Fig. 6. Detection of APN activity with hyperpolarized Ala-[1-¹³C]Gly-d₂-NMe₂ in vivo.

(A) Schematic representation of the experimental outline. i.v., intravenously. (B and C) Time series of ¹³C NMR spectra acquired in vivo with the coil placed over the leg tumor after intravenous injection of hyperpolarized probe 3. Inset: an example of the anatomical images from the observed area (¹H MRI). (D and E) Time course plots of ¹³C signals of Ala-[1-¹³C]Gly-d₂-NMe₂ (3) (red line) and [1-¹³C]Gly-d₂-NMe₂ (4) (orange line) in (B) and (C). (F) Dot plot of the AUC ratio on days 1 and 2 (n = 3 and P = 0.009). The experiments were performed using 40 μl (n = 1) and 80 μl (n = 2) of the probe solution for hyperpolarization. AUC, area under the curve. N.T., nontreated. G) CSI of a mouse leg bearing xenograft tumor (MIA PaCa-2). Left: Anatomical image from the observed area (T₂-weighted ¹H MRI). Middle: Image of the product (4) to the probe (3) ratio. Right: Expanded spectra in representative voxels a to d. The voxel size is 2.8 mm × 2.8 mm × 10 mm. The left peak is Ala-[1-¹³C]Gly-d₂-NMe₂ (3; red circle), and the right peak is [1-¹³C]Gly-d₂-NMe₂ (4; orange circle). ¹³C spectra are with denoising process. The image was acquired at 18 to 26 s after injection of the hyperpolarized probe.