, MRS-mediated biochemical evaluation is expected to become available for even routine clinical practice.

Direct Production of a Hyperpolarized Metabolite on a Microfluidic Chip

Microfluidic systems hold great potential for the study of live microscopic cultures of cells, tissue samples, and small organisms. Integration of hyperpolarization would enable quantitative studies of metabolism in such volume limited systems by high-resolution NMR spectroscopy. We demonstrate, for the first time, the integrated generation and detection of a hyperpolarized metabolite on a microfluidic chip. The metabolite [1-¹³C]fumarate is produced in a nuclear hyperpolarized form by (i) introducing para-enriched hydrogen into the solution by diffusion through a polymer membrane, (ii) reaction with a substrate in the presence of a ruthenium-based catalyst, and (iii) conversion of the singlet-polarized reaction product into a magnetized form by the application of a radiofrequency pulse sequence, all on the same microfluidic chip. The microfluidic device delivers a continuous flow of hyperpolarized material at the 2.5 μL/min scale, with a polarization level of 4%. We demonstrate two methods for mitigating singlet–triplet mixing effects which otherwise reduce the achieved polarization level.

Anti-Inflammatory and Anti-Oxidant Effect of Dimethyl Fumarate in Cystic Fibrosis Bronchial Epithelial Cells

Cystic Fibrosis (CF) is caused by mutations on the CF transmembrane conductance regulator (CFTR) gene and is associated with chronic infection and inflammation. Recently, it has been demonstrated that LPS-induced CFTR dysfunction in airway epithelial cells is due to an early oxidative stress. Dimethyl fumarate (DMF) is an approved anti-inflammatory and anti-oxidant drug for auto-immune and inflammatory diseases, but its role in the CF has never been investigated. In this study, we examined the effect of DMF on CF-related cytokines expression, ROS measurements and CFTR channel function. We found that DMF reduced the inflammatory response to LPS stimulation in both CF and non-CF bronchial epithelial cells, both as co-treatment and therapy, and restored LPS-mediated decrease of Trikafta™-mediated CFTR function in CF cells bearing the most common mutation, c.1521_1523delCTT (F508del). DMF also inhibited the inflammatory response induced by IL-1β/H₂O₂ and IL-1β/TNFα, mimicking the inflammatory status of CF patients. Finally, we also demonstrated that DMF exhibited an anti-oxidant effect on CF cells after different inflammatory stimulations. Since DMF is an approved drug, it could be further investigated as a novel anti-inflammatory molecule to ameliorate lung inflammation in CF and improve the CFTR modulators efficacy.

Constant-adiabaticity pulse schemes for manipulating singlet order in 3-spin systems with weak magnetic non-equivalence

Parahydrogen-induced polarization (PHIP) is a source of nuclear spin hyperpolarization, and this technique allows for the preparation of biomolecules for in vivo metabolic imaging. PHIP delivers hyperpolarization in the form of proton singlet order to a molecule, but most applications require that a heteronuclear (e.g. ¹³C or ¹⁵N) spin in the molecule is hyperpolarized. Here we present high field pulse methods to manipulate proton singlet order in the [1-¹³C]fumarate, and in particular to transfer the proton singlet order into ¹³C magnetization. We exploit adiabatic pulses, i.e., pulses with slowly ramped amplitude, and use constant-adiabaticity variants: the spin Hamiltonian is varied in such a way that the generalized adiabaticity parameter is time-independent. This allows for faster polarization transfer, and we achieve 96.2% transfer efficiency in thermal equilibrium experiments. We demonstrate this in experiments using hyperpolarization, and obtain 6.8% ¹³C polarization. This work paves the way for efficient hyperpolarization of nuclear spins in a variety of biomolecules, since the high-field pulse sequences allow individual spins to be addressed.

Multimodal Molecular Imaging Detects Early Responses to Immune Checkpoint Blockade

Immune checkpoint blockade (ICB) has become a standard therapy for several cancers, however, the response to ICB is inconsistent and a method for noninvasive assessment has not been established to date. To investigate the capability of multimodal imaging to evaluate treatment response to ICB therapy, hyperpolarized ¹³C MRI using [1-¹³C] pyruvate and [1,4-¹³C2] fumarate and dynamic contrast enhanced (DCE) MRI was evaluated to detect early changes in tumor glycolysis, necrosis, and intratumor perfusion/permeability, respectively. Mouse tumor models served as platforms for high (MC38 colon adenocarcinoma) and low (B16-F10 melanoma) sensitivity to dual ICB of PD-L1 and CTLA4. Glycolytic flux significantly decreased following treatment only in the less sensitive B16-F10 tumors. Imaging [1,4-¹³C2] fumarate conversion to [1,4-¹³C2] malate showed a significant increase in necrotic cell death following treatment in the ICB-sensitive MC38 tumors, with essentially no change in B16-F10 tumors. DCE-MRI showed significantly increased perfusion/permeability in MC38-treated tumors, whereas a similar, but statistically nonsignificant, trend was observed in B16-F10 tumors. When tumor volume was also taken into consideration, each imaging biomarker was linearly correlated with future survival in both models. These results suggest that hyperpolarized ¹³C MRI and DCE MRI may serve as useful noninvasive imaging markers to detect early response to ICB therapy. SIGNIFICANCE: Hyperpolarized ¹³C MRI and dynamic contrast enhanced MRI in murine tumor models provide useful insight into evaluating early response to immune checkpoint blockade therapy.See related commentary by Cullen and Keshari, p. 3444.

