The bromodomain containing proteins TRIM24 (Tripartite motif containing protein 24) and BRPF1 (bromodomain and PHD finger containing protein 1) are involved in the epigenetic regulation of gene expression and have been implicated in human cancer. Overexpression of TRIM24 correlates with poor patient prognosis and BRPF1 is a scaffolding protein required for the assembly of histone acetyltransferase complexes, where the gene of MOZ (monocytic leukemia zinc finger protein) was first identified as a recurrent fusion partner in leukemia patients (8p11 chromosomal rearrangements). Here, we present the structure guided development of a series of N,N-dimethyl benzimidazolone bromodomain inhibitors through the iterative use of X-ray cocrystal structures. A unique binding mode enabled the design of a potent and selective inhibitor, 8i (IACS-9571) with low nanomolar affinities for TRIM24 and BRPF1 (ITC Kd = 31 nM and 14 nM, respectively). With its excellent cellular potency (EC50 = 50 nM) and favorable pharmacokinetic properties (F = 29%), 8i is a high-quality chemical probe for the evaluation of TRIM24 and/or BRPF1 bromodomain function in vitro and in vivo.

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Indoleamine 2,3-dioxygenase 1 (IDO1), a heme-containing enzyme that mediates the rate-limiting step in the metabolism of l-tryptophan to kynurenine, has been widely explored as a potential immunotherapeutic target in oncology. We developed a class of inhibitors with a conformationally constrained bicyclo[3.1.0]­hexane core. These potently inhibited IDO1 in a cellular context by binding to the apoenzyme, as elucidated by biochemical characterization and X-ray crystallography. A SKOV3 tumor model was instrumental in differentiating compounds, leading to the identification of IACS-9779 (62) and IACS-70465 (71). IACS-70465 has excellent cellular potency, a robust pharmacodynamic response, and in a human whole blood assay was more potent than linrodostat (BMS-986205). IACS-9779 with a predicted human efficacious once daily dose below 1 mg/kg to sustain >90% inhibition of IDO1 displayed an acceptable safety margin in rodent toxicology and dog cardiovascular studies to support advancement into preclinical safety evaluation for human development.

Increased expression of IDO1 is believed to create a tumor microenvironment that is immunosuppressive. In the course of our research directed at identifying potent and selective inhibitors of IDO1, we identified a class of compounds that inhibited IDO1 activity in a cellular context, but not in isolated enzymatic assays. We have conducted detailed mechanistic studies and shown that these molecules inhibit IDO1 by binding to the apo-enzyme, thus preventing the incorporation of the heme-cofactor into the active site of the holo-enzyme. Through an extensive medicinal chemistry campaign, we optimized a series of orally bioavailable, highly potent and selective inhibitors of IDO1 that possess excellent pharmacological properties. For several lead molecules, pharmacokinetic (PK) - pharmacodynamic (PD) relationships were established in whole blood and SKOV3 xenograft assays. The inhibition of IDO1 in a human whole-blood assay correlated well with the suppression of tumor kynurenine (KYN) that was observed in SKOV3 xenografts. At plasma concentrations of 3 µM, IACS-9779 supressed tumor KYN levels by 90%. IACS-9779 was well tolerated with excellent in vivo PK properties across multiple preclinical species, and a human PK prediction consistent with a low daily dose needed for full suppression of KYN production via IDO1. Note: This abstract was not presented at the meeting. Citation Format: Faika Mseeh, Matthew M. Hamilton, Joseph R. Marszalek, Norma E. Rogers, Connor A. Parker, Simon S. Yu, Zhen Liu, Naphtali J. Reyna, Timothy McAfoos, Brett W. Virgin-Downey, Paul G. Leonard, Jason B. Cross, Ningping Feng, Angela L. Harris, Andy M. Zuniga, Keith Mikule, Martin Tremblay, Yongying Jiang, Mikhila Mahendra, Jihai Pang, Qi Wu, Quanyun Xu, Timothy P. Heffernan, Philip Jones, Richard T. Lewis. IACS-9779, a development candidate that inhibits 2,3-dioxygenase (IDO) activity by blocking heme incorporation into IDO apoenzyme [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3277.

MTH1 is a protein that sanitizes oxidized dNTPs in the cell. It preferentially hydrolyzes 8-oxo-dGTP and 2-OH-dATP to their corresponding monophosphates and thereby prevents the incorporation of oxidized nucleotides into DNA or RNA. The functional result is a reduction in down-stream mutations, or DNA damage, thus preventing cell death. Recent publications suggest that MTH1 is a non-essential enzyme in normal cells, but is required for the survival of cancer cells as a consequence of being subjected to high levels of oxidative stress; hence its relevance as an oncology target. Gad et al., 2014 The interesting target rationale combined with a perceived high chemical tractability of the target resulting from availability of x-ray crystallographic information for the protein, led to a decision to undertake, in parallel, target validation, assay development and drug discovery. This effort resulted in the structure-based design of potent, cell active MTH1 small molecule inhibitors. This poster will describe the discovery and optimization of these inhibitors, and their use to evaluate the potential of MTH1 as an oncology target. This work was complemented by parallel genetic studies. Pharmacodynamic evaluation of target engagement using proximal biomarkers will be presented, as will phenotypic responses across a range of cancer cell lines. Citation Format: Elisabetta Leo, Alessia Petrocchi, Jennifer Bardenhagen, Maria Alimova, Xi Shi, Connor Parker, Naphtali Reyna, Matthew Hamilton, Edward Felix, Andrzej Mazan, Christian Dillon, Faika Mseeh, Joseph R. Marszalek, Carlo Toniatti, Giulio Draetta, Phil Jones, Richard T. Lewis. Identification of potent, cell active MTH1 inhibitors and their use in target validation studies. [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 B48.