Ilwoo Park¹, Llewellyn E Jalbert¹, Tomoko Ozawa², C. David James², Joanna J Phillips², Daniel B Vigneron^1,3, Russell O Pieper², Sabrina M Ronen¹, and Sarah J Nelson^1,3
1Surbeck Laboratory of Advanced Imaging, Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA, United States,²Brain Tumor Research Center, Department of Neurological Surgery, University of California, San Francisco, San Francisco, CA, United States, ³Department of Bioengineering and Therapeutic Sciences, University of California, San Francisco, San Francisco, CA, United States

We have demonstrated that hyperpolarized 13C MR metabolic imaging using [1-13C]-pyruvate can provide an early surrogate marker of MGMT activity and response to TMZ treatment. The inhibition of pyruvate metabolism in MGMT-deficient tumors was seen as early as day one after TMZ treatment, and occurred long before the delayed apoptotic response induced by TMZ. The results from this study suggest that this technique may allow neuro-oncologists to quickly evaluate patient response to TMZ and enable them to tailor customized therapies for individual patients with brain tumors.

Sarah E Bohndiek^1,2, De-en Hu^1,2, Mikko I Kettunen^1,2, and Kevin M Brindle^1,2
1Department of Biochemistry, University of Cambridge, Cambridge, Cambridgeshire, United Kingdom, ²Cambridge Research Institute, Cancer Research UK, Cambridge, Cambridgeshire, United Kingdom

Hyperpolarization is a new technique that can substantially increase the sensitivity of in vivo MRS measurements of 13C labeled metabolic substrates and their metabolites, promising new insights into tumor metabolism and rapid detection of treatment response. We show here that measurements of hyperpolarized [1-13C]pyruvate and [1,4-13C2]fumarate metabolism in xenograft colorectal cancer models can detect altered tumor metabolism following treatment with the anti-angiogenic agent Bevacizumab. Our results suggest that hyperpolarized markers may inform on acute responses to anti-angiogenic therapy and more importantly, provide a means to differentiate responders and non-responders at an early stage in the treatment time course.

Aaron Keith Grant¹, Pankaj K Seth², Elena Vinogradov¹, Xiaoen Wang¹, Vikas P Sukhatme², and Robert E Lenkinski^1
1Radiology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, United States, ²Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, United States

The Warburg phenomenon is the tendency of many cancers to preferentially metabolize pyruvate into lactate rather than oxidizing it in the TCA cycle. This tendency may confer a survival advantage on cancer cells. Reversing the Warburg effect may selectively harm cancer cells. Dichloroacetate (DCA) is a drug that may accomplish this by increasing the rate of oxidative metabolism. Hyperpolarized pyruvate provides a tool to monitor changes in metabolism resulting from DCA. We present preliminary data in the TRAMP model of prostate cancer that show signatures of increased oxidative metabolism, including reduced lactate signal and increased bicarbonate signal, following DCA treatment.

Ralph E Hurd¹, Daniel Spielman², Sonal Josan³, Yi-Fen Yen¹, Adolf Pfefferbaum^3,4, and Dirk Mayer^2,3
1GE Healthcare, Menlo Park, CA, United States, ²Department of Radiology, Stanford University, Stanford, CA, United States, ³Neuroscience Program, SRI International, Menlo Park, CA, United States, ⁴Psychiatry and Behavioral Sciences, Stanford University, Stanford, CA, United States

Three-dimensional dynamic metabolic images were obtained following injection of 80 mM hyperpolarized [1-13C]pyruvate, prepared with, and without, 40 mM sodium lactate in the dissolution buffer. Comparisons were made on the basis of apparent rate constants, lactate signal, and contrast-to-noise ratio. In a second experiment, metabolic images of hyperpolarized 40 mM [1-13C]lactate, were compared, with and without 80 mM sodium pyruvate in the dissolution buffer. This set of exchange-linked dissolution agents and controls was investigated as a potential quantitative measure of steady-state pool size limits and isotopic exchange, as well as for improvement in metabolic imaging signal and contrast-to-noise ratio.

Peder Eric Zufall Larson¹, Adam B Kerr², John M Pauly², and Daniel B Vigneron^1
1Radiology and Biomedical Imaging, UC - San Francisco, San Francisco, CA, United States, ²Electrical Engineering, Stanford University, Stanford, CA, United States

In hyperpolarized 13C metabolic imaging, the metabolic profile is assumed from indirect observations of converted metabolites. We have developed a method using the stimulated echo for directly observing localized conversion/label exchange from hyperpolarized [1-13C]pyruvate to [1-13C]lactate and [1-13C]alanine in vivo. It is based on a phase-sensitive stimulated-echo tagging, which also selects only stationary metabolites. Metabolites generated from stationary pyruvate during the mixing interval have a 90-degree phase shift from those present prior to the tagging. Generated metabolites are separated using a phase-sensitive reconstruction. In vivo experiments have demonstrated direct observation of both alanine and lactate generation, allowing for a more accurate metabolic characterization.