Monitoring tumor cell death in murine tumor models using deuterium magnetic resonance spectroscopy and spectroscopic imaging

2H magnetic resonance spectroscopic imaging has been shown recently to be a viable technique for metabolic imaging in the clinic. We show here that 2H MR spectroscopy and spectroscopic imaging measurements of [2,3-2H2]malate production from [2,3-2H2]fumarate can be used to detect tumor cell death in vivo via the production of labeled malate. Production of [2,3-2H2]malate, following injection of [2,3-2H2]fumarate (1 g/kg) into tumor-bearing mice, was measured in a murine lymphoma (EL4) treated with etoposide, and in human breast (MDA-MB-231) and colorectal (Colo205) xenografts treated with a TRAILR2 agonist, using surface-coil localized 2H MR spectroscopy at 7 T. Malate production was also imaged in EL4 tumors using a fast 2H chemical shift imaging sequence. The malate/fumarate ratio increased from 0.016 ± 0.02 to 0.16 ± 0.14 in EL4 tumors 48 h after drug treatment (P = 0.0024, n = 3), and from 0.019 ± 0.03 to 0.25 ± 0.23 in MDA-MB-231 tumors (P = 0.0001, n = 5) and from 0.016 ± 0.04 to 0.28 ± 0.26 in Colo205 tumors (P = 0.0002, n = 5) 24 h after drug treatment. These increases were correlated with increased levels of cell death measured in excised tumor sections obtained immediately after imaging. 2H MR measurements of [2,3-2H2]malate production from [2,3-2H2]fumarate provide a potentially less expensive and more sensitive method for detecting cell death in vivo than 13C MR measurements of hyperpolarized [1,4-13C2]fumarate metabolism, which have been used previously for this purpose.

Rapid hyperpolarization and purification of the metabolite fumarate in aqueous solution

Magnetic resonance imaging is hindered by inherently low sensitivity, which limits the method for the most part to observing water molecules in the body. Hyperpolarized molecules exhibit strongly enhanced MRI signals which opens the door for imaging low-concentration species in vivo. Biomolecules can be hyperpolarized and injected into a patient allowing for metabolism to be tracked in real time, greatly expanding the information available to the radiologist. Parahydrogen-induced polarization (PHIP) is a hyperpolarization method renowned for its low cost and accessibility, but is generally limited by low polarization levels, modest molecular concentrations, and contamination by polarization reagents. In this work we overcome these drawbacks in the production of PHIP-polarized [1-¹³C]fumarate, a biomarker of cell necrosis in metabolic ¹³C MRI.

Hyperpolarized fumarate is a promising biosensor for carbon-13 magnetic resonance metabolic imaging. Such molecular imaging applications require nuclear hyperpolarization to attain sufficient signal strength. Dissolution dynamic nuclear polarization is the current state-of-the-art methodology for hyperpolarizing fumarate, but this is expensive and relatively slow. Alternatively, this important biomolecule can be hyperpolarized in a cheap and convenient manner using parahydrogen-induced polarization. However, this process requires a chemical reaction, and the resulting solutions are contaminated with the catalyst, unreacted reagents, and reaction side-product molecules, and are hence unsuitable for use in vivo. In this work we show that the hyperpolarized fumarate can be purified from these contaminants by acid precipitation as a pure solid, and later redissolved to a desired concentration in a clean aqueous solvent. Significant advances in the reaction conditions and reactor equipment allow for formation of hyperpolarized fumarate at ¹³C polarization levels of 30–45%.

Singlet-Contrast Magnetic Resonance Imaging: Unlocking Hyperpolarization with Metabolism*

Hyperpolarization-enhanced magnetic resonance imaging can be used to study biomolecular processes in the body, but typically requires nuclei such as 13 C, 15 N, or 129 Xe due to their long spin-polarization lifetimes and the absence of a proton-background signal from water and fat in the images. Here we present a novel type of 1 H imaging, in which hyperpolarized spin order is locked in a nonmagnetic long-lived correlated (singlet) state, and is only liberated for imaging by a specific biochemical reaction. In this work we produce hyperpolarized fumarate via chemical reaction of a precursor molecule with para-enriched hydrogen gas, and the proton singlet order in fumarate is released as antiphase NMR signals by enzymatic conversion to malate in D2 O. Using this model system we show two pulse sequences to rephase the NMR signals for imaging and suppress the background signals from water. The hyperpolarization-enhanced 1 H-imaging modality presented here can allow for hyperpolarized imaging without the need for low-abundance, low-sensitivity heteronuclei.

