Supplementary Information. Detecting tumor response to treatment using hyperpolarized 13 C magnetic resonance imaging and spectroscopy

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1 Supplementary Information Detecting tumor response to treatment using hyperpolarized 13 C magnetic resonance imaging and spectroscopy Sam E. Day, Mikko I. Kettunen, Ferdia A. Gallagher, De-En Hu, Mathilde Lerche, Jan Wolber, Klaes Golman, Jan Henrik Ardenkjaer-Larsen and Kevin M. Brindle Figure 1 Effect of pulse flip angle on the apparent T 1 of hyperpolarized [1-13 C]pyruvate. The z magnetizations of hyperpolarized [1-13 C]pyruvate samples were sampled successively using: 1) TR = 1 s, nominal flip angle = 5 ; 2) TR = 3 s, nominal flip angle = 5 ; 3) TR = 1 s, nominal flip angle = 2.5. The apparent T 1 s for these experiments were 41 s, 46 s and 52 s, respectively. The solid line represents a fit of all of the data to: S(t) = S 0 * exp (t /T 1) * cos(α) n, where S (t) is the observed z magnetization at time t, S 0 is the initial z magnetization, α is the flip angle and n is the number of preceding r.f. pulses. For the last experiment, the data were fit to α/2. The fitted T 1, using all the data gave a T 1 of 55 s and a value for α of 6.3. These data show that decreasing TR or increasing the flip angle leads to an underestimate of the T 1. However, this effect is small, moreover it has little effect on the estimated rate constants calculated from the two-site exchange model shown in the paper (equations 2 & 3 in the paper). Figure 2 shows the effect on the fitted rate constants, and, of varying the T 1 s of the lactate and pyruvate carboxyl carbons between 20 and 60 s for experiments on cells and tumors. There is little effect on the apparent rate constants over this range of T 1 s. 1

2 Figure 2 Effect on the fitted rate constants of varying the T 1 s of the lactate and pyruvate carboxyl carbons. The carboxyl carbon T 1 s were varied between 20 and 60 s (ρ P = ρ L = 0.05 to s 1 ) on the fitted rate constants, and. The open and filled circles represent the optimum fitted values (largest R 2 value) when relaxation rate was also fitted for the data obtained from cells (a) and tumors (b). The same optimal values were obtained regardless of the initial guesses. Measurements of exchange in cell suspensions using 1 H NMR and [3-13 C]pyruvate It has been widely assumed that lactate dehydrogenase catalyzes a reaction that is nearto-equilibrium in the cell. This assumption has been used to calculate cytosolic NADH/NAD + ratios from measurements of tissue lactate/pyruvate ratios 1. The equilibrium constant for the reaction catalysed by lactate dehydrogenase is 2 : Keq = [Pyr][NADH ][H + ] [Lac][NAD + ] =1.11x10 11 Thus if we assume that the reaction is near-to-equilibrium then we can calculate the expected pyruvate, lactate and NADH concentrations, using measured values for tumor cell NAD+ concentration and intracellular ph, following the addition of 40 mm lactate and 40 mm pyruvate to an EL4 cell suspension. These are similar concentrations to those that we added in the cell experiments described in the manuscript i.e. 2

