In vivo Hyperpolarized 13C MRS of Tumor Response to DCA Treatment

MRS was performed on either a Bruker 7 T horizontal bore micro-imaging system or a Philips 3 T clinical scanner. In vivo tumor implantation and DCA treatment: Human HT29 carcinoma or SW1222 colon carcinoma cells (5×10⁶) were propagated subcutaneously in NCr nude mice. Tumors were scanned on day one, mice were then treated on days two and three with 200 mg/kg DCA p.o. and a final dose was given on day four, one hour before the post-treatment scan. MR Coils: Mice bearing cancer xenografts of volume 250–300 mm³ were positioned with their tumor within either a custom made 1.8 cm diameter (Bruker 7 T) or 2 cm diameter (Philips 3 T) ¹³C transmit/receive surface coil at the isocentre of the spectrometer. Hyperpolarized ¹³C in vivo: A solution weighing 26 mg [1-¹³C]pyruvic acid (99% isotopically enriched, Sigma Aldrich, United Kingdom) containing 15 mM trityl free radical OX63 (GE Healthcare) and 1.5 mM gadolinium Dotarem-DOTA (Guerbet, United Kingdom) was polarized in a HyperSense® DNP polarizer (Oxford Instruments Molecular Biotools Ltd, UK) for 1 hour. The hyperpolarized pyruvic acid was dissolved in 4 ml Trizma buffer containing 80 mM NaOH, 1 mM EDTA, 50 mM NaCl resulting in a 80 mM pyruvate solution at pH 7, 37°C. A solution of 175 µl 80 mM hyperpolarized [1-¹³C]pyruvate was administered in situ via a lateral tail vein over approximately 5 s. A series of 128 ¹³C spectra were recorded at 75 MHz (Bruker 7 T), every 2 s using a 20° pulse-and-acquire sequence (1 transient, 32 k time domain points, 15 kHz spectral width) or at 32 MHz (Philips 3 T) every 3 s using a 20° slice selective pulse-and-acquire sequence (10 mm slice thickness, 1 transient, 2048 time domain points, 8 kHz spectral width).