Metabolomics in renal cell carcinoma: From biomarker identification to pathomechanism insights

Renal cell carcinoma (RCC) is a frequently diagnosed cancer with high prevalence, which is inversely associated with survival benefit. Although myriad studies have shed light on disease causality, unfortunately, thus far, RCC diagnosis is faced with numerous obstacles partly due to the insufficient knowledge of effective biomarkers, hinting deeper mechanistic understanding are urgently needed. Metabolites are recognized as final proxies for gene-environment interactions and physiological homeostasis as they reflect dynamic processes that are ongoing or have been taken place, and metabolomics may therefore offer a far more productive and cost-effective route to disease discovery, particularly within the arena for new biomarker identification. In this review, we primarily expatiate recent advances in metabolomics that may be amenable to novel biomarkers or therapeutic targets for RCC, which may expand our armaments to win more bettles against RCC.

Imaging Cell Death: Focus on Early Evaluation of Tumor Response to Therapy

Cell death plays a prominent role in the treatment of cancer, because most anticancer therapies act by the induction of cell death including apoptosis, necrosis, and other pathways of cell death. Imaging cell death helps to identify treatment responders from nonresponders and thus enables patient-tailored therapy, which will increase the likelihood of treatment response and ultimately lead to improved patient survival. By taking advantage of molecular probes that specifically target the biomarkers/biochemical processes of cell death, cell death imaging can be successfully achieved. In recent years, with the increased understanding of the molecular mechanism of cell death, a variety of well-defined biomarkers/biochemical processes of cell death have been identified. By targeting these established cell death biomarkers/biochemical processes, a set of molecular imaging probes have been developed and evaluated for early monitoring treatment response in tumors. In this review, we mainly present the recent advances in identifying useful biomarkers/biochemical processes for both apoptosis and necrosis imaging and in developing molecular imaging probes targeting these biomarkers/biochemical processes, with a focus on their application in early evaluation of tumor response to therapy.

Direct and indirect assessment of cancer metabolism explored by MRI

Magnetic resonance-based approaches to obtain metabolic information on cancer have been explored for decades. Electron paramagnetic resonance (EPR) has been developed to pursue metabolic profiling and successfully used to monitor several physiologic parameters such as pO₂ , pH, and redox status. All these parameters are associated with pathophysiology of various diseases. Especially in oncology, cancer hypoxia has been intensively studied because of its relationship with metabolic alterations, acquiring treatment resistance, or a malignant phenotype. Thus, pO₂ imaging leads to an indirect metabolic assessment in this regard. Proton electron double-resonance imaging (PEDRI) is an imaging technique to visualize EPR by using the Overhauser effect. Most biological parameters assessed in EPR can be visualized using PEDRI. However, EPR and PEDRI have not been evaluated sufficiently for clinical application due to limitations such as toxicity of the probes or high specific absorption rate. Hyperpolarized (HP) ¹³ C MRI is a novel imaging technique that can directly visualize the metabolic profile. Production of metabolites of the HP ¹³ C probe delivered to target tissue are evaluated in this modality. Unlike EPR or PEDRI, which require the injection of radical probes, ¹³ C MRI requires a probe that can be physiologically metabolized and efficiently hyperpolarized. Among several methods for hyperpolarizing probes, dissolution dynamic nuclear hyperpolarization is a widely used technique for in vivo imaging. Pyruvate is the most suitable probe for HP ¹³ C MRI because it is part of the glycolytic pathway and the high efficiency of pyruvate-to-lactate conversion is a distinguishing feature of cancer. Its clinical applicability also makes it a promising metabolic imaging modality. Here, we summarize the applications of these indirect and direct MR-based metabolic assessments focusing on pO₂ and pyruvate-to-lactate conversion. The two parameters are strongly associated with each other, hence the acquired information is potentially interchangeable when evaluating treatment response to oxygen-dependent cancer therapies.

