A small molecule that inhibits OGT activity in cells.

O-GlcNAc transferase (OGT) is an essential mammalian enzyme that regulates numerous cellular processes through the attachment of O-linked N-acetylglucosamine (O-GlcNAc) residues to nuclear and cytoplasmic proteins. Its targets include kinases, phosphatases, transcription factors, histones, and many other intracellular proteins. The biology of O-GlcNAc modification is still not well understood, and cell-permeable inhibitors of OGT are needed both as research tools and for validating OGT as a therapeutic target. Here, we report a small molecule OGT inhibitor, OSMI-1, developed from a high-throughput screening hit. It is cell-permeable and inhibits protein O-GlcNAcylation in several mammalian cell lines without qualitatively altering cell surface N- or O-linked glycans. The development of this molecule validates high-throughput screening approaches for the discovery of glycosyltransferase inhibitors, and further optimization of this scaffold may lead to yet more potent OGT inhibitors useful for studying OGT in animal models.