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Purpose: Serine is a major source of one‐carbon units needed for the synthesis of nucleotides and the production of intramitochondrial nicotinamide adenine dinucleotide phosphate (NADPH), and it plays an important role in cancer cell proliferation. The aim of this study was to develop a deuterium (2H) MRS imaging method for imaging tumor serine metabolism. Methods: Sequential (2H) spectra and spectroscopic images were used to monitor the metabolism of [2,3,3‐2H3]serine in patient‐derived glioblastoma cells in vitro and in tumors obtained by their orthotopic implantation in mouse brain. Results: [14,14‐2H2] 5,10‐methylene‐tetrahydrofolate, [2H]glycine, [2H]formate, and labeled water were detected in cell suspensions and water labeling in spectroscopic images of tumors. Studies in cells and tumors with variable mitochondrial content and inhibitor studies in cells demonstrated that most of the labeled serine was metabolized in the mitochondria. Water labeling in the cell suspensions was correlated with formate labeling; therefore, water labeling observed in tumors could be used to provide a surrogate measure of flux in the pathway of one‐carbon metabolism in vivo. Conclusion: The method has the potential to be used clinically to select patients for treatment with inhibitors of one‐carbon metabolism and subsequently to detect their early responses to such treatment. [ABSTRACT FROM AUTHOR]

Imaging the metabolism of [2,3‐2H2]fumarate to produce malate can be used to detect tumor cell death post‐treatment. Here, we assess the sensitivity of the technique for detecting cell death by lowering the concentration of injected [2,3‐2H2]fumarate and by varying the extent of tumor cell death through changes in drug concentration. Mice were implanted subcutaneously with human triple negative breast cancer cells (MDA‐MB‐231) and injected with 0.1, 0.3, and 0.5 g/kg [2,3‐2H2]fumarate before and after treatment with a multivalent TRAlL‐R2 agonist (MEDI3039) at 0.1, 0.4, and 0.8 mg/kg. Tumor conversion of [2,3‐2H2]fumarate to [2,3‐2H2]malate was assessed from a series of 13 spatially localized 2H MR spectra acquired over 65 min using a pulse‐acquire sequence with a 2‐ms BIR4 adiabatic excitation pulse. Tumors were then excised and stained for histopathological markers of cell death: cleaved caspase 3 (CC3) and DNA damage (terminal deoxynucleotidyl transferase dUTP nick end labeling [TUNEL]). The rate of malate production and the malate/fumarate ratio plateaued at tumor fumarate concentrations of 2 mM, which were obtained with injected [2,3‐2H2]fumarate concentrations of 0.3 g/kg and above. Tumor malate concentration and the malate/fumarate ratio increased linearly with the extent of cell death determined histologically. At an injected [2,3‐2H2]fumarate concentration of 0.3 g/kg, 20% CC3 staining corresponded to a malate concentration of 0.62 mM and a malate/fumarate ratio of 0.21. Extrapolation indicated that there would be no detectable malate at 0% CC3 staining. The use of low and nontoxic fumarate concentrations and the production of [2,3‐2H2]malate at concentrations that are within the range that can be detected clinically suggest this technique could translate to the clinic. [ABSTRACT FROM AUTHOR]

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 2H MRS and MRSI measurements of increased [2,3‐2H2]malate production following intravenous injection of [2,3‐2H2]fumarate. We show here that cell death can be detected with similar sensitivity following oral administration of the 2H‐labeled fumarate. Methods: Mice with subcutaneously implanted EL4 tumors were fasted for 1 h before administration (200 μl) of [2,3‐2H2]fumarate (2 g/kg bodyweight) via oral gavage without anesthesia. The animals were then anesthetized, and after 30 min, tumor conversion of [2,3‐2H2]fumarate to [2,3‐2H2]malate was assessed from a series of 13 2H spectra acquired over a period of 65 min. The 2H spectra and 2H 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 [2,3‐2H2]fumarate can be used to detect tumor cell death noninvasively following treatment with a sensitivity that is similar to that obtained with intravenous administration. [ABSTRACT FROM AUTHOR]

Purpose: The performance of pulse sequences in vivo can be limited by fast relaxation rates, magnetic field inhomogeneity, and nonuniform spin excitation. We describe here a method for pulse sequence optimization that uses a stochastic numerical solver that in principle is capable of finding a global optimum. The method provides a simple framework for incorporating any constraint and implementing arbitrarily complex cost functions. Efficient methods for simulating spin dynamics and incorporating frequency selectivity are also described. Methods: Optimized pulse sequences for polarization transfer between protons and X‐nuclei and excitation pulses that eliminate J‐coupling modulation were evaluated experimentally using a surface coil on phantoms, and also the detection of hyperpolarized [2‐13C]lactate in vivo in the case of J‐coupling modulation‐free excitation. Results: The optimized polarization transfer pulses improved the SNR by ~50% with a more than twofold reduction in the B1 field, and J‐coupling modulation‐free excitation was achieved with a more than threefold reduction in pulse length. Conclusion: This process could be used to optimize any pulse when there is a need to improve the uniformity and frequency selectivity of excitation as well as to design new pulses to steer the spin system to any desired achievable state. [ABSTRACT FROM AUTHOR]