Combining Hyperpolarized Real-Time Metabolic Imaging and NMR Spectroscopy To Identify Metabolic Biomarkers in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is a deadly cancer that progresses without any symptom, and oftentimes, it is detected at an advanced stage. The lack of prior symptoms and effective treatments have created a knowledge gap in the management of this lethal disease. This issue can be addressed by developing novel noninvasive imaging-based biomarkers in PDAC. We explored in vivo hyperpolarized (HP) ¹³C MRS of pyruvate to lactate conversion and ex vivo ¹H NMR spectroscopy in a panel of well-annotated patient-derived PDAC xenograft (PDXs) model and investigated the correlation between aberrant glycolytic metabolism and aggressiveness of the tumor. Real-time metabolic imaging data demonstrate the immediate intracellular conversion of HP ¹³C pyruvate to lactate after intravenous injection interrogating upregulated lactate dehydrogenase (LDH) activity in aggressive PDXs. Total ex vivo lactate measurement by ¹H NMR spectroscopy showed a direct correlation with in vivo dynamic pyruvate-to-lactate conversion and demonstrated the potential of dynamic metabolic flux as a biomarker of total lactate concentration and aggressiveness of the tumor. Furthermore, the metabolite concentrations were very distinct among all four tumor types analyzed in this study. Overexpression of LDH-A and hypoxia-inducible factor (HIF-1α) plays a significant role in the conversion kinetics of HP pyruvate-to-lactate in tumors. Collectively, these data identified aberrant metabolic characteristics of pancreatic cancer PDXs and could potentially delineate metabolic targets for therapeutic intervention. Metabolic imaging with HP pyruvate and NMR metabolomics may enable identification and classification of aggressive subtypes of patient-derived xenografts. Translation of this real-time metabolic technique to the clinic may have the potential to improve the management of patients at high risk of developing pancreatic diseases.

Assessing Therapeutic Efficacy in Real-time by Hyperpolarized Magnetic Resonance Metabolic Imaging

Precisely measuring tumor-associated alterations in metabolism clinically will enable the efficient assessment of therapeutic responses. Advances in imaging technologies can exploit the differences in cancer-associated cell metabolism as compared to normal tissue metabolism, linking changes in target metabolism to therapeutic efficacy. Metabolic imaging by Positron Emission Tomography (PET) employing 2-fluoro-deoxy-glucose ([18F]FDG) has been used as a routine diagnostic tool in the clinic. Recently developed hyperpolarized Magnetic Resonance (HP-MR), which radically increases the sensitivity of conventional MRI, has created a renewed interest in functional and metabolic imaging. The successful translation of this technique to the clinic was achieved recently with measurements of 13C-pyruvate metabolism. Here, we review the potential clinical roles for metabolic imaging with hyperpolarized MRI as applied in assessing therapeutic intervention in different cancer systems.

Hyperpolarized 13C MRI: State of the Art and Future Directions

Hyperpolarized (HP) carbon 13 (¹³C) MRI is an emerging molecular imaging method that allows rapid, noninvasive, and pathway-specific investigation of dynamic metabolic and physiologic processes that were previously inaccessible to imaging. This technique has enabled real-time in vivo investigations of metabolism that are central to a variety of diseases, including cancer, cardiovascular disease, and metabolic diseases of the liver and kidney. This review provides an overview of the methods of hyperpolarization and ¹³C probes investigated to date in preclinical models of disease. The article then discusses the progress that has been made in translating this technology for clinical investigation. In particular, the potential roles and emerging clinical applications of HP [1-¹³C]pyruvate MRI will be highlighted. The future directions to enable the adoption of this technology to advance the basic understanding of metabolism, to improve disease diagnosis, and to accelerate treatment assessment are also detailed.

MARCH1 encourages tumour progression of hepatocellular carcinoma via regulation of PI3K-AKT-β-catenin pathways

Membrane‐associated RING‐CH‐1 (MARCH1) is a membrane‐anchored E3 ubiquitin ligase that is involved in a variety of cellular processes. MARCH1 was aberrantly expressed as a tumour promoter in ovarian cancer, but the signalling about the molecular mechanism has not yet been fully illuminated. Here, we first determined that MARCH1 was obviously highly expressed in human hepatocellular carcinoma samples and cells. In addition, our findings demonstrated that the proliferation, migration and invasion of hepatocellular carcinoma were suppressed, but the apoptosis was increased, as a result of MARCH1 knockdown by either siRNA targeting MARCH1 or pirarubicin treatment. Conversely, the proliferation, migration and invasion of hepatocellular carcinoma were obviously accelerated, and the apoptosis was decreased, by transfecting the MARCH1 plasmid to make MARCH1 overexpressed. Moreover, in vivo, the results exhibited a significant inhibition of the growth of hepatocellular carcinoma in nude mice, which were given an intra‐tumour injection of siRNA targeting MARCH1. Furthermore, our study concluded that MARCH1 functions as a tumour promoter, and its role was up‐regulated the PI3K‐AKT‐β‐catenin pathways both in vitro and in vivo. In summary, our work determined that MARCH1 has an important role in the development and progression of hepatocellular carcinoma and may be used as a novel potential molecular therapeutic target in the future treatment of hepatocellular carcinoma.

