New Quinolinone O-GlcNAc Transferase Inhibitors Based on Fragment Growth

Abstract

O-GlcNAcylation is an important post-translational and metabolic process in cells that must be carefully regulated. O-GlcNAc transferase (OGT) is ubiquitously present in cells and is the only enzyme that catalyzes the transfer of O-GlcNAc to proteins. OGT is a promising target in various pathologies such as cancer, immune system diseases, or nervous impairment. In our previous work we identified the 2-oxo-1,2-dihydroquinoline-4-carboxamide derivatives as promising compounds by a fragment-based drug design approach. Herein, we report the extension of this first series with several new fragments. As the most potent fragment, we identified 3b with an IC₅₀ value of 116.0 μM. If compared with the most potent inhibitor of the first series, F20 (IC₅₀ = 117.6 μM), we can conclude that the new fragments did not improve OGT inhibition remarkably. Therefore, F20 was used as the basis for the design of a series of compounds with the elongation toward the O-GlcNAc binding pocket as the free carboxylate allows easy conjugation. Compound 6b with an IC₅₀ value of 144.5 μM showed the most potent OGT inhibition among the elongated compounds, but it loses inhibition potency when compared to the UDP mimetic F20. We therefore assume that the binding of the compounds in the O-GlcNAc binding pocket is likely not crucial for OGT inhibition. Furthermore, evaluation of the compounds with two different assays revealed that some inhibitors most likely interfere with the commercially available UDP-Glo™ glycosyltransferase assay, leading to false positive results. This observation calls for caution, when evaluating UDP mimetic as OGT inhibitors with the UDP-Glo™ glycosyltransferase assay, as misinterpretations can occur.

Keywords: O-GlcNAc; O-GlcNAc transferase; fragments growth; molecular docking; protein glycosylation.

Figure 1

Schematic depiction of fragment screening and workflow of the fragment-based design approach; synthesis and evaluation of 1^st set of 22 compounds (evaluation at 1 mM by UDP-Glo™ assay) and 2^nd set of 15 compounds (evaluation at 100 μM by fluorescence activity assay). 2^nd set includes compounds based on F20 elongated with various amines.

Figure 2

Reagents and conditions (a) acetic acid, malonic acid, reflux, overnight; (b) and (f) corresponding amine, DIPEA, TBTU, DMF, RT, overnight; (c) ethyl chloroformate, TEA, DMF, corresponding amine, RT, overnight; (d) and (h) NaOH, EtOH, RT, overnight; (e) TBAF, THF, RT, overnight; (g) corresponding amine, HOBt, EDC, Et₃N, DMF, RT, overnight.

Figure 3

Comparison of 6b (A,C) and UDP-5S-GlcNAc (C,D) binding mode in the OGT binding site (PDB entry: 4GYY); predicted binding pose for 3b (B). The ligand and the neighboring protein side-chains are shown as stick models, colored according to the chemical atom type (blue, N; red, O; orange, S; green, Cl). Hydrogen bonds are indicated by black dotted lines. Thr922 is doubled due to static disorder.