Fig. 2.
Reversal of immune resistance by systemic inhibition of TDO. (A) Structure, activity, physicochemical features, and bioavailability of TDO inhibitors 680C91 and LM10. Ki were measured on recombinant human TDO (hTDO) (16). A cellular assay based on mouse P815B-mTDO, mouse P815B-mIDO, or human 293E-hTDO cells was used to measure IC50, defined as the concentration giving 50% inhibition of TDO activity at a l-tryptophan concentration of 80 μM. Values ± SEM are shown corresponding to the mean of three independent experiments. LD50 was estimated by an MTT assay evaluating cell viability in the same cultures. Solubility was evaluated at room temperature as described in ref. 16. Bioavailability was estimated by measuring plasma concentration of the compounds after 1, 2, or 7 d of oral administration of 160 mg/kg/day. Mice (n = 10) received either normal drinking water or a solution of 1 mg/mL 680C91 at pH 2.5 or 1 mg/mL LM10 at pH 9, of which they drank an average of 4 mL/day. (B) Tumor progression in immunized mice (n = 45 per group) challenged by i.p. injection of 4 × 105 cells from either P815B-mTDO cl8 (diamonds, Left), P815B-mTDO cl12 (triangles, Center), or P815B cl1 (circles, Right) and treated (black symbol) or not (white symbol) with 160 mg/kg/day LM10 in the drinking water, starting one day before the injection of tumor cells. Shown are the compiled results of three experiments, each involving groups of 15 mice. The untreated groups are identical to those shown on Fig. 1A. Mice received either normal drinking water or a solution of LM10 at 1 mg/mL P = 0.001, P < 0.001, and P = 0.006 for treated versus untreated mice after challenge with cl8, cl12 and cl1, respectively (Logrank test).