ABSTRACT
Cancer cells are highly reliant on NAD+-dependent processes, including glucose metabolism, calcium signaling, DNA repair, and regulation of gene expression. Nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme for NAD+ salvage from nicotinamide, has been investigated as a target for anticancer therapy. Known NAMPT inhibitors with potent cell activity are composed of a nitrogen-containing aromatic group, which is phosphoribosylated by the enzyme. Here, we identified two novel types of NAM-competitive NAMPT inhibitors, only one of which contains a modifiable, aromatic nitrogen that could be a phosphoribosyl acceptor. Both types of compound effectively deplete cellular NAD+, and subsequently ATP, and produce cell death when NAMPT is inhibited in cultured cells for more than 48 hours. Careful characterization of the kinetics of NAMPT inhibition in vivo allowed us to optimize dosing to produce sufficient NAD+ depletion over time that resulted in efficacy in an HCT116 xenograft model. Our data demonstrate that direct phosphoribosylation of competitive inhibitors by the NAMPT enzyme is not required for potent in vitro cellular activity or in vivo antitumor efficacy. Mol Cancer Ther; 16(7); 1236-45. ©2017 AACR.
Subject(s)
Colorectal Neoplasms/drug therapy , Cytokines/antagonists & inhibitors , Enzyme Inhibitors/administration & dosage , Nicotinamide Phosphoribosyltransferase/antagonists & inhibitors , Adenosine Triphosphate/genetics , Adenosine Triphosphate/metabolism , Animals , Calcium Signaling/genetics , Colorectal Neoplasms/genetics , Colorectal Neoplasms/pathology , Cytokines/genetics , DNA Repair/drug effects , Enzyme Activation/drug effects , Gene Expression Regulation, Neoplastic/drug effects , HCT116 Cells , Humans , Mice , NAD/metabolism , Nicotinamide Phosphoribosyltransferase/genetics , Xenograft Model Antitumor AssaysABSTRACT
Herein we disclose SAR studies of a series of dimethylamino pyrrolidines which we recently reported as novel inhibitors of the PRC2 complex through disruption of EED/H3K27me3 binding. Modification of the indole and benzyl moieties of screening hit 1 provided analogs with substantially improved binding and cellular activities. This work culminated in the identification of compound 2, our nanomolar proof-of-concept (PoC) inhibitor which provided on-target tumor growth inhibition in a mouse xenograft model. X-ray crystal structures of several inhibitors bound in the EED active-site are also discussed.
Subject(s)
Polycomb Repressive Complex 2/antagonists & inhibitors , Polycomb Repressive Complex 2/metabolism , Pyrrolidines/pharmacology , Sulfonamides/pharmacology , Animals , Antineoplastic Agents/chemical synthesis , Antineoplastic Agents/chemistry , Antineoplastic Agents/pharmacology , Cell Line, Tumor , Humans , Ligands , Mice , Microsomes, Liver/drug effects , Microsomes, Liver/metabolism , Polycomb Repressive Complex 2/chemistry , Protein Binding , Pyrrolidines/chemical synthesis , Pyrrolidines/chemistry , Stereoisomerism , Structure-Activity Relationship , Sulfonamides/chemical synthesis , Sulfonamides/chemistry , Xenograft Model Antitumor AssaysABSTRACT
Polycomb repressive complex 2 (PRC2) is a regulator of epigenetic states required for development and homeostasis. PRC2 trimethylates histone H3 at lysine 27 (H3K27me3), which leads to gene silencing, and is dysregulated in many cancers. The embryonic ectoderm development (EED) protein is an essential subunit of PRC2 that has both a scaffolding function and an H3K27me3-binding function. Here we report the identification of A-395, a potent antagonist of the H3K27me3 binding functions of EED. Structural studies demonstrate that A-395 binds to EED in the H3K27me3-binding pocket, thereby preventing allosteric activation of the catalytic activity of PRC2. Phenotypic effects observed in vitro and in vivo are similar to those of known PRC2 enzymatic inhibitors; however, A-395 retains potent activity against cell lines resistant to the catalytic inhibitors. A-395 represents a first-in-class antagonist of PRC2 protein-protein interactions (PPI) for use as a chemical probe to investigate the roles of EED-containing protein complexes.
