Abstract 5245: Identification and characterization of the IDO1 inhibitor LY3381916

Abstract

Indoleamine 2,3-dioxygenase 1 (IDO1) is a heme-dependent enzyme that catalyzes the initial and rate-limiting step of tryptophan catabolism resulting in the local depletion of tryptophan and the concomitant production of kynurenine, both of which are immunosuppressive. Targeting IDO1 in combination with PD-1/PD-L1-targeted antibodies has shown promise in early phase clinical trials in several cancers and strongly suggests that, in some patients, IDO1 expression restrains PD-1/PD-L1-targeted checkpoint therapies. While some cancers extrinsically express IDO1 in response to IFN-γ produced from an ongoing, yet ineffective immune response, others select for the intrinsic expression of IDO1, independent of an immune response. We identified several cancer cell lines that intrinsically expressed either IDO1 or the related isozyme TDO2. Using these cell lines, we discovered LY3381916, a potent and selective inhibitor of cell-based IDO1 activity (IDO1 7 nM; TDO2 >20 µM). Using a variety of techniques, we demonstrated that LY3381916 binds to newly synthesized apo-IDO1 lacking heme, but does not inhibit mature heme-bound IDO1. Protein x-ray crystallography confirmed that LY3381916 binds to apo-IDO1 where it occupies the heme-binding pocket of IDO1. As a result of this novel mechanism of action, substantial inhibition of IDO1 in tumors requires the turn-over of mature heme-bound IDO1. Modeling of the pre-clinical PK/PD relationship suggests QD dosing of LY3381916 will maintain greater than 90% inhibition over 24 hours. In addition, due to the favorable properties of the drug, significant central nervous system (CNS) penetration has been measured for LY3381916 (rodent kp,uu 0.26). Kynurenine-mediated agonism of the aryl hydrocarbon receptor (AHR) is immunosuppressive in the tumor microenvironment. Inhibition of IDO1 and the subsequent reduction of kynurenine can relieve this immunosuppression. However, several heme-binding IDO1 inhibitors have been shown to replace kynurenine as an AHR agonist potentially limiting their ability to relieve this IDO1-dependent immunosuppressive mechanism. LY3381916 shows no confounding agonism of AHR up to 100 µM. Additionally, we characterized LY3381916 in pre-clinical tumor models and demonstrated that it was able to enhance LY3300054, anti-PD-L1 antibody (LY3300054) activity, which was associated with an enhanced T cell response. Based on these characteristics, LY3381916 is currently being investigated in a Phase I clinical trial. These data suggest further development of LY3381916 may be warranted. Citation Format: Frank C. Dorsey, Karim A. Benhadji, Lillian L. Sams, Debra A. Young, John F. Schindler, Karen L. Huss, Alexander Nikolayev, Carmine Carpenito, David Clawson, Bonita Jones, Andrew L. Faber, James E. Thomas, Steven A. Haney, Gaiying Zhao, William T. McMillen, Tod Smeal, Daniel J. Sall, Michael D. Kalos, Sandaruwan Geeganage, James R. Henry. Identification and characterization of the IDO1 inhibitor LY3381916 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5245.

The therapeutic potential of targeting tryptophan catabolism in cancer

“…Recently pharmacodynamics data from a preclinical study in solid tumours were released, which revealed that LY3381916 does not bind the mature IDO1 enzyme but rather binds to the haem-binding pocket of the apo-IDO1 protein, thus preventing protein maturation. 151 …”

“…Such data are not available for epacadostat. Evaluation of the intra-tumoural concentrations of epacadostat would be important, as intra-tumoural penetrance of IDO1 inhibitors could be hindered due to diminished blood supply 143 , 151 or elevated oncotic pressure in solid tumours 8 , 143 (Fig. 2a , left).…”

X-ray Structure-Guided Discovery of a Potent, Orally Bioavailable, Dual Human Indoleamine/Tryptophan 2,3-Dioxygenase (hIDO/hTDO) Inhibitor That Shows Activity in a Mouse Model of Parkinson’s Disease

“…(A) Current mechanistic proposals for IDO/TDO-mediated oxidative cleavage of tryptophan, where the initial indole activation is either by an electrophilic or radical addition . (B) Representative hIDO1/hTDO inhibitors: epacadostat (INCB024360), navoximod (NLG-919), I-1 , linrodostat (BMS-986205), , PF-06840003, LY3381916, NLG8189, I-2 , I-3 , LM10, I-4 , I-5 , I-6 , I-7 , I-8 , and I-9 , of which the potency values are from the corresponding cited references.…”

“…Since hIDO1 inhibitors have great potential for cancer immunotherapy other than CNS disorders, a number of highly potent and selective hIDO1 inhibitors have been developed, many of which have entered clinical development, such as epacadostat (INCB024360), navoximod (NLG-919), linrodostat (BMS-986205), PF-06840003, and LY3381916 (Figure B). Very recently, several structurally novel hIDO1 inhibitors (e.g., I-1 , I-2 , and I-3 ) were continuously identified by the DNA-encoded library technology, virtual screening, or other strategies (Figure B), providing new candidates for drug development. − Mechanistic studies of hIDO1 inhibitors have revealed distinct inhibition modes, for example, via binding to chelate with heme iron, ,− binding to heme without iron chelation, binding to trigger heme release, , or only binding with apo -hIDO1, suggesting different perspectives in inhibitor development.…”

Discovery of the First Potent IDO1/IDO2 Dual Inhibitors: A Promising Strategy for Cancer Immunotherapy

“…Indoleamine 2,3-dioxygenase-1 (IDO1), indoleamine 2,3-dioxygenase-2 (IDO2), and tryptophan 2,3-dioxygenase (TDO) are the first rate-limiting enzymes in the KP that catalyze the conversion of Trp to kynurenine (Kyn). − IDO1, the most well-characterized enzyme, is frequently overexpressed in the vast majority of cancers, and IDO1 overexpression is associated with poor prognosis. , Extensive preclinical evidence has demonstrated that IDO1-expressing dendritic cells (DCs) mediate immune tolerance mainly via the degradation of Trp and its metabolites, which results in the inhibition of effector T cell proliferation and the induction of regulatory T cell (Treg) differentiation and activation. − Therefore, the development of IDO1 inhibitors as immunotherapeutic agents has attracted considerable attention. Several selective and highly potent IDO1 inhibitors have been developed, and some of them have successfully advanced into clinical trials as a single agent or in combination with other drugs in the past decade, such as navoximod (NLG919), epacadostat (Epa), linrodostat (BMS-986205), PF-06840003, and LY3381916 (Figure ). Due to the failure of Epa to improve clinical responses in a phase III trial (ECHO-301), many efforts have been made to search for novel and more potent IDO1 inhibitors.…”