3 Table 1 Starting concentrations (mm) Calculated equilibrium concentrations (mm) NADH 0 NADH eq 5.59 x 10 5 Pyr 40 Pyr eq 40 Lactate 40 Lac eq 40 NAD NAD eq ph 7.1 K 1.11 x (M) (The NAD + concentration was measured at 0.4 mm, assuming that 5 x 10 8 cells contains 0.64 ml intracellular water 3. The ph was based on 31 P NMR measurements on CHO cells 4 ). Thus chemical equilibrium is achieved by the conversion of just 5.59 x 10 8 M lactate into pyruvate (1.4 x 10 4 % of the total lactate pool; 21 nmols in the 4 ml of medium containing 10 8 cells). Given the measured flux in the cell experiment, in untreated cells 54 nmols/s/10 8 cells, chemical equilibrium will be achieved in ~0.4 sec. For isotopic equilibrium to be achieved the whole lactate pool must turn over. Experimental demonstration of label exchange in an EL4 cell suspension. EL-4 cells were washed twice in RPMI 1640 medium at 37 C and then resuspended in 600 µl of the same medium, at a cell density of 10 8 cells/ml, containing unlabeled lactate (40 mm) and [3-13 C]pyruvate (40 mm) in a 5 mm NMR tube. Successive 1D 1 H NMR spectra were acquired across a spectral width of 8 khz into 16K complex data points using the NOESY pulse sequence: Relaxation Delay (RD)-90-t 1-90-t m -90-acquire; RD = 2.5s, t 1 =5 ms, t m =150 ms. The water resonance was suppressed by low power irradiation during the t m and RD periods. An additional delay of 300 ms was added prior to RD which, with an acquisition delay of 2.048s, gave a total recycle time of 4.952s. One transient was acquired per spectrum and the sample temperature was maintained at 37 C. The cells were maintained in suspension by periodically bubbling air through the NMR tube. The 13 C label in pyruvate and lactate was detected through splitting of their respective methyl 1 H resonances by spin-spin coupling with the 13 C label. The spin-coupled 13 C satellites are indicated in the 1 H NMR spectra shown in Figure 3. 3

4 Figure 3 Experimental demonstration of 13 C label exchange in an EL4 cell suspension. Exchange of 13 C label between 40 mm [3-13 C]pyruvate and 40 mm unlabeled lactate following their addition to an EL4 cell suspension. The spectra were collected after 1 minute (a) and 40 minutes (b). The pyruvate and lactate peak integrals are shown as a function of time in (c). The spikes in these traces were due to air bubbles passing through the receiver coil. There was no change in the total pyruvate concentration but a decrease in the concentration of [3-13 C]pyruvate and an increase in the concentration [3-12 C]pyruvate, demonstrating exchange of 13 C label between pyruvate and lactate. The increase in lactate concentration is due to its production from glucose in the medium. Fitted rate constants and relaxation times for flux data obtained with cells in vitro and tumors in vivo following injection of hyperpolarized [1-13 C]pyruvate The tables here show the fitted parameters for the data presented in the paper. Table 2 4

5 Cells Effect of lactate concentration Added lactate concentration (mm) s 1 (x 10 3 ) s 1 (x 10 3 ) ρl = ρp *[Pyr] nmol/s/10 8 cells 0 (n=2) 37 ± ± ± ± (n=2) 12 ± ± ± ± (n=2) 6 ± ± ± ± 26 Treatment s 1 (x 10 3 ) s 1 (x 10 3 ) ρl = ρp *[Pyr] nmol/s/10 8 cells Untreated (n=4) 9 ± ± ± ± 15 Etoposide (n=5) 11 ± ± ± ± 1.5 ** 0.01 ** Etoposide+Nicotinamide 12 ± ± ± ± 11 (n=4) Etoposide + 3 Aminobenzamide (n=2) 22 ± ± ± ± 2 Pyruvate (37.5 mm) was added to 4 ml medium containing 10 8 cells. This corresponds to 150 mol pyruvate. Mean ± SD. ** p<0.01. Different from untreated cells (Student s unpaired t-test) Tumors Fitted values for treated and untreated animals p L =p P Untreated ± ± ± (n=8) (T 1 = 30 ± 2 s) Treated ± ± ± (n=8) ** ( 25%) (T 1 = 30 ± 4 s) Mean ± SD. ** p<0.01 (Student s unpaired t-test) / 4.0 ± ± 0.4 Fitted values for the same animals before and after treatment (n=4) ρ L = ρ P Untreated ± ± ± (T 1 = 30 ± 1 s) Treated ± ± ± ** ( 39%) (T 1 = 29 ± 7 s) Mean±SD. ** p<0.01 (Student s paired t-test) / 2.2 ± ± 0.7 5