Hyperpolarized (HP) 13C magnetic resonance enables non‐invasive probing of metabolism in vivo. To date, only 13C‐molecules hyperpolarized with persistent trityl radicals have been injected in humans. We show here that the free radical photo‐induced in alpha‐ketoglutaric acid (α‐KG) can be used to hyperpolarize photo‐inactive 13C‐molecules such as [1‐13C]lactate. α‐KG is an endogenous molecule with an exceptionally high radical yield under photo‐irradiation, up to 50 %, and its breakdown product, succinic acid, is also endogenous. This radical precursor therefore exhibits an excellent safety profile for translation to human studies. The labile nature of the radical means that no filtration is required prior to injection while also offering the opportunity to extend the 13C relaxation time in frozen HP 13C‐molecules for storage and transport. The potential for in vivo metabolic studies is demonstrated in the rat liver following the injection of a physiological dose of HP [1‐13C]lactate. [ABSTRACT FROM AUTHOR]

Purpose: Imaging tumor metabolism in vivo using hyperpolarized [1‐13C]pyruvate is a promising technique for detecting disease, monitoring disease progression, and assessing treatment response. However, the transient nature of the hyperpolarization and its depletion following excitation limits the available time for imaging. We describe here a single‐shot multi spin echo sequence, which improves on previously reported sequences, with a shorter readout time, isotropic point spread function (PSF), and better signal‐to‐noise ratio. Methods: The sequence uses numerically optimized spectrally selective excitation pulses set to the resonant frequencies of pyruvate and lactate and a hyperbolic secant adiabatic refocusing pulse, all applied in the absence of slice selection gradients. The excitation pulses were designed to be resistant to the effects of B0 and B1 field inhomogeneity. The gradient readout uses a 3D cone trajectory composed of 13 cones, all fully refocused and distributed among 7 spin echoes. The maximal gradient amplitude and slew rate were set to 4 G/cm and 20 G/cm/ms, respectively, to demonstrate the feasibility of clinical translation. Results: The pulse sequence gave an isotropic PSF of 2.8 mm. The excitation profiles of the optimized pulses closely matched simulations and a 46.10 ± 0.04% gain in image SNR was observed compared to a conventional Shinnar–Le Roux excitation pulse. The sequence was demonstrated with dynamic imaging of hyperpolarized [1‐13C]pyruvate and [1‐13C]lactate in vivo. Conclusion: The pulse sequence was capable of dynamic imaging of hyperpolarized 13C labeled metabolites in vivo with relatively high spatial and temporal resolution and immunity to system imperfections. [ABSTRACT FROM AUTHOR]

Mesothelin overexpression in lung adenocarcinomas correlates with the presence of activating KRAS mutations and poor prognosis. Hence SS1P, a mesothelin-targeted immunotoxin, could offer valuable treatment options for these patients, but its use in solid tumor therapy is hampered by high immunogenicity and non-specific toxicity. To overcome both obstacles we developed RG7787, a de-immunized cytotoxic fusion protein comprising a humanized SS1 Fab fragment and a truncated, B-cell epitope silenced, 24 kD fragment of Pseudomonas exotoxin A (PE24). Reactivity of RG7787 with sera from immunotoxin-treated patients was >1000 fold reduced. In vitro RG7787 inhibited cell viability of lung cancer cell lines with picomolar potency. The pharmacokinetic properties of RG7787 in rodents were comparable to SS1P, yet it was tolerated up to 10 fold better without causing severe vascular leak syndrome or hepatotoxicity. A pharmacokinetic/pharmacodynamic model developed based on NCI-H596 xenograft studies showed that for RG7787 and SS1P, their in vitro and in vivo potencies closely correlate. At optimal doses of 2–3 mg/kg RG7787 is more efficacious than SS1P. Even large, well established tumors (600 mm 3 ) underwent remission during three treatment cycles with RG7787. Also in two patient-derived lung cancer xenograft models, Lu7336 and Lu7187, RG7787 showed anti-tumor efficacy. In monotherapy two treatment cycles were moderately efficacious in the Lu7336 model but showed good anti-tumor activity in the KRAS mutant Lu7187 model (26% and 80% tumor growth inhibition, respectively). Combination of RG7787 with standard chemotherapies further enhanced efficacy in both models achieving near complete eradication of Lu7187 tumors. [ABSTRACT FROM AUTHOR]