Jamie D. Walls

Pseudorandom selective excitation in NMR.

In this work, average Hamiltonian theory is used to study selective excitation under a series of small flip-angle θ-pulses [θ≪π/3] applied either periodically [corresponding to the DANTE pulse sequence] or aperiodically to a spin-1/2 system. First, an average Hamiltonian description of the DANTE pulse sequence is developed that is valid for frequencies either at or very far from integer multiples of 1τ, where τ is the interpulse delay. For aperiodic excitation, a single resonance, νsel, can be selectively excited if the θ-pulse phases are modulated in concert with the interpulse delays. The conditions where average Hamiltonian theory can be accurately applied to describe the dynamics under aperiodic selective pulses, which are referred to as pseudorandom-DANTE or p-DANTE sequences, are similar to those found for the DANTE sequence. Signal averaging over different p-DANTE sequences improves the apparent selectivity at νsel by reducing the excitations at other frequencies. Experimental demonstrations of p-DANTE sequences and comparisons with the theory are presented.

Abstract 1840: Metabolomic profiling of gastrointestinal stromal tumor (GIST) T1 cell lines in response to imatinib therapy

Background: There is a growing need for novel drugs to treat drug resistant GIST. The aim of this study was to evaluate chronological metabolic changes in GIST cells treated with imatinib mesylate. Methods: Human GIST T1 cells were incubated with imatinib 0.5 mM. Metabolomic profiling was performed in extracted cell pellets at 12, 24 and 48 hours, after viability and cell counting was done, and compared with controls via acquisition of 1 H-NMR spectra using a 500MHz spectrometer equipped with a 5mm TCI 500S2 H-C/N-D-05 Z cryoprobe head at 298 K. Standard, one-dimensional NOESYpr1D pre-saturation pulse program was used. Spectra were further processed in an NMR suite processor; Partial Least Squares Discriminant Analysis (PLS-DA) model was used for characterization of chronological biochemical differences. Results: By 48 hours of exposure of cells to imatinib, glucose initially increased then significantly decreased with gradual decrease of lactate production and minimal changes in pyruvate and succinate denoting shifting from cytosolic to mitochondrial glycolysis, this was echoed with consumption of glutamine and glutamate. Glutathione and cell membrane phospholipids as phosphocholine gradually decreased by a factor of 1.6 for each, suggesting inhibited growth and invasiveness. Aspartate, myo-inositol, glycerophosphocholine and taurine gradually increased by a factor of 1.6, 1.7, 2.6 and 1.3, respectively. Tyrosine, valine and leucine showed minimal changes. Cell viability was directly correlated to changes in choline, creatine phosphate, myo-inositol and taurine (Pearson9s R >0.65). PLS-DA model suggested that changes in myoinositol, glycerophosphocholine, glutamate, aspartate, phosphcholine and glutathione were the metabolites mostly influencing the differential chronological global metabolic profiles of the cells with continued exposure to imatinib (R 2 X = 0.76, R 2 Y = 0.60, Q 2 (cum) = 0.20). Conclusion: Metabolomic profiling of GIST cells exposed to signal transduction modulators supplements molecular findings and provides further mechanistic insights into longitudinal changes of the mitochondrial and glycolytic pathways of oncogenesis, it can potentially provide novel as well as complementary therapeutic targets. Citation Format: Vered Marks, Gregory Tiesi, Ana Paz Mejia, Jonathan Trent, Jamie Walls, Alan Livingstone, Danny Yakoub. Metabolomic profiling of gastrointestinal stromal tumor (GIST) T1 cell lines in response to imatinib therapy. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1840. doi:10.1158/1538-7445.AM2015-1840

1H NMR studies distinguish the water soluble metabolomic profiles of untransformed and RAS-transformed cells

Metabolomic profiling is an increasingly important method for identifying potential biomarkers in cancer cells with a view towards improved diagnosis and treatment. Nuclear magnetic resonance (NMR) provides a potentially noninvasive means to accurately characterize differences in the metabolomic profiles of cells. In this work, we use 1H NMR to measure the metabolomic profiles of water soluble metabolites extracted from isogenic control and oncogenic HRAS-, KRAS-, and NRAS-transduced BEAS2B lung epithelial cells to determine the robustness of NMR metabolomic profiling in detecting differences between the transformed cells and their untransformed counterparts as well as differences among the RAS-transformed cells. Unique metabolomic signatures between control and RAS-transformed cell lines as well as among the three RAS isoform-transformed lines were found by applying principal component analysis to the NMR data. This study provides a proof of principle demonstration that NMR-based metabolomic profiling can robustly distinguish untransformed and RAS-transformed cells as well as cells transformed with different RAS oncogenic isoforms. Thus, our data may potentially provide new diagnostic signatures for RAS-transformed cells.

Breakdown of linear response theory under low-power excitation in NMR. I. The case of long-lived signals in inhomogeneously broadened spin systems

In this work, we examine the application of linear response theory to the problem of low-power excitation in inhomogeneously broadened spin systems when the strength of the radiofrequency (RF) pulse, νRF, is smaller than the inhomogeneous linewidth. Even for small overall excitations [Θ = 2πνRFTp ≪ 1 where Tp is the RF pulse length], linear response theory is shown to break down for spins with resonance frequencies that are on the order of νRF, which is due to the fact that the RF interaction cannot be treated as a small perturbation in this case. This breakdown in linear response theory can be partially corrected for by enforcing unitarity in the linear response. Furthermore, the nature of the spin echo generated by a πX-pulse applied immediately after a low-power pulse is investigated. Numerical calculations and experiments performed in an inhomogeneously broadened H2O/D2O solution confirm the theoretical predictions presented in this work.

Conditional rotations of heteronuclear coupled spins

We present a new pulse sequence that conditionally excites I spin magnetization only in the presence of a nonzero heteronuclear coupling to an S spin. The pulse sequence, referred to as the reverse INEPT pathway selective pulse or RIPSP, generates a pure I spin rotation by an angle that depends upon the heteronuclear coupling constant in InS spin systems. Experimental demonstrations are shown in (13)C labeled chloroform, dichloromethane, and toluene samples and in unlabeled 2,3-dibromopropionic acid and brucine samples.