6 Measurements of hyperpolarized 13 C-labeled pyruvate and lactate in underlying muscle and in a slice though the abdomen. The labeled lactate observed in the tumor could have been formed elsewhere in the body and washed into the tumor via the circulation. However, spectroscopic measurements from a 5 mm thick slice above the tumor, in treated and untreated animals, which included the liver, showed only relatively low levels of lactate labeling when compared to the tumor (Figs. 4a and 4b). Similarly, measurements from muscle underlying the tumor site also showed only relatively low levels of lactate labeling (Figs. 4c and 4d). A signal from alanine was observed in the muscle spectra (Fig. 4d). Figure 4 Measurements of hyperpolarized 13 C-labeled pyruvate and lactate in underlying muscle and in a slice though the abdomen. Changes in pyruvate and lactate signals measured from a slice through the abdomen in an untreated (a) and in a treated (b) animal, and in muscle tissue in an animal with no tumor (c), following injection of hyperpolarized [1-13 C]pyruvate. A representative spectrum from muscle is shown in (d). The solid lines represent the best fits of the data to the two-site exchange model. (Note that data for the abdomen were collected using a 35 mm diameter 1 H/ 13 C volume coil (Rapid Biomedical GmbH, Würzburg, Germany), which gives a lower signal-to-noise ratio than the surface coil used to acquire the muscle data. 6

7 These and other measurements were fitted in order to obtain the apparent rate constants for the exchange between pyruvate and lactate i.e. Table 3 Muscle (n=2) Abdomen (n=10) ρ L = ρ P ± ± ± (T 1 19 ± 1 s) ± ± ± (T 1 19 ± 3 s) Observation of heterogeneity in the lactate/pyruvate ratio in spectra derived from a spectroscopic image These spectra, from a representative tumor, indicate that the observed heterogeneity in the lactate/pyruvate ratio is not simply a consequence of a poor signal-to-noise ratio for the pyruvate signal. Figure 5 Observation of heterogeneity in the lactate/pyruvate ratio in spectra derived from a spectroscopic image. Color maps representing [1-13 C]lactate and [1-13 C]pyruvate peak intensities (a) and corresponding lactate/pyruvate intensity ratios (c) obtained from 13 C chemical shift data (b) in an untreated animal. The 1 H image, shown in grayscale, was used to define the tumor margins (indicated by the white lines). 7