Francisco M Martinez-Santiesteban¹, Lanette Friesen Waldner², and Timothy James Scholl^1,2
1Department of Medical Biophysics, University of Western Ontario, London, ON, Canada, ²Imaging Research Laboratories, Robarts Research Institute, University of Western Ontario, London, ON, Canada

An important characteristic of hyperpolarized contrast agents is that they possess a suitably long T1 relaxation time to permit sufficient time for transportation, injection, metabolism and imaging. While T1 times can be readily measured at clinical field strengths, very little data, if any, exists at very low fields (< 10mT) where they are dispensed from the polarizing apparatus and transported to the fringe field of the MRI. The results presented here are some of the first T1 nuclear magnetic resonance dispersion measurements reported for hyperpolarized [1-13C] pyruvate.

Albert P Chen¹, Ralph E Hurd², Marie A Schroeder^3,4, Angus Z Lau^4,5, Yi-Ping Gu⁴, Wilfred W Lam⁴, Jennifer Barry⁴, James Tropp⁶, and Charles H Cunningham^4,5
1GE Healthcare, Toronto, ON, Canada, ²GE Healthcare, Menlo Park, CA, United States, ³Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom, ⁴Imaging Research, Sunnybrook Health Sciences Centre, Toronto, ON, Canada, ⁵Deptartment of Medical Biophysics, University of Toronto, Toronto, ON, Canada, ⁶GE Healthcare, Fremont, CA, United States

Utilization of either C1 or C2 labeled pre-polarized pyruvate as a tracer can only afford a partial view of cardiac pyruvate metabolism. If pyruvate was labeled at both C1 and C2 positions, then it would be possible to observe the down stream metabolites that were the results of both PDH and Krebs cycle flux with a single tracer bolus. Intracellular pH could also be estimated from the same data, provided the ¹³CO₂ signal has adequate SNR. This study demonstrated the feasibility of simultaneous investigation of cardiac PDH flux, Krebs cycle metabolism and intracellular pH in vivo, by using hyperpolarized [1,2-¹³C₂]pyruvate.

Daniel Ball¹, Michael Dodd¹, Helen Atherton², Marie Schroeder¹, Carolyn Carr¹, George Radda¹, Kieran Clarke¹, and Damian Tyler^1
1Department of Physiology, Anatomy and Genetics, Oxford University, Oxford, Oxfordshire, United Kingdom, ²Department of Biochemistry, Cambridge University

The use of hyperpolarized pyruvate has been demonstrated to be extremely useful for the assessment of cardiac carbohydrate metabolism, but it is unable to probe cardiac fatty acid metabolism. Therefore, the aim of this study was to develop an appropriate probe to allow assessment of short-chain fatty acid metabolism. Hyperpolarized butyrate, a 4-carbon short chain fatty acid was chosen as its small molecular size ensured high levels of polarization and a sufficiently long relaxation time for application. Metabolism of hyperpolarized [1-13C]butyrate was demonstrated in the perfused rat heart through the visualization of butyrate incorporation into the TCA cycle.

Sadia Asghar Butt¹, Lise Vejby Søgaard¹, Peter Magnusson¹, Mette Lauritzen¹, Per Åkeson¹, and Jan Henrik Ardenkjær-Larsen^2
1Danish Research Centre for Magnetic Resonance, Hvidovre, Denmark, ²GE Healthcare, Broendby, Denmark

Metabolic imaging of hyperpolarized [1-13C]ketoisocaproate and [1-13C]pyruvate was performed in the normal rat brain. A chemical shift imaging (CSI) sequence was acquired after injection of [1-13C]ketoisocaproate or [1-13C]pyruvate. The metabolite CSI maps showing biodistribution of metabolites reveal that [1-13C]leucine (formed by transamination of injected [1-13C]ketoisocaproate) is located in the brain tissue. Further the [1-13C]pyruvate metabolites, [1-13C]lactate and 13C-bicarbonate also showed brain localization. This study is the first to show hyperpolarized [1-13C]ketoisocaproate as a viable substance for rat brain imaging.

Mor Mishkovsky^1,2, Arnaud Comment^1,2, and Rolf Gruetter^1,3
1Laboratory for Functional and Metabolic Imaging, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland, ²Department of Radiology, Université de Lausanne, Lausanne, Switzerland, ³Department of Radiology, Universités de Lausanne et de Genève, Lausanne and Genève, Switzerland

Acetate brain metabolism was studied in vivo in rats following the infusion of hyperpolarized 1-¹³C and ¹³C₂ sodium acetate solutions, leading to the first direct observation of the brain TCA cycle intermediate 2-oxoglutarate (2OG). The observation of 2OG and the lack of glutamate (Glu) signal imply that the reactions leading to ¹³C-label incorporation into Glu are operating, in the glial compartment in vivo, at a rate much lower than that of transaminase. We deduced from this observation that transport across the inner mitochondria membrane is rate limiting.