Secalonic Acid-F, a Novel Mycotoxin, Represses the Progression of Hepatocellular Carcinoma via MARCH1 Regulation of the PI3K/AKT/β-catenin Signaling Pathway

Liver cancer is a very common and significant health problem. Therefore, powerful molecular targeting agents are urgently needed. Previously, we demonstrated that secalonic acid-F (SAF) suppresses the growth of hepatocellular carcinoma (HCC) cells (HepG2), but the other anticancer biological functions and the underlying mechanism of SAF on HCC are unknown. In this study, we found that SAF, which was isolated from a fungal strain in our lab identified as Aspergillus aculeatus, could inhibit the progression of hepatocellular carcinoma by targeting MARCH1, which regulates the PI3K/AKT/β-catenin and antiapoptotic Mcl-1/Bcl-2 signaling cascades. First, we confirmed that SAF reduced the proliferation and colony formation of HCC cell lines (HepG2 and Hep3B), promoted cell apoptosis, and inhibited the cell cycle in HepG2 and Hep3B cells in a dose-dependent manner. In addition, the migration and invasion of HepG2 and Hep3B cells treated with SAF were significantly suppressed. Western blot analysis showed that the level of MARCH1 was downregulated by pretreatment with SAF through the regulation of the PI3K/AKT/β-catenin signaling pathways. Moreover, knockdown of MARCH1 by small interfering RNAs (siRNAs) targeting MARCH1 also suppressed the proliferation, colony formation, migration, and invasion as well as increased the apoptotic rate of HepG2 and Hep3B cells. These data confirmed that the downregulation of MARCH1 could inhibit the progression of hepatocellular carcinoma and that the mechanism may be via PI3K/AKT/β-catenin inactivation as well as the downregulation of the antiapoptotic Mcl-1/Bcl-2. In vivo, the downregulation of MARCH1 by treatment with SAF markedly inhibited tumor growth, suggesting that SAF partly blocks MARCH1 and further regulates the PI3K/AKT/β-catenin and antiapoptosis Mcl-1/Bcl-2 signaling cascade in the HCC nude mouse model. Additionally, the apparent diffusion coefficient (ADC) values, derived from magnetic resonance imaging (MRI), were increased in tumors after SAF treatment in a mouse model. Taken together, our findings suggest that MARCH1 is a potential molecular target for HCC treatment and that SAF is a promising agent targeting MARCH1 to treat liver cancer patients.

Hyperpolarized 13C MRI: Path to Clinical Translation in Oncology

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.

Development of methods and feasibility of using hyperpolarized carbon-13 imaging data for evaluating brain metabolism in patient studies

Purpose

Hyperpolarized 13C metabolic imaging is a non-invasive imaging modality for evaluating real-time metabolism. The purpose of this study was to develop and implement experimental strategies for using [1-13C]pyruvate to probe in vivo metabolism for patients with brain tumors and other neurological diseases.

Methods

The 13C RF coils and pulse sequences were tested in a phantom and were performed using a 3T whole body scanner. Samples of [1-13C]pyruvate were polarized using a SPINlab system. Dynamic 13C data were acquired from eight patients previously diagnosed with brain tumors, who had received treatment and were being followed with serial MR scans.

Results

The phantom studies produced good quality spectra with a reduction in signal intensity in the center due to the reception profiles of the 13C receive coils. Dynamic data obtained from a 3 cm slice through a patient’s brain following injection with [1-13C]pyruvate showed the anticipated arrival of the agent, its conversion to lactate and bicarbonate, and subsequent reduction in signal intensity. A similar temporal pattern was observed in 2D dynamic patient studies, with signals corresponding to pyruvate, lactate and bicarbonate being in normal appearing brain but only pyruvate and lactate being detected in regions corresponding to the anatomic lesion. Physiological monitoring and follow-up confirmed that there were no adverse events associated with the injection.

Conclusions

This study has presented the first application of hyperpolarized 13C metabolic imaging in patients with brain tumor and demonstrated the safety and feasibility of using hyperpolarized [1-13C]pyruvate to evaluate in vivo brain metabolism.

Development of methods and feasibility of using hyperpolarized carbon-13 imaging data for evaluating brain metabolism in patient studies

PURPOSE

Hyperpolarized ¹³C metabolic imaging is a non-invasive imaging modality for evaluating real-time metabolism. The purpose of this study was to develop and implement experimental strategies for using [1-¹³C]pyruvate to probe in vivo metabolism for patients with brain tumors and other neurological diseases.

METHODS

The ¹³C RF coils and pulse sequences were tested in a phantom and were performed using a 3T whole body scanner. Samples of [1-¹³C]pyruvate were polarized using a SPINlab system. Dynamic ¹³C data were acquired from eight patients previously diagnosed with brain tumors, who had received treatment and were being followed with serial MR scans.

RESULTS

The phantom studies produced good quality spectra with a reduction in signal intensity in the center due to the reception profiles of the ¹³C receive coils. Dynamic data obtained from a 3 cm slice through a patient’s brain following injection with [1-¹³C]pyruvate showed the anticipated arrival of the agent, its conversion to lactate and bicarbonate, and subsequent reduction in signal intensity. A similar temporal pattern was observed in 2D dynamic patient studies, with signals corresponding to pyruvate, lactate and bicarbonate being in normal appearing brain but only pyruvate and lactate being detected in regions corresponding to the anatomic lesion. Physiological monitoring and follow-up confirmed that there were no adverse events associated with the injection.

