Figure 2. On-Target Inhibition of RBC LDH Ex Vivo and Tumor LDH In Vivo.

(A–C) Ex vivo lactate secretion assay using mouse (m) RBCs. Mice were dosed orally (PO) (A) or intravenously (IV) (B and C) with NCI-006. (B) includes LDHi dosing between 1 and 50 μM; (C) includes 50 and 100 μM doses. At 2 h after LDH inhibitor administration, blood was drawn, and ex vivo lactate production in mRBCs was determined (see Method Details). Lactate production in RBCs obtained from mice treated with 50–200 mg/kg NCI-006 in the PO group and 10–50 mg/kg NCI-006 in the IV group was significantly reduced compared with lactate production in mice treated with PBS (n = 3 for each group, *p < 0.05, t test). By 24 h after LDH inhibitor administration, lactate production returned to normal levels, except in the PO group treated with 100 or 200 mg/kg NCI-006, and in the IV group treated with 50 or 100 mg/kg NCI-006. The data are displayed as means ± SEM (n = 3 for each group; *p < 0.05, t test). ^†50% reduction in RBC counts was seen in mice treated with 200 mg PO and 100 mg/kg IV of the LDH inhibitor.

(D) Ex vivo lactate recovery time measured using mRBCs. Mice were orally administered 50 mg/kg LDHi or PBS. Lactate production returned to baseline between 15 and 24 h after LDHi administration.

(E and F) Correlation between intra-tumor concentration of LDH inhibitor and LDH activity in MIA PaCa-2 xenografts, comparing oral (E) and IV (F) drug administration. Tumors were excised 1 h after NCI-006 administration, and the LDH activity in the tumor and the NCI-006 concentration in the plasma and tumor were measured.