8 Methods Cell culture EL-4 murine lymphoma cells were grown in RPMI 1640 medium supplemented with 10% fetal calf serum, 2mM glutamine and penicillin (100 units/ml)/streptomycin (100 g/ml). Cell viability was assessed following staining with trypan blue. Apoptosis and necrosis were visualized by staining with acridine orange (10 g/ml) and propidium iodide (50 g/ml) respectively 35. For flow cytometry cell pellets (10 6 cells) were washed in ice-cold HEPES-buffered saline and resuspended in 100 L buffer (10 mm HEPES, 140 mm NaCl, 2.5 mm CaCl 2, ph 7.4). Annexin V-FITC (Molecular Probes, USA), which was used according to the manufacturer s instructions, and propidium iodide (1 g/ml) were added, prior to incubation for 10 min at 20 C. The resulting mixture was kept briefly on ice and then analyzed using Flow Cytometry in a Cyan ADP-MLE cytometer (Dako, Ely, Cambridgeshire, UK), with 20,000 cells counted per event. Tumor extracts Immediately after completion of imaging the mouse was sacrificed and the tumors rapidly excised and snap-frozen in a liquid nitrogen-cooled mortar. Frozen tumors were weighed, crushed and, for metabolite determinations, extracted using 7% ice-cold perchloric acid. The extracts were neutralized using 2M K 2 CO 3, treated with Chelex 100 resin and then lyophilized. Dried samples were dissolved in 1 ml 2 H 2 O and, for 1 H NMR measurements, 150 l of the sample was combined with 500 l of a buffer containing 0.1 M Na 2 HPO 4 and 0.1 M KH 2 PO 4, ph 8.0, and 4.2 mm TSP (as a chemical shift and intensity standard) in 2 H 2 O. 1 H NMR spectra were acquired at 500 MHz into 32 k complex data points using a 90 o pulse, 6 s recycle time, a spectral width of 8 khz and were the sum of 32 transients. For measurements of lactate dehydrogenase activity approximately 0.2 g of snap-frozen tissue was thawed in 830 µl buffer containing 50 mm Tris-HCl, ph 8.2, 2 mm dithiothreitol, 2 mm EDTA and 1% Triton X-100, and then homogenized using a tight-fitting Potter homogenizer. After 10 strokes with the pestle, the resulting tumor extracts were centrifuged for 1 min at 4500 g. The supernatants were removed, diluted, and assayed immediately by monitoring the reduction in absorbance of NADH at 340 nm 6. The samples were diluted so that reduction of A 340 was linear over the first ten minutes. The assay mixture was comprised of 830 l of 80 mmol/l Tris, ph 7.2, 200 mmol/l NaCl, 0.2 mmol/l NADH, 1.6 mmol/l pyruvate and 17 l of the diluted protein extract. Cell Extracts. EL-4 cells (6 x 10 8 ), treated with drug solvent, etoposide or etoposide plus nicotinamide, were extracted using 7% ice-cold perchloric acid. The extracts were neutralized using 2M K 2 CO 3, treated with Chelex 100 resin and then lyophilized. Dried samples were dissolved in 1 ml 2 H 2 O and 2.5 ml of a buffer containing 50 mm triethanolamine HCl, ph 8.0, and 5 mm Na 2 EDTA. Samples were run with a capillary tube containing 100 mm MDP as a chemical shift and intensity standard. 31 P NMR spectra were acquired at 161 MHz into 15 k complex data points using a 90 o pulse, 11.5 s recycle time, a spectral width of 10 khz and were the sum of 4000 transients. For measurements of lactate dehydrogenase activity, 10 7 cells were resuspended in 1 ml of buffer containing 50 mm Tris-HCl, ph 8.2, 2 mm dithiothreitol, 2 mm EDTA and 8

9 1% Triton X-100, and then homogenized using a tight-fitting Potter homogenizer. The supernatants were removed, diluted, and assayed immediately by monitoring the reduction in absorbance of NADH at 340 nm, using the assay system described above. References 1. Veech, R. L., Lawson, J. W. R., Cornell, N. W. & Krebs, H. A. Cytosolic phosphorylation potential. J. Biol. Chem. 254, (1979). 2. Williamson, D. H., Lund, P. & Krebs, H. A. The redox state of free nicotinamideadenine dinucleotide in the cytoplasm and mitochondria of rat liver. Biochem. J. 103, (1967). 3. Reitzer, L. J., Wice, B. M. & Kennell, D. Evidence that glutamine, not sugar, is the major energy source for cultured HeLa cells. J. Biol. Chem. 254, (1979). 4. Williams, S. N. O., Anthony, M. L. & Brindle, K. M. Induction of apoptosis in two mammalian cell lines results in increased levels of fructose-1,6-bisphosphate and CDP-choline as determined by 31 P MRS. Magn. Reson. Med. 40, (1998). 5. Anthony, M. L., Zhao, M. & Brindle, K. M. Inhibition of phosphatidylcholine biosynthesis following induction of apoptosis in HL-60 cells. J. Biol. Chem. 274, (1999). 6. Vassault, A. Lactate dehydrogenase. in Methods of Enzymatic Analysis Vol. 3 (ed Bergmeyer, H. U.) (Verlag Chemie, Deerfield Beach, FL, 1983). 9