Abstract LB-B14: Characterization of next generation IDO1 and TDO inhibitors as novel cancer immunotherapeutic agents
Authors: McGuinness Barry E. , Cowley Phillip M. , Wise Alan , Brown Thomas J. 
Published: May 2016

Abstract
Introduction
The enzymes indoleamine 2,3-dioxygenase (IDO1) and tryptophan 2,3-dioxygenase (TDO) catalyse oxidation of the essential amino acid tryptophan (Trp) leading to the formation of immunosuppressive kynurenine (Kyn) pathway metabolites that dampen the immune response in the tumor microenvironment. Both IDO1 and TDO have been shown to be up-regulated in a variety of cancers and blockade of their activity has been shown to stimulate the anti-tumor immune response in pre-clinical animal models. We have discovered and optimized multiple novel chemical series of both highly selective and dual-acting inhibitors of IDO1 and TDO. Herein we describe the in vitro and in vivo characterization of molecules that we are progressing into the clinic.
Methods
In vitro assays measured the effects of IDO1/TDO inhibitors on Kyn production in cancer cells, hPBMCs and effects on T-cell proliferation in co-culture systems. In vitro ADME properties and in vivo PK/PD profiles were measured by standard methods. In the LPS model of Kyn stimulation, LPS was administered at 0.75-3 mg/kg IP simultaneously with oral administration of IDO1 inhibitors. Plasma and tissue samples were collected 20 hours after dosing. In the PAN02 model of tumor growth compounds were orally administered at 100 mg/kg BID once a mean tumor volume of 90 mm3 was reached.
Results
We have characterized the IDO1 and TDO-selective inhibitors and dual-acting inhibitors which demonstrate nM potencies. In IFNγ-stimulated A172 glioblastoma cells expressing both enzymes, the dual-acting molecules fully inhibit Kyn production, whilst selective inhibitors yield only a partial response, demonstrating the utility of dual enzyme blockade in cancer cells. The compounds also relieve inhibition of T-cell proliferation in cancer cell/T-cell co-culture assays and demonstrate highly favourable physico-chemical and pharmacokinetic properties. These properties translate to superior PK/PD effects following oral dosing in rodents with profound and sustained modulation of plasma Kyn and Trp levels compared to existing clinical molecules. In a mouse model of LPS-induced IDO1 activation, our highly selective IDO1 inhibitors fully ablate the elevation of Kyn in both plasma and lung in a dose-dependent manner. This lung Kyn modulation is more potent and efficacious than that observed for an IDO1 inhibitor currently in clinical trials. In addition, the IOmet IDO1 inhibitors provide superior tumor growth control in a PAN02 syngeneic model.
Conclusions
We describe the characterisation of novel potent, selective and dual-acting IDO1 and TDO inhibitors. The drug-like properties of these candidate-quality molecules translate to superior rodent in vivo PK/PD and anti-tumor profiles compared to compounds in clinical trials. This clear advantage is expected to translate to a significantly better PK/PD effect in humans, especially in lung cancer - a major opportunity for α-PD-1/PD-L1 and IDO1 inhibitor combination therapy.
Citation Format: Barry E. McGuinness, Phillip M. Cowley, Alan Wise, Thomas J. Brown. Characterization of next generation IDO1 and TDO inhibitors as novel cancer immunotherapeutic agents. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr LB-B14.