Figure 3. Monitoring LDH Inhibitor On-Target Activity in Tumor Xenografts Using ¹³C MR Spectroscopy with Hyperpolarized (HP) [1-¹³C] Pyruvate (Pyr).

(A) A schematic representation of the HP [1-¹³C]Pyr MR study. The ¹³C MR studies were performed with mice bearing MIA PaCa-2 tumors. Except for (E), each mouse was imaged 24 h before and 30 min after LDHi administration, thus serving as its own control.

(B and C) Representative ¹³C-MR spectra (B) and signal intensity curves (C) of [1-¹³C]pyruvate (Pyr), [1-¹³C]lactate (Lac), [1-¹³C]alanine (Ala), and H¹³CO₃- (Bic) detected in a MIA PaCa-2 xenograft after HP [1-¹³C]Pyr injection.

(D) ¹³C MR spectroscopy showed dose-dependent LDH inhibitor suppression of the tumor Lac/Pyr ratio.

(E) Lactate recovery time following a single dose (IV) of 50 mg/kg NCI-006 was determined by ¹³C MR spectroscopy. The [1-¹³C]Lac/Pyr ratio returned to baseline within 12–16 h after IV dosing.

(F) Representative ¹³C-MR spectra (top) and signal intensity curves (bottom) were obtained from before (left) and after (right) evaluations, as described above. The scale bar of the MR image insert (white bar, left side of image) is 8 mm. For a magnified MR image and scale bar (the same for all MR images), please refer to Figure S1E. Conversion of [1-¹³C]Pyr to [1-¹³C]Lac was clearly suppressed by IV NCI-006 administration.

(G) [1-¹³C]Lac/Pyr ratio is significantly decreased after in vivo NCI-006 administration (IV, 50 mg/kg) to mice bearing MIA PaCa-2 (n = 3) or HT29 (n = 3) xenografts.

(H) Average inhibition of tumor LDH activity ± standard deviation (vehicle group, n = 3; treated group, n = 4), determined by biochemical assay of tumors removed from mice 1 h after an IV dose of 50 mg/kg NCI-006 is 79.3% ± 7.4% (**p < 0.01, t test).

See also Figure S1.