Discovery of indoximod prodrugs and characterization of clinical candidate NLG802

A series of different prodrugs of indoximod, including estesrs and peptide amides were synthesized with the aim of improving its oral bioavailability in humans. The pharmacokinetics of prodrugs that were stable in buffers, plasma and simulated gastric and intestinal fluids was first assessed in rats after oral dosing in solution or in capsule formulation. Two prodrugs that produced the highest exposure to indoximod in rats were further tested in Cynomolgus monkeys, a species in which indoximod has oral bioavailability of 6-10% and an equivalent dose-dependent exposure profile as humans. NLG802 was selected as the clinical development candidate after increasing oral bioavailability (>5-fold), C_max (6.1-3.6 fold) and AUC (2.9-5.2 fold) in monkeys, compared to equivalent molar oral doses of indoximod. NLG802 is extensively absorbed and rapidly metabolized to indoximod in all species tested and shows a safe toxicological profile at the anticipated therapeutic doses. NLG802 markedly enhanced the anti-tumor responses of tumor-specific pmel-1 T cells in a melanoma tumor model. In conclusion, NLG802 is a prodrug of indoximod expected to increase clinical drug exposure to indoximod above the current achievable levels, thus increasing the possibility of therapeutic effects in a larger fraction of the target patient population.

Implementation of the CYP Index for the Design of Selective Tryptophan-2,3-dioxygenase Inhibitors

A class of imidazoisoindole (III) heme-binding indoleamine-2,3-dioxygenase (IDO1) inhibitors were optimized via structure-based drug design into a series of tryptophan-2,3-dioxygenase (TDO)-selective inhibitors. Kynurenine pathway modulation was demonstrated in vivo, which enabled evaluation of TDO as a potential cancer immunotherapy target. As means of mitigating the risk of drug-drug interactions arising from cytochrome P450 inhibition, a novel property-based drug design parameter, herein referred to as the CYP Index, was implemented for the design of inhibitors with appreciable selectivity for TDO over CYP3A4. We anticipate the CYP Index will be a valuable design parameter for optimizing CYP inhibition of any small molecule inhibitor containing a Lewis basic motif capable of binding heme.