CONCLUSIONS

This study has presented the first application of hyperpolarized ¹³C metabolic imaging in patients with brain tumor and demonstrated the safety and feasibility of using hyperpolarized [1-¹³C]pyruvate to evaluate in vivo brain metabolism.

Assessment of bevacizumab resistance increased by expression of BCAT1 in IDH1 wild-type glioblastoma: application of DSC perfusion MR imaging

BCAT1 (branched-chain amino acid trasaminase1) expression is necessary for the progression of IDH1 wild-type (WT) glioblastoma multiforme (GBM), which is known to be associated with aggressive tumors. The purpose of our study is to investigate the bevacizumab resistance increased by the expression of BCAT1 in IDH1 WT GBM in a rat model, which was evaluated using DSC perfusion MRI. BCAT1 sh#1 inhibits cell proliferation and limits cell migration potential in vitro. In vivo MRI showed that the increase in both tumor volume and nCBV after bevacizumab treatment in IDH1 WT tumors was significantly higher compared with BCAT1 sh#1tumors. In a histological analysis, more micro-vessel reformation by bevacizumab resistance was observed in IDH1 WT tumors than BCAT1 sh#1 tumors. These findings indicate that BCAT1 expression in IDH1 WT GBM increases resistance to bevacizumab treatment, which could be assessed by DSC perfusion MRI, and that nCBV can be a surrogate imaging biomarker for the prediction of antiangiogenic treatment in GBM.

Simultaneous imaging of hyperpolarized [1,4-13 C2 ]fumarate, [1-13 C]pyruvate and 18 F-FDG in a rat model of necrosis in a clinical PET/MR scanner

A co-polarization scheme for [1,4-¹³ C₂ ]fumarate and [1-¹³ C]pyruvate is presented to simultaneously assess necrosis and metabolism in rats with hyperpolarized ¹³ C magnetic resonance (MR). The co-polarization was performed in a SPINlab polarizer. In addition, the feasibility of simultaneous positron emission tomography (PET) and MR of small animals with a clinical PET/MR scanner is demonstrated. The hyperpolarized metabolic MR and PET was demonstrated in a rat model of necrosis. The polarization and T₁ of the co-polarized [1,4-¹³ C₂ ]fumarate and [1-¹³ C]pyruvate substrates were measured in vitro and compared with those obtained when the substrates were polarized individually. A polarization of 36 ± 4% for fumarate and 37 ± 6% for pyruvate was obtained. We found no significant difference in the polarization and T₁ values between the dual and single substrate polarization. Rats weighing about 400 g were injected intramuscularly in one of the hind legs with 200 μL of turpentine to induce necrosis. Two hours later, ¹³ C metabolic maps were obtained with a chemical shift imaging sequence (16 × 16) with a resolution of 3.1 × 5.0 × 25.0 mm³ . The ¹³ C spectroscopic images were acquired in 12 s, followed by an 8-min ¹⁸ F-2-fluoro-2-deoxy-d-glucose (¹⁸ F-FDG) PET acquisition with a resolution of 3.5 mm. [1,4-¹³ C₂ ]Malate was observed from the tissue injected with turpentine indicating necrosis. Normal [1-¹³ C]pyruvate metabolism and ¹⁸ F-FDG uptake were observed from the same tissue. The proposed co-polarization scheme provides a means to utilize multiple imaging agents simultaneously, and thus to probe various metabolic pathways in a single examination. Moreover, it demonstrates the feasibility of small animal research on a clinical PET/MR scanner for combined PET and hyperpolarized metabolic MR.

Magnetic resonance imaging with hyperpolarized agents: methods and applications

In the past decade, hyperpolarized (HP) contrast agents have been under active development for MRI applications to address the twin challenges of functional and quantitative imaging. Both HP helium (³He) and xenon (¹²⁹Xe) gases have reached the stage where they are under study in clinical research. HP ¹²⁹Xe, in particular, is poised for larger scale clinical research to investigate asthma, chronic obstructive pulmonary disease, and fibrotic lung diseases. With advances in polarizer technology and unique capabilities for imaging of ¹²⁹Xe gas exchange into lung tissue and blood, HP ¹²⁹Xe MRI is attracting new attention. In parallel, HP ¹³C and ¹⁵N MRI methods have steadily advanced in a wide range of pre-clinical research applications for imaging metabolism in various cancers and cardiac disease. The HP [1-¹³C] pyruvate MRI technique, in particular, has undergone phase I trials in prostate cancer and is poised for investigational new drug trials at multiple institutions in cancer and cardiac applications. This review treats the methodology behind both HP gases and HP ¹³C and ¹⁵N liquid state agents. Gas and liquid phase HP agents share similar technologies for achieving non-equilibrium polarization outside the field of the MRI scanner, strategies for image data acquisition, and translational challenges in moving from pre-clinical to clinical research. To cover the wide array of methods and applications, this review is organized by numerical section into (1) a brief introduction, (2) the physical and biological properties of the most common polarized agents with a brief summary of applications and methods of polarization, (3) methods for image acquisition and reconstruction specific to improving data acquisition efficiency for HP MRI, (4) the main physical properties that enable unique measures of physiology or metabolic pathways, followed by a more detailed review of the literature describing the use of HP agents to study: (5) metabolic pathways in cancer and cardiac disease and (6) lung function in both pre-clinical and clinical research studies, concluding with (7) some future directions and challenges, and (8) an overall summary.

Multiparametric human hepatocellular carcinoma characterization and therapy response evaluation by hyperpolarized (13) C MRSI

Individual tumor characterization and treatment response monitoring based on current medical imaging methods remain challenging. This work investigates hyperpolarized (13) C compounds in an orthotopic rat hepatocellular carcinoma (HCC) model system before and after transcatheter arterial embolization (TAE). HCC ranks amongst the top six most common cancer types in humans and accounts for one-third of cancer-related deaths worldwide. Early therapy response monitoring could aid in the development of personalized therapy approaches and novel therapeutic concepts. Measurements with selectively (13) C-labeled and hyperpolarized urea, pyruvate and fumarate were performed in tumor-bearing rats before and after TAE. Two-dimensional, slice-selective MRSI was used to obtain spatially resolved maps of tumor perfusion, cell energy metabolic conversion rates and necrosis, which were additionally correlated with immunohistochemistry. All three injected compounds, taken together with their respective metabolites, exhibited similar signal distributions. TAE induced a decrease in blood flow into the tumor and thus a decrease in tumor to muscle and tumor to liver ratios of urea, pyruvate and its metabolites, alanine and lactate, whereas conversion rates remained stable or increased on TAE in tumor, muscle and liver tissue. Conversion from fumarate to malate successfully indicated individual levels of necrosis, and global malate signals after TAE suggested the washout of fumarase or malate itself on necrosis. This study presents a combination of three (13) C compounds as novel candidate biomarkers for a comprehensive characterization of genetically and molecularly diverse HCC using hyperpolarized MRSI, enabling the simultaneous detection of differences in tumor perfusion, metabolism and necrosis. If, as in this study, bolus dynamics are not required and qualitative perfusion information is sufficient, the desired information could be extracted from hyperpolarized fumarate and pyruvate alone, acquired at higher fields with better spectral separation. Copyright © 2016 John Wiley & Sons, Ltd.

Assessing inflammatory liver injury in an acute CCl4 model using dynamic 3D metabolic imaging of hyperpolarized [1-(13)C]pyruvate

To facilitate diagnosis and staging of liver disease, sensitive and non-invasive methods for the measurement of liver metabolism are needed. This study used hyperpolarized (13)C-pyruvate to assess metabolic parameters in a CCl4 model of liver damage in rats. Dynamic 3D (13)C chemical shift imaging data from a volume covering kidney and liver were acquired from 8 control and 10 CCl4-treated rats. At 12 time points at 5 s temporal resolution, we quantified the signal intensities and established time courses for pyruvate, alanine, and lactate. These measurements were compared with standard liver histology and an alanine transaminase (ALT) enzyme assay using liver tissue from the same animals. All CCl4-treated but none of the control animals showed histological liver damage and elevated ALT enzyme levels. In agreement with these results, metabolic imaging revealed an increased alanine/pyruvate ratio in liver of CCl4-treated rats, which is indicative of elevated ALT activity. Similarly, lactate/pyruvate ratios were higher in CCl4-treated compared with control animals, demonstrating the presence of inflammation. No significant differences in metabolite ratios were observed in kidney or vasculature. Thus this work shows that metabolic imaging using (13)C-pyruvate can be a successful tool to non-invasively assess liver damage in vivo.

Preclinical imaging and translational animal models of cancer for accelerated clinical implementation of nanotechnologies and macromolecular agents

The majority of animal models of cancer have performed poorly in terms of predicting clinical performance of new therapeutics, which are most often first evaluated in patients with advanced, metastatic disease. The development and use of metastatic models of cancer may enhance clinical translatability of preclinical studies focused on the development of nanotechnology-based drug delivery systems and macromolecular therapeutics, potentially accelerating their clinical implementation. It is recognized that the development and use of such models are not without challenge. Preclinical imaging tools offer a solution by allowing temporal and spatial characterization of metastatic lesions. This paper provides a review of imaging methods applicable for evaluation of novel therapeutics in clinically relevant models of advanced cancer. An overview of currently utilized models of oncology in small animals is followed by image-based development and characterization of visceral metastatic cancer models. Examples of imaging tools employed for metastatic lesion detection, evaluation of anti-tumor and anti-metastatic potential and biodistribution of novel therapies, as well as the co-development and/or use of imageable surrogates of response, are also discussed. While the focus is on development of macromolecular and nanotechnology-based therapeutics, examples with small molecules are included in some cases to illustrate concepts and approaches that can be applied in the assessment of nanotechnologies or macromolecules.

Biomarkers in preclinical cancer imaging

In view of the trend towards personalized treatment strategies for (cancer) patients, there is an increasing need to noninvasively determine individual patient characteristics. Such information enables physicians to administer to patients accurate therapy with appropriate timing. For the noninvasive visualization of disease-related features, imaging biomarkers are expected to play a crucial role. Next to the chemical development of imaging probes, this requires preclinical studies in animal tumour models. These studies provide proof-of-concept of imaging biomarkers and help determine the pharmacokinetics and target specificity of relevant imaging probes, features that provide the fundamentals for translation to the clinic. In this review we describe biological processes derived from the “hallmarks of cancer” that may serve as imaging biomarkers for diagnostic, prognostic and treatment response monitoring that are currently being studied in the preclinical setting. A number of these biomarkers are also being used for the initial preclinical assessment of new intervention strategies. Uniquely, noninvasive imaging approaches allow longitudinal assessment of changes in biological processes, providing information on the safety, pharmacokinetic profiles and target specificity of new drugs, and on the antitumour effectiveness of therapeutic interventions. Preclinical biomarker imaging can help guide translation to optimize clinical biomarker imaging and personalize (combination) therapies.

Improving tumour heterogeneity MRI assessment with histograms

By definition, tumours are heterogeneous. They are defined by marked differences in cells, microenvironmental factors (oxygenation levels, pH, VEGF, VPF and TGF-α) metabolism, vasculature, structure and function that in turn translate into heterogeneous drug delivery and therapeutic outcome. Ways to estimate quantitatively tumour heterogeneity can improve drug discovery, treatment planning and therapeutic responses. It is therefore of paramount importance to have reliable and reproducible biomarkers of cancerous lesions' heterogeneity. During the past decade, the number of studies using histogram approaches increased drastically with various magnetic resonance imaging (MRI) techniques (DCE-MRI, DWI, SWI etc.) although information on tumour heterogeneity remains poorly exploited. This fact can be attributed to a poor knowledge of the available metrics and of their specific meaning as well as to the lack of literature references to standardised histogram methods with which surrogate markers of heterogeneity can be compared. This review highlights the current knowledge and critical advances needed to investigate and quantify tumour heterogeneity. The key role of imaging techniques and in particular the key role of MRI for an accurate investigation of tumour heterogeneity is reviewed with a particular emphasis on histogram approaches and derived methods.

A polymer-based magnetic resonance tracer for visualization of solid tumors by 13C spectroscopic imaging

Morphological imaging precedes lesion-specific visualization in magnetic resonance imaging (MRI) because of the superior ability of this technique to depict tissue morphology with excellent spatial and temporal resolutions. To achieve lesion-specific visualization of tumors by MRI, we investigated the availability of a novel polymer-based tracer. Although the ¹³C nucleus is a candidate for a detection nucleus because of its low background signal in the body, the low magnetic resonance sensitivity of the nucleus needs to be resolved before developing a ¹³C-based tracer. In order to overcome this problem, we enriched polyethylene glycol (PEG), a biocompatible polymer, with ¹³C atoms. ¹³C-PEG40,000 (¹³C-PEG with an average molecular weight of 40 kDa) emitted a single ¹³C signal with a high signal-to-noise ratio due to its ability to maintain signal sharpness, as was confirmed by in vivo investigation, and displayed a chemical shift sufficiently distinct from that of endogenous fat. ¹³C-PEG40,000 intravenously injected into mice showed long retention in circulation, leading to its effective accumulation in tumors reflecting the well-known phenomenon that macromolecules accumulate in tumors because of leaky tumor capillaries. These properties of ¹³C-PEG40,000 allowed visualization of tumors in mice by ¹³C spectroscopic imaging. These findings suggest that a technique based on ¹³C-PEG is a promising strategy for tumor detection.

Metabolic effects of antiangiogenic drugs in tumors: therapeutic implications

Antiangiogenic therapy has become a mainstay of cancer therapeutics, but clinical responses are generally short-term owing to the development of secondary resistance. Tumor starvation by antiangiogenic drugs is largely attributed to increased hypoxia and impaired nutrients supply, suggesting that angiogenesis inhibition causes remarkable metabolic perturbations in the tumor microenvironment. We review here recent acquisitions concerning metabolic effects of angiogenesis blockade in tumors and discuss the possibility that some metabolic features of tumor cells - i.e. their dependency from glucose as primary energy substrate - might affect tumor responses to anti-vascular endothelial growth factor treatment. Moreover, we discuss the hypothesis that anti-angiogenic therapy might foster metabolic evolution of tumors. The therapeutic implications of this hypothesis will be